metal-organic compounds
(2,2′-Bipyridine-κ2N,N′)[2-tert-butylanilinato(2−)]dichloridooxidomolybdenum(VI) dichloromethane hemisolvate
aChemistry, Institute of Natural Sciences, Massey University at Albany, PO Box 102904, North Shore Mail Centre, Auckland, New Zealand
*Correspondence e-mail: j.waters@massey.ac.nz
The MoVI atom in the title structure, [Mo(C10H13N)Cl2O(C10H8N2)]·0.5CH2Cl2, has a distorted octahedral coordination sphere with cis-orientated oxide and imide ligands, trans-chloride ligands and the 2,2′-bipyridine (bipy) ligand N atoms lying trans to the oxide and imide ligands. An imide-ligand tert-butyl-methyl-group H atom makes a close approach with the oxide ligand (distance = 2.53 Å) and the imide-ligand N atom (distance = 2.41 Å). Another imide-ligand tert-butyl-methyl-group H atom makes a close approach to a chloride ligand (distance = 2.82 Å). One bipy-ligand α-H atom makes a close approach to the oxide ligand (distance = 2.4 Å) and the other α-H atom makes a close approach to the imide-ligand phenyl-ring ortho-H atom (distance = 2.52 Å). These close approaches suggest the presence of weak intramolecular hydrogen bonds. The solvent molecule has been modelled under consideration of half-occupancy.
Related literature
For other oxo-imido complexes, see: Bell et al. (1994); Barrie et al. (1999); Bradley et al. (1987); Clegg et al. (1993); Chatt et al. (1979); Clark et al. (1996,). For the trans-influence effect, see: Nugent & Mayer (1988). For close approaches of hydrogen atoms in transition metal complexes and the relationship to weak hydrogen bonds to oxygen atoms, see: Desiraju (1996); to chlorine atoms, see: Aakeroy et al. (1999); and to N atoms, see: Demers et al. (2005).
Experimental
Crystal data
|
Refinement
|
|
Data collection: SMART (Siemens, 1995); cell SAINT (Siemens, 1995); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1999); software used to prepare material for publication: SHELXL97.
Supporting information
https://doi.org/10.1107/S1600536810047392/bv2152sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536810047392/bv2152Isup2.hkl
Na2MoO4.2H2O (2.0 g, 8.3 mmol) was dried under vacuum by heating at 100°C for 1 h to yield anhydrous Na2MoO4 (1.7 g, 8.3 mmol). 2-tert-butylaniline (2.46 g, 16.5 mmol) was added followed by 1,2-dimethoxyethane (50 cm3) and then triethylamine (4.6 cm3 33.0 mmol) and the mixture was stirred rapidly while chlorotrimethylsilane (8.4 cm3 66.0 mmol) was added dropwise. The mixture was stirred for 16 h, refluxed for 8 h and then filtered while the mixture was still hot and the solvent removed to give a deep red crystalline solid (4.43 g). 0.76 g of this material was added to 2,2'-bipyridine (0.214 g, 1.4 mmol), CH2Cl2 (30 cm3) was added and the mixture stirred for 5 h. The solution was filtered, the solvent removed and the deep-red crystalline solid washed with petroleum spirit. The solid was dissolved in CH2Cl2 (20 cm3) the volume reduced to ca one-half and the solution allowed to stand at room temperature yielding a red-brown crystalline solid (0.55 g). A crystal was chosen from the mass and the X-ray
obtained.H atoms were placed in calculated positions riding on the atoms to which they are attached. The CH2Cl2 solvent was located close to a centre of symmetry requiring that it be no more than half-weighted. No attempt was made to refine its site occupancy factor.
Complexes of molybdenum containing oxo and imido functions in the same molecule are still fairly rare. However they are relatively easy to prepare by a conproportionation reaction between bis-imido complexes of the form [Mo(NR)2Cl2(dme)] (dme =1,2- dimethoxyethane) and the bis-oxo complexes [Mo(O)2Cl2(dme)] (Bell et al., 1994). During attempts to prepare bis-imido complexes in which the imido ligand carried substituents on the aryl ring possessing potentially sterically hindering ortho-substituents, we reacted Na2MoO4 with two equivalents of 2-tert-butylaniline in the presence of 8 equivalents of SiMe3Cl and 4 equivalents of NEt3 in dme as solvent which is the normal protocol for producing [Mo(NR)2Cl2(dme)] complexes in good yield. A red solid was obtained which had the characteristic features of the complex. This complex was then reacted with 2,2'-bipyridine (bipy) to produce the complex [Mo(NC6H4CMe3-2)2Cl2(bipy)]. This type of complex was of interest as our studies of bis-imido tungsten complexes of the form [W(NC6H5)2Cl2(bipy)] had shown there was a steric interaction between the bipy α-H atoms and the ipso-carbon of the phenyl ring (Bradley et al., 1987). Whereas the imido ligand nitrogen atoms were bent away from each other as expected, the ipso-carbon atoms of the phenyl were bent inwards towards each other [W—N—C bond angles 165.6 (12) and 164.4 (12)°] apparently to reduce contact with the bipy α-H atoms. The imido ligand phenyl groups were also apparently rotated to reduce contact of the ortho-H atoms with the bipy α-H atoms. The product obtained from the reaction with bipy crystallized nicely but did not give particularly good C, H and N analytical data. The NMR spectra suggested the bulk sample was indeed [Mo(NC6H4CMe3-2)2Cl2(bipy)] but the spectra also indicated a small amount of a second species was present. A crystal picked out from the mass and subjected to an X-ray analysis was found not to be the bis-imido complex but instead the oxo-imido complex [Mo (NC6H4CMe3-2)(O)Cl2(bipy)](1). The oxo-imido function could have arisen as a by-product during the preparation of [Mo(NC6H4CMe3 2)2Cl2(dme)] by incomplete oxo-imido exchange or by hydrolysis of one of the imido functions during the exchange of the dme ligand for the bipy ligand as this ligand was not dried after obtaining it from commercial sources.
