Formation of Alkyl and Aryl Titanium-Carbon Bond ... - ACS Publications

Formation of Alkyl and Aryl Titanium-Carbon

Bond

Compounds

DANIEL F. HERMAN

Downloaded by MICHIGAN STATE UNIV on February 18, 2015 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0023.ch024

Research Laboratory, National Lead Co., New York, Ν. Y.

The first compound synthesized and isolated, contain ing a titanium-carbon bond was phenyltitanium triisopropoxide. Much information was accumulated related to the preparation and properties of organotitanium compounds of the type R TiX , where R could be alkyl or aryl groups and X could be alkoxy groups or halogen. The organotitanium compounds can exist at various valence levels. Compounds of the type R TiX can exist when the sum of n and m is 2 or 3. These materials, although more stable than quadrivalent organotitanium compounds, exhibit some thermal instability and act as catalysts for polymerization. Reduction of titanium com pounds by organometallic reagents takes place through the intermediate formation of an organo titanium compound. Reduction proceeds only to the extent of giving a mixture of bi- and trivalent compounds even in the presence of excess Grignard reagent. Reaction of the lower valent titanium com pounds with the solvent may account for this. n

n

4-n

m

A l k y l and aryl organometallic compounds containing direct carbon to titanium bonds are discussed. These carbon-metal bonds are of at least partial covalent character. New work is described which further elucidates the nature of the organotitanium com pounds formed on reaction of organometallic reagents with titanium esters or chlorides at varying molar ratios. Conclusions or proposed structures are based upon diagnostic tests and chemical analyses similar to those by Herman and Nelson (8). Although most of the compounds described are diffcult to handle and even more difficult to isolate in purified state, they are increasingly important as catalysts in heterogeneous polymerization. This field has grown rapidly since Ziegler's announce ment (18) of the low pressure polymerization of ethylene by means of catalysts formed by the interaction of organometallic reagents, such as org a no aluminum compounds, with various derivatives of titanium. The initial attempt to prepare a stable and isolatable organotitanium compound was made in 1861 by Cahours (3). Many further attempts were also unsuccessful (1, 2, 4, 7, 10-14, 16)· Under some circumstances, organotitanium products of a transi tory nature may have been formed in solution, especially in the reactions of titanium 265

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

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ADVANCES IN CHEMISTRY SERIES

salts w i t h v a r i o u s o r g a n o m e t a l l i c reagents (7, 13). A successful s y n t h e s i s was r e p o r t e d i n 1952 a n d 1953 b y H e r m a n a n d N e l s o n (8). T h e i s o l a t i o n o f p h e n y l t i t a n i u m t r i i s o p r o p o x i d e was d e s c r i b e d , a n d c o m p o u n d s o f t h e t y p e R T i X _ were discussed. S u m m e r s a n d U l o t h (17) d e s c r i b e d a n u n u s u a l series o f c o m p o u n d s o f t h e class ( C H ) T i R 2 , where R is phenyl, p - t o l y l , and p - d i m e t h y l a m i n o p h e n y l . These m a terials possessed a n u n u s u a l s t a b i l i t y t o w a r d s h y d r o l y s i s w h e n c o m p a r e d t o t h e s i m p l e r o r g a n o t i t a n i u m c o m p o u n d s . T h i s is a t t r i b u t e d t o t h e s a n d w i c h s t r u c t u r e o f t h e t w o c y c l o p e n t a d i e n e r i n g s . F r i e d l a n d e r a n d O i t a (6) d e s c r i b e d t h e r e a c t i o n p r o d u c t s o f a l k y l l i t h i u m compounds and t i t a n i u m tetrachloride a t v a r y i n g molar ratios a n d o b t a i n e d evidence p o i n t i n g t o w a r d s t r a n s i e n t t i t a n i u m - c a r b o n b o n d s . Diagnostic m e t h o d s e m p l o y e d were s i m i l a r t o those d e s c r i b e d p r e v i o u s l y (8). T h e s e m a t e r i a l s were a c t i v e c a t a l y s t s for t h e p o l y m e r i z a t i o n o f e t h y l e n e . n

