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Tungsten Complexes

JOSEPH

L.

TEMPLETON

W. R. Kenan, Jr. Laboratory, Department of Chemistry, University of North Carolina, Chapel Hill, N C 27514

Tricarbonylbis(N,N-dimethyldithiocarbamato)tungsten, (W(CO) (dmtc) ), has been synthesized, and two distinct intramolecular dynamic processes have been identified by variable temperature C NMR studies of this seven-coordinate molecule. The sodium salt of dimethyldithiocarbamate reacts with tetracarbonyldiiodotungsten to form the above product, W(CO) (dmtc) . Analytical, IR and NMR data confirm this formulation. The C NMR spectrum at —110°C has three distinct resonances, two of which initially coalesce independently of the third (∆G≠ = 8.1 kcal mol ) as the temperature is increased. All three carbon monoxide signals are averaged at higher temperatures(∆G≠= 9.0 kcal mol ). Reversible loss of one CO occurs upon heating to form an insoluble blue W(CO) (dmtc) compound. 3

2

13

3

2

13

-1

-1

2

A

2

s u b s t a n t i a l n u m b e r o f stable seven-coordinate m e t a l c o m p l e x e s h a v e n o w been isolated a n d structurally characterized. A comprehensive

r e v i e w b y D r e w ( I ) systematizes

t h e s t r u c t u r a l d a t a that h a s b e e n

a c c u m u l a t e d f o r seven-coordinate c o m p o u n d s .

M o r e recently W r e f o r d

has c o n t r i b u t e d t o u n r a v e l i n g t h e details o f d y n a m i c processes w h i c h c a n o c c u r f o r s u c h complexes ( 2 ) . I n o n e case, d y n a m i c N M R studies o f TaCl(7 -C oH )[(CH3)2PC H P(CH3)2]2 7

4

1

8

2

4

w e r e i n t e r p r e t e d i n terms o f

a n i n t e r c o n v e r s i o n o f t h e ground-state p e n t a g o n a l b i p y r a m i d t o a n i n t e r m e d i a t e m o n o c a p p e d t r i g o n a l p r i s m ( 3 ) . I n another s t u d y , site e x c h a n g e 0-8412-0429-2 /79 / 33-173-263$05.00/ 0 © 1979 American Chemical Society King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

264

INORGANIC

COMPOUNDS WITH UNUSUAL PROPERTIES

i n s e v e n - c o o r d i n a t e species of t h e t y p e M X ( C O ) ( L ^ L / ) 2

2

II

w a s consistent

w i t h a nondissociative mechanism involving a polytopal rearrangement (4). A l t h o u g h t h e n a t u r e of s e v e n - c o o r d i n a t e c o m p o u n d s is of i n t r i n s i c interest, p e r h a p s of greater significance is t h e role of e x p a n d e d c o o r d i n a t i o n spheres as intermediates i n t h e c h e m i s t r y of o c t a h e d r a l c o m p l e x e s . T h e p r e p a r a t i o n of t h e t h e r m o d y n a m i c a l l y u n f a v o r a b l e

£rans-Mo(CO) 2

( d i p h o s ) i s o m e r ( 5 ) v i a a seven-coordinate i n t e r m e d i a t e is a n e x e m p l a r y 2

case of s t e r e o c h e m i c a l c o n t r o l . P l a u s i b l e seven-coordinate

intermediates

i n t h e reactions of olefins w i t h p e n t a c a r b o n y l t u n g s t e n p h e n y l c a r b e n e

(6)

c a n exert s t e r e o c h e m i c a l c o n t r o l of the p r o d u c t d i s t r i b u t i o n s . Although

M o (II)

a n d W ( I I ) e x h i b i t t h e most

extensive

seven-

c o o r d i n a t e c h e m i s t r y y e t k n o w n (consistent w i t h the a p p l i c a t i o n of t h e effective a t o m i c n u m b e r r u l e to these d

4

s y s t e m s ) , a s u r v e y of t h e s u b -

s t i t u t e d m e t a l c a r b o n y l complexes of m o l y b d e n u m a n d t u n g s t e n reveals n o s t r u c t u r a l d a t a f o r c o m p o u n d s of t h e t y p e M ( C O ) ( B - B ) 3

2

where B - B

is a b i d e n t a t e m o n o a n i o n i c l i g a n d . N o t u n g s t e n t r i c a r b o n y l s of this t y p e h a v e b e e n r e p o r t e d to date, b u t M c D o n a l d a n d c o - w o r k e r s h a v e synthes i z e d a n d s t u d i e d t h e closely r e l a t e d W ( C O ) ( P P h ) ( B - B ) 2

3

2

compounds

w h e r e B - B is a c h e l a t i n g d i t h i o c a r b a m a t e ( 7 ) , xanthate, o r d i t h i o p h o s phate

(8).

F o r m o l y b d e n u m , the compounds

R o N C S o " ) ( 9 ) are examples of t h e M ( C O ) ( B - B ) 3

[S P(i-Pr) ] 2

2

2

Mo(CO) (dtc) (dtc = 3

2

2

t y p e as is M o ( C O ) 3

( 1 0 ) , w h i c h has b e e n w e l l c h a r a c t e r i z e d i n s o l u t i o n .