The structure of (1) consists of a distorted-octahedral array about the molybdenum atom with a cis-orientation of the organoimido and oxo ligands, trans-chloro ligands and the nitrogen atoms of the bipyridyl ligand lying trans to the organoimido and oxo ligands (Fig. 1). The overall structure is similar to that observed for the tungsten-bipy complex [WCl2(NCMe3)(O)(bipy)] (Clegg et al., 1993) and also the molybdenum complexes [MoCl2(NH)(O)(OPPh2Et)] (Chatt et al. 1979) and [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] (Clark et al. 1996). The Mo—Nimido bond length [1.735 (3) Å] and Mo—Ooxo bond length [1.686 (2) Å] are similar to those found in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [1.756 (7) and 1.700 (6) Å] (Clark et al. 1996). The Mo—Cl(1) bond length [2.3580 (9) Å] is slightly shorter than the Mo—Cl(2) bond length [2.3745 (9) Å]. The longer Mo—Cl bond length is similar in distance to the shorter Mo—Cl bond in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [2.375 (3) Å] but both bonds are shorter than those found in [MoCl2(NH)(O)(OPPh2Et)] [average 2.391 (7) Å] or the bis-imido complex [MoCl2(NC10H15)(NC6F5)(dme)] (C10H15 = adamantyl) [average 2.397 (2) Å] (Bell et al. 1994). The Mo—N bond trans to the oxo ligand is slightly longer than that trans to the imido function [2.283 (3) and 2.255 (3) Å respectively] which suggests that the oxo ligand may exert the stronger trans -influence (Nugent & Mayer, 1988). However this may not be a trans -influence effect as there are close approaches of the two α-hydrogen atoms of the bipy ligand with other parts of the molecule.
The N(1)—Mo—O(1) bond angle [104.7 (1)°] and Cl(1)—Mo—Cl(2) bond angle [160.08 (3)°] in (1) are similar to those found in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [bond angles 104.2 (4) and 159.7 (1)° respectively] and the two chloro ligands push away from both the Mo—O(1) and Mo—N(1) multiple bonds. In this respect, the O(1)—Mo—Cl(1) and O(1)—Mo—Cl(2) bond angles (oxo ligand and chloro ligands) are essentially equivalent [96.83 (8) and 97.41 (8)° respectively] but the N(1)—Mo—Cl(1) angle [99.78 (9)°] is greater than the N(1)—Mo—Cl(2) angle [90.00 (9)°] and this appears to be related to a
arising from the proximity of the 2-tert-butyl substituent on the imido ligand aryl ring (see later). The angles associated with the coordinated nitrogen atoms of the bipy rings show there is nothing unusual for the way this ligand coordinates to the metal with the O(1)—Mo—N(3), N(1)—Mo—N(2) and N(2)—Mo—N(3) bond angles [159.2 (1), 164.4 (1) and 69.97 (9)° respectively] being similar to those found for [WCl2(NCMe3)(O)(bipy)] [157.9 (2), 165.9 (2) and 69.1 (2)° respectively] (Clegg et al., 1993) or for the bis-imido tungsten complex [WCl2(NPh)2(bipy)] [161.2 (5), 164.3 (5) and 69.8 (4)° respectively] (Bradley et al. 1987). These angles do not differ significantly from those associated with the coordination mode of the 1,2-dimethoxyethane ligand in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)]- [Ooxo—Mo—O, Nimido—Mo—O and O—Mo—O angles 160.3 (3), 165.9 (3) and 70.6 (2) respectively]. The coordinated bipy ligand is essentially planar with the difference between the two planes made by the two rings being only 3.9 (2)°.The phenyl ring of the organoimido ligand is bent back towards Cl(2) and also N(3) of the bipy ring with the Mo—N(1)—C(11) bond angle being 165.8 (2)ωhich is smaller than in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [172.2 (7)°] (Clark et al., 1996) and the tungsten bipy analogue [WCl2(NCMe3)(O)(bipy)] [170.6 (5)°] (Clegg et al., 1993) but similar to that found in the bis-imido complexes [Mo(NC6H3Cl2-2,6)(S2CNEt2)2][162.2 (7) and 162.9 (7)/%] (Barrie et al., 1999) and [WCl2(NPh)2(bipy)] [165.6 (12) and 164.4 (11)°] (Bradley et al., 1987). However in these complexes the M—N—C bond angles are such that the phenyl or alkyl group bends in towards the adjacent oxo or imido ligand whereas in the present complex the bend is away from the oxo ligand. This appears to be caused by the tert-butyl substituent which in the crystal prefers to orientate over Cl(1) and O(1) rather than Cl(2) and O(1) which appears to be another possible orientation (Fig 1). The rotation of the organoimido phenyl ring is such that the plane of the ring deviates from the plane made by the bipy rings by 46.5 (1)° (Fig 1). The orientation of the phenyl ring and the orientation of the 2-tert-butyl substituent has some interesting consequences for intramolecular contacts. For the 2-tert-butyl substituent the rotation about C(16) and C(17) is such that one of the equatorially positioned methyl groups [C(18)] lies directly above the oxo ligand and H(18a) makes a contact of 2.53 Å with it. This distance lies within the range of distances considered to involve weak hydrogen bonding to oxygen atoms (Desiraju, 1996)). There is an even shorter separation of 2.41 Å between H(18) and the imido nitrogen atom, N(1) and the separation is well within the range of values considered to involve weak hydrogen bonding to nitrogen [2.65%A (Demers et al., 2005)]. It is interesting to note that even though the nitrogen lone pair will be mostly involved in donation to molybdenum to make the imido ligand multiple bond, the bend made by the Mo—N(1)—C(11) system [165.8 (2)°] is such that any remaining lone pair is pointing in the direction of H(18a). The other equatorially positioned methyl group of the 2-tert-butyl substituent lies above Cl(1) with the H(19c) to Cl(1) separation of 2.82 Å. This distance is also within the range of values suggested as weak hydrogen bonding to chlorine (Aakeroy et al. 1999). The separation between H(19c) and the imido nitrogen N(1) is 2.39Å which suggests potential weak hydrogen bonding may also be involved. There is a similar approach of H(18a) to N1 (2.41 Å). However it should be realised that these close approaches are forced on the system by the molecular geometry of the tert-butyl group which may or may not imply the existence of attractive H-bonding. The remaining methyl group of the 2-tert-butyl substituent, which lies in an axial position, is rotated to give a gearing effect which removes any interaction of the H atoms with the nearest neighbour H atoms. Thus H(20a) is positioned so as to bisect the C(18)—C(17)—C(19) angle and this allows H(20b) and H(20c) to lie in front of, but to either side of, the bipy α-hydrogen H(15). As a result of the positioning of the 2-tert-butyl substituent, H(12), which lies in the other ortho-position of the aromatic ring, makes a close contact with Cl(2) with the distance of 3.06 Å being just outside the limit of the H and Cl van der Waals radii (3.0 Å) but still representing a weak hydrogen bond (Aakeroy, 1999). H(12) also makes a close contact of 2.52 Å with the α-hydrogen of the nearby bipy ring which is just outside the van der waals radii of 2.4 Å (Aakeroy, 1999). On the other side of the molecule there is a close approach of the weak hydrogen bonding type, for H(1) which is the other α-hydrogen of the bipy ring, with the terminal oxo ligand oxygen [O(1)]. This arises since the bipy rings are essentially co-planar with the Mo—O multiple bond. The atomic separation is 2.44 Å which is even shorter than the distance the 2-tert-butyl substituent H(18a) atom makes with O(1) (2.53 Å). The separation for this type of interaction in [WCl2(NCMe3)(O)(bipy)] is 2.42 Å (Clegg, et al., 1993). There are no other significant intramolecular contacts in the structure. The disordered partial CH2Cl2 molecule lies across a centre of symmetry in the but its H atoms make no significant approaches to the chlorine complex.
