η³-Propargyl/Allenyl Complexes of Platinum and Palladium of the Type [(PPh₃)₂M(η³-CH₂CCR)]⁺

Abstract

A study is reported on the synthesis, spectroscopic properties, molecular structure, and reaction chemistry of η 3 -propargyl/allenyl complexes of platinum and palladium of the type [(PPh 3 ) 2 M(η 3 -CH 2 CCR)] + (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 -(PPh 3 ) 2 PtBr(η 1 -CH 2 C⋮CPh) with AgO 3 SCF 3; (ii) treatment of (PPh 3 ) 2 Pt(η 2 -PhC⋮CCH 2 OMe) with BF 3 ·OEt 2; (iii) addition of RC⋮CCH 2 OS(O) 2 C 6 H 4 Me- p to (PPh 3 ) 2 Pt(η 2 -C 2 H 4 ) in solution. Complexes 2a,b resulted upon (i) abstraction of Br - from trans -(PPh 3 ) 2 PdBr(η 1 -CH 2 C⋮CR)/ trans -(PPh 3 ) 2 PdBr(η 1 -C(R) C CH 2 ) with AgBF 4 and (ii) treatment of Pd 2 (dba) 3 ·CHCl 3 with PPh 3 and RC⋮CCH 2 OS(O) 2 C 6 H 4 Me- p . The structures of 1a (OTf)·CH 2 Cl 2 (Tf = O 2 SCF 3 ) and 2a (BF 4 ) 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 C 3 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 Et 2 NH to afford the corresponding complexes [(PPh 3 ) 2 Pt(η 3 -CH 2 C(X)CHR)] + (X = OMe, NEt 2 ); 2a,b behave analogously, except that the reaction with MeOH requires trace amounts of NaOMe or NEt 3 . 1 H and 13 C NMR spectroscopic data suggest that the reaction products are best formulated as resonance hybrids of η 3 -allyl and metallacyclic structures.