Tris triphenylphosphine halorhodium I

RhCl3 -I- 4P(C6H6)3 - RhCl[P(C6H6),l3 + Cl2P(C6H5)3 

Rhodium(III) chloride trihydrate (2 g.) is dissolved in 70 ml. of ethanol (95%) in a 500-ml. round-bottomed flask fitted with gas inlet tube, reflux condenser, and gas exit bubbler, A solution of 12 g. of triphenylphosphine (freshly crystallized from ethanol to remove triphenylphosphine oxide) in 350 ml. of hot ethanol is added and the flask purged with nitrogen. The solution is refluxed for about 2 hours, and the crystalline product which forms is collected from the hot solution on a Buchner funnel or sintered-glass filter. The product is washed with small portions of 50 ml. of anhydrous ether yield 6.25 g. (88% based on Rh). This crystalline product is deep red in color. 

An isomeric species which is orange is obtained if the total volume of ethanol used is 200 ml. or less and the solution is refluxed for a period of about 5 minutes. This substance often contains small amounts of the red product and, on continued refluxing, the orange crystals are slowly converted to the red form. 

The excess triphenylphosphine used in the preparation can be recovered by addition of water to the ethanol filtrates until precipitation begins. After allowing the solutions to stand 2 to 3 days in a stoppered flask, the triphenylphosphine crystallizes out. Recrystallization from ethanol and ethanol-benzene (1 1) removes triphenylphosphine oxide contaminant. 

The red and orange forms of RhCl[P(C6H5)3]3 have apparently identical chemical properties the difference is presumably due to different crystalline forms, and possibly bonding in the solid. The complex is soluble in chloroform and methylene chloride (dichloromethane) to about 20 g./l. at 25°. The solubility in benzene or toluene is about 2 g./l. at 25° but is very much lower in acetic acid, acetone, and other ketones, methanol, and lower aliphatic alcohols. In paraffins and cyclohexane, the complex is virtually insoluble. Donor solvents such as pyridine, dimethyl sulfoxide, or acetonitrile dissolve the complex with reaction, initially to give complexes of the type RhCl[P(C6H6)3]2L, but further reaction with displacement of phosphine may occur. 

---

JA Osborn, FH Jardin, JF Young, G Wilkinson. Preparation and properties of tris(triphenylphosphine)halorhodium(I) and some reactions thereof including catalytic homogeneous hydrogenation of olefins and acetylenes and their derivatives. J Chem Soc A 1711, 1966. 

---