Photoactivation of Polymer-Anchored Catalysts - American Chemical

2 Photoactivation of Polymer-Anchored Catalysts

Interfacial Photoprocesses: Energy Conversion and Synthesis Downloaded from pubs.acs.org by CORNELL UNIV on 09/02/16. For personal use only.

I r o n C a r b o n y l C a t a l y z e d Reactions

of

Alkenes

ROBERT D. SANNER, RICHARD G. AUSTIN, and MARK S. WRIGHTON 1

Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 1

WILLIAM D. HONNICK and CHARLES U. PITTMAN, JR.

Department of Chemistry, University of Alabama, University, A L 35486

Photoactivation of polymer-anchored iron carbonyl catalysts is reported. Prototypic reactions are 1-pentene isomerization and reaction of 1-pentene with HSiEt , which can be photocatalyzed at 2 5 ° C by near-UV irradiation of suspensions of the polymer-anchored catalyst systems. The basic polymer system is a styrene-1% divinylbenzene resin derivatized with either -PPh or -P(Ph)CH CH PPh anchoring sites for catalyst precursors. Fe(CO) 's (n = 3, 4) are attached to the phosphine sites by reaction with Fe (CO) . The poly mer-anchored catalysts show turnover numbers exceeding 2 X 10 in some cases and observed quantum yields exceed unity, indicating the photogeneration of a thermal catalyst. From the data we conclude that the anchoring Fe-P bond is relatively photoinert and that the catalysis is initiated by the photoinduced dissociation of C O . 3

2

2

2

2

n

3

12

4

Coordinatively ^

unsaturated transition metal organometallic

complexes

a r e b e l i e v e d to p l a y a k e y r o l e i n h o m o g e n e o u s c a t a l y t i c processes

(I).

C o o r d i n a t i v e u n s a t u r a t i o n c a n b e generated p h o t o c h e m i c a l l y b y 1

To whom correspondence should be addressed. 0-8412-0474-8/80/33-184-013$05.00/0 © 1980 American Chemical Society

14

INTERFACIAL

PHOTOPROCESSES

l i g h t - i n d u c e d l i g a n d dissociation a n d m e t a l - m e t a l b o n d cleavage

(2,3).

S u c h p h o t o c h e m i s t r y has b e e n e x p l o i t e d to i n i t i a t e c a t a l y t i c processes under relatively m i l d thermal conditions ( 4 , 5 , 6 ) .

Light-generated cata

lysts m a y b e g e n u i n e l y u n i q u e since t h e catalyst is t h e result of some excited-state d e c a y process.

F u r t h e r , c a t a l y t i c processes that are r u n at

l o w e r temperatures m a y y i e l d greater p r o d u c t d i s t r i b u t i o n s e l e c t i v i t y w h e n m o r e t h a n one p r o d u c t c a n b e f o r m e d .

L i g h t also offers a d e g r e e

of c o n t r o l over c a t a l y t i c processes n o t necessarily a t t a i n a b l e i n c o n v e n


t i o n a l c a t a l y t i c systems, since the p r o d u c t f o r m a t i o n d e p e n d s

on

two

s t i m u l i , l i g h t a n d heat. E x a m p l e s of o r g a n o m e t a l l i c p h o t o c a t a l y s i s h a v e d e m o n s t r a t e d the c o n c e p t of i n i t i a t i n g catalysis u n d e r r e l a t i v e l y m i l d c o n d i t i o n s i n t h e reactions of olefins w i t h h y d r o g e n a n d s i l i c o n h y d r i d e s a n d i n u n i m o l e c u l a r i s o m e r i z a t i o n reactions of olefins

(4,5,6).

I n this c h a p t e r w e s u m m a r i z e o u r recent findings (7)

o n the e x p l o i t a

t i o n of p h o t o c h e m i c a l catalyst g e n e r a t i o n i n situations w h e r e t h e catalyst p r e c u r s o r is a n c h o r e d to a p o l y m e r .

A d d i t i o n a l l y , w e present n e w , d a t a

to f u r t h e r c h a r a c t e r i z e s u c h systems.

A l a r g e n u m b e r of examples

of

t h e r m a l l y a c t i v a t e d , p o l y m e r - a n c h o r e d catalyst systems h a v e b e e n s t u d i e d (8,9,10).

A n c h o r i n g a catalyst to a p o l y m e r takes a d v a n t a g e of

the

m o l e c u l a r specificity of o r g a n o m e t a l l i c catalysts w h i l e s t i l l b e i n g a b l e to separate the p r o d u c t s easily f r o m the catalyst system. V i e w i n g t h e p o l y m e r as a l i g a n d , a l b e i t a n u n u s u a l one, one c a n also effect s o m e c o n t r o l o v e r the c a t a l y t i c processes b y

the n a t u r e of

the p o l y m e r - a n c h o r i n g

system. P h o t o c h e m i c a l a c t i v a t i o n of p o l y m e r - a n c h o r e d catalyst systems a l l o w the g e n e r a t i o n of u n i q u e catalyst systems. I t has b e e n d e m o n s t r a t e d that extensive, m u l t i p l e , c o o r d i n a t i v e u n s a t u r a t i o n c a n b e p h o t o g e n e r a t e d b y i r r a d i a t i n g m e t a l c a r b o n y l s i n situations w h e r e the complexes matrix

isolated

(11,12,13).

