Experimental Organometallic Chemistry - American Chemical Society

Chapter 1

Development of Techniques in Organometallic Chemistry D . F . Shriver

Downloaded by PRINCETON UNIV on July 8, 2013 | http://pubs.acs.org Publication Date: November 24, 1987 | doi: 10.1021/bk-1987-0357.ch001

Department of Chemistry, Northwestern University, Evanston, IL 60201

As in all physical sciences, advances in organometallic chemistry have been strongly coupled to advances in techniques. The field is flourishing in large part because of the development of versatile, user-friendly NMR and IR spectrometers and X-ray diffractometers. Similarly, steady improvements in the techniques for synthesizing and handling organometallics have greatly increased the efficiency of our research. Many organometallics are air sensitive, so the development of techniques which permit synthesis and characterization in a vacuum or inert atmosphere are central to the f i e l d . Even though the manipulation of a i r - s e n s i t i v e compounds has been successfully practiced for a long time, the techniques have undergone constant improvement. For convenience these may be c l a s s i f i e d as vacuum line, bench-top inert atmosphere, and glove box techniques but as shown in this book combinations of them are common. One of the most elegant and rigorous methods for handling volatile air-sensitive materials is the chemical vacuum line, which was developed in the early 1900's by Alfred Stock for the synthesis of nonmetal hydrides, including those of boron and s i l i c o n . When Stock began these investigations around 1902 at Berlin, the rotary oil-sealed mechanical vacuum pump had been recently developed, but the assembly of the rest of the apparatus was not as simple. For example, the complex series of traps and valves, which Stock eventually devised, Figure 1, had to be constructed on the spot from soft glass, material which is highly subject to breakage by thermal shock. Stock's designs for chemical vacuum line apparatus were widely disseminated. A leading American inorganic chemist, Professor L . M. Dennis at Cornell University became familiar with Stock's apparatus in the course of trips to Europe and he utilized chemical vacuum l i n e s to investigate the hydrides of germanium i n the late 1920's(l). About this same time chemical vacuum line techniques were

0097-6156/87/0357-0001 $06.00/0 © 1987 American Chemical Society

In Experimental Organometallic Chemistry; Wayda, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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EXPERIMENTAL ORGANOMETALLIC CHEMISTRY

