Substituted metal carbonyls. Part 24. Heteropolymetallic oligomers [(OC)xM′(µ-L–L)M(CO)4(µ-L–L)M′(CO)x] and [(OC)5Mn–Mn(CO)4(µ-L–L)M(CO)4(µ-L–L)(OC)4Mn–Mn(CO)5][M = Cr, Mo or W; M′= Cr, Mo, W (x= 5) or Fe (x= 4); L–L = Fe(C5H4PPh2)2 or Ph2P(CH2)mPPh2(m= 2 or 3)], with metal carbonyl and diphosphine repeating units

Abstract

A series of soluble oligomeric complexes of formulae [(OC)_xM′(µ-L–L)M(CO)₄(µ-L–L)M′(CO)_x][L–L = Fe(C₅H₄PPh₂)₂: M = Cr, M′= Cr, Mo, W, Fe, or Mn₂; M = Mo, M′= Cr, Mo, Fe or Mn₂; M = W, M′= Cr or W. L–L = Ph₂P(CH₂)_mPPh₂: M = Cr, M′= Mo, m= 2 or 3. M′= Cr, Mo, or W, x= 5; M′= Fe, x= 4; M′= Mn₂, x= 9) has been isolated either as by-products in the syntheses of the bimetallics [(OC)_xM′(µ-L–L)M(CO)_x] or in a designed synthesis from cis-[M(CO)₄(solv)₂](solv = solvent)(yields 1–18%). The repeating units are ferrocenyl or alkyl-chain diphosphine and metal carbonyl fragments and sometimes the oligomeric chains are supported by a M–M bond. The longest polymeric chain consists of seven metal atoms, Fe₂MMn₄. The linearity of the oligomeric propagation depends on the geometry of the central M(CO)₄ unit, which is cis for Mo but trans for Cr or W. The geometrical preference is explained on steric and thermodynamic grounds, and the fluxionality of the five-co-ordinate intermediate. Nucleophilic attack by Me₃NO on the bimetallics did not give oligomers through decarbonylation, but rather the phosphine oxide complexes [M(CO)₅{Fe(C₅H₄PPh₂)(C₅H₄PPh₂O)}] through dephosphination.