Reaction of Dihalodiboranes(4) with a N‐Heterocyclic Silylene: Facile Construction of 1‐Aryl‐2‐Silyl‐1,2‐Diboraindanes

Abstract

Dihalodiboranes(4) react with a N-heterocyclic silylene (NHSi) to generate NHSi adducts of 1-aryl-2-silyl-1,2-diboraindanes, as was confirmed by X-ray crystallography, featuring the functionalization of both B-X (X=halogen) bonds and a sp - or sp -C-H bond under mild conditions. Coordination of a third NHSi to the proposed 1,1-diaryl-2,2-disilyldiborane(4) intermediates, generated by a twofold B-X insertion, may be crucial for the C-H borylation that leads to the final products. Notably, our results demonstrate the first C-H borylation with a strong B-F bond activated by silylene insertion.

Synthesis and Reactivity of Carboranylsilylene Stabilized Boranes: Construction of Carborane-Fused Silaboracycles

“…The results clearly show the formation of a Si→B dative bond with the distances of 1.999(6) Å in 2 , 1.952(6) Å in 3 , and 2.048(2) Å in 4 , which are associated with the crowdedness around the boron atom. These measured data fall in the range of typical Si–B bond distances (1.623–2.065 Å) observed in the reported silylene-borane adducts. − Both Si(1) and B(13) atoms adopt a distorted tetrahedral geometry. The Si(1)–C(1) distances of 1.911(5) Å in 2 , 1.916(4) Å in 3 , and 1.925(2) Å in 4 are barely shorter than that of 1.988(2) Å in 1 .…”

“…On the basis of the aforementioned experimental data and literature reports, − a plausible reaction mechanism for the formation of 5 – 7 is proposed in Scheme . Reaction of 2 or 4 with 1 equiv of LiHMDS affords a four-membered ring intermediate A .…”

“…Silylene (divalent silicon compound) has one lone pair of electrons and one empty p-orbital, acting as both Lewis acid and base. This class of compounds has received considerable attention in coordination/organometallic chemistry, small molecule activation, and stabilization of low-valent main-group compounds. − On the other hand, silylenes are capable of inserting into element-halide bonds in alkyl, − aryl, silyl, stannyl, and boron halides. − The diverse reactivity patterns between silylenes and organoborane halides has also been documented. Representative examples are illustrated in Scheme .…”

“…In 1996, Denk described a slow insertion of an N-heterocyclic silylene (NHSi) into the B–C bond in the silylene-borane adduct . Later, the Braunschweig group reported the oxidative addition reaction of NHSi with ArBX 2 or dihalodiboranes(4) via silylene insertion into the B-X bond. , The groups of Iwamoto and So also disclosed silylene insertion into the B–Cl bond of ArBCl 2 . Roesky reported that amidinate-supported silylene could undergo amidinate ligand rearrangement from Si to B atom and halide migration from B to Si atom to give borylhalosilanes .…”

N-Heterocyclic Silylene Coordinated Dialkyl Borenium Equivalent

“…Highly reactive diarylsilylene was found to undergo B–E (E = B, H, Cl) bond insertions with various boranes. − Metzler and Braunschweig have also reported similar reactions for stable N - heterocyclic silylenes (NHSi) (Scheme ). − The coordination of stable NHSi to B­(C 6 F 5 ) 3 yielded a Lewis acid–base adduct that gradually transformed into a silyl borane via migration of the C 6 F 5 group from boron to silicon. The B–Cl bond insertion was observed when NHSi was allowed to react with haloboranes.…”