Remarks on the process of homogeneous carbonylation of rhodium compounds by N,N-dimethylformamide Yuri S. Varshavsky * , Tatiana G. Cherkasova Institute of Chemistry, St. Petersburg State University, Petrodvorets, Universitetskii pr., 26, 198504 St. Petersburg, Russia Received 20 May 2006; received in revised form 11 July 2006; accepted 19 October 2006 Available online 25 October 2006 Abstract Reductive carbonylation of rhodium(III) chloride complexes, commercial RhCl 3 Æ nH 2 O neutralized with BaCO 3 , (Me 2 NH 2 ) 2 - [RhCl 5 (DMF)], (PPh 4 )[RhCl 4 (H 2 O) 2 ], RhCl 3 (DMF) 3 , RhCl 3 (CH 3 CN) 3 , RhCl 3 (CH 3 CN) 2 (DMF), [Rh(CO) 2 Cl 3 ] 2 , and rhodium(I) com- plex, Rh(PPh 3 ) 3 Cl, by N,N-dimethylformamide (DMF) is studied. The data obtained support the conception of direct carbonyl group transfer from DMF molecule to the Rh metal center. The mechanistic scheme of carbonylation process is refined and discussed with regard of new experimental results. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Rhodium; Dimethylformamide; Carbonylation 1. Introduction Reductive carbonylation of platinum metal halides on heating their solutions in alcohols has been discovered in 1960s. Specifically for rhodium compounds, this reaction has been described in several papers [1–6]. In 1965 Rusina and Vlc ˇek [7] revealed that N,N-dimethylformam- ide (DMF) is also a powerful agent for reductive carbon- ylation of rhodium(III) chloride. In all these works carbonylation was carried out in the presence of stabiliz- ing ligand, usually triphenylphosphine, to prevent excess reduction and metal black deposition. Soon after Rusina and Vlc ˇek publication, we attempted to heat rho- dium(III) chloride solution in DMF without any stabiliz- ing ligand and obtained a clear yellow solution containing rhodium in the form of the [Rh(CO) 2 Cl 2 ]  anion. Consecutive addition of acetylacetone and water to the reaction mixture resulted in the precipitation of known complex, Rh(Acac)(CO) 2 , in good yield [8]. In our further communications [9–13] we reported syntheses of a variety of analogous dicarbonyl rhodium(I) com- plexes with bidentate monoanionic ligands and salts of the [Rh(CO) 2 Cl 2 ]  anion. Within the following four dec- ades this method has gained wide acceptance and has become a routine laboratory practice (see for example [14–26]) and a subject of industrially oriented studies [27]. The mechanistic scheme we suggested [28,29] involved direct carbonyl group transfer from a DMF molecule to a rhodium atom. The recent publications [30,31] contributed some new facts and ideas to this chemistry and brought forward another mechanistic con- ception based on the HCl-mediated decarbonylation of DMF and subsequent carbonylation of rhodium by free carbon monoxide. We considered briefly this alternative and presented our new data concerning carbonylation of several individual rhodium(III) complexes in the report [32]. The revival of interest in these problems prompted us to verify and extend our old experimental studies, to prove our mechanistic conception, and to pub- lish it in a more widely available edition. 0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jorganchem.2006.10.040 * Corresponding author. Tel.: +7 812 428 4710; fax: +7 812 2743445. E-mail address: yurel@peterlink.ru (Y.S. Varshavsky). www.elsevier.com/locate/jorganchem Journal of Organometallic Chemistry 692 (2007) 887–893