Alkoxy-substituted group 6 allenylidene complexes – Synthesis and properties

Abstract

Bis(alkoxy)allenylidene complexes, [(CO) 5M C C C(OR′)OR], as well as mono(alkoxy)allenylidene complexes, [(CO) 5M C C C(OR′)Ph], of chromium and tungsten are accessible from propynones [H C C C( O)Ph] or propynoic acid esters [H C C C( O)OR; R = Et, (−)-menthyl, endo-bornyl] by the following reaction sequence: (a) deprotonation of the alkynes, (b) reaction with [(CO) 5M-THF] (M = Cr, W), and (c) alkylation of the resulting alkynyl metallate, [(CO) 5M C C C( O)R], with Meerwein salts. Vinylidene complexes, [(CO) 5M C C(R′)C( O)OR], are formed as a by-product by C β-alkylation of the alkynyl metallate. Dimethylamine displaces one alkoxy substituent of the bis(alkoxy)allenylidene complexes to give dimethylamino(alkoxy)allenylidene complexes, [(CO) 5M C C C(OR)NMe 2]. The analogous reaction of dimethylamine with a mono(alkoxy)-substituted allenylidene complex affords the aminoallenylidene complex [(CO) 5Cr C C C(NMe 2)Ph]. When the amine is used in large excess, the α,β-unsaturated aminocarbene complex [(CO) 5Cr C(NMe 2) C(H) C(NMe 2)Ph] is additionally formed by addition of the amine across the C α C β-bond of the allenylidene ligand. The reaction of [(CO) 5M C C C(OEt) 2] with dimethyl ethylenediamine offers access to bis(amino)allenylidene complexes, in which C γ 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 β C γ bond of [(CO) 5M C C C(OEt)OMethyl] to give alkenylallenylidene complexes. Subsequent acid-catalyzed intramolecular cyclization affords a pyranylidene complex.