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UBC Theses and Dissertations

Bis(hydrocarbyl) and alkylidene complexes of iridium Massey, Roberta Lynn 1989

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B I S ( H Y D R O C A R B Y L ) A N D A L K Y L I D E N E C O M P L E X E S O F I R I D I U M B y R o b e r t a L y n n M a s s e y B . Sc . , T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1986 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S ( D E P A R T M E N T O F C H E M I S T R Y ) W e accept this thesis as c o n f o r m i n g to the r e q u i r e d standard T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A M a r c h 1989 © R o b e r t a L y n n M a s s e y , 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of CkdW) 17>tp The University of British Columbia Vancouver, Canada DE-6 (2/88) i i Abstract T h e i r i d i u m ( m ) b i s ( h y d r o c a r b y l ) c o m p l e x e s I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] f o r R = C H 3 , C 6 H 5 , C H 2 P h , a n d R ' = C H 3 , C6H5, C H 2 P h , C H 2 C M e 3 , C H 2 S i M e 3 were s y n t h e s i z e d i n h i g h y i e l d s f r o m the h y d r o c a r b y l h a l i d e p r e c u r s o r s I r ( R ) X [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , w h e r e X = I o r B r , b y r e a c t i o n w i t h the a p p r o p r i a t e o r g a n o l i t h i u m sal t L i R 1 . T h e g e o m e t r y o f the f i v e - c o o r d i n a t e c o m p l e x e s w a s d e t e r m i n e d to be t r i g o n a l b i p y r a m i d a l b o t h i n s o l u t i o n , o n the bas is o f N O E D I F F e x p e r i m e n t s , and i n the s o l i d state b y c o m p a r i s o n to the p r e v i o u s l y d e t e r m i n e d X - r a y structures o f the m e t h y l n e o p e n t y l a n d d i b e n z y l d e r i v a t i v e s . T h e c o m p l e x e s w e r e f o u n d to be t h e r m a l l y stable, h o w e v e r , they d i d react w h e n e x p o s e d to sunl ight to g i v e the a l k y l i d e n e c o m p l e x e s I r ( = C H R ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] f o r R = H , P h . A l t h o u g h the b e n z y l i d e n e c o m p l e x ( R = P h ) has not yet been i s o l a t e d i n the p u r e state, the = C H P h l i g a n d w a s f o u n d to be rotat ing about the I r=C b o n d axis o n the ! H N M R t ime scale w i t h a AG+rot = 9.3 k c a l / m o l . T h e reac t iv i ty o f the m e t h y l i d e n e c o m p l e x ( R = H ) w a s a l so b r i e f l y e x p l o r e d w i t h CH3I , C 2 H 4 , C 2 H 2 , C O , P M e 3 , and H 2 . O n the basis o f the o b s e r v e d s p e c t r o s c o p i c d a t a , severa l o f these r e a c t i o n s i n v o l v e c a r b o n - c a r b o n b o n d f o r m a t i o n , and the methyl idene carbon appears to be n u c l e o p h i l i c i n nature. i i i T A B L E O F C O N T E N T S A b s t r a c t i i T a b l e o f Contents i i i L i s t o f Tables v i L i s t o f F i g u r e s v i i G l o s s a r y o f A b b r e v i a t i o n s . . . . . ix A c k n o w l e d g e m e n t x i C H A P T E R 1. C A R B E N E A N D A L K Y L I D E N E C O M P L E X E S 1 1.1 Introduct ion 1 1.2 B a c k g r o u n d and N o m e n c l a t u r e 3 1.3 R e a c t i v i t y Patterns 4 1.4 B o n d i n g 7 1.5 Synthes is 7 1.5.1 Synthet ic Routes 7 1.5.2 Synthes is o f H e t e r o a t o m - S u b s t i t u t e d C a r b e n e C o m p l e x e s 8 1.5.3 Synthes is o f A l k y l i d e n e C o m p l e x e s 11 1.6 T h e s i s Content 14 1.7 References 15 C H A P T E R 2. S Y N T H E S I S A N D C H A R A C T E R I Z A T I O N O F I R I D I U M B I S ( H Y D R O C A R B Y L ) C O M P L E X E S I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 18 2.1 Introduct ion 18 2.2 Other H y d r o c a r b y l C o m p l e x e s o f I r i d i u m 18 2.3 Synthes is o f I r ( R ) R , [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 19 iv 2.4 Characterization 20 2.4.1 1H and 1 3 C{ 1 H} NMR Data 20 2.4.2 Solution Structure 24 2.4.3 Solid State Structure 30 2.5 Experimental..... 32 2.5.1 General Information 32 2.5.2 Synthesis of Iridium Bis(hydrocarbyl) Complexes 33 2 .6 References 36 CHAPTER 3 . PHOTOREACTIVTTY OF IRIDIUM BIS(HYDROCARBYL) C O M P L E X E S Ir(R)R ,[N(SiMe2CH2PPh2)2] 39 3.1 Photochemical Versus Thermal Reaction Conditions 39 3.2 Thermal Stability 4 0 3.3 Photochemical Reactivity 40 3.3.1 Photolysis of Ir(CH3)2[N(SiMe2CH2PPh2)2] (2) 42 3.3.2 Photolysis of Ir(CH2Ph)2[N(SiMe2CH2PPh2)2] (9) 42 3.3.3 Photolysis of Ir(CH2Ph)(CH3)[N(SiMe2CH2PPh2)2] (8) 43 3.4 Deuterium Labelling Studies 44 3.5 Ultraviolet/Visible Spectroscopy 45 3.6 Possible Mechanism for the Photoreactions 47 3.5 Experimental 50 3.5.1 Thermolysis Studies 50 3.5 .2 Photolysis Studies 50 3.5.3 UV7VIS Spectrophotometry 50 3.5.4 Synthesis of Deuterium Labelled Samples 50 3.6 References 51 V C H A P T E R 4. I R I D I U M A L K Y L I D E N E C O M P L E X E S I r ( = C H R ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , R = H , P h 52 4.1 I r i d i u m B e n z y l i d e n e C o m p l e x I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 52 4.1.1 Synthes is a n d C h a r a c t e r i z a t i o n 52 4 .1 .2 D e t e r m i n a t i o n o f I r=C R o t a t i o n a l B a r r i e r 53 4 .2 I r i d i u m M e t h y l i d e n e C o m p l e x I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 55 4.2.1 O t h e r Isolated T r a n s i t i o n - M e t a l M e t h y l i d e n e C o m p l e x e s 55 4 .2 .2 R e a c t i v i t y o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 57 4.2.2.1 R e a c t i o n w i t h M e t h y l Iod ide 58 4.2.2.2 R e a c t i o n w i t h E t h y l e n e 62 4.2.2.3 R e a c t i o n w i t h A c e t y l e n e 65 4.2.2.4 R e a c t i o n w i t h C a r b o n M o n o x i d e 66 4.2.2.5 R e a c t i o n w i t h T r i m e t h y l p h o s p h i n e 70 4.2.2.6 R e a c t i o n w i t h D i h y d r o g e n 73 4.2.2.7 