Colton's work w i t h the tricarbonylbisdithiocarbamatomolybdenum series ( 9 ) a n d M c D o n a l d ' s success i n s t u d y i n g t h e t r i p h e n y l p h o s p h i n e s u b s t i t u t e d t u n g s t e n analogs

( 8 ) l e d us to a t t e m p t t h e synthesis a n d

c h a r a c t e r i z a t i o n of a n analogous t u n g s t e n t r i c a r b o n y l c o m p l e x ( i ) t h e m o l y b d e n u m d e r i v a t i v e s r e v e r s i b l y lose c a r b o n m o n o x i d e

since: (11);

( i i ) t h e tungsten analogues s e e m e d l i k e l y to e x h i b i t different b e h a v i o r t h a n t h e m o l y b d e n u m series ( e a r l i e r p r e p a r a t i v e attempts suggested that t u n g s t e n d i t h i o c a r b a m a t e s s h o u l d b e c a p a b l e of existence b u t i n d i c a t e d that t h e y w o u l d b e d i f f i c u l t to c h a r a c t e r i z e (7,12); c o o r d i n a t e features of M ( C O ) ( B - B ) 3

2

N M R t e c h n i q u e s at e a c h of t h e l i g a n d sites. (CO) [(CH ) NCS ] 3

3

2

2

2

a n d ( i i i ) t h e seven-

complexes c o u l d b e p r o b e d v i a A s y n t h e t i c route to W -

a n d r e l e v a n t s p e c t r o s c o p i c d a t a are r e p o r t e d here.

Experimental Materials. T u n g s t e n h e x a c a r b o n y l , i o d i n e , t r i p h e n y l p h o s p h i n e , C O gas, a n d s o d i u m N , N - d i m e t h y l d i t h i o c a r b a m a t e w e r e o b t a i n e d f r o m c o m m e r c i a l sources a n d u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n . Solvents w e r e p u r g e d w i t h a stream of p u r i f i e d n i t r o g e n p r i o r to use. A l l s o l u t i o n m a n i p u l a t i o n s w e r e p e r f o r m e d u n d e r a n i t r o g e n atmosphere u s i n g S c h l e n k techniques.

King; Inorganic Compounds with Unusual Properties—II Advances in Chemistry; American Chemical Society: Washington, DC, 1979.

22.

TEMPLETON

Seven-Coordinate

Tungsten

265

Complexes

Physical Measurements. I R spectra w e r e r e c o r d e d o n a B e c k m a n 4250 I R S p e c t r o p h o t o m e t e r . S o l i d spectra w e r e o b t a i n e d as N u j o l m u l l s on C s l plates or as K B r pellets. S o l u t i o n spectra i n the r e g i o n 2 4 0 0 1600 c m " w e r e o b t a i n e d i n sealed K B r cells of 0.10 m m p a t h l e n g t h . P o l y styrene was u s e d as a c a l i b r a t i o n m a r k e r i n a l l cases. N M R spectra w e r e r e c o r d e d w i t h a V a r i a n X L - 1 0 0 F o u r i e r t r a n s f o r m spectrometer. Carb o n - 1 3 spectra w e r e o b t a i n e d at a spectrometer f r e q u e n c y of 25.16 M H z w i t h the H s i g n a l of d e u t e r o m e t h y l e n e c h l o r i d e s e r v i n g as a n i n t e r n a l lock. B r o a d b a n d proton d e c o u p l i n g was routinely used for C measurements. S p e c t r a w e r e r e c o r d e d at v a r i o u s temperatures d o w n to — 1 1 0 ° C w i t h a solvent m i x t u r e c o n s i s t i n g of C D C l 2 : C D C l : C C l 4 i n a ratio of 6 0 : 2 7 : 1 3 w i t h a trace of M e S i a d d e d to serve as a n i n t e r n a l reference. Trisacetylacetonatochromium(III) (10 m g ) w a s a d d e d to e a c h s a m p l e as a p a r a m a g n e t i c r e l a x a t i o n agent i n v i e w of the l o n g T i values characteristic of m e t a l c a r b o n y l c a r b o n atoms. A n a l y s e s w e r e p e r f o r m e d b y G a l b r a i t h L a b o r a t o r i e s , K n o x v i l l e , Tennessee. 1

