20 The Effect of Coordination Pattern and 5f Electron Configuration on
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Organoactinide Reactivity TOBIN J. MARKS Northwestern University, Evanston, Ill. 60201
This article discusses developments in two fields of organo actinide chemistry: sigma-bonded actinide organometallics and actinide ions as templates in ligand cyclization reactions. The marked thermal stability of (η -C H ) U-R and (η C H ) Th-R compounds results largely from coordinative saturation which thwarts decomposition via β-hydride elim ination as well as other routes. Thermolysis of these com pounds occurs by intramolecular elimination of R-H. The coordinatively unsaturated UR and ThR compounds are less thermally stable, and they decompose where possible by hydride elimination. The organometallic product of (η C H ) ThR thermolysis is (η -C H ) Th(η :η -C H ) Th(η CH) which suggests the importance of an intermediate (η -C H4)Th(η -C H ) carbene complex-ylid species. When phthalocyanine condensations are carried out in the pres ence of uranyl ion, a complex of the macrocyclic super -phthalocyanine ligand, a five-subunit, expanded analog of phthalocyanine, is obtained. 5
5
5
5
5
5 3
3
4
4
5
5
5
5
5
5
3
1
5
5 2
5
5
5
4 2
2
1
5
5
5
5 2
' " p h e great flowering i n t r a n s i t i o n m e t a l o r g a n o m e t a l l i c c h e m i s t r y d u r i n g A
t h e last 20 years has, u n t i l v e r y r e c e n t l y , l a r g e l y i g n o r e d t h e a c t i n i d e
elements. F u l l interest i n a c t i n i d e o r g a n o m e t a l l i c c h e m i s t r y d i d n o t f u l l y a w a k e n u n t i l t h e recent synthesis of the n o v e l c o m p o u n d uranocene.
Since
t h e n i t has b e c o m e i n c r e a s i n g l y a p p a r e n t t h a t the a c t i n i d e s h a v e a r i c h a n d d i v e r s e o r g a n o m e t a l l i c c h e m i s t r y (1-7). have u n i q u e stereochemical
M o r e o v e r , these m e t a l ions
( h i g h coordination numbers, unusual co
o r d i n a t i o n geometries ) a n d e l e c t r o n i c ( 5 / v a l e n c e o r b i t a l s ) features t h a t are u n k n o w n i n t h e d t r a n s i t i o n series w h i c h suggest i n t e r e s t i n g prospects f o r t h e i r use as reagents a n d catalysts. T h i s p a p e r presents recent d e v e l 232 In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
20.
Organoactinide
MARKS
233
Reactivity
opments i n two burgeoning
fields:
actinide-to-carbon sigma bonds a n d
a c t i n i d e ions as t e m p l a t e s i n c y c l o o l i g o m e r i z a t i o n reactions. T h e p r i n c i p a l focus is o n those c o o r d i n a t i v e as w e l l as e l e c t r o n i c features w h i c h c o n t r o l t h e rates a n d selectivities of t h e c h e m i c a l t r a n s f o r m a t i o n s t h a t are u n d e r g o n e w h e n o r g a n i c l i g a n d s are c o o r d i n a t e d t o a c t i n i d e ions. Actinide-to-Carbon
Sigma Bonds
P r i o r to a n d d u r i n g t h e M a n h a t t a n P r o j e c t , c o n s i d e r a b l e effort
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d i r e c t e d t o w a r d the synthesis of v o l a t i l e u r a n i u m a l k y l c o m p o u n d s as U ( C H ) 2
5
4
was such
for use i n isotope s e p a r a t i o n . T h e s e a t t e m p t s w e r e u n s u c
cessful {8,9)
a n d i t w a s a s s u m e d that the u r a n i u m a l k y l b o n d w a s i n
t r i n s i c a l l y u n s t a b l e . T h u s , f o r s e v e r a l decades the n a t u r e of t h e u r a n i u m t o - c a r b o n l i n k a g e r e m a i n e d u n e x p l o r e d , a n d t h e r e w a s e v e n some q u e s t i o n as to w h e t h e r s u c h b o n d i n g c o u l d t a k e p l a c e . T h e s e p r e c o n c e p t i o n s w e r e d i s p e l l e d b y t h e synthesis of t h e r e m a r k a b l y t h e r m a l l y stable u r a n i u m o r g a n o m e t a l l i c s of the f o r m u l a U - R via R e a c t i o n 1 ( 1 0 , I I , 1 2 , 1 3 , 14).