For other oxo-imido complexes see: Bell et al. (1994); Barrie et al., (1999); Bradley et al., (1987); Clegg et al. (1993); Chatt et al. (1979); Clark et al. (1996,). For the trans-influence effect, see: Nugent & Mayer, (1988). For close approaches of hydrogen atoms in transition metal complexes and the relationship to weak hydrogen bonds to oxygen atoms, see: Desiraju (1996); to chlorine atoms, see: Aakeroy et al. (1999); and to N atoms, see: Demers et al. (2005).
Data collection: SMART (Siemens, 1995); cell
SAINT (Siemens, 1995); data reduction: SAINT (Siemens, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1999); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).Fig. 1. ORTEP diagram, at the 50% probability level, of the mlecule showing the numbering system. |
[Mo(C10H13N)Cl2O(C10H8N2)]·0.5CH2Cl2 | F(000) = 2136 |
Mr = 528.7 | Dx = 1.630 Mg m−3 |
Orthorhombic, Pbcn | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -P 2n 2ab | Cell parameters from 8192 reflections |
a = 17.4207 (2) Å | θ = 2–25° |
b = 14.9657 (1) Å | µ = 1.00 mm−1 |
c = 16.5237 (1) Å | T = 150 K |
V = 4307.94 (6) Å3 | Needle, yellow |
Z = 8 | 0.26 × 0.06 × 0.06 mm |
Siemens SMART diffractometer | 4459 independent reflections |
Radiation source: fine-focus sealed tube | 3438 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.084 |
Area detector ω scan | θmax = 26.6°, θmin = 1.8° |
Absorption correction: multi-scan (Blessing, 1995) | h = 0→21 |
Tmin = 0.651, Tmax = 0.963 | k = 0→18 |
40908 measured reflections | l = 0→20 |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.043 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.102 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | w = 1/[σ2(Fo2) + (0.054P)2 + 1.7768P] where P = (Fo2 + 2Fc2)/3 |
4459 reflections | (Δ/σ)max = 0.008 |
280 parameters | Δρmax = 0.64 e Å−3 |
0 restraints | Δρmin = −1.54 e Å−3 |
[Mo(C10H13N)Cl2O(C10H8N2)]·0.5CH2Cl2 | V = 4307.94 (6) Å3 |
Mr = 528.7 | Z = 8 |
Orthorhombic, Pbcn | Mo Kα radiation |
a = 17.4207 (2) Å | µ = 1.00 mm−1 |
b = 14.9657 (1) Å | T = 150 K |
c = 16.5237 (1) Å | 0.26 × 0.06 × 0.06 mm |
Siemens SMART diffractometer | 4459 independent reflections |
Absorption correction: multi-scan (Blessing, 1995) | 3438 reflections with I > 2σ(I) |
Tmin = 0.651, Tmax = 0.963 | Rint = 0.084 |
40908 measured reflections |
R[F2 > 2σ(F2)] = 0.043 | 0 restraints |
wR(F2) = 0.102 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.03 | Δρmax = 0.64 e Å−3 |
4459 reflections | Δρmin = −1.54 e Å−3 |
280 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
Mo1 | 0.353791 (15) | 0.84420 (2) | 0.150599 (16) | 0.02018 (11) | |
Cl1 | 0.31084 (5) | 0.72649 (6) | 0.06725 (5) | 0.0299 (2) | |
Cl2 | 0.41115 (5) | 0.98134 (6) | 0.19018 (5) | 0.0291 (2) | |
N1 | 0.26663 (15) | 0.87982 (19) | 0.18979 (16) | 0.0208 (6) | |
N2 | 0.46431 (15) | 0.83274 (18) | 0.08033 (16) | 0.0218 (6) | |
N3 | 0.34325 (15) | 0.91836 (19) | 0.03034 (16) | 0.0226 (6) | |
O1 | 0.39213 (13) | 0.77987 (16) | 0.22394 (13) | 0.0257 (5) | |
C1 | 0.52275 (19) | 0.7863 (2) | 0.1095 (2) | 0.0269 (8) | |
H1 | 0.5178 | 0.7587 | 0.1610 | 0.032* | |
C2 | 0.5900 (2) | 0.7769 (3) | 0.0679 (2) | 0.0298 (8) | |
H2 | 0.6311 | 0.7430 | 0.0900 | 0.036* | |
