[Journal logo]

Volume 70 
Part 2 
Pages 165-168  
February 2014  

Received 23 September 2013
Accepted 2 January 2014
Online 9 January 2014

Bis{2-[(3,5-diphenyl-1H-pyrrol-2-yl­idene-[kappa]N)amino]-3,5-di­phenyl­pyrrol-1-ido-[kappa]N}palladium(II): a homoleptic four-coordinate tetra­phenyl­aza­di­pyrromethene complex of palladium

aDepartment of Pharmaceutical and Medicinal Chemistry, Royal College of Surgeons in Ireland, 123 St Stephen's Green, Dublin 2, Ireland, and bSchool of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland
Correspondence e-mail: paul.evans@ucd.ie, donalfoshea@rcsi.ie

The structural chemistry of the title compound, [Pd(C32H22N3)2], at 173 K is described. The compound is com­prised of two deprotonated (3,5-diphenyl-1H-pyrrol-2-yl)(3,5-di­phenyl­pyrrol-2-yl­idene)amine ligands coordinated to a central PdII cation, which lies on an inversion centre and has distorted square-planar geometry. The Pd-N bond lengths range from 2.008 (4) to 2.014 (4) Å and the bite angle is 84.16 (14)°. The chelate plane makes a dihedral angle of 45.3 (2)° with respect to the central PdN4 plane, giving a stepped conformation to the mol­ecule. The complex displays simple intra­molecular C-H...N hydrogen bonds, while the unit cell consists of discrete monomeric Pd(C32H22N3)2 units which display inter­molecular C-H...[pi] inter­actions and limited intra- and inter­molecular [pi]-[pi] stacking.

1. Introduction

Bidentate aza­dipyrromethenes are a developing class of organic ligands valued for their spectroscopic properties as chromophores in the visible red and near-infrared (NIR) spectroscopic regions (Teets et al., 2008[Teets, T. S., Partyka, D. V., Updegraff, J. B. III & Gray, T. G. (2008). Inorg. Chem. 47, 2338-2346.], 2009[Teets, T. S., Updegraff, J. B. III, Esswein, A. J. & Gray, T. G. (2009). Inorg. Chem. 48, 8134-8144.]; Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]). The use of this class of compound as a framework for coordination of a BF2 chelate confers sufficient structural rigidity on the resultant compound to limit radiation-less transitions and allow the exploitation of excited states (Hall et al., 2005[Hall, M. J., McDonnell, S. O., Killoran, J. & O'Shea, D. F. (2005). J. Org. Chem. 70, 5571-5578.], 2006[Hall, M. J., Allen, L. T. & O'Shea, D. F. (2006). Org. Biomol. Chem. 4, 776-780.]; McDonnell & O'Shea, 2006[McDonnell, S. O. & O'Shea, D. F. (2006). Org. Lett. 8, 3493-3496.]). In particular, the excellent photostability, high extinction coefficients and high fluorescence quantum yields observed in BF2-chelated tetra­aryl­aza­dipyrromethenes have encouraged their study and potential application in photodynamic therapy, fluorescent chemosensors and in vitro fluoro­phores (Killoran et al., 2002[Killoran, J., Allen, L., Gallagher, J. F., Gallagher, W. M. & O'Shea, D. F. (2002). Chem. Commun. pp. 1862-1863.]; McDonnell & O'Shea, 2006[McDonnell, S. O. & O'Shea, D. F. (2006). Org. Lett. 8, 3493-3496.]; Loudet et al., 2008[Loudet, A., Badnichhor, R., Burgess, K., Palma, A., McDonnell, S. O., Hall, M. J. & O'Shea, D. F. (2008). Org. Lett. 10, 4771-4774.]; Frimannsson et al., 2010[Frimannsson, D. O., Grossi, M., Murtagh, J., Paradisis, F. & O'Shea, D. F. (2010). J. Med. Chem. 53, 7337-7343.]; Palma et al., 2011[Palma, A., Alvarez, L. A., Scholz, D., Frimannsson, D. O., Grossi, M., Quinn, S. J. & O'Shea, D. F. (2011). J. Am. Chem. Soc. 133, 19618-19621.], and references therein). It is these photophysical characteristics and the ability to incorporate readily other metals into the organic framework that has led to the exploration of their transition metal complexes in efforts to attune the photophysical properties and lead to new potential catalysts, and optical data storage and electrochromic devices (Teets et al., 2008[Teets, T. S., Partyka, D. V., Updegraff, J. B. III & Gray, T. G. (2008). Inorg. Chem. 47, 2338-2346.], 2009[Teets, T. S., Updegraff, J. B. III, Esswein, A. J. & Gray, T. G. (2009). Inorg. Chem. 48, 8134-8144.]; Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]). However, despite being known in the literature [the tetra­aryl­aza­dipyrromethene used in this study was first reported by Rogers (1943[Rogers, M. A. T. (1943). J. Chem. Soc. pp. 590-596.])], and unlike the analogous dipyrrin class of compounds (Wood & Thompson, 2007[Wood, T. E. & Thompson, A. (2007). Chem. Rev. 107, 1831-1861.]), metal complexes of tetra­aryl­aza­dipyrromethenes remain limited in the literature to a few examples of tricoordinate group 11 (CuI, AgI and AuI) (Teets et al., 2009[Teets, T. S., Updegraff, J. B. III, Esswein, A. J. & Gray, T. G. (2009). Inorg. Chem. 48, 8134-8144.]) and first-row bidentate (CoII, CuII, NiII and ZnII) complexes (Teets et al., 2008[Teets, T. S., Partyka, D. V., Updegraff, J. B. III & Gray, T. G. (2008). Inorg. Chem. 47, 2338-2346.]; Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]; Bessette et al., 2012[Bessette, A., Ferreira, J. G., Giguère, M., Bélanger, F., Désilets, D. & Hanan, G. S. (2012). Inorg. Chem. 51, 12132-12141.]). In the latter case, the aim of the study was to detect any potential impact of inter-ligand and metal-ligand sterics and subsequent effects on spectroscopic properties. Herein, we describe an extension of this early work in the synthesis and structural chemistry of the first structurally characterized PdII-tetra­aryl­aza­dipyrromethene complex, the title compound, (II)[link].

