Coordination modes and catalytic carbonylative [4+1] cycloaddition of vinylallenes

(Vinylallene)rhodium complexes with three kinds of coordination modes, that is, eta(2)-coordination of the terminal pi-bond of the allenyl group, eta( 4)-coordination of the conjugated diene skeleton, and planar sigma(2)-coord ination, were synthesized by ligand substitution of RhCl(PPh3)(3) with viny lallenes of specific substitution patterns. Their structures were determine d by X-ray crystallography. Coordination preferences can be explained in te rms of spatial interactions between the vinylallene substituents and the ph osphine ligands as well as effective delocalization of the pi-electrons of the endo- and exocyclic double bonds. The structural studies were extended to the development of the rhodium-catalyzed carbonylative [4 + 1] cycloaddi tion reaction of vinylallenes, affording five-membered carbocycles. With a nonsymmetrical vinylallene, face-selective eta(4)-coordination from the les s hindered side of the allenyl group was observed. The achievement of [4 1] carbonylation can be attributed to (i) the substantial facility of subst ituted vinylallenes for eta(4)-coordination and (ii) the significant contri bution of a metallacyclo-3-pentene resonance form. to the intermediate comp lex. A platinum(0) complex also catalyzed the [4 + 1] cycloaddition of viny lallenes as efficiently as rhodium.