Heteroleptic Nickel Complexes for the Markovnikov-Selective Hydroboration of Styrenes

Abstract

First-row transition metal catalysis offers a cheaper, more environmentally sustainable alternative to second- and third-row transition metal catalysts. Nickel has shown great promise as a tool for the borylation of unsaturated compounds to yield boronic esters, but Markovnikov-selective hydroborations of simple styrenes have not been well-explored. Herein, we report the synthesis of benzyl boronic esters via nickel-catalyzed hydroboration of styrenes using a heteroleptic N-heterocyclic carbene (NHC)–phosphine nickel complex, IMes­(Cy3P)­NiCl2. The IMes­(Cy3P)­NiCl2 complex displays a broad substrate scope and maintains the integrity of yield and regioselectivity when challenged with substrates bearing increased steric hindrance. The heteroleptic complexes also tolerate both electron-withdrawing and -donating groups, in contrast to traditional bis-phosphine and Ni(0) complexes.

Recent Advances in Hydrometallation of Alkenes and Alkynes via the First Row Transition Metal Catalysis

“…[288] In 2018, Cárdenas and co-workers disclosed an iron-catalyzed hydroborylative cyclization of 1,6-enynes with 2,2'-biquinoline (129) as the ligand, allowing the construction of carbo-and heterocycles bearing a homoallylic boryl unit (Scheme 104). [288] In 2018, Cárdenas and co-workers disclosed an iron-catalyzed hydroborylative cyclization of 1,6-enynes with 2,2'-biquinoline (129) as the ligand, allowing the construction of carbo-and heterocycles bearing a homoallylic boryl unit (Scheme 104).…”

Cobalt‐Catalyzed Regioselective Hydroboration of Terminal Alkenes

“…The vast majority of known nonprecious metal catalysts have been found to promote the hydroboration of terminal alkenes with anti‐Markovnikov selectivity. However, a few catalysts based on earth‐abundant metals were recently shown to promote the unusual Markovnikov alkene hydroboration . Following reports of Cu I catalysts, our group reported the first manganese‐catalyzed hydroboration of terminal alkenes with Markovnikov selectivity in 2016 .…”

“…Following reports of Cu I catalysts, our group reported the first manganese‐catalyzed hydroboration of terminal alkenes with Markovnikov selectivity in 2016 . In the same year, nickel and iron complexes with N‐heterocyclic carbene (NHC) ligands were reported to catalyze the Markovnikov hydroboration of a range of aromatic terminal alkenes ,. [10a] Very recently, Lu's group also reported an iron‐catalyzed Markovnikov hydroboration of alkenes using amide‐based tridentate ligands.…”

“…Further efforts were dedicated to the development of new cobalt catalysts based on pincer‐type NNN ligands instead of conventional PNP ligands, which are expensive and not readily available (Scheme ). Although rigid tridentate ligands containing pyridine or imine groups have been found to have unique applications in catalytic hydrofunctionalization reactions, the use of flexible tridentate NNN ligands in hydroboration remains scarce. In this paper, we report the synthesis of new dinuclear Co II ‐alkyl complexes based on flexible NNN ligands, and the regiodivergent hydroboration of aromatic terminal alkenes by using the Co‐PNP and Co‐NNN complexes.…”

Cobalt-catalysed Markovnikov selective hydroboration of vinylarenes

“…In most cases, these reactions are either highly anti-Markovnikov selective or give a mixture of both Markovnikov and anti-Markovnikov products. [5][6][7][8][9][10][11][12][13][14][15][16][17][18] Huang reported that bipyridyl-phosphine cobalt complexes show high activity in the anti-Markovnikov hydroboration of alkenes. 5 Additionally, Chirik developed bis(imino)pyridine cobalt methyl complexes for the anti-Markovnikov selective hydroboration of alkenes (Scheme 1A).…”