Studies of Asymmetric Homogeneous Catalysts - Advances in

20 Studies of Asymmetric Homogeneous Catalysts Catalytic Aspects of Metal Phosphine Complexes Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 01/03/18. For personal use only.

W. S. K N O W L E S , W. C. C H R I S T O P F E L , K. E . K O E N I G , and C. F. H O B B S Monsanto Company, Corporate Research Laboratories, St. Louis, M O 63166

A number of chiral bisphosphines related to DiPAMP(1) were prepared and evaluated in asymmetric catalysis. Many variants were closely equivalent but none were superior to the parent compound. In addition, some monophosphines containing sulfone substituents were quite effective. These had the particular advantage of being usable in water solution. Several new DIOP derivatives were tried in the hydroformylation of vinyl acetate but only modest enantiomeric excesses were achieved. A 72% enantiomeric excess was achieved on dehydrovaline under relatively forcing conditions using DiCAMP(3). This result was remarkable since these phosphine ligands generally work very poorly, if at all, on tetrasubstituted olefins.

O

ver the past decade the use of chiral phosphine ligands c o m plexée! with r h o d i u m to effect an asymmetric hydrogénation of enamide precursors o f α-amino acids has been h i g h l y effective (J, 2). E v e n though the enantiomeric excess (ee) has turned out to be a very sensitive function of ligand structure, a considerable number of h i g h l y successful phosphines have been discovered. T h e field as a p p l i e d to enamides has matured now to a program o f finding ligands with mar ginal improvements such as water solubility, faster rates, ease of syn thesis, and also a study of mechanisms. W h e n one turns to other prochiral unsaturates not related to enamides, o p t i m i z i n g b y varying ligand structure has been only mar ginally productive, and the 9 0 - 9 5 % ee so easily obtained w i t h ena mides has remained w e l l out o f reach for the most part. In several cases these low results persist i n spite of having been the subject of a considerable research effort. 0065-2393/82/0196-0325$05.00/0 © 1982 American Chemical Society

326

METAL PHOSPHINE COMPLEXES

O v e r the past d e c a d e w e have e x p l o r e d a n u m b e r o f p h o s p h i n e l i g a n d s for i n c r e m e n t a l i m p r o v e m e n t s o f p r e s e n t s y s t e m s a n d f o r s t u d ies i n n e w types o f r e d u c t i o n s a n d h y d r o f o r m y l a t i o n s . E v e n t h o u g h bisphosphines continue to dominate the efficient

monophosphines.

systems that w e have

field,

w e have found fairly

T h i s chapter deals

w i t h these a n d other

explored

for a - p h e n y l a c r y l i c a c i d ,

dehydro-

v a l i n e , a n d h y d r o f o r m y l a t i o n o f v i n y l acetate. E v e n t h o u g h w e h a v e

Catalytic Aspects of Metal Phosphine Complexes Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 01/03/18. For personal use only.

not solved efficiently

a n y o f these cases, w e ' v e l e a r n e d a l o t a b o u t

the b e h a v i o r o f a variety o f l i g a n d s a n d hope that this k n o w l e d g e c o n t r i b u t e t o these a n d other u n s o l v e d p r o b l e m s i n this

will

field.

Experimental

All compounds were characterized by MS and by NMR. In most cases only small amounts were needed for catalytic studies. In Situ Catalyst. Bisphosphine (.05 mmol) and Rh(COD)AcAc (17, 18) (.05 mmol) were weighed into a 6-mL vial. Air was displaced with nitrogen and 5 mL of peroxide-free, 88% isopropyl alcohol (IPA) was added while bubbling through a small stream of nitrogen. The vial was sealed with a septum and supersonically stirred until solution was complete. For a standard run, 0.5 mL (0.005 mmol of complex) was used to hydrogenate 1.0 g (4.88 mmol) of AAC in 25 ml of 88% IPA at 50°C and 3 atm. The ee was measured by diluting to 100 mL and comparing the optical rotation with a blank run in the same manner (3). This in situ catalyst is suitable for reducing acids which provide a proton source to release the AcAc. When reducing neutral substrates, one must either add .005 mmol of HCl or use a preformed solid catalyst of the type [Rh(COD)(Bisphosphine)] B F 4 (3). (R,R)-l,2-Ethanediylbis[o-hydroxyphenyl)phenylphosphine] (Com pound 12). In a flame-dried, nitrogen-purged 100-mL round bottom flask equipped with a nitrogen inlet, magnetic stirring bar, and syringe septum was placed 3.0 g (16.12 mmol) diphenylphosphine in 50 ml of the T H F (freshly distilled from sodium ketyl). A solution of η-butyl lithium in hexane (10 mL, 16.1 mmol) was syringed in over several minutes. After stirring at room tem perature for 5 min, 2.5 g (5.45 mmol DiPAMP(l) was added in one portion, and the resulting solution stirred at room temperature for 60 h. The solvent was removed under reduced pressure and the resulting material was taken up in H 0 - N a O H - C H C l . Sodium hydroxide was added until both layers were homogeneous. The water layer was separated and carefully acidified with HCl, and the phosphine was extracted with CH C1 . The organic layer was separated and dried with potassium carbonate, and the solvent was removed under reduced pressure to give 1.54 g of white foam. Final purification was accomplished by crystallization from C H O H (4 mL)/acetone (2 mL)/deionized water (1 mL) at - 3 ° C . Within 2 h 1.09 g of product were obtained (crys tallized with 1.5 mol of acetone per mole of product). +

2

2

2

2

2

3

m

p

= 148-149.5°C, [ α β ° = + 5 5 . 9 ° C (0.85, C H C 1 ) 3

The same procedure could be used on DiPAMPO to give (S,S)-l,2-ethanediylbis[(o-hydroxyphenyl)phenylphosphine oxide.].

