Issue 41, 2021

Hydroboration of carbonyls and imines by an iminophosphonamido tin(ii) precatalyst

Abstract

A novel three-coordinated tin(II) chloride [Ph2P(NtBu)2]SnCl (1) supported by an N,N′-di-tert-butyliminophosphonamide having two phenyl groups on the phosphorus atom was synthesized by the reaction of the starting lithium iminophosphonamide [Ph2P(NtBu)2]Li with SnCl2·(dioxane) in toluene. The molecular structure of 1 was established by X-ray diffraction analysis. Tin(II) chloride 1 can act as an efficient precatalyst for the hydroboration of a wide variety of aldehydes, ketones, and imines at −10 °C. DFT calculations propose that hydroboration involves hydride transfer from the corresponding tin(II) hydride intermediate [Ph2P(NtBu)2]SnH (10) to the carbonyl substrates via four-membered transition states (TS-12), affording three-coordinated tin(II) alkoxide intermediates [Ph2P(NtBu)2]SnOR (13), followed by the stepwise reaction of 13 with HBpin (pin = pinacolate) to release the boronate esters and regenerate the tin(II) hydride 10. The stoichiometric reaction of the in site-generated 10 with benzophenone 2a at −10 °C led to the formation of 13. Moreover, 13 also stoichiometrically reacted with HBpin at −10 °C, forming the corresponding boronate ester 3a and 10 based on the 1H NMR spectrum of the reaction mixture.

Graphical abstract: Hydroboration of carbonyls and imines by an iminophosphonamido tin(ii) precatalyst

Supplementary files

Article information

Article type
Paper
Submitted
07 Jūn. 2021
Accepted
10 Sept. 2021
First published
13 Sept. 2021

Dalton Trans., 2021,50, 14810-14819

Author version available

Hydroboration of carbonyls and imines by an iminophosphonamido tin(II) precatalyst

K. Nakaya, S. Takahashi, A. Ishii, K. Boonpalit, P. Surawatanawong and N. Nakata, Dalton Trans., 2021, 50, 14810 DOI: 10.1039/D1DT01856F

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