The electronic features and photochemistry of TpTiCl3 (1) (Tp = hydrotris(pyrazol-1-yl)borate) and Tp*TiCl3 (2) (Tp* = hydrotris( 3,5-dimethylpyrazol-1-yl)borate) were studied in THF. Reactive decay of the excited states produced either HBpz3· (or HBpz3°* and metal center Ti(III) radicals via homolytic cleavage of the Tp -Ti (Tp* - Ti) bond. Cleavage of the Tp - Ti and the Tp*- Ti bond as a primary photoprocess is shown to be consistent with LMCT Tp - Ti and Tp*- Ti excitation. TpTiCl2(THF) (3) and Tp*TiCl2(THF) (4) were also prepared by stoichiometric reduction of 1 and 2 with Li3N. The THF ligand in 3 and 4 was replaced by the stable nitroxyl radical TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to provide the new complexes TpTiCl2-(TEMPO) (5) and Tp*TiCl2(TEMPO) (6) in which the TEMPO ligand is eta1 coordinated to Ti(IV). Photolysis of 5 and 6 generate Ti(III) and the TEMPO radical in the primary photochemical step.
Photochemistry of tris(pyrazolyl)borate titanium(IV) complexes
GAZZI, Roberto;PERAZZOLO, Francesca;SOSTERO, Silvana;TRAVERSO, Orazio
2005
Abstract
The electronic features and photochemistry of TpTiCl3 (1) (Tp = hydrotris(pyrazol-1-yl)borate) and Tp*TiCl3 (2) (Tp* = hydrotris( 3,5-dimethylpyrazol-1-yl)borate) were studied in THF. Reactive decay of the excited states produced either HBpz3· (or HBpz3°* and metal center Ti(III) radicals via homolytic cleavage of the Tp -Ti (Tp* - Ti) bond. Cleavage of the Tp - Ti and the Tp*- Ti bond as a primary photoprocess is shown to be consistent with LMCT Tp - Ti and Tp*- Ti excitation. TpTiCl2(THF) (3) and Tp*TiCl2(THF) (4) were also prepared by stoichiometric reduction of 1 and 2 with Li3N. The THF ligand in 3 and 4 was replaced by the stable nitroxyl radical TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to provide the new complexes TpTiCl2-(TEMPO) (5) and Tp*TiCl2(TEMPO) (6) in which the TEMPO ligand is eta1 coordinated to Ti(IV). Photolysis of 5 and 6 generate Ti(III) and the TEMPO radical in the primary photochemical step.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
