Rings, Clusters, and Polymers of the Main Group Elements - American

7 Multihapto Bonding Between Main Group Elements and Carbocyclic Ligands Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 27, 2016 | http://pubs.acs.org Publication Date: September 30, 1983 | doi: 10.1021/bk-1983-0232.ch007

An Approach to the Bonding in Main Group Cluster Compounds S. G. BAXTER, A. H. COWLEY, and J. G. LASCH The University of Texas at Austin, Department of Chemistry, Austin, TX 78712

MNDO calculations have been performed on a number of main-group capping moieties for C H , C H , C H , and C H carbocyclic rings. Perhapto bonding is predicted when the number of interstitial electrons (comprising ring-π plus relevant main-group fragment electrons) totals six. Some cases of intermediate hapticity are discussed in the context of the C H ring. 3

6

3

4

4

5

5

6

5

5

The d i s c o v e r y o f t h e t r a n s i t i o n m e t a l s a n d w i c h m o l e c u l e s f e r r o c e n e a n d d i b e n z e n e c h r o m i u m r a n k s a s one o f t h e more i m p o r t a n t c h e m i c a l d i s c o v e r i e s o v e r t h e p a s t t h r e e d e c a d e s . The c h e m i s t r y o f t h e s e a n d o t h e r d- a n d f - b l o c k c a r b o c y c l i c π-complexes h a s been i n v e s t i g a t e d i n t e n s i v e l y i n the ensuing y e a r s . Significant p r o g r e s s h a s a l s o b e e n made t o w a r d u n d e r s t a n d i n g t h e e l e c t r o n i c s t r u c t u r e s and p a t t e r n s o f s t a b i l i t y o f t h e s e i n t e r e s t i n g com pounds ( 1 ) . However, compared w i t h t h e d - a n d f - b l o c k e l e m e n t s , much l e s s i s known a b o u t t h e m u l t i h a p t o i n t e r a c t i o n o f t h e m a i n group e l e m e n t s w i t h c a r b o c y c l i c l i g a n d s . M i n k i n a n d M i n y a e v (2) have s u g g e s t e d t h a t a n n u l e n e - c a p p e r h a p t o b o n d i n g w i l l b e f a v o r e d when t h e t o t a l number o f ring-π p l u s m a i n - g r o u p m o i e t y e l e c t r o n s i s e q u a l t o e i g h t , w h i l e S c h l e y e r e t a l . ( 3 ) f a v o r a n optimum number o f s i x i n t e r s t i t i a l e l e c t r o n s ( 4 ) . S e v e r a l m a i n - g r o u p π-complexes h a v e b e e n i n v e s t i g a t e d u s i n g various l e v e l s o f theory. T h u s , C 5 H 5 L 1 (5) a n d C s H s B e H (6) h a v e b e e n computed u s i n g ab i n i t i o m e t h o d s , a n d Dewar a n d R z e p a (7) h a v e e x p l o r e d t h e i n t e r a c t i o n o f BeX m o i e t i e s w i t h c y c l o p e n t a d i e n y l , i n d e n y l , a n d f l u o r e n y l g r o u p s . The MNDO method h a s a l s o b e e n employed f o r t h e i n v e s t i g a t i o n o f v a r i o u s c a r b o c y c l i c b e r y l l i u m d e r i v a t i v e s , (8) a n d t h e PRDDO method has b e e n u t i l i z e d i n c o n j u n c t i o n w i t h C s H s B e R compounds ( 9 ) . The t i n c a t i o n [ C 5 H 5 S n ] has b e e n s t u d i e d w i t h t h e EHMO method, (10) a n d Hoffmann +

0097-6156/83/0232-0111 $06.00/0 © 1983 American Chemical Society

Cowley; Rings, Clusters, and Polymers of the Main Group Elements ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

