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Nuclear magnetic resonance investigations of organosilicon compounds Hunter, Brian K. 1966

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NUCLEAR MAGNETIC RESONANCE  INVESTIGATIONS  OF ORGANOSILICON COMPOUNDS  by  BRIAN K. HUNTER B.Sc.(hons.), U n i v e r s i t y o f B r i t i s h Columbia, 196^  A THESIS SUBMITTED I N P A R T I A L FULFILMENT  OF  THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department of Chemistry  We a c c e p t t h i s t h e s i s a s c o n f o r m i n g required  standard  THE U N I V E R S I T Y OF B R I T I S H COLUMBIA S e p t e m b e r , 1966  to the  In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e  requirements  for an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study,  I f u r t h e r agree t h a t p e r m i s s i o n - f o r e x t e n s i v e c o p y i n g o f t h i s  t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e Head o f my Department o r by h i s r e p r e s e n t a t i v e s .  Tt i s understood  or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l w i t h o u t my w r i t t e n p e r m i s s i o n .  Department o f  v.  \iLiAAJL*i'f\r\j  The U n i v e r s i t y o f " B r i t i s h Columbia Vancouver 8, Canada  that  copying  g a i n s h a l l n o t be a l l o w e d  i  ABSTRACT The  n u c l e a r m a g n e t i c r e s o n a n c e s p e c t r a o f a number o f  o r g a n o s i l i e o n compounds a r e e x a m i n e d . 29  The  7.95  Mcs.  s p e c t r a a r e o b t a i n e d f o r t h e s e compounds and  shifts  are considered  trends observed opposing  in detail.  the  chemical  I t i s proposed that  the  are the r e s u l t of a c o m p e t i t i o n between  e f f e c t s ; a paramagnetic s h i f t  i n f l u e n c e d by  i n t h e e f f e c t i v e n u c l e a r c h a r g e on s i l i c o n and shift  silicon-  i n f l u e n c e d by  (p—»d)TT  bonding.  The  a  changes  diamagnetic  concept  of  c o m p e t i t i v e s h i f t mechanism r a t i o n a l i z e s t h e c h e m i c a l observed OEt,  f o r s e r i e s of the type  OAc,  C l , P and  C^H^)  M  e  s x  i^L _ r  x  two  (where:  X =  the  shifts OMe,  but does not e x p l a i n the s h i f t s  of  s i l i c o n h y d r i d e s . T h i s concept a l s o r a t i o n a l i z e s the trends 119 observed i n S n c h e m i c a l s h i f t s b u t , l o g i c a l l y , does not 1 7  apply to  J  C  must v a n i s h .  chemical  be  inadequate  molecules. methyl J  r  .„„  where t h e d - o r b i t a l c o n t r i b u t i o n  None o f t h e o b s e r v e d  w i t h the ^ S i chemical to  shifts  A new  g r o u p s on  shifts.  coupling constants  A v a i l a b l e t h e o r i e s are  to describe the coupling constants long range c o u p l i n g i s observed s i l i c o n a t t a c h e d t o o x y g e n and  o f a b o u t 0.35  c.p.s.  correlate found  i n these  between the  chlorine with  ii  TABLE OF CONTENTS Page 1  INTRODUCTION G e n e r a l T h e o r y o f N.M.R.  5  Chemical S h i f t Theory  9  Spin-Spin (p — * d ) T T  Coupling Bonding  Theory  12  i n O r g a n o s i l i e o n Compounds  1*+  N.M.R. o f O r g a n o s i l i e o n  Systems  16 20  EXPERIMENTAL N u c l e a r M a g n e t i c Resonance Measurements  20  Sample P r e p a r a t i o n  23  RESULTS  25  DISCUSSION  30 30  R e l a x a t i o n Times Accuracy o f Silicon-29  Chemical S h i f t Data  32  S i l i c o n - 2 9 Chemical S h i f t s  3*+  Coupling  *+5  Constants  BIBLIOGRAPHY  hQ  APPENDICES  52  S i l i c o n - 2 9 Chemical S h i f t s  52  Tln-119 Chemical S h i f t s  5^  Lead-207  55  Chemical S h i f t s  iii  L I S T OF TABLES Page  Table 1.  C a l c u l a t e d and Observed  S i - X a n d Sn-X Bond L e n g t h s  2.  N.M.R. a n d Bond L e n g t h D a t a f o r S i l L ^ F ^  3.  Signs of Coupling Constants i n Organosilicon  15  Compounds  17  Systems h. 5.  18  Preparation of Fluorosilanes -*C a n d  1  2  9  Si  2h  R e l a x a t i o n Times  25  6.  N.M.R. D a t a f o r M e S i ( 0 M e ) ^  x  25  7.  N.M.R. D a t a f o r M e ^ K O E t ) ^  26  8.  N.M.R. D a t a f o r M e S l ( 0 A c ) i _  9.  N.M.R. D a t a f o r Me S i C l ^ .  x  x  +  N.M.R. D a t a f o r Me S i F  11. 12.  N.M.R. D a t a f o r M e S i H ^ _ N.M.R. D a t a f o r ( 6 5)h,_  13.  Miscellaneous  lk.  Paramagnetic S h i f t s  x  M E  S I  X  2  _  27  10.  l f  26  x  28  x  28  x  C  H  2  7  x  ^ S i Chemical S h i f t s . and Percentage Observed  29 35  iv  LIST OF FIGURES Figure 1.  Page The L a b o r a t o r y Coordinate System f o r the N.M.R. Experiment  2. 3.  h,  (p-*d)Tf  Bonding O r b i t a l s i n ( S i H ^ N  F Chemical S h i f t s f o r R S i F _ Compounds x  1 3  C  and  2 9  Si  (a)  2 9  Si  lf  <x  18  Chemical S h i f t s i n 19  Compounds  Spectrum  of Me^SiH w i t h  (MeO)^Si as I n t e r n a l Standard (b)  2 9  Si  Spectrum  22  of Me^SiH with  (MeO)^Si as E x t e r n a l Standard 6.  9.  1  Measurement Of ( M e ^ S i ) 0 2  P l o t Of I n ( 1 + I / I ) v s . t f o r t  and 8.  22  Recorder Traces For A d i a b a t i c F a s t Passage T  7.  16  1 9  MeJM(OR)^ 5.  6  2 9  Si  2 9  Si  Q  C 31  Compounds  Spectrum  of C ^ S i h ^  S i Chemical S h i f t Of Series  2 9  1 3  23  33  Me^KOMe)^ 3 ^  Figure 10.  Page 2  9  Si  C h e m i c a l S h i f t o f Me  Difference i n  SiX vs.  Electronegativity  36  o f S i and X 11.  2  9  Si  Chemical S h i f t of  i n Terms o f ^<Tp 12. 13.  A <f  and  x  1 1 9  Sn  J  1 1 9  15.  1 3  Sn  C  (x  l +  38  y  l f - x  39  h2  x  Chemical S h i f t s  Chemical S h i f t s x  x  Chemical S h i f t s f o r  x  16.  x  Chemical S h i f t of M e S i C l  (n-Bu) SnCl __ [k.  Me Si(0Me)^_  of M e ^ n V i ^  o f CH^X  vs.  - x )  hh  c  High F i e l d  1 3  C  (a) M e S i ( 0 M e ) 2  h2  S a t e l l i t e s of 2  and  (b) Me^SKOMe)  h7  vi  ACKNOWLEDGEMENTS  I w i s h t o t h a n k D r . L. W. R e e v e s f o r h i s h e l p a n d encouragement d u r i n g t h e course o f t h i s A l s o , I would l i k e  investigation.  t o t h a n k A. L e e S m i t h o f t h e  D o w - C o r n i n g C o r p o r a t i o n who k i n d l y d o n a t e d a number o f compounds u s e d i n t h i s  work.  1  INTRODUCTION Nuclear Magnetic two decades,  Resonance (N.M.R.) has, i n the past  become one o f the most commonly a p p l i e d s p e c t r o s c o p i c  techniques used by chemists.  However, a t p r e s e n t , chemists use  o n l y f o u r n u c l e i on a r o u t i n e b a s i s ; Hydrogen-1, F l u o r i n e - 1 9 , Phosphorus-31, and B o r o n - 1 1 .  Of the 130 "non-routine" n u c l e i ,  o n l y one, Carbon-13? has r e c e i v e d any l a r g e amount o f a t t e n t i o n . S t u d i e s o f non-routine n u c l e i are' hampered by the low i n h e r e n t n u c l e a r s e n s i t i v i t i e s o f most o f these n u c l e i . 1 2 a b r i e f c o n s i d e r a t i o n o f the B l o c h equations  J  From  one may c a l c u l a t e  the r e l a t i v e N.M.R. s i g n a l s t r e n g t h f o r a g i v e n n u c l e u s . s e n s i t i v i t y i s u s u a l l y expressed r e l a t i v e t o p r o t o n s . c o n s i d e r the slow passage a b s o r p t i o n mode experiment  We s h a l l usually  19  1  used f o r r o u t i n e  H and  7  F N.M.R. s p e c t r a .  From the o r i g i n a l B l o c h treatment o f Magnetic the v o l t a g e induced i n the r e c e i v e r c o i l may be w r i t t e n ,  V= where:  This  Kwtf, X"  Resonance,  o  V - induced v o l t a g e which i s out o f phase w i t h the a p p l i e d r a d i o frequency f i e l d K = a constant which depends upon the geometry o f the apparatus  CO  =  angular frequency, i n r a d i a n s sec."* , 1  of  the a p p l i e d r a d i o frequency  H, = magnitude,  X-  frequency  field  i n gauss, o f the r a d i o  field  B l o c h magnetic  susceptibility  2  a  1  -  z  T .  W.X  7?  (M,  -  (2) where: = Larmor  e q u i l i b r i u m paramagnetic  T, T,  3T  secT  precession frequency i n radians suceptibility.  - l o n g i t u d i n a l or s p i n - l a t t i c e r e l a x a t i o n time i n seconds.  = transverse or s p i n - s p i n r e l a x a t i o n time in  seconds.  magnetogyric r a t i o  i n r a d i a n s gauss  -1  sec.  Therefore: To  V =  (3) T h i s v o l t a g e r e a c h e s a maximum f o r two w h i c h may  be r e a c h e d 1.  conditions  simultaneously;  At resonance, (4)  where: f-/^ = m a g n i t u d e in 2.  At beginning  of the a p p l i e d magnetic  gauss. of s a t u r a t i o n ,  field  -1  1  3 T h u s , f o r maximum s i g n a l ;  K y W, HO X>  W'O  T  4  *  2.  2.  (fa)  2.  4  (7) For non-viscous  so  liquids;  that,  F r o m t h e C u r i e Law:  -  A/  o  ) r  3kT ft  1  where:  A/ x  = number o f n u c l e i p e r c . c . = nuclear  spin  = n u c l e a r m a g n e t i c moment i n n u c l e a r magnetons  k  = Boltzmann's = 1.38 X 1 0  7  constant gm.cm. sec."* deg." 2  2  1  "J*" = a b s o l u t e t e m p e r a t u r e i n d e g r e e s  Kelvin  Thus;  V=  I  3 k T  +1  do)  F o r c o n s t a n t K, H , a n d T, D  F o r c o n s t a n t K , o J > a n d T, 0  (IX)  One  may c a l c u l a t e  the r e l a t i v e s i g n a l s t r e n g t h o f a  g i v e n n u c l e u s u s i n g t h e a b o v e e q u a t i o n s a n d known m a g n e t i c 29 moments a n d i s o t o p i c a b u n d a n c e s . F o r S i i n T e t r a m e t h y l s i l a n e y  the s e n s i t i v i t y a t constant magnetic for  1 3  C i n B e n z e n e i t i s 1.71+  V 10  _ 1 +  field  i s -#. 15* 10"-^ a n d  .  In s p i t e o f these l o ws e n s i t i v i t i e s , the nuclear magnetic  resonances  Three reviews o f  o f many n o n - r o u t i n e n u c l e i h a v e b e e n *+ ") 6  Carbon-13 N.M.R. h a v e a p p e a r e d .  observed.  