Catalytic Aspects of Metal Phosphine Complexes - American

1

Applications of P-31 NMR to the Study of Metal-Phosphorus Bonding ALAN PIDCOCK

Downloaded by 203.64.11.45 on May 16, 2015 | http://pubs.acs.org Publication Date: June 1, 1982 | doi: 10.1021/ba-1982-0196.ch001

School of Molecular Sciences, University of Sussex, Brighton BN1 9QJ, U.K.

Evidence is presented that 1JM-P is Fermi dominated and a molecular orbital (MO) expression derived from that term is used to discuss the relation between 1JPt-P and the Pt-P length for platinum(II) and (IV) complexes, the dependence of coupling constants on the nature of ligands in trans and cis relationship to the detector ligand, and the dependence on 1JM-P on groups attached to phosphorus (M = platinum(II), tungsten(O), and hydrogen). New results are included for the following series of complexes: cis-[PtPh(SnX )(PPh ) , cis- and trans-[PtCl(SnX )(PPh3) cis-[PtCl (PX )(PEt )], and trans-[PtCl2(PX )(PCy )](Cy = cyclohexyl). 3

3

3

2],

3

2

2]

3

3

3

T

he characterization a n d assignment o f structures o f coordination c o m p o u n d s w i t h p h o s p h o r u s l i g a n d s is a i d e d strongly b y P - 3 1 N M R spectra e s p e c i a l l y w h e n c o u p l i n g constants b e t w e e n the m e t a l a n d p h o s p h o r u s V M - P or b e t w e e n p h o s p h o r u s a n d other l i g a n d donor atoms / p - c a n b e m e a s u r e d ( 1 , 2 ) . T h e c o u p l i n g constants vary c o n s i d e r a b l y i n m a g n i t u d e , a n d w h e n trends or correlations h a v e b e e n established the c o u p l i n g constants c a n p r o v i d e important structural information b e y o n d that d e r i v e d from the s y m m e t r y o f the spectra. T h e c o u p l i n g constants (particularly those i n v o l v i n g d i r e c t l y b o n d e d atoms) also m a y b e u s e d to investigate b o n d i n g i n coordination c o m p o u n d s , a n d the variation i n the m a g n i t u d e o f the c o u p l i n g s V M - P b e t w e e n a m e t a l i n a s i n g l e o x i d a t i o n state a n d a g i v e n p h o s p h o r u s l i g a n d (e.g., f r o m c a . 1 5 0 0 H z t o 5 5 0 0 H z f o r p l a t i n u m ( I I ) a n d P R ) i s a reflection o f the w i d e variation i n b o n d strengths i n c o o r d i n a t i o n c o m p o u n d s . I n studies o f h o m o g e n e o u s catalysis there are m a n y examples o f c o m p l e x identification v i a c o u p l i n g constants i n v o l v i n g phosphorus, a n d a greater u n d e r s t a n d i n g o f the l a b i l i t y o f l i g a n d s also has c o m e t h r o u g h greater k n o w l e d g e o f ground-state b o n d i n g patterns g a i n e d b y m e a s u r i n g c o u p l i n g c o n s t a n t s (3). 2

L

3

0065-2393/82/0196-0001$05.50/0 © 1982 American Chemical Society In Catalytic Aspects of Metal Phosphine Complexes; Alyea, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

2

METAL PHOSPHINE COMPLEXES

T h i s chapter emphasizes the establishment o f trends i n c o u p l i n g constants b e t w e e n transition metals a n d phosphorus a n d the interpre tation o f such trends i n terms o f the appropriate m o l e c u l a r orbital ( M O ) treatments that are c u r r e n t l y available. Framework for

Interpretation

Interpretations o f c o u p l i n g constants generally are f o u n d e d o n the assumption that the c o u p l i n g derives essentially from the F e r m i con t a c t t e r m . T h i s a s s u m p t i o n is s u p p o r t e d b y t h e e x i s t e n c e o f a n u m b e r o f correlations b e t w e e n 7M-P a n d other c o u p l i n g s for w h i c h n o n - F e r m i terms are expected

t o b e s m a l l e r (4). E x a m p l e s o f c o r r e l a t i o n s

that


e x t e n d o v e r a s i z e a b l e range o f m a g n i t u d e o f 7M-P are those b e t w e e n 7ΡΙ-Ρ for t h e p h o s p h o n a t o l i g a n d s i n trans-

[PtX{P(0)(OPh) }(PBu ) ] 2

3

2

a n d / P T - C - H for t h e m e t h y l l i g a n d s i n trans- [ P t X ( C H ) ( P E t ) ] (X = C I , 2

3

3

2

B r , I, O N 0 , N , N C O , N C S , N 0 , a n d C N ) (5), a n d b e t w e e n V m - p for 2

PBu

3

3

i n trans-

2

[ P t C l L ( P B u ) l a n d Ϋ ^ - Ν i n trans2

3

[PtCl L(NH C H 2

2

e

1 3

)]

( L = P R , A s R , M e S O , N H R ) (6) (see F i g u r e s 1 a n d 2). T h e s e a n d 3

3

2

2

other correlations i n v o l v i n g d i r e c t c o u p l i n g to h y d r i d e l i g a n d

UPÎ-H

a n d i n d i r e c t c o u p l i n g s t o fluorine h a v e b e e n e x a m i n e d b y D i x o n e t a l . (7), w h o h a v e s h o w n t h a t t h e n o n z e r o i n t e r c e p t s o f s o m e o f t h e c o r r e l a tions are consistent w i t h F e r m i - d o m i n a t e d c o u p l i n g s .

Figure 1. Graph of [PtX{P(0)(OPh) }(PBu ) ] 2

3 2

'J t-p for against P

the phosphonato ligand in trans] -c-Hfor trtins-[Pt(CH )X(PEt ) ] (5) 2

Pt

3

In Catalytic Aspects of Metal Phosphine Complexes; Alyea, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1982.

3 2


1.

PIDCOCK

P-31 NMR

and Metal-Phosphorus

3

Bonding

T h e e v a l u a t i o n o f the F e r m i contact t e r m i n v a l e n c e b o n d or

MO

t h e o r y i n v o l v e s s e v e r a l s i m p l i f y i n g a s s u m p t i o n s ( s u c h as t h e a v e r a g e excitation

energy

approximation)

especially

for

complexes

of

low

s y m m e t r y (I ), b u t t h e f o r m o f t h e F e r m i t e r m is s u c h t h a t t h e c o u p l i n g s m u s t d e p e n d strongly o n the s o r b i t a l content of the b o n d b e t w e e n the c o u p l e d atoms. A c o n v e n i e n t form o f the M O expression (adapted P o p l e a n d S a n t r y (4))

is g i v e n i n E q u a t i o n 1; t h e c o n s t a n t C

from

involves

the m a g n e t o g y r i c ratios of the c o u p l e d n u c l e i a n d other constants,

3

ΔΕ

is a n a v e r a g e e x c i t a t i o n e n e r g y , | S ( 0 ) | a n d | Sp(0) | a r e t h e m a g n i t u d e s M

o f the valence

state s - o r b i t a l b a s i s f u n c t i o n s e v a l u a t e d at t h e

nuclei, and P's s m

p

parent

is t h e M O b o n d o r d e r b e t w e e n t h e s o r b i t a l s o f

Î/M-P = C ( A E ) - ' | S ( 0 ) | | S P ( 0 ) | ( P ' 3

2

m

the c o u p l e d atoms. T h e term ( P ' s s ) M

P

2

2

S M S P

)

(1)

2

increases d i r e c t l y w i t h a p , the s

c h a r a c t e r o f t h e d o n o r o r b i t a l o f t h e p h o s p h o r u s l i g a n d , a n d w i t h o&, the s character of the acceptor

orbital of the metal (M).

