C25

Journal of Organometallic Chemistry, 217 (1981) C25-C28 Ekevier Sequoia S.A., Lausanne -Printed in The Netherlands

Prebninary communication

DYNAMIC BEHAVIOUR OF BIS(DI0P)PALLADIU-M AND ITS REACTION

KATHLEEN BROWN and PENNY A_ CHALONER*

Dyson Pen--ins Labomtory, South Parks Road, Ox ford,

(Received May Sth, 1981)

0x1 3QY (Great Bn-tain)

The dynamic behaviour of bis(DIOP)palladium is studied by complete line-shape analysis of its 3*P NMR spectrum_ Its reaction with trans-disuhsti- tuted alkenes gives diastereomeric complexes, the selectivity depending on the

nature of the substituents.

A number of asymmetric syntheses have been achieved in the presence of tetralds(triphenylphosphine)palladium and excess 2,3-isopropylidene-2,3-trczns- dihydroxy-1,4-bis(diphenylphosphino)butane, DIOP, I [l] . More recently, asymmetric addition of hydrogen cyanide to norbomadiene has been reported, catalysed by an isolated DIOP-palladium complex [Z] . The catalyst was prep- ared by the reduction of ((+)-DIOP)PdCl, with sodium borohydride in acetone solution in the presence of (+)-DIOP. The 31P NMR spectrum of the complex showed a singlet at room temperature but two signals below -70°C. On the basis, together with microanalytical data, the authors assigned to it the struc- ture ((+)-DIOP)Pd, though they have since concluded that the complex was ((+)-DIOP),Pd [3]. In view of -the apparent difference between their original suggestion and the kn&vn (DIOP),Pt [4] we investigated this compound in more detail.

H 1

PPh2

PPh,

0022-328X/81/0000-0000/$02.~0,~ 1981, Elsevier Sequoia S.A.

TABLE1

RESULTSaFTHRREA~TXO~OFCOMPLRX~

WIT

~A~K

~NE

S

Alk

end

% P

d co

nver

ted

to

nlke

ne

com

plex

1:1a

&la

Dhs

texo

omer

3i

P N

MR

In

toiu

ono

rntia

nt

300

K (

pp

m)

CO

OM

e

4 COO

Me

0 c 0 0

MeO

QC

a

CO

OM

e

li CO

Oi

BO

OC

co

ot -

Bu

t-B

UO

OC

P

CN

F x C

F3

F

CF

3

6 60

40

28 6

100

16

-

100

-

a0

3:2

70

3:2

la

2:r

100

1:1

X0

Bra

nd

at t

i te

mpe

r&w

ee

10.6

2 (d

)J(P

A-P

S)

= 1

7 H

Z

7,28

(d)

1X,7

(d)

b,c

J(P

A-P

J$

E 8

Hz

8.6

(d)

9.42

*

9,3!

Se68

94

1

9,21

8,

28

8,26

b

7.77

a R

atio

al

kcnw

mlh

dium

; (D

IOP)

,Pd

- 0,

016

M,

b 22

8 K

, ’

Spec

trum

re

cord

ed

In a

ceto

ne.

’ 20

8 K

, e

263

K,

C27

((-)-DIOP)PdCI, was reduced with sodium borohydride in acetone or hydrazine hydrate in ethanol in the presence of (-)-DIOP. Recrystahisation (toluene) and prolonged drying in vacua gave in both cases yehow prisms (m.pt. 99-102°C,dec;~ = f 56.3~ = 0.49, CsHs.((-)-DIOP),Ptgives aD = +18.67 c = O-08, C.&I, ) w ic analyzed correctly for ((-)-DIOP),Pt. h h A monomeric formula was confirmed by the field desorption mass spectrum; the characteristic palladium isotope pattern was noted with M’ = 1102 for *06Pd.

The 31P NMR spectrum was recorded at various temperatures (Fig. 1). At 300 K a singlet (S = 0.32 ppm [5] was observed while at 190 K an A,B,

T =277 K

*=60000 s-1

T = 252 K

k = 16000 s-’

T =22a K

Ii = n-50 s-1

?- ~215 K

k =290 s-’

T ~203 K

k = 65 s-’

T =190 K

k = 35 s-’

Fizz_l.Observedandcalculated "PNMR spectra of<<---)_DIOP),Pd_

C28

multiplet (6 (PA) = 7.57 ppm, 6 (Pn) = -5.22 ppm, J(PA-pB) = 24 Hz) was resolved. The dynamic exchange did not involve free phosphine. Complete line shape analysis [S] gave AG* (228 K) = 41.2 kJ mol-‘. This compares closely with the process and activation energy for the analogous platinum complex and is consistent with a tetrahedral complex ((-)-DIOP),Pd, II, in which exchange is occnrring between different conformations of the seven- membered chelate rings. It is noteworthy that when DIOP is added to tetrakis- (triphenylphosphine)palladium, as in most alkylation reactions [ 11, (DIOP)* Pd is also obtained, showing identical dynamic behaviour to the isolated complex_

The displacement of one molecule of DIOP from II by an alkene leads to a mixed complex. With a symmetrically cis-disubstituted alkene an AB pattern is expected in the 31P NMR spectrum, whereas with a symmetrical trans-alkene two diastereomeric complexes may be observed_ Results are given in Table 1. In the case of dimethyl maleate slow isomerisation occurs to give the dimethyl fumarate complex. The degree of binding is highest for alkenes bearing the most electron-withdrawing groups. Lower equilibrium constants but higher di- astereomeric preference are observed for more hindered alkenes. The coordina- tion of an alkene to palladium makes it more susceptible to nucleophilic attack and the binding of these simple substrates may provide a model for the role of DIOP palladium complexes as asymmetric catalysts.

Acknowledgements

Kl3 thanks the Lancashire Education Authority for a grant and PAC thanks the Cephelasporm Trust for the award of a fellowship.

References

B.M. Trost and T-J_ Dietsche. J_ Amer. Chem. SGC.. 95 (1973) 8200; B.M. Trost and P-E. Strege. J. Amer. Chem. SOL. 99 (1977) 1649. P.S. EImes and W-R. Jackson. J. Amer. Chem. Sot.. 101 (1979) 6128. W-R. Jackson. private communication_ J-M. Brown and P-A. Chaloner, J. Amer. Chem. Sot.. 100 (1978) 4307. 31P chemical shifts are recorded in ppm downfield from external H,PO, _ Simulated spectra WZI-CZ calc&ted using tie program DNMRS; G. Binsch. J. Amer. Chem. SOL. 91 (Z969) 1304.