Most o f  the work o n ^ C h a s i n v o l v e d the s t u d y o f c h e m i c a l s h i f t s i n 1  p a r t i c u l a r s e r i e s o f o r g a n i c molecules. F o r example, s u b s t i t u t e d 7 - 1 0 a r o m a t i c systems have r e c e i v e d c o n s i d e r a b l e a t t e n t i o n . ' C a r b o n y l compounds h a v e a l s o • b e e n e x a m i n e i n d e t a i l . ^ The 13 c a r b o n y l c a r b o n i s i d e a l y s u i t e d t o C N.M.R. i n v e s t i g a t i o n s i n t h a t i t u s u a l l y gives s i n g l e t resonances which are c h e m i c a l l y 13 s h i f t e d f r o m most o t h e r C r e s o n a n c e s . 13 Most o f the C work t o date h a s examined e l e c t r o n i c 13 e f f e c t s on s h i e l d i n g s i n r a t h e r c o m p l i c a t e d systems. However, 17 S p i e s e c k e a n d S c h n e i d e r ' h a v e e x a m i n e d a number o f CH^X a n d CH-jCH^X compounds f o r e f f e c t s o f e l e c t r o n e g a t i v i t y a n d m a g n e t i c 1 1 " } a n i s o t r o p y o f s u b s t i t u e n t s upon the H and C c h e m i c a l s h i f t s . 18 1 ~\ I n a d d i t i o n , Grant and P a u l have r e p o r t e d the -C chemical 1  1  1 1  1  J  J  J  J  >  s h i f t s f o r some 50 c a r b o n s i n a l k a n e s y s t e m s u s i n g a n i m p r o v e d 19 13 t e c h n i q u e . ' No a t t e m p t s h a v e b e e n made t o c o r r e l a t e C shifts w i t h the remainder o f group I V because o f the l i m i t e d d a t a J  available. O t h e r n u c l e i i n g r o u p I V h a v e b e e n e x a m i n e d a n d some chemical s h i f t s reported.  Silicon-29  resonances  have been examined  i cr o n  by L a u t e r b u r a n d c o - w o r k e r s ^ '  and a l i s t  of  29 7  S i chemical 21  s h i f t s h a s b e e n c o m p i l e d . ( S e e A p p e n d i x A.) observed  2  Si  9  Baker  s p e c t r a u s i n g t h e INDOR ( i n t e r n u c l e a r  has double  r e s o n a n c e ) method b u t h a s n o t r e p o r t e d a n y c h e m i c a l s h i f t s . Germanium-73 i s n o t l i k e l y shift  t o b e t o o u s e f u l f o r N.M.R. c h e m i c a l  i t s l a r g e s p i n (9/2)  s t u d i e s because  and l o w magnetogyric  r a t i o (2^ r a d i a n s gauss"" s e c . " f o r '-'Ge v s . 655 r a d i a n s g a u s s " -1 1 73 sec. f o r H) make o b s e r v a t i o n o f ' G e r e s o n a n c e s v e r y d i f f i c u l t . J  '  2  2  Tin-119 h a s b e e n o b s e r v e d b y L a u t e r b u r a n d B u r k e and c o - w o r k e r s . '  A table of  J  and b y Reeves  119  <y\ oh.  7  S n chemical s h i f t s  appears i n  a p p e n d i x B. Lead-207 h a s b e e n o b s e r v e d b y P i e t t e a n d Weaver 26 207 and b y R o c a r d and c o - w o r k e r s and a f e w 'Pb c h e m i c a l s h i f t s h a v e b e e n c o m p i l e d . ( S e e A p p e n d i x C.) The n u c l e a r m a g n e t i c r e s o n a n c e s o f many o t h e r n u c l e i y  27  have been o b s e r v e d , i n c l u d i n g : ' 2  37 i  H  9 3  C  «Co  Hb  127  «Cu  1 9 9  x  Hg  205  7 Al 3*<a 2  8 1  T1  Br  G e n e r a l T h e o r y Of N.M.R. The n u c l e a r m a g n e t i c r e s o n a n c e e x p e r i m e n t i s b e s t described ^' 2  f i g u r e 1.  2 9  b y c o n s i d e r i n g a c o o r d i n a t e s y s t e m a s shown i n  The s t a t i c m a g n e t i c f i e l d ,  z d i r e c t i o n and t h e o s c i l l a t i n g along the x d i r e c t i o n .  H , i s applied i n the Q  radio frequency f i e l d  The r a d i o f r e q u e n c y ( r . f . ) f i e l d i s  given by:  2H,C/0  =  i s applied  2 Hi (to* co-t)  (is)  Ho  X F i g u r e 1.  The l a b o r a t o r y c o o r d i n a t e system f o r the N.M.R. experiment.  The r . f . f i e l d may a l s o be w r i t t e n as the sum o f two v e c t o r s o f magnitude, ±  , r o t a t i n g i n the xy plane w i t h angular f r e q u e n c i e s  . We now c o n s i d e r a r o t a t i n g r e f e r e n c e frame, S', which  r o t a t e s about the l a b o r a t o r y z a x i s w i t h an angular + <JL>  .  One r . f . component i s now f i x e d along the x  the other r o t a t e s with an angular frequency of ignored.  1  -2<*>  frequency a x i s and and may be  The e f f e c t i v e magnetic f i e l d , H ., may be w r i t t e n : ff  (14) where;  1  i f we  write, =  - n  then,  (lb)  -  sL  where:  The a n g l e , © , between H  Q  and H  on whether one i s sweeping below resonance.  SUA©  =•  The angle  goes from 0 to TT  e f f  depending  the magnetic f i e l d from above or 0  may  cos  be c a l c u l a t e d  e  from:  =  In the r o t a t i n g r e f e r e n c e frame the m a g n e t i z a t i o n precesses about H" £ w i t h an angular v e l o c i t y , ef  li*0 0  at  e  resonance,  below resonance,  If H  Q  to H .  i s f a r above resonance, H- ff e  I f we now  ^  above resonance,  is practically  0  90°  = 90o >  90  parallel  sweep down through resonance, the m a g n e t i z a t i o n  8  w h i c h was e n d s up  p a r a l l e l to H ,  remains p a r a l l e l  Q  a n t i p a r a l l e l to H .  During  Q  a magnetization  i s induced  to  and  the passage of  i n the x'y  finally  resonance  plane which i n t u r n  !  induces  a v o l t a g e i n the r e c e i v e r c o i l which i s a l i g n e d along the y i B l o c h h a s shown t h a t t h i s v o l t a g e i s p r o p o r t i o n a l t o :  axis.  t  i  where:  The  $ = H  - /r w  H  s i g n o f the v o l t a g e depends upon whether H  g r e a t e r than or l e s s than Slichter  29  ' has  Q  is initially  . shown t h a t i f ,  t h e r e w i l l be a c o m p l e t e i n v e r s i o n o f m a g n e t i z a t i o n . r e p r e s e n t s an a d i a b a t i c passage. passage occurs  i n s u c h a way  m a g n e t i z a t i o n and K ff above r e s o n a n c e ,  0  resonance the angle  P h y s i c a l l y , the a d i a b a t i c  that the angle,  remains constant.  Q  &  , between the  Beginning  e q u a l s 0 ° and b e g i n n i n g &  This  the  passage  the passage below  equals 1 8 0 ° .  F a s t p a s s a g e r e q u i r e s t h a t t h e t i m e r e q u i r e d t o sweep through  r e s o n a n c e be v e r y s h o r t w i t h r e s p e c t t o T^,  l a t t i c e r e l a x a t i o n time.  1  i s l o n g , one  s a t i s f y the c o n d i t i o n ,  ^LMs  for  and  respect to  few  resonance.  can e a s i l y s a t i s f y the c o n d i t i o n s f o r  a d i a b a t i c f a s t p a s s a g e b e c a u s e one  reasonable  spin-  T h i s c o n d i t i o n means t h a t v e r y  n u c l e i change energy l e v e l d u r i n g the passage o f When T  the  values of  c a n sweep s l o w e n o u g h t o j 2f  still  be  sweeping f a s t  with  T^. In  t h e above d i s c u s s i o n i t has  system i s i n thermal  b e e n assumed t h a t  e q u i l i b r i u m at the beginning  of the  the  sweep.  2.  F o r many n u c l e i ,  Silicon-29,  including  the s p i n - l a t t i c e  t i m e , T.j, i s l o n g ; o f t h e o r d e r o f a m i n u t e .  relaxation  T h i s means t h a t  one  m u s t w a i t s e v e r a l m i n u t e s b e t w e e n sweeps i n o r d e r t o a l l o w t h e s y s t e m t o r e a c h t h e r m a l e q u i l i b r i u m . Now, if,  i n s t e a d of a l l o w i n g the system to e q u i l i b r a t e a f t e r  initial  sweep, we  sweep b a c k t h r o u g h  i initial to  c o n s i d e r what h a p p e n s our  resonance s h o r t l y a f t e r  i  passage of resonance.  The  i n i t i a l signal i s proportional  the e q u i l i b r i u m m a g n e t i z a t i o n , M  passage, the magnetization  .  A f t e r the a d i a b a t i c  i s i n v e r t e d t o -M  .  I f we  now  allow  t h e s y s t e m t o r e l a x , t h e z component o f t h e m a g n e t i z a t i o n , M is  g i v e n by: M  The  •  -  l  _  M,(l-2e  _  \  (22)  i n t e n s i t y o f t h e s e c o n d s i g n a l i s p r o p o r t i o n a l t o -M t Ar  Thus,  I i  »  _ H z  /  so t h a t ,  T  A p l o t of s l o p e 1/T^ Chemical  -  (\-i<r  ')  h  J \  i n t e r c e p t of I n  Shift  i  2.  s h i f t s were f i r s t  observed  by K n i g h t  S i n c e t h e n , t h e r e h a v e b e e n many a t t e m p t s  chemical  shifts.  Most t h e o r i e s of c h e m i c a l  to  p r o p o s e d i n 1950-^ u s i n g p e r t u r b a t i o n t h e o r y .  3 0  in  calculate  s h i f t are  u p o n m o d i f i c a t i o n s o f Ramsey's t h e o r y w h i c h was shift  with  Theory  Chemical 19^9.  =  .  \  vs. t should give a s t r a i g h t l i n e and  based  first The  chemical  i s u s u a l l y c a l c u l a t e d as a s c r e e n i n g c o n s t a n t ; w h e r e :  U  c  _  U  our  0  ( l - o r )  <*r>  ,  10  where: |4t  =  resonant f i e l d  U  -  applied  (f- 32 Pople^  of i ^ *  1  species  field  screening constant of i  species  ' has e x p r e s s e d t h i s  b y S a i k a and  Slichter.^  s c r e e n i n g u s i n g the breakdown proposed  3  where: (f^  -  screening constant f o r nucleus A  CJL*  -  diamagnetic contribution  (Tp**  C  A olUoc  paramagnetic  =  contribution  =  c o n t r i b u t i o n from c i r c u l a t i o n s  =  o t h e r atoms c o n t r i b u t i o n from  interatomic  c i r c u l a t i o n s w h i c h c a n n o t be ^ ^ i s  on  localized  a l s o known a s t h e Lamb^^ t e r m and f o r r a n d o m l y  t u m b l i n g m o l e c u l e s i t may  3mc  l  be c a l c u l a t e d a s  J  follows:  I  where:  f  r  =  d i s t a n c e from nucleus  (r)  =  electron density at distance  The d i a m a g n e t i c t e r m d e p e n d s o n t h e e l e c t r o n d e n s i t y n e a r  the  n u c l e u s and c o n s e q u e n t l y upon t h e e l e c t r o n e g a t i v i t y o f s u b s t i t u e n t s a t t a c h e d t o the nucleus under c o n s i d e r a t i o n . paramagnetic term,Up  , r e s u l t s from the mixing of the  g r o u n d and e x c i t e d e l e c t r o n i c  states i n the applied  field.  