Unprecedented Formation of Azulenylidene Ligands by Reaction of the Vinylidene Ligand in Arylvinylidene Pentacarbonyl Complexes of Chromium and Tungsten with Alkoxyacetylenes

Abstract

Arylvinylidene(pentacarbonyl)chromium and -tungsten complexes [(CO)5MCC(C6H4R1-p)R2] (M = Cr, W; R1 = H; R2 = Me, C6H4R3-p [R3 = H, Me, OMe, Cl, tBu]; R1 = Me; R2 = C6H4Cl-p) react with alkoxyacetylenes, HC⋮COR‘ (R‘ = Et, tBu, adamantyl), by 1,3-addition of the CC triple bond to the vinylidene ligand and ring expansion to give azulenylidene complexes When monosubstituted and unsymmetrically bis-substituted bis(aryl)vinylidene complexes are employed, mixtures of two isomers are obtained. In the two isomers the substituent either is attached to the seven-membered ring or resides in the para position of the phenyl group. In general, the selectivity of the reactions is low; the isomeric ratio varies between 0.5 and 2 depending on the metal and the substituent. DFT calculations on the reaction mechanism indicate that the reactions are initiated by a nucleophilic addition of the terminal carbon atom of the alkoxyacetylene to the metal-bound Cα atom of the vinylidene ligand. The low selectivity of the reactions ...