An Effective Route to Cycloruthenated N-Ligands under Mild Conditions

Abstract

C 6 H 6 )Ru(C∧N)CH 3 CN] + PF 6 -(C∧N ) C 6 H 4 -2-CH 2 NMe 2 , (R)-(+)-C 6 H 4 -2-CH(Me)NMe 2 , C 6 H 2 -3,4-(OCH 3 ) 2 -2-CH 2 -NMe 2 ) are readily obtained by the intramolecular C-H activation of N,N-dimethylbenzylamine derivatives with [(η 6 -C 6 H 6 )RuCl 2 ] 2 in up to 53% isolated yields. Under similar conditions, 8-methylquinoline also led to a cycloruthenated complex, though in lower yield (12%) and after a longer reaction time. Reaction with the optically active (R)-(+)-N,N-dimethyl-1-phenylethylamine led to a 48% diastereomeric excess in the cycloruthenated product. Under the same conditions, and after 14 and 65 h of reaction time, respectively, 2-phenyl-and 2-benzylpyridine are cyclometalated, leading to the formation of complexes in which the benzene ligand has been substituted by three acetonitriles: [(C∧N)Ru(CH 3 CN) 4 ] + -PF 6 -(C∧N ) C 6 H 4 -2-C 5 H 4 N, C 6 H 4 -2-(CH 2 )-C 5 H 4 N) were obtained in 40 and 24% isolated yields, respectively.

Ruthenacycles and Iridacycles as Catalysts for Asymmetric Transfer Hydrogenation and Racemisation

“…Complexes 1-3 [12][13][14], 4a [15,16], 4b [17], 6 [18], 7 [19], 8a-c [20] were prepared according to literature procedures.…”

“…The diastereomeric ratio (dr) of the ruthenacycle depends of course on the ligands. In the case of 1a the dr was 74:26 [19].…”

“…3 This ruthenacycle, which is surprisingly stable is very easily synthesised from [Ru(arene)Cl 2 ] 2 according to Scheme 1 [19]. A simple flash column over alumina gave essentially pure material.…”

“…It is clear that this high temperature is not compatible with the enzyme. Much better results were obtained with catalyst 6 developed by Park and co-workers which was capable of full racemisation of both alcohols within half an hour at room temperature [19]. Unfortunately, the catalyst failed completely under aqueous conditions.…”

The Combinatorial Approach to Asymmetric Hydrogenation: Phosphoramidite Libraries, Ruthenacycles, and Artificial Enzymes

“…These chiral ruthenacycles are easily synthe-A C H T U N G T R E N N U N G sised from an enantiopure aromatic compound with an aminoalkyl side chain and a commercially available ruthenium precursor in a single step as shown in Scheme 5. [38] It turns out these compounds are remarkably good catalysts for the asymmetric transfer hydrogenation of ketones. [39] Better still, it is possible to perform the catalyst synthesis in the robot, immediately followed by screening of its catalytic activity for the substrate of interest.…”