Naphthylaminoborane: from structural switches to frustrated Lewis pair reactivity

Abstract

A series of naphthyl-bridged amino-borane derivatives, namely 1-(dimethylamino)-8-naphthylboranes (1, 3, 5, 7) and 5-(dimethylamino)-6-acenaphthylboranes (2, 4, 6, 8, 10, 11), differing in the steric and electronic properties of the boryl moiety, have been synthesized and fully characterized by spectroscopic and crystallographic means. Structural X-ray analysis of the peri-atom displacement and ring torsion angles served to experimentally assess the presence and magnitude of the B-N interactions. The reversible quaternarization of nitrogen has been explored and was found to provide an efficient switch corresponding to different molecular organizations. The electronic characteristics of the nature of B-N interactions were further studied by Natural Bonding Orbital analysis derived from the theoretically calculated electron densities. This real-space bonding indicator discriminates the bonding B-N contact in 5 from the nonbonding in 8, which correlates with the flexibility of the naphthyl scaffold to respond to the Lewis acidity of boron allowing shorter peri interactions. Whereas, the steric shielding imposed by the two mesityl groups, and/or the rigidity of the acenaphthene framework disrupt B-N interaction. Thus, this communication reports on the modulation of the B-N bonding continuum by means of structural tuning leading to a molecular switch, as well as its implications towards revealing FLP reactivities through the isolation of intermediates of a stepwise mechanism.

Insights into Frustrated and Regular peri‐Substituted (Ace‐)Naphthylaminoboranes and (Ace‐)Naphthylphosphinoboranes

“…Besides their relevance for frustrated Lewis pair chemistry, some of the functionalized (ace-)naphthylphosphinoboranes have been the starting point for the synthesis of interesting new compound classes, such as P 2 B 2 heterocycles, [12,16] borenium ions, [18,20,21] and boron-centered radicals. [19] A selection of these peri-substituted (ace-)naphthylaminoboranes (1)(2)(3)(4)(5)(6) and (ace-)naphthylphosphinoboranes (7)(8)(9)(10)(11)(12) are shown in Schemes 1 and 2. These compounds can be divided into regular LPs (1, 2, 3, 7, 8, 10, 12) and FLPs (4,5,6,9,11), which can be easily distinguished by their N-B and P-B peri distances.…”

“…[19] A selection of these peri-substituted (ace-)naphthylaminoboranes (1)(2)(3)(4)(5)(6) and (ace-)naphthylphosphinoboranes (7)(8)(9)(10)(11)(12) are shown in Schemes 1 and 2. These compounds can be divided into regular LPs (1, 2, 3, 7, 8, 10, 12) and FLPs (4,5,6,9,11), which can be easily distinguished by their N-B and P-B peri distances. In two cases, a minute variation from a naphthyl scaffold to the more rigid acenaphthyl scaffold induced a change from LP to FLP (3 vs. 6 [11] and 8 vs. 11 [15] ), whilst the other substituents remained the same.…”

Di‐(2‐picolyl)‐N‐(2‐quinolinylmethyl)amine‐Functionalized Triarylboron: Lewis Acidity Enhancement and Fluorogenic Discrimination Between Fluoride and Cyanide in Aqueous Solution

“…Aryl organoboron compounds are increasingly exploited as a class of promising materials because of their intriguing optical and electronic properties, which arise from the interactions between the empty p orbital of boron and attached π‐conjugated systems . Furthermore, the inherent Lewis acidic nature derived from the coordinated unsaturation of trivalent organoboron can be utilized for the complexation of certain nucleophilic anions . In particular, triarylboranes containing the −BMes 2 unit (Mes=2,4,6‐Me 3 C 6 H 2 ) have been widely studied in molecular sensors for the fluoride anion, due to their moisture‐stability and the large steric encumbrance, which prevents the coordination of larger anions to boron.…”

“…[1][2][3][4][5][6][7] Furthermore, the inherent Lewisa cidic nature derived from the coordinated unsaturation of trivalent organoboron can be utilized fort he complexation of certain nucleophilic anions. [8][9][10][11][12][13] In particular, triarylboranes containing the ÀBMes 2 unit (Mes = 2,4,6-Me 3 C 6 H 2 )h ave been widely studied in molecular sensors for the fluoridea nion, [14][15][16][17] due to their moisture-stability and the large steric encumbrance, which prevents the coordination of larger anions to boron. In the past decade, many studies have been executed to enhancet he Lewis acidity ande lectron-accepting ability of ArB(Mes 2 )t o overcome the hydration enthalpy of fluoridei ons for applications in aqueouss olutiona ss ensors.…”

“…The title compound QB was readilys ynthesized throughaconventional Suzuki reaction by reacting compound 2 with 4. QB is stable in ambient air and H 2 Oi nb oth solution and the solid state, and was characterized by 1 H, 13 C, 11 BNMR, elemental analysis, and X-ray single-crystallography.A sr evealed by the crystal structure shown in Figure1,t wo mesityl planesa nd ap henylp lane are arranged in ap ropeller-like fashion around the central boron, whereas the boron center is sterically protectedb yt he four ortho-methyl groups. Also, the Ba tom and its three-bonded C atoms exhibit perfectc o-planarity.…”