Bis(diphenylphosphino)methane-assisted synthesis of iron–platinum and –palladium clusters. Crystal structures of [Fe2Pt(µ-dppm)(CO)8] and [FePt2(µ-dppm)(CO)6](dppm = Ph2PCH2PPh2)

Abstract

Reactions of [MCl₂(dppm-PP′)](dppm = Ph₂PCH₂PPh₂) complexes with iron carbonyl reagents afforded dppm-bridged Fe–M mixed-metal complexes: [Fe₂Pt(µ-dppm)(CO)₈](1) was best obtained using [Fe₂(CO)₉], [FePt₂(µ-dppm)(CO)₆](2) by the reaction with K[Fe(CO)₃(NO)], [FePt₂(µ-dppm)₂(CO)₄](4) by the reaction with Na₂[Fe(CO)₄], and [Fe₂Pd(µ-dppm)₂(CO)₆](5) by the reaction with Na₂[Fe₂(CO)₈]. Reactions of [PdM(µ-dppm)₂Cl₂] with Na₂[Fe(CO₄)] afforded [FeMPd(µ-dppm)₂(CO)₄](6; M = Pd) and (7; M = Pt) in high yields. Cluster (7) was shown to exist in two isomeric forms. The kinetic isomer, isolated pure at –20 °C, contains a terminal Pd-bound carbonyl whereas the thermodynamic isomer has a terminal Pt-bound carbonyl ligand. A 1 : 1 ratio is observed at equilibrium. The cluster [Fe₂Pt(µ-dppm)₂(CO)₆](3) was obtained quantitatively by reaction of (1) or [Fe₂Pt(CO)₉(PPh₃)] with 1 or 2 equivalents of dppm. These reactions were shown to occur first by substitution of the Pt-bound carbonyl ligand. Low-yield interconversion of (1) and (2) was observed as a result of metal-exchange reactions. The structures of clusters (1) and (2) have been established by single-crystal X-ray diffraction studies. In (1) a Fe–Pt bond is bridged by the dppm ligand and Fe(1)–Fe(2) 2.740(2), Pt–Fe(1) 2.542(1), and Pt–Fe(2) 2.557(1)Å. In (2) the Pt–Pt bond is bridged by the dppm ligand and Fe–Pt(1) 2.541(3), Fe–Pt(2) 2.541(4), and Pt(1)–Pt(2) 2.581 (1)Å. The i.r. and n.m.r. spectra (¹H, ¹H-{³¹P}, and ³¹P-{¹H}) of the new compounds are reported and discussed.