Homogeneous Catalytic Hydrogenation of Amides to Amines

Abstract

Hydrogenation of amides in the presence of [Ru(acac)3] (acacH=2,4-pentanedione), triphos [1,1,1-tris- (diphenylphosphinomethyl)ethane] and methanesulfonic acid (MSA) produces secondary and tertiary amines with selectivities as high as 93% provided that there is at least one aromatic ring on N. The system is also active for the synthesis of primary amines. In an attempt to probe the role of MSA and the mechanism of the reaction, a range of methanesulfonato complexes has been prepared from [Ru(acac)3], triphos and MSA, or from reactions of [RuX(OAc)(triphos)] (X=H or OAc) or [RuH2(CO)(triphos)] with MSA. Crystallographically characterised complexes include: [Ru(OAc-κ(1)O)2(H2O)(triphos)], [Ru(OAc-κ(2)O,O')(CH3SO3-κ(1)O)(triphos)], [Ru(CH3SO3-κ(1)O)2(H2O)(triphos)] and [Ru2(μ-CH3SO3)3(triphos)2][CH3SO3], whereas other complexes, such as [Ru(OAc-κ(1)O)(OAc-κ(2)O,O')(triphos)], [Ru(CH3SO3-κ(1)O)(CH3SO3-κ(2)O,O')(triphos)], H[Ru(CH3SO3-κ(1)O)3(triphos)], [RuH(CH3SO3-κ(1)O)(CO)(triphos)] and [RuH(CH3SO3-κ(2)O,O')(triphos)] have been characterised spectroscopically. The interactions between these various complexes and their relevance to the catalytic reactions are discussed.

Selective Methylation of Amines with Carbon Dioxide and H2

“…As shown in Scheme 1 a, 5 a was fully converted and 2 a was the major product in 64 % yield. [26] Based on these results, we propose that the consecutive methylation reaction proceeds under our reaction conditions with both formamide (major) and methanol (minor) as intermediates (Scheme 3). Interestingly, this reaction occurred in low yield in the presence of H 2 (Scheme 1 b).…”

“…[14,[22][23][24][25][26][27][28] Initially, we investigated the reaction of carbon dioxide, H 2 , and aniline (1 a) in the presence of in situ formed ruthenium complexes as a model system (Table 1 and Tables S1-S4 in the Supporting Information). [14,[22][23][24][25][26][27][28] Initially, we investigated the reaction of carbon dioxide, H 2 , and aniline (1 a) in the presence of in situ formed ruthenium complexes as a model system (Table 1 and Tables S1-S4 in the Supporting Information).…”

“…Since it is known that CO 2 can be hydrogenated to formic acid and methanol in the presence of ruthenium complexes, the reduction of the formamide 5 a and methylation from methanol were investigated. [26] To understand the influence of electronic effects, the competition reaction of para-substituted aniline derivatives was investigated. [30a] Meanwhile, it was found that methanol can also act as the source of the methyl group.…”

Multifaceted catalytic hydrogenation of amides via diverse activation of a sterically confined bipyridine–ruthenium framework

“…Cole-Hamilton 12, 13 , Leitner/Klankermayer 13–15 , and Beller 16 have developed different (triphos)Ru catalyst systems (triphos = CH 3 C[CH 2 PPh 2 ] 3 ; Ph = C 6 H 5 ) for selective cleavage of the C=O bond of amides. When combined with catalytic Yb(OSO 2 CF 3 ) 3 , hydrogen pressure ( P H2 ) can be reduced as low as ca.…”

Hydrogen

“…78, 79 The reaction is sensitive to the nature of the substrates with selectivities varying significantly (eq 32). 80 Despite this, direct amide reduction has significant potential as an environmentally sustainable technique in the future, but continued research in this area is required. In a related reaction, direct methylation of amines has been achieved using CO 2 and hydrogen.…”