trans-Carbonylchlorobis[diphenyl(4-tolyl)phosphine]rhodium(I)

Abstract

The title compound, [RhCl(C19H17P)2(CO)], can be characterized as a Vaska-type complex containing a diphenyl(4-tolyl)phosphine ligand. The rhodium(I) metal centre has a square-planar coordination. The molecule is disordered, with the Rh atom lying on an inversion centre. The most important bond lengths and angles include Rh—P = 2.3315 (9) Å, Rh—Cl(trans CO) = 2.405 (2) Å, Rh—C(carbonyl) = 1.724 (11) Å and Rh—C—O = 178.0 (6)°.

The Impact of Weak CH⋅⋅⋅Rh Interactions on the Structure and Reactivity of trans‐[Rh(CO)2(phosphine)2]+: An Experimental and Theoretical Examination

“…Whereas complex 3 features a markedly distorted coordination geometry (see above), complex 6 exhibits a virtually perfect square-planar arrangement (see Table 2), which is consistent with its centrosymmetric molecular structure (C i point group, with the inversion center at rhodium). Of particular relevance to the current discussion is the fact that the OC À Rh À CO fragment in the crystal structure of 6 is practically linear (aC1-Rh1-C1a = 180.08 [36] and aRh1-C1-O1 = aRh1-C1a-O1a = 177.81(18)8), which is in agreement with previously reported crystal structures of trans-dicarbonyl bisphosphine Rh I complexes, [8] but in clear contrast to 3, in which the two conformers have significantly distorted OC À Rh À CO fragments. It is worth noting that the bond lengths associated with the CO ligands in 6 (i.e., Rh À C and C À O) are practically identical to those in 3 (see Table 2).…”

“…The arene moieties of the phosphine ligands were found to point in opposite directions on either side of the metal center (anti configuration). However, unlike the few reported crystal structures of cationic trans-dicarbonyl bisphosphine Rh I complexes, [8] all of which have a nearly perfect squareplanar geometry, complex 3 was found to exhibit a significantly distorted coordination geometry.…”

“…[27] However, further work by Hoffmann and co-workers has demonstrated that whereas this prediction holds for neutral complexes, positively charged complexes with strongly donating ligands should actually favor square-planar geometry. [28] This difference in structure was linked to the lower d orbital energies of cationic metals relative to neutral ones (e.g., Rh + versus Ru 0 ), making the former more electronegative (i.e., a better s acceptor and worse p donor) with respect to CO. More recent work by Eisenstein, Caulton and co-workers has focused on a neutral d 8 [29] in which the coordination sphere is very similar to that of 3. As predicted by Hoffmann and co-workers, this complex exhibits a sawhorse structure with a remarkably acute C-Ru-C angle of 133.3(4)8, [30] in marked distinction from 3.…”