20.

KNOWLES ET AL.

Asymmetric


m p = 3 2 7 ° C , [a]?

0

Homogeneous

Catalysts

327

+ 20.8°C (1, C F C O O H ) 3

T h e diacetate ( C o m p o u n d 13) was prepared b y acetylating C o m p o u n d 12, a n d since it d i d not crystallize, it was used w i t h o u t purification. (R)-(o-Methoxyphenyl)methyl(morpholinosulfonylmethyl)phosphine (Compound 18). To a solution of morpholinomethanesulfonamide (13) (14.0 g, 84.9 m m o l ) i n 100 m L d r y T H F at 15°C was a d d e d η-butyl l i t h i u m (50.9 m L 1.6M solution i n hexane (81.5 mmol). T h e n ( S ) p - m e n t h y l o-methoxyp h e n y l m e t h y l p h o s p h i n a t e (11.0 g, 34.0 m m o l ) i n 50 m L dry T H F was a d d e d at 15°C a n d the mass was h e l d at 20°-25°C for 16 h g i v i n g a clear y e l l o w solu tion. T h e product was p u r i f i e d on a dry silica c o l u m n b y e l u t i n g w i t h e t h y l acetate. N M R ( C D C 1 ) S 1.96 ( d , 3 H , J = 14 H z ) 3 . 2 0 - 3 . 9 0 ( m , 8 H ) , 3 . 5 5 ( d , 2 H , J = 1 4 . H ) , 3 . 9 2 (S, 3 H ) , a n d 6 . 7 4 - 8 . 1 1 ( m , 4 H ) . 3

T h e above s o l i d (2.26 g, 6.8 m m o l ) was dissolved i n 150 m l of dry acetonitrile and 6 m l of S i C l s l o w l y were a d d e d at 70°C. T h e mixture then was h e l d for 30 m i n , c o o l e d , a n d a d d e d to 100 m l of 2 5 % N a O H at 0°-5°C. T h e layers were separated a n d the aqueous phase was extracted w i t h C H C 1 . After removal of the solvent, 1.9 g of clear y e l l o w o i l was obtained. It was c r y s t a l l i z e d from ethanol to give a product, m p 76°-77°C, [a]J° = +123.8°C (0.8, C H C 1 ) . M S and N M R were consistent. F u r t h e r crystallization d i d not i m p r o v e the rotation. 2

e

2

2

3

T h e p h y s i c a l constants for related c o m p o u n d s were made b y the same procedure. (R)-(o-Methoxyphenyl)methyl(methylsulfonylmethyl)phosphine pound 14):

(Com

m p 1 1 2 - 1 1 3 , [a]£° = + 131.0°C (0.4, E t O H ) . (R)-(o-Methoxyphenyl)methyl(IV,N-dimethylsulfonylmethyl)phosphine (Compound 16). T h i s c o m p o u n d is not c r y s t a l l i n e ; it formed a crystalline derivative of the type L R h A c A c , w h i c h was used for the catalyst. 2

C o m p o u n d s 15 a n d 17 were made i n a s i m i l a r manner but d i d not purify readily. (2S,4S)-N-Methanesulfonyl-4-diphenylphosphino-2-diphenylphosphinomethylpyrolidine (Compound 21). T h e f - B O C group on A c h i w a s B P P M (5, 6) was r e m o v e d w i t h formic a c i d a n d the free base reacted w i t h C H S 0 C 1 . D u r i n g purification on a silica c o l u m n the b i s p h o s p h i n e was o x i d i z e d to the b i s p h o s p h i n e oxide. T h i s product was readily r e d u c e d w i t h S i C l i n C H C N to give the d e s i r e d b i s p h o s p h i n e ( C o m p o u n d ; m p 124°-126°C 21), [a\l° = -46.7°C (0.3, C H C I 3 ) . A n X-ray structure of the r h o d i u m c o m p l e x is d e s c r i b e d i n Ref. 8. 3

2

e

2

3

(R^t)-4,5-Bis(p-tosyloxymethyl)-2,2-diphenyl-l,3-dioxolane (Compound 30). A mixture of 4.3 g (.01 mol) o f (R,R )-1,2,3,4 butane tetrol-l,4-ditosylate a n d 2.4 g (.01 mol) of d i c h l o r o d i p h e n y l methane i n 25 m L of o-dichlorobenzene was refluxed u n d e r nitrogen for 12 h w i t h e v o l u t i o n of H C 1 . After evaporation of the solvent, the residue was crystalized from benzene/heptane to obtain 3.6 g (60.5% of product); m p 121°-122°C. [α]%> = - 6 . 6 3 (1, C H ) . e