Of

course

a n a l o g o u s e x p r e s s i o n s c a n b e w r i t t e n for o t h e r c o u p l i n g s s u c h as 1/M-C a n d JM—N> a n d t h e m a g n i t u d e s o f i n d i r e c t c o u p l i n g s s u c h as l

2

/ -C-H M

often are d i s c u s s e d i n terms o f a n expression o f s i m i l a r form, w h e r e C t h e n i n c l u d e s factors a f f e c t i n g t h e t r a n s m i s s i o n o f c o u p l i n g t h r o u g h t h e intervening bonds.


4


T h u s , t h e c o r r e l a t i o n s b e t w e e n c o u p l i n g c o n s t a n t s (see F i g u r e s 1 a n d 2) i m p l y p a r a l l e l c h a n g e s i n t h e p a r a m e t e r s o f E q u a t i o n 1 i n t h e different series o f c o m p l e x e s , b u t n e i t h e r the accurate correlations nor the more qualitative establishment of similar trends i n c o u p l i n g con s t a n t s i n r e l a t e d sets o f c o m p l e x e s

gives a clear indication of w h i c h

t e r m s i n E q u a t i o n 1 a r e t h e i m p o r t a n t v a r i a b l e s for a p a r t i c u l a r set o f c o u p l i n g c o n s t a n t s . I n a set o f c o m p l e x e s t h e s i t e a n d t y p e o f v a r i a t i o n o f s t r u c t u r e c a n d e t e r m i n e to s o m e e x t e n t w h i c h v a r i a b l e s o f E q u a t i o n 1 a r e d o m i n a n t for t h a t set. H o w e v e r , i f p o s s i b l e , a t t e m p t s a l s o s h o u l d b e m a d e t o i d e n t i f y b y e x p e r i m e n t or c a l c u l a t i o n t h e i m p o r t a n t v a r i


a b l e s for e a c h k i n d o f s t r u c t u r e v a r i a t i o n . Metal Oxidation

State and Phosphorus Ligand

Constant

W h e r e t h e p h o s p h o r u s l i g a n d is h e l d c o n s t a n t , i t is n o r m a l to as s u m e t h a t t h e s c h a r a c t e r o f t h e p h o s p h o r u s d o n o r o r b i t a l (ap),

which

c o n t r i b u t e s d i r e c t l y to ( P ' s s ) a n d |Sp(0)| , d o e s n o t v a r y s i g n i f i c a n t l y M

P

2

2

as o t h e r l i g a n d s o n t h e m e t a l are c h a n g e d (8).

It s e e m s r e a s o n a b l e t h a t

c h a n g e s at t h e m e t a l p r i n c i p a l l y s h o u l d affect t e r m s i n E q u a t i o n 1 t h a t a r e a s s o c i a t e d w i t h t h e m e t a l a n d t h a t v a r i a t i o n s i n d u c e d i n t h e state o f t h e p h o s p h o r u s d o n o r s h o u l d b e s m a l l i n c o m p a r i s o n . H o w e v e r , i t is clear from studies o f c o u p l i n g constants w i t h i n the phosphorus donor t h a t s o m e v a r i a t i o n s i n t h e p h o s p h o r u s d o n o r d o o c c u r . T h u s , ^ P - C for PBu

3

is c a . 3 8 H z w h e n t r a n s to n i t r o g e n or c h l o r i n e i n d i c h l o r o -

p l a t i n u m ( I I ) c o m p l e x e s a n d is c a . 3 2 H z w h e n t r a n s to P R d r a w a l o f σ-electrons f r o m P B u

3

3

(9). W i t h

b y p l a t i n u m is s t r o n g e r for P B u

3

trans

to n i t r o g e n o r c h l o r i n e , a n d t h e s i m p l e s t i n t e r p r e t a t i o n o f t h e r e s u l t s is t h a t a p | S ( 0 ) | for P - C b o n d s is l a r g e r i n t h e s e c o m p l e x e s . A n i n c r e a s e 2

P

i n ap (for t h e P - C b o n d s ) is e x p e c t e d f r o m B e n t ' s r u l e s (10)

since a

stronger acceptor s h o u l d i n v o l v e larger p- a n d s m a l l e r s character i n the p h o s p h o r u s orbital of the P t - P b o n d , a n d there s h o u l d be a c o m p l e m e n t a r y c h a n g e i n the orbitals o f the P - C bonds. E l e c t r o n w i t h drawal from P B u

3

a l s o is e x p e c t e d to c o n t r a c t t h e r a d i a l p a r t s o f t h e

p h o s p h o r u s (basis) o r b i t a l s a n d i n c r e a s e |S (0)| ( i i ) . P

t w o factors affect ^ ( P C )

A l t h o u g h these

2

i n t h e s a m e w a y , t h e i r effects o n t h e p h o s

p h o r u s d o n o r o r b i t a l u s e d i n t h e b o n d to p l a t i n u m t e n d to c a n c e l i n 7 M - P : |S (0)| i n c r e a s e s a n d a% d e c r e a s e s P

2

as t h e a c c e p t o r s t r e n g t h o f

p l a t i n u m i n c r e a s e s . T h i s i m p l i e s t h a t t h e p r o d u c t a | S ( 0 ) | for t h e P t P 2

2

P

b o n d s m a y not vary significantly i n c o m p a r i s o n w i t h changes i n the p l a t i n u m p a r a m e t e r s for a r a n g e o f c o m p l e x e s o f a g i v e n p h o s p h o r u s donor. The

values

of J _ l

Ag

P

for c o m p l e x e s

[Ag(PBu ) ] 3

n

+

(n = 2, 3 ,

4),

w h i c h are i n c o m m o n w i t h s e v e r a l o t h e r c o u p l i n g c o n s t a n t s b e t w e e n d i r e c t l y b o n d e d a t o m s (22), d e p e n d o n t h e c o o r d i n a t i o n n u m b e r η i n a m a n n e r that suggests d o m i n a n c e o f the s character o f the s i l v e r h y b r i d orbital a

2

Ag

( w h i c h c o n t r i b u t e s d i r e c t l y to t h e ( P ' s g S ) o f E q u a t i o n 1). A

P

2


1.

PIDCOCK

P-31 NMR


Bonding

5

400 1 J(AGP)

(HZ)

200 1


0

0.50

0,25

0

1/N Figure 3. Graph of J . for_[Ag(PBu )J (BF )-( 12) against 1/n, the s character of the idealized sp hybrid orbital of silver. Results for other silver(I) complexes are similar ( 13, 14). 1

Ao P

+

3

n

4

1

T h u s t h e g r a p h o f H A S - P a g a i n s t 1/n, t h e i d e a l i z e d s c h a r a c t e r o f t h e silver s p

n _ 1

h y b r i d o r b i t a l s , is a c c u r a t e l y l i n e a r (see F i g u r e 3). R e s u l t s

o f this k i n d (especially

for ^ C - H ) p r o b a b l y h a v e b e e n p r e e m i n e n t

in

l e a d i n g to t h e g e n e r a l a c c e p t a n c e o f t h e i d e a t h a t c o u p l i n g c o n s t a n t s b e t w e e n d i r e c t l y b o n d e d atoms a c c u r a t e l y reflect s-orbital contents o f b o n d s . H o w e v e r , i n t e r m s o f t h e M O e x p r e s s i o n (see E q u a t i o n 1) ( a n d especially

i n terms

terms w i t h different

of more 3

ΔΕ),

accurate treatments

involving

several

s u c h results appear almost coincidental,

since a n accurate c o r r e l a t i o n appears to r e q u i r e a rather i m p r o b a b l e constancy i n the p r o d u c t |S (0)| / AE a n d i n the r e l a t i v e c o n t r i b u t i o n s 2