i n t r o d u c e d t o t h e U.S.A. f o r t h e i n v e s t i g a t i o n o f boron h y d r i d e s by Anton Burg, who worked a t t h e U n i v e r s i t y o f C h i c a g o , f i r s t as a s t u d e n t w i t h S c h l e s i n g e r and l a t e r a s t a f f member. Burg a c q u i r e d t h e s e t e c h n i q u e s by c a r e f u l l y r e a d i n g S t o c k ' s papers and adding innovations of h i s own(l). S e v e r a l other former S c h l e s i n g e r s t u d e n t s , such as H. C. Brown, R i l e y S c h a f f e r , and Grant U r r y , have a l s o made major c o n t r i b u t i o n s t o t h e development o f vacuum-line and inert-atmosphere apparatus. In a d d i t i o n t o a s o u r c e o f vacuum, a c h e m i c a l vacuum l i n e may i n c l u d e a s e r i e s o f U - t r a p s t o s e p a r a t e compounds o f d i f f e r e n t v o l a t i l i t y , r e a c t i o n v e s s e l s o f v a r i o u s t y p e s , and p r o v i s i o n f o r t h e s t o r a g e o f v o l a t i l e s o l v e n t s and gases. Vacuum systems o f t h i s t y p e have been e x t e n s i v e l y used t o prepare and c h a r a c t e r i z e l o w m o l e c u l a r weight o r g a n o m e t a l l i c s . Some o f t h e major problems i n vacuum l i n e work have been t h e e r o s i o n o f s t o p c o c k grease by n o n p o l a r s o l v e n t s and t h e m e c h a n i c a l i n f l e x i b i l i t y o f t h e a p p a r a t u s . In r e c e n t y e a r s these problems have been reduced by t h e use o f O-ring j o i n t s , v a l v e s w i t h T e f l o n stems and g l a s s b o d i e s , a n d f l e x i b l e s t a i n l e s s s t e e l t u b i n g . The c h a p t e r by Andrea Wayda i n t h i s volume p r e s e n t s an e x c e l l e n t example o f how these components c a n be u t i l i z e d i n an apparatus w i t h p r o v i s i o n f o r both h i g h vacuum and inert-atmosphere manipulations. In c o n t r a s t w i t h high-vacuum l i n e s , i n e r t - a t m o s p h e r e apparatus i s more o f t e n used t o handle l i q u i d s than gases o r v a p o r s . As w i t h the c h e m i c a l vacuum l i n e , i n e r t - a t m o s p h e r e bench-top t e c h n i q u e s were o r i g i n a l l y developed i n Europe, b u t t h e r e i s no s i n g l e o r i g i n a t o r f o r t h i s d i v e r s e s e t o f apparatus and t e c h n i q u e s . The r e a c t i o n tube w i t h a s i d e arm f o r t h e i n t r o d u c t i o n o f i n e r t g a s , F i g u r e 2 a , was d e s c r i b e d by W a l t e r Schlenk i n 1913, and i s s t i l l i n use today b u t i t has been t r a n s f o r m e d t o a more c o n v e n i e n t form by modern O - r i n g j o i n t s and T e f l o n - g l a s s v a l v e s , F i g u r e 2b. In t h e l a t e I960's P r o f e s s o r James B u r l i c h and I , as c o n s u l t a n t s to Ace G l a s s Co. and Kontes G l a s s Co. r e s p e c t i v e l y , a s s i s t e d w i t h t h e commercial i n t r o d u c t i o n o f complete l i n e s o f i n e r t - a t m o s p h e r e g l a s s ware. From these companies and, more r e c e n t l y , A l d r i c h Chemical Co., i t i s p o s s i b l e t o o r d e r a i n e r t - a t m o s p h e r e setup a l l t h e way from an i n e r t gas p u r i f i e r t o f i l t e r s and Schlenk f l a s k s . A t h i r d major t e c h n o l o g y , t h e i n e r t - a t m o s p h e r e g l o v e - b o x was developed i n i t s modern form d u r i n g World War 2 i n c o n n e c t i o n w i t h f i s s i o n weapons programs. Glove boxes a r e e s p e c i a l l y s u i t e d f o r h a n d l i n g s o l i d s , but they a l s o a r e w i d e l y used i n t h e U.S.A. f o r s o l u t i o n c h e m i s t r y . E x c e l l e n t i n e r t - a t m o s p h e r e g l o v e boxes have been c o m m e r c i a l l y a v a i l a b l e f o r many y e a r s . One o f t h e reasons t h a t i n e r t - a t m o s p h e r e t e c h n i q u e s c o n t i n u e t o e v o l v e i s t h e a v a i l a b i l i t y o f new m a t e r i a l s . The i n t r o d u c t i o n o f b o r o s i l i c a t e g l a s s i n t h e 1920*s l e d t o g r e a t improvements i n vacuum l i n e s and a l l types o f l a b o r a t o r y g l a s s w a r e . Modern O - r i n g j o i n t s would be v i r t u a l l y u s e l e s s i f i t were n o t f o r s y n t h e t i c r u b b e r 0 - r i n g s , t h a t a r e r e s i s t a n t t o a r e a s o n a b l e range o f s o l v e n t s . S i m i l a r l y , b u t y l r u b b e r , which i s d u r a b l e and has a r e l a t i v e l y low p e r m e a b i l i t y t o a i r , i s used as a g l o v e m a t e r i a l f o r i n e r t - a t m o s p h e r e boxes. T e f l o n has made t h e c o n s t r u c t i o n o f g r e a s e l e s s v a l v e s p o s s i b l e , and i n many a p p l i c a t i o n s these have r e p l a c e d greased s t o p c o c k s and S t o c k ' s e x p e n s i v e and cumbersome mercury f l o a t v a l v e s . Some new



1. SHRIVER

Techniques in Organometallic Chemistry

F i g u r e 1. An e a r l y , c a . 1913, d e s i g n f o r S t o c k ' s vacuum l i n e . The items c o n t a i n i n g a p a i r o f d a r k l y shaded f l o a t s a r e mercury f l o a t v a l v e s . The mercury r e s e r v o i r below each o f these has been omitted. The sources o f vacuum and i n e r t atmosphere a l s o have been o m i t t e d . (Reproduced w i t h p e r m i s s i o n from Ref. 7. C o p y r i g h t 1933 C o r n e l l U n i v e r s i t y Press.)

(a)

(b)

F i g u r e 2. ( a ) The o r i g i n a l d e s i g n f o r a Schlenk t u b e , ( b ) A modern Schlenk tube w i t h g r e a s e - f r e e j o i n t and v a l v e and p e a r shaped chamber t o f a c i l i t a t e s t i r r i n g and s o l v e n t removal under vacuum.


