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

• Published in: Organometallics Vol. 35; no. 9; pp. 1301 - 1312
• Main Authors: Riddlestone, Ian M, McKay, David, Gutmann, Matthias J, Macgregor, Stuart A, Mahon, Mary F, Sparkes, Hazel A, Whittlesey, Michael K
• Format: Journal Article
• Language: English
• Published: American Chemical Society 09.05.2016
• ISSN: 0276-7333; 1520-6041
• 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.