2

1 3

3

2

4

Preparative Procedures. T R I C A R B O N Y L B I S ( N , N - D I M E T H Y L D I T H I O C A R B A M A T O ) T U N G S T E N ( I I ) . T h e W ( C O ) I reagent was p r e p a r e d p h o t o c h e m i c a l l y a c c o r d i n g to the m e t h o d of C o l t o n a n d R i x (13). T h e s o l i d reactants W ( C O ) I , 1 . 5 0 g (2.72 m m o l ) , a n d N a ( d m t c ) ( E a s t m a n C h e m i c a l s ) , (0.80 g, 5.60 m m o l ) w e r e p l a c e d i n a flask u n d e r n i t r o g e n p r i o r to a d d i n g 30 m L of T H F w h i c h h a d b e e n f r e s h l y d i s t i l l e d f r o m c a l c i u m h y d r i d e u n d e r a n i t r o g e n atmosphere. T h e solids d i s s o l v e d to f o r m a r e d s o l u t i o n , a n d gas e v o l u t i o n c o m m e n c e d . W i t h i n 30 m i n the r e a c t i o n w a s j u d g e d c o m p l e t e b a s e d o n the cessation of gas e v o l u t i o n , w i t h the a m o u n t of gas c o l l e c t e d a p p r o x i m a t e l y e q u a l to that e x p e c t e d f o r t h e loss of one C O p e r m o l e of W ( C O ) I i n i t i a l l y present. T h e s o l u t i o n was filtered p r i o r to r e m o v a l of the T H F solvent b y v a c u u m e v a p o r a t i o n . T h e s o l i d that r e m a i n e d was c h r o m a t o g r a p h e d o n a n a l u m i n a c o l u m n u s i n g b e n z e n e as the eluent. V a c u u m e v a p o r a t i o n of the b e n z e n e s o l u t i o n p r o d u c e d a s o l i d w h i c h w a s p u r i f i e d b y r e c r y s t a l l i z a t i o n f r o m toluene b y c o o l i n g a s o l u t i o n that h a d b e e n saturated at 5 0 ° C . T h e i n i t i a l y i e l d was 5 0 % after c h r o m a t o g r a p h i n g the c r u d e m a t e r i a l . T h e final y i e l d was 3 0 % after r e c r y s t a l l i z a t i o n . A n a l y s i s : C a l c d f o r C H N o 0 S W : C , 21.27; H , 2.38; N , 5.51; S, 25.23; W , 36.17. F o u n d : C , 21.97"; H , 2.53; N , 5.57; S, 23.92; W , 35.63. 4

4

2

2

4

2

9

1 2

3

4

D l C A R B O N Y L B I S ( JV, N - D I M E T H Y L D I T H I O C ARB A M A T O ) T U N G S T E N ( I I ) .

A

s o l i d s a m p l e of W ( C O ) ( d m t c ) , 50 m g (0.1 m m o l ) , w a s p l a c e d i n a t u b e a n d h e a t e d u n d e r v a c u u m . A t e m p e r a t u r e of 1 0 0 ° C w a s sufficient to cause a c o l o r change w i t h i n m i n u t e s . T h e i n i t i a l orange crystals b e c a m e d a r k b l u e - g r e e n a n d the I R s p e c t r u m of the n e w m a t e r i a l s h o w e d n e w b a n d s g r o w i n g i n the c a r b o n y l s t r e t c h i n g r e g i o n at 1930 a n d 1803 c m " , b u t the b a n d s a t t r i b u t e d to the s t a r t i n g m a t e r i a l w e r e of almost e q u a l intensity. H e a t i n g at 170 ° C f o r 2 h r p r o d u c e d a s o l i d that d i s p l a y e d o n l y the t w o c a r b o n y l absorptions at 1930 a n d 1803 c m " . T h e b l u e - g r e e n s o l i d r e s u l t i n g f r o m t h e r m a l loss of C O was i n s o l u b l e i n c o m m o n o r g a n i c solvents, a n d q u a n t i t a t i v e c o n v e r s i o n of W ( C O ) ( d m t c ) to W ( C O ) ( d m t c ) was not a c c o m p l i s h e d w i t h o u t some a c c o m p a n y i n g d e c o m p o s i t i o n to m a t e r i a l w i t h no c a r b o n y l s . 3

2

1

1

3

2

2

2

TRIPHENYLPHOSPHINEDICARBONYLBIS ( N , N - D I M E T H Y L D I T H I O C A R B A M A -

TO)TUNGSTEN(II).

( M e t h o d A ) . E q u i m o l a r amounts of W ( C 0 ) ( d m t c ) , 3


2

266

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

II

250 m g (0.5 m m o l ) a n d P ( C H ) , 130 m g (0.5 m m o l ) w e r e p l a c e d i n a flask f o l l o w e d b y a d d i t i o n of 10 m L of C H C 1 as a solvent. A f t e r s t i r r i n g at r o o m t e m p e r a t u r e f o r 12 h r the s o l u t i o n w a s filtered. T h e s o l i d p r o d u c t w a s c h a r a c t e r i z e d b y I R after r e m o v a l of t h e C H C 1 solvent u n d e r v a c u u m . T h e s o l i d state I R s p e c t r u m of W ( C O ) ( P P h ) ( d m t c ) showed t w o s t r o n g absorptions a t t r i b u t e d to C O s t r e t c h i n g f r e q u e n c i e s at 1910 a n d 1820 c m " i n a g r e e m e n t w i t h the values r e p o r t e d p r e v i o u s l y b y C h e n , Y e l t o n , a n d M c D o n a l d ( 8 ) , w h o s y n t h e s i z e d this a n d r e l a t e d c o m p o u n d s f r o m s u b s t i t u t i o n reactions of W ( C O ) ( P P h ) C l w i t h u n i - n e g a t i v e c h e l a t i n g l i g a n d s . ( M e t h o d B ) T h e r m a l loss of C O w a s i n d u c e d to f o r m the blue-green W ( C O ) ( d m t c ) f r o m W ( C O ) ( d m t c ) , 50 m g (0.1 m m o l ) . A d d i t i o n of P ( C H ) , 30 m g (0.1 m m o l ) a n d toulene ( 5 m L ) c a u s e d the b l u e - g r e e n s o l i d to dissolve, a n d the s o l u t i o n I R s p e c t r u m s h o w e d o n l y t w o b a n d s i n the c a r b o n y l r e g i o n : 1930 a n d 1840 c m " , as f o u n d previously for W ( C O ) ( P P h ) ( d m t c ) p r e p a r e d a c c o r d i n g to Method A . 6

