Iron pyrrole-based PNP pincer ligand complexes as catalyst precursors.

The structure of a pincer ligand consists of a backbone and two `arms' which typically contain a P or N atom. They are tridentate ligands that coordinate to a metal center in a meridional configuration. A series of three iron complexes containing the pyrrole-based PNP pincer ligand 2,5-bis[(diisopropylphosphanyl)methyl]pyrrolide (PNP) has been synthesized. These complexes are possible precursors to new iron catalysts. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κP,N,P'}carbonylchlorido(trimethylphosphane-κP)iron(II), [Fe(CHNP)Cl(CHP)(CO)] or [Fe(PNP)Cl(PMe)(CO)], (I), has a slightly distorted octahedral geometry, with the Cl and CO ligands occupying the apical positions. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κP,N,P'}chlorido(pyridine-κN)iron(II), [Fe(CHNP)Cl(CHN)] or [Fe(PNP)Cl(py)] (py is pyridine), (II), is a five-coordinate square-pyramidal complex, with the pyridine ligand in the apical position. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κP,N,P'}dicarbonylchloridoiron(II), [Fe(CHNP)Cl(CO)] or [Fe(PNP)Cl(CO)], (III), is structurally similar to (I), but with the PMe ligand replaced by a second carbonyl ligand from the reaction of (II) with CO. The two carbonyl ligands are in a cis configuration, and there is positional disorder of the chloride and trans carbonyl ligands.