Structure and reactivity of rhodium(l1) complexes - CiteSeerX

Pure & Appl. Chem., Vol. 61, No. 5, pp. 795-804, 1989.

Printed in Great Britain.

0 1989 IUPAC

Structure and reactivity of rhodium(l1) complexes F l o r i a n P. P r u c h n i k I n s t i t u t e o f C h e m i s t r y , U n i v e r s i t y o f Wroclaw, C u r i e S t r e e t , 50-383 Wroctaw, P o l a n d

14 Joliot

A b s t r a c t - Complexes c o n t a i n i n g t h e Rh24+ c o r e a r e e x t e n s i v e l y i n v e s t i g a t e d b o t h f r o m t h e t h e o r e t i c a l and p r a c t i c a l p o i n t s o f v i e w . P r o p e r t i e s q + r e a c t h y i t y and 5 i e c t r o n i c s t r u c t u r e o f c o m p l e x e s w i t h Rh , Rh2 a n d R h 2 : [Rh2X ( 0 0 C R ) 2 ( N - N ) 2 ] n ? n = 1 , 0 , - 1 ) a r e d i s c u s s e d . T2e c a l c u l a t i o n s and [Rh2(00CR)4] c o n f i r m e d t h e r e a s o n a b l e s t a b i l i t y o f CRh2(00CR)41 compounds. The e f f e c t o f a x i a l a n d e q u a t o r i a l I i g a n d s o n e l e c t r o n i c s t r u c t u r e o f c o m p l e x e s a n d on s t a b i l i t y o f t h e Rh-Rh b o n d was i n v e s t i g a t e d . Assignment o f t h e p(Rh-Rh) s t r e t c h i n g frequenc y i s d i s c u s s e d on t h e g r o u n d o f t h e n o r m a l c o o r d i n a t e a n a l y s i s a n d p o t e n t i a l e n e r g y d i s t r i b u t i o n c a l c u l a t i o n s . The r e d o x r e a c t i o n s o f complexes under s t u d y were examined. T h e i r c a t a l y t i c p r o p e r t i e s i n r e d u c t i o n r e a c t i o n s o f o l e f i n s and k e t o n e s w e r e i n v e s t i g a t e d . The m e c h a n i s m o f f o r m a t i o n o f c a t a l y t i c a l l y a c t i v e complexes i s d i s c u s s e d .

