METAL-ORGANIC COMPOUNDS

Organoboron Compounds ROY M. ADAMS Callery Chemical Co., Callery, Pa., and Geneva College, Beaver Falls, Pa.

Downloaded by STANFORD UNIV GREEN LIBR on March 16, 2013 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch010

In this paper the definition of organoboron compounds is limited to those containing boron-carbon bonds. The nomenclature is that proposed by Wartik and Schaeffer and the Organic Subcommittee on Boron Nomenclature (116, 159). Preparations Trialkylboranes or Triarylboranes. The first report of the preparation of boron-carbon bonds was made by Frankland almost one hundred years ago. Triethylborane was prepared by the reaction of diethyl zinc with ethyl borate. 3(C H ) Zn + 2B(OC H ) --> 2(C H ) B + 3Zn(OC H ) 2

5

2

2

5 3

2

5

3

2

5 2

As a result, the alkylboranes are sometimes referred to as Frankland reagents by European writers (52). Many alkyl- and arylboranes have been prepared by similar methods using alkoxy- or haloboranes as the boron source, an alkyl or aryl halide as the carbon source, and an active metal as the condensing agent. B Y + 6M + 3RX

BR + 3MY + 3MX

3

3

Y = halide, oxide or alkoxide; X = halide; M = Li, Na, Mg, Zn, or Al; R is alkyl or aryl. In most cases the intermediate metal alkyl or alkyl metal halide was isolated. In the first preparations of arylboranes, diarylmercury compounds were used (16, 37, 69, 77-80, 82, 83, 99, 106, 107, 148, 162). In the case of hydrocarbons which react with active metals, the hydrocarbon has sometimes been used as the carbon source—e.g., naphthalene (88). Ethylene has also been used as the carbon source in forming an intermediate alkylaluminum halide (124). Al + AlCls + C H 2

C H A1C1 + (C H ) A1C1

4

2

5

2

2

5 2

The preparation of a boron-carbon bond directly from a boron compound and a hydrocarbon was first reported by Pace. Attempts to reproduce this preparation have been unsuccessful (118). Arnold has patented the reaction of acetylene with trichloroborane in the presence of mercurous chloride to form chlorovinylborane (2). Hg Cl BCI3 + C H > CI—CH=CH—BC1 The ease of elimination of acetylene, by these compounds, in the presence of bases limits their usefulness (12). 2

2

H

2

2

2

H

Cl—C=C—BC1 + 3 0 H - -» B(OH) + C H + 3C1~ 2

3

2

2

Hurd has reported the preparation of triethylborane from ethylene and diborane. The kinetics of this reaction was studied by Whatley and Pease (64, 161). B H + 6C H -» 2(C II ) B 87 2

6

2

4

2

f)

3

In METAL-ORGANIC COMPOUNDS; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

88

ADVANCES IN CHEMISTRY SERIES

O t h e r s h a v e s t u d i e d t h e r e a c t i o n of d i b o r a n e w i t h u n s a t u r a t e d o r g a n i c c o m p o u n d s , b u t t h e p r o d u c t s a r e u s u a l l y p o l y m e r i c (114, 147, 14&)S c h l e s i n g e r f o u n d t h a t t h e r e a c t i o n of d i b o r a n e w i t h m e t a l a l k y l s g e n e r a l l y g a v e m e t a l b o r o h y d r i d e s a n d a l k y l boranes (141)—e.g., ( C H ) A 1 + 2 B H -> A 1 ( B H ) + ( C H ) B 3

3

2

6

4

3

3

B r o k a w a n d Pease f o u n d t r i e t h y l b o r a n e a m o n g a l u m i n u m borohydride w i t h ethylene.

3

the products

of the reaction of

A 1 ( B H ) + 1 2 C H -> A 1 ( C H ) + 3 ( C H ) B


4

3

2

4

2

5

3

2

5

3

M o n o - or Dialkylboranes or M o n o - or Diarylboranes. I n general, the preceding p r e p a r a t i o n s c a n be m o d i f i e d t o g i v e chiefly m o n o - o r d i a l k y l b o r a n e s by p r o p e r r e a c t a n t stoichiometry (167). BY

+ 6 M + R X -> B R Y

3

+ M Y+ M X

2

W i b e r g a n d F i s c h e r h a v e also f o u n d t h a t m o n o - o r d i a l k y l b o r a n e s m a y be p r e p a r e d b y t h e r e d i s t r i b u t i o n o f t r i a l k y l b o r a n e s w i t h h a l o - o r a l k o x y b o r a n e s (45-48, 162). BRg + B X

3

+ Β (OR) ;

>ioo° c .

3BR(X)OR

k

H C — € H B B r 3

6

4

3

3

6

3

4

+ (H CC H ) BBr

2

3

6

4

2

T h e only reported preparation of a mixed t r i a l k y l b o r a n e was b y K r a u s f r o m d i b u t y l b o r y l s o d i u m a n d m e t h y l i o d i d e (6). (C H ) BNa + CH I - » (C H ) BCH 4

9

2

3

4

9

2

+ Nal

3

L e t s i n g e r w a s able t o p r e p a r e p h e n y l ( l - n a p h t h y l ) h y d r o x y b o r a n e l-naphthyldialkoxyborane with phenyllithium. C H L i + ( 1 — C i o H ) B ( O R ) -> L i C H ( l — C i H ) B ( O R ) 6

