Isolation of intermediates in the dicobalt octacarbonyl-catalyzed cyclotrimerization of cyclooctyne. Crystal and molecular structure of a cobaltacyclopentadiene complex

Magnetic Hydrogels from Alkyne/Cobalt Carbonyl-Functionalized ABA Triblock Copolymers

“…While freshly prepared PES n [Co 2 (CO) 6 ] x - b -EO 800 - b -PES n [Co 2 (CO) 6 ] x samples are soluble in common organic solvents (including CHCl 3 , toluene, THF, and DMF), samples that have been aged at room temperature for 1–2 weeks or longer invariably become insoluble in the same solvents, indicating that the PPES/Co domains have become cross-linked. , Oxidative decomposition of the alkyne/dicobalt hexacarbonyl moieties might also occur to a very small extent during the drop-casting and drying procedure, as evidenced by the broadening of 1 H NMR peaks consistent with the formation of paramagnetic Co­(II) species, , observed for the cobalt-complexed polymers (Figure S8) as compared to the corresponding uncomplexed triblock copolymers (Figure S3). Moreover, cobalt carbonyl-alkyne complexes can undergo a variety of addition or cyclization reactions to produce structures, including cyclopentadienones, quinones, aromatic rings, and polymers that, were they to occur in an intermolecular fashion, would lead to cross-linking of the PPES/(Co 2 (CO) 6 domains. − While the exact mechanism for cross-linking is not yet known, it occurs to a sufficient extent to preserve block copolymer morphology upon subsequent thermolytic formation of cobalt nanoparticles.…”

Mechanistic Studies of Transition-Metal-Catalyzed [2 + 2 + 2] Cycloaddition Reactions

“…In contrast to the previously reported examples that used asymmetrically substituted alkynes, , the symmetrically substituted 1,3,5-triphenyltris­(acetyl)­benzene 21 was isolated, and also the fly-over complex 20a was symmetrically substituted. The authors postulated the mechanism shown in Scheme , which involved an elusive bimetallic cobaltacyclopentadiene complex 18c , analogous to the ones isolated earlier, , formed upon head-to-tail oxidative cyclization from monoalkyne complex 17b . Upon coordination of a third alkyne, 18c formed the fly-over complex 20a , which provides reasonable amounts of the cyclotrimer 21 under relatively mild conditions and short reaction times and was thus postulated as an intermediate in the reaction.…”

“…In the previously commented set of studies of the [Co 2 (CO) 8 ]-catalyzed cyclotrimerization reaction, only complexes involving one or three alkynes were isolated. Bennet and Donaldson 83 studied the cyclotrimerization of cyclooctyne, which is cyclotrimerized under very mild conditions, with the same catalyst. When the reaction was carried out under nearly stoichiometric conditions, the reaction product was isolated together with monoalkyne complex 17a and a new organocobalt complex that after X-ray diffraction analysis was assigned as bimetallic cobaltacyclopentadiene complex 18a (Scheme 10, equation a).…”

Nitrous Oxide Mediated Oxygen Atom Insertion into a Ruthenium−Hydride Bond. Synthesis and Reactivity of the Monomeric Hydroxoruthenium Complex (DMPE)2Ru(H)(OH)

“…Many catalytic processes involve intermediates that are proposed to contain late transition metal−heteroatom (N, O, S) bonds. − Recent work has been directed toward the synthesis of these potentially reactive species, but there remain few examples of monomeric late metal hydroxide complexes, − species which are thought to be important in the hydration of olefins to alcohols, the hydration of nitriles to carboxamides, and the Wacker process. ,− …”