Structure and Reactivity Patterns of Polyphosphine Ligands and Their

28

Structure and Reactivity Patterns of Polyphosphine Ligands and Their Complexes of Rhodium and Cobalt(I) Downloaded by MONASH UNIV on November 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch028

DEVON W. MEEK, DANIEL L. DuBOIS, and JACK TIETHOF The Ohio State University, Columbus, Ohio 43210

In

the

presence

of

free

phosphorus-hydrogen cleanly vinyl

and readily derivatives

ligands. usual

provides:

transition

phosphine,

(a)

useful

polyphosphine of

more

ligands

on the

-phosphorus

and phosphorus-phosphorus and

and bonding

protonation

PhP(CH CH CH PPh ) , 2

2

2

that have strikingly of

Co(I)

complexes

phos)(CO)2] ,

and

+

characterized

with

different of

2

number, complex;

at the metal; via

coupling of

and metal

constants.

RhCl(ttp),

ttp

Several

new

series [Co(tri-

[Co(triphos)(monophos)(CO)]

were

+

2 3

and

=

complexes

Co(triphos)H(CO),

each of the three

a

simultaneously

information

behavior.

types

un-

with

coordination

reactions

CH C(CH PPh ) , PhP(CH2CH2PPh2)2, 3

accentuate

yield alkyl and hydride

2 2

of

chelating

Compared

(or nucleophilicity)

structural

add

bonds

of the resulting

(c) detailed Alkylation

AIBN,

polydentate

a polyphosphine

control

basicity

double

metals.

and stereochemistry

(b) increased

from bonds

to the carbon-carbon

Chelating

stoichiometry,

generated

sulfur-hydrogen

to produce

properties

monodentate

radicals

and

triphosphine

ligands

PhP(CH2CH 2

CH PPh ) . 2

2 2

Τ T n u s u a l p r o p e r t i e s i n t r a n s i t i o n metals a r e often i n d u c e d b y ^

phine ligands.

tert-phos-

F o r example, monodentate phosphines have

been

use extensively for s t a b i l i z i n g b o t h h i g h a n d l o w o x i d a t i o n states of t h e m e t a l (e.g.

N i ( I V ) a n d N i ( O ) ( J ) , for p r o d u c i n g a h i g h trans influence

( 2 , 3 ) , a n d for a c t i v a t i n g s m a l l molecules s u c h as H , 0 , a n d olefins 2

2

(4).

I n recent years, m a n y investigations of o r g a n o m e t a l l i c c h e m i s t r y a n d 335 In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

336

INORGANIC

t r a n s i t i o n m e t a l complexes

COMPOUNDS

used

p a r t i c u l a r , i n v e s t i g a t i o n s of

WITH

UNUSUAL

chelating phosphines

five-coordinate

PROPERTIES

as l i g a n d s .

In

complexes revealed that the

stability, stereochemistry, a n d magnetic properties d e p e n d on a subtle b l e n d of e l e c t r o n i c a n d steric effects ( 5 , 6, 7, 8, 9 ) . d e v e l o p m e n t of the c o o r d i n a t i o n c h e m i s t r y of

Consequently, further terf-phosphines

depends

g r e a t l y o n the c o n c u r r e n t d e v e l o p m e n t of s y n t h e t i c p h o s p h o r u s c h e m i s t r y . A p r o p e r l y d e s i g n e d p o l y p h o s p h i n e c a n a c c e n t u a t e the s p e c i a l effects of p h o s p h i n e l i g a n d s as i t a c c o m p l i s h e s

simultaneously: (a)

a

more

p r e d i c t a b l e c o o r d i n a t i o n n u m b e r a n d s t o i c h i o m e t r y i n the r e s u l t i n g c o m plexes since the c h e l a t e effect m i n i m i z e s t h e p o s s i b i l i t y t h a t one or m o r e

