PN3P Rhodium Pincer Complexes: Coordination Chemistry and Reactivity

Abstract

Abstract: The choice ofsuitable ligand platforms is crucial to organometallic coordination chemistry and homogeneous catalysis. Among the various ligand platforms available, pincer ligands offer a convenient route to manipulate the properties of the resulting complexes. The pincer chemistry of rhodium has attracted attention for over 40 years, and Rh complexes are dominated by Rh(I) and Rh(III) low-spin states, thus they are more predictable than other paramagnetic species. Compared to other pincer ligand platforms, pyridine-based pincer complexes are particularly attractive as they exhibit diverse reactivities. Our group realized a new class of the PN3 (P) pincer system, with altered the unique catalytic performances, thermodynamic and kinetic properties due to their pseudo-dearomatized nature. In Chapter 2, selective carbonylation of benzene to benzaldehyde using a phosphorus nitrogen PN3P Rh(I) complex was realized. The PN3P Rh pincer chloride complex cPePN3PRhCl was capable of activating C−H bond of benzene to give the phenyl complex cPePN3PRh(C6H5) using KN(SiMe3)2 as a base. Furthermore, the benzoyl complex cPePN3PRh(CO)(C6H5) was obtained by treating a benzene solution of cPePN3PRh(C6H5) with CO gas. In dilute HCl, a high yield of 90% benzaldehyde was formed with regeneration of the cPePN3PRhCl. This is the first example of selective carbonylation of benzene into benzaldehyde accomplished by directly inserting CO without irradiation. In Chapter 3, the ligand-centered reactivity of a pseudo-dearomatized PN3P *rhodium complex towards molecular oxygen wasrealized. For the dearomatized rhodium carbonyl complex (tBuPN3P*RhCO), one of the C−H bonds of the pseudo-dearomatized pyridine ring was oxidized by O2 to create an α, β-unsaturated carbonyl functionality. Moreover, the resulting metal complex with the post-modified PN3P ligand could react with thiophenol and 4-methylaniline to afford the corresponding oxidative Michael addition products. In Chapter 4, to further explore the ligand-centered reactivity of tBuPN3P *RhCO, a series of second-generation diimine-amido PN3P-pincer carbonyl complexes were synthesized by reaction of tBuPN3P*RhCO and various alkyl/benzyl halides via a post-modification strategy, and these complexes were well characterized by NMR, HRMS, FT-IR, and single crystal diffraction. Moreover, a plausible mechanism for the formation of 2nd -generation PN3P complexes was proposed

Date of Award	Aug 2021
Original language	English (US)
Awarding Institution	Physical Sciences and Engineering
Supervisor	Kuo-Wei Huang (Supervisor)