Platinum allenylidene complexes and formation of platinum and palladium acetonitrile alkynyl complexes

The platinum(0) complex [Pt(PPh3)4] reacts with brominated propargylic amides and esters in benzene by oxidative addition to give trans-[Br(PPh3)2Pt–CC–C(O)R] complexes whereas no reaction occurs when halogenated solvents (CH2Cl2, CHCl3) are used. The cis-ligands PPh3 can be replaced by P(iPr)3 and the bromide by trifluoroacetate. O-Alkylation of those trans-[X(PR′3)2Pt–CC–C(O)R] complexes (X = Br, CF3COO; R′ = Ph, iPr) derived from propargylic amides with MeOTf or [Me3O]BF4 in CH2Cl2 gives the first cationic monoallenylidene complexes of platinum, trans-[X(PR′3)2PtCCC(OMe)NR2]+Y− (Y = OTf, BF4). In contrast, trans-[Br(PPh3)2Pt–CC–C(O)OMenthyl] derived from a propargylic ester does not react with MeOTf in CH2Cl2. However, in acetonitrile instead of O-methylation the substitution of acetonitrile for the bromide ligand to yield the cationic acetonitrile alkynyl platinum complex trans-[MeCN(PPh3)2Pt–CC–C(O)OMenthyl]+OTf− is observed. The related palladium complexes trans-[X(PR′3)2Pd–CC–C(O)OR] (X = Br, CF3COO; R′ = Ph, iPr, R = menthyl, Et) react with MeOTf or [Et3O]BF4 analogously affording trans-[MeCN(PR′3)2Pd–CC–C(O)OR]+Y− (Y = OTf, BF4).