112

RINGS, C L U S T E R S , A N D P O L Y M E R S

Z +

e t a l . (11) have examined t h e m o t i o n o f a [ C H ] fragment a c r o s s a IC5H5]" r i n g . The p r e s e n t c o n t r i b u t i o n r e p r e s e n t s a n a t t e m p t t o d e v e l o p f u r t h e r a model f o r t h e m u l t i h a p t o b o n d i n g o f main-group element f r a g m e n t s t o c a r b o c y c l i c r i n g s , ( C H ) (n=3-6) u s i n g t h e MNDO program system (12). One o f t h e a d v a n t a g e s o f t h i s method i s t h a t i t p e r m i t s study o f t h e capping o f c a r b o c y c l i c r i n g s by t h e h e a v i e r main-group elements. E m p h a s i s i s p l a c e d b a s i c a l l y o n two themes: ( i ) whether a s i x - o r e i g h t - e l e c t r o n counting procedure i s more a p p r o p r i a t e , a n d ( i i ) w h e t h e r c o n f o r m i t y w i t h o t h e r c l u s t e r e l e c t r o n counting procedures i s achieved. I t i s on t h e l a t t e r p o i n t t h a t R a l p h R u d o l p h made o n e o f h i s s e m i n a l c o n t r i butions t o inorganic chemistry. I n d e p e n d e n t l y h e ( 1 3 ) a n d Wade (14) a r r i v e d a t a method o f c o u n t i n g s k e l e t a l e l e c t r o n s w h i c h p r o v i d e d m a j o r new i n s i g h t s i n t o t h e s y s t e m a t i c s o f m a i n - g r o u p a n d t r a n s i t i o n metal c l u s t e r chemistry. 2

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n

Computational Procedures A l l c o m p u t a t i o n s w e r e c a r r i e d o u t u s i n g t h e MNDO method ( 1 2 ) and p u b l i s h e d p a r a m e t e r s ( 1 5 ) . For the c y c l i c structures, t r a n s i t s o f a p e r p e n d i c u l a r main-group moiety a c r o s s t h e v a r i o u s r i n g s g e n e r a t e η s t r u c t u r e s ( n = l - 6 ) a s shown b e l o w . η

η

1

This approach has been d i s c u s s e d p r e v i o u s l y f o r t h e c y c l o p e n t a d i e n y l r i n g and has been r e f e r r e d t o as a h a p t o t r o p i c s e a r c h (11,6). The g e o m e t r y d e f i n i t i o n s w e r e a s f o l l o w s : Perhapto S t r u c t u r e s . I n a l l s t r u c t u r e s , t h e c a r b o n atoms o f t h e ( C H ) r i n g (n=3-6) w e r e c o n s t r a i n e d a s a r e g u l a r p o l y g o n , b u t i n e a c h c a l c u l a t i o n t h e C-C bond d i s t a n c e s w e r e r e l a x e d . To e n s u r e a p e r h a p t o f i n a l s t r u c t u r e , t h e p o s i t i o n o f t h e c e n t r a l atom, M, was m i n i m i z e d a l o n g t h e p r i n c i p a l a x i s o f t h e r i n g . The h y d r o g e n s w e r e h e l d symmetry - e q u i v a l e n t (_ι.£. a l l C-H bond l e n g t h s a n d a l l C-C-H bond a n g l e s e q u a l ) , b u t w e r e a l l o w e d t o b e n d o u t o f t h e plane o f t h e r i n g . n

Dihapto S t r u c t u r e s . F o r these c a l c u l a t i o n s , t h e r i n g carbon atoms w e r e f r o z e n i n t o t h e g e o m e t r i e s o b t a i n e d i n t h e p e r h a p t o calculations. A g a i n , s y m m e t r y - e q u i v a l e n t h y d r o g e n atoms w e r e c o n s t r a i n e d t o h a v e e q u a l C-H bond l e n t h s a n d C-C-H bond a n g l e s . However, no t o r s i o n a n g l e l i m i t a t i o n s w e r e i m p o s e d . The c e n t r a l atom was m a i n t a i n e d i n a d i h a p t o c o n f i g u r a t i o n b y r e l a x a t i o n o f i t s p o s i t i o n o n a l i n e p e r p e n d i c u l a r t o t h e r i n g p l a n e and w h i c h b i s e c t e d a C-C b o n d .