[Scheme 1]
[Figure 1]
Figure 1
(a) The mol­ecular structure of (II)[link], showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. (b) A view of the PdN4 coordination plane and the N-C-N-C-N chelation plane geometry, showing the stepped conformation between the chelation planes of the ligands and the Pd atom. (c) A view looking down the N1/N3 vector, showing the puckering of the pyrrolide rings with respect to the chelation plane. [Symmetry code: (i) -x + 2, -y + 2, -z.]
[Figure 2]
Figure 2
The unit-cell packing in (II)[link], viewed down a. The N and Pd atoms are represented by small ellipsoids drawn at the 50% probability level, while C atoms are represented by large spheres of arbitary size. H atoms have been omitted for clarity.

2. Experimental

2.1. Synthesis and crystallization

Pd(OAc)2 (30 mg, 0.134 mmol, 1.03 equivalents) was added to a stirred solution of ligand (I)[link] (58 mg, 0.130 mmol, 1 equivalent) in AcOH (5 ml) and heated at 373 K for 2 h with vigorous stirring. The dark-coloured solution was then cooled to room temperature, CH2Cl2 (25 ml) and H2O (25 ml) were added, the product was extracted with CH2Cl2 (2 × 15 ml) and the combined organic phases were dried over MgSO4. The solution was filtered and the solvent removed in vacuo, and the product was purified by flash column chromatography on silica gel with cyclo­hexane-EtOAc (19:1 v/v) to give the product, (II)[link], as a metallic brown solid [yield 41 mg, 63%; RF = 0.15 (cyclo­hexane-EtOAc; 19:1 v/v)]. 1H NMR (300 MHz, CDCl3): [delta] 6.91 (1H, s), 7.15-7.19 (3H, m), 7.39 (1H, t, J = 7.5 Hz), 7.53 (2H, t, J = 7.5 Hz), 7.72-7.78 (2H, m), 8.39 (2H, d, J = 7.5 Hz); (ES+) m/z 554 [M - L]+, 554 (C32H22N3106Pd 554); UV-Vis (CH2Cl2): [lambda]max 611 nm.

Obtaining a crystal of (II)[link] suitable for X-ray analysis was challenging, but one was grown by the slow evaporation of a CH2Cl2 solution of (II)[link]. The majority of the compound failed to give crystals and was obtained as a noncrystalline gum.

