Synthesis of coordination complexes using mixed donor chalcogenoether macrocycles to investigate hard/soft metal to ligand interactions

Abstract

Improvements to the synthesis of Group 16 mixed donor macrocycles are reported. The mixed donor chalcogenoether macrocycles [15]aneO3S2, [18]aneO2S4 and [18]aneO4E2 (E= S, Se and Te) can coordinate a range of both soft and hard Lewis acids. Complexes investigating hard Lewis acids focussed on Ca(II), Sr(II), Sc(III) and Y(III) halides. The Group 2 metals are coordinated to all the donors in the macrocycle, importantly the metal centres showed an affinity for the softer donor (S, Se) as well as the harder donor (O). This interaction was maintained even after trace ingress of water. The lattice energies of the starting metal precursors were important in accessing the coordination chemistry of Ca(II) and Sr(II), CaI2 and SrI2 both gave products of the type [MI2(macrocycle)]. Similarly ScI3 was reacted with the macrocyclic ligands to give ionic solids [ScI2(macrocycle)][I]. The analogous Y(III) and Sc(III) chlorides were also synthesised by using the halide abstractor FeCl3 and [ScCl3(THF)3] and [YCl2(THF)5][YCl4(THF)2] to give complexes of the type [MCl2(macrocycle)][FeCl4]. The macrocycles bind hexadentate (pentadentate in case of [15]aneO3S2) to the Group 3 cations. Softer and borderline Lewis acids Sn(XFn)2 and Pb(XFn)2 (X=B, P; n= 4, 6 respectively) form complexes with the Group 16 donor macrocycles. The coordination compounds exhibit a range of unusual coordination modes for the weakly coordinating fluoroanions ([BF4]- ?2, ?2 and ?1; [PF6]- ?3 and ?2). Pb(II) and Sn(II) were shown to encourage the hydrolysis of the [PF6]- anion and the decomposition of [18]aneO4Te2. Sn(II) also cleaved the other [18]aneO4E2 (E= S, Se) macrocycles, the complex [Sn([18]aneO4S2)(HO(CH2)2OH)][BF4]2 is the first structural evidence for metal mediated ring opening of a saturated oxa-thia macrocycle. A series of coordination complexes of Sb(III), a soft Lewis acid, halides were investigated. Structural comparisons between the analogous fluoro-, chloro- and iodo- antimony(III) complexes showed the corresponding halide greatly influenced the Lewis behaviour of Sb(III). X-ray crystallography, 1H (and where appropriate 19F, 31P, 45Sc, 77Se and 125Te) NMR spectroscopy, elemental analysis, conductivity measurements and IR spectroscopy were used to characterise the complexes in this study.

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ORCID for Gillian Reid: orcid.org/0000-0001-5349-3468

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