Iron pyrrole-based PNP pincer ligand complexes as catalyst precursors

摘要

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[(diisopropylphosphan-yl)methyl]pyrrolide (PN~(pyr)P) has been synthesized. These complexes are possible precursors to new iron catalysts. {2,5-Bis[(diisopropylphosphanyl)meth-yl]pyrrolido-κ~3P,N,P'}carbonylchlorido(trimethylphosphane-κP)iron(II), [Fe-(C_18H_34NP_2)Cl(C_3H_9P)(CO)] or [Fe(PN~(pyr)P)Cl(PMe_3)(CO)], (I), has a slightly distorted octahedral geometry, with the Cl and CO ligands occupying the apical positions. {2,5-Bis[(diisopropylphosphanyl)methyl]pyrrolido-κ~3P,N,P'}chlorido-(pyridine-κN)iron(II), [Fe(C_18H_34NP_2)Cl(C5H5N)] or [Fe(PN~(pyr)P)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-κ~3P,N,P'}dicarbonylchloridoiron(II), [Fe(C_18H_34NP_2)Cl(CO)_2] or [Fe(PN~(pyr)P)-Cl(CO)_2], (III), is structurally similar to (I), but with the PMe_3 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.