14 Structure and Reactivity of Ni(II)-d Complexes 8
Inorganic Compounds with Unusual Properties—II Downloaded from pubs.acs.org by UNIV OF MASSACHUSETTS AMHERST on 03/01/17. For personal use only.
with Monodentate Tertiary Phosphine:CO Fixation
C. SAINT-JOLY, M. DARTIGUENAVE, and Y. DARTIGUENAVE Laboratoire de Chimie de Coordination du CNRS et Université P. Sabatier, 205 Rte de Narbonne, 31030 Toulouse, France
Nickel(II) phosphine complexes have been reported to be efficient catalysts in carbonylation reactions. To investigate this reaction mechanism, we have studied the reaction of C O on the related Ni(II) complexes: NiX (PMe ) (n = 2,3) and [NiX(PMe ) ]BF4 (m = 3,4). Pentacoordinate carbonyl nickel(II) species (without reduction of Ni(II) to Ni(O)) were isolated (1) by direct substitution of PMe by C O in the pentacoordinate complex and (2) by addition of C O on the trans square-planar tetracoordinate complex. These compounds are trigonal-bipyramidal complexes with C O in equatorial position. The N i - C O distance (1.73 Å) is the shortest reported N i - C O distance. Since these carbonylation reactions can be viewed as substitution of an equatorial PMe by CO in a d TBP, they can be related to the substitution reactions in square-planar d metal complexes. 2
3
3
n
m
3
8
3
8
l ^ T u m e r o u s c a r b o n y l a t i o n reactions a r e k n o w n that a r e c a t a l y z e d b y ^
nickel, p a l l a d i u m , a n d p l a t i n u m complexes.
T h e reaction products
c a n b e a v a r i e t y of o r g a n i c c o m p o u n d s s u c h as esters, a l d e h y d e s , etc. (1,2).
S i n c e v e r y f e w d e t a i l e d studies o n t h e p o s s i b l e m e c h a n i s m of
these reactions h a v e b e e n r e p o r t e d , i t is c o m m o n l y a s s u m e d that a c y l m e t a l c o m p l e x e s are t h e basic i n t e r m e d i a t e s i n t h e reactions. F o r e x a m p l e , S c h e m e 1 outlines t h e m e c h a n i s m p r o p o s e d b y G a r r o u a n d H e c k f o r t h e p a l l a d i u m - c a t a l y z e d c o n v e r s i o n of a r y l h a l i d e s i n t o esters 0-8412-0429-2/79/33-173-152$05.00/0 © 1979 American Chemical Society
(1,2).
14.
SAINT-JOLY
Ni(II)-d
E T AL.
153
Complexes
8
Scheme 1 P d X ( P P h ) + C O + 2 n - B u O H -> P d ( C O ) ( P P h ) + 2 H X + ( n - B u O ) C O 2
3
2
3
2
2
Pd(CO) (PPh ) + R X - +P d R X ( P P h ) + C O 3
2
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3
2
3
2
+ C O - * Pd(RCO)X(PPh ) 3
2
Pd(RCO)X(PPh )
2
+ n-BuOH-> PdHX(PPh ) + n-BuCOOR
PdHX(PPh )
2
+ C O - * Pd(CO) (PPh )
3
3
3
3
2
2
+ H X neutralized b y N R
3
I n t h e n i c k e l c h e m i s t r y , attempts to isolate a c y l n i c k e l ( I I ) c o m p o u n d s h a v e f a i l e d f o r a l o n g t i m e (1,2,3,4).
Moreover, the resulting organic
c o m p o u n d s w e r e c a r b o n y l free, i n d i c a t i n g a n a p p a r e n t i n s t a b i l i t y of t h e supposed acylnickel(II)
intermediate
H o w e v e r , i n 1972
(1,2,5,6,7).
P a n k o w s k i a n d Bigorgne (8) succeeded i n isolating the pentacoordinate NiI (CO)(PMe ) 2
3
2
c o m p l e x , a n d i n 1973 K l e i n
prepared the
(5,6,7)
stable a c y l n i c k e l ( I I ) complexes N i X ( C H C O ) ( P M e ) 3
3
2
i n normal condi-
tions of t e m p e r a t u r e a n d pressure. NiX(CH ) (PMe ) + CO 3
3
2
pentane >N i X ( C H C O ) (PMe ) fast d PCO - 1635-1650 cm" X = Cl,Br,I 3
3
1
a
T h e c r y s t a l structure d e t e r m i n a t i o n ( 9 )
2
shows t h e presence of a
trans s q u a r e - p l a n a r N i ( I I ) c o m p l e x w i t h n o r m a l b o n d lengths a n d angles. T h e a c e t y l p l a n e is p e r p e n d i c u l a r to t h e c o o r d i n a t i o n p l a n e o f t h e N i ( I I ) . T h e N i - C distance of 1 . 8 4 ( 1 ) A c a n b e c o m p a r e d d i r e c t l y w i t h t h e values of 1 . 8 2 ( 3 ) a n d 1.80 A o b t a i n e d i n t h e N i ( 0 ) : N i ( C O ) a n d N i ( C O ) 4
2
6
( P P h ) complexes w h e r e TT b a c k b o n d i n g is o p e r a t i v e a n d t o t h e m e a n 2
4
v a l u e of 1.84 A o b t a i n e d f o r N i - C i n t h e N i ( I I ) c o m p l e x e s a n d 1.82(2) A i n N i I ( C O ) ( F d m a )
(10)
2
bis(dimethylarsine)).
(11)
[Ni(CN) ] " 5
3
( F d m a — ferrocene-1,1'-
I t is t e m p t i n g to relate t h e s t a b i l i z a t i o n of t h e
acylcomplex N i X ( C H C O ) ( P M e ) 3
3
2
to t h e presence i n t h e m o l e c u l e of
the h a l i d e l i g a n d since K l e i n d i d n o t succeed, u n t i l n o w , t o isolate stable a c y l c o m p l e x e s b y r e a c t i o n of C O o n t h e N i ( C H ) ( P M e ) 3
(CH )(PMe ) ] 3
3
4
+
2
3
3
and [ N i -
complexes.
S i n c e t h e i n s e r t i o n o f C O i n a m e t a l - c a r b o n b o n d is a w e l l k n o w n r e a c t i o n , its m e c h a n i s m is s t i l l n o t w e l l u n d e r s t o o d a n d t h e c h o i c e b e t w e e n C O i n s e r t i o n i n a M - C b o n d o r a l k y l m i g r a t i o n to t h e C O b o n d e d o n M is d i f f i c u l t (12).
However, i n the only reported example—the
( C O ) / C O s y s t e m — t h e authors f a v o r t h e s e c o n d h y p o t h e s i s . 5
CH -Mn3
Thus, if
t h e a c y l c o m p l e x N i X ( C H C O ) ( P M e ) is c o n s i d e r e d t h e result of m i g r a 3
3
2
t i o n of t h e C H l i g a n d to t h e C O g r o u p b o n d e d o n t h e n i c k e l center, a 3
p o s s i b l e m e c h a n i s m f o r this r e a c t i o n is r e p o r t e d i n F i g u r e 1.
154
INORGANIC
COMPOUNDS
WITH
UNUSUAL
PROPERTIES
II
Table I. Analytical D a t a and Physical Properties for C(%) Color NiI (CO) (PMe ) NiBr (CO) (PMe ) NiCl (CO)(PMe ) [NiBr(CO)(PMe ) ]BF [NiCl(CO) (PMe ) ]BF
Inorganic Compounds with Unusual Properties—II Downloaded from pubs.acs.org by UNIV OF MASSACHUSETTS AMHERST on 03/01/17. For personal use only.
2
3
2
2
3
2
2
3
2
3
3
3
3
4 4
MP(°C)
Calc.
a
brown red brown red brown orange orange
Found
17.03 17.07 20.78 21.09 26.92 27.14 24.40 24.99 unstable
160 172
° A l l melting points are uncorrected.
T h i s m e c h a n i s m is r e l a t e d to the l i g a n d r e p l a c e m e n t square-planar d
8
complexes
reaction i n
w h e r e the first step is a d d i t i o n o n a
(13)
s q u a r e - p l a n a r c o m p l e x g i v i n g t w o t r i g o n a l - b i p y r a m i d a l isomers.
Isomer
1 is t h e m o r e p r o b a b l e since m i g r a t i o n of t h e C H g r o u p f r o m a n e q u a 3
t o r i a l site to a n o t h e r e q u a t o r i a l site p r o d u c e s the s q u a r e - p l a n a r l i g a n d a r r a n g e m e n t that is o b s e r v e d e x p e r i m e n t a l l y . O n the o t h e r h a n d , i s o m e r 2 w o u l d produce an approximately tetrahedral l i g a n d arrangement, w h i c h is t h e e x c i t e d state of the stable s q u a r e - p l a n a r species
(14).
A l t h o u g h , to o u r k n o w l e d g e , no p e n t a c o o r d i n a t e N i X R ( C O ) ( P R ) 3
2
complexes h a v e b e e n r e p o r t e d ( b u t some are w i t h P d ( I I ) or P t ( I I ) ) , b u t f o l l o w i n g H e c k t h e i r existence c a n b e d e d u c e d f r o m t h e c h e m i c a l reactions. T h u s , w e h a v e i n v e s t i g a t e d the r e l a t e d r e a c t i o n of C O w i t h t h e Ni(II)
complexes:
NiX (PMe ) 2
3
n
(n —
1,2;
PMe CHq
V
PMe
3
'
PMe
3
— halide)
^CO
Me P
PMeq +
and [ N i X -
3
>
CH
Ni'
X
3
NT
CO
MeoP.
CH
PMe
3
3
Figure 1. Possible mechanism for formation of acyl complex. Application of substitution mechanism on square planar d complexes. 8
14.
SAINT-JOLY
Ni(II)-d
ET AL.
155
Complexes
8
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X(%) Calc.
Found
Calc.
Found
Calc.
Found
3.69 4.55 5.86 5.65
3.56 4.65 5.82 5.69
12.57 15.54
12.57 15.23
51.52 40.09 22.89
51.78 39.88 23.62
( P M e ) ] B F , k e e p i n g i n m i n d the p r e v i o u s i s o l a t i o n of t h e 3
(PMe ) 3
4
4
NiI (CO)2
compound by Pankowski and Bigorgne.
2
Besides N i I ( C O ) ( P M e ) , f e w N i ( I I ) complexes of C O h a v e b e e n 2
3
2
r e p o r t e d i n the l i t e r a t u r e : N i X ( C H C O ) ( P M e ) 3
(PR ) 3
2
3
( F d m a ) (11). complexes. of N i ( I I )
3
N i X ( C O ) ( ^ - a l l y l ) (3);
(15);
2
NiPh(CO)-
(5,6,7,9);
NiX(CO)
fo -C H ) 5
5
5
(4); N i I ( C O ) 2
T h e y are u s u a l l y p r e p a r e d b y o x i d a t i v e a d d i t i o n o n N i ( 0 )
U s u a l l y , the r e p o r t e d attempts to isolate c a r b o n y l c o m p l e x e s h a v e l e d to r e d u c t i o n either i n the v a l e n c e state of
( N i ( I I ) - * N i ( 0 ) ) or i n the l i g a n d (16,17).
Ni(II)
T h e s e authors are u s e d to
relate this a p p a r e n t r e l u c t a n c e of N i ( I I ) to c o o r d i n a t e C O to t w o f a c t o r s : ( 1 ) the r e l a t i v e stable a n d c o n t r a c t e d 3d orbitals of N i ( I I ) i o n that r e n d e r b a c k d o n a t i o n i n t o the c a r b o n y l 77* f u n c t i o n less effective; ( 2 ) the k i n e t i c i n s t a b i l i t y of the c a r b o n y l complexes (15,16,17).
W e w i l l , i n this s t u d y ,
p u t the emphasis o n the s e c o n d factor. A l l of the m o l e c u l a r c a r b o n y l N i ( I I ) complexes h a v e b e e n p r e p a r e d by dissolving the molecular N i X ( P M e ) 2
plexes i n b e n z e n e ( X = temperature.
3
(X =
n
Cl,Br,I; n =
Br,I) and/or i n ethanol ( X =
2,3)
com-
C l , B r , I ) at r o o m
T h e solutions r a p i d l y react w i t h C O at r o o m t e m p e r a t u r e
a n d a t m o s p h e r i c pressure, w i t h a c o l o r c h a n g e f r o m g r e e n - b l u e to g r e e n a n d b r o w n . B r o w n crystals of N i X ( C O ) ( P M e ) , i n s o l u b l e i n e t h a n o l , 2
are i s o l a t e d b y
filtration
3
2
a n d w a s h e d w i t h e t h a n o l saturated w i t h C O .
W h e n p r e p a r e d i n b e n z e n e , a d d i t i o n of p e n t a n e saturated w i t h C O is necessary to p r e c i p i t a t e the b r o w n complexes ( T a b l e
I).
R e a c t i o n of the c a t i o n i c [ N i X ( P M e ) ] B F complexes ( X = 3
4
4
Cl,Br,I)
w i t h C O was c a r r i e d out i n a m i x t u r e of b e n z e n e - d i c h l o r o m e t h a n e
at
r o o m t e m p e r a t u r e a n d a t m o s p h e r i c pressure. C O is i m m e d i a t e l y a b s o r b e d a n d a n i m p u r e b r o w n s o l i d c a n b e p r e c i p i t a t e d b y a d d i t i o n of p e n t a n e . H o w e v e r , r e c r y s t a l l i z a t i o n of this b r o w n c o m p l e x i n d i c h l o r o m e t h a n e saturated
with
C O gives y e l l o w - t o - g o l d m i c r o c r y s t a l s of
[NiX(CO)-
( P M e ) ] B F , w h i c h are stable e n o u g h to b e i s o l a t e d i n the p r e s e n c e of 3
CO
3
4
for X =
(PMe ) ]BF 3
4
Br. 4
When X =
I, because of the d i s s o c i a t i o n of [ N i l -
f o l l o w i n g the r e a c t i o n :
156
INORGANIC
2[NiI(PMe )4]BF 3
COMPOUNDS
WITH UNUSUAL
PROPERTIES
C H Cl ^-4 N i l 2 ( P M e , ) + [ N i ( P M e a ) 4 ] ( B F )
4
8
4
a
II
+ PMe,,
insoluble o n l y t h e m o l e c u l a r N i I ( C O ) ( P M e ) w a s isolated ( 1 9 ) . A l l of these complexes h a v e b e e n c h a r a c t e r i z e d as t r u l y p e n t a c o o r d i nate l o w s p i n N i ( I I ) complexes ( T a b l e I I ) . T h e m o l e c u l a r complexes are r e a s o n a b l y stable i n t h e s o l i d state a n d c a n b e h a n d l e d i n a i r f o r a short t i m e . T h e c a t i o n i c complexes m u s t b e k e p t u n d e r C O t o p r e v e n t d i s s o c i a t i o n . A l l are unstable i n s o l u t i o n , i f C O is n o t present i n excess.
