Preparation, Characterization, and Reactions of Dialkylamides and

23 Preparation, Characterization, and Reactions of Dialkylamides and Alkoxides of Molybdenum and Tungsten

Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch023

M. H. CHISHOLM, M. EXTINE, and W. REICHERT Frick Inorganic Chemical Laboratories, Princeton University, Princeton, N. J. 08540

The preparation and characterization of Mo L where L = NMe , NMeEt, NEt OBu , OSiMe OCMe Ph, and W (NMe ) are reported. Physical measurements including single-crystal x-ray studies indicate that in this series dimerization occurs by metal-metal triple bond formation in the absence of bridging ligands. H NMR studies on M (NR ) reveal the large diamagnetic anisotropy induced by the metal-metal triple bond. Reactions of W(NMe ) are presented and compared with those of W(Me) . The reaction of W(NMe ) with carbon dioxide leads to W(NMe ) (O CNMe ) which contains a fac-WN O moiety and very short W-N bonds. A general mechanism for the insertion of carbon dioxide into the covalent metal-nitrogen bond is proposed. 2

6

t

2

2,

2

2

3,

2

6

1

2

2

6

2

6

6

2

2

W7"e

3

2

2

6

3

3

3

set o u t to synthesize a series c o m p o u n d s o f t h e g e n e r a l f o r m u l a

M L , M L , andM L 3

4

6

where M =

m o l y b d e n u m a n d tungsten a n d

L — alkyl, ( R ) , dialkylamide, ( N R ) , a n d alkoxide ( O R ) ligands. W e 2

t h e n w a n t e d t o c o m p a r e i n d e t a i l t h e c h e m i s t r y associated w i t h c o v a l e n t m e t a l - c a r b o n , - n i t r o g e n , a n d - o x y g e n b o n d s b a s e d o n ( a ) the r e a c t i v i t y of t h e o r g a n i c l i g a n d a n d ( b ) t h e c o o r d i n a t i o n p r o p e r t i e s o f t h e t r a n s i t i o n m e t a l . T h i s s u m m a r y covers o u r first t w o years' w o r k w h i c h f o c u s e d o n t h e synthesis a n d c o o r d i n a t e properties o f t h e M o L

3

series a n d t h e

reactions o f W ( N M e ) . 2

6

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

274

INORGANIC

The

MoL

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

Series

s

W i l k i n s o n a n d co-workers

( J , 2) r e c e n t l y d e s c r i b e d the p r e p a r a t i o n

a n d c h a r a c t e r i z a t i o n of a n u m b e r of stable a l k y l c o m p l e x e s of t h e e a r l y t r a n s i t i o n elements. R

=

T h e r e a c t i o n of M o C l

w i t h L i R or R M g X w h e r e

5

a ^ - h y d r i d e e l i m i n a t i o n s t a b i l i z e d a l k y l l e d to the i s o l a t i o n

of

d i m e r i c d i a m a g n e t i c orange c r y s t a l l i n e c o m p o u n d s M o R o ( 1 ) · F o r the 2

t r i m e t h y l s i l y l m e t h y l d e r i v a t i v e , c r y s t a l structure (3)

r e v e a l e d the p r e s

ence of a v e r y short M o - M o b o n d (2.167 A ) a n d the staggered a r r a n g e m e n t of the M o C m o i e t y . 2

It o c c u r r e d to us that i t m i g h t be p o s s i b l e t o

6

m a k e s t r u c t u r a l l y r e l a t e d d i a l k y l a m i d o a n d a l k o x y c o m p o u n d s , thus p r o viding a

u n i q u e o p p o r t u n i t y for the s t u d y of strong h o m o n u c l e a r i n t e r

actions i n the closely r e l a t e d series L M o = = M o L Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch023

3

where L =

3

R,

NR

2 >

and O R . However

there are c e r t a i n p e r t i n e n t factors

that w o u l d seem

to

d i s c o u n t this v i e w . F i r s t , d i m e r i z a t i o n , or m o r e g e n e r a l l y p o l y m e r i z a t i o n , b y m e t a l - m e t a l b o n d f o r m a t i o n i n the absence of b r i d g i n g l i g a n d s w a s unprecedented

i n the c h e m i s t r y of m e t a l alkoxides a n d d i a l k y l a m i d e s

S e c o n d , i t h a d a l r e a d y b e e n s h o w n (6)

(4,5).

with L i N M e

and L i N E t

2

(dialkylamido)molybdenum(IV) t i o n of

Mo R 2

6

from

M0CI5).

compounds

diethylamides

undergo

tetrakis-

Wilkinsons prepara

(cf.

T h i r d , i n the c h e m i s t r y of

v a n a d i u m , a n d t i t a n i u m , i t is k n o w n (4,7) and

that the r e a c t i o n of M 0 C I 5

l e d to the i s o l a t i o n of m o n o m e r i c

2

chromium,

that the d i m e r i c d i m e t h y l -

disproportionation

under

relatively

mild

c o n d i t i o n s ( h i g h v a c u u m a n d w a r m i n g to ca. 6 0 ° C ) via R e a c t i o n 1 w i t h resultant i s o l a t i o n of the m o n o m e r i c m e t a l ( I V ) d i a l k y l a m i d e s . R Ν

R N 2

\

/

2

NR \

M R

2

N

/

2

/ M

N j ^

>· M ( N R ) 2

X

N R

4

+

[M(NR ) L 2

2

(D

2

where M

R2

=

Ti, V, Cr

A c o n s i d e r a t i o n of the s e c o n d a n d t h i r d of these factors l e d us t o use M o C l

a n d to a t t e m p t l o w t e m p e r a t u r e c r y s t a l l i z a t i o n s i n the p r e p a

3

r a t i o n of M o ( N M e ) . 2

3

A t y p i c a l synthesis is o u t l i n e d b e l o w .

T h e a d d i t i o n of M o C l of L i N M e

2

3

to a n i c e - c o o l e d , m a g n e t i c a l l y s t i r r e d s o l u t i o n

(three mole equivalents i n 50:50 T H F : h e x a n e ) gave a dark

b r o w n s o l u t i o n . T h e r e a c t i o n m i x t u r e w a s s t i r r e d 12 h r at 0 ° C u n d e r a n atmosphere of d r y , oxygen-free n i t r o g e n .

Solvent w a s t h e n r e m o v e d

by

v a c u u m d i s t i l l a t i o n , a n d the r e s i d u e w a s d r i e d u n d e r h i g h v a c u u m at 60 ° C .