Other Reac t ions A t t e m p t e d 73 4.2.3 S u m m a r y o f R e a c t i v i t y o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 76 4 .3 E x p e r i m e n t a l 76 4.3.1 G e n e r a l 76 4 .3 .2 A t t e m p t e d Iso lat ion o f I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 77 4 .3 .3 . C a l c u l a t i o n o f Rota t iona l B a r r i e r for I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 77 4.3.4 R e a c t i o n o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] w i t h V a r i o u s S u b s t r a t e s 78 4 .4 References 78 C H A P T E R 5. C O N C L U S I O N S 82 v i List of Tables Table 2-1. * H N M R D a t a f o r I r i d i u m B i s ( h y d r o c a r b y l ) C o m p l e x e s 21 Table 2-II. " C p H J N M R D a t a f o r I r i d i u m B i s ( h y d r o c a r b y l ) C o m p l e x e s 22 Table 3-1. P h o t o l y s i s R e s u l t s f o r I r i d i u m B i s ( h y d r o c a r b y l ) C o m p l e x e s 41 Table 3-II. U V / V I S Spec t ra l D a t a f o r I r i d i u m B i s ( h y d r o c a r b y l ) C o m p l e x e s 45 Table 4-1. S p e c t r o s c o p i c D a t a for I r i d i u m A l k y l i d e n e C o m p l e x e s . . 53 Table 4-II. O t h e r R e p o r t e d Isolated M e t h y l i d e n e C o m p l e x e s 56 v i i List of Figures Figure 1-1. E x a m p l e s o f the t w o types o f carbene c o m p l e x e s : F i s c h e r carbene and S c h r o c k a l k y l i d e n e 3 Figure 1-2. T y p i c a l r e a c t i v i t y patterns f o r e l e c t r o p h i l i c carbene and n u c l e o p h i l i c a l k y l i d e n e c o m p l e x e s 4 Figure 1-3. L i m i t i n g f o r m s w h i c h contr ibute to s tab i l iza t ion o f the carbene carbon 5 Figure 1-4. T w o b o n d i n g v i e w s f o r the carbene m o i e t y : donor/acceptor b o n d and covalent b o n d 7 Figure 2-1. N M R spec t rum f o r c o m p l e x 3 23 Figure 2-2. J H N M R spec t rum and N O E D I F F spec t rum f o r c o m p l e x l b 26 Figure 2-3. * H N M R spec t rum and N O E D I F F spectra f o r c o m p l e x l c 27 Figure 2-4. * H N M R spec t rum a n d N O E D I F F spectra f o r c o m p l e x 10 28 Figure 2-5. * H N M R spec t rum a n d N O E D I F F spec t rum for c o m p l e x 9 29 Figure 2-6. M o l e c u l a r structure o f the m e t h y l - n e o p e n t y l d e r i v a t i v e (3) as d e t e r m i n e d b y X - r a y c r y s t a l l o g r a p h i c a n a l y s i s 8 31 Figure 2-7. M o l e c u l a r structure o f the d i b e n z y l d e r i v a t i v e (9) as d e t e r m i n e d b y X - r a y c r y s t a l l o g r a p h i c a n a l y s i s 1 2 31 Figure 3-1. O r b i t a l sp l i t t ing d iagrams for a d 6 m e t a l c o m p l e x 46 Figure 3-2. P o s s i b l e effects o n the m e t a l - h y d r o c a r b y l bonds due to the absorpt ion o f v i s i b l e rad ia t ion 47 Figure 4-1. lH N M R spec t rum o f I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] at 298 K , a n d the peaks due to the s i l y l m e t h y l protons ( in the r e g i o n 0.0 - 0.5 p p m ) as the temperature i s l o w e r e d to 178 K 54 Figure 4-2. lH N M R spec t rum o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + C H 3 I after 9 0 minutes at r o o m temperature 59 v i i i Figure 4-3. * H N M R spec t rum o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] under 1 atmosphere o f C O after a f e w minutes at r o o m temperature 68 Figure 4-4. l H N M R s p e c t r u m o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + P M e 3 a t - 2 0 ° C 71 Figure 4-5. * H N M R spec t rum o f I r ( H ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + A l M e 3 75 i x Glossary of Abbreviations: A A n g s t r o m , 1 0 - 8 cent imetre a t m a t m o s p h e r e B L e w i s base br b r o a d B u l tert iary b u t y l , C ( C H 3 ) 3 °C degree C e l s i u s c m c e n t i m e t r e C O E c y c l o o c t e n e , r i 2 - C 8 H i 4 C p c y c l o p e n t a d i e n y l , T jS - C s H s -C p * p e n t a m e t h y l c y c l o p e n t a d i e n y l , T i 5 - C 5 M e 5 " A h e a t A G ^ r o t free energy o f rotat ion d d o u b l e t d d double t o f doublets d t double t o f triplets E e l ec t rophi le E t e t h y l , C2H5 p H } p r o t o n d e c o u p l e d h v l i g h t energy (photo lys is ) H z H e r t z , s e c o n d s - 1 J c o u p l i n g constant Japp apparent c o u p l i n g constant (v i r tua l c o u p l i n g ) Jgem g e m i n a l c o u p l i n g constant k c a l / m o l k i l o c a l o r i e s per m o l e X. w a v e l e n g t h ^max w a v e l e n g t h o f m a x i m u m absorpt ion X L anc i l l a ry l i g a n d L n a n c i l l a r y l igands m m u l t i p l e t M central meta l a tom o f a c o m p l e x M e m e t h y l , C H 3 m g m i l l i g r a m m L m i l l i l i t r e m m H g m i l l i m e t r e s o f m e r c u r y (pressure) m o l m o l e N u n u c l e o p h i l e n m n a n o m e t r e N M R nuc lear magnet ic resonance N O E nuc lear Overhauser effect N O E D I F F nuc lear Overhauser effect di f ferem P h p h e n y l , Q5H5 p p m parts per m i l l i o n q quar te t R a l k y l or a r y l group ref re ference s s i n g l e t t t r ip le t t t t r iplet o f tr iplets T c temperature o f coalescence T H F te trahydrofuran, C4H8O u v / v i s u l t r a v i o l e t - v i s i b l e w w a t t X an ion ic l i g a n d , usua l ly ha l ide x i A c k n o w l e d g e m e n t I w i s h to express m y s incere a p p r e c i a t i o n to m y r e s e a r c h s u p e r v i s o r , D r . M i c h a e l D . F r y z u k , f o r a l l o f h i s i n s t r u c t i o n , pat ience a n d g u i d a n c e throughout the course o f this w o r k . I a m also extremely t h a n k f u l to M r . Jesse N g , D r . N e i l M c M a n u s , D r . G r a h a m W h i t e , M r . D a v e M c C o n v i l l e , M r . M u r u g e s a p i l l a i M y l v a g a n a m , M r s . K i r a n J o s h i , M r . T i m H a d d a d , D r . B r i a n L l o y d and the rest o f the F r y z u k lab group for their exce l lent c r i t i c i s m , h e l p f u l d iscuss ions and, most o f a l l , their f r i e n d s h i p . A s p e c i a l thanks to M o m and D a d , T a n and R o n , Jan and C e c , and a l l o f m y f a m i l y f o r their c o n t i n u a l l o v e and encouragement. xii T o m y husband, Dan ie l , for his uncondit ional love and never -ending patience, support, and prayers for m e . 