Hydrides of numerous transition metal complexes can be generated by the heterolytic cleavage of H2 gas such that they offer alternatives to using main group hydrides in the regeneration of ammonia borane, a compound that has been intensely studied for hydrogen storage applications. Previously, we reported that HRh(dmpe)2 (dmpe = 1,2-bis(dimethylphosphinoethane)) was capable of reducing a variety of BX3 compounds having a hydride affinity (HA) greater than or equal to the HA of BEt3. This study examines the reactivity of less expensive cobalt and nickel hydride complexes, HCo(dmpe)2 and [HNi(dmpe)2]+, to form B-H bonds. The hydride donor abilities (ΔGH-°) of HCo(dmpe)2 and [HNi(dmpe)2]+ were positioned on a previously established scale in acetonitrile that is cross-referenced with calculated HAs of BX3 compounds. The collective data guided our selection of BX3 compounds to investigate and aided our analysis of factors that determine favorability of hydride transfer. HCo(dmpe)2 was observed to transfer H- to BX3 compounds with X = H, OC6F5, and SPh. The reaction with B(SPh)3 is accompanied by the formation of dmpe-(BH3)2 and dmpe-(BH2(SPh))2 products that follow from a reduction of multiple B-SPh bonds and a loss of dmpe ligands from cobalt. Reactions between HCo(dmpe)2 and B(SPh)3 in the presence of triethylamine result in the formation of Et3N-BH2SPh and Et 3N-BH3 with no loss of a dmpe ligand. Reactions of the cationic complex [HNi(dmpe)2]+ with B(SPh)3 under analogous conditions give Et3N-BH2SPh as the final product along with the nickel-thiolate complex [Ni(dmpe)2(SPh)] +. The synthesis and characterization of HCo(dedpe)2 (dedpe = Et2PCH2CH2PPh2) from H 2 and a base is also discussed, including the formation of an uncommon trans dihydride species, trans-[(H)2Co(dedpe) 2][BF4].
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry