Homopolar dihydrogen bonding in ligand stabilized diberyllium hydride complexes, Be-2(CH3)(2)H2L2 (L = H-, CO, N-heterocyclic carbene and CN-)

摘要

The structure and bonding of diberyllium hydride complexes Be-2(CH3)(2)H(2)L2, where L = H- (2), CO (3), NHC (4) and CN- (5) were studied in detail and compared with isostructural diborane (1). The bonding in Be-2(CH3)(2)H2L2 was analyzed considering the interaction of two Be(CH3)L fragments with the bridging (mu-H)(2) fragment. The geometrical and molecular orbital (MO) analyses indicate that the extent of back donation from Be L (L = CO, NHC and CN-) is less in Be-2(CH3)(2)H2L2 as compared to that in Be(CH3)L fragments. The NBO, MO and QTAIM analyses indicate a significant charge concentration at the bridging (mu-H)(2) in Be-2(CH3)(2)H2L2, whereas charge depletion is observed at the (mu-H)(2) fragment in diborane. The accumulation of electron density at the bridging (mu-H)(2) is duly reflected in the detection of a (mu-H)-(mu-H) bond path in Be-2(CH3)(2)H2L2, in spite of having longer (mu-H)-(mu-H) distances. The interaction between the bridging H-atoms in diberyllium hydride complexes can be considered as homopolar hydride hydride dihydrogen bonding. The direction of the charge flow is from (mu-H)(2) to BH2 in diborane, whereas from Be(CH3)L to (mu-H)(2) in Be-2(CH3)(2)H2L2. Hence, the bridging (mu-H)(2) fragments in Be-2(CH3)(2)H2L2 are electron rich as compared to the (mu-H)(2) fragment in diborane. The experimental report of the ring opening of the (NHC)-N-Ar (Ar = 2,4,6-trimethylphenyl) ligand through hydride transfer from [Be(CH3)H((NHC)-N-Ar)](2) corroborates well with the presence of electron rich bridging (mu-H)(2) in diberyllium hydride complexes.