1 C H A P T E R 1. C A R B E N E A N D A L K Y L I D E N E C O M P L E X E S 1.1 Introduction C a r b e n e s ( : C R 2 ) are v e r y energe t i c spec ies w h i c h p l a y a r o l e i n m a n y reac t ions a n d c a n serve as b u i l d i n g b l o c k s i n o r g a n i c s y n t h e s i s . 1 B e c a u s e o f their s h o r t - l i v e d n a t u r e , carbenes are d i f f i c u l t to s t u d y a n d c a n o n l y be i s o l a t e d b y e n t r a p m e n t i n l o w t e m p e r a t u r e m a t r i c e s . 2 H o w e v e r , they c a n be s t a b i l i z e d b y c o o r d i n a t i o n to a m e t a l centre , a l l o w i n g charac ter iza t ion o f the carbene as a l i g a n d . T h e f i rs t studies o f such c o m p l e x e s began just over t w o decades a g o , 3 a n d s ince then, c o m p l e x e s c o n t a i n i n g t r a n s i t i o n m e t a l - c a r b o n d o u b l e b o n d s ( M = C ) h a v e b e c o m e w i d e s p r e a d i n o r g a n o m e t a l l i c c h e m i s t r y . 4 N o t o n l y are they o f theoret ical importance f r o m the p o i n t o f v i e w o f b o n d i n g , but they a lso d i s p l a y interest ing r e a c t i v i t y patterns. M e t a l c a r b e n e 5 c o m p l e x e s have been f o u n d to par t i c ipa te i n a v a r i e t y o f d i f ferent processes as r e a c t i o n in termedia tes a n d a l s o h a v e p o t e n t i a l a p p l i c a t i o n i n o r g a n i c s y n t h e s i s . 6 - 7 A v e r y u s e f u l s y n t h e t i c r e a c t i o n i s the s t o i c h i o m e t r i c f o r m a t i o n o f c y c l o p r o p a n e s o b t a i n e d f r o m the i n t e r a c t i o n o f an o l e f i n w i t h a m e t a l c a r b e n e 8 ( e q u a t i o n 1-1). A l t e r n a t i v e l y , o ther c a r b e n e c o m p l e x e s are k n o w n to c a t a l y z e metathesis reac t ions w h e n i n the presence o f o l e f i n s (equat ion 1 - 2 ) . 9 - 1 0 T h e c h a i n OR R + ( 1 - D R R R R' I M = C 2 p r o p a g a t i o n step i n the Z i e g l e r - N a t t a p o l y m e r i z a t i o n o f alkenes has t r a d i t i o n a l l y been p r o p o s e d to p r o c e e d b y m i g r a t o r y i n s e r t i o n o f the o l e f i n i n t o a m e t a l - c a r b o n s ing le b o n d , 1 1 as s h o w n i n path (a) o f S c h e m e 1-1. H o w e v e r , the i s o l a t i o n o f an a l k y l i d e n e -Scheme 1-1 L nM—CH 2R + ) c = ( / L nM—CH 2R I I L p M - C - C - C H g R (a) H U M = C \ H R I I LnM-C-C—CH 2 R (b) h y d r i d e c o m p l e x w h i c h p o l y m e r i z e s e t h y l e n e 1 2 lends support to an alternative f o r m for the act ive catalyst (path (b)). A v e r y r e m a r k a b l e and u s e f u l reac t ion o f a l k y n e s w i t h ( a l k o x y a r y l ) c h r o m i u m carbene c o m p l e x e s was r e p o r t e d 1 3 i n 1975 (equation 1-3), and s i n c e then , the c o - c y c l i z a t i o n process has been u s e d i n the synthes i s o f v a r i o u s n a t u r a l p r o d u c t s . 7 I n a d d i t i o n , c a r b e n e c o m p l e x e s h a v e b e e n p r o p o s e d as intermediates i n the F i s c h e r - T r o p s c h reduct ion o f C O b y H 2 , 1 4 i n the rearrangement o f s m a l l - r i n g h y d r o c a r b o n s , 1 5 and i n m e t a l - c a t a l y z e d d e c o m p o s i t i o n o f d i a z o c o m p o u n d s w i t h o le f ins to f o r m c y c l o p r o p a n e s . 1 6 ( C O ) 5 C r = C . P- CO R R ' C = C R " c o § R* I C = C r — (CO) 3 C OH * d - 3 ) Cr (CO)3 3 1.2 Background and Nomenclature I n 1964 , F i s c h e r a n d M a a s b o l r e p o r t e d 3 the s y n t h e s i s a n d i s o l a t i o n o f p e n t a c a r b o n y l [ m e t h o x y ( p h e n y l ) c a r b e n e ] t u n g s t e n ( 0 ) w h i c h w a s t h e f i r s t c h a r a c t e r i z e d m e t a l carbene c o m p l e x ( F i g u r e l - l ( a ) ) . T h i s l e d to a d i s c o v e r y o f a vas t n u m b e r 1 7 ' 1 8 o f c o m p o u n d s i n v o l v i n g meta ls f r o m groups 6-8 c o o r d i n a t e d to a h e t e r o a t o m - s u b s t i t u t e d carbene l i g a n d a n d , as a r e s u l t , carbenes o f th is t y p e are a p p r o p r i a t e l y re ferred to as " F i s c h e r - t y p e carbenes" . ^ O M e H (CO)5 W = C ( lBuCH2)3 T a = C ( a ) ( b ) F i g u r e 1-1. E x a m p l e s o f the t w o t y p e s o f c a r b e n e c o m p l e x e s (a) F i s c h e r carbene and (b) S c h r o c k a l k y l i d e n e . I n contras t , S c h r o c k m o r e r e c e n t l y d i s c o v e r e d a series o f c o m p o u n d s a lso c o n t a i n i n g a f o r m a l m e t a l - c a r b o n d o u b l e b o n d w h i c h w e r e f o u n d to be s i g n i f i c a n t l y d i f ferent f r o m those o f F i s c h e r and o t h e r s . 1 9 These n e w c o m p l e x e s are d e r i v e d f r o m meta l a l k y l s b y r e m o v a l o f an a - h y d r o g e n a t o m , resu l t ing i n the carbene carbon h a v i n g o n l y a l k y l and/or h y d r o g e n substituents ( F i g u r e l - l ( b ) ) , a n d hence are of ten referred to as " S c h r o c k - t y p e a l k y l i d e n e s " . T h e y are m o r e c o m m o n a m o n g the earl ier transi t ion m e t a l s a n d s h o w r e m a r k a b l e d i f f e r e n c e s i n r e a c t i v i t y as c o m p a r e d to the p r e v i o u s F i s c h e r carbene c o m p l e x e s . T h e k e y d i f f e r e n c e between the t w o types o f c o m p l e x e s l i e s i n the reac t ive nature o f the carbene c a r b o n ; i n the F i s c h e r - t y p e c o m p o u n d s , i t is e l e c t r o p h i l i c , and i n the S c h r o c k - t y p e , i t i s n u c l e o p h i l i c . 