Intramolecular metathesis of a vinyl group with vinylidene C=C double bond in Ru complexes

Article abstract of DOI:10.1021/ja054994a

The cationic complex {[Ru]=C=CHCPh₂CH₂CH=CH ₂}BF₄ (3a, [Ru] = (η⁵-C₅H ₅)(PPh₃)₂Ru) in solution transforms to {[Ru]=C=CHCH₂CPh₂CH=CH₂}BF₄ (4a) via a new metathesis process of the terminal vinyl group with the C=C of the vinylidene group which is confirmed by ¹³C labeling studies. This transformation is irreversible as revealed by deuteration and decomplexation studies. The cationic complex {[Ru]=C=CHCPh₂CH₂CMe=CH ₂}BF₄ (3b) undergoes a cyclization process yielding 6b containing a η²-cyclic allene ligand which is fully characterized by single-crystal X-ray diffraction analysis. Analogous complexes 4a′ and 6b′ ([Ru] = (η⁵-C₅H₅)(dppe)Ru) containing dppe ligands were similarly obtained from protonation of the corresponding acetylide complexes via formation of vinylidene intermediate. Protonation of the acetylide complex containing a terminal alkynyl group [Ru]-C≡CCPh₂CH₂C≡CH (2c) generates the vinylidene complex {[Ru]=C=CHCPh₂CH₂C≡CH}BF ₄ (3c) which again undergoes an irreversible transformation to give {[Ru]=C=CHCH₂CPh₂C=CH}BF₄ (4c) possibly via a π-coordinated alkynyl complex followed by hydrogen and metal migration. No similar transformation is observed for the analogous dppe complex 3c′. With an extra methylene group, complex {[Ru]=C=CHCPh₂CH ₂CH₂CH=CH₂}BF₄ (3d) and complex {[Ru]=C=CHCPh₂CH₂Ph}BF₄ (3e) are stable. The presence of a gem-diphenylmethylene moiety at the vinylidene ligand with the appropriate terminal vinyl or alkynyl group along with the correct steric environment implements such a novel reactivity in the ruthenium vinylidene complexes.