[12257-42-0] · C14H16Cl2Rh2 · Bis(bicyclo[2.2.1]hepta-2,5-diene)dichlorodirhodium · (MW 461.00)
(catalyst for valence isomerization2 and N-heterocyclization;3 in combination with phosphorus ligands are catalysts for hydrogenation of many functional groups5,6 and hydroformylation; with chiral ligands are catalysts for asymmetric hydrogenation7-11)
Alternate Name: dichlorobis(norbornadiene)dirhodium.
Physical Data: mp 240 °C dec.
Solubility: sol chloroform and benzene; insol ether and light petroleum.
Form Supplied in: yellow crystals.
Preparative Methods: Rhodium(III) Chloride and bicyclo[2.2.1]hepta-2,5-diene in aq ethanol, when shaken for 2 days, give a yellow deposit.
Purification: recrystallized from chloroform and light petroleum.
Handling, Storage, and Precautions: air stable up to 240 °C.
The rhodium chloride dimer is easily prepared from rhodium trichloride and the diene has been well used as a catalyst for valence isomerization of quadricyclanes to bicyclo[2.2.1]hepta-2,5-dienes (eq 1).2
The reverse isomerization is catalyzed by Copper(I) Chloride under irradiation.2c This cycle has attracted much attention as a solar energy storage system. The rhodium dimer catalyzes the reaction between aminoarenes and alkanals to give quinolines (eq 2).3 The rhodium dimer is easily transformed into a monomeric neutral form in combination with neutral donor ligands, which turns into a cationic form in the presence of such salts as Potassium Hexafluorophosphate and NaClO4 (eq 3).
These rhodium complexes of two types show high catalytic activities for hydrogenation of many unsaturated groups5-11 such as C=C, C&tbond;C, C=O, and C=N. In particular, cationic rhodium complexes are efficient under mild conditions (at ambient temperature and 1 atm of H2).5 The original rhodium dimer is readily modified into a selection of active catalysts by use of a wide range of phosphorus ligands including chiral,7-11,13 polymer-supported,14 and water-soluble types.15,16
With a variety of chiral ligands, such substrates as alkenes,7 ketones,8 a-keto amides,9 a-keto esters,10 and imines11 are hydrogenated highly enantioselectively (eqs 4-7).
Hydroformylation of alkenes proceeds with a rhodium catalyst,12 even asymmetrically.13 A polymer-supported rhodium catalyst is efficient for hydrogenation of benzenes to cyclohexanes.14 Water-soluble phosphine ligands are applicable for asymmetric hydrogenation of alkenes15 and hydroformylation of alkenes.16
Kyoto University, Japan