C3 | 0.5975 (2) | 0.8169 (3) | −0.0060 (2) | 0.0300 (8) | |
H3 | 0.6436 | 0.8111 | −0.0362 | 0.036* | |
C4 | 0.53740 (19) | 0.8656 (2) | −0.0355 (2) | 0.0258 (8) | |
H4 | 0.5416 | 0.8943 | −0.0865 | 0.031* | |
C5 | 0.47099 (19) | 0.8728 (2) | 0.00858 (18) | 0.0197 (7) | |
C6 | 0.40356 (18) | 0.9217 (2) | −0.01916 (18) | 0.0197 (7) | |
C7 | 0.4003 (2) | 0.9672 (2) | −0.0908 (2) | 0.0258 (8) | |
H7 | 0.4441 | 0.9698 | −0.1250 | 0.031* | |
C8 | 0.3339 (2) | 1.0088 (2) | −0.1132 (2) | 0.0282 (8) | |
H8 | 0.3311 | 1.0415 | −0.1623 | 0.034* | |
C9 | 0.2717 (2) | 1.0023 (3) | −0.0635 (2) | 0.0327 (9) | |
H9 | 0.2243 | 1.0289 | −0.0784 | 0.039* | |
C10 | 0.2782 (2) | 0.9575 (3) | 0.0072 (2) | 0.0300 (8) | |
H10 | 0.2347 | 0.9539 | 0.0417 | 0.036* | |
C11 | 0.20734 (19) | 0.9275 (2) | 0.22186 (19) | 0.0225 (7) | |
C12 | 0.2068 (2) | 1.0188 (2) | 0.2053 (2) | 0.0341 (9) | |
H12 | 0.2446 | 1.0435 | 0.1705 | 0.041* | |
C13 | 0.1527 (2) | 1.0727 (3) | 0.2388 (3) | 0.0425 (10) | |
H13 | 0.1533 | 1.1352 | 0.2290 | 0.051* | |
C14 | 0.0974 (2) | 1.0355 (3) | 0.2866 (3) | 0.0415 (10) | |
H14 | 0.0589 | 1.0725 | 0.3097 | 0.050* | |
C15 | 0.0967 (2) | 0.9464 (3) | 0.3014 (2) | 0.0327 (9) | |
H15 | 0.0568 | 0.9227 | 0.3341 | 0.039* | |
C16 | 0.15120 (18) | 0.8890 (2) | 0.27117 (19) | 0.0219 (7) | |
C17 | 0.15032 (18) | 0.7900 (2) | 0.2892 (2) | 0.0241 (7) | |
C18 | 0.2222 (2) | 0.7626 (3) | 0.3349 (2) | 0.0294 (8) | |
H18A | 0.2676 | 0.7779 | 0.3028 | 0.044* | |
H18B | 0.2212 | 0.6980 | 0.3446 | 0.044* | |
H18C | 0.2241 | 0.7941 | 0.3868 | 0.044* | |
C19 | 0.1439 (2) | 0.7378 (3) | 0.2113 (2) | 0.0324 (9) | |
H19A | 0.0978 | 0.7567 | 0.1820 | 0.049* | |
H19B | 0.1404 | 0.6738 | 0.2236 | 0.049* | |
H19C | 0.1893 | 0.7489 | 0.1778 | 0.049* | |
C20 | 0.0821 (2) | 0.7650 (3) | 0.3419 (2) | 0.0374 (10) | |
H20A | 0.0853 | 0.7971 | 0.3935 | 0.056* | |
H20B | 0.0826 | 0.7005 | 0.3520 | 0.056* | |
H20C | 0.0344 | 0.7813 | 0.3141 | 0.056* | |
C21 | 0.4547 (10) | 0.5417 (12) | 0.0336 (9) | 0.088 (5) | 0.50 |
H21A | 0.428 (7) | 0.558 (9) | 0.007 (7) | 0.080* | 0.50 |
H21B | 0.452 (7) | 0.562 (8) | 0.074 (7) | 0.080* | 0.50 |
Cl3 | 0.4319 (3) | 0.4302 (3) | 0.0347 (4) | 0.0822 (14) | 0.50 |
Cl4 | 0.5425 (4) | 0.5541 (6) | −0.0196 (6) | 0.162 (4) | 0.50 |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mo1 | 0.01602 (16) | 0.02499 (18) | 0.01954 (16) | −0.00289 (12) | 0.00123 (11) | 0.00364 (12) |
Cl1 | 0.0277 (5) | 0.0339 (5) | 0.0282 (4) | −0.0058 (4) | −0.0006 (3) | −0.0033 (4) |
Cl2 | 0.0271 (4) | 0.0320 (5) | 0.0281 (4) | −0.0105 (4) | 0.0059 (4) | −0.0008 (4) |
N1 | 0.0183 (14) | 0.0206 (15) | 0.0234 (14) | −0.0059 (11) | 0.0018 (11) | 0.0032 (12) |
N2 | 0.0175 (14) | 0.0252 (16) | 0.0226 (14) | −0.0013 (12) | −0.0004 (11) | −0.0001 (12) |
N3 | 0.0173 (14) | 0.0274 (16) | 0.0230 (14) | −0.0006 (12) | 0.0021 (11) | 0.0040 (12) |
O1 | 0.0206 (12) | 0.0298 (14) | 0.0267 (12) | −0.0048 (11) | −0.0016 (9) | 0.0044 (10) |
C1 | 0.0205 (18) | 0.034 (2) | 0.0264 (18) | 0.0011 (15) | −0.0027 (14) | 0.0007 (16) |
C2 | 0.0201 (18) | 0.038 (2) | 0.0318 (19) | 0.0040 (16) | −0.0035 (15) | −0.0048 (16) |
C3 | 0.0172 (18) | 0.037 (2) | 0.036 (2) | −0.0023 (16) | 0.0038 (15) | −0.0102 (17) |
C4 | 0.0251 (18) | 0.030 (2) | 0.0217 (17) | −0.0070 (15) | 0.0037 (14) | −0.0045 (14) |