4 1.3 Reactivity Patterns T h e reac t iv i ty b e h a v i o r w h i c h is t y p i c a l l y f o u n d f o r F i scher -carbene c o m p l e x e s i s s u m m a r i z e d i n F i g u r e l -2 (a) . T h e carbene c a r b o n i s v u l n e r a b l e to attack b y E * S- h+/ &f 6 - / , j v ) L n M = c L ^ C ^ - ^ E ;(v) Nu H t(iii) B B (a) (b) Figure 1-2. T y p i c a l r e a c t i v i t y patterns f o r (a) e l e c t r o p h i l i c carbene; and (b) n u c l e o p h i l i c a l k y l i d e n e . n u c l e o p h i l e s , w h i c h c a n result i n heteroatom subst i tut ion , or b y L e w i s bases l e a d i n g to adduct f o r m a t i o n ( F i g u r e l - 2 ( i ) ) . F o r e x a m p l e , ca t ion ic carbene c o m p l e x e s tend to u n d e r g o s i m p l e a d d i t i o n processes , as is s h o w n f o r the i r o n m e t h o x y c a r b e n e u p o n r e a c t i o n w i t h m e t h y l l i t h i u m 2 0 (equation 1-4). N e u t r a l c o m p l e x e s c a n react b y either a d d i t i o n ( e q u a t i o n 1-5), o r a d d i t i o n - e l i m i n a t i o n to g i v e a s u b s t i t u t e d c a r b e n e 7 'x , . CH 3 Li I r ^ n ° C / e + ^ / H - ° C F e ^ / O C H a ( 1 4 ) / \ / 7 ^ C H 3 C O CCHj C O H ( C O ) 5 W = C OMe PMe 3 Me PMe 3 I ( C O ) 5 W — C — O M e I Me (1-5) 5 (equat ion 1-6). A l t e r n a t i v e l y , e lec t rophi les can coordinate to the carbene heteroatom ( F i g u r e l - 2 ( i i ) ) , w h i c h c a n resul t i n c a r b y n e ( M = C ) f o r m a t i o n i f the substi tuent i s a b s t r a c t e d ( e q u a t i o n 1-7).7 I f o n e o f the substi tuents o n the carbene c a r b o n i s an (CO) 'OMe (CO) 5Cr—C- •Nu -OMe" (CO) 5 Cr=C Nu Ph (1-6) Nu' - RS' , R 2N' , Ph' M .Y •R + E - M = C — R + X" ( Y - E - ) X—Ms=C—R M = Cr, Mo,W (1-7) Y = OMe, OH, CI R = Me, Ph E - BX 3 , Ag+ X = halide a l k y l g r o u p , the a l k y l hydrogens tend to be quite a c i d i c , and deprotonat ion b y a L e w i s base c a n l e a d to an a n i o n i c c o m p l e x ( F i g u r e l - 2 ( i i i ) ) . T h e a f o r e m e n t i o n e d c y c l o p r o p a n e f o r m a t i o n (equation 1-1) is a t y p i c a l react ion o f carbene c o m p l e x e s w i t h o l e f i n s a n d arises f r o m the interact ion o f the e lec tron densi ty o f the C = C d o u b l e b o n d w i t h the e l e c t r o p h i l i c carbene a tom. T h e r e a c t i v i t y o f F i s c h e r - c a r b e n e c o m p l e x e s has l e d to the ass ignment o f a p a r t i a l n e g a t i v e c h a r g e o n the m e t a l a n d a p a r t i a l p o s i t i v e charge o n the carbene c a r b o n ( F i g u r e l - 2 a ) . 1 3 « 1 7 T h e r o l e o f the heteroatom substituents i s b e l i e v e d to be f o r s t a b i l i z a t i o n o f the c o m p l e x b y 7t-donation to the e l e c t r o n d e f i c i e n t c a r b o n as s h o w n i n F i g u r e 1-3, and i n d e e d , i n the f irst x - r a y c r y s t a l l o g r a p h i c s tudy o f a carbene M = M-X M-•Y + Figure 1-3. L i m i t i n g f o r m s w h i c h c o n t r i b u t e t o s tab i l i za t ion o f the carbene carbon . 6 c o m p l e x the distances be tween the carbene c a r b o n a n d heteroatom substituents were f o u n d to be short re la t ive to s ing le b o n d s . 1 7 In contrast , a l k y l i d e n e c o m p l e x e s d i s p l a y r e a c t i v i t y patterns consistent w i t h a n u c l e o p h i l i c c a r b o n a t o m , a n d a t y p i c a l react ion o f an a l k y l i d e n e w i t h an o l e f i n results i n the f o r m a t i o n o f a m e t a l l a c y c l o b u t a n e in te rmedia te l e a d i n g to o l e f i n metathesis (equat ion 1-2). T h e o b s e r v e d di f ferences i n reac t iv i ty have l e d to the ass ignment o f a r e v e r s e d b o n d p o l a r i t y as c o m p a r e d to the carbene c o m p l e x e s , this t i m e w i t h the e lec t ron dens i ty o n the carbon a t o m and a par t ia l p o s i t i v e charge o n the m e t a l (F igure l - 2 b ) . A charac ter i s t i c r e a c t i o n o f an a l k y l i d e n e c o m p l e x i s w i t h e l e c t r o p h i l e s as s h o w n i n F i g u r e l - 2 ( i v ) , o r w i t h L e w i s a c i d s s u c h as A l M e 3 to f o r m adducts (equat ion 1 - 8 ) . 2 1 In fact , m a n y a l k y l i d e n e c o m p l e x e s are t rans i t ion-meta l analogues o f the c l a s s i c o r g a n i c y l i d e s that u n d e r g o W i t t i g - t y p e r e a c t i o n s w i t h c a r b o n y l f u n c t i o n a l i t i e s , 2 2 * 2 3 and the a l k y l i d e n e s have e v e n been f o u n d to react w i t h esters and a m i d e s 2 4 (equation 1-9). F i n a l l y , r e m o v a l o f an a - h y d r o g e n o n the a l k y l i d e n e carbon b y a s t rong base o r b y i n t r a m o l e c u l a r r e d u c t i v e - e l i m i n a t i o n i s a route to a l k y l i d y n e ( M = C - R ) c o m p l e x e s 2 5 ( F i g u r e l - 2 ( v ) ) . ^ C H g CH3 Cp2Ta + AIMe3 • Cp2fa AIMe 3 ( 1 - 8 ) ^ C H 2 ^ C H 2 ^ O II + C H 3 C C H 3 C H 3 H • [R3Ta(0)]x + C = C C H 3 ^ C M e 3 H / (1 - 9 ) R 3 T a = C \ o 'CMe. 3 \ II + Me 2NCH Me 2N H • [R3Ta(0)]x + J ^ c = C ^ VT ^ C M e 3 ( R - Me 3 CCH 2 ) 7 1.4 Bonding T h e o b s e r v e d d i f f e r e n c e s i n r e a c t i v i t y b e t w e e n the t w o d i s t i n c t g r o u p s o f carbene c o m p l e x e s h a v e resul ted i n contras t ing b o n d i n g v i e w s f o r the m e t a l - c a r b o n in terac t ions , a n d d i f f e r e n t f o r m a l charges assoc ia ted w i t h the t w o l i g a n d types . A v a l e n c e b o n d v i e w 2 6 - 2 7 f o r the meta l -carbene b o n d i n the F i s c h e r - t y p e c o m p l e x e s i n v o l v e s a s inglet-state carbene d o n a t i n g an e lec t ron p a i r to the m e t a l f r o m an s p 2 h y b r i d o r b i t a l , a n d i n re turn , the m e t a l donates a p a i r o f d e lectrons b a c k to the e m p t y p o r b i t a l o f the c a r b e n e ( F i g u r e l - 4 a ) . I n contras t to t h i s , the S c h r o c k - t y p e c o m p l e x e s h a v e a c o v a l e n t - t y p e d o u b l e b o n d , r e s u l t i n g f r o m the t w o u n p a i r e d e lec t rons f r o m a tr iplet-state carbene s p i n - c o u p l i n g to t w o e lec t rons o n the m e t a l centre ( F i g u r e l - 4 b ) . I n support o f these b o n d i n g theories , ca l cu la t ions o n a var ie ty o f f ree carbenes h a v e s h o w n that h e t e r o a t o m subst i tuents s t a b i l i z e the s i n g l e t state w h e r e a s a l k y l subst i tuents s t a b i l i z e the t r ip le t s t a t e . 