The  1  The  paramagnetic  transfer  term i s l a r g e  1  only  i f the e x c i t a t i o n  o f an e l e c t r o n between p o r d - o r b i t a l s . ^  hydrogen,  the p character  of the hydrogen  orbitals  involves  For i s small  1  so t h a t  the paramagnetic  negligible. 7  contribution  internuclear  contribution,  ( 7 " *  B and a l s o t h e i n t e r n u c l e a r for  1  H.  a 1 / r  B  only  i tw i l l  The  depends upon t h e n a t u r e o f  ,  separation,  contribution,  f o r ring currents  t e r m we s h a l l c o n s i d e r w i l l  since  ones  term i s dominant.  r ^ , but since i t  term t h i s c o n t r i b u t i o n w i l l  3  The d e l o c a l i z e d  significant only  H chemical s h i f t s i s  However, f o r most n u c l e i e x c e p t t h e l i g h t 9  s u c h a s ' L i and 'Be t h e p a r a m a g n e t i c  involves  to  be s m a l l  cr*'** ' ', 6 06  ±  s  except  probably  i n aromatic systems.  be t h e p a r a m a g n e t i c  The  part  be most s e n s i t i v e t o c h a n g e s i n c h e m i c a l  environment.' S c h n e i d e r and Buckingham c a l c u l a t e d shieldings  f o r mercury,  formula:  CT  P  =  t h a l l i u m , and l e a d u s i n g L ( L - M )  k  —  ^—  12  paramagnetic  T T *  m  c  2  2  A  the following  I r  <v  E  where: ^  0  =  ground  s t a t e wave  function 7.  =  t h e sum o f t h e s q u a r e s o f t h e t o t a l o r b i t a l a n g u l a r momenta o f t h e electrons  A El  =  average  w i t h o( a n d {3 s p i n s .  e x c i t a t i o n energy, i n ergs  Since,  -3 is  t h e v a l u e o f r -3 f o r  -r  3  2_M  ^1  -3  a.,  LA^U+'A)  a_n e l e c t r o n w h i c h  I™)  c o n t r i b u t e s to the  12 o r b i t a l a n g u l a r momentum, where: Z ~ =  effective nuclear  r  %  -  Bohr r a d i u s  =  0.529  n,l- =  charge  Angstroms  quantum numbers  of the c o n t r i b u t i n g  orbitals S u b s t i t u t i n g , one o b t a i n s :  ~  T h e y compare t h e c a l c u l a t e d  s h i f t s with experimental  values  b y c o n s i d e r i n g t h e p a r a m a g n e t i c s h i f t t o be z e r o f o r t h e 2+ 3+ 2+ s p h e r i c a l i o n s Hg , T1 , a n d Pb . T h e i r agreement i s J  remarkably  good when one c o n s i d e r s t h e s i m p l i c i t y o f t h e i r  treatment. A more r e c e n t t r e a t m e n t  by Jameson and G u t o w s k y ^  7  b a s e d o n v a l e n c e b o n d a n d L.C.A.O. c a l c u l a t i o n s h a s b e e n a p p l i e d t o Xenon f l u o r i d e s . -  3  This approach i s r a t h e r  c o m p l i c a t e d a n d i s f a r t o o cumbersome t o be a p p l i e d i n most cases.  W i t h p r e s e n t t h e o r i e s one c a n , a t b e s t ,  e x p l a i n observed  chemical  qualitatively  s h i f t s f o r most n o n - r o u t i n e  nuclei.  Spin-Spin Coupling Theory Much o f t h e f i n e  s t r u c t u r e i n N.M.R. s p e c t r a i s a  r e s u l t of i n t e r a c t i o n s between the n u c l e a r s p i n s . c o u p l i n g a r i s e s from the s m a l l magnetic f i e l d  Spin  induced  at  a g i v e n n u c l e u s b y o t h e r n u c l e a r moments w i t h i n t h e m o l e c u l e . 1  T h i s e f f e c t i s t r a n s m i t t e d v i a t h e b o n d i n g e l e c t r o n s and g e n e r a l l y a t t e n u a t e s r a p i d l y a s t h e number o f i n t e r v e n i n g b o n d s increases.  The m a g n i t u d e o f t h i s i n t e r a c t i o n , w h i c h i s indepen-.  dent of the a p p l i e d f i e l d , J,  i n c y c l e s per second.  i s g i v e n by t h e c o u p l i n g  constant,  13 Most e a r l y t h e o r e t i c a l treatments•of stants involved proton/proton  - c o u p l i n g s and  t o c o u p l i n g s between other n u c l e i . 9  However, J u a n  applied  and  J 29o,-u f r o m a bin ^ other workers ' , have  Lti  bond t r e a t m e n t .  c a n n o t be  con-  J 13r-rr and  G u t o w s k y ^ * ^ have c o n s i d e r e d valence  coupling  2  T h e s e , and hi  a s s u m e d t h a t , i n Ramsey's Fermi contact  treatment  J  term i s dominant.  of s p i n c o u p l i n g ,  T h i s t e r m may  the  be w r i t t e n a s :  (SI)  where: $y  Afc \f\ o/u.  =  m a g n e t o g y r i c r a t i o o f X,  =  average e l e c t r o n i c e x c i t a t i o n  = =  H energy  a normalization factor s  c h a r a c t e r of o r b i t a l s used f o r bonding  |v\S^( )) [  =  0  value  '  o f s e l e c t r o n wave f u n c t i o n a t  nucleus  hh  Smith  has  assumed t h a t t h e J u a n and  Gutowsky f o r m u l a t i o n a l s o  a p p l i e s t o JY_CH*  J  co*sl  =  o£  a. (m) K  info)  t  ^  where: c/ C L  X  ( A S )  y  =  s c h a r a c t e r of X  =  hyperfine  coupling constant  e l e c t r o n on OL  hyperfine ^  =  of  ns  X  coupling constant  e l e c t r o n on A  orbital  of 1 s  H  average e x c i t a t i o n energy of e l e c t r o n on  X  1^  We  can see from the above two  i n c o u p l i n g constants  equations  r e f l e c t e i t h e r changes i n e x c i t a t i o n  energy or h y b r i d i z a t i o n of the coupled (p ->d) TT  t h a t changes  nuclei.  Bonding i n O r g a n o s i l i e o n Compounds The  p o s s i b i l i t y of the d - o r b i t a l s of s i l i c o n  used i n the f o r m a t i o n of (p-*d)TT  bonds has  c o n s i d e r a b l e l e n g t h i n a number of a r t i c l e s .  being  been, d i s c u s s e d a t The  J  need t o  modify the simple cr bond p i c t u r e becomes apparent when one compares c a l c u l a t e d and l e n g t h s . Schomaker and  experimental  v a l u e s of Si-X bond  S t e v e n s o n ^ have shown t h a t one  c a l c u l a t e bond l e n g t h s from c o n s i d e r a t i o n of c o v a l e n t 1+8  and P a u l i n g  may  lf7  radii ' 1  electronegativities,  where: dA 8 f  A  % Table  , f$ p(  =  A  =  -  B  bond l e n g t h  c o v a l e n t r a d i i of A and  g  =  Pauling  p  =  a constant =  1 g i v e s c a l c u l a t e d and  f o r a number of Si-X and I t can be  Sn-X  B  electronegativities 0.09  observed v a l u e s of bond  lengths  bonds.  seen t h a t while a c o r r e c t i o n f o r e l e c t r o -  n e g a t i v i t y and hence i o n i c c h a r a c t e r g i v e s some i d e a of bond l e n g t h , t h e r e are s t i l l problems.  For example, t h e r e i s a  n o t i c e a b l e s h o r t e n i n g of the S i - 0 and  S i - F bonds and  bond i s l o n g e r than the c a l c u l a t e d v a l u e . lengthening  of the Si-H bond i s p r o b a b l y  The not  the  Si-H  apparent  significant  because of the f a c t t h a t both the c o v a l e n t r a d i u s of hydrogen and  i t s e l e c t r o n e g a t i v i t y are r a t h e r i n d e f i n i t e l y d e f i n e d .  For example i f one uses one-half  the bond l e n g t h i n the  hydrogen molecule as the c o v a l e n t r a d i u s one  obtains a  bond l e n g t h of 1 . 5 0 Angstroms which i s too l o n g .  Si-H  However, the  15 Table-J  C a l c u l a t e d And O b s e r v e d .calcj  Bond  S i - X And Sn-X Bond • obs. (»*9)  1A8  Lengths  Compound  Si-H  1A2  Si-C  1.88  1.89  Si(CH )^  Si-0  1.76  1.6W  Si(OMe)  Si-P  1.69  1.56  SiF  Sl-Cl  2.05  2.01  SiCl;  Si-Br  2.22  2.15  SiBr  Si-I  2.kk  2A6  Sn-H  1.66  1.70  CH^SnH^  Sn-C  2.11  2.18  SnCCH^  Sn-F  1.92  ionic  SnF^.  Sn-Cl  2.28  2.31  SnCl^  Sn-Br  2M  2.kh  SnBr^  Snll  2.67  2.6h  A  A 3  h  s h o r t e n i n g o f t h e S i - 0 a n d S i - F b o n d s m u s t be a c c o u n t e d f o r in  some way. her  A number o f w o r k e r s  cv\  _  cro y  j  have d e s c r i b e d t h e r o l e  and e f f e c t s o f t h e d - o r b i t a l s upon t h e b o n d i n g and c h e m i s t r y o f silicon.  The m o s t o b v i o u s c a s e r e q u i r i n g t h e u s e o f some  h i g h e r h y b r i d i z a t i o n beyond 3sp^ on s i l i c o n i s t h e h e x a f l u o r o 2s i l i c a t e i o n S1F7 . T h i s h a s b e e n shown^ t o be o c t a h e d r a l : 3 2 2p r o b a b l y u s i n g sp d h y b r i d i z e d s i l i c o n . W h i l e S i F ^ and t h e t r i m e t h y l a m i n e a d d u c t s o f f l u o r o s i l a n e s - ^ ' - ^ do n o t r e q u i r e t h e u s e o f (p-»d)TT b o n d i n g , t h e y do show t h a t t h e energies  o f t h e d - o r b i t a l s a r e l o w enough, a t l e a s t i n t h e  presence of e l e c t r o n e g a t i v e groups, t o enter  i n t o 3spd  type  hybrids. T r i s - s i l y l a m i n e and t r i m e t h y l a m i n e interesting arrangement.  show a number o f  c o n t r a s t s w h i c h p o i n t t o w a r d a (p-»d)"7T b o n d i n g ( S i E % K N i s a much w e a k e r e l e c t r o n d o n o r  than  16 ( C H ^ ) ^ N a n d (SiH^)-^N  i s p l a n a r ^ ' whereas (CH^)^N i s p y r a m i d a l .  T h e s e r e s u l t s c a n b o t h be e x p l a i n e d o n t h e b a s i s o f t h e f o l l o w i n g bonding  scheme:  Figure 2  (p  —»d)TT  Bonding O r b i t a l s I n ( S i H - ^ N  p  The  n i t r o g e n i s sp  from the remaining silicons.  This  hybridized with the lone p a i r d e l o c a l i z e d p-orbital into a d  same t y p e  type  a result of steric  on t h e  o f d e r e a l i z a t i o n c o u l d a l s o be  r e s p o n s i b l e f o r t h e l a r g e S i - O - S i bond a n g l e hexamethyldisiloxane  orbital  and d i s i l o x a n e .  (130  ) i n 7  T h i s e f f e c t c o u l d a l s o be  repulsion but i t i s not l i k e l y that the  e f f e c t would be so l a r g e i n t h e l i g h t o f t h e c o n s i d e r a b l e l o n e p a i r / l o n e p a i r r e p u l s i o n w h i c h would be i n t r o d u c e d . b o n d i n g may i n v o l v e s p -<f lone p a i r s i n the remaining silicon  The  bonds o n oxygen t o s i l i c o n w i t h t h e p - o r b i t a l s back-donating  into the  d-orbitals.  