Transition Metal Methylene Complexes. 36. Chelate-Type Bridging α-Diazo Ketones through Cleavage of a Metal-Metal Triple Bond

Cleavage of the metal-metal triple bond of bis[dicarbonyl(η⁵-pentamethylcyclopentadienyl)molybdenum](Mo≡Mo) (1a) is effected by the α-ketodiazoalkanes 2a-d resulting in the formation of the chelate-type dinuclear insertion products 3a-d. An X-ray crystallographic study of the key compound 3a revealed the central structural frame [formula omitted] to be composed of an essentially planar five-membered metallacyclic unit that coordinates to the second metal atom via a terminal nitrogen group (Mo(2)−N(2) = 183.6 (17) pm; N(1)−N(2) = 124.4 (24) pm). No molybdenum-molybdenum bond is present after α-diazo ketone addition to the unsaturated organometallic precursor 1a, with the nonbonding MoMo distance being longer than 380 pm. Metal-metal bond cleavage appears to be prevalent in the reactions of metal-metal triple bonds with carbonyl-flanked diazoalkanes capable of chelating mononuclear organometallic fragments.