CD212-slides-1.pdf - Inorganic and Physical Chemistry

CD212 Aug 2013 Inorganic Chemistry

E. D. Jemmis, Department of Inorganic and Physical Chemistry

Indian Institute of Science Bangalore 560012

BORON SLIDES

1

Tetrahedral Carbon 1874 Van’t Hoff and LeBel

Sp3 Hybridisation

Diamond (Bragg, 1920s)

C C C

H

H H H

H

H H

H H

H

H H

C

2 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore

2-D Aromaticity

Hückel’s 4n + 2 π Electron Rule

E. Hückel

2л 2л 6л

6л 6л 6л

+2 + -

+ +2


Condensed Aromatics and Hückel Rule

Sp2 Hybridisation Mixed Condensation

14π 6π 10π

- + - - -


RULES OF CARBON CHEMISTRY-sp2

CARBYNE CCCCCCCCCC sp


A SIMILAR UNDERSTANDING IN THE CHEMISTRY OF BORON NEEDED

What are the modes of understanding? What are the equivalents of sp2 & sp3 hybridizations, and Hückel 4n+2 Rule? Is it possible to relate boranes to elemental boron à la benzene to graphite, methane to diamond and sp2 hybridisation to carbon nanotubes? Boron-rich solids vs boranes


REST OF THE LECTURE Molecular Chemistry of Boron compared to carbon Polyhedral Boranes and Wade’s Rule Condensed Polyhedral Boranes - mno Rule Elemental Boron and Boron Rich Solids


9

A preview of things to come - structures from boron chemistry

BB B

B

BB

Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore

10

B

B

C

C C

B B

B B

B B

CC

C C

- +

+2

C


C

CC

B

C C

C

B B

B

B

B

B B

B

BB

B

+ + +

(4n+2) π electrons The Diphenylcyclopropenyl Cation.

Ronald Breslow, Joyce Lockhart, Hai Won Chang J. Am. Chem. Soc., 1961, 83 (10), pp 2375–2379


E.D. Jemmis, G. Subramanian and G.N. Srinivas, Boron Analogs of Cyclopropenium Cation: B3H6

+, the First Three Membered Nonplanar 2π Aromatic, J. Am. Chem. Soc., 114, 7939-7941 (1992).

BB

B

+

Schulenberg, N., Wadepohl, H. and Himmel, H.-J. (2011), Synthesis and Characterization of a Doubly

Base-Stabilized B3H6+ Analogue. Angew. Chem. Int.

Ed. Engl. doi: 10.1002/anie.201104834, 2011.


13

C

CC

B

C C

C

B B

B

B

B

B B

B

BB

B

+ + +

CC

C

C

BB

B

B

(4n+2) π electrons


14

C C

CC

CC CC

CC

C

CC

C

-2

+3

+

(4n+2) π electrons

B B

B

B B

MgB2

XCC

C

CC

+

X-

acid

Stock, 1912

Masamune, 1974


15

CC

C

CC

+ C

C

CC

C

-

(4n+2) π electrons

- 2 e

(4n+2) electrons

B B

B

B B


16

B B

B

B B

C C

CC

CC CC

CC

C

CC

C

-2

+3

+

(4n+2) π electrons

XCC

C

CC

+

X-

MgB2 acid

Stock, 1912-32

Masamune, 1974


17

C

-1

+3

(4n+2) π electrons

CCCC C

C

C

CC

C

CC C

C

C C

+2

+

2 X-

BB B

B

BB

X

X

CC C

C

C C

Hogeveen 1975

2

Stock

MgB2 acid


18

+2

(4n+2) π electrons

- 2 e

(4n+2) electrons

C

C

C

C

C

C

CC C

C

C C B

B B

B

BB

BBBBBB


Li Be B CHHH

+ 2+

3

1 58

o

o

oo


CC

C

CC

CC C

C

C C

BB B

B

BB


M

H θ2

CCOO

COθ1

n 3 4 5 6

M Co Fe Mn Cr

θ1

θ2

104.0

25.0

97.0

6.0

92.0

0.0

88.0

-3.0

M M More DiffuseLess Diffuse

CnHnM(CO)3


22

+2

(4n+2) π electrons

- 2 e

(4n+2) electrons

C

C

C

C

C

C

CC C

C

C C B

B B

B

BB

BBBBBB


23

+2

(4n+2) π electrons

- 2 e

(4n+2) electrons

C

C

C

C

C

C

CC C

C

C C

BBBBBB

- 2 e C C

C

C

C C

+4

B

B

B B

B

B

-2

B B

B

C

C B


24

The ring – cap matching becomes more crucial when there are two caps interacting from either side of the ring

