Learning objectives
Knowledge and uderstanding: To provide students with the basic knowledge related to organometallic chemistry, the preparation, characterization and reactivity of the main classes of organometallic compounds. At the end of the course, the student will be able to recognize the role played by metal within synthesis protocols (mainly organic), both in stoichiometric and catalytic reactions. They will also be able to evaluate the importance of ligands combined with the metal in direct the process towards high performance in terms of yield and selectivity.
Applying knowledge and understanding: students are encouraged to use all the knowledge deriving from the course program but also from the previously attended course programs (Inorganic Chemistry and Organic Chemistry) to understand the structural and reactive properties of organometallic compounds. They will therefore be able to evaluate the different reactivity that an organic molecule shows when "free" (uncoordinated) compared to when it is interacting with a metallic nucleus (coordinate), and as a function of the metallic nucleus (type of element and its oxidation state) and its coordinative neighborhood. They will have the ability to understand the scientific bibliography concerning synthesis processes promoted by metal complexes, identifying the key role played by the chosen metal species.
Making judgments: the students will acquire the ability to carefully choose the type of metal (type of element and its oxidation state) most suitable for promoting a specific reaction involving a particular organic substrate, according to the reactive steps expected in the mechanism of reaction. They will also acquire skills relating to how to carry out a correct monitoring of the reaction, to determine its efficiency both in terms of conversion / yield and selectivity.
Communication skills: the students will acquire the ability to describe in detail and precisely the structures of organometallic compounds, highlighting the peculiarities deriving from the metal-ligand interaction. They will therefore be able to propose and describe a plausible reaction mechanism for common metal-promoted processes (both stoichiometric and catalytic), justifying the expected performances (productivity and selectivity). Finally, They will be able to illustrate the advantages deriving from metal-promoted reactions with respect to classical organic synthesis protocols.
Learning skills: the students will be able to program metal-catalyzed synthesis experiments, to critically evaluate their performance and to intervene on structural changes and experimental conditions for the optimization of the reaction. They will have the ability to critically analyze literature results, using them for a better optimization of the reactions of interest.
Prerequisites
Knowledge of the fundamental concepts of inorganic, organic and coordination chemistry
Course unit content
Review of some basic knowledge of coordination chemistry (metal-ligand bonding, coordination geometries, chelation).
Metal-carbon interaction based on the type of C-ligand (sigma-donor, sigma-donor/pi-acceptor, pi-donor/pi-acceptor), 18e rule.
Organometallic chemistry of some s and p-blocks metals: organolithium compounds, organomagnesium compounds, organoalluminium compounds, organisilicon compounds, organophosphorious compounds.
Sistematic study of the main classes of C-based ligands for transition metals: alkyls and aryls, carbonyls, monoolefins, dienes, allens, alkynes, cyclopentadienyls, arenes, carbenes, isonitriles.
Agostic interactions, beta-elimination, alfa-elimination.
Substitution reaction is octahedral and square-planar complexes.
Nucleophilic and electrophilic addition reactions to coordinated ligands.
Oxidative addition, migratory insertion, reductive elimination.
Organometallic catalysis:main differences between homogeneous and heterogeneous catalysis, role played by an organometallic catalyst (ligand and metal effect), efficiency of a catalyst. Homogeneous hydrogenation, hydrogen trabsfer recation, hydroformilation, coupling reactions (Heck, Suzuki, Sonogashira, Negishi), nucleophilic addition to coordinated allenes, addition of HCN (hydrocyanation), R3SiH (hydrosilylation) and RNH2 (hydroammination) to olefins.
Full programme
Review of some basic concepts of Coordination Chemistry, such as Lewis donor/acceptor, coordination geometries, crystal filed theory, ligands filed theory, magnetism of the coordination compounds, trans-influence and trans-effect, reactivity of the coordinated ligand.
Concept of ligand-to-metal electron donation and metal-to-ligand back-donation (sigma-donor ligands, sigma/pi donor ligands, sigma-donor/pi-acceptor, pi-donor/pi-acceptor ligands). 18 electron-rule, coordinatively saturated/unsaturated complexes.
