Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(H) and ruthenium(II) halides to generate. complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl-2 (1) in CD2Cl2 features sa tridentate binding mode as established by P-31{H-1} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br-2 (2) revealed a pseudo-octahedral, cis-alpha geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD2Cl2 solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru-(K-4-DPPEPM)Cl-2 (3) is obtained from rac-DPPEPM and either [RuCl2(COD)](2) [COD = 1,5-cyclooctadiene] or RuCl2-(PPh3)(4). The structure of 3 in both the solid state and in CD2Cl2 solution features a folded K-4-DPPEPM. This binding mode was also observed in cis-[Fe(K-4-DPPEPM)(CH3CN)(2)](CF3SO3)(2) (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(k(4)-DPPEPM)Cl(CO)] (Cl) (5). The same reaction in CH2Cl2 produces a mixture of 5 and [Fe(K-3-DPPEPM)Cl-2,(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of k(4)-DPPEPM.