The nickel bis(dithiolene) complex Ni(S2C2(CF3)2)2 employs its sulfur centers in reactions with alkenes, and stable interligand S-bonded alkene adducts can be formed. The present study shows that the selectivity of alkene binding to charge-neutral Ni(S2C2(CF3)2)2 is influenced by the anion [Ni(S2C2(CF3)2)2]-. In the absence of anion, formation of substituted dihydrodithiins (intraligand addition) dominates, whereas the presence of anion allows for the formation of stable interligand adducts. Mechanistic implications are discussed. The X-ray crystal structure of the ethylene adduct of Ni(S2C2(CF3)2)2 is presented, displaying interligand binding of ethylene to sulfur centers in the bis(dithiolene) complex.
Cobalt fluorocarbene complexes CpCo(═CFR(F))(PPh2Me) (Cp = η(5)-C5H5, R(F) = F or CF3) react with tetrafluoroethylene to give the metallacyclobutanes CpCo(κ(2)-CFR(F)CF2CF2-)(PPh2Me) in the first examples of cycloaddition reactions between perfluoroalkenes and metal perfluorocarbenes. The metallacyclic products undergo a variety of reactions upon activation of the C-F bonds, including Brønsted acid-catalyzed C-F/Co-C scrambling. Implications for metal-catalyzed metathesis and polymerization of perfluoroalkenes are discussed.
Four perfluoroalkyl cobalt(III) fluoride complexes have been synthesized and characterized by elemental analysis, multinuclear NMR spectroscopy, X-ray crystallography, and powder X-ray diffraction. The remarkable cobalt fluoride (19)F NMR chemical shifts (-716 to -759 ppm) were studied computationally, and the contributing paramagnetic and diamagnetic factors were extracted. Additionally, the complexes were shown to be active in the catalytic fluorination of p-toluoyl chloride. Furthermore, two examples of cobalt(III) bis(perfluoroalkyl)complexes were synthesized and their reactivity studied. Interestingly, abstraction of a fluoride ion from these complexes led to selective formation of cobalt difluorocarbene complexes derived from the trifluoromethyl ligand. These electrophilic difluorocarbenes were shown to undergo insertion into the remaining perfluoroalkyl fragment, demonstrating the elongation of a perfluoroalkyl chain arising from a difluorocarbene insertion on a cobalt metal center. The reactions of both the fluoride and bis(perfluoroalkyl) complexes provide insight into the potential catalytic applications of these model systems to form small fluorinated molecules as well as fluoropolymers.
Unusual nucleophilic cobalt fluorocarbene complexes ([CoI]CFR; R = F, CF3) are described. Only a
handful
of fluorocarbenes of first-row transition metals have been reported,
and these have exhibited electrophilic reactivity
at the metal–carbene bonds. The title compounds are the first
persistent/isolable cobalt fluorocarbenes and also rare examples of
metal fluorocarbenes with relatively nucleophilic MC bonds
(vs other metal fluorocarbene complexes), demonstrated by their reactions
with H+ and Me+ and their unusual stability
toward water. X-ray crystal structures reveal the shortest terminal
cobalt–carbene bonds reported to date, and DFT studies provide
details into the nature of these bonds.
Among established methods for transforming Si-H bonds, carbonyl hydrosilylation and heterodehydrogenative coupling with alcohols catalysed by B(C6F5)3 are shown to provide exceptionally clean routes to the derivatisation of tetra-substituted disilanes such as [Ph2SiH]2, giving no products resulting from Si-Si bond cleavage. Even higher activity is observed for the borane-catalysed dehydrogenative coupling of silanes with alkyl- and arylthiols, the first examples of such Si-S bond formation in the absence of a transition metal catalyst. Clean, quantitative syntheses of a range of thiosilanes are reported, and the lability of the Si-S linkage toward subsequent alcoholysis is investigated. The crystal structure of 2,3-disila-2,2,3,3-tetramethyl-1,4-benzodioxane is presented.
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