Downloaded by MONASH UNIV on November 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch028

p h o s p h i n o groups w i l l be d i s p l a c e d d u r i n g a c h e m i c a l r e a c t i o n ; ( b ) i n c r e a s e d b a s i c i t y ( o r n u c l e o p h i l i c i t y ) of t h e m e t a l a t o m ; a n d ( c ) c o n t r o l over t h e s t e r e o c h e m i s t r y of t h e r e s u l t i n g c o m p l e x (10). tion,

p o l y (f e r f - p h o s p h i n e )

s t u d y of

ligands have

tremendous

more

In addi-

potential i n

the

d y n a m i c processes a n d i n o b t a i n i n g m e t a l - p h o s p h o r u s

phosphorus-phosphorus

N M R c o u p l i n g constants t h a t w o u l d b e

t a i n a b l e for analogous c o m p l e x e s of m o n o d e n t a t e p h o s p h i n e s

and unob-

(11).

T h i s p a p e r is c o n c e r n e d w i t h a l l these five aspects of p o l y p h o s p h i n e s . I n a d d i t i o n , the m e t h o d s for s y n t h e s i z i n g p o l y p h o s p h i n e l i g a n d s are d i s cussed b r i e f l y . Poly (tert-phosphine)

Ligands

A n o b j e c t i v e of o u r r e s e a r c h w a s to s y n t h e s i z e a series of r e l a t e d , flexi b l e p o l y d e n t a t e l i g a n d s that c o n t a i n e i t h e r - C H 2 C H 2 - or - C H C H C H 2

2

2

c o n n e c t i n g u n i t s a n d different types of d o n o r groups so t h a t s y s t e m a t i c variations the

of

the catalytic, sterochemical, a n d spectral properties

metal c o u l d be

studied.

Until

1971

most

polyphosphines

of

were

prepared b y treating organic polyhalides w i t h alkali metal dialkyl

or

d i a r y l p h o s p h i d e s — e . g . , t h e r e l a t i v e l y easy p r e p a r a t i o n of P h P C H C H 2 2

PPh

2

(12).

2

H o w e v e r , use of this m e t h o d f o r m o r e c o m p l i c a t e d t r i - a n d

t e t r a p h o s p h i n e s is severely l i m i t e d b y the difficulties i n o b t a i n i n g t h e a p p r o p r i a t e o r g a n i c p o l y h a l i d e or i n effecting the p h o s p h i d e r e a g e n t (13).

complete

reaction w i t h

T h e v a r i e t y of p o l y p h o s p h i n e s t h a t c o n -

t a i n P C H C H P u n i t s w a s g r e a t l y i n c r e a s e d b y K i n g et al. (14,

15,

16)

b y t h e b a s e - c a t a l y z e d a d d i t i o n s of p h o s p h o r u s - h y d r o g e n b o n d s to

the

2

2

carbon-carbon

double

bonds

i n various v i n y l

phosphine

derivatives.

K i n g a n d C l o y d r e c e n t l y u s e d the b a s e - c a t a l y z e d m e t h o d to p r e p a r e the first

extensive

series

of

methylated polyphosphines

(17,

18).

The

syntheses of the m e t h y l a t e d p h o s p h i n e l i g a n d s i n v o l v e s the c o n v e r s i o n of a P - H b o n d t o a P C H C H P ( C H ) 2

2

3

2

u n i t via

the potassium

b u t o x i d e c a t a l y z e d a d d i t i o n to C H = C H P ( S ) ( C H ) 2

furization w i t h L i A l H

4

3

2

tert-

followed by desul-

i n b o i l i n g dioxane (Reactions 1 a n d 2 ) .

In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.

28.

MEEK

Polyphosphine

E T AL.

\

/ C H /

Ρ

—

H

337

Ligands jj^g

3

v

CH2=CH—

+

yCH

•

/

I

I

C

X

H

/

P

C

H

C

2

H

P

2

s \

/ >

C

H

C

2

H

,

P

C

H

C

X

H

3

s LiAlH

S

\

4

(

•

>

"ll^CHa

/

(1)

H

χ

3

3

^

C

H

C

2

H

P

2

(

C

H

)

3

4, with positive numbers being downfield from the standard. Resolution for the coupling constants is ± 1 H z . P i is the unique central phosphorus atom of P h P ( C H 2 C H C H P P h ) 2 . * P refers to the two equivalent terminal phosphorus atoms of P h P ( C H C H CH PPh ) . 2

b

2

3

0

d

2

2

2

2

2

2

2

2


2

28.

