Binolate complexes of lithium, zinc, aluminium, and titanium; preparations, structures, and studies of lactide polymerization

The reaction of racemic 5,5',6,6'-tetramethyl-3,3'-di-tert-butyl-1,1'-biphenyl-2,2'-diol (biphenolate-H-2) with 4 mol equiv. of (BuLi)-Bu-n yields [(mu(3),mu(3)-biphenolate)(2)Li-4((BuLi)-Bu-n)(4)] (1) in high yield. I further reacts with 4 mol equiv. of 2,4dimethyl-3-pentanol in the presence of tetrahydrofuran (THF) or cyclohexene oxide (CyHO) to give the lithium aggregate [(mu,mu-biphenotate)Li-2(mu(3)-OCH(Pr-i)(2))(2)Li-2(L)(2)] (2-THF, L = THF; 2-CyHO, L = CyHO). Treatment of biphenolate-H2 with 3 mol equiv. of ZnEt2, followed by addition of 2 mol equiv. of 2,4-dimethyl-3-pentanol provides the zinc complex [(mu,mu-biphenolate)Zn(mu-OCH(Pr-i)(2))(2)Zn2Et2] (3). Aluminium alkoxide incorporating biphenolate ligand can also be obtained via a similar synthetic route. The compound [(mu-biphenolate)AlMe(mu-OCH(Pr-i)(2))AlMe2] (4) is prepared from the reaction of biphenolate-H2 with 2 mol equiv. of AlMe, in the presence of I mol equiv. of 2,4dimethyl-3-pentanol. The titanium (4+) binolate complex [(biphenolate)Ti2Cl6] (5) is synthesized from the reaction of biphenolate-H-2 and 2 mol equiv. of TiCl4. In addition, 2-THF, 3, and 4 have been examined for rac-lactide polymerization, and the comparative studies of polymerization are also presented.