INTRODUCTION The c h e m i s t r y o f r h o d i u m i s among t h e m o s t d i v e r s e o f a l l t h e t r a n s i t i o n met a l s a n d i s b e i n g v i g o r o u s l y i n v e s t i g a t e d a t t h e p r e s e n t t i m e . The m o s t coma n d + 3 . The m o n o m e r i c r h o d i u m ( l 1 ) common o x i d a t i o n s t a t e s o f r h o d i u m a r e +I pounds a r e u n s t a b l e , c o n t r a r y t o t h e d i m e r i c r h o d i u m complexes c o n t a i n i n g t h e r h o d i u m - r h o d i u m b o n d . Among t h e m t h e m o s t i m p o r t a n t a r e t h e R h 2 ( 0 0 C R ) 4 c a r b o x y l a t e s a n d t h e i r a n a l o g s . The s t u d i e s o f t h e s e compounds l e d t o t h e c r e a t i o n o f c h e m i s t r y o f t h e new o x i d a t i o n s t a t e s o f t h e o t h e r p l a t i n u m m e t a l s , t h a t i s , R u ( I ) , Os(I), P t ( l I I ) . The d e v e l o p m e n t o f c h e m i s t r y o f t h e r h o d i u m ( I I ) d i m e r s o b s e r v e d r e c e n t l y , i s due t o t h e i n t e r e s t i n t h e t h e o r y o f t h e e l e c t r o n i c s t r u c t u r e o f c l u s t e r s w i t h t h e s i n g l e m e t a l - m e t a l bond, t h e i r spect r o s c o p i c p r o p e r t i e s a n d r e a c t i v i t y as w e l l as t h e i r p o s s i b l e p r a c t i c a l a p p l i c a t i o n s ( r e f . 1 - 3 ) . B i n u c l e a r r h o d i u m ( l 1 ) complexes a r e e f f e c t i v e c a t a l y s t s i n r e d u c t i o n o f o l e f i n s and k e t o n e s and i n o x i d a t i o n o f a l k e n e s and a l k y l - a r o m a t i c h y d r o c a r b o n s ; t h e y a l s o c a t a l y z e t h e r e a c t i o n s o f t h e d i a z o compounds w i t h RXH (X=O,S,NH) a n d w i t h o l e f i n s t o p r o d u c e c y c l o p r o p a n e d e r i v a t i v e s . They a r e t h e c a t a l y s t s o f s i l y l a t i o n , o f t h e p h o t o c a t a l y t i c d e c o m p o s i t i o n o f w a t e r , e t c . The r h o d i u m ( l 1 ) c a r b o x y l a t e s R h 2 ( 0 0 C R l 4 a r e a l s o t h e m o s t p r o m i s i n g a n t i t u m o r compounds. The m a j o r i t y o f t h e r h o d i u m ( l 1 ) c o m p l e x e s c o n t a i n s b r i d g e I i g a n d s , m o s t f r e q u e n t l y t h e c a r b o x y l a t e I i g a n d s [Rh2(l-OOCR) L ] where L i s t h e L e w i s base. The compounds c o n t a i n i n g e i t h e r l o w e r n u m b e r 4 0 f & r i d g e s , e . g . : CRh ( O A c ) ( P Y ) ~ ] C F S O ~( ,r e f . 4 ) , CRh X,(OOCR) ( ~ h e l ) ~( X] = C I , B r , I , ; R = H,6le, CH?OH)C6H5; c h e l = 2 , 2 - b i p y r i d i n e ? b p y ) , l , ? O - p h e n a n t h r o l i n e ( p h e n ) a n d i t s d e r i v a t i v e s ) ( r e f . 5 - 9 ) , o r + n o t c o n t a i n i n g b r i d g e I i g a n d s , e . g . : CRh2(dmg)41 ( r e f . I - 3 ) , CRh L l 4 ( r e f . 4 , 1 1 ) a r e a l s o known. The Rh-Rh b o n d l e n g t h d e p e n d s u p o n t h e $u%er a n d p r o p e r t i e s o f t h e b r i d g e I i g a n d s . F o r c o m p l e x e s w i t h 4 b r i d g e I i g a n d s t h e v a l u e o f bond l e n g t h l i e s i n t h e l i m i t s f r o m 235.9 pm f o r Rh ( m h p ) 4 (mhp = 2-oxy-6-methylpyridinate) t o 249 pm f o r CRh ( H PO ) ( H 0)2].?n t h e c o m p l e x e s w i t h t w o RCOO b r i d g e s t h e Rh-Rh d i s t a n c e ? s 2 5 5 $ 262 pm ( r e f . 9 , 1 2 , 1 3 ) ; i n t h e b r i d g e - f r e e compounds i t c h a n g e s f r o m 2 6 2 . 5 pm f o r R h 2 ( C 2 2 H 2 2 N 4 ) 2* 3C6H6 t o 2 9 3 . 6 pm f o r [ R h 2 ( d m g ) 4 ( P P h 3 ) 2 J * C 3 H 7 0 H * H 2 0 . The Rh-Rh b o n d i n a l l r h o d i u m ( l 1 ) d i m e r s i s now assumed t o b e s i n g l e , a l t h o u g h t h e d i s t a n c e b e t w e e n t h e r h o d i u m a t o m s was f o u n d t o v a r y w i t h i n v e r y b r o a d l i m i t s . T h i s was c o n f i r m e d b y t h e e x t e n d e d HGckel ( r e f . 1 4 ) , SCs-Xf-Sb) ( r e f . 1 5 ) and ab i n i t i o ( r e f . 1 6 , 1 7 ) c a l c u l a t i o n s , w h i c h g a v e t h e 6 J'i b 795

F. P. PRUCHNIK

796

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configurations. The r e s u l t s i n d i c a t e t h a t t h e e l e c t r o n i c s t r u c t u r e depends on t h e n a t u r e o f n o t o n l y a x i a l , b u t a l s o o f o t h e r I i g a n d s . Somewhat d o u b t f u l i s a l s o t h e a s s i g n ment, o f t h e g ( R h 2 ) s t r e t c h i n g y j b r a t i o n , w h i c h was e s t i m a t e d t o b e a b o u t 300 cm ( r e f . 1 8 ) o r as 1 5 0 - 1 8 0 cm (ref.19,20).