M

3

o f t h e m e t a l a n d p h o s p h o r u s a t o m i c o r b i t a l s to t h e M O s . A l t h o u g h t h e fact t h a t t h e c o r r e l a t i o n b e t w e e n ^Ag-p a n d 1/n d o e s n o t p a s s t h r o u g h t h e o r i g i n (see F i g u r e 3) i n d i c a t e s s o m e f a i l u r e o f t h i s s i m p l e

frame

w o r k of interpretation, it seems p r o b a b l e that some fortuitous c a n c e l l a t i o n o f c h a n g e s i n |S (0)| a n d Δ Ε 2

M

overlooked

is i n v o l v e d a l s o . It s h o u l d n o t b e

3

that E q u a t i o n 1 itself a n d the s i m p l e interpretation

in

terms of h y b r i d i z a t i o n i n v o l v e substantial approximations. H o w e v e r , w h e r e the energies of the valence-state orbitals of met als are r e a s o n a b l y s i m i l a r , w e c a n e x p e c t that the coefficients atomic

orbitals ( w h i c h

affect

P's s ) can undergo M

P

large

of the

numerical

changes w h i l e the energy differences b e t w e e n b o n d i n g a n d a n t i b o n d i n g o r b i t a l s (e.g., Δ Ε ) c h a n g e o n l y f r a c t i o n a l l y . T h e r e f o r e c h a n g e s i n 3

! / M - P i n a series o f c o m p l e x e s oxidation

state,

and

of a given

coordination

number

phosphorus donor, may

be

metal,

dominated

by

changes i n the s c o m p o n e n t o f the M - P b o n d s rather t h a n b y |S (0)| M


2


6 or

3

ΔΕ.

This

interpretation can be

supported

strongly

for

square-

p l a n a r a n d octahedral transition m e t a l c o m p l e x e s w h e r e the b i n d i n g of phosphorus ligands ligand

trans

complexes

to

of

is i n f l u e n c e d

phosphorus,

platinum(II)

[PtCl -n(PR3)n] " ( n

6

strongly b y the nature of

in

the

4

nonequivalent

( n

n

Table

and

2 ) +

similar

3

ΔΕ

terms.

P t - P bonds Therefore

ences i n the s components

complexes

(trans to c h l o r i n e

the

c o u p l i n g constants w i t h i n these c o m p l e x e s

platinum(IV)

I) (15). T h e

p h o s p h o r u s ) that are associated w i t h a c o m m o n probably

the

chloro(trialkylphosphine)

[PtCl - (PR3)n] ~

(n = 1, 2 , 3) (see

2 ) +

w i t h η = 3 have

as

| Spt(0) |

large

2

and

term

and

differences

must derive from

in

differ

o f t h e P t - P b o n d s t r a n s to c h l o r i n e a n d

p h o s p h o r u s . T h e s e differences

must originate

p r i m a r i l y i n t h e ap\

t e r m s , s i n c e t h e p r o d u c t « p | S p ( 0 ) | is e x p e c t e d t o b e n e a r l y i n v a r i a n t .


2

The

strong dependence

o f 1/pt-p o n t h e n a t u r e o f t h e t r a n s

ligand

derives from changes i n the hybridization of p l a t i n u m . W h e r e c o u p l i n g constants from different c o m p l e x e s are c o m p a r e d , i t is n o t p o s s i b l e to e l i m i n a t e | S ( 0 ) | / A E as a n i m p o r t a n t

variable.

3

M

H o w e v e r t h e fact t h a t i/pt-p t r a n s to a g i v e n l i g a n d ( p h o s p h o r u s

or

c h l o r i n e , T a b l e I) is s i m i l a r i n a l l o f t h e c o m p l e x e s o f a g i v e n o x i d a t i o n state s u g g e s t s t h a t t h e ( P ' s p t s ) t e r m s d e p e n d e s s e n t i a l l y o n t h e t r a n s P

2

l i g a n d a n d that other terms o f E q u a t i o n 1 are s i m i l a r e v e n i n different complexes

o f a g i v e n o x i d a t i o n state. T h i s a r g u m e n t , w h i c h r e c e i v e s

some support from bond-length measurements complexes

(see

T a b l e II),

for t h e

platinum(II)

p r e s u m e s t h a t t h e b o n d s to P R

3

t r a n s to a

g i v e n l i g a n d are s i m i l a r i n the different c o m p l e x e s . T h e lengths o f the Pt-P

b o n d s trans to c h l o r i n e are not s i g n i f i c a n t l y different

[ P t C l ( P E t ) ] (16) 2

3

and [PtCl (PEt ) ]

2

3

3

2 +

in

cis-

(17), w h e r e the c o u p l i n g con

s t a n t s a r e v e r y s i m i l a r . T h e P t - P b o n d is s h o r t e r i n [ P t C l ( P E t ) ] 3

3

(18),

_

w h e r e t h e c o u p l i n g is c a . 2 0 0 H z l a r g e r , s u g g e s t i n g t h a t t h i s b o n d h a s a s l i g h t l y l a r g e r s c o m p o n e n t , w h i c h is r e f l e c t e d i n t h e s h o r t e r b o n d a n d i n the larger c o u p l i n g constant. T h e s m a l l e r c o u p l i n g constants for

Pt-P

bonds

trans to

[ P t C l ( P E t ) ] (19) 2

3

2

phosphorus

The

of ]M-P 1

3

3

+

and

trans-

l i k e w i s e correlate w i t h b o n d s that are l o n g e r t h a n

for P t - P t r a n s to c h l o r i n e (see T a b l e Correlation

in [PtCl(PEt ) ]

with Bond

I).

Length

s u b s t a n t i a l l y l a r g e r v a l u e s o f ! / - P for p h o s p h o r u s t r a n s to M

c h l o r i n e c o m p a r e d w i t h p h o s p h o r u s t r a n s to p h o s p h o r u s c o r r e l a t e w i t h s h o r t e r M - P b o n d s t r a n s t o c h l o r i n e for a n u m b e r o f m e t a l s a n d o x i d a t i o n states: t u n g s t e n ( I V ) ,

r h o d i u m ( I ) a n d (III), p l a t i n u m ( I I ) a n d

a n d linear mercury(II) (i5).

B y analogy

w i t h the discussion o f

(IV), the

r e s u l t s for t h e p l a t i n u m ( I I ) c o m p l e x e s , t h i s i n d i c a t e s t h e d o m i n a n c e o f t h e ( P ' s s ) t e r m i n E q u a t i o n 1 for c o u p l i n g s w i t h a v a r i e t y o f M , b u t as M

P

2

d i s c u s s e d e a r l i e r i t is d i f f i c u l t t o d e t e r m i n e t h e e x t e n t o f v a r i a t i o n o f



Pt-P

ipt-p

'J

Pt-P

T a b l e I.

3704 2.215(4) (18) [PtClsP]" 2085

3

[PtCl P]~ 2

2

3508 2.258(2) (16) cis-[PtCl4P ] 2070 2 . 3 3 9 ( 4 ) (20)

2

cis-[PtCl P ] 3

[PtClP ] +

1

3474,2261 2.251(3), 2.354(3) mer-tPtClaPs]" " 2049, 1374

P l a t i n u m ( I I ) a n d (IV)

(17)

2

2

2

2400 ca. 2 . 3 1 5 (19) trans-[¥tC\^ ] 1475 2.393(5) (21 )

t r a n s - [Pt Cl P

'/Κ-Ρ (in Hertz) a n d P t - P B o n d Lengths (in Angstroms) i n Trialkylphosphine Complexes o f


]

-α

00

ο g-

CO

ί ο Co ί ο

"β ι CO

ο ο ο ο

8


I S ( 0 ) | a n d Δ Ε e i t h e r for t h e s e s y s t e m s or i n c o m p a r i s o n s o f c o u p l i n g 2

M

3

constants i n different c o m p l e x e s o f a single m e t a l . If variations o f c o u p l i n g c o n s t a n t s 7M-P d e r i v e s o l e l y f r o m c h a n g e s i n (P's s ) > a n d t h e M