6

7

2

6

6

0

7

b y the reaction of a

2

IHOH LiOH + 2ROH +C H (1—Ci H )BOH 6

6

0

7

A t t e m p t s t o p r e p a r e m i x e d a l k y l a r y l b o r a n e s were u n s u c c e s s f u l (88). T h e dialkylhaloboranes c a n be prepared b y reaction of the t r i a l k y l b o r a n e w i t h a hydrogen halide. ( C H ) B + H C 1 -> ( C H ) B C 1 + C H 3

3

3

2

4

T h e a d d i t i o n of a l u m i n u m halide a n d increased temperatures result i n the r e m o v a l of a second m o l e c u l e o f t h e a l k a n e (11, 52, 143, 162). (CH ) BC1 + HC1 ^ 3

CH BC1

2

3

2

+ CH

4

L o n g has r e p o r t e d t h e p r e p a r a t i o n of d i p r o p y l i o d o b o r a n e f r o m t r i p r o p y l b o r a n e a n d iodine at 140°C. ( C H ) B + I -> ( C H ) B I + B H I 3

7

3

2

3

7

2

3

7

T h e iodine m a y be replaced b y chlorine o r bromine b y reaction w i t h the appropriate a n t i m o n y h a l i d e (95). 3 ( C s H ) B I + S b C l -> 3 ( C H ) B C 1 + S b l 7

2

3

3

7

2

3


ADAMS-ORGANOBORON COMPOUNDS

89

T h e a l k y l fluoroboranes were first p r e p a r e d b y B u r g f r o m t r i f l u o r o b o r a n e a n d t h e a n h y d r i d e of t h e c o r r e s p o n d i n g h y d r o x y b o r a n e (20). (CH BO) 3

3

+ 3 B F -> C H B F 3

3

+ (FBO)

2

3

3 ( C H ) , B O B ( C H ) , + 3 B F -> 6 ( C H ) B F + ( F B O ) 3

3

3

3

2

3

M c C u s k e r f o u n d t h a t B u r g ' s m e t h o d was g e n e r a l l y s a t i s f a c t o r y f o r p r e p a r i n g the a l k y l d i f l u o r o b o r a n e s a n d t h a t t h e y were stable t o d i s p r o p o r t i o n a t i o n . T h e s e c o n d a r y a n d t e r t i a r y c o m p o u n d s were s p o n t a n e o u s l y flammable. The trialkylboroxins and alu m i n u m c h l o r i d e gave e v i d e n c e of the f o r m a t i o n of a l k y l d i c h l o r o b o r a n e s (98).


A l k y l a l k o x y b o r a n e s . T h e m o n o a l k y l d i a l k o x y b o r a n e s m a y be p r e p a r e d b y the slow o x i d a t i o n o f a l k y l b o r a n e s (52) R B + 0 -> R B ( O R ) 3

2

2

o r b y t h e a l c o h o l y s i s of t h e m o n o a l k y l h a l o b o r a n e s o r t h e m o n o a l k y l d i b o r a n e s . CH BC1 3

CH B H 3

2

+ 2 H O C H -> C H B ( O C H )

2

2

5

+ 5HOC H

5

2

3

2

5

6

3

2

+ 2HC1

2

CH B(OC H ) 6

+ B(OC H ) + 5H

2

2

5

3

2

T h e m o n o a l k y l d i a l k o x y b o r a n e s are e v i d e n t l y i n t e r m e d i a t e s i n t h e r e a c t i o n s of t h e m e t a l a l k y l s w i t h excess t r i a l k o x y b o r a n e , b u t t h e y h a v e s e l d o m b e e n i s o l a t e d (llfi). W i t h m o i s t a i r the t r i a l k y l b o r a n e s are r e p o r t e d t o y i e l d d i a l k y l a l k o x y b o r a n e s (67). (C H ) B + 0 4

9

3

2

m

°

1 S t U r e

> (C H ) BOC H 4

9

2

4

9

D i - n - b u t o x y p h e n y l b o r a n e r e a c t e d w i t h p h o s p h o r u s p e n t a c h l o r i d e t o give p h e n y l dichloroborane. S i m i l a r r e a c t i o n s were o b t a i n e d w i t h b o t h m - a n d p- b i s - ( d i b u t o x y b o r y l ) benzenes. A t t e m p t s t o reduce t h e p h e n y l d i c h l o r o b o r a n e s w i t h l i t h i u m a l u m i n u m h y d r i d e d i d not give phenylborane. P h e n y l d i f l u o r o b o r a n e was p r e p a r e d b y the r e a c t i o n of d i m e t h o x y p h e n y l b o r a n e w i t h t r i f l u o r o b o r a n e (99). C H B(OC H ) 6

5

4

9

3C H B(OCH ) 6

6

3

+ P C 1 -> C H B C 1 + ( C H 0 ) P C 1 ?

