Macrocyclic Complexes of Niobium(III): Synthesis, Structure, and Magnetic Behavior of Mononuclear and Dinuclear Species That Incorporate the [P2N2] System

Abstract

The coordination chemistry of the two mixed donor macrocyclic ligands R[P2N2] (where R[P2N2] = RP(CH2SiMe2NSiMe2CH2)2PR, R = cyclohexyl (Cy) or phenyl (Ph)) with niobium(III) is presented. The reaction of the dilithio precursors R[P2N2]Li2(S) (R = Cy, S = THF; R = Ph, S = 1,4-dioxane) with NbCl3(DME) (DME = 1,2-dimethoxyethane) generates the complexes R[P2N2]NbCl (R = Cy, 1; R = Ph, 2). For R = Cy, single-crystal X-ray diffraction studies and variable-temperature magnetic susceptibility measurements indicate that 1 is mononuclear in the solid state; however, analogous variable-temperature magnetic data suggest that 2 is dinuclear in the solid state due to the observation of antiferromagnetic exchange. In solution, 2 is apparently monomeric similar to 1. Adduct formation between these mononuclear complexes is also evident; reaction of 2 with neutral donors and coordinating solvents produces the mononuclear derivatives Ph[P2N2]NbCl(L) (L = py, CO, PMe3, THF, MeCN), of which the pyridine adduct, 3e, has been...