2 6 A s f o r f o r m a l charges , the F i s c h e r - t y p e carbene i s c o n s i d e r e d to be a n e u t r a l l i g a n d a n d the S c h r o c k - t y p e i s ass igned a charge o f - 2 . 2 8 1.5 Synthesis 1.5.1 Synthetic Routes S i n c e research f i r s t began i n this f i e l d , hundreds o f carbene c o m p l e x e s have been synthes ized a n d a large n u m b e r o f methods has been d e v e l o p e d to p r o d u c e these ( a ) (b) Figure 1-4. T w o b o n d i n g v i e w s f o r the c a r b e n e m o i e t y (a) donor/acceptor b o n d ; and (b) covalent b o n d . 8 c o m p o u n d s f o r a v a r i e t y o f t r a n s i t i o n m e t a l s . 1 8 - 2 6 H o w e v e r , there are three bas ic strategies u s e d to synthes ize carbene and a l k y l i d e n e c o m p l e x e s : (1) t r a n s f o r m a t i o n o r m o d i f i c a t i o n o f a c o o r d i n a t e d c a r b o n l i g a n d ( i .e . , o f a m e t a l c a r b o n s ingle b o n d ) ; (2) a d d i t i o n o f a carbene p r e c u r s o r to a c o o r d i n a t i v e l y unsa tura ted m e t a l c o m p l e x ; and (3) m o d i f i c a t i o n o f an e x i s t i n g carbene c o m p l e x ; T h e s p e c i f i c strategy i n use w i l l be re ferred to as character is t ic e x a m p l e s o f the m o s t c o m m o n synthetic methods are d i scussed f o r the di f ferent types o f carbene c o m p l e x e s . 1.5.2 Synthesis of Heteroatom-Substituted Carbene Complexes T h e m e t h o d F i s c h e r and M a a s b o l o r i g i n a l l y u s e d 3 to prepare the f irst carbene c o m p l e x is s t i l l one o f the m o s t c o m m o n synthet ic routes f o r e l e c t r o p h i l i c carbene c o m p o u n d s . U t i l i z i n g strategy (1) above , i t i n v o l v e s the r e a c t i o n o f r e a d i l y a v a i l a b l e meta l c a r b o n y l c o m p o u n d s w i t h o r g a n o l i t h i u m reagents, g i v i n g the a n i o n i c a c y l l i t h i u m sa l t s w h i c h are t h e n a l k y l a t e d w i t h e l e c t r o p h i l e s s u c h as t r i a l k y l o x o n i u m tetraf luoroborates (equat ion 1-10). T h i s s t ra ight forward preparat ive route g i v e s h i g h y i e l d s o f the d e s i r e d carbene c o m p l e x a n d has been e x t e n d e d 1 7 to a w i d e range o f o r g a n o l i t h i u m r e a g e n t s a n d m e t a l centres i n c l u d i n g c h r o m i u m , m o l y b d e n u m , m a n g a n e s e , t e c h n e t i u m , r h e n i u m a n d i r o n . T h e same t y p e o f r e a c t i o n c a n be p e r f o r m e d w i t h stable n e u t r a l a c y l , i m i d o y l , a n d t h i o a c y l c o m p l e x e s o f o s m i u m , r u t h e n i u m o r i r i d i u m u s i n g v a r i o u s a l k y l a t i n g reagents to g i v e c a t i o n i c he teroatom-subst i tuted carbene s p e c i e s . 2 9 O L i + Me30BF4 M(CO)6 + LiR (CO)5M=C - LiBF4 - Me20 (CO)5M=C (1-10) R 9 A n o t h e r strategy (1) m e t h o d , w h i c h a lso has been a p p l i e d to both m i d d l e 1 8 and l a t e 2 9 t rans i t ion-meta l c o m p o u n d s , i s the n u c l e o p h i l i c a d d i t i o n o f a l c o h o l s , amines o r t h i o l s to c o o r d i n a t e d i s o c y a n i d e l igands (equation 1-11). C o m m o n carbene precursors u s e d f o r strategy (2) syntheses are the e l e c t r o n -r i c h o l e f i n s s u c h as the one s h o w n i n e q u a t i o n 1-12. T h e y h a v e b e e n u s e d to s y n t h e s i z e a great v a r i e t y o f m o n o - , b i s - , t r i s - , a n d te t rak iscarbene c o m p l e x e s f o r di f ferent meta l c e n t e r s . 2 9 ' 3 0 (1-11) . N H R LnM—CssN—R + RmXH |_ n M=C^ ( X - N , O , S) X Rm CH2Ph CH2Ph I I RuCI3(NO)(PPh3) + | ) = ( J • CI(NO)RuJ=( | U 1 " 1 2 ) t > 0 I I CHaPh CH2Ph T h e r e are n u m e r o u s w a y s i n w h i c h n e w carbene c o m p l e x e s c a n be obta ined b y the m o d i f i c a t i o n o f e x i s t i n g carbene c o m p o u n d s (strategy (3)). T h e carbene l i g a n d i t se l f can be m o d i f i e d as i l lus t ra ted i n S c h e m e s 1-2 and 1-3, o r the other l i g a n d s o n Scheme 1-2 MeNH2 -NHMe (CO)5Cr=C. "Me 1. THF, -20°C, „ _ 'OMe / MeONa ^ O M e (CO)5Cr=C L _ • (CO) 5 Cr=C^ ^ \ 2. Me3OBF4 ^ C H n M e 3 . n n-1,2,3 ^CMe • (CO) 5Cr=C^ MeONa ^ CD. 10 Scheme 1-3 MesNH M=Ru, X=F M=Os, X=CI CI2(CO)(PPh3)2M=CX2 { M = > R ^ x = F *~ CI2(CO)(PPh3)2M==C^ CI2(CO)(PPh3)2M=C, " ' NMe2 X OMe NaSEt F the m e t a l c a n be c h a n g e d o r substi tuted. T h e diha locarbene c o m p l e x e s o f S c h e m e 1-3 c o m p r i s e a recent ly d e v e l o p e d c lass o f carbene c o m p l e x e s w h i c h are m o r e c o m m o n a m o n g the later t rans i t ion metals r u t h e n i u m , o s m i u m and i r i d i u m . 