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

An intramolecular phosphine-borane frustrated Lewis pair (FLP) chelate, i Pr2 P(C6 H4 )BCy2 or PB (Cy = cyclohexyl), was used to coordinate aminoborane (H2 BNH2 ) 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 H2 BNH2 complex supported by a modified FLP chelate bearing a geometrically constrained bicyclic 9-borabicyclo(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 }].