Syntheses and structural characterizations of iron(II) complexes containing cyclic diphosphine ligands with positioned pendant nitrogen bases

A series of new iron(II) complexes that contain cyclic diphosphine ligands with pendant amine bases, (P2N2R ')-N-R, have been synthesized and characterized (where (P2N2R)-N-R' are substituted 1,5-diaza-3,7-diphosphacyclooctanes). These compounds include [Fe((P2N2Ph)-N-Ph)(CH3CN)(4)](BF4)(2) (5), cis-[Fe((P2N2Ph)-N-Ph)(2)(CH3CN)(2)](BF4)(2) (6a), cis-[Fe((P2N2Bz)-N-Ph)(2)(CH3CN)(2)] (BF4)(2) (6b), cis-[Fe((P2N2Bz)-N-Cy)(2)(CH3CN)(2)](BF4)(2) (6c), trans[HFe((P2N2)-N-Ph (Ph))(2)(CH3CN)](BF4) (7), and cis-Fe((P2N2Ph)-N-Ph)(2)(Cl)(2) (8). The molecular structures of 5, 6b, and 7 have been confirmed by X-ray diffraction studies. For all complexes the cyclic diphosphine ligands contain one six-membered ring in a chair conformation and one six-membered ring in a boat conformation. For complex 7, the two rings that are in boat conformations result in N-H distances between the pendant amine nitrogens and the hydride ligand of 2.6 to 2.7 angstrom. Protonation of the pendant bases in complex 7 has been found to form several products. A structural assignment for a dominant protonated isomer has been assigned on the basis of H-1, P-31, and N-15 NMR spectroscopic techniques.