Neutral and cationic organometallic aluminium and indium complexes of mono-pendant arm triazacyclononaneligands

Abstract

Organometallic monomeric and dimeric, neutral and cationic, κ²- and κ⁴-coordinated mono-pendant arm triazacyclononane complexes of aluminium and indium have been prepared, along with three new mono-pendant arm triazacyclononane ligand precursors HL⁴, HL⁵ and HL⁶ (HL⁴ = 1-(2-hydroxy-2-methylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane; HL⁵ = 1-(2-hydroxy-2-methylethyl)-4,7-dimethyl-1,4,7-triazacyclononane; HL⁶ = 1-(2-hydroxy-2,2-diphenylethyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of HL⁴ or HL⁵ with AlMe₃ or AlMe₃·py gives the μ-alkoxide bridged dimeric complexes [Al₂(κ²-L⁴)₂Me₄] and [Al₂(κ²-L⁵)₂Me₄]. Reaction of HL⁴ with two equivalents of AlMe₃ gives the monomeric compound [Al(κ²-L⁴·AlMe₃)Me₂] which can also be prepared by treating [Al₂(κ²-L⁴)₂Me₄] with two equivalents of AlMe₃. Reaction of HL² with AlMe₃·py gives [Al(κ²-L²)Me₂], whereas AlMe₃ reacts with one or two equivalents of HL¹ to give exclusively [Al(κ²-L¹)₂Me] which contains two κ²-L¹ ligands (HL¹ = 1-(2-hydroxy-3,5-dimethylbenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane; L² = 1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-diisopropyl-1,4,7-triazacyclononane). Reaction of AlMe₃ with HL⁶ gives low yields of the monomeric derivative [Al(κ²-L⁶)Me₂]. The κ²-coordination mode of the triazacyclononane ligands in all these compounds is unique in the chemisty of these ligands. The crystal structures of four of them are discussed. Methyl group abstraction from [Al(κ²-L⁴·AlMe₃)Me₂] or [Al(κ²-L²)Me₂] using B(C₆F₅)₃ gives the κ⁴-coordinated cationic derivatives [Al(κ⁴-L²)Me][MeB(C₆F₅)₃] and [Al(κ⁴-L⁴·AlMe₃)Me][MeB(C₆F₅)₃], and the latter undergoes reaction with pyridine or MeCN to form [Al(κ⁴-L⁴)Me][MeB(C₆F₅)₃]. The cationic centres in the last three compounds are unreactive to unsaturated substrates and aprotic Lewis bases. Reaction of In(CH₂Ph)₃ with HL¹ or HL² affords the four-coordinate complexes [In(κ²-L¹)(CH₂Ph)₂] and [In(κ²-L²)(CH₂Ph)₂] in which the L^1,2 ligand is κ² bound to In. With the sterically less demanding HL³ [1-(3,5-di-tert-butyl-2-hydroxybenzyl)-4,7-dimethyl-1,4,7-triazacyclononane], however, the six-coordinate complex [In(κ⁴-L³)(CH₂Ph)₂] is formed. The compound [In(κ²-L²)(CH₂Ph)₂] reacts with B(C₆F₅)₃ to form [In(κ⁴-L²)(CH₂Ph)][(PhCH₂)B(C₆F₅)₃].

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