Aromatic boron heterocycles and their metal complexes.

Abstract

In analogy to the ansa-metallocenes of group 4 metals, a number of bridged group 4 metal complexes of boratabenzenes have been synthesized and tested as homogeneous catalysts for olefin polymerization. These include [bis(eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl)dimethylsilane]zirconium dichloride, [(eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl) (eta-3 '-t-butylcyclopentadienyl)dimethylsilane]zirconium dichloride, [(eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl) (eta-3'-trimethylsilylcyclopentadienyl)dimethylsilane]zirconium dichloride, (eta-N,N-dimethyl-1-amino-2-tri-methylsilyl-4-isopropylboratabenezene) (eta-pentamethylcyclopentadienyl)zirconium dichloride, eta-t-butylamido(eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl)dimethylsilane]zirconium dichloride, eta-t-butylamido(eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl)dimethylsilane]zirconium dichloride, eta-t-butylamido (eta-N,N-diisopropyl-1-aminoboratabenzen-4-yl)dimethylsilane]titanium dichloride, eta-t-butylamido(eta-1-butylboratabenzen-4-yl)dimethylsilane]zirconium dichloride, [eta-t-butylamido(eta-1-(2'S,5 'S)-dimethylpyrrolidinylboratabenzen-4-yl)dimethylsilane]titanium dichloride, and [eta-t-butylamido(eta-1-(2'S,5 'S)-dimethylpyrrolidinylboratabenzen-4-yl)dimethylsilane]zirconium dichloride. These complexes catalyze ethylene and propylene polymerization with good activities in the presence of co-catalyst methylaluminoxane (MAO). Activities qualitatively decrease with increase of steric congestion at the active metal center. Diisopropylaminoboron bridged bis(cyclopentadienyl)zirconium dichloride, rac-bis(indenyl)zirconium dichloride, and rac-bis(tetrahydroindenyl)zirconium dichloride have been synthesized and tested for olefin polymerization. These complexes are remarkably stable and have open wedges around zirconium. They rapidly polymerize ethylene and propylene in the presence of MAO. In particular the later two complexes produce isotactic polypropylene. Further fine-tuning of these complexes should be of particular interest. Novel anionic aromatic boron heterocycles related to thiophene have been prepared and coordinated to transition metals. Specifically N,N-diisopropyl-3-amino-1,3-benzothiaborolide, N,N-diisopropyl-3-amino-4-trimethylsilyl-1,3-thiaborolide, and N,N-diisopropyl-3-amino-1,3-thiaborolide were synthesized by efficient routes. NMR spectra data suggest the anions are strongly stabilized by pi bond to boron but the negative charge is not extensively delocalized over the rings. Several Fe(II), Ru(II), and Zr(IV) complexes from these anions have been synthesized in which the thiaborolides serve as eta5 ligands. Of particular interest is the (eta-pentamethylcyclopentadienyl) (eta-1,3-thiaborolyl)zirconium dichloride which polymerizes ethylene in the presence of MAO. The activity is comparable to that of the respective boratabenzene zirconium complex. This demonstrates the potential of this type of ligand in homogeneous catalysis for olefin polymerization. As an application of the methodology developed in the synthesis of above thiaborolides, remarkably simple yet novel 1,3-thiaphosphole and 1,3-thiaarsole have been synthesized. These heterocycles are aromatic as evidenced by their NMR and UV spectroscopic data. Ab initio molecular orbital calculations have been performed on these compounds. A new synthesis of 1-N-t-butyl-2-methyl-1,2-azaborine has been developed. This aromatic heterocycle can serve as a ligand towards Mo(CO)3.Ph.D.Organic chemistryPolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123322/2/3069002.pd