2

5

2

+ 2BF

6

5

2

3C H BF

3

6

6

4

2

9

2

3

+ 2B(OCH ) 3

3

L e t s i n g e r has p r e p a r e d a n u m b e r of d i a r y l a m i n o e t h o x y b o r a n e s a n d f o u n d t h e m t o be u n u s u a l l y stable because of the i n t e r n a l d a t i v e b o n d Ar

I ArB

Ο

î

I

H N

C H

2

H

2

2

H e f o u n d these c o m p o u n d s c o n v e n i e n t f o r i s o l a t i n g d i a r y l h y d r o x y b o r a n e s , a n d t h e d i e t h a n o l a m i n e d e r i v a t i v e s f o r t h e i s o l a t i o n of t h e a r y l d i h y d r o x y b o r a n e s (90). H e also r e p o r t e d t h e i s o l a t i o n of the first r e p o r t e d h e t e r o c y c l i c c o m p o u n d w i t h o n l y c a r b o n a n d b o r o n i n the r i n g , b y the f o l l o w i n g r e a c t i o n (91 ) : CH

2

C H

2

(J^J) + ( C H 0 ) B 4

9

3


90

ADVANCES IN CHEMISTRY SERIES K u i v i l a has i n v e s t i g a t e d t h e ethers o f p h e n y l d i h y d r o x y b o r a n e w i t h s e v e r a l p o l y a l -

cohols, i n c l u d i n g s o r b i t o l , m a n n i t o l , p i n a c o l , c a t e c h o l , p e n t a e r y t h r i t o l , d i e t h y l D - t a r t r a t e , a n d c i s - i n d a n - l , 2 - d i o l . T h e s e were p r e c i p i t a t e d b y m e r e l y a d d i n g the p h e n y l d i h y d r o x y b o r a n e t o a s a t u r a t e d s o l u t i o n of t h e p o l y o l (86). O—CR ArB(OH)

+ (R COH)

2

2

2

+

-> A r — Β

2

O—CR

2H 0 2

2

H e also f o u n d t h a t α - h y d r o x y i s o b u t y r i c a c i d ties u p p h e n y l d i h y d r o x y b o r a n e as a c o m p l e x a n i o n (84).


OH

o C H B(OH) 6

6

3

2

I o-

CH CH

H 0

+

c=o

CGHB- - B

+ H(CH ) —CH(OH)COOH •

2

3

+

3

3

Recent w o r k b y Letsinger has demonstrated t h a t the d i a l k y l a l k o x y b o r a n e s m a y be p r e p a r e d f r o m G r i g n a r d reagents a n d a l k o x y b o r a n e s b y t h e use o f 1,2-ethandiol t o s e p arate the d i a l k y l f r o m the m o n o a l k y l a t e d p r o d u c t . T h e r e s u l t i n g ethers differ w i d e l y i n v o l a t i l i t y (89). 2(C H ) BOCH 4

9

2

C H B(OCH ) 4

9

3

2

+ H O C H C H O H -» ( C H ) B O C H C H O B ( C H )

3

2

4

2

+ HOCH CH OH 2

9

2

2

- C H B(OCH -)

2

4

9

2

2

9

+

2

2CH OH 3

2CH OH

+

2

4

3

M e e r w e i n found i n a n u n u s u a l reaction t h a t trialkylboranes reacted w i t h aldehydes t o give d i a l k y l a l k o x y b o r a n e s

(102).

(0 Η ) Β + C H C H O -> ( C H ) B O C H C H 2

Δ

3

6

5

2

5

2

2

6

5

+

C H 2

4

B o r o n b o n d s t o m o s t elements o t h e r t h a n c a r b o n h y d r o l y z e to f o r m the h y d r o x y b o r a n e s (41, 43, 70, 134, 139, 142). R BY 2

+ H O H -> R B O H +

H Y

2

R = a l k y l or a r y l , Y = halogen, a l k o x i d e , h y d r i d e , amide, or oxide. T h e a l k y l h y d r o x y b o r a n e s lose w a t e r r e a d i l y (43). 2R BOH

H O H +

2

3RB(OH)

(RBO)

2

R BOBR 2

3

2

+ 3H 0 2

cyclic

T h e t r i a l k y l b o r o x i n s c a n also b e p r e p a r e d f r o m b o r i c o x i d e a n d t h e t r i a l k y l b o r a n e (58). B 0 2

3

+ (CH ) B ^± (CH ) B 0 3

3

3

3

3

3

Alkylboranes with F u n c t i o n a l Groups i n the Side C h a i n . L y l e has s t u d i e d t h e p r e p a r a t i o n o f t r i a l k y l boranes w i t h t e r m i n a l o r a l p h a d o u b l e b o n d s or e t h e r e a l g r o u p s i n t h e side c h a i n . H e f o u n d t h a t the s t a b i l i t y of t h e G r i g n a r d reagent w a s g e n e r a l l y l i m i t i n g i n these p r e p a r a t i o n s . P h y s i c a l p r o p e r t i e s a n d i n f r a r e d s p e c t r a g a v e evidence of i n t r a m o l e c u l a r a s s o c i a t i o n (97). H H C — C 2

Η,Ο^ \

/ CH3OC3H6

- C H

H C

C H

I

Ο—CH Β

H C 2

2

il

2

3

•

\

2

/

B-

\

C4H7

0 Η 4

7

0 ΗβΟΟΗ3 3


91


R o t h s t e i n a n d S a v i l l e obtained b i s ( d i a l l y l b o r y l ) oxide a n d t r i - n - b u t y l b o r a n e r a t h e r t h a n the expected a l l y l d i - n - b u t y l b o r a n e f r o m the reaction of allylmagnesium bromide with di-n-butylbromoborane.

T h e e v i d e n t course o f t h e r e a c t i o n w a s

2 C H M g B r + 3 ( C H ) B B r -> 2 ( C H ) B + ( C H ) B B r + 2 M g B r 3

6

4

9

2

4

9

3

3

5

2

2 ( C H ) B B r + H O H -> 2 H B r + ( C H ) B O B ( C H 5 ) 3

5

2

3

5

2

3

2

2

B i s ( d i a l l y l b o r y l ) o x i d e w a s also o b t a i n e d f r o m t h e r e a c t i o n o f a l l y l m a g n e s i u m b r o mide with trifluoroborane

(123).

