ELECTRON TRANSFER IN THE REACTIONS OF TITANOCENE-BIS(TRIMETHYLSILYL) ACETYLENE COMPLEXES WITH 2,2'-BIPYRIDINE AND 4,5-DIAZAFLUORENE - THE CRYSTAL STRUCTURE OF (4,5-DIAZAFLUORENYL)BIS(PENTAMETHYLCYCLOPENTADIENYL)TITANIUM(III)

摘要

The titanocene-bis(trimethylsilyl)acetylene complexes Cp(2)'Ti[eta(2)-C-2(SiMe(3))(2)] (Cp' = C5H5, C(5)HMe(4), and C(5)Me(5)) react with 2,2'-bipyridine (bpy) to give the corresponding Cp(2)'Ti(bpy) complexes 1-3. EPR evidence of the electronic triplet state in 1-3 implies the transfer of one of the Ti d(2) electrons to the bpy ligand. An analogous electron transfer to 4,5-diazafluorene (dafH) affords (4,5-diazafluorenyl)titanocene (Ti-III) complexes Cp(2)'Ti(daf) (Cp' = C5H5 (4), C(5)HMe(4) (5), and C(5)Me(5) (6)) with a release of one hydrogen atom from the sp(3) carbon atom of the ligand. EPR spectra of 4-6 in toluene solutions are characterized by g = 1.9798-1.9820, coupling to Ti-47 and Ti-49 isotopes a(Ti) = 11.9-12.6 G, and for 4 and 6 also by the coupling to two equivalent nitrogen atoms a(N) = 2.0 G. Rhombic g-tensors with g(av) in the range 1.981-1.982 were obtained in frozen toluene glass. The X-ray crystal structure of 6 (monoclinic, P2(1)/c (No. 14), a = 11.7309(9) Angstrom, b = 14.7075(10) Angstrom, c = 14.7893(11) Angstrom, beta = 94.68(6)degrees, V = 2543.1(4) Angstrom(3), Z = 4) proved that both nitrogen atoms of an approximately planar 4,5-diazafluorenyl ligand coordinate to a pseudotetrahedrally coordinated titanium atom, The electronic absorption spectra of 4-6 in solution showed a well-resolved vibrational structure of the (daf)(-) anion with positions of all vibronic bands shifted to longer wavelength by ca. 20-30 nm, and a low intensity band probably of the d-d transition in the range 820-940 nm. [References: 27]