Laboratoire de Chimie de Coordination UPR 8241


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Thématiques

Keywords : Tris(pyrazolyl)borate (Tp’) ligands, Fluorinated ligands, Imido ligands, CH and CC agostic interactions, CH activation and functionalization, Oligomerization, Polymerization, Hydroamination, Yttrium, Titanium, Zirconium, Vanadium, Niobium

- CH and CC agostic interactions, CH activation and functionalization

We use the fantastic possibilities of tuning the steric and electronic properties of tris(pyrazolyl)borate ligands to induce unusual ligand coordination, stabilize reactive intermediates and eventually discover new reactions of Early Transition Metal complexes. In particular, C-H and C-C agostic interactions are studied with their consequences on the dynamics and reactivity of alkyl groups in the field of the catalytic polymerization of olefins, and CH bond activation and functionalization.

Beyond α-CH or β-CH agostic interactions, rare cases of α-CC agostic complexes have been described. The importance of ring strain in the cyclopropyl group of TpMe2NbCl(c-C3H5)(MeCCMe) has been emphasized. The key to assigning the α-CC agostic interaction was the ability to measure and compute JCC coupling constants.

A review

  • Intramolecular C–C Agostic Complexes : C–C Sigma Interactions by Another Name. M. Etienne, A. S. Weller. Chem. Soc. Rev. 2014, 43, 242
  • C-C Coupling Constants, JCC, are Reliable Probes for -C-C Agostic Structures C. Boulho, T. Keys, Y. Coppel, L. Vendier, M. Etienne, A. Locati, F. Bessac, F. Maseras, D. A. Pantazis, J. E. McGrady. Organometallics 2009, 28, 940.
  • An Unprecedented α-C–C Agostic Interaction in a Cyclopropyl Tris(pyrazolyl)boratoniobium Complex. J. Jaffart, M. Etienne, M. Reinhold, J. E. McGrady, F. Maseras. Chem. Commun. 2003, 876.
  • Agostic Interactions in Sterically Hindered Early Transition Metal Alkyl Complexes. M. Etienne, J. E. McGrady, F. Maseras. Coord. Chem. Rev. 2009, 253, 635.

Related cyclopropyl methyl complexes activate the CH bond of benzene via a rare -H abstraction / 1,3-addition sequence under very mild conditions (room temperature !), linking the structure of the complex to its reactivity.

  • C-H Bond Activation of Benzene by Unsaturated 2-Cyclopropene and 2-Benzyne Complexes of Niobium. C. Boulho, P. Oulié, L. Vendier, M. Etienne, V. Pimienta, A. Locati, F. Bessac, F. Maseras, D. A. Pantazis, J. E. McGrady. J. Am. Chem. Soc. 2010, 132, 14239.
  • CH Bond Activation by a Transient 2-Cyclopropene Niobium Complex. P. Oulié, C. Boulho, L. Vendier, Y. Coppel, M. Etienne. J. Am. Chem. Soc., 2006, 128, 15962.

More recently, a unique case of a heterobimetallic bis(cyclopropyl) LiY complex exhibiting two types of CC agostic interactions has been obtained. The interaction with Li has an electrostatic character whereas that with Y has a more covalent nature (DFT and NBO analysis). The latter is also supported by a CH agostic interaction in a Y(η3-CCH) manner. The right hand side of the picture shows the optimized structure of 1 with relevant calculated parameters : CC bond length (Å), 1st line ; JCC (Hz), 2nd line, italics.

  • An Unsymmetrical bis CC Agostic Heterobimetallic LiY Complex. Y. Escudié, C. Dinoi, O. Allen, L. Vendier, M. Etienne. Angew. Chem. Int. Ed, 2012, 51, 2461.


Our interest in CH bond activation expands to catalytic functionalization of alkanes.
Highly fluorinated hydrotris(indazolyl)borates have been synthesized. Extremely electrophilic copper(I) and silver(I) complexes are catalysts for the insertion of carbene into alkane CH bonds. This includes a mild catalytic functionalization of methane to ethylpropanoate under supercritical conditions (sc-CO2) with TON approaching 103, one of the most challenging problems of modern chemistry.

  • Functionalization of Non-Activated C-H Bonds of Alkanes : an Effective and Recyclable Catalytic System Based on Fluorinated Silver Catalysts and Solvents. M. Á. Fuentes, B. K. Muñoz, K. Jacob, L. Vendier, A. Caballero, M. Etienne, P. J. Pérez. Chem. Eur. J. 2013, 19, 1327
  • Silver-Catalyzed C-C Bond Formation between Methane and Ethyl Diazoacetate in Supercritical CO2. A. Caballero, E. Despagnet-Ayoub, A. Díaz, M. M. Díaz-Requejo, M. E. González-Núñez, R. Mello, B. K. Muñoz, W.-S. Ojo, G. Asensio, M. Etienne, P. J. Pérez. Science 2011, 332, 835.
  • A New Perfluorinated F21-Tp Scorpionate Ligand : Enhanced Alkane Functionalization by Carbene Insertion with (F21-Tp)M Catalysts (M = Cu, Ag). E. Despagnet-Ayoub, K. Jacob, L. Vendier, M. Etienne, E. Álvarez, A. Caballero, M. M. Díaz-Requejo, P. J. Pérez. Organometallics 2008, 27, 4779.

 

- Tuning the electronic, steric and coordinative properties of imido ligands

We have been exploring synthetic routes to early-transition complexes containing imides. Particularly, titanium imides are undergoing a renaissance of their chemistry given their ability to conduct catalytic processes. For that purpose it is desirable to have in hands a large diversity of new complexes with various properties (electronic, steric, coordination mode…) such as those reported below. We have developed a very convenient one-step procedure that allows the synthesis of various imido complexes of Ti(IV) and V(IV). A number of unprecedented imido complexes have been prepared, in particular electron deficient tosyl-imido, chiral imido, di-imido, η6-arene-imido, and hemilabile imido complexes (Figures 1 and 2). Some of these new complexes have found application as precatalysts in olefin polymerization or in alkyne hydroamination.

We have also established for the first time, the propensity of group 4 and 5 amido precursors toward the formation of unique dimer complexes with two distinct bridging μ-imido ligands, as well as heterobimetallic species bridged by μ-imido ligands (Figure 3). These results point out a number of new avenues to explore in the synthesis of homo- and heterodinuclear complexes.

  • C. Lorber, R. Choukroun, L. Vendier, Eur. J. Inorg. Chem. 2006, 4503 (link pdf).
  • C. Lorber, L. Vendier, Organometallics 2010, 29, 1127 (link pdf).
  • C. Lorber, L. Vendier, Inorg. Chem., 2011, 50, 9927 (link pdf).
  • V.-H. Nguyen, L. Vendier, M. Etienne, E. Despagnet-Ayoub, P.-A. R. Breuil, L. Magna, D. Proriol, H. Olivier-Bourbigou, C. Lorber, Eur. J. Inorg. Chem. 2012, 97 (link pdf).

 

- Non-metallocene ligands for vanadium olefin polymerization catalysis

Ancillary ligands play a pivotal role in catalysis by transition metal complexes by modulating the steric and electronic environment around the metal center. We are involved in the synthesis of non-metallocene vanadium catalysts for olefin polymerization with supporting ligands like the amine(bisphenolate) below that has proven to catalyze the copolymerization of ethylene with norbornene.

  • C. Lorber, Pure Appl. Chem., 2009, 81, 1205 (link pdf).