Syntheses and crystal structures of mononuclear [2.2]paracyclophane complexes of rhodium and iridium supported by the pentamethylcyclopentadienyl ligand [M(η6-pcp)(η5-C5Me5)](BF4)2 (M=Rh and Ir)

Abstract

Mononuclear [2.2]paracyclophane complexes of Rh and Ir, [M(η6-pcp)(η5-C5Me5)](BF4)2 (M=Rh (1) and Ir (2); pcp=[2.2]paracyclophane) were crystallized and their structures were first characterized crystallographically. On both pcp complexes the metal atom is bonded to the benzene ring on one side of the pcp ligand in the η6-coordination mode. The metal atom is also supported by the η5-C5Me5 ligand to afford a triple-decker sandwich structure. In Rh pcp complex 1 the average Rh-C(pcp) and Rh-C(C5Me5) distances are 2.284(2) and 2.161(2) Å, respectively. The average C(pcp)=C(pcp) distance of 1.407(4) Å with the Rh atom is longer than that (1.388(4) Å) without a Rh atom. Similarly, the average Ir-C(pcp) and Ir-C(C5Me5) distances in Ir pcp complex 2 are 2.275(3) and 2.174(3) Å, respectively. The average C(pcp)=C(pcp) distance of 1.410(4) Å with the Ir atom is longer than that (1.388(4) Å) without an Ir atom. It is interesting that the average interannular distances of 2.97 Å for 1 and 2 between two decks of the pcp ligand are shorter than that (3.09 Å) of the metal-free pcp ligand, indicative of the decrease of the repulsive π-interaction between benzene rings. The Rh pcp complex gave the well-resolved 1H NMR signals of [Rh(η6-pcp)(η5-C5Me5)]2+, whereas the Ir pcp complex exhibited two kinds of 1H NMR signals which were assigned as [Ir(η6-pcp)(η5-C5Me5)]2+ and [Ir2(η6-pcp)(η5-C5Me5)2]4+ in (CD3)2CO at 23°C.