Heterotrinuclear Oxo-Bridged Fe(III)ORu(IV)OFe(III) Complexes of Ruthenium Porphyrin and Borylated Low-Spin Iron Dioximes(1).
The synthesis, structure, spectra, and reactivity of diamagnetic linear chain heterotrinuclear oxo-bridged complexes L-Fe(III) N(4)-O-Ru(IV)(TPP')-O-Fe(III)N(4)-L are described where TPP' is tetrakis(4-methoxyphenylporphyrinate), N(4) is one of the borylated bis(dioximate) macrocycles, N(4) = ((DMG)BF(2))(2) in 1, ((DMG)BPh(2))(2) in 2, and ((DPG)BF(2))(2) in 3, and L is a monodentate terminal ligand, L = BuNH(2), CH(3)CN, Py, 1-MeIm, (BuO)(3)P, etc. Crystal data for 3-(BuNH(2))(2) = [(BuNH(2))Fe((DPG)BF(2))(2)-O](2)Ru(TPP') monoclinic space group P2(1)/n, a = 16.845 Å, b = 27.184 Å, c = 24.593 Å, beta = 90.41 degrees, Fe-O = 1.79(1) Å, Ru-O = 1.80(1) Å, Fe-O-Ru = 175 degrees. Large porphyrin and phenyl ring current shifts permit ready characterization of the materials by (1)H NMR. A red-shifted Soret band at 433 nm and two charge transfer transitions in the 650-850 nm region are observed in the visible spectra. Clean reduction of 1, 2, and 3-(CH(3)CN)(2) with 4-tert-butylcatechol is observed giving Fe(II) and Ru(II) products. The kinetics of reduction parallel those of low-spin (&mgr;-oxo)diiron FeN(4) systems showing a 1/[CH(3)CN] dependence, but the rates are 10(3)-10(5) times slower. The Ru(IV) is proposed to stabilize the &mgr;-oxo-Fe bonds toward reductive cleavage via delocalization of the oxo pi electrons onto the ruthenium. Electrochemical data for the heterotrinuclear Fe-O-Ru-O-Fe systems are compared with those for the binuclear Fe-O-Fe systems. The HOMO is stabilized by 120 mV over the corresponding Fe-O-Fe system.
Vernik
Isak
I
Department of Chemistry York University, North York, Ontario, Canada M3J 1P3.
Stynes
Dennis V.
DV