Ring-opening polymerisation of silver-diphosphine [M2L3] coordination cages to give [M2L3](infinity) coordination polymers

[M2L3] coordination cages and linear [M2L3] polymers of the rigid, bridginf diphosphines bis(diphenyl-phosphono)acetylene (dppa) and trans-1,2-bis(dip henylphosphino)ethylene (dppet) with silver(1) salts have been investigated in the solution and solid states. Unlike flexible diphosphines, 1:1 dppa/A gX mixtures do not selectively form discrete [Ag-2(diphos)(2)(X)(2)] macroc ycles; instead dynamic mixtures of one-, two- and three-coordinate complexe s are formed. However, 3:2 dppa/AgX ratios (X=SbF6, BF4, O3SCF3 or NO3) do lead selectively to new [M2L3] triply bridged cage complexes [Ag-2(dppa)(3) (X)(2)] 1a-d (X=SbF6 a, BF4 b, O3SCF3 c, NO3 d), which do not exhibit Ag-P bond dissociation at room temperature on the NMR time scale (121 MHz). Comp lexes 1a-d were characterized by X-ray crystallography and were found to ha ve small internal cavities, helical conformations and multiple intramolecul ar aromatic interactions. The nucleophilicity of the anion subtly influence s the cage shape: Increasing nucleophilicity from SbF6 (1a) through BF4 (1b ) and O3SCF3 (1c) to NO3 (1d) increases the pyrmidal distortion at the AgP3 centres, stretching the cage framework (with Ag...Ag distances increasing from 5.48 in 1a to 6.21 Angstrom in 1d) and giving thinner internal cavitie s. Crystal packing strongly affected the size of the helical twist angle, a nd no correlation between this parameter and the Ag-Ag distance was observe d. When crystalline 1c was stored in its supernatant for 16 weeks, conversi on occured to the isostoichiometric [M2L3](chi) coordination polymer [Ag(dp pa)(2)Ag(dppa)(O3SCF3)(2)](chi) (1c ') X-ray crystallography revealed a str ucture with ten-membered Ag-2(dppa)(2) rings linked into infinite one-dimen sional chains by a third dppa unit. The clear structural relationship betwe en this polymer and the precursor cage 1c suggests a novel example of ring- opening polymerization. With dppet, evidence for discrete [M2L3] cages was also found in solution, although P-31 NMR spectroscopy suggested some Ag-P bond dissociation. On crystallation only the corresponding ring-opened poly meric structures [M2L3](chi) could be obtained. This may be because the gre ater steric bulk of dppet versus dppa destabilises the cage and favors the ring-opening polymerisation.