The Influence of N‐Heterocyclic Carbenes (NHC) on the Reactivity of [Ru(NHC)₄H]⁺ With H₂, N₂, CO and O₂

Abstract

The five-coordinate ruthenium N-heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr(2)Me(2))(4)H][BAr(F) (4)] (1; IiPr(2)Me(2)=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; Ar(F)=3,5-(CF(3))(2)C(6)H(3)), [Ru(IEt(2)Me(2))(4)H][BAr(F) (4)] (2; IEt(2)Me(2)=1,3-diethyl-4,5-dimethylimidazol-2-ylidene) and [Ru(IMe(4))(4)H][BAr(F) (4)] (3; IMe(4)=1,3,4,5-tetramethylimidazol-2-ylidene) have been synthesised following reaction of [Ru(PPh(3))(3)HCl] with 4-8 equivalents of the free carbenes at ambient temperature. Complexes 1-3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about delta -41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe(4))(4)(MeCN)H][BAr(F) (4)], 4. The reactivity of 1-3 towards H(2) and N(2) depends on the size of the N-substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H(2) and N(2) only at low temperature and incompletely, while 3 affords [Ru(IMe(4))(4)(eta(2)-H(2))H][BAr(F) (4)] (7) and [Ru(IMe(4))(4)(N(2))H][BAr(F) (4)] (8) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1-3 to give [Ru(NHC)(4)(CO)H][BAr(F) (4)] (9-11). Addition of O(2) to solutions of 2 and 3 leads to rapid oxidation, from which the Ru(III) species [Ru(NHC)(4)(OH)(2)][BAr(F) (4)] and the Ru(IV) oxo chlorido complex [Ru(IEt(2)Me(2))(4)(O)Cl][BAr(F) (4)] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO >> O(2) > N(2) > H(2).

Ruthenium Bidentate Phosphine Complexes for the Coordination and Catalytic Dehydrogenation of Amine– and Phosphine–Boranes

“…After removal of the solvent, the residue was dissolved in benzene (10 mL) and filtered. [28] The solution was concentrated to half volume and layered with hexane to afford dark orange crystals of 12 in 45 % yield (42 mg).…”

“…After removal of the solvent, the residue was dissolved in benzene (10 mL) and filtered. [28] The solution was concentrated to half volume and layered with hexane to afford dark orange crystals of 12 in 45 % yield (42 mg). 1 H NMR (500 MHz,[D 6 ]benzene, 298 K): d = À25.63 (br m, 1 H; RuH), 0.65 (m, 1 H; Cy-CHH agostic ), 0.94-1.16 (m, 4 H; Cy-CH 2 ), 1.…”

Metal–Ligand Cooperation in the Catalytic Dehydrogenative Coupling (DHC) of Polyalcohols to Carboxylic Acid Derivatives

“…, [14] or bearing bidentate phosphane ligands, [HRuA C H T U N G T R E N N U N G (dppe) 2 A C H T U N G T R E N N U N G (OTf)] (7, dppe = 1,2-bis(diphenylphosphanyl)ethane, OTf = triflate), [15] showed little activity (entries 3 and 4, Table 1). Based on previous findings, we investigated a number of diolefin amide rhodium complexes (1-3) in the catalytic DHC of polyols.…”

Computation provides chemical insight into the diverse hydride NMR chemical shifts of [Ru(NHC)4(L)H]0/+species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H−, F−and Cl−) and their [Ru(R2PCH2CH2PR2)2(L)H]+congeners

“…4 The ability of these [Ru(NHC) 4 H] + fragments to bind small molecules, L, at the vacant coordination site trans to H varies considerably according to the NHC substituents. 5 and all three complexes irreversibly bind CO. For the saturated 18e [Ru(NHC) 4 (L)H] + species with L = H 2 , N 2 and CO the hydride signals appear in the range δ = -4 ppm to δ = -10 ppm. However, the hydride in [Ru(I i Pr 2 Me 2 ) 4 (η 2 -O 2 )H] + resonates at δ = + 4.8 ppm.…”