2 9 - 3 1 T h e p r i n c i p a l m e t h o d f o r d iha locarbene synthesis i s the abstract ion or e l i m i n a t i o n o f a h a l i d e f r o m a t r i h a l o m e t h y l l i g a n d , as s h o w n i n the e x a m p l e i n S c h e m e 1-4. Scheme 1-4 Ru(CO)2L3 Hg(CF3)2 -L O C ^ I ^HgCF 3 Ru O C ^ I X C F 3 L C l s -HgCI(CF3) C l ^ I ^ C l Ru O C ^ I ^ C F 2 L HCI, gas -HF, -CO O C ^ I Ru O C ^ I X C F , 11 1.5.3 Synthesis of Alkylidene Complexes E q u a t i o n s 1-13 a n d 1-14 s h o w e x a m p l e s o f the t w o m a i n routes to a l k y l i d e n e c o m p l e x e s : b y r e m o v a l o f an a - h y d r o g e n o n a c o o r d i n a t e d a l k y l l i g a n d (strategy (1)), o r by r e a c t i o n w i t h d i a z o a l k a n e c o m p o u n d s , R 2 C N 2 (strategy (2)) . T h e f i rs t route Ta(CH 2CMe 3) 3Cl2 + 2LiCH 2 CMe 3 ( M e 3 C C H 2 ) 3 T a = C + C M e 4 ( i _ i 3 ) " 2 L i C I ^ C M e 3 C = N = N OsCI(NO)(PPh3)3 - C I ( N O ) ( P P h 3 ) 2 O s = C ^ (1-14) - P P h 3 , - N 2 H (R = H, Me, p-tolyl) a p p l i e s a l m o s t e x c l u s i v e l y to the e a r l y t r a n s i t i o n - m e t a l c o m p l e x e s as demonst ra ted b y S c h r o c k a n d c o w o r k e r s . 1 9 - 3 2 W h i l e the latter route has been a p p l i e d to a w i d e r a n g e o f t r a n s i t i o n m e t a l centres , i t i s the p r i n c i p a l m e t h o d u s e d f o r p r e p a r i n g a l k y l i d e n e s o f the la ter m e t a l s . 2 9 - 3 1 H o w e v e r , there are a f e w e x c e p t i o n s w o r t h m e n t i o n i n g . A d d i t i o n o f m i n e r a l and organic acids across the meta l carbon tr iple bonds o f r u t h e n i u m a n d o s m i u m a r y l c a r b y n e c o m p l e x e s has been s u c c e s s f u l i n g i v i n g the s e c o n d a r y a l k y l i d e n e c o m p l e x e s s h o w n i n equat ions 1-15 a n d 1 - 1 6 . 3 3 S h a w and C I ( C O ) ( P P h 3 ) 2 M = C — R H C I » C I 2 ( C O ) ( P P h 3 ) 2 M = C ^ ^ (1-15) M=Os;R=H,Me ^ ^ R M=Ru; R^OMe MeCOoH , , , CI(CO)(PPh 3 ) 2 Os=CPh — * - [fa -0 2CMe)(CO)(PPh 3) 2Os=CHPh] CI0 4 (1-16) 12 c o w o r k e r s r e p o r t e d 3 4 * 3 5 a n u n u s u a l c a r b e n e d e r i v e d i n l o w y i e l d f r o m a c y c l o m e t a l l a t e d i r i d i u m h y d r i d e c o m p l e x u p o n t h e r m o l y s i s ( equat ion 1-17). T h e i r r e p r o d u c i b i l i t y o f the reac t ion has prevented an i n - d e p t h study o f this c o m p o u n d but, o n the basis o f s tructural a n d ^ C f 1 ! ! } N M R data , the authors f a v o u r the ass ignment o f the y l i d e structure f o r the c o m p o u n d rather than the carbene. C i H — C — I r — C I < ^ l , ^ — P B u 2 200-C 15 mm Hg ( -H 2 ) " (+H2) r P'Bua I = l r—CI I, carbene P , B u 2 Ir— CI P l Bu 2 ylide (1-17) T h e genera t ion o f i s o l a b l e t e r m i n a l m e t h y l i d e n e ( M = C H 2 ) c o m p l e x e s o f the m i d d l e a n d late meta l s b y m e t h o d s other than u s i n g d i a z o m e t h a n e i s q u i t e rare . G l a d y s z et a l r e p o r t e d 3 6 the f i r s t i s o l a b l e e l e c t r o p h i l i c m e t h y l i d e n e c o m p l e x , s y n t h e s i z e d b y a - h y d r o g e n abstract ion f r o m a c o o r d i n a t e d m e t h y l group o n r h e n i u m (equat ion 1-18). I r i d i u m m e t h y l i d e n e c o m p l e x e s have been postula ted b y T h o r n and / R e \ ON | PPh 3 C H a Ph 3 C + PF 6 " CH 2 CI 2 ON || PPh 3 H H (1-18) PFc T u l i p 3 7 ' 3 8 as i n t e r m e d i a t e s i n t w o separate r e a c t i o n s , b o t h o f w h i c h u n d e r g o rearrangements to m o r e stable products , as s h o w n i n S c h e m e s 1-5 a n d 1-6. S u c h use o f a l k o x y m e t h y l c o m p l e x e s to generate a m e t h y l i d e n e has also been a p p l i e d to metals o f g r o u p s 6 - 8 , 3 9 b u t the r e s u l t i n g c o m p l e x e s are , at best , c h a r a c t e r i z e d b y spectroscopic methods o n l y . 13 Scheme 1-5 O-feOMe C H 2 -(EOMe) CHP \f I CH2 H I L,lr (L=PMe3, E+=electrophile, '-postulated intermediate) Scheme 1-6 CH3 , ' - - L r~-l r — C H 2 O C K 3 Si BrCH2OMe 1 -MeCCHjjOMe CH3 1 . * Br—I r =CH 2 Br ..L Br—I r—CH2ChU Br—lr—CH 2CH 3 (L=PMe3, '-postulated intermediate) 14 1.6 Thesis Content I n 1985 , o u r research g r o u p r e p o r t e d 4 0 the f o r m a t i o n o f an i s o l a b l e i r i d i u m m e t h y l i d e n e c o m p l e x p r o d u c e d u p o n p h o t o l y s i s o f an i r i d i u m (III) d i a l k y l , as s h o w n i n equat ion 1-19. N o t o n l y i s i t the f irst e x a m p l e o f a square p lanar i r i d i u m m e t h y l i d e n e , but i t a lso appears to f o r m v i a cc-hydrogen e l i m i n a t i o n (or abstraction) f r o m one o f the a l k y l l i g a n d s , based o n l a b e l l i n g studies a n d p r o d u c t a n a l y s i s . A l t h o u g h this i s a general synthet ic route f o r m a n y a l k y l i d e n e s o f the ear ly t rans i t ion-meta ls , i t appears to be qui te rare f o r m e t a l a l k y l s o f groups 8-10. T h e u n u s u a l s tab i l i ty w h i c h a l l o w s i s o l a t i o n o f the m e t h y l i d e n e can be attributed to the u n i q u e tridentate l i g a n d s y s t e m 4 1 o n the i r i d i u m center. T h e b u l k y p h e n y l substituents o n the p h o s p h i n e donors p r o v i d e a " p o c k e t " to protect the m e t h y l e n e uni t , a n d the w e a k trans i n f l u e n c e o f the a m i d e s tab i l izes the o t h e r w i s e reac t ive l i g a n d . In order to exp lore further the m e c h a n i s m o f the i r i d i u m m e t h y l i d e n e f o r m a t i o n , as w e l l as attempt to d i s c o v e r n e w a l k y l i d e n e species , a series o f b i s ( h y d r o c a r b y l ) (where h y d r o c a r b y l i s the genera l t e r m f o r an a l k y l o r a r y l l i g a n d ) c o m p o u n d s o f i r i d i u m (IJJ) w e r e s y n t h e s i z e d , f u l l y charac ter ized a n d m o n i t o r e d under p h o t o l y s i s b y N M R s p e c t r o s c o p y . A s a r e s u l t , a b e n z y l i d e n e c o m p l e x ( I r = C H P h ) has been s y n t h e s i z e d but not i s o l a t e d i n a p u r e state, as yet . I n a d d i t i o n , a p r e l i m i n a r y 45 % + H2C=CHCMe3 + CMe4 (1-19) 15 i n v e s t i g a t i o n o f the p o l a r i t y and nature o f the i r i d i u m - c a r b o n d o u b l e b o n d w a s under taken b y s u r v e y i n g the reac t iv i ty o f the m e t h y l i d e n e c o m p l e x w i t h several s m a l l m o l e c u l e s , e lec t rophi les a n d n u c l e o p h i l e s . 