Coordination Chemistry of Diindole Ligands: Synthesis and Reactivity of a Di(indolyl)bicyclononylborate Ligand and Explorations in Main Group Diindolylmethane Chemistry

Abstract

Chapter One gives a brief overview of established coordination chemistry of pyrrole and indole-based ligands, and of the ansa-metallocene chemistry of ligands featuring a heteroatom in the bridging position. Proposals for syntheses of coordination compounds of two different ansa-indolyl ligand systems are outlined. Chapter Two describes the synthesis and characterization of an anionic diindolylborate ligand and outlines attempted reactivity with transition metal and main group halides. Spectroscopic results from these reactions as well as reactions to synthesize variants of this ligand are presented. The final section details syntheses of variants of a known diindolylmethane ligand. Chapter Three presents the first well-characterized Group 13 coordination compounds of the di(3-methylindol-2-yl)-4-bromophenylmethane ligand. Hydrogen-elimination reactions producing borane and alane complexes in high yield were employed. Spectroscopic characterization is presented, as well as solid-state structural characterization of the borane. Further reactivity with trimethylaluminum is explored but results are not as definitive. Chapter Four details the first explored reactivity of the diindolylmethane ligand with metals from the s-block. Dinuclear compounds of lithium, sodium, and potassium were obtained by reaction of di(3-methylindolyl)-4-bromophenylmethane with common amides of the metals. All three compounds proved reactive with metal halides and their utility as precursors to further coordination complexes was demonstrated by reaction with calcium iodide. The potassium salt yielded a calcium complex of di(3-methylindolyl)-4-bromophenylmethane, the first known Group 2 complex of diindolylmethane. Chapter Five explores reactivity with Group 15 phosphine and stibine reagents. Phosphine halides of both di(3-methylindolyl)-4-bromophenylmethane and di(3-methylindolyl)- 4-fluorophenylmethane were synthesized and characterized spectroscopically. A solid-state structure of di-(3-methylindol-2-yl)chlorophosphine-4-bromophenylmethane was obtained. The purposes of targeting these compounds was to establish diindolylmethane as a viable supporting framework for Group 15 compounds, to examine relative Lewis basic properties of the diindolylmethane ligand system, and to determine if they were a suitable route to phosphenium cations. A diindolylmethane complex of an amidostibine was also obtained and characterized by spectroscopic and elemental analysis. Attempts toward both phosphenium and stibenium cations through halide abstraction and substituent protonation, respectively, did not yield the expected cations.