Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemistry

Supervisor

Dr. Richard J. Puddephatt

Abstract

This thesis describes a study of monometallic and bimetallic dimethylplatinum(II) complexes containing ditopic nitrogen donor ligands. This work details the design and synthesis of side-to-side and cofacial arranged ligands and their respective coordination chemistry. The study of the synthesis, characterization and reaction mechanisms of the various dimethylplatinum(II) complexes is outlined in detail with special emphasis focused on the reactivity of the complexes towards oxidative addition.

The ditopic ligand 6-dppd, 1,4-di(2-pyridyl)-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine, was observed to coordinate only a single equivalent of a platinum(II) center. The inability to coordinate a second equivalent, even through an assisted bridging atom, is presumed to be due to a steric clash between the free pyridyl group and the cyclooctyl backbone. In attempts to make heterobimetallic complexes of 6-dppd, the complex [PtMe2(6-dppd)] was observed to react preferentially with mercuric halides by oxidative addition rather than coordination of the mercuric salt in the second coordination site giving complexes [PtXMe2(HgX)(6-dppd)] where X = Br, Cl, OAc. This indicates that the platinum center is actually a better nucleophile than the free pyridyl nitrogen atom. The oxidative addition of solvent dichloromethane was also observed showing the enhanced reactivity of [PtMe2(6-dppd)]. Finally, [PtMe2(6-dppd)] was treated with DCl at low temperature to give the deuteridoplatinum(IV) complex. The deuteridoplatinum(IV) complex reductively eliminates methane in solution and extensive H/D exchange occurs into the CH4 product at low temperature indicating very easy reversibility of the exchange between hydridomethylplatinum(IV) and methaneplatinum(II) complexes.

The abstraction of a chloride ligand from [PtClMe(6-dppd)] led to the formation of a complex dimer structure endo,endo-[Pt2Me223-6-dppd)2][OTf]2. This process allowed for the formation of a bimetallic platinum(II) complex which retained the initial stereochemistry. The protonolysis of [PtMe2(6-dppd)] with one equivalent of HOTf led to the generation of methane gas and the concomitant formation of both endo,endo-[Pt2Me223-6-dppd)2][OTf]2 and exo,exo-[Pt2Me223-6-dppd)2][OTf]2. The structures of the exo isomeric clamshell dimers appeared much less sterically hindered in the solid state and were observed experimentally and computationally to be the thermodynamically preferred isomers. The mechanism, selectivity and reversibility of this isomerism process was explored in detail.

The reactions of [PtMe2(6-dppd)] with alkyl bromides RCH2Br, which possess hydrogen bonding functionality, result in the formation of stable organoplatinum(IV) complexes capable of forming supramolecular structure via hydrogen bonding. Both intra and inter molecular hydrogen bonding is observed in the formation of supramolecular architectures which self-assemble in the solid state through additional π-stacking and weak secondary interactions.

The new anthracene derived ditopic ligands, bpad = N1,N8-bis(pyridin-2-ylmethylene)anthracene-1,8-diamine and adpa = (N,N)-4,4’-(anthracene-1,8-diylbis(ethyne-2,1-diyl))-bis(N-(pyridin-2-ylmethylene)aniline) were prepared, characterized and used to coordinate dimethylplatinum(II) centers giving cofacial bimetallic complexes of dimethylplatinum(II). [Pt2Me4(bpad)] was shown to degrade over time in solution through a proposed metalation event involving the anthracene backbone. The oxidative addition of a variety of substrates was performed using [Pt2Me4(adpa)] giving stable diplatinum(IV) complexes as characterized by 1H NMR spectroscopy. The new xanthene derived ditopic ligands, ppxda = 2,7-di-tert­-butyl-9,9-dimethyl-N4,N5-bis(4-(pyridin-2-ylmethyleneamino)phenyl)-xanthene-4,5-dicarboxamide and pmxda = 2,7-di-tert-butyl-9,9-dimethyl-bis(pyridine-2-ylmethylene)-9H-xanthene-4,5-diamine were prepared, characterized and used to ligate two equivalents of a dimethylplatinum(II) center. Diplatinum complexes of both ligands were shown to easily undergo oxidative addition to give the corresponding diplatinum(IV) complexes which adopt the anti orientation. The syn alignment of metal centers was accessible through the abstraction of halides ligands and incorporation of bridging groups as is the case for the pyrazine bridged bimetallic platinum complex [Pt2Me6(C4H4N2)(pmxda)][OSO2CF3]2.


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