The Exploration of Metal Ligand Cooperation and Bond Activations by Late Transition Metal Complexes Containing the PNpyrP Ligand

<p>Pincer ligands have become a reliable class of ligands in organometallic chemistry due to their ability to bind a metal center at three coordination sites, providing structural and electronic support to the metal complex. This dissertation describes the synthesis of late transition metal complexes containing a new PNP ligand comprised of a central pyrrole unit and di-<i>iso</i>-propylphosphine donors, bis[(dimethylamino)methyl]pyrrole, ((PN^pyrP)H), <b>1</b>.</p><p>With this ligand, multiple transmetallation reagents including [(PN^pyrP)Li]₂ (<b>7</b>), (PN^pyrP)Tl (<b>8</b>), and [(PN^pyrP)Ag]₂ (<b>12</b>) were synthesized in order to afford group 10 metal complexes of the form (PN^pyrP)MCl (M = Ni (<b>2</b>), Pd (<b>3</b>), Pt (<b>4</b>)) as well as (PN^pyrP)Ir(COD) (<b>6</b>) and (PN^pyrP)Ru(PPh₃)Cl (<b>12</b>). Compounds <b>2</b>, <b>6</b>, and <b>12</b> were the platform from which a library of transition metal (PN^pyrP) complexes were generated and studied in stoichiometric and catalytic H-H and C-H bond activation reactions. </p><p>The ability for the (PN^pyrP) framework on late transition metals to engage in metal-ligand cooperation was assessed. We determined that nickel, iridium, and ruthenium complexes containing this ligand exhibit reversible structural changes of the backbone depending on the reaction environment (i.e. acid/base, atmosphere). Upon addition of HCl or Brookhart’s acid ([H-(Et₂O)₂][BAr₄F]), protonation of the ß-pyrrole position induces formation of an imine in the PNP backbone and a change in coordination mode of the N-donor from anionic to dative. An analogous rearrangement is observed upon addition of a hydride abstracting reagent ([Ph₃C][PF₆]) to <b>2</b> or <b>12 </b>in which electrophilic aromatic addition to the ß-pyrrole position of the (PN^pyrP) backbone occurs. </p><p>Further, complex <b>12</b> was found to activate H₂ at room temperature to afford (PN^pyrP)^HRu(PPh₃)(H)Cl (<b>44</b>), a Ru(II) hydride compound containing the protonated pyrrole backbone. Overall, the ability of late transition metal complexes containing the (PN^pyrP) ligand to undergo reversible structural changes was investigated as a means to leverage metal-ligand cooperation for the activation of small molecules and typically inert bonds.</p>