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

The reaction of the digold(I) diacetylide (AuCCCH2OC6H4)2CMe2] 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)xPPh2, the simple ring complex Au2(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)] is formed selectively when x = 2, but the 2]catenanes Au2(CCCH2OC6H4)2CMe2](Ph2P(CH2)xPPh2)]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, Au4(CCCH2OC6H4)2CMe2]2(Ph2P(CH2)3PPh2)2] and a "hexamer" Au2(CCCH2OC6H4)2CMe2](Ph2P(CH2)3PPh2)]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)2CMe2] was treated with a mixture of two diphosphane ligands, or when two 2]catenane complexes Au2(CCCH2OC6H4)2CMe2](diphosphane)]2] were allowed to equilibrate, only the symmetrical 2]catenanes were formed. The diphosphanes Ph2PCCPPh2, trans-Ph2PCH=CHPPh2] and (Ph2PC5H4)2Fe give the corresponding ring complexes Au2(CCCH2OC6H4)2CMe2](diphosphane)], and the chiral, unsymmetrical diacetylide Au2(CCCH2OC6H4C(Me)(CH2CMe2)C6H3OCH2CC)] gives macrocyclic ring complexes with all diphosphane ligands Ph2P(CH2)xPPh2 (x = 2-5).