Phosphine- and Amine-Borane Dehydrocoupling Using a Three-Coordinate Iron(II) β-Diketiminate Precatalyst

Abstract

Dehydrocoupling of phosphine- and amine-boranes is reported using an iron­(II) β-diketiminate complex. Dehydrocoupling of amine-boranes is far more facile than the phosphine counterpart, the former proceeding at room temperature with 1 mol% iron precatalyst. This low loading is sufficient to allow in situ kinetic analysis and deuterium labeling studies to be carried out. An iron amido-borane complex has also been isolated, which is believed to be the catalyst resting state. Overall, this has allowed us to postulate a catalytic cycle which proceeds via release of diborazane, iron hydride, and iron amido-borane intermediates.

Magnesocenophane‐Catalyzed Amine Borane Dehydrocoupling

“…These KIEs are different to those reported by Kays et al. for their magnesium‐based catalyst IV , but are similar to those observed for an iron diketiminate catalyst . This suggests that cleavage of the N−H bond might occur in the rate‐determining step.…”

A Highly Active Bidentate Magnesium Catalyst for Amine‐Borane Dehydrocoupling: Kinetic and Mechanistic Studies

“…This stands in contrast to, for example, the iron-catalyzed dehydrocoupling of Me 2 NH·BH 3 reported by Webster et al,w hich displayed aK IE of 2.5 AE 0.2 with Me 2 ND·BH 3 . [45] The distinctive 1:1:1t riplet of HD was also observed by 1 HNMR as the sole by-product in reactions with Me 2 ND·BH 3 ( Figure S32). It was not possible to obtain ap ure sample of Me 2 NH·BD 3 from the literature procedure, whicha fforded mixtures of Me 2 NH·BD 3 and Me 2 NH·BH 3 (Supporting Information, section S4.1.4).…”

“…The formation of iPr 2 N=BH 2 has been observed in previousw ork on the catalytic dehydrogenation of iPr 2 NH·BH 3 . [45][46][47] Scheme1.Synthesis of compounds 1 (a) and 2 (b), and catalytic dehydrocoupling/dehydrogenation of Me 2 NH·BH 3 (c) and iPr 2 NH·BH 3 (d) by 1. To put this reactivity into context, the most effective previous alkalinee arth catalystf or the reaction in Scheme 1c was published by Hill et al in 2010.…”

NHI- and NHC-Supported Al(III) Hydrides for Amine–Borane Dehydrocoupling Catalysis

“…This synthesis was adapted from general literature procedures [48], with the exception that this was solely carried out in hexanes rather than THF. Diisopropyl amine (1.00 g, 1.3 mL, 9.88 mmol) was placed in a Schlenk flask followed by 10 mL of hexanes.…”