MEEK

ET

Polyphosphine

AL.

347

Ligands

t r i p h o s p h i n e l i g a n d a n d c h l o r i d e f o r m the b a s a l p l a n e a n d t h e a l k y l g r o u p o c c u p i e s the a p i c a l p o s i t i o n . T h e p r o t o n N M R d a t a of containing added

CH CN

[Rh(ttp)HCl(C H OH)] 2

+

5

in

r e v e a l that a c e t o n i t r i l e replaces

3

e t h a n o l m o l e c u l e q u a n t i t a t i v e l y a n d that the r e s u l t i n g c a t i o n HC1(CH CN)] 3

I n contrast

CH N0 3

the

2

labile

[Rh(ttp)-

does not exchange C H C N r a p i d l y at r o o m t e m p e r a t u r e .

+

3

to the h y d r i d e , the m e t h y l c o m p l e x

exchanges C H C N r a p i d l y d o w n to ~ 3

[Rh(ttp)Cl(CH )]

+

3

— 50°C. T h e corresponding

ethyl

c o m p l e x does not f o r m a stable C H C N or C O a d d u c t ; thus, t h e t e n d e n c y 3

of the

five-coordinate

species to a d d a sixth l i g a n d decreases m a r k e d l y

i n the series h y d r i d e > m e t h y l > e t h y l w h i c h p r o b a b l y reflects i n c r e a s i n g Downloaded by MONASH UNIV on November 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch028

steric interactions rather t h a n electronic factors.

Proton N M R and IR

studies also d e m o n s t r a t e d that, for a g i v e n h y d r i d e or a l k y l c o m p l e x , the s t a b i l i t y of the six-coordinate CH CN > 3

The

3 1

2

>

5

P N M R spectra of the t w o m e t h y l cations

(L = CH CN, 3

complexes decreases i n the o r d e r C O

C H OH. CO)

r e v e a l that the

[Rh(ttp)Cl(CH )L] 3

terminal phosphino

groups

e q u i v a l e n t w h i c h requires a p l a n a r a r r a n g e m e n t of t t p ( F i g u r e 5 ) . a d d i t i o n , the c o u p l i n g constant plexes t h a n that of J

R h

.

P 2

1

]

J i h

.

P l

are In

is 24r-25 H z larger for b o t h c o m -

, w h i c h strongly suggests that the w e a k e r l i g a n d CH

3

+

Rh-R

Figure 5. Proton-noise decoupled, Fourier transform P NMR spectrum of [Rh(ttp)CH Cl(CH CN)]FS0 in CD CN 31

s

3

3

3


348

INORGANIC

is trans to P i .

UNUSUAL

C o n s e q u e n t l y , s t r u c t u r e V I I is p r o p o s e d for

(CH )(CO)] ;

PROPERTIES

[Rh(ttp)Cl-

this is a different i s o m e r f r o m t h a t of t h e

+

3

COMPOUNDS WITH

analogous

h y d r i d e , i.e. V I .


CH

3

3HE Cobalt (I) Complexes of Tri(tert-pbosphine) A s a p a r t of o u r efforts

Ligands

to s t u d y s y s t e m a t i c a l l y the p h y s i c a l a n d

c h e m i c a l p r o p e r t i e s of a m e t a l i n different s t e r e o c h e m i c a l

environments,

w e s y n t h e s i z e d a n d c h a r a c t e r i z e d several n e w series of C o ( I )

complexes

of

and

the

types

C o ( t r i p h o s ) H ( C O ),

( triphos ) ( monophos ) ( C O ) ] CH C(CH PPh ) , 3

2

2

( monophos =

3

[Co(triphos) ( C O ) ] , 2

+

[Co-

w i t h the t h r e e t r i ( ter*-phosphine ) l i g a n d s

+

PhP(CH CH PPh ) , 2

2

the m o n o d e n t a t e

2

2

and

PhP(CH CH CH PPh )