R i t t e r has prepared several v i n y l - t y p e boranes b y the reaction of v i n y l s o d i u m o r propenyllithium with dimethylbromoborane. C H = C H N a + ( C H ) B B r -> ( C H ) B C H = C H


2

3

2

3

2

2

+ NaBr

T h e p r o d u c t s were u n u s u a l l y s t a b l e t o d i s p r o p o r t i o n a t i o n , a p p a r e n t l y because of p i bonding between the v i n y l group a n d the boron H C 3

H C

\

/

H H H B — C = C H ^± H

3

C \

3

/

H H B-=C—CH

C

3

M e t h y l d i v i n y l , t r i v i n y l , a n d t r i m e t h y l b o r a n e s were o b t a i n e d as w e l l as t h e u n u s u a l b i s ( d i m e t h y l b o r y l ) ethane, p r o b a b l y f r o m ethenyldisodium, w h i c h is k n o w n t o be a n i m purity i n vinylsodium preparations (115). 2 ( C H ) B B r + N a C H = C H N a -> 2 N a B r + ( C H ) B C H = C H B ( C H ) 3

2

3

2

3

Schlesinger prepared

Diborylalkanes a n d Diborylbenzenes.

2

bis(dichloroboryl)-

e t h a n e b y t h e r e a c t i o n of d i b o r o n t e t r a c h l o r i d e w i t h e t h y l e n e B C1 + C H 2

4

2

4

-> C 1 B C H C H B C 1 2

2

2

2

T h e chlorines m a y be replaced b y methoxy groups b y treatment w i t h methanol a n d b y m e t h y l groups b y treatment w i t h d i m e t h y l zinc. C1 BCH CH BC1

2

+ 4 C H O H -> ( C H 0 ) B C H C H B ( O C H )

C1 BCH CH BC1

2

+ 2 ( C H ) Z n -> 2 Z n C l

2

2

2

2

2

2

3

3

3

2

2

2

2

2

3

+ 4HC1

2

+ (CH ) BCH CH B(CH ) 3

2

2

2

3

2

T h e m e t h y l d e r i v a t i v e decomposes s l o w l y t o give t r i m e t h y l b o r a n e a n d unidentified b y products. S i m i l a r p r o d u c t s h a v e been p r e p a r e d b y t h e r e a c t i o n of d i b o r o n t e t r a c h l o r i d e w i t h propene, 2-butene, cyclopropane, a n d acetylene (154). T h e r e p l a c e m e n t of t h e c h l o r i n e s b y h y d r o g e n h a s n o t g i v e n a s t a b l e p r o d u c t (131). M c E w e n h a s also p r e p a r e d t h e m- a n d p - b i s d i h y d r o x y b o r y l benzenes f r o m t h e corresponding dibromobenzenes. T h e d i l i t h i u m b e n z e n e s were p r e p a r e d b y exchange w i t h b u t y l l i t h i u m . T h e l i t h i u m c o m p o u n d was then treated w i t h m e t h y l borate. A similar preparation was carried out using G r i g n a r d procedures. T h e s t r u c t u r e of e a c h c o m p o u n d w a s p r o v e d b y cleavage w i t h b r o m i n e t o t h e r e s p e c t i v e d i b r o m o b e n z e n e a n d b o r i c a c i d . T h e s e c o m p o u n d s were also p r e p a r e d f r o m t h e i n t e r m e d i a t e b r o m o p h e n y l boroxins

(99).

Br— 4

9

LifSu

+ 2C H Br 4

9

L i — / ~ Λ — L - Lii + B B (( O OC CH H )) - > ( C ( C H sHO ^ 0B ) fB / ~ ^B \ ( O C H , ) i " + 2Li+ 33

33

3

2

\=/

Ι6 6HOH

(HO) B C H H B H B H C H 3

2

3

2

+ 2(CH ) 0 :B H

3

3

2

3

R o s e n b l u m found that t r i b u t y l b o r a n e decomposed o n heating t o give butene a n d d i b u t y l d i b o r a n e (122). 2 ( C H ) B -> 4 C H 4

9

3

4

8

+ (C H ) B H 4

9

2

2

4

Reactions M a n y o f t h e r e a c t i o n s of t h e a l k y l - a n d a r y l b o r a n e s h a v e b e e n c o v e r e d i n t h e p r e c e d i n g sections. W i t h H y d r o g e n . T h e a l k y l b o r a n e s d o n o t react w i t h h y d r o g e n a t o r d i n a r y t e m p e r a t u r e a n d pressure ; h o w e v e r , s o l i d p y r o l y s i s p r o d u c t s m a y be f o r m e d u n d e r e x t r e m e c o n d i t i o n s (5). W i t h M e t a l s . K r a u s e first r e p o r t e d a r e a c t i o n b e t w e e n s o d i u m a n d t r i p h e n y l borane t o give a colored crystalline product, sodium t r i p h e n y l b o r a t e ( - l ) ether

(C H ) B + N a 6

5

3

> NaB(C H ) 6

5

3

T h e product reacted i n s t a n t l y w i t h oxygen. I t w a s t i t r a t a b l e w i t h i o d i n e i n ether a n d r e a c t e d w i t h a l k y l halides a n d c a r b o n d i o x i d e . T h e e t h e r e a l s o l u t i o n c o n d u c t e d elec t r i c i t y . T h e sodium could be removed b y shaking w i t h m e r c u r y . T r i - p - t o l y l b o r a n e b e h a v e d s i m i l a r l y (81). B e n t s t u d i e d s i m i l a r r e a c t i o n s w i t h t r i n a p h t h y l b o r a n e a n d f o u n d t h a t a second a t o m of s o d i u m c o u l d b e a d d e d . H e s t u d i e d t h e c o n d u c t i v i t i e s of t h e o t h e r s o l u t i o n s o f b o t h t h e m o n o - a n d d i s o d i u m c o m p l e x e s (9, 36). B(l—GoH ) 7