1.7 References 1. W . K i r m s e , " C a r b e n e C h e m i s t r y " , 2 n d E d . , A c a d e m i c Press , Inc . , N e w Y o r k ( 1 9 7 1 ) . 2. (a) O . M . N e f e d o v , A . K . M a l t s e v and R . G . M i k a e l y a n , Tet . L e t t . , 4 4 (1971) 4 1 2 5 . (b) A . M . T r o z z o l o and W . A . G i b b o n s , J . A m . C h e m . S o c . , 89 (1967) 239 . 3. E . O . F i s c h e r and A . M a a s b o l , A n g e w . C h e m . , Int. E d . E n g l . , 3 (1964) 580 . 4. I. H a i d u c a n d J . J . Z u c k e r m a n , " B a s i c O r g a n o m e t a l l i c C h e m i s t r y " , W a l t e r de G r u y t e r , N e w Y o r k (1985); p . 252 . 5 . " C a r b e n e " w i l l be the general t e r m u s e d to refer to a c o m p o u n d w i t h a m e t a l c a r b o n d o u b l e b o n d , L n M = C X Y , w h e r e X a n d Y are not any s p e c i f i c type o f substituents. " A l k y l i d e n e " w i l l refer to a class o f carbenes i n w h i c h X a n d Y are h y d r o c a r b y l and/or h y d r o g e n substituents. 6. J . P . C o l l m a n , L . S. H e g e d u s , J . R . N o r t o n a n d R . G . F i n k e , " P r i n c i p l e s and A p p l i c a t i o n s o f O r g a n o t r a n s i t i o n M e t a l C h e m i s t r y " , U n i v e r s i t y Sc ience B o o k s , M i l l V a l l e y , C a . (1987); chapter 16. 7. K . H . D o t z , A n g e w . C h e m . , Int. E d . E n g l . , 23 (1984) 587. 8. E . O . F i s c h e r and K . H . D o t z , C h e m . B e r . , 105 (1972) 3966 . 9 . R . H . G r u b b s , D . D . C a r r , C . H o p p i n and P . L . B u r k , J . A m . C h e m . S o c , 98 (1976) 3478 . 10. R . R . S c h r o c k , R . T . D e P u e , J . F e l d m a n , C . J . Schaver ien , J . C . D e w a n and A . H . L i u , J . A m . C h e m . Soc . , 110 (1988) 1423. 11. r e f . 6 , p . 5 8 0 . 16 12. H . W . T u r n e r , R . R . S c h r o c k , J . D . F e l l m a n n and S. J . H o l m e s , J . A m . C h e m . S o c . , 105 (1983) 4942 . 13. K . H . D o t z , A n g e w . C h e m . , Int. E d . E n g l . , 14 (1975) 644. 14. ref. 6, p . 654. 15. ref. 6, pp .816-820 . 16. ref. 6, p p . 800-806. 17. E . O . F i s c h e r , A d v . Organomet . C h e m . , 14 (1976) 1. 18. D . J . C a r d i n , B . C e t i n k a y a and M . F . Lapper t , C h e m . R e v . , 72 (1972) 545 . 19. R . R . S c h r o c k , A c c . C h e m . Res . , 12 (1979) 98 . 20 . C . P . C a s e y and W . M . M i l e s , J . Organomet . C h e m . , 117 (1976) 189. 2 1 . R . R . S c h r o c k a n d P . R . Sharp, J . A m . C h e m . Soc . , 100 (1978) 2389. 22 . R . R . S c h r o c k , J . A m . C h e m . Soc . , 98 (1976) 5399. 23 . F . N . T e b b e , G . W . P a r s h a l l and G . S. R e d d y , J . A m . C h e m . S o c . , 100 (1978) 3611 . 24 . R . H . G r u b b s , J . O r g . C h e m . , 50 (1985) 2316. 25 . r e f . 6 , p . l 4 0 . 26 . T . E . T a y l o r and M . B . H a l l , J . A m . C h e m . Soc . , 106 (1984) 1576. 27 . E . A . Car ter and W . A . G o d d a r d III, J . A m . C h e m . Soc . , 108 (1986) 4746 . 28. re f .6 , p p . 27-28 . 29 . M . A . G a l l o p and W . R . R o p e r , A d v . Organomet . C h e m . , 25 (1986) 121. 30 . M . F . L a p p e r t , J . Organomet . C h e m . , 100 (1975) 139. 31 . W . R . R o p e r , J . Organomet . C h e m . , 300 (1986) 167. 32. C . D . W o o d , S . J . M c L a i n and R . R . S c h r o c k , J . A m . C h e m . Soc . , 101 (1979) 3210. 33 . G . R . C l a r k , K . M a r s d e n , W . R . R o p e r and L . J . W r i g h t , J . A m . C h e m . Soc . , 102 (1980) 6570 . 34. H . D . E m p s a l l , E . M . H y d e , R . M a r k h a m , W . S. M c D o n a l d , M . C . N o r t o n , B . L . 17 S h a w and B . W e e k s , J . C h e m . S o c . C h e m . C o m m u n . , (1977) 589 . 35 . C . C r o c k e r , H . D . E m p s a l l , R . J . E r r i n g t o n , E . M . H y d e , W . S. M c D o n a l d , R . M a r h a m , M . C . N o r t o n , B . L . S h a w and B . W e e k s , J . C h e m . S o c . D a l t o n Trans . , (1982) 1217. 36. W . T a r n , G.-Y. L i n , W . - K . W o n g , W . A . K i e l , V . K . W o n g a n d J . A . G l a d y s z , J . A m . C h e m . Soc . , 104 (1982) 141. 37. D . L . T h o r n , O r g a n o m e t a l l i c s , 1 (1982) 879. 38 . D . L . T h o r n a n d T . H . T u l i p , J . A m . C h e m . Soc . , 103 (1981) 5984 . 39. (a) P . W . J o l l y and R . Pett i t , J . A m . C h e m . S o c , 88 (1966) 5044 . (b) M . L . H . G r e e n , M . Ishaq and R . N . W h i t e l y , J . C h e m . So c . ( A ) , (1967) 1508. (c) P . E . R i l e y , C . E . C a p s h e w , R . Pettit and R . E . D a v i s , Inorg . C h e m . , 17 (1978) 408 . (d) M . B r o o k h a r t , J . R . T u c k e r , T . C . F l o o d and J . Jensen, J . A m . C h e m . Soc . , 102 (1980) 1203. 40 . M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , J . A m . C h e m . S o c , 107 (1985) 6708. 4 1 . M . D . F r y z u k and P . A . M a c N e i l , O r g a n o m e t a l l i c s , 2 (1983) 355 . 