P

2

M - P b o n d lengths correlate w i t h this term also, a correlation b e t w e e n ! / M - P a n d t h e M - P l e n g t h is to b e e x p e c t e d for c o m p l e x e s o f a g i v e n M , o x i d a t i o n state, a n d p h o s p h o r u s l i g a n d . It is n e c e s s a r y to r e s t r i c t c o m p a r i s o n s t o c o m p l e x e s o f a s i n g l e p h o s p h o r u s l i g a n d (or s i m i l a r p h o s p h o r u s l i g a n d s ) b e c a u s e , for e x a m p l e , t h e b o n d l e n g t h s a r e u n l i k e l y to b e e q u a l l y s e n s i t i v e to c h a n g e s

i n the s character of the m e t a l a n d

p h o s p h o r u s o r b i t a l s , a n d t h e t e r m |S (0)| is l i k e l y t o d e p e n d o n t h e P

2

nature of the groups on phosphorus. W h e n this correlation proposed

the

(15),

first

r e s u l t s for p l a t i n u m ( I I ) t r i a l k y l p h o s p h i n e

was com


p l e x e s w e r e s u c h that a satisfactory c o r r e l a t i o n c o u l d b e c o n s t r u c t e d , b u t the form o f the correlation was i l l - d e f i n e d because the u n c e r t a i n ties i n the b o n d lengths w e r e not s m a l l c o m p a r e d w i t h the total range of lengths. Subsequently, accurate b o n d lengths a n d c o u p l i n g con stants h a v e complexes Figure 4

become available of

for

a large

trialkylphosphines, and

the

number results

of

platinum(II)

are

plotted

in

(22).

N o s i m p l e c o r r e l a t i o n is c a p a b l e o f fitting t h e r e s u l t s t o w i t h i n t h e e x p e r i m e n t a l e r r o r s , a n d w i t h i n t h e f r a m e w o r k o f i n t e r p r e t a t i o n t h a t is suggested, it m u s t b e c o n c l u d e d that either there are significant v a r i a tions i n |S (0)| / AE M

2

3

or t h a t t h e c o r r e l a t i o n b e t w e e n ( P ' s p t s ) a n d b o n d P

2

l e n g t h is p o o r . H o w e v e r , t h e o v e r a l l t r e n d i n t h e r e s u l t s i n w h i c h i n c r e a s i n g v a l u e s o f î/pt-p a r e a s s o c i a t e d w i t h s h o r t e r b o n d s is l i k e l y to d e r i v e f r o m t h e s e n s i t i v i t y o f b o t h !/pt-p a n d t h e b o n d l e n g t h s to t h e s - o r b i t a l b o n d o r d e r . T h e w i d e r a n g e o f ^pt-p

f o u n d for t h e s h o r t P t - P

b o n d s suggests that the b o n d lengths b e t w e e n p l a t i n u m ( I I ) a n d trial k y l p h o s p h i n e s m a y r e a c h a l o w e r l i m i t o f ca. 2.21 À a n d that the b o n d l e n g t h s t h e r e f o r e b e c o m e v i r t u a l l y i n d e p e n d e n t o f (P'sptSp) ( a n d l/m-p) 2

i n t h i s r e g i o n . I t is p o s s i b l e t h a t m o r e a c c u r a t e c o r r e l a t i o n s b e t w e e n !/M-p a n d t h e M - P l e n g t h m a y b e f o u n d for m o r e r e s t r i c t e d sets c o m p l e x e s . I n F i g u r e 4 m o s t o f the p o i n t s c o r r e s p o n d to

of

complexes

w i t h p h o s p h o r u s t r a n s t o p h o s p h o r u s or p h o s p h o r u s t r a n s t o c h l o r i n e so t h a t w i t h i n t h e s e sets t h e l i g a n d s c i s t o p h o s p h o r u s v a r y . C a l c u l a t i o n s b y S h u s t o r o v i c h , w h o treats t h e e n e r g y d i f f e r e n c e b e t w e e n L a n d X i n M X

n

L as a p e r t u r b a t i o n , s u g g e s t t h a t a c o r r e l a t i o n b e t w e e n 1/M-P a n d

t h e M - P l e n g t h is to b e e x p e c t e d w h e n t h e l i g a n d s t r a n s t o p h o s p h o r u s a r e v a r i e d , b u t t h a t a c o r r e l a t i o n is n o t e x p e c t e d w h e n l i g a n d s c i s t o p h o s p h o r u s a r e v a r i e d (25,

26).

A l t h o u g h the perturbation m u s t

m u c h more c o m p l i c a t e d t h a n the single energy difference

be

parameter

u s e d i n t h e s e c a l c u l a t i o n s , i t is c l e a r l y d e s i r a b l e t h a t a s e r i e s o f c o m p l e x e s is e x a m i n e d i n w h i c h o n l y t h e l i g a n d t r a n s t o P R

3

varies.

The

c a l c u l a t i o n s a n d the b r o a d a g r e e m e n t f o u n d b e t w e e n trans influence


1.

P-31 NMR

PIDCOCK


9

Bonding


2.Ί0

2.20

2000

3000 :

4000

J(PTP)

5000

(HZ)

Figure 4. Graph of Pt-P length (shown with standard deviation limits) against 'JPÎ-P for platinum(II) complexes of trialkylphosphines: phosphorus trans to phosphorus; phosphorus trans to chlorine; Φ, phosphorus trans to other donor atoms; O, trans-[Ptl (PCy ) ], For discussion see Ref 23; the point with ] > 5000 Hz is for [Ρί (μCl) (COEt) (PMe Ph) ] (24). Some platinum(IV) complexes have been included, O. 2

3

2

Pt P

2

2

2

2

2

s e r i e s b a s e d o n ^pt-p (or o t h e r c o u p l i n g c o n s t a n t s ) a n d o t h e r p h y s i c a l p a r a m e t e r s (3) p r o v i d e s o m e g r o u n d s for e x p e c t i n g t h a t a m o r e a c c u r a t e c o r r e l a t i o n b e t w e e n J -p l

a n d the M - P l e n g t h then w i l l

M

emerge.

R e s u l t s for a f e w p l a t i n u m ( I V ) c o m p l e x e s h a v e b e e n i n c l u d e d i n F i g u r e 4. W e h a v e k n o w n for s o m e t i m e t h a t c o u p l i n g c o n s t a n t s !/pt-p are s m a l l e r i n p l a t i n u m ( I V ) t h a n i n r e l a t e d p l a t i n u m ( I I )

complexes

a n d that the ratio o f the c o u p l i n g s w a s c a . 0.6, c l o s e to the ratio 0.67 expected

for i d e a l i z e d d s p 2

3

and dsp

2

hybridization schemes

(8).

H o w e v e r , t h e c a n c e l l a t i o n o f | S ( 0 ) | / A E t e r m s for t h e t w o o x i d a t i o n Pt

states a p p e a r s i m p r o b a b l e , as d o e s

2

3

the correlation w i t h

idealized

s - o r b i t a l c o n t e n t s for s u c h a s y m m e t r i c c o m p l e x e s . P e r h a p s o f m o r e s i g n i f i c a n c e is t h e a p p a r e n t c o n f o r m i t y o f t h e p l a t i n u m ( I V ) r e s u l t s w i t h t h e p l a t i n u m ( I I ) c o r r e l a t i o n (see F i g u r e 4) w h i c h h i g h l i g h t s t h e près-


10


e n c e o f l o n g e r P t - P b o n d s i n t h e p l a t i n u m ( I V ) c o m p l e x e s (20, 21, R e s u l t s for p l a t i n u m ( O )

complexes

cannot be

27).

included properly

in

F i g u r e 4 b e c a u s e b o n d l e n g t h s a r e n o t a v a i l a b l e for s i m p l e t r i a l k y l p h o s p h i n e complexes. H o w e v e r , despite some variation of the phos phorus

l i g a n d , the

coupling

constants

for

platinum(O)

complexes

[ P t ( P X ) ] v a r y w i t h η i n t h e m a n n e r e x p e c t e d from a s i m p l e h y b r i d i 3

n

zation scheme

(28).

