Synthesis and characterization of iron complexes based on bis-phosphinite PONOP and bis-phosphite PONOP pincer ligands

A series of bis-phosphinite and bis-phosphite PONOP iron complexes were prepared and characterized by NMR and IR spectroscopy. Bis-phosphinite PONOP iron dichloride complexes (RPONOP)FeCl2 ((PONOP)-P-R = 2,6-(R2PO)(2)(C5H3N) and R = Tr, tBu) were prepared through complexation of the free ligands with FeCl2 and their solid-state structures were determined. Bis-phosphite PONOP iron complexes (c1E1PONOP)Fe(PMe3)2 and (ca1PONOP)Fe(PMe3)2 (Cat = catechol) were synthesized through complexation of the free ligands to Fe(PMe3)(4). Carbonyl complexes of both bis-phosphinite and bis-phosphite PONOP were prepared and characterized by IR. The monocarbonyl ((PONOPFe)-P-OEt(CO)(2) was accessed through exposure of (111`PONOP)FeCl2 to an atmosphere of CO and the CO stretching frequency was observed at 1969 cm -1. Dicarbonyl complexes ((PONOP)-P-iPr)Fe(C0)2 and ((PONOPFe)-P-OEt(CO)(2) were accessed through reduction of the corresponding chloride complexes with sodium amalgam under a CO atmosphere. Carbonyl stretching frequencies for (RIPONOP)Fe(C0)2 and ( E1PONOPFe)(C0)2 were observed at 1824 and 1876 cm -1, and at 1871 and 1927 cm(-1) respectively. The bis-phosphite PONOP complexes exhibit a less electron rich metal center than the bis-phosphinite PONOP complexes, as would be expected based on the stronger pi-acceptor character of these ligands. The electronic properties of the bisphosphinite PONOP and bis-phosphite PONOP iron complexes are intermediate between previously reported PNP and PDI iron complexes, with the PONOP ligands exhibiting stronger electron donating ability than PDI ligands, but promoting a less electron rich metal center than found in analogous PNP iron complexes. (c) 2014 Elsevier BY. All rights reserved.