Bis(alkynyl), Metallacyclopentadiene, and Diphenylbutadiyne Complexes of Ruthenium

Heating diphenylbutadiyne with [Ru(CO)2(PPh3)3] or [Ru(CO)3(PPh3)2] in toluene under reflux provides
respectively the ruthenacyclopentadiene [Ru{κ2-CRCPhCPhCR}(CO)2(PPh3)2] (R = C⋮CPh) or the
cyclopentadienone complex [Ru{η4-OCC4Ph2R2}(CO)2(PPh3)], the latter via [2 + 2 + 1] alkyne and
CO cyclization. The bis(alkynyl) complex cis,cis,trans-[Ru(C⋮CPh)2(CO)2(PPh3)2] is not formed in either
of these reactions but is the product of the reaction of [RuCl2(CO)2(PPh3)2] with LiC⋮CPh or of cis,mer-[Ru(C⋮CPh)2(CO)(PPh3)3] with CO. Although the bis(alkynyl) complex does not undergo reductive
elimination to provide the diyne complex, thermolysis of cis,cis,trans-[Ru(C⋮CPh)(HgC⋮CPh)(CO)2(PPh3)2] (obtained from [Ru(CO)2(PPh3)3] and [Hg(C⋮CPh)2]) provides a noninterconvertible 1:1 mixture
of cis,cis,trans-[Ru(C⋮CPh)2(CO)2(PPh3)2] and [Ru(η-PhC⋮CC⋮CPh)(CO)2(PPh3)2].