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 pK a 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.

An Acidity Scale of Tetrafluoroborate Salts of Phosphonium and Iron Hydride Compounds in [D2]Dichloromethane

“…3 5.1 [14] 4.0 trans-[RuClA C H T U N G T R E N N U N G (dppe) 2 7.2 [14] 7.2 [14] [Ru ( 8.1 [15] 8.1 [Ru(Cp)(H) 2 8.4 [15,16] 8. 8.9 [17] 8.9…”

Dihydrogen bonding formed by (hydrido)[hydrotris(pyrazolyl)borato]ruthenium. The effect of ligands on the proton-accepting ability of ruthenium complexes

“…The nonclassical structure of complex 2 has been identified by 1 H NMR spectroscopy. 9 The formation of complex 2 is confirmed by the disappearance of the  RuH band in the IR spectrum; in addition, the  BH band of the Tp ligand is shifted to the higher frequencies (by 19 cm -1 ). Note that addition of an excess of a weaker acid, (CF 3 ) 2 CHOH, also results in proton transfer to hydride 1, despite a low basicity factor.…”

“…Complex 1 was prepared ac cording to a known procedure. 9 IR spectra were recorded on a Nicolet 6700 FTIR spectro meter; for cooling samples, a Carl Zeiss Jena cryostat (CaF 2 cells) was used. 1 H NMR spectra were recorded on an Avance 600 spectrometer.…”

“…3-8 Similar complexes with the Tp ligand do always have nonclassical structures. 2, [9][10][11] Earlier, 12,13 we have demonstrated that hydrogen bond ing (MH ... HX) to a hydride ligand precedes proton trans fer giving rise to complexes with molecular hydrogen. The ligand environment is crucial for both the proton accept ing ability of the hydride ligand and the stability of the complexes MH ... HX formed by dihydrogen bonds (DHB) 14 as well as for the stability of complexes with molecular hydrogen.…”

A comparison of Cp*- and Tp-ruthenium carbyne complexes prepared via site selective electrophilic addition to neutral ruthenium vinylidenes

“…Similar effects have been observed in ruthenium dihydrogen complexes, where increasingly stronger donor co-ligands yield an increase in H-H separation [19]. Thus, [CpRu(g 2 -H 2 )(dppe)] + (dppe = Ph 2 PCH 2 CH 2 PPh 2 ) has a more ''stretched'' H-H bond ( 1 J HD = 24.9 Hz, d(HH) calc $ 1.00 Å ) [19] than [TpRu(g 2 -H 2 )(dppe)] + ( 1 J HD = 32.5 Hz, d(HH) calc $ 0.88 Å ) [20]. An increase in electron density at the metal centre should also translate into longer C-C bonds for metal-bound p-co-ligands.…”