Reduced Bis imino pyridine Iron Chemistry

It is useful to compare the molecular and electronic stmctures of the bis(imino)pyridine iron dinitrogen complexes with those of the ruthenium congeners reported by Berry and coworkers [32]. Stirring K -( PDI)Ru(q -arene) complexes in non-arene solvents under a dinitrogen atmosphere furnished the bimetallic ruthenium dinitrogen complex [( PDI)Ru]2(P2 l dimeric 

As discussed above, introduction of alkyl substituents larger than methyl onto the imine carbon resulted in a preference for four-coordinate iron dinitrogen 

As with the ketimine variant of the pincer, we initiated this chemistry by the reduction of the iron dibromide complex ( PDAl)FeBr2 ( PDAl = 2,6(2,6- Pr2-CgH3N=CH)2C5H3N) [40], 

The dimeric iron compound proved to be robust both in solution and the soHd state. Although catalyticaUy inactive, the electronic structure of [( PDAl)Fe]2 was of interest Observation of a single Mdssbauer doublet with an isomer shift of 0.84mms i estabhshed equivalent high-spin iron centers. These data, in combination with the distortions to the pincer ligand observed by X-ray diffraction, estabhshed overall two-electron reduction of the chelate, one in the unperturbed portion of the ligand and the other in the q -imine coordinated to the adjacent iron. 

The unusual structure of [( PDAl)Fe]2 presented a unique opportunity to study electronic communication between two iron centers bearing redox-active bis(aldimino)pyridine pincer Hgands. Variable-temperature solid-state magnetic susceptibihty measurements established an essentially invariant effective magnetic moment of 4.3 pg between 100 and 300 K. Below 100 K, decreases monotonically 

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