Bonding in Transition-Metal Methylene Complexes. 3. Comparison of Cr and Ru Carbenes; Prediction of Stable LnM(CXY) Systems’
نویسندگان
چکیده
The electronic structure of the lowest carbene state of a representative early-transition-metal complex, CrCH2+ (6A1 symmetry), has been examined by using ab initio techniques. Its properties reveal a complex with a single u-donor bond from singlet CH2 to high-spin (d5) Cr+ and no *-back-bond, resulting in a low bond energy (38.7 kcal/mol) and a large carbenealkylidene state splitting (18.8 kcal/mol). These results are contrasted with Ru carbene (possessing both uand r-donor bonds) properties [D,(Ru=C) = 65.8 kcal/mol and A.E(carbene-alkylidene) = 12.9 kcal/mol]. This comparison enables, for the first time, a separation of u-donor bond strengths from *-donor bond strengths. Finally, using only valence electron properties, we are able to predict stabilities of L,M(CXY) complexes (e&, how substituents at carbon affect the preference for bridging vs. terminal CXY), discussing trends for the entire transition series.
منابع مشابه
Bonding in transition-metal-methylene complexes. 2. (RuCH2)+, a complex exhibiting low-lying methylidene-like and carbene-like states.
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