Self-assembly of gold(I) rings and reversible formation of organometallic [2]catenanes

The reaction of the digold(I) diacetylide [(AuCCCH2OC6H4)(2)CMe2] with diphosphane ligands can lead to formation of either macrocyclic ring complexes or [2]catenanes by self-assembly. This gives an easy route to rare organometallic [2]catenanes, and the effect of the diphosphane ligand on the selectivity of self-assembly is studied. With diphosphane ligands Ph2P-(CH2)(x)PPh2, the simple ring complex [Au-2[(CCCH2OC6H4)(2)CMe2)(Ph2P-(CH2)(x)PPh2)] is formed selectively when x=2, but the [2]catenanes [Au-2[(CCCH2OC6H4)(2)CMe2](Ph2P(CH2)(x)PPh2)](2) are formed when x = 4 or 5. When x = 3, a mixture of the simple ring and [2]catenane is formed, along with the "double-ring" complex, [Au-4[(CCCH(2)OC7(6)H(4))(2)CMe2](2)(Ph2P(CH2)(3)PPh2)(2)] and a "hexamer" [{Au-2[(CCCH2OC6H4)(2)CMe2]- (Ph2P(CH2)(3)PPh2)}(6)] Whose structure is not determined. A study of the equilibria between these complexes by solution NMR techniques gives insight into the energetics and mechanism of [2]catenane formation. When the oligomer [(AuCCCH2OC6H4)(2)CMe2] was treated with a mixture of two diphosphane ligands, or when two [2]catenane complexes [{Au-2[(CCCH2OC6H4)(2)CMe2]-(diphosphane)}(2)] were allowed to equilibrate, only the symmetrical [2]catenanes were formed. The diphosphanes Ph2PCCPPh2, trans-[Ph2PCH=CHPPh2] and (Ph2PC5H4)(2)Fe give the corresponding ring complexes [Au-2{(CCCH2OC6H4)(2)CMe2}(diphosphane)], and the chiral, unsymmetrical diacetylide [Au-2[(CCCH2OC6H4CMe)(CH2CMe2)- C6H3OCH2CC)] gives macrocyclic ring complexes with all diphosphane ligands Ph2P(CH2)(x)PPh2 (x = 2 - 5).