Organometallic compounds of some elements of the s and p blocks (synthesis, solid and solution structure, reactivity): organolithium, organomagnesium, organoaluminum (Grignard and binary compounds), organosilicon.
Systematic study of the main classes of organometallic ligands: hydrides, phosphines, alkyls and aryls, carbonyls, mono-olefins, poly-olefins (dienes and allyls), cyclopentadienes, arenes, carbenes and isonitriles. For each class of ligands the structural features (solid state and solution), the main synthetic protocols and the main reactive behaviors will be addressed.
Alpha-aghostic interaction, beta-aghostic interaction, beta-elimination, their role in organometallic synthesis and (catalytic) reactivity.
Substitution reactions in octahedral and square-planar complexes: dissociative mechanism and associative mechanism, hybrid mechanisms.
Nucleophilic and electrophilic addition reactions onto coordinated ligands (CO, olefins, arenes, cyclopentadienes, dienes and allenes)
Oxidative addition (concerted mechanism, Sn2, ionic mechanism, radical and oxidative coupling), migratory insertion (1.1 and 1.2 mechanisms), reductive elimination (in octahedral and tetracoordinated complexes).
Metallorganic catalysis: comparison between homogeneous and heterogeneous catalysis (advantages and drawbacks). Role of the organometallic catalyst. Efficiency and selectivity of a catalyst (turnover number, turnover frequency, enantiomeric (diasteromeric) excess, chemoselectivity, regioslectivity). Homogeneous hydrogenation (Wilkinson catalyst and further generations), hydrogen transfer (internal and external sphere mechanism, Noyori mechanism), hydroformylation (Co and Rh-based catalysts), olefins metathesis, coupling reactions (Heck, Suzuki, Sonogashira, Negishi). Crytical discussion about the true homogeneous nature of some organometallic catalytic processes.
Bibliography
- The Organometallic Chemistry of the Transition Metals Robert H. Crabtree, Wiley
- Organometallics, A Coincise Introduction Ch. Elschenbroich, A. Salzer, Wiley VCH
- Fundamentals of Organometallic Catalysis, Steinborn D., Wiley-VCH
Teaching methods
Oral lessons (48 hours), with the possibility of following the lesson remotely (via Teams). The didactical supports (slides, audio and video recordings) will be made available on the web-platform Elly. Some exercises are scheduled during the lessons, aimed at reinforcing the knlowedge acquired by the students. Discussions with the audience will be strongly motivated by the teacher to reinforce tha abality of the student to analyze the different solution strategies.
Assessment methods and criteria
Oral exam, where the following points will be addressed: Learning of the basic concepts of organometallic chemistry, with particular emphasis to the ligand to metal electronic donation and metal to ligand back-donation, in order to understand the different reactivity shown by a free ligand (not coordinated organic molecule) and metal-bound organic molecule. Analysis of the effect played by all the actors involved in the reaction that's, type of organic ligand, substituents directly attached to the C-atoms bound to the metal, type of metal (its position in the Periodic Table and its electronegativity), type of ancillary (spectators) ligands. Definition of a possible synthetic strategy for the preparation of simple organometallic compounds, taking into consideration the type of ligand, metal and experimental conditions (temperature, solvent) required for getting the requested molecular structure and chemical reactivity. Ability to rationalize the most convenient spectroscopic and analytical techniques for the characterization of a given organometallic compounds. Ability to use the acquired concepts in order to understand some catalytic mechanisms governing some useful metal-catalyzed organic syntheses.
The exam will be conducted in the following way:
the student will receive a week before the exam a short paper that will be discussed during the exam through a ppt presentation. Some examples of structures, reactions or characterization techniques will be object of discussion (example shared by the teacher through a ppt file). General questions about the class of ligands, synthetic pathways ecc. will then be analyzed.
Other information
The slides of the lessons are available on the web. The teacher is available for tutoring (upon agreement).
