Dibenzylzirconium complexes of chelating aminodiolates. Synthesis, structural studies, thermal stability, and insertion chemistry

Aminodiolate ligands, RN(CH2CH2C(O)R'(2))(2) (1a-e), allow the isolation of soluble, monomeric zirconium dialkyl complexes, [RN(CH2CH2C(O)R'(2))(2)]Zr R "(2) (2a-e, 5, 6). The fluxional behavior and thermal stability of these complexes are strongly dependent on the nature of the substituents at the n itrogen center, with smaller substituents (R = Me; 2a,b, 5, 6) increasing t he rigidity and thermal stability of the complexes. Complexes bearing tert- butyl groups (2c,d) readily undergo thermal decomposition by elimination of isobutene. Thermal ortho metalation of the chiral complex Zr[((S)-PhC(H)Me )N(CH2CH2C(O)Me-2][CH2Ph](2) (2e) affords the chiral metallacycle Zr[N(CH2C H2C(O)Me-2}(2){((S)-2-C6H4C(H)Me}][CH2Ph] (7), which has been structurally characterized. Reaction of 7 with 1 equiv of aryl aldehyde (ArC(O)H; Ar = P h, beta-naphthyl) results in regiospecific insertion of the aldehyde into t he phenylzirconium bond. The resulting aminotriolate complex Zr[N{CH2CH2C(O )Me-2}(2){((S)-2-((R)-(beta-naphthyl)CH(O))-C6H4C(H)Me}][CH2Ph] (8b) is for med in 91% de and has been characterized by X-ray crystallography. Further insertion of ArC(O)H into the remaining Zr-benzyl bond of 8b proceeds with poorer stereochemical control. Complex 7 also catalyzes the slow cyclotrime rization of phenylacetylene to 1,2,4- and 1,3,5-triphenylbenzene (2.5 turno vers/day). Complexes 2b,d and 7 function as precatalysts for ethylene polym erization when treated with MAO activator, although the activity is very lo w.