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

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 t ransfer of one of the Ti d(2) electrons to the bpy ligand. An analogou s electron transfer to 4,5-diazafluorene (dafH) affords (4,5-diazafluo renyl)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 fr om 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 an d Ti-49 isotopes a(Ti) = 11.9-12.6 G, and for 4 and 6 also by the coup ling 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 gl ass. 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) Angs trom, beta = 94.68(6)degrees, V = 2543.1(4) Angstrom(3), Z = 4) proved that both nitrogen atoms of an approximately planar 4,5-diazafluoreny l ligand coordinate to a pseudotetrahedrally coordinated titanium atom , The electronic absorption spectra of 4-6 in solution showed a well-r esolved 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 820-94 0 nm.