Bent metallocenes containing ancillary ligands in ring-bridging chains. Synthesis, spectroscopy, and X-ray crystal structure of [2,6-pyridinediylbis(methylcyclopentadienyl)]chromium(II)

Cr[(eta5-C5H4CH2)2-2,6-C5H3N] (CrL) has been obtained by metathesis reaction between CrCl2 and Na2[(C5H4CH2)2-2,6-C5H3N] in THF at room temperature. Low-temperature H-1 NMR studies of CrL are reported. The solid state structure of CrL was determined by single crystal X-ray analysis (monoclinic, C2/c, a = 13.662(3) angstrom, b = 8.975(2) angstrom, c = 21.085(3) angstrom, beta = 95.11(4)-degrees, V = 2575.1(9) angstrom3, z = 8, R = 0.041, R(w) = 0.052 for 1619 measured reflections with I > 3sigma(I)). The ligand is bound to the metal atom via the two bent cyclopentadienyl rings with distances Cr-Cg(1) (Cg = gravity center) of 1.849(5) angstrom and Cr-Cg(2) of 1.840(5) angstrom, with the pyridine nitrogen at a distance Cr-N of 2.521(4) angstrom, which is the longest Cr-N value yet reported. The effects of the reduction in symmetry of this bent chromocene with respect to the unsubstituted one, which results in the perturbation of the axial ligand field typical of the undistorted metallocenes, are discussed in view of magnetic and optical investigations.