5

3

2

2

2

2

2

3

2

1

3

2

3

2

2

6

5

2

3

2

3

1

2

3

2

TRICARBONYLBIS(N,]V-DIMETHYLDITHIOCARBAMATO)TUNGSTEN(II),

1 3

CO

E N R I C H E D . A toluene s o l u t i o n of the i s o t o p i c a l l y n o r m a l W ( C O ) ( d m t c ) was s t i r r e d at 50 ° C f o r 45 m i n u n d e r a C O atmosphere. T h e s o l u t i o n w a s a l l o w e d to c o o l a n d c y c l o h e x a n e w a s a d d e d to p r e c i p i t a t e the e n riched C O sample. 3

2

1 3

1 3

Results and

Discussion

T h e p r e p a r a t i o n of seven-coordinate W(CO) (B-B) 3

W(II)

complexes of the t y p e

was p u r s u e d v i a a route s i m i l a r to C o l t o n s

2

for isolating M o ( C O ) ( d t c ) 3

2

(9).

scheme

W e selected N , I V - d i m e t h y l t h i o c a r b a -

m a t e ( d m t c ) since it p r o v i d e s a b i d e n t a t e l i g a n d w i t h a c h a r g e of — 1, a n d it was k n o w n to f o r m s e v e n - c o o r d i n a t e

c o m p o u n d s of the t y p e w e

sought. T h e ease of p r e p a r a t i o n of W ( C O ) I 4

+

I

2

d i c t a t e d that W ( C O ) I

(13)

4

2

2

b y p h o t o l y s i s of W ( C O )

b e u s e d i n i t i a l l y as the W ( I I )

6

halo-

c a r b o n y l reactant of c h o i c e . I R analysis of the r e a c t i o n m i x t u r e c o n s i s t i n g of W ( C O ) I 4

a n d N a ( d m t c ) w a s e n c o u r a g i n g i n v i e w of t h e t r i c a r b o n y l

2

p a t t e r n o b s e r v e d , a n d w h e n c o u p l e d w i t h the C O e v o l u t i o n a n d

the

f o r m a t i o n of i n s o l u b l e N a l that o c c u r r e d u p o n s t i r r i n g the T H F s o l u t i o n , the d a t a suggested

that i n d e e d W ( C O ) ( d m t c ) 3

2

had formed.

Minor

c a r b o n y l c o n t a i n i n g i m p u r i t i e s w e r e e v i d e n t i n the s o l u t i o n I R s p e c t r u m b e t w e e n 2200 a n d 1700 c m " , b u t the three s t r o n g b a n d s at 2020,

1944,

1

a n d 1926 c m ' d o m i n a t e d . C h r o m a t o g r a p h y o n a l u m i n a affected p u r i f i c a 1

t i o n s u c h that o n l y these three b a n d s

observed i n solution.

A

f u r t h e r r e c r y s t a l l i z a t i o n of the m a t e r i a l e l i m i n a t e d a s m a l l a m o u n t

of

insoluble blue-green W(CO) (dmtc) 3

2

were

m a t e r i a l that f o r m e d after e l u t i o n .

The

orange

c o u l d be d r i e d under v a c u u m a n d dissolved i n organic

solvents w i t h no loss of c a r b o n y l l i g a n d s . T h e s t a b i l i t y of the t r i c a r b o n y l i n s o l u t i o n p r o v i d e d a n o p p o r t u n i t y to observe b o t h the s o l u t i o n I R a n d N M R b e h a v i o r of the c o m p l e x . ported for M o ( C O ) ( d t c ) 3

2

S i m i l a r s o l u t i o n s t a b i l i t y has b e e n

re-

i n o r g a n i c solvents i n a r e c e n t p u b l i c a t i o n (14).


22.

TEMPLETON

Seven-Coordinate

Tungsten

T h e I R s p e c t r u m of W ( C O ) ( d m t c ) 3

267

Complexes

w a s t y p i c a l of s u b s t i t u t e d cis

2

t r i c a r b o n y l s i n the absence of t h r e e f o l d s y m m e t r y . T h e A± a n d E n o r m a l m o d e s generated b y a C

3

axis p r o d u c e t w o a l l o w e d absorptions.

Depar-

t u r e f r o m the t h r e e f o l d s y m m e t r y splits the degenerate E b a n d i n t o t w o components.

F i g u r e 1 r e p r o d u c e s this s i m p l e p a t t e r n t h a t was o b s e r v e d

i n the c a r b o n y l r e g i o n f o r W ( C O ) ( d m t c ) . 3

2

T h e s o l i d state I R s p e c t r u m

o b t a i n e d as a K B r p e l l e t f o r purposes of c o m p a r i s o n w i t h s i m i l a r m o l y b d e n u m d a t a d i s p l a y e d f o u r d i s t i n c t absorptions

(2010, 1932,

1909,

1880 c m " ) w h i l e o n l y three w e r e r e p o r t e d f o r M o ( C O ) ( d m t c ) 1

3

1920, a n d 1882 c m " )

and

(2020,

T h e a d d i t i o n a l solid-state a b s o r p t i o n b a n d

(12).

1

2

is p r o b a b l y the result of solid-state s p l i t t i n g of the three f u n d a m e n t a l m o d e s , b u t the p o s s i b i l i t y of m o r e t h a n one isomer also exists. Heating solid W ( C O ) ( d m t c ) 3

i n vacuo resulted i n an abrupt color

2

c h a n g e f r o m o r a n g e to b l u e - g r e e n .

