1. Ch 13. Group 13

2. Element properties

3. Elemental forms Boron has 3 polytypes, all contain B12 icosahedra.
Two major sources of B are in the Mohave desert, Turkey.
Al to Tl All are cp metal structures (except Ga - mp 30°C, bp 2403°C)

4. Al metal Ellingham diagram
Al3+ is abundant in the crust, but Al is very electropositive
Al(0H)4¯ / Al E0 = −2.3 V
Reduction with C or CO requires t > 2000 °C
Ellingham diagram

5. Al (m) production by electrolysis
Price $ / kg Al
Hall Herault process (1888)
Al2O  Al (m)
+e¯ , ~5V
Na3AlF6(liq)

6. Halides
BX3 : Lewis acidity BBr3 > BCl3 > BF3
This is the opposite of expected inductive effect
B(s) /2 F2(g)  BF3(g) −1109
3F(g)  3/2 F2(g) −3/2 D(F-F) = −233
B(g)  B(s) −406
B(g) F(g)  BF3(g) −1748
So Davg (B-F) = note for comparison that D(C-F) ~ 490 kJ/mol
But ΔH (BF3(g) + F− (g)  BF4− (g)) = −380
The lower LA is attributed to loss of π-bonding upon D3h  Td geometry change
Only BF3 is stable in aqueous solution:
BCl3 + 3H2O  B(OH)3 + 3HCl
Similarly, BF4− is stable in aqu acid, but not BCl4−,BBr4−
AlF4− Td
AlF63 − Oh (only period 3 and higher can be hypervalent

7. Borates B(OH)3 + 2H2O → H3O+ + B(OH)4− pK ~ 9 (weak BA and LA)
B3O3(OH)4− 2 B with CN=3, 1 B with CN=4
Borate esters B(OR)3 ex: B(OCH3)3 a weak LA

8. Graphite / BN structures

9. BN compounds Cl3B = :NH3  Cl3B−NH3 (s) 
1/3 B3N3H3Cl3 (s) HCl (g) (trichloroborazine)
 
BN (s) + HCl (g)
Note: there are also cubic BN and BN analogs to fullerenes, nanotubes

10. Heavier congeners

11. Borides
CaB6
AlB2

12. Borohydride clusters

13. Wade’s rules

14. 11B NMR for nido [B11H14]-

15. Geometric isomers

16. Cluster chemistry

17. Stack compounds

18. Organoaluminum compounds
Al2R6 dimeric except for large R groups
Al2R6 ↔ 2 AlR3
K ~ for R = CH3
K ~ for R = C4H9
K > for R = C6H3(CH3)3
Al2Me HCl  Al2Cl2Me CH4
+ 2 ROH  Al2(OR)2Me CH4
preference for bridging sites is OR- ~ X- > H- > Ph- > R-
Need good e- donor and small size to bridge

19. Organometallic compoundsΔ
Al(iso-C4H9)3  Al2H2(iso-C4H9) H2C=C(CH3)2 alkene elimination
3 Al2Cl2Me Na  2 Al2Me Al NaCl
Tl(CH3)3 Tl(CH3)2+ is linear, stable in aqu base, isoelectronic w/ Hg(CH3)2
(η5-C5H5)Tl is air stable monomeric in gas phase, chain structure in solid state

20. Ziegler-Natta catalysis
½ Al2R6 + C2H4  R2Al(CH2CH2)R
R2Al(CH2CH2)R + C2H4  R2Al(CH2CH2)2R
etc..
3n C2H  Al[(CH2CH2)n(CH2CH3]  NaO(CH2CH2)nCH3
n C2H  (C2H4)n (HDPE)
n CH2=C(H)CH3  (CH2C(H)CH3)n PP (isotactic)
HDPE = 50 x 106 tons/yr ≈10 lbs / person
≈500 x 106 barrels oil / yr (US consumes 720 x 106 barrels / day)
Al2R6
H2O, NaOH
Al2Et6, TiCl4
heptane
n=7-10
detergents, soaps