Text

theses

The activation of carbon-hydrogen (C-H) bonds mediated by transition metal complexes is a fundamental step in a vast array of chemical transformations and industrial processes. As such, research into the understanding of the factors governing both efficiency and selectivity of these reactions has been intense. The work presented in this thesis comprises results of experiments designed to evaluate the ability of a pincer-ligated iridium complex to activate the C-H bonds of several classes of aryl substrates. The pincer-ligated iridium fragment (PCP)Ir (PCP = {κ3-2,6-bis[(di-tert-butylphosphino)methyl]phenyl}) rapidly and reversibly adds the C-H bond of benzene, giving a kinetically labile addition product. The kinetics and thermodynamics of C-H activation of a series of halogen-, alkyl-, and trifluoromethyl-substituted arenes were studied with a particular focus on determining whether “directing” effects play a significant role. In regard to electronic effects, it was observed that electron withdrawing aryl substituents favor C-H activation. Products of C-H activation ortho to weakly or non-coordinating substituents (e.g., Cl, Br, CF3) are kinetically more stable than those of the meta- and para-substituted analogs, due to steric crowding in the transition state for addition and elimination. However, there is no thermodynamic preference for the ortho-substituted complexes. In addition to C-H activation, (PCP)Ir also activates C-X bonds (X = Cl, Br) under certain conditions, yielding product mixtures through a mechanism that remains unclear. Several series of polycyclic aromatic substrates (naphthalenes, biphenyls, bipyridines, and associated tricyclic analogs) were also studied, giving insight into the utility of aryl C-H activation and preferred binding modes of the (PCP)Ir fragment. Not surprisingly, steric effects play a significant role in the regioselectivity of polycyclic aromatic C-H bond activation by (PCP)Ir. Cyclometalation reactions resulting from single or double C-H activation processes yield particularly stable products. Additional results included an unexpected C-C activation, and several products stabilized by heteroatom (N, O) coordination to iridium. Activation of large polycycles like terpyridine yielded stable, κ2 chelates that may be of value in research on organic light emitting diodes (OLEDs). Finally, several congested (PCP)Ir dimers were synthesized by taking advantage of the remarkable stability of the products from cyclometalation to the (PCP)Ir complex.

ETD_4708

Ph.D.

Includes bibliographical references

Includes vita

by David Alan Laviska

http://hdl.rutgers.edu/1782.1/rucore10001600001.ETD.000068902

doi:10.7282/T31N7ZQM

ETD doctoral

The author owns the copyright to this work.