Synthesis and spectroscopic characterization of diruthenium .sigma.,.pi.-vinyl complexes Ru2[.mu.-O:C(NMe2),.mu.-.sigma.,.pi.-C(Ar):C(Ar)H](CO)5PPh3, (Ar = phenyl, p-tolyl) and Ru2[.mu.-O:C(NMe2), .mu.-.sigma.,.pi.-C(Ph):CH2](CO)5PPh3. Crystal and molecular structures of Ru2[.mu.-O:C(NMe2), .mu.-.sigma.,.pi.-C(C6H4Me-p):C(C6H4Me-p)H](CO)5PPh3 and Ru2[.mu.-O:C(NMe2),.mu.-.sigma.,.pi.-C(Ph):CH2](CO)5PPh3