N.M.R. Of O r g a n o s i l i e o n The  Systems  most s t r i k i n g  o b s e r v a t i o n one c a n make a b o u t t h e  N.M.R. s t u d i e s o f o r g a n o s i l i e o n s y s t e m s i s t h a t i t i s v i r t u a l l y impossible t o c o r r e l a t e the chemical  shifts  and c o u p l i n g  JLZ constants w i t h any parameter.  F o r example,  considerthe  data i n t a b l e 2 on t h e s e r i e s , S i H F Y . which Ebsworth has ^ ^8^0 ' x H~x c o m p i l e d . T h e p r o t o n s h i f t o f S i H ^ and t h e f l u o r i n e 7  chemical s h i f t  of S i F ^ are both d i s t i n c t l y  rest of the series.  The S i - H c o u p l i n g  regular but the Si-F coupling  d i f f e r e n t from the  constants are f a i r l y  constants are irregular i n  t h a t a maximum o c c u r s f o r S i H F . 2  The S i - H a n d S i - F b o n d  2  l e n g t h s d e c r e a s e a s one g o e s f r o m S i H ^ t o S i F ^ . Table 2  N.M.R. And Bond L e n g t h D a t a F o r SiH^F), £(a) H  £(b) F  T  (c)  T  °SiE  (c) SiF  T  d  --  , ( c ) ,(d) SiH SiF a  —  a  l.h-77 A —  SiH^  6.80  —  SiH F  5.2^5.29  217 151  229.0 281 ^5.8 1.1+73 282 297.8 60.5 1.^7  5A9  109.5  381.7  —  163.3  3  SiH F 2  SiHF  2  3  SiF^  202.5  (c) HF  —  (a)  i n T" u n i t s , r e f . 58  (c)  ref.  59  27^.8  178(e)  i n the  9  (d) r e f .  F shifts  1.^6  —  —  1.565  1.5^  53  ( e ) r e f . 60  have observed s i m i l a r  effects  i n t h e s e r i e s , R ^ - S i F ^ , w i t h R = Me o r E t  a n d x = 0, 1, 2, o r 3. been p a r t i a l l y  96.3  1.59^ A 1.577  ( b ) i n p.p.m. f r o m C F C l ^ r e f . 58  S c h n e l l a n d Rochow 1  Compounds  ( S e e F i g u r e 3.)  These r e s u l t s  have  e x p l a i n e d on t h e b a s i s o f changes i n ( p - * d ) T T  b o n d i n g b u t no f i r m c o n c l u s i o n s h a v e b e e n r e a c h e d . Bruhe coupling  has examined  constants i nthe series, Cl (CH ) _ SiOR. n  o b s e r v e s changes i n t h e e f f e c t i v e oxygen (p-*d)TT  t h e c h e m i c a l s h i f t s and 3  3  n  He  electronegativity of the  i n t h e s e m o l e c u l e s and a t t r i b u t e s t h e s e changes t o bonding f r o m c h l o r i n e and oxygen  i n coupling  to silicon.  constant are attributed t o v a r i a t i o n s  t h r o u g h (p-*d)TT chemical s h i f t s (p-»d)"TT b o n d i n g  bonding.  Schmidbaur  Changes  i n hybridization  h a s a l s o examined t h e  a n d c o u p l i n g c o n s t a n t s a n d p o i n t s o u t how can p l a y an important p a r t i n changing  both  18  1.00-  p.p.  150  -  100  T? <^F  -R^Fj  3  Figure 3 . chemical  1 9  F  Chemical S h i f t s For R S i F v  s h i f t s and  coupling constants.  double resonance, determined the constants 13  but  C H  J  J  J  29  S i g n s Of  Coupling  J  2 9  SiCCH  HCH  by are  to that  ' S i and  J  C  expected. Systems  Molecule  Me^SiF  (assumed)  2  +  (  t  r  a  n  Me SiHCl  (assumed)  2  Me.Si 3  ( c i s )  s  of  are  Me SiHCl  HCSiH SiCCH  J  i s opposite  signs  Constants In Organosilicon  +  SiH  2 9  has,  Me^SiF  SiF  J  and  Sign  HCSiF 2 9  Couplings  29Q.?U  J  s i g n , t h i s i s t o be  Coupling J  s i g n of  Compounds.  D a n y l u k ^>  s i n c e the magnetogyric r a t i o s of  of opposite Table 3  The  v  signs of s e v e r a l c o u p l i n g  i n o r g a n o s i l i c o n systems.  g i v e n i n t a b l e 3« J  k  C=C  )  CI  H  \  \  H  12 5  Lauterbur^'  20  has  measured the  29 S i chemical  shifts  7  o f a number o f o r g a n o s i l i e o n compounds. He p o i n t s o u t a m a j o r -lo 29 d i f f e r e n c e between C and S i . s h i f t s f o r t h e s e r i e s Me^jMCOR)^ J  where M  i s C or S i .  F i g u r e h.)  7  (He d o e s n o t  Lauterbur  s t a t e what R i s . )  e x p l a i n s t h i s d i f f e r e n c e on t h e b a s i s  d-orbital participation i n back-coordination. phenyl  and  (See  v i n y l groups s h i e l d  s i l i c o n and  of  In a d d i t i o n ,  deshield  carbon,  consistent with donation  f r o m the TT-bonds i n t o  d-orbitals.  a t t e m p t s h a v e b e e n made t o e x p l a i n t h e  To d a t e , no 29 d e t a i l s of ' S i chemical  F i g u r e h.  1 3  C  and  2  9  Si  silicon  shifts.  Chemical S h i f t s  In Me^l(OR)^  Compounds  ;  20  EXPERIMENTAL Nuclear Magnetic  Resonance Measurements  P r o t o n N.M.R. s p e c t r a w e r e r u n a t 100 M c s . o n a V a r i a n A s s o c i a t e s HA-100 s p e c t r o m e t e r .  Benzene ( d r y ,  redistilled  reagent  g r a d e ) was u s e d a s a n i n t e r n a l s t a n d a r d u n l e s s  otherwise  noted.  H o w e v e r , a l l c h e m i c a l s h i f t s a r e r e p o r t e d i n p.p.m.  f r o m t e t r a m e t h y l s i l a n e (T.M.S.); a n e g a t i v e v a l u e denotes a s h i f t t o low f i e l d .  S p e c t r a were r u n o n f i e l d  sweep mode u s i n g  the benzene s i g n a l t o p r o v i d e a n i n t e r n a l f i e l d  frequency  lock.  L i n e p o s i t i o n s were m e a s u r e d b y r u n n i n g t h e s p e c t r a o n 50 c . p . s . —2 sweep w i d t h a n d 1000 s e c o n d sweep t i m e second  ) and p l a c i n g f r e q u e n c y  s i d e o f t h e peak.  ( 1 . 2 X 10  milligauss  c a l i b r a t i o n markers on e i t h e r  I n t h i s way, c o u p l i n g c o n s t a n t s may be  measured t o ±0.05 c.p.s.  and chemical s h i f t s t o b e t t e r than  ± 0.01 p.p.m. F l u o r i n e N.M.R. s p e c t r a were r u n o n t h e V a r i a n A s s o c i a t e s HA-100 o p e r a t i n g o n HR mode a t 9^.1 M c s . M o n o f l u o r o t r i c h l o r o m e t h a n e ( F r e o n - 1 1 ; M a t h e s o n C a n a d a L i m i t e d ) was u s e d a s a n i n t e r n a l standard.  Coupling constants and chemical s h i f t s  measured u s i n g t h e a u d i o s i d e b a n d method.  were  By t h i s method,  c o u p l i n g c o n s t a n t s may b e m e a s u r e d t o — 0 . 1 c . p . s .  and chemical  s h i f t s t o ± 0 . 0 1 p.p.m;  /  S i l i c o n - 2 9 N.M.R. s p e c t r a w e r e r u n o n a  spectrometer  system assembled i n t h e department; l a r g e l y from V a r i a n A s s o c i a t e s parts.  The s y s t e m o p e r a t e s a t 7«95 M c s .  this field  corresponds  a n d 9«+1 K i l o g a u s s ; l  t o ^0.0 Mcs. resonance f o r protons.  Field  sweep i s p r o v i d e d b y a V a r i a n M o d e l V3507 s l o w sweep u n i t a n d s p e c t r a a r e r e c o r d e d o n a V a r i a n G-10 r e c o r d e r . stability  Good b a s e l i n e  i s a c h i e v e d b y u s i n g r e g u l a t e d power s u p p l i e s f o r t h e  V^-311 r a d i o - f r e q u e n c y u n i t .  B+ v o l t a g e (+300 v o l t s d . c . ) i s  21  p r o v i d e d b y a Lambda E l e c t r o n i c s C o r p . , M o d e l 3 2 p o w e r s u p p l y and  the +12.0  E l e c t r o n i c Research  v o l t s d.c.  (1$  f i l a m e n t v o l t a g e by 32-*+  A s s o c i a t e s , I n c . , M o d e l T.R.  r e g u l a t i o n ) power s u p p l y .  regulation) a  (0.01$  A l l s p e c t r a a r e r u n a t h i g h power •i  (>100  m i l l i g a u s s ) and  d i s p e r s i o n mode.  The  signals probably  mode b u t t h e r e i s v e r y l i t t l e (See F i g u r e 5»)  (A/1  r a p i d passage  d i s t o r t i o n of the  pyrex tubes  w a l l t e s t tube (MeCO^Si).  liquids  w i t h i n a c o n c e n t r i c 15  mm.  o.d.  pyrex  silicon-29  The  l i n e s w i t h a s p a c i n g o f 18*+  mm.  thin  used  as  spectrum  c.p.s. (measured from  t o 23 p.p.m. a t 7 . 9 5  F o r r o u t i n e measurements the f o l l o w i n g p r o c e d u r e s a m p l e was  10  (usually  A s a m p l e o f t r i m e t h y l s i l a n e , M e ^ S i H , was  p r o t o n spectrum) which corresponds standard  the  i n thin wall  c o n t a i n i n g the e x t e r n a l standard  a s t a n d a r d f o r sweep c a l i b r a t i o n . g i v e s two  of  nuclei. Samples were r u n as n e a t  o.d.  peaks,  5 minutes  to wait approximately  b e t w e e n sweeps b e c a u s e o f t h e l o n g r e l a x a t i o n t i m e s Silicon-29  ) in  c o n t a i n some a b s o r p t i o n  apparent  I t i s necessary  gauss minute  r u n o n i n c r e a s i n g and  was  the  Mcs.  used.  The  d e c r e a s i n g sweep  and  t h e s a m p l e t o be m e a s u r e d was  t h e n r u n a t t h e same sweep r a t e  setting  at least four times.  The  again.  By  standard  s a m p l e was  comparing the peak s e p a r a t i o n s i n the s t a n d a r d  the sample, the s i l i c o n - 2 9 The  s h i f t s may  be m e a s u r e d t o ± 29  r e l a x a t i o n times of the ^,'Si i n  s i l o x a n e , t e t r a m e t h o x y s i l a n e , and  i n c r e a s e d a s h i g h as p o s s i b l e w i t h o u t  changing  sweep r a t e i n c r e a s e d t o a b o u t 10  the  for  r o u t i n e measurement.  The  field  was  A f t e r a time, t , the f i e l d  resonance i n the opposite d i r e c t i o n . recorded  o n a S a n b o r n M o d e l 151  power l e v e l  1.0  p.p.m.  probe  t h e n swept  balance  was  swept  through  through  These s i g n a l s I  was  times the value used  r e c o r d e r and  measure t h e change i n i n t e n s i t y f r o m  one  were  i s able  to  t o 1^. a t t i m e t .  w a i t i n g f o r s e v e r a l m i n u t e s a f t e r t h e s e c o n d sweep, one repeat the process  and  t e t r a m e t h y l s i l a n e were The  and  run  hexamethyldi-  measured by t h e f o l l o w i n g p r o c e d u r e .  resonance.  then  again f o r a d i f f e r e n t value of t .  By can  Two  22  £ - — 7 9.5~ f>f>** Figure  5b.  ? S i spectrum of Me^Si w i t h 9  standard  (MeCO^Si a s e x t e r n a l  s u c h p a i r s o f s i g n a l s a r e shown i n f i g u r e 6. In  (1 -  I^/I ) Q  v s . t i s a s t r a i g h t l i n e with slope  i n t e r c e p t I n 2. processes estimate  Figure 6  and  Because o f t h e complicated r e l a x a t i o n  w h i c h may go o n , t h i s m e t h o d p r o b a b l y of  magnitude  A plot of  a n d s h o u l d n o t be u s e d e x c e p t  gives only an  as an order o f  value.  Recorder Traces F o r A d i a b a t i c F a s t Passage T M e a s u r e m e n t Of ( M e ^ S D p O  1  s p e c t r a w e r e r u n a t 7»95 M c s . u s i n g t h e 29 same p r o c e d u r e a s f o r S i e x c e p t t h a t t h e m a g n e t i c f i e l d was Carbon-13  7  r e d u c e d t o 7.^5 percent  Kilogauss.  The s a m p l e s were r u n a s 60 v o l u m e  s o l u t i o n s i n CSg a n d a c o n v e n i e n t  s a m p l e was u s e d f o r sweep c a l i b r a t i o n .  v a l u e o f J 13QJJ i n t h e  I n t h e compounds o f  i n t e r e s t , m e t h y l c h l o r o s i l a n e s , t h e C resonances a r e quartets J  13  and  a r e r a t h e r d i s t o r t e d . The a c c u r a c y  of the C shifts i s J  r e d u c e d t o ±. 5 p.p.m. b y t h i s d i s t o r t i o n . times  relaxation  were m e a s u r e d f o r B e n z e n e , C S , . a n d t h e c a r b o n y l 29 9  i n a c e t o n e u s i n g t h e same p r o c e d u r e u s e d f o r  y  carbon  S ir e l a x a t i o n  times. Sample P r e p a r a t i o n i  Many o r g a n o s i l i c o n compounds were p u r c h a s e d  from  2it several sources.  (N.M.R. S p e c i a l t i e s C o . ; P e n i n s u l a r Chem-  R e s e a r c h C o r p ; A l d r i c h C h e m i c a l Co.)  S e v e r a l samples  k i n d l y d o n a t e d b y t h e Dow C o r n i n g C o r p o r a t i o n . and d o n a t e d  samples were used w i t h o u t f u r t h e r  were  The p u r c h a s e d purification.  S e v e r a l s a m p l e s w e r e p r e p a r e d by s t a n d a r d t e c h n i q u e s ^ as l i s t e d  below.  necessary.  7  S t a n d a r d vacuum t e c h n i q u e s w e r e u s e d where  S a m p l e s were u s u a l l y p u r i f i e d b y d i s t i l l a t i o n a n d  p u r i t i e s c h e c k e d b y N.M.R. s p e c t r a r u n o n a V a r i a n A - 6 0 . The  silanes,  (CgH^SiHg,  (CgH^SiH^,  S i H ^ , Me^SiH,  M e S i H , and MeSiH^ were p r e p a r e d by r e d u c t i o n o f t h e c o r r e s p o n d 2  ing  2  c h l o r i d e s w i t h L i A l H ^ under a d r y n i t r o g e n  environment.  The m e t h y l a n d p h e n y l f l u o r i d e s w e r e p r e p a r e d f r o m the  c h l o r i d e s u s i n g v a r i o u s f l u o r i n a t i n g a g e n t s a s shown i n  t a b l e h.  Silicon Tetrafluoride  (SiF>,) was p r e p a r e d f r o m t h e fiP> r e a c t i o n o f N a S i F ^ a n d HgSO^ o n s i l i c a - g e l . The p h e n y l m e t h y l 2  s i l a n e s were p r e p a r e d f r o m P h e n y l l i t h i u m and t h e c o r r e s p o n d i n g methylchlorosilanes. Phenyl'magnesium Table h  T r i p h e n y l s i l a n e was p r e p a r e d f r o m  Bromide  and T r i c h l o r o s i l a n e .  P r e p a r a t i o n Of F l u o r o s i l a n e s Compound Me SiF 2  MeSiF 2  2  2  PbF /reflux 2  HF/EtpO  3  4> S i F  Agent  AgF/Et 0  3  Me SiF  Fluorinating  2  HF/Et 0 2  (low y i e l d )  21  RESULTS Table 5  C and  1 3  2 9  Si  R e l a x a t i o n Times  Compound  T^  Benzene  1*+ sec,  Acetone ( c a r b o n y l carbon)  19  CS (MeO^Si (Me Si) 0 Me^Si  35  2  3  Table 6  73 hO 16  2  N.M.R. Data F o r Me^Si(OMe)),  ^™"^™~~^~—"  '  '"  <f(a)  6  Me^Si Me^SiOMe Me Si(0Me) MeSKOMe)^ Si(OMe)^ 2  2  _X_  »I1.PI1I«III  Si  6  r (b) Me  6  —  r (b) OMe  '  -r  d  (  "  O Q  ^SiCH  p.p.m. p.p.m. p. p. r..  c.p.s.  -79.5 -96.5  0.0 -0.21  6.62 6.65  -77  -0.19 -0.12  -38 0  -3A9 -3.55 -3.58 -3.60  7.2  8.35  J  T oo ^SiOCH  c.p.s.  13 3.90 3.82 3.55 H-.  (a) S i l i c o n - 2 9 c h e m i c a l s h i f t i n p.p.m. f r o m ( M e O V S i (b) H c h e m i c a l s h i f t i n p.p.m. from T.M.S. (c) J 1 3  C H  i s f o r m e t h y l group.  J  1 J  T  CH  1^  c.p.s.  118.1 118.0 118.5 119.1  Cc)  26 Table 7  N.M.R. Data F o r , M e ^ S i C O E t ) f  { (a) Si  0  C (b) Me  J  d  l f - x  2 9  SiCH  J  1 3  CH  p.p.m.  p.p.m.  c.p.s.  c.p.s.  Me^Si  -79.5  6.62  118.1  Me^SiOEt  -93 -72  0.0 -0.23 -0.20 -0.16  6.67 7.08  118.0 118.2  8.35  119.2  i n p.p.m. f r o m  (MeO VSi  Me Si(0Et) 2  MeSi(OEt)  2  -3h  3  +k  SKOEt)^ Silicon-29  (a) (b)  chemical s h i f t  H chemical s h i f t  Table 8  i n p.p.m. f r o m  N.M.R. D a t a F o r Me C (a)  OS i  Me^Si Me^SiOAc Me Si(0Ac) 2  MeSi(OAC)  2  3  SKOAc)^  Silicon-29  (a)  T.M.S.  Si(0Ac)^  C (b) Me  J J  2 9  SiCH  1  3  C  H  p.p.m.  p.p.m.  c.p.s.  c.p.s.  -79.5 -103  0 -0.36  6.62 7.10  118.1  -85 -35 -5  -0.53 -0.67  7.77 9.5  —  chemical s h i f t  (b) H c h e m i c a l s h i f t 1  0  v  123.^ —  —  i n p.p.m. f r o m  i n p.p.m. f r o m  119.5 121.3  T.M.S.  (MeO^Si  22  Table 9  N.M.R. D a t a F o r Me S l C l )  Me SiCl 3  2  MeSiCl  2  3  SiCl^  (a)  c (b) OC  p.p.m.  p.p.m.  -79.5 -115 -120 -96 -63  Me^Si Me SiCl  r (a) 0 Si  _  f  r (c) O Me  T J  p.p.m.  190 176 190 210  O  1 3  (c)  1  Me Si4> 2  MeSi4>  3  2  —  —  (MeO)^Si 2  C (a) Si  Me Si(C H V x  C (b) °Me  6  J  2 9  5  _  x  SiCH  J  (b) (c)  2  9  -i  Si  1 3  CH  c.p.s.  p .p.m.  p.p.m.  c.p.s.  -79.5 -75  0 -0.26  -0.52  6.62 6.60 6.60  119.0 120.5  -0.7^  6.6*t  (c)  -72 -67  118.1  (c) (a)  118.1 120.77 123.6 125.5  i n p.p.m. f r o m T.M.S.  d  M e ^ S i 4>  CE  c.p.s.  7.00 7.61 9.07  —  N.M.R. D a t a F o r  Me^Si  , 15  6.62  C c h e m i c a l s h i f t i n p.p.m. f r o m C S  H shift  1 J  c.p.s.  " S i c h e m i c a l s h i f t i n p.p.m. f r o m  (b)  T  V  0 -0.39 -0A5 -1.05  —  Q  ^ SiCH  chemical s h i f t r e l a t i v e t o (MeOVSi  H chemical s h i f t r e l a t i v e t o Me^Si  t o o i n s o l u b l e t o be measured  ^  T a b l e 10  N.M.R. D a t a F o r M e S i F ^ _ v  Sl  )  p.p.m. Me^Si  <f Me^  ^ F  p.p.m.  p.p.m.  -6%  -0.19 -28  MeSiF^  (d)  +0.2  SiF^  (d)  3  Me SiF 2  (a) (O  2  1  2  S i chemical  9  F  9  chemical  C  )  J  2 9  SiF  J  c.p.s.  2 9  SiCH  276  158  1 3  CH  J  278  133 161.8  ] c.p.s  6.62  c.p.s. 118.1  7.*+0  120.0  7.23  7.60  130  s h i f t r e l a t i v e to  J  c.p.s.  0  -79.5 -110  Me SiF  v  6.25  -  8.8  178 (b)  (MeO)^Si  s h i f t f r o m CFC1-,  (d)  —  1  s h i f t f r o m T.M.S. H chemical t o o v o l a t i l e t o be m e a s u r e d  T a b l e 11 N.M.R. D a t a F o r Me^SiH),, S i p.p.m.  6  Me^Si Me^SiH Me SiH 2  MeSiH  3  (c)  X ^  Me p.p.m.  6  0  2  9  H p.p.m.  SiH c.p.s.  J  J  3 H c.p.s.  J  1  C  HCS3H c.p.s.  J  118.1  183.8  7.20  3.76  -h.03  188.5  7.5  119.35 120.8  -3.71 (c)  19^.6  7.9  123.6  h.67  -0.20  20  -38  -0.26  (c)  -0.27  S i chemical s h i f t from (MeO^Si  t o o v o l a t i l e t o be m e a s u r e d  SiCH c.p.s. 2 9  6.62  0  -79.5 -61  (c)  SiH^ (a)  2  X ^  202.5 (b)  1  H chemical  s h i f t f r o m T.M.S.  >+.i5  22 Table 13  Miscellaneous  2 9  S i Chemical S h i f t s . Chemical S h i f t ^  Compound ViSi(OEt) C H^SiR" 6  (p.p.m.) -15.5  3  -18  3  C H^Si(0Et) 6  (MeO) Si 6  ( C  6 5 2 H  )  -19  3  -27  2  S i H  2  (C H ) Si(0Et) 6  5  2  (C H ) SiF 6  5  2  2  -^9  2  -57  Vi^Si Me Si 6  -»+5  -59  2  Me(C H^) SiH  -60  [(MeOjgMeSi]  -72  Et SiF  -80  6  2  2  2  2  ClCH SiMe 2  -81.5  3  (Me Si) 0 Me Si 3  -83.5  2  3  —  O  —(^--1-8*.  (a) r e l a t i v e t o (Mefc^Si  -92  30  DISCUSSION Relaxation  times 13  The  r e l a x a t i o n t i m e s measured f o r  J  29  C  and  S i are  7  c a l c u l a t e d f r o m t h e s l o p e s o f t h e p l o t s o f I n (1 +  vs. t 69  shown i n f i g u r e 7 and a r e l i s t e d 13 have d i s c u s s e d shielding. and  J  C  |  i n table  r e l a x a t i o n i n terms  T h e y e s t i m a t e t h e T^  5.  M c C o n n e l l and Holm  of a n i s o t r o p i c  of CS  t o be a b o u t  2  controlling  seconds  one n u c l e u s b y a n o t h e r . field,  induced magnetic  field  levels.  r e l a x a t i o n t i m e i s p r o p o r t i o n a l t o (jU,y*z) magnetic so T  J  C  induced  i n the  field  results  In CS ,  The  induce  and r ^ ; w h e r e r 2  t h e r e a r e no  0  in a  e f f e c t upon the  n u c l e i i n the molecule to c o n t r i b u t e t o the  i s long.  1  separation.  dipolar  a t t h e n u c l e u s w h i c h may  i n the n u c l e a r energy  the i n t e r n u c l e a r  field  As t h e m o l e c u l e t u m b l e s  this  modulation of the magnetic transitions  factor  the magnitude of the r e l a x a t i o n time i s the  a p p l i e d magnetic  the  60  most c a s e s o b s e r v e d h e r e , t h e dominant  s p i n - s p i n c o u p l i n g . T h i s a r i s e s from the magnetic  is  chemical  "apparently long" f o r CCl^. In  at  1  2  other J  C  relaxation  I n b e n z e n e and f o r t h e c a r b o n y l c a r b o n i n a c e t o n e ,  i s c o u p l e d t o one  reduction i n T .  o r more p r o t o n s w h i c h l e a d s t o a  In (MeO^Si,  1  so t h a t t h e d i p o l a r  coupling  the internuclear distance i s large  i s less  means f o r t h e n u c l e i t o r e l a x .  effective  i n providing  I n ( M e ^ S i ^ O and  i n t e r n u c l e a r d i s t a n c e i s r e d u c e d , r e d u c i n g T^.  i n Me^Si,  The  a the  s h o r t e r T^  in  M e ^ S i t h a n i n ( M e ^ S i ^ O . i s a r e s u l t o f a g r e a t e r number o f p r o t o n s ;  coupled to the The  1 3  silicon.  C  T^s  are shorter than those f o r  compounds m e a s u r e d . T h i s d i f f e r e n c e  2  9  Si  i n the  i s probably a result  the  g r e a t e r n u c l e a r m a g n e t i c moment o f C a r b o n - 1 3 and a l s o 13  the  l o w e r symmetry o f t h e  chemical s h i f t In  7  C molecules measured.  