Abstract
Two new dendrimer series were prepared and characterized. These dendrimers contain a single bis(cyclopentadienyl)cobalt(III) (cobaltocenium, Cob+) unit covalently attached to the apical (focal) position of Newkome-type dendrons, ranging in size from first to third generation. The dendrimers in the first series (1ECob + − 3ECob +) are hydrophobic and have 3, 9, and 27 tert-butyl esters on their peripheries, whereas the dendrimers in the second series (1Cob + − 3Cob +) are hydrophilic with 3, 9, and 27 carboxylic acid groups on their surfaces, respectively. In voltammetric experiments, all dendrimers showed the expected one-electron reversible reduction of the cobaltocenium center, and the heterogeneous rate of electron transfer decreased with generation in both dendrimer series. The host−guest binding interactions between water-soluble dendrimers 1Cob + − 3Cob + and the cucurbit[7]uril (CB7) host were investigated using 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and electrochemical techniques. The association equilibrium constants (K) for all dendrimer guests were significantly lower than that measured for the inclusion complex between underivatized Cob + and CB7 (K = 5.7 × 109 M-1). Nonetheless, among the three dendrimers surveyed, the second-generation dendrimer, 2Cob +, afforded optimum stabilization for the CB7 inclusion complex.