BAXTER

7.

113

Multihapto Bonding

ETA L .


Monohapto S t r u c t u r e s . As i n t h e c a s e o f t h e d i h a p t o s t r u c t u r e s , the geometries o f the r i n g carbons were c o n s t r a i n e d t o those emerging from the perhapto c a l c u l a t i o n s , and symmetry-equivalent h y d r o g e n s were f o r c e d t o m a i n t a i n e q u a l C-H bond l e n g t h s a n d C-C-H bond a n g l e s . M o n o h a p t i c i t y was i m p o s e d b y m i n i m i z i n g t h e p o s i t i o n o f t h e c e n t r a l atom a l o n g a l i n e p e r p e n d i c u l a r t o t h e r i n g p l a n e and p a s s i n g t h r o u g h a r i n g c a r b o n . S t r u c t u r e s w i t h MH M o i e t i e s . For perhapto s t r u c t u r e s t h e h y d r o g e n was c o n f i n e d t o t h e same l i n e as t h e c e n t r a l atom. The d i h a p t o a n d monohapto c a l c u l a t i o n s a l s o u s e d i n p u t s t r u c t u r e s w i t h t h e h y d r o g e n o n t h e same l i n e u s e d t o c o n s t r a i n t h e c e n t r a l atom, b u t h e r e t h e p o s i t i o n o f t h e h y d r o g e n atom was t o t a l l y r e l a x e d . S t r u c t u r e s w i t h MH2 M o i e t i e s . optimized basis. Qualitative

These were h a n d l e d o n a g e o m e t r y -

Considerations

Due t o t h e a v a i l a b i l i t y o f a p p r o p r i a t e o r g a n o m e t a l l i c r e a g e n t s , b y f a r t h e l a r g e s t number o f a n n u l e n e c o m p l e x e s o f t h e main-group elements i n v o l v e t h e c y c l o p e n t a d i e n y l group. L e t us s t a r t the d i s c u s s i o n , t h e r e f o r e , by c o n s i d e r i n g q u a l i t a t i v e l y t h e π-type c o o r d i n a t i o n o f a C5H5 r i n g t o a m a i n - g r o u p e l e m e n t , M. As shown i n F i g u r e l a , b o n d i n g i n t e r a c t i o n s i n symmetry a r e e x p e c t e d between the v a l e n c e s o r b i t a l o f M and t h e t o t a l l y s y m m e t r i c π-ΜΟ o f C 5 H 5 , a n d b e t w e e n t h e d e g e n e r a t e n p and n p AO's o f M a n d t h e e^ MO o f C 5 H 5 . The 2a\ MO r e s u l t s f r o m m i x i n g o f t h e a n t i b o n d i n g component o f t h e laχ MO a n d a b o n d i n g MO w h i c h r e s u l t s from i n t e r a c t i o n between the v a l e n c e p o r b i t a l and the a j r i n g MO. The r e l a t i v e e n e r g i e s o f t h e e j a n d 2a\ M 0 s a r e g o i n g t o depend o n e.g. t h e e n e r g i e s o f t h e v a l e n c e s a n d ρ o r b i t a l s o f M. Somewhat s i m i l a r d i a g r a m s can b e c o n s t r u c t e d f o r t h e i n t e r a c t i o n between a c y c l o p e n t a d i e n y l group and l i g a t e d main-group m o i e t i e s , MI^. T h a t f o r a 05Η ····ΜΗ i n t e r a c t i o n i s i l l u s t r a t e d in Figure l b . O b v i o u s l y , e i g h t e l e c t r o n s c a n b e accommodated i n e i t h e r t h e ( n - C H 5 ) M o r (n -C5H5)MH b o n d i n g scheme. However, t h e q u e s t i o n of whether a s i x - o r e i g h t - e l e c t r o n i n t e r s t i t i a l e l e c t r o n count i s more v a l i d w i l l depend o n (a) w h e t h e r t h e 2a\ MO i s o c c u p i e d , and (b) i f t h e 2 a i MO i s o c c u p i e d w h e t h e r i t i n v o l v e s s i g n i f i c a n t ring-M i n t e r a c t i o n . R e a l i z i n g t h a t t h e b a s i c p a t t e r n o f a and e l i g a n d π MO's p e r s i s t s t h r o u g h o u t t h e c a r b o c y c l i c r i n g s y s t e m s , C H (n=3-6) (16), i t i s c l e a r t h a t t h e i n t e r a c t i o n o f a n s,p b a s i s s e t o f a m a i n - g r o u p e l e m e n t w i t h C 3 H 3 , C 4 H 4 , and CeHe r i n g s s h o u l d p r o d u c e lai, lei, d 2 a i MO s i n a v e r y s i m i l a r f a s h i o n t o t h e c y c l o p e n t a d i e n y l s y s t e m s i l l u s t r a t e d i n F i g u r e 1. x

