Organometallics [Andy Johnson]

labile - anion and cation exchange easily high Zeff strongly electrophilic and oxophilic few redox reactions polar and v. reactive M-C bonds preference for “hard” σ-donors (non-polarisable) weak complexation of π-acceptors typical catalysis = polymerisation

ligands bound strongly strong, not v. reactive M-C bonds preference for σ-donor/π-acceptor combinations typical catalysis = alkene and alkyne metathesis

easy ligand association/dissociation weak - not v. reactive M-C bonds even weaker/reactive M-O/M-N bonds preference for s-donor/weak π-acceptor ligands typical catalysis = hydroformylation

lowers activation barrier by introducing a new reaction pathway ** doesn’t change thermodynamics **

they overlap between different classes of orbitals (i.e. net overlap = 0)

correct symmetry spatial overlap - must occupy same region in space similar energy

all available orbitals on C are involved in C-H/C-R bonding

it would disrupt the aromaticity of the phenyl ring

18 e- involved in bonding orbital 0 e- involved in anti-bonding orbital

both electrons provided by ligand = dative covalent bond

one electron provided by ligand and by metal = normal covalent bond

both electrons provided by metal = dative covalent bond

[metal separate from ring] metal “on” rather than “in” e.g. ferrocene

metal “in” ring

(number of X ligands) + (charge on complex)

halides often bridge between 2 metal centres using a lone pair = LX X = sigma bond L = donor bond

[doesn’t add to oxidation state] assign one of the electrons of the electron pair in a single to each metal centre double, triple, quadruple -> 2,3,4 respectively

radical BENT - acts as a 1 electron X ligand (l.p. on nitrogen not used) LINEAR - l.p. now can be used (LX)

late TM d8 -> square planar d10 -> trigonal -as Z increases, d-shell is stabilised -occupied dx2 orbital (perpendicular to plane) no longer involved in ligand bonding

early TM have less d-electrons -> must achieve 18 e- count via larger ligands if ligands = too bulky, low-electron count complexes are formed

ligand donates sigma/non-bonding e- to metal while accepting e- density through overlap of metal t2g orbital and ligand π* ^ ligand = both sigma donor and π acceptor

more backhanding/electron density in ligand anti bonding orbital weakens CO bond bond lengthens lowers CO stretching frequency

d orbital energies decrease/increase in electron density on M energies of dπ and π* orbitals separate back bonding becomes worse

major interaction = σ-donation from CO 5σ orbital (anti-bonding, l.p. on CO) to metal stretching frequency > free CO