Chiral cyclopentadienyl hydrogenation catalysts: crystal structures of rhodium complexes [Rh(C5R4R*)Cl2]2 (R = H, R* = neomenthyl; R = Me, R* menthyl)

The synthesis and crystal structure of the title compounds are reported. The corresponding tetramethylmenthyl derivative was co-crystallized with triphenylphosphineoxide, ie. as [Rh{C5Me4-(menthyl)}Cl2]2·2[(C6H5)3PO]. Both compounds are active hydrogenation catalysts in the presence of Et3N but with prochiral alkenes the enantioselectivity is low (i.e. ≤ 13% ee).