Journal
ORGANOMETALLICS
Volume 36, Issue 15, Pages 2996-3004Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.organomet.7b00521
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Funding
- MINECO of Spain [CTQ2014-52799-P, CTQ2016-81797-REDC]
- Diputacion General de Aragon [E-35]
- FEDER
- European Social Fund
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The preparation of new osmium hydride complexes, starting from OsH6((PPr3)-Pr-i)(2) (1) and OsH2Cl2((PPr3)-Pr-i)(2) (2), and their catalytic activity in acceptorless dehydrogenative coupling of alcohols and amines and in dehydrogenation of cyclic amines are reported. Complex 1 reacts with acetylacetone (Hacac) to give the classical trihydride OsH3(acac)((PPr3)-Pr-i)(2) (3). The protonation of 3 with triflic acid (HOTf) produces the release of H-2 and the formation of the unsaturated osmium(IV) dihydride [OsH2(acac)((PPr3)-Pr-i)(2)]OTf (4), which is also prepared by starting from 2 via the intermediate OsH2Cl(acac)((PPr3)-Pr-i)(2) (5). Treatment of an acetylacetone solution of 5 with KOH affords Os(acac)(2)((PPr3)-Pr-i)(2) (6). In the presence of 5 mol % of KOH, complexes 3-6 promote the coupling of benzyl alcohol and aniline to give N-benzylideneaniline and H-2. Under the same conditions, complex 3 catalyzes a wide range of analogous couplings to afford a variety of imines, including aliphatic imines, with yields between 90 and 40% after 1-48 h. Complex 3 also catalyzes the dehydrogenation of cyclic amines. According to the amount of H-2 released by each 1 g of employed substrate, the amines have been classified into three classes: poor (1,2,3,4-tetrahydroquinaldine, 2-methylindoline, and 2,6-dimethylpiperidine), moderate (1,2,3,4-tetrahydroquinoline and 6-methyl-1,2,3,4-tetrahydroquinoline), and good hydrogen donors (1,2,3,4-tetrahydroisoquinoline).
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