ligands P h P H , 2

T a b l e V lists some of the i s o l a t e d c o m p o u n d s ,

2

2

(MeO) P,

2

and

3

2

2

Et P). 3

the m o s t d i a g n o s t i c

IR

d a t a for t h e c o b a l t h y d r i d e a n d c a r b o n y l s t r e t c h i n g frequencies, a n d the c o n d u c t i v i t y or mass s p e c t r a l d a t a for the c a t i o n i c or t h e n e u t r a l c o m plexes r e s p e c t i v e l y . The C o ( t r i p h o s ) H ( C O ) the c o r r e s p o n d i n g

complexes c a n b e p r e p a r e d b y

C o ( triphos ) C l

2

complexes w i t h

NaBH

4

reducing

i n ethanol

w h i l e b u b b l i n g carbon monoxide through the solution. T h e yellow, airsensitive c o m p l e x e s w e r e c h a r a c t e r i z e d b y e l e m e n t a l analysis a n d b y N M R , I R , a n d mass s p e c t r o s c o p y .

T h e corresponding deuterated

Ή

com

plexes w e r e also p r e p a r e d i n o r d e r to v e r i f y t h e I R b a n d s assigned to t h e Co-Η

stretching mode.

Co(etp)H(CO)

T h e proton

w i t h / φ ρ . = 65 H z a n d / Φ Η

N M R of the h y d r i d e r e g i o n

for

consists of a n o v e r l a p p i n g d o u b l e t of t r i p l e t s at τ 21.7 2 Ρ

.

Η

= 44 H z ( F i g u r e 6 ) .

T h e spectra i n F i g

ure 6 s h o w that the t w o types of p h o s p h o r u s n u c l e i c a n b e

decoupled

selectively. T h e N M R d a t a i n d i c a t e that the t w o t e r m i n a l d i p h e n y l p h o s p h i n o groups are e q u i v a l e n t a n d are consistent w i t h either a t r i g o n a l b i p y r a m i d or a square p y r a m i d c o n t a i n i n g a p l a n e of s y m m e t r y . T r e a t m e n t of the h y d r i d e complexes w i t h the w e a k acids or N H P F 4

6

NH BF 4

4

i n the presence of another l i g a n d p r o v i d e s a g e n e r a l a n d

selective m e t h o d for p r e p a r i n g the series of c o m p l e x e s

[ C o ( triphos ) -


28.

MEEK

E T

Table V .

Polyphosphine

AL.

349

Ligands

D i a g n o s t i c C h a r a c t e r i z a t i o n D a t a o n the C o ( I ) C o m p l e x e s of Three Tri(tert-phosphines) 0

Compound

vco

b

v -H,M-i> M

HCo(etp)(CO) DCo(etp)(CO) HCo(ttp) (CO) DCo(ttp)(CO) H C o (tripod) (CO) DCo(tripod) (CO)

Parent Ion in Mass Spectrum

1920 1380 1920(sh) 1370 1930 1380

1870 1870 1880 1880 1857 1857

c

622 650 712


vco

CH2C12

NujolMull [Co(etp) ( C O ) ] B F [Co(etp) ( P ( O M e ) ) ( C O ) ] B F [Co(etp)(P H)(CO)]PF [Co(etp)(PEt )(CO)]BF [Co(ttp) ( C O ) ] B F [ C o (ttp) ( P ( O M e ) s ) ( C O ) ] B F [Co(ttp)(P H)(CO)]BF [ C o (tripod) ( C O ) ] P F [Co(tripod)(P(OMe) )(CO)]BF [Co(tripod) (Ρφ Η) ( C O ) ] B F [ C o (tripod) ( P E t ) ( C O ) ] B F 2

1980,2020 1945 1925 1930 1940,2000 1920 1930 1953,2026 1930 1905 1890

4

8

4

2

c

3

4

2

4

4

2

4

2

0

3

2

4

4

3

4

Solution

AM

1980,2024 1950 1936 1928 1949,2004 1932 1928 1969,2026 1928 1915 1908

82 84 67 76 84 80 82 80 84 81 82

d

" T h e three triphosphine ligands are P h P ( C H C H P P h ) , etp; P h P ( C H C H C H P P h ) , ttp; and C H C ( C H P P h ) , tripod. The spectra of the hydride complexes were obtained on Nujol mulls whereas the spectra of the deuterated species were recorded on K B r discs. Hexachlorobutadiene reacts with these hydrides. °sh, shoulder on a more intense absorption. Molar conductance values on ~10~ M nitromethane solutions. 2