THE STRUCTURE OF R h * X 2 ( 0 0 C R ) 2 ( N - N ) * COMPLEXES I n o r d e r t o g a i n some a d d i t i o n a l i n f o r m a t i o n a b o u t t h e p r o p e r t i e s , s t r u c t u r e a n d r e a c t i v i t y o f t h e R h ( I I ) c o m p l e x e s , we h a v e s t u d i e d t h e R h 2 X 2 ( 0 0 C R ) 2 ( N - N ) 2 dimers : X = C I , R=H, N - N = b p y ; 2: C I , H , p h e n ; 3 : B r , H, p h e n ; 4 : C I , M e , - b p y ; 5 : B r , Me, b p y ; 6 : I , Me, b p y ; C I , Me, p h e n ; 8 : B r , Me, p h e n ; 9 : I,Me p h e n ; 1 0 : C I , CH(OH)Ph, b p y ; 11: B r , CH(OH)Ph, b p y ; 12: I , CH(OH)Ph, b p y ; -1 -3 : CI;-CH(OH)Ph, p h e n ; 1 4 : B r , CH(OH)Ph, p h e n ; 1 5 : I , CH(OH)Ph, p h e n ) a n d (16; R=H; R=Me; 18: Rh (OOCR) ( H 0 ) R=EH(OH)Pk) f r e 8 . 5 - 7 6 ) .The exchange o f I i g a n d s , b o t h a x i a l and e q u a t o r i a l ones, a l l o w s t h e e l u c i d a t i o n o f t h e r e l a t i o n between the p r o p e r t i e s o f c o m p l e x e s a n d t h e n a t u r e o f I i g a n d s a n d t h e compar i s o n o f t h e p r o p e r t i e s o f complexes under t h e 0 s t u d y w i t h t h o s e o f Rh (OOCR)4 c o m p l e x e s . T h e s t r u c t u r e o f c o m p l e x e s w i t 2 two c a r b o x y l a t o I i a n d s i s shown i n F i .I.The Rh-Rh d i s t a n c e f o r YRh C 1 2 (OOCH) ( p h e n ) ( r e f . 5 , 9 ) , [Rh C I (OOCH) ( b p y ? 1. XX 4H 0 ? r e f . 9 , $ 1 ) , ( R h C I (OOCC&(O&)C H ) 2 ( b p y ) E i s 6 H 2 6 ( r e f .22), [ R h 2 ( 0 A 2 ) 2 f p h e n ) ( m i d . ) 6 ] ? C ? 0 ) 2 ( m i d = N-methyl i m i d a z o l e ) ( r e f . ? 3 ) , [Rg2(0Acf2(3,4,7,8-Me phen) ( m i d ) ] ( C 1 0 4 ) 2 ( r e f . 1 3 ) and [Rh2(0Ac) ($mg)2(6Ph ) f - H 2 0 ( s e e r e f . 1-3) a r e e q u a l t o $ 5 7 . 6 pm, 2 2 7 ? 8 pm, 2 5 7 . 0 pm, 2 5 5 . 6 pm Fig.1. Structure of the 2 5 6 . 4 pm a n d 2 6 1 . 8 pm, r e s p e c t i v e l y . [Rh2X2 (OOCR) ( N - N ) 2 ] complexes. The R h - 0 d i s t a n c e a r e somewhat l o q g e r ( u p t o 4 pm) t h a n i n [Rh2(00CR) c o m p l e x g s , w h i l e t h e Rh-CI d i s t a n c e i s b y 7 - 9 pm s h o r t e r t h a n i n t h e [ R h 2 ( 0 6 ~ e ) 4 ~ ~ 2d]i m e r . The Rh-Rh b o n d l e n g t h s i n c o m p l e x e s w i t h two b r i d g e s e x c e e d b y c a . 17 pm t h o s e i n t h e a p p r o p r i a t e [ R h 2 ( 0 0 C R ) 4 ] t e t r a c a r b o x y l a t e s . I n o r d e r t o e l u c i d a t e t h e e l e c t r o n i c s t r u c t u r e o f [Rh2X2(OOCR) ( N - N ) ] ( N - N = b p y , p h e n ) c o m p l e x e s , a n d t o c o m p a r e i t w i t h t h e s t r u c t u r e o ? R h 2 ( 6 O C R l 4 compounds, we h a v e p e r f o r m e d t h e c a l c u l a t i o n s o f t h e e l e c t r o n i c s t r u c t u r e o f c o m p l e x e s 1 6 , [ 5 b 2 X (OOCH)2(HN=CH-CH=NH) (X = CI, Br, I ) a n d [Rh2(OOCH)2(HN=CH-CH=NH)2L2] = H 2 0 , NH3, PH3, As&,] by t h e Fens k e - H a l l m e t h o d ( r e f . 2 3 ) . F o r diaquatetrafgrmtto$irhgdluT(II) t h e f o l l o w i n g m o l e c u l a r o r b i t a l s s e q u e n c e was a c h i e v e d : d 6 5* ( r e f . 24), that

(1

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7

3

1,

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F*

TABLE 1.

