Chemical Overview

 Complexes of gold and silver containing selenium donors


In contrast to the great number of known gold-sulfur complexes, the chemistry of selenium donors to gold has been neglected. Recent reports by Woollins of the facile preparation of bis(diphenylphosphino)amine chalcogenide ligands prompted us to probe the reactivity of the coinage metals with this ligand class.

Using the deprotonated ligand K[Ph2P(Se)NP(Se)Ph2], the complex [{N(Ph2PSe)2-Se,Se'}AuPPh3] shown below was generated from ClAuPPh3. Both selenium donors were found to bind to the metal centre to give an almost symmetrical metallacycle. After initial formation of the analogous trimethylphosphine complex, a rearrangement occurs to give the four-coordinate species [{N(Ph3PSe)2-Se,Se'}Au(PMe3)2]. Both species display a twisted conformation when viewed side-on. Treatment of the compound [(dppm)(AuOTf)2], prepared in situ, with the K[Ph2P(Se)NP(Se)Ph2] ligand leads to the formation of a 10-membered ring in which a short gold-gold transannular bond is found. Further interactions between the gold centres and a selenium atom on a neighbouring molecule brings pairs of molecules together to form a dimer.

[{N(Ph2PSe)2-Se,Se'}AuPPh3]

[{N(Ph2PSe)2-Se,Se'}Au2(dppm)]OTf

 

A literature search revealed that the very little had been done with the protonated mixed-donor ligand class [Ph2P(=Se)HNP(A)Ph2] (A = lone pair, O, S, Se). This led to an investigation of the reactivity of ligands bearing both hard (O) and soft (S, Se) donors towards silver(I) centres. The structures of two representative examples are shown below. The silver centre of the complex on the left is bound solely through selenium donors whereas that on the right has a combination of phosphorus and selenium donors forming 5-membered metallacycles. Both species show hydrogen bonding interactions from the protons on the amine ligands which form infinite chains linked through a linear arrangement of bromide counteranions and solvent molecules.

[{HN(Ph2PSe)2-Se,Se'}2Ag]Br

[{HN(Ph2PSe)(Ph2P)-Se,P}2Ag]Br

Interestingly, an attempt to prepare the analagous mixed-donor complex [{HN(Ph2PSe)(Ph2PS)-Se,S}2Ag]Br failed and yielded instead the neutral, bromide bridged complex shown below. Disorder in the positions of the chalcogen atoms prevented unambiguous assignment. No supramolecular interactions were observed.

[{HN(Ph2PSe)(Ph2PS)-Se,S}AgBr]2

 

Further details of this work can be found in the following articles:

J. D. E. T. Wilton-Ely, A. Schier and H. Schmidbaur. Two, three and four-coordination at gold (I) supported by the bidentate selenium ligand K[Ph2P(Se)NP(Se)Ph2]. Inorg. Chem. 2001, 40, 1058.

J. D. E. T. Wilton-Ely, A. Schier and H. Schmidbaur. Silver(I) coordination by variants of the bis(diphenylphosphino)amine chalcogenide ligand. J. Chem., Soc., Dalton Trans., 2001, 3647.

 

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