Mechanistic Investigations of Gold(I)-catalyzed Carbene Transfer and Hydrofunctionalization Reactions

Widenhoefer, Ross A

Carden, Robert Gerard

2020-01-27T16:52:10Z

2020-09-12T08:17:11Z

2019

Chemistry

Cationic gold(I) complexes have been recognized as efficient catalysts for a wide array of transformations, including carbene transfers to form cyclopropanes and hydrofunctionalization reactions. While there have been great strides made in the development of these reactions, far less is understood about the mechanisms by which these transformations occur. Here are reported kinetic and mechanistic analyses of gold(I)-catalyzed reactions as well as the interrogation of the properties of cationic gold(I) carbene complexes, which are commonly proposed intermediates in gold(I)-catalyzed transformations.

A series of gold(I) sulfonium benzylide complexes were synthesized by nucleophilic substitution of -chloro gold(I) carbenoid complexes with sulfides. These complexes reacted efficiently with alkenes and dimethylsulfoxide to form cyclopropanes and benzaldehyde, respectively. Kinetic analysis of these reactions is consistent with the intermediacy of cationic gold(I) benzylidene complexes. Further mechanistic analysis revealed that alkene stereochemistry is preserved during cyclopropanation and a Hammett analysis of the reaction suggests a concerted mechanism for cyclopropanation.

To evaluate the electron donor ability of (L)Au fragments in cationic gold(I) carbene complexes, a series of cationic gold (β,β‐disilyl)vinylidene complexes and cationic gold (fluorophenyl)methoxycarbene complexes were synthesized. 29Si and 19F NMR analysis of these complexes compared to organic model compounds revealed that (L)Au fragments are significantly more inductively donating and comparably π‐donating as p-substituted aryl groups. A comparison of various ligands showed that (P(t-Bu)2-o-biphenyl)Au fragments are nominally stronger electron donors than (IPr)Au fragments, both of which are significantly more electron donating that (PPh3)Au and [P(OMe)3]Au fragments.

Kinetic and mechanistic analysis of the gold(I)-catalyzed hydrofunctionalization of 3-methyl-1,2-butadiene with alcohols and anilines was performed. Experimental data suggest a mechanism for the gold(I)-catalyzed hydroalkoxylation involving endergonic allene displacement of triflate from gold, followed by an outer-sphere attack of alcohol on gold(I)--allene complex, followed by rapid protodeauration. In contrast, for the gold(I)-catalyzed hydroamination, the active catalyst is the gold(I) bound nucleophile complex and a buildup of bis(gold) vinyl complex suggests a slow protodeauration.

A brief study evaluating student learning in the classroom is also presented. A series of team-based learning applications based on the spiropyran to merocyanine transformation were developed and assessed relative to a series of control application problems. There was no statistically significant difference in student outcomes based on the applications used in class, but student feedback suggests that the interconnected, and real-life examples were more engaging.

https://hdl.handle.net/10161/19832

Chemistry

Mechanistic Investigations of Gold(I)-catalyzed Carbene Transfer and Hydrofunctionalization Reactions

Dissertation

7.4958904109589035