Tertiary phosphine oxide complexes of lanthanide diiodides and dibromides

Robert D Bannister,William Levason,Mark E Light,Gillian Reid

doi:10.1016/j.poly.2018.07.057

Robert D Bannister, William Levason + Show 2 more

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https://doi.org/10.1016/j.poly.2018.07.057

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Abstract

The reaction of OPR3 (R = Me, Ph) with YbI2, EuI2 and EuBr2 in rigorously anhydrous MeCN under N2 produces the divalent lanthanide complexes [LnX2(OPR3)4] (Ln = Yb, Eu, X = I; Ln = Eu, X = Br) in moderate to good yield, whilst [SmI2(OPR3)4] were obtained from SmI2 and OPR3 in dry, degassed thf. These are the first examples involving divalent lanthanide ions and the complexes have been characterised by microanalysis, IR, UV–Vis and 31P{1H} NMR spectroscopy. The X-ray crystal structure of [EuI2(OPPh3)4]·MeCN confirmed the six-coordinate Eu(II) species with a cis-octahedral geometry, which IR spectroscopy suggests is present in all of the OPPh3 complexes. In contrast the [LnX2(OPMe3)4] complexes appear to be trans isomers. The OPPh3 complexes are readily oxidised by dry O2 or I2, yielding the corresponding trivalent cations, [LnX2(OPPh3)4]+; a crystal structure of the product formed by oxidation of [EuI2(OPPh3)4] in MeCN solution confirms this to be [EuI2(OPPh3)4]I3·1.5MeCN, containing a trans-octahedral cation.

Highlights

While the overwhelming majority of lanthanide coordination chemistry involves the Ln(III) state [1,2,3], the last twenty five years have seen a steady growth of complexes of divalent lanthanides, mostly based upon Eu, Yb and Sm, but with a small number of complexes of Dy, Nd and Tm characterised [4,5]
Tertiary phosphine oxides (OPR3) have proved to be popular ligands for trivalent lanthanides, and many examples with a range of R groups are known as oxo-anion salts, diketonates and halides, as described in a very recent comprehensive review [9]
The [EuBr2(OPR3)4] complexes were made the reactions needed overnight stirring due to the poorer solubility of the EuBr2 in MeCN

Summary

Introduction

While the overwhelming majority of lanthanide coordination chemistry involves the Ln(III) state [1,2,3], the last twenty five years have seen a steady growth of complexes of divalent lanthanides, mostly based upon Eu, Yb and Sm, but with a small number of complexes of Dy, Nd and Tm characterised [4,5]. Taking OPPh3 (the most thoroughly investigated ligand) as an example, all the LnCl3 complexes are six-coordinate, with both mer-[LnCl3(OPR3)3] and trans-[LnCl2(OPR3)4]Cl characterised for all (except Pm). The former type is preferred for the early lanthanides, with the cations becoming more favoured later in the series [10], whilst the [LnX2(OPPh3)4]X (X = Br, I) are favoured for the heavier halides [11,12]. No examples of divalent lanthanide phosphine oxide complexes have been reported [9], hexamethylphosphoramide. We report the preparations and properties of complexes of OPPh3 and OPMe3 with the divalent LnI2 (Ln = Yb, Eu and Sm) and EuBr2

Experimental

X-ray experimental

Results and discussion

Conclusions