6

328

M E T A L PHOSPHINE COMPLEXES

(R,R )-4,5-Bis(diphenylphosphinomethyl)-2,2-diph^ ( C o m p o u n d 23). A solution of 12.8 m m o l o f l i t h i u m d i p h e n y l p h o s p h i d e i n 65 m L of T H F was prepared u s i n g 2-chloropropane to destroy the p h e n y l l i t h i u m . T h i s mixture was stirred for 16 h at 25°C w i t h the above bis-tosylate. Evapora tion of the solvent f o l l o w e d by hydrolysis a n d extraction gave a product w h i c h crystallized from ethanol; m p 135-137°C, [a]J° = -40.4°C (1, C H ) . Hydroformylation s. T h e hydroformylation of v i n y l acetate was run at 6 to 7 atm w i t h a 4 4 : 5 6 C O / H mixture at 80°-100°C u s i n g benzene as a solvent and an 8 x 1 0 ~ M concentration of r h o d i u m and a 3 . 4 5 M concentration of v i n y l acetate. T h e ratio o f l i g a n d to metal was varied from 1 to 6 a n d the best results were obtained only at h i g h ratios. Isolated yields i n the hydroformylation ran about 7 5 - 8 5 % . Rotations were measured on d i s t i l l e d aldehyde a n d compared w i t h a standard for pure α-acetoxypropanal: [a] ° = -34.9°C (5.0, toluene). T h i s standard was obtained i n two ways. A n asymmetric hydroformylation was r u n and the aldehyde was o x i d i z e d to S-α-acetoxypropionic a c i d . A comparison of the rotation obtained w i t h the literature (19) for pure S-acid [a]l° = -49.3°C (7.2, C H C 1 ) was used to arrive at the 34.9°C figure for pure S-aldehyde. T h i s n u m b e r was c h e c k e d u s i n g an N M R shift reagent. 6

e

2


4

2

D

3

Results The following evaluation:

asymmetric

reactions

were considered

for t h i s

Z—AAC H^

^COOH

^COOH

C=C C H E

— C6H5CH2—CH^ K

NHCOCH3

5

NHCOCH3

Ε ir Z — B A C

H Z-

C H E

COOH /

\

5

COOH /

\ NHCOC H \ E

5

C H CH —CH 6

/ Ε -

/

H

—

E

2

\HCOQH,

χ

NHCOC H

5

5

π

20.

Asymmetric

KNOWLES E T A L .

Homogeneous

329

Catalysts

DHV CH

COOCH3

3

^COOCHa

^ C = C ^ CH

NHCOC H

3

6

(CH ) CH-CH^ 3

2

NHCOC H

5

6

5

III


a-Phenylacrylic A c i d ^ O O H CH2

= =

C

\

^COOH —* C H 3 — C H

C H 6

\

5

C H 6

5

IV V i n y l Acetate OCOCH3

I CH =CHOCOCH 2

3

CH CH 3

CHO

O f t h e s e r e a c t i o n s o n l y I a n d I I - Z a n d t h e c o r r e s p o n d i n g ee's w o r k w i t h h i g h e f f i c i e n c y . T h e b e s t p h o s p h i n e a v a i l a b l e to u s for t h e s e c o n v e r s i o n s w a s (R,R) -l,2-ethanediylbis-[(2-methoxyphenyl)-phenylp h o s p h i n e ] ( D i P A M P ) (3). S i n c e a n u m b e r o f v a r i a n t s o f t h i s m o l e c u l e w e r e r e a d i l y a v a i l a b l e f r o m a c o m m o n , r e s o l v e d i n t e r m e d i a t e , it s e e m e d w o r t h w h i l e to m a k e a f e w o f t h e s e w i t h t h e h o p e o f a c h i e v i n g m a r g i n a l g a i n s as w e l l as i m p r o v i n g o u r u n d e r s t a n d i n g o f t h i s r e m a r k a b l e catalysis. T a b l e I s h o w s a n u m b e r of b i s p h o s p h i n e s that w e r e p r e p a r e d for this s t u d y . S u b s t i t u t i n g a l i p h a t i c g r o u p s for t h e p h e n y l i n D i P A M P , as i n C o m p o u n d s 2 a n d 3 , g a v e a s u r p r i s i n g l y i n f e r i o r c a t a l y s t for r e d u c i n g α-acetamidocinnamic a c i d ( A A C ) (see R e a c t i o n I). S u b s t i t u t i n g t h e p h e n y l w i t h a n e l e c t r o n - d o n a t i n g s p e c i e s as i n C o m p o u n d 4 or a n e l e c t r o n - w i t h d r a w i n g g r o u p as i n C o m p o u n d 5 or 6 a p p e a r e d to h a v e n o m a r k e t effect. T h e 4 - d i m e t h y l a m i n o s u b s t i t u e n t i n C o m p o u n d 7 w a s d e s i g n e d to b e a n e l e c t r o n - d o n a t i n g s p e c i e s i n b a s e a n d a n e l e c t r o n - w i t h d r a w i n g s p e c i e s i n a c i d . It w a s s u r p r i s i n g t h a t t h i s p h o s p h i n e s h o w e d s u c h a m a r k e d difference b e t w e e n the a c i d a n d b a s e m o d e w h e n C o m p o u n d 4 or 5 (as d i d D i P A M P ) s h o w e d o n l y m i n o r differences.