2.2. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1[link]. H atoms were placed in calculated positions and refined using a riding model, with C-H = 0.95 Å and Uiso(H) = 1.2Ueq(C). The phenyl ring defined by atoms C5-C10 shows some indication of disorder, particularly the elongated displacement ellipsoids for atoms C8, C9 and C10. Attempts to model and refine the disorder using restraints led to unreasonably high correlations; it was thus decided to retain an ordered model. The initial rapid data collected at the start of the experiment suggested that the crystal would be very weakly diffracting at high [theta] angles, so that the chosen [theta]max for the full data collection was set lower than normally desired. Upon completion of the data collection, it was unfortunately not recognized that additional significant reflection intensities might have been available at higher angles.

3. Results and discussion

The mol­ecular structure of (II)[link] and the atom-labelling scheme are shown in Fig. 1[link](a), with selected geometric parameters listed in Table 2[link]. Complex (II)[link] crystallizes as brown prism-shaped crystals in the space group P21/c (No. 14) with two inverted N,N'-bidentate chelating tetra­aryl­aza­di­pyrro­methene ligands. The PdII cation is located on a crystallographic inversion centre (with one half of the mol­ecule residing in the asymmetric unit), tetra­coordinated by two pyrrole N atoms of each ligand.

In spite of the two sterically bulky ligands, a distorted square-planar geometry is observed at the metal centre, with angles falling in the range 84-96° for various groupings of N-M-N angles (Table 2[link]). In order to maintain this preferred square-planar geometry, the N1/C1/N2/C17/N3 chelation plane is splayed back, forming a dihedral angle of 45.3 (2)° with the mean metal coordination plane (PdN4), giving the complex a stepped conformation (Fig. 1[link]b). This stepped geometry has been observed in structurally analogous PdII dipyrrin and di­pyridyl­iminate complexes (Freeman & Snow, 1965[Freeman, H. C. & Snow, M. R. (1965). Acta Cryst. 18, 843-850.]; March et al., 1971[March, F. C., Couch, D. A., Emerson, K., Fergusson, J. E. & Robinson, W. T. (1971). J. Chem. Soc. A, pp. 440-448.]; Wood & Thompson, 2007[Wood, T. E. & Thompson, A. (2007). Chem. Rev. 107, 1831-1861.]; Hall et al., 2010[Hall, J. D., McLean, T. M., Smalley, S. J., Waterland, M. R. & Telfer, S. G. (2010). Dalton Trans. 39, 437-445.]), with such a geometry predicted to be favoured over the distorted tetra­hedron detected in NiII and ZnII analogues of this ligand (Teets et al., 2008[Teets, T. S., Partyka, D. V., Updegraff, J. B. III & Gray, T. G. (2008). Inorg. Chem. 47, 2338-2346.]; Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]).

The phenyl substituents on the pyrrole rings are parallel with respect to each other and show dihedral angles of 41.4 (2) and 62.95 (17)° (pyrrole positions C2 and C18), and 53.64 (15) and 56.55 (16)° (pyrrole positions C4 and C20), with the PdN4 plane, respectively. Additionally, the phenyl substituents on the pyrrole C4 and C20 positions are almost coplanar with the chelation plane, showing dihedral angles of 8.51 (17) and 11.31 (18)°, respectively. This gives an indication that the stepped geometry of this structure can overcome the inter­molecular steric repulsions of the bulky phenyl substituents used in this study and may allow further modification of the ligand to tune the desired properties without compromising the ideal structural conformation. However, a slight deviation of the ligand from planarity was detected (Fig. 1[link]c), with a folding of the two pyrrole rings away from the chelation plane (N1/C1/N2/C17/N3) by 15.72 (18) and 16.48 (8)° along the N1-C1 and N3-C17 bonds, respectively. The chelate ring shows very minor puckering, with atom N3 lying out of the mean N1/C1/N2/C17 plane by 0.035 (9) Å, while the PdN4 coordination plane is planar. The Pd-N bond lengths of 2.014 (4) and 2.008 (4) Å observed for (II)[link] are typical for PdII complexes of this type and are related to those detected in structurally characterized palladium(II) dipyrrin, dipyrromethene and metallo-tetra­pyrrole complexes (March et al., 1971[March, F. C., Couch, D. A., Emerson, K., Fergusson, J. E. & Robinson, W. T. (1971). J. Chem. Soc. A, pp. 440-448.], 1972[March, F. C., Fergusson, J. E. & Robinson, W. T. (1972). Dalton Trans. pp. 2069-2076.]; Stolzenberg et al., 1992[Stolzenberg, A. M., Schussel, L. J., Summers, J. S., Foxman, B. M. & Petersen, J. L. (1992). Inorg. Chem. 31, 1678-1686.]; Lord et al., 2000[Lord, P. A., Olmstead, M. M. & Balch, A. L. (2000). Inorg. Chem. 39, 1128-1134.]; Wood & Thompson, 2007[Wood, T. E. & Thompson, A. (2007). Chem. Rev. 107, 1831-1861.]).

