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Home > Members > Permanents > Yann Sarazin

Dr Yann Sarazin

CNRS Research Fellow (level CR1)

Institut des Sciences Chimiques de Rennes
UMR 6226 CNRS - Université Rennes 1
Campus de Beaulieu
Building 10C, Room 921
35042 Rennes Cedex. France

Phone : 33 (0) 2 23 23 30 19
Email: yann.sarazin@univ-rennes1.fr

ORCID ID 0000-0003-1121-0292
Researcher ID Q-2202-2015

Education and professional experience

  • 2012 (Oct.) Research Habilitation, University of Rennes, France
  • 2008 CNRS Research Fellow, Institut des Sciences Chimiques de Rennes UMR 6226 CNRS – University of Rennes 1
  • 2007–2008 Post-doc research associate (Prof. JF Carpentier), Institut des Sciences Chimiques de Rennes - UMR CNRS 6226 – University of Rennes 1
  • 2004–2007 Post-doc research associate (Prof. M Bochmann), University of East Anglia (UK)
  • 2000-2004 Ph. D. in coordination and macromolecular chemistry Supervisor Prof. M Bochmann, University of East Anglia, United Kingdom
  • 1999-2000 M. Sc. in organic and macromolecular chemistries, University of Lille, France

Ongoing collaborations

  • Prof. M. Bochmann, University of East Anglia, Norwich, UK: polymerisation kinetics
  • Prof. M. Etienne, LCC Toulouse, France: calcium chemistry, syntheses and catalysis
  • Prof. A. Silvestru, Univ. Babeş-Bolyai, Cluj, Romania: chalcogenates for main group metal complexes
  • Dr. S. Tobisch, University of Saint Andrews, UK: DFT computations and reaction mechanisms
  • Prof. A. Trifonov, University of Nizhny-Novgorod, Russia: divalent lanthanides, syntheses and catalysis
  • On occasion, we are also collaborating with Prof. L. Maron (INSA Toulouse, France), Prof. J. Okuda (Aachen, Germany), Dr. T. K. Panda (IIT Hyderabad, India) and Prof. D. B. Leznoff (Burnaby, Canada)

Scientific production

  • 63 publications (h-index = 24; 1850+ citations) in international peer-reviewed journals, including: 1 Chem. Rev., 2 JACS, 3 Angew. Chem. Int. Ed., 16 Chem. Eur. J., 9 Organometallics, 1 Chem. Rec.
  • 6 families of PCT Int. Appl. WO patents
  • 3 book chapters
  • 4 review articles
  • 5 invited lectures (incl. plenary) and 9 oral presentations in international conferences
  • 9 invited seminars in international universities

Contributions to the scientific community

  • Co-chairman and coordinator of Journées Chimie de Coordination de la Société Chimique de France 2014
  • Co-chairman and coordinator of GECOM-CONCOORD, Rennes, 2019
  • Member of the Advisory Board for the International Conference on Germanium, Tin and Lead
  • External examiner for Ph. D. theses

Funding

  • Agence Nationale de la Recherche (ANR)
  • Ministère de l’Enseignement Supérieur et de la Recherche
  • European Union (Marie Skłodowska-Curie Actions)
  • Total Petrochemicals (with Prof. JF Carpentier)

Research interests

The many research interests within our group chiefly lie in the coordination chemistry of main group metals, with applications in homogeneous catalysis.
We devise discrete complexes using metals of group 2 (calcium, strontium and barium), group 13 (aluminium, gallium and indium) and group 14 (germanium, tin and lead), and we implement them as molecular precatalysts for atom-efficient reactions: ring-opening polymerisations, hydroelementation and heterodehydrocoupling. We are also investigating fundamental aspects of the organometallic chemistry of groups 2, 12 and 14 metals.

See below for a description of the four main topics that are currently captivating our attention

Current students and PDRA

  • Hanieh Roueindeji: PhD student, 2015-2018 (organometallic chemistry of large alkaline earths)
  • Erwann Le Coz: PhD student, 2016-2019 (large alkaline earths complexes: design and catalysis)
  • Fatima Abou Khalil: MSc student, 2016-2017 (coordination chemistry of stannylenes and plumbylenes)

Alumni

Ph. D. students

  • Valentin Poirier: 2008-2011; now NMR Research engineer, Structuralis, Paris, France
  • Nicolas Maudoux: 2011-2014; now Research engineer, Triskem, Rennes, France
  • Sorin Roşca: 2012-2015; now PDRA UBC Vancouver, Canada (with L. L. Schafer)
  • Clément Bellini: PhD 2013-2016

