Carbyne complexes kinetics

H. Fischer, J. Organomet. Chem., 1980,195, 55. From carbene to carbyne complexes kinetic study of the C, Cr migration of the SnPha group in [(OC)5Cr(CSnPii3NEt2)]. 

The migration of a triphenyltin group from a carbene (CO)5Cr C(SnPh3)NEt2, on treatment with PPh3 with loss of CO, leads to a carbyne complex, trans-[(CO)4Cr(SnPh3)( CNEt2)] the reaction follows a first order kinetics . ... 

The mechanism of ligand substitution reactions in the carbyne complexes /rar7.v-M(CR)X(CO)4 (M = Cr, W R = Me, Ph, NEtj X = Cl, Br, 1, SePh) was investigated by H, Fischer and co-workers (JOO). The influence of the metal center, the trans ligand, and the carbyne substituent on the M—CO dissociation step was determined. The reactions with PPhj in 1,1,2-trichloroethane [Eq. (62)] all follow first-order kinetics, with activa-... 

By isoelectronic replacement of the nitrosyl ligand with a carbyne unit, we derived a new type of system, which was realized in the form of the complex W(sCMes)(dmpe)2H [41]. A strong 7t-accepting ability is also attributed to the carbyne ligand, so that a electronically related environment of the hydride could be expected, compared to related nitrosyl substituted species. It turns out that W(NO)(dmpe)2H reacts with excess benzophenone about five times faster than the corresponding carbyne complexes. This factor of enhancement, however, is in kinetic terms a minor one, which means that these complexes have overall comparable reactivity. For the insertion of benzophenone into the W-H bond of W(CMes)(dmpe)2H, an inverse and very pronounced deuterium isotope effect is observed (kj /k = 1/3). This points to existence of a late transition state in the rate determining step, which must have to do with the actual H-transfer. 

Dr. M.T. Duarte (Institute Superior Tecnico) for the X-ray diffraction analysis of one of the isocyanide complexes, Dr.R. Henderson (Nitrogen Fixation Laboratory, Univ. Sussex) for stopped-flow kinetic studies. Dr. E.G. Bakalbassis and Prof. C.A. Tsipis (Aristotle Univ., Thessaloniki)for the extended Huckel MO calculations, as well as, from our laboratory, Dr. M.F.N.N. Carvalho (some isocyanide and aminocarbyne complexes, and stopped-flow studies). Lie. M.A.N.D.A. Lemos (electrochemical studies). Lie. S.P.R. Almeida and Lie. M.F.C. Guedes da Silva (some vinylidene and carbyne complexes, and electrochemical studies). 

Note I Metathesis polymerization is most often metal-catalyzed and the kinetic-chain carriers alternate between metal carbene complexes and melallacyclobutanes or metal carbyne complexes and metallacyclobutenes. 

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