5

5

w

2

Previous attempts to form R T i X _ c o m p o u n d s were unsuccessful, because t h e c o n d i t i o n s selected f o r r e a c t i o n were t o o s t r i n g e n t . T h e r e f o r e , t h e i n i t i a l r e a c t i o n s t u d i e d was one i n v o l v i n g e q u i m o l a r q u a n t i t i e s o f p h e n y l m a g n e s i u m b r o m i d e a n d b u t y l t i t a n a t e i n ether a t a b o u t 8 ° C . Evidence indicated that a phenyl-titanium b o n d o f m o d e r a t e s t a b i l i t y h a d been f o r m e d in situ. T h e s o l u t i o n gave a s l o w l y d e v e l o p i n g b u t e v e n t u a l l y s t r o n g c o l o r test w i t h M i c h l e r ' s k e t o n e . B e c a u s e G r i g n a r d reagents e x h i b i t a v e r y r a p i d p o s i t i v e test, i t was a s s u m e d t h a t p h e n y l m a g n e s i u m b r o m i d e was n o l o n g e r p r e s e n t a n d t h a t a n e w o r g a n o m e t a l l i c c o m p o u n d — i . e . , a n o r g a n o t i t a n i u m c o m p o u n d o f lesser a c t i v i t y — h a d b e e n f o r m e d . S u b s t a n t i a t i n g t h i s , carbonation of a phenylmagnesium bromide yielded 70 t o 9 0 % benzoic acid, a n d c a r b o n a t i o n o f the G r i g n a r d - t i t a n a t e r e a c t i o n m i x t u r e y i e l d e d o n l y 0 t o 2 % benzoic a c i d . H i g h y i e l d s of benzoic a c i d w o u l d b e e x p e c t e d i f t h e r e was n o r e a c t i o n o f t h e G r i g n a r d reagent. O x i d a t i o n o f t h e r e a c t i o n m i x t u r e r e s u l t e d i n 20 t o 2 5 % y i e l d s o f p h e n o l a l o n g w i t h some b i p h e n y l a n d benzene. T h e s e results are i d e n t i c a l t o w h a t is o r d i n a r i l y o b t a i n e d o n o x i d a t i o n o f p h e n y l m a g n e s i u m b r o m i d e . A s t h e G r i g n a r d reagent is n o l o n g e r present, these o x i d a t i o n p r o d u c t s m u s t b e a t t r i b u t e d t o a n e w type of organometallic c o m p o u n d . T h e a u t h o r s c o n c l u d e d t h a t t h i s c o m p o u n d was a p h e n y l t i t a n i u m c o m p o u n d f o r m e d a c c o r d i n g t o E q u a t i o n 1. n


4

4

w

C H M g B r + ( C H 0 ) T i -> C H T i ( O C H ) 6

5

4

9

4

6

5

4

9

3

+ C H OMgBr 4

9

(1)

T h e o x i d a t i o n a n d h y d r o l y s i s r e a c t i o n s are s h o w n i n E q u a t i o n s 2 a n d 3. C H Ti(OC H ) 6

5

4

9

3

+ i 0 -> C H O T i ( O C H ) 2

6

5

4

9

C H OTi(OC H )

3

+ H 0 -> C H O H + T i 0

C H Ti(OC H )

3

+ H 0 -> C H

6

5

6

4

5

4

9

9

2

6

2

6

9

(2b)

hydrate + 3 C H O H

(3)

5

+ Ti0

6

2

(2a)

3

2

hydrate + 3 C H O H 4

4

7

E q u a t i o n 2 has been s u b s t a n t i a t e d b y i n f r a r e d evidence. I n the G r i g n a r d r e a g e n t - b u t y l titanate reaction m i x t u r e , reduced t i t a n i u m c o m p o u n d s are f o r m e d g r a d u a l l y o n storage a t r o o m t e m p e r a t u r e a n d i n e r t a t m o s p h e r e (Figure 1). T h i s d e c o m p o s i t i o n w i l l b e discussed l a t e r , b u t t w o p o i n t s s h o u l d b e e m p h a s i z e d here. ( 1 ) T h e r e is e s s e n t i a l l y no f o r m a t i o n o f r e d u c e d t i t a n i u m i m m e d i a t e l y a f t e r c o m p l e t i n g t h e a d d i t i o n of G r i g n a r d reagent to t h e t i t a n a t e . ( 2 ) A t t h i s p o i n t , t h e G r i g n a r d reagent h a d r e a c t e d c o m p l e t e l y t o f o r m o r g a n o t i t a n i u m c o m p o u n d s . Therefore, the e n s u i n g f o r m a t i o n of l o w e r v a l e n t t i t a n i u m c o m p o u n d s is n o t a t t r i b u t e d t o a d i r e c t r e d u c i n g a c t i o n of the G r i g n a r d reagent b u t t o a h o m o l y t i c cleavage o f t h e c a r b o n - m e t a l b o n d , as i n E q u a t i o n 4. C H Ti^-» C H · 6

5

6

\

5

—Ti ·

(4)

/

T h e f o r m a t i o n o f free p h e n y l r a d i c a l s a n d l o w e r v a l e n t t i t a n i u m c o m p o u n d s c o n t a i n i n g o d d electrons i s p o s t u l a t e d . T h e d e c o m p o s i t i o n is b e l i e v e d t o b e u n i m o l e c u l a r r a t h e r t h a n b i m o l e c u l a r , because i n b i m o l e c u l a r c o u p l i n g r e a c t i o n s b i p h e n y l is o b t a i n e d


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É1

ΓζΤΠ


ο

1 0.25: 15

Ik

20

TIME-DAYS

Figure 1.