v

z

T

5

5

5

5

n

a

n

Five-Membered R i n g

n

1

Systems.

I n terms o f h a p t o t r o p i c

searches,



ηΡ

χ

y

np

z

X

ν

^

Λ

(a)

5

5

u

\ (Π5 -C „H )M

1

Λ

»

^

\

/

5

C ηH

f\ 5

a

i

"l

2

5

5

^

Ν

A

1

5

^

/

/

^

'

_

/

with a main group

(b)

5

„ MyiU (η -C H )MH / - . ^ Γ ,

Figure 1. Qualitative scheme for the pentahapto interaction ofC H ττ-orbitals element M (left) or an M-H σ-bond (right).

np

e


s

V i _ U M-H

n

σΜ-Η

χ

ηΡ , nP

y

( a

.

i>

,

m

Ζ Ο

Η W

^

η r

oo

*

115

Multihapto Bonding

BAXTER ET A L .

7.

both C 5 H 5 B and C5H5AI adopt η ground s t a t e geometries (Table I ) . Furthermore, the η preference p r e v a i l s f o r both molecules when a complete geometry o p t i m i z a t i o n i s c a r r i e d out. Only minimal d i s t o r t i o n of the r i n g s takes place d u r i n g the geometry o p t i m i z a tion. Both C 5 H 5 B and C H A 1 are unknown molecules; however, the h e a v i e r congeners C H I n and C H T 1 have been known f o r s e v e r a l years. Although C H I n and C H T1 are polymeric i n the s o l i d s t a t e (17), these molecules adopt η s t r u c t u r e s i n the vapor s t a t e (18). Although C H B and C H A 1 both adopt η geometries, i t i s i n t e r e s t i n g to note that the sequence o f MO s d i f f e r s i n the two molecules; i n C H B the HOMO i s o f e symmetry, w h i l e that o f the aluminum analog i s a . A NOCOR MO c a l c u l a t i o n (19) on C H T 1 i n d i c a t e s that the HOMO i s of a i symmetry; however, U V PES s p e c t r a l data ( 2 0 ) and Χα scattered-wave c a l c u l a t i o n s ( 2 1 ) f o r C s H s I n and C 5 H 5 T I suggest that the HOMO i s o f e symmetry. We now turn to some charged systems. The anion [ C s H s B e ] " i s i s o e l e c t r o n i c w i t h C5H5B and, l i k e the boron compound, e x h i b i t s a preference f o r the η geometry. T h i s p r e f e r e n c e p e r s i s t s when the geometry i s completely optimized. The c a l c u l a t i o n s on [ C s H s S i ] * were undertaken because the h e a v i e r congeneric c a t i o n f M e s C s S n ] * i s known and has been found t o e x h i b i t a pentahapto s t r u c t u r e on the b a s i s o f X-ray c r y s t a l l o g r a p h y ( 1 0 ) . The MNDO h a p t o t r o p i c search i n d i c a t e s a minimum at η ; moreover, the pentahapto s t r u c t u r e p e r s i s t s w i t h only minor changes o f energy when the geometry i s optimized. The [ C s H s S i ] " * " c a t i o n has a l s o been i n v e s t i g a t e d by ab i n i t i o methods ( 3 c ) . The c a l c u l a t i o n s on [CsHsBH]"*" were undertaken because boron c a t i o n s o f the type [ M e s C s B X ] * (X=C1, Br, I ) are known ( 2 2 ) , and s p e c t r o s c o p i c evidence i n d i c a t e s that the BX* moiety i s pentahapto-bonded t o the MesCsring. Moreover, C s H s B e H , which i s i s o e l e c t r o n i c with [ C 5 H 5 B H ] + has been shown t o possess a n η geometry (23). Our MNDO c a l c u l a t i o n s o n [ C H B H ] + i m p l y t h a t t h e η and η geometries are very c l o s e i n energy. P r e v i o u s l y , i t has been suggested (24) that the a d d i t i o n o f boron Lewis Acids t o C s H s I n causes a change from η t o η attachment. 5

