The hydrodefluorination of CF 3-substituted alkenes can be catalyzed by a nickel(II) hydride bearing a pincer ligand. The catalyst loading can be as low as 1 mol%. gem-Difluoroalkenes containing a number of functional groups can be formed in good to excellent yields by a radical mechanism initiated by H • transfer from the nickel hydride. The relative reactivity of various substrates supports the proposed mechanism, as does a TEMPO trapping experiment.
The diagonal relationship in the periodic table between phosphorus and carbon has set an expectation that the triple-bonded diatomic diphosphorus molecule (P
2
) should more closely mimic the attributes of acetylene (HC≡CH) rather than its group 15 congener dinitrogen (N
2
). Although acetylene has well-documented coordination chemistry with mononuclear transition metals, coordination complexes that feature P
2
bound to a single metal center have remained elusive. We report the isolation and x-ray crystallographic characterization of a mononuclear iron complex featuring P
2
coordination in a side-on, η
2
-binding mode. An analogous η
2
-bound bis-timethylsilylacetylene iron complex is reported for comparison. Nuclear magnetic resonance, infrared, and Mössbauer spectroscopic analysis—in conjunction with density functional theory calculations—demonstrate that η
2
-P
2
and η
2
-acetylene ligands exert a similar electronic demand on mononuclear iron centers but exhibit different reactivity profiles.
It has long been
recognized that the first intermediate in chemical
reactions mediated by Fe(CO)5 is Fe(CO)4. However,
the extreme instability of this unsaturated, high-spin species has
hampered detailed structural and stoichiometric reactivity studies.
The previously reported heteroleptic complex Fe(N2)(CO)2(CNArTripp2)2 (ArTripp2 =
2,6-(2,4,6-(i-Pr)3C6H2)2C6H3), which is isolobal to Fe(CO)5, is shown here to possess a labile dinitrogen ligand that
allows it to perform reactions analogous to Fe(CO)4. Specifically,
Fe(N2)(CO)2(CNArTripp2)2 oxidatively adds dihydrogen, white phosphorus, and the Si–H
bonds of triethylsilane and phenylsilane readily at room temperature
and also binds tetrahydrofuran in the absence of N2. Accordingly,
Fe(N2)(CO)2(CNArTripp2)2 effectively serves as a masked form of Fe(CO)4, allowing
for well-defined reactivity and structurally characterizable reaction
products.
The first consistent series of mononuclear 17electron complexes of three Group 7 elements has been isolated in crystalline form and studied by X-ray diffraction and spectroscopic methods. The paramagnetic compounds have a composition of [M 0 (CO)(CNp-F-Ar DArF2 ) 4 ] (M = Mn, Tc, Re; Ar DArF2 = 2,6-(3,5-(CF 3 ) 2 C 6 H 3 ) 2 C 6 H 2 F) and are stabilized by four sterically encumbering isocyanides, which prevent the metalloradicals from dimerization. They have a square pyramidal structure with the carbonyl ligands as apexes. The frozen-solution EPR spectra of the rhenium and technetium compounds are clearly anisotropic with large 99 Tc and 185,187 Re hyperfine interactions for one component. High-field EPR (Q band and W band) has been applied for the elucidation of the EPR parameters of the manganese(0) complex.
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