- Effect of ligand modification on the reactivity of phosphinoamide-bridged heterobimetallic Zr/Co complexes
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The effect of modifying the N-aryl substituent (aryl = mesityl vs. m-xylyl) of the phosphinoamide ligands linking Zr and Co in tris(phosphinoamide)-linked heterobimetallic complexes has been investigated. Treatment of the metalloligand (iPr2PNXyl)3ZrCl (2) (Xyl = m-xylyl) with CoI2 affords the iodide-bridged product ICo(iPr 2PNXyl)2(μ-I)Zr(η2-iPr2PNXyl) (3) rather than the C3-symmetric isomer observed using the N-mesityl derivative, ICo(iPr2PNMes)3ZrCl. Upon two-electron reduction of complex 3, ligand rearrangement occurs to generate the three-fold symmetric reduced complex N2Co(iPr 2PNXyl)3Zr(THF) (4). Comparison of 4 with the previously reported mesityl-substituted complex N2Co(iPr 2PNMes)3Zr(THF) (1) reveals similar structural features but with a less sterically hindered Zr apical site in complex 4. An obvious electronic difference between these two complexes is also present based on the drastically different infrared N2 stretching frequencies of 1 and 4. These notable differences lend themselves to different reactivity in both stoichiometric and catalytic reactions. Alkyl halide addition to complex 4 results in homo-coupling products resulting from alkyl radicals rather than the alkyl-bridged or intramolecular C-H activation products formed upon addition of RX to 1. This difference in reactivity with alkyl halides renders complex 3 a less effective catalyst for the Kumada cross-coupling of alkyl halides with n-octylMgBr than ICo(iPr2PNMes)3ZrCl, as a greater proportion of homocoupling products are formed under catalytic conditions.
- Zhou, Wen,Saper, Noam I.,Krogman, Jeremy P.,Foxman, Bruce M.,Thomas, Christine M.
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p. 1984 - 1989
(2014/01/17)
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- A catalytic application of Co/Zr heterobimetallic complexes: Kumada coupling of unactivated alkyl halides with alkyl grignard reagents
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Tris(phosphanylamide) early/late heterobimetallic Zr/Co complexes, ClZr(R′NPR2)3CoI [R′ = iPr, R = Ph (1), R′ = 2,4,6-trimethylphenyl, R = iPr (2), R′ = R = iPr (3)], have been utilized as catalysts for the cross-coupling of alkyl halides with n-octylmagnesium bromide. While yields are consistently higher for alkyl bromide substrates, it is found that these unusual heterobimetallic complexes are also active towards more challenging alkyl chloride substrates. This is particularly interesting in light of the fact that monometallic cobalt complexes are inert towards these substrates, suggesting that Zr also plays a role in catalysis. Radical trapping studies suggest that a one-electron transfer radical oxidative addition pathway is operative.
- Zhou, Wen,Napoline, Jonathan Wesley,Thomas, Christine M.
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scheme or table
p. 2029 - 2033
(2011/06/25)
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- Cobalt-catalyzed cross-coupling reaction between functionalized primary and secondary alkyl halides and aliphatic Grignard reagents
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The coupling of primary and secondary unactivated alkyl bromides with alkyl-Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (CoCl2·2 LiI, 4TMEDA). The reaction is very chemoselective since ketone, ester and nitrile functions are tolerated.
- Cahiez, Gerard,Chaboche, Christophe,Duplais, Christophe,Giulliani, Arianna,Moyeux, Alban
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supporting information; experimental part
p. 1484 - 1488
(2009/07/01)
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- The radical-chain addition of aldehydes to alkenes by the use of N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst
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Hydroacylation of simple alkenes with aldehydes via a radical process was successfully achieved by the use of N-hydroxyphthalimide (NHPI) as a polarity-reversal catalyst. Thus, 5-tridecanone was obtained by the reaction of oct-1-ene with pentanal in the presence of small amounts of NHPI and dibenzoyl peroxide (BPO).
- Tsujimoto,Iwahama,Sakaguchi,Ishii
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p. 2352 - 2353
(2007/10/03)
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