Date of Award

January 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Irina P. Smoliakova

Abstract

Cyclopalladation of organic ligands followed by reactions at the C–Pd bond with MPR2 (M = Li, K, or H) or other reagents (e.g. oxidants) is a desirable strategy for the synthesis of hemilabile bidentate ligands due to the large library of known cyclopalladated complexes (CPCs). This dissertation is composed of three projects on the functionalization of cyclopalladated ligands.

In the first study, a new method for (sp3)C–P bond formation using diphenylphosphine was studied. Conditions for the synthesis of aminophosphines were optimized for the reactions of dinuclear chloro-bridged (sp3)C–Pd CPCs and HPPh2. The best yields were obtained with 9 equivalents of phosphine in methylene chloride in the presence of cesium carbonate at 35 у. The scope of the reaction was explored with a range of enantiopure and achiral C,N and C,P CPCs. The corresponding N,P and P,P ligands or their oxides were isolated in 30–65% yields. Reactions of HPPh2 in toluene with CPCs derived from D-camphor methyloxime and 2-tert-butyl-4,4-dimethyl-2-oxazoline provided unique mononuclear Pd(II) complexes with a terminal PPh2 ligand in 16 and 52% yield, respectively.

The electronic and steric effect of secondary phosphines were studied in phosphination reactions of cyclopalladated ligands. HPR2 with electron-donating and -withdrawing aryl groups (R = p-MeOC6H4 or p-CF3C6H4), bulky groups (R = mesityl or 1-adamantyl) and non-equavalent substituents (R1 = t-Bu, R2 = Ph) were reacted with CPCs derived from N,N-dimethylbenzylamine and enantiopure L-fenchone methyloxime, 1-(N,N-dimethylamino)ethylphenyl, and di-2,4-tert-butyl-2-oxazoline. With large molar ratios of phosphine to CPC (9:1 or 4.5:1), C–PR2 bond formation occurred to produce the corresponding aminophosphines or phosphine oxides in 56–61% and 12–44% yields, respectively. For both (sp2)C–Pd and (sp3)C–Pd CPCs, the reaction was tolerant to electronic differences in the phosphine substituents, but the sterically hindered phosphines dimesitylphosphine and HPt-BuPh reacted only with the fenchone-derived CPC to give the N,P ligand products in 32 and 12% yield, respectively.

Finally, an approach to the synthesis of N,O ligands was studied via the oxygenation of (S)-4-tert-butyl- and (S)-4-ethyl-2-phenyl-2-oxazoline CPCs with meta-chloroperoxybenzoic acid (m-CPBA). Reactions were performed at room temperature in methylene chloride, ethyl acetate, or acetonitrile followed by workup with lithium chloride. Oxidation products formed in these reactions included dinuclear complexes (S,S)-di-μ-Cl(κ2-N,O)2Pd2, (S,S)-di-μ-oxo(κ2-N,O)2Pd2Cl2, and (S,S)-di-μ-(m-Cl-C6H4CO2)(κ2-N,O)2Pd2, as well as mononuclear derivatives (S,S)-bis(κ2-N,O)Pd and dinuclear monooxidation complexes (S,S)-di-μ-Cl(κ2-N,O)(κ2-C,N)Pd2. Each complex was isolated in low yield (6−46%) with the combined yield of oxidation products reaching up to 64%. The best selectivity in product distribution was observed for the reactions of μ-OAc-CPCs with 2.7 equivalents of m-CPBA in acetonitrile.

All new compounds were characterized by 1H, 13C{1H}, and 31P{1H} NMR spectrometry, and their purity was proven by satisfactory elemental analysis. X-ray crystallographic data were obtained for a new cyclopalladated complex derived from O-methyloxime L-fenchone having HP(mesityl)2 as an ancillary ligand.

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