2

2

2

3

2

2

2

2

2

2

2

3

6

S

d

(CO) ] 2

and [ C o ( t r i p h o s ) ( m o n o p h o s ) ( C O ) ]

+

(Equations 6 and 7).

+

Δ H C o (etp) C O +

NH4BF4 +

CO

>

CH OH + N H 8

[Co(etp) ( C O ) ] B F 2

4

+ H

2

(6)

3

Δ H C o (triphos) C O + N H B F

4

+ PR

[ C o (triphos) ( P R ) C O ] B F

4

+ H

4

> CH OH + N H 3

3

3

2

3

(7)

T h i s p r e p a r a t i v e m e t h o d offers d i s t i n c t advantages over the m o r e c o m monly

u s e d d i r e c t c o m b i n a t i o n of

Co (CO) . 2

8

ligand

with

compounds

s u c h as

Difficulties s u c h as p o l y m e r i c complexes are often e n c o u n -


350

COMPOUNDS

WITH

UNUSUAL

PROPERTIES


INORGANIC

Figure 6. Proton NMR spectra of Co[PhP(CH CH PPh ) ~\H(CO) in tetrahydrofuran (a), two phosphorus nuclei decoupled at 40.4846 MHz (b), one phosphorus nucleus decoupled at 40.4860 MHz (c), and all three phosphorus nuclei decoupled at 40.4888 (d). The tentatively proposed structure has the hydride and carbonyl ligands at axial and equatorial sites of a trigonal bipyramid, respectively. 2

t e r e d b y t h e latter p r e p a r a t i v e m e t h o d s (e.g.

2

E q u a t i o n 8)

2 2

(28).

The

or hv » C Η

Δ

Co (CO) 2

+ PhP(CH CH PPh )

8

2

2

[Co (etp) (CO) ] BPh 2

3

4

+

4

2

2

(>

6


(8)

28.

M E E K

Polyphosphine

E TA L .

351

Ligands

H C o ( t r i p h o s ) C O + N H X r o u t e is p a r t i c u l a r l y u s e f u l f o r syntheses o f 4

the m i x e d complexes

[Co(triphos)(monophos)(CO)]

since s u c h c o m -

+

plexes w o u l d b e v e r y difficult to o b t a i n f r o m other C o ( I ) reagents. T h e [Co(triphos)(CO) ] 2

+

and [Co(triphos)(monophos)(CO)]

complexes

+

are a l l y e l l o w or orange, air-stable solids, b u t t h e i r solutions are m o d e r ately sensitive to oxygen. T h e d i c a r b o n y l cations m a y h a v e e i t h e r s q u a r e - p y r a m i d a l , t r i g o n a l b i p y r a m i d a l , o r s o m e w h a t d i s t o r t e d structures ( 2 9 ) . I R studies of t h e T a b l e V I . B o n d A n g l e s o f the [ C o ( t r i p h o s ) ( C O ) ] C o m p l e x e s C a l c u l a t e d f r o m the R e l a t i v e Intensities o f the T w o C a r b o n y l B a n d s Downloaded by MONASH UNIV on November 20, 2015 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch028

2

+

Compound [ C o (tripod) ( C O ) ] P F [Co(etp)(CO) ]PF [Co(etp)(CO) ]BF [Co(ttp)(CO) ]PF [ C o (ttp) ( C O ) ] B F 2

2

88° 96° 95° 115° 114°

(

6

2

4

2

6

2

4

"Calculated according to Cotton and Wilkinson (30). 2026 cm-1

1949

7

T

0

60

1969

2023 1981

f

UJ

2004

< cr CD

(/) 4 0 — CD

Structure and Reactivity Patterns of Polyphosphine Ligands and Their

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