Crystal structure and stereochemistry of the solvated complex dichlorodipyridine-[o-(di-o-tolylphosphino)benzyl]rhodium(III)–0·61 chloroform: the trans-influence of ligands in octahedral complexes

Abstract

The complex [RhCl₂(C₆H₅N)₂{P(o-C₆H₄Me)₂(o-C₆H₄CH₂)}] crystallises from chloroform–ethanol as monoclinic crystals containing a monstoicheiometric amount of chloroform. The cell dimensions are a= 18·43, b= 10·22, c= 19·15, β= 112·4 ± 0·1°; the space group is P2₁/c with one molecule of metal complex per asymmetric unit.

A three-dimensional X-ray analysis, based on 2430 independent diffractometer-measured reflections, has converged to a final weighted R of 0·077. The value of σ for the Rh–Cl and Rh–P bond distances is 0·004 Å, and for Rh–C and Rh–N is 0·013–0·016Å; within the pyridine and tolyl groups the mean σ for bond distances is 0·027 Å.

The steric requirements of the five-membered chelate ring and the methyl groups of the nonchelating tolyl groups give rise to several significant deviations from the C_2v symmetry of the carbon skeleton of free toluene. The trans-influence exerted by a saturated carbon ligand is evidenced by the significant difference between the Rh–Cl bond lengths, one chlorine being trans to a pyridine (Rh–Cl 2·339 Å), the other trans to the benzyl carbon (Rh–Cl 2·531 Å). A general discussion of the trans-influence in octahedral complexes is provided.

The molar ratio, within the crystal, complex:chloroform, determined from a least squares refinement of the chloroform group population parameter, is 1 :0·61 ± 0·02. Complete disorder of the solvents chloroform appears to be prevented by a weak hydrogen bond between the proton of the chloroform group and one of the chlorine atoms co-ordinated to the metal.