The cleavage of coordinated organoisothiocyanates to give heteronuclear clusters containing organoisocyanides as ligands: Preparation, spectra and structure of [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}( μ3-S){ μ3-CNC(O)C 6H 5}], [{Co( η-C 5H 5)} 2{Fe(CO)(CNC 6H 4Me-4)(PPh 3)}( μ3-S)( μ3-CO)], and related complexes

Abstract

Two equivalents of [Co( η-C 5H 5)(PPh 3) 2] cleave the coordinated C–S bond of [Fe(PPh 3) 2(CO) 2( η 2-SCNR)] complexes to give clusters having the general formulae [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}(S)(CNR)], I. Those where RNC=(a) MeNC and (b) 4-Me 2NC 6H 4NC exist in both the solid state and in solution as the [{Co( η-C 5H 5)} 2{Fe(CO)(CNR)(PPh 3)}( μ 3-S)( μ 3-CO)] isomer, I I. Those where R=(f) MeC(O)NC, (g) 4-Me 2NC 6H 4C(O)NC and (h) C 6H 5C(O)NC exist as the [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}( μ 3-S)( μ 3-CNR)] isomer, I II, and those where RNC=(c) 4-MeC 6H 4NC, (d) C 6H 5NC and (e) 4-ClC 6H 4NC exist as a mixture of I I and I II in fluxional equilibrium in solution with the proportion of I II increasing with increasing electron-withdrawing ability of R. Variable temperature 1H-NMR spectroscopy shows that apart from the I I=I II interconversion (Δ G *=ca. 77–88 kJ mol −1), the I I isomer undergoes a further fluxional process which inverts the configuration at Fe (ΔG *=ca. 65 kJ mol −1). All I react with MeOSO 2CF 3 to give salts of the [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}( μ 3-S){ μ 3-CN(Me)R}] + cations except for Ig which is alkylated at the NMe 2 group to give [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}( μ 3-S)( μ 3-CNC(O)C 6H 4NMe 3] +. The new complexes are characterized by IR and NMR spectroscopy, and by X-ray crystallography for [{Co( η-C 5H 5)} 2{Fe(CO)(CNC 6H 4Me-4)(PPh 3)}( μ 3-S)( μ 3-CO)], Ic, and [{Co( η-C 5H 5)} 2{Fe(CO) 2(PPh 3)}( μ 3-S){ μ 3-CNC(O)C 6H 5}], Ih. In both the structure is based on a FeCo 2 triangle capped on one face by a μ 3-S ligand and on the other by a μ 3-CNC(O)Ph (Ih) or μ 3-CO (Ic) ligand with S and CO are disordered in Ic. In both cases the C ligand acts as a 2e donor in these 48e complexes. The bridging isocyanide ligand is bent at N indicating that it is acting as a strong electron acceptor, unlike the μ 3-CNMe ligand in [Ni 3(Ph 2PCH 2PPh 2) 2(CNMe) 2( μ 3-I)( μ 3-CNMe)] + which is almost linear and probably only a weak acceptor but a strong donor.