New Ligand System Based on a Bipyridine-Functionalized Calix[4]arene Backbone Leading to Mono- and Bimetallic Complexes

The synthesis of a new ligand system for mono- and bimetallic complexes based on a calixarene is described. Ligand BBPC (3, bis(bipyridine)-calix[4]arene) is obtained in three steps in 40% overall yield by first brominating one of the methyl groups of the 4,4ʹ-dimethyl-2,2ʹ-bipyridine in two steps and subsequently reacting it with p-tertbutylcalix[4]arene under basic conditions. Reaction of BBPC (3) with 2 equiv of [Rh(NBD)2)BF4 or [Rh(NBD)(CHsCN)2]BF4 (NBD = norbomadiene) produces the bimetallic compound BBPC[Rh(NBD)BF4]2 (4). Treatment of the ligand with PdCCHsC leads to the isolation of the bimetallic complex BBPCpdC (5). When the nickel precursor NI DME) (DME = dimethoxyethane) is reacted with BBPC, the bimetallic complex BBPC (6) is isolated which, upon crystallization from methanoi, gives the mononuclear bis(bipyridine) complex BBPC[NiBr(OMe)] (7). Full characterization includes X-ray structural studies of complexes 4,5, and 7. The bimetallic compounds 4 and 5 show metal to metal distances of 4.334 A (for 4) and 3.224 A (for 5). For all three complexes, unique molecular packing arrangements were found, based on hydrophobic/hydrophilic interactions.