Stasch S-Block Metals

Question 1

alkali metal reactivity (generally)

Answer 1

air and moisture sensitive - potentially pyrophoric

Question 2

solubility of RLi compounds

Answer 2

hydrocarbon solvents and aprotic donor solvents

Question 3

How to produce organolithium products (large scale)

Answer 3

nBuCl + 2Li —> nBuLi + LiCl

Question 4

basicity of organolithiums

Answer 4

MeLi < nBuLi < sBuLi < tBuLi

Question 5

two useful RLi reactions

Answer 5

B-hydride elimination [with heat] // simplified ether cleavage

Question 6

what do donor solvents do to the reactivity of RLi?

Answer 6

enhance it // can cause degradation

Question 7

what is an aggregation state?

Answer 7

fundamental states of matter + some others

Question 8

how does a low T affect aggregation state of RLi

Answer 8

lower aggregation state

Question 9

How does TMEDA (donor molecule) affect reactivity of lithium alkyls?

Answer 9

improves kinetic basicity - so improves reactivity.

Induces break up of BuLi clusters to form lower coordinated species to increase LiC polarity.

Question 10

which has a faster metallation rate: PhCh2Li or CH3Li? [in THF] Why?

Answer 10

benzyllithium!
due to monomeric form of its aggregation (cf tetrameric methyl)
(despite methyl anion being stronger and smaller base than benzyl anion)

Question 11

what is a superbase?

Answer 11

a mixture of strong bases that can react as stronger bases/nucleophiles together.
By increasing kinetic acidity of RLi

Question 12

example of a “Schlosser” superbase + “special talent”

Answer 12

KOtBu + nBuLi - capable of deprotonating inert CH bonds

Question 13

synthesis of nBuNa (/K)

Answer 13

NaOtBu + nBuLi

Question 14

does nBuLi prefer 1,2 or 1,4 addition?

Answer 14

1,2

Question 15

Which aryl halides can do M-X exchange with Li reagents?

Answer 15

Br or I

Question 16

How do you drive an M-X exchange to completion?

Answer 16

use 2 x tBuLi - prevents other RX in the mixture

Question 17

What type of alkali metal amides would you use for deprotonations? Why?

Answer 17

sterically demanding - as they are strong bases but poorer electrophiles

Question 18

Examples of sterically demanding alkali metal amides?

Answer 18

LDA // LHMDS // LTMP

Question 19

how does directed ortho-metallation work?

Answer 19

donor atoms can direct the Li to the ortho position on a benzene by donating electron density into the lithium

Question 20

What is Corey Seebach?

Answer 20

converting an aldehyde to a 1,3-dithiane —> generates a C-H acidic compound that’d readily deprotonated with nBuLi to form an acyl anion

Question 21

how would you standardise an RLi solution from decomposition effects?

Answer 21

diphenylacetic acid // N-pivaloyl-o-toluidine

with titration.

Question 22

What do Lithium Napthalenide (+diide) species do?

Answer 22

reversibly reduces the extended pi systems that accommodate extra electrons

Question 23

How to make MgR2 species?

Answer 23

direct synthesis (grignard) followed by salt metathesis // metallation // redox-transmetallation

Question 24

What is the Schlenk equilibrium related to and what is it?

Answer 24

grignard reagents: 2RMgX MgR2 + MgX2 (+ various other MgXR mixes)

Question 25

what compound could be added to grignard solutions (eg in Et2O) to precipitate out all the MgX compounds and leave MgR2 only?

Answer 25

Dioxane

Question 26

typical aggregation state of RMgX in a) THF and b) Et2O?

Answer 26

a) monomeric over a wide conc. range

b) dimeric over a wide conc. range

Question 27

What is single electron transfer?

Answer 27

another method of forming grignard reagents
by transferring a single electron from Mg metal to the sigma* orbital of X-R then the X- transfers to Mg to leave R. to combine with .MgX.

Question 28

Order of reactivity of halides in RX

Answer 28

I>Br>Cl»F

Question 29

What is Wurtz coupling? (RI can do in side reactions)

Answer 29

2RX + 2Na —> R-R + 2NaX

Question 30

How can Mg metal be activated?

Answer 30

reduction of MgX2 with K or Na (in THF)

Question 31

how do grignard reagents work with ketones?

Answer 31

the ketone coordinates to Mg2+ before the addition

Question 32

how would a grignard reagent form an enolate?

Answer 32

hindered grignard + carbonyl compounds with a-acidic C-H units causes deprotonation

Question 33

how would you observe a hydride transfer using a carbonyl and a grignard reagent?

Answer 33

if grignard contains B-hydrogen atoms and is quite basic + reacting with hindered ketones.

Question 34

What is the “turbo-grignard” reagent?

Answer 34

iPrMgCl.LiCl

Question 35

what does the “turbo-grignard” reagent do?

Answer 35

good for exchange reactions. Highly reactive, selective and functional group tolerant.

Question 36

what is a “turbo-Hauser” reagent?

Answer 36

the amide base “R2NMgCl2Li” prepared from the turbo grignard

Question 37

what can a turbo-hauser reagent do?

Answer 37

capable of deprotonating functionalised aromatics to generate grignard reagents

Question 38

How would you alkylate an RLi and RMgX?

Answer 38

use an alternative leaving group (eg tosylate) to improve reactivity or use R groups without B-hydrogens or add metal salts instead

Question 39

why would an alkylation of RLi and RMgX be difficult?

Answer 39

side reactions: metal halide exchange and HX eliminations with B-hydrogens

Question 40

what is Mg-Anthracene?

Answer 40

An intermediate formed by the direct synthesis of MgR2 with anthracene and Mg