Homoleptic complexes rhodium

When the stoichiometry is changed and 2 equiv. of phosphino functionahsed imidazo-lium salt reacted with 1 equiv. of rhodium(I), a homoleptic, cationic rhodium(l) complex is formed where the carbenes are trans to each other [300]. 

The reaction of 1 with Rh(PPh3)3CI proceeds directly to the homoleptic complex 18, which has been fully characterized, and we have not been able to detect any intermediate in this reaction. The analogous reaction of 2 with Rh(PPh3)3Cl can be separated into two steps first a trinuclear metal entity 19 is formed, and at higher molar ratios of 2 the homoleptic tin substituted rhodium( 1) complex 20 is formed, which contains six metal atoms clustered at the center of the molecule. The compounds 18, 19 and 20 have been characterized by X-ray structure determination techniques. In 18, the central unit is an almost square planar germanium arrangement in the middle of which the rhodium atom is situated. One of the edges... 

The most common homoleptic rhodium complexes are Rli4(CO)i2 and Rh6(CO)i6. Rli4(CO)i2 can be used in catalysis directly or can serve as a catalyst precursor. It can also be used to synthesize other rhodium carbonyl clusters. 

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