REDUCTION CHEMISTRY OF ORGANOMETALLIC MOLYBDENUM, TUNGSTEN, AND RUTHENIUM BROMO COMPLEXES OF THE BULKY, PERARYLATED CYCLOPENTADIENYL LIGANDETA(5)-C5PH4HQME2 - EVIDENCE FOR THE INTERMEDIACY OF METAL-CENTERED RADICALS AND NUCLEOPHILIC REACTIONS OF PRODUCT METALATE ANIONS WITH CHLORINATED SOLVENT

The bromo complexes (C5Ph4hqMe2)M(CO)(n)Br (1, M = Mo, n = 3, 2, M = W , n = 3; 3, M = Ru, n = 2) have been prepared and are reduced via the (C5Ph4-hqMe2)M(CO)n.radicals in a two-electron (ECE) process to the co rresponding metalate (C5Ph4hqMe2)M(CO)n- (4-6) and bromide anions at - 1.76 V (Mo), -1.84 V (W) and -1.92 V (Ru). Reduction of 3 with cobalto cene in THF affords the dimer {(C5Ph4hqMe2)Ru(CO)2}2 (7). Anions 4 and 5 and dimer 7 show electrochemically quasi-reversible (C4Ph4hqMe2)M(C O)n./(C5Ph4hqMe2)M(CO)n- couples at -0.54 V (Mo), -0.52 V (W) and -1.3 0 V (Ru). Anion 4 does not react with 1,2-dichloroethane on the bulk e lectrolysis time scale (3-10 min); 5 reacts slightly, and 6 reacts com pletely, in accord with the anticipated nucleophilicities of these met alate anions.