C5 | 0.0205 (17) | 0.0202 (17) | 0.0185 (16) | −0.0042 (14) | 0.0007 (13) | −0.0035 (13) |
C6 | 0.0213 (17) | 0.0194 (17) | 0.0185 (15) | −0.0040 (13) | 0.0015 (13) | −0.0022 (13) |
C7 | 0.0291 (19) | 0.0259 (19) | 0.0223 (17) | −0.0049 (16) | 0.0030 (14) | −0.0010 (14) |
C8 | 0.038 (2) | 0.026 (2) | 0.0207 (17) | −0.0007 (16) | −0.0037 (15) | 0.0039 (15) |
C9 | 0.0254 (18) | 0.039 (2) | 0.0340 (19) | 0.0058 (17) | −0.0035 (16) | 0.0096 (16) |
C10 | 0.0212 (18) | 0.039 (2) | 0.0294 (19) | 0.0022 (17) | −0.0004 (15) | 0.0065 (16) |
C11 | 0.0191 (17) | 0.0248 (19) | 0.0234 (17) | −0.0022 (14) | −0.0032 (13) | 0.0015 (14) |
C12 | 0.036 (2) | 0.025 (2) | 0.041 (2) | −0.0031 (17) | 0.0010 (17) | 0.0089 (17) |
C13 | 0.049 (3) | 0.022 (2) | 0.057 (3) | 0.0062 (19) | −0.001 (2) | 0.0035 (19) |
C14 | 0.038 (2) | 0.034 (2) | 0.053 (3) | 0.0149 (19) | 0.0056 (19) | −0.0036 (19) |
C15 | 0.0252 (19) | 0.039 (2) | 0.034 (2) | 0.0035 (17) | 0.0060 (16) | −0.0007 (17) |
C16 | 0.0199 (17) | 0.0242 (18) | 0.0215 (16) | −0.0030 (14) | −0.0010 (13) | −0.0007 (14) |
C17 | 0.0193 (17) | 0.0249 (19) | 0.0279 (18) | −0.0042 (14) | 0.0045 (14) | 0.0030 (14) |
C18 | 0.0279 (19) | 0.031 (2) | 0.0293 (19) | 0.0032 (16) | 0.0030 (15) | 0.0080 (15) |
C19 | 0.0224 (19) | 0.031 (2) | 0.044 (2) | −0.0076 (16) | 0.0045 (16) | −0.0087 (17) |
C20 | 0.030 (2) | 0.038 (2) | 0.044 (2) | −0.0088 (18) | 0.0117 (17) | 0.0087 (18) |
C21 | 0.096 (11) | 0.084 (11) | 0.085 (11) | 0.034 (9) | −0.031 (8) | −0.035 (9) |
Cl3 | 0.054 (2) | 0.065 (3) | 0.127 (3) | −0.001 (2) | −0.021 (2) | −0.001 (3) |
Cl4 | 0.123 (6) | 0.162 (6) | 0.200 (7) | −0.087 (5) | −0.108 (5) | 0.089 (5) |
Mo1—O1 | 1.686 (2) | C12—C13 | 1.359 (5) |
Mo1—N1 | 1.735 (3) | C12—H12 | 0.9500 |
Mo1—N2 | 2.255 (3) | C13—C14 | 1.364 (6) |
Mo1—N3 | 2.283 (3) | C13—H13 | 0.9500 |
Mo1—Cl1 | 2.3580 (9) | C14—C15 | 1.356 (5) |
Mo1—Cl2 | 2.3745 (9) | C14—H14 | 0.9500 |
N1—C11 | 1.363 (4) | C15—C16 | 1.375 (5) |
N2—C1 | 1.323 (4) | C15—H15 | 0.9500 |
N2—C5 | 1.334 (4) | C16—C17 | 1.511 (5) |
N3—C10 | 1.332 (4) | C17—C19 | 1.510 (5) |
N3—C6 | 1.332 (4) | C17—C18 | 1.519 (5) |
C1—C2 | 1.366 (5) | C17—C20 | 1.520 (4) |
C1—H1 | 0.9500 | C18—H18A | 0.9800 |
C2—C3 | 1.365 (5) | C18—H18B | 0.9800 |
C2—H2 | 0.9500 | C18—H18C | 0.9800 |
C3—C4 | 1.365 (5) | C19—H19A | 0.9800 |
C3—H3 | 0.9500 | C19—H19B | 0.9800 |
C4—C5 | 1.371 (4) | C19—H19C | 0.9800 |
C4—H4 | 0.9500 | C20—H20A | 0.9800 |
C5—C6 | 1.458 (4) | C20—H20B | 0.9800 |
C6—C7 | 1.367 (4) | C20—H20C | 0.9800 |
C7—C8 | 1.363 (5) | C21—Cl4i | 1.453 (17) |
C7—H7 | 0.9500 | C21—Cl3 | 1.715 (19) |
C8—C9 | 1.363 (5) | C21—Cl4 | 1.77 (2) |
C8—H8 | 0.9500 | C21—H21A | 0.70 (12) |
C9—C10 | 1.350 (5) | C21—H21B | 0.74 (11) |
C9—H9 | 0.9500 | Cl3—Cl4i | 0.563 (9) |
C10—H10 | 0.9500 | Cl4—Cl3i | 0.563 (9) |
C11—C12 | 1.393 (5) | Cl4—C21i | 1.453 (17) |
C11—C16 | 1.397 (4) | Cl4—Cl4i | 2.287 (12) |
O1—Mo1—N1 | 104.71 (12) | C9—C10—H10 | 118.7 |
O1—Mo1—N2 | 89.34 (10) | N1—C11—C12 | 116.2 (3) |
N1—Mo1—N2 | 164.37 (11) | N1—C11—C16 | 122.8 (3) |
O1—Mo1—N3 | 159.24 (10) | C12—C11—C16 | 121.0 (3) |
N1—Mo1—N3 | 96.03 (11) | C13—C12—C11 | 120.5 (4) |
N2—Mo1—N3 | 69.97 (9) | C13—C12—H12 | 119.8 |
O1—Mo1—Cl1 | 96.83 (8) | C11—C12—H12 | 119.8 |
