fac , cis -Bromidotricarbonylbis(tribenzylphosphine)-rhenium(I)

Crystals of the title compound, fac,cis-[ReBr(C21H21P)2(CO)3], were obtained by recrystallization of a sample from CHCl3 layered with hexane. The geometry about the d6 ReI centre is (distorted) octa­hedral with the three CO ligands fac and the two tribenzyl­phosphine ligands cis. In accordance with the trans influence, the Re—C bond trans to Br is significantly shorter than those trans to the organophos­phine ligands.

The molecular structure of (I) is shown in Fig. 1. The overall fac,cis geometry about an octahedral d 6 Re I centre, as was indicated by earlier spectroscopic (IR and NMR) evidence, is confirmed by this crystallographic study. The octahedral geometry is considerably distorted [cis angles range from 81.055 (14) to 98.32 (2) , with P1-Re1-P2 the largest, and trans angles range from 169.03 (8) to 173.81 (8) ], but bond lengths and angles are well within previously reported ranges for related compounds (Beckett et al., 2003;Carballo et al., 2001;Gibson et al. 2001). The Re1-C1 bond trans to Br is significantly shorter than the Re1-C2 and Re1-C3 bonds trans to P. Experimental fac,cis-[ReBr(CO) 3 {P(CH 2 C 6 H 5 ) 3 } 2 ], (I), was prepared by adapting a standard literature method (Angelici et al., 1963) and its physical and spectroscopic properties have been reported previously (Beckett et al., 2003). Orange single crystals suitable for X-ray diffraction studies were obtained by slow diffusion of hexane (layered) into a chloroform solution of (I) at 279 K.
Crystal data [ReBr(C 21  All H atoms were placed in idealized positions (C-H = 0.95-0.99 Å ) and refined using a riding model, with U iso (H) = 1.2U eq (C). The deepest residual electron-density hole is located 0.93 Å from atom Re1.
The authors thank the EPSRC for a studentship (DSB).

Special details
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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.