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Flashcards in part 1 Deck (99):
1

general properties of s-block metals in compounds

1. typically ionic bonding (non-directional)
2. flexible metal ligand interaction
3. various coord. modes and metal coord. nos
4. redox inert

2

what is organometallic chemistry?

study of compounds that have at least one interaction/bond between a carbon and metal centre

3

organometallics

compounds with M-C bonds

4

metalorganics

compounds that contain metal and organic groups but don't have direct M-C bond

5

properties of M-C bonds depend on

1. bond polarity (electronegativity differences)
2.bond length
3.bond strengths (atomic/ionic radii, orb size and overlaps)

6

covalent contribution in bonds

orb overlap (wavefunctions)

7

ionic contribution in bonds

attraction from opposite charges

8

what type of bonds make up main group organometallics?

largely M-C σ bonds of various strengths and polarity

9

electronegativity of element increases with

higher oxidation state
eg Ti(IV) > Ti(I)

10

is electronegativity of element such as carbon constant?

no- depends on the amount of s-contribution to hybrid orbs (s-orb more strongly affected by effective nuclear charge than other orbs)
the more s character, the more electronegatiive and the stronger the M-C bond strength

11

polarity trends in main group organometallics

1. M-C bond polarity decreases from left to right in table
2. M-C bond polarity increases down a group

12

bond strength trends in main group organometallics

decreases down a group

13

what does mean bond energy do going a group and why?

energy decreases due to different radical expansion and poorer orb overlap for heavier metals and period 2 elements eg carbon

14

are organometallic compounds stable/unstable with respect to oxidation to MOn, CO2, H2O

organometallic compounds are thermodynamically unstable

15

generally what types of organometallics are reactive towards air and moisture?

organometallics with e-poor metal centres and vacant coord. sites (low-lying vacant orbs, free e- pairs and highly polar M-C bonds

16

`is M-C interaction hard or soft?

quite soft

17

why are ionic R- groups preferred to covalent ones?

prefer good distribution of anionic charge on R

18

what do the aggregation states of lithium alkyls in solution depend on?

solvent (hydrocarbon vs donor solvent) and temperature

19

why can RLi compounds be more reactive at low temperatures compared with at RT in donor solvent?

due to a lower aggregation state at low temperatures. driving force is (-TΔS) towards more free donors and higher RLi aggregation at higher temp.

20

why are deprotonations of toluene/benzene very slow?

kintetically hindered

21

how can the kinetic basicity of lithium alkyls be increased?

use donor molecules eg THF, chelating amines or MOtBu

22

how can the speed of deprotonation of benzene be improved

addition of TMEDA- induces break up of (nBuLi)6 cluster, breaking Li-C interactions to form a lower coordinated species. Polarity of Li- bond is increased and reactivity of nBuLi is increased

23

superbase

mixtures of strong bases (different alkali metals or alkaline earth metals) can react as strong bases/nucleophiles

24

schlosser base

mixtures of nBuLi and KOtBu

25

what can schlosser bases be used for?

deprotonate quite inert CH bonds eg synthesis of benzylpotassium from toluene

26

why are sterically demanding alkali amides strong bases but poorer nuleophiles

due to donor atom with e- lone pair in the amide, kinetic barriers are less of an issue

27

Corey-Seebatch reaction

synthesis of ketone from aldehyde- convert aldehyde to a 1,3-dithiane to generate a CH-acidic compound that is readily deprotonated with nBuLi to form an acyl anion equivalent

28

how can you estimate the concentration of RLi solutions?

titrations- need to be air and moisture free
eg use diphenylacetic acid and N-pivaloyl-o-toluidine

29

what does the reaction of lithium metal and naphthalene give?

lithium naphthalenide (radical anion) and lithium naphthalenediide (dianion) species

30

what "holds together" s-block metals coordinating to neutral/anionic π-systems?

electrostatic (ionic) interactions

31

common donor solvents for Schlenk equillibrium, grignard reagents

diethyl ether, tetrahydrofuran (THF), dimethoxyethane (DME), 1,4-dioxane

32

ways to synthesise MgR2 compounds

1. grignard formation followed by formation of salt
2. metallation
3. redox-transmetallation

