Conversion of long-chain terminal alcohols and secondary amines into tertiary amines using ruthenium(II) tertiary phosphine complexes as homogeneous catalysts

Cyclopentadienyl RuII Complexes as Highly Efficient Catalysts for the N‐Methylation of Alkylamines by Methanol

“…[1,5,8,11,12] The hydrogen produced in the dehydrogenation process is then transferred to the imine to give the alkylated secondary amine. With secondary amines, the condensation reaction with the aldehyde should give a transient immonium ion.…”

“…[1,5,8,11,12] In a second step the condensation product of the aldehyde with the primary amine is hydrogenated by a RuϪH/RuϪH 2 system to the secondary amine. This product can re-enter the catalytic cycle to be converted into a 3 OD on treatment of 1 with excess cyclohexylamine.…”

“…[19] Finally, we found appreciable amounts of free imine in the reaction mixtures, unlike previous observations in which the imine is formed at the metal centre, by condensation between coordinated amine and aldehyde, and then, without decoordination, immediately hydrogenated to the corresponding amine. [1,5,8,11,12] …”

“…Thus, the reaction between amines and alcohols has been investigated in detail, particularly using homogeneous catalysts based on late transition metals; [1Ϫ12] those based on ruthenium have been the most widely investigated, including the ruthenium() complexes [RuCl 2 (PPh 3 ) 3 ], [1,3,5Ϫ12] [RuH 2 (PPh 3 ) 4 ], [2,4,5Ϫ7] [RuHCl(CO)(PPh 3 ) 3 ], [5,11] [RuBr 2 -(PPh 3 ) 3 ], [6] [RuHCl(PPh 3 ) 3 ], [6] [RuH 2 {P(OEt) 3 } 4 ], [7] [RuCl 2 (CO) 2 (PPh 3 ) 2 ], [8] [RuCl 2 (PϪN) 2 ], [8] (PϪN ϭ o-diphenylphosphanyl-N,N-dimethylaniline) [RuH 2 (CO)-(PPh 3 ) 3 ], [11] [{RuCl 2 (η 5 -C 5 Me 5 )} 2 ], [11] as well as those bearing terdentate NPN or NNЈN type ligands, [12] the ruthenium(0) derivatives [Ru(CO) 3 (PPh 3 ) 2 ], [5] [Ru 3 -(CO) 12 ], [11] and [Ru(cot)(cod)], [11] and, finally, ''in situ'' generated systems [RuCl 3 /phosphane [6,7] or RuCl 3 /P(OR) 3 [6,7] ] exhibit catalytic activity in the N-alkylation of amines by alcohols. Although the reaction is commonly performed in an autoclave at 120Ϫ215°C, long reaction times are often required to obtain high yields of products.…”

Borrowing Hydrogen in the Activation of Alcohols

“…[17] The same catalyst has also been reported to work in other N-alkylation reactions. [18] Selectivity for mono-alkylation was improved using the ruthenium complex RuA C H T U N G T R E N N U N G (cod)A C H T U N G T R E N N U N G (cot), where the ethylation of 2-aminopyridine 3 was achieved to give the product 4 in 85 % yield. [19] The addition of phosphines and phosphites to this complex increased the amount of di-alkylation.…”