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4-Tetrafluorobenzobarrelene)-η1-((tri-4-fluorophenyl)phosphine)-η1-(2-phenylphenyl)rhodium(I): A Catalyst for the Living Polymerization of Phenylacetylenes

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Published copy (DOI)

Author(s)

  • Nicholas Sheng Loong Tan
  • Gareth L. Nealon
  • Stephen A. Moggach
  • Jason M. Lynam
  • Mark I. Ogden
  • Massimiliano Massi
  • Andrew B. Lowe

Department/unit(s)

Publication details

JournalMACROMOLECULES
DateAccepted/In press - 7 Jun 2021
DateE-pub ahead of print - 23 Jun 2021
DatePublished (current) - 13 Jul 2021
Issue number13
Volume54
Pages (from-to)6191–6203
Early online date23/06/21
Original languageEnglish

Abstract

(η4-Tetrafluorobenzobarrelene)-η1-((tri-4-fluorophenyl)phosphine)-η1-(2-phenylphenyl)rhodium(I), Rh(tfb)(biph)(PAr3), was prepared and evaluated as a catalyst in the controlled, stereospecific (co)polymerization of arylacetylenes. Following recrystallization, the complex was characterized by single-crystal X-ray diffraction, elemental analysis, and multinuclear NMR spectroscopy, including 103Rh and 31P-103Rh{1H, 103Rh} heteronuclear multiple quantum coherence (HMQC) experiments. Single-crystal X-ray diffraction indicated that Rh(tfb)(biph)(PAr3) adopts a slightly distorted square-planar geometry consistent with previously reported tetracoordinate rhodium(I)-aryl and -vinyl complexes. 103Rh and 2D 31P-103Rh{1H} HMQC NMR spectroscopy confirmed the purity and stability of the new complex in solution. In the presence of excess P(4-FC6H4)3 as a rate modifier, the Rh(I)-aryl catalyst mediated the homopolymerization of phenylacetylene, PhC2H, in a controlled manner as evidenced from the linearity of the pseudo-first-order kinetic plots, the evolution of molecular weight and dispersity, and the quantitative crossover efficiency in a self-blocking experiment. The broader utility of Rh(tfb)(biph)(PAr3) was demonstrated in the polymerization of a series of functional arylacetylenes, including 4-trifluoromethoxyphenylacetylene and 3,4-dichlorophenylacetylene, as well as in the preparation of well-defined AB diblock copolymers of phenylacetylene with the trifluoromethoxy and dichloro derivatives. Computational studies using density functional theory allowed a quantitative comparison between Rh(tfb)(biph)(PAr3) and the 2,5-norbornadiene (nbd) analogue, Rh(nbd)(biph)(PAr3). Results indicated that the former has a lower HOMO energy compared to the nbd derivative and is consistent with the enhanced π-acidity of the tetrafluorobenzobarrelene ligand species. Calculations similarly indicated that Rh(tfb)(biph)(PAr3) has a slightly higher binding affinity for PhC2H. Finally, we highlight the role the biph aryl ligand plays in stabilizing the rhodium complex through a C-H agostic and η2-πinteractions and different steps in the catalyst initiation process.

Bibliographical note

Funding Information:
A.B.L. thanks the Research Office at Curtin for a Ph.D. stipend for NSLT. The authors acknowledge the facilities and the scientific and technical assistance of Microscopy Australia at the Centre for Microscopy, Characterization and Analysis (CMCA), the University of Western Australia, a facility funded by the University, State and Commonwealth Governments. The authors are grateful to the EPSRC for funding the computational equipment used in this study (grants EP/H011455/1 and EP/K031589/1). S.A.M. thanks the Australian Research Council (ARC) for a Future Fellowship (FT200100243).

Publisher Copyright:
© 2021 American Chemical Society.

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