Frustrated Lewis Pair Chelation and Reactivity of Complexed Parent Iminoborane and Aminoborane

Abstract

An intramolecular phosphine−borane frustrated Lewis pair (FLP) chelate, i Pr 2 P(C 6 H 4 )BCy 2 or PB (Cy = cyclohexyl), was used to coordinate aminoborane (H 2 BNH 2 ) and iminoborane (HBNH) units via donor−acceptor stabilization. Attempts to induce dehydrogenation from these B−N adducts with known metal catalysts (or pre-catalysts) have been unsuccessful thus far, and related observations were noted with an H 2 BNH 2 complex supported by a modified FLP chelate bearing a geometrically constrained bicyclic 9borabicyclo(3.3.1)nonane (BBN) unit. Treatment of the iminoborane adduct [PB{HBNH}] with a chlorinating agent led to ligand activation via B−C bond cleavage instead of the expected H/Cl exchange at boron to give [PB{ClBNH}]. Nucleophilic attack at the boron center in [PB{HBNH}] was observed upon addition of BnK (Bn = benzyl), yielding the amidoborate complex [PB{H(Bn)BNH}{K(THF) 2 }].

Frustrated Lewis pair-ligated tetrelenes

“…Previously, our group reported the use of frustrated Lewis pairs (FLPs) 6 to isolate rare examples of “donor–acceptor” stabilized dihydridotetrelenes (EH 2 ). 7,8 Of relevance to the current study, the intramolecular FLP, i Pr 2 P(C 6 H 4 )BCy 2 9 (Cy = cyclohexyl), abbreviated as PB , can be used to access [PB{EH 2 }] adducts (E = Si, Ge), 7 and these hydrides can deposit films of elemental silicon and germanium, respectively, upon mild heating (<110 °C) in toluene (Scheme 1). 7…”

Strain-Release Promoted Thermal [2 + 2] Cycloaddition and Photochemical [2 + 2] Cycloreversion of a Tetraorganylaminoborane

“…In materials chemistry, they act as monomers or intermediates in the catalytic synthesis of poly(aminoborane)s 3−7 and their carbene-catalyzed decomposition 8,9 and as monomers for oligo(iminoborane)s. 10−13 Aminoboranes were discussed in the context of hydrogen storage 14−16 and are potential precursors for boron nitride. 17 Aminoboranes are also useful in synthesis, e.g., of aldimines 18 and iminium ions. 19 They are also used in aza-Matteson reactions, 20 as dienophiles in Diels− Alder reactions, 21−23 and in form of their dimers for alkyne hydroboration.…”

“…24 Likewise, they are important in the synthesis of BN-fused aromatics and 1,2-dihydro-1,2-azaborine derivatives. 25 They found application as Lewis acids, 26 complexes with frustrated Lewis pairs, 17 and further inorganic syntheses. 27 Aminoboranes carrying hydrogen and/or halogen atoms are often dimeric in solution and in the solid state.…”

“…Likewise, they are important in the synthesis of BN-fused aromatics and 1,2-dihydro-1,2-azaborine derivatives . They found application as Lewis acids, complexes with frustrated Lewis pairs, and further inorganic syntheses …”

“…Aminoboranes are an important class of boron–nitrogen containing compounds that are related to alkenes by the substitution of the CC double bond by an isoelectronic and isosteric BN bond. , The applications of aminoboranes are broad and encompass a number of areas of current research. In materials chemistry, they act as monomers or intermediates in the catalytic synthesis of poly­(aminoborane)­s – and their carbene-catalyzed decomposition , and as monomers for oligo­(iminoborane)­s. – Aminoboranes were discussed in the context of hydrogen storage – and are potential precursors for boron nitride . Aminoboranes are also useful in synthesis, e.g., of aldimines and iminium ions .…”