The

polymer-anchored

complex

can

are be

v i e w e d as a s i t u a t i o n w h e r e t h e c o m p l e x c a n b e " m a t r i x i s o l a t e d / ' p r o v i d e d the r i g i d i t y of the p o l y m e r is great e n o u g h a n d t h e d e n s i t y of c o m p l e x e s o n the p o l y m e r is l o w e n o u g h to p e r m i t i s o l a t i o n .

Homoge

neous o r g a n o m e t a l l i c c a t a l y t i c species h a v e p r e v i o u s l y b e e n a t t a c h e d to p o l y m e r m a t r i c e s a n d there is e v i d e n c e for v a r y i n g degrees of m a t r i x i s o l a t i o n (14-19). photogenerated

H o w e v e r , this a p p r o a c h has n e v e r b e e n a p p l i e d to c a t a l y t i c species.

Of

course, t h e e x p l o i t a t i o n of

any

p h o t o a c t i v a t i o n of a p o l y m e r - a n c h o r e d catalyst d e p e n d s o n t h e p h o t o inertness of the a n c h o r b o n d .

P h o t o i n d u c e d selective loss of

ligands

o t h e r t h a n the p o l y m e r l i g a n d is the objective. D e t a i l e d results h a v e b e e n o b t a i n e d for F e ( C O )

r t

(n =

3, 4 )

bound

to a p h o s p h i n a t e d s t y r e n e - d i v i n y l b e n z e n e r e s i n . T w o types of a n c h o r i n g sites h a v e b e e n u s e d a n d are r e p r e s e n t e d i n I a n d I I . M o s t of the w o r k thus f a r has i n v o l v e d the p h o s p h i n a t e d p o l y m e r I . T h i s a n c h o r i n g system a p p r o x i m a t e s a t r i p h e n y l p h o s p h i n e l i g a n d ; c o n s e q u e n t l y the F e ( C O ) n


2.

SANNER E T A L .

(PPh3) . 5

w

Photoactivation

of Polymer-Anchored

Polymer

Polymer

I

II

(n =

15

Catalysts

3, 4 ) complexes h a v e b e e n u s e d as h o m o g e n e o u s m o d e l s

for t h e p o l y m e r - a n c h o r e d system. A d i r e c t c o m p a r i s o n of these p h o s p h i n e derivatives w i t h F e ( C O )

5

also has b e e n m a d e to assess t h e effect of

h a v i n g t h e p h o s p h i n e l i g a n d ( s ) i n t h e c o o r d i n a t i o n sphere.

The

probe

c a t a l y t i c c h e m i s t r y is 1 - p e n t e n e i s o m e r i z a t i o n a n d r e a c t i o n w i t h H S i E t . 3

B o t h reactions c a n b e p h o t o c a t a l y z e d u s i n g F e ( C O ) precursor

5

as t h e c a t a l y s t

(6).

Experimental T h e g e n e r a l p r o c e d u r e s a n d synthesis associated w i t h C a t a l y s t S y s t e m I (see T a b l e I) h a v e b e e n d e t a i l e d elsewhere ( 7 ) , i n c l u d i n g t h e synthesis a n d c h a r a c t e r i z a t i o n of the d e r i v a t i z e d p o l y m e r . T h e i r r a d i a t i o n source Table I. Anchoring' System

%of Phenyl Rings Substituted

Catalyst System

%Fe

P:Fe

I I

3.3 29

A B

0.92 4.47

0.58 4.10

2.9 2.0

II II II II

11.9 3.1 11.9 3.1

C D E F

3.91 1.73 4.32 1.51

6.79 1.40 1.10 0.42

1.0 2.2 7.1 6.5

See text.