A n I R s p e c t r u m , after h e a t i n g

at

100 ° C for 2 hr, i n d i c a t e d that n e w absorptions h a d g r o w n i n at 1930 a n d 1803

cm"

1

w h i l e m u c h of the o r i g i n a l t r i c a r b o n y l w a s s t i l l

unreacted.

P r o l o n g e d h e a t i n g at 170 ° C p r o d u c e d a n i n s o l u b l e s o l i d w i t h o n l y the t w o n e w absorptions i n the c a r b o n y l r e g i o n .

T h i s was i n t e r p r e t e d

as

c o n v e r s i o n to W ( C O ) ( d m t c ) , analogous to the m o l y b d e n u m d i c a r b o n y l 2

2

derivatives characterized previously where v ( C O ) for M o ( C O ) ( d m t c ) 2

was o b s e r v e d at 1930 a n d 1840 c m "

2

(12).

1

T h e loss of C O f r o m W ( C O ) ( d m t c ) 3

2

was reversible, as e v i d e n c e d

b y the d i s s o l u t i o n of the i n s o l u b l e b l u e - g r e e n d i c a r b o n y l i n toluene w h e n CO

w a s a d d e d to the r e a c t i o n vessel.

The

solution spectrum w h i c h

r e s u l t e d was that of the t r i c a r b o n y l w h i l e no d i s s o l u t i o n of the d i c a r b o n y l (dmtc) WCCO) 2

2000 Figure

1.

1800

3

2000

IR spectrum of from 1800 to 2100

1800

W(CO) (dmtc) cm' 3

2

1


268

INORGANIC

COMPOUNDS WITH UNUSUAL

PROPERTIES

o c c u r r e d i n the absence of C O . T h e i n s o l u b i l i t y of W ( C O ) ( d m t c ) 2

2

II

in

o r g a n i c solvents is s o m e w h a t s u r p r i s i n g i f i n d e e d the c o m p l e x is m o n o m e r i c since W ( C O ) ( d m t c ) 3

v a r i e t y of

solvents.

The

has excellent s o l u b i l i t y a n d s t a b i l i t y i n a

2

p o s s i b i l i t y of

d i m e r or p o l y m e r f o r m a t i o n

t h r o u g h b r i d g i n g s u l f u r atoms b y d a t i v e b o n d f o r m a t i o n u s i n g one of the sulfur lone pairs (15)

c o u l d m a i n t a i n a n effective a t o m i c n u m b e r of 18,

as occurs i n [ W ( C O ) I ] 4

2

2

v i a iodine bridges.

If i n d e e d s u c h a n i n t e r -

a c t i o n occurs, it m u s t b e w e a k a n d u n f a v o r a b l e r e l a t i v e to C O c o o r d i n a t i o n , as e v i d e n c e d b y the r a p i d u p t a k e of C O that occurs almost i n s t a n t a n e o u s l y w h e n the d i c a r b o n y l s o l i d interacts w i t h a s o l u t i o n c o n t a i n i n g dissolved C O .

A m o n o m e r - d i m e r e q u i l i b r i u m has b e e n

M c D o n a l d a n d co-workers for M o ( C O ) ( d t c ) 2

e l e c t r o n i c spectra as a f u n c t i o n of c o n c e n t r a t i o n (14). absorptions of s o l i d W ( C O ) ( d m t c ) 3

presence

a n d the v ( C - N ) f r e q u e n c y of

reflects the p a r t i a l d o u b l e b o n d c h a r a c t e r

1

on

The remaining IR

w e r e consistent w i t h the

2

of b i d e n t a t e d i t h i o c a r b a m a t e l i g a n d s (16), 1523 c m '

proposed by

i n solution based

2

of the C N b o n d

t y p i c a l i n this d e l o c a l i z e d l i g a n d system. The

1

H N M R of W ( C O ) ( d m t c ) 3

2

s h o w e d o n l y a s i n g l e t at r o o m

t e m p e r a t u r e (8 = 3.20 p p m ) as w o u l d b e a p p r o p r i a t e f o r the m e t h y l p r o tons of d m t c (17),

a n d further H N M R investigations were not p u r s u e d J

b e c a u s e of the greater s e n s i t i v i t y of environment.

The initial

1 3

1 3

C N M R to s m a l l differences

C N M R s p e c t r u m at r o o m t e m p e r a t u r e

in dis-

p l a y e d three resonances i n a d d i t i o n to those a t t r i b u t a b l e to solvent a n d M e S i . T h e m e t h y l g r o u p s w e r e easily a s s i g n e d to the singlet at 39.2 p p m 4

w h i l e t h e c e n t r a l carbons of the d i t h i o c a r b a m a t e l i g a n d s ( r e f e r r e d to as C carbons t h r o u g h o u t the d i s c u s s i o n ) w e r e a s s i g n e d at 208.7 p p m a n d t h e c a r b o n y l carbons at 233.1 p p m i n v i e w of t y p i c a l values f o r these l i g a n d s (18,19).

