supplementary materials


sj5366 scheme

Acta Cryst. (2013). E69, m654    [ doi:10.1107/S1600536813030328 ]

Tetra­chlorido­[N2,N2'-(di­methyl­silanedi­yl)bis­(N-tert-butyl-3-methyl­benzimid­amid­ato)-[kappa]2N2,N2']hafnium(IV)

T. Wang, J.-P. Zhao and S.-D. Bai

Abstract top

The symmetric title mol­ecule, [Hf(C26H40N4Si)Cl4], lies about a twofold rotation axis. The HfIV and Si atoms lie on the rotation axis with all other atoms being in general positions. The HfIV atom is six-coordinated by two N atoms from the N2,N2'-(di­methyl­silanedi­yl)bis­(N-tert-butyl-3-methyl­benz­imid­amidate) ligand and four Cl- ions in a slightly distorted octa­hedral geometry. The two amidinate moieties are connected through the central Si atom with Si-N bond length of 1.762 (3) Å, generating the characteristic N-C-N-Si-N-C-N skeleton of a silyl-linked ansa-bis­(amidine) species.

Comment top

Anionic N,N-chelating amidinate ligands, have been widely used in the synthesis of organometallic complexes of the s-, p-, d-, and f-block metals for a number of years (Edelmann, 2012; Münch et al., 2008). Their steric and electronic properties can easily be modified by a simple variation of the substitution pattern (Liu et al., 2013; Qian et al., 2010). In the search for ancillary ligands to replace cyclopentadienyls to create non-metallocene species, amidinate anions have found many applications in coordination chemistry, and also as ancillary ligands to form metal complexes which act as catalysts in organic transformations and ethylene polymerizations (Lei et al., 2011).

Linked bis(amidinate) ligands are a very special branch of this class of compound and their chemistry has been developed in recent years. We explored a class of silyl linked bis(amidinate) ligands, and applied them to the synthesis of metal complexes. They imposed a close contact between the two amidinate moieties and had the advantage of affording binuclear complexes analogous to an "ansa-metallocene" (Bai et al., 2013). Here, the synthesis and characterization of the Hf(IV) complex SiMe2[NC(m-MePh)N(But)H]2HfCl4 bearing the silyl-linked ansa-bis(amidine) ligands will be described.

N',N''-(dimethylsilanediyl)bis(N-tert-butyl-3-methylbenzimidamide SiMe2[NC(m-MePh)NH(tBu)]2 was prepared by treating tBuNH2 with one equivalent of LiBun, m-MePhCN, and half equivalent of SiMe2Cl2 in a one-pot reaction. Treating the ansa-bis(amidine) SiMe2[NC(m-MePh)NH(tBu)]2 with HfCl4 in CH2Cl2 gave the title compound. Crystals suitable for X–ray investigation were obtained by recrystallization from toluene and its molecular structure is presented in Fig. 1. It is a symmetric molecule lying about a 2-fold rotation axis (e in Wyckoff notation). The Hf1 and Si1 atoms lie on this axis with all other atoms on general positions. The two amidinate moieties connect the central Si atom with Si–N2 distances 1.762 (3) Å, which matched our original proposal of forming a dianionic N–C–N–Si–N–C–N framework. The structure shows that all the substituents and the silyl bridge are on the same side of the N—C—N skeletons, resulting in two E-anti forms of the amidinate units. The two inner nitrogen atoms bind to Hf1 at a distance of 2.233 (3) Å, and the N2—Hf2—N2i angle is 69.28 (11)° (i = -x + 1, y, -z + 1/2). The Hf center also exhibits a slightly distorted octahedral geometry.

Related literature top

For reviews of related amidinate ligands and their applications, see: Edelmann (2012); Lei et al. (2011); Münch et al. (2008). For a review of the modification of the steric and electronic properties of amidinate ligands by varying their substitution patterns, see: Liu et al. (2013); Qian et al. (2010). For related silyl-linked bis (amidinate) ligands and the synthesis of their metal complexes, including a closely related Hf complex, see: Bai et al. (2013).

