BIS(DIPHENYLPHOSPHINO)METHANE-ASSISTED SYNTHESIS OF IRON-PLATINUM AND IRON-PALLADIUM CLUSTERS - CRYSTAL-STRUCTURES OF [FE2PT(MU-DPPM)(CO)8] AND [FEPT2(MU-DPPM)(CO)6] (DPPM = PH2PCH2PPH2)

Reactions of [MCl2 (dppm-PP')] (dppm = Ph2PCH2PPh2) complexes with iron carbonyl reagents afforded dppm-bridged Fe-M mixed-metal complexes: [Fe2Pt(mu-dppm) (CO)8] (1) was best obtained using [Fe2(CO)9], [FePt2(mu-dppm)(CO)6] (2) by the reaction with K[Fe(CO)3(NO)], [FePt2(mu-dppm)2(CO)4] (4) by the reaction with Na2[Fe(CO)4], and [Fe2Pd(mu-dppm)2(CO)6] (5) by the reaction with Na2[Fe2(CO)8]. Reactions of [PdM(mu-dppm)2CI2] with Na2[Fe(CO)4] afforded [FeMPd(mu-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-degrees-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(mu-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) angstrom. 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) angstrom. The i.r. and n.m.r. spectra (H-1, H-1-{P-31}, and P-31-{H-1}) of the new compounds are reported and discussed.