Palladium complexes with germylene ligands: Synthesis, structure and reactivity

A series of novel palladium complexes of the form L2PdGe[N(SiMe 3)2]2 (L is a monodentate or bidentate phosphine ligand) were synthesized to explore the cooperative reactivity of the Pd germylene bond. (Ph3P)2PdGe[N(SiMe3)2] 2 (1) was synthesized by ligand substitution of (Ph 3P)4Pd, whereas (Et3P)PdGe[N(SiMe3) 2]2 (2) and {lcub}dppePdGe[N(SiMe3) 2]2{rcub}2 (3b) (dppe = diphenylphosphinoethane) were synthesized by photolytic reduction of their corresponding phosphine oxalato complexes followed by addition the germylene ligand. In solution, 3b exists in equilibrium with the monomeric dppePdGe[N(SiMe3) 2]2 (3a). The germylene ligand of 2 was found to be one order of magnitude more labile than the analogous Pt system, and two orders of magnitude less labile than the analogous Ni system. Reactivity of these new palladium germylenes towards O2 is described.; The palladium germylene complexes display a phosphine dependent reactivity with COS to generate sulfide bridged species. Complexes 2 and 3a react with COS to give the sulfide bridged species (Et3P) 2Pd(muS)Ge[N(SiMe3)2]2 (8) and (dppe)Pd(muS)Ge[N(SiMe3)2]2 ( 11) (dppe = (diphenylphosphino)ethane), respectively. Complex 1 reacts with COS to give the disulfide bridged complex (Ph3P) 2Pd(muS)2Ge[N(SiMe3)2]2 (10) resulting in Pd-Ge bond cleavage. In the presence of excess germylene, complexes 8 and 10 are shown to partially regenerate their parent palladium germylene complexes, 2 and 1 respectively, via photolysis or heating.; Addition of SO2 to 8 results in the insertion of SO2 into the Pd-Ge bond to give the O-germyl-S-sulfoxylate insertion isomer (Et3P)2Pd(muS)S(O)OGe[N(SiMe3) 2]2 (13). Heating solutions of 8 results in the formation of the 8-membered metallocycle (Et3P)Pd(SGe[N(SiMe 3)2]2OSOGe[N(SiMe3)2] 2S) (14) and a LnPd(0) fragment.; The reaction of 8 with paraformaldehyde under photolytic conditions results in the insertion of formaldehyde into the Pd-Ge bond to give (Et3P)2Pd(muS)(muCH2O)Ge[N(SiMe 3)2]2 (15). Subsequent addition of CO results in migratory insertion into the Pd-C bond, followed by rapid reductive elimination to regenerate the Pd(0) metal center and give a unique five-membered organic heterocycle, Ge[N(SiMe3)2] 2SC(O)CH2O (18).; X-ray crystal structures of 2, 3b, 8 , 10, 11, 13, 14, the dppe derivative of 15 ((dppe)Pd(muS)(muCH2O)Ge[N(SiMe 3)2]2 (16)), and the dimeric form of complex 8 ({lcub}(Et3P)Pd(muS)Ge[N(SiMe3) 2]2{rcub}2 (12)) are reported.