Electron transfer in the reactions of titanocene-bis(trimethylsilyl) acetylene complexes with 2,2'-bipyridine and 4,5-Diazafluorene (cas 245-37-4). The crystal structure of (4,5-diazafluorenyl) bis(pentamethylcyclopentadienyl) titanium(III)

Add time:09/29/2019    Source:infona.pl

The titanocene-bis(trimethylsilyl)acetylene complexes Cp' 2 Ti[η 2 -C 2 (SiMe 3 ) 2 ] (Cp' = C 5 H 5 , C 5 HMe 4 , and C 5 Me 5 ) react with 2,2'-bi-pyridine (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 I I I ) complexes Cp' 2 Ti(daf) (Cp' = C 5 H 5 (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 4 7 Ti and 4 9 Ti isotopes a T i = 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 a v 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) Å, b = 14.7075(10) Å, c = 14.7893(11) Å, β = 94.68(6) o , V = 2543.1(4) Å 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.

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