SNS ligand-assisted catalyst activation in Zn-catalysed carbonyl hydroboration

Abstract

Zinc amido and thiolate SNS complexes exhibit distinct ligand-assisted pre-catalyst activation pathways for carbonyl hydroboration using pinacolborane.

Comparing B–H Bond Activation in NiIIX(NNN)-Catalyzed Nitrile Dihydroboration (X = Anionic N-, C-, O-, S-, or P-donor)

“…The stoichiometric reaction of 1 with HBpin afforded an insoluble black precipitate and N-borylated L 1 , as confirmed by EI-MS (Figure S15). In the previous work with a Zn­(SNS) 2 hydroboration precatalyst, we also showed that the basic amido group binds strongly to the Bpin group, reducing the ligand’s ability to coordinate the metal . As a result, we turned to the less basic pyrrolyl group in L 2 . ,− …”

“…In the previous work with a Zn(SNS) 2 hydroboration precatalyst, we also showed that the basic amido group binds strongly to the Bpin group, reducing the ligand's ability to coordinate the metal. 42 As a result, we turned to the less basic pyrrolyl group in L 2 . 47,51−53 Treatment of HL 2 with 1 equiv of NiBr 2 (DME) afforded Ni II Br(κ 3 -NNN) (2) as a brown solid (Scheme 3).…”

“…Organoboron intermediates are very important in synthetic chemistry, enabling many important transformations, such as the formation of C–C , and C–N − bonds, alcohols, − imines, , and amines. − Hydroboration of unsaturated CC and CX bonds is one primary route for the production of key organoboron intermediates. − Reduction of nitriles, for example, has received much attention due to the importance of amines as precursors for the production of pharmaceutical compounds and as components of industrial processes for the production of polyesters, dyes, and agrochemicals. , The poor functional group compatibility of traditional hydroboration reagents such as diborane or alkylboranes , led to development of less reactive catecholborane (HBcat) and pinacolborane (HBpin), which do not readily reduce aldehydes at ambient temperature. , To selectively elevate the reactivity of the latter reagents, a number of first row metal and main group complexes have been employed. − Over the past decade, metal–ligand cooperation (MLC) has been shown to be particularly well-suited for catalyzed hydroboration of polar CX bonds. − In one common type of MLC, an anionic ligand X functions as a Lewis base, converting the B–H bond into a B–X bond and a metal hydride. In this type of mechanism, the formed B–X bond either has a productive role in the catalytic cycle, − known as bifunctional catalysis, or just initiates the reaction and leaves the catalytic cycle (bifunctional catalyst activation). − …”

Spin-state crossover in photo-catalyzed nitrile dihydroboration via Mn-thiolate cooperation

“…15 Given the literature precedence for imine hydroboration 33 in addition to a previous report of the activity of a ligand backbone for H 2 activation, 34 the observed hydroboration of the imine backbone in the S Me NS ligand is not unexpected. Additionally, the hydroborated ligand was previously isolated and characterized in our lab, 35 and its presence in this reaction mixture was conrmed by comparison of 1 H and 11 B NMR data. It is of note that this intermediate is preferentially formed over Mn-H derived from traditional bifunctional B-H activation by 41.2 kcal mol −1 (Fig.…”

Solvent-free Zn (NSNO) complex-catalysed dihydroboration of nitriles

“…3 Zinc, as an abundant and economically accessible first row metal, is one of the most environmentally friendly and biocompatible elements that can be employed in synthetic and catalytic processes. 4 Indeed, various hydroboration reactions of N-heterocycles, 5 carbonyls, 6 isocyanates, 7 carbon dioxide 8 and alkynes 9 have been catalysed using zinc-based systems. Reports to date of zinc complex-catalysed dihydroboration of nitriles both involve dimeric precatalysts (A, 10 B 11 ) with strongly donating ligands (Scheme 1).…”