Di-and Triborolyl Ligands

The ruthenium starting materials of composition nido-[(r] -MQCeii4Fr-/)Ru(2,3-Et2C2B3H4-5-R)] (R = Me, Cl) with tert-butyl lithium and then 

R =R = Et]. The methyl-containing starting material after a similar sequence of transformations but with nickel chloride gives the nickel analogue of 7 [ML = = Ru(/7 -cymene) M = Ni, R = R = H R = 

In the complexes of 1,3-boroles containing the unsaturated substituents (89CB633, 90CB2273, 94CB2393), the coordination mode is in the case of iron tricarbonyl complexes 10 and 11 (R = H, Me). 

The reactions of the Group VIII di- and triborolyl or carboranes sandwiches are directed basically to their extension to multidecker derivatives. 

Similar triple-decker complexes are known, e.g., [( -/ -MeC6H4CHMe2) Ru( -Et2C2B3H3)Ru( - 7-MeC6H4CHMe2)] and [( -Cp)Co( j -Et2C2 B3H3) 

When species Wo-[(/ 5-Cp )Co(Et2C2B3H4-5-X)] (X= Me, Cl) are deprotonated with -butyl lithium and then reacted with iron(II) chloride, 

R = R = R = R = R = Me] also reacts with [( -C2H4)2RhCl] to give the tetranuclear product 3 formulated as a pentadecker species with two central bridging chlorine atoms. 

---

The di- and triborolyl ligands tend to i -coordination in sandwichforming reactions. There is a clear-cut tendency for stacking processes followed by the formation of multidecker species and often stabilization of the unusual oxidation states of the transition metals. The route to the linked sandwich and multidecker complexes is attractive for materials chemistry. Thia- and azaborolyl organome-tallic chemistry follows the same trends, although in the azaborolyl complexes the i -rather than i -coordination is sometimes realized. Moreover, coordination via the boron atom is known. In the B, N, Si-heterocycles, the heteroring is j " -coordinated. 

---