i s a d i r e c t i o n a l p r o p e r t y i t may  be  i n the l i q u i d  an average v a l u e .  causes the observed  H o w e v e r , t h i s a n i s o t r o p y may  of  Since the anisotropic.  m o s t N.M.R. w o r k , t h i s a n i s o t r o p y i s n o t i m p o r t a n t  random m o t i o n  of  because  shielding  to  have a marked  be  31  Figure 7  P l o t Of  I n (1  + I /I ) t  Q  v s  »  *  F o r  c  And  ^ S i Compounds  32 69 '  e f f e c t on in effect  As t h e m o l e c u l e t u m b l e s , t h e m a g n e t i c  nuclei,  " s e e " a v a r y i n g m a g n e t i c f i e l d w h i c h may i n d u c e 13  t r a n s i t i o n s between t h e n u c l e a r energy l e v e l s .  A l l of the  J  C  compounds, f o r w h i c h T^'s w e r e m e a s u r e d , w o u l d be e x p e c t e d t o e x h i b i t a n i s o t r o p i c s h i e l d i n g s ; CS^ and Me C0 on t h e b a s i s o f 2  m o l e c u l a r symmetry a n d b e n z e n e b e c a u s e I t w o u l d be u s e f u l t o m e a s u r e  of the ring  current.  f o r analogous carbon and s i l i c o n 29 A-\ compounds t o c l a r i f y w h i c h shows l o n g e r T ^ s ; S i o r ^C. 1  Accuracy o f S i l i c o n - 2 9 Chemical S h i f t  Data  29 The  error i n the  t o be ±1 p.p.m.  S i s h i f t measurements i s e s t i m a t e d  T h i s e s t i m a t e i s b a s e d o n two f a c t s .  F i r s t , the  s t a n d a r d d e v i a t i o n on a s e r i e s o f seven measurements o f t h e chemical s h i f t  i n a ( M e O V S i / T , M . S . s a m p l e was f o u n d t o be 29 0.M- p.p.m. S e c o n d , many s a m p l e s g i v e S i spectra which a r e s p l i t i n t o m u l t i p l e t s by d i r e c t S i - H coupling. ( S e e F i g u r e 8.) The 29 c o u p l i n g c o n s t a n t s may be m e a s u r e d f r o m t h e S i s p e c t r u m a n d 7  2 9  7  •i  compared t o t h e v a l u e o b t a i n e d f r o m t h e H s p e c t r u m . 29 from  7  S i s p e c t r a c o n s i s t e n t l y agree t o ± 5 c.p.s. w i t h  obtained from H spectra. 1  was  The v a l u e s  found, from  2  9  Si  F o r example,  J 29  S i H  those  i n (C^H^^SiMeH  s p e c t r u m , t o b e 190-200 c . p . s . a n d , f r o m  1  H  s p e c t r u m , 196 c . p . s . I n some c a s e s , f o r e x a m p l e t h e m e t h y l 29 chlorosilanes, the very fast  7  S i s p e c t r u m c a n n o t be o b s e r v e d e x c e p t  sweep a n d h i g h e r t h a n n o r m a l power c o n d i t i o n s .  e r r o r s a r e c o n s e q u e n t l y somewhat l a r g e r ; a b o u t ± 5 p.p.m.  under The Also,  some s i g n a l s , p a r t i c u l a r l y t e t r a v i n y l s i l a n e , a r e c o n s i d e r a b l y broadened  b y s p i n c o u p l i n g a n d t h e e r r o r i s i n c r e a s e d t o ± 3 p.p.m. 29 W h i l e t h e random e r r o r i n t h e  7  S i measurements i s  i 1 p.p.m., t h e r e i s a s y s t e m a t i c e r r o r i n t h e m e a s u r e m e n t s which has n o t been t a k e n i n t o account.  Since an e x t e r n a l  s t a n d a r d i s b e i n g u s e d , a c o r r e c t i o n s h o u l d be made f o r d i f f e r ences  i n b u l k s u s c e p t i b i l i t y o f t h e v a r i o u s samples.-'  This  21  Figure 8  2  9  Si  S p e c t r u m Of C ^ S i R ^  c o r r e c t i o n may be a p p l i e d u s i n g t h e f o l l o w i n g e q u a t i o n ,  where: & sphere & X  obs v ref  9( v s a m p l e  =  s p h e r i c a l or true chemical  =  observed chemical  =  v  o  =  v  °l  The b u l k s u s c e p t i b i l i t y and c a n p r o b a b l y  l  u  m  e  u m e  shift  shift  s u s c e p t i b i l i t y of reference s u s c e p t i b i l i t y o f sample  c o r r e c t i o n w i l l be l e s s t h a n 1 p.p.m.  be i g n o r e d .  As a c h e c k , t h e c h e m i c a l  shift  b e t w e e n M e ^ S i H a n d ( M e O ^ S i was m e a s u r e d f o r i n t e r n a l a n d external standards.  For internal  standard  62.6 p.p.m. a n d f o r e x t e r n a l s t a n d a r d  the s h i f t i s  i t i s 6 1 . 5 p.p.m.  It  i s q u e s t i o n a b l e , whether o r n o t t h i s d i f f e r e n c e i s s i g n i f i c a n t , In any case, t h e s m a l l e r r o r i n t r o d u c e d by f a i l u r e t o apply a bulk s u s c e p t i b i l i t y  c o r r e c t i o n i s b o u n d t o be p r e f e r a b l e t o  the p o s s i b i l i t y o f l a r g e r e r r o r s introduced by s o l v e n t  effects,  S i l i c o n - 2 9 Chemical  Shifts  29 Any a t t e m p t t o e x p l a i n t h e o b s e r v e d S i chemical s h i f t s m u s t be v e r y q u a l i t a t i v e a n d somewhat s p e c u l a t i v e . We 29 s h a l l attempt t o e x p l a i n general trends i n S i chemical s h i f t 119 13 and w i l l b r i e f l y examine t h e S n and C c h e m i c a l s h i f t s f o r s i m i l a r i t i e s and d i f f e r e n c e s . y  1  7  The are l i s t e d figure for  2 9  Si'chemical shifts  J  f o r t h e s e r i e s Me  Si(OMe)^  i n t a b l e 6 a n d t h e t r e n d i s shown g r a p h i c a l l y i n  9.  T h i s t r e n d i s a l s o f o l l o w e d f o r Me S i C O E t ) ^ ^ a n d  Me S i ( 0 A c )  L  .  ( S e e t a b l e s 7 a n d 8.)  minimum i n t h e c h e m i c a l s h i f t e f f e c t s being  The e x i s t e n c e o f a  i s i n d i c a t i v e o f two c o m p e t i n g  present.  X Figure 9  2  9  Si  Chemical  Shift  Of Me S K O M e ) ^  Series  I t h a s b e e n shown t h a t t h e p a r a m a g n e t i c to  the chemical s h i f t w i l l  contribution. paramagnetic  i n m o s t c a s e s be t h e d o m i n a n t  Using the Schneider-Buckingham t r e a t m e n t , ^ the 3  shifts  maybe c a l c u l a t e d f o r m o s t n u c l e i .  number o f s u c h s h i f t s centage  contribution  are l i s t e d i n table  t h a t the observed  A  1*f, w i t h t h e p e r -  chemical s h i f t range forms of t h e  12 T a b l e 1H-  P a r a m a g n e t i c S h i f t s And P e r c e n t a g e  Observed  -1175 -2300 -1750  27$ 27%  -Moo  h5%  8%  -¥fOO  300%  c a l c u l a t e d paramagnetic term.  The  l a r g e Pb c h e m i c a l s h i f t  r a n g e i n c l u d e s a number o f s o l i d s a n d l e a d m e t a l so t h a t i t i s  29  not s u r p r i s i n g that the simple theory f a i l s .  The v e r y s m a l l  c h e m i c a l s h i f t range i n d i c a t e s t h a t w h i l e the t o t a l shielding  i s l a r g e t h e o b s e r v e d changes  relatively of  small.  Si  paramagnetic  i n shielding  are  I t i s important to r e a l i z e that the  selection  a s t a n d a r d from w h i c h c h e m i c a l s h i f t s a r e measured i s a r b i -  trary.  The  t r u e z e r o of c h e m i c a l s h i f t i s an u n s h i e l d e d n u c l e u s . 29 In the case of ' S i t h e r e i s no s p e c i e s f o r w h i c h t h e p a r a m a g n e t i c s h i e l d i n g w o u l d be s m a l l . S c h n e i d e r and B u c k i n g h a m assume 2+ t h a t Pb  i n s o l u t i o n would have a s m a l l paramagnetic  so t h a t t h e may of  3000  shielding  p.p.m. s h i f t b e t w e e n PbNO^ s o l u t i o n a n d P b C M e ) ^  be u s e d a s a m e a s u r e o f t h e p a r a m a g n e t i c s h i e l d i n g . 29 t h e s i l i c o n compounds f o r w h i c h t h e  A l l  ' S i s h i f t s have been  measured c o n t a i n s i l i c o n i n a t e t r a c o o r d i n a t e d environment of I f we t a k e t h e p o i n t o f v i e w t h a t we a r e o b s e r v i n g c o v a l e n t bonds. H e n c e , t h e p a r a m a g n e t i c c o n t r i b u t i o n w i l l be s m a l l changes i n p a r a m a g n e t i c s h i e l d i n g i t i s r e a s o n a b l e t o large i n a l l cases. assume t h a t o t h e r f a c t o r s may a l s o s i g n i f i c a n t l y a f f e c t t h e total  shielding.  I n a n a t t e m p t t o m i n i m i z e t h e number o f  v a r i a b l e s we h a v e e x a m i n e d  compounds o f t h e t y p e Me  SiXu  as a f u n c t i o n o f e l e c t r o n e g a t i v i t y w i t h o u t w o r r y i n g about major  changes  i n m o l e c u l a r geometry.  I n f i g u r e 10 we  have  and  36  plotted  ( Me^Si  2  b e t w e e n S i and X.  -  Me^SiX) v s . t h e e l e c t r o n e g a t i v i t y The p o i n t s  f o r S i , I , B r , and C l l i e w i t h i n  1 3 p.p.m. o f a s t r a i g h t l i n e , i m p l y i n g the  N, 0, and F l i e on a  s t r a i g h t l i n e which i s not p a r a l l e l  and d o e s n o t p a s s t h r o u g h t h e o r i g i n . with  a l i n e a r dependence o f  c h e m i c a l s h i f t on e l e c t r o n e g a t i v i t y .  different  t h e known a b i l i t y o f n i t r o g e n ,  donate t o s i l i c o n using We  s h a l l now  difference  (p-» d)7T  to the f i r s t  This deviation  line  coincides  o x y g e n and f l u o r i n e t o b a c k bonds.  consider the observed s h i e l d i n g  t o be  21 divided  i n t o two  0"  parts  as  -  p  cr  follows:  +  cr*  where: CT  =  observed  Op"  =  paramagnetic  shielding  =  contribution  to  shielding shielding  from  substituents I n our  c o n t e x t , <7" w i l l be  c o n s i d e r e d as  s h i e l d i n g which r e s u l t s from the 3d-orbitals of  the  the  diamagnetic  d o n a t i o n of e l e c t r o n s  into  <T^ i s n e g a t i v e so t h a t  silicon.  the  increases  i n Z .~ c a u s e d by s u b s t i t u t i o n o f e l e c t r o n e g a t i v e g r o u p s on t o en pg s i l i c o n w i l l l e a d t o low f i e l d s h i f t s of the ' S i resonances. < T i s p o s i t i v e and i n c r e a s e s i n o c c u p a n c y o f t h e d - o r b i t a l s af  X  29  will  lead  to high f i e l d  a c o m b i n a t i o n of d o n a t i o n on  to  The  shifts  of the  s u b s t i t u t i o n of e l e c t r o n e g a t i v e  o b s e r v e d c h e m i c a l s h i f t w i l l be  between X I f we  dependent upon the and  S i and  assume t h a t ,  CI determines the  will  for  M e ^ S i F , Me^Si-O-R and  contribution  change l i n e a r l y 10,  dependence of  extrapolate  i t and  now  diffenence i n  in figure  can  We  the Op  line  3  from back-donation.  