Reactivity of the dimesityl-1,8-naphthalenediylborate anion: isolation of the borataalkene isomer and synthesis of 1,8-diborylnaphthalenes

Abstract

The anionic boron peri-bridged naphthalene derivative, namely dimesityl-1,8-naphthalenediylborate (1), undergoes a hydrolysis reaction to afford dimesityl-1-naphthylborane (2) whose structure has been determined. Upon standing at room temperature in toluene for an extended period of time, 1 undergoes a ring expansion reaction to afford 8,10,11a-trimethyl-7-mesityl-11aH-7-boratabenzo[de]anthracene (3). As shown by its crystal structure, compound 3 constitutes a rare example of a borataalkene and features a carbon-boron double bond of 1.475(6) Angstroms incorporated in a conjugated hexa-1-boratatriene system. The reaction of 1 with 9-chloro-9-borafluorene and 5-bromo-10,11-dihydrodibenzo[b,f]borepin results in the formation of diboranes 4 and 5 which bear two different boryl moieties at the peri-positions of naphthalene. These diboranes have been characterized by multinuclear NMR spectroscopy and X-ray single crystal analysis. The boron center of the borafluorenyl moiety is pi-coordinated to the ipso-carbon of a mesityl group with which it forms a contact of 2.730(3) Angstroms. The cyclic voltammogram of 2 in THF shows a quasi-reversible reduction wave at E(1/2)-2.41 V (vs. Fc/Fc+) corresponding to the formation of the radical anion. In the case of diboranes 4, 5 and 1-(dimesitylboryl)-8-(diphenylboryl)naphthalene (6), two distinct waves are observed at E(1/2)-2.14 and -2.56 V for 4, E(1/2)-2.26 and -2.78 V for 5, and E(1/2)-2.41 and -2.84 V for 6. The first reduction wave most likely indicates the formation of a radical anion in which the unpaired electron is sigma-delocalized over the two boron centers.

Structural Changes Accompanying the Stepwise Population of a BC π Bond

“…This salt is extremely air-sensitive and has been isolated in a crystalline form by diffusion of hexane into a THF solution. In the 11 B NMR spectrum, the resonance which appears at d = 40 ppm is close to those reported for [Mes 2 BCH 2 ] À (d = 35 ppm) [1] and 8,10,11a-trimethyl-7-mesityl-11aH-7-boratabenzo[de]anthracene (d = 45.5 ppm), [2] thus reinforcing a borataalkene formulation for 1 À . The 1 H resonance of the N-methyl group of 1 À at d = 3.09 ppm is shifted upfield by 1.9 ppm when compared to that of 1 + .…”

“…Since the structure of 1C has been previously determined, [19] the present structural analysis of 1-OTf and 1-[K(db- [18]crown-6)(thf) 2 ] allows us to analyze the structural changes induced by reduction of 1 + into 1C and 1 À (Figure 2). …”

Dibenzometallacyclopentadienes, boroles and selected transition metal and main group heterocyclopentadienes: Synthesis, catalytic and optical properties

“…53 and 54) and shows an 1 -coordination of the ipso-carbon of one of the Mes groups to the boron atom of the dibenzoborole moiety [100]. Electrochemical reduction generated a radical anion with the unpaired electron delocalized over the two B centers.…”

Fluoride Ion Recognition by Chelating and Cationic Boranes

“…These reactions afford unsymmetrically substituted 1,8-diborylnaphthalene species such as 3, 4, 5, and 6 where the boron centers are separated by 3.2-3.4 Å. [47][48][49] In a similar way, 2 reacts with 10-bromo-9-oxa-10-boranthracene (7) or 10-bromo-9-thia-10-boranthracene (8) to afford diboranes The reaction of diboranes 3, 9, and 10 with [S(NMe 2 ) 3 ]-[Me 3 SiF 2 ] (TASF) has been investigated and found to afford the anionic chelate complexes [3-µ 2 -F] -, [9-µ 2 -F] -and [10-µ 2 -F] -(Scheme 3). 26,49,50 Complexation of larger halides or polyatomic anions such as NO 3 -and H 2 PO 4 -is not observed thus indicating that fluoride anion complexation is selective.…”

“…However, it had been firmly established that bifunctional diboranes with rigid aromatic backbones [39][40][41] Figure 1) rather than the targeted diborane. [45][46][47][48] Because of the strain present in the four-membered ring, this borate is very reactive and undergoes ringopening reactions with electrophiles including boron halide reagents. These reactions afford unsymmetrically substituted 1,8-diborylnaphthalene species such as 3, 4, 5, and 6 where the boron centers are separated by 3.2-3.4 Å.…”