5

5

5

5

5

b

5

5

5

5

5

5

5

5

5

5

5


1

5

5

x

5

5

5

2

5

5

5

5

1

Six o r Eight I n t e r s t i t i a l

Electrons?

For the systems considered i n Table I , a l l e i g h t e l e c t r o n s would be counted a c c o r d i n g t o the Minkin and Minyaev model ( 2 ) . In the model o f Schleyer e t a l . , (3) a main-group element lone p a i r o f C 5 H 5 B , C 5 H 5 A I , [ C H B e ] " , and [ C 5 H S i ] and the B-H σ-bond of [C5H5BH]"*" would be excluded from the count on the b a s i s that they are not i n t e r s t i t i a l e l e c t r o n s . Χα-SW c a l c u l a t i o n s on e.g. ( n - C H 5 ) I n and ( n - C H 5 ) B e X support the views o f Schleyer et a l . (3a). Thus, the 5ai MO o f ( n - C s H 5 ) I n , which i s predominantly lone p a i r c h a r a c t e r , and the 4 a i MO o f (n -CsH )BeX, which i s the Be-X σ-bond, f e a t u r e only minor c o n t r i b u t i o n s from the C5H5 r i n g . I t should a l s o be noted that a s i x - e l e c t r o n r u l e a f f o r d s conformity w i t h the e l e c t r o n counting procedures o f Rudolph (13) +

5

5

5

5

5

5

5

5

5

b



RINGS,

CLUSTERS,

A N D POLYMERS

Heats o f Formation ( k c a l / m o l ) , R e l a t i v e Energies ( k c a l / m o l ) , a n d η G e o m e t r i e s (Â) f o r C5H5 Compounds. 5

HAPTICITY

AH

r

(RELATIVE ENERGY

η

5

GEOMETRY

112. 21 112. 83 103. 92 103. 90

(8.29) (8.91) (0.00)

B-•C = 1.904 C--C = 1.446 C-•H = 1.081

n n n optimized

76.59 76.11 70.98 70.97

(5.61) (5.13) (0.00)

Al- •C = 2.215 C--C = 1.442 C--H = 1.082

1

75.53 75.01 68. 84 68.84

(6.69) (6.17) (0.00)

Be--C = 2.188 C--C = 1.439 C-•H = 1.083

n n n optimized

213.02 205. 05 189. 89 189. 89

(23.13) (15.16) (0.00)

S i - •C = 2.089 C--C 1.453 C--H = 1.086

1

277. 97 268. 18 269. 24 269. 23

(9.79) (0.00) (1.06)

1

n n n optimized 2

5

1

2

5

n n n optimized 2

5

1

2

5

n n n optimized 2

5

1.784 B--C C--C = 1.471 C--H = 1.086 B--H = 1.161


7.

BAXTER ET A L .