+ N a - > NaB(l—Ci H )

3

0

NaB(l—Ci H ) 0

7

3

7

3

+ N a -> N a B ( l — C i H ) 2

9

7

3

C h u has s t u d i e d t h e m a g n e t i c s u s c e p t i b i l i t y a n d v i s i b l e s p e c t r u m of s o d i u m t r i phenylborate(-l). H e found t h a t it was not paramagnetic a n d assumed t h a t the anions m u s t be d i m e r i c . S o d i u m t r i m e s i t y l b o r a t e ( - 1 ) w a s f o u n d t o h a v e one u n p a i r e d e l e c t r o n . L a c k o f d i m e r i z a t i o n i s a p p a r e n t l y due t o steric f a c t o r s . T r i s - l ( 2 - m e t h y l n a p h t h y l ) b o r a n e r e m o v e d t h e s o d i u m f r o m s o d i u m t r i m e s i t y l b o r a t e ( - 1 ) , p r e s u m a b l y because o f h i g h e r e l e c t r o n a f f i n i t y (32, 33). B ( C n H ) , + NaB(CeHii) -> N a B ( C n H ) + B ( C H ) 9

8

1 0

3

9

n

3

K r a u s e r e p o r t e d t h a t u n l i k e t h e t r i a r y l b o r a n e s , t h e t r i a l k y l b o r a n e s d i d n o t react w i t h m e t a l s (80). H o w e v e r , K r a u s has r e p o r t e d t h e r e a c t i o n of d i b u t y l c h l o r o b o r a n e i n ether w i t h sodium-potassium alloy t o give d i b u t y l b o r y l (C H ) BC1 + M - » M C I + (C H ) B 4

9

2

4

9

2

where M is 1 equivalent of sodium potassium alloy. I n comparison W i b e r g found t h a t the reaction of dimethylchloroborane w i t h g a v e t r i m e t h y l b o r a n e a n d a p o l y m e r i c m a t e r i a l (167).


sodium

93


B u r g found that u p o n contact w i t h sodium i n l i q u i d a m m o n i a at —7 8 ° C . t e t r a m e t h y l d i b o r a n e is s p l i t e q u a l l y i n t o a m m o n i a - d i m e t h y l b o r a n e a n d a n u n u s u a l s a l t . (CH ) BH B(CH ) 3

2

2

3

+ 2 N a + N H -> ( C H ) H B — N H

2

3

3

2

+ NaBH(CH )

3

3

2

T h i s salt is stable as a w h i t e s o l i d i n \^acuum e v e n a t 9 0 ° C . I t h y d r o l y z e s r a p i d l y a n d quantitatively to dimethylhydroxyborane, hydrogen, a n d sodium hydroxide. T r i m e t h y l b o r a n e is a d d e d i n l i q u i d a m m o n i a t o f o r m a y e l l o w s o l i d w h i c h is also s t a b l e i n v a c u u m a t 1 0 0 ° C . {23). Na BH(CH )

2

+ 3 H O H -> 2 N a O H + 2 H + ( C H ) B O H

Na BH(CH )

2

+ B(CH ) -* Na BH(CH ) B(CH )

2

3


2

3

2

3

3

2

3

3

2

3

2

3

T h e c o r r e s p o n d i n g p o t a s s i u m salt w a s p r e p a r e d b y t h e same m e t h o d s , b u t a t t e m p t s t o p r e p a r e t h e l i t h i u m salt were u n s u c c e s s f u l . T h e s o d i u m s a l t reduces c h l o r o s i l a n e t o silane a n d reacts w i t h a q u e o u s h y d r o c h l o r i c a c i d t o f o r m a p p a r e n t l y p o l y m e r i c s o d i u m d i m e t h y l b o r y l (30). Na HB(CH ) 2

3

+ C l S i H -> N a C l + S i H

2

3

S o d i u m d i m e t h y l b o r y l reacted h i g h l y r e d u c i n g residue (25).

+ [NaB(CH ) ]x

4

3

with ammonia to form

NaB(CH ) 3

+ N H -> ( C H ) B N H

2

3

3

2

2

aminodimethylborane

and a

+ NaH?

2

Reactions with M e t a l H y d r i d e s or Organometallics. Fisher prepared lithium b o r o h y d r i d e b y t h e h y d r o g é n a t i o n of a l i t h i u m h y d r i d e - t r i e t h y l b o r a n e a d d u c t a t 2 4 0 ° C . u n d e r 2000 p . s . i . i n c y c l o h e x a n e (50). LiBH(C H ) 2

5

+ 3H

3

2 4

2

°° > LiBH C ,

+ 3C H

4

2

6

3000 p.s.i.

