Aromatic boron heterocycles and their metal complexes.

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

Slurry Discharge Pipeline Damage and Wear Due to Transporting Rock Particles during Slurry Shield Tunneling: A Case Study Based on In Situ Observed Results

Rock particles in excavated materials can damage and wear down slurry discharge pipelines when slurry shield tunneling occurs in a pebble layer and rock ground. This pipeline damage and wear, if not properly dealt with, can lead to a broken-down tunneling machine. Based on a slurry shield tunneling project in China, damage and wear were thoroughly examined. The observed pipeline wear and leaks, transported rock particles, mechanical properties, and flow rate of the carrier slurry were presented. The measured results showed that the wear rates of a straight pipe, a pipe along a curved tunnel, a 60° inclined pipe, and a 90° elbow pipe in pebble ground were approximately 0.71 mm/100 rings, 1 mm/100 rings, 2.14 mm/100 rings, and 4 mm/100 rings, respectively. When the machine drove into rock ground, the wear rates increased by one to two times, which could be attributed to the sharper particle shapes. Countermeasures to address these issues, such as adjusting the pipeline layout, welding reinforcement plates in advance, and preparing additional pipes, were highlighted. The wear rates of different types of pipes, the effectiveness of new pipeline fixing methods, and the probability of pipeline leaks in different strata were discussed in detail