VARIABLE PRESSURE OXYGEN-17 FTNMR AND STOPPED-FLOW KINETIC STUDY OF WATER EXCHANGE AND DMSO SUBSTITUTION ON SQUARE-PLANAR TETRAAQUA-PALLADIUM (II) AND -PLATINUM (II)

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VARIABLE PRESSURE OXYGEN-17 FTNMR AND STOPPED-FLOW KINETIC STUDY OF WATER

EXCHANGE AND DMSO SUBSTITUTION ON SQUARE-PLANAR TETRAAQUA-PALLADIUM (II)

AND -PLATINUM (II)

Y. Ducommun, P. Nichols, L. Helm, L. Elding, A. Merbach

To cite this version:

Y. Ducommun, P. Nichols, L. Helm, L. Elding, A. Merbach. VARIABLE PRESSURE OXYGEN-17 FTNMR AND STOPPED-FLOW KINETIC STUDY OF WATER EXCHANGE AND DMSO SUB- STITUTION ON SQUARE-PLANAR TETRAAQUA-PALLADIUM (II) AND -PLATINUM (II).

Journal de Physique Colloques, 1984, 45 (C8), pp.C8-221-C8-224. �10.1051/jphyscol:1984842�. �jpa- 00224343�

JOURNAL DE PHYSIQUE

Colloque C8, supplément au n ° l l , Tome 45, novembre 1984 page C8-221

VARIABLE PRESSURE OXYGEN-17 FTNMR AND STOPPED-FLOW KINETIC STUDY OF WATER EXCHANGE AND DMSO SUBSTITUTION ON SQUARE-PLANAR

TETRAAQUA-PALLADIUM(II) AND - P L A T I N U M ( I I )

Y. Ducommim, P . J . N i c h o l s , L. Helm, L . I . E l d i n g * and A.E. Merbach

Institut de Chimie Minerale et Analytique, 3, plaee du Ch&teau, CE-1005 Lausanne, Switzerland

* University of Lund, Sweden

Résumé - L'échange t r è s l e n t d'eau sur P t ( H20 ) ^+ a été é t u d i é dans l e domaine de températures 273 à 334 K e t de pressions 0 , 1 à 228 MPa, par RMN de l ' o x y g è - ne-17, en suivant l'accroissement du s i g n a l de l ' e a u l i é e obtenu l o r s du mé- lange de s o l u t i o n s de p l a t i n e ( I I ) avec de l ' e a u e n r i c h i e en 1 70 . L'échange beaucoup plus r a p i d e d'eau sur Pd(H20)i;+ a été é t u d i é dans l e domaine de tem- pératures 240 à 345 K et de pressions 0 , 1 à 260 MPa, par mesure de l a largeur du p i c de l ' e a u l i é e , à 27,11 e t 48,78 MHz. La f o r m a t i o n du complexe de Pd(H20)?+ avec l e OMSO a été étudiée par s t o p p e d - f l o w , dans l e domaine de tem- pératures 288 à 309 K, et de pressions 0 , 1 à 175 MPa. Les r é s u l t a t s sont i n t e r p r ê t é s , dans les t r o i s cas, en termes de modes d ' a c t i v a t i o n a s s o c i a t i f s ( a ) .

Abstract - The very slow water exchange on Pt(H20)t;+ was s t u d i e d i n t h e tempe- r a t u r e range 273 t o 334 K and pressure range 0 . 1 t o 228 MPa by 1 70 FTNMR, f o l - lowing the increase i n height of the s i g n a l from bound water observed when p l a t i n u m ( I T ) s o l u t i o n s are mixed w i t h 1 70 enriched water. The much f a s t e r wa- t e r exchange on Pd(H20)?+ was s t u d i e d i n the temperature range 240 t o 345 K and pressure range 0 . 1 t o 260 MPa, by measuring the 1 70 FTNMR l i n e w i d t h s o f the bound water resonance at 27.1 and 48.7 MHz. Complex f o r m a t i o n between DMSO and Pd(H20)i;+ was studied by s t o p p e d - f l o w , i n t h e temperature range 288 t o 309 K and pressure range 0.1 t o 175 MPa. I n the t h r e e cases, the r e s u l t s are i n t e r p r e t e d i n terms of a s s o c i a t i v e a c t i v a t i o n modes ( a ) .

