The preparation of primary amines from nitriles has been a subject of continuing interest, and many different methods have been reported for this process. We report in this paper an alternative method for transforming nitriles into primary amines. In this work, a wide range of nitriles were reduced to primary amines by 1.2 equiv of ammonia borane under thermal decomposition conditions without any catalyst and the corresponding primary amines were isolated in good to excellent yields. The reactions are environmentally benign with H 2 and NH 3 generated as byproducts. The reactions are also tolerant of many functional groups. Nitriles are likely reduced by the in situ-generated aminodiborane, the application of which in organic synthesis has never been reported before. By using our protocol, primary amines containing multifluorinated aromatic rings, which are greatly important in pharmaceutical synthesis and have rarely been prepared via catalytic processes, were successfully prepared.
A PNCNP pincer-ligated platinum(II) chloride complex [2,6-( t Bu 2 PNH) 2 C 6 H 3 ]PtCl (1a) was synthesized and fully characterized. Complex 1a was applied to the catalytic hydrosilylation of unsaturated carbon-heteroatom bonds. For comparison, the corresponding hydride complex [2,6-( t Bu 2 PNH) 2 C 6 H 3 ]PtH (1b) and the related POCOP pincer chloride complex [2,6-( t Bu 2 PO) 2 C 6 H 3 ]PtCl (1c) were also used to catalyze the reactions. It was found that 1a is a good catalyst for the hydrosilylation of both C�O and C�N bonds. Wide ranges of aldimines, ketimines, aldehydes, and ketones were hydrosilylated, and the expected amine or alcohol products were obtained in good to excellent yields. The reactions also feature good functional group compatibility. Complex 1a represents the most effective transition metal catalyst for the hydrosilylation of the C�N bond and is among the best transition metal catalysts for the hydrosilylation of the C�O bond. The reactions are likely catalyzed by a cationic platinum(II) species generated from complex 1a during the reactions.
In order to develop efficient protocols for CO 2 reduction with less expensive and more convenient hydrogen sources, the catalytic reactivities of group 10 metal hydride complexes supported by a PNCNP pincer ligand, [2,6-( t Bu 2 PNH) 2 C 6 H 3 ]MH (M = Ni, 1a; Pd, 1b; Pt, 1c), against the hydroboration of CO 2 with NH 3 •BH 3 and NaBH 4 have been explored. Both 1a and 1b readily react with CO 2 at room temperature to form the corresponding formato complexes, [2,6-( t Bu 2 PNH) 2 C 6 H 3 ]MOC(O)H (M = Ni, 2a; Pd, 2b), in nearly quantitative yields. Treatment of NH 3 •BH 3 with CO 2 (1 atm) in 1,4-dioxane or THF at room temperature in the presence of 0.05−1.0 mol % of 1b followed by hydrolysis of the resulting mixtures produces formic acid in 105−186% yields, and initial turnover frequencies of up to 2000 h −1 are observed. In the presence of 1.0 mol % of 1b, NaBH 4 reacts with CO 2 (1 atm) in THF at room temperature to form NaB[OC(O)H] 4 (3) in 87% isolated yield. In situ NMR spectroscopy indicates that the reactions proceed through the insertion of the C�O bond in CO 2 into the Pd−H bond in 1b to form 2b, which sequentially reacts with the hydrides in NH 3 •BH 3 or NaBH 4 to produce boron formato species and regenerate 1b. This work represents one of the rare examples of catalytic transfer hydrogenation of CO 2 with NH 3 •BH 3 to the formic acid level under very mild conditions without any additives and also the first example of 4 equiv of CO 2 uptake by NaBH 4 in a reaction.
A palladium(II) hydride complex supported by a benzene-based PNCNP pincer ligand, [2,6-(tBu2PNH)2C6H3]PdH (1), has been synthesized via two different routes: the reaction of the corresponding chloride complex with LiAlH4 and...
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