Scandium complex, bonding features

This chapter is devoted to the most significant developments of early-transition metal compounds ligated by N-heterocyclic carbene ligands (from group 3 to group 7 scandium to rhenium) [10]. When appropriate and available, the structural features of these metal complexes will be discussed. The synthetic pathways, bonding nature of the Ccarbene-M> reactivity, and applications of such derivatives (with a special emphasis on their use in catalysis) will be discussed [11]. 

The molecular structure of Sc2-naph (Fig. 11) was reminiscent of previously reported yttrium naphthalene complexes (Fryzuk et al., 2000). The naphthalene is distorted from planarity with C2/C3 and C2A/C3A bending in opposite directions from the plane composed of the other six carbon atoms (ca. 20° torsion angle). The C-C bonds within the naphthalene are best described as two isolated double bonds (C2=C3 and C2A=C3A), with short distances averaging 1.37 A, and a 6C, 871-electron system for the six coplanar center carbon atoms. Each scandium ion binds to Cl through C4 (or CIA through C4A) with similar distances averaging 2.51 A. These features are also reminiscent of those of the lithium naphthalene dianion [Li(TMEDA)]2(p-ri ri -CioH8) (TMEDA = tetramethylethylenediamine) (Melero et al., 2009). 

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