Carbodicarbenes and related divalent carbon(0) compounds.
Quantum-chemical calculations using DFT and ab initio methods have been carried out for fourteen divalent carbon(0) compounds (carbones), in which the bonding situation at the two-coordinate carbon atom can be described in terms of donor-acceptor interactions L-->C<--L. The charge- and energy-decomposition analysis of the electronic structure of compounds 1-10 reveals divalent carbon(0) character in different degrees for all molecules. Carbone-type bonding L-->C<--L is particularly strong for the carbodicarbenes 1 and 2, for the "bent allenes" 3 a, 3 b, 4 a, and 4 b, and for the carbocarbenephosphoranes 7 a, 7 b, and 7 c. The last-named molecules have very large first and large second proton affinities. They also bind two BH(3) ligands with very high bond energies, which are large enough that the bis-adducts should be isolable in a condensed phase. The second proton affinities of the complexes 5, 6, and 8-10 bearing CO or N(2) as ligand are significantly lower than those of the other molecules. However, they give stable complexes with two BH(3) ligands and thus are twofold Lewis bases. The calculated data thus identify 1-10 as carbones L-->C<--L in which the carbon atom has two electron pairs. The chemistry of carbones is different from that of carbenes because divalent carbon(0) compounds CL(2) are pi donors and thus may serve as double Lewis bases, while divalent carbon(II) compounds are pi acceptors. The theoretical results point toward new directions for experimental research in the field of low-coordinate carbon compounds.
Klein
Susanne
S
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Strasse, 35043 Marburg, Germany.
Tonner
Ralf
R
Frenking
Gernot
G