Investigations of the reactivity of palladium and platinum complexes with molecular oxygen and characterization of a gold(III)-alkene complex

Abstract

Understanding the reactivity of metal complexes with molecular oxygen will facilitate the

development of catalysts that can enable the widespread use of molecular oxygen as an oxidant

for organic synthesis. This thesis presents two new classes of reactions between metal complexes

and molecular oxygen. Neutral five-coordinate Pt complexes were tested for reactivity in the

presence of molecular oxygen. In arene solution, the complexes (tBuMe2nacnac)PtMe3 (1,

tBuMe2nacnac- = [((4-tBu-2,6-Me2C6H2)NC(CH3))2CH]-), (Me3Me-nacnac)PtMe3 (2,

Me3Me-nacnac- = [((2,4,6-Me3C6H2)NC(CH3))2CCH3]-), and (tBu2PyPyr)PtMe3 (3,

tBu2PyPyr- = 3,5-di-tert-butyl-2-(2-pyridyl)pyrrolide) reacted immediately with oxygen to form

peroxo species in which two oxygen atoms bridge between the metal center and a carbon atom in

the ligand backbone. In contrast, no reaction between (iPr2AnIm)PtMe3 (4a, iPr2AnIm- = [o- C6H4-{N(C6H3iPr2)}(CH=NC6H3iPr2)]-) or (Me3AnIm)PtMe3 (4b, Me3AnIm- = [o-C6H4-

{N(C6H2Me3)}(CH=NC6H2Me3)]-) and oxygen was observed. As activation of oxygen by five- coordinate PtIV species was found to involve cooperation between the metal center and the

ligand, the ability of the ligand to participate in the oxygen binding appears to be a vital

component. Oxygen atom transfer reactions of the novel peroxo species are also presented. In a

separate study, an unusual reaction involving the activation of both molecular oxygen and a C-H

bond at the same metal center was investigated. Pd(P(Ar)(tBu)2)2 (15, Ar = naphthyl) was found

to react with molecular oxygen at room temperature in arene solvent to form a hydroxide dimer

in which one equivalent of phosphine per Pd was lost and the remaining phosphine was

cyclometalated through the naphthyl ring. At low temperature, two intermediates were observed.

The nature of these intermediates suggests a mechanism involving initial reaction of Pd(P(Ar)

(tBu)2)2 with O2 followed by the C-H activation step. In a final chapter unrelated to oxygen

reactivity, the generation and characterization of a goldIII-alkene complex by NMR and X-ray

crystallography is presented. Such species have been proposed as intermediates in catalytic

reactions but until recently none had been observed.