Syntheses, Structures, and Reactivity of Dinuclear Molybdenum−Platinum and Tungsten−Platinum Complexes with Bridging Carbonyl, Sulfur Dioxide, Isonitrile, and Aminocarbyne Ligands and a dppa Backbone (dppa = Ph2PNHPPh2)

The heterodinuclear μ-carbonyl complexes [(OC) 4 M(μ-CO)(μ-dppa)Pt(PPh 3 )] ( 3a, M = Mo; 3b, M = W) are formed upon the reaction of [(OC) 5 M(η 1 -dppa)] ( 1a, M = Mo; 1b, M = W) with [Pt(C 2 H 4 )(PPh 3 ) 2 ]. After addition of p -tosylmethyl isonitrile to 3, the CO bridge is replaced by a bridging isonitrile ligand to afford [(OC) 4 W(μ-C NCH 2 SO 2 p -tolyl)(μ-dppa)Pt(PPh 3 )] ( 4a, M = Mo; 4b, M = W). If stronger electron-donating isonitriles such as benzyl or 2,6-xylyl isonitrile are added to 3, fragmentation into mononuclear complexes occurs. Protonation of 4 leads to the μ-aminocarbyne complexes [(OC) 4 M{μ-CN(H)CH 2 SO 2 p -tolyl}(μ-dppa)Pt(PPh 3 )][BF 4 ] ( 5a, M = Mo; 5b, M = W), which react further with isonitriles to yield the μ-aminocarbyne complexes [(OC) 3 (RNC)W{μ-CN(H)CH 2 SO 2 p -tolyl}(μ-dppa)Pt(PPh 3 )][BF 4 ] 6, (R = 2,6-xylyl, benzyl). Purging a solution of 4a with SO 2 yields the complex [(OC) 4 Mo(μ-SO 2 )(μ-dppa)Pt(PPh 3 )], 7a, in which a triphenylphosphine oxide ligand is bound via a hydrogen bridge to the N−H group of the dppa backbone. X-ray diffraction studies performed on 4b and 7a reveal that the μ-CNR and the μ-SO 2 ligands bridge the metal centers in an asymmetric manner, the Pt−μ-C or Pt−μ-S distances being significantly shorter than the corresponding W−μ-C or Mo−μ-S distances, respectively.