Alkoxido-, amido-, and chlorido derivatives of zirconium- and hafnium bis(amido)cyclodiphosph(V)azanes: Ligand ambidenticity and catalytic productivity

Abstract

Bis(tert-butylamido)cyclodiphosph(III)azanezirconium- and hafnium dichloride are good polyethylene pre-catalysts, but due to the basicity of their phosphorus(III) atoms they suffer from ligand degradation. To lessen the Lewis-acid attacks on these complexes, the phosphorus-nitrogen ligands were oxidized with sulfur to afford the corresponding bis(tert-butylamido)cyclodiphosph(V)azanes, which are devoid of such very Lewis-basic sites. These modified ligands, however, no longer bind the metals in the desired κ2N,N′ fashion, but laterally in the catalytically inactive κN,κEl mode. Treatment of the Group 4 metal dichlorides with sodium tert-butoxide afforded the bis(tert-butylamido)cyclodiphosph(III)azanemetal di-tert-butoxides in high yields. These compounds were amenable to sulfur oxidation, yielding bis(tert-butylamido)cyclodiphosph(V)azanemetal di-tert-butoxides in equally high yields. The oxidized complexes retain the κ2N,N′ structure, prompting us to reinvestigate a similar oxidation of the bis(tert-butylamido)cyclodiphosph(III)azanemetal dichlorides. The dichloride complexes were more difficult to oxidize, but ultimately bis(tert-butylamido)cyclodiphosph(V)azanezirconium- and hafnium dichlorides were obtained and shown to be more productive catalysts than their phosphorus(III) counterparts.