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

The cationic complex {[Ru]=C=CHCPh2CH2CH CH2}BF4 (3a, [Ru] = (eta(5)-C5H5)(PPh3)(2)Ru) 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 C-13 labeling studies. This transformation is irreversible as revealed by deuteration and decomplexation studies. The cationic complex {[Ru]=C=CHCPh2CH2CMe=CH2}BF4 (3b) undergoes a cyclization process yielding 6b containing a eta(2)-cyclic allene ligand which is fully characterized by single-crystal X-ray diffraction analysis. Analogous complexes 4a' and 6b' ([Ru] = (eta(5)-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}BF4 (3c) which again undergoes an irreversible transformation to give {[Ru] C=CHCH2CPh2C CH}BF4 (4c) possibly via a g-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=CHCPh2CH2CH2CH=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.