Decomposition rates of phenylmagnesium bro mide a n d butyltitanate 1 to 1 to 4 to 1 molar ratios

i n h i g h y i e l d s (5). I n t h e present i n s t a n c e , t y p i c a l d e c o m p o s i t i o n p r o d u c t s a r e 3 3 to 3 4 % benzene, 25 t o 3 7 % b i p h e n y l , a n d u p t o 1 5 % of h i g h e r a r o m a t i c h y d r o c a r b o n s . T h e m o s t s t r i k i n g evidence f o r s u c h a t h e r m a l cleavage of t h e t i t a n i u m - c a r b o n b o n d i s the a b i l i t y of the reaction fragments t o catalyze the p o l y m e r i z a t i o n of v i n y l monomers. T h e a c t u a l i s o l a t i o n o f a p h e n y l t i t a n i u m c o m p o u n d f r o m these r e a c t i o n m i x t u r e s was a c h i e v e d b y t h e r e a c t i o n o f p h e n y l l i t h i u m w i t h i s o p r o p y l t i t a n a t e a t 8 ° t o 1 5 ° C . A t r a n s i e n t orange c o l o r w a s p r o d u c e d w h i c h w a s f o l l o w e d b y t h e d e p o s i t i o n o f w e l l f o r m e d w h i t e c r y s t a l s a n a l y z i n g as C H T i ( O C H ) 3 - L i O C 3 H - L i B r - ( C H ) 0 . P h e n y l t i t a n i u m triisopropoxide was isolated from this complex b y reaction w i t h t i t a n i u m t e t r a c h l o r i d e o r a l u m i n u m c h l o r i d e . I t w a s o b t a i n e d as a w h i t e c r y s t a l l i n e s u b s t a n c e , m e l t i n g p o i n t 8 8 ° t o 9 0 ° C , w h i c h w a s stable o n storage a t 1 0 ° C . R a p i d d e c o m p o s i t i o n t o t i t a n o u s p r o d u c t s t o o k place o n h e a t i n g a t 100° t o 1 2 0 ° C . T h e p r o d u c t e x h i b i t e d a l l o f t h e r e a c t i o n s p r e v i o u s l y d e s c r i b e d i n t h e in situ f o r m a t i o n o f phenyltitanium compounds. Therefore, the diagnostic methods previously described are r e l i a b l e , a n d t h i s a p p r o a c h m a y b e u s e d w i t h reasonable confidence i n d e m o n s t r a t i n g t h e existence o f o r g a n o t i t a n i u m b o n d s i n r e a c t i o n m i x t u r e s o f o r g a n o m e t a l l i c reagents w i t h t i t a n i u m d e r i v a t i v e s . 6

5

3

7

7

2

5

2

T h e stabilities of t i t a n i u m - c a r b o n bonds i n compounds of t h e general f o r m R T i X _ were s t u d i e d . R g r o u p s were v a r i e d f r o m a l k y l t o a r y l , a t t e m p t s were m a d e to l i n k m o r e t h a n one R g r o u p t o t h e t i t a n i u m a t o m , a n d X w a s v a r i e d f r o m a l k o x i d e t o h a l i d e . T h e general c o n c l u s i o n w a s t h a t t i t a n i u m - c a r b o n b o n d s o f v a r i a b l e s t a b i l i t y e x i s t e d i n a l l cases. W i t h v a r i a t i o n i n t h e R g r o u p , s t a b i l i t y i n c r e a s e d : b u t y l < m e t h y l < acetylenyl < p - a n i s y l < p h e n y l < 2 - n a p h t h y l < i n d e n y l . T h e i n d e n y l g r o u p is a s p e c i a l case, b e i n g a c o n g e n e r o f c y c l o p e n t a d i e n e w h i c h f o r m s c o m p o u n d s o f u n u s u a l s t a b i l i t y w i t h t h e t r a n s i t i o n elements. T h e effect of changes i n t h e X g r o u p o n t h e s t a b i l i t y of t h e p h e n y l t i t a n i u m b o n d w a s as f o l l o w s : b u t o x y ~ i s o b u t o x y p r o p o x y ^ i s o p r o p o x y > m e t h o x y , c h l o r i d e > fluoride. S t u d y of changes i n η s h o w e d t h a t greatest s t a b i l i t y w a s o b t a i n e d w h e n η = 1. S t a b i l i t y f e l l off s h a r p l y w h e n η = 2, a n d q u a d r i v a l e n t c o m p o u n d s were v i r t u a l l y n o n e x i s t e n t w i t h m o r e t h a n t w o R g r o u p s b o u n d t o t h e t i t a n i u m a t o m . H o w e v e r , l o w e r v a l e n t c o m p o u n d s of t i t a n i u m w h i c h s t i l l c o n t a i n e d c a r b o n - m e t a l b o n d s were i n d i c a t e d . n

