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′ = (PPh 3) 2, dppe, and CO,PPh 3) produced the corresponding dicationic dihydrogen complexes [ RCnRu(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 [ RCnRu(H 2)(L)(L′)] 2+ and monocationic dihydrogen complexes [TpRu(H 2)(L)(L′)] + (L,L′ = dppe, (PPh 3) 2, CH 3CN,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. [ MeCnRu(H 2)(CO)(PPh 3)] 2+ was found to be more acidic than [ HCnRu(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 pK a values well above that of H 3O + can be deprotonated by H 2O 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 2O.