A study is reported on the synthesis, spectroscopic properties, molecular structure, and reaction chemistry of η3-propargyl/allenyl complexes of platinum and palladium of the type [(PPh3)2M(η3-CH2CCR)]+ (M = Pt, R = Ph (1a), Me (1b); M = Pd, R = Ph (2a), Me (2b)). Complexes 1a,b were obtained by each of the following methods:  (i) reaction of trans-(PPh3)2PtBr(η1-CH2C⋮CPh) with AgO3SCF3; (ii) treatment of (PPh3)2Pt(η2-PhC⋮CCH2OMe) with BF3·OEt2; (iii) addition of RC⋮CCH2OS(O)2C6H4Me-p to (PPh3)2Pt(η2-C2H4) in solution. Complexes 2a,b resulted upon (i) abstraction of Br- from trans-(PPh3)2PdBr(η1-CH2C⋮CR)/trans-(PPh3)2PdBr(η1-C(R)CCH2) with AgBF4 and (ii) treatment of Pd2(dba)3·CHCl3 with PPh3 and RC⋮CCH2OS(O)2C6H4Me-p. The structures of 1a(OTf)·CH2Cl2 (Tf = O2SCF3) and 2a(BF4) were determined by X-ray diffraction techniques. Both cationic metal complexes show remarkably similar structures, the salient features being the attachment to the metal of all three propargyl/allenyl carbon atoms of the nonlinear C3 fragment (C(1)−C(2)−C(3) bond angles:  152.2(9)° for 1a, 154.7(5)° for 2a) and the essentially coplanar arrangement of the three carbon, two phosphorus, and platinum or palladium atoms. 1a,b react readily with MeOH and Et2NH to afford the corresponding complexes [(PPh3)2Pt(η3-CH2C(X)CHR)]+ (X = OMe, NEt2); 2a,b behave analogously, except that the reaction with MeOH requires trace amounts of NaOMe or NEt3. 1H and 13C NMR spectroscopic data suggest that the reaction products are best formulated as resonance hybrids of η3-allyl and metallacyclic structures.

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