INTRODUCTION

The only two square-planar hydrated cations known so f a r are t h o s e - o f palladium ( I I ) and p l a t i n u m ( I I ) . Although l i g a n d s u b s t i t u t i o n r e a c t i o n s o f f o u r - c o o r d i n a t e square-planar complexes, e x p e c i a l l y those of p l a t i n u m , have been e x t e n s i v e l y i n v e s t i - g a t e d , only very few studies of solvent exchange k i n e t i c s Of such complexes have been r e p o r t e d1'2, and the e f f e c t of pressure on the k i n e t i c s of these systems i s not known. We r e p o r t the volumes of a c t i v a t i o n f o r water exchange on P t ( H20 ) 2+ 3 and f o r water exchange1* and DMSO m o n o - s u b s t i t u t i o n on Pd(H20}2r'" i n aqueous s o l u t i o n .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984842

JOURNAL DE PHYSIQUE

RESULTS

Water exchange on Pt2+ (scheme 1 ) was s t u d i e d a t v a r i - able temperature and v a r i a b l e pressure u s i n g slow samp-

l i n g 170 NMR. I n t h e v a r i a b l e temperature work, t h e r a t e o f exchange was t o o f a s t t o measure i n t h i s way a t t h e h i g e r temperatures, and a r a p i d m i x i n g device had t o be used (see f i g u r e I).' I t c o n s i s t s o f an i n j e c t o r mounted on t h e NMR spectrometer, and c o n t a i n i n g 0.7 g o f a 0.58 m s o l u t i o n o f pt2' i n o r d i n a r y water which i s r a p i d e l y i n j e - c t e d i n t o 0.55 g o f 20 % 170 enriched water. The increase i n h e i g h t (hb) o f t h e bound water s i g n a l (-124.3 ppm from f r e e water s i g n a l , 27.1 MHz, 324 K ) i s measured as a f u n c t i o n o f time. T h i s increase i s due t o chemical exchan-

kbared emitter

-

ge between bound and f r e e water molecules. F i g u r e 2 shows

&

t h e temperature dependence, and f i g u r e t h e pressure de- 1

1. F a s t i n j e c t i o n dev i c e

2. E y r i n g p l o t f o r kex (1.5 m HC104.) 3. E f f e c t o f pressure on kex

(a) represents f a s t i n j e c t i o n data. i n 1.5 m HC1O4 a t 297.2 K.

pendence of kex. Water exchange on Pd2+ (scheme 2 ) was s t u d i e d b y v a r i a b l e tempera-

t u r e and v a r i a b l e pressure 170 NMR, measuring t h e line-broadening o f t h e bound water s i g n a l a t 27.1 and 48.8 MHz, i n presence o r absence o f ~ n ~ + , added as b u l k water r e - l a x a t i o n agent. F i g u r e 4 and 5 r e s p e c t i v e l y show t h e temperature and pressure depen- dence o f kex. The k i n e t i c parameters obtained f o r water exchange on both pd2+ and Pt2f are summarized i n Table I . The complex f o r m a t i o n r e a c t i o n o f pd2+ w i t h dimethyl-

4. Temperature dependence o f t h e bound 5. Pressure dependence o f t h e water water r e l a x a t i o n r a t e a t low [H']. 0.8 exchange on pd(H20):+ a t 27.1 MHz m HC104, w i t h ( 0 ) and w i t h o u t ( 0 , A ) (0) a t 325.3 K, and (e) a t 323.2 K.

added ~ n * + ( 0 , 0 ) 27.1, (A) 48.8 MHz.