R e c e n t l y c o u p l i n g constants b e t w e e n the m e t a l a n d l i g a n d atom n u c l e i h a v e b e e n r e p o r t e d for sets o f l i n e a r m e r c u r y ( I I ) c o n t a i n i n g the Ph(OC H 4

9

-

detector

ligands

n) a n d P ( 0 ) ( O E t )

C H , CF , PMe , 3

(29,

2

3

30,

complexes

P(0)Bu' ,

3

P(O)-

2

a n d a variety of

61)

other


a n i o n i c l i g a n d s . T h e orders o f trans influence f o u n d w e r e a l m o s t i n d e p e n d e n t o f the detector l i g a n d a n d the c o u p l i n g m e a s u r e d , a n d w e r e s i m i l a r t o t h e t r a n s i n f l u e n c e o r d e r s e s t a b l i s h e d for p l a t i n u m ( I I ) a n d o t h e r t r a n s i t i o n - m e t a l c o m p l e x e s (3, 7, 31-36).

A s w e p o i n t e d o u t ear

l i e r , t h e t r a n s i n f l u e n c e o r d e r is n o t e x p e c t e d to b e c o m p l e t e l y

inde

p e n d e n t o f t h e d e t e c t o r l i g a n d or t h e c o u p l i n g (29), a n d i n a d d i t i o n t h e r e s u l t s for s p - h y b r i d i z e d m e r c u r y ( I I ) c o m p l e x e s

s h o w that the trans

i n f l u e n c e p h e n o m e n o n d o e s n o t r e q u i r e t h e u s e o f do- o r b i t a l s i n t h e f o r m a l h y b r i d i z a t i o n s c h e m e o f t h e m e t a l . A c c o r d i n g to t h e p e r t u r b a t i o n c a l c u l a t i o n s o f S h u s t o r o v i c h (25),

the d

a

a n d s orbitals, w h i c h are

t h e m o s t i m p o r t a n t b o n d i n g o r b i t a l s for m e t a l s s u c h as respond

platinum(II),

i n p a r a l l e l to a c h a n g i n g trans l i g a n d , a n d i n l i n e a r

sp-

h y b r i d i z e d m e r c u r y ( I I ) c o m p l e x e s t h e s - o r b i t a l b e h a v i o r is e x p e c t e d t o c l o s e l y p a r a l l e l that i n earlier transition metal complexes. T h u s , i n a l l o f these

complexes

t h e m e t a l s o r b i t a l is e i t h e r d o m i n a n t o r

i m p o r t a n t i n t h e b o n d i n g a n d is t h e p r i n c i p a l c o n t r i b u t o r t o t h e

very NMR

c o u p l i n g constants. Dependence of l / - p on cis M

Ligands

W h i l e it appears w e l l e s t a b l i s h e d that changes i n the σ-bonding a r e at l e a s t m a i n l y r e s p o n s i b l e for t h e effects o f t r a n s l i g a n d s o n 1/M-P a n d other parameters of m e t a l - l i g a n d bonds, the relative o f σ,

importance

π, a n d s t e r i c c o n t r i b u t i o n s t o t h e effects o f c i s l i g a n d s r e m a i n s

unclear.

Although

[PtCl - (PR3)n] " 4

( n

w

2 ) +

in

some

systems,

such

and [PtCl -n(PR3)n] " ( n

e

2 ) +

as

in

the

complexes

w h i c h were discussed

e a r l i e r , c h a n g e o f t h e c i s l i g a n d s h a s r e l a t i v e l y l i t t l e effect o n Î / M - P o r on

the

M-P

lengths,

considerable

variations

in

Î/M-P a n d

other

c o u p l i n g s c a n b e i n d u c e d b y cis l i g a n d s . M o r e r e c e n t l y changes

in

b o n d lengths i n d u c e d b y cis ligands have been s t u d i e d systematically i n cis- [ P t C l L ( P R ) ] c o m p l e x e s (11, 37, 2

There

3

38).

a r e g o o d c o r r e l a t i o n s b e t w e e n t h e v a l u e s o f l / m - p for t h e

p h o s p h i n e l i g a n d s i n trans- [ P t ( C H ) X ( P E t 3 ) 2 ] , f r a n s - [ P t { P ( 0 ) ( O P h ) } 8

X ( P B u ) ] , trans3

2

2

[ P t ( S C F ) X ( P E t ) ] , a n d trans- [ P t ( C F ) X ( P E t ) ] for 3

3

2

2

3


3

2

1.

PIDCOCK

P-31 NMR


11

Bonding

h a l i d e a n d p s e u d o h a l i d e l i g a n d s X , a n d b e t w e e n the latter t w o

series

for a w i d e r r a n g e o f a n i o n i c l i g a n d s ( 5 , 3 2 ) . T h e o r d e r o f d e c r e a s i n g c i s i n f l u e n c e (as m e a s u r e d b y l/pt-p for t h e C F 2

P(OPh) > P(OMe) 3

SCF

3

Hz

(X = C O )

> P(OEt)

3

> Br > CI > N

complexes

to

> N0

3

2603

Hz

2

3

> PPh

3

complexes

> C N > PEt

3

> O N 0 , w i t h J^-p The

2

3

r e s u l t s for

the

3

> H > Ph > C H

3

>

SCF

i n d i c a t e that the series c o n t i n u e s to g r o u p s o f e v e n

cis influence: C F

>

changing from 2021

2

(X = O N 0 ) .

was C O

> pyridine > I

3

lower

W i t h some m i n o r variations,

(32).

s i m i l a r s e r i e s h a v e b e e n f o u n d for l/pt-p c i s t o X i n [ P t ( C H ) X ( d p p e ) ] 3

( d p p e = P h P C H C H P P h ) (33) a n d i n [ P t X ( t t p ) l 2

2

2

C H C H P P h ) ] (34). 2

2

2


correlation

+

[ttp =

PhP(CH

o f î/pt-p c i s to X

between

i n these

1/pt-p a n d t h e

series o f c o m p l e x e s ,

Pt-P

length

i n the

series

[ P t C l L ( P E t ) ] is r e l a t i v e l y p o o r (see F i g u r e 5). T h i s m a y b e 2

r

A l t h o u g h t h e r e is a g o o d m e a s u r e o f c o n s i s t e n c y

2

i n the behavior

2

3

the cis-

because

t h e t o t a l o v e r l a p p o p u l a t i o n ( a n d h e n c e t h e b o n d l e n g t h ) c i s to t h e l i g a n d does not correlate

w i t h the s-orbital b o n d order (and

hence

î/pt-p) as s u g g e s t e d b y S h u s t o r o v i c h (26), b u t i t w o u l d b e u n w i s e t o a t t a c h s i g n i f i c a n c e t o t h e w e a k n e s s o f t h e c o r r e l a t i o n for v a r y i n g c i s l i g a n d s u n t i l a b e t t e r c o r r e l a t i o n is o b t a i n e d for v a r y i n g t r a n s l i g a n d s . A l t h o u g h the calculations o f S h u s t o r o v i c h do not suggest a general r e l a t i o n s h i p b e t w e e n c o u p l i n g s c i s a n d t r a n s to a v a r y i n g l i g a n d X

(26),

2.28

2.26

A

PT-P LENGTH

(A)

2.24

ÇIS-IPTCL L(PET )] 2

3

2.22

2600

3000

3400 2

Figure

5.

Graph against

of Pt-P ^pt-pfor

J(PT-P)

3800

(Hz)

(shown with standard deviation the cis-[PtCl L(PEt )] complexes 2

3


limits)


12


3

J(PTSCF)

(HZ)

40

80 3

Figure

Graph of J cFcis ]ptscF trans to Xin

6.

