The eta3-propargyl/allenyl complex [(Ph3-P)2Pt(eta3-CH2CCPh)]+ (4), formed by reaction of trans-(PPh3)2PtBr(eta1-CH2C=CPh) with AgO3SCF3 or (Ph3-P)2Pt(eta2-PhC=CCH2OMe) with BF3.OEt2, reacts with Br-to yield 9:1 cis-/trans-(Ph3P)2PtBr(eta1-CH2C=CPh), with excess PMe3 to give [(Me3P)3Pt(eta1-C(Ph)=C=CH2)]+, and with CO to afford 1:1 [trans-(Ph3P)2Pt(CO)(eta1-CH2C=CPh)]+/[trans- (Ph3P)2Pt(CO) (eta1-C(Ph)=C=CH2)]+. With Et2NH, ROH (R = Me, Et), and CH(CO2Me)2-, 4 undergoes nucleophilic addition to the central C atom with transfer of hydrogen to the CPh atom of eta3-CH2CCPh to produce eta3-allyl complexes as single syn or anti isomers.