Nucleophilic Substitution at a Coordinatively Saturated Five-Membered NHC∙Haloborane Centre

Abstract

In this paper, we have used a saturated five-membered N-Heterocyclic carbene (5SIDipp = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-ylidine) for the synthesis of SNHC-haloboranes adducts and their further nucleophilic substitutions to put unusual functional groups at the central boron atom. The reaction of 5-SIDipp with RBCl2 yields Lewis-base adducts, 5-SIDipp·RBCl2 [R = H (1), Ph (2)]. The hydrolysis of 1 gives the NHC stabilized boric acid, 5-SIDipp·B(OH)3 (3), selectively. Replacement of chlorine atoms from 1 and 2 with one equivalent of AgOTf led to the formation of 5-SIDipp·HBCl(OTf) (4) and 5-SIDipp·PhBCl(OTf) (5a), where all the substituents on the boron atoms are different. The addition of two equivalents of AgNO3 to 2 leads to the formation of rare di-nitro substituted 5-SIDipp·BPh(NO3)2 (6). Further, the reaction of 5-SIDipp with B(C6F5)3 in tetrahydrofuran and diethyl ether shows a frustrated Lewis pair type small molecule activated products, 7 and 8.

Versatile chemistry of six-membered NHC with boranes: bromination at sp3 borane, activation of the B–H bond of HBpin, and ring expansion of NHC

“…[5][6][7][8][9][10][11] In the same line, Radius and coworkers established carbene•alane/gallane chemistry and its facile halogenation. [12][13][14] Due to our current interest in boron chemistry, [15][16][17][18][19] we proceeded to study the chemistry of 6-SIDipp with boranes. In our previous communication, we have shown that the reaction of a saturated six-membered N-heterocyclic carbene (6-SIDipp) with BH 3 led to the formation of an adduct, 6-SIDipp•BH 3 .…”

Access to NHC–Boryl Mono‐ and Bis‐Selenide and Utility as Mild Selenium Transfer Reagent Including to the C−F Bond

“…Due to our recent success in saturated N-heterocyclic carbenes, [15][16][17][18] we commenced our study by evaluating the reaction between 5-SIDipp • BH 3 (1) and diphenyldiselenide (PhSeÀ SePh). Monitoring the reaction by 11 B NMR spectroscopy revealed the formation of mixture of both mono and bis selenides (Scheme 2).…”

Barium phosphidoboranes and related calcium complexes

“…§ Complex 6 is a rare example of a heteroleptic, monometallic barium alkoxide. The ring-opening of thf has been previously reported for a number of systems built around oxophilic metals, [25][26][27][28][29][30] frustrated Lewis pairs based on phosphines [31][32][33][34] or NHCc, 48 even middle-to-late transition metals. 49,50 The formation of 6 presumably occurs via nucleophilic attack by the phosphorus atom on the thf α-carbon atom, resulting in ring opening, while the increased negative charge on the now Ba-coordinated oxygen atom also results in borane migration from the phosphine to generate a more stable Lewis adduct.…”