604808-12-0Relevant articles and documents
Rapid ketone transfer hydrogenation by employing simple, in situ prepared iridium(I) precatalysts supported by "non-N-H" P,N ligands
Lundgren, Rylan J.,Stradiotto, Mark
, p. 10388 - 10395 (2008)
The catalytic utility in ketone transfer hydrogenation (TH) of the preformed complexes [Ir(cod)(κ2-2-NMe2-3-PiPr 2-indene)]+X- ([2a]+X-; X: PF6, BF4, and OTf; cod: η4-1,5- cyclooctadiene; OTf: trifluoromethanesulfonate), [Ir(cod)(κ2-1- PiPr2-2-NMe2-indene)]+OTf- ([2b]+OTf-), [Ir-(cod)(κ2-2-NMe 2-3-PiPr2-indenide)] (3), and [Ir(cod) (κ2-o-tBu2P-C6H4-NMe 2)]+ PF6- ([4]+PF 6-), as well as of related mixtures prepared from [{IrCl(cod)}2] and various P,N-substituted indene or phenylene ligands, was examined. Whereas [2a]+X-, [2b] +OTf-, 3, and related in situ prepared Ir catalysts derived from P,N-indenes proved to be generally effective in mediating the reduction of acetophenone to 1-phenylethanol in basic iPrOH at reflux (0.1 mol% Ir; 81-99% conversion) in a preliminary catalytic survey, the structurally related Ir catalysts prepared from (o-R2P-C6H 4)NMe2 (R: Ph, iPr, or tBu) were observed to outperform the corresponding P,N-indene ligands under similar conditions. In the course of such studies, it was observed that alteration of the substituents at the donor fragments of the supporting P,N ligand had a pronounced influence on the catalytic performance of the derived catalysts, with ligands featuring bulky dialkylphosphino donors proving to be the most effective. Notably, the crystallographically characterized complex [4]+PF6 -, either preformed or prepared in situ from a mixture of [{IrCl-(cod)}2], NaPF6, and (o-tBu2P-C 6H4)NMe2, proved to be highly effective in mediating the catalytic transfer hydrogenation (TH) of ketones in basic iPrOH, with near quantitative conversions for a range of alkyl and/or aryl ketones and with very high turnover-frequency values (up to 230000 h-1 at > 50% conversion); this thereby enabled the use of Ir loadings ranging from 0.1 to 0.004 mol %. Catalyst mixtures prepared from [{IrCl-(cod)}2], NaPF6, and the chiral (αS,αS)-1,1'-bis[α- (dimethylamino)benzyl]-(R,R)-2,2'-bis(dicyclohexylphosphino)-ferrocene (Cy-Mandyphos) ligand proved capable of mediating the asymmetric TH of aryl alkyl ketones, including that of the hindered substrate 2,2- dimethylpropiophenone with an efficiency (0.5 mol % Ir; 95% conversion, 95% ee) not documented previously in TH chemistry.
