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Ring‐Opening Polymerisation of Silver–Diphosphine [M 2 L 3 ] Coordination Cages To Give [M 2 L 3 ] ∞ Coordination Polymers
Author(s) -
Lozano Elvira,
Nieuwenhuyzen Mark,
James Stuart L.
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010618)7:12<2644::aid-chem26440>3.0.co;2-3
Subject(s) - diphosphines , crystallography , chemistry , intramolecular force , dissociation (chemistry) , polymer , stereochemistry , catalysis , organic chemistry , biochemistry
[M 2 L 3 ] coordination cages and linear [M 2 L 3 ] ∞ polymers of the rigid, bridging diphosphines bis(diphenylphosphino)acetylene (dppa) and trans ‐1,2‐bis(diphenylphosphino)ethylene (dppet) with silver( I ) salts have been investigated in the solution and solid states. Unlike flexible diphosphines, 1:1 dppa/AgX mixtures do not selectively form discrete [Ag 2 (diphos) 2 (X) 2 ] macrocycles; instead dynamic mixtures of one‐, two‐ and three‐coordinate complexes are formed. However, 3:2 dppa/AgX ratios (X=SbF 6 , BF 4 , O 3 SCF 3 or NO 3 ) do lead selectively to new [M 2 L 3 ] triply bridged cage complexes [Ag 2 (dppa) 3 (X) 2 ] 1 a–d (X=SbF 6 a , BF 4 b , O 3 SCF 3 c , NO 3 d ), which do not exhibit Ag−P bond dissociation at room temperature on the NMR time scale (121 MHz). Complexes 1 a–d were characterised by X‐ray crystallography and were found to have small internal cavities, helical conformations and multiple intramolecular aromatic interactions. The nucleophilicity of the anion subtly influences the cage shape: Increasing nucleophilicity from SbF 6 ( 1 a ) through BF 4 ( 1 b ) and O 3 SCF 3 ( 1 c ) to NO 3 ( 1 d ) increases the pyramidal distortion at the AgP 3 centres, stretching the cage framework (with Ag⋅⋅⋅Ag distances increasing from 5.48 in 1 a to 6.21 Å in 1 d ) and giving thinner internal cavities. Crystal packing strongly affected the size of the helical twist angle, and no correlation between this parameter and the Ag–Ag distance was observed. When crystalline 1 c was stored in its supernatant for 16 weeks, conversion occured to the isostoichiometric [M 2 L 3 ] ∞ coordination polymer [Ag(dppa) 2 Ag(dppa)(O 3 SCF 3 ) 2 ] ∞ ( 1 c′ ). X‐ray crystallography revealed a structure with ten‐membered Ag 2 (dppa) 2 rings linked into infinite one‐dimensional chains by a third dppa unit. The clear structural relationship between this polymer and the precursor cage 1 c suggests a novel example of ring‐opening polymerisation. With dppet, evidence for discrete [M 2 L 3 ] cages was also found in solution, although 31 P NMR spectroscopy suggested some Ag−P bond dissociation. On crystallisation, only the corresponding ring‐opened polymeric structures [M 2 L 3 ] ∞ could be obtained. This may be because the greater steric bulk of dppet versus dppa destabilises the cage and favours the ring‐opening polymerisation.