An unusual reaction of A π-complexed lithio-arene: the characterization and structure of μ-(2,2'-difluoro-5,5'-dimethylbenzophenone)bis(tricarbonylchromium(0))

Article abstract of DOI:10.1016/S0022-328X(00)85839-8

(π-Lithioarene)tricarbonychromium(0) complexes are suggested to be in equilibrium with carbene-bridged dimers at low temperature; the dimers can be trapped with acid chlorides or chloroformate esters yielding bis[(arene)tricarbonylchromium(0)]-carbinols or -ketones, respectively. Thus, the lithiation of (p-fluorotoluene)tricarbonylchromium(0) followed by addition of methyl chloroformate yields μ(2,2'-difluoro-5,5'-dimethylbenzophenone)bis(tricarbonylchromium(0)); crystals of C₂₁H₁₂Cr₂F₂O₇ are monoclinic space group P2₁/_c, with a = 7.170(2), b = 21.832(5), c = 13.428(2) A, β = 98.91(2)°. The structure has been determined by the analysis of 1959 observed reflections recorded on a Syntex P2₁ automatic diffractometer and refined by full-matrix least-squares to R = 0.054, R_w = 0.045. The two Cr(CO)₃ tripods are oriented differently with respect to the bound arene rings. This shows that the orientation of the Cr(CO)₃ moiety is not governed primarily by the electronic properties of the ring substituents.