33

synthesis of MgR2 compounds : direct synthesis

grignard formation : Mg + nBuCl → nBuMgCl
salt formation: nBuMgCl + nBuLi → MgnBu2 + LiCl

34

synthesis of MgR2 compounds : metallation

MgnBu2 + 2RH → MgR2 +2nBuH

35

synthesis of MgR2 compounds : redox- transmetallation

Mg + HgR2 → MgR2 + Hg

36

Schlenk equilibrium

2RMgX ↔ MgR2 + MgX2

37

addtion of dioxane to grignard solutions gives?

solutions of MgR2
2RMgX + 2 dioxane → MgR2 + MgX2(dioxane)2

38

aggreation state of RMgX in THF

monomeric eg 1 Mg (Mg has coordination number of ~5/6

39

aggreation state of RMgX in Et2O

dimeric eg 2 Mg - bridging groups
Mg coordination number ~4

40

what side of schlenk equil. does it lie on in Et2O?

reagents side- RMgX

41

what side of schlenk equil. does it lie on in THF?

products - MgR2 + MgX2

42

grignard formation mechanism

1. reaction initiated by single e- transfer from Mg to σ* orb on R-X
2. Get ransfer of X to Mg leaving radical R°, which combines with MgX to give RMgX

43

grignard formation mechanism - order of reactivity of RX

I> Br> Cl> > F (RF is typically unreactive)

44

Problem associated with using RI as RX in grignard formation?

it is fastest however gives most Wurtz coupling

45

Wurtz coupling

2RX + 2Na → R-R + 2NaX

46

in the reaction of RMgX with ketones what type of transition states are favoured?

6-memembered - 1 ketone: 2 grignard

47

why is the 1:1 mechanism for the reaction of RMgX with ketones not favoured?

can have more side reactions eg enolisation and reduction

48

why is the 1:2 mechanism for the reaction of RMgX with ketones favoured?

favours nucleophilic addition

49

how can the the addition of nucleophiles to ketones be improved?

through the addition of anhydrous salts eg Li+, Zn2+, Ln3+ - can supress side reactions through the lewis-acid activation of the ketone by coordination to the salt

50

what do you get from the reaction of more hindered/basic grignard reagents with carbonyl compounds with acidic CH in the alpha position?

enolates

51

what do you get from the reaction of grignards with β-hyrogens and hindered ketones?

hydride transfer- reduction of carbonyl to "alcohol"

52

Turbo-Grignard

iPrMgCl.LiCl
highly selective, reactive and has high functional group tolerance
can be used in Mg-halogen exchange reactions

53

Turbo-Hauser bases

R2NMgCl.LiCl - strong base
made from turbo grignard
used to deprotonate functionalisaed aromatic molecules to give grignard reagents

54

synthesis of ZnR2 compounds

direct synthesis, salt-formation, redox-transmetallation

55

Simmons-smith reaction

converts alkenes into cyclopropane via an organozinc carbenoid X-CH2-M from diiodomethane and Zn(Cu)

56

reformatsky reaction

reaction of zinc with α-bromoester to give zinc enolate. Which can go on to to react with carbonyl group to give β- hydroxyester

57

RCd and RHg compounds

highly toxic, typically linear geometry

58

CdR2 + acid chlorides

givers ketones

59

mechanism of RX substitution by Me2CuLi and product

product = R-Me
occurs via cross-coupling mechanism, involves redox reaction - oxidative adddition and reductive elimination

60

synthesis of AlR3

3RLi + AlCl3 → AlR3 + 3LiCl

61

synthesis of AlMe3

4Al + 6MeCl → 2Me3Al2Cl3 → Me4Al2Cl2 + Me2Al2Cl4

62

Reduction to give AlMe3

3Me4Al2Cl2 + 6Na → 2Me6Al2 + 2Al + 6NaCl occurs via disproportionation reaction

63

structure of AlMe3 in solid/liquid/gas

solid and soultion: dimeric (3c2e bond for bridging methyl groups)
gas: monomeric

