Synthesis and reactivity of dinuclear iron–platinum, chromium–platinum, molybdenum–platinum and tungsten–platinum complexes with bridging carbonyl, isocyanide and aminocarbyne ligands. An empirical study on the parameters decisive for the bonding mode of

The dppm-bridged heterobimetallic μ-carbonyl complexes [(OC)4M(μ-CO)(μ-dppm)Pt(PPh3)] (1a, M=Cr; 1b, M=Mo; 1c, M=W) have been prepared by the reaction of [M(CO)5(η1-dppm)] (M=Cr, Mo, W) with [Pt(CH2CH2)(PPh3)2]. The outcome of stoichiometric isocyanide addition to 1 is electronically controlled by the π-accepting propensity of CNR. Addition of isocyanide ligands with strongly electron withdrawing substituents R affords the isonitrile-bridged complexes [(OC)4M(μ-CN–R)(μ-dppm)Pt(PPh3)] 2 (M=W; R=CF3), 3 (3a, M=Cr; 3b M=Mo, 3c M=W; R=CH2SO2p-tolyl), and 4 (M=W; R=[CH2PPh3][PF6]. With less π-accepting isocyanides (R=CH2Ph, C6H11, CH2PO(OEt)2,) the labile complexes [(RNC)(OC)3W(μ-CO)(μ-dppm)Pt(PPh3)] (5–7) ligated by a terminal isonitrile ligand are formed. In contrast, treatment of [(OC)3Fe(μ-CO)(μ-dppm)Pt(PPh3)] with CNCH2PO(OEt)2 yields exclusively [(OC)3Fe{μ-CNCH2PO(OEt)2}(μ-dppm)Pt(PPh3)] (9) with the isocyanide ligand in a bridging bonding mode. Upon protonation of 2 and 3b with HBF4, the stable μ-aminocarbyne complexes [(OC)4M(μ-CN(H)R′)(μ-dppm)Pt(PPh3)][BF4] (10–11) are formed by electrophilic addition of H+ on the basic isonitrile nitrogen atom. The molecular structures of 1a,c, 2 and 3c have been determined by X-ray diffraction methods. The μ-CO and the μ-CNR ligands bridge the metal centres in an asymmetric manner, the Pt–μ-C distances being significantly shorter than the corresponding M–μ-C distances. In contrast, the μ-CNCH2PO(OEt)2 ligand of [(OC)3Fe{μ-CN–CH2PO(OEt)2}(μ-dppm)Pt(PPh3)] (9) bridges symmetrically the two metal centres. Furthermore, the molecular structure of cis-[(benzylNC)(OC)4W(η1-dppm)] (8a) resulting from degradation of 5 has been determined.