Experimental top

A solution of LiBun (2.2 M, 2.27 ml, 5.0 mmol) in hexane was added to a stirred solution of tBuNH2 (0.53 ml, 5.0 mmol) in THF (ca 30 ml) by syringe at 273 K. The reaction mixture was warmed to room temperature and kept stirring for 4 h and then m-MePhCN (0.59 ml, 5.0 mmol) was added by syringe at 273 K. The reaction mixture was warmed to room temperature and kept stirring for 4 h. Then SiMe2Cl2 (0.3 ml, 2.55 mmol) was added by syringe at 273 K. After stirring at room temperature for 4 h, it was dried in vacuum to remove all volatiles. The residue was extracted with CH2Cl2 (30 ml) and then HfCl4 (0.812 g, 2.5 mmol) was added to this stirred solution at 273 K. The reaction mixture was warmed to room temperature, after stirring for 4 h the solution was dried in vacuum to remove all volatiles. The residue was dissolved with toluene and then concentrated to yield colorless crystals of the title compound. Yield: 0.422 g (22.3%). 1H NMR (30 MHz, CDCl3) δ (p.p.m.): 8.813 (s, 2H; NH), 7.398, 7.204 (d, 8H; m-Mephenyls), 2.511 (s, 6H; m-Mephenyls), 1.034 (s, 18H; tBu), -0.272 (s, 6H; SiMe2). 13C NMR (75 MHz, CDCl3) δ (p.p.m.): 172.566 (N-C-N), 139.174–126.831 (m-Mephenyl), 78.569–77.724 (m-Mephenyls), 57.109 (CMe3), 32.080, 22.363 (CMe3), 3.012 (SiMe2). Anal. Calcd. for C26H40Cl4HfN4Si (Mr = 757.00): C, 45.25; H, 5.33; N, 3.30%. Found: C, 45.56; H, 5.48; N, 3.44%.

Refinement top

The methyl H atoms were constrained to an ideal geometry, with C—H distances of 0.96 Å and Uiso(H) = 1.5Ueq(C), but each group was allowed to rotate freely about its C–C and C–Si bonds. The amino H atoms were constrained with N—H distances of 0.86 Å and Uiso(H) = 1.2Ueq(N). The phenyl H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C—H distances of 0.93 Å and Uiso(H) = 1.2Ueq(C).

Computing details top

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL/PC (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. The molecular structure, showing the atom–numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.
Tetrachlorido[N2,N2'-(dimethylsilanediyl)bis(N-tert-butyl-3-methylbenzimidamide)-κ2N2,N2']hafnium(IV) top
Crystal data top
[Hf(C26H40N4Si)Cl4]F(000) = 1512
Mr = 757Dx = 1.524 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2ycCell parameters from 2487 reflections
a = 9.4373 (14) Åθ = 2.5–22.1°
b = 17.992 (3) ŵ = 3.54 mm1
c = 19.966 (3) ÅT = 296 K
β = 103.276 (3)°Block, colorless
V = 3299.5 (8) Å30.08 × 0.05 × 0.05 mm
Z = 4
Data collection top
Bruker SMART area-detector
diffractometer
2920 independent reflections
Radiation source: fine-focus sealed tube2446 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.035
φ and ω scansθmax = 25.1°, θmin = 2.3°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 117
Tmin = 0.765, Tmax = 0.843k = 2119
7121 measured reflectionsl = 2323
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.028Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.061H-atom parameters constrained
S = 1.02 w = 1/[σ2(Fo2) + (0.0266P)2]
where P = (Fo2 + 2Fc2)/3
2920 reflections(Δ/σ)max = 0.001
169 parametersΔρmax = 0.53 e Å3
0 restraintsΔρmin = 0.29 e Å3
Crystal data top
[Hf(C26H40N4Si)Cl4]V = 3299.5 (8) Å3
Mr = 757Z = 4
Monoclinic, C2/cMo Kα radiation
a = 9.4373 (14) ŵ = 3.54 mm1
b = 17.992 (3) ÅT = 296 K
c = 19.966 (3) Å0.08 × 0.05 × 0.05 mm
β = 103.276 (3)°
Data collection top
Bruker SMART area-detector
diffractometer
2920 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
2446 reflections with I > 2σ(I)
Tmin = 0.765, Tmax = 0.843Rint = 0.035
7121 measured reflectionsθmax = 25.1°
Refinement top
R[F2 > 2σ(F2)] = 0.028H-atom parameters constrained
wR(F2) = 0.061Δρmax = 0.53 e Å3
S = 1.02Δρmin = 0.29 e Å3
2920 reflectionsAbsolute structure: ?
169 parametersAbsolute structure parameter: ?
0 restraintsRogers parameter: ?
Special details top

