Tungsten-Tungsten Multiple-Bond Functionalities Supported by a Polyoxo Surface Modeled by Calix[4]arene

This report deals with the stepwise reduction of the parent compound [cis-Cl2W{p-Bu-t-calix[4]-(O)(4)}], 2, leading to metal-metal-bonded metalla-calix[4]arene dimers containing the W=W, W=W, and W4/W functionalities. The reduction of 2 with 1 equiv of K led to a W(V) derivative with an unchanged W-coordination sphere in [cis-Cl2W{p-Bu-t-calix[4]-(O)(4)}K], 4, where the alkali metal cation, hosted inside the cavity, experiences eta(6)-interactions with the arene rings. The reduction of 2 with 2 equiv of Na led to the dianion [W-2(mu-Cl)(2){p-Bu-t-calix[4]-(O)(4)}(2)](2-), hosting two sodium cations inside the calix[4]arene cavities in [W-2(mu-Cl)(2){p-Bu-t-calix[4]- (O)(4)}(2)Na-2], 5 [W-W 2.614(1) Angstrom]. A neutral W=W-calix[4]arene dimer was generated by photochemical labilization of ethylene from [(eta(2)-C2H4)W{p-Bu-t-calix[4]-(O)(4)}] and isolated as the (BuNC)-N-t adduct [W-2{mu-p-Bu-t-calix[4]-(O)(4)}(2)((BuNC)-N-t)(2)], 7 [W-W 2.582(1) Angstrom], containing a bridging oxygen from each calix[4]arene ligand. Further reduction of 5 or the reduction of 2 with 3 equiv of Na led to [W-2{p-Bu-t-calix[4]-(O)(4)}(2)(mu-Na)(2)], 8 [W-W 2.313(1) Angstrom], containing two sodium cations shared by the two calix[4]arene ligands. Further reduction of 8 led to [W-2{p-Bu-t-calix[4]-(O)(4)}(2)(mu-Na)(4)], 9 [W-W 2.292(1) Angstrom], containing four bridging sodium cations. All the species reported occur in the ion-pair form with the alkali metal cation complexed either in the cavity or at the lower rim of calix[4]arene ligand. The additional solvent molecules around the alkali metal cation are not specified in this abstract. Extended Huckel calculations have been performed to elucidate the electronic configuration of the metal-metal functionalities when sandwiched by two calix[4]arene tetraanions.