Neutral and Cationic Molybdenum Imido Alkylidene Cyclic Alkyl Amino Carbene (CAAC) Complexes for Olefin Metathesis

Koushani Kundu; Janis V Musso; Mathis J Benedikter; Wolfgang Frey; Katrin Gugeler; Johannes Kästner; Michael R Buchmeiser

doi:10.1002/chem.202301818

Neutral and Cationic Molybdenum Imido Alkylidene Cyclic Alkyl Amino Carbene (CAAC) Complexes for Olefin Metathesis

Chemistry. 2023 Sep 15;29(52):e202301818. doi: 10.1002/chem.202301818. Epub 2023 Aug 9.

Authors

Koushani Kundu¹, Janis V Musso¹, Mathis J Benedikter¹, Wolfgang Frey², Katrin Gugeler³, Johannes Kästner³, Michael R Buchmeiser^{1

4}

Affiliations

¹ Institute of Polymer Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
² Institute of Organic Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
³ Institute of Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany.
⁴ German Institutes of Textile and Fiber Research (DITF), Körschtalstr. 26, 73770, Denkendorf, Germany.

PMID: 37366606
DOI: 10.1002/chem.202301818

Abstract

The first neutral and cationic Mo imido alkylidene cyclic alkyl amino carbene (CAAC) complexes of the general formulae [Mo(N-Ar)(CHCMe₂ Ph)(X)₂ (CAAC)] and [Mo(N-Ar)(CHCMe₂ Ph)(X)(CAAC)][B(Ar^F )₄ ] (X=Br, Cl, OTf, OC₆ F₅ ; CAAC=1-(2,6-iPr₂ -C₆ H₃ )-3,3,5,5-tetramethyltetrahydropyrrol-2-ylidene) have been synthesized from molybdenum imido bishalide alkylidene DME precursors. Different combinations of the imido and "X" ligands have been employed to understand synthetic peculiarities. Selected complexes have been characterized by single-crystal X-ray analysis. Due to the pronounced σ-donor/π-acceptor characteristics of CAACs, the corresponding neutral and cationic molybdenum imido alkylidene CAAC complexes do not require the presence of stabilizing donor ligands such as nitriles. Calculations on the PBE0-D3BJ/def2-TZVP level for PBE0-D3BJ/def2-SVP optimized geometries revealed partial charges at molybdenum similar to the corresponding molybdenum imido alkylidene N-heterocyclic carbene (NHC) complexes with a slightly higher polarization of the molybdenum alkylidene bond in the CAAC complexes. All cationic complexes have been tested in olefin metathesis reactions and showed improved activity compared to the analogous NHC complexes for hydrocarbon-based substrates, allowing for turnover numbers (TONs) up to 9500 even at room temperature. Some Mo imido alkylidene CAAC complexes are tolerant towards functional groups like thioethers and sulfonamides.

Keywords: alkylidene; cyclic alkyl amino carbenes; halides; molybdenum; olefin metathesis.

Abstract

Grants and funding