the  difference  between  t h e n the  contribution  that  change i n C T  the  substituents p o i n t e d out silicon will (p—*d)TT  to the the  A<Tp  f r o m Ao*"*. X  silicon.  c a u s e an The  As  sum  of  the  Op  is  electronegativity with  substitution.  through S i , Br,  I,  2  the  we  compounds i f t h e r e were  We  can  then extrapolate See  From f i g u r e  11,  Craig^  a partial  i n c r e a s e i n the  and  be  no  the  figure  11.  observed chemical s h i f t  0  and  chemical s h i f t would  becomes more e f f e c t i v e as  f o r m a t i o n of  bonding.  and  effects.  assume t h a t  change i n s h i f t f r o m Me^Si to Me^SiX t o S i X ^ . The  two  back-  upon e l e c t r o n e g a t i v i t y ,  d e t e r m i n e what t h e Me Si-NR  Thus,  g r o u p s and  s i l i c o n l e a d s to a c o m p e t i t i o n of  c h a n g e s i n s c r e e n i n g , A o~p and A d " * . linearly  S i resonances.  7  is  i t i s apparent one  a d d s more  Ebsworth^  3  have  p o s i t i v e charge at effectiveness  of  s u b s t i t u t i o n of e l e c t r o n e g a t i v e  the  the groups  2d will  tend t o i n c r e a s e the p o s i t i v e charge  t h e change i n to  (j~  x  on t h e s i l i c o n .  g o i n g f r o m M e ^ S i t o M e ^ S i X w o u l d be  be l e s s t h a n t h e c h a n g e g o i n g f r o m M e S i X ^ t o S i X ^ .  Thus,  expected This i s  what i s e x p e r i m e n t a l l y o b s e r v e d . Jaffe^ Si-F is  and  has  S i - C l bonds.  0 . 2 0 and  bonding  2  calculated overlap integrals f o r S i - 0 , F o r S i - 0 and  for Si-Cl i t is 0.15.  S i - F the overlap Therefore, while  i s p o s s i b l e f o r S i C l bonds i t i s l i k e l y  e f f e c t i v e t h a n i n S i - 0 or S i - F bonds. s e r i e s i s g i v e n i n t a b l e 9 and ically.  Si(OMe)),  of  Cl.  v  t o be  less  d a t a f o r t h e Me  1 2 shows t h e t r e n d  s e r i e s because of the s m a l l e r  A l s o , the  the l e s s e r a b i l i t y in  (p^d)TT SiCl^. graph-  A cTp c o n t r i b u t i o n i s s m a l l e r t h a n f o r t h e  The  Me  figure  The  integral  A <f  electronegativity  c o n t r i b u t i o n i s much s m a l l e r b e c a u s e o f  of c h l o r i n e to back donate.  the chemical s h i f t occurs at M e ~ S i C l . 0  T h u s , t h e minimum  ko The 10.)  table  d a t a f o r t h e s e r i e s Me S i F ^ i s i n c o m p l e t e (See PQ t-x  but from the three  l e a s t comment o n t h e t r e n d .  7  S i s h i f t s a v a i l a b l e one c a n a t  I n spite of the greater  n e g a t i v i t y o f f l u o r i n e over  chlorine, the chemical  M e ^ S i F i s v i r t u a l l y t h e same a s t h a t o f M e ^ S i C l . chemical T.M.S. term.  s h i f t of Me SiF 2  2  electro-  shift of Also, the  i s o n l y k.5 p.p.m. t o l o w f i e l d o f CT*  Both of these f a c t s a r e c o n s i s t e n t w i t h a l a r g e Since f l u o r i n e  i s known t o b a c k - d o n a t e v e r y r e a d i l y , a  h i g h occupancy o f t h e s i l i c o n d - o r b i t a l s i s n o t unexpected. The  in  12.  table  field  chemical The  shifts f o r the  M e  S i x  ( 6 5')L _ C  H  r  a  r  given  e  x  s i l i c o n - 2 9 r e s o n a n c e moves r e g u l a r l y t o h i g h  b u t t h e c h a n g e s a r e q u i t e s m a l l ; 13 p.p.m. f r o m M e ^ S i t o  MeSitC^H^)^.  S i n c e , t h e s i l i c o n i s bound t o f o u r c a r b o n s i n  a l l members o f t h e s e r i e s term w i l l  i ti snot l i k e l y  e x h i b i t much c h a n g e .  Phenyl  t h a t the paramagnetic  groups have e l e c t r o n s i n  t h e i r T T - b o n d i n g o r b i t a l s w h i c h may b a c k - d o n a t e i n t o t h e d orbitals of s i l i c o n .  However, any b a c k - d o n a t i o n  w i l l b e much  s m a l l e r t h a n f o r t h e h a l o g e n s a n d w i l l n o t become more as t h e s u b s t i t u t i o n i s i n c r e a s e d . expected  effective  A s i m i l a r e f f e c t w o u l d be  f o r t h e v i n y l s i l a n e s , a n d i t s h o u l d be o f t h e same  general order o f magnitude. The  methylsilanes,  increase i n chemical  shift  are both very v o l a t i l e The be  6  Si  chemical  shifts  2  f  2  9  Si  shifts arenot available.  shifts  i s n o t known b u t a p p e a r s t o  F o r example, ( C ^ H ^ S i H ^ i s t o  13 a n d a p p e n d i x A l i s t  of Me(C H^) SiH. 6  2  a number o f m i s c e l l a n e o u s  s h i f t s a n d a number o f comments c a n be made. t o p.p.m. f r o m  G e n e r a l l y , speaking  s u b s t i t u t i o n leads t o a high f i e l d  shift.  phenyl  The  (MeOj^Si and v i n y l  F o r example,  a n d C H ^ S i ( 0 E t ) ^ a r e a b o u t 15 p.p.m. t o h i g h f i e l d o f  ViSKOEt)^  6  3  and V i S i ( 0 E t )  (C Ry Si(0Et) 6  However, MeSiH^ and S i H ^  which i s t o high f i e l d  2  s u b t r a c t i n g 58 p.p.m.  Also,  x  i n a p p e n d i x A may b e c o n v e r t e d  MeSi(0Et)  a p p e a r t o show a g e n e r a l  H  13.)  table  Table  by  and t h e  of (C H^) SiH  i L _ >  toward SiH^.  g e n e r a l f o r S i - H compounds.  (See 9  s x  reason f o r these high f i e l d  high f i e l d  2  M e  2  2  3  i st o high f i e l d  of C H^Si(0Et) .  i s 25 p.p.m. t o h i g h f i e l d  6  3  of Me Si(0Et) . 2  2  H o w e v e r , Me (C£H^)SiH  and M e ( C ^ H ^ ) S i H  2  same r e s o n a n c e p o s i t i o n a s M e ^ S i H . groups f o r m e t h y l groups u s u a l l y 29 the  leads t o a high f i e l d s h i f t of  ( M e O ) ^ S i , (MeOpMeSiJg a n d Me^Si,^.  The o r d e r o b s e r v e d  2  (MeO) Si 6  field. is  The s u b s t i t u t i o n o f m e t h o x y l  S i resonance b u t t h i s i s not s t r a i g h t forward f o r the  series is  are both a t v i r t u a l l y the  2  2  to high f i e l d of M e S i 6  The c h e m i c a l s h i f t  with  2  of SiBr^  (MeO)^IeSi a tlow  (+ 10 p.p.m. f r o m  (MeO)^Si)  somewhat d i f f i c u l t t o r a t i o n a l i z e u n l e s s t h e h i g h e r p o l a r i z -  ability  o f bromine  favourable.  than chlorine  b o n d i n g more  While t h e concept o f a c o m p e t i t i o n between t h e  paramagnetic s h i e l d i n g from  makes ( p - ? d ) T T  ( p - * d)TT  and a d i a m a g n e t i c s h i e l d i n g  resulting  bonding, explains the gross features of  chemical s h i f t s ,  2 < 7  Si  t h e r e a r e a f e w minor p o i n t s w h i c h cannot be  explained. T h i s concept o f c h e m i c a l s h i f t a l s o appears t o a p p l y 119 to the S n c h e m i c a l s h i f t s o f t h e s e r i e s (n-Bu) SnClu x w h i c h 22 have been measured b y L a u t e r b u r . ( S e e A p p e n d i x B.) I n f i g u r e 119 13 we h a v e p l o t t e d t h e S n c h e m i c a l s h i f t o f (n-Bu) S n C l ^ „ 7  7  a g a i n s t x. (-  2  2  a r e f o r acetone  77 p.p.m.) a n d C S ( - 11*+ p.p.m.) s o l u t i o n s .  Since acetone i s  2  a polar  solvent i t 'i s l i k e l y t o exhibit a larger 119  than CS . 2  the  The t w o v a l u e s f o r n - B u S n C l  I n any case, t h e  7  Sn shifts  same t r e n d a s t h e Me S i ( O M e ) ^  of this  series.  solvent series  effect follow  Since t i n has  v a c a n t ^ - d - o r b i t a l s , ( p - * d)TT  bonding i s p o s s i b l e  be more e f f e c t i v e f o r c h l o r i n e  t o t i n back-donation than f o r 119  chlorine chlorides  to silicon.  Therefore, the  7  Sn shifts  and s h o u l d  f o r the t i n  b e h a v e more l i k e t h e s i l i c o n a l k o x i d e s t h a n t h e  s i l i c o n chlorides.  The c h e m i c a l s h i f t  of Me SnCl 2  measured o n l y i n acetone s o l u t i o n and MeSnCl^  2  has been  only i n acetone  and  i n water s o l u t i o n .  The g e n e r a l t r e n d i s t h e same a s f o r  the  n - b u t y l c h l o r i d e s i f one c o n s i d e r s t h a t s o l v a t i o n  effects  l e a d to. h i g h f i e l d s h i f t s . The s u b s t i t u t i o n o f p h e n y l a n d v i n y l groups f o r m e t h y l groups l e a d t o h i g h f i e l d s h i f t s o f 119 the  7  S n resonance and v i n y l ,  a g a i n , a p p e a r s t o be more  e f f e c t i v e t h a n p h e n y l . F o r example, M e S n V i and M e S n ( C g H ^ ) a r e s h i f t e d 7 9 . ^ p.p.m. a n d 59.8 p.p.m. r e s p e c t i v e l y t o h i g h 2  2  2  2  k2  i  cm • soo-  -STO  .  0  4  Figure  field  13  1 1 9  Sn  o f Me^Sn.  almost l i n e a r .  Chemical S h i f t s For  (n-Bu) SnCl _ x  For the methylvinylstannaries ( S e e f i g u r e 1*+.)  two  l f  x  the trend i s  Thus, the c o m p e t i t i o n  of  s h i e l d i n g s gives a r a t i o n a l , but q u a l i t a t i v e , d e s c r i p t i o n o f t h e g e n e r a l f e a t u r e s o f 119 Sn c h e m i c a l s h i f t s .  i  hi  If  the preceeding  e x p l a n a t i o n of chemical s h i f t i s  Carbon-13 c h e m i c a l s h i f t s .  c o r r e c t , i t should not apply to In  other words, analogous  carbon  compounds s h o u l d n o t  t h e same t r e n d s a s s i l i c o n o r t i n . The t h a t t h e d - o r b i t a l c o n t r i b u t i o n , (T*, ( p a g e 19)  Figure h  s h i f t s f o r t h e two  discussion. Me^C  The  to C(0R)i  1 3  J  C  C  zero f o r  and  2  Si  carbon.  chemical  s t a t e d , i t makes no d i f f e r e n c e t o  s h i f t s e x h i b i t a general decrease  c o n s i s t e n t w i t h an i n c r e a s e i n  +  9  (CH^^COR)^^.