S u b s e q u e n t e x t r a c t i o n of this d r i e d r e s i d u e w i t h pentane y i e l d e d

a dark, red-brown

solution w h i c h , w h e n

concentrated

and cooled

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

to

23.

CHiSHOLM

—78 ° C ,

Molybdenum

E T AL.

gave

a

very

dark,

and

powdery

M o ( N M e ) 3 . This was collected b y

filtration

2

Analytically pure M o ( N M e )

in vacuo.

Tungsten

2

3

275

crystalline

product—crude

(Schlenk technique) a n d d r i e d is p a l e y e l l o w ; i t w a s o b t a i n e d

f r o m the c r u d e p r o d u c t b y v a c u u m s u b l i m a t i o n ( 1 0 0 ° C , 10r

cm

4

Hg).

D u r i n g the v a c u u m s u b l i m a t i o n of M o ( N M e ) 3 , s m a l l q u a n t i t i e s of 2

the p u r p l e m o n o m e r i c

Mo(NMe ) 2

4

were

initially evolved

H H c m H g ) . B e c a u s e of its greater v o l a t i l i t y , M o ( N M e ) 2

s e p a r a t e d f r o m M o ( N M e ) . I t is not c l e a r w h y M o ( N M e ) 2

3

2

formation could result from impurities i n our M o C l

( 50-60°C,

c o u l d b e easily

4

forms.

4

r e a c t i o n w h i c h competes w i t h the f o r m a t i o n of M o ( N M e ) . 2

ever, q u i t e c e r t a i n t h a t M o ( N M e ) 2

I t is, h o w -

3

is n o t f o r m e d f r o m M o ( N M e )

4

Its

or f r o m some r e d o x

3

2

3

by


a d i s p r o p o r t i o n a t i o n r e a c t i o n s u c h as R e a c t i o n 1. T h e a d d i t i o n of alcohols to h y d r o c a r b o n solutions of

Mo(NMe ) 2

3

causes q u a n t i t a t i v e f o r m a t i o n of a l k o x i d e s via R e a c t i o n 2. T h e n a t u r e of t h e a l k o x i d e d e p e n d s o n the n a t u r e of R (see Mo(NMe ) 2

where R =

+

3

3 ROH

below). The

M(OR)

3

+

3 HNMe

Me, Et, Pr",Pr ,Bu', C M e P h , SiMe 1

2

teri-butoxide (2)

2

3

a n d t r i m e t h y l s i l o x i d e are v o l a t i l e orange c r y s t a l l i n e solids t h a t are r e a d i l y purified by vacuum sublimation (100°C, 1 0 The

molybdenum (III)

where R =

derivatives

cm H g ) .

- 4

Mo(NMe ) 2

and

3

Mo(OR) , 3

B u * a n d S i M e , are m o i s t u r e - a n d oxygen-sensitive

diamag-

3

netic compounds. z e n e a n d mass

Cryoscopic molecular weight determinations i n benspectral data demonstrate

t h a t these

compounds

are

d i m e r i c (i.e. M o L ) i n s o l u t i o n a n d i n t h e v a p o r state. T h e mass s p e c t r a 2

6

r e v e a l strong p a r e n t ions, M o L 2

species. denum

6

+

,

a n d several other

Mo -containing 2

I n d e e d t h e v i r t u a l absence of ions c o n t a i n i n g o n l y one is v e r y s t r i k i n g .

I n this c o n n e c t i o n ,

M o - and

molyb-

Mo -containing 2

species are r e a d i l y d i s t i n g u i s h a b l e b e c a u s e of the s e v e r a l isotopes molybdenum.

T h e mass d i s t r i b u t i o n of t h e i o n M o ( O S i M e ) 2

s e n t e d i n F i g u r e 1.

T h e basic M o

the presence of s i l i c o n ( S i , 2 8

2 9

2

3

e

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

S i , and

3 0

S i ) w h i c h causes the

of

is p r e -

+

by

complex

envelope. T h e d i a m a g n e t i c n a t u r e of these m o l y b d e n u m ( I I I )

compounds and

the presence of o n l y M o - c o n t a i n i n g ions i n the mass s p e c t r u m constitute 2

good evidence

for strong m e t a l - m e t a l b o n d i n g .

Further evidence

m e t a l - m e t a l b o n d i n g was sought b y R a m a n s p e c t r o s c o p y . resonance

R a m a n enhancements

were noted recently (8, 9 ) . L =

of

for

Remarkable

m e t a l - m e t a l stretching vibrations

F o r the d i m e r i c compounds M o L , 2

where

6

N M e , O B u ' , a n d O S i M e , the R a m a n spectra d o n o t i n d i c a t e this 2

3

t y p e of resonance e n h a n c e m e n t ; not i m m e d i a t e l y obvious.

i n d e e d , assignment of v t r ( M o - M o ) s

T h e c o l o r of M o ( N M e ) 2

2

6

and

is

Mo (OR) ,


2

6

276

INORGANIC


,

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

Jj

Figure 1. Parent ion of Mo (OSiMe ) as observed (top) and calculated (bot tom) for naturally occurring isotopes of Mo, Si, O, and C 2

where R =

s 6

B u * a n d S i M e , is a t t r i b u t a b l e to a t a i l i n g of a U V a b s o r p t i o n 3

i n t o t h e v i s i b l e [cf.

i n R e f s . 10 a n d J J M o ( 0 C R ) 2

2

4

and related com

p o u n d s w h i c h s h o w δ - » δ* transitions i n t h e v i s i b l e ] . C o n s e q u e n t l y laser l i g h t i n the v i s i b l e r e g i o n of the s p e c t r u m does n o t i n d u c e a resonance e n h a n c e m e n t of v

8 t r

(Mo-Mo).

s a m p l e of M o ( N M e ) 2

230 c m

- 1

1,600

Figure

2

6

are a l l p o l a r i z a b l e , a n d q u a l i t a t i v e l y w e assign these to

1,300

2.

I n t h e R a m a n s p e c t r u m of a c r y s t a l l i n e

( F i g u r e 2 ) , the s t r o n g b a n d s at 550, 320, a n d

Raman spectrum

1,000

TOO

(100-1600 cm' ) Mo (NMe ) 1

2

1+00

of a polycrystalline

100

sample

2 6


v

8 t r

-

cm'

of

23.

cmsHOLM E T A L .

Molybdenum

and

( M o - N ) , v t r ( M o - M o ) , and p ( N C ) 2

s

277

Tungsten

respectively.