3

PtS

3

J(PTSCF)

120

(HZ)

TRAN_S

TO

X

to Xin trans-[Pt(SCF )X(PEt ) ] cis-[Pt(SCF )X(PEt ) ] (7, 39j 3

3

t h e c o u p l i n g Jpt-scF cis t o X i n c i s - [ P t ( S C F ) X ( P E t ) ] 3

3

c r e a s i n g f u n c t i o n o f /pt-scF t r a n s to X 3

against

3 2

3 2

3

in

is a l i n e a r d e

2

trans-[Pt(SCF )X(PEt ) ] 3

3 2

(39). S u b s e q u e n t r e s u l t s h a v e r e v e a l e d a s i m i l a r b u t s l i g h t l y less p r e c i s e c o r r e l a t i o n for t h e d i r e c t c o u p l i n g s l/pt-p (see F i g u r e s 6 a n d 7) (32). In

studies

of

the

reactions

of

organotin

compounds

with

platinum(O) a n d p l a t i n u m ( I I ) c o m p l e x e s , w e h a v e o b t a i n e d a series o f ci5-bis(triphenylphosphine)platinum(II)

complexes

IJ(PTP) TRANS

Figure

7.

Graph

3

which

one

(HZ) TO X

of *] -Ρ cis to X against ^pt-p [Pt(SCF )X(PEt ) ] (32) Ρ(

in

trans

to X in cis-

3 2


1.

PIDCOCK

P-31 NMR and Metal-Phosphorus

Bonding

13

a n i o n i c l i g a n d v a r i e s t h r o u g h a r a n g e o f c a r b o n o r t i n d o n o r s (40, 41, L i n e a r r e l a t i o n s h i p s w e r e f o u n d b e t w e e n l/pt-p c i s t o t h e c a r b o n

42).

l i g a n d i n t h e t w o series d s - [ P t C l ( C X ) ( P P h ) ] a n d n

3

frans-[PtCl(CX )-

2

n

( P P h ) ] a n d cis t o t h e t i n l i g a n d i n t h e t w o s e r i e s cis- [ P t C l ( S n X ) 3

2

3

( P P h ) ] a n d f r a n s - [ P t C l ( S n X ) ( P P h ) ] (see F i g u r e s 8 a n d 9 ) . F u r t h e r 3

2

3

more, i n complexes

where the P P h

3

2

3

l i g a n d , w h i c h is c i s t o c a r b o n o r

t i n , is a l s o t r a n s t o c h l o r i n e , ! / - p c i s t o c a r b o n o r t i n is a l i n e a r P t

d e c r e a s i n g f u n c t i o n o f î/m-p t r a n s t o c a r b o n o r t i n (see F i g u r e s 1 0 a n d 11).

For the complexes

cis- [ P t P h ( S n X ) ( P P h ) ] , 3

3

where

2

the

PPh

3

l i g a n d c i s t o t i n is t r a n s t o t h e p h e n y l l i g a n d , t h e r e is n o d i s c e r n i b l e c o r r e l a t i o n b e t w e e n i/pt-p c i s a n d t r a n s to t i n (see F i g u r e 12). T h i s w a s


also t h e case

for ! / - p c i s a n d trans to v a r y i n g

carbon

P t

ligands i n

[ P t C H ( C X ) ( d p p e ) ] ( 3 3 ) , w h e r e a g a i n t h e p h o s p h o r u s l i g a n d is t r a n s 3

n

to a c a r b o n σ d o n o r . F o r t h e cis-[PtPh(SnX )(PPh ) ] 3

complexes

3 2

(see

F i g u r e 12) ^ H - P t r a n s t o t i n v a r i e s b y a s i m i l a r a m o u n t t o ! / - p t r a n s t o P t

t i n i n c i s - [ P t C l ( S n X ) ( P P h ) ] (see F i g u r e 9 ) , b u t 7 p t - c i s t o t i n i n t h e 3

3

2

P

former c o m p l e x e s varies b y a m u c h s m a l l e r a m o u n t t h a n for t h e corre s p o n d i n g l i g a n d i n the latter c o m p l e x e s .

T h i s a n d the results o f A p -

p l e t o n a n d B e n n e t t ( 3 3 ) s u g g e s t t h a t w h e n P R is t r a n s t o a c a r b o n cr 3

donor, t h e b o n d s a l o n g this axis o f the m o l e c u l e are m u c h m o r e resis tant to p e r t u r b a t i o n t h a n w h e n P R

3

is t r a n s t o P R

or c h l o r i n e . T h e

3

a m o u n t o f s c a t t e r o n t h e c o r r e l a t i o n s is n u m e r i c a l l y s i m i l a r i n e a c h

C

I

PHTP

^ ( P T - P ) (HZ)

L

Ρτ

PPH

3

c i s το ( X . — N

I Figure

8.

Graph of ' ] ,cis to C X„ in cis- [PtCl(C X )(PPh ) ] 'Jp -pcis to CX in trans-[PtCKCX„)(PPh ) ](41) P

t

P

a

n

3

3 2

2


against



14



1.

PIDCOCK


Bonding

15

1600

£4000

3500

X

Figure

11.

Graph

of

J(PT-P)

(HZ) C I S το SN

] -p trans to SnX cis- [PtCl(SnX )(PPh ) ]

1

Pt

3

3

4500

3 2

against *Jpt-pcis (41)

to SnX

3

in

c a s e , b u t i t is s u f f i c i e n t t o o b s c u r e a n y c o r r e l a t i o n w h e r e t h e o v e r a l l changes i n d u c e d b y cis l i g a n d s are s m a l l . T h e r e s u l t s for t h e t i n - c o n t a i n i n g c o m p l e x e s (41, 42) a l s o p e r m i t the

examination of the relationship b e t w e e n

trans to the t i n

JP%-P

1

l i g a n d a n d the i n d i r e c t c o u p l i n g constant /p-pt-sn- T h e r e are accurate 2

l i n e a r r e l a t i o n s h i p s for t w o s e r i e s o f c o m p l e x e s (see F i g u r e 13) t h a t

3000^(PT-P)

(HZ)

TRANS το SN

25001

2000 -

2000

2050

2100

2150

2200

^ ( Ρ τ - Ρ ) (HZ) TRANS TO PH

Figure

12.

Plot of ^pt-ptrans to SnX against ^pt-pcis [PtPh(SnX )(PPh ) ] (41) 3

3

to SnX

3

3 2


in cis-



16

—ι

1—

1

2000

2500

A

J

3000

( P T P ) ( H Z ) TRANS

TO S N

Figure 13. Graphs of Jp-ptsn for PPh trans to tin against 'Jpt-pfor PPh trans to tin for the cis- [PtCl(S η X )(PPh ) ] and cis- [PtPh( S η X )(PPh ) ] complexes (41) 2

3

3

3

3 2

3

3 2

extend over sizeable

ranges

of magnitude.

I n these

series o f c o m

plexes, t h e p r i n c i p a l variables are e x p e c t e d to b e (P's sp) (and p a r t i c u Pt

2

l a r l y t h e c o n t r i b u t i o n o f the p l a t i n u m orbitals) for t h e P t - P c o u p l i n g , a n d | S ( 0 ) | a s n for t h e i n d i r e c t c o u p l i n g . A s t h e e l e c t r o n e g a t i v i t y Sn

2

of

2

t h e g r o u p s o n t i n i n c r e a s e s |S (0)| a n d a § f o r t h e S n - P t b o n d b o t h Sn

2

n

increase a n d t h e trans i n f l u e n c e o f the t i n l i g a n d decreases l e a d i n g to the observed

correlation. Perhaps further correlations w i l l b e f o u n d

w h e n r e s u l t s for l/pt-sn for t h e s e c o m p l e x e s b e c o m e a v a i l a b l e .

