Picolyl−NHC Hydrotris(pyrazolyl)borate Ruthenium(II) Complexes: Synthesis, Characterization, and Reactivity with Small Molecules

Abstract

Ruthenium(II) hydrotris(pyrazolyl)borate chloro complexes bearing picolyl-functionalized N-heterocyclic carbenes [TpRu- (κ2-C,N-picolyl-RI)Cl] (picolyl-MeI = 3-methyl-1-(2-picolyl)imidazol-2- ylidene) (1a), picolyl-iPrI = 3-isopropyl-1-(2-picolyl)imidazol-2-ylidene (1b), picolyl-Me45DClI = 3-methyl-1-(2-picolyl)-4,5-dichloroimidazol- 2-ylidene (1c), picolyl-PhI = 3-phenyl-1-(2-picolyl)imidazol-2-ylidene (1d), picolyl-MeBI = 3-methyl-1-(2-picolyl)benzoimidazol-2-ylidene (1e)) have been synthesized and characterized. Furthermore, cationic carbonyl derivatives 2a−e have been prepared, characterized, and used to study the donor properties of the picolylcarbene ligands (picolyl-RI) via infrared spectroscopy. Also, the reactivity of the 16-electron species [TpRu(κ2-C,N-picolyl-RI)]+, in situ generated using NaBArF 4 (ArF = 3,5-bis(trifluoromethyl)phenyl) as a halide scavenger, toward N2, CH3CN, H2, CH2CH2, S8, and O2 was studied indicating a strong influence of the NHC wingtip and backbone substituents in the product distribution. The crystal structures of [TpRu(κ2- C,N-picolyl-iPrI)Cl] (1b), [TpRu(κ2-C,N-picolyl-MeI)CO][BArF 4] (2a), [TpRu(κ2-C,N-picolyl-PhI)CO][BArF 4] (2d), [{TpRu(κ2- C,N-picolyl-MeI}2(μ-N2)][BArF 4]2 (3′a), [{TpRu(κ2-C,N-picolyl-PhI)}2(μ-N2)][BArF 4]2 (3′d), [TpRu(κ2-C,N-picolyl-iPrI)(η2- CH2CH2)][BArF 4] (5b), and [{TpRu(κ2-C,N-picolyl-MeI)}2(μ-S2)][BArF 4]2 (6) are reported.