Comparison of the data for the free (3,5-diphenyl-1H-pyrrol-2-yl)(3,5-di­phenyl­pyrrol-2-yl­idene)amine ligand, (I)[link] (Bandi et al., 2013[Bandi, V., El-Khouly, M. E., Ohkubo, K., Nesterov, V. N., Zandler, M. E., Fukuzumi, S. & D'Souza, F. (2013). Chem. Eur. J. 19, 7221-7230.]), and its PdII complex, (II)[link], shows minor structural differences in bond lengths and angles. As a representative sample, a deviation of only 0.034 Å is detected in the bond lengths of the pyrrole rings between (I)[link] and (II)[link]. As observed in (I)[link], the five-membered pyrrole rings (N1/C1-C4 and N3/C17-C20) are essentially planar, with the largest deviations being 0.024 (7) and 0.012 (9) Å for atoms C1 and C17, respectively. The backbone C1-N2-C17 bond angle (where N2 is the bridging N atom not involved in metal ligation) of 122.6 (4)° in (II)[link] is comparable with the value in (I)[link] [122.93 (11)°], larger than that reported for the analogous BF2-aza­dipyrromethene compound [119.7 (1)°; Li et al., 2010[Li, Y., Dolphin, D. & Patrick, B. O. (2010). Tetrahedron Lett. 51, 811-814.]] but smaller than in the corresponding previously reported metal(II) bis-chelates of (I)[link] [124.9 (3)-129.3 (2)°; Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]]. These larger angles in the metal-coordinated systems indicate flexibility in the coordinated ligand. It is of inter­est that the C-N bond lengths of the ligand are comparable for (II)[link] and the analogous NiII complex (Palma et al., 2009[Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.]), suggesting the dominant feature for the ligand may be [pi]-delocalization, irrespective of any deformation of the ligand in the complex (March et al., 1971[March, F. C., Couch, D. A., Emerson, K., Fergusson, J. E. & Robinson, W. T. (1971). J. Chem. Soc. A, pp. 440-448.]).

The unit cell of (II)[link] (Fig. 2[link]) consists of discrete monomeric Pd(C32H22N3)2 units [the shortest Pd...Pd distance being 9.1975 (3) Å] that pack into two anti­parallel running stacks which are offset to accommodate the torsion angle of the aromatic rings in the mol­ecule. Limited [pi]-[pi] stacking between adjacent pyrrole-aryl rings and aryl-aryl rings, with perpendicular ring-to-ring distances of ca 3.6 Å, completes the host of weaker inter­molecular inter­actions detected in (II)[link].

Examination of the structure with PLATON (Spek, 2009[Spek, A. L. (2009). Acta Cryst. D65, 148-155.]) shows the presence of two intra­molecular phenyl C-H...N hydrogen bonds (C10-H10...N2 and C26-H26...N2), two longer (weaker) C-H...[pi](arene) and two C-H...Pd inter­actions (Table 3[link]). Both C-H...[pi](arene) inter­actions are inter­molecular, with phenyl atoms C13 and C29 acting as donors to the N1/C1-C4 and C21-C26 rings of adjacent mol­ecules, thereby linking mol­ecules in the unit cell into extended chains. The two C-H...Pd inter­actions are both intra­molecular and connect atoms H16 and H32 of the phenyl rings adjacent to the Pd metal centre, with H...Pd lengths of 2.76 and 2.79 Å, respectively (Table 3[link]). Brookhart et al. (2007[Brookhart, M., Green, M. L. H. & Parkin, G. (2007). Proc. Natl Acad. Sci. USA, 104, 6908-6914.]) categorized such M...H-C bonds as anagostic inter­actions (M...H [asymptotically equal to] 2.3-2.9 Å), largely electrostatic in nature and typical of square-planar d8 transition metal centres.

