Chloro(1,5‐Cyclooctadiene)Rhodium(I) Dimer

Abstract

[12092-47-6] C16H24Cl2Rh2 (MW 493.08) InChI = 1S/2C8H12.2ClH.2Rh/c2*1-2-4-6-8-7-5-3-1;;;;/h2*1-2,7-8H,3-6H2;2*1H;;/q;;;;2*+1/p-2/b2*2-1-,8-7-;;;; InChIKey = QSUDXYGZLAJAQU-MIXQCLKLSA-L (catalyst precursor for reactions involving heteroatom nucleophiles, aryl boronic acids, alkenes, alkynes, and a variety of organometallic reagents; most notably cross-couplings, asymmetric hydrogenations, Pauson–Khand annulations, carbonyl 1,2- and 1,4-additions, cycloisomerizations, and various tandem processes) Alternate Names: 1,5-cyclooctadienerhodium(I) chloride dimer and rhodium(I) chloride 1,5-cyclooctadiene complex dimer. Physical Data: mp 243 °C. It exists as hygroscopic yellow to orange crystals. Solubility: soluble in dichloromethane; moderately soluble in chloroform, acetic acid, and acetone; slightly soluble in ether, methanol, ethanol and benzene; insoluble in water. Analysis of Reagent Purity: strong infrared bands at 819, 964 and 998 cm−1 (Nujol mull). 1H NMR: 4.3 ppm and 2.6–1.7 ppm (CDCl3). Preparative Method: prepared by refluxing RhCl3·3H2O and excess cis,cis-1,5-cyclooctadiene in ethanol for 3–18 h. The solution is then cooled, the orange solid filtered, washed with ethanol and dried. Recrystallization from dichloromethane/diethyl ether or acetic acid gives orange prisms.1-3 Note that if the RhCl3·3H2O is particularly acidic, Na2CO3 can be added to the solution of rhodium complex in refluxing ethanol to obtain satisfactory results. Handling, Storage and Precautions: although the catalyst is quite air-stable, it should be handled under an inert atmosphere, and stored at reduced temperature (2–8 °C), to ensure optimal catalytic activity. The complex is susceptible to slow oxidation upon exposure to air, and appropriate precautions should be taken to maintain its catalytic efficacy. Reproducible results are best obtained when the catalyst is prepared fresh and used immediately. Standard good laboratory practices should be used when working with this reagent.