a

Analytical D a t a for Polymer Catalyst Systems

16

INTERFACIAL

PHOTOPROCESSES

i n t h e experiments d e s c r i b e d h e r e i n w a s a G E B l a c l d i t e e q u i p p e d w i t h t w o 1 5 - W b u l b s w i t h p r i n c i p a l o u t p u t at 355 n m ; the i n t e n s i t y at the s a m p l e ( s t i r r e d for p o l y m e r systems) w a s a p p r o x i m a t e l y 1 0 ' e i n / m i n m e a s u r e d b y f e r r i o x a l a t e a c t i n o m e t r y ( 7 ) . T h e samples themselves w e r e solutions or suspensions of the catalyst p r e c u r s o r i n neat 1-pentene ( C h e m i c a l S a m p l e s C o . , > 9 9 . 9 % ) s u c h that a b o u t 1 0 " M F e w a s present. S a m p l e size w a s t y p i c a l l y 1.0 m L ; the a l i q u o t s w e r e p l a c e d i n 13 X 1 0 0 - m m a m p u l e s , f r e e z e - p u m p - t h a w degassed, a n d h e r m e t i c a l l y s e a l e d p r i o r to i l l u m i n a t i o n at 298 K . A n a l y s e s w e r e a l l b y gas c h r o m a t o g r a p h y using equipment described previously (7). P o l y m e r S y s t e m I I has not b e e n p r e v i o u s l y d e s c r i b e d a n d its synthesis is d e s c r i b e d b e l o w . T e t r a h y d r o f u r a n ( T H F ) w a s d i s t i l l e d f r o m potass i u m / b e n z o p h e n o n e u n d e r n i t r o g e n . A l l other solvents a n d c h e m i c a l s w e r e u s e d as r e c e i v e d , except for d i p h e n y l v i n y l p h o s p h i n e , w h i c h w a s p r e p a r e d b y the r e a c t i o n of c h l o r o d i p h e n y l p h o s p h i n e w i t h v i n y l m a g n e s i u m b r o m i d e a c c o r d i n g to the l i t e r a t u r e m e t h o d (23). Styrene-1%d i v i n y l b e n z e n e beads w e r e p u r c h a s e d f r o m B i o - R a d L a b o r a t o r i e s ( S X - 1 , 2 0 0 - 4 0 0 m e s h ) a n d w e r e b r o m i n a t e d a c c o r d i n g to l i t e r a t u r e m e t h o d s (24). M i c r o a n a l y t i c a l analyses w e r e p e r f o r m e d b y S c h w a r z k o p f M i c r o a n a l y t i c a l L a b o r a t o r i e s , W o o d s i d e , N e w Y o r k . A l l reactions a n d m a n i p u lations i n v o l v i n g p h o s p h i n e s w e r e c a r r i e d out u n d e r n i t r o g e n . Preparation of C H 5 P ( H ) C H C H P ( Q H ) . A neat s o l u t i o n of p h e n y l p h o s p h i n e (36.0 g, 0.33 m o l ) a n d d i p h e n y l v i n y l p h o s p h i n e (36.8 g, 0.17 m o l ) c o n t a i n i n g A I B N (0.30 g ) w a s i r r a d i a t e d u n d e r n i t r o g e n for 2 h r w i t h a 1 0 0 - W H a n o v i a U V l a m p . T h e excess d i p h e n y l p h o s p h i n e w a s d i s t i l l e d f r o m the r e s u l t i n g s o l u t i o n at a t m o s p h e r i c pressure a n d t h e l - p h e n y l p h o s p h i n o - 2 - d i p h e n y l p h o s p h i n o e t h a n e w a s v a c u u m d i s t i l l e d at 1 9 0 - 1 9 5 ° C / 0 . 0 5 t o r r , y i e l d : 35.0 g ( 6 3 % ) . T h e o n l y other m a j o r b y p r o d u c t w a s bis ( 2 - d i p h e n y l p h o s p h i n o e t h y l ) p h e n y l p h o s p h i n e p r o d u c e d b y the r e a c t i o n of t w o moles of d i p h e n y l v i n y l p h o s p h i n e p e r m o l e of p h e n y l p h o s p h i n e . T h e r a t i o of the t w o p r o d u c t s f o r m e d b y this r e a c t i o n is v e r y sensitive to the r a t i o of the t w o reactants, w i t h a n excess of p h e n y l p h o s p h i n e f a v o r i n g p r o d u c t i o n of bis chelate p h o s p h i n e . Preparation of P - P ( P h ) C H C H P P h . L i t h i u m m e t a l (5.0 g, 0.72 m o l ) w a s s u s p e n d e d i n T H F (25 m L ) a n d a s o l u t i o n of 1 - p h e n y l p h o s p h i n o - 2 - d i p h e n y l p h o s p h i n o e t h a n e (22.0 g, 68.3 m m o l ) d i s s o l v e d i n T H F (50 m L ) was a d d e d dropwise. A yellow solution initially formed a n d s l o w l y b e c a m e d a r k r e d . T h e reactants w e r e s t i r r e d together for t w o days at r o o m t e m p e r a t u r e a n d t h e n refluxed for 1 d a y . T h e excess l i t h i u m m e t a l w a s r e m o v e d , a n d the s o l u t i o n w a s a d d e d d r o p w i s e to a b r o m i n a t e d s t y r e n e - l % - d i v i n y l b e n z e n e (11.9 g ~ 3 0 % of the p o l y s t y r y l r i n g s b r o m i n a t e d ). T h e m i x t u r e w a s s t i r r e d for 2 days at r o o m t e m p e r a t u r e a n d t h e n refluxed for 1 d a y . T h e m i x t u r e w a s c o o l e d a n d h y d r o l y z e d s l o w l y w i t h 100 m L of d e o x y g e n a t e d w a t e r , filtered, a n d w a s h e d w i t h 500 m L p o r t i o n s of the f o l l o w i n g d e o x y g e n a t e d solvents: w a t e r , acetone-water ( 1 : 1 ) , acetone, b e n z e n e , a n d m e t h a n o l . T h e p h o s p h i n a t e d r e s i n b e a d s w e r e d r i e d i n v a c u o at r o o m t e m p e r a t u r e for 24 h r . A n a l y s i s f o u n d 0 . 3 7 % B r a n d 5 . 1 6 % P , w h i c h corresponds to 1 1 . 9 % of the p o l y s t y r y l rings containing a b o u n d - P ( P h ) C H C H P P h group. A s i m i l a r p r o c e d u r e w a s f o l l o w e d to p r e p a r e a p h o s p h i n a t e d r e s i n c o n t a i n i n g b o u n d - P ( P h ) C H C H P P h groups w i t h 3 . 1 % of t h e p o l y styryl rings substituted. 6