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Hf10.50000.540155 (12)0.25000.03621 (10)
Cl10.63951 (14)0.53649 (6)0.36889 (6)0.0584 (3)
Cl20.33063 (15)0.63063 (6)0.27686 (7)0.0666 (4)
Si10.50000.37014 (8)0.25000.0430 (4)
N10.2205 (4)0.47999 (19)0.33427 (18)0.0510 (10)
H10.21860.51760.30740.061*
N20.3964 (3)0.43808 (16)0.28086 (16)0.0363 (8)
C10.1179 (5)0.4877 (3)0.3814 (2)0.0589 (13)
C20.2003 (7)0.4884 (4)0.4547 (3)0.120 (3)
H2A0.23350.43900.46830.180*
H2B0.13790.50550.48330.180*
H2C0.28250.52100.45960.180*
C30.0055 (7)0.4271 (3)0.3680 (4)0.112 (3)
H3A0.03780.42460.31960.168*
H3B0.06850.43750.39260.168*
H3C0.05090.38040.38320.168*
C40.0435 (7)0.5621 (3)0.3634 (3)0.0891 (19)
H4A0.11460.60120.37320.134*
H4B0.02790.56930.39010.134*
H4C0.00330.56300.31530.134*
C50.3128 (4)0.4280 (2)0.32526 (19)0.0337 (9)
C60.3272 (5)0.3587 (2)0.3673 (2)0.0415 (10)
C70.4307 (5)0.3561 (2)0.4283 (2)0.0510 (11)
H70.48600.39840.44290.061*
C80.4556 (7)0.2921 (3)0.4691 (3)0.0682 (15)
C90.3727 (8)0.2312 (3)0.4451 (3)0.089 (2)
H90.38670.18790.47120.107*
C100.2714 (8)0.2312 (3)0.3850 (3)0.088 (2)
H100.21820.18830.37060.105*
C110.2455 (6)0.2957 (2)0.3440 (3)0.0652 (14)
H110.17600.29600.30260.078*
C120.5689 (8)0.2921 (4)0.5360 (3)0.112 (2)
H12A0.57690.24300.55540.167*
H12B0.54080.32640.56740.167*
H12C0.66110.30680.52760.167*
C130.6240 (6)0.3125 (3)0.3154 (2)0.0676 (15)
H13A0.69200.28720.29430.101*
H13B0.56810.27680.33400.101*
H13C0.67610.34390.35170.101*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Hf10.04771 (16)0.03029 (14)0.03166 (14)0.0000.01126 (11)0.000
Cl10.0724 (8)0.0574 (7)0.0391 (6)0.0115 (6)0.0002 (5)0.0005 (5)
Cl20.0921 (10)0.0479 (7)0.0683 (8)0.0238 (7)0.0361 (8)0.0044 (6)
Si10.0556 (11)0.0302 (8)0.0490 (11)0.0000.0241 (9)0.000
N10.056 (2)0.056 (2)0.048 (2)0.0136 (19)0.0266 (19)0.0120 (17)
N20.0409 (19)0.0351 (17)0.0345 (18)0.0027 (15)0.0123 (16)0.0020 (14)
C10.054 (3)0.080 (3)0.049 (3)0.014 (3)0.025 (2)0.000 (2)
C20.109 (5)0.207 (7)0.044 (4)0.072 (5)0.018 (4)0.010 (4)
C30.096 (5)0.095 (4)0.174 (8)0.010 (4)0.093 (5)0.014 (5)
C40.091 (4)0.092 (4)0.100 (5)0.042 (4)0.055 (4)0.014 (3)
C50.035 (2)0.037 (2)0.028 (2)0.0086 (19)0.0047 (18)0.0062 (16)
C60.058 (3)0.036 (2)0.039 (3)0.004 (2)0.028 (2)0.0045 (18)
C70.061 (3)0.047 (3)0.048 (3)0.000 (2)0.020 (2)0.005 (2)
C80.097 (4)0.062 (3)0.054 (3)0.020 (3)0.035 (3)0.015 (3)
C90.174 (7)0.041 (3)0.076 (4)0.008 (4)0.076 (5)0.011 (3)
C100.160 (7)0.041 (3)0.080 (4)0.033 (3)0.062 (5)0.015 (3)
C110.085 (4)0.058 (3)0.061 (3)0.023 (3)0.032 (3)0.013 (3)
C120.134 (6)0.123 (5)0.072 (5)0.036 (5)0.013 (4)0.039 (4)
C130.084 (4)0.062 (3)0.071 (4)0.030 (3)0.045 (3)0.025 (3)
Geometric parameters (Å, º) top
Hf1—N22.233 (3)C3—H3C0.9600
Hf1—N2i2.233 (3)C4—H4A0.9600
Hf1—Cl2i2.4261 (11)C4—H4B0.9600