Post-doctoral research assistants

  • Pierre de Frémont: 2008-2009; now CNRS Research Fellow, University of Strasbourg, France
  • Liana Annunziata: 2009-2010; now Project manager, SICPA, Switzerland
  • Amelia Cortes: 2009-2010; now Associate Professor, University of Rennes, France
  • Bo Liu: 2010-2013; now Associate Professor, Changchun Institute of Applied Chemistry, PR China
  • Lingfang Wang: 2011-2014; now Associate Professor, Yancheng, PR China
  • Nuria Romero: 2015-2016; now Associate Professor, Autonomous University of Barcelona, Spain

Master students

  • Dragos Roşca: 2009-2010; PhD University of East Anglia, UK (with M. Bochmann)
  • Sorin Roşca: 2012; PhD University of Rennes, France (with Y. Sarazin)
  • Sami Fadlallah: 2013-2014; PhD University of Lille, France (with M. Visseaux)
  • Yuya Hu: 2014-2015; PhD University of Geneva, Switzerland (with C. Mazet)
  • Eric Tan: 2011-2014; PhD Institute of Chemistry of Catalonia (ICIQ), Spain (with A. M. Echavarren)


Topic 1 - Coordination chemistry of large alkaline earth metals

Well-defined heteroleptic complexes of the large, oxophilic and electropositive alkaline earth metals (Ae) calcium, strontium and barium are highly ionic and exhibit a d0 electronic configuration. They display remarkable catalytic activities in polymerisation, terminal alkyne coupling, hydrogenation and hydroelementation of alkenes. Intimate knowledge of the structure of the precatalysts has opened up access to detailed mechanistic studies.

We are taking advantage of the high reactivity of Ae metals (Ae = Ca, Sr, Ba) to design molecular precatalysts for organic transformations. LXAeN(SiMe3)2 heteroleptic precatalysts stabilised by bulky multidentate ligands can be made, but their synthesis is often impeded by ligand scrambling equilibria.

To overcome this limitation, we are utilising the bulky N(SiMe3)2 amido group, or more often its derivative N(SiMe2H)2 which allows the stabilisation of otherwise kinetically labile heteroleptic species thanks to intramolecular anagostic Ae∙∙∙H–Si interactions. This has enabled the production of a myriad of Ca-Ba complexes supported by phenolato, alkoxo or N-containing (imino-anilide, diketiminate) ligands that are stable under conditions relevant to catalysis. The existence of Ae∙∙∙H–Si contacts in these complexes is attested to by XRD crystallography and NMR and FTIR spectroscopies; it is also backed up by state-of-the-art DFT computations:

We are also keen on alkaline earth ion pairs of the type [LOAe]+∙∙∙[H2NB(C6F5)32]− with a cationic metal centre very loosely associated to a weakly-coordinating anion. We have reported procedures for the synthesis of solvent-free Mg−Ba (and Zn) cationic complexes. Besides, cationic Ae metals bearing fluorinated alkoxides are stabilised by intramolecular AeF–C interactions:

We have then taken full advantage of these non-covalent, secondary interactions to stabilise highly electron-deficient alkaline earth complexes. We have been able to prepare the first series of olefin and alkyne complexes of calcium and strontium, where  ligands are coordinated to the d0 metal ions in the solid state and in solution. These results represent fundamental advances in the organometallic chemistry of the alkaline earths.

Selected references for topic 1

  • (1) Ligands in Alkaline Earth Complexes
    S.-C. Roşca et al., ASAP article
  • (2) Alkaline Earth-Olefin Complexes with Secondary Interactions
    S.-C. Roşca et al., Chem. Eur. J. (2016) 22, 6505. DOI: 10.1002/chem.201601096
  • (3) Highly fluorinated tris(indazolyl)borate silylamido complexes of the heavier alkaline earth metals: Synthesis, characterization, and efficient catalytic intramolecular hydroamination (Hot Paper)
    N. Romero et al., Chem. Eur. J. (2015) 21, 4115. DOI: 10.1002/chem.201405454
  • (4) Potassium and well-defined neutral and cationic calcium fluoroalkoxide complexes: Structural features and reactivity
    S.-C. Roşca et al., Organometallics (2014) 33, 5630. DOI: 10.1021/om500343w
  • (5) Discrete divalent rare-earth cationic ROP catalysts: Ligand-dependent redox behavior and discrepancies with alkaline-earth analogues in a ligand-assisted activated monomer mechanism
    B. Liu et al., Chem. Eur. J. (2013) 19, 3986. DOI: 10.1002/chem.201204340
  • (6) Heteroleptic silylamido phenolate complexes of calcium and the larger alkaline-earth metals: -agostic Si–H···Ae stabilization and activity in the ring-opening polymerization of L-lactide
    B. Liu et al., Chem. Eur. J. (2012) 18, 6289. DOI: 10.1002/chem.201103666
  • (7) Discrete, solvent-free alkaline-earth metal cations: Metal···fluorine interactions and ROP catalytic activity
    Y. Sarazin et al., J. Am. Chem. Soc. (2011) 133, 9069. DOI: 10.1021/ja2024977