3

6

2

2

2

2

2

2

2

2

5

2

2

2

2

2.

SANNER E T A L .

Photoactivation

of Polymer-Anchored

17

Catalysts

Preparation of P - [ P ( P h ) C H C H P P h 2 ] ^ F e ( C O ) ] . Fe (CO)i (0.55 g, 3.28 m m o l F e ) w a s d i s s o l v e d i n 25 m L of T H F a n d r e a c t e d w i t h 1.0 g of p h o s p h i n a t e d r e s i n c o n t a i n i n g b o u n d - P ( P h ) C H C H P P h groups ( 1 1 . 9 % of the rings s u b s t i t u t e d , 1.67 m m o l P ) . T h e m i x t u r e w a s refluxed f o r 1 h r , c o o l e d , a n d filtered. T h e r e s i n b e a d s t h e n w e r e w a s h e d r e p e a t e d l y w i t h alternate p o r t i o n s of d r y , d e o x y g e n a t e d T H F a n d m e t h a n o l , a n d t h e n d r i e d i n v a c u o at 8 0 ° C for 24 h r . A n a l y s i s f o u n d : 3 . 9 1 % P a n d 6 . 7 9 % F e c o r r e s p o n d i n g to a P : F e r a t i o of 1.0. T h r e e other p o l y m e r - a t t a c h e d catalyst resins w e r e p r e p a r e d s i m i l a r l y u s i n g different F e ( C O ) : p h o s p h i n a t e d r e s i n ratios. C a t a l y s t r e s i n f o r C a t a l y s t S y s t e m D (see T a b l e I ) w a s p r e p a r e d b y t h e r e a c t i o n of Fe (CO) (0.10 g, 5.0 m m o l F e ) w i t h p h o s p h i n a t e d r e s i n (2.0 g, 3 . 1 % r i n g s s u b s t i t u t e d , 1.08 m m o l P ) . C a t a l y s t r e s i n for C a t a l y s t S y s t e m E (see T a b l e I ) w a s p r e p a r e d b y the r e a c t i o n of F e ( C O ) i (0.032 g, 0.19 m m o l F e ) w i t h p h o s p h i n a t e d r e s i n (1.0 g, 1 1 . 9 % r i n g s s u b s t i t u t e d , 1.67 m m o l P ) . C a t a l y s t r e s i n for C a t a l y s t S y s t e m F (see T a b l e I ) w a s p r e p a r e d b y the r e a c t i o n of F e ( C O ) i (0.023 g, 0.13 m m o l F e ) w i t h p h o s p h i n a t e d r e s i n (2.0 g, 3 . 1 % r i n g s s u b s t i t u t e d , 1.08 m m o l P ) . 2

2

n

3

y

2

2


3

3

2

2

1 2

1 2

3

3

Results and

2

2

Discussion T h e p o l y m e r u s e d i n t h i s w o r k is a c o m

Polymer Systems Studied.

mercially available ( B i o - R a d Laboratories S X - 1 , 200-400 mesh) styrene1%

divinylbenzene, microporous

resin. It was brominated and

func-

t i o n a l i z e d a c c o r d i n g to the p r o c e d u r e s r e p r e s e n t e d i n E q u a t i o n s 1-3.

The

(i)

(2) I

(

^

B

,

r

i

f

n ^

!

(

^

p

(

p

|

i

)

C

H

!

C

H

!

p

p

h

!

m

II p h o s p h i n a t e d m a t e r i a l I a n d I I w e r e separately r e a c t e d t h e r m a l l y w i t h Fe (CO)i 3

2

i n T H F to i n c o r p o r a t e F e ( C O )

to the p h o s p h i n e l i g a n d s (see Fe (CO)i 3

2

n

(n =

Equations 4 and 5).

3, 4 ) b y a t t a c h m e n t T h e r m a l r e a c t i o n of

w i t h p h o s p h i n e l i g a n d s is k n o w n to p r o d u c e

i r o n c a r b o n y l species (20).

