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Lookup NU author(s): Dr Simon DohertyORCiD, Mark Waugh, Thomas Scanlan, Professor William Clegg, Dr Mark Elsegood
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Addition of tert-BuN≡C to the σ-η-allenyl complex [Fe2(CO)6(μ-PPh2){μ-η 1:ηα,β2-(H)-Cα=Cβ=CγH 2}] results in nucleophilic addition to Cα to give the μ-η1:η1-∥-alkyne [Fe2(CO)6-(μ-PPh2){μ-η 1:η1-(tert-BuN≡C)C=CCH3}] (2) and the β,γ-unsaturated amide [Fe2(CO)6(6(μ-PPh 2)(μ-η1:η2-{tert-BuNHC(O)CH 2}C=CH2)] (3). Compounds 2 and 3 are proposed to form via initial nucleophilic attack at Cα to give [Fe2(CO)6(μ-PPh2){μ-η 1:η1-(tert-BuNC)-HC=C=CH2}], an unstable zwitterionic allene-bridged intermediate which subsequently undergoes either a 1,3-hydrogen migration to give 2 or hydrolysis by extraneous water to give the β,γ-unsaturated amide 3. An alternative pathway involving initial nucleophilic attack at Cβ to give the metallacyclopentene intermediate [Fe2(CO)6(μ-PPh2){μ-η 1:η1-HC=C(tert-BuNC)CH2}], followed by 1,3-hydrogen migration and Cβ to Cα tert-BuN≡C migration has been considered. Isotope labeling experiments using [Fe2(CO)6(μ-PPh2){μ-η 1:ηα,β2-(D)-Cα=Cβ=CγH 2}] (1-d1) are consistent with a large primary kinetic isotope effect for the transfer of hydrogen between Cα and Cγ. Addition of excess isopropylamine to a hexane solution of 2 gave the amidinium-substituted μ-η1:η1-parallel alkyne derivative [Fe2(CO)6(μ-PPh2){μ-η 1:η1-C(tert-BuHNC)(NHPri)C=CCH 3}] (4), in near quantitative yield via addition of N-H across the C-N multiple bond. Chloroform solutions of 3 smoothly decarbonylate over several days to afford [Fe2(CO)5(μ-PPh2)(μ-η 1(C):η1(O):η2(C)-{tert-BuNHC(O)CH 2}C=CH2)] (5), which contains a five-membered metallacycle by virtue of coordination of the amide carbonyl oxygen atom. The single-crystal X-ray structures of 2, 4, and 5 are reported.
Author(s): Doherty S, Hogarth G, Waugh M, Scanlan TH, Clegg W, Elsegood MRJ
Publication type: Article
Publication status: Published
Journal: Organometallics
Year: 1999
Volume: 18
Issue: 16
Pages: 3178-3186
Print publication date: 02/08/1999
ISSN (print): 0276-7333
ISSN (electronic): 1520-6041
Publisher: American Chemical Society
URL: http://dx.doi.org/10.1021/om9901630
DOI: 10.1021/om9901630
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