86392-66-7Relevant articles and documents
Reactivity and conformation of a phosphine-substituted dihalocarbene complex. X-ray crystal structures of [(η5-C5H5)Fe(CO)(PPh3)(CF 2)][BF4] and [(η5-C5H5)Fe(CO)2(CCl 2)][BCl4]
Crespi, Ann M.,Shriver, Duward F.
, p. 1830 - 1835 (2008/10/08)
The difluorocarbene complex [CpFe(CO)(PPh3)(CF2)][BF4] (1) was prepared by halide abstraction from CpFe(CO)(PPh3)(CF3) using BF3. The structures of this compound and [CpFe(CO)2(CCl2)][BCl4], 2, determined by single-crystal X-ray diffraction, show the effect of ligand asymmetry on the dihalocarbene orientation. For 1 the plane of the CF2 ligand is tilted 18° away from coplanarity with the CO. Complex 2 adopts a vertical conformation with the plane of the CCl2 ligand bisecting the OC-Fe-CO angle. The orientations of CX2 in 1 and 2 agree with the conformations predicted by the MO treatment of Hoffmann and co-workers; however, low-temperature NMR measurements of 1 indicate that the CF2 group is rapidly rotating in solution, so the energy barrier between the various conformers is low. The reaction of CpFe(CO)(PPh3)(CF3) with BCl3 at low temperatures was followed by low temperature NMR, which indicates the successive formation of CF2, CFCl, and CCl2 complexes. These results substantiate a previously postulated mechanism for halide exchange. Crystal data for 1: space group, monoclinic, P21/c; a = 9.035 (3) A?, b = 24.390 (11) A?, c = 10.745 (5) A?, β = 102.20 (3)°; Z = 4. Crystal data for 2: space group, monoclinic, P21/c; a = 12.238 (4) A?, b = 9.444 (4) A?, c = 13.440 (4) A?, β = 113.55 (3)°; Z = 4.