E l e m e n t a l analyses

mononuclear

(Schwarzkopf

Micro-

a n a l y t i c a l L a b o r a t o r i e s ) a n d I R spectra i n the c a r b o n y l r e g i o n h a v e b e e n u s e d to c h a r a c t e r i z e these systems.

18

INTERFACIAL

Fe (C0)i2 > THF

/-^ (pVPPh ) .Je(CO),

3

II

F

e

3

(

C

Q

h

)

PHOTOPROCESSES

2

(4)

B

n = 3, 4

(p)-P(Ph)CH CH PPh ) [Fe(CO)„]

2

2

2

2

I

(5)

v

THF aj — l , 2 ; n — 3 , 4 ; y — 1 , 2


T a b l e I s u m m a r i z e s t h e essential a n a l y t i c a l results f o r t h e several p o l y m e r c a t a l y s t systems d e s c r i b e d h e r e i n , a n d T a b l e I I gives I R s p e c t r a l d a t a f o r p o l y m e r systems a n d other r e l e v a n t c o m p l e x e s .

T h e I R data

( b a n d positions a n d r e l a t i v e i n t e n s i t i e s ) f o r a n c h o r i n g system I r e v e a l t h a t t h e r e is a r a t i o of ( p ) - P P h F e ( C O ) 4 2

between about 2-6 where the F e ( C O ) Table II.

3

frans 2

2

2

2

3

>

2045(—); 1968(—); 1932 ( — ) ; 1876 (—) 2049 (—); 1976 (—); 1934 (—) 1992 (—); 1923 ( — ) ; 1901 (—)

® - P (Ph) C H C H P P h ) . [ F e (CO) „]„ ( s — l , 2 ; n —3,4;y —1,2) 2

2

2

(C)

2055 ( — ) ; 1 9 8 2 ( — ) ; 1934 (—)

(D)

2050 ( — ) ; 1975 ( — ) ; 1935 ( — ) ; 1880 (—)

(E)

2050 ( — ) ; 1 9 8 0 ( — ) ; 1935 (—)

(F)

2040 ( — ) ; 1 9 7 5 ( — ) ; 1935 ( — ) ; 1885 (—)

'Polymer systems measured as Nujol mulls; other complexes measured in hydro carbon solution. 'Data from Refs. 26 and 26.

2.

SANNER E T AL.

agent.

Photoactivation

of Polymer-Anchored

T h e d i s t r i b u t i o n of F e ( C O )

19

Catalysts

species f o r a n c h o r i n g system II is

n

m o r e c o m p l e x , o w i n g to the p o s s i b i l i t y t h a t t h e d i p h o s p h i n e a n c h o r m a y or m a y n o t b e a c h e l a t i n g reagent.

C o m p a r i s o n of t h e I R s p e c t r a f o r

catalyst systems IIC-IIF suggest t h a t there are a t t a c h e d F e ( C O ) T h e b a n d at 1880 o r 1885 c m "

serves as a c r o s s - l i n k i n g reagent as i n system I, m i m i c k i n g t h e fran$-Fe(CO) (PPh ) 3

3

2

species.

units.

4

i n IIB a n d IIF suggests t h a t F e ( C O )

1

T h e d a t a seem to r u l e out a n i m p o r t a n t

c o n t r i b u t i o n f r o m a n c h o r i n g system II as a chelate to b i n d F e ( C O ) t h e systems

studied.

3

model

D e l i b e r a t e v a r i a t i o n i n the d i s t r i b u t i o n of

in

3

the


c o o r d i n a t i o n sphere of the a t t a c h e d i r o n i n I a n d II is c l e a r l y a c h i e v a b l e b y c a r e f u l c o n t r o l at the f u n c t i o n a l i z a t i o n stages, b u t t h e w o r k to date has f o c u s e d m a i n l y o n first e s t a b l i s h i n g some of the q u a n t i t a t i v e p h o t o c a t a l y t i c b e h a v i o r i n these systems. Primary Photoprocesses

Equation 6

in Iron Carbonyl Complexes.

represents the p r i m a r y c h e m i c a l result of o p t i c a l l y e x c i t i n g

Fe(CO) , r

hv

Fe(CO)

T h e r e a c t i o n occurs

(2,11,12).

p r i m a r y step i n the F e ( C O ) g e n a t i o n (21), been

>Fc(CO)

5

+

4

CO

(6)

efficiently a n d is b e l i e v e d to b e

p h o t o c a t a l y z e d i s o m e r i z a t i o n (21),

5

the

hydro-

a n d h y d r o s i l a t i o n ( 6 ) of alkenes. B u t i n these cases i t has

postulated

Fe(CO) (alkene) 4

that a b s o r p t i o n

of

an

or F e ( C O ) ( H ) ( R )

to effect the a l k e n e c h e m i s t r y

additional photon

by

some

H , S i ( a l k y l ) ) is r e q u i r e d

(R =

4

3

(6,21).