^  s e r i e s o f compounds  the R group i s not 13  While  reason f o r t h i s i s  must be  shows t h e t r e n d s i n  show  our  from  paramagnetic  s h i e l d i n g a s e l e c t r o n e g a t i v e g r o u p s a r e a d d e d . S p i e s e c k e and 17 13 S c h n e i d e r ' h a v e m e a s u r e d the' C c h e m i c a l s h i f t s o f a number 13 J  of  s u b s t i t u t e d methanes.  c h e m i c a l s h i f t o f CH^X  15  In figure  we  have p l o t t e d the  r e l a t i v e t o the t e r m i n a l carbons  J  C  in  neopentane a g a i n s t the d i f f e r e n c e i n e l e c t r o n e g a t i v i t i e s , 13 X  - X .  While  the  J  C  s h i f t s do n o t e x h i b i t a s i m p l e  ence upon e l e c t r o n e g a t i v i t y , t h e d e v i a t i o n s w h i c h c e r t a i n l y d i f f e r e n t from the s i m i l a r p l o t f o r (See F i g u r e 10.)  M e . S i X compounds.  The  2  Si  are  shifts in 13  Schneider  t e r m s o f c h a n g e s i n m a g n e t i c a n i s o t r o p y and b y  For these  do a p p e a r  deviations i n 17  s h i f t h a v e b e e n d e s c r i b e d b y S p i e s e c k e and co-workers  9  depend-  0  C  ' in  Schaefer ^  and  7  i n terms of i n t r a m o l e c u l a r d i s p e r s i o n e f f e c t s . 13 s i m p l e examples t h e t r e n d s i n • C c h e m i c a l s h i f t s J  are  29 d i f f e r e n t from  those i n  7  S i and  a r e e x p l a i n e d on a  different  basis. The  1 3  C  chemical s h i f t s of the M e S i C l x  e x h i b i t a trend i n chemical s h i f t which to the in The  the  2  9  Si  shifts.  same e f f e c t .  l f  _  x  series  a p p e a r s t o be  similar  H o w e v e r , i t i s u n l i k e l y t o be a r e s u l t  More l i k e l y ,  the  1 3  C  of  s h i f t s r e f l e c t a change  t h e e f f e c t i v e e l e c t r o n e g a t i v i t y o f t h e s i l i c o n bound t o i t . e l e c t r o n e g a t i v i t y o f t h e s i l i c o n w i l l be  number o f c h l o r i n e s bound t o i t and donation from  chlorine.  More  1 3  C  g o v e r n e d by  the  a l s o the extent of back-  s h i f t s w i l l have t o  be  m e a s u r e d f o r c a r b o n bound t o s i l i c o n and o t h e r g r o u p f o u r e l e m e n t s b e f o r e t h i s b e h a v i o r c a n be e x p l a i n e d .  hi  Coupling  Constants 39  13QJJ  Gutowsky and Juan-" have c o n s i d e r e d J J 29 ^ S  and  from a v a l e n c e bond t r e a t m e n t and have reached  H  following conclusions.  The magnitude of the c o u p l i n g i s  dependent almost e n t i r e l y upon the s - c h a r a c t e r of t h e or carbon.  The  p o l a r i t y of the bond does not a f f e c t  coupling constant.  the  The  silicon the  a d d i t i o n of an e l e c t r o n e g a t i v e sub-  s t i t u e n t t o methane i n p r e a s e s t h e s - c h a r a c t e r by, i n e f f e c t , i n c r e a s i n g the p - c h a r a c t e r o f t h e C-X  bonding o r b i t a l s .  however, has a l e s s e r a f f i n i t y f o r t h e s e l e c t r o n s on T h e r e f o r e , J 13 £ i s reduced  t h a n does hydrogen.  c.p.s.).  carbon  i n Me^Si (118.1  C  c.p.s.) f r o m methane (125  Silicon,  I f the e f f e c t i v e n u c l e a r  charge of s i l i c o n , w h i c h amounts t o i t s e l e c t r o n e g a t i v i t y , i n c r e a s e s one would expect t h e v a l u e o f the v a l u e s of J 1 3  From examining Me  Si(OAc)^  and Me  S  i  C  l  i n the s e r i e s Me  C H  , t a b l e s 6,  u  to increase.  13QJJ  J  8 and 9> one  t h a t indeed t h e r e i s a r e g u l a r i n c r e a s e i n J 13 JJ. C H  can  ,  see  Furthermore,  C  the v a l u e s of J 1 3  Si(OMe)^  i n d i c a t e t h a t t h e o r d e r of i n c r e a s i n g  e f f e c t i v e n u c l e a r charge on s i l i c o n i s C l ^ O A c ^ O M e .  This i s  29  t h e same o r d e r p r e d i c t e d f r o m t h e Me^SiX compounds. and  M e  s x  T h i s s i m p l e approach breaks down f o r  i( 6 5 )lj._ > c  H  ' S i c h e m i c a l s h i f t s i n the  ,  x  t a b l e s 11  and  12,  f a c t t h a t l i t t l e or no change i n % ££ e  J  M e  s x  iHL,._  where, i n s p i t e o f the i s expected  1 3QJJ shows a r e g u l a r i n c r e a s e toward MeSiX^.  on  silicon,  At p r e s e n t ,  t h i s r e s u l t i s unexplained. I f we use e q u a t i o n 3 2 , f a c t o r s governing J  page 1 3 ,  s h o u l d be a b l e t o make some  w e  comment on the changes i n J 2 9 ^ Q J J . s  t h e compounds measured, a  g i  as a guide t o the  It i s unlikely that, for  ( 3 s ) , a^ ( 1 s ) ,  orAE  x  will  change.  We must t h e r e f o r e c o n s i d e r changes i n s - c h a r a c t e r a l o n e t o be r e s p o n s i b l e f o r changes i n J 2 9  S i C  jj.  I f the  electronegativity  o f s u b s t i t u e n t s on s i l i c o n a f f e c t s J 2 9 g g i n the same way i C  electronegative substituents affect J 13Q methanes, J 2 9 a r e added.  S i C H  The  should  H  as  i n substituted  i n c r e a s e as e l e c t r o n e g a t i v e groups  expected b e h a v i o r i s observed  f o r Me  SiX^^;  x  h6 where: the J  S = OMe,  OEt,  OAc  series Me Si(C^H^)i _ x  29  S i C  +  and  C I , t a b l e s 6,  c h a r g e on  a general  silicon.  increase i n J 9  The  2  g i  s e r i e s ' Me  Q .  SiRY  I t must be  H  This  and  9.  Also,  change i n  change i n e f f e c t i v e  t h e o r i e s o f s p i n - s p i n c o u p l i n g c a n n o t be i n v o l v i n g heavy n u c l e i .  8,  e x h i b i t s v i r t u a l l y no  x  j j w h i c h i s c o n s i s t e n t w i t h no  nuclear  7,  Y  ,  again,  assumed t h a t  extended to  i s probably  shows simple  systems  because of the  a s s u m p t i o n s w h i c h must be made w i t h r e s p e c t  to the  gross  electron  wave f u n c t i o n s . A c a r e f u l examination  of the  1 3  C  s a t e l l i t e s of  m e t h y l s i l i c o n compounds r e v e a l s f i n e s t r u c t u r e due range HCSiCH c o u p l i n g . and  Me^SiX (where:  l i t e s which are  (See F i g u r e  X = OMe,  split  OEt,  16.)  OAc  The  and  to a  The  long  compounds,  CI) have  i n t o seven l i n e s .  several  1 3  C  (Me^Si^O  satel-  compounds M e S i X 0  0  13  ( w h e r e : X = OMe, O E t , OAc and C I ) h a v e C s a t e l l i t e s w h i c h a r e quartets. I n a l l cases, J^CSiCH °»35 0.1 c.p.s. T h i s c o u p l i n g i s observable because protons attached t o C are not e q u i v a l e n t 1 2 J  =  1 3  to protons probably  attached  to  r e l a t e d to the  C. (p  The  magnitude of t h i s c o u p l i n g  d)TTbonding i n t h e s e  I n g e n e r a l , the c o u p l i n g constant the  environment of the  s i l i c o n i n these  b e t w e e n n u c l e i i s d o m i n a t e d by and  a f f e c t e d i n the  which dominate the chemical  s h i f t data  w h i c h c a n n o t be be  Silicon-29  compounds.  d a t a does not  compounds.  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Chem.  52 APPENDIX A Si  2 9  Chemical S h i f t s  [(CH ) SiO] Si* SiBr^  81.5 68  Sodium s i l i c a t e s o l u t i o n  6k  (C-E^\S±  59.5  3  l f  [(CH ) SiO] SiCH C H SiH (C H 0) SiCH 3  6  3  5  3  *f 2.5 39 2115  3  3  2  5  3  3  C H^(CH )SiH (CH SiHO) (C^SiHO)^ 6  3  3  1*f.8 13.1  2  5  1 2  11.-8 0 -2.2  (C H ) SiH [(CH ) Si0} [(CH^SiO]^ 6  5  2  3  2  2  x  [CgHyCH^SiO]^ C H^(CH ) SiH SiCl^ [(CH ) SiO] (C H (CH ) SiCH==CH 6  3  3  3  3  6  3  2  [(CH ) SiH] 0 (CH ) SiC H (C H ) CH SiOC H [(CH ) SiNH] [(CH ) Si] NH (CH ) SiCH OH (CH^Si 3  3  6  2  3  5  3  2  3  3  3  2  6  2  5  3  2  3  2  3  2  [(CH ) Si] CH (CH ) SiCH NH 3  3  3  3  2  2  3  2  2  6  5  6  solution) J  1  5  >  1  -17.2 -1?.8 -18.2 -18.7 -19.8 -21.8 _22.0 -22.5 -23.2  2  (CH ) SiCH C H 3  -2.3 -k.5 -6 -12.1  2  2  2  Chemical S h i f t (p.p.m.)  Compound  3  ^>  5  -23.k  21  APPENDIX A (Cont'd) Si  (CH ) Si(CH ) CH (CH ) SiCH Cl (CH ) SiCH NCS t(CH ) Si] 0 (CH ) SiOC H^ [ ( C H ) S i 6 ] SiCH" CH SiCl [(CH^^Siql^Si (CH ) SiI (CH3) Si(CH C1)CHC1 3  3  2  3  3  2  3  3  2  3  3  3  2  3  3  3  2  3  3  3  2 9  3  3  3  3  3  2  2  2  Chemical Shifts ^ '  -23.8 -25.5 -28.2 -28.7 -29.h -29.+ -30. -30. h -30.6 -31.2  [(CH ) Sid] PO (CH ) SiBr  -35 -WA  (CH3)3SiCl  -51  (CH ) ,SiP (CH ) SiCl (CH.KSiOSO.H  -53.1 -5+ -57.6  3  3  3  3  3  3  3  3  2  2  2 0  5k APPENDIX B 1 1 9  Sn  Chemical S h i f t s  2 2  ' ^ 2  Me^Sn = 0 Chemical S h i f t Compound  Snl^  (CS  (p.p.m.)  solution)'  2  1701  SnSO^ (aqueous)  909  SnBr^  638  Na [Sn(0H) ] 2  (aqueous)  6  592  K Q S n ( 0 H ) l (aqueous)  590  SnCl .2H 0  521  2  6  (aqueous, I+.85M)  2  2  CH SnCl^. (aqueous) 3  SnCl  (tetrahydrofuran)  2  (n-C H ) 3n(0Ac) l f  9  2  2  *+80 236 195  Vi^Sn  165  SnCl^  150  (C H^) (cyclohexyl)Sn  11*+  (CH ) Sn  109  6  3  3  6  Vi S Bu 2  n  2  86. *f  2  (nrBu) Sn 6  79.5  2  (CH ) Sn -Vi 3  2  79.*+  2  (CH ) Sn(C Hy 3  2  6  2  59.8  (C H ) SnCl ,  1+6.0  Vi SnCl  1+0.9  6  ?  3  2  2  35A  (CH ) SnVi 3  3  (CH ) SnC H -  30.3  (n-Bu^Sn  12  3  n-BuSnCl  6  3  3  (CH ) SnCl 3  2  n-Bu SnCl 2  2  2  (acetone s o l u t i o n ) (acetone s o l u t i o n )  2  (CH ) SnBr 3  5  2  (CH ) SnBr 3  3  -71  -7I+.3  2  n - B u S n C l (CS s o l u t i o n ) 2  -.36  2  -11^  -130.7  n-Bu SnCl 3  (CH.KSnCl  -158.6  51 APPENDIX C 2  ° P b Chemical 7  Shifts ^' 2  Chemical Compound  +6,900 +7,+00  PbO y e l l o w  +8,700 +10,100  PbSe  PbS PbTe Pb(C H 0 ) 2  3  2  2  single crystal  +10,800 +10,900  PbO r e d  +11,200  P M C H ^  +11,1+00  Pb(Zirconate) s o l i d  +12,300 +12,300 +12,500  Pb(ClO^  +1^,100  Pb(C R" 0 ) 2  3  Pb(C 0 2  l f  )  2  2  solution  PbCO^ s i n g l e Pb(N0 ) 3  2  solution  solid  2  crystal  solution  +1 +,lf00 l  + 1 +, K)0 l  l  Pb(N0 ).'H 0  +15,200  PbNO.  +15,200  3  2  3 6  Shift  0  powder  2  '  (p.p.m.)  Pb m e t a l Pb0  2 6  

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