However, a consid

e r a b l e d e g r e e of m i x i n g is possible, a n d a q u a n t i t a t i v e i n t e r p r e t a t i o n of this s p e c t r u m a w a i t s f u t u r e c a l c u l a t i o n s . T h e variable temperature

Ή

N M R s p e c t r a of M o ( O R ) , 2

6

where

R — B u ' , C M e P h , a n d S i M e , i n toluene-ds r e v e a l s i n g l e m e t h y l reso 2

nances

3

at t e m p e r a t u r e s

of

+90°

to

— 90 ° C .

T h e s e s p e c t r a are

consistent w i t h the presence of o n l y t e r m i n a l l y b o n d e d L Mo==MoL3.

H o w e v e r , the o b s e r v a t i o n of a s i n g l e m e t h y l

resonance


3

Β

Figure 3. Variable temperature H NMR spectrum of Mo (NMe ) recorded in toluene-d at 100 MHz and A at 30°, Β at -20°, and C at -60°C. For A , S(Me) — 3.3 ppm; for C, S(Me) = 2.4 and 4.2 ppm rehtive to hexamethyldisiloxane. 1

2

thus

alkoxy ligands

g 6

8


278

INORGANIC

does n o t e x c l u d e

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

t h e p o s s i b i l i t y of r a p i d ( N M R t i m e s c a l e )

bridge-

t e r m i n a l l i g a n d exchange, n o r , of course, c a n w e e x c l u d e the p o s s i b i l i t y of a c c i d e n t a l m a g n e t i c d e g e n e r a c y of b r i d g i n g a n d t e r m i n a l l i g a n d s for d i m e r i c molecules ture Ή 3).

(RO) MO(/A-OR) MO(OR) . 2

2

2

2

6

is h o w e v e r , d e f i n i t i v e ( F i g u r e

A t 2 0 ° C a n d a b o v e , a s i n g l e s h a r p resonance

from hexamethyldisiloxane. at ~

T h e variable tempera

2

N M R s p e c t r u m of M o ( N M e )

is o b s e r v e d

O n c o o l i n g , this resonance

at

broadens

3.3δ until

— 20 ° C i t v i r t u a l l y d i s a p p e a r s i n t o t h e base l i n e . O n f u r t h e r c o o l i n g

to — 4 0 ° C , t w o resonances of 1:1.

a p p e a r at 4.2 a n d 2.4 δ i n the i n t e g r a l r a t i o

N o f u r t h e r c h a n g e is o b s e r v e d

w h e n t h e s a m p l e is c o o l e d to

— 8 0 ° C . T h e N M R s p e c t r u m is i n d e p e n d e n t of M o ( N M e ) 2

t i o n a n d is unaffected b y a d d e d H N M e . 2

2

concentra

6

T h e s e observations are i n c o m


p a t i b l e w i t h a fluxional d i m e r i c m o l e c u l e t h a t has a g r o u n d state g e o m e t r y involving

bridging

[Al(NMe ) ] 2

3

2

dimethylamido

i n R e f s . 4 a n d 12).

s p e c t r u m of M o ( N M e ) 2

2

dimethylamido ligands.

6

ligands

[Ti(NMe ) ]

(cf.

2

3

T h e variable temperature Ή

2

and NMR

is consistent w i t h t h e p r e s e n c e of o n l y t e r m i n a l

T h e low temperature limiting spectrum, w h i c h

consists of t w o resonances i n t h e i n t e g r a l r a t i o of 1:1, i n d i c a t e s f r e e z i n g o u t of p r o x i m a l a n d d i s t a l m e t h y l groups w i t h respect to the m e t a l - m e t a l triple bond.

T h e large c h e m i c a l shift difference

(ca.

2.0 p p m )

p r o x i m a l a n d d i s t a l m e t h y l groups results f r o m the l a r g e

Figure 4. Molecular structure of Mo (NMe ) . Bond lengths: Mo-Mo 2.142(2) A , Mo-N 1.98(1) A , and N-C 1.48(2) A; angles: Mo-Mo-N 103.7(3)% a 133(1)% β 116(1)° and y 110(1)° 2

between

diamagnetic

$ 6


23.

Molybdenum

CHiSHOLM E T AL.

and

279

Tungsten

a n i s o t r o p y i n d u c e d b y the m e t a l - m e t a l t r i p l e b o n d ( 1 3 ) .

A t this p o i n t ,

a c r y s t a l s t r u c t u r e w a s o b v i o u s l y necessary to v e r i f y these p r e d i c t i o n s . F i g u r e 4 is a n O R T E P d r a w i n g of the s t r u c t u r e of M o ( N M e ) 2

d e t e r m i n e d b y C o t t o n et al. (14).

2

6

as

C e r t a i n aspects of the s t r u c t u r e are

e v i d e n t f r o m this v i e w of the m o l e c u l e :

(a)

t h e a b s e n c e of b r i d g i n g

d i m e t h y l a m i d o l i g a n d s : the M o - M o - N angles are 103.7°; ( b )

the short

m o l y b d e n u m - m o l y b d e n u m b o n d l e n g t h [ 2 . 2 1 4 ( 2 ) A ] a n d t h e staggered a r r a n g e m e n t of the M o N 2

moiety; and (c) M o N C

6

units are p l a n a r a n d

2

l e a d to six p r o x i m a l a n d six d i s t a l m e t h y l g r o u p s w i t h respect to the metal-metal triple bond.

Both (a)

and (b)

c o n f i r m the presence of a

m o l y b d e n u m - m o l y b d e n u m triple bond.


T h e a r r a n g e m e n t of the M o - N C Figure 5 in which M o ( N M e ) 2

2

6

planes is r e v e a l e d m o r e c l e a r l y i n

2

is v i e w e d d o w n the m e t a l - m e t a l axis.

Figure 5. Molecular structure of Mo (NMe ) viewed along the Mo-Mo axis showing the Mo-NC planes; Mo (NC ) has S symmetry that differs little from D 2

2

2

g

6

2

6

6

sd

T h i s v i e w of t h e m o l e c u l e c l e a r l y demonstrates the s t a g g e r e d e t h a n e - l i k e c o n f o r m a t i o n of the M o N 2

6

m o i e t y , a n d i t also shows t h a t t h e M o - N C

2

planes are almost c o l i n e a r w i t h t h e m e t a l - m e t a l b o n d .

I n fact, t h e y are

t i l t e d 7 ° out of c o l i n e a r i t y w h i c h leads to absolute S

symmetry for the

Mo (NC ) 2

2

6

moiety.

distal M o - N - C

6

F i n a l l y , i t s h o u l d b e n o t e d t h a t the p r o x i m a l a n d

angles differ: « =

133°

and β —

116°.

