Three‐Coordinate Rhodium Complexes in Low Oxidation States

• Published in: Chemistry : a European journal 2020-03, Vol.26 (15), p.3270-3274
• Main Authors: Varela‐Izquierdo, Víctor, López, José A., Bruin, Bas, Tejel, Cristina, Ciriano, Miguel A.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemists; Gold; low-valent; Metals; metal–metal bond; NHC ligands; Oxidation; Rhodium; Salts; Silver; tri-coordinate
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202000387

The isolation of simultaneously low‐coordinate and low‐valent compounds is a timeless challenge for preparative chemists. This work showcases the preparation and full characterization of tri‐coordinate rhodium(‐I) and rhodium(0) complexes as well as a rare rhodium(I) complex. Reduction of [{Rh(μ‐Cl)(IPr)(dvtms)}2] (1, IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolyl‐2‐ylidene; dvtms=divinyltetramethyldisiloxane) with KC8 gave the trigonal complexes K[Rh(IPr)(dvtms)] and [Rh(IPr)(dvtms)], whereas the cation [Rh(IPr)(dvtms)]+ results from their oxidation or by ion of chloride from 1 with silver salts. The paramagnetic Rh0 complex is a unique fully metal‐centered radical with the unpaired electron in the dz2 orbital. The Rh(‐I) complex reacts with PPh3 with replacement of the NHC ligand, and behaves as a nucleophile, which upon reaction with [AuCl(PPh3)] generates the trigonal pyramidal complex [(IPr)(dvtms)Rh‐Au(PPh3)] with a metal–metal bond between two d10 metal centers. Trigonal‐planar rhodium complexes in low oxidation states are feasible by combination of a highly flexible diolefin and a bulky ligand. One‐electron oxidation of the diamagnetic Rh(‐I) complex gives the paramagnetic Rh0 counterpart, a unique metal‐centered radical with the unpaired electron in the dz2 orbital. Code color: Rh (yellow), K (pink), Si (green), O (red), N (blue), C (gray).