Bimetallic systems. Part 20. Synthesis of group 6 metal(0)-iridium(I) or -rhodium(I) complexes bridged by Ph2PCH2PPh2

Abstract

Complexes of the type [(OC)₃M′(µ-dppm)₂M(CO)X](M′= Cr, Mo, or W; M = Rh or Ir; dppm = Ph₂PCH₂PPh₂) were synthesised by two independent routes. When M′= Mo, M = Ir, treatment of [Ir(CO)(dppm-PP′)₂]X (X = Cl, Br, or I) with [Mo(CO)₃(cht)](cht =η⁶-cyclohepta-1,3,5-triene) or ring opening of fac- or mer-[Mo(CO)₃(dppm-PP′)(dppm-P)] with [IrCl(CO)₂(H₂NC₆H₄Me-p)] gave moderate yields. The complex [(OC)₃W(µ-dppm)₂Ir(CO)Cl] was made similarly but could not be isolated pure by either method. Treatment of [Rh(CO)(dppm-PP′)2]Cl with [Mo(CO)₃(cht)] did not give the corresponding molybdenum–rhodium complex. However, [(OC)₃Mo(µ-dppm)₂Rh(CO)Cl] was obtained on transmetallation of [ClAg(µ-dppm)₂Rh(CO)Cl] with [Mo(CO)₃(cht)], and more readily and in superior yield from fac- or mer-[Mo(CO)₃(dppm-PP′)(dppm-P)] and [Rh₂Cl₂(CO)₄]. The corresponding chromium and tungsten complexes were prepared similarly in high yield. Spectroscopic evidence suggests that [(OC)₃W(µ-dppm)₂Rh(CO)X](X = Cl, Br, or I) occur in two isomeric forms. Treatment of [(OC)₃M′(µ-dppm)₂Rh(CO)Cl] with carbon monoxide and NH₄PF₆, in polar solvents, gave [(OC)₃M′(µ-dppm)₂Rh(CO)₂] PF₆(M′= Cr, Mo, or W). These cationic species were readily prepared in one step from fac- or mer-[M′(CO)₃(dppm-PP′)(dppm-P)]. Similarly, treatment of fac- or mer-[M′(CO)₃(dppm-PP′)(dppm-P)] with [IrCl(CO)₂(H₂NC₆H₄Me-p)], in the presence of CO and NH₄PF₆, gave the analogous iridium cationic complexes. The cationic species [(OC)₃M′(µ-dppm)₂M(CO)₂]PF₆(M′= Cr, Mo, or W; M = Rh or Ir) were found to react with Cl^– to give the corresponding neutral species [(OC)₃M′(µ-dppm)₂M(CO)Cl]; thus [(OC)₃W(µ-dppm)₂lr(CO)Cl] was obtained analytically pure by this method.