330

M E T A L PHOSPHINE

COMPLEXES

S u b s t i t u t i o n o f the p h e n y l w i t h a 2 - n a p h t h y l gave a n i d e n t i c a l catalyst

(Compound

8).

Replacement

of the

2-methoxy

w i t h a 2-

m e t h y l t h i o ( C o m p o u n d 9) d e s t r o y e d t h e c a t a l y s i s , a l t h o u g h t h e c o r r e 10) w a s f a i r l y e f f e c t i v e . T h e

2-fluoro-

p h e n y l , as s e e n i n C o m p o u n d 1 1 , g a v e o n l y a m o d e r a t e l y

sponding sulfone ( C o m p o u n d

efficient

catalyst. S i n c e V a r i a n t 9 p r o b a b l y d e s t r o y e d the catalysis b y

forming

a tight complex w i t h the metal, w e

e x p e c t e d that the free p h e n o l ,


C o m p o u n d 12 w o u l d b e h a v e i n a s i m i l a r m a n n e r . A s i t t u r n e d o u t , t h i s c o m p o u n d w a s a fairly efficient, t h o u g h s l u g g i s h , catalyst. I n o u r early w o r k w e f o u n d that v a r y i n g the s m a l l , m e d i u m , a n d l a r g e g r o u p s o n t h e p h o s p h o r u s w a s u n p r o d u c t i v e (4). T h i s l e d to o u r c h o i c e o f the h i g h l y successful o - a n i s y l group. P e r h a p s other hetero atoms i n the s u b s t i t u e n t m i g h t l e a d to catalysts w i t h n e w a n d u s e f u l properties. We

explored

a few

sulfone

substituents a n d f o u n d that

these w e r e i n t e r e s t i n g b u t not s u p e r i o r to o u r present m o d e l s . T a b l e shows

that i f w e

substitute the c y c l o h e x y l

group

cyclohexyl-2-methoxyphenylmethylphosphine)

of C A M P

II

((R)-

(28) ( J ) w i t h a m e t h y l

s u l f o n y l m e t h y l , as i n C o m p o u n d 14, w e c a n o b t a i n a v e r y r e s p e c t a b l e 92%

ee o n Z - A A C . T h e

and

17 s h o w

that the

T a b l e I.

low

results a c h i e v e d w i t h C o m p o u n d s

o-anisyl

group

Bisphosphines

is s t i l l

necessary

\

/

P—CH CH P 2

(R,R)

2

\ Compound Vo.

R

R4

2

R4

« 3

2

1

C

e

H

5

2-CH OC H

4

R.

R

2

2 3 4

C

2

H

5

2-CH OC H

4

Ri

R

2

4

Ri

R R

5

3-ClC H

C e H

3

3

2-CH OC H

n

3

4-CH OC H 3

e

e

4

4

6

4-CH S0 C H

7

4*.(CH ) NC H

8

2-naphthyl

3

2

3

e

2

e

2-CH3SCgH 2-CH3S0 CgH

11 12

2-FC H CeH

13

CeH

a 6

4

4

2

e

5

4

4

2

2-CH OC H

4

Ri

R

2

2-CH OC H

4

Ri

R

2

2-CH OC H

4

3

e

4

3

e

4

3

4

e

2-CH OC H 2-CH OC H

3

CeH CeH CeH

e

e

Ri Ri

R

2

2

Ri

R

2

5

Ri

R

2

5

Ri

R

2

3

9 10

5

e

e

e

5

2-HOC„H 2 - C H C O O C H 4

3

15

good

R3

Ri

R

for

e

4

Best ee %

a

96%

S

60S 64S 92 S 96 S 89 S

8 3 (acid 1 5 (base 95 S N R 73 S 60S

Ri Ri

R R

2

84 S*

Ri

R

2

63 S

The % ee was measured for the hydrogénation of A A C . The % ee was measured for the hydrogénation of B A C .

2

6

20.

Asymmetric

KNOWLES ET AL.

T a b l e II.

Homogeneous

Sulfone Based Phosphines ( ^

^

x

R


R 2-CH OC H

15 16 17 18

C H 2-CH OC H CeH 2-CH OC H

19

R,R-l,2-Ethanediylbis[(2-methoxy-4-sodium sulfonylphenyl)phenylphosphine] R,R-l,2-Ethanediylbis[2-methoxy-4-dimethylaminosulfonylphenyl)phenylphosphine] (C H ) P. P(C H )

3

e

e

4

s

3

e

4

5

3

21

e

4

CH C C C C

H H H H

E

C H S 0 C H

3

3

C H (CH (CH / (3

3

3

3

3

3

5

2

VoforAAC

S 0 C H ) NS0 CH ) NS0 CH \ S0 CH Ν 2

Acid

9 2 (0°) 8 3 (50°)

2

2

2

2

3

2

2

2

2

84(50°) 90(0°)

2

2

E

L> C H

I

5

(50°)

79 S S 19 S 78 S 26 S 79 S

2

3

\

/

3

Base (Temp.)

