Frustrated Lewis pair chemistry of hydride sponges

An improved synthesis for 1,8-bis(dimethylboranyl)naphthalene ( 1 , hydride sponge) was developed avoiding the use of tin( iv ) reagents. The related 1,2-bis(dimethylboranyl)benzene ( 2 ) was prepared. 1 combined with 1,8-bis(dimethylamino)naphthalene ( 3 , proton sponge) is a Frustrated Lewis pair (FLP) that forms adducts [ 1 -EH n −1 ][ 3 -H] with the protic compounds EH n = H 2 O, NH 3 , H 2 S, PH 3 , H 2 Se, HCN. Their structures show the chelation of the deprotonated substrates, except for CN − (binds to one B atom of 1 ). The mechanisms of formation of [ 1 -EH n −1 ][ 3 -H] were explored by NMR spectroscopy. Similar reactions took places for the FLP system 2 + 3 , but the adducts [ 2 -EH n −1 ][ 3 -H] are less stable; only the PH 3 adduct was isolated and AsH 3 forms a chelated adduct [ 2 -N&z.dbd;C(CD 3 )AsH 2 ][ 3 -H]. FLP 1 + 3 does not react with molecular hydrogen, but the formal adduct [ 1 -H][ 3 -H] was isolated via salt metathesis from K[ 1 -H] and [ 3 -H]Cl; it is stable towards water, atmospheric oxygen and up to 100 °C; its thermal decomposition proceeds without formation of H 2 . The stabilities of both, the mixture 1 + 3 + H 2 and the formal adduct [ 1 -H][ 3 -H], allow concluding that hydrogen activation of FLP 1 + 3 is kinetically prevented. Hydride and proton sponges together form a Frustrated Lewis pair that cleaves NH 3 , H 2 O, PH 3 , H 2 S, H 2 Se and HCN but not dihydrogen, although the formal dihydrogen adduct, obtained in a synthetic detour, is stable to air and moisture and up to 100 °C.