A N‐Heterocyclic Carbene‐Supported Zinc Catalyst for the 1,2‐Regioselective Hydroboration of N‐Heteroarenes

Mondal, Sumana; Singh, Tejender; Baguli, Sudip; Ghosh, Soumya; Mukherjee, Debabrata

doi:10.1002/chem.202300508

Cited by 11 publications

(5 citation statements)

References 124 publications

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“… [19] Efforts to obtain Zn‐thiolate complexes were unsuccessful due to Zn‐NHC bond scission. During the submission of our work, Mukherjee and coworkers reported the formation of a Zn(II) hydride species from fluorenyl‐tethered NHC⋅ZnBrN(TMS) 2 complex upon reaction with HBpin, and the resultant zinc hydride species has been employed as a catalyst for the regioselective hydroboration of N‐heteroarenes [20] . In the same vein, we have also reacted 1 with pinacolborane (HBpin) to prepare the zinc hydride, however, the reaction led to the extrusion of ZnEt 2 and 6‐SIDipp mediated B−H activation of HBpin took place, which was recently reported by our group [14] .…”

Section: Resultsmentioning

confidence: 99%

Six‐Membered NHC Stabilized Monomeric Zinc Complexes

et al. 2023

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This paper describes the rare use of a 6‐membered saturated N‐heterocyclic carbene (NHC) known as 1,3‐di(2,6‐diisopropylphenyl) tetrahydropyrimidine‐2‐ylidene (abbreviated as 6‐SIDipp) as a ligand in zinc chemistry. We report on the investigation of the reactions between 6‐SIDipp and ZnX2, which resulted in a range of new monomeric 6‐SIDipp⋅ZnX2 complexes (X=Et (1), Cl (2), Br (3), and I (4)). We also prepared a new NHC zinc complex where the two substituents of the zinc atom are different, 6‐SIDipp⋅Zn(Et)Br (7) through the reaction of the proligand [6‐SIDippH]Br with ZnEt2. We have observed that the reactions of complex 1 with sulfur and HBpin led to the removal of the ZnEt2 moiety, resulting in the formation of a C=S double bond and a B−H activation product, respectively. Lastly, the reaction of 1 with five‐membered NHCs led to the exchange of carbene and the formation of either 5‐IDipp⋅ZnEt2 (8) or 5‐SIDipp⋅ZnEt2 (9).

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Section: Resultsmentioning

confidence: 99%

Six‐Membered NHC Stabilized Monomeric Zinc Complexes

et al. 2023

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“…We also plan to test 8 in other hydroelementation catalyses. A few more zinc catalysts for carbonyl hydroboration are known. A conjugated bis-guanidinate-supported zinc hydride dimer (0.05 mol % loading) gives a TOF of 5800 h –1 for the same reaction…”

Section: Results and Discussionmentioning

confidence: 99%

2-Anilidomethylpyridine-Derived Three-Coordinate Zinc Hydride: The Journey Unveils Anilide Backbone’s Reactive Nature

Mandal,

Joshi,

Das

et al. 2023

Inorg. Chem.

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Low-coordinate heteroleptic zinc hydrides are catalytically important but rare and synthetically challenging. We herein report three-coordinate monomeric zinc hydride on a 2anilidomethylpyridine framework ( NN L). The synthetic success comes through systematically screening a few different routes from different precursors. During the process, the ligand's anilide backbone interestingly appears to be more reactive than Zn's terminal site to electrophilic Lewis and Brønsted acids. The proligand NN LH reacts with [Zn{N(SiMe 3 ) 2 } 2 ] and ZnEt 2 to give [( NN L)ZnA] (A = N(SiMe 3 ) 2 (1), Et(2)). Both are inert to PhSiH 3 and H 2 but react with HBpin only through the internal Zn−N anilide bond to give the borylated ligand NN LBpin (3). The reactions of 1 and 2 with Ph 3 EOH (E = C, Si) afford a series of divergent compounds like [( NN LH)Zn(OSiPh 3 ) 2 ] (4), [Zn 3 (OSiPh 3 ) 4 Et 2 ] (5), and [EtZn(OCPh 3 )] (6). But in all cases, it is invariably the Zn−N anilide bond protonated by the −OH with equal or higher preference than the terminal Zn−N or Zn−C bonds. A DFT analysis rationalizes the origin of such a reactivity pattern. Realizing that an acidfree route might be the key, reacting [( NN L)Li] with ZnBr 2 gives [( NN L)Zn(μ-Br)] 2 (7), which on successively treating with KOSiPh 3 and PhSiH 3 gives the desired [( NN L)ZnH] (8) as a three-coordinate monomer with a terminal Zn−H bond. Estimating the ligand steric in 8 shows the openness in Zn's coordination sphere, a desired criterion for efficient catalysis. This and a positive influence of the pyridyl sidearm is reflected in 8's superior activity in hydroborating PhC(O)Me by HBpin in comparison to Jones' two-coordinate anilido zinc hydride.

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“…Motivated by the earlier precedence of Zn‐catalyzed hydroelementation of N‐heteroarenes, [59–60] Mukherjee and coworkers synthesized the NHC‐supported Zn(II) complexes ( 23 and 23’ ) and applied them as a catalyst for hydroboration of N‐heteroarenes (Scheme 33). [63] This Zn catalysts exhibited high 1,2‐regioselectivity and good productivity at 25 °C with regard to the dearomative reduction of pyridines and (iso)quinolines. This work represents the first NHC‐ligated metal catalysts for 1,2‐hydroboration of N‐heteroarenes (Scheme 33a).…”

Section: Recent Studiesmentioning

confidence: 94%

First‐Row Transition Metal‐Catalyzed Single Hydroelementation of N‐Heteroarenes

Park

2024

ChemCatChem

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Catalytic partial reduction of N‐heteroarenes with H2 or H[E] (E = Si, B‐based) has been a useful and general method for synthesis of a broad range of dihydropyridines (DHP) and dihydroquinolines (DHQ). In recent seven years, one of the most notable advances in this context is being able to utilize earth‐abundant and inexpensive first‐row transition metal‐based catalytic systems. These catalytic procedures are generally considered more environmentally benign and sustainable when compared to conventional catalytic systems relying on precious metals. This Review describes 20 molecular catalytic systems based on first‐row transition metals for selective single hydroelementation of pyridines and quinolines with H2 surrogate, hydrosilanes, and hydroboranes providing 1,2‐ or 1,4‐dihydropyridines and ‐dihydroquinolines. The observed reaction profiles such as scope and activity are briefly presented, while the proposed working modes over a series of elemental steps ‐ H−[E] bond cleavage, hydride (H‐) or hydrogen atom (H·) transfer, and product release, are discussed in detail on the basis of experimental and/or computational mechanistic observations and insights.

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A N‐Heterocyclic Carbene‐Supported Zinc Catalyst for the 1,2‐Regioselective Hydroboration of N‐Heteroarenes

Cited by 11 publications

References 124 publications

Six‐Membered NHC Stabilized Monomeric Zinc Complexes

Six‐Membered NHC Stabilized Monomeric Zinc Complexes

2-Anilidomethylpyridine-Derived Three-Coordinate Zinc Hydride: The Journey Unveils Anilide Backbone’s Reactive Nature

First‐Row Transition Metal‐Catalyzed Single Hydroelementation of N‐Heteroarenes

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