Topic 2 - Alkaline earth complexes in homogeneous catalysis

Catalysed heterofunctionalisations of unsaturated substrates are of tremendous interest, not least because of their atom efficiency. Our calcium, strontium and barium complexes constitute excellent precatalysts for the inter- and intramolecular hydroamination of alkenes, hydrophosphination of activated alkenes and hydrophosphonylation of aldehydes and ketones. They range amongst the most effective to date for these catalysed reactions, converting large amounts of substrate in record time and under mild conditions.

For instance, they catalyse the anti-Markovnikov addition of phosphines to activated alkenes at 60 °C; this reaction is otherwise difficult to catalyse with other systems:

Similarly, the regiospecific addition of amines to activated alkenes is also very efficiently catalysed by phenolate and imino-anilide alkaline-earth complexes under mild conditions (25–60 °C):

Cyclisation in the cyclohydroamination of aminoalkenes is also catalysed competently. Ring-closure occurs according to Baldwin rules, and typical gem-disubstituted effects are observed:

Our alkaline earth complexes also act as competent precatalysts for the chemoselective N–H/H–Si cross-dehydrocoupling of amines and hydrosilanes. The benchmark couplings of triphenylsilane with pyrrolidine or tert-butylamine has enabled us to delineate several key reactivity trends and highlight the extreme efficiency of barium catalysts.

In the light of the results exhibited by our systems in monofunctional amine/hydrosilane dehydrocouplings, we became interested in the barium-promoted production of polycarbosilazanes from difunctional substrates. The rapid and controlled syntheses of either linear or cyclic polymers by dehydropolymerisation of p-xylylenediamine and diphenylsilane are achieved using our most effective dehydrocoupling precatalyst, BaCH(SiMe3)22•(THF)2.

SELECTED REFERENCES FOR TOPIC 2

  • (1) Amino ether–phenolato precatalysts of divalent rare earths and alkaline earths for the single and double hydrophosphination of activated alkenes
    I. V. Basalov et al., Organometallics 2016, asap. DOI: 10.1021/acs.organomet.6b00252
  • (2) Sequential barium-catalysed N-H/H-Si dehydrogenative cross-couplings: cyclodisilazanes vs linear oligosilazanes
    C. Bellini et al., Chem. Eur. J. 2016, asap. DOI: 10.1002/chem.201603191
  • (3) Tailored cyclic and linear polycarbosilazanes via barium-catalysed N-H/H-Si dehydrocoupling reactions
    C. Bellini et al., Angew. Chem. Int. Ed. 2016, 55, 3744. DOI: 10.1002/anie.201511342
  • (4) Alkaline-earth catalysed cross-dehydrocoupling of amines and hydrosilanes: Reactivity trends, scope and mechanism
    C. Bellini et al., Chem. Eur. J. 2016, 22, 4564. DOI: 10.1002/chem.201504316
  • (5) Barium-mediated cross-dehydrocoupling of hydrosilanes with amines - A complementary approach by theory and experiment
    C. Bellini et al., Angew. Chem. Int. Ed. 2015, 54, 7679. DOI: 10.1002/anie.201502956
  • (6) Highly active, chemo- and regioselective Yb(II) and Sm(II) catalysts for the hydrophosphination of styrene with phenylphosphine
    I. V. Basalov et al., Chem. Eur. J. 2015, 21, 6033. DOI: 10.1002/chem.201500380
  • (7) Divalent heteroleptic ytterbium complexes - effective catalysts for intermolecular styrene hydrophosphination and hydroamination
    I. V. Basalov et al., Inorg. Chem. 2014, 53, 1654. DOI: 10.1021/ic4027859
  • (8) Heteroleptic alkyl and amide iminoanilide alkaline earth and divalent rare earth complexes for the catalysis of hydrophosphination and (cyclo)hydroamination reactions
    B. Liu et al., Chem. Eur. J. 2013, 19, 13445. DOI: 10.1002/chem.201301464
  • (9) Cyclohydroamination of aminoalkenes catalyzed by disilazide alkaline-earth metal complexes: Reactivity patterns and deactivation pathways
    B. Liu et al., Chem. Eur. J. 2013, 19, 2784. DOI: 10.1002/chem.201203562
  • (10) Highly effective alkaline earth catalysts for the sterically governed hydrophosphonylation of aldehydes and non-activated ketones
    B. Liu et al., Chem. Eur. J. 2012, 18, 13259. DOI: 10.1002/chem.201201489
  • (11) When bigger is better: Intermolecular hydrofunctionalizations of activated alkenes catalyzed by heteroleptic alkaline-earth complexes
    B. Liu et al., Angew. Chem. Int. Ed. 2012, 51, 4943. DOI: 10.1002/anie.201200364


