[19584-30-6] · C12O12Rh4 · Dodecacarbonyltetrarhodium · (MW 747.76)
(catalyst for hydrogenation, hydroformylation, silylformylation, hydroboration, aldol reactions)
Solubility: sol hexane, benzene, toluene, acetone, dichloromethane.
Form Supplied in: dark red crystalline solid; commercially available.
Preparative Method: prepared from Tetracarbonyl(di-m-chloro)dirhodium4
Handling, Storage, and Precautions: air sensitive; should be handled under nitrogen or argon; water sensitive (decomposes to Rh6(CO)16 in the presence of water); heat sensitive; store in refrigerator under carbon monoxide. Use in a fume hood.
Rh4(CO)12, either in solution or bound to alumina, is an effective catalyst for the hydrogenation of alkenes to alkanes5 in good yield. Asymmetric hydrogenations with enantioselectivities up to 70% have also been achieved by using Rh4(CO)12 in combination with chiral phosphines such as (1) and (2).6
Alkenes are hydroformylated to aldehydes under mild conditions using Rh4(CO)12 as the catalyst,7 while alkynes react under water-gas shift conditions to give furan-2(5H)-ones (eq 1) as a mixture of isomers when unsymmetrical alkynes are used.8 Both mono- and disubstituted alkynes have also been found to undergo cross-hydroformylation with ethylene to give exclusively trans-a,b-unsaturated ketones in good yield.9
The addition of trialkylsilanes and carbon monoxide across the carbon-carbon triple bond of alkynes (silylformylation) is catalyzed by Rh4(CO)12. b-Silylacrylaldehydes are formed in good yield with a high degree of stereocontrol for the (Z) isomer (eq 2) (see also Dodecacarbonyltetrarhodium-Dimethyl(phenyl)silane-Carbon Monoxide).10 In the presence of a base such as 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) and the highly hindered silane t-butyldimethylsilane, propargyl alcohols11 and propargyl amines12 can be cyclized to a-silylmethylene-b-lactones and lactams (eq 3; Z = O, NR3) in good yield. The addition of hydrosilanes across the double bond of alkenes is also catalyzed by Rh4(CO)12.13
1,3-Dienes undergo hydroboration with Catecholborane in the presence of Rh4(CO)12 to give, exclusively, (Z)-allylic boronates in good yield.14 These compounds react with aldehydes to give erythro-alcohols (eq 4).
Crossed aldol reactions of enol trimethylsilyl ethers and aldehydes and ketones occur rapidly in the presence of a catalytic amount of Rh4(CO)12 to give b-trimethylsiloxyalkanones (eq 5), while the reaction of enol trimethylsilyl ethers with acetals yields b-methoxy ketones.15
Michael S. Shanklin & Michael P. Doyle
Trinity University, San Antonio, TX, USA