3

14

20

^

ee

Com pound No.

331

Catalysts

85 S 79 S ?1R(IPA) 88 R ( H 0 )

2

2

2

so

2

CH

3

(Achiwa

Sulfone)

Since displacement of (R) menthyl ester and the S i C l reduction both occur with inversion, all products are presumably of the R-configuration. a

2

p

e

c a t a l y s i s . O t h e r s u b s t i t u t e d s u l f o n e s s u c h as C o m p o u n d s 16 a n d 18 behave almost identically. O n e

difference

b e t w e e n these

sulfones

a n d o u r p r e v i o u s c a t a l y s t s is t h e i r s o l u b i l i t y i n a q u e o u s m e d i a . W i t h a h o m o g e n e o u s c a t a l y s t i t is o n l y n e c e s s a r y for t h e s u b s t r a t e t o b e m a r g i n a l l y s o l u b l e . I n fact, i t is v e r y c o n v e n i e n t to go f r o m a s l u r r y o f reactant to a s l u r r y o f p r o d u c t . W i t h sulfones u n l i k e D i P A M P a n d DIOP modify

o n e c a n u s e w a t e r as t h e s l u r r y i n g m e a n s . W e

attempted

D i P A M P w i t h a s u l f o n y l g r o u p as w e l l as A c h i w a ' s

to

BPPM

( i , 5, 6 ) . C o m p o u n d s 1 9 , 2 0 , a n d 2 1 w e r e s u c c e s s f u l m o d i f i c a t i o n s , performing i n water a n d g i v i n g only m a r g i n a l l y poorer results than the parent c o m p o u n d . S i n c e D I O P (22) ( i , 7 ) a n d its c l o s e d e r i v a t i v e s a r e t h e m o s t effec t i v e l i g a n d s for n o n c h e l a t i n g o l e f i n s l i k e a - p h e n y l a c r y l i c a c i d (I, ( R e a c t i o n I V ) a n d for h y d r o f o r m y l a t i o n s ( R e a c t i o n V ) (1 ), w e

7)

decided

to t r y a f e w v a r i a n t s o f t h i s v e r s a t i l e m o l e c u l e as s h o w n i n T a b l e

III.

332



W e w e r e a b l e to s u b s t i t u t e the g e m - m e t h y l s i n t h e k e t a l r i n g w i t h g e m - p h e n y l s . C o m p o u n d 2 3 shows that this perturbation was quite h a r m f u l to b o t h R e a c t i o n s I a n d V . T h i s r e s u l t w a s u n e x p e c t e d s i n c e X - r a y s t r u c t u r e s h o w e d t h e g e m - m e t h y l s to b e w e l l r e m o v e d f r o m t h e site o f a c t i o n (8) a n d o n e w o u l d e x p e c t g e m - p h e n y l s to b e s i t u a t e d similarly. Meta-substitution on the p h e n y l groups of D I O P gave marginal i m p r o v e m e n t ( i ) , a n d t h e β-naphthyl m o i e t y s h o u l d s i m u l a t e a m e t a s u b s t i t u e n t . A c t u a l l y C o m p o u n d 2 4 t u r n s o u t to b e b e t t e r t h a n D I O P s i n c e it g i v e s a 8 3 % y i e l d u n d e r a c o n d i t i o n w h e r e D I O P w o u l d g i v e o n l y a 7 6 % y i 4 d (3 a t m a n d 50°C). T h e α-naphthyl w a s , as m i g h t b e e x p e c t e d for so h i n d e r e d a m o l e c u l e , q u i t e i n f e r i o r . T h e m - t r i fluoromethyl p r o d u c t (see C o m p o u n d 26) g a v e s i g n i f i c a n t l y faster h y d r o f o r m y l a t i o n s , b u t at b e s t w a s o n l y m a r g i n a l l y b e t t e r . A n o t h e r D I O P d e r i v a t i v e w a s p r e p a r e d to c h e c k w h e t h e r t h e r i g i d i t y o f t h e acetonide r i n g was really necessary. T h e adjacent m e t h y l s i n C o m p o u n d 2 7 m i g h t b e e x p e c t e d to i n f l u e n c e a p r e f e r r e d c o n f o r m a t i o n as i n B o s n i e n ' s c h i r a p h o s (1, 9 ) . A c t u a l l y , u n d e r b a s e c o n d i t i o n s C o m p o u n d 27 gave a respectable 6 6 % suggesting that w i t h sufficiently large groups C o m p o u n d 2 7 m i g h t b e c o m e a n efficient l i g a n d . W i t h r e s p e c t to R e a c t i o n I V , C o m p o u n d 2 7 g a v e 5 5 % e e as c o m p a r e d w i t h 6 0 % for D I O P (7). Hydroformylations were r u n under a variety of temperature, pressure, a n d excess-ligand conditions. Table III shows o n l y the best e e ' s o b t a i n e d after a l i m i t e d s t u d y . I n n o case w e r e w e a b l e to e x c e e d results p u b l i s h e d b y others i n other systems ( i ) . f Table III.

