Réactions d'insertion du cyanoacétylène et du dicyanoacétylène dans les deux liaisons métalhydrogène des dihydrures [(C 5H 5) 2MH 2] (M  Mo ou W)

Abstract

Only alkyne or alkene insertion reactions into one MH bond of [(C 5H 5) 2MH 2] (M  Mo or W) have been reported up to now. The insertion of alkynes with low steric hindrance, cyanoacetylene (HCCCN) and dicyanoacetylene (NCCCCN) into both MH of [(C 5H 5) 2MH 2] bonds are described in this paper. The first, as well as the second insertion of the same alkyne (either HCCCN or NCCCCN) is stereoselective. The (C 5H 5) 2M(H)AAH or (C 5H 5) 2M(AAH) 2 complexes are formed. In the case of mixed diinsertion complexes, ([(C 5H 5) 2M(σ-C 3H 2N)(σ-C 4HN 2)]) containing both cyanoacetylene and dicyanoacetylene, the geometry of the final products depends on the order of addition of the reactants. Thus, the insertion of (HCCCN) into [(C 5H 5) 2MH(σ- trans-C(CN)CHCN)] is stereoselective, while in the reaction of (NCCCCN) with [(C 5H 5) 2MH(σ-C(CN)CH 2] two stereoisomers [(C 5H 5) 2M(σ- trans- and - cis-C(CN)CHCN)(σ-C(CN)CH 2)] are formed. Insertions of cyanoacetylene and dicyanoacetylene into a MH bond of (C 5H 5) 2M(H)AAH complexes (AA  HCCCF 3, CH 3O 2CCCCO 2CH 3, NCCHCHCN, CH 3O 2CCHCHCO 2CH 3) are also reported. The stereochemistry of the various complexes is proposed on the basis of 1H and 13C NMR spectra, and the mechanisms of the various insertion reactions are discussed.