Synthesis, Characterization, and Acidity of Ruthenium Dihydrogen Complexes with 1,4,7-Triazacyclononane, 1,4,7-Trimethyl-1,4,7-triazacyclononane, and Hydrotris(pyrazolyl)borato Ligands

Abstract

Protonation of [RCnRuH(L)(L‘)]+ (RCn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane; L,L‘ = (PPh3)2, dppe, and CO,PPh3) produced the corresponding dicationic dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+. Protonation of TpRuH(dppe) (Tp = hydrotris(pyrazolyl)borato) yielded the new monocationic dihydrogen complex [TpRu(H2)(dppe)]+. The acidity of the dihydrogen complexes [RCnRu(H2)(L)(L‘)]2+ and monocationic dihydrogen complexes [TpRu(H2)(L)(L‘)]+ (L,L‘ = dppe, (PPh3)2, CH3CN,PPh3, and CO,PPh3) has been studied. It was found that the dicationic complexes are more acidic than their monocationic Tp and Cp counterparts. [MeCnRu(H2)(CO)(PPh3)]2+ was found to be more acidic than [HCnRu(H2)(CO)(PPh3)]2+, probably due to the stronger H−H interaction in the latter complex. It is also noted that triazacyclononane and hydrotris(pyrazolyl)borato dihydrogen complexes with pseudo aqueous pKa values well above that of H3O+ can be deprotonated by H2O to form the corresponding monohydride complexes in organic/aqueous mixed solvents. It is believed that deprotonation of the dihydrogen ligands in these complexes is assisted by strong solvation of H+ by H2O.