CO-Migration in the Ligand Substitution Process of the Chelating Diphosphite Diiron Complex (μ-pdt)[Fe(CO)3][Fe(CO){(EtO)2PN(Me)P(OEt)2}

Abstract

Selective synthetic routes to isomeric diiron dithiolate complexes containing the (EtO) 2PN(Me)P(OEt) 2 (PNP) ligand in an unsymmetrical chelating role, for example, (mu-pdt)[Fe(CO) 3][Fe(CO)(kappa (2)-PNP)] ( 3) and as a symmetrically bridging ligand in (mu-pdt)(mu-PNP)[Fe(CO) 2] 2 ( 4), have been developed. 3 was converted to 4 in 75% yield after extensive reflux in toluene. The reactions of 3 with PMe 3 and P(OEt) 3 afforded bis-monodentate P-donor complexes (mu-pdt)[Fe(CO) 2PR 3][Fe(CO) 2(PNP)] (PR 3 = PMe 3, 5; P(OEt) 3, 7), respectively, which are formed via an associative PMe 3 coordination reaction followed by an intramolecular CO-migration process from the Fe(CO) 3 to the Fe(CO)(PNP) unit with concomitant opening of the Fe-PNP chelate ring. The PNP-monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex (mu-pdt)(mu-PNP)[Fe(CO)PR 3][Fe(CO) 2] (PR 3 = PMe 3, 6; P(OEt) 3, 8) on release of 1 equiv CO when refluxing in toluene. Variable-temperature (31)P NMR spectra show that trisubstituted diiron complexes each exist as two configuration isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.