N1—Mo1—Cl1 | 99.78 (9) | C12—C13—C14 | 118.9 (4) |
N2—Mo1—Cl1 | 85.03 (7) | C12—C13—H13 | 120.5 |
N3—Mo1—Cl1 | 80.17 (7) | C14—C13—H13 | 120.5 |
O1—Mo1—Cl2 | 97.41 (8) | C15—C14—C13 | 120.8 (4) |
N1—Mo1—Cl2 | 90.00 (9) | C15—C14—H14 | 119.6 |
N2—Mo1—Cl2 | 81.28 (7) | C13—C14—H14 | 119.6 |
N3—Mo1—Cl2 | 81.57 (7) | C14—C15—C16 | 122.9 (4) |
Cl1—Mo1—Cl2 | 160.08 (3) | C14—C15—H15 | 118.5 |
C11—N1—Mo1 | 165.8 (2) | C16—C15—H15 | 118.5 |
C1—N2—C5 | 119.5 (3) | C15—C16—C11 | 115.9 (3) |
C1—N2—Mo1 | 120.6 (2) | C15—C16—C17 | 122.3 (3) |
C5—N2—Mo1 | 119.9 (2) | C11—C16—C17 | 121.8 (3) |
C10—N3—C6 | 118.5 (3) | C19—C17—C16 | 109.9 (3) |
C10—N3—Mo1 | 122.2 (2) | C19—C17—C18 | 110.2 (3) |
C6—N3—Mo1 | 119.3 (2) | C16—C17—C18 | 110.7 (3) |
N2—C1—C2 | 122.0 (3) | C19—C17—C20 | 107.6 (3) |
N2—C1—H1 | 119.0 | C16—C17—C20 | 111.2 (3) |
C2—C1—H1 | 119.0 | C18—C17—C20 | 107.1 (3) |
C3—C2—C1 | 119.1 (3) | C17—C18—H18A | 109.5 |
C3—C2—H2 | 120.5 | C17—C18—H18B | 109.5 |
C1—C2—H2 | 120.5 | H18A—C18—H18B | 109.5 |
C4—C3—C2 | 118.7 (3) | C17—C18—H18C | 109.5 |
C4—C3—H3 | 120.6 | H18A—C18—H18C | 109.5 |
C2—C3—H3 | 120.6 | H18B—C18—H18C | 109.5 |
C3—C4—C5 | 120.0 (3) | C17—C19—H19A | 109.5 |
C3—C4—H4 | 120.0 | C17—C19—H19B | 109.5 |
C5—C4—H4 | 120.0 | H19A—C19—H19B | 109.5 |
N2—C5—C4 | 120.7 (3) | C17—C19—H19C | 109.5 |
N2—C5—C6 | 115.8 (3) | H19A—C19—H19C | 109.5 |
C4—C5—C6 | 123.5 (3) | H19B—C19—H19C | 109.5 |
N3—C6—C7 | 121.2 (3) | C17—C20—H20A | 109.5 |
N3—C6—C5 | 115.0 (3) | C17—C20—H20B | 109.5 |
C7—C6—C5 | 123.8 (3) | H20A—C20—H20B | 109.5 |
C8—C7—C6 | 119.8 (3) | C17—C20—H20C | 109.5 |
C8—C7—H7 | 120.1 | H20A—C20—H20C | 109.5 |
C6—C7—H7 | 120.1 | H20B—C20—H20C | 109.5 |
C7—C8—C9 | 118.6 (3) | Cl3—C21—Cl4 | 107.9 (9) |
C7—C8—H8 | 120.7 | Cl4i—C21—H21A | 106 (10) |
C9—C8—H8 | 120.7 | Cl3—C21—H21A | 101 (10) |
C10—C9—C8 | 119.3 (3) | Cl4—C21—H21A | 103 (10) |
C10—C9—H9 | 120.4 | Cl4i—C21—H21B | 123 (10) |
C8—C9—H9 | 120.4 | Cl3—C21—H21B | 112 (10) |
N3—C10—C9 | 122.6 (3) | Cl4—C21—H21B | 118 (10) |
N3—C10—H10 | 118.7 | H21A—C21—H21B | 113 (10) |
Symmetry code: (i) −x+1, −y+1, −z. |
D—H···A | D—H | H···A | D···A | D—H···A |
C18—H18A···O1 | 0.98 | 2.53 | 3.492 (4) | 167 |
C18—H18A···N1 | 0.98 | 2.41 | 3.070 (5) | 124 |
C19—H19C···Cl1 | 0.98 | 2.82 | 3.762 (4) | 162 |
C19—H19C···N1 | 0.98 | 2.39 | 3.036 (5) | 123 |
Experimental details
Crystal data | |
Chemical formula | [Mo(C10H13N)Cl2O(C10H8N2)]·0.5CH2Cl2 |
Mr | 528.7 |
Crystal system, space group | Orthorhombic, Pbcn |
Temperature (K) | 150 |
a, b, c (Å) | 17.4207 (2), 14.9657 (1), 16.5237 (1) |
V (Å3) | 4307.94 (6) |
Z | 8 |
Radiation type | Mo Kα |
µ (mm−1) | 1.00 |
Crystal size (mm) | 0.26 × 0.06 × 0.06 |
Data collection | |
Diffractometer | Siemens SMART |
Absorption correction | Multi-scan (Blessing, 1995) |
Tmin, Tmax | 0.651, 0.963 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 40908, 4459, 3438 |
Rint | 0.084 |
(sin θ/λ)max (Å−1) | 0.629 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.043, 0.102, 1.03 |
No. of reflections | 4459 |
No. of parameters | 280 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.64, −1.54 |
Computer programs: SMART (Siemens, 1995), SAINT (Siemens, 1995), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 1999).
