Synthesis and structural determination of [Rh(opo)(CO)(PR<sub>3</sub>)] complexes (opo<sup>−</sup> = 2-oxopyridin-1-olate) and <i>in situ</i> isomeric behavior from preliminary kinetic study of iodomethane oxidative addition
Creators: name: Elmakki, Mohammed A. E.
name: Orbett T. Alexander
name: Gertruida J. S. Venter
name: Venter, Johan A.
name: Roodt, Andreas
Publisher: name: Taylor & Francis
Year: 2021
Subjects: subject: Biophysics
subject: Biochemistry
subject: Space Science
subject: 29999 Physical Sciences not elsewhere classified
subject: FOS: Physical sciences
subject: FOS: Physical sciences
subject: Medicine
subject: Microbiology
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Immunology
subject: FOS: Clinical medicine
subject: FOS: Clinical medicine

description: A range of complexes, [Rh(opo)(CO)(PR<sub>3</sub>)], with opo<sup>−</sup> = 2-oxopyridin-1-olate, and [Rh(opo)(CO)<sub>2</sub>] (<b>1</b>), [Rh(opo)(CO)(PPh<sub>3</sub>)] (<b>2A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo)(CO)(PPh<sub>2</sub>Cy)] (<b>3A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo)(CO)(PPhCy<sub>2</sub>)] (<b>4A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo) (CO)(PCy<sub>3</sub>)] (<b>5A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo)(CO)(P(<i>o</i>-Tol)<sub>3</sub>)] (<b>6A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo)(CO) (P(<i>m</i>-Tol)<sub>3</sub>)] (<b>7A<sub>I</sub>/B<sub>I</sub></b>), [Rh(opo)(CO)(P(<i>p</i>-Tol)<sub>3</sub>)] (<b>8A<sub>I</sub>/B<sub>I</sub></b>), and <i>cis</i>-[Rh(opo)(CO)(CH<sub>3</sub>)(I)(PPh<sub>3</sub>)] (<b>2A<sub>II</sub></b>), were synthesized and characterized by IR and NMR spectroscopy. Two isomers (<b>A</b> = major, MaI; <b>B</b> = minor, MiI) were observed in <i>ca.</i> 2:1 ratios for complexes <b>2–8</b> due to the similar characteristics of the chelating O-donors, yet non-symmetric within the bidentate ligand. Single crystal X-ray diffraction yielded the solid-state structures of the major isomers of <b>4A<sub>I</sub></b>, <b>5A<sub>I</sub></b>, <b>6A<sub>I</sub></b>, and <b>2A<sub>II</sub></b>. Metallophilic interactions were observed between neighboring Rh(I) centers in [Rh(opo)(CO)<sub>2</sub>] (<b>1</b>) with an intermolecular Rh···Rh distance of 3.5780(5) Å. These interactions do not occur in the crystal structures of <b>4A<sub>I</sub></b>, <b>5A<sub>I</sub></b>, <b>6A<sub>I</sub></b>, and <b>2A<sub>II</sub></b>, attributed to the steric bulk of the phosphine ligands and the interactions observed in the crystal lattice of these structures. Preliminary iodomethane oxidative addition (OA) to the rhodium(I) complexes [Rh(opo)(CO)(PR<sub>3</sub>)] was investigated by IR, NMR, and UV-Vis spectroscopy, yielding corresponding <i>alkyl</i> intermediate species (n<b>A<sub>II</sub></b>/<b>B<sub>II</sub></b>) or <i>acyl</i> products (n<b>A<sub>III</sub></b>/<b>B<sub>III</sub></b>), respectively, for <i>n</i> = <b>2–8</b> and PR<sub>3</sub> = PPh<sub>3</sub> (<b>2</b>), PPh<sub>2</sub>Cy (<b>3</b>), PPhCy<sub>2</sub> (<b>4</b>), PCy<sub>3</sub> (<b>5</b>), P(<i>o</i>-Tol)<sub>3</sub> (<b>6</b>), P(<i>m</i>-Tol)<sub>3</sub> (<b>7</b>), P(<i>p</i>-Tol)<sub>3</sub> (<b>8</b>). The rates of OA and assumed subsequent migratory carbonyl insertion (CI) reactions were identical within standard deviations, suggesting the CI to be fast relative to the OA. Moreover, the interconversion between the two isomers A and B seemed to be a slower process, governed by the relative steric strain induced by the tertiary phosphine ligands and not by the rates.