Preparation, structural studies, and some reactions of new heterobinuclear complexes containing molybdenum, tungsten, or manganese and rhodium or copper; X-ray crystal structures of [MoRh(CO)(µ-CO)2(PPh3)2(η-C5H5)] and two isomers of [CuW(CO)3(PPh3)2(η-C5H5)]

Abstract

Reaction of the anions [M(CO)₃(η-C₅H₅)]^– or [Mn(CO)₅]^– with [RhCl(PPh₃)₃] in tetrahydrofuran produces the formally unsaturated bimetallic complexes [MRh(CO)(µ-CO)₂(PPh₃)₂(η-C₅H₅)][M = Mo (1) or W (2)] or [MnRh(CO)₂(µ-CO)₂(PPh₃)₃](3) respectively. An X-ray diffraction study of (1) has established its molecular structure: monoclinic, space group P2₁/c, a= 18.102(2), b= 10.407(1), c= 20.736(2)Å, β= 104.99(1)°, and Z= 4. The structure, determined from 5 233 independent intensities, was refined to R= 0.036 (R¹= 0.074). It comprises a Mo(CO)(η-C₅H₅) group bonded to Rh(PPh₃)₂ with a short Mo–Rh separation 2.588(1)Å and two asymmetric (µ-CO) ligands with Mo–C 1.980(6) and 2.026(5)Å and Rh–C 2.182(6) and 2.092(5)Å; the Mo(µ-CO)₂Rh framework has a dihedral angle (Mo–Rh–C/Mo–Rh–C) of 161°. I.r., ¹H and ³¹P-{¹H} n.m.r. spectra of complexes (1)–(3) are presented and discussed in relation to their structures: formal metal–metal multiple bonds, Rh[grahpic omitted]M, are proposed. Complex (1) acts as a catalyst in hydrogenation of cyclohexene and reactions involving the cleavage of M–Rh bonds are described for complexes (1) and (3). Reactions of [M(CO)₃(η-C₅H₅)]^– with [{CuCl(PPh₃)}₄] give the bimetallic products [CuM(CO)₃-(PPh₃)₂(η-C₅H₅)][M = Mo (4) or W (5)] in relatively low yields. Complex (5) has been obtained in two isomeric crystalline forms, (5a) and (5b), for which X-ray crystal structure determinations have been undertaken: (5a), triclinic, space group P(no. 2), a= 12.404(4), b= 11.756(3), c= 14.208(3)Å, α= 101.4(2), β= 79.5(2), γ= 110.3(2)°, and Z= 2; (5b), monoclinic, space group P2¹/c(no. 14), a= 17.991 (3), b= 10.098(2), c= 21.608(2)Å, β= 105.66(1)°, with Z= 4. The structures of (5a) and (5b) have been refined to residuals R= 0.058 and 0.034 from 3 997 and 4 009 unique reflections, respectively. Both isomers contain W(CO)₃(η-C₅H₅) groups bonded to Cu(PPh₃)₂ units. The carbonyl ligands are essentially terminally bound to W but two CO groups show some semibridging interactions with Cu, especially in structure (5b); Cu–C 2.309(13) and 2.405(13)Å in (5a), 2.260(8) and 2.197(9)Å in (5b). In (5a) the Cu(PPh₃)₂ unit occupies the position typical of a ligand to W in a complex with ‘four-legged piano stool’ geometry [W–Cu 2.721(1)Å; dihedral angle (W–Cu–C/W–Cu–C′) 139.8°]. In (5b) the W(µ-CO)₂Cu fragment is almost planar (W–Cu–C/W–Cu–C′ 170.9°) and W–Cu [2.771 (1)Å] is longer. The structures and bonding of complexes (4) and (5) are discussed in relation to i.r. and n.m.r. spectral data; in solution,¹³C-{¹H} n.m.r. spectra support a non-rigid structure for complex (5).