4

n



268

T o establish more f i r m l y the i d e n t i t y of the organic derivatives of reduced t i t a n i u m and t o examine their catalytic activity, phenylmagnesium bromide was added to b u t y l titanate a n d t i t a n i u m tetrachloride at 1 to 1 to 4 t o 1 m o l a r ratios.

Decomposition

rates a r e s h o w n i n F i g u r e 1, a n d a s u m m a r y of t h e d a t a o b t a i n e d a t t h e 4 t o 1 m o l a r ratios is given i n T a b l e I .

Table I.

I n t h e reactions of phenylmagnesium bromide a n d b u t y l

Reaction of 4 Moles of Phenylmagnesium Bromide with 1 Mole of Butyl Titanate a n d 1 Mole of Titanium Tetrachloride (% d i s t r i b u t i o n of p h e n y l groups after storage) Reaction I, Butyl Titanate 20-Hr. Storage


2-Hr. Storage Free in ether soin.

Phenyl recovered as Unreacted Grignard Benzene Bi phenyl Other aromatics Total recovery

Bound in solid with T i , Mg, Br, Bu

Total

16.0 7.0 13.9 36.9

10.5 33.6 26.5 13.9 84.5

10.5 17.6 19.5 —

Free in ether soin. 2.0 23.2 24.3« —.

Bound in solid with Ti, Mg, Br, Bu

Total

11.2 7.5 14.7 33.4

2.0 34.4 31.8« 14.7 82.7«

Reaction II, Titanium Tetrachloride, 20-Hr. Storage, Total Recovery 2.4 23.5 50.0 75.9

« 2 % higher values obtained in a duplicate run.

titanate at 1 to 1 a n d 2 to 1 molar ratios, b o t h monophenyl—e.g., C H T i X — a n d d i p h e n y l — e . g . , ( C H ) T i X — t i t a n i u m species o f q u a d r i v a l e n t t i t a n i u m were f o r m e d (#). A t h i g h e r r a t i o s of r e a c t a n t s , t h e r e a c t i o n s a r e c o m p l i c a t e d i n t h a t d e c o m p o s i t i o n 6

6

5

2

5

3

2

of t h e q u a d r i v a l e n t o r g a n o t i t a n i u m c o m p o u n d leads t o t h e f o r m a t i o n o f t i t a n i u m c o m p o u n d s w h i c h m a y be a r y l a t e d . E q u a t i o n s 5 t o 8 are p o s t u l a t e d . T l R M g X + T1X4 - > R n T l X 4 _ n R TiX _n - » R -lTiX _n + R· n

4

n

4

R _ i T i X _ n + R M g X -> R T i X _ n n

4

reduced

(5) (6)

3

(7)

R · —> organic b y - p r o d u c t s

(8)