Topic 3 - Alkaline earth complexes in polymerisation catalysis

Growing concern towards environmental issues, depletion of the fossil feedstocks and unstable crude oil prices have prompted research groups to investigate the use of biopolymers as an alternative to the already existing synthetic commodity materials. The ring-opening polymerisation (ROP) of lactide, a bio-renewable resource produced by fermentation from sugar-roots and corn, has attracted the most attention, including ours.

Our alkaline earth complexes display excellent catalytic performances in the controlled immortal ring-opening polymerisation of “green” cyclic esters: lactide, -butyrolactone, -caprolactone etc. These precatalysts rank amongst the best ones known to date for this catalysis, allowing efficient access to versatile biopolymers with controllable microstructures and predictable molecular weights.

Both heteroleptic charge-neutral and cationic alkaline earth complexes yield effective ROP catalysts, and thorough mechanistic studies (combining NMR, DFT, kinetics etc.) have enabled us to discriminate between the two families and ascertain the pertaining respective mechanisms.

SELECTED REFERENCES FOR TOPIC 3

  • (1) Discrete divalent rare-earth cationic ROP catalysts: Ligand-dependent redox behavior and discrepancies with alkaline-earth analogues in a ligand-assisted activated monomer mechanism
    B. Liu et al., Chem. Eur. J. 2013, 19, 3986. DOI: 10.1002/chem.201204340
  • (2) Alkali aminoether-phenolate complexes: synthesis, structural characterization and evidence for an activated monomer ROP mechanism
    S.-C. Roşca et al., Dalton Trans. 2013, 42, 9361. DOI: 10.1039/c2dt32726k
  • (3) Heteroleptic silylamido phenolate complexes of calcium and the larger alkaline-earth metals: -Agostic Si–H···Ae stabilization and activity in the ring-opening polymerization of L-lactide
    B. Liu et al., Chem. Eur. J. 2012, 18, 6289. DOI: 10.1002/chem.201103666
  • (4) Well-defined, solvent-free cationic barium complexes: Synthetic strategies and catalytic activity in the ring-opening polymerization of lactide
    B. Liu et al., Inorg. Chim. Acta 2012, 380, 2 DOI: 10.1016/j.ica.2011.09.020 Young Investigator Award, art cover
  • (5) Discrete, solvent-free alkaline-earth metal cations: Metal···fluorine interactions and ROP catalytic activity
  • Y. Sarazin et al., J. Am. Chem. Soc. 2011, 133, 9069. DOI: 10.1021/ja2024977
  • (6) Bis(dimethylsilyl)amide complexes of the alkaline-earth metals stabilized by β-Si-H agostic interactions: Synthesis, characterization, and catalytic activity
    Y. Sarazin et al., Organometallics 2010, 29, 6569. DOI: 10.1021/om100908q
  • (7) Discrete, base-free, cationic alkaline-earth complexes – Access and catalytic activity in the polymerization of lactide
    Y. Sarazin et al., Eur. J. Inorg. Chem. 2010, 3423. DOI: 10.1002/ejic.201000558

Topic 4 - Divalent tin(II) and lead(II) complexes for ROP catalysis

Industrially, the cheap and robust tin(II) bis(2-ethyl-hexanoate) is the sole ROP catalyst used to prepare aliphatic polyesters. We have undertaken detailed mechanistic studies using our own tin(II) precatalysts in order to best mimic industrially relevant systems and to understand what happens in batch-scale polymerisation reactors.

