Axial Tri-tert-butylphosphane Coordination to Rh-2(OAc)(4): Synthesis, Structure, and Catalytic Studies

• Published in: Organometallics Vol. 35; no. 18; pp. 3139 - 3147
• Main Authors: Tan, Jiantao, Kuang, Yi, Wang, Yi, Huang, Qingfei, Zhu, Jin, Wang, Yuanhua
• Format: Journal Article
• Language: English
• Published: WASHINGTON Amer Chemical Soc 26.09.2016
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; CINCHONA ALKALOIDS; CARBENE; LIGANDS; DIRHODIUM(II) COMPLEXES; ASYMMETRIC ADDITION; DIAZO-COMPOUNDS; ALDEHYDES; ARYLBORONIC ACIDS; H INSERTION REACTION; C-H
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.6b00477

The introduction of strong sigma-donor axial ligands to the Rh-Rh metal bond has been utilized as an effective way to provide new chemical reactivities to bimetallic dirhodium(II) complexes. In this report, Rh-2(OAc)(4) complexes with axial bulky alkylphosphane ligands (PR3), in particular P(t- Bu)(3), were prepared and characterized. The net sigma-donation from the PR3 to the Rh-Rh bond is the result of the competition between the electron-donating ability of the R group and the steric profile of the PR3 at the Rh-2 core. Analysis of the crystal structure data showed that the strong sigma-donor P(t-Bu)(3) coordinates to the rhodium with an amount of sigma-donation to the rhodium similar to that of the aryl phosphane ligand PPh3, but has an unusually long Rh-P bond distance (2.663 angstrom). During catalytic trials to synthesize 3-aryl-3-hydroxy-2-oxindole by the addition of arylboronic acids to isatin derivatives, this longer Rh-P bond distance in Rh-2(OAc)(4)(P(t-Bu)(3))(2) (Cat-1) facilitates substitution of one of the axial phosphane ligands by the arylboronic acid. This sigma-donating effect greatly accelerated the arylation reaction in comparison to alternative catalysts. Additionally, Rh-2(OAc)(4) was easily recovered after completion of the reaction.