T h e larger

p r o x i m a l angle p r o b a b l y reflects the greater i n t e r n a l steric congestion i n this m o l e c u l e . The bonding in M o ( N M e ) 2

2

6

c a n b e q u a l i t a t i v e l y d e s c r i b e d as f o l

l o w s . E a c h m o l y b d e n u m forms f o u r σ b o n d s i n v o l v i n g a p p r o x i m a t e


sp

3

280

INORGANIC

COMPOUNDS WITH

UNUSUAL

PROPERTIES

h y b r i d i z a t i o n . T h e n , i f w e define the M o - M o axis as the ζ axis, m o l y b d e num d

and d

xz

yz

a t o m i c orbitals f o r m t w o m e t a l - m e t a l π b o n d s . T h e

molybdenum-molybdenum

t r i p l e b o n d so f o r m e d p a r a l l e l s t h e s i t u a t i o n

w i t h W i l k i n s o n s M o ( C H S i M e ) e (1,3). 2

2

W i t h M o ( N M e ) , however,

3

2

2

the l o n e pairs o n n i t r o g e n m a y also enter i n t o b o n d i n g . state c o n f i g u r a t i o n

(i.e. F i g u r e 4) m o l y b d e n u m

orbitals m a y a c c o m m o d a t e f o u r electrons

and

d

xy

the M o - N C

2

atomic

d 2. * X

y

from lone pairs o n nitrogen.

T h i s leads to 16 valence s h e l l electrons p e r m o l y b d e n u m . of

e

I n the ground

units a n d t h e s o m e w h a t short

T h e planarity

M o - N bond

lengths

[1.98(1) A ] suggest t h a t n i t r o g e n - t o - m e t a l π b o n d i n g is significant. I n this s i t u a t i o n , l i g a n d π electrons are d o n a t e d to m e t a l orbitals w h i c h a r e δ a n d δ* orbitals w i t h respect to m e t a l - m e t a l b o n d i n g . Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch023

fact

that

accounts

Mo (NMe ) 2

2

for the significantly

[2.214(2) A ]

6

[2.167(?) A ] .

than

longer

I t is p e r h a p s this Mo-Mo

i n Wilkinsons

bond

in

Mo (CH SiMe )e 2

I t i s , o f course, difficult to estimate

2

3

t h e difference i n

m e t a l - m e t a l b o n d l e n g t h w h i c h m i g h t arise solely f r o m differences i n t h e steric r e q u i r e m e n t s o f t h e l i g a n d s . W i t h this i n m i n d , w e e x t e n d e d o u r synthesis o f M o ( N R ) 2

3

to b u l k i e r N R g r o u p s — N R 2

=

2

NMeEt,

N E t , and NPr *. 2

2

T h e p h y s i c a l properties

of M o ( N M e E t )

and M o ( N E t )

3

2

3

closely

p a r a l l e l those of M o ( N M e ) . T h e y are d i m e r i c d i a m a g n e t i c c o m p o u n d s . 2

2

6

The low-temperature-limiting Ή

N M R spectrum of M o ( N M e E t ) 2

6

is

consistent w i t h a g r o u n d state g e o m e t r y t h a t has s i x p r o x i m a l m e t h y l groups a n d six d i s t a l e t h y l groups. trum of M o ( N E t ) 2

2

6

T h e h i g h - t e m p e r a t u r e - l i m i t i n g spec

shows t h e t i m e - a v e r a g e d p r o x i m a l a n d d i s t a l reso

nances b u t also c o m p l e x p r o t o n - p r o t o n motions

about the N - C H

m o d e l of M o ( N E t ) 2

2

e

bond

2

couplings

a r e severely

w h i c h suggest t h a t

hindered.

A

indicates that there is i n d e e d severe

O u r characterization of

ΜΟ(ΝΡΓ *) 2

3

molecular congestion.

is i n c o m p l e t e , b u t i t does

appear

that this c o m p o u n d is q u i t e different f r o m t h e d i m e t h y l a m i d e . F i n a l l y w e should comment o n the mechanism d i s t a l a l k y l interconversions

in M o ( N R ) 2

2

of p r o x i m a l a n d

compounds.

6

A t t h e most

e l e m e n t a r y l e v e l , this c o u l d b e d e s c r i b e d b y M o - N b o n d r o t a t i o n . sophisticated

treatment

o f this t y p e

of intramolecular

A

rearrangement

r e q u i r e s the a p p r o a c h a d o p t e d b y M i s l o w a n d co-workers i n t h e i r g r a p h i c a l analyses o f t h e d y n a m i c stereochemistry f o r m A r Z (15, 16) a n d A r C (17). 3

4

of a r y l compounds of the

I n this context, w e note t h e stereo

chemical correspondence between M o ( N M e ) 2

2

6

and S i P h 2

6

How

(18).

ever, i n a d d i t i o n t o flip rearrangements ( M o - N b o n d r o t a t i o n ) , a

fluxional

process i n w h i c h d i m e t h y l a m i d o g r o u p s are t r a n s f e r r e d f r o m o n e m o l y b d e n u m to t h e other c o u l d b e operative.

T h e most attractive

fluxional

m e c h a n i s m i n v o l v e s t h e c o n c e r t e d p a i r w i s e i n t e r c h a n g e o f l i g a n d s , i.e. a transition

state

that

has the b r i d g e d

Al (NMe ) 2

2

6

structure.


For

23.

CHisHOLM E T A L .

Molybdenum

and

281

Tungsten

M o ( N M e ) e , these m e c h a n i s m s are p e r m u t a t i o n a l l y i n d i s t i n g u i s h a b l e . 2

2

H o w e v e r , w e h o p e to b e able to synthesize M o ( N M e ) ( N R ) w h i c h , 2

2

5

2

b a r r i n g a c c i d e n t a l a n i s o c h r o n y , s h o u l d e n a b l e us to d i s t i n g u i s h b e t w e e n t h e flipping a n d the

fluxional

mechanisms.

T h e i m p o r t a n c e of steric factors i n d e t e r m i n i n g the c o o r d i n a t e p r o p erties of the m e t a l i n t h e M L b u l k y ligands L =

series c a n n o t b e o v e r e m p h a s i z e d .

3

For

CH SiMe , C H C ( C H ) , NMe , NMeEt, NEt , OBu', 2

3

2

3

3

2

2

O S i M e , a n d O C M e P h , m o l y b d e n u m adopts the L M o = = M o L 3

2

3

structure.

3

I n c r e a s i n g the steric d e m a n d of the l i g a n d s e v e n f u r t h e r s h o u l d g r e a t l y w e a k e n t h e m e t a l - m e t a l i n t e r a c t i o n a n d c o u l d e v e n l e a d to the i s o l a t i o n of m o n o m e r i c


(19),

compounds

MoL —cf.

