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

Protonation of [ R CnRuH(L)(L‘)] + ( R Cn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane; L,L‘ = (PPh 3 ) 2, dppe, and CO,PPh 3 ) produced the corresponding dicationic dihydrogen complexes [ R CnRu(H 2 )(L)(L‘)] 2+ . Protonation of TpRuH(dppe) (Tp = hydrotris(pyrazolyl)borato) yielded the new monocationic dihydrogen complex [TpRu(H 2 )(dppe)] + . The acidity of the dihydrogen complexes [ R CnRu(H 2 )(L)(L‘)] 2+ and monocationic dihydrogen complexes [TpRu(H 2 )(L)(L‘)] + (L,L‘ = dppe, (PPh 3 ) 2, CH 3 CN,PPh 3, and CO,PPh 3 ) has been studied. It was found that the dicationic complexes are more acidic than their monocationic Tp and Cp counterparts. [ Me CnRu(H 2 )(CO)(PPh 3 )] 2+ was found to be more acidic than [ H CnRu(H 2 )(CO)(PPh 3 )] 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 p K a values well above that of H 3 O + can be deprotonated by H 2 O 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 H 2 O.