Melding of Experiment and Theory Illuminates Mechanisms of Metal-Catalyzed Rearrangements: Computational Approaches and Caveats

This review summarizes approaches and caveats in computational modeling of transition-metal-catalyzed sigmatropic rearrangements involving carbene transfer. We highlight contemporary examples of combined synthetic and theoretical investigations that showcase the synergy achievable by integrating experiment and theory.1 Introduction2 Mechanistic Models3 Theoretical Approaches and Caveats3.1 Recommended Computational Tools3.2 Choice of Functional and Basis Set3.3 Conformations and Ligand-Binding Modes3.4 Solvation4 Synergy of Experiment and Theory – Case Studies4.1 Metal-Bound or Free Ylides?4.2 Conformations and Ligand-Binding Modes of Paddlewheel Complexes4.3 No Metal, Just Light4.4 How To ‘Cope’ with Nonstatistical Dynamic Effects5 Outlook

Tuning Catalytic Activity of Dimolybdenum Paddlewheel Complexes by Ligands:Mechanism Study on the Radical Addition Reaction of CCl4 to 1-Hexene

The detailed catalytic mechanism of a series of paddlewheel complexes [Mo2L4] featuring Mo-Mo quadruply-bond on radical addition of CCl4 to 1-hexene was studied using density functional theory. Different ligands of Mo-Mo bond are investigated to illustrate the ligand effect on the catalytic activity. The results show that the Mo-Mo quadruply-bond paddlewheel complexes have high catalytic activity on the title reaction. The whole reaction involves 4 steps. Firstly, the C-Cl bond of first CCl4 is activated by [Mo2L4] catalyst, [Mo2L3Cl] and CH3COOCCl3 are obtained; Then the second CCl4 adds to [Mo2L3Cl] to produce [Mo2L3Cl2] and CCl3 radical; CCl3 radical interacts with 1-hexene to get an addition, the addition product which reacts with one Cl atom of [Mo2L3Cl2] to get the last product nBuCHClCH2CCl3 and regenerate [Mo2L3Cl]. The addition of the first CCl4 to [Mo2L4] catalyst is the rate-determining step of the whole reaction. Because this step is not in the catalytic cycle, the reaction would speed up after a certain period of time. The catalytic activity of dimolybdenum paddlewheel complex is depended on the natural population analysis (NPA) charge of Mo and the redox potential E(Mo24+/Mo25+). The higher NPA of Mo atom and higher E(Mo24+/Mo25+) of the catalyst, the higher catalytic activity it has. Our calculated results provide an explanation for experimental observations and useful insights for further development of bimetallic catalysts in radical addition reactions.

Mixed-Ligand Dirhodium(II,II) Paddlewheel Complexes as Carbene Transfer Catalysts

This review highlights the applications of dirhodium(II,II) paddlewheel complexes with a mixed-ligand scaffold. Dirhodium(II,II) paddlewheel complexes are well-known as highly efficient and selective carbene transfer catalysts. While the majority of...

Two mixed valence diruthenium (II,III) isomeric complexes show different anticancer properties

In this paper it is demonstrated that the nature of the ligands of two Ru2 (II,III) paddlewheel complexes drammatically affects the overall anticancer properties in cells. Herein, the complex [Ru2(EB776)4Cl]...

Tuning Rh(II)-Catalyzed Cyclopropanation with Tethered Thioether Ligands

Dirhodium(II) paddlewheel complexes have high utility in diazo-mediated cyclopropanation reactions and ethyl diazoacetate is one of the most commonly used diazo compounds in this reaction. In this study, we report our efforts to use tethered thioether ligands to tune the reactivity of Rh-carbene mediated cyclopropanation of olefins with ethyl diazoacetate. Microwave methods enabled the synthesis of a family of Rh-complexes in which tethered thioether moieties were coordinated to axial sites of the complex. Different tether lengths and thioether substituents were screened to optimize cyclopropane yeilds and minimize side product formation. Furthermore, good yields were obtained when equimolar diazo and olefin were used. Structural and spectroscopic investigation revealed that tethered thioethers changed the electronic structure of the rhodium core, which was instrumental in the performance of the catalysts. Computational modeling of the catalysts provided further support that the tethered thioethers were responsible for increased yields.

Tuning Rh(II)-Catalyzed Cyclopropanation with Tethered Thioether Ligands

Dirhodium(II) paddlewheel complexes have high utility in diazo-mediated cyclopropanation reactions and ethyl diazoacetate is one of the most commonly used diazo compounds in this reaction. In this study, we report our efforts to use tethered thioether ligands to tune the reactivity of Rh-carbene mediated cyclopropanation of olefins with ethyl diazoacetate. Microwave methods enabled the synthesis of a family of Rh-complexes in which tethered thioether moieties were coordinated to axial sites of the complex. Different tether lengths and thioether substituents were screened to optimize cyclopropane yeilds and minimize side product formation. Furthermore, good yields were obtained when equimolar diazo and olefin were used. Structural and spectroscopic investigation revealed that tethered thioethers changed the electronic structure of the rhodium core, which was instrumental in the performance of the catalysts. Computational modeling of the catalysts provided further support that the tethered thioethers were responsible for increased yields.