Ruthenium Catalyzed Selective Hydroboration of Carbonyl Compounds

Abstract

Using the [Ru(p-cymene)Cl2]2 (1) complex, catalytic hydroboration of aldehydes and ketones with pinacolborane under neat and mild conditions is reported. At rt, chemoselective hydroboration of aldehydes over the ketones is also attained. Mechanistic studies confirmed the immediate formation of monohydride bridged dinuclear complex [{(η(6)-p-cymene)RuCl}2(μ-H-μ-Cl)] (1b) from the reaction of 1 with pinacolborane, which catalyzed the highly efficient hydroboration reactions. The catalytic cycle containing mononuclear Ru-H species and intramolecular 1,3-hydride transfer is postulated.

Ruthenium-Catalyzed Regioselective 1,4-Hydroboration of Pyridines

“…20 monohydride bridged dinuclear complex [{(η 6 -p-cymene)-RuCl} 2 (μ-H-μ-Cl)] 6 (Scheme 4c). 18,21 To ascertain any role of complex 6 in catalysis, the regioselective 1,4-hydroborations of pyridine catalyzed by complexes 2 and 3 (3 mol %) 22 were monitored using 1 H NMR, which confirmed the formation and presence of only monohydride complex 5 throughout the catalysis in both experiments. 23 On the basis of the above-mentioned experimental observations, a catalytic cycle is proposed as depicted in Scheme 5.…”

Hydroboration, Cyanosilylation, and Sequential Cyanosilylation and Hydroboration of Carbonyl Compounds in the Presence of a TiIV Amido Complex as an Efficient Catalyst

“…The addition of a second equivalent of HBpin did not lead to further hydroboration of the pyridine ring even after prolonged heating, possibly due to the preferential coordination of the borate ester to the metal center through the oxygen atoms. [26] The reaction between 4-acetylbenzaldehyde and HBpin also further confirms the selective reduction of the aldehyde (Scheme 5). Similar results were obtained when we treated ferrocene-2-carbaldehyde with HBpin (Table 3, Entry 7, FS 90-92 in the Supporting Information).…”

“…[13] However, these protocols have no tolerance for other active functional groups such as nitro groups, nitriles, and amides. In addition, cata- lysts based on transition metals such as titanium, [17][18][19][20][21] manganese, [22] iron, [23] molybdenum, [24] rhodium, [25] ruthenium, [26] copper, [27] and zinc, [28] as well as on main group metals such as aluminum, [29] gallium, [30] germanium, [31] and tin, [31] are known for the hydroboration of carbonyl compounds. In addition, cata- lysts based on transition metals such as titanium, [17][18][19][20][21] manganese, [22] iron, [23] molybdenum, [24] rhodium, [25] ruthenium, [26] copper, [27] and zinc, [28] as well as on main group metals such as aluminum, [29] gallium, [30] germanium, [31] and tin, [31] are known for the hydroboration of carbonyl compounds.…”

1‐Alkali‐metal‐2‐alkyl‐1,2‐dihydropyridines: Soluble Hydride Surrogates for Catalytic Dehydrogenative Coupling and Hydroboration Applications

“…Notably the analogous reaction of 2‐methoxybenzaldehyde using DIPPnacnac‐Mg n Bu (0.5 mol %) is complete in one hour 19. Further, the hydroboration of 2‐naphthaldehyde is faster than that catalysed by the ruthenium complex [Ru( p ‐cymene)Cl 2 ] 2 (0.1 mol %, 4 h),33 albeit lower catalyst loadings were used in each case. Hydroboration of 4‐bromobenzaldehyde (entry 5) is also complete within 15 min, indicating a tolerance to Li/halogen exchange under the reaction conditions, thereby increasing the range of useful substrates able to participate in these reactions.…”

“…Furthermore this reaction occurs quicker than those using either 0.05 mol %A r*N-(Si(iPr) 3 )SnOtBu, [34] in 4.5h (Ar* = (C 6 H 2 {C(H)Ph 2 } 2 iPr-2,6,4), (IPr)-CuOtBu, [35] (0.1 mol %, 1h)o r[ Ru(p-cymene)Cl 2 ] 2 (0.1 mol %, 3h), although again 1tLi has ah igher loading (5 mol %). [33] Interestingly,h ydroboration of mesitaldehyde (entry 6) takes longer for complete conversion (24 ha t7 0 8C). We attribute this to the steric hindrance of two ortho-mesityl methyl groups,w hich slows down the process, presumably by either inhibiting the hydrometallation step and/orb yp reventing efficient reformation of the putative active DHP catalyst.…”