n

T o e s t a b l i s h t h e v a l i d i t y o f these e q u a t i o n s , t h e f o l l o w i n g f a c t o r s m u s t b e d e t e r m i n e d : c o m p l e t e n e s s o f u t i l i z a t i o n o f t h e G r i g n a r d reagent, e x t e n t o f r e d u c t i o n o f t h e o r g a n o t i t a n i u m c o m p o u n d s , i d e n t i t y of t h e p u r e l y o r g a n i c p r o d u c t s o f d e c o m p o s i t i o n , a n d i d e n t i t y o f t h e t i t a n i u m p r o d u c t s of t h e d e c o m p o s i t i o n , p a r t i c u l a r l y these r e d u c e d t i t a n i u m p r o d u c t s w h i c h a r e s t i l l o r g a n o m e t a l l i c i n n a t u r e . F i n a l l y , i t w a s necessary to relate t h e various identifiable products t o t h e i n d i v i d u a l equations shown. D i a g n o s t i c experiments were c a r r i e d o u t . T h e p r o d u c t w a s carbonated t o d e t e r m i n e t h e e x t e n t o f G r i g n a r d reagent r e a c t e d . T h e u n b o u n d p u r e l y o r g a n i c m a t e r i a l w a s s e p a r a t e d b y f i l t r a t i o n f r o m t h e s o l i d o r g a n o m e t a l l i c p r o d u c t s before a n y hydrolysis o r oxidation was allowed to take place. T h e o r g a n o t i t a n i u m product was h y d r o l y z e d subsequent t o t h e r e m o v a l of the u n b o u n d organic m a t e r i a l . T h e organic m a t e r i a l so l i b e r a t e d w a s i s o l a t e d a n d r e l a t e d t o t h e i n i t i a l presence of o r g a n o t i t a n i u m compounds. O x i d a t i o n f o l l o w e d b y h y d r o l y s i s w a s also u s e d s i m i l a r l y ( E q u a t i o n s 2 and 3 ) . T h e v a l u e s l i s t e d i n T a b l e I a r e t h e p e r cents of t h e p h e n y l g r o u p s o r i g i n a l l y c h a r g e d as G r i g n a r d reagent w h i c h are i s o l a t e d i n t h e f o r m s i n d i c a t e d . A t o t a l r e c o v e r y of 1 0 0 % w o u l d i n d i c a t e a c o m p l e t e a c c o u n t i n g f o r a l l t h e G r i g n a r d r e a g e n t . A c t u a l l y recoveries r a n g e f r o m 8 2 t o 8 4 % , w h i c h is e n t i r e l y s a t i s f a c t o r y i n v i e w o f t h e n u m b e r of steps i n v o l v e d a n d t h e d i f f i c u l t y of h a n d l i n g these m a t e r i a l s . I n a r e a c t i o n m i x t u r e ( R e a c t i o n I ) w h i c h w a s a n a l y z e d 2 h o u r s a f t e r c o m p l e t i o n of t h e a d d i t i o n o f t h e G r i g n a r d reagent, c a r b o n a t i o n s h o w e d t h a t 8 8 t o 9 0 % o f t h e G r i g n a r d h a d b e e n u t i l i z e d . F u r t h e r storage f o r a t o t a l o f 2 0 h o u r s s h o w e d t h a t t h i s u t i l i z a t i o n i n c r e a s e d t o 9 8 % . T h e r e a c t i o n is t h e r e f o r e v e r y r a p i d a n d e s s e n t i a l l y c o m p l e t e . A n y organo-