T h e c r u c i a l q u e s t i o n here w i t h respect to p o l y m e r - a n c h o r e d F e ( C O ) species is w h e t h e r t h e F e - P b o n d is p h o t o i n e r t .

n

I f t h e F e - P is c l e a v e d

p h o t o c h e m i c a l l y , t h e n the a n c h o r e d species c a n b e released to the b u l k s o l u t i o n a n d s i m p l y effect t h e same c h e m i s t r y as t h a t f o u n d b e g i n n i n g with F e ( C O )

5

i n s o l u t i o n . T h r e e lines of e v i d e n c e s u p p o r t the c o n c l u s i o n

t h a t t h e F e - P b o n d is r e l a t i v e l y p h o t o i n e r t for the catalyst systems s t u d i e d here.

F i r s t , E q u a t i o n s 7 a n d 8 represent t h e c h e m i s t r y o c c u r r i n g u p o n

Fe(CO) PPh 4

hw, P(OMe) 3

3

> Fe(CO) (PPh ) (P(OMe) ) ± 0.04 3

* 55nm =0.4 3

3

3

+ CO

(7)

(benzene) h», HSiEt Fe(CO) PPh > F e ( C O ) ( P P h ) (H) (SiEt ) + C O (8) n e a r - U V p h o t o e x c i t a t i o n of F e ( C O ) P P h i n the presence of P ( O M e ) 3

4

3

3

4

3

3

3

3

a n d H S i E t , respectively; i n the former no F e ( C O ) ( P ( O M e ) ) 3

was

d e t e c t e d a n d i n the latter no F e ( C O ) ( H ) ( S i E t ) w a s f o u n d ( 7 ) .

Thus,

3

4

4

for F e ( C O ) ( p h o s p h i n e ) 4

optical excitation.

3

t h e e x t r u s i o n of C O is t h e p r i n c i p a l r e s u l t of

S i m i l a r results w e r e o b t a i n e d for

Fe(CO) (PPh ) , 3

3

2

20

INTERFACIAL

b u t loss of P P h

3

PHOTOPROCESSES

here has a n efficiency of a b o u t o n e - t e n t h t h a t of

loss. S e c o n d , i r r a d i a t i o n of t h e p o l y m e r - a n c h o r e d F e ( C O ) not y i e l d d e t e c t a b l e a m o u n t s of F e ( C O ) w h e n the s o l u t i o n c o n t a i n s P P h

3

n

complexes

n

CO

species does

i n solution, even

as a p o t e n t i a l s e q u e s t e r i n g

F i n a l l y , t h e c a t a l y t i c c h e m i s t r y f o r the p o l y m e r - a n c h o r e d

reagent.

systems

inconsistent w i t h t h a t o b t a i n e d f r o m F e ( C O ) ; t h e d a t a suggest 5

is the

r e t e n t i o n of at least one p h o s p h i n e i n t h e c o o r d i n a t i o n sphere d u r i n g a c t u a l c a t a l y t i c reactions.


Qualitative Photocatalytic Behavior.

Polymer-anchored F e ( C O )

n

species h a v e b e e n s h o w n to serve as p h o t o c h e m i c a l sources of c a t a l y t i c a l l y a c t i v e species t h a t are c a p a b l e of effecting 1-pentene i s o m e r i z a t i o n , E q u a t i o n 9, a n d 1-pentene r e a c t i o n w i t h H S i E t , E q u a t i o n 10. 3

The

hp

V c a t a l y t i c c h e m i s t r y c a n be i n d u c e d w i t h n e a r - U V (355 n m ) at 25 ° C w h e r e t h e r e is n o d e t e c t a b l e d a r k r e a c t i o n ; n o

irradiation

photoinduced

r e a c t i o n of the 1-pentene is f o u n d b y i r r a d i a t i n g suspensions of a n c h o r i n g m a t e r i a l p r i o r to a t t a c h m e n t of the F e ( C O )

n

units.

the

Solvent

i n t e r a c t i o n s are s u b s t a n t i a l b u t h a v e n o t yet b e e n f u l l y e v a l u a t e d .

The

i m p o r t a n c e of p o l y m e r s o l v a t i o n is reflected i n t h e f a c t t h a t 0 . 1 M 1-pen tene i n a n isooctane s u s p e n s i o n of C a t a l y s t S y s t e m A (see

Table I) under

goes m u c h less t h a n 1 % i s o m e r i z a t i o n after 12 h r of i r r a d i a t i o n , w h e r e a s more than 2 5 %

i s o m e r i z a t i o n results u n d e r t h e same c o n d i t i o n s

b e n z e n e as the solvent. B e n z e n e is a n excellent s w e l l i n g solvent.

with

There

fore, reactions i n b e n z e n e are s u i t a b l e f o r c o m p a r i s o n w i t h h o m o g e n e o u s cases.

F o r t h e w o r k d e s c r i b e d h e r e t h e solutions are g e n e r a l l y neat

1-pentene o r a neat 1:1 m o l r a t i o of 1-pentene : H S i E t . 3

C a t a l y t i c a c t i o n d e p e n d s o n t h e r i g o r o u s e x c l u s i o n of 0 ; 2

w e r e r u n i n h e r m e t i c a l l y sealed, f r e e z e - p u m p - t h a w - d e g a s s e d

reactions ampules.