LOSnN(SiMe3)2 phenolato ROP tin(II) precatalysts promote the ROP of lactide, trimethylene carbonate etc. Mechanistic issues related to the nature of the active species and operative pathways in such polymerisations have been elucidated, notably through the abundant use of 119Sn NMR spectroscopy. Kinetic monitoring and comprehensive DFT computations have been performed to rationalise our experimental observations.

119Sn NMR spectroscopy has enabled unambiguous catalyst speciation. All of the several tin(II) species found in the reaction medium under real polymerisation conditions have been authenticated. This was not trivial, since as many as 5 different catalytically active species can potentially be found at once!

Tin(II) ROP precatalysts are ideally suited to the monitoring of ROP reactions by 1H NMR spectroscopy. Long-term efforts have led to the first comprehensive kinetic modelling of catalysed ROP reactions. We are now able to perfectly fit experimental data to a set of simple mathematical equations. This powerful method gives access at once to the various reaction rate constants (initiation, propagation, exchange) which characterise immortal ROP reactions.

In relation with these kinetic and mechanistic studies, we have also developed of related divalent tetrel complexes that can act as ROP precatalysts. The use of amino(ether) phenolate ligands associated to Met(N(SiMe3)2)2 (Met = Ge, Sn or Pb) affords the divalent complexes LOSnN(SiMe3)2, which serve as precursors to unusual heterobimetallic complexes. All these compounds mediate the ROP of cyclic esters.

We have also designed several “ligand-free” tin(II) and lead(II) alkoxides, such as the bis(isopropoxide) [Sn(-OiPr)2]∞ and the heteroleptic [Sn(-OiPr)(N(SiMe3)2]2 or their lead(II) congeners [Pb(-OiPr)2]∞ and [Pb(-OiPr)(N(SiMe3)2]2. These simple compounds are excellent (pre)catalysts for the ROP of lactide, and in particular the lead(II) alkoxides displayed turnover frequencies amongst the highest ones to this day. Dozens of such complexes have been synthesised and structurally characterised, and their 119Sn NMR or 207Pb NMR data were scrupulously recorded.

To enhance our understanding of structural patterns and NMR chemical shifts in these compounds, and ultimately to facilitate catalyst development, we have devised a DFT methodology that enables us to link the structural features of these complexes to their 119Sn NMR chemicals shifts, and to model the data with good accuracy.

SELECTED REFERENCES FOR TOPIC 4

  • (1) Structurally characterized lead(II) alkoxides as potent ring-opening polymerization catalysts
    L. Wang et al., Organometallics 2015, 34, 1321. DOI: 10.1021/acs.organomet.5b00052
  • (2) Structure vs 119Sn NMR chemical shift in three-coordinated tin(II) complexes: Experimental data and predictive DFT computations
    L. Wang et al., Organometallics 2015, 34, 2139. DOI: 10.1021/om5007566
  • (3) On the coordination chemistry of organochalcogenolates RNMe2^E− and RNMe2^E^O− (E = S, Se) onto lead(II) and lighter divalent tetrel elements
    A. Pop et al., Dalton Trans. 2014, 43, 16459. DOI: 10.1039/c4dt02252a
  • (4) Kinetic analysis of the immortal ring-opening polymerization of cyclic esters: A case study with tin(II) catalysts
    L. Wang et al., Macromolecules 2014, 47, 2574. DOI: 10.1021/ma500124k
  • (5) Stable divalent germanium, tin and lead amino(ether)-phenolate monomeric complexes: structural features, inclusion heterobimetallic complexes, and ROP catalysis
    L. Wang et al., Dalton Trans. 2014, 43, 4268. DOI: 10.1039/c3dt51681d
  • (6) Heteroleptic tin(II) initiators for the ring-opening (co)polymerization of lactide and trimethylene carbonate: Mechanistic insights from experiments and computations
    L. Wang et al., Chem. Eur. J. 2013, 19, 13463. DOI: 10.1002/chem.201301751
  • (7) Synthetic and mechanistic aspects of the immortal ring-opening polymerization of lactide and trimethylene carbonate with new homo- and heteroleptic tin(II)-phenolate catalysts
    V. Poirier et al., Chem. Eur. J. 2012, 18, 2998. DOI: 10.1002/chem.201102261  

Publications referenced in HAL