CrL

3

N P r * (20, 2 1 ) , a n d N ( S i M e ) 2

3

sterically demanding

2

where L

3

(22).

=

CH(SiMe ) 3

2

O n the other h a n d , less

l i g a n d s s h o u l d a l l o w the m e t a l to

increase

its

c o o r d i n a t i o n n u m b e r b y the f o r m a t i o n of m e t a l - l i g a n d - m e t a l b r i d g e s . T h i s i n d e e d appears to b e the case for M o ( O R ) a n d P r . These

3

where R =

Me, Et,

are b l a c k , p o l y m e r i c , n o n v o l a t i l e , p a r a m a g n e t i c

1

com-

p o u n d s for w h i c h p o l y m e r i z a t i o n p r o b a b l y occurs b y t h e f o r m a t i o n of Mo0

6

u n i t s [cf.

difference

Cr(OR)

between

molybdenum (III)

3

(4, 5 ) w h e r e R — M e a n d E t ] . A

w h a t r e l u c t a n t l y , f o r m t e t r a h e d r a l complexes 2

(III)

and

is the f o l l o w i n g : c h r o m i u m ( I I I ) w i l l , t h o u g h s o m e -

where L — C H S i M e

as i n t h e salts

a n d O B u * (20, 23),

(1,2)

3

prefers to a d o p t the L M o = = M o L 3

forming

notable

the c o o r d i n a t i o n c h e m i s t r y of c h r o m i u m ( I I I )

a fourth M o - L bond.

3

LiCrL , 4

whereas m o l y b d e n u m -

s t r u c t u r e at the expense of

T h i s p r e s u m a b l y reflects

the

greater

a b i l i t y of m o l y b d e n u m to f o r m strong m e t a l - m e t a l m u l t i p l e b o n d s i n its tervalent state. I n d e e d to o u r k n o w l e d g e there are no k n o w n c h r o m i u m chromium multiple bonded compounds

W

2

(NMe ) 2

of c h r o m i u m ( I I I ) .

6

T h e great p r o p e n s i t y of m o l y b d e n u m to f o r m m e t a l - m e t a l m u l t i p l e b o n d e d c o m p o u n d s m i g h t l e a d one to expect the same of tungsten. T h i s , h o w e v e r , does not a p p e a r to b e the case (24).

I n d e e d , at t h e start of

this w o r k o n l y W ( C H S i M e ) h a d b e e n p r e p a r e d , a n d i t w a s r e p o r t e d 2

2

3

6

as f o r m i n g crystals i s o m o r p h o u s to those of M o ( C H S i M e ) (3). 2

2

3

6

The

v i r t u a l absence of W - W m u l t i p l e b o n d e d c o m p o u n d s leads to i n t r i g u i n g questions.

Are W - W

m u l t i p l e b o n d s i n h e r e n t l y w e a k e r t h a n those

of

m o l y b d e n u m a n d , i f so, for w h a t reasons, or, h a v e c e r t a i n s u b t l e factors of

the

coordination

c h e m i s t r y of

tungsten thus f a r p r e c l u d e d

their

preparation? I n 1969 w e r e p o r t e d ( 2 5 ) W(NMe ) 2

6

the p r e p a r a t i o n a n d c h a r a c t e r i z a t i o n of

f r o m the r e a c t i o n of W C 1 w i t h L i N M e . W e n o t e d t h a t this 6

2


282

INORGANIC

COMPOUNDS WITH

reaction was always accompanied

UNUSUAL

PROPERTIES

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

o n the basis of a n a l y t i c a l d a t a , w e f o r m u l a t e d t h a t t h e r e d u c e d t u n g s t e n was

of

the form

W(NMe ) . 2

O u r c h a r a c t e r i z a t i o n of

3

e n c o u r a g e d us to p u r s u e the synthesis of W ( N M e ) 2

could

clearly

reveal invaluable information

Mo (NMe )6 2

about

tungsten-tungsten

bonding and allow a direct comparison w i t h molybdenum. tions i n v o l v i n g W C 1

and L i N M e

6

2

since this c o m p o u n d

3

Since reac

proceeded w i t h some reduction

2

t u n g s t e n , i t s e e m e d that a r e a c t i o n u s i n g a r e d u c e d

tungsten

of

halide

m i g h t w e l l l e a d to o n l y , or at least to the p r e d o m i n a n c e of, W ( N M e ) . 2

3

S u c h was not the case. W h e n they w e r e r e a c t e d w i t h f o u r e q u i v a l e n t s of L i N M e , W C 1 ( T H F ) 2

4

W(NMe )

6

W(NMe )

3

with two

e q u i v a l e n t s of


2

2

W(NMe ) . 2

3

samples

as

the

and W C i 4 ( O E t )

(26)

2

only

2

isolatable

was o b t a i n e d .

2

yielded

(26)

dimethylamide

of

T h e r e a c t i o n of the cluster c o m p o u n d LiNMe

2

2

from

reactions

f o u n d that i f W C l ( O E t ) 4

2

2

that involved W C 1 .

2

and

6

than many

6

However,

6

no

WC1

g a v e a m i x t u r e of W ( N M e )

2

This mixture was m u c h richer i n W ( N M e )

obtained

pure

tungsten;

we

is a l l o w e d to d e c o m p o s e i n ether u n d e r a

n i t r o g e n a t m o s p h e r e at r o o m t e m p e r a t u r e a n d the resultant b l a c k s l u d g e is t h e n r e a c t e d w i t h three e q u i v a l e n t s of L i N M e , a m i x t u r e of W ( N M e ) 2

and

W(NMe ) 2

W(NMe ) 2

3

is

6

obtained

with W ( I I I ) : W ( V I ) =

to isolate p u r e W ( N M e ) 2

and

W(NMe ) 2

W(NMe ) 2

3

which

a

high

percentage

2:1 b a s e d o n tungsten. A l l attempts 2

and

chromatography

cocrystallize.

Attempts

have failed; W ( N M e ) 2

3

to

s i l ) w h i c h a l l o w s the i s o l a t i o n of W ( N M e ) . 2

erties of the m i x t u r e w e r e , h o w e v e r , 2

observed

6

is t h e

more

for W ( N M e ) 2

2

c

+

T h e spectroscopic

floriprop

i n f o r m a t i v e w i t h r e g a r d to

I n the mass s p e c t r u m

3

3

isolate

reactive c o m p o u n d a n d it decomposes on the c o l u m n (dehydrated

n a t u r e of W ( N M e ) .

