Issue 36, 2018

Cyclooctatetraenyl calcium and strontium amido complexes

Abstract

This paper reports the synthesis and structural characterisation of a series of cyclooctatetraenyl (C8H8) complexes of calcium and strontium, most of them containing the bis(trimethylsilyl)amido ligand. Mixing MI2 (M = Ca, Sr), KN(SiMe3)2 and K2(C8H8) in thf in a 2 : 2 : 1 ratio gave the inverse sandwich amido complexes [[{(Me3Si)2N}M(thf)x]2(μ-C8H8)] (M = Ca, x = 1; M = Sr, x = 2) (1-Ca, 1-Sr) in fair to good yields. From a 1 : 1 : 1 ratio, the mixed potassium calcium complex [[{(Me3Si)2N}Ca(thf)](μ-C8H8)K] (2) was obtained in good yield. The reaction of 2 with a 1 : 1 mixture of CaI2 and KN(SiMe3)2 yielded 1-Ca confirming that the reaction could be carried out stepwise. Attempts at making heterobimetallic calcium strontium amido complexes from the reaction of 2 with Sr{N(SiMe3)2}2 led to redistribution reactions which afforded the potassium strontium complex [[K{(Me3Si)2N}2Sr]2(μ-C8H8)] (3) among other species. Complex 3 was more conveniently synthesised in fair yield starting from a 2 : 4 : 1 molar mixture of SrI2, KN(SiMe3)2 and K2(C8H8), respectively. Treatment of 2 with PhC[triple bond, length as m-dash]CH in benzene yielded an insoluble complex tentatively formulated as the polymeric complex [CaK(CCPh)(C8H8)(thf)x]n (4). Upon dissolution in thf, 4 underwent a redistribution reaction yielding the X-ray characterised [{Ca(μ-C8H8)2}K2(thf)2] (5) and a homoleptic calcium alkynyl complex [Ca(CCPh)2(thf)x]. Several compounds were characterised by X-ray diffraction as discrete or polymeric structures where Ca⋯Cπ interactions were identified in some cases. Despite identified drawbacks, such as the lability of the coordinated thf ligands and facile redistribution reactions, this study represents the first synthetic approach to cyclooctatetraenyl heavy alkaline-earth metal amido complexes.

Graphical abstract: Cyclooctatetraenyl calcium and strontium amido complexes

Supplementary files

Article information

Article type
Paper
Submitted
01 Qas 2018
Accepted
12 Qas 2018
First published
13 Qas 2018

Dalton Trans., 2018,47, 12587-12595

Cyclooctatetraenyl calcium and strontium amido complexes

F. M. Sroor, L. Vendier and M. Etienne, Dalton Trans., 2018, 47, 12587 DOI: 10.1039/C8DT02257G

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