Chemistry of the metal carbonyls. Part 81. Homonuclear and heteronuclear di- and tri-metal carbonyl complexes derived from dicarbonyl-(pentamethylcyclopentadienyl)rhodium; X-ray crystal structure of [ Mn-Rh(µ-CO)2(CO)2(η-C5H5)(η-C5Me5)]

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Abstract
Treatment of [Rh(CO)2(η-C5Me5)] with [Mn(CO)2(thf)(η-C5H5)](thf = tetrahydrofuran) affords [MnRh(µ-CO)2(CO)2(η-C5H5)(η-C5Me5)], the structure of which has been determined by an X-ray diffraction study. The crystals are orthorhombic, space group Pnam(non-standard setting of Pnma, No. 62), in a unit cell with a= 16.851(12), b= 9.338(5), c= 11.566(9)Å, U= 1 820(2)Å3 at 220 K, and Z= 4. The structure was solved to R 0.057 (R′ 0.058) from 1 860 observable independent reflections [I 3.0σ(I)]. The molecule possesses C, symmetry; one terminal carbonyl ligand on each of the metal atoms, together with the Rh–Mn bond [2.703(2)Å], define the mirror plane. The cyclopentadienyl ligand on the Mn atom is in a trans relationship to the pentamethylcyclopentadienyl ligand on the Rh atom and both lie astride (perpendicular to) the mirror plane. The two other carbonyl ligands are terminal to the Mn atom but are strongly semi-bridging to the Rh atom [Mn–C(9) 1.866(7), Rh–C(9) 2.172(7)Å], and define planes which are nearly perpendicular to the mirror plane. A distortion of the Rh–C5 geometry towards a ‘diolefin’ type attachment is discussed. Reaction of [Rh(CO)2(η-C5Me5)] with [Fe2(CO)9] in thf affords the compounds [FeRh(µ-CO)2(CO)4(η-C5Me5)] and [Fe2Rh(µ-CO)2(CO)7(η-C5Me5)]. The latter is also formed, together with [FeRh2(µ3-CO)(µ-CO)2(CO)3(µ-C5Me5)2], on treatment of [Rh2(µ-CO)2(η-C5Me5)2] with excess [Fe2(CO)9]. The trirhodium complex [Rh3(µ3-CO)(µ-CO)2(η-C5Me5)3] was obtained in high yield by pyrolysis of [Rh(CO)2(η-C5Me5)] and undergoes dynamic behaviour in solution. Protonation of the trirhodium cluster or [Rh2(µ-CO)2(η-C5Me5)2] affords quantitatively the cation [Rh3(µ-H)(µ3-CO)(µ-CO)2(η-C5Me5)3]+ which can be deprotonated with NaOMe in MeOH.

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