HHH H

H H

Si2B4 B62- C2B4


25

Explanation of relative stability of positional isomers

0.0 35.3 57.1

0.0 9.7

65.8 41.5

0.0

16.6

Relative stabilization energy in kcal/mol

BB

C

C

BBB

B

B

C

CB

B

B

B

CC

C

B

C

BB

BB

B

B

CCB

BBB

B

B

CC

BB

B

B

C

BC

BB B

C

C

B B

B

C

C

B B


BB B

B

BB

BB

B

BB B

BB B

B

B B

B B

B

B BB


26.6

24.2


COMMONLY FOUND BORANES ARE BASED ON POLYHEDRA. ICOSAHEDRAL B12H12

-2 MOST FAVOURED.

ELEMENTAL BORON HAS MOSTLY ICOSAHEDRAL UNITS

BnHn-2


Longuet-Higgins 1955

B12H12-2


Synthesis, Structure, Bonding, Reactions, Theoretical Studies

styx formalism to predict the structure of boranes s # BHB 3c-2e t # BBB 3c-2e y # BB 2c-2eh x # BH 2c-2e BpHp+q s=p-t, x=q-s, 2y=s-x

W. N. Lipscomb 30 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science,

Bangalore

Rudolf Diagram

R. E. Williams


Wade’s n+1 Skeletal Electron Pair Rule

Mol Formul

a

n ep

BH CH

ep q

B12H12 12 13 12 0 12 -2

B11H11 11 13 11 0 11 -4

C2B9H11 11 13 9 3 12 -2

C3B8H11 11 13 8 4.5

12.5

-1

n + 1 n + 2

Wade, Williams, Mingos, Rudolf

H

H H

n

2n

n-1

n


C6H6 C6H6+2

C4B2H6 B6H10

C6H6+4

C2B4H6 B6H6

-2

The Organic Connection


COMMONLY FOUND BORANES ARE BASED ON POLYHEDRA. ICOSAHEDRAL B12H12

-2 MOST FAVOURED. THIS IS CHANGED WHEN OTHER ELEMENTS ARE INTRODUCED. THE BRICKS ARE NOT THE SAME.

BnHn-2


39

Structure of some commonly found polyhedral boranes


40

1. M(R)-C2B4H6 a) Ga(CH3)-2,3-C2B4H6 b) Ga(CMe3)-2,3-(CSiMe3)2B4H4 (c) Ga(CMe3)-2,4-(CSiMe3)2B4H4 d) Ga(C10N2H8)(tBu)-2,3-(CSiMe3)2B4H4. 2C6H6 e) Ga(C10N2H8)(tBu) -2,4-(CSiMe3)2B4H4. 2C6H6 f) Ga(C8N4H6)(tBu)-2,4-(CSiMe3)2B4H4 g) Ga(Cl)(CH2NMe2)2-2,3-(CSiMe3)2B4H4.C6H6 h) Ga(Cl)(CH2NMe2)2-2,4-(CSiMe3)2B4H4.C6H6 i) In(CH3)-2,3-C2B4H6 j) In(CHMe2)-2,3-(CSiMe3)B4H4 k) In(CHMe2)-2,4-(CSiMe3)B4H4 l) In(C10N2H8)(CHMe2)-2,3-(CSiMe3)2B4H4 m) In(C10N2H8)(CHMe2)-2,4-(CSiMe3)2B4H4 n) In(C8N4H6) (CHMe2)-2,3- (CSiMe3)2B4H4

