Microwave mediated rhodium-catalysed hydroboration of trans-4-octene with pinacolborane

(N‐Phosphinoamidinate)cobalt‐Catalyzed Hydroboration: Alkene Isomerization Affords Terminal Selectivity

“…In particular we sought to identify catalysts of this type that are useful in promoting alkene isomerization/hydroboration processes that transform linear internal aliphatic alkenes and related substrates selectively into 1-alkylboronate products-a challenging yet useful reaction class that at the time had only proved feasible with either rhodium or iridium catalysts. [19][20][21][22][23] Herein we report on the successful application of the three-coordinate (N-phosphinoamidinate)cobalt(amido) pre-catalyst (1-Co) in the room-temperature addition of HBPin to linear and branched mono-substituted terminal alkenes, gem-disubstituted terminal alkenes, linear internal octenes, and cyclic alkenes with or without added solvent and with excellent anti-Markovnikov selectivity (where relevant); the hydroboration of selected ketones using 1-Co is also presented. The remarkable ability of 1-Co to promote alkene isomerization/hydroboration processes involving linear internal alkenes, leading to the selective terminal addition of the BPin group, is demonstrated.…”

“…In keeping with these results, the hydroboration of an equimolar mixture of 2 a-c with HBPin in the presence of 1-Co (2.5 mol %) afforded 3 cleanly over the course of one hour at room temperature under neat reaction conditions. It is worthy of mention that while synthetically useful, yet challenging, net alkene isomerization/hydroboration processes of this type catalyzed by rhodium or iridium complexes are known, [19][20][21][22][23] such processes promoted by cobalt complexes are limited only to a very recent publication by Obligacion and Chirik [14] that appeared while this manuscript was in preparation, who employed tridentate (bis(imino)pyridine)CoMe catalysts.…”

[Cp*IrCl2]2 catalyzed hydroborations of alkenes using a bulky dioxaborocine

“…More significantly, the C(24)-C(29) bond length of 1.559(3) Å is typical for a single bond. Attempts to affect the hydroboration of limonene [30] using 1 and [Cp*IrCl 2 ] 2 proved unsuccessful, even when reactions were carried out at elevated temperatures using a microwave reactor [18], and additions appear to be remarkably selective for unhindered aliphatic alkenes.…”

“…Since this remarkable discovery, a considerable amount of research has focussed on investigating the mechanism and scope of catalyzed hydroboration reactions [6,[10][11][12][13]. Much less studied, however, is the use of alternate borane sources [14][15][16][17][18]. Indeed, pinacolborane, (4,4,5,5-tetramethyl-1,3,2-dioxaborolane or HBpin) is occasionally used as a replacement for HBcat as the resulting organoborane products are stable to air and chromatography.…”

Microwave Assisted Heterofunctionalization of Alkenes and Alkynes

“…The vinyl-Bpin products are formed regioselectively and stereoselectively. Recently, Robinson reported the MW assisted hydroboration of an internal alkene using O 2 -treated (Ph 3 P) 3 RhCl as the catalyst, THF as the solvent, and HBpin as the substrate (eqn 41) [82]. After irradiating the reaction mixture for 20 minutes (100 W) in a focused microwave reactor, the intended addition product was not formed.…”