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Treatment of [PdI(Ph)(PPh3)]2 with allenes CH2═C═CHR (R = CMe3, CO2Et, P(O)(OEt)2, and SO2Ph) in dichloromethane at room temperature produces a mixture of cis and trans isomers of the π-allyl palladium complexes PdI(η3-CH2C(Ph)CHR)(PPh3) in which the R group is anti to the Ph group. The disubstituted allenes MeCH═C═CHR (R = P(O)(OEt)2 and SO2Ph) similarly react with [PdI(Ph)(PPh3)]2 to give the π-allyl palladium complexes PdI(η3-MeCHC(Ph)CHR)(PPh3) in which the R group is anti and the Me group is syn to the Ph group. PdI(Ph)(dppe) alone was found to be unreactive toward allenes such as CH2═C═CHSO2Ph and MeCH═C═CHSO2Ph at room temperature. In contrast, in the presence of TlPF6, PdI(Ph)(dppe) readily reacts with allenes CH2═C═CHR (R = CMe3, CO2Et, COPh, and SO2Ph) and MeCH═C═CHSO2Ph to give the π-allyl palladium complexes [Pd(η3-CH2C(Ph)CHR)(dppe)]PF6 and [Pd(η3-MeCHC(Ph)CHR)(dppe)]PF6, respectively. Although mechanistically possible, vinyl complexes were not observed as the insertion products in all cases....

Treatment of RuHCl(CO)(PPh3)3 with CH2CCHCO2Me gives the allyl complex Ru(η3-CH2CHCHCO2Me)Cl(CO)(PPh3)2. The analogous allyl complexes Os(η3-CH2CHCHR)Cl(CO)(PPh3)2 (R = Ph, CH2Ph) are also produced from the reactions of OsHCl(CO)(PPh3)3 with CH2CCHR. In contrast, MHCl(PPh3)3 (M = Ru, Os) react with CH2CCHR to give the vinyl complexes MCl(C(CH3)CHR)(CH2CCHR)(PPh3)2 (M = Ru, R = CMe3, M = Os, R = CMe3, Ph, CO2Et). The difference in the reaction pathways for the reactions of allenes with MHCl(CO)(PPh3)3 and MHCl(PPh3)3 (M = Ru, Os) has been studied by computational chemistry. The theoretical study shows that the observed different reactivity can be related to the significant difference in the electron density increase at the central carbon of the allene ligand upon coordination to the metal fragments.