S u s t a i n e d catalysis r e q u i r e s c o n t i n u o u s i r r a d i a t i o n ; i.e., w h e n t h e l i g h t is t u r n e d off t h e r e a c t i o n appears to stop, b u t i t c a n b e r e i n i t i a t e d b y l i g h t .

2.

SANNER E T A L .

Photoactivation

of Polymer-Anchored

21

Catalysts

Q u a n t u m y i e l d s often exceed u n i t y , t h o u g h , i n d i c a t i n g that i r r a d i a t i o n p r o d u c e s a t h e r m a l l y a c t i v e c a t a l y s t c a p a b l e of effecting a n u m b e r of t u r n o v e r s b e f o r e r e a c t i v a t i o n w i t h l i g h t is necessary. E x c e p t for C a t a l y s t Systems D , E , a n d F (see

T a b l e I ) , w e have observed a large amount

of substrate r e a c t i o n c o m p a r e d w i t h t h e n u m b e r of i r o n atoms i n i t i a l l y present.

W e have observed more than 2 X

10

4

1-pentene

molecules

r e a c t e d p e r i r o n a t o m present. F i n a l l y , t h e catalyst system is u s e d as a s t i r r e d suspension i n the substrate s o l u t i o n , a n d this results i n d i f f i c u l t y i n m e a s u r i n g the q u a n t u m y i e l d s . S i n c e the suspension m a y scatter l i g h t , Interfacial Photoprocesses: Energy Conversion and Synthesis Downloaded from pubs.acs.org by CORNELL UNIV on 09/02/16. For personal use only.

w e t a k e the r e a c t i o n q u a n t u m y i e l d s as t h e n u m b e r of 1-pentene m o l e cules c o n s u m e d p e r p h o t o n i n c i d e n t o n t h e s a m p l e .

These

y i e l d s are thus a l o w e r l i m i t f o r t h e a c t u a l q u a n t u m y i e l d .

quantum Table III

shows the q u a n t u m y i e l d s as a f u n c t i o n of the a m o u n t of C a t a l y s t S y s t e m B

(see

Table I)

s u s p e n d e d i n the neat 1-pentene.

W i t h i n the r a n g e

1 0 - 4 0 m g there is l i t t l e c h a n g e i n t h e o b s e r v e d q u a n t u m y i e l d r e c o r d e d at a b o u t 3 0 %

conversion.

B e l o w 5 m g the q u a n t u m yields fall

off,

consistent w i t h s u b s t a n t i a l t r a n s m i s s i o n of the i n c i d e n t i r r a d i a t i o n . E v e n t h o u g h suspensions are u s e d , g o o d r e p r o d u c i b i l i t y has b e e n a c h i e v e d .

Table III.

Dependence of Observed Q u a n t u m Yield for 1-Pentene Reaction on Weight of Polymer U s e d 0

Wt of Polymer

% Conversion

5 10 20 30 40

&

(trans:cis)

2.2 5.3 6.5 6.7 6.2

1.76 1.78 1.71 1.68 1.47

b

33.8 25.4 30.8 31.6 29.4

°

"Stirred suspensions of Catalyst System B in 1.00 mL of degassed 1-pentene irra diated at 25°C using a G E Blacklite (355 nm) irradiation source. Observed quantum yield for consumption of 1-pentene; number of 1-pentene molecules consumed per photon incident on the sample. Observed ratio of trans- to cis-2-pentene products. 5

0

1-Pentene Isomerization.

D a t a for the p h o t o c a t a l y z e d i s o m e r i z a t i o n

of neat 1-pentene f o r several c a t a l y s t precursors are s h o w n i n T a b l e IV. A l l of the catalyst p r e c u r s o r s h a v i n g a p h o s p h i n e i n t h e c o o r d i n a t i o n sphere y i e l d a n i n i t i a l r a t i o of 2-pentenes that is different f r o m t h a t w h e n Fe(CO)

5

is u s e d as the c a t a l y s t p r e c u r s o r .

T h i s result u n e q u i v o c a l l y

establishes that the p h o s p h i n e c o m p l e x e s d o r e t a i n the p h o s p h i n e i n t h e c o o r d i n a t i o n sphere d u r i n g the a c t u a l i s o m e r i z a t i o n process.

Further,

the r a t i o of the 2-pentenes for the p o l y m e r systems is b e t w e e n t h a t f o u n d for the F e ( C O ) P P h a n d F e ( C O ) ( P P h ) 4

3

d i s t r i b u t i o n of s u c h species

3

3

2

species, consistent w i t h t h e

a n c h o r e d to t h e p o l y m e r .

decline i n isomerization quantum yield F e ( C O ) ( P P h ) 3

3

The 2

2 X 1 0 ) i n d i c a t e g o o d catalyst l i f e t i m e 4

for s y n t h e t i c a p p l i c a t i o n s .

