Structural diversity of calcium organocuprates(I): synthesis of mesityl cuprates via addition and transmetalation reactions of mesityl copper(I).

The addition of [(L)(4)Ca(I)Mes] (Lewis base L=thf, Et(2)O) to mesityl copper(I) and the transmetalation reaction of mesityl copper(I) with activated calcium are suitable pathways for the synthesis of dimesityl cuprates(I) of calcium. However, the structures of the calcium cuprates(I) depend on the preparative procedure. The transmetalation reaction leads to the formation of [Mes-Cu-Mes](-) anions whereas the addition yields dinuclear [(Mes-Cu)(2)(mu-Mes)](-) anions. The solvent-separated counterions are [Ca(thf)(6)](2+) and [(thf)(5)CaI](+), respectively. In contrast to these findings, the addition of [(L)(4)Ca(I)Mes] to mesityl copper(I) in an Et(2)O/toluene mixture led to formation of tetrameric solvent-free iodocalcium dimesityl cuprate(I) [ICa(mu-eta(1),eta(6)-Mes(2)Cu)](4), representing a rare example of a heavy Normant-type organocuprate.