New structural motifs in chromium(iii) calix[4 and 6]arene chemistry

Abstract

The reactions of either p-tert-butylcalix[4]areneH(4) [Cax(OH)(4)], 1,3-dimethoxy-p-tert-butylcalix[4]areneH(2) [Cax(OH)(2)(OMe)(2)] or p-tert-butylcalix[6]areneH(6) [Cax[6](OH)(6)] with alkali metal cations and the chromium complexes [CrCl(3)(THF)(3)] or [CrCl(2)(THF)] (THF = tetrahydrofuran) are described. In particular, the treatment of [Cax(OH)(4)] with in situ generated M[Cr(Ot-Bu)(4)] (M = Li or K) affords, after work-up, the complex {[CrCax(O)(4)(NCMe)](2)[Li(THF)](2)[Li(NCMe)](2)Cl(2)(micro(4)-O)}.2.25(MeCN) and two forms of {K(MeCN)(x)[CrCax(O)(4)(NCMe)][CrCax(OH)(O)(3)(NCMe)]}.MeCN (x = 3 or 4) , respectively. The potassium salt of [Cax(OH)(4)] reacts with [CrCl(2)(THF)] to afford a highly sensitive complex, which on exposure to air gives rise to the compound {[CrCax(O)(4)K(THF)(2)](2)H(micro-O)(H(2)O)K(THF)(H(2)O)(micro-THF)}(2).6THF , that possesses four chromium calixarene units, two sets of K(+) ions that are coordinated in two very different environments together with terminal and bridging THF ligands. The reaction of n-BuLi with [Cax(OH)(4)], followed by the addition of [CrCl(3)(THF)(3)] affords, after work-up, the complex {Cr[micro-Cax(OH)(O)(3)](NCMe)}(2).4Me(2)C[double bond, length as m-dash]O.0.5H(2)O (). Complex is also available via the hydrolysis of complex . Interaction of [Cax(OH)(2)(OMe)(2)] with NaH or n-BuLi in THF affords, following the addition of [CrCl(3)(THF)(3)], the demethylated dimer {Cr[micro-Cax(OH)(O)(3)](NCMe)}(2).4MeCN (), which is a different solvate of , or the monomeric salt {Cax(O)(2)(OMe)(2)CrCl(2)[Li(NCMe)(2)]}.2MeCN (), respectively. The reaction of 1,3-dipropoxy-p-tert-butylcalix[4]areneH(2), [Cax(OH)(2)(On-Pr)(2)], with n-BuLi followed by [CrCl(3)(THF)(3)] affords the monomeric complex [CrCl(2)Cax(O)(2)(On-Pr)(2)Li(NCMe)(2)].3MeCN (). Interaction of the mono-methoxy ligand [Cax(OH)(3)(OMe)] with n-BuLi in diethyl ether followed by addition of [CrCl(3)(THF)(3)] in THF affords, upon work-up, the complex [CrCax(OMe)(O)(3)(NCMe)](2).MeCN (). Interaction of p-tert-butylcalix[6]areneH(6) [Cax[6](OH)(6)] with Na[Cr(Ot-Bu)(4)] (formed in situ from [CrCl(3)(THF)(3)] and excess NaOt-Bu) affords the complex {CrCax[6](O)(3)(OH)(3)Na(NCMe)(2)(micro-OH)}(2).4MeCN (). Complexes - have been structurally characterised; for and , it was necessary to use synchrotron radiation. Screening of - for ethylene polymerisation using either methylaluminoxane (MAO) or dimethylaluminium chloride (DMAC) as co-catalyst afforded only very poor catalytic activities (<or= 1 g mmol(-1) hr(-1) bar(-1)).