Cyclodextrin Phosphanes as First and Second Coordination Sphere Cavitands

摘要

The binding properties of two alpha-cyclodextrins each containing two C(5)-linked "CH_2PPh_2" units L19A,D-substituted) and L2 (A,C-substituted)have been investigated Both ligands readily form transition-metal chelated complexes in which the methal centres are immoblised at the cavity entrance Althouth diphosphane L1 displays a marked tendency to behave only as a trans-spanning ligand the ligadn possesses sa certain eegree of flexibility for example allowing the ligand possesses a certain degree of flexibility for example allowing the stabilistation fo trigonal silver(I) complex inwhich the bite angle drops to 143 Another feature of Li concenrns its ability to functin as an hemilabile ligand Together 3ith four methoxy groups anchored onto the primary face te two P~III centres fo L1 from a circularly arranged P_2O_4 12-electron donor set able to complex an Ag~+ ion in a dynamic way each of the four oxygen atoms coordinating successively to the silver ion Furthermore the particular structure fo L1 and L2 characterised gy the presence of P~III units lying close to the cavity entrance lea upon comlexatin to complexes where by the first coordination sphere is partly entrapped in the cycloddextrin Thus when treated with metal chlorides both ligands systematically produced complexes in which the M-Cl unit is maintained inside the cyclodextrin through weak Cl...H-5 interactions The chelated complex (Ag(L1)]BF_4 reacts with acetonitrile in excess to afford a mizture of two equilibration complexes [Ag(acetonitrile)(L1)]BF_4 and [Ag(acetonitrile)(L1)]BF_4 whose coordinated nitriles ilie inside the cyclodextrin cavity the inner-cavity ligands can be substituted by a benzonitrile molecule The present study provides the first identification of an [Ag(acetonitrile)_2(phosphane)_2]~+ ion The unexpected stabilisation of this species probably rests on a cavity effecdt the cyclodextrin wals favouring recombination of hte comples after facile dissociation of the nitrile ligands.