Multihapto

117

Bonding

and Wade (14). According t o these r u l e s , a l l the compounds i n Table I are p r e d i c t e d t o adopt nido s t r u c t u r e s s i n c e each possesses n+2 s k e l e t a l e l e c t r o n p a i r s . Each CH group c o n t r i b u t e s three s k e l e t a l e l e c t r o n s , hence only one valence e l e c t r o n i s r e q u i r e d from B, A l , Be", Si+, or BH"" to achieve a t o t a l o f s i x electrons. 1


Consequences o f Increasing Main-Group Fragment

the Number of Valence E l e c t r o n s on the

A l l the systems considered i n Table I feature a main-group fragment e l e c t r o n count o f three, only one e l e c t r o n o f which i s involved i n i n t e r s t i t i a l bonding. We now explore the consequences of i n c r e a s i n g the t o t a l e l e c t r o n count o f the main-group fragment to f i v e e l e c t r o n s . Two examples o f t h i s e l e c t r o n count are represented by C5H5MH2 (M=B, A l ) . For both molecules the minimum energy geometry i s η and the M««««C(2) and M««-«C(5) distances 1

Ε = Β C ( 1 )

Ε = Al

C(2) >

C(3)

C(4)

B-C(l) C(l)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(l)-C(5)

1.55 1.52 1.36 1.47 1.36 1.53

Â Â Â Â Â Â

Al-C(l) C(l)-C(2) C(2)-C(3) C(3)-C(4) C(4)-C(5) C(l)-C(5)

1.84 1.51 1.37 1.47 1.37 1.52

Â Â Â Â Â Â

exceed the sum of covalent r a d i i f o r Β and C (1.57 Â) o r A l and C (-2.00 Â ) . Previous ab i n i t i o work (25) had i n d i c a t e d a minimum at η ; however the b a r r i e r s between η , η , and η s t r u c t u r e s were found t o be small. An EHMO i n v e s t i g a t i o n (11) of the system [C5H5]"«··[CH2l a l s o i n d i c a t e d an η minimum but no minimum was found a t the η geometry. The experimental data f o r a number o f Group IIIA compounds of the type (C Rs)MXY (R=H, Me; X, Y=alkyl, C 5 H 5 , CI) have been assembled i n Table I I . C o l l e c t i v e l y , these data i n d i c a t e that the energies o f η , n , and η geometries are r a t h e r c l o s e . S i m i l a r conclusions have emerged from MNDO c a l c u l a t i o n s (35) on phosphenium ions o f the type [(MesCs)(R)P] , namely ( i ) that the g l o b a l minimum i s η , ( i i ) η and η s t r u c tures do not correspond to minima, and ( i i i ) the b a r r i e r to circumannular migration o f the RP moiety i n the η s t r u c t u r e s ( v i a an η intermediate) i s very small (


X

=

X

2 +

2 +

6

6

6

6

+

2

b

6

6

6

Acknowled gment The authors are g r a t e f u l to the Petroleum Research Fund f o r generous f i n a n c i a l support.

Literature Cited 1. For reviews, see (a) Mingos, D.M.P. Adv. Organomet. Chem. 1977, 15, 1; (b) Haaland, A. Acc. Chem. Res. 1979, 12, 415. 2. Minkin, V. I.; Minyaev, R. M. Zh. Org. Khim. 1979, 15, 225, 1569. 3. (a) Jemmis, E. D.; Schleyer, P. v. R. J. Am. Chem. Soc. 1982, 104, 4781. For related papers, see (b) Collins, J. B.; Schleyer, P. v. R. Inorg. Chem. 1977, 16, 152 (c) Krogh -Jespersen, K.; Chandrasekhar, J.; Schleyer, P. v. R. J. Org. Chem. 1980, 45, 1608. 4. Interstitial electrons have been defined (3b) as electrons which bind π-bonding ligands to a central atom. 5. (a) Janoschek, R.; Diercksen, G.; Preuss, H. Int. Quantum Chem. Symp. 1967, 1, 205 (b) Alexandratos, S.; Streitwieser, Α., Jr.; Schaefer, H. F., III J. Am. Chem. Soc. 1976, 98, 7959. 6. Jemmis, E. D.; Alexandratos, S.; Schleyer, P. v. R.; Streit wieser, A. Jr.; Schaefer, H. F., III J. Am. Chem. Soc. 1978, 100, 5695.