Some u p p e r v a l e n c e e n e r g y l e v e l s ( e V ) a n d c h a r g e d i s t r i b u t i o n s . Rh2C12(OOCH)2(C2N2H4)2

D4h energy % I eve I 2Rh

charge Iigands

:2v I eve I

energy

% charge 2Rh I i g a n d s

Rh2Br2(OOCH)2(C2N2H4)2 C2v I eve I

energy

% charge 2Rh I i g a n d s

5a

-11.25

77

23

13al

-13.96

57

43

13al

-13.04

64

36

%

-10.73

81

19

14al 3-i

-12.84

54

46

14al

-12.54

56

44

-12.33

71

29

Ilb2

-12.00

75

25

z*

13bl

-11.29

45

55

13bl

-10.86

63

37

15al

-10.43

76

24

10a2

-10.31

46

54

ci l g

d

d

7c

-

9.96

91

9

-

7.80

75

25

5e

-

7.76

90

10

lzal

-10.61

75

25

P g 4a 6*2U

-

2.39

82

18

15bl

- 9.33

68

32

0.36

68

32

Ila2

-

9.16

50

50

15bl

- 9.10

62

38

0.48

64

36

18a

-

7.33

17

83

-

7.03

15

85

16b

- 6.51

24

76

- 6.29

24

76

-

63

37

18a 5*N? 16b Z*N? 17bl

- 2.97

60

40

2Sb2g 2b 6" l u

2kKo

' 2 2

b*

>y*

x*N? 3" Ni! 17bl

b*

2.85

JT

n* d

J7*

5*

6*

797

Structure and reactivity of rhodium(//)complexes

i s t h e same as t h a t o b t a i n e d b y t h e e x t e n d e d H G c k e l ( r e f . 1 4 ) a n d ab i n i t i o SCF/CI ( r e f . 1 7 ) m e t h o d s . The o b t a i n e d e n e r g y v a l u e s o f 6' a n d P* o r b i t a l s a r e o n l y s l i g h t l y d i f f e r e n t , l i k e i n t h e case o f t h e o t h e r methods ( r e f . 1 4 , 1 5 , 1 7 1 . The 1 , 4 - d i a z a - 1 , 3 - b u t a d i e n e m o l e c u l e , l i k e t h e 2 , 2 ' - b i p y r i d i n e one,cont a i n s t h e c o n j u g a t e d s y s t e m o f d o u b l e b o n d s N=C-C=N, a n d t h u s t h e r e s u l t s o f c a l c u l a t i o n s f o r c o m p l e x e s w i t h HN=CH-CH=NH a n d 2 , 2 - b i p y r i d i n e s h o u l d b e s i m i l a r . S u b s t i t u t i o n o f two f o r m a t o I i g a n d s b y t w o HN=CH-CH=NH m o l e c u l e s r e moves t h e d e g e n e r a c y o f 4 F ( R h - R h ) a n d S?*(Rh-Rh) o r b i t a l s . B e t w e e n t h e A* a n d f * o r b i t a l s o f t h e Rh2 core there a r e the emptyfl* o r b i t a l s o f the d i e ne I i g a n d , w i t h c o n s i d e r a b l e c o n t r i b u t i o n o f d;r o r b i t a l s o f r h o d i u m . T h i s i s i n d i c a t i v e f o r t h e Z - a c c e p t o r p r o p e r t i e s o f 1,4-diaza-1,3-butadiene. The b o n d i n g L , B , 6 o r b i t a l s , as we1 I as t h e a n t i b o n d i n g K * , F * , 5 " o r b i t a l s i n t h e [Rh2X2 ( OOCH) (HN=CH-CH=NH) 2 ] comp I e x e s c o n t a i n c o n s i d e r ab I e c o n t r i b u t i o n s o f I i g a n d o r b i t a l s , as c o m p a r e d w i t h [Rh2(00CH) ( H O ) , ] (Table 1). A l s o the c o n t r i b u t i o n o f d o r b i t a l s o f rhodium i n R h - l i $ a n $ o r b i t a l s grows. I t i s e s p e c i a l l y s t r o n g i n t h e case o f 6 , T , 6 * and J 7 * 4 9 r b i t a l s . Such a s i t u a t i o n i s due