Nickel(II) Catalyzed Hydroboration: A Route to Selective Reduction of Aldehydes and N‐Allylimines

Abstract

A cationic [(iminophosphine)nickel(allyl)] + complex was found to be sufficiently electrophilic to activate aldehydes and N-allylimines to undergo hydroboration with pinacolborane (HBpin) under mild reaction conditions. The catalyst displayed excellent selectivity toward aldehydes in the presence of ketones. A wide variety of functional groups were tolerated, includ- [a] I. 1877 ing halogens, NO 2 , CN, OMe, and alkenes for both aldehydes and imines. Electron-rich substrates were found to be significantly more reactive than their electron poor counterparts, a feature that was correlated to their enhanced ability to coordinate to the Lewis acidic nickel center. [40] Colorless liquid (60 mg, 81 % isolated yield). 1 H NMR (600 MHz, CDCl 3 ): δ = 7. 33-7.30 (m, 4H), 7.25-7.22 (m, 1H), 5.92 (ddt, 3 J HH = 17.2, 3 J HH = 10.2, 3 J HH = 6.0 Hz, 1H), 5.19 (dq, 3 J HH = 17.2, 4 J HH = 2 J HH = 1.5 Hz, 1H), 5.10 (dq, 3 J HH = 10.2, 4 J HH = 2 J HH = 1.5 Hz, 1H), 3.78 (s, 2H), 3.27 (dt, 3 J HH = 6.0, 4 J HH = 1.5 Hz, 2H), 1.47 (br s, 1H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ = 140. 3, 136.9, 128.5, 128.3, 127.1, 116.1, 53.4, 51.9. [30a] Colorless liquid (74 mg, 92 % isolated yield). 1 H NMR (600 MHz, CDCl 3 ): δ = 7.22 (d, 3 J HH = 7.9 Hz, 2H), 7.15 (d, 3 J HH = 7.9 Hz, 2H), 5.94 (ddt, 3 J HH = 17.2, 3 J HH = 10.2, 3 J HH = 6.0 Hz, 1H), 5.20 (dq, 3 J HH = 17.2, 4 J HH = 2 J HH = 1.6 Hz, 1H), 5.12 (dq, 3 J HH = 10.2, 4 J HH = 2 J HH = 1.6 Hz, 1H), 3.76 (s, 2H), 3.28 (dt, 3 J HH = 6.0, 4 J HH = 1.6 Hz, 2H), 2.35 (s, 3H), 1.52 (br s, [41] Colorless liquid (81 mg, 91 % isolated yield). 1 H NMR (600 MHz, CDCl 3 ): δ = 7.24 (d, 3 J HH = 8.3 Hz, 2H), 6.86 (d, 3 J HH = 8.3 Hz, 2H), 5.93 (ddt, 3 J HH = 17.3, 3 J HH = 10.4, 3 J HH = 6.0 Hz, 1H), 5.19 (dq, 3 J HH = 17.3, 4 J HH = 2 J HH = 1.6 Hz, 1H), 5.11 (dq, 3 J HH = 10.4, 4 J HH = 2 J HH = 1.6 Hz, 1H), 3.79 (s, 3H), 3.73 (s, 2H), 3.26 (dt, 3 J HH = 6.0, 4 J HH = 1.6 Hz, 2H), 1.45 (br s, 1H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ = 158. 7, 136.9, 132.5, 129.5, 116.1, 113.8, 55.4, 52.8, 51.8. N-Benzylprop-2-en-1-amine (2b): N-(4-Methylbenzyl)prop-2-en-1-amine (2c): N-(4-Methoxybenzyl)prop-2-en-1-amine (2d): N-(4-N,N-Dimethylaminobenzyl)prop-2-en-1-amine(2e): [30a] Pale yellow liquid (87 mg, 91 % isolated yield). 1 H NMR (600 MHz, CDCl 3 ): δ = 7.20 (d, 3 J HH = 8.6 Hz, 2H), 6.72 (d, 3 J HH = 8.6 Hz, 2H), 5.94 (ddt, 3 J HH = 16.8, 3 J HH = 10.1, 3 J HH = 6.1 Hz, 1H), 5.19 (dq, 3 J HH = 16.8, 4 J HH = 2 J HH = 1.6 Hz, 1H), 5.10 (dq, 3 J HH = 10.1, 4 J HH = 2 J HH = 1.6 Hz, 1H), 3.70 (s, 2H), 3.27 (dt, 3 J HH = 6.1, 4 J HH = 1.6 Hz, 2H), 2.94 (s, 6H), 1.38 (br s, 1H). 13 C{ 1 H} NMR (151 MHz, CDCl 3 ): δ = 149.9, 136.9, 129.2, 128.2, 115.9, 112.7, 52.8, 51.7, 40.8. N-(4-Fluorobenzyl)prop-2-en-1-amine (2f):[30a] Colorless liquid (71 mg, 86 % isolated yield). 1 H NMR (600 MHz, CDCl 3 ): δ = 7.32-7.27 (m, 2H), 7.04-6.98 (m, 2H), 5.92 (ddt, 3 J HH = 17.1, 3 J HH = 10.2, 3 J HH = 5.9 Hz, 1H), 5.19 (dq, 3 J HH = 17.1, 4 J HH = 2 J HH = 1.4 Hz, 1H), 5.12 (dq, 3 J HH = 10.2, 4 J HH = 2...

Iron-catalysed hydroboration of non-activated imines and nitriles: kinetic and mechanistic studies

“…However, no successful hydroboration of ketimine is reported by this catalyst. 42 Significantly, across all reports there have been limited examples of successful application of hydroboration strategies employing ketimine substrates; strongly indicating an ongoing need for more active/selective catalysts to be developed. The low abundance, high cost and toxicity of precious metal elements has prompted the catalytic community to focus heavily on an examination of the use of base metals in catalysis.…”

Applications of catalysis in hydroboration of imines, nitriles, and carbodiimides

“…Slightly sluggish reaction rates were observed in substrates with electron withdrawing groups. 100 In that same year, the Gade group reported an iron alkyl precatalyst (Fig. 4d) in the enantioselective hydroboration of N-alkyl imines.…”

Hydrosilylation and hydroboration in a sustainable manner: from Earth-abundant catalysts to catalyst-free solutions

“…His contribution opened up a new method for preparing several boron derivatives. [89][90][91][92][93] The innumerable catalytic solutions have been implemented over many years, starting with those based on transition metals, [94][95][96][97][98][99][100][101][102] through those utilizing rare-earth element complexes, [103][104][105][106][107][108] up to the main group species-catalyzed approaches. [109][110][111][112][113] Once more, our attention was drawn in particular to the procedures utilizing Earth-abundant s-block species.…”