T h e f a c i l e i n t e r c o n v e r s i o n routes a v a i l a b l e to

seven-

c o o r d i n a t e c o m p o u n d s s u g g e s t e d that a d y n a m i c process w a s a v e r a g i n g t h e e n v i r o n m e n t s of the three c a r b o n y l l i g a n d s o n t h e N M R t i m e scale s i n c e a structure w i t h three e q u i v a l e n t C O l i g a n d s s e e m e d h i g h l y i m probable. A

temperature-dependent

1 3

C N M R study was undertaken.

original data were obtained on natural abundance

1 3

The

C a n d are r e p r o d u c e d

i n F i g u r e 2. I n d e e d the c a r b o n y l s i g n a l at 233.1 p p m b r o a d e n e d s u b s t a n t i a l l y at — 27 ° C a n d n o c a r b o n y l resonance w a s o b s e r v e d at either or — 7 4 ° C .

—37°

C o o l i n g to — 1 0 4 ° C p r o d u c e d a t o t a l of three resonances i n

the l o w field r e g i o n : the 248.7 p p m resonance c l e a r l y assignable to C O , w h i c h h a d n o w r e a p p e a r e d i n t h e s l o w exchange l i m i t ; the 206.1

ppm

resonance i n t e r p r e t a b l e as a s l i g h t n e g a t i v e t e m p e r a t u r e d e p e n d e n c e f o r t h e c e n t r a l d i t h i o c a r b a m a t e c a r b o n ( C ) ; a n d the 203.7 p p m

resonance

w h i c h w o u l d b e a s s i g n e d t o a u n i q u e c a r b o n y l p o s i t i o n i n o r d e r that the w e i g h t e d average of the c a r b o n y l c h e m i c a l shifts r e p r o d u c e the r o o m


22.

TEMPLETON

Seven-Coordinate

Tungsten

269

Complexes

C-13 nmr 35C

207

233

-37C

2 0 9

OC

-74C 249

-27C

PPM

250 Figure 2. abundance

200

-104C

206. 904

PPM

250

200

Variable temperature ^C-^H} NMR spectra of natural W(CO) (dmtc) in the low-field region displaying resonances attributed to CO and R N CS ~ s

2

13

temperature value ( J ( 2 X

248.7 +

2

13

2

203.7) — 233.7, cf. 233.1

observed).

T h e m e t h y l singlet r e m a i n e d s h a r p at — 74 ° C b u t at — 104 ° C t w o signals h a d r e p l a c e d the o r i g i n a l singlet. O n e c a n i n t e r p r e t the a b o v e d a t a , a d m i t t e d l y l i m i t e d b y the s m a l l n u m b e r of different temperatures a n d t h e signal-to-noise r a t i o present f o r exchanging

1 3

C sites w i t h no a t t a c h e d protons to enhance these resonance

signals, as i n d i c a t i v e of t w o u n i q u e sites f o r the c a r b o n y l s i n a r a t i o of 2 : 1 , e q u i v a l e n t sites f o r b o t h c e n t r a l d m t c carbons, a n d t w o sites f o r t h e f o u r d m t c m e t h y l s i n a 1:1 r a t i o . A l t h o u g h the

1 3

C O - e n r i c h e d N M R study

c o n t r a d i c t s e a c h of these c o n c l u s i o n s f o r the l o w t e m p e r a t u r e s t r u c t u r e , v i d e i n f r a , the a b o v e case offers a c o n v e n i e n t p o i n t of d e p a r t u r e

for

a n a l y z i n g the s t e r e o c h e m i c a l n o n r i g i d i t y of these c o m p l e x e s . T h e l a c k of s t r u c t u r a l d a t a f o r the g r o u n d state of m o l e c u l e s of t h e type M ( C O ) ( B - B ) 3

2

necessitates that reasonable

postulates r e g a r d i n g

l i g a n d d i s t r i b u t i o n serve as a basis f o r the i n t e r p r e t a t i o n of t h e N M R data.

T h e preference

exhibited b y carbonyl ligands w h i c h favor

cis

geometries to e n h a n c e the 7r-acceptor p r o p e r t i e s of these l i g a n d s is w e l l documented (20).

T h e o b s e r v e d p a t t e r n a n d intensities of the I R

ab-

sorptions f o r t h e three c a r b o n y l s are consistent w i t h s u c h a cis a r r a n g e m e n t , a n d w e suggest that a u s e f u l s t a r t i n g p o i n t f o r s t r u c t u r a l c o n s i d e r a tions is the 4 : 3 geometry.

T h e cis a r r a n g e m e n t of the three C O l i g a n d s

w i l l p r o v i d e t h e p l a n a r g r o u p of three d o n o r atoms b y d e f i n i t i o n , r e g a r d less of the details of t h e i r l o c a t i o n . T h e t w o b i d e n t a t e l i g a n d s are t h e n r e q u i r e d to f u r n i s h the f o u r r e m a i n i n g d o n o r atoms i n a p l a n e p a r a l l e l to


270

INORGANIC COMPOUNDS W I T H UNUSUAL PROPERTIES

II

that of the three c a r b o n d o n o r atoms i f the strict 4 : 3 d e f i n i t i o n is to a p p l y . I n fact, there is n o reason to assume p l a n a r i t y f o r the f o u r S atoms, b u t as p o i n t e d out b y D r e w , the 4 : 3 g e o m e t r y is sufficiently close to b o t h the c a p p e d o c t a h e d r o n a n d the c a p p e d t r i g o n a l p r i s m ( C T P ) that i t n e e d n o t b e c o n s i d e r e d a separate g e o m e t r y .