m a i n l y t o t h e i n t e r a c t i o n b e t w e e n t h e R h 2 c o r e o r b i t a l s and HN=CH-CH=NH o r b i t a l s as w e l l as w i t h t h e a x i a l I i g a n d o r b i t a l s ( C I , B r , I ) . This i s responsible f o r the lowering o f energy of 6 , 3 7 a n d X * o r b i t a l s , b u t , s i n c e t h e g r e a t e r c o n t r i b u t i o n o f I i g a n d o r b i t a l s i t changes t h e c h a r a c t e r o f Rh-Rh b o n d , a n d , f i n a l l y , l e a d s t o t h e w e a k e n i n g o f t h e b o n d b e t w e e n c e n t r a l a t o m s . The c o n t r i b u t i o n o f 6 + ( R h - R h ) ( 1 7 b l ) o r b i t a l t o the b(Rh-X)(12bl) o r b i t a l grows i n t h e o r d e r C l c B r C l . T h i s i s c o n s i s t e n t w i t h t h e e l e c t r o n e g a t i v i t y d e c r e a s e o f h a l o g e n s i n t h e same d i r e c t i o n . I t means, t h a t w e a k e s t becomes t h e 6(Rh-C1) b o n d , u n d e r t h e e f f e c t o f t h e t r a n s d ( R h - R h ) b o n d . A s t h e r e s u l t o f i n t e r a c t i o n w i t Q + t h e empty .Ji*(CN) o r b i t a l s , t h e X ( 1 4 a l ) a n d Z * ( 1 3 b l ) o r b i t a l s o f t h e Rh2 c o r e , d e r i v i n g f r o m J ' ( 6 e ) and Z * ( 5 e ) o r b i t a l s o f t h e [ R h 2 ( 0 0 C H ) 4 ( H 2 0 ) 2 ] c o m p l e x , r e s p e c t i v e l y , a r g s t a b i I ized! T h i s s t a b i l i z a t i o n i s a d d i t i o n a l l y i n c r e a s e d by i n t e r a c t i o n w i t h p o r b i t a l s o f t h e ha1 i d e I i g a n d s . I n t h e c a t i o n i c [ R h 2 ( 0 0 C H ) (HN=CH-CH=NH) L 1 2 + c o m p l e x e s ( L = H20, NH3, PH , A s H 3 ) , t h e d e g e n e r a c y o f t 2 e 5i a n d Z* o f 2 R 2 2 4 + c o r e i s a l s o r e m o v e d a n d ?he e l e c t r o n d e n s i t y i s s h i f t e d t o w a r d s t h e HN=CH-CH=NH l i z + gands; i n t h i s case, however t h e m i x i n g o f t h e I i g a n d s o r b i t a l s w i t h t h e Rh2 c o r e o r b i t a l s i s s m a l l e r . The m u t u a l i n t e r a c t i o n o f t h e a x i a l I i g a n d s w i t h r h o d i u m o r b i t a l s i s u n u s u a l l y e f f e c t i v e i n t h e c a s e o f PH3 a n d AsH3 ( F i g . 2 ) . F o r

Lt

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In

OsCHI

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4-12

L* - 20

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F i g . 2 . M o s t i m p o r t a n t e n e r g y l e v e l s o f [ R h 2 ( 0 0 C H ) (H 0 ) 1 - a , [ R h X (OOCH)2(HN=CH-CH=yy) I ( X = CI - b , B r - c , I - d f a 6 d ?Rh2(00C?12?( H N = C H - C H = N H ) ~ L ~ I ?L = H ~ O- e , NH3 - f , P H ~- 9 ) .

F. P. PRUCHNIK

798

5

t 9 e s quence o f t h e m o l e c u l a r o r b i t a l s i s t h e f o l complexes w i t y20 a g d b)H 6 6*' c * NC) Z 2 * ( N C ) d*. B e c a u s e o f t h e i n c r e a s e l o w i n g flI2T2 6 XI* i n the order H O