Differences and Similarities of Structures, Bond Dissociation Energy, and Molecular Orbitals of Borane Complexes with Tetrylone and Tetrylene Ligands: Do Divalent Tetrylenes(II) Have Hidden Divalent Tetrylones(0) Chemistry Character?s
T. A. N. Nguyen, T. P. L. Huynh, T. H. Tran, T. Q. Duong, T. H. Dang and V. T. Pham

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Quantum chemical calculations at the gradient-corrected (BP86) density-functional calculations with various basis sets (SVP, TZVPP) were carried out for BH3 complexes of carbodiphosphorane-analogues (called tetrylones) [H3B-{E(PH3)2}] (B3-EP2) and N-heterocyclic carbene-analogues (called tetrylenes) [H3B-{NHEMe}] (B3-NHEMe) when E = C–Pb. The calculated equilibrium structures of tetrylone complexes B3-EP2showed that all ligands {E(PH3)2} (EP2) were bonded in a tilted orientation relative to the fragment BH3 and the tilting angle became much more acute when E became heavier. In contrast, the slighter complexes B3-NHEMe possessed end-on-bonded NHEMe ligands when E = C–Ge with the bending angles, α, were 180° while the heavier adducts B3-NHSnMe and B3-NHPbMe exhibited side-on-bonded ligands which the bending angle, α, became more acute. The bond dissociations energies (BDEs) for the B-E bonds in B3-EP2system slightly decreased for the heavier homologues from the strongest bonded carbon complex, B3-CP2 (De = 40.5 kcal/mol) to the weakest bonded lead adduct, B3-PbP2 (De = 31.6 kcal/mol). The trend of the BDEs for the B-E bonds in tetrylene complexes B3-NHEMe were observed the same trend compared with tetrylone complexes which is B3-NHCMe >> B3-NHSiMe >> B3-NHGeMe > B3-NHSnMe > B3-NHPbMe. Density functional calculations predicted that tetrylenes B3-NHEMe had some degree of hidden tetrylones(0) character which were supported by significant values for the BDEs, structures, and molecular orbitals of both systems B3-EP2 andB3-NHEMe. The results of this work not only gave insight into the structures and energies of the molecules investigated, but also provided challenges to test the skills of experimental researchers.

Key words: Tetrylones; tetrylenes; bond dissociation energy; density-functional cal-culations; quantum chemical calculations; equilibrium structures


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