TY - JOUR
T1 - The Lewis basicity of diaminocarbene - A theoretical study of donor- acceptor complexes of C(NH2)2, NH3 and CO with the Lewis acids EF3, ECl3 (E = B, Al, Ga, In), TiF4 and TiCl4
AU - Beste, Ariana
AU - Krämer, Oliver
AU - Gerhard, Anja
AU - Frenking, Gernot
PY - 1999
Y1 - 1999
N2 - 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(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)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(NH2)2 > NH3 > CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, 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 aye found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on-going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
AB - 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(NH2)2 have been calculated to be 14-27 kcal/mol higher than those of NH3. The most strongly bonded complex is Cl3Al-C(NH2)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(NH2)2 > NH3 > CO, but the ordering of Lewis acid strength of EX3 depends on the coordinated Lewis base. TiF4 and TiCl4 have similar Lewis acidities as BF3, 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 aye found for the diaminocarbene complexes. The covalent character of the X3E-CO bond increases on-going from E = boron to the heavier Group 13 elements, while the opposite order is found for the X3E-NH3 and X3E-C(NH2)2 bonds.
KW - Ab initio calculations
KW - Diaminocarbenes
KW - Donor-acceptor complexes
KW - Lewis basicity
UR - http://www.scopus.com/inward/record.url?scp=0038568231&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1099-0682(199911)1999:11<2037::AID-EJIC2037>3.0.CO;2-T
DO - 10.1002/(SICI)1099-0682(199911)1999:11<2037::AID-EJIC2037>3.0.CO;2-T
M3 - 文章
AN - SCOPUS:0038568231
SN - 1434-1948
SP - 2037
EP - 2045
JO - European Journal of Inorganic Chemistry
JF - European Journal of Inorganic Chemistry
IS - 11
ER -