3

of

f r o m this m i x t u r e h a v e f a i l e d so f a r ; W ( N M e )

3

cosublime

6

by

2

contains

the

a s t r o n g p a r e n t i o n is

, and variable temperature Ή

N M R studies

r e v e a l p r o p e r t i e s analogous to those o b s e r v e d for M o ( N M e ) , n a m e l y 2

a s i n g l e m e t h y l resonance

2

6

at r o o m t e m p e r a t u r e w h i c h broadens

when

t h e s a m p l e is c o o l e d a n d finally gives t w o peaks i n t h e i n t e g r a l r a t i o of 1:1 s e p a r a t e d b y ca. 2.0 p p m . graphy

techniques.

Recent

reveal that W ( N M e ) 2

6

A t this p o i n t w e r e s o r t e d to c r y s t a l l o

findings

of

and W ( N M e ) 2

2

m o l e c u l a r s t r u c t u r e of W ( N M e ) 2

2

6

c

C o t t o n a n d co-workers

(27)

do indeed cocrystallize.

The

p a r a l l e l s t h a t of M o ( N M e ) 2

2

c

with

a W - W b o n d l e n g t h of 2.30 A . A l t h o u g h this b o n d l e n g t h is s i g n i f i c a n t l y l o n g e r t h a n t h a t of M o - M o i n M o ( N M e ) , i t is n o w c l e a r that t u n g s t e n 2

tungsten m u l t i p l e b o n d i n g

2

6

is not i n h e r e n t l y w e a k .

F u r t h e r m o r e , the

a b u n d a n c e of M o - a n d t h e p a u c i t y of W - m u l t i p l e b o n d e d 2

m u s t reflect s u b t l e differences

2

complexes

i n the c o o r d i n a t i o n c h e m i s t r y of

metals.


these

23.

Molybdenum

CHISHOLM E T AL.

Reactions

of

and

283

Tungsten

W(NMe )

2 6

T h e c h e m i s t r y of W ( N M e ) 2

(25)

6

and W ( M e )

(28)

e

provides a

great o p p o r t u n i t y for c o m p a r i n g c o v a l e n t t r a n s i t i o n m e t a l - n i t r o g e n a n d - c a r b o n σ bonds.

I n s o m e w a y s t h e i r reactions are s i m i l a r ; f o r e x a m p l e ,

b o t h c o m p o u n d s react w i t h alcohols to f o r m alkoxides W ( O R ) . e

ever, i n most reacts

(28)

(0 N Me) 2

2

2

instances t h e i r reactions

differ; for e x a m p l e ,

w i t h N O to g i v e the e i g h t - c o o r d i n a t e whereas W ( N M e ) 2

W(Me)

complex

6

W(Me 4

does not react w i t h N O u n d e r

6

How

com

parable conditions. Superficially W ( M e )

is t h e m o r e r e a c t i v e c o m p o u n d .

6

I t is p y r o -

p h o r i c i n a i r , t h e r m a l l y u n s t a b l e at r o o m t e m p e r a t u r e , a n d e v e n Downloaded by UNIV OF BATH on July 3, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/ba-1976-0150.ch023

to d e t o n a t i o n ( 2 9 ) . u p to 2 0 0 ° C ,

W(NMe ) 2

a n d i t is a p p r e c i a b l y less m o i s t u r e - s e n s i t i v e t h a n other

metal dimethylamides. However, W ( N M e ) 2

6

is the m o r e r e a c t i v e c o m

p o u n d t o w a r d some substrates. F o r e x a m p l e , w h i l s t W ( M e ) in C S

2

prone

o n the other h a n d is t h e r m a l l y stable

6

a n d acetone ( 2 8 ) , W ( N M e ) 2

o r g a n i c substrates. W ( N M e ) 2

6

reacts w i t h C S

6

is s o l u b l e

6

r e a d i l y reacts w i t h b o t h of these 2

to give W ( S C N M e ) . 2

2

4

R e d u c t i o n of t u n g s t e n is a c c o m p a n i e d b y o x i d a t i o n of the d i t h i o c a r b a m a t o l i g a n d to M e N C ( S ) S - S ( S ) C N M e . 2

2

A r a t h e r r e m a r k a b l e r e a c t i o n occurs w i t h C 0 .

E v e n i n the pres

2

ence of six or m o r e e q u i v a l e n t s of C 0 , o n l y three e q u i v a l e n t s of

C0

2

2

are c o n s u m e d w h i c h y i e l d s the n o v e l c o m p o u n d W ( N M e ) ( 0 C N M e ) . 2

3

2

2

3

T u n g s t e n r e m a i n s i n its h e x a v a l e n t state. T h i s r e a c t i o n is r e m a r k a b l e i n several w a y s .

F i r s t , a l l other d i m e t h y l a m i d e s of the e a r l y t r a n s i t i o n

elements react a c c o r d i n g to t h e g e n e r a l r e a c t i o n , R e a c t i o n 3.

M (NMe ) 2

n

+

nC0

2

-> M ( 0 C N M e ) 2

2

(3)

n

M = T i , Zr, H f , V , M o

where η = 4

M = N b and T a

where η =

5

M = M o and W

where η =

3

i n s e r t i o n occurs w h i c h y i e l d s the f u l l y s u b s t i t u t e d c a r b a m a t o Second, W ( N M e ) 2

reacts w i t h C 0

2

6

Complete

compounds.

is a n e x t r e m e l y s t e r i c a l l y c o n g e s t e d m o l e c u l e yet i t

v e r y r a p i d l y , m u c h m o r e r a p i d l y t h a n i t reacts

alcohols w h i c h g i v e W ( O R ) . 6

T h i r d , although W ( N M e ) 2

with

consumes

6

o n l y three m o l e e q u i v a l e n t s of C 0 , the p r o d u c t , W ( N M e ) ( 0 C N M e ) , 2

exchanges C 0

2

(Reaction 4).

2

3

2

T h i s exchange is r e a d i l y f o l l o w e d b y


2

3

Ή

284


INORGANIC

(T )

COMPOUNDS WITH

UNUSUAL

PROPERTIES

*o

Figure 6. * H NMR spectrum of W(NMe ) (0 CNMe ). in the region of 2.5-5.5 ppm TMS (bottom) and scale expanded (top) to show W coupling to the W-NMe protons and C coupling to the O CNMe protons g s

13

2

2

183

2

13

13

t

9


23.