Table I . K i n e t i c parameters f o r H20 exchange on square- p l a n a r hydrated c a t i o n s a t 297 ( a ) and 324 K (b).

k 2 9 8 / s - 1 c

ex (5.6 + 0.4)*102 (3.9 + ^0.3)

AH*/ k Jmo 1-

'

A S * / J K - ' ~ O ~ - ' -26 ? 6 -9 + 8 A ~ * / c m ~ m o l -

'

( c ) Exchange o f a p a r t i c u l a r H20 on ~(~20);'.

s u l f o x i d e (DMSO) (scheme 3) was s t u d i e d by stopped-flow

[pd(H20) I+]" + DMSO [ P ~ ( H ~ o ) ~ ( D M S O ) 12+ ⁺ H20 ( 3 )

w i t h U V - v i s i b l e d e t e c t i o n a t v a r i a b l e temperature and v a r i a b l e pressure. For t h e v a r i a b l e pressure work, a com- p l e t e stopped-flow u n i t has been introduced i n t o a pres- sure vessel6, a l l o w i n g t h e s t u d y o f r e a c t i o n s w i t h h a l f - l i v e s > 4 ms, up t o 200 MPa, and between 173 and 473 K (see f i g u r e 6 ) . t h e pressure dependence o f k f and kr i s shown i n f i g u r e 7 and t h e k i n e t i c parameters a r e l i s t e d

i n Table 11.

.

(28-224 JOURNAL DE PHYSIQUE

ld -

16 -

I" Lf T a b l e 11. K i n e t i c parameters f o r DMSO mono-

s u b s t i t u t i o n on ~ d ( ~ ~ 0 ) ' ; ' .

Forward r e a c t i o n Reverse r e a c t i o n

4 k 2 9 8 2.45 + 0.04 M - ~ S - ' 0.24 + 0.01 s-'

AH* +58 + ¹ k ~ m o l - ' +69 2 1 k ~ m o l - ' AS* -44 + 3 JK-'mol-' -25 + 3 J~-'rnol-'

-15 AV* -10.4 + 0.5 cm3mol-' -0.9 + 0.2 cm3mol-'

50 loo 150

P(MFU1

7. E f f e c t of p r e s s u r e on t h e f o r w a r d ( k f ) and r e v e r s e (kr) r a t e c o n s t a n t s f o r r ~ d ( ~ 2 0 ) 3 ~ ~ ~ 0 ] 2 + f o r m a t i o n a t 238 K.

DISCUSSION

pd2+ exchanges i t s aqua-ligands 1.4.10~ t i m e s f a s t e r t h a n pt2+. T h i s agrees e x c e l l e n t l y w i t h p r e v i o u s l y observed r e a c t i v i t y d i f f e r e n c e s between pd2+ and p t 2 + aqua-halide complexes7y8. The n e g a t i v e v a l u e s o f AS* and AV* a r e c o m p a t i b l e w i t h a s s o c i a t i v e a c t i v a t i o n mode f o r w a t e r exchange and f o r DMSO s u b s t i t u t i o n . Other k i n e - t i c d a t a a l s o i n d i c a t e t h a t an I, mechanism i s v e r y l i k e l y f o r s u b s t i t u t i o n reac- t i o n s o f p l a t i n u m ( I 1 ) and p a l l a d i u m ( I 1 ) complexes. The s u b s t i t u t i o n r a t e s depend s t r o n g l y on t h e n a t u r e o f t h e e n t e r i n g l i g a n d , b u t t h e r e i s a l s o a l e a v i n g l i g a n d e f f e c t . The e x t r e m e l y s l o w r a t e o f e n t r y o f t h e d i m e t h y l s u l f o x i d e m o l e c u l e i n t o t h e c o o r d i n a t i o n sphere o f p a l l a d i u m ( I 1 ) can p r o b a b l y be a t t r i b u t e d t o oxygen-bonding o f t h e m o l e c u l e i n t h e r a t e - d e t e r m i n i n g step.

REFERENCES

( 1 ) M. Tubino & A.E. Merbach, I n o r g . Chim. A c t a

2,

Drakenberg & L.1 E l d i n g , I n o r g . Chem. 21, 1820 (1982). ( 3 ) L. Helm, L.I. E l d i n g &

A.E. Merbach, I n o r g . Chem. i n press. ( 4 ) L. Helm, L.I. E l d i n g & A.E.Merbach, Helv.

Chim. A c t a 67, 1453 (1984). ( 5 ) P. Bernhard, L. Helm, A. L u d i & A.E.Merbach, J. Amer.

Chem. Soc. i n press. ( 6 ) P.J. N i c h o l s , Y. Oucommun & A.E. Merbach, I n o r g . Chem. 22, 3993 (1983). ( 7 ) L.I. E l d i n g , I n o r g . Chim. A c t a

1,