2.

SANNER E T A L .

Photoactivation

of Polymer-Anchored

Photocatalyzed Reaction of 1-Pentene and H S i E t

3

Catalysts

25

a

(Pentyl)SiEts' (n-Pentyl)SiEt '

III

IV

V

16.5 17.5

21.3 16.1

52.4 51.2

9.8 15.2

8.1 10.5

16.2 16.0

62.0 58.1

13.6 15.4

19.8 11.1

14.8 17.3

50.5 57.9

14.8 13.6

8.4 14.7

21.1 15.5

58.7 55.4

11.8 14.4

11.3

16.4

55.0

17.3


s

* Similar product distributions were found for catalysis using Catalyst System B. Experiments with C were conducted in w-xylene solutions of 1.1M 1-pentene and I.IM HSiEt . c

3

Acknowledgments W e t h a n k t h e Office o f N a v a l R e s e a r c h f o r s u p p o r t o f this r e s e a r c h at t h e U n i v e r s i t y o f A l a b a m a ( O N R I n o r g a n i c P o l y m e r s P r o g r a m ) a n d the Massachusetts Institute of Technology.

M S W acknowledges

support

as a D r e y f u s T e a c h e r - S c h o l a r grant r e c i p i e n t , 1975-1980. Literature

Cited

1. Cotton, F. A.; Wilkinson, G.; "Advanced Inorganic Chemistry," 3rd ed.; Interscience: New York, 1972; pp. 770-800. 2. Wrighton, M. Chem. Rev. 1974, 74, 401. 3. Wrighton, M. S. Top. Curr. Chem. 1976, 65, 37. 4. Austin, R. G.; Paonessa, R. S.; Giordano, P. J.; Wrighton, M. S. Adv. Chem. Ser. 1978, 168, 189. 5. Wrighton, M.; Ginley, D. S.; Schroeder, M. A.; Morse, D. L. Pure Appl. Chem. 1975, 41, 671. 6. Schroeder, M. A.; Wrighton, M. S. J. Organomet. Chem. 1977, 128, 345. 7. Sanner, R. D.; Austin, R. G.; Wrighton, M. S.; Honnick, W. D.; Pittman, C. U., Jr. Inorg. Chem. 1979, 18, 928. 8. Pittman, C. U., Jr.; Hanes, R. M. Ann. N.Y. Acad. Sci. 1974, 239, 76. 9. Pittman, C. U., Jr.; Smith, L. R. In "Organotransition-Metal Chemistry"; Ishii, Y., Tsutsui, M., Eds.; Plenum: New York, 1975; pp. 143-156. 10. Grubbs, R. H.; Kroll, L. C. J. Am. Chem. Soc. 1971, 93, 3062. 11. Poliakiff, M. J. Chem. Soc. Dalton Trans. 1974, 210. 12. Poliakoff, M.; Turner, J. J. J. Chem. Soc. Dalton Trans. 1974, 2276. 13. Perutz, R. N.; Turner, J. J. J. Am. Chem. Soc. 1975, 97, 4791.


26

INTERFACIAL

PHOTOPROCESSES

14. Gubitosa, G.; Boldt, M.; Brintzinger, H. H . J. Am. Chem. Soc. 1977, 99, 5174. 15. Grubbs, R.; Lau, C. P.; Cukier, R.; Brubaker, C., Jr. J. Am. Chem. Soc. 1977, 99, 4517 16. Jarrell, M. S.; Gates, B. C.; Nicholson, E . D. J. Am. Chem. Soc. 1978, 100, 5727. 17. Pittman, C. U., Jr.; Ng, Q. J. Organomet. Chem. 1978, 153, 85. 18. Jayalekshmy, P.; Mazur, S. J. Am. Chem. Soc. 1976, 98, 6710. 19. Scott, L. T.; Rebek, J.; Ovsyanki, L.; Sims, C. L. J. Am. Chem. Soc. 1977, 99, 625. 20. Angelici, R. J.; Siefert, E. E. Inorg. Chem. 1966, 5, 1457. 21. Wrighton, M. S.; Schroeder, M. A., J. Am. Chem. Soc. 1976, 98, 551. 22. Harrod, J. F.; Chalk, A. J. "Organic Synthesis via Metal Carbonyls"; Wender, I., Pino, P., Eds.; Wiley: New York, 1977; Vol. 2, pp. 673-704. 23. Berlin, K. D.; Butler, G. G. J. Org. Chem. 1961, 26, 2537. 24. Pittman, C. U., Jr.; Smith, C. R.; Hanes, R. M. J. Am. Chem. Soc. 1975, 97, 1742. 25. Reckziegel, A.; Bigorgne, M. J. Organomet. Chem. 1965, 3, 341. 26. Manuel, T. A. Inorg. Chem. 1963, 2, 854. RECEIVED October 2, 1978.

Photoactivation of Polymer-Anchored Catalysts - American Chemical

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