CBBBGaBC

CB

B

B

Ga

BC


41

2. M(R)-C2B9H11 a)  Ga(C2H5)-2,3-C2B10H11 b) [Al (Me) B11H11]2-. [AsPh3]2 c) Al(Me)-2,3-C2B9H11 d) Al(C2H5)-2,3-C2B9H11 e) Al(Me)2-2,3-C2B9H11 f) Al(Et)(PEt3)2-2,3-C2B9H11 g) Tl-2,3-C2B9H11. PPh3

CBBBGaBC

BB

C B

B

B

BB

Ga

C

B

B


Elemental boron - B12 units Condensed polyhedral Boranes What are the electronic requirements? Electron Counting Rules for Condensed polyhedral boranes


B12H12-2

N+1 electron pairs - Wade

B20H16

B30H24


The mno Rule for Polycondensed Boranes, Metallaboranes, and Metallocenes

m+n+o skeletal electron pairs m à number of polyhedra n à number of vertices o à number of single atom bridging


m+n+o = 2+21+0 = 23 ep 18BH + 3B à 18+4.5 = 22.5 ep -1 charge B12H12

2- m=1, n=12, o=0 à Wades n+1 Rules

B21H18-

m = # polyhedra n = # vertices o = # single atom bridges


B30H24 m+n+o = 3+30+0 = 33 ep 24BH + 6B à 24 + 9 =33 ep.

neutral


m + n + o =2 + 20 +0 = 22ep 16BH + 4B 16 + 6 = 22ep, Neutral

Synthesised 40 years ago by Lipscomb and Muettertties. Neutral Molecule.

B20H16


Co(C2B9H11)2-1

3 + 12 + 36 +1 = 52 e

m+n+o2+23+126 epairs52e

Examples for Single atom bridge (single vertex sharing)


C & E News


B19H22-1 and

not B19H20-1

m+n+o = 2+19+0+2 = 23ep

(BH)17B2H3- =

17+3+1.5+0.5 = 22ep

J. A. Dopke, D. R. Powell, D. Gaines, Inorganic Chemistry, 39, 463 (2000), J. T. Spencer etal, Inorg. Chem. Commun. 5, 274, (2002).

The two electron deficiency is not noticed because it was not anticipated. The X-ray structure was refined assuming B19H20

-.The Mass spectra gave

consistently two mass units higher than calculated. The structure should be B19H22

-


B12H16 B13H19

B16H20 B18H20

2-

n-B18H22 iso-B18H22


C6H6 C6H6+2

C4B2H6 B6H10

C6H6+4

C2B4H6 B6H6

-2

The Organic Connection


Hückel 4n+2 p Electron Rule A subset of the mno Rule

B14H12 -2, two hexagonalbipyramids sharing an edge

m+n +o =2+14 =16ep 12(BH) + 2B =12+3 =15ep -2 charge


m+n+o+p = 2+12+0+2 = 16 ep 10(BH) +2(B) = 10+ 3 = 13ep -6 charge

m+n+o+p = 2+10+0+4=16ep

8(BH) +2B =8 + 3 =11ep -10 charge

B12H10-6, C4B8H10

-2

B10H8-10 ,C10H8

(4n+2)π =10e + 22 C-C bonding electrons =16ep 58 Eluvathingal D. Jemmis, Dept of Inorganic and Physical Chemistry, Indian Institute of Science,

Bangalore

26.6

24.2

-2


If Buckminster Fuller had his way, boron would have the structure

Everything in the universe seems to be made up of icosahedron, including viral capsids.


Even the universe is of icosahedral symmetry?


α-Rhombohedral Boron - B12

6 borons from 2c-2e B-B bonds 6 borons from 3c-2e B-B-B bonds. This leaves 6-(2/3)6 = 2 electrons for the B12 skeletal bondings


Ideally elemental boron should have each B12 surrounded by 12 B12 , but this creates problem in space filling; this is present in Y24B1584 but with many defects. (YB66)24 will not be discussed today - we do not understand it enough. Structure of beta-rhombohedral boron and related slides will be in another presentation.


CD212-slides-1.pdf - Inorganic and Physical Chemistry

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