Structural Distortion of the TpCo-L Fragment (Tp = tris(pyrazolyl)borate). Analysis by X-ray Diffraction and Density Functional Theory

The crystal structures of coordinatively unsaturated
[(TpNpCo)2(μ-N2)] and
TpNpCo(CO) show “bent”
molecules, in which the fourth ligand (N2, CO) is bent away
from the pseudo-threefold axis of the TpCo-moiety by
27−38°. Magnesium reduction of
Tpt-Bu,MeCo(CO) yielded
[Tpt-Bu,MeCo(μ-CO)]2Mg(THF)4
which was also structurally
characterized; the reduced carbonyl is “linear”. Extended
Hückel theory (EHT) and density functional theory
(DFT)
have been used to analyze the electronic structures and structural
preferences of the TpCo-L fragment with L = CO
(CoI, d8), COLi (Co0,
d9), and I (CoII, d7). The
actual and theoretical structure determinations were in good
agreement.
Based on these results we suggest that d8 TpCo-L
complexes and, by analogy, isoelectronic CpM-L complexes
assume “bent” structures.