G14 Flashcards
What are the 4 G14 elements used in NMR?
Si (silicon) - Non-metal
Ge (germanium) - Metalloid
Sn (tin) - Metal
Pb (lead) - Metal
What are features of p-block?
- Increase in metallic properties on descending the group
- This is due to the increasing atomic radius and associated decrease in ionization energy down the group
- The valance configuration for these elements is ns2 np2, so their common oxidation states will be +4 and +2
- The +4 oxidation state is more common for the lighter elements
- The +2 oxidation state is more common for the heavier elements – the inert pair effect
What is a carbene?
- Carbenes contains a neural carbon atom with 2 valence electrons
- Carbenes can be stabilised with heteroatoms
- NHC’s are generally strong sigma donors
- Commercially available
What are the uses of N-Heterocyclic carbenes?
- Ligands (commerically available)
- To stabilise high/low valent complexes
- Organocatalysis (reduction of carbon dioxide)
What are tetrylenes?
Like carbenes but with G14 elements where the C is
Diavalent species in +2 oxidation state
heavier analougues display increased stabiity due to inert pair effect
How is the divalent state in N-heterocyclic systems stabilised?
- Nitrogen atoms donate π-electrons to the metal centre (reducing σ-electron density at the metal centre)
- Stabilisation through mesomeric and inductive effects
How to synthesise heavy tetrylenes (draw diagram)?
- Dilithiation - followed by addition of the appropriate metal chloride
- Transamination of preiligand with M[N(SiMe3)2]
What are features of silylenes?
- Stable as a monomer in the solid-state
- Readily undergoes oxidative addition:
Draw diagram of silylene [1+4] cycloaddition
Draw a diagram of silylene adduct formation
Draw a diagram of silylene insertion adduct formation
What are features of stable germanone (heavy ‘ketone’)?
- Can react with N2O to give E=O bond
- Reactive
Draw Stable Germanone addition reaction with H2O
Draw Stable Germanone cycloaddition reaction with CO2
What are features of stable stannylenes?
- No dimerization in the solid-state
- Readily undergoes oxidative addition:
Draw stannylene oxidative addition reaction
Draw stannylene insertion oxidative addition reaction with metal substrates
Features of R2E=ER2 molecule?
- Structure is not a simple extension of the bonding situation in ethylene i.e. not sp2-hybridized tin with simple s,p-overlap
- Singlet state is more stable in the monomeric form for the heavier group 14 elements
- Trans-bent geometry (electron pairs not shared equally between atoms in each bond - primarily located on one rather than two atoms)
What are features of the R2E=ER2 trans-bent geometry?
(readily dissociate into monomers in solution)
* Result = POLAR DATIVE bonds that represent weak dipolar interaction
* As you descend the group a considerable weakening of the bond occurs
* Many tin and lead derivatives have Sn-Sn and Pb-Pb bond distances close to that of
single bonds in the solid state
e.g. Sn=Sn in previous example : 2.77 Å
typical Sn-Sn single bond : 2.81 Å
How to synthesise disilenes? Draw diagram
By ‘trapping’ reactions of non-isolable intermediates from retero-Diels Alder
Recall the element-element multiple bonding general trends diagram
Largest to shortest contraction, compound features and what R group corresponds
