SYNTHESIS AND CHARACTERIZATION OF WATER-SOLUBLE [PD(TRIPHOSPHINE)(CH3CN)](BF4)(2) COMPLEXES FOR CO2 REDUCTION

The syntheses of the triphosphine ligands RP(CH(2)CH(2)PR'(2))(2) (R = CH2CH2CH2OH and R' = Et, HOPetpE; R = Ph and R' = CH2CH2P(O)(OEt)(2), etpEPO; R = Me(2)N and R' = Et, MNetpE; R = i-Pr2N and R' = Et, IPNetpE; R = Ph and R' = NMe(2), etpMN) are described. The reaction of [Pd(CH3CN)(4)(BF4)2 with these ligands forms [Pd(triphosphine)(CH3CN)](BF4)(2) complexes that are all water soluble with the exception of [Pd(IPNetpE)(CH3-CN)](BF4)(2). The labile acetonitrile ligands are easily substituted by triethylphosphine to form [Pd(triphosphine)(PEt(3))](BF4)2 complexes. The triethylphosphine complexes undergo quasi-reversible two-electron reductions while the corresponding acetonitrile complexes undergo two, closely spaced, irreversible, one-electron reductions. [Pd(HoPetpE)(CH3CN)](BF4)(2) and [Pd(etpEPO)(CH3CN)](BF4)(2) are catalysts for the electrochemical reduction of CO2 to CO in both dimethylformamide and buffered aqueous solutions. Kinetic studies are reported for [Pd(HoPetpE)(CH3CN)](BF4)(2) in dimethylformamide.