Lutidine-Derived Ru-CNC Hydrogenation Pincer Catalysts with Versatile Coordination Properties

Abstract

Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC–pincer complexes (Ru-CNC’s) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4–6. Nitrile adduct 4 shows reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H2 to form the bis-hydrido complex 8. Finally, these Ru-CNC’s are active in catalytic hydrogenation of CO2 to formate salts, and unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols.

Ruthenium(II) Complexes Containing Lutidine‐Derived Pincer CNC Ligands: Synthesis, Structure, and Catalytic Hydrogenation of CN bonds

“…The facial coordination of the pincer in complexes 3 is unusual in light of previously reported metal complexes containing structurally related CNC11, 12, 18 and CNN ligands 9. 10 To compare the structure of the coordinated CNC ligands in complexes 3 with that observed in derivatives with a mer arrangement of the pincer, as well as to have RuCNC complexes without coordinated PPh 3 available for mechanistic studies, we have prepared complexes 4 d and 4 e .…”

“…The latter group has also reported the formation of Ru‐CNC complexes that exhibit a moderate activity in the dehydrogenation of alcohols 11. Recently, during the progress of our work, Pidko and co‐workers have described the use of Ru‐CNC complexes in the hydrogenation of CO 2 and esters 12…”

Ru–Ag and Ru–Au dicarbene complexes from an abnormal carbene ruthenium system

“…of P-NHC × HBr in THF in the presence of NaOAc (88% yield). Notably, 2 is a rare example of a Ru-NHC complex bearing both a normal and an abnormal carbene ligand, 16 which may form on account of steric factors involving the bulky mesityl group.…”

“…14,15 For Ru only few aNHC-species have been described, [16][17][18][19][20][21] and some display high catalytic activity in transfer hydrogenation. 17 Compared to NHCs, the aNHC ligands show stronger σ-donating properties and therefore are complementary ligands of widespread relevance for catalysis.…”

Mechanistic insights into catalytic carboxylic ester hydrogenation with cooperative Ru(II)-bis{1,2,3-triazolylidene}pyridine pincer complexes

“…General procedure for catalytic ester hydrogenation reactions: The catalyst (3,75 and THF (2 mL) were added. A needle was used to puncture the cap and a set of four vials was placed in a stainless steel autoclave (200 mL) under argon gas.…”