T r i e t h y l b o r a n e f o r m s a l i q u i d 1 t o 1 a d d u c t w i t h s o d i u m h y d r i d e w h i c h has n o t b e e n c h a r a c t e r i z e d . L i t h i u m h y d r i d e dissolves i n a d i e t h y l e t h e r s o l u t i o n of t r i m e t h y l b o r a n e a n d is r e c o v e r e d as l i t h i u m h y d r i d e u p o n e v a p o r a t i o n of t h e s o l u t i o n . E v i d e n t l y a r e v e r s i b l y f o r m e d l i t h i u m h y d r i d e - t r i m e t h y l b o r a n e a d d u c t i s r e s p o n s i b l e (19). L i H + B ( C H ) ^± L i B H ( C H ) 3

3

3

3

A l u m i n u m h y d r i d e i n ether a n d t r i m e t h y l b o r a n e reacted; however, t h e p r o d u c t could n o t be freed f r o m the ether (132). Schlesinger found t h a t t r i m e t h y l b o r a n e reacted w i t h l i t h i u m a l u m i n u m h y d r i d e t o form lithium methyltrihydroaluminate and dimethylaluminum hydride (160). LiAlH

4

+ ( C H ) B -> L i A l H C H 3

3

3

+ (CH ) A1H

3

3

2

T r i m e t h y l b o r a n e reacted w i t h u r a n i u m b o r o h y d r i d e t o give m e t h y l a t e d derivatives. M e t h y l t r i h y d r o b o r a t o t r i s ( t e t r a h y d r o b o r a t o ) u r a n i u m is t h e m o s t v o l a t i l e k n o w n c o m p o u n d of u r a n i u m . T e t r a k i s ( m o n o m e t h y l t r i h y d r o b o r a t o ) u r a n i u m w a s also i s o l a t e d . T h e s e m a t e r i a l s r e a c t e d w i t h w a t e r a n d h y d r o g e n c h l o r i d e as follows (129): U ( B H ) ( B H C H ) + 1 2 H 0 -> U ( O H ) + 1 5 H + C H B ( O H )

2

U ( B H ) ( B H C H ) + 6HC1 -> U C 1 + 6 H + 3/2 B H

3

4

4

3

3

3

3

3

2

4

3

2

4

3

2

2

U ( B H C H ) + 1 2 H C 1 -> U C 1 + 1 2 H + 4 C H B C 1 3

3

4

2

3

6

+ 3HB0

+ CH BC1

2

2

2

E a r l y a t t e m p t s t o react t r i m e t h y l b o r a n e w i t h m e t a l a l k y l s a n d a r y l s f a i l e d (153). H o w e v e r , Johnson found that t r i b u t y l b o r a n e reacted exothermally w i t h d i p h e n y l m a g nesium i n ether. Separation into t w o layers occurred. O n l y o n e m o l e of t r i b u t y l b o r a n e r e a c t e d w i t h o n e m o l e of d i p h e n y l m a g n e s i u m . T r i b u t y l b o r a n e r e a c t e d e x o t h e r m a l l y w i t h e t h y l l i t h i u m , b u t less v i g o r o u s l y w i t h b u t y l l i t h i u m a n d b u t y l m a g n e s i u m b r o m i d e . T r i b u t y l b o r a n e d i d n o t react w i t h d i b u t y l z i n c (69). LiC H 2

5

+ B(C H ) 4

Mg(C H ) 6

5

2

9

LiB(C H ) C H

3

4

9

3

2

5

+ B ( C H ) -> C H M g B ( C H ) C H 4

9

3

6

5

4

9

3

6

ô


94


Schlesinger found that e t h y l l i t h i u m added equal m o l a r quantities of t r i m e t h y l borane to form a white crystalline adduct (128). LiC H


2

+ B ( C H ) -> L i B ( C H ) C H

6

3

3

3

3

2

6

H u r d prepared l i t h i u m tetramethylborate b y the reaction of m e t h y l l i t h i u m w i t h t r i m e t h y l b o r a n e i n e t h y l ether. T h i s m a t e r i a l was stable i n v e r y d r y air, b u t sometimes ignited i n moist a i r . I t was soluble i n ether a n d dissolved w i t h o u t reaction i n water. A c i d i f i c a t i o n of t h e aqueous solution resulted i n t h e e v o l u t i o n of t r i m e t h y l b o r a n e . E l e c t r o l y s i s o f t h e a q u e o u s s o l u t i o n g a v e m e t h a n e , e t h a n e , a n d c y c l o p r o p a n e (65). W i t t i g f o u n d t h a t t r i p h e n y l b o r a n e forms stable complexes w i t h l i t h i u m h y d r i d e a n d b u t y l l i t h i u m (70). W i t t i g first reported the p r e p a r a t i o n of a t e t r a p h e n y l b o r a t e a n i o n b y t h e reaction of t r i p h e n y l b o r a n e w i t h p h e n y l l i t h i u m . LiC H 6

+ Β(Ο Η ) -> Li+B(C»H.)r

5

β

δ

3

H e also p r e p a r e d t h e h y d r o t r i p h e n y l b o r a t e a n i o n b y t h e r e a c t i o n o f l i t h i u m h y d r i d e with triphenylborane. L i H + B ( C H ) -> Li+ + B H ( C H ) r 6

6

3

6

5

A n u m b e r o f salts o f t h e t e t r a p h e n y l b o r a t e a n i o n were p r e p a r e d b y m e t a t h e s i s a n d t h e usefulness o f t h i s i o n i n t h e g r a v i m e t r i c d e t e r m i n a t i o n of p o t a s s i u m , r u b i d i u m , c e s i u m , a n d a m m o n i u m ions w a s p o i n t e d o u t . T h e u n u s u a l c o m p o u n d t e t r a p h e n y l p h o s p h o n i u m tetraphenylborate was prepared b o t h metathetically a n d b y the reaction of p e n t a phenylphosphorus a n d triphenylborane. P(C H ) 6

