Bis(allenylidene) Complexes of Palladium and Platinum

trans-Bis(alkynyl)palladium complexes, trans-[(PEt3)2Pd(−CCC{O}NR2)2] (NR2 = NMe2 (2a), N(CH2)4 (2b)), were synthesized
by two different methods: (a) by copper-catalyzed reaction of HCCC(O)NR2 with [PdCl2(PEt3)2] under
basic conditions and (b) by treating HCCC(O)NR2 with AgNO3 followed by transmetalation of the
alkynyl ligand from silver to [PdCl2(PEt3)2]. The reaction of AgCCC(O)NMe2 (3a) with trans-[Br(PiPr3)2PdCCC(O)N(CH2)4] (5) affords a complex containing
two different alkynyl ligands, trans-[(PiPr3)2Pd{−CCC(O)NMe2}{−CCC(O)N(CH2)4}] (6). Methylation of 2a,b and 6 with MeOTf or [Me3O]BF4 yields dicationic bisallenylidene complexes of palladium, trans-[(PEt3)2Pd{CCC(OMe)NR2}2]2+ 2X− (X = OTf,
BF4; NR2 = NMe2, N(CH2)4) and trans-[(PEt3)2Pd{CCC(OMe)NMe2}{CCC(OMe)N(CH2)4}]2+2OTf− (7-OTf). In contrast to the reaction of 3a with
[PdCl2(PEt3)2], that of 3a with the platinum complex [PtCl2(PPh3)2] gives cis- and trans-[(PPh3)2Pt(−CCC{O}NMe2)2] (8a (cis) and 9a (trans)), depending on the reaction conditions
and, upon subsequent alkylation with MeOTf, the cis and trans isomers of the first allenylidene platinum
complexes, cis- and trans-[(PPh3)2Pt{CCC(OMe)NMe2}2]2+2OTf−.