(R,fl)-DIOP

Com pound No. 22 23 24 25 26 27

Derivatives

V

Structure

CH C H CH CH CH CH3—

«

2

3

e

5

3

3

3

C H (DIOP) C H 2- N a p h t h y l 1-Naphthyl C H —3C e H4 5 ) - H C FP (CC H e

5

e

5

2

I

3

e

X ) — C H — C H P (R )2 2

2

\ ) — C H — C H

2

P (R2)

2

>

;

Hydro génation ofAAC Best ee %

Hydrofor mylation of Vinyl Acetate Best ee %

83 i l 38 R 83 R NR 7R

40 S 29 S 39 S 6S 42 S

0

2

*(S,S)»

(

49 S (acid) 6 6 S (base)

C H 3 — CH—CH P(CeH5) A l l hydroformylations were run with excess ligand (1-6 moles). Best ee's were obtained with 6 moles of ligand at the expense of slow reactions. Ref. 16. 2

α

6

2

Asymmetric

KNOWLES E T A L .

20.

Table IV.

333

Catalysts

D e h y d r o v a l i n e (Reaction

Compound No.

III)

Ligand

28 29 30


Homogeneous

ee

(C H )(2-CH OC H )(CH )P(CAMP) (CeHnXiso-PrOCeHJiCHa)? [(C H )(2-CH OC H )PCH -] (DiCAMP) e

1 1

e

3

1 1

e

3

4

23 44 72

3

e

4

2

%

2

W h e n o n e t r i e s a s y m m e t r i c hydrogénations o n a h i n d e r e d a m i n o a c i d as i n R e a c t i o n I I I , a l l o f t h e w e l l - k n o w n l i g a n d s ( i )

give

very

s l o w reactions a n d p o o r ee's. Hydrogénations g e n e r a l l y d o n ' t

finish

D i P A M P . T a b l e I V s h o w s t h a t u s i n g t h e i s o p r o p y l e t h e r o f C A M P (28) ( J O ) g a v e m u c h faster r e a c t i o n s a n d m o d e s t e f f i c i e n c y . T h e d i m e r o f C o m p o u n d 28, [ D i C A M P ( 3 ) ] ,

a catalyst w h i c h was disappointingly

p o o r for A A C {see R e a c t i o n I ) , g a v e 7 2 % e e for R e a c t i o n I I I at a c c e p t a b l e rates u n d e r r e l a t i v e l y f o r c i n g c o n d i t i o n s (75°C a n d 4 a t m p a r t i a l pressure o f hydrogen). T h i s l e a d indicates that some further structural modification m i g h t solve this system i f there was sufficient i n c e n t i v e . Synthetic

Methods

A l l o f the b i s p h o s p h i n e s i n T a b l e I w e r e p r e p a r e d b y the reaction of the appropriate G r i g n a r d reagent on a resolved m e n t h y l phosphinate e s t e r as d e s c r i b e d i n o u r p r e v i o u s w o r k (3). R ' w a s e i t h e r p h e n y l (11 ) or o - a n i s y l (3). R

x

c o r r e s p o n d s t o R i g r o u p i n T a b l e I.

Ο

Ο

R'—Ρ—Ο Men CH

3

Ο

R ' - P - ^

\

C H

(CH ) 0 3

3

+

3

» * f t?*^

(R'-P—CH ) 2

Ri

BF "

Si Cl

4

2

O

'

2

6

^ M g X II

R'—P—OCH

3

(R'—P—CH _) 2

CH

2

3

Ri

W h e n t h e G r i g n a r d r e a g e n t w a s t o o h i n d e r e d for f a c i l e r e a c t i o n , t h e m e n t h y l e s t e r w a s c o n v e r t e d first to t h e m e t h y l e s t e r b y t h e m e t h o d o u t l i n e d b y D e B r u i n (12). this m a n n e r .

P h o s p h i n e s 9 , 1 0 , a n d 11 w e r e p r e p a r e d i n

334


C o u p l i n g b y p r e p a r i n g the anion w i t h l i t h i u m followed by C u C l Phosphine

diisopropylamide

o x i d a t i o n w o r k e d n i c e l y i n a l l cases

2

(I).

10 w a s p r e p a r e d b y o x i d i z i n g C o m p o u n d 9 as t h e

phosphine oxide w i t h K M n 0

a n d t h e n r e d u c i n g the p h o s p h i n e o x i d e

4

w i t h S i C l . T h e s u l f o n e w a s i n e r t to this s i l a n e reagent. 2

e

Phosphine DiPAMP

12 w a s

with

prepared

lithium

b y cleaving the m e t h y l ether

diphenylphosphide

in

on

tetrahydrofuran


( T H F ) at a m b i e n t t e m p e r a t u r e s . M e l t i n g p o i n t s a n d rotations o f these p h o s p h i n e s a n d t h e i r corre s p o n d i n g oxides are r e p o r t e d i n T a b l e V. For catalytic w o r k o n l y a few m i l l i g r a m s o f l i g a n d w e r e r e q u i r e d for e v a l u a t i o n so t h a t o n l y