R
R =
= = = = =
C H 7&-C H allyl t-C H vinyl 4
3
8
= = = = =
3
9
7
5
4
6
9
5
3
2
5
T h e m o l e c u l a r s t r u c t u r e of t h e
r
neopentyl ter£-C H C H C F C CoH G
5
RLi -» ( C , H ) U - R RMgX
(C«H ) UC1 5
(τ; -0 Η )3-
= = = =
5
(1)
3
p-tolyl benzyl -2-cis-2—butenyl -2-£rarw-2-butenyl
5
p h e n y l a c e t y l i d e c o m p l e x is d e p i c t e d i n F i g u r e 1 ( 1 5 ) . A l t h o u g h t h e y
are e x c e e d i n g l y a i r sensitive, these c o m p o u n d s
generally have very h i g h
t h e r m a l s t a b i l i t y . F o r e x a m p l e , t h e h a l f - l i f e of t h e R =
η-butyl c o m p o u n d
i n t o l u e n e s o l u t i o n at 97 ° C exceeds 1000 h r . T h a t s u c h m o n o h a p t o o r g a n o m e t a l l i c s are n o t u n i q u e t o u r a n i u m w a s d e m o n s t a r t e d b y the h i g h y i e l d synthesis of t h e t h o r i u m ( I V ) ( R e a c t i o n 2 ) (16,17).
analogs
T h e s e c o m p l e x e s h a v e e v e n greater t h e r m a l s t a b i l RLi
(C H ) ThCl 5
R
= = = =
5
3
> (C H ) Th-R RMgX 5
n-C H allyl i-C H neopentyl 4
3
= = = =
9
7
ity t h a n the ( C H ) U R compounds. 5
5
3
5
3
-2-cis-2-butenyl -2-£rcms-2-butenyl 5-hexenyl n-C H 3
7
F o r example, i n toluene solution
( s e a l e d t u b e ) at + 1 7 0 ° C ( C H ) T h ( n - b u t y l ) has a h a l f - l i f e of 5
5
3
t h a n 95 h r . T h e t h o r i u m c o m p l e x e s
(2)
more
offer a n i n t r i g u i n g o p p o r t u n i t y t o
In Inorganic Compounds with Unusual Properties; King, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1976.
234
INORGANIC
Figure 1.
The structure of (v -C H UC C H (15) 5
2
6
5
COMPOUNDS
WITH
UNUSUAL PROPERTIES
).-
5
5
e x a m i n e t h e effects of t w o 5f electrons ( T h ( I V ) is 5 f ; U ( I V ) is 5 f )
on
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t h e p r o p e r t i e s of a c t i n i d e a l k y l s . I n v i e w of the r e p o r t e d i n s t a b i l i t y of u r a n i u m t e t r a - a l k y l s , w e u n d e r t o o k a n i n v e s t i g a t i o n of those factors w h i c h s t a b i l i z e a c t i n i d e - t o - c a r b o n s i g m a b o n d s (13,17).
T h e a p p r o a c h w a s to s t u d y the k i n e t i c aspects of
( C H ) M R t h e r m o l y s i s i n s o l u t i o n a n d to s c r u t i n i z e t h e t h e r m a l d e c o m 5
5
3
p o s i t i o n p r o d u c t s , i n c l u d i n g those i n w h i c h d e u t e r i u m a n d s t e r e o c h e m i c a l labels w e r e i n c o r p o r a t e d . S e v e r a l significant patterns e m e r g e d .
Thermoly-
sis of b o t h ( C H ) U R a n d ( C H ) T h R c o m p o u n d s i n toluene s o l u t i o n 5
5
3
5
5
3
does n o t o c c u r via the c o m m o n l y o b s e r v e d ^ - h y d r o g e n eh'mination seq u e n c e ( R e a c t i o n 3 sometimes f o l l o w e d b y R e a c t i o n 4 ) (18-28). CH2=CHR i M - C H 0 C H 3 R ^ M — H ^± M - H +
M - H +
M - C H C H R -> 2 M + 2
3
Rather,
CH2=CHR
(3)
CH CH R 3
f o r b o t h M — T h a n d U , R - H is e l i m i n a t e d (13,17).
(4)
2
Deuterium-labelling
s t u d i e s — e . g . ( C D ) M R t h e r m o l y z e d i n toluene a n d ( C H ) M R t h e r 5
5
3
5
5
3
m o l y z e d i n t o l u e n e - d — i n d i c a t e t h a t a b s t r a c t i o n of a c y c l o p e n t a d i e n y l 8
r i n g h y d r o g e n takes p l a c e .
C r o s s o v e r experiments (e.g.
Reaction 5) i n -
d i c a t e t h a t a b s t r a c t i o n is p r e d o m i n a n t l y i n t r a m o l e c u l a r . S o m e (C H ) MR' 5
5
5
5
R'-H
3
(C D ) MR
crossover
->
(5)
R-D
3
w a s o b s e r v e d i n the p r o d u c t s of t h e t h o r i u m e x p e r i m e n t . H o w e v e r , mass s p e c t r a of s t a r t i n g m a t e r i a l i s o l a t e d f r o m p a r t i a l l y t h e r m o l y z e d samples i n d i c a t e s t h a t this s c r a m b l i n g occurs p r i o r to t h e r m a l
decomposition.
E x p e r i m e n t s w e r e also d e s i g n e d i n v i e w of t h e f a c t t h a t v i n y l i c free r a d i cals are k n o w n to i n v e r t at a rate w h i c h is c o m p e t i t i v e w i t h d i f f u s i o n o u t of solvent cages a n d i n t e r c e p t i o n b y the most p o t e n t r a d i c a l scavengers
