The complexes M(PNP)22+ (M = Pd, Pt, PNP = Et2PCH2N(Me)CH2PEt2) were synthesized by addition of PNP to Pd(CH3CN)4(BF4)2 and (COD)PtCl2, respectively. Pd(PNP)2 was synthesized by reaction of Pd(PNP)22+ with H2 and tetramethylguanidine (TMG) in CH3-CN. The thermodynamic hydride donor ability, ΔG°H-, for HPt(PNP)2+ (54.7 kcal/mol) was measured by heterolytic cleavage of hydrogen in the presence of NEt3 in CH3CN. The hydride donor ability of HPd(PNP)2+ (51.1 kcal/mol) was determined by measuring the equilibrium constant for direct hydride transfer to Pt(PNP)22+. The M(II) complexes undergo reversible, two-electron reductions in benzonitrile. The measured reduction potentials were used in a thermodynamic cycle to estimate pKa values of 22.1 and 27.6 for deprotonation of HPd-(PNP)2+ and HPt(PNP)2+, respectively. The palladium hydride has an acidity equal to that of the nickel hydride and is a better hydride donor than both the nickel and platinum analogues. This shows that it is possible for transition metal hydrides to act simultaneously as both acids and hydride donors.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry