(Phenylalkyl)palladium Complexes Containing β-Hydrogen Atoms: Synthesis and Characterization of [PdR2(dppe)], [PdR(SPh)(dppe)] (R = CH2CH2Ph, CH2CH2CH2Ph, CH2CHMePh), and [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, Br, Cl)

Abstract

Reactions of HgR2 (R = CH2CH2Ph, 1a; CH2CH2CH2Ph, 1b; CH2CHMePh, 1c) (prepared from HgCl2 and the requisite Grignard compounds) with lithium in toluene afforded (phenylalkyl)lithium compounds LiR (2a−c) in yields of between 64 and 81%. At −30 °C, they react with [PdCl2(dppe)] [dppe = 1,2-bis(diphenylphosphanyl)ethane] yielding bis(phenylalkyl)palladium(II) complexes [PdR2(dppe)] (3a−c) which were isolated (Tdec = 159 °C, 3a; 80 °C, 3b; 145 °C, 3c) and fully characterized by 1H, 13C, and 31P NMR spectroscopy. Single-crystal X-ray diffraction of [Pd(CH2CH2Ph)2(dppe)] (3a) showed that the palladium atom is square-planar coordinated by two 2-phenylethyl ligands and the dppe ligand. The two CH2CH2Ph ligands exhibite nearly a fully staggered conformation. Overall, a good approximation for the complex is that it has C2 symmetry with the C2 axis defined by the Pd atom and the midpoint of the central C−C bond of the dppe ligand. Bis(phenylalkyl)palladium complexes 3a and 3b reacted with PhSH in a 1:1 ratio yielding [PdR(SPh)(dppe)] (R = CH2CH2Ph, 5a; CH2CH2CH2Ph, 5b), whereas in the case of complex 3c, besides [Pd(CH2CHMePh)(SPh)(dppe)] (5c), a considerable amount of [Pd(SPh)2(dppe)] (6a) was formed. Reactions of 3b with the less acidic alkanethiols iPrSH and tBuSH resulted in the formation of [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = iPr, 5d; tBu, 5e) along with smaller amounts of [Pd(SR′)2(dppe)] (6) and [Pd(dppe)2] (7). Furthermore, complex 3b was found to react in THF with disulfides R′SSR′ (R′ = Ph, Bz, Me), yielding [Pd(CH2CH2CH2Ph)(SR′)(dppe)] (R′ = Ph, 5b; Bz, 5f, Me, 5g) with small amounts (3−13%) of [Pd(SR′)2(dppe)] (6) as side products. The corresponding reaction with MeSeSeMe afforded [Pd(CH2CH2CH2Ph)(SeMe)(dppe)] (8a) and 3% of [Pd(SeMe)2(dppe)] (9a) and [Pd(dppe)2] (7). Reactions of complex 5b with MeI and H2C=CHCH2Br in tetrahydrofuran and with neat H2C=CHCH2Cl readily proceeded at −30 °C to give halo(3-phenylpropyl)palladium complexes [Pd(CH2CH2CH2Ph)X(dppe)] (X = I, 10a; Br, 10b; Cl, 10c). They were isolated as pale yellow powdery/microcrystalline substances and fully characterized by 13C and 31P NMR spectroscopy. Solutions of complexes 10 in THF decompose rapidly above −30 °C. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)