Zirconium Complexes of a Cross-Bridged Cyclam

Abstract

The acid−base reaction of tetrabenzylzirconium with 1,4,8,11-tetraazabicyclo[6.6.2]hexadecane (H2(CBC), 1) produces (CBC)Zr(CH2Ph)2, 2. Similarly, reaction of 2 with phenols yields (CBC)Zr(CH2Ph)(O-2,6-C6H3But2),3, and (CBC)Zr(O-2,6-C6H3Me2)2, 5. Prolonged heating of 3 leads to the metalated product (CBC)Zr[κ2(C,O)-OC6H3(6-But)(2-CMe2CH2)], 4. Reaction of ZrCl2[N(SiMe3)2]2 with H2(CBC) leads to (CBC)ZrCl2, 6, which subsequently affords (CBC)Zr(X)(Y) by salt metathesis (7, X = Cl, Y = N(SiMe3)2; 8, X = Y = CH3; 9, X = Y = CH2Si(CH3)3). Compounds 3 and 7 show restricted rotation about the Zr−O and Zr−N bonds, respectively, on the NMR time scale. For 3, the energy of activation for this process was determined to be 69 ± 1 kJ/mol. Neither 6 nor 8 shows ethylene polymerization activity when treated with 500 equiv of MAO. Reaction of 6 with 2 equiv of n-BuLi in the presence of excess diphenylacetylene leads to the zirconacyclopentadiene 10, (CBC)Zr(C4Ph4). The structures of 5, 9, and 10 have been determined by ...