Bandeau LBPB

Pincer complexes, Non-innocent ligands and Cooperative catalysis

    • Efficient Synthesis of Unsaturated δ- and ε-Lactones/Lactams by Catalytic Cycloisomerization: When Pt Outperforms Pd
      Ke, N. Á. Espinosa, S. Mallet-Ladeira, J. Monot, B. Martin-Vaca*, D. Bourissou*
      Adv. Synt. Catal. 2016, 358, 2324-2331.

      ASC 2016 Platine

      Platinum pincer complexes featuring an SCS indenediide backbone have been prepared and evaluated in the catalytic cycloisomerization of alkynoic acids and N-tosyl alkynylamides. One of the platinum complexes significantly outperforms its palladium analogue for the formation of 6- and 7-membered rings. The catalytic system takes advantage of the alkynophilicity of Pt and of the non-innocent character of the indenediide framework. Like for Pd, the catalytic performance is significantly improved by using an H-bond donor additive such as pyrogallol. For the first time, a large variety of ω-unsaturated δ- and ε-lactones/lactams could be prepared with high selectivities and in very good yields.

    • A case study of proton shuttling in palladium catalysis
      Monot, P. Brunel, C. E. Kefalidis, N. Á. Espinosa-Jalapa, L. Maron*, B. Martin-Vaca*, D. Bourissou*
      Chem. Sci., 2016, 7, 2179-2187.

      Chemical Science 2016

      The mechanism of alkynoic acid cycloisomerization with SCS indenediide Pd pincer complexes has been investigated experimentally and computationally. These studies confirmed the cooperation between the Pd center and the backbone of the pincer ligand, and revealed the involvement of a second molecule of substrate. It acts as a proton shuttle in the activation of the acid, it directs the nucleophilic attack of the carboxylic acid on the π-coordinated alkyne and it relays the protonolysis of the resulting vinyl Pd species. A variety of H-bond donors have been evaluated as external additives, and polyols featuring proximal hydroxyl groups, in particular catechol derivatives, led to significant catalytic enhancement. The impact of 4-nitrocatechol and 1,2,3-benzenetriol is particularly striking on challenging substrates such as internal 4- and 5-alkynoic acids. Endo/exo selectivities up to 7.3/1 and 60-fold increase in reactivity were achieved.

    • Enhanced Catalytic Performance of Indenediide Palladium Pincer Complexes for Cycloisomerization: Efficient Synthesis of Alkylidene Lactams
      N. Á. Espinosa-Jalapa, D. Ke, N. Nebra, L. Le Goanvic, S. Mallet-Ladeira, J. Monot, B. Martin-Vaca,* D. Bourissou*
      ACS Catalysis, 2014, 4, 3605-3611.

      Pincer-5

      New SCS Pd pincer complexes featuring a non-innocent indenediide backbone show high catalytic activity in cycloisomerization. A variety of alkylidene lactams (5 to 7 membered rings) have been prepared efficiently from N-tosyl alkynylamides and good results have also been obtained with challenging alkynoic acids.

    • Metal–Ligand Cooperation in the Cycloisomerization of Alkynoic Acids with Indenediide Palladium Pincer Complexes
      N. Nebra , J. Monot , R. Shaw , B. Martin-Vaca,* D. Bourissou *
      ACS Catalysis, 2013, 3, 2930-2934.

      Pincer-4

      Indenediide Pd complexes 1a-c are shown to very efficiently catalyze the cycloisomerization of alkynoic acids into alkylidene lactones via metal-ligand cooperation (TON up to 2000). 1a-c are competent towards a broad range of alkynoic acids, including functionalized and internal ones, and give access to 5- as well as 6- and 7-membered lactones in excellent yields and with very high selectivities.

    • Walking Metals in d8⋅⋅⋅d8 Hetero-bimetallic Complexes: An Original Dynamic Phenomenon
      N. Nebra, S. Ladeira, L. Maron,* B. Martin-Vaca,* D. Bourissou*
      Chem. Eur. J., 2012, 18, 8474-8481.

      Pincer-3

      Starting from the indenylidene chloropalladate [{Ind(Ph2P=S)2}PdCl] 1, the new Pd(II)∙∙∙Rh(I) hetero-bimetallic pincer complex {PdCl[Ind(Ph2P=S)2]Rh(nbd)} 2 was prepared. According to multinuclear variable temperature NMR experiments, the pendant [Rh(nbd)] fragment of 2 readily shifts in solution at room temperature between the two edges of the SCS tridentate ligand. To assess the role of the pincer-based polymetallic structure on this fluxional behavior, the related monometallic Rh complex {[IndH(Ph2P=S)2]Rh(nbd)} 3 was prepared. No evidence for a metal shift was observed in that case even at high temperature, indicating that in-plane pincer coordination to Pd plays a crucial role. DFT calculations have been performed to shed light into the mechanism of such metal shifts and to identify the factors influencing the associated activation barriers. Significantly different pathways were found for the bimetallic complexes 2 and 4 on one hand, and the monometallic complex 3 on the other hand. The corresponding activation barriers predicted computationally are in very good agreement with the experimental observations.