Hf1—Cl22.4261 (11)C4—H4C0.9600
Hf1—Cl1i2.4366 (11)C5—C61.491 (5)
Hf1—Cl12.4366 (11)C6—C71.377 (6)
Hf1—Si13.0588 (16)C6—C111.390 (6)
Si1—N2i1.762 (3)C7—C81.399 (6)
Si1—N21.762 (3)C7—H70.9300
Si1—C13i1.857 (5)C8—C91.368 (8)
Si1—C131.857 (5)C8—C121.507 (8)
N1—C51.318 (5)C9—C101.351 (8)
N1—C11.504 (5)C9—H90.9300
N1—H10.8600C10—C111.409 (7)
N2—C51.327 (5)C10—H100.9300
C1—C21.491 (7)C11—H110.9300
C1—C31.502 (7)C12—H12A0.9600
C1—C41.516 (7)C12—H12B0.9600
C2—H2A0.9600C12—H12C0.9600
C2—H2B0.9600C13—H13A0.9600
C2—H2C0.9600C13—H13B0.9600
C3—H3A0.9600C13—H13C0.9600
C3—H3B0.9600
N2—Hf1—N2i69.32 (16)H2A—C2—H2C109.5
N2—Hf1—Cl2i164.88 (9)H2B—C2—H2C109.5
N2i—Hf1—Cl2i97.96 (9)C1—C3—H3A109.5
N2—Hf1—Cl297.96 (9)C1—C3—H3B109.5
N2i—Hf1—Cl2164.88 (9)H3A—C3—H3B109.5
Cl2i—Hf1—Cl295.71 (6)C1—C3—H3C109.5
N2—Hf1—Cl1i94.22 (9)H3A—C3—H3C109.5
N2i—Hf1—Cl1i83.21 (9)H3B—C3—H3C109.5
Cl2i—Hf1—Cl1i92.23 (4)C1—C4—H4A109.5
Cl2—Hf1—Cl1i89.86 (4)C1—C4—H4B109.5
N2—Hf1—Cl183.21 (9)H4A—C4—H4B109.5
N2i—Hf1—Cl194.22 (9)C1—C4—H4C109.5
Cl2i—Hf1—Cl189.86 (4)H4A—C4—H4C109.5
Cl2—Hf1—Cl192.23 (4)H4B—C4—H4C109.5
Cl1i—Hf1—Cl1176.89 (5)N1—C5—N2120.5 (3)
N2—Hf1—Si134.66 (8)N1—C5—C6119.6 (3)
N2i—Hf1—Si134.66 (8)N2—C5—C6119.9 (3)
Cl2i—Hf1—Si1132.14 (3)C7—C6—C11119.6 (4)
Cl2—Hf1—Si1132.14 (3)C7—C6—C5118.7 (4)
Cl1i—Hf1—Si188.45 (3)C11—C6—C5121.5 (4)
Cl1—Hf1—Si188.45 (3)C6—C7—C8122.2 (5)
N2i—Si1—N292.2 (2)C6—C7—H7118.9
N2i—Si1—C13i116.87 (18)C8—C7—H7118.9
N2—Si1—C13i108.80 (19)C9—C8—C7116.7 (5)
N2i—Si1—C13108.80 (19)C9—C8—C12122.9 (5)
N2—Si1—C13116.87 (18)C7—C8—C12120.4 (5)
C13i—Si1—C13112.1 (3)C10—C9—C8122.8 (5)
N2i—Si1—Hf146.09 (10)C10—C9—H9118.6
N2—Si1—Hf146.09 (10)C8—C9—H9118.6
C13i—Si1—Hf1123.93 (17)C9—C10—C11120.6 (5)
C13—Si1—Hf1123.93 (17)C9—C10—H10119.7
C5—N1—C1133.8 (4)C11—C10—H10119.7
C5—N1—H1113.1C6—C11—C10117.9 (5)
C1—N1—H1113.1C6—C11—H11121.0
C5—N2—Si1127.0 (3)C10—C11—H11121.0
C5—N2—Hf1131.4 (2)C8—C12—H12A109.5
Si1—N2—Hf199.25 (14)C8—C12—H12B109.5
C2—C1—C3111.6 (5)H12A—C12—H12B109.5
C2—C1—N1110.4 (4)C8—C12—H12C109.5
C3—C1—N1110.6 (4)H12A—C12—H12C109.5
C2—C1—C4109.5 (5)H12B—C12—H12C109.5
C3—C1—C4109.2 (5)Si1—C13—H13A109.5
N1—C1—C4105.2 (4)Si1—C13—H13B109.5
C1—C2—H2A109.5H13A—C13—H13B109.5
C1—C2—H2B109.5Si1—C13—H13C109.5
H2A—C2—H2B109.5H13A—C13—H13C109.5
C1—C2—H2C109.5H13B—C13—H13C109.5
Symmetry code: (i) x+1, y, z+1/2.
Selected bond lengths (Å) top
Hf1—N22.233 (3)Si1—C131.857 (5)
Hf1—Cl22.4261 (11)N1—C51.318 (5)
Hf1—Cl12.4366 (11)N1—C11.504 (5)
Hf1—Si13.0588 (16)N1—H10.8600
Si1—N21.762 (3)
Acknowledgements top

We acknowledge financial support by the Natural Science Foundation of China (20702029) and the Natural Science Foundation of Shanxi Province (2008011024).

references
References top

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