Syntheses, characterizations and reactivity of trans-dioxorhenium(V) and -(VI) complexes
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The synthesis, electronic structure and reactivity of trans-dioxorhenium(V) and -(VI) complexes have been examined in detail. An improved general synthesis of trans-[ReO2(L)4]X complexes is presented. The amine complex [ReO2(en)2]I can be made in 90% yield from ReO2(PPh3)2I and ethylenediamine in less than 15 minutes at room temperature. Refluxing methanol suspensions of ReO2(PPh3)2I with 12-50 equivalents of electron-rich pyridines results in the formation of [ReO2L4]I compounds in 50 to 85% yield. Systematic substituent studies reveal the influence of ancillary ligands on the physical properties of trans-[ReO2(L)4][PF6] compounds. The Re(VI)/Re(V) redox couple is a linear function of pyridine ligand [...] (ReVI/Re/V) = (0.96 + [...]) V vs. Fc+/Fc. The dxy/dxz,dyz energy gap is also a linear function of pyridine [...]; increasing the pyridine basicity lowers the energy of the dxy [...] dxz,dyz transition and the energy of the [...] excited state. The excited-state properties of trans-[ReO2(L)4][PF6] pyridine complexes follow a trend consistent with the energy-gap law. Strongly basic 4-dialkylaminopyridine ligands stabilize d(1) trans-dioxorhenium(VI) complexes. Analysis of the X-ray structure of trans-[...] shows that there is considerable shortening (0.04 Ã) in the Re-N bond lengths relative to Re(V) analogues, but the Re-oxo bond lengths are virtually the same in both oxidation states. The EPR spectrum of the d(1) ion trans-[...] (dmap = 4-dimethylaminopyridine) has been measured in a 50% DMSO/H2O glass at 7 K. Analysis of the spectrum gives g[...] = 1.91, A[...] = 0.031 cm(-1), g|| = 1.83, A|| = 0.060 cm(-1), and Qz = 0.0075 cm(-1). Because of the large quadrupole coupling, the forbidden ([...] = Â±1, Â±2) transitions are quite intense and some are stronger than the allowed ([...] = 0) transitions. Comparison of Qz values and dxy [...] dxz,dyz transition energies for trans-[reO2(dmap)4](2+) and related monooxo and mononitrido complexes confirms that the ligand-field splitting associated with the multiply bonded units increases in the order ReO(4+) < ReN(3+) < ReO2(2+).
Advisor:Harry B. Gray; Jay Richmond Winkler
School:California Institute of Technology
School Location:USA - California
Source Type:Master's Thesis
Date of Publication:10/17/1990