ISSN:
1434-1948
Keywords:
Diaminocarbenes
;
Lewis basicity
;
Ab initio calculations
;
Donor-acceptor complexes
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 Do = 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 are 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.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
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