122

RINGS, CLUSTERS,

A N D POLYMERS

7. (a) Dewar, M. J. S.; Rzepa, H. S. J. Am. Chem. Soc. 1978, 100, 777 (b) Dewar, M. J. S.; Rzepa, H. S. Inorg. Chem. 1979, 18, 602. 8. Bews, J. R.; Glidewell, C. J. Organomet. Chem. 1981, 219, 279. See also, Glidewell, C. J. Organomet. Chem. 1981, 217, 273. 9. Marynick, D. S. J. Am. Chem. Soc. 1981, 103, 1328. 10. Jutzi, P.; Kohl, F.; Hofmann, P.; Krüger, C.; Tsay, Y.-H. Chem. Ber. 1980, 113, 757. 11. Anh, N. T.; Elian, M.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 110. 12. Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4899. For a discussion of the validity of the MNDO method, see Dewar, M. J. S.; McKee, M. L. Inorg. Chem. 1978, 17, 1075. 13. Rudolph, R. W. Acc. Chem. Res. 1976, 9, 446. 14. (a) Wade, K. J. Chem. Soc. Chem. Commun. 1971, 792 (b) Wade, K. Adv. Inorg. Chem. and Radiochem. 1976, 18, 1. 15. (a) Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4907 (b) Dewar, M. J. S.; McKee, M. L. ibid. 1977, 99, 5231 (c) Dewar, M. J. S.; Rzepa, H. S. J. Am. Chem. Soc. 1978, 100, 58 (d) Davis, L. P.; Guidry, R. M.; Williams, J. R.; Dewar, M. J. S.; Rzepa, H. S. Journal of Computational Chemistry 1981, 2, 433. 16. Cotton, F. A. "Chemical Applications of Group Theory" 2nd. Ed. Wiley-Interscience 1971. 17. Frasson, E.; Menegus, F.; Panattoni, C. Nature 1963, 199, 1087, 18. (a) Shibata, S.; Bartell, L. S.; Gavin, R. Μ., Jr. J. Chem. Phys. 1964, 41, 717 (b) Tyler, J. K.; Cox, A. P.; Sheridan, J. Nature 1959, 183, 1182. 19. Ewig, C. S.; Osman, R.; Van Wazer, J. R. J. Am. Chem. Soc. 1978, 100, 5017. 20. (a) Evans, S., D. Phil. Thesis Oxford University, 1972 (b) Egdell, R. G.; Fragala, I.; Orchard, A. F. J. Electron Spectrosc. and Relat. Phenom. 1978,14, 467 (c) Cradock, S. Duncan, W. J. Chem. Soc. Faraday Trans. 2 1978, 74, 194. 21. Cowley, A. H.; Lattman, M. To be published. 22. Jutzi, P.; Seufert, A. Angew. Chem. Int. Ed. Engl. 1977, 16, 330. 23. Bartke, T.; Bjørseth, Α.; Haaland, Α.; Marstokk, Κ. M.; Møllendal, H. J. Organomet. Chem. 1975, 85, 271. 24. Contreras, J. G.; Tuck, D. G. Inorg. Chem. 1973, 12, 2596. 25. Gropen, O.; Haaland, A. J. Organomet. Chem. 1975, 92, 157. 26. Grundke, H.; Paetzold, P. I. Chem. Ber. 1971, 104, 1136. 27. Drew, D. Α.; Haaland, A. Acta Chem. Scand. 1973, 27, 3735. 28. Stadelhofer, J . ; Weidlein, J . ; Fischer, P.; Haaland, A. J. Organomet. Chem. 1976, 116, 55. 29. Mertz, K.; Zettler, F.; Hausen, H. D.; Weidlein, J. J. Organomet. Chem. 1976, 122, 159. 30. Teclé, B.; Corfield, P. W. R.; Oliver, J. P. Inorg. Chem. 1982, 21, 458.



