Complexes of Group 2 dications with soft thioether- and selenoether-containing macrocycles

Abstract

A new route to cationic complexes of Mg, Ca, Sr and Ba with 18-membered ring O₄S₂, O₄Se₂ and O₂S₄ donor macrocycles from metal acetonitrile complexes with weakly coordinating [BAr^F]⁻ anions is described. The precursors used were [M(MeCN)_x][BAr^F]₂ (M = Mg, x = 6; M = Ca, x = 8) and [M′(acacH)(MeCN)₅][BAr^F]₂ (M′ = Sr or Ba). Reaction of these with the heterocrowns, [18]aneO₄S₂ (1,4,10,13-tetraoxa-7,16-dithiacyclooctadecane), [18]aneO₄Se₂ (1,4,10,13-tetraoxa-7,16-diselenacyclooctadecane) or [18]aneO₂S₄ (1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane) in anhydrous CH₂Cl₂ solution gave [M(heterocrown)(MeCN)₂][BAr^F]₂ for M = Mg, Ca or Sr, whilst the larger Ba forms [Ba(heterocrown)(acacH)(MeCN)][BAr^F]₂. The complexes have been characterised by microanalysis, IR, ¹H and ¹³C{¹H} NMR spectroscopy. X-ray crystal structures are reported for [Ca([18]aneO₂S₄)(MeCN)₂][BAr^F]₂, [Ca([18]aneO₄Se₂)(MeCN)₂][BAr^F]₂, [Sr([18]aneO₄S₂)(MeCN)₂][BAr^F]₂, and [Sr([18]aneO₄Se₂)(MeCN)₂][BAr^F]₂ which contain 8-coordinate metal centres with trans-nitrile ligands and κ⁶-heterocrowns, and for the 9-coordinate [Ba([18]aneO₄Se₂)(acacH)(MeCN)][BAr^F]₂. Adventitious hydrolysis of the magnesium complexes in solution results in six-coordinate complexes, [Mg(κ³-[18]aneO₄Se₂)(OH₂)₂(MeCN)][BAr^F]₂ and [Mg(κ³-[18]aneO₄S₂)(OH₂)₂(MeCN)][BAr^F]₂, whose structures were determined. X-ray crystal structures are also reported for [Mg(MeCN)₆][BAr^F]₂, [M(MeCN)₈][BAr^F]₂ (M = Ca, Sr) and [Ca(18-crown-6)(MeCN)₂][BAr^F]₂.