Coordination Modes and Catalytic Carbonylative [4 + 1] Cycloaddition of Vinylallenes

Abstract

(Vinylallene)rhodium complexes with three kinds of coordination modes, that is, η 2-coordination of the terminal π-bond of the allenyl group, η 4-coordination of the conjugated diene skeleton, and planar σ 2-coordination, were synthesized by ligand substitution of RhCl(PPh3)3 with vinylallenes of specific substitution patterns. Their structures were determined by X-ray crystallography. Coordination preferences can be explained in terms of spatial interactions between the vinylallene substituents and the phosphine ligands as well as effective delocalization of the π-electrons of the endo- and exocyclic double bonds. The structural studies were extended to the development of the rhodium-catalyzed carbonylative [4 + 1] cycloaddition reaction of vinylallenes, affording five-membered carbocycles. With a nonsymmetrical vinylallene, face-selective η 4-coordination from the less hindered side of the allenyl group was observed. The achievement of [4 + 1] carbonylation can be attributed to (i) the substantial facility of substituted vinylallenes for η 4-coordination and (ii) the significant contribution of a metallacyclo-3-pentene resonance form to the intermediate complex. A platinum(0) complex also catalyzed the [4 + 1] cycloaddition of vinylallenes as efficiently as rhodium.

Rhodium‐Catalyzed Ring Expansion of Cyclopropanes to Seven‐membered Rings by 1,5 CC Bond Migration

“…Formation of η 4 -(vinylal-lene) rhodium complex 5 can initiate an oxidative cyclization to yield alkylidene metallacyclopentene 6 . This transformation has been documented in the rhodium-catalyzed [4+1] cycloaddition of vinylallenes with CO, [22] and also the corresponding alkylidene metallacyclopentene complexes were isolated and characterized in the absence of CO. [23, 24] Alkylidene metallacyclooctadiene 7 can be obtained by the cleavage of the strained cyclopropane ring in complex 6 . Reductive elimination of metallacycle 7 then yields the desired seven-membered-ring 3 .…”

Intermolecular Tandem Pd‐Catalyzed Cross‐Coupling/[4+4] and [4+2] Cycloadditions: A One‐Pot, Five‐Component Assembly of Bicyclo[6.4.0]dodecanes

“…A Pd‐catalyzed [4+4] cycloaddition reaction with a vinyl allene as the starting material was reported recently 11. In this reaction, the vinyl allene was obtained from the reaction of 1‐phenylvinylmagnesium bromide with propargyl bromide in the presence of a Pd 0 catalyst 12. However, preparation of the vinyl allene in situ by inversion of the charge polarization of the reaction components (α‐bromostyrene and propargyl bromide) was applied in the present method.…”

Reaction Chemistry of the Carbenoid Butadienyl Complex Ion [CpCo(σ,η4‐C4HMe4)]+ Formed by Protonation of the Cyclobutadiene Complex [CpCo(C4Me4)]

“…A stereoisomerization related to the transformation 5 Ǟ 14 has been described for vinylallene complexes of the [RhCl(PPh 3 )] fragment. [17] M. Murakami et al argue that the isomerization occurs via a 14e complex with a 2,5-σ 2 -coordinated vinylallene (1,2,4-pentatriene) ligand and present an example where this arrangement becomes the groundstate of the molecular system. Most likely the isomerization 5 Ǟ 14 follows the same path.…”