Cationic aluminum alkyl complexes incorporating aminotroponiminate ligands

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N'-diisopropylaminotroponiminate ligand (Pr-i(2)-ATI(-)) are described. The reaction Of ( Pr-i(2)-ATI)AIR(2) (1a-e,g,h; R = H (a), Me (b), Et (c), Pr (d), Bu-i (e), Cy (g), CH2Ph (h)) with (Ph3C][B(C6F5)(4)] yields (Pr-i(2)-ATI)AlR+ species whose fate depends on the properties of the R ligand. la and lb react with 0.5 equiv of [Ph3C][B(C6F5)(4)] to produce dinuclear monocationic complexes [{(Pr-i(2)-ATI)AlR}(2)(mu -R)][(C6F5)(4)] (2a,b). The cation of 2b contains two (Pr-i(2)-ATI)AIMe+ units linked by an almost linear Al-Me-Al bridge; 2a is presumed to have an analogous structure. 2b does not react further with [Ph3C][B(C6F5)(4)]. However, 1a reacts with 1 equiv of [Ph3C][B(C6F5)(4)] to afford (Pr-i(2)-ATI)Al(C6F5)(mu -H)(2)B(C6F5)(2) (3) and other products, presumably via C6F5-transfer and ligand redistribution of a [(Pr-i(2)-ATI)AlH][(C6F5)(4)] intermediate. 1c-e react with 1 equiv of [Ph3C][B(C6F5)(4)] to yield stable base-free [(Pr-i(2)-ATI)AlR][B(C6F5)(4)] complexes (4c-e). 4c crystallizes from chlorobenzene as 4c(CIPh).0.5PhCl, which has been characterized by X-ray crystallography. In the solid state the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph T-stacking interaction. 1g,h react with [Ph3C][B(C6F5)(4)] to yield (Pr-i(2)-ATI)Al(R)(C6F5) (5c,h) via C6F5- transfer of [(Pr-i(2)-ATI)AlR][(BC6F5)(4)] intermediates. 1c,h react with B(C6F5)3 to yield (Pr2-ATI)Al(R)(C6F5) (5c,h) via C6F5- transfer of [(Pr-i(2)-ATI)AlR][RB(C6F5)(3)] intermediates. The reaction of 4c-e with MeCN or acetone yields [(Pr-i(2)-ATI)Al(R)(L)][B(C6F5)(4)] adducts (L = MeCN (8c-e), acetone (9c-e)), which undergo associative intermolecular L exchange. 9c-e undergo slow beta -H transfer to afford the dinuclear dicationic alkoxide complex [{(i)(Pr(2)ATI)Al(mu -(OPr)-Pr-i)}(2)][B(C6F5)(4)](2) (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization of tert-butyl acetylene by an insertion/sigma -bond metathesis mechanism involving [(Pr-i(2)-ATI)Al(C dropC' Bu)][B(C6F5)(4)] (13) and [(Pr-i(2)-ATI)Al(CH=C(' Bu)C dropC' Bu)][B(C6F5)(4)] (14) intermediates. 13 crystallizes as the dinuclear dicationic complex [ (Pr-i(2)-ATI)Al(mu -C dropC' BU)](2)][B(C6F5)(4)](2). 5PhCl from chlorobenzene. 4e catalyzes the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react with ethylene-d(4) by beta -H transfer to yield ((Pr-i(2)-ATI)AlCD2CD2H][B(C6F5)(4)] initially. Polyethylene is also produced in these reactions by an unidentified active species.