D—H···A | D—H | H···A | D···A | D—H···A |
C18—H18A···O1 | 0.98 | 2.53 | 3.492 (4) | 167 |
C18—H18A···N1 | 0.98 | 2.41 | 3.070 (5) | 124 |
C19—H19C···Cl1 | 0.98 | 2.82 | 3.762 (4) | 162 |
C19—H19C···N1 | 0.98 | 2.39 | 3.036 (5) | 123 |
Acknowledgements
We are grateful to Ms T. Groutso of the University of Auckland for the data collection
References
Aakeroy, C. B., Evans, T. A., Seddon, K. R. & Palinko, I. (1999). New J. Chem. 23, 145–152. Web of Science CrossRef CAS Google Scholar
Barrie, A., Coffey, T. A., Forster, G. D. & Hogarth, G. (1999). J. Chem. Soc. Dalton Trans. p. 4159. Google Scholar
Bell, A., Clegg, W., Dyer, P. W., Elsegood, M. R. J., Gibson, V. C. & Marshall, E. L. (1994). J. Chem. Soc. Chem. Commun. pp. 2247–2248. CrossRef Web of Science Google Scholar
Blessing, R. H. (1995). Acta Cryst. A51, 33–38. CrossRef CAS Web of Science IUCr Journals Google Scholar
Bradley, D. C., Errington, R. J., Hursthouse, M. B., Short, R. L., Ashcroft, B. R., Clark, G. R., Nielson, A. J. & Rickard, C. E. F. (1987). J. Chem. Soc., Dalton Trans. pp. 2067–2075. Google Scholar
Chatt, J., Choukroun, R., Dilworth, J. R., Hyde, J., Vella, P. & Zubieta, J. (1979). Transition Met. Chem. 4, 59–63. CSD CrossRef CAS Web of Science Google Scholar
Clark, G. R., Nielson, A. J. & Rickard, C. E. F. (1996). J. Chem. Soc. Dalton Trans. pp. 4265–4268. CSD CrossRef Web of Science Google Scholar
Clegg, W., Errington, R. J., Hockless, D. C. R. & Redshaw, C. (1993). J. Chem. Soc. Dalton Trans. pp. 1965–1971. CSD CrossRef Web of Science Google Scholar
Demers, E., Maris, T., Cabana, J., Fournier, J.-H. & Wuest, J. D. (2005). Cryst. Growth Res. Des. 5, 1237–1245. Web of Science CSD CrossRef CAS Google Scholar
Desiraju, G. R. (1996). Acc. Chem. Res. 29, 441–449. CrossRef CAS PubMed Web of Science Google Scholar
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838. CrossRef CAS IUCr Journals Google Scholar
Nugent, W. A. & Mayer, J. M. (1988). In Metal-Ligand Multiple Bonds. New York: Wiley. Google Scholar
Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Web of Science CrossRef CAS IUCr Journals Google Scholar
Siemens (1995). SAINT and SMART. Siemens Analytical X-ray Instruments Inc., Madison, Wisconsin, USA. Google Scholar
This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited.
Complexes of molybdenum containing oxo and imido functions in the same molecule are still fairly rare. However they are relatively easy to prepare by a conproportionation reaction between bis-imido complexes of the form [Mo(NR)2Cl2(dme)] (dme =1,2- dimethoxyethane) and the bis-oxo complexes [Mo(O)2Cl2(dme)] (Bell et al., 1994). During attempts to prepare bis-imido complexes in which the imido ligand carried substituents on the aryl ring possessing potentially sterically hindering ortho-substituents, we reacted Na2MoO4 with two equivalents of 2-tert-butylaniline in the presence of 8 equivalents of SiMe3Cl and 4 equivalents of NEt3 in dme as solvent which is the normal protocol for producing [Mo(NR)2Cl2(dme)] complexes in good yield. A red solid was obtained which had the characteristic features of the complex. This complex was then reacted with 2,2'-bipyridine (bipy) to produce the complex [Mo(NC6H4CMe3-2)2Cl2(bipy)]. This type of complex was of interest as our studies of bis-imido tungsten complexes of the form [W(NC6H5)2Cl2(bipy)] had shown there was a steric interaction between the bipy α-H atoms and the ipso-carbon of the phenyl ring (Bradley et al., 1987). Whereas the imido ligand nitrogen atoms were bent away from each other as expected, the ipso-carbon atoms of the phenyl were bent inwards towards each other [W—N—C bond angles 165.6 (12) and 164.4 (12)°] apparently to reduce contact with the bipy α-H atoms. The imido ligand phenyl groups were also apparently rotated to reduce contact of the ortho-H atoms with the bipy α-H atoms. The product obtained from the reaction with bipy crystallized nicely but did not give particularly good C, H and N analytical data. The NMR spectra suggested the bulk sample was indeed [Mo(NC6H4CMe3-2)2Cl2(bipy)] but the spectra also indicated a small amount of a second species was present. A crystal picked out from the mass and subjected to an X-ray analysis was found not to be the bis-imido complex but instead the oxo-imido complex [Mo (NC6H4CMe3-2)(O)Cl2(bipy)](1). The oxo-imido function could have arisen as a by-product during the preparation of [Mo(NC6H4CMe3 2)2Cl2(dme)] by incomplete oxo-imido exchange or by hydrolysis of one of the imido functions during the exchange of the dme ligand for the bipy ligand as this ligand was not dried after obtaining it from commercial sources.
The structure of (1) consists of a distorted-octahedral array about the molybdenum atom with a cis-orientation of the organoimido and oxo ligands, trans-chloro ligands and the nitrogen atoms of the bipyridyl ligand lying trans to the organoimido and oxo ligands (Fig. 1). The overall structure is similar to that observed for the tungsten-bipy complex [WCl2(NCMe3)(O)(bipy)] (Clegg et al., 1993) and also the molybdenum complexes [MoCl2(NH)(O)(OPPh2Et)] (Chatt et al. 1979) and [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] (Clark et al. 1996). The Mo—Nimido bond length [1.735 (3) Å] and Mo—Ooxo bond length [1.686 (2) Å] are similar to those found in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [1.756 (7) and 1.700 (6) Å] (Clark et al. 1996). The Mo—Cl(1) bond length [2.3580 (9) Å] is slightly shorter than the Mo—Cl(2) bond length [2.3745 (9) Å]. The longer Mo—Cl bond length is similar in distance to the shorter Mo—Cl bond in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [2.375 (3) Å] but both bonds are shorter than those found in [MoCl2(NH)(O)(OPPh2Et)] [average 2.391 (7) Å] or the bis-imido complex [MoCl2(NC10H15)(NC6F5)(dme)] (C10H15 = adamantyl) [average 2.397 (2) Å] (Bell et al. 1994). The Mo—N bond trans to the oxo ligand is slightly longer than that trans to the imido function [2.283 (3) and 2.255 (3) Å respectively] which suggests that the oxo ligand may exert the stronger trans -influence (Nugent & Mayer, 1988). However this may not be a trans -influence effect as there are close approaches of the two α-hydrogen atoms of the bipy ligand with other parts of the molecule.