NMR

a n d M S analyses w e r e u s e d . W h e n e v e r possible the products w e r e p u r i f i e d b y c r y s t a l l i z a t i o n to constant m e l t i n g p o i n t s . I n the case

of

o i l s , t h e r e a l w a y s w i l l r e m a i n s o m e d o u b t as to o p t i c a l p u r i t y . T h e p h o s p h i n e s w e r e a i r - s e n s i t i v e a n d h a d to b e c r y s t a l l i z e d u n d e r n i t r o gen. A c t u a l l y , i n m u c h o f o u r earlier w o r k the p h o s p h i n e s w e r e c o n t a m i n a t e d w i t h 5 - 1 0 % o x i d e w h i c h c a u s e d n o c h a n g e i n e e ' s o r rates as l o n g as t h e w e i g h t s w e r e a d j u s t e d p r o p e r l y . T h e sulfones w e r e p r e p a r e d b y the f o l l o w i n g reactions:

Ο

Ο

Il

II

R ^ O z C H , + R'—Ρ—Ο Men — CH

R'—Ρ—CH S0 Ri 2

CH

3

i

2

3

Si Cl 2

6

II R'—P—CH S0 Ri 2

2

I

CH R ' w a s e i t h e r p h e n y l (11) m o r p h o l i n o as i n R

3

of Table

or o - a n i s y l (3). R

t

3

w a s C H , ( C H ) N , or 3

3

2

II.

C o m p o u n d 14 c o u l d b e m a d e t h i s w a y or a l t e r n a t e l y f r o m a n i o n o f d i m e t h y l s u l f o x i d e (13)

f o l l o w e d b y o x i d a t i o n to t h e

w i t h K M n 0 . T h i s c o m p o u n d , although n i c e l y crystalline, was 4

ficult

the

sulfone dif

to p u r i f y a n d w e f o u n d i t b e t t e r t o m a k e t h e m o r p h o l i n o d e r i v a

t i v e , C o m p o u n d 18, w h i c h h a n d l e d m u c h b e t t e r . C o m p o u n d 19 w a s o b t a i n e d b y d i r e c t s u l f o n a t i o n o f C o m p o u n d 1 w i t h concentrated

H S0 2

4

at 25°C. T h e

d i m e t h y l a m i n o sulfone

was

p r e p a r e d b y c h l o r o s u l f o n a t i n g a n d a m i n a t i n g D i P A M P as t h e b i s oxide followed b y silane reduction. The

sulfone derivative

o f A c h i w a ' s R P P M (5, 6) w a s

f r o m t h e free b a s e a n d m e t h a n e s u l f o n y l c h l o r i d e .

prepared

Table V.


Com pound No. 2 3 4 5 6 7 8 9 10 11 12 13

Asymmetric

KNOWLES E T A L .

20.

335

Catalysts

Physical Data on Bisphosphine Oxides

( R , R ) -Bisphosphine M.P.

Homogeneous

(°C)

Oxide

[a]%°(l,

188-9 222-4 oil oil oil 222-5 217-220 179-80 noncrystalline 193-4 327

(R,R)-Bisphosphine,

MeOH)

-76. Γ -52.7° -30.4°

oil 84-6 122-3 89-91 oil 175-80 133-4 127- 9 noncrystalline 1 2 8 - 3 0 (not p u r e ) 1 4 8 - 9 [a]%> = + 5 6 . 7 ° (1, C H C 1 ) oil

+95° -30.5° -61.3° -14.2° + 70.8° ( C F 3 C O O H )

The benzophenone

m.p.(°C)

3

k e t a l o f D I O P ( C o m p o u n d 23) c o u l d n o t b e

m a d e d i r e c t l y f r o m t h e c o r r e s p o n d i n g d i o l b u t w a s p r e p a r e d as f o l lows: HO—CH—CH OTs

C H

2

6

+ (C H ) CC1 6

5

2

5

O—CH—CH OTs 2

2

C H/0—CH—CH OTs

HO—CH—CH,OTs

6

2

30 T h e b i s - t o s y l a t e ( C o m p o u n d 30) t h e n w a s c o n v e r t e d t o C o m p o u n d 23 i n the phide

usual manner

by

reacting

with lithium

diphenylphos-

(7).

T h e a- a n d / 3 - n a p h t h y l d e r i v a t i v e s , C o m p o u n d s 2 4 a n d 2 5 , as w e l l as C o m p o u n d 2 6 w e r e p r e p a r e d from t h e b i s - t o s y l a t e (7) a n d t h e c o r r e sponding lithium diarylphosphide. T h e d i m e t h y l derivative, C o m p o u n d 27, was prepared from r a c e m i c 1,2 d i m e t h y l s u c c i n i c a c i d b y first r e s o l v i n g w i t h q u i n i n e (14, 15, 16), p r e p a r i n g t h e d i m e t h y l ester, a n d t h e n p r o c e e d i n g e x a c t l y b y t h e s a m e s e q u e n c e u s e d for D I O P f r o m d i m e t h y l tartrate (7). T a b l e V I gives m e l t i n g points a n d rotations o f the c o m p o u n d s i n T a b l e III. Table VI. Compound No. 23 24 25 26 27

M.P.

