Chemistry of the metal carbonyls. Part 82. Synthesis of complexes with bonds between rhodium and the sub-group 6 metals; X-ray crystal structure of [CrRh(µ-CO)2(CO)2(η-C5Me5)(η-C6H6)]

Abstract

Irradiation with u.v. light of mixtures of [Cr(CO)₃(η-arene)](arene = C₆H₆, C₆H₃Me₃-1,3,5, or C₆Me₆) and [Rh(CO)₂(η-C₅Me₅)] in tetrahydrofuran (thf) affords the dimetal compounds [CrRh(µ-CO)₂(CO)₂(η-C₅Me₅)(η-arene)]; the complex [CrRh(µ-CO)₂(CO)₂(η-C₉H₇)(η-C₆H₃Me₃-1,3,5)](C₉H₇= indenyl) has been similarly prepared from [Rh(CO)₂(η-C₉H₇)] and [Cr(CO)₂(thf)(η-C₆H₃Me₃-1,3,5)]. The i.r. and n.m.r. data for these species are reported and discussed in relation to the molecular structure of [CrRh(µ-CO)₂(CO)₂(η-C₅Me₅)(η-C₆H₆)] which has been established by an X-ray diffraction study : crystals are orthorhombic, space group Pnma(no. 62), in a unit cell with a= 10.635(4), b= 11.690(3), c= 15.275(5)Å, and Z= 4. The structure has been refined to R 0.051 from 1 584 independent intensities [I 2.5σ(I)]. The molecule is constrained crystallographically to C_s, symmetry, the mirror plane being defined by the terminal carbonyl ligand on each metal atom, the Rh–Cr bond [2.757(2)Å], and the centroids of the two cyclic ligands. The pentamethylcyclopentadienyl ligand on the Rh atom is in a trans relationship to the η⁶-benzene ligand on the Cr atom, and both lie astride (perpendicular to) the mirror plane. The two other carbonyl ligands are terminal to the Cr atom, but are strongly semi-bridging to the Rh atom [Cr–C 1.902(7), Rh–C 2.200(7)Å], and define planes which are nearly perpendicular to the mirror plane. Some distortion of the Rh–C₅ geometry towards a ‘diolefin’ type attachment is noted and discussed. Reaction of the compounds [M(CO)₅(thf)](M = Cr or W) and [Mo(NCMe)(CO)₅] with [Rh₂(µ-CO)₂(η-C₅Me₅)₂] affords the heteronuclear trimetal cluster complexes [MRh₂(µ-CO)₂(CO)₅(η-C₅Me₅)₂] in high yield. These species may be regarded as molecules in which an M(CO)₅ fragment, isolobal with CH₂, is ‘complexed’ by an ethylene-like [Rh₂(µ-CO)₂(η-C₅Me₅)₂] fragment.