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

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 NaBAr4F (BAr4F = B{C6H3(3,5-CF3)(2)}(4)) gave the salt [Ru(IPr)(2)(CO)H]BAr4F (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 center dot center dot center dot eta(3)-H2C xi-agostic interaction involving one Pr-i 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, H-2, and the amine-boranes H3B center dot NR2H (R = Me, H) gave [Ru(IPr)(2)(CO)(3)H]BAr4F (3), [Ru(IPr)(2)(CO)(eta(2)-H-2)H]BAr4F (4), and [Ru(IPr)(2)(CO)(kappa(2)-H2BH center dot NR2H)H]BAr4F (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)]BAr4F (7). X-ray characterization of 3 and 5-7 was complemented by DFT calculations, and the mechanism of H-2/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)] BAr4F (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 center dot center dot center dot eta(2)-HC xi-agostic interaction.