Alkoxy-substituted group 6 allenylidene complexes - Synthesis and properties

摘要

Bis(alkoxy)allenylidene complexes, [(CO)(5)M=C=C=C(OR')OR], as well as mono(alkoxy)allenylidene complexes, [(CO)(5)M=C=C=C(OR')Ph], of chromium and tungsten Lire accessible from propynones [H-C&3bond; C-C(=O)Ph] or propynoic acid esters [H-C&3bond; C-C(=O)OR; R = Et, (-)-menthyl, endo-bornyl] by the following reaction sequence: (a) deprotonation of the alkynes, (b) reaction with [(CO)(5)M-THF] (M = Cr, W), and (c) alkylation of the resulting alkynyl metallate, [(CO)(5)M-C&3bond; C-C(=O)R], with Meerwein salts. Vinylidene complexes, [(CO)(5)M=C=C(R')C(=O)OR], are formed as it by-product by C-beta-alkylation of the alkynyl metallate. Dimethylamine displaces one alkoxy substituent of the bis(alkoxy)allenylidene complexes to give dimethylamino(alkoxy)allenylidene complexes, [(CO)(5)M=C=C=C(OR)NMe2]. The analogous reaction of dimethylamine with a mono(alkoxy)-substituted allenylidene complex affords the aminoallenylidene complex [(CO)(5)Cr=C=C=C(NMe2)Ph]. When the amine is used in large excess, the alpha,beta-unsaturated aminocarbene complex [(CO)(5)Cr=C(NMe2)-C(H)=C(NMe2)Ph] is additionally formed by addition of the amine across the C-alpha-C-beta-bond of the allenylidene ligand. The reaction of [(CO)(5)M=C=C=C(OEt)(2)] with dimethyl ethylenediamine offers access to bis(amino)allenylidene complexes, in which C-gamma is part of a five-membered heterocycle. Photolysis of bis(alkoxy)allenylidene complexes in the presence of triphenylphosphine yields tetracarbonyl- and tricarbonyl{bis(phosphine)}allenylidene complexes. Diethylaminopropyne inserts into the C-beta=C-gamma bond Of [(CO)(5)M=C=C=C(OEt)OMethyl] to give alkenylallenylidene complexes. Subsequent acid-catalyzed intramolecular cyclization affords a pyranylidene complex. (c) 2005 Elsevier B.V. All rights reserved.