Dependence on the Phosphorus

Ligand

T h e t e r m s o f E q u a t i o n 1 t h a t a r e e x p e c t e d t o b e c h a n g e d m o s t as g r o u p s o n p h o s p h o r u s a r e v a r i e d a r e |S (0)| a n d t h e s c h a r a c t e r o f t h e P

2

p h o s p h o r u s d o n o r o r b i t a l ap, w h i c h c o n t r i b u t e s d i r e c t l y t o ( P ' s s ) M

B o t h o f these terms are e x p e c t e d to increase w i t h i n c r e a s i n g l y tronegative

substituents o n phosphorus—|S (0)| P

2

P

2

elec

b y contraction o f the


1.

PIDCOCK


17

Bonding

p h o s p h o r u s 3s o r b i t a l a n d a p b y r e h y b r i d i z a t i o n o f t h e p h o s p h o r u s o r b i t a l s i n a c c o r d w i t h B e n t ' s r u l e s (JO). I n m o s t i n s t a n c e s c o u p l i n g c o n s t a n t s J -p l

increase w i t h increasing electronegativity o f the s u b -

M

stituents o n the phosphorus donor, b u t the opposite t r e n d has b e e n n o t e d for c o m p l e x e s o f t h e l i g a n d s P P h R _ n

3

( R = a l k y l a n d η = 1-3)

n

in mercury(II) complexes

[ H g X L ] (43). I n c o o r d i n a t i v e l y s a t u r a t e d

cadmium(II),

a n d tin(IV) complexes the M - P bonds are

2

indium(III),

2

r a t h e r l o n g a n d , t h e r e f o r e , p r e s u m a b l y m u c h w e a k e r t h a n for t h e t r a n s i t i o n m e t a l s (44, 45, 46). I t s e e m s t h a t t h e a n o m a l o u s t r e n d i n c o u p l i n g c o n s t a n t s for [ H g X L ] m a y b e c o m m o n t o s u c h c o m p l e x e s a n d m a y 2

2

arise f r o m i n c r e a s i n g steric pressure o n the r e l a t i v e l y w e a k M - P b o n d s


as t h e n u m b e r o f p h e n y l s u b s t i t u e n t s o n t h e p h o s p h o r u s i n c r e a s e s . C o u p l i n g c o n s t a n t s a r e m u c h l a r g e r for p h o s p h i t e t h a n for p h o s p h i n e l i g a n d s a n d the ratio o f the c o u p l i n g constants i n otherwise s i m i l a r c o m p l e x e s l i e s i n t h e 1 . 5 - 1 . 8 r a n g e for a v a r i e t y o f a c c e p t o r s (e.g., r h o d i u m ( I ) a n d ( I I I ) , p l a t i n u m ( I I ) , s i l v e r ( I ) , a n d B H ) (1, 2). A p 3

p r o x i m a t e c o n s t a n c y o f t h e r a t i o is e x p e c t e d i f c h a n g e s i n | S ( 0 ) | a p a r e 2

P

d o m i n a n t . F o r c o m p l e x e s o f a g i v e n m e t a l a n d o x i d a t i o n state, t h e r a t i o o f c o u p l i n g c o n s t a n t s b e t w e e n p h o s p h i t e a n d p h o s p h i n e c o m p l e x e s is n o t r i g o r o u s l y c o n s t a n t . H o w e v e r for p l a t i n u m ( I I ) c o m p l e x e s w e h a v e f o u n d t h a t for P ( O P h )

3

a n d P P h complexes, a n d a variety o f other pairs 3

o f p h o s p h o r u s donors, that there are accurate l i n e a r relationships b e t w e e n t h e c o u p l i n g constants for c o m p l e x e s

o f different

phosphorus

d o n o r s (e.g., see F i g u r e 14) (47). W h e r e s u f f i c i e n t r e s u l t s a r e a v a i l a b l e s u c h l i n e a r c o r r e l a t i o n s a r e b e s t l i m i t e d to sets o f c o m p l e x e s o f a g i v e n s t e r e o c h e m i s t r y . T h u s for c o m p l e x e s o f P P h ferent

correlations

for

3

trans-[PtAB(PR ) ],

and PEt

the three

3

cis-[PtAB(PR ) ],

3 2

3

2

[ P t A B C ( P R ) ] c o m p l e x e s are g i v e n b y E q u a t i o n s 2 (correlation 3

dif and

coeffi

c i e n t r = 1.00, 1 7 p o i n t s ) , 3 (r = 1.00, 14 p o i n t s ) , a n d 4 (r = 0 . 9 9 , 1 0 points). !/pt-PPh trans 3

!/pt-PPh

3 c

is

7pt-pph

3

=

1-155

!/pt-PEt trans ~

=

1125

!/pt-PEt

3 c

=

1-120

ypt-PEt

3

^7

(2)

215

(3)

3

is ~ ~~

(4)

378

T h e g r a d i e n t is l a r g e r for E q u a t i o n 2 t h a n for E q u a t i o n s 3 a n d 4 b e c a u s e t h e trans i n f l u e n c e o f P P h

3

is l o w e r t h a n t h a t o f P E t . T h e s e 3

relationships are sufficiently accurate to m a k e a useful c a l c u l a t i o n o f a n u n k n o w n c o u p l i n g c o n s t a n t w h e n t h e r e s u l t for a n a n a l o g o u s

complex

w i t h a d i f f e r e n t p h o s p h o r u s d o n o r is a v a i l a b l e . R e s u l t s a l s o h a v e b e e n o b t a i n e d for cis- [ P t C l L ( P E t ) ] 2

3

and

trans-

[ P t C l L ( P C y ) ] ( C y = cyclohexyl) complexes, where L i n the cis c o m 2

3

p l e x e s v a r i e s o v e r t h e f u l l r a n g e o f p h o s p h o r u s d o n o r s from P H P h PF

3

2

to

a n d for t h e t r a n s c o m p l e x e s f r o m P R t o P ( O R ) (22). T h e c o u p l i n g 3

3


18


6000'

1

J(PT-PPH ) 3

(Hz)


mo A

2000

»

1

WOO

i

6000

I

J(PT-P(0PH) )

Figure 14. Graph of Jpt-pfor bonds to PPh in platinum(II) against 'Jpt-pfor bonds to P(OPh) in otherwise similar ^Pt-pphs = 0.530 ^pt-pwph^ + 517 (correlation coefficient 3

3

2

J(PTP)

( H Z ) FOR

10000

(HZ)

3

1

·

S000

L

IN

complexes complexes: 0.99) (41)

TRANS-[PTCL L(PCY )] 2

3

Figure 15. Graph of 'Jpt-p for bonds to the ligand L in c i s [PtCl L(PEt )] against *J t-p for bonds to the ligand L in trans[PtCl L(PCy )](Cy = cyclohexyl) (22) 2

3

P

2

3


1.

PIDCOCK



8000

Figure 16. [PtCl L(PEt )] 2

3

19

Bonding

J

Graph of 'Jpt-p against ^w-pfor

for bonds to the ligand L in c i s bonds to the ligand L in [W(CO) L] (22) 5

constants to the c h a n g i n g p h o s p h o r u s donor i n the t w o series are re l a t e d l i n e a r l y (see F i g u r e 15), a n d t h e r e i s a n a c c u r a t e l i n e a r r e l a t i o n s h i p b e t w e e n t h e r e s u l t s for t h e c i s p l a t i n u m ( I I ) c o m p l e x e s a n d t h e tungsten(O)

[ W ( C O ) L ] c o m p l e x e s (21, 4 8 , 4 9 , 5 0 , 51) o v e r t h e f u l l 5

r a n g e o f p h o s p h o r u s d o n o r s (see F i g u r e 16). T h e s e c o r r e l a t i o n s p r i n c i p a l l y r e f l e c t t h e d o m i n a n c e o f t h e p h o s p h o r u s - c e n t e r e d t e r m s |S (0)| ap 2

