Ruthenium complexes of hexakis(cyanophenyl)[3]radialenes and their di(cyanophenyl)methane precursors: synthesis, photophysical, and electrochemical properties

摘要

The coordination chemistry of cross-conjugated ligands and the effect of cross-conjugation on the nature of metal-metal and metal-ligand interactions have received limited attention. To explore the effects of cross-conjugation eight ruthenium complexes were synthesized, mononuclear complexes of two isomeric cross-conjugated [3]radialenes [RuCp(PPh_3)_2(L)]PF_6 and [{RuCp*(dppe)}(L)]PF_6 (L = hexakis(4-cyanophenyl)[3]radialene, 2; hexakis(3-cyanophenyl)[3]radialene, 3), and dinuclear complexes [{RuCp(PPh_3)_2}_2(L)](PF_6)_2 and [{RuCp*(dppe)}_2(L)](PF_6)_2 of the diarylmethane precursors (L = 4,4'-dicyanodiphenylmethane, 4; 3,3'-dicyanodiphenylmethane, 5) to the [3]radialenes. Considerable synthetic challenges allowed only clean isolation of mononuclear complexes of the multidentate radialenes 2 and 3. As expected, coordinating a positively charged metal induces a red shift for the n-it* transition in complexes of ligand 2, but unexpectedly a blue shift for the same transition in complexes of 3 was observed. This points to conformational differences for the [3]radi-alene in the ruthenium complexes of the para- (2) versus meta- (3) substituted hexaaryl[3]radialenes. Cyclic voltammetry indicates that the methylene spacer in 4 and S does not enable any interaction between metal centers and the absorption behavior is essentially as observed for [Ru(NCPh) (PPh_3)_2Cp]PF_6 and [Ru(NCPh)(dppe)Cp*]PF_6 but generally with a slight red shift in absorbance