Molybdenum-based alkyne-isocyanide coupling reactions: synthesis of a reactive diiminometallacyclopentene complex

The complex [Mo(CO)(PhC=CPh)(2)(eta -C5Me5)][BF4] reacted with three equivalents of 2,6-dimethylphenyl isocyanide, CNxyl, to give the tris(isocyanide) complex [Mo(PhC=CPh)(CNxyl)(3)(eta -C5Me5)][BF4] 1. With four equivalents of CNxyl, alkyne-isocyanide coupling leads to the formation of the diiminometallacyclopentene [Mo{C(=Nxyl)C(Ph)=C(Ph)C=Nxyl}(CNxyl)(2)(eta -C5Me5)][BF4] 2 which decomposes in thf at room temperature to give the tetrakis(isocyanide) complex [Mo(CNxyl)(4)(eta -C5Me5)][BF4] 3. In dichloromethane, 2 gives the diiminocyclobutene xylN=CC(Ph)=C(Ph)C=Nxyl 4, the eta (2)-iminoacyl complex [MoCl(CNxyl)(2)(eta (2)-xylN=CCH2Cl)(eta -C5Me5)][BF4] 5, formed by an addition reaction with dichloromethane, and the metallacyclobutene complex [Mo{C(Ph)=C(Ph)C=N(H)xyl}(CNxyl)(3)(eta -C5Me5)][BF4](2) 6. Complex 5 is more efficiently synthesized by photolysis of 3 in dichloromethane, but the same reaction in chloroform produces the dichloromethyl complex [MoCl(CHCl2)(CNxyl)(3)(eta -C5Me5)][BF4] 7 which thermally decomposes to [MoCl2(CNxyl)(3)(eta -C5Me5)][BF4] 8. Reaction of 2 with HCl in diethyl ether results in protonation of the metallacyclic ring and formation of the iminium metallacyclopentene [MoCl{C(=Nxyl)C(Ph)=C(Ph)C=N(H)xyl}(CNxyl)(2)(eta -C5Me5)][BF4] 9. Compound 3 is oxidised by AgBF4 to give the molybdenum(IV) complex [MoF(CNxyl)(4)(eta -C5Me5)][BF4](2) 10. The molecular structures of 3-6, 7/8 and 10 have been determined by X-ray crystallography.