Synthesis of the labile rhenium(I) complexes fac-Re(CO)3(L)[κ2-O,O-FcC(O)CHC(O)Me] (where Fc = ferrocenyl; L = THF, H2O, alkyne) and alkyne addition to the diketonate ligand

Silvia Atim, Li Yang, Volodymyr Nesterov, Xiaoping Wang, Michael G. Richmond

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Abstract

Refluxing equimolar amounts of 1-ferrocenyl-1,3-butanedione (Fcacac) with BrRe(CO)5 in THF yielded the labile solvent complex fac-Re(CO)3 (THF)[κ2-O,O-FcC(O)CHC(O)Me] (1) in 80% isolated yield. 1 may also be prepared in quantitative yield using fac-BrRe(THF)2(CO)3 as the starting rhenium complex. The THF molecule in 1 is replaced by H2O during chromatographic purification to furnish the corresponding aqua complex fac-Re(CO)3(H2O)[κ2-O,O-FcC(O)CHC(O)Me] (2) while the reaction of 1 with PPh3 gives fac-Re(CO)3(PPh3)[κ2-O,O-FcC(O)CHC(O)Me] (3). Treatment of 1 with the terminal alkynes phenylacetylene and methyl propiolate proceeds rapidly at room temperature to give the π intermediates fac-Re(CO)3 (alkyne)[κ2-O,O-FcC(O)CHC(O)Me] [4 (PhC≡CH); 6 (MeO2CC[tbnd]CH)] that are not stable and undergo a 1,4-addition with regiospecific alkyne attack at the γ-methine site of the Fcacac moiety to afford fac-Re(CO)33-C,O,O-FcC(O)CH(E-PhC = CH)C(O)Me] (5) and fac-Re(CO)33-C,O,O-FcC(O)CH(Z-HC=CCO2Me)C(O)Me] (7). The solid-state structure for 5 and 7 was established by X-ray crystallography, and the computed mechanisms that account for the formation of these two products from 1 and alkyne are presented. 1 reacts with the internal alkyne dimethyl acetylenedicarboxylate (DMAD) to furnish the novel dimeric compound [fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)}]2 (9). The structure of 9 confirms the linking of the monomeric fac-Re(CO)3{FcC(O)CH2C(CO2Me)C(CO2Me)} fragments through the intermolecular coordination of the ester oxygen atom associated with the α-carbomethoxy moiety of the E-metalated alkene; the latter moiety is traced to the initial DMAD insertion into the 6-membered metallocyclic ring in the π precursor fac-Re(CO)3 (MeO2CC[tbnd]CCO2Me)[κ2-O,O-FcC(O)CHC(O)Me]. The labile solvent complex fac-Re(CO)3 (THF)[κ2-O,O-FcC(O)CHC(O)Me] (1) has been prepared and investigated in ligand substitution reactions. Terminal alkynes displace the THF ligand in 1 to afford the metalated alkenyl compounds fac-Re(CO)33-C,O,O-FcC(O)CH(alkenyl)C(O)Me]. The regiochemistry attendant in the formal 1,4-addition reaction has been explored by electronic structure calculations.

Original languageEnglish
Pages (from-to)87-100
Number of pages14
JournalJournal of Organometallic Chemistry
Volume874
DOIs
StatePublished - Nov 1 2018

Funding

Financial support from the Robert A. Welch Foundation (Grant B-1093-MGR ) is greatly appreciated. The DFT calculations were performed at UNT through CASCaM, which is an NSF-supported facility ( CHE-1531468 ). X.P.W. acknowledges support by the U.S. Department of Energy , Office of Science, under Contract No. DE-AC05-00OR22725 managed by UT Battelle, LLC. Financial support from the Robert A. Welch Foundation (Grant B-1093-MGR) is greatly appreciated. The DFT calculations were performed at UNT through CASCaM, which is an NSF-supported facility (CHE-1531468). X.P.W. acknowledges support by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC05-00OR22725 managed by UT Battelle, LLC.

Keywords

  • DFT
  • Labile ligands
  • Regiospecific alkyne addition
  • Rhenium-iron
  • X-ray crystallography

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