Molybdenum

CHISHOLM E T A L .

and

W(NMe ) (0 CNMe ) 2

3

2

2

3

W(NMe ) (0 *CNMe ) (0 CNMe ) _ 2

3

2

2

n

2

2

3

285

Tungsten

+ 3*C0 n

^±

2

+ nC0

(4)

+

2

(3 -

n)*C0

where η = NMR 3

7i3 . c

spectroscopy

since

H

recorded i n toluene-d S i n c e the

1 3

C0

presence of 0 abundance =

1 2

2

hgand

2

N M R s p e c t r u m of W ( N M e ) ( 0 2

3

2

shows

CNMe )

1 3

2

3

at 30 ° C a n d 60 M H z is p r e s e n t e d i n F i g u r e 6.

8

C N M e l i g a n d s is also o b s e r v e d .

14%,

3

served for W ( N M e ) 2

We

C-labelled 0 * C N M e

1 3

0-3

w a s o n l y 9 2 % p u r e , a s m a l l p e a k a t t r i b u t a b l e to t h e

2

2

note t h a t the W - N M e


the

— 3.0 H z . T h e Ή

2

6

protons s h o w c o u p l i n g to

2

/ i 8 3

W

I t is i n t e r e s t i n g to W; I =

3.0 H z . C o u p l i n g to

—

H

1 8 3

1 8 3

but was noted (28) for W ( M e ) , 6

believe that W ( N M e ) ( 0 C N M e ) 2

3

2

2

3

2

/i83

provides

u n d e r s t a n d i n g of i n s e r t i o n reactions i n v o l v i n g C 0

2

V4, n a t u r a l

W w a s not o b w

.

H

6 Hz.

—

a k e y to

the

a n d covalent m e t a l -

n i t r o g e n b o n d s . T h e m e c h a n i s m of these i n s e r t i o n reactions has r e c e i v e d r e l a t i v e l y l i t t l e a t t e n t i o n (30)

a l t h o u g h i t is reasonable t h a t i t s h o u l d

i n v o l v e a four-center t r a n s i t i o n state as i n d i c a t e d b y R e a c t i o n 5. S u c h a m e c h a n i s m is s i m i l a r to that g e n e r a l l y a c c e p t e d (31)

for the i n s e r t i o n of

olefins a n d acetylenes i n t o m e t a l - h y d r o g e n a n d m e t a l - c a r b o n σ b o n d s , b u t i t differs w i t h r e g a r d to the role of the lone p a i r o n n i t r o g e n . C l e a r l y , b o t h steric a n d e l e c t r o n i c factors s h o u l d b e i m p o r t a n t i n R e a c t i o n 5.

JL

0 = C = 0

M-NMe

2

+

C0

M e

±M—N

2

^ - ^ M e We

obtained

numerous

spectroscopic

data

on

W(NMe ) (0 2

3

C N M e ) , a l l of w h i c h i n d i c a t e d the e q u i v a l e n c e of the t h r e e 2

l i g a n d s a n d the e q u i v a l e n c e of the three 0 C N M e 2

2

ligands.

2

NMe

3

2

Classical

t e c h n i q u e s c o u l d not, h o w e v e r , r e a d i l y d i s t i n g u i s h b e t w e e n s i x - c o o r d i n a t e t u n g s t e n , i.e. a f a c - W N 0 3

3

octahedron, and a nine-coordinate

geometry

i n v o l v i n g b i d e n t a t e c a r b a m a t o l i g a n d s . W e d e c i d e d to resolve t h i s i n t e r esting a n d i m p o r t a n t s t r u c t u r a l q u e s t i o n b y u s i n g c o m m e r c i a l c r y s t a l l o g r a p h y services ( M o l e c u l a r S t r u c t u r e C o r p . , C o l l e g e S t a t i o n , T e x a s ) . A n O R T E P v i e w of W ( N M e ) ( 0 C N M e ) 2

7. T h e m o l e c u l e has C

3

3

2

2

3

is p r e s e n t e d i n F i g u r e

s y m m e t r y . T u n g s t e n is s i x - c o o r d i n a t e a n d the

l o c a l g e o m e t r y a b o u t tungsten is s u i t a b l y d e s c r i b e d as a f a c - W N 0

3

hedron.

O f p a r t i c u l a r note are t h e f o l l o w i n g observations: t h e

N(2)-

W-N(2)

angles ( 9 4 . 8 ( 3 ) ° ) are greater t h a n the 0 ( 1 ) - W - 0 ( 1 )

angles

3

(82.1(2)°), (b)

the W - N ( 2 )

octa

b o n d distances ( 1 . 9 2 2 ( 7 ) A ) are c o n s i d -



286

INORGANIC

COMPOUNDS

WITH

UNUSUAL

PROPERTIES

Figure 7. Molecular structure of W(NMe ) (O CNMe ) showing facWN O moiety; the molecule has C symmetry. Bond lengths: W-N(2) 1.922(7) A and W-O(l) 2.041(6) A; angles: 2 V - W - N 94.8°, O-W-0 82.1°, N-W-O 170.3°, N-W-0 93.2°, and N-W-0 89.3°. g

3

s

3

g

2

s

3

e r a b l y shorter t h a n the W - O ( l ) the 0 C N C o a n d W - N C 2

2

b o n d distances ( 2 . 0 4 1 ( 6 ) A ) , a n d

(c)

moieties are p l a n a r .

T h e structures of W ( N M e ) 2

6

(25)

and

W(NMe ) (0 CNMe ) 2

3

2

2

3

suggest that steric factors are not the sole c o n t r o l l i n g factors i n h m i t i n g i n s e r t i o n . W e b e l i e v e that i n s e r t i o n is l i m i t e d b y the n u c l e o p h i l i c i t y of the N M e

ligands.

2

Six d i m e t h y l a m i d o l i g a n d s , " N M e , offer t u n g s t e n a 2

t o t a l of 24 electrons a l t h o u g h a v a i l a b l e m e t a l v a l e n c e orbitals c a n a c c o m m o d a t e o n l y 18 electrons nonbonding

a n d 6 electrons

o c c u p y a t r i p l y degenerate

m o l e c u l a r o r b i t a l . T h u s for W ( N M e ) , l i g a n d - t o - m e t a l ττ 2

6

b o n d i n g m a y l e a d to a m a x i m u m W - N b o n d order of 1.5. H o w e v e r , w i t h W ( N M e ) ( 0 C N M e ) , replacement of three N M e 2

3

2

2

3

2

ligands b y weaker

ττ-donating o x y g e n l i g a n d s leads to greater N - t o - W ττ b o n d i n g as is e v i d e n c e d b y the v e r y short W - N b o n d l e n g t h of 1.922(7) A , cf. W - N b o n d


23.

