Syntheses, structures, and reactivity of dinuclear molybdenum-platinum andtungsten-platinum complexes with bridging carbonyl, sulfur dioxide, isonitrile, and aminocarbyne ligands and a dppa backbone (dppa = Ph2PNHPPh2)

The heterodinuclear mu-carbonyl complexes [(OC)(4)M(mu-CO)(mu-dppa)Pt(PPh3) ] (3a, M = Mo; 3b, M = W) are formed upon the reaction of [(OC)(5)M(eta(1)- dppa)] (1a, M = Mo; 1b, M = W) with [Pt(C2H4)(PPh3)(2)]. After addition of p-tosylmethyl isonitrile to 3, the CO bridge is replaced by a bridging ison itrile ligand to afford [(OC)(4)W(mu-C=NCH(2)SO(2)p-tolyl)(mu-dppa)Pt(PPh3) ] (4a, M = Mo; 4b, M = W). If stronger electron-donating isonitriles such a s benzyl or 2,6-xylyl isonitrile are added to 3, fragmentation into mononuc lear complexes occurs. Protonation of 4 leads to the mu-aminocarbyne comple xes [(OC)(4)M{mu-CN(H)CH(2)SO(2)p-tolyl}(mu-dppa)Pt(PPh3)][BF4] (5a, M = Mo ; 5b, M = W), which react further with isonitriles to yield the mu-aminocar byne complexes [(OC)(3)(RNC)W{mu-CN(H)CH(2)SO(2)p-tolyl}(mu-dppa)Pt(PPh3)][ BF4] 6, (R = 2,6-xylyl, benzyl). Purging a solution of 4a with SO2 yields t he complex [(OC)(4)Mo(mu-SO2)(mu-dppa)Pt(PPh3)], 7a, in which a triphenylph osphine 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 tha t the mu-CNR and the mu-SO2 ligands bridge the metal centers in an asymmetr ic manner, the Pt-mu-C or Pt-mu-S distances being significantly shorter tha n the corresponding W-mu-C or Mo-mu-S distances, respectively.