Dimethyl Acetylenedicarboxylate (dmad) Reactivity with the Mixed-Metal Cluster Co_2Rh_2(CO)_(12):Facile Cluster Fragmentation and Highly Specific Metal Redistribution to Give the Butterfly Cluster Co_3Rh(CO)_(10)(mu-dmad) and the Planar Cluster CoRh_

摘要

The reaction between the tetrahedral cluster Co_2Rh_2(CO)_(12) (1) and a 2-fold excess of dimethyl acety-lenedicarboxylate (dmad) proceeds rapidly at room temperature to give alkyne-substituted clusters Co_3Rh(CO)_(10)-(mu-dmad) (3) and CoRh_3(CO)_9(mu-dmad)3 (4) as the major products in good yield.Cluster 3 was characterized in solution by IR and ~1H NMR spectroscopies and by comparison to an independently prepared sample of 3 from the reaction of dmad with the known tetrahedral cluster Co_3Rh(CO)_(12) (2).Cluster 4 was characterized by IR and NMR (~2H and ~(13)C) spectroscopies and FAB mass spectrometry,and the solid-state structure was established by X-ray diffraction analysis.The structure of CoRh_3(CO)_9(mu-dmad)_3 consists of a square planar array of metals where two of the three dmad ligands cap both of the CoRh_3 faces and the remaining dmad ligand bridges one of the Rh-Rh edges.The nine ancillary CO groups are all terminally bound,with one Co(CO)_3 and three Rh(CO)_2 moieties structurally found.The facile cluster fragmentation / metal redistribution observed upon reaction with dmad is briefly discussed relative to other alkyne ligands that react with cluster 1 to furnish the arachno clusters Co_2Rh_2(CO)_(10)(mu_4-alkyne).