5

+ Β ( 0 Η ) -> ( C H ) P + + B ( C H ) -

8

6

δ

3

6

5

4

6

6

4

A t e t r a p h e n y l b i s m u t h o n i u m a n d a d i p h e n y l i o d o n i u m s a l t were s i m i l a r l y p r e p a r e d . H e also p r e p a r e d c y a n o t r i p h e n y l b o r a t e s b y t h e r e a c t i o n o f t r i p h e n y l b o r a n e w i t h m e t a l c y a n i d e s a n d c y a n o t r i h y d r o b o r a t e s b y t h e r e a c t i o n of l i t h i u m b o r o h y d r i d e w i t h h y d r o cyanic acid. These complex cyanoborates a r e r e m a r k a b l y stable t o h y d r o l y s i s a n d thermal decomposition. B ( C H ) + N a C N -> Na+ + B ( C N ) ( C H ) e

6

6

L1BH4

+ H O N -> L i

+ BH CN- + H

+

3

6

3

2

T h e h y d r o x y t r i p h e n y l b o r a t e a n i o n a n d t h e p h e n y l e t h y n y l t r i p h e n y l b o r a t e s were pared similarly.

pre

O H " + ( C H ) B -> B ( O H ) ( C H ) 6

5

3

6

5

3

C H C = C - + ( C H ) B -> B ( C = C — C I I ) ( C H ) 6

5

6

5

3

6

5

6

5

3

T h e s e c o m p o u n d s were u s u a l l y a n a l y z e d b y d e c o m p o s i t i o n w i t h a q u e o u s m e r c u r i c c h l o r i d e (172). (C H ) B- + 4HgCl 6

5

4

2

+ 3 H O H -> 4 C H H g C l + 4C1" + 3H+ + 3 B ( O H ) 6

5

8

T h e use o f t h e t e t r a p h e n y l b o r a t e a n i o n t o p r e c i p i t a t e t h e h e a v i e r a l k a l i m e t a l s w a s p a t e n t e d b y H e y l (62). A g r e a t d e a l of s t u d y h a s b e e n m a d e o f t h i s i o n as a n a n a lytical tool f o r the alkali metals. T h e analysis m a y be carried o u t gravimetrically, t i t r i m e t r i c a l l y w i t h s i l v e r n i t r a t e , o r c o n d u c t o m e t r i c a l l y (4, 51, 54, 57). K r a u s has studied the electrolytic properties of several t r i a r y l b o r a n e complexes w i t h s m a l l a n i o n s s u c h as h y d r o x i d e , fluoride, a n d a m i d e (72). Reactions with Oxygen a n d O x i d i z i n g Agents. G r u m m i t t r e p o r t e d t h a t t h e ease of o x i d a t i o n o f a l k y l b o r a n e s decreased w i t h i n c r e a s i n g a l k y l c h a i n l e n g t h a n d i n creased r a p i d l y i n t h e o r d e r p r i m a r y , s e c o n d a r y , t e r t i a r y . H e f o u n d i n d i c a t i o n o f p e r o x i d e i n t e r m e d i a t e s (60). B a m f o r d a n d N e w i t t f o u n d t h a t t r i m e t h y l b o r a n e o x i d i z e d m u c h less r e a d i l y t h a n


95

ADAMS—ORGANOBORON COMPOUNDS

t r i p r o p y l b o r a n e , t h a t t h e r e a c t i o n w a s a c h a i n process b e g i n n i n g a n d e n d i n g o n w a l l s , a n d t h a t i t w a s s t r o n g l y i n h i b i t e d b y m i x t u r e s of t r i f l u o r o b o r a n e a n d w a t e r ( 7 ) . T h e y found indications that trimethylborane formed a 1 to 1 addition product w i t h oxygen. Verhoek has corroborated this a n d isolated the adduct. H e f o u n d i t t o b e stable t o a i r a t r o o m t e m p e r a t u r e a n d a t m o s p h e r i c pressure a n d t o b e e q u i v a l e n t i n o x i d i z i n g p o w e r t o a t y p i c a l h y d r o p e r o x i d e o f t h e same m o l e c u l a r w e i g h t [157). T h e d i a r y l h y d r o x y b o r a n e s react w i t h c h l o r i n e w a t e r o r b r o m i n e w a t e r t o y i e l d t h e aryldihydroxyborane according to the following equation. Ar BOH + X 2

+ H 0 -> A r B ( O H ) + H X + A r X

2

2

2


I n t h e presence of excess h a l o g e n t h e a r y l d i h y d r o x y b o r a n e is d e c o m p o s e d t o b o r i c a c i d a c c o r d i n g t o t h e e q u a t i o n (1, 103) ArB(OH)

2

+ X

2

+ H 0 -> A r X + H X + B ( O H ) 2

3

K r a u s e r e p o r t e d t h a t t r i b e n z y l b o r a n e is s i m i l a r t o a l k y l b o r a n e s i n i t s l o w m e l t i n g point a n d reactivity w i t h oxygen. A l t h o u g h 1 - n a p h t h y l b o r a n e i s s t a b l e i n a i r , m o s t of the a r y l b o r a n e s o x i d i z e i n a i r t o f o r m t h e a r y l b o r o n o x i d e , b u t d o n o t i g n i t e . T h e y also react r a p i d l y w i t h alcohols (78, 79, 80, 82). A r B + 1/2 0 + H 0 -> A r B O + 2 A r O H 3

