Beyond the Nucleophilic Role of Metal–Boryl Complexes in Borylation Reactions

Abstract

Transition metal–boryl complexes play an important role as reactive intermediates in catalytic borylation processes and have enjoyed tremendous exploration. Over the years, it has been well established that a boryl ligand possesses strong nucleophilicity in copper­(I)–boryl complexes. Thus, the role played by boron’s “empty” p orbital has often been overlooked and d-electrons’ effect from the metal is even more seldom mentioned, despite the fact that they in theory should also have influence on the reactivity of a metal–boryl complex. In this work, the reactivity of metal–boryl complexes has been systematically studied with the aid of density functional theory calculations. We have revealed that when the metal is more electronegative, the nucleophilic feature of boryl is diminished and will no longer be active, whereas when the boryl is not substituted with π-donating groups, the “empty” p orbital of boron will be active and can serve as the electrophilic site. In addition, when the metal center changes from relatively inert d10 to d8, the d electrons can also play the role of a nucleophile. With a much more comprehensive understanding of metal–boryl complexes, this work will benefit the future catalyst design related to transition-metal-catalyzed borylation reactions.

Robust dicopper(i) μ-boryl complexes supported by a dinucleating naphthyridine-based ligand

“…Finally, the electron distribution in the Cu–B bonds was investigated, since studies attribute the high nucleophilicity and reactivity exhibited by these complexes to the Cu-boryl σ-bonding electrons. Computational work by Carbó and Fernández in 2012, 33 and Sheong and Lin in 2021, 34 revealed that the contribution of B-based orbitals to the M–BR 2 bond is remarkably high ( ca. 70%, with a p/s ratio ≈ 0.9) 35 in the case of mononuclear Cu-boryl species, whereas in other examples like Au- or Pd-boryl compounds, the contribution of B is 56% and 53%, respectively.…”

Gold-Aluminyl and Gold-Diarylboryl Complexes: Bonding and Reactivity with Carbon Dioxide

“…Notably, gold-boryl complex III involving aryl substituents is expected to differ from typical dioxy- and diamino-boryls such as Bpin (pin = pinacolate: 2,3-dimethyl-2,3 butanediolate), Bcat (cat = 1,2-O 2 C 6 H 4 ), Bneop (neop = (OCH 2 ) 2 CMe 2 ), Bdan (dan = 1,8-diaminonaphthalene), etc., mainly in the role played by boron’s “empty” p orbitals and to exhibit stronger Lewis acidity at the boron center. 4 Although experimental evidence for the reaction of complex III with carbon dioxide has not been reported, the reduction of CO 2 to CO catalyzed by a copper boryl complex [IPrCu(Bpin)] has been observed to occur in solution under mild conditions, 5 and the reaction mechanism has been computationally studied. 6 Very recently, some of us have computationally investigated the analogous reactivity with isostructural gold-aluminyl, gold-gallyl, and gold-indyl complexes, [ t Bu 3 PAuX( Si NON)] − (X = Al, Ga, and In, Si NON = [O(SiMe 2 NDipp) 2 ] 2– , Dipp = 2,6- i Pr 2 C 6 H 3 ), demonstrating that this is kinetically and thermodynamically favorable only for the gold-aluminyl complex.…”

Iridium‐Catalyzed β‐C(sp2)−H Borylation of Enamides – Access to 3,3‐Dihalogeno‐2‐methoxypiperidines

“…The reaction insertion of the metal‐complex occurred at the more nucleophilic site of the double bond. As described in the literature, when the boryl in the metal complex is not substituted with a π‐donating group, the empty p orbital of boron remains active and can serve as the electrophilic site [12] . The C−H borylation of aromatics is well documented, in contrast fewer studies described analogous reactions for alkenes.…”

“…As described in the literature, when the boryl in the metal complex is not substituted with a π-donating group, the empty p orbital of boron remains active and can serve as the electrophilic site. [12] The CÀ H borylation of aromatics is well documented, in contrast fewer studies described analogous reactions for alkenes. However, we assume that the insertion reaction occurred with an in situ generated tris(boryl)Ir(III) complex as depicted in the literature.…”