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] = (η5-C5H5)(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CH2}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}BF4 (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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.