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269

metallic m a t e r i a l found a t this point must be o r g a n o t i t a n i u m i n nature. A n a l y s i s of t h e v a l e n c e levels of t h e t i t a n i u m p r o d u c t s shows t h a t c o m p l e t e r e d u c t i o n t o t h e t i t a n o u s state h a s t a k e n p l a c e w i t h i n t h e 2 - h o u r p e r i o d . T h e t e r m t i t a n o u s i n c l u d e s b o t h b i - a n d t r i v a l e n t t i t a n i u m . I n the 20-hour reaction, such a reduced product contained 8 8 % trivalent and 1 2 % bivalent t i t a n i u m compounds. Assuming that e a c h e q u i v a l e n t o f G r i g n a r d reagent is c a p a b l e o f r e d u c i n g t h e v a l e n c e l e v e l of t i t a n i u m b y one u n i t , 1.12 e q u i v a l e n t s o f G r i g n a r d reagent s h o u l d b e i n v o l v e d i n r e d u c t i o n out of t h e 4 moles consumed. T h e r e f o r e , s l i g h t l y m o r e t h a n o n e e q u i v a l e n t of p h e n y l s h o u l d b e i s o l a t e d as a r o m a t i c h y d r o c a r b o n s , a n d b e t w e e n t w o a n d t h r e e e q u i v a l e n t s s h o u l d b e b o u n d t o t i t a n i u m i n the t i t a n o u s state as a n o r g a n o m e t a l l i c compound. H o w e v e r , i n R e a c t i o n I a t o t a l of 3 7 . 1 % of the p h e n y l e q u i v a l e n t s ( 1 7 . 6 % benzene, 1 9 . 5 % b i p h e n y l ) were i s o l a t e d f r o m the f i l t e r e d e t h e r s o l u t i o n s . T h i s v a l u e increases t o 4 7 . 5 % o n storage f o r 2 0 h o u r s . E q u a t i n g t h i s l a t t e r q u a n t i t y t o a r e d u c t i o n r e a c t i o n m e a n s t h a t a l m o s t 2 m o l e s of reagent h a v e been c o n s u m e d . There fore, the t i t a n i u m s h o u l d b e r e d u c e d c o m p l e t e l y t o t h e b i v a l e n t s t a t e . A s t h i s w a s n o t the case, i t a p p e a r s t h a t p a r t o f t h e G r i g n a r d reagent i s d e s t r o y e d c a t a l y t i c a l l y b y the t i t a n i u m compounds. T h i s effect is e v e n m o r e s t r i k i n g w h e n t i t a n i u m t e t r a c h l o r i d e ( R e a c t i o n I I ) is used i n p l a c e of b u t y l t i t a n a t e . T h e s o l i d p o r t i o n o f t h e p r o d u c t c o n t a i n e d o v e r 9 0 % of t h e t i t a n i u m a n d m a g n e s i u m u s e d i n t h e r e a c t i o n . B e c a u s e t h i s h a d been s e p a r a t e d a l r e a d y f r o m t h e e t h e r s o l u t i o n a n d w a s h e d , a l l free benzene a n d b i p h e n y l f o r m e d d u r i n g r e d u c t i o n s h o u l d h a v e been r e m o v e d . A n y additional organic m a t e r i a l formed o n hydrolysis m u s t be a t t r i b u t e d t o the presence o f o r g a n o t i t a n i u m c o m p o u n d s i n the t i t a n o u s s t a t e . A n a l y sis o f R e a c t i o n I a f t e r 2 h o u r s shows t h a t 36.9 m o l e % o f the p h e n y l e q u i v a l e n t s u s e d were b o u n d t o t h e t i t a n i u m . T h i s m a t e r i a l was i s o l a t e d as 1 6 . 0 % benzene, 7 . 0 % b i p h e n y l , a n d 1 3 . 9 % h i g h b o i l i n g a r o m a t i c residue. A n a l y s i s o f t h e 2 0 - h o u r r u n s h o w e d t h a t 33.4 m o l e % of the p h e n y l e q u i v a l e n t s u s e d were b o u n d t o t h e t i t a n i u m . I n t h e 2 - h o u r r u n a n a v e r a g e o f 1.49 p h e n y l g r o u p s were b o u n d t o each t i t a n i u m a t o m . T h i s d r o p s t o 1.3 p h e n y l g r o u p s p e r t i t a n i u m o n storage f o r 20 h o u r s . F r o m these figures a n d f r o m t h e a n a l y s i s o f t h e v a l e n c e levels o f t i t a n i u m , t h e f o l l o w i n g c o m p o u n d s are i n d i c a t e d : C H T i X , ( C H ) T i X , a n d ( C H ) T i X . T h e decrease of b o u n d p h e n y l g r o u p s o n storage i n d i c a t e s a slow b r e a k d o w n o f these c o m p o u n d s . B y i n c r e a s i n g t h e storage t i m e f r o m 2 t o 2 0 h o u r s , the a s y e t u n r e a c t e d p o r t i o n o f t h e G r i g n a r d reagent i s c o n s u m e d a n d gives a n a p p r o x i m a t e l y e q u i v a l e n t a m o u n t o f b i p h e n y l w i t h o u t a n y a p p a r e n t change i n t h e v a l e n c e levels o f t h e t i t a n i u m . A d i s c r e p a n c y h a s been s h o w n b e t w e e n the e x t e n t o f r e d u c t i o n of t h e t i t a n i u m a n d t h e a m o u n t of organic m a t e r i a l obtained w h i c h can be equated t o reduction. A l l of this i n d i c a t e s c a t a l y t i c d e s t r u c t i o n o f t h e G r i g n a r d reagent b y t h e t i t a n i u m c o m p o u n d s , w h i c h t a k e s p l a c e a f t e r t h e t i t a n i u m has been r e d u c e d t o l o w e r v a l e n c e levels. T h i s m a y be e x p l a i n e d b y p i c t u r i n g t h a t i n a n o r g a n i c s y s t e m t h e t i t a n i u m is n o t r e d u c e d b e l o w a v a l e n c e l e v e l o f b e t w e e n t w o a n d t h r e e ; once t h i s l e v e l is r e a c h e d , the t i t a n i u m is r e o x i d i z e d b y r e a c t i o n w i t h t h e s o l v e n t . C o n t i n u e d r e a c t i o n o f the o x i d i z e d m a t e r i a l w i t h G r i g n a r d reagent i s t h e n possible. 6

5

2

6

5

2

6

5

T h e f o l l o w i n g t y p e s o f r e a c t i o n s are p o s t u l a t e d : RTiX TiX

2

—> R - + T i X

2

+ C2H5OC2H5 -> T i X O C H

5

2

TiX TiX OC H 2

2

2

5

2

2

2

5

2

5

6

5

2

(10) (11)

+ H R -» TiX H + R .

+ C H M g B r -> C H T i X 6

(9) + C H -

+ C H OMgBr 2

5

(12) (13)

E q u a t i o n s 10 a n d 11 are h y p o t h e t i c a l r e a c t i o n s s h o w i n g o x i d a t i o n o f t h e b i v a l e n t t i t a n i u m c o m p o u n d s b y e i t h e r d i e t h y l e t h e r o r a h y d r o c a r b o n s o l v e n t . E q u a t i o n s 12



270 and

13 i l l u s t r a t e t h e c o n t i n u e d r e a c t i o n w i t h t h e G r i g n a r d r e a g e n t .