Table 1
Experimental details

Crystal data
Chemical formula [Pd(C32H22N3)2]
Mr 1003.45
Crystal system, space group Monoclinic, P21/c
Temperature (K) 100
a, b, c (Å) 13.9269 (4), 11.9137 (3), 14.0158 (5)
[beta] (°) 96.665 (3)
V3) 2309.80 (12)
Z 2
Radiation type Cu K[alpha]
[mu] (mm-1) 3.64
Crystal size (mm) 0.06 × 0.03 × 0.02
 
Data collection
Diffractometer Agilent SuperNova Dual diffrac­tom­eter (Cu at zero) with an Atlas detector
Absorption correction Analytical [CrysAlis PRO (Agilent, 2011[Agilent (2011). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England.]), based on expressions derived by Clark & Reid (1995[Clark, R. C. & Reid, J. S. (1995). Acta Cryst. A51, 887-897.])]
Tmin, Tmax 0.842, 0.945
No. of measured, independent and observed [I > 2[sigma](I)] reflections 8633, 3515, 2879
Rint 0.040
[theta]max (°) 62.2
(sin [theta]/[lambda])max-1) 0.574
 
Refinement
R[F2 > 2[sigma](F2)], wR(F2), S 0.050, 0.125, 1.08
No. of reflections 3515
No. of parameters 322
H-atom treatment H-atom parameters constrained
[Delta][rho]max, [Delta][rho]min (e Å-3) 0.90, -0.54
Computer programs: CrysAlis PRO (Agilent, 2011[Agilent (2011). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England.]), SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]), ORTEPIII (Burnett & Johnson, 1996[Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.]) and publCIF (Westrip, 2010[Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.]).

Table 2
Selected geometric details for bonds and contacts (Å, °)

Pd1-N1 2.014 (4) N2-C17 1.326 (6)
Pd1-N3 2.008 (4) N3-C17 1.402 (6)
Pd1...N2 3.235 (5) N3-C20 1.352 (6)
N1-C1 1.380 (6) C1-C2 1.459 (6)
N1-C4 1.354 (6) C2-C3 1.377 (7)
N2-C1 1.330 (6) C3-C4 1.416 (7)
       
N1-Pd1-N3 84.16 (14) N1-C4-C3 109.4 (4)
N1-Pd1-N3i 95.84 (14) C1-N1-C4 108.2 (4)
N1-C1-N2 126.4 (4) C1-N2-C17 122.6 (4)
N2-C17-N3 125.8 (4) C17-N3-C20 107.3 (4)
N1-C1-C2 108.4 (4)    
       
N1-C1-N2-C17 6.4 (7) N3-C17-N2-C1 -6.8 (7)
Symmetry code: (i) -x + 2, -y + 2, -z.

Table 3
Hydrogen-bond geometry (Å, °)

Cg1 is the centroid of the N1/C1-C4 five-membered ring and Cg2 is the centroid of the C21-C26 phenyl ring. Atom C10 is involved in an unrefined disorder.

D-H...A D-H H...A D...A D-H...A
C10-H10...N2 0.95 2.39 3.029 (9) 124
C26-H26...N2 0.95 2.67 3.115 (6) 109
C13-H13...Cg1ii 0.95 2.93 3.528 (6) 122
C29-H29...Cg2iii 0.95 2.90 3.710 (6) 144
C16-H16...Pd1 0.95 2.76 3.366 (5) 122
C32-H32...Pd1 0.95 2.79 3.409 (4) 123
Symmetry codes: (ii) -x + 2, y + [{1\over 2}], -z + [{1\over 2}]; (iii) -x + 2, -y + 1 - z.

Supporting information for this paper is available from the IUCr electronic archives (Reference: GZ3242 ).


Acknowledgements

The authors thank the Irish Research Council for Postdoctoral Fellowship No. PD/2011/2132, and Science Foundation Ireland for financial support.