    • 1,3-Bis(thiophosphinoyl)indene: A Unique and Versatile Scaffold for Original Polymetallic Complexes
      N. Nebra, N. Saffon, L. Maron,* B. Martin−Vaca,* D. Bourissou*
      Inorg. Chem. 2011, 50, 6378-6383.

      Pincer-2

      The coordination of tridentate ligands featuring lateral coordination sites prone to act as bridging ligands was explored with the aim of obtaining original polymetallic species in a straightforward and controlled manner. Accordingly, the 2-indenylidene chloro-palladate [{Ind(Ph2P=S)2}PdCl]was found to behave as a k2-C,S bidentate ligand towards metal fragments, giving access to homo- and hetero-polymetallic complexes. X-ray diffraction analyses reveal the presence of short metal-metal contacts in all these complexes. DFT calculations unambiguously substantiate that the metals engage into unusual d8∙∙∙d8 interactions with quasi-perpendicular arrangement of their coordination planes.

    • The 2-Indenylidene Chloropalladate {PdCl[Ind(Ph2P═S)2]}(nBu4N): A Versatile Pincer Complex with “Innocent” and “Noninnocent” Behavior
      P. Oulié, N. Nebra, S. Ladeira, B. Martin-Vaca*, D. Bourissou*
      Organometallics, 2011, 30, 6416-6422.

      Pincer-1

      The chloro-palladate pincer complex {PdCl[Ind(Ph2P=S)2]}(nBu4N) 2 has been prepared and its reactivity has been thoroughly investigated. Alkyl halides such as iodomethane and benzyle chloride react at the electron-rich 2-indenylidene moiety, leading to the 2-indenyl pincer complexes {PdI[IndMe(Ph2P=S)2]} 3 and {PdCl[IndBn(Ph2P=S)2]} 4, respectively. Nucleophiles such as PPh3 and NHCy2 also react readily with 2, to give the corresponding 2-indenylidene complexes by displacement of the chloride at Pd. In addition, treatment of 2 with PhC≡CLi affords complex {Pd(C≡CPh)[Ind(Ph2P=S)2]}(nBu4N) 8, the first alkynyl-palladate to be isolated. All the new compounds have been characterized by multi-nuclear NMR spectroscopy and mass spectrometry. The structure of complexes 3 and 8 has been further analyzed by means of X-Ray diffraction studies.

      Selected publications:

      Enhanced Catalytic Performance of Indenediide Palladium Pincer Complexes for Cycloisomerization: Efficient Synthesis of Alkylidene Lactams.
      N. Á. Espinosa-Jalapa, D. Ke, N. Nebra, L. Le Goanvic, S. Mallet-Ladeira, J. Monot, B. Martin-Vaca,* D. Bourissou*
      ACS Catalysis 2014, 4, 3605-3611.

      Metal-Ligand Cooperation in the Cycloisomerization of Alkynoic Acids with Indenediide Palladium Pincer Complexes.
      Nebra, N.; Monot, J.; Shaw, R.; Martin-Vaca, B.;* Bourissou, D.*
      ACS Catalysis 2013, 3, 2930-2934.

      Influence of the Ligand Backbone in Pincer Complexes: Indenediide-, Indolyl-, and Indenyl-Based SCS Palladium Complexes.
      Lisena, J.; Monot, J.; Mallet-Ladeira, S.; Martin-Vaca, B.;* Bourissou, D.*
      Organometallics 2013, 32, 4301-4305.

      Walking Metals in d8…d8 Hetero-bimetallic Complexes: An Original Dynamic Phenomenon
      Nebra, N.; Ladeira, S.; Maron, L.; Martin-Vaca, B.;* Bourissou, D*
      Chem. Eur. J. 2012, 18, 8474-8481.

      The 2-indenylidene chloropalladate {PdCl[Ind(Ph2P:S)2]}(nBu4N): a versatile pincer complex with "innocent" and "noninnocent" behavior.
      Oulie, P.; Nebra, N.; Ladeira, S.; Martin-Vaca, B.;* Bourissou, D.*
      Organometallics 2011, 30, 6416-6422.

      Original palladium pincer complexes deriving from 1,3-bis(thiophosphinoyl)indene proligands: Csp3-H versus Csp2-H bond activation.
      Nebra, N.; Lisena, J.; Saffon, N.; Maron, L.;* Martin-Vaca, B.;* Bourissou, D.*
      Dalton Trans. 2011, 40, 8912-8921.

      1,3-Bis(thiophosphinoyl)indene : A unique and Versatile Scaffold for Original Polymetallic Complexes
      Nebra, N.; Saffon, N.; Maron, L.;* Martin-Vaca, B.;* Bourissou, D.*
      Inorg. Chem. 2011, 50, 6378-6383.

      2-Indenylidene Pincer Complexes of Zirconium and Palladium
      Oulie, P.; Nebra, N.; Saffon, N.; Maron, L.;* Martin-Vaca, B.;* Bourissou, D.*
      J. Am. Chem. Soc. 2009, 131, 3493-3498.

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