T h e products

f o r m e d go b a c k i n t o t h e c y c l e w h i c h s t a r t s w i t h E q u a t i o n 9. S u c h a scheme i s s i m i l a r t o t h a t u s e d b y K h a r a s c h (9) t o e x p l a i n t h e a p p a r e n t c a t a l y t i c d e c o m p o s i t i o n of

phenylmagnesium bromide

b y cobalt

c h l o r i d e i n t h e presence

of

bromobenzene.

I n t h i s case, a c o b a l t s u b h a l i d e , C o X , i s a s s u m e d t o b e a c a r r i e r f o r a c h a i n r e a c t i o n . C o X is constantly regenerated t o C o X b y e x t r a c t i n g t h e b r o m i n e of bromobenzene. 2

E x t r a c t i o n o f a h y d r o g e n b y b i v a l e n t t i t a n i u m i s w e l l k n o w n i n t h e case o f o x i d a t i o n b y w a t e r . F u r t h e r s u p p o r t f o r t h e e x t r a c t i o n of h y d r o g e n b y r e d u c e d m e t a l c o m pounds is the f o r m a t i o n of n i c k e l h y d r i d e i n the reaction of p h e n y l m a g n e s i u m b r o m i d e , n i c k e l c h l o r i d e , a n d h y d r o g e n {15).


I n f r a r e d t e c h n i q u e s c a n b e u s e d as a d i a g n o s t i c test f o r t h e presence of t h e p h e n y l g r o u p l i n k e d t o t i t a n i u m . A series of b a n d s a t 3.2, 9.3, 10.7, 12.1, 13.8, a n d 14.3 m i c r o n s is f o u n d i n p h e n y l t i t a n i u m t r i i s o p r o p o x i d e , w h i c h d i s a p p e a r o n o x i d a t i o n . T h e o x i d a tion product is shown to be p h e n o x y t i t a n i u m triisopropoxide b y comparison w i t h the s p e c t r a of a k n o w n s a m p l e . T h e v a r i o u s b a n d s a r e b e l i e v e d t o b e c h a r a c t e r i s t i c o f strains imposed o n the p h e n y l ring i n being b o u n d t o t i t a n i u m rather t h a n of t h e t i t a n i u m - c a r b o n b o n d itself. C o m p a r i s o n w i t h t h e a b s o r p t i o n spectra of " s a n d w i c h " c y c l o p e n t a d i e n y l t i t a n i u m c o m p o u n d s suggests a t y p e of d e l o c a l i z e d work will be described i n detail i n another publication.

bonding.

This

M o s t q u a n t i t a t i v e d a t a c o n c e r n i n g t h e c o m p o u n d s of class R T i X h a v e been obtained i n t h e reaction of p h e n y l G r i g n a r d w i t h b u t y l titanate o r t i t a n i u m t e t r a n

m

c h l o r i d e . T h i s reagent w a s selected because of i t s ease i n h a n d l i n g a n d t h e ease w i t h w h i c h p r o d u c t s c o u l d b e i d e n t i f i e d . I n w o r k i n g w i t h o t h e r G r i g n a r d reagents a n d o r g a n o a l u m i n u m a n d l i t h i u m compounds, similar reactions are indicated q u a l i t a t i v e l y . A n o t a b l e difference w a s t h e u n u s u a l s t a b i l i t y i n r e a c t i o n s w i t h o r g a n o l i t h i u m compounds. T h i s p r o b a b l y r e s u l t s f r o m c o m p l e x i n g a c t i o n , w h i c h w a s first n o t e d b y H e r m a n a n d N e l s o n (8) a n d l a t e r r e p o r t e d b y F r i e d l a n d e r a n d O i t a {6) i n r e a c t i o n s w i t h alkyllithium compounds. O r g a n o m e t a l l i c reagents w h i c h are c o n s i d e r e d a l k y l a t i n g o r a r y l a t i n g agents s h o u l d f o r m c o m p o u n d s o f t h e class R T i X w h e n r e a c t e d w i t h t i t a n i u m esters o r h a l i d e s . T h e reactions occur a t r o o m temperature a n d are v e r y r a p i d . W i t h t h e exception of s t a b i l i z a t i o n b y c o m p l e x i n g a c t i o n , s t a b i l i t y of t h e R - T i c o m p o u n d s i n t h e q u a d r i v a l e n t s t a t e f a l l s off r a p i d l y w i t h increases i n n. H o w e v e r , s t a b i l i t y i s c o n s i d e r a b l y g r e a t e r for the b i - a n d t r i v a l e n t compounds. I n r e a c t i o n s o f o r g a n o m e t a l l i c reagents a t u p to a 4 t o 1 m o l a r ratio, compounds of the R T i X , R T i X , a n d R T i X types are i n d i n

