Bond Activation in Iron(II)‐Coordinated Polypodal Phosphane Ligands

Abstract

AbstractA mononuclear iron(II) complex is readily formed when combining equimolar amounts of iron(II) tetrafluoroborate hexahydrate, the pyridine‐derived triphosphane C5H3N{2‐[CMe(CH2PMe2)2]}{6‐[CMe2(CH2PMe2)]} (2) and diethylphosphane (Et2PH) in methanol at room temperature. The chelate ligand is in fact pentadentate, as one of the methyl groups of the neopentyl‐like sidearm engages in a C–H‐bonded contact (agostic interaction) with the metal centre, in addition to the expected NP3 coordination. The remaining site of what is a distorted coordination octahedron is occupied by monodentate Et2PH. The autoclave reaction of this purple complex with CO (10 bar, ethanol solvent, 65 °C) yields a yellow microcrystalline precipitate, whose analysis reveals a mixture of two products, in an approximate ratio of 40:1. One of the products is the cis‐dicarbonyl complex[Fe(2)(CO)2](BF4)2 (4), in which the chelate ligand acts as an NP3 donor, and the other is the monocarbonyl complex of the tetrapodal pentadentate NP4 ligand 1. The latter ligand is formed from 2 by incorporation of an additional PMe2 donor, in what, in effect, is a metal‐mediated phosphenium group transfer. A mechanism is suggested for this reaction. Other species in the reaction mixture have been identified on the basis of mass spectra, and the full NMR spectroscopic assignment of complex 4 (1H, 31P, 13C) is reported.