2

2

P h e n y l d i h y d r o x y b o r a n e reacts w i t h h y d r o g e n p e r o x i d e t o y i e l d p h e n o l a n d b o r i c a c i d . I t also reacts w i t h 5 0 % s o d i u m h y d r o x i d e , w a t e r u n d e r p r e s s u r e , o r b o i l i n g c o n c e n t r a t e d h y d r o c h l o r i c a c i d t o g i v e b e n z e n e a n d b o r i c a c i d (1). C H B(OH) 6

6

+ H 0

2

2

>C H OH + B(OH)

2

6

+ H 0 ^-^> C H 2

6

5

+ B(OH)

6

3

3

T h e d i a r y l h y d r o x y b o r a n e s react w i t h hydrogen peroxide t o y i e l d a r y l d i h y d r o x y boranes a c c o r d i n g t o t h e e q u a t i o n : R B O H + H 0 -> R B ( O H ) + R O H 2

2

2

2

I n t h e presence of excess h y d r o g e n p e r o x i d e b o r i c a c i d i s f o r m e d (101) : RB(OH)

2

+ H 0 -> R O H + B ( O H ) 2

2

3

T h e acid dissociation constants of a large n u m b e r of t h e a r y l d i h y d r o x y b o r a n e s h a v e b e e n s t u d i e d (173). Several a r y l d i h y d r o x y boranes are r a p i d l y oxidized b y alkaline potassium p e r m a n g a n a t e a t r o o m t e m p e r a t u r e . B o t h t h e 1- a n d 2 - n a p h t h y l d e r i v a t i v e s g i v e p h t h a l i c a c i d . o - T o l y l a n d o- a n d p - p h e n e t y l d e r i v a t i v e s a r e also r a p i d l y o x i d i z e d . T h e r a t e of o x i d a t i o n w i t h m - p h e n e t y l is m o d e r a t e , w h i l e p h e n y l a n d m - a n d p - t o l y l a r e r e s i s t a n t t o o x i d a t i o n of t h e benzene r i n g . T h e r e a c t i o n p r o b a b l y p r o c e e d s t h r o u g h t h e r e m o v a l of t h e d i h y d r o x y b o r y l g r o u p b y o x i d a t i o n . P h e n o l s a r e p r o d u c e d w h i c h a r e i n g e n e r a l r a p i d l y o x i d i z e d (10). T h e t o l y l d i h y d r o x y b o r a n e s are oxidized b y potassium permanganate t o the c a r b o x y l p h e n y l d i h y d r o x y b o r a n e (71). B e n z y l - a n d n a p h t h y l d i h y d r o x y b o r a n e s reduce s i l v e r n i t r a t e (70, 108). C i o H B ( O H ) + 2Ag+ + 2 H O H -> C i H O H + B ( O H ) + 2 A g + 211+ 7

2

0

7

3

Reactions with Ammonia and Amines T h e r e a c t i o n s of a l k y l b o r a n e s w i t h a m m o n i a a n d a m i n e s h a v e b e e n s t u d i e d e x t e n s i v e l y . F r a n k l a n d first r e p o r t e d t h e a d d u c t of t r i e t h y l b o r a n e a n d a m m o n i a (53). C o p l e y first discussed t h e i s o s t e r i s m of b o r o n - n i t r o g e n c o m p o u n d s w i t h c a r b o n c o m p o u n d s (38). B r o w n h a s m a d e a n e x t e n s i v e s t u d y i n t h i s field a n d h a s s h o w n steric effects o n m a n y o r g a n i c r e a c t i o n m e c h a n i s m s b y u s i n g s t e r i c a l l y s i m i l a r a l k y l -



96


b o r a n e - a l k y l a m i n e r e a c t i o n s . A s a r e s u l t t h e s t a b i l i t i e s a n d d i s s o c i a t i o n pressures o f m a n y a m i n e - b o r a n e s h a v e b e e n m e a s u r e d {17). H e reports t h a t trimethylborane a n d triethylborane are most easily handled a n d p u r i f i e d as t h e t r i m e t h y l a m i n e a n d a m m o n i a a d d u c t s , r e s p e c t i v e l y . T h e t r i m e t h y l b o r a n e w a s freed f r o m t r i m e t h y l a m i n e b y a series o f r a p i d d i s t i l l a t i o n s . T h e t r i e t h y l b o r a n e w a s freed f r o m a m m o n i a b y t r e a t m e n t w i t h h y d r o g e n c h l o r i d e (16). Schlesinger reports t h a t the alkyldiboranes a d d t w o moles of a m m o n i a a n d t h a t the s t a b i l i t y of the diammoniates of methyldiborane, dimethyldiborane, t r i m e t h y l d i borane, a n d tetramethyldiborane t o pyrolysis a n d disproportionation is greater t h a n t h a t of t h e m e t h y l diboranes themselves. T h e s t a b i l i t y increases w i t h i n c r e a s i n g n u m ber of m e t h y l groups. O n p y r o l y s i s these m a t e r i a l s m a y b e c o n v e r t e d t o B - m e t h y l a m i n o b o r a n e s a n d b o r a z i n e s (138, 139)—e.g. (CH ) B H 3

4

2

+ 2NH

2

>2H N : B(CH ) H

3

3

3

2

200° C .

H N :B(CH ) H 3

3

>H NB(CH )

2

2

3

+ H

2

2

350° C .

CH

+ 1/3 ( H N B C H )

4

3

METAL-ORGANIC COMPOUNDS

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