Niobium and tantalum (V) complexes supported with aryloxide ancillary ligation: Synthesis; structure; 2-vinylpyridine insertion reactions. Oxorhenium (V) oxazoline complexes: Reactivity, mechanism, and application towards catalytic hydrolysis and alcoholysis of organic silanes

Rex Aaron Corbin, Purdue University

Abstract

Part I. of the dissertation focuses upon the preparation of new group (5) η2–pyridylethyl metallacyclic complexes supported with aryloxide ancillary ligation. A series of Tantalum and Niobium metallacyclic derivitized complexes were obtained from reaction of mixed chloro bis/tris aryloxides with nBu3SnH in the presence of 2-vinylpyridine. In situ hydride formations, resulting from H/Cl exchanges, were found to provide a platform for regioselective olefin insertion and subsequent hydride migration to the β olefin carbon to yield 4-membered metallacycles. This methodology represents a new and efficient synthetic route to transition metal pyridylalkyl derivitized complexes. In the course of this work a new synthetic strategy was developed and optimized to yield pure gram quantities of product that were fully characterized by NMR, elemental analysis, and X-ray crystallography. Isotope labeling experiments (H/D) and VT NMR techniques were utilized to gain additional mechanistic and structural insight. Part II. of the dissertation presents work relating to the discovery that a series of primary, secondary, and tertiary alkyl/aryl silanes undergo rapid hydrolysis and alcoholysis to yield dihydrogen and silanols or silyl ethers in the presence of catalytic amounts of a monooxo Re (V) oxazoline complex: [Re(O)(hoz)2]+ [B(C6F5 )4]-. This catalytic system embodies great potential for on demand hydrogen production applications. In addition to the robust nature of the Rhenium catalyst and the efficiency of the transformation, advantageous system characteristics include kinetic control and H2 production originating from organic liquids with water or an alcohol as the only coreagent under ambient temperature and pressure. Spectroscopic and kinetic characterizations in conjunction with isotope labeling experiments were utilized to elucidate mechanistic details and revealed the most viable reaction pathway for activation of silane (Si-H) by oxorhenium (V) complexes. Kinetic investigations and isotope labeling studies employed direct monitoring in real time of H 2 or H-D evolution via residual gas analysis (RGA) quadrupole mass spectrometry. To gain additional mechanistic insight, substrate induced electronic and steric effects upon the organosilicon center were probed and correlated using the Taft and analogous linear free energy relationships.

Degree

Ph.D.

Advisors

Abu-Omar, Purdue University.

Subject Area

Inorganic chemistry|Organic chemistry

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