New Metallacarborane Chemistry: Molybdenum and Tungsten Carbonyl Multidecker Sandwiches. Cluster Dimers Linked via Metal-Metal Bonds(1).

This article reports the synthesis, characterization, and chemistry of the first molybdenum and tungsten complexes bearing small carborane ligands, including novel M−M-linked dicluster species. The reaction of the nido-2,3-Et2C2B4H42- dianion with (RCN)3M(CO)3 reagents (M = Mo, W; R = Me, Et) gave the (Et2C2B4H4)M(CO)32- anions, which were isolated as lithium (12-crown-4) salts 1b (M = Mo) and 2b (M = W). Treatment of 1b and 2b with Ph4PX (X = Cl, Br, I) followed by triflic acid afforded the dimeric products [(Et2C2B4H4)Mo(CO)2]2(μ-X)2 (X = Cl (3a), Br (3b), I (3c)) and the corresponding tungsten dimers 4a−c, all of which are red or orange air-stable crystalline solids. X-ray crystallography on 3b revealed a geometry without precedent in small metallacarborane dimers, in which two MC2B4 pentagonal pyramidal clusters are linked via an intercluster metal−metal bond. From NMR and other spectroscopic evidence, the remaining dimeric products 3a, 3c, and 4a−c are proposed to have structures similar to 3b. Decap...