(MU-OXO)DIIRON COMPLEXES OF BORYLATED DIMETHYLGLYOXIMES - STEPWISE LIGATION TO ALLOSTERICALLY LINKED BINDING-SITES AND H-1-NMR SPECTRA OF PARAMAGNETIC NITRILE, AMINE, IMIDAZOLE, AND PYRIDINE-DERIVATIVES

(mu-Oxo)diiron complexes of [Fe((DMG)BPh(2))(2)]O-2 (1) bind one or tw o axial ligands within cyclophane-like cavities which lie trans to the oxo bridge. Nonbonded interactions between the bound ligand and the B Ph(2) superstructure are elucidated. Hindered ligands at one site sign ificantly reduce ligation at the remote site via peripheral contacts o perating between the two superstructures surrounding the binding sites . Ligated species are characterized on the basis of visible spectra an d paramagnetic shifts in the H-1 NMR spectra. The BPh(2) phenyl proton shifts were fit to a simple dipolar model. The DMG methyl, imidazole, and pyridine ligand H-1 resonances experience contact shifts which di ffer in magnitude and sign for the various ligated forms, LFe-O-Fe, LF e-O-FeL, and LFe-O-Fe(CH3CN). Contact shifts are consistent with spin transfer from a single unpaired electron on each low-spin iron to pi o rbitals of the ligands. Restricted rotation of bound ligands within th e cyclophane-like cavities is evident.