SYNTHESIS AND STRUCTURE OF EVEN-ELECTRON PARAMAGNETIC CHROMIUM(II) COMPLEXES

In an effort to develop the coordination chemistry of Cr(II), we have prepared the starting chloro-bridged dimer {[(Ph(2)PCH(2)SiMe(2))(2)N] Cr}(2)(mu-Cl)(2) by reaction of the lithium salt LiN-(SiMe(2)CH(2)PPh( 2))(2) with CrCl2 . THF. Subsequent replacement of the remaining chlor ide leads to the formation of mononuclear organochromium complexes of the general formula CrR-[N(SiMe(2)CH(2)PPh(2))(2)] (R = Me, CH(2)Ph, C 5H5). The methyl and benzyl complexes display nearly planar geometries around each Cr(II) and both show high-spin (spin-only) d(4) configura tions; the solid-state structure of the benzyl derivative shows that t he benzyl ligand is bound in an eta(2) fashion. The cyclopentadienyl d erivative is low spin (two unpaired electrons) and shows a geometry wi th the tridentate ligand in a distorted facial orientation and the cyc lopentadienyl unit eta(5)-bound. Semiempirical ZINDO restricted open-s hell Hartree-Fock studies confirm the stabilities of the various spin states of the isolated complexes.