Cobalt-catalysed Markovnikov selective hydroboration of vinylarenes

Abstract

A bipyridiyl-oxazoline cobalt catalyst BPOCoCl has been developed for the Markovnikov selective hydroboration of alkenes using pinacolborane and NaOBu as the in situ activator with up to >98 : 2 branched : linear selectivity (24 examples, 45-92% isolated yield).

Visible‐Light Controlled Divergent Catalysis Using a Bench‐Stable Cobalt(I) Hydride Complex

“…We elected to investigate the visible‐light promoted hydroboration of alkenes: an atom‐economical, value‐adding transformation which has provoked substantial research. Examples of both Markovnikov and anti‐Markovnikov cobalt‐catalysed hydroborations have been reported previously. Many of these examples, however, rely on complex ligand systems or use an air sensitive cobalt complex that must be manipulated in a glovebox .…”

Cobalt‐Catalyzed Regioselective Hydroboration of Terminal Alkenes

“…The majority of cobalt‐catalyzed hydroboration reactions of alkenes have been reported to take place with anti‐Markovnikov selectivity, but recent work has indicated that selective Markovnikov hydroboration of alkenes can be achieved through the use of Co‐NNN complexes. [4d], Nevertheless, there is still a great need to develop new cobalt catalysts for Markovnikov hydroboration.…”

Cobalt–Pincer Complexes in Catalysis

“…When the bipyridyl-oxazoline cobalt complex 31 c was applied for the hydroboration of different substituted styrene derivatives the Markovnikovs electivity could be significantly improved. [56] Thus, the hydroboration of styrenew ith pinacolboranep roceeded with excellent yields and high selectivity for the Markovnikov regioisomer( entry 6). With the terpyridine cobalt complex 32 a moderate yield and ag ood Markovnikov selectivity for styrene was obtained (entry 7).…”

“…Interestingly, the air‐stable Co–CCC‐NHC‐pincer complex 29 and the cobalt–alkyl‐NNN‐pincer complex 30 bearing the 2,2′:6′,2′′‐terpyridine ligand hydroborate styrene favouring the Markovnikov regiochemistry (Table , entries 4 and 5) instead of the usual anti‐Markovnikov product. When the bipyridyl–oxazoline cobalt complex 31 c was applied for the hydroboration of different substituted styrene derivatives the Markovnikov selectivity could be significantly improved . Thus, the hydroboration of styrene with pinacolborane proceeded with excellent yields and high selectivity for the Markovnikov regioisomer (entry 6).…”

“…After this influential work of Chirik, variouso ther systems have been published utilising cobalt NNN, PNN, CCC pincer complexes for the hydroboration of alkenes (Figure 4a [56] 32 [1] NaOtBu [2]T HF r.t. 60 69 (9:91) 8 [57] 10 a [1] -Et 2 O25 60 > 99 (92:8) 9 [57] 33 [0.5]-Et 2 O25 240 99 (5:95) 10 [59] 34 [2.5]-benzene r.t. 60 88 (100:0) olefins with HBPin. [53] Most reactions proceeded to completion with 0.005-0.05mol %o f28 with or without solventu pon activation with NaBHEt 3 .I nalarger scale experiment the hydroboration of styrene (50 mmol) with HBPin was realised with a very low catalyst loading of 28 (0.005 mol %) providing ane xcellent turnover number (TON) of 19 800.…”