Ζ


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EXPERIMENTAL ORGANOMETALLIC CHEMISTRY

m a t e r i a l s w h i c h s h o u l d l e a d t o u s e f u l new equipment d e s i g n s a r e c e r a m i c s t h a t can be shaped by m a c h i n i n g , p l a s t i c s w i t h h i g h c h e m i c a l r e s i s t a n c e and h i g h s e r v i c e t e m p e r a t u r e s , and e l a s t o m e r s t h a t a r e r e s i s t a n t t o a wide range o f s o l v e n t s . S e v e r a l r e v i e w s d e s c r i b e t h e equipment and t e c h n i q u e s f o r t h e m a n i p u l a t i o n o f a i r - s e n s i t i v e compounds.(2-6) The p r e s e n t volume d i f f e r s from these by t h e p r e s e n t a t i o n o f i n d i v i d u a l i s t i c accounts o f equipment and t e c h n i q u e s . Both t h e b e g i n n e r and t h e e x p e r t s h o u l d f i n d many u s e f u l i d e a s h e r e . Bear i n mind, however, t h a t the manipul a t i o n o f a i r - s e n s i t i v e compounds i s l e s s f l e x i b l e than open beaker c h e m i s t r y and t h e r e f o r e i t i s n e c e s s a r y t o pay c a r e f u l a t t e n t i o n t o the i n t e g r a t i o n o f a p p a r a t u s so t h a t a c o m p a t i b l e s e t o f o p e r a t i o n s can be performed. T h i s c a n be a c h i e v e d by p l a n n i n g each experiment i n detail. Sometimes, s k e t c h e s o f t h e apparatus a t each s t e p i n a s y n t h e s i s s e r v e t o c a t c h p o t e n t i a l problems. The e x p e r t i n h a n d l i n g a i r - s e n s i t i v e systems s h o u l d be a b l e t o d e s i g n new a p p a r a t u s , and c o n s t r u c t s m a l l items which might o t h e r w i s e t a k e days t o r u n through a g l a s s shop. V e r s a t i l i t y i s a g r e a t virtue i n this field. F o r e x a m p l e , some c h e m i s t s c o n s i d e r i t i m p o s s i b l e t o s t a r t s e r i o u s r e s e a r c h on a i r - s e n s i t i v e compounds b e f o r e a c o s t l y d r y box system has been a c q u i r e d . T h i s view cont r a s t s w i t h t h a t o f a l e a d i n g European l a b o r a t o r y , which I v i s i t e d r e c e n t l y . A d r y box t h a t hadn't been used i n s e v e r a l y e a r s s a t i n a c o r n e r , even though v e r y a i r - s e n s i t i v e compounds were b e i n g s y n t h e s i z e d and c h a r a c t e r i z e d i n t h a t l a b o r a t o r y . To emphasize the q u a l i t y of t h e i r i n e r t - a t m o s p h e r e t e c h n i q u e s , my h o s t d i s p l a y e d a s e a l e d v i a l c o n t a i n i n g a b e a u t i f u l c r y s t a l l i n e compound which h i s co-worker had prepared. He then c r a c k e d t h e v i a l open t o demonstrate t h a t t h e compound b u r s t s i n t o flames when exposed t o a i r . C l e a r l y , t h e w e l l d e s i g n e d i n e r t - a t m o s p h e r e g l a s s w a r e , and good l a b o r a t o r y t e c h n i q u e s p r a c t i c e d i n t h a t l a b o r a t o r y a r e p e r f e c t l y s a t i s f a c t o r y and p r o b a b l y more e f f i c i e n t than t h e use o f g l o v e - b o x e s . The s p l e n d i d c o l l e c t i o n o f t e c h n i q u e s p r e s e n t e d i n t h i s volume should provide a stimulus to f u r t h e r i n n o v a t i o n s .

Literature Cited 1. I appreciate correspondence with Professors E. G. Rochow and A. B. Burg who provided information about developments at Cornell University and the University of Chicago. 2. Gysling, H. G.; Thunberg, A. L. In Physical Methods of Chemistry, Vol 1: Components of Scientific Instruments and Applications of Computers to Chemistry, Rossiter, B. W., Ed.; John Wiley Inc.: New York, 1986; p 373. 3. Shriver, D. F . ; Drezdzon, M. A. The Manipulation of A i r Sensitive Compounds, 2nd edn, John Wiley Inc.: New York, 1986. 4. Eisch, J. J.; King, R. B . , Eds.; Organometallic Syntheses, Academic: New York, Vol. 1 by R. B. King, 1965; V o l . 2 by J.J. Eisch, 1982. 5. Brown, H. C.; Kramer, G. W.; Levy, A. B . ; Midland, M. M. Organic Synthesis via Boranes, Wiley-Interscience Inc.: 1973, Chapter 9; p. 119.


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Techniques in Organometallic Chemistry

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6. Herzog, S.; Dehnert, J.; Luhder, K. In In Technique of Inorganic Chemistry, Jonassen, H. B . ; Weissberger, Α., Eds.; WileyInterscience Inc.: New York, 1968; p. 119. 7. Stock, A. The Hydrides of Boron and Silicon; Cornell university Press: Ithaca, NY, 1933.


RECEIVED September 1, 1987


Experimental Organometallic Chemistry - American Chemical Society

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