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The Lewis Basicity of Diaminocarbene – A Theoretical Study of Donor–Acceptor Complexes of C(NH 2 ) 2 , NH 3 and CO with the Lewis Acids EF 3 , ECl 3 (E = B, Al, Ga, In), TiF 4 and TiCl 4
Author(s) -
Beste Ariana,
Krämer Oliver,
Gerhard Anja,
Frenking Gernot
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199911)1999:11<2037::aid-ejic2037>3.0.co;2-t
Subject(s) - chemistry , lewis acids and bases , acceptor , covalent bond , ionic bonding , boron , frustrated lewis pair , bond order , computational chemistry , crystallography , bond length , organic chemistry , crystal structure , ion , catalysis , physics , condensed matter physics
Quantum chemical calculations at the MP2 level using large valence basis sets up to TZ+2P quality have been carried out in order to predict the geometries and bond energies of the title compounds. The nature of the donor–acceptor bond has also been investigated. The calculations show clearly that diaminocarbenes are much stronger Lewis bases than amines. The complexation energies of C(NH 2 ) 2 have been calculated to be 14–27 kcal/mol higher than those of NH 3 . The most strongly bonded complex is Cl 3 Al–C(NH 2 ) 2 , which has a theoretically predicted Al–C bond energy D o = 59.1 kcal/mol. In all the complexes, the strength of the Lewis bases is C(NH 2 ) 2 > NH 3 > CO, but the ordering of Lewis acid strength of EX 3 depends on the coordinated Lewis base. TiF 4 and TiCl 4 have similar Lewis acidities as BF 3 , but the titanium tetrahalides may bind one or two donor molecules with almost the same bond strength. The investigated donor–acceptor bonds have a high degree of ionic character. The largest covalent contributions are found for the diaminocarbene complexes. The covalent character of the X 3 E–CO bond increases on going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X 3 E–NH 3 and X 3 E–C(NH 2 ) 2 bonds.