Isolation of [Ru(IPr)2(CO)H]+ (IPr = 1,3-Bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and Reactivity toward E-H (E = H, B) Bonds

Article abstract of DOI:10.1021/acs.organomet.6b00173

Halide abstraction from the ruthenium N-heterocyclic carbene complex Ru(IPr)₂(CO)HCl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) with NaBAr₄^F (BAr₄^F = B{C₆H₃(3,5-CF₃)₂}₄) gave the salt [Ru(IPr)₂(CO)H]BAr₄^F (2), which was shown through a combined X-ray/neutron structure refinement and quantum theory of atoms in molecules (QTAIM) study to contain a bifurcated Ru···η³-H₂C ξ-agostic interaction involving one ⁱPr substituent of the IPr ligand. This system complements the previously reported [Ru(IMes)₂(CO)H]⁺ cation (IMes =1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene), where a non-agostic form is favored. Treatment of 2 with CO, H₂, and the amine-boranes H₃B·NR₂H (R = Me, H) gave [Ru(IPr)₂(CO)₃H]BAr₄^F (3), [Ru(IPr)₂(CO)(η²-H₂)H]BAr₄^F (4), and [Ru(IPr)₂(CO)(κ²-H₂BH·NR₂H)H]BAr₄^F (R = Me, 5; R = H, 6), respectively. Heating 5 in the presence of Me₃SiCH-CH₂ led to alkene hydroboration and formation of the C-H activated product [Ru(IPr)(IPr)′(CO)]BAr₄^F (7). X-ray characterization of 3 and 5-7 was complemented by DFT calculations, and the mechanism of H₂/H exchange in 4 was also elucidated. Treatment of 2 with HBcat resulted in Ru-H abstraction to form the boryl complex [Ru(IPr)₂(CO)(Bcat)] BAr₄^F (8), which proved to be competent in the catalytic hydroboration of 1-hexene. In 8, a combined X-ray/neutron structure refinement and QTAIM analysis suggested the presence of a single Ru···η²-HC ξ-agostic interaction.