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2
NiX PMe
3
(CO) ( P M e )
2
3
2
2
^ NiX
2
(PMe ) 3
2
+ CO
is a better l i g a n d t h a n C O as s h o w n b y t h e r e a c t i o n :
3
NiX (CO) (PMe ) + PMe 2
3
2
3
^± N i X ( P M e ) 2
3
3
+ CO
T o u n d e r s t a n d t h e C O fixation m e c h a n i s m at t h e N i ( I I ) center, i t is essential to d e t e r m i n e t h e stereochemistry of t h e complexes. If, as i t is m o r e l i k e l y , t h e t r i g o n a l - b i p y r a m i d a l g e o m e t r y of N i X ( P M e ) (18) a n d [ N i X ( P M e ) ] ( B F ) (19) is p r e s e r v e d f o r the c a r b o n y l complexes, the p r o b a b l e isomers w i l l b e those w i t h t h e halogens i n t h e e q u a t o r i a l positions of t h e t r i g o n a l b i p y r a m i d , i n absence o f s p e c i a l l i g a n d r e q u i r e ments (19,20). 2
3
4
3
3
4
Table II. Characterization D a t a Mf(BM) (25°C) a
NiI (CO)(PMe ) 2
3
NiBr (CO)(PMe ) 3
NiCl (CO)(PMe ) 2
1
a/
2015 s
2
0.64 2
vcofcm
3
2
0.49
4
[NiCl(CO) (PMe ) ]BF
4
3
0.34
1960 w 2005 s 1955 w
1.02
2030 s
2
[NiBr(CO)(PMe ) ]BF 3
1965 w 2010 s
3
3
Dipole Moment
0
3.90
3.95
I n the solid state, corrected from the diamagnetism of the ligands {15). In the solid state, as nujol mull. In C H saturated with C O . I n C H C 1 saturated with C O ; positive shift downfield from 62.5% H P 0 . The slow exchange limit is not reached. a
6
c
d
6
6
2
2
3
4
(*)
14.
SAINT-JOLY
ET
Ni(II)-d
AL.
157
Complexes
8
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Scheme 2
X
PMo
1
PMc
3
2
PMe
3
3
X
: i
4
5
F o r t h e m o l e c u l a r N i X ( C O ) ( P M e ) complexes ( S c h e m e 2 ) , o n l y 2
3
2
i s o m e r 2 is consistent w i t h t h e presence of one v X =
I) a n d a s i n g l e
c o
P { H } N M R l i n e at - 8 0 ° C
3 1
v i b r a t i o n (2015
cm" ,
(6.55 p p m , X =
X
1
I).
T h i s N M R l i n e is i n t h e p p m r a n g e of a x i a l P M e
3
pentacoordinate complexes [ N i X „ ( P R ) . ]
as s h o w n i n F i g u r e 2.
3
5
n
(29)
ligand i n the Ni(II)
T h u s t h e presence of a s t i l l fast p h o s p h i n e exchange process at — 8 0 ° C ( e i t h e r i n t e r - or i n t r a m o l e c u l a r ) is v e r y u n l i k e l y since t h e signal should be i n between the P
a x
a n d P«,
r e s u l t — s t a b i l i z a t i o n of i s o m e r 2—has b e e n s t u d y of P M e
by P ( O M e )
3
variable-temperature torial P M e
3
3 1
3
3 1
P { H } range. 1
P{ H}NMR 1
A n identical
obtained i n the
i n the N i X ( P M e ) 2
3 1
3
3
exchange
complexes, w h e r e the
P { H } N M R has s h o w e d s u b s t i t u t i o n of t h e e q u a -
by P ( O M e )
1
3
(22).
for the Carbonyl N i ( I I ) Complexes P{ H}FT (-80°C)
S1
NMR
1
4
6.55
16.6
21.6 + 2.4 ( - 8 0 ° C ) + 15.7 ( - 1 2 0 ° C ) -26.5 + 6.1 ( - 8 0 ° C )
Molecular Weight (g)' 408
(398)
436
(492)
Electronic (26°C,10*
Transitions cm' (