P

i n J ( M L ) , b u t i t a p p e a r s t h a t a n y i n d u c e d c h a n g e s i n t h e t e r m s asso X

ciated w i t h the metal must be closely parallel i n the cis-platinum(II) a n d t h e tungsten(O) c o m p l e x e s . T h a t c h a n g e s i n t h e m e t a l orbitals o c c u r is e v i d e n t f r o m c h a n g e s i n t h e b o n d l e n g t h s t o t h e r e m a i n i n g ligands

for b o t h p l a t i n u m ( I I )

complexes

(see

Figure

17) a n d f o r

chromium(O) c o m p l e x e s , w h i c h are p r e s u m a b l y very s i m i l a r to the a n a l o g o u s tungsten(O) c o m p l e x e s ( 5 3 ) . I n recent years the a v a i l a b i l i t y of strongly a c i d i c solvents has facil i t a t e d t h e d e t e r m i n a t i o n o f ^ H - P for a f u l l r a n g e o f p r o t o n a t e d p h o s p h o r u s d o n o r s [ H L ] + (54, 55, 56) a n d t h e g r a p h o f ^ H - P a g a i n s t

JPX-P

1

for t h e c i s - p l a t i n u m ( I I ) c o m p l e x e s is g i v e n i n F i g u r e 18. T h e c u r v a t u r e o f t h e g r a p h is o p p o s i t e t o t h a t w h i c h is e x p e c t e d

from


synergic

20


2.m

2.361 2.258

2.361

Ετ,Ρ-

2.357

2.272

Ετ,Ρ-

2.182

2.258

PET

2.305

2.355

2.

Ρ(0ΡΗ)?

3

Figure 17. Pt-L bond lengths (in angstroms) in cis-[PtCl (PEt ) ] cis-[PtCl (PEt ) {P(OPh) }] (52), and c\s-[PtCl (PEt )(PF )] 2

2

Ml

3

3

2

3

3 2

3

( 16), (\\)


strengthening of the P t - P σ bond through π b o n d i n g i n the P t - P F

3

system. T h e nonlinearity probably derives from i n d u c e d changes i n the p l a t i n u m orbitals w h i c h are p r e s u m a b l y greater than any changes i n d u c e d i n t h e I s a c c e p t o r o r b i t a l o f h y d r o g e n . I t is n o t s u r p r i s i n g t h a t some changes

i n the orbitals o f p l a t i n u m have to b e i n v o k e d

three g r o u p s o n p h o s p h o r u s are v a r i e d i n these

systems

since

a n d large

changes i n the character o f the phosphorus donor orbital are e v i d e n t from the changes i n t h e c o u p l i n g constants, t h e energies o f the phos p h o r u s l o n e - p a i r o r b i t a l s (57, 5 8 , 5 9 ) , a n d i n h y p e r f i n e c o u p l i n g c o n stants i n c o b a l t c o m p l e x e s

o f various phosphorus donors (60). S i n c e

8000 Η

J(HP) (Hz) IN [ΗΡΧ ]

2

+

3

Figure 18. Graph of '1 _ρ [PtCl L(PEt )] against 'J -pfor and PPhCl , Ρί

2

3

H

2

for bonds to the ligand [HL] . Values of'Jn-pforL may be unreliable (55) +

L in c i s = PPh Cl


2

1.

PIDCOCK

P-31 NMR


21

Bonding

! / M - p a n d t h e h y p e r f i n e c o u p l i n g c o n s t a n t s (60)

d e p e n d on the p r o d u c t

«p|Sp(0)| , i t is n o t p o s s i b l e t o d e t e r m i n e w h i c h o f t h e t e r m s a% or 2

|S (0)| is t h e m o r e s e n s i t i v e t o t h e g r o u p s a t t a c h e d t o p h o s p h o r u s . W e P

2

expect that the coefficients of the orbitals a

2

P

vary more than the elec

t r o n d e n s i t y |S (0)| , a n d i t is p r o b a b l e t h a t α ρ v a r i e s m o r e t h a n is P

2

i m p l i e d b y t h e h y b r i d o r b i t a l s c o n s t r u c t e d to f o l l o w k n o w n X P X b o n d a n g l e s . T h u s i t is m o r e l i k e l y t h a t t h e c h a n g e s i n 7 M - P d e r i v e m o r e t h a n « ρ t h a n f r o m |S (0)| , b u t s i n c e t h e t e r m s c h a n g e i n t h e s a m e w a y P

2

for M - P b o n d s , d i s c u s s i o n i n t e r m s o f t h e p r o d u c t a | S ( 0 ) | 2

P

2

is m o r e

a p p r o p r i a t e at p r e s e n t .


Literature

Cited

1. Nixon, J. F.; Pidcock, A. Ann. Rev. NMR Spectrosc. 1969, 2, 346. 2. Pregosin, P. S.; Kunz, R. W.; "13P and 13C N M R of Transition Metal Phos phine Complexes"; Springer-Verlag: Berlin, 1979. 3. Appleton, T. G.; Clark, H. C.; Manzer, L. E . Coord. Chem. Rev. 1973, 10, 335. 4. Pople, J. Α.; Santry, D. P. Mol. Phys. 1964, 8, 1. 5. Allen, F. H.; Pidcock, Α.; Waterhouse, C. R. J. Chem. Soc. (A) 1970, 2087. 6. Motschi, H.; Pregosin, P. S.; Venanzi, L. M. Helv. Chim. Acta 1979, 62, 667. 7. Dixon, K. R.; Moss, K. C.; Smith, M . A. R.; J. Chem. Soc. Dalton 1975, 990. 8. Pidcock, Α.; Richards, R. E . ; Venanzi, L. M. J. Chem. Soc. (A) 1966, 1707. 9. Balimann, G.; Pregosin, P. S. J. Mag. Res. 1976, 22, 235. 10. Bent, H . A. Chem. Rev. 1961, 61, 275. 11. Hitchcock, P. B.; Jacobson, B.; Pidcock, A. J. Chem. Soc. Dalton 1977, 2043. 12. de Bie, M. J. Α., unpublished data. 13. Colquhoun, I. J.; McFarlane, W. Chem. Comm. 1980, 145. 14. Alyea, E . C.; Dias, S. Α.; Stevens, S. Inorg. Chim. Acta 1980, 44, L203. 15. Mather, G. G.; Pidcock, Α.; Rapsey, G. J. N. J. Chem. Soc. Dalton 1973, 2095. 16. Manojlović-Muir, Lj.; Muir, K. W.; Solomun, T. J. Organometal. Chem. 1944, 142, 265. 17. Mazid, Μ. Α.; Russell, D. R. J. Chem. Soc. Dalton 1980, 1737. 18. Bushnell, G. W.; Pidcock, Α.; Smith, M. A. R.; J. Chem. Soc. Dalton 1975, 572. 19. Messmer, G. G.; Amma, E . L. Inorg. Chem. 1966, 5, 1775. 20. Hitchcock, P. B.; Jacobson, B.; Pidcock, A. J. Organometal. Chem. 1977, 136, 397. 21. Aslanov, L.; Mason, R.; Wheeler, A. G.; Whimp, P. O.; Chem. Comm. 1970, 30. 22. Jacobson, B. Ph. D. Thesis, Sussex, Brighton, U.K., 1977. 23. Hitchcock, P. B.; Jacobson, B.; Pidcock, A. J. Chem. Soc. Dalton 1977, 2038. 24. Anderson, G. K.; Cross, R. J.; Manojlović-Muir, Lj.; Muir, K. W.; Solomun, T. J. Organometal. Chem. 1979, 170, 385. 25. Shustorovich, E. J. Amer. Chem. Soc. 1979, 101, 792. 26. Shustorovich, E . Inorg. Chem. 1979, 18, 1039. 27. Muir, K. W.; Walker, R. J. Chem. Soc. Dalton 1975, 272. 28. Ref. 2, p 92. 29. Goggin, P. L.; Goodfellow, R. J.; McEwan, D. M.; Griffith, A. J.; Kessler, K. J. Chem. Res. (M) 1979, 2315.



22

M E T A L PHOSPHINE COMPLEXES

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