References

Agilent (2011). CrysAlis PRO. Agilent Technologies Ltd, Yarnton, Oxfordshire, England.
Bandi, V., El-Khouly, M. E., Ohkubo, K., Nesterov, V. N., Zandler, M. E., Fukuzumi, S. & D'Souza, F. (2013). Chem. Eur. J. 19, 7221-7230.  [CSD] [CrossRef] [ChemPort] [PubMed]
Bessette, A., Ferreira, J. G., Giguère, M., Bélanger, F., Désilets, D. & Hanan, G. S. (2012). Inorg. Chem. 51, 12132-12141.  [Web of Science] [CSD] [CrossRef] [ChemPort]
Brookhart, M., Green, M. L. H. & Parkin, G. (2007). Proc. Natl Acad. Sci. USA, 104, 6908-6914.  [CrossRef] [PubMed] [ChemPort]
Burnett, M. N. & Johnson, C. K. (1996). ORTEPIII. Report ORNL-6895. Oak Ridge National Laboratory, Tennessee, USA.
Clark, R. C. & Reid, J. S. (1995). Acta Cryst. A51, 887-897.  [CrossRef] [IUCr Journals]
Freeman, H. C. & Snow, M. R. (1965). Acta Cryst. 18, 843-850.  [CSD] [CrossRef] [ChemPort] [IUCr Journals]
Frimannsson, D. O., Grossi, M., Murtagh, J., Paradisis, F. & O'Shea, D. F. (2010). J. Med. Chem. 53, 7337-7343.  [Web of Science] [CrossRef] [ChemPort] [PubMed]
Hall, M. J., Allen, L. T. & O'Shea, D. F. (2006). Org. Biomol. Chem. 4, 776-780.  [CrossRef] [PubMed] [ChemPort]
Hall, M. J., McDonnell, S. O., Killoran, J. & O'Shea, D. F. (2005). J. Org. Chem. 70, 5571-5578.  [CSD] [CrossRef] [PubMed] [ChemPort]
Hall, J. D., McLean, T. M., Smalley, S. J., Waterland, M. R. & Telfer, S. G. (2010). Dalton Trans. 39, 437-445.  [CrossRef] [ChemPort]
Killoran, J., Allen, L., Gallagher, J. F., Gallagher, W. M. & O'Shea, D. F. (2002). Chem. Commun. pp. 1862-1863.  [CSD] [CrossRef]
Li, Y., Dolphin, D. & Patrick, B. O. (2010). Tetrahedron Lett. 51, 811-814.  [Web of Science] [CSD] [CrossRef] [ChemPort]
Lord, P. A., Olmstead, M. M. & Balch, A. L. (2000). Inorg. Chem. 39, 1128-1134.  [Web of Science] [CSD] [CrossRef] [PubMed] [ChemPort]
Loudet, A., Badnichhor, R., Burgess, K., Palma, A., McDonnell, S. O., Hall, M. J. & O'Shea, D. F. (2008). Org. Lett. 10, 4771-4774.  [Web of Science] [CSD] [CrossRef] [PubMed] [ChemPort]
March, F. C., Couch, D. A., Emerson, K., Fergusson, J. E. & Robinson, W. T. (1971). J. Chem. Soc. A, pp. 440-448.  [CSD] [CrossRef]
March, F. C., Fergusson, J. E. & Robinson, W. T. (1972). Dalton Trans. pp. 2069-2076.  [CSD] [CrossRef]
McDonnell, S. O. & O'Shea, D. F. (2006). Org. Lett. 8, 3493-3496.  [Web of Science] [CSD] [CrossRef] [PubMed] [ChemPort]
Palma, A., Alvarez, L. A., Scholz, D., Frimannsson, D. O., Grossi, M., Quinn, S. J. & O'Shea, D. F. (2011). J. Am. Chem. Soc. 133, 19618-19621.  [Web of Science] [CrossRef] [ChemPort] [PubMed]
Palma, A., Gallagher, J. F., Müller-Bunz, H., Wolowska, J., McInnes, E. J. L. & O'Shea, D. F. (2009). Dalton Trans. pp. 273-279.  [CSD] [CrossRef]
Rogers, M. A. T. (1943). J. Chem. Soc. pp. 590-596.  [CrossRef]
Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.  [CrossRef] [ChemPort] [IUCr Journals]
Spek, A. L. (2009). Acta Cryst. D65, 148-155.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Stolzenberg, A. M., Schussel, L. J., Summers, J. S., Foxman, B. M. & Petersen, J. L. (1992). Inorg. Chem. 31, 1678-1686.  [CSD] [CrossRef] [ChemPort] [Web of Science]
Teets, T. S., Partyka, D. V., Updegraff, J. B. III & Gray, T. G. (2008). Inorg. Chem. 47, 2338-2346.  [Web of Science] [CSD] [CrossRef] [PubMed] [ChemPort]
Teets, T. S., Updegraff, J. B. III, Esswein, A. J. & Gray, T. G. (2009). Inorg. Chem. 48, 8134-8144.  [Web of Science] [CSD] [CrossRef] [PubMed] [ChemPort]
Westrip, S. P. (2010). J. Appl. Cryst. 43, 920-925.  [Web of Science] [CrossRef] [ChemPort] [IUCr Journals]
Wood, T. E. & Thompson, A. (2007). Chem. Rev. 107, 1831-1861.  [Web of Science] [CrossRef] [PubMed] [ChemPort]


Acta Cryst (2014). C70, 165-168   [ doi:10.1107/S2053229614000084 ]