T h u s , i n o u r case, w e c a n use

the

c o n c e p t u a l s i m p l i c i t y of the 4 : 3 d i s t r i b u t i o n i n terms of the n a t u r a l d i v i s i o n of S : C a n d alter the b i d e n t a t e l i g a n d positions a c c o r d i n g l y to r e a l i z e 4

3

a n y of the i d e a l i z e d geometries accessible w i t h i n the constraint of cis c a r b o n y l groups. C o n s i d e r the 4 : 3 projections s h o w n b e l o w as A a n d B . I n b o t h cases, r o t a t i o n of the t h r e e C O l i g a n d s w i l l a v e r a g e C O ( l ) w i t h C O ( 2 ) CO(3).

T h e same r o t a t i o n a l m o t i o n w i l l average a l l C H

3

and

groups w h e n

one considers that e q u i v a l e n t m i n i m a are accessible after e a c h r o t a t i o n of 6 0 ° .

I n case B , w h e r e C ( l )

is n o t e q u i v a l e n t to C ( 2 ) , a v e r a g i n g of

C O (2)

C O (3)

CH (2) 3

\ /

CH (3) 3

N

C(2)—N

-C(l)

\

CH (4)

CH (1)

3

3

com A

C O (2) CH (2) 3

CHa(l)

\

CH (3) 3

N—C(l)

C(2)—N

CO(l)

\

CH (4) 3

C O (3) B


22.

TEMPLETON

Seven-Coordinate

Tungsten

271

Complexes

these signals w i l l also occur. H e n c e , o n l y one s i g n a l w i l l b e seen f o r e a c h of the three d i s t i n c t types of carbons i n the fast e x c h a n g e l i m i t f o r b o t h A a n d B . U p o n c o o l i n g the s a m p l e to o b t a i n the h'miting s p e c t r u m , b o t h case A a n d B w i l l p r o d u c e t w o separate C O signals i n a ratio of 2 : 1 a n d t w o C H signals i n a ratio of 1:1, b u t case B w o u l d p r e d i c t t w o different 3

C

e n v i r o n m e n t s a n d h e n c e t w o signals w h i l e A has b o t h C atoms i n

m a g n e t i c a l l y e q u i v a l e n t sites i n t h e f r o z e n geometry. p o s s i b l e geometries provides a geometry

Although

other

c o u l d b e a n a l y z e d , suffice it to n o t e that case A that is consistent

w i t h the p o s s i b l e

d i s c u s s e d w i t h respect to the n a t u r a l a b u n d a n c e T h e i n c o r p o r a t i o n of

1 3

1 3

assignments

C data above.

C O i n t o the s a m p l e p r o c e e d e d as e x p e c t e d i n

v i e w of the l a b i l i t y of the C O i n the t r i c a r b o n y l w h e n h e a t e d

under

v a c u u m or w h e n r e a c t e d w i t h t r i p h e n y l p h o s p h i n e . T h e I R s p e c t r u m c o m p a r i s o n i n F i g u r e 1 c l e a r l y reflects s u b s t a n t i a l

1 3

C O enrichment, probably

i n the n e i g h b o r h o o d of 15 to 2 0 % , a n e s t i m a t e d b a s e d o n N M R d a t a . The

room-temperature

(CO) (dmtc) 3

2

s p e c t r u m of the

isotopically enriched

p r o v i d e d d e f i n i t i v e e v i d e n c e t h a t the e x c h a n g e

W-

process

d i d not i n v o l v e a dissociative loss of C O to f o r m a six-coordinate i n t e r mediate.

T h e p r e s e n c e of

1 8 3

produced a doublet w i t h J (

W (I =

1 8 3

W—

1 3

1/2) C)

=

i n 14.4%

natural abundance

119 H z , i n d i c a t i n g that

any

e x c h a n g e was necessarily i n t r a m o l e c u l a r i n o r d e r that t h e c o u p l i n g b e r e t a i n e d . T h e i n t e n s i t y of the d o u b l e t r e l a t i v e to the t o t a l

1 3

C O intensity

was a p p r o x i m a t e l y 1 5 % , a n d the c o u p l i n g constant of 119 H z is i n t h e r a n g e t y p i c a l of W - C c o u p l i n g constants (21), of these s i d e b a n d s .

The enriched

temperature for W ( C O ) ( d m t c ) 3

2

1 3

thus c o n f i r m i n g the o r i g i n

C O N M R spectra as a f u n c t i o n of

are i l l u s t r a t e d i n F i g u r e s 3, 4, a n d 5.

T h e i m p r o v e d signal-to-noise r a t i o i n the l a b e l l e d species a l l o w e d us to o b t a i n u s e f u l d a t a over a b r o a d t e m p e r a t u r e range. T h e c o u l d b e seen at e a c h of t h e 11 temperatures

1 3

C O signal

chosen f o r s t u d y , a n d

the a d d i t i o n a l d a t a d i c t a t e d that the d y n a m i c processes w e r e m o r e c o m plex than originally formulated.