Physical Constants D I O P CC)

135-137 110-125 104-106 oil 96-97

Derivatives

[ ]f a

-40.4° 13.9° -.46° 3.24° 47°.

(1, (2, (2, (1, (1,

C H )(R,R) C H )(fl,R) C H )(R,R) toluene)(R,R) CHC1 )(S,S) e

e

e

e

e

e

3

336

METAL PHOSPHINE COMPLEXES

Conclusions It is f a i r l y w e l l e s t a b l i s h e d t h a t t h e s u c c e s s a c h i e v e d w i t h R e a c t i o n s I a n d I I - Z a r e f a c i l i t a t e d b y t h e a b i l i t y o f t h e s u b s t r a t e to c h e l a t e w i t h the m e t a l ( J , 3 , 8). T h e c a r b o n y l o f the a m i d e a n d the o l e f i n are s i t u a t e d p e r f e c t l y for b o n d f o r m a t i o n a n d t h e c a r b o x y l o r its e q u i v a l e n t forms a t h i r d p o i n t o f t i e - d o w n . T h i s three-point l a n d i n g a p p a r e n t l y forms a r i g i d s t r u c t u r e that e n a b l e s a rather s i m p l e l i g a n d to

achieve


s t e r i c c o n t r o l . F o r t u n a t e l y , t h i s s p e c i a l c a s e is a p p l i c a b l e t o s y n t h e s i z i n g α-amino a c i d s w h e r e t h e i m p o r t a n c e o f t h e c o m p o u n d s offsets t h e l a c k o f g e n e r a l i t y . I n R e a c t i o n s I I I , I V , a n d V t h e t i e - d o w n is e i t h e r h i g h l y h i n d e r e d or n o n e x i s t e n t , a n d p e r h a p s o n e c a n o n l y

achieve

success i n these m o r e difficult systems w i t h a l i g a n d o f m u c h greater complexity. I n t h e h y d r o f o r m y l a t i o n r e a c t i o n , V , t h e s i t u a t i o n is e v e n Here

there

is n o d e f i n i t e

stereochemistry

b e t w e e n the

worse.

phosphine

l i g a n d a n d the m e t a l . O n e o f the reactants, c a r b o n m o n o x i d e , c o m p e t e s so w e l l w i t h t h e p h o s p h i n e for sites o n t h e m e t a l t h a t it is d i f f i c u l t to i n s u r e t h a t t h e c h i r a l a g e n t is p r e s e n t w h e n t h e n e w a s y m m e t r i c c e n t e r is f o r m e d . Literature

Cited

1. Valentine, D.; Scott, J. W. Synthesis 1978, 5, 329. 2. Koenig, K. E . ; Sabacky, M . J . ; Bachman, G. L.; Christopfel, W. C.; Barnstorff, H . D.; Friedman, R. B.; Knowles, W. S.; Stults, B. R.; Vineyard, B. D.; Weinkauff, D. J. Ann. N.Y. Acad. Sci. 1980, 333, 16. 3. Vineyard, B. D.; Knowles, W. S.; Sabacky, M. J . ; Bachman, G. L.; Wein kauff, D. J. J. Am. Chem. Soc. 1977, 99, 5946. 4. Knowles, W. S.; Sabacky, M. J.; Vineyard, B. D. Ann. N.Y. Acad. Sci. 1973, 214, 119. 5. Achiwa, K. J. Am. Chem. Soc. 1976, 98, 845. 6. Ojima, I.; Kogure, T.; Yoda, N. J . Org. Chem. 1980, 45, 4728. 7. Kagan, H . B.; Dang, T. P. J. Am. Chem. Soc. 1972, 94, 6429. 8. Knowles, W. S.; Vineyard, B. D.; Sabacky, M. J.; Stultz, B. R. "Fundamen tal Research in Homogeneous Catalysis", Plenum: New York, 1979; Vol. 3, p. 537. 9. Fryzuk, M. D.; Bosnich, B. J. Am. Chem. Soc. 1977, 99, 6262. 10. Knowles, W. S.; Sabacky, M. J . ; Vineyard, B. D. In "Homogeneous Catalysis—II", Adv. Chem. Ser. 1974, 132, 274. 11. Korpiun, O.; Lewis, R. Α.; Chickos, J.; Mislow, K. J. Am. Chem. Soc. 1968, 90, 4842. 12. DeBruin, Κ. E.; Perrin, D. E . J. Org. Chem. 1975, 40, 1523. 13. Corey, E . J . ; Chaykovsky, M. J . Am. Chem. Soc. 1965, 87, 1345. 14. Korver, O.; Joberg, S. Tetrahedron 1975, 31, 2603. 15. Berner, Ε.; Leonardson, R. Ann. 1939, 538, 1. 16. Carnmalm, B. Chem. Ind. (London) 1956, 1093. 17. Cramer, R. J. Am. Chem. Soc. 1964, 86, 217. 18. Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1971, 93, 2397. 19. Cohen, S. G.; Crossley, J . ; Khedouri, E . ; Zand, R.; Klee, L. H . J . Am. Chem. Soc. 1963, 85, 1685. RECEIVED July 10, 1980.

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