CHISHOLM

Molybdenum

E T A L .

length of 2.032(25) A i n W ( N M e ) 2

the f a c - W N 0 3

geometry allows

3

e n h a n c e d nitrogen-to-tungsten the

dimethylamido

6

287

and Tungsten

I t s h o u l d also b e n o t e d t h a t

(25).

for m a x i m u m

W - N bonding.

This

π bonding reduces the nucleophilicity of

lone pairs, a n d further

insertion of C 0

is n o t

2

favored. I n v i e w of t h e p r e v i o u s o b s e r v a t i o n that W ( N M e ) 2

r e a d i l y reacts

6

w i t h alcohols to g i v e W ( O R ) , i t w o u l d seem t h a t t h e W 0 6

m o r e t h e r m o d y n a m i c a l l y stable t h a n either t h e W N moieties

of W ( N M e ) 2

6

and W ( N M e ) ( 0 C N M e ) 2

3

2

2

2

3

m o i e t y is 3

respectively.

3

sertion of C 0 i n t o W - N b o n d s i n W ( N M e ) ( 0 C N M e ) 2

6

or the f a c - W N 0

6

2

2

3

3

In

m u s t present

a r e l a t i v e l y h i g h e n e r g y o f a c t i v a t i o n . I t is therefore p a r t i c u l a r l y p e r t i n e n t to ask b y w h a t m e c h a n i s m does W ( N M e ) ( 0 C N M e ) 2


C0

2

3

2

2

exchange w i t h

3

i n R e a c t i o n 4. K i n e t i c d a t a suggest that this e x c h a n g e

reaction

involves a n i n n e r s p h e r e process w i t h a r a t e - d e t e r m i n i n g step t h a t i n v o l v e s expulsion of C 0

2

w h i c h m a y be described b y the deinsertion

reaction

(Reaction 6 ) . W(NMe ) (0 CNMe ) 2

We

3

2

2

— W(NMe ) (0 CNMe )

3

2

c o n c l u d e that W ( M e )

different m e c h a n i s m s .

W(Me) 2

2

2

and W ( N M e ) 2

6

2

+ C0

2

g e n e r a l l y react

(6) via

reacts (28) via i n i t i a l n u c l e o p h i l i c attack

6

at tungsten w h e r e a s W ( N M e )

6

4

6

reacts via e l e c t r o p h i l i c attack o n n i t r o

g e n n o n b o n d i n g lone p a i r s .

Literature Cited 1. Mowat, W., Shortland, A. J., Yagupsky, G., Hill, N. J., Yagupsky, M., Wilkinson, G.,J.Chem. Soc. Dalton Trans. (1972) 533. 2. Mowat, W., Shortland, A. J., Hill, N. J., Wilkinson, G., J. Chem. Soc. Dalton Trans. (1973) 770. 3. Huq, F., Mowat, W., Shortland, A. J., Skapski, A. C., Wilkinson, G., Chem. Commun. (1971) 1079. 4. Bradley, D. C., Adv. Inorg. Chem. Radiochem. (1972) 15, 259. 5. Bradley, D. C., Fisher, K., in "MTP International Review of Science," Vol. 5, p. 65, Butterworths, London, 1972. 6. Bradey, D. C., Chisholm, M. H.,J.Chem. Soc. A (1971) 2741. 7. Basi, J. S., Bradley, D. C., Chisholm, M. H., J. Chem. Soc. A (1971) 1433. 8. Angell, C. Α., Cotton, F. Α., Frenz, Β. Α., Webb, T. R., J. Chem. Soc. Chem. Commun. (1973) 399 9. Clark, R. J. H., Franks, M. L., J. Chem. Soc. Chem. Commun. (1974) 316. 10. Cowman, C. D., Gray, H. B., J. Am. Chem. Soc. (1973) 95, 8177. 11. Norman, Jr., J. G., Kolari, H. J., J. Chem. Soc. Chem. Commun. (1974) 303. 12. Lappert, M. F., Sanger, A. R., J. Chem. Soc. A (1971) 874. 13. Filippo, J. S., Inorg. Chem. (1972) 11, 3140. 14. Chisholm, M. H., Reichert, W., Cotton, F. Α., Frenz, Β. Α., Shive, L., J. Chem. Soc. Chem. Commun. (1974) 480. 15. Gust, D., Mislow, K.,J.Am. Chem. Soc. (1973) 95, 1535.



288

INORGANIC COMPOUNDS WITH UNUSUAL PROPERTIES

16. Mislow, K., Gust, D., Finocchiaro, P., Boetcher, R. J., Top. Current Chem. (1974) 47, 1. 17. Hutchings, M. G., Mislow, K., Nourse, J. G., Tetrahedron (1974) 30, 1535. 18. George, M. V., Peterson, D. J., Gilman, H., J. Am. Chem. Soc. (1960) 82, 403. 19. Barker, G. K., Lappert, M. F., J. Organomet. Chem. (1974) 76, C45. 20. Alyea, E. C., Basi, J. S., Bradley, D. C., Chisholm, M. H., Chem. Commun. (1968) 495. 21. Bradley, D. C., Hursthouse, M. B., Newing, C. W., Chem. Commun. (1971) 411. 22. Bradley, D. C., Hursthouse, M. B., Rodesiler, P. F., Chem. Commun. (1969) 14. 23. Chisholm, M. H., Ph.D. Thesis, London, 1969. 24. Cotton, F. Α., Chemical Society Centenary Lecture, 1974; Chem. Soc. Rev. (1975) 4, 27. 25. Bradley, D.C.,Chisholm, M. H., Heath, C. E., Hursthouse, M. B., Chem. Commun. (1969) 1261. 26. Grahlert, W., Thiele, Κ. H., Z. Anorg. Allg. Chem. (1971) 383, 144. 27. Cotton, F. Α., personal communication; J. Amer. Chem. Soc. (1975) 97, 1242. 28. Shortland, A. J., Wilkinson, G.,J.Chem. Soc. Dalton Trans. (1973) 872. 29. Wilkinson, G., private communication. 30. Lappert, M. F., Prokai, B., Adv. Organomet. Chem. (1967) 5, 225. 31. Cotton, F. Α., Wilkinson, G., in "Advanced Inorganic Chemistry," 3rd ed., Chap. 24, Interscience, New York, 1972. RECEIVED January 24, 1975. Work supported by the Research Corp., the Petroleum Research Fund administered by the American Chemical Society (grant PRF-7722 AC3), and the National Science Foundation (grant GP42691X). M. Extine was the recipient of a graduate student fellowship from the American Can Co.


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