Iron(II) and Ruthenium(II) Complexes Containing Bidentate, Tied-Back Diphosphonite Ligands. X-ray Structure of cis-FeMe2[(−OCH2CEt2CH2O−)PCH2CH2P(−OCH2CEt2CH2O−)]2

trans-RuCl2(PP)2 (2) and cis-FeCl2(PP)2 (4) have been synthesized by the reaction of the diphosphonite 1,2-bis((2,2-diethyl-1,3-propanedioxy)phosphino)ethane (PP) with RuCl2(Ph3P)3 and FeCl2, respectively. Complex 4 was converted to cis-FeMe2(PP)2 (5), for which a molecular structure was obtained.