Electronic structure and bonding in neutral and dianionic boradiphospholes: R'BC2P2R2 (R = H, tBu, R' = H, Ph).
Classical and non-classical isomers of both neutral and dianionic BC(2)P(2)H(3) species, which are isolobal to Cp(+) and Cp(-), are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311++G(d,p) for BC(2)P(2)H(3) is based on a vinylcyclopropenyl-type structure, whereas BC(2)P(2)H(3)(2-) has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC(2)P(2)H(3): 1) tricyclopentane, 2) nido and 3) vinylcyclopropenyl-type structures, all within 1.7 kcal mol(-1) of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp(+) and H(n)C(n)P(5-n)(+) isomers, BC(2)P(2)H(3) shows a competition between pi-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC(2)P(2)H(3) increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC(2)P(2)H(3)(2-) merely favours different positional isomers of the cyclic planar geometry, as observed in 1) isoelectronic neutral heterodiphospholes EtBu(2)C(2)P(2) (E = S, Se, Te), 2) monoanionic heterophospholyl rings EtBu(2)C(2)P(2) (E = P(-), As(-), Sb(-)) and 3) polyphospholyl rings anions tBu(5-n)C(n)P(5-n) (n = 0-5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC(2)P(2)H(3) isomers appear to be: 1) relative bond strengths, 2) availability of electrons for the empty 2p boron orbital and 3) steric effects of the tBu groups in the HBC(2)P(2)tBu(2) systems.
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India).|School of Chemistry, University of Hyderabad, Hyderabad 500046 (India).
Dandamudi
D
Usharani
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India).
Anne
A
Poduska
Chemistry Department, School of Life Sciences, University of Sussex, Falmer, Brighton, Sussex, BN1 9QJ (UK).
John F
JF
Nixon
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India).|Indian Institute of Science Education and Research Thiruvananthapuram, CET Campus, TVM 695016, Kerala (India), Fax: (+91) 471-2597442.
Eluvathingal D
ED
Jemmis
D000838:Anions / Q000737:chemistry*; D001880:Boranes / Q000737:chemistry*; D002412:Cations / Q000737:chemistry; D003517:Cyclopentanes / Q000737:chemistry*; D004583:Electrons; D007536:Isomerism; D008958:Models, Molecular; D013329:Structure-Activity Relationship
D000838:Anions; D001880:Boranes; D002412:Cations; D003517:Cyclopentanes