Principal Reaction Types

1) Salt Elimination 2) Protonolysis 3) Oxidative addition 4) Reductive Elimination 5) Oxidative Coupling 6) Reductive Cleavage 7) Migratory Insertion 8) Elimination Reactions 9) σ-bond metathesis

Reductive Elimination

reductive cleavage

Elimination reactions

an organometallic compound, through reacting a metal halide with alkyl lithium or grignard Produces a inorganic salt as side product

• Thermodynamics: Salts have high lattice energy, hence highly stable • Kinetics: le chatelier’s principle, the salts of formed as solid, hence removed from the reaction solution, driving the reaction forward

• The alkoxide/amide/alkyl becomes protonated • The conjugate base and metal form a new bond • (sometimes you can make the protonate species volatile meaning it will bubble off, driving the reaction forward)

• This is the simultaneous addition of two ligands into the coordination sphere of a metal, it is an overall process with no mechanistic implications • The synthesis of Grignard reacts, RMgX, from Mg and RX is an O.A. reaction

Going from a 16e to an 18e complex (typical for the oxidation state of the metal to increase by 2 during an oxidative addition)

• Non-bonding electron density at the metal • A vacant coordination site • A metal with accessible oxidation states separated by 2 units

• Heavier elements of a group (more electron rich) • When the metal is electron rich (π-basic) • When hard or strong σ-donor ligands are present (push more e- density onto metal) • Small ligands are present (adding ligands - less steric hindrance the better) • The metal is large (less sterics the better) • For storng M-A and M-B and weak A-B bonds

• Oxidation state: decreases by 2 • Coordination number: decreases by 2 • Valance electron count: decreases by 2

…the ligands that you’re eliminating are cis to one another e.g. the hydrogen and silicon are close enough together to allow the elimination to happen

It generally involves an early transition metal with a d² configuration with unsaturated substrates (i.e. alkenes or alkynes or nitriles) which are coupled together to form an additional C-C bond, forming a metallocycle

formation of a new metallocycle gone from Zn (II) to Zn (IV)

…. C-C and C-N bonds

• oxidation state has not changed • gone from a 18e- to a 16e complex

β-hydride elimination is the most common way for a metal alkyl to decompose (due to the stabiliity of the square transition state and final product) Involves the transfer of a hydride from the β-position on a ligand to the metal centre (most common is alkyl/alkoxide complexes) Has to have a hydride on the β-position for this reaction to occur

• A complex must be coordinatively unsaturated for β-hydride elimination to occur • The metal complex must usually have <18 electrons, otherwise a 20-electron alkene-hydride intermediate would be formed

• This is the transfer of a hydride from the α-position on a ligand to the metal centre • Forming a double bond between carbon and metal centre - carbene • Formally, the process is a type of O.A. reaction as oxidation state of the metal increases by 2 • (Hence cannot occur in a d⁰ or d¹ metal complex)

• For d⁰ or d¹ metal complexes α-abstraction does not result in a change of oxidation state • Due to metal starting and ending with 2x M-C bonds • The α-hydrogen transfers directly to an adjaent ligand instead of the metal centre

γ-, δ-, ε-eliminations

• Essentially it is a swappint of the group attached to different σ-bonds • Occurs through a square transition state • Common reaction for early transition metals/lanthanides/actinides in high oxidation states where oxidative addition and reductive elimination are not viable