64

synthesis of AlEt3: Zielger direct process

Al + 1.5 H2 +3C2H4 → AlEt3

65

organoaluminium from hydroalumination order of reactivity of alkenes

CH2=CR2 < CH2=CHR < CH2=CH2

66

reaction for hydroaluminium to organoaluminium

Al + 1.5H2 + 3 C4H8 → AliBu3

67

hydroalumination

reverse reaction of β-hydride elimination
ie gives alkenes from alkynes

68

DIBAH

iBu2AlH

69

hydroalumination reaction + product

alkyne + iBu2AlH → alkene
cis- adition and Al adds on to least substituted carbon

70

Aufbau reaction

growth of alkyl chains using AlEt3 and then displacement to release AlEt3

71

Aufbau reaction + 1-alkenes

only get single insertion into Al-C bond

72

Ziegler-Natta polymerisation of alkenes -reaction steps

-migration of Me onto alkyl chain
-insertion of alkene into alykl chain

73

Methyl alumoxane (MAO) structure, uses

(MeAlO)n, can come in polymer chains, rings or cages
synthesised from hydrolysis of water
used to activate catalysts eg in Zieglar-Natta polymerisation

74

Role of MAO during polumerisation

1. alkylating agent (M-Cl to M-Me)
2. lewis acid (abstract CH3- from M)
3. picks up impurities

75

Tebbe Reagent

Cp2Ti- (CH2, Cl) bridge- AlMe2

76

use of Tebbe reagent

can be used to transfer a methylene to a ketone - replaces double bond O

77

Group 14 organometallics ER4

1. stable - not e- deficient
2. less reactive/nucleophilic due to low bond polarity of E-C
3. E-C bond strength decreases down the group
E-C bond polarity decreases down the group
4.thermal stability of ER4 decreases down the group

78

Uses and synthesis of PbEt4

used as anti-knocking agent in petrol
4 NaPb + 4EtCl → PbEt4 + 3Pb + 4NaCl

79

SnR4 compounds

undergo transmetallation reactions with alkyl/phenyl lithium
C3H6SnPh3 + PhLi → C3H6Li + SnPh4
RLi attacks Sn via 5-coordinate intermediate

80

hydrogermylation

addition of Ge-R over alkene double bond

81

hydrostannation

addition of Sn-R over alkene double bond

82

group 15 ER3

lewis bases

83

group 15 ER5

hypervalent
+5 oc state is less stable going down group due to inert pair effect

84

inert pair effect

2 electrons in outer most s orb do not ionise or react

85

group 15 R2EH compounds

don't undergo hydroelementation reactions due to not having strong polarisation of E-H bond

86

λ

total number of bonds oe can be ox state

87

σ

number of simga-bonded substituents

88

Group 15 preparation of organoelement (III) compounds

EX3 + 3MeBr → ER3 + 3MgX2/LiX

89

lanthanoid contraction

ion size decreases with increasing atomic number

90

lanthanoids

form ionic complexes - hard metal cations
+3 common ox state

91

formation of cyclopentadienyl- Ln complexes

salt metathesis and redox-transmetallations

92

Ziegler-Natta polymerisation what metal can be used as precatalyst? what is structure of precatalyst?

uses Cp2MCl2 M= Ti, Zr, Hf as precataylst

93

formation of Tebbe reagent

Cp2TiCl2 + 2AlMe3 → Cp2Ti - (Cl and Me) bridge - AlMe2 + Me2AlCl + MeH

94

synthesis of PbEt4

4NaPb + 4EtCl → PbEt4 + 3Pb + 4NaCl

95

decomposition of PbEt4

decomposes at evelated temperatures
PbEt4 → Et• + •PbEt3
PbEt4 + •Et → H3C-CH3 + Et3PbCh2Ch2•

96

what is the intermediate when RLi attacks Sn

5-coordinate intermediate
SnMe4 + MeLi → Li[SnMe5]

97

synthesis of Cp lanthanoid complexes - salt metathesis

LnCl3 + 3Cp M → Cp3Ln

98

synthesis of Cp lanthanoid complexes - redox transmetallation

Ln metal + 3CpTi → Cp3Ln

99

why are group 14 ER4 molecules stable?

aren't electron deficient and don't posses an element based lone pair