m

2

2

c a t e d . T h e l o w e r v a l e n t t i t a n i u m c o m p o u n d s a p p e a r t o b e free r a d i c a l i n n a t u r e a n d b y v i r t u e of a n o d d electron are capable of reacting w i t h t h e solvent. Complete r e d u c t i o n t o t h e b i v a l e n t state is n o t realized under t h e conditions examined. T i t a n i u m i s r e d u c e d b y a scission of t h e c a r b o n - m e t a l b o n d t o y i e l d free R r a d i c a l s a n d generally insoluble h i g h l y reactive t i t a n i u m compounds of lower valence. C o m p o u n d s o f t h e class R T i X a c t as c a t a l y s t s f o r t h e p o l y m e r i z a t i o n o f s t y r e n e b u t a d i e n e , e t h y l e n e p r o p y l e n e , a n d o t h e r s . S i n c e Z i e g l e r ' s a n n o u n c e m e n t {18) i n w

w

1954 o f t h e l o w p r e s s u r e p o l y m e r i z a t i o n o f e t h y l e n e , m a n y l a b o r a t o r i e s h a v e b e e n s t u d y i n g c a t a l y s t s c o n s i s t i n g o f m i x t u r e s o f v a r i o u s o r g a n o m e t a l l i c reagents w i t h t i t a n i u m h a l i d e s o r esters. O r g a n o t i t a n i u m c o m p o u n d s o f t h e t y p e p o s t u l a t e d as p l a y i n g a d o m i n a n t role i n t h i s t y p e of p o l y m e r i z a t i o n .

described are

T h e c h a r a c t e r i s t i c r e a c t i o n s o f R - T i b o n d s , s u c h as h o m o l y t i c scission a n d t h e c h a i n r e a c t i o n s h i f t s i n v a l e n c e l e v e l , m a y b e r e s p o n s i b l e f o r t h e i n i t i a t i o n of p o l y merization.

Acknowledgment T h e a u t h o r wishes t o express h i s a p p r e c i a t i o n t o U n o K r u s e f o r h i s c o l l a b o r a t i o n o n t h e e x p e r i m e n t a l phases of t h i s p a p e r a n d t o H . H . B e a c h a m a n d D a n i e l K a u f m a n f o r t h e i r m a n y h e l p f u l suggestions a n d a d v i c e .


HERMAN-TITANIUM-CARBON BOND COMPOUNDS

271

Literature Cited (1) (2) (3) (4) (5) (6)


(7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18)

Browne, O. H., Reid, E. F., J. Am. Chem. Soc. 49, 830 (1927). Buckton, J. Chem. Soc. 1863, 17. Cahours, Μ. Α., Ann. chim. (3) 62, 280 (1861). Challenger, F., Pritchard, F., Jinks, J. R. Α., J. Chem. Soc. 125, 864 (1924). Cotton, F. Α., Chem. Revs. 55, 582 (1955). Friedlander, Η. N., Oita, K., Abstracts of Papers, 130th Meeting, ACS, Atlantic City, N . J., September 1956, p. 13S. Gilman, H., Jones, R. C., J. Org. Chem. 10, 505 (1945). Herman, D. F., Nelson, W. K., Am. Chem. Soc. 74, 2693 (1952) ; 75, 3877, 3882 (1953). Kharasch, M. S., Fields, Ε. K., Ibid., 63, 2316 (1941). Kohler, H., Ber. deut. chem. Ges. 13, 1626 (1880). Levy, L., Ann. chim. et phys. (6) 25, 433 (1892). Paterno, E., Peratoner, Α., Ber. deut. chem. Ges. 22, 467 (1889). Plets, V. Μ., J. Gen. Chem. U.S.S.R. (Eng. Transl.) 8, 1298 (1938). Razuvaev, G. Α., Bogdanov, I. F., Ibid., 3, 367 (1933). Schlenk, W., Weichselfelder, T., Ber. deut. chem. Ges. 56, 2230 (1923). Schumann, Α., Ibid., 21, 1079 (1888). Summers, R., Uloth, R. H., J. Am. Chem. Soc. 76, 2278 (1954). Ziegler, K., Brit. Patent 713,081 (Aug. 4, 1954). RECEIVED for review May 10, 1957. Accepted June 1, 1957.


Formation of Alkyl and Aryl Titanium-Carbon Bond ... - ACS Publications

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