Département de chimie moléculaire

The redn. of water to H2 by the tris(pyrazol-1-yl)borate complex [Pd(CH2CH2CH2CH2){\{}(pz)3BH-N,N'{\}}]- with concomitant formation of the palladium(IV) complex Pd(CH2CH2CH2CH2)(OH){\{}(pz)3BH-N,N',N''{\}} has been studied theor. at the MP2//SCF level using [PdMe2{\{}(H2C:N-NH)3BH{\}}]- as a model for the pallada(II)cyclopentane reagent. The calcns. suggest that the uncoordinated pyrazole group has a major role as an intramol. nucleophile in delivering 2H+ (per mole of H2 formed) to the palladium center, with an eventual role as a coordinated group in the palladium(IV) product. Thus, initial protonation leads to formation of a N-protonated palladium(II) species Pd(CH2CH2CH2CH2){\{}(pz)2(pzH)BH-N,N'{\}} contg. a "Pd···H-N" interaction, followed by hydroxide coordination and hydrido ligand formation to give a palladium(IV) species trans-[Pd(CH2CH2CH2CH2)(H)(OH){\{}(pz)3BH-N,N'{\}}]-, a second protonation to form trans-Pd(CH2CH2CH2CH2)(H)(OH){\{}(pz)2(pzH)BH-N,N'{\}} prepd. for a dihydrogen bond interaction "Pd-H···H-N", and finally by elimination of H2 and coordination of the pyrazole group to form Pd(CH2CH2CH2CH2)(OH){\{}(pz)3BH-N,N',N''{\}}. [on SciFinder(R)]