A f t e r i n i t i a l b r o a d e n i n g to a n u n s y m -

m e t r i c a l d o u b l e t at — 6 5 ° C , t w o signals w i t h a n intensity r a t i o of 1:2 w e r e o b s e r v e d at — 78 ° C , w i t h the less intense s i g n a l at l o w field c o r r e s p o n d i n g to the 248.7 p p m s i g n a l f r o z e n out i n the earlier s t u d y . T h e — 7 8 ° C spect r u m also s h o w e d b r o a d e n i n g of the d i t h i o c a r b a m a t e c a r b o n C resonance. F u r t h e r c o o l i n g p r o d u c e d a d o u b l e t for the C atoms ( t h e h i g h field s i g n a l of this p a i r h a d earlier b e e n i n c o r r e c t l y a t t r i b u t e d to the u n i q u e c a r b o n y l ligand).

A g a i n t w o signals of a p p r o x i m a t e l y e q u a l i n t e n s i t y

appeared

f o r t h e m e t h y l g r o u p s i n the l o w t e m p e r a t u r e r e g i o n . T h e u n i q u e C O resonance at l o w

field

c o n t i n u e d to s h a r p e n

temperatures b e l o w — 7 8 ° C . C o u p l i n g to b o t h t u n g s t e n ( / ( 100 H z ) a n d c a r b o n ( / ( C - C ) 1 3

1 3

^

10 H z ) w a s o b s e r v e d .

1 8 3

W-

1 3

C)

at «

The upfield


272

INORGANIC

COMPOUNDS

WITH

UNUSUAL PROPERTIES

-46C

(dmtc) W( CO). 13

2

233 ppm

-25C

7

îS^**!^^^

8

.249

-88C

3.

Figure

Variable temperature enriched W(CO) (dmtc) s

1 3

2

C - { H } NMR spectra of from - 2 5 ° C to - 8 8 ° C 1

CO-

13

-93 C

-99C |249ppm

-105 C 23

218^

J (dmtc^WÔ^

-HOC

ijw Figure

4.

Variable temperature riched W(CO) (dmtc) s

C-{ H} NMR spectra of from -93° to - 110°C

1S

2

X

CH

-78C

Figure 5. Variable temperature ^ C - j / / ) N M R specrtra 0/ W (CO) (dmtc) displaying the CH resonance 1

3

2

3

"

_ 8

8

C

3

39.2pp,r

, I

CO-en-

ls

-99C t " 105 ^(î^^Î^

~ HQQi.x.iAiUjiu..uii


l

II

22.

TEMPLETON

Seven-Coordinate

Tungsten

273

Complexes

C O resonance w i t h t w i c e t h e i n t e n s i t y o f t h e l o w f i e l d s i g n a l u n d e r w e n t a s e c o n d b r o a d e n i n g process at l o w e r temperatures, h o w e v e r . W h i l e t h e lowest temperature attained (—-110°C)

f a i l e d to p r o d u c e a l i n e w i d t h

sufficiently n a r r o w to m e a s u r e c o u p l i n g constants f o r these t w o c a r b o n y l l i g a n d s , t h e c h e m i c a l shifts w e r e a c c u r a t e l y d e t e r m i n e d , a n d rate c o n stants w e r e e x t r a c t e d f r o m t h e c o a l e s c e n c e t e m p e r a t u r e a n d l i n e w i d t h measurements.

C l o s e i n s p e c t i o n o f t h e m e t h y l r e g i o n suggests that t h e

t w o signals o b s e r v e d at — 9 9 ° C m a y b e b r o a d e n i n g a g a i n at l o w e r t e m peratures, i n d i c a t i n g that m o r e t h a n t w o sites c a n exist f o r t h e f o u r m e t h y l groups. I n s u m m a r y t h e n , t h r e e c a r b o n y l l i g a n d s u n d e r g o t w o d i s t i n c t exc h a n g e processes w h i l e t h e d i t h i o c a r b a m a t e l i g a n d s p r o v i d e t w o a d d i t i o n a l sites at w h i c h t o a c c u m u l a t e exchange d a t a , carbons C a n d C H . 3

T a b l e I lists t h e a c t i v a t i o n b a r r i e r , A G ^ , c a l c u l a t e d f r o m t h e E y r i n g e q u a tion ( 1 ) , where k

ex

was calculated according to the G u t o w s k y - H o l m

e q u a t i o n at t h e coalescence t e m p e r a t u r e ( 2 2 ) , a n d t h e fast exchange a n d

Table I. C CH

T(°C)

a

Activation Barriers kexfsec- )* 1

70 50 28

-88 -91* -99

3

AGifkcalmol ) 1

9.1 9.1 8.9 9.0 ± 0 . 1 *

R NCS 2

2

-65 -78 -83* -93 -99

1300 290 141 60 25

9.1 9.1 9.1 8.9 8.9 9.0 ± 0.1

CO 1,2,3

-65* -78 -88

1290 310 110

9.1 9.0 8.9 9.0 ± 0.1

CO 2,3

-91* -93 -99 -105 -110

840 760 220 110 70

8.0 8.2 8.1 8.0 8.0 8.1 ± 0.1

° The * identifies the coalescence temperature, T . Rate constants were calculated as indicated in the text. The ± values of AGr listed serve only as an indication of the agreement of these determinations and do not represent error limits. c

b

9


274

INORGANIC

COMPOUNDS WITH UNUSUAL PROPERTIES

II

fc --^-exp(-AGVR2 )

T>T

C

r =r

(1)

T

ex

c

k

e

x

^ ^ ^ ) l

k

e

x

=

C

fc ,

2

^^L

=

V T

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