Syntheses and reactions of acyclic and cyclic carbene complexes cis-[MI(CMeNHMe)(CO)2(η-C5H5)](M = Mo or W) and cis-[MI{C(CH2)nNMe}(CO)2(η-C5H5)](M = Mo, n= 3 or 4; M = W, n= 3) obtained through alkyl migration to methyl isocyanide co-ordinated to molybdenum or tungsten. X-Ray structure of cis-[MoI{C(CH2)3NMe}(CO)2(η-C5H5)]

Abstract

Reaction of the isonitrile anion [M(CNMe)(CO)₂(η-C₅H₅)]^–(M = Mo or W) with I(CH₂)₃I in tetrahydrofuran solution results in good yields of the carbene complexes cis-[MI{[graphic omitted]Me}(CO)₂(η-C₅H₅)]. The structure of the molybdenum compound was studied by X-ray crystallography. It crystallises as red needles, triclinic, a= 7.824(3), b= 13.363(6), c= 14.559(6)Å, α= 78.62(4), β= 77.37(3), and γ= 80.99(4)°; R converged to 0.0385 for 2 378 independent reflections. There are two essentially similar independent molecules within the asymmetric unit. The cyclic carbene ligand and the iodine atom are mutually cis. The carbene ligand adopts a reverse orientation relative to the cyclopentadienyl ring in that the NMe substituent is orientated below the basal plane away from the cyclopentadienyl ring in contrast to the O substituent in related oxacyclopentylidene complexes. The molecule fails to interconvert from the observed cis configuration to the expected trans complex. An important feature of the formation of this molecule is a facile migration reaction of the alkyl chain to an isonitrile ligand. The six-membered carbene ring complex cis-[Mol{[graphic omitted]Me}(CO)₂(η-C₅H₅)] is formed in the analogous reaction of [Mo(CNMe)(CO)₂(η-C₅H₅)]^– with I(CH₂)₄I. Both molybdenum carbene complexes react with Li(BEt₃H) by attack at the carbene affording [[graphic omitted]Me}(CO)₂(η-C₅H₅)](n= 3 or 4). Treatment of these complexes with acid results in the evolution of the organic heterocycle N-methylpyrrolidine (n= 3) or N-methylpiperidine (n= 4). The acyclic carbene compounds cis-[MI(CMeNHMe)(CO)₂(η-C₅H₅)](= Mo or W) are formed in high yield in the reaction of the corresponding anion [M(CNMe)(CO)₂(η-C₅H₅)]^– with MeI followed by MeCO₂H and LiI.