Syntheses and spectroscopic characterizationof fac-[Re(CO)_3(phen)(L)]PF_6, L = trans- and cis-1,2-bis(4-pyridyl)ethylene

摘要

The complex fac-[Re(CO),(phenflt-bpe)]PF6 (t-bpe = trans-i .2-bis(4-pyridyl)ethylene, phen = 1 ,10-phenanthroline) was synthe-sized, purified and characterized by UV—Vis, ‘H NMR. Raman and IR spectroscopy. ‘H NMR resonance spectrum of fac-[Re(CO)3(phen)(t-bpe)]~ reveals a clear electronic communication of the metal center across the coordinated t-bpe with upfield shift of the ligand signals upon complexation. The CO stretching frequencies are in accord with facial geometry of the rhenium complex. The photochemical behavior of free trans-l,2-bis(4-pyridyl)ethylene and of its protonated form is also reported. The quantum yield for the trans —~ cis photoinduced isomerization of free ligand in methanolic solutions at 313 nm irradiation is 0.17 + 0.03. The average values for the photoisomerization of the protonated ligand (pH 1.9) are 0.19 + 0.02 and 0.15 ± 0.01, respectively at 313 and 334 nm excitation. The photoassisted trans —. cis isomerization of t-bpe in the fac-I7Re(CO)3(phen)(t-bpe)]~complex was achieved with higher quantum yields at lower energy irradiation by exploiting the red shifted absorption upon formation of the complex. The photoproducts cis-l,2-bis(4-pyridyl)ethylene and fac-[Re(CO)3(phen)(c-bpe)]PF6 were synthesized and identified by UV—Vis, ‘H NMR and luminescence properties.