Two‐Coordinate NHC‐Supported Zn^IIOrganocations: Steric and Electronic Tunability and Use in Alkyne Hydroboration Catalysis

Abstract

Dedicated to Professor Rinaldo Poli on the occasion of his 65th birthday.We herein report on the synthesis, structure, and use in alkyneled to with robust and stable two-coordinate Zn II cations [(IPrCl)ZnÀ R] + (3 a, R=Et; 3 b, R=Me) and [(ItBu)ZnÀ Et] + (4), respectively, all isolated as [B(C 6 F 5 ) 4 ] À salts. Further derivatization of alkyl cations 3 b and 4 by reaction with one equivalent of [B(C 6 F 5 ) 3 ] afforded cations [(IPrCl)ZnÀ C 6 F 5 ] + (5) and [(ItBu)ZnÀ C 6 F 5 ] + (6) as [B(C 6 F 5 ) 4 ] À salts,with cation 6 displaying a limited stability in solution. The molecular structures of cations 3 b, 4 and 5 were confirmed through X-ray diffraction studies. Among stable cations, Fluoride ion affinity (FIA) estimations agree with cation 5 being the most Lewis acidic in thus far reported [(IPrCl)ZnÀ R] + cations. In the presence of pinacol borane and 1-octyne, cations 3 a-b, 5 and [(IPrCl)ZnÀ C 6 F 5 ] + (5 mol%) slowly catalyze the selective cishydroboration of 1-octyne to the vinylborane product A. Cation 5 also mediates 2-hexyne hydroboration to afford a mixture of hydroboration products B and C. In the case of hydroboration catalysis mediated by cations 5 and [(IPrCl)ZnÀ C 6 F 5 ] + , experimental data and preliminary DFT calculations are consistent a Lewis-acid-type catalysis.

Ligand and metal-centred reactivity in 2,6-bis(imino)-1,4-dihydropyridinate Zn(ii) alkyls: the dual behaviour of an intriguing type of complex

“…BF 4 − or SbF 6 − ). However, the shortest Zn⋯F–C were found in four ionic complexes with organic fluorinated anions, 30 with the hitherto closest approach, 2.471 Å, corresponding to the interaction of a linear cation [(NHC)Zn(C 6 F 5 )] + with [B(C 6 F 5 ) 4 ] − as its counteranion. 30 a Most of the remaining Zn⋯F–C contacts (192 = 86%) fall within the range of 2.7–3.0 Å.…”

Magnesium(ii) complexes supported by indole- and pyrrole-containing Schiff-base ligands: syntheses, structures, and applications as precatalysts in the hydroboration of nitriles and alkynes

“…30,31 Since Nikonov and coworkers discovered that a Mo(IV) complex could catalyse the hydroboration of nitriles in 2012, 32,33 research on the hydroboration of nitriles or alkynes has been increasing. A plethora of transition-metal complexes, such as zirconium, 34 manganese, 35 iron, 36,37 cobalt, 22,[38][39][40][41][42][43] nickel, [44][45][46] zinc, [47][48][49][50][51][52][53] ruthenium, [54][55][56] palladium, 57 and many rare-earth metal complexes, [58][59][60] can catalyse the hydroboration of nitriles or alkynes. In recent years, earth-abundant, nontoxic and inexpensive main group-metal compounds have become favourable catalysts in these research fields.…”

Tri-coordinated zinc alkyl complexes with N^S/Se coordination of imino-phosphanamidinate chalcogenide ligands as precursors for efficient hydroboration of nitriles and esters

“…Recently zinc complexes have also started to gain the attention of researchers as potential catalysts for hydroboration reactions. [33][34][35][36][37][38][39] Yao et al and Mukherjee et al independently reported multidentate phenolate ligand-supported zinc alkyl complexes and N-heterocyclic carbine-based zinc complexes as catalysts for regioselective hydroboration of N-heteroarenes. 40,41 The Nembenna group established a conjugated bis-guanidinate zinc hydride complex as a catalyst for the hydroboration of isonitriles, nitriles and esters.…”