Syntheses and Structural Characterizations of Iron(II) Complexes Containing Cyclic Diphosphine Ligands with Positioned Pendant Nitrogen Bases

Abstract

A series of new iron(II) complexes that contain cyclic diphosphine ligands with pendant amine bases, P2RN2R‘, have been synthesized and characterized (where P2RN2R‘ are substituted 1,5-diaza-3,7-diphosphacyclooctanes). These compounds include [Fe(P2PhN2Ph)(CH3CN)4](BF4)2 (5), cis-[Fe(P2PhN2Ph)2(CH3CN)2](BF4)2 (6a), cis-[Fe(P2PhN2Bz)2(CH3CN)2](BF4)2 (6b), cis-[Fe(P2CyN2Bz)2(CH3CN)2](BF4)2 (6c), trans-[HFe(P2PhN2Ph)2(CH3CN)](BF4) (7), and cis-Fe(P2PhN2Ph)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 Å. 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 1H, 31P, and 15N NMR spectroscopic techniques.