The N(1)—Mo—O(1) bond angle [104.7 (1)°] and Cl(1)—Mo—Cl(2) bond angle [160.08 (3)°] in (1) are similar to those found in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [bond angles 104.2 (4) and 159.7 (1)° respectively] and the two chloro ligands push away from both the Mo—O(1) and Mo—N(1) multiple bonds. In this respect, the O(1)—Mo—Cl(1) and O(1)—Mo—Cl(2) bond angles (oxo ligand and chloro ligands) are essentially equivalent [96.83 (8) and 97.41 (8)° respectively] but the N(1)—Mo—Cl(1) angle [99.78 (9)°] is greater than the N(1)—Mo—Cl(2) angle [90.00 (9)°] and this appears to be related to a steric effect arising from the proximity of the 2-tert-butyl substituent on the imido ligand aryl ring (see later). The angles associated with the coordinated nitrogen atoms of the bipy rings show there is nothing unusual for the way this ligand coordinates to the metal with the O(1)—Mo—N(3), N(1)—Mo—N(2) and N(2)—Mo—N(3) bond angles [159.2 (1), 164.4 (1) and 69.97 (9)° respectively] being similar to those found for [WCl2(NCMe3)(O)(bipy)] [157.9 (2), 165.9 (2) and 69.1 (2)° respectively] (Clegg et al., 1993) or for the bis-imido tungsten complex [WCl2(NPh)2(bipy)] [161.2 (5), 164.3 (5) and 69.8 (4)° respectively] (Bradley et al. 1987). These angles do not differ significantly from those associated with the coordination mode of the 1,2-dimethoxyethane ligand in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)]- [Ooxo—Mo—O, Nimido—Mo—O and O—Mo—O angles 160.3 (3), 165.9 (3) and 70.6 (2) respectively]. The coordinated bipy ligand is essentially planar with the difference between the two planes made by the two rings being only 3.9 (2)°.
The phenyl ring of the organoimido ligand is bent back towards Cl(2) and also N(3) of the bipy ring with the Mo—N(1)—C(11) bond angle being 165.8 (2)ωhich is smaller than in [MoCl2(NC6H2Ph3-2,4,6)(O)(dme)] [172.2 (7)°] (Clark et al., 1996) and the tungsten bipy analogue [WCl2(NCMe3)(O)(bipy)] [170.6 (5)°] (Clegg et al., 1993) but similar to that found in the bis-imido complexes [Mo(NC6H3Cl2-2,6)(S2CNEt2)2][162.2 (7) and 162.9 (7)/%] (Barrie et al., 1999) and [WCl2(NPh)2(bipy)] [165.6 (12) and 164.4 (11)°] (Bradley et al., 1987). However in these complexes the M—N—C bond angles are such that the phenyl or alkyl group bends in towards the adjacent oxo or imido ligand whereas in the present complex the bend is away from the oxo ligand. This appears to be caused by the tert-butyl substituent which in the crystal prefers to orientate over Cl(1) and O(1) rather than Cl(2) and O(1) which appears to be another possible orientation (Fig 1). The rotation of the organoimido phenyl ring is such that the plane of the ring deviates from the plane made by the bipy rings by 46.5 (1)° (Fig 1). The orientation of the phenyl ring and the orientation of the 2-tert-butyl substituent has some interesting consequences for intramolecular contacts. For the 2-tert-butyl substituent the rotation about C(16) and C(17) is such that one of the equatorially positioned methyl groups [C(18)] lies directly above the oxo ligand and H(18a) makes a contact of 2.53 Å with it. This distance lies within the range of distances considered to involve weak hydrogen bonding to oxygen atoms (Desiraju, 1996)). There is an even shorter separation of 2.41 Å between H(18) and the imido nitrogen atom, N(1) and the separation is well within the range of values considered to involve weak hydrogen bonding to nitrogen [2.65%A (Demers et al., 2005)]. It is interesting to note that even though the nitrogen lone pair will be mostly involved in donation to molybdenum to make the imido ligand multiple bond, the bend made by the Mo—N(1)—C(11) system [165.8 (2)°] is such that any remaining lone pair is pointing in the direction of H(18a). The other equatorially positioned methyl group of the 2-tert-butyl substituent lies above Cl(1) with the H(19c) to Cl(1) separation of 2.82 Å. This distance is also within the range of values suggested as weak hydrogen bonding to chlorine (Aakeroy et al. 1999). The separation between H(19c) and the imido nitrogen N(1) is 2.39Å which suggests potential weak hydrogen bonding may also be involved. There is a similar approach of H(18a) to N1 (2.41 Å). However it should be realised that these close approaches are forced on the system by the molecular geometry of the tert-butyl group which may or may not imply the existence of attractive H-bonding. The remaining methyl group of the 2-tert-butyl substituent, which lies in an axial position, is rotated to give a gearing effect which removes any interaction of the H atoms with the nearest neighbour H atoms. Thus H(20a) is positioned so as to bisect the C(18)—C(17)—C(19) angle and this allows H(20b) and H(20c) to lie in front of, but to either side of, the bipy α-hydrogen H(15). As a result of the positioning of the 2-tert-butyl substituent, H(12), which lies in the other ortho-position of the aromatic ring, makes a close contact with Cl(2) with the distance of 3.06 Å being just outside the limit of the H and Cl van der Waals radii (3.0 Å) but still representing a weak hydrogen bond (Aakeroy, 1999). H(12) also makes a close contact of 2.52 Å with the α-hydrogen of the nearby bipy ring which is just outside the van der waals radii of 2.4 Å (Aakeroy, 1999). On the other side of the molecule there is a close approach of the weak hydrogen bonding type, for H(1) which is the other α-hydrogen of the bipy ring, with the terminal oxo ligand oxygen [O(1)]. This arises since the bipy rings are essentially co-planar with the Mo—O multiple bond. The atomic separation is 2.44 Å which is even shorter than the distance the 2-tert-butyl substituent H(18a) atom makes with O(1) (2.53 Å). The separation for this type of interaction in [WCl2(NCMe3)(O)(bipy)] is 2.42 Å (Clegg, et al., 1993). There are no other significant intramolecular contacts in the structure. The disordered partial CH2Cl2 molecule lies across a centre of symmetry in the crystal lattice but its H atoms make no significant approaches to the chlorine complex.