34788-98-2Relevant academic research and scientific papers
Experimental and Computational Characterization of the Transition State for C-X Bimetallic Oxidative Addition at a Cu-Fe Reaction Center
Karunananda, Malkanthi K.,Parmelee, Sean R.,Waldhart, Greyson W.,Mankad, Neal P.
, p. 3857 - 3864 (2015)
The heterobimetallic complex (IPr)Cu-Fp (IPr = N,N′-bis(2,6-diisopropylimidazol-2-ylidene, Fp = FeCp(CO)2) was identified previously as a nonprecious metal catalyst for C-H borylation. To better understand the nature of the bimetallic reaction pathways operative in this system, we have conducted a thorough mechanistic study of alkyl halide activation by the Cu-Fe heterobimetallic reaction center. Use of cyclopropylmethyl halide substrates as radical clocks established that alkyl halide activation occurs by a two-electron mechanism for alkyl bromides and chlorides but not iodides. Eyring analysis of the activation of benzyl chloride allowed for experimental determination of activation parameters, including a large and negative entropy of activation (ΔS? = -36 eu). A Hammett study with para-substituted benzyl chlorides revealed a reaction constant of ρ = 1.6, indicating accumulation of negative charge in the transition state on the alkyl halide carbon. The Ru analogue, (IPr)Cu-Rp (Rp = RuCp(CO)2), was found to react approximately 17-25 times more slowly with selected benzyl chlorides than (IPr)Cu-Fp, indicating that the relative nucleophilicities of the free metal carbonyl anions are predictive of the relative reactivities of their heterobimetallic counterparts. Synthesis and characterization of the new Ag and Au analogues, (IPr)Ag-Fp and (IPr)Au-Fp, are reported along with the observation that these more covalent congeners are significantly less reactive toward alkyl halides. DFT calculations were used to model a transition state for the Cu-Fe reaction, which was identified as stereoinvertive at the alkyl halide carbon. NBO calculations indicate crucial roles played by the CO ligands within the Fp group: they both act as redox noninnocent ligands and also provide structural templating to stabilize the transition state as the metal-metal bond breaks. (Chemical Equation Presented).
Formal transfers of hydride from carbon-hydrogen bonds. Synthesis, structure, and reactions of [Cp(CO)2FeCH2]3CH
Kobayashi, Michio,Wuest, James D.
, p. 2843 - 2850 (2008/10/08)
The reaction of Cp(CO)2FeNa with (CH3SO2OCH2)3CH (4) provided [Cp(CO)2FeCH2]3CH (3) in 50% yield. Thermal decomposition of compound 3 occurred rapidly in solution at 25°C and produced approximately equimolar amounts of [Cp(CO)2Fe]2 (5) and dicarbonyl(cyclopentadienyl)(cyclopropylmethyl)iron (6). These products presumably result from decarbonylation of compound 3, formation of carbonyl-bridged intermediate 8, and reductive elimination. The reaction of compound 3 with 2 equiv of Ph3C+PF6- yielded the Cp(CO)2Fe+ complex 11 of Cp(CO)2FeCH2CH2CH=CH2 and negligible amounts of triphenylmethane. Ph3C+ may accept an electron from compound 3, triggering loss of Cp(CO)2Fe* and a shift of Cp(CO)2FeCH2 that converts the isobutyl skeleton of the starting material into the n-butyl skeleton of product 11. Irradiation of compound 3 at 350 nm produced [Cp(CO)2Fe]2 (5) and an exo/endo mixture of carbonyl(cyclopentadienyl)(η3-2-methyl-2-propenyl)iron (34). These products appear to result from decarbonylation, formation of carbonyl-bridged intermediate 8, further decarbonylation, formation of iron hydride 33 by β-elimination, reductive elimination, and further irradiation of dicarbonyl(cyclopentadienyl)(2-methyl-2-propenyl)iron (21).