7.

BAXTER ET A L .

Multihapto Bonding

123

31. Schonberg, P. R.; Paine, R. T.; Campana, C. J . Am. Chem. Soc. 1979, 101, 7726. 32. Schonberg, P. R.; Paine, R. T.; Campana, C. F.; Duesler, Ε. N. Organometallics 1982, 1, 799. 33. Einstein, F. W. B.; Gilbert, M. M.; Tuck, D. G. Inorg. Chem. 1972, 11, 2832. 34. Jutzi, P.; Kohl, F.; Krüger, C.; Wolmershäuser, G.; Hofmann, P.; Stauffert, P. Angew. Chem. Int. Ed. Engl. 1982, 21, 70. 35. (a) Baxter, S. G.; Cowley, A. H.; Mehrotra, S. K. J. Am. Chem. Soc. 1981, 103, 5572 (b) Cowley, A. H.; Mehrotra, S. K. J. Am. Chem. Soc. 1983, 105, 2074. 36. See, for example, (a) Soluki, B.; Rosmus, P.; Bock, H.; Maier, G. Angew. Chem. Int. Ed. Engl. 1980, 19, 51 (b) Maier, G.; Mihm, G.; Reisenauer, H. P. Angew. Chem. Int. Ed. Engl. 1980, 19, 52. 37. For a review, see Ashe, A. J., III Acc. Chem. Res. 1978, 11, 153. 38. Cuthbertson, A. F.; Glidewell, C. J. Organomet. Chem. 1981, 221, 19. 39. Cowley, A. H.; Ebsworth, Ε. Α. V.; Mehrotra, S. K.; Rankin, D. W. H.; Walkinshaw, M. D. J. Chem. Soc. Chem. Commun. 1982, 1099. 40. Davison, Α.; Rakita, P. E. Inorg. Chem. 1970, 9, 289. 41. (a) Rossi, A. R.; Hoffmann, R. Inorg. Chem. 1975, 14, 365 (b) Elian, M.; Maynard, M. L.; Chen, D.; Mingos, D. M. P.; Hoffmann, R. Inorg. Chem. 1976, 15, 1148. 42. Maier, G.; Pfriem, S.; Schaefer, U.; Matusch, R. Angew. Chem. Int. Ed. Engl. 1978, 17, 520. 43. (a) Stohrer, W. D.; Hoffmann, R. J. Am. Chem. Soc. 1972, 94, 1661 (b) Kollmar, H.; Smith, H. O.; Schleyer, P. v. R., J. Am. Chem. Soc. 1973, 95, 5834 (c) Dewar, M. J. S.; Haddon, R. C. J. Am. Chem. Soc. 1973, 95, 5836 (d) Hehre, W. J.; Schleyer, P. v. R. J. Am. Chem. Soc. 1973, 95, 5837. 44. (a) Masamune, S.; Sakai, M.; Ona, H.; Jones, A. J. J. Am. Chem. Soc. 1972, 94, 8956 (b) Masamune, S.; Sakai, M.; Kemp -Jones, Α. V.; Ona, H.; Venot, Α.; Nakashima, T. Angew. Chem. Int. Ed. Engl. 1973, 12, 769. 45. (a) Luth, H.; Amma, Ε. L. J. Am. Chem. Soc. 1969, 91, 7515 (b) Weininger, M. S.; Rodesiler, P. E.; Gash, A. G.; Amma, E. L. J. Am. Chem. Soc. 1972, 94, 2135 (c) Rodesiler, P. F.; Auel, Th.; Amma, E. L. J. Am. Chem. Soc. 1975, 97, 7405. RECEIVED June 16, 1983


Rings, Clusters, and Polymers of the Main Group Elements - American

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