18 C H A P T E R 2. S Y N T H E S I S A N D C H A R A C T E R I Z A T I O N O F I R I D I U M B I S ( H Y D R O C A R B Y L ) C O M P L E X E S I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 2.1 Introduction F o l l o w i n g t h e d i s c o v e r y 1 o f t h e i r i d i u m m e t h y l i d e n e c o m p l e x I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] u p o n p h o t o l y s i s o f an i r i d i u m d i a l k y l spec ies , o u r research g r o u p set out to synthes ize other b i s ( h y d r o c a r b y l ) c o m p l e x e s ( a l k y l and/or a r y l ) w h i c h w o u l d h o p e f u l l y l ead to n e w a l k y l i d e n e c o m p o u n d s . A s a resul t , a general s y n t h e t i c r o u t e w a s d e v e l o p e d f o r the p r e p a r a t i o n o f c o m p l e x e s o f the f o r m u l a I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] where R = C H 3 , C 6 H 5 , C H 2 P h and R" = C H 3 , C 6 H 5 , CH2PI1, C H 2 C M e 3 , C H 2 S i M e 3 . S u c h b i s ( h y d r o c a r b y l ) c o m p l e x e s o f i r i d i u m are ac tua l ly qui te u n i q u e i n the l i terature. 2.2 Other H y d r o c a r b y l Complexes of Iridium T h e f i rs t o - b o n d e d o r g a n o i r i d i u m c o m p l e x e s were prepared i n the ear ly 1960's b y o x i d a t i v e a d d i t i o n o f o r g a n i c ha l ides to V a s k a ' s c o m p o u n d . 2 3 - 0 S i n c e then, m a n y a l k y l a n d a r y l i r i d i u m species have been reported and the n u m b e r s are i n c r e a s i n g as the interest i n t rans i t ion meta l h y d r o c a r b y l c o m p l e x e s f o r a p p l i c a t i o n i n cata lys is and o r g a n i c synthes is cont inues to g r o w . 3 * 4 B y far , most o f the a l k y l a n d a r y l c o m p l e x e s k n o w n f o r i r i d i u m are o f Ir (UI) where the meta l center i s c o o r d i n a t i v e l y saturated i n an o c t a h e d r a l 2 o r p s e u d o - o c t a h e d r a l 5 ( " p i a n o - s t o o l " ) e n v i r o n m e n t . O n e i m p o r t a n t e x a m p l e o f the latter type i s the c o m p l e x C p * I r ( C O ) H ( C H 3 ) , w h i c h i s p r o d u c e d u p o n the a c t i v a t i o n o f m e t h a n e b y C p * I r ( C O ) 2 u n d e r p h o t o l y s i s c o n d i t i o n s . 5 6 Square p l a n a r Ir(I) a l k y l s a n d a r y l s h a v e a l s o b e e n p r e p a r e d . 6 T h e s e i n c l u d e the a l k y l analogues o f V a s k a ' s c o m p o u n d w h i c h tend to be m o r e react ive than I r C l ( C O ) ( P P h 3 ) 2 due to the increased e lec t ron densi ty at the meta l centre w h e n a C I i s r e p l a c e d b y an a l k y l g r o u p R . 6 h R e m a r k a b l y , there are o n l y a f e w e x a m p l e s o f f i v e - c o o r d i n a t e 19 h y d r o c a r b y l d e r i v a t i v e s and those reported thus f a r conta in jus t a s ing le a l k y l o r a r y l l i g a n d . 7 2.3 Synthesis of I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] T h e p r e p a r a t i o n o f i r i d i u m ( I I I ) m e t h y l h y d r o c a r b y l c o m p l e x e s I r ( C H 3 ) R [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] b y r e a c t i o n o f R L i w i t h the green , s q u a r e - p y r a m i d a l m e t h y l i o d i d e c o m p l e x I r ( C H 3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (la) w a s p r e v i o u s l y d e v e l o p e d a n d r e p o r t e d . 1 ' 8 T o e x t e n d this c lass o f b i s ( h y d r o c a r b y l ) d e r i v a t i v e s , routes to other f i v e - c o o r d i n a t e , h y d r o c a r b y l h a l i d e der iva t ives have a lso been d e v e l o p e d . T h e br ight green, b e n z y l b r o m i d e c o m p l e x I r ( C H 2 P h ) B r [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (lb) i s p r o d u c e d i n 8 0 % i s o l a t e d y i e l d b y the o x i d a t i v e a d d i t i o n o f P h C H 2 B r to Ir(T|2-C g H i 4 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] i n c o m p l e t e a n a l o g y to the prepara t ion o f l a . 9 T h e p h e n y l i o d i d e c o m p l e x I r ( C 6 H s ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (lc) cannot be accessed by o x i d a t i v e a d d i t i o n , but rather hea t ing the m e t h y l i o d i d e d e r i v a t i v e i n p u r e benzene results i n the e l i m i n a t i o n o f m e t h a n e 1 0 and the f o r m a t i o n o f the o l i v e green c o m p l e x lc. T h e s t ructures o f the n e w h y d r o c a r b y l h a l i d e s l b a n d lc are c o m p l e t e l y ana logous to that o f la p r e v i o u s l y d e s c r i b e d 9 : the geometr ies are square p y r a m i d a l w i t h the h y d r o c a r b y l group o c c u p y i n g the apica l p o s i t i o n . N I r X + Li Ft' (2-1) R X R R' 1 a CH3 1 b CH2Ph 1 c C 6 H 5 Br 2 CH3 3 CH3 4 CH3 5 CH3 6 CeH5 7 C 6 H S 8 CHjPh 9 CHgPh 1 0 CHzPh 1 1 CHjPh C H 3 CHfcCMes C 6 H S CH2SiMe3 C 6 H 5 C H 3 CHgPh CH2SiMe3 C6H5 2 0 T h e b i s (hydxocarbyl ) c o m p l e x e s are generated s t ra ight forwardly b y a d d i t i o n o f one e q u i v a l e n t o f the a p p r o p r i a t e o r g a n o l i t h i u m d e r i v a t i v e to the c o r r e s p o n d i n g h y d r o c a r b y l h a l i d e 1 (equation 2-1) . T h e react ions c a n be c o n v e n i e n t l y f o l l o w e d b y the dramat i c c o l o u r changes f r o m green to deep r e d o r p u r p l e . B y * H a n d 3 1 P { ^ H ) N M R s p e c t r o s c o p y , these r e a c t i o n s are q u a n t i t a t i v e ; h o w e v e r , i s o l a t e d y i e l d s are genera l ly l o w e r , 6 0 - 8 0 % , because o f the h i g h s o l u b i l i t y o f these c o m p l e x e s . These c r y s t a l l i n e mater ia l s can be stored for several m o n t h s under an inert a tmosphere , but i n s o l u t i o n , they are ex t remely a i r and mois ture sensi t ive . 2.4 Characterization 2.4.1 1H and 1 3 C { * H } N M R Data T h e p r o t o n N M R spectra o f the b i s ( h y d r o c a r b y l ) c o m p l e x e s p r o v i d e a v a l u a b l e a n d s t r a i g h t f o r w a r d m e t h o d f o r the ir c h a r a c t e r i z a t i o n . F o r the resonances o f the l i g a n d b a c k b o n e , there are t w o p o s s i b l e patterns that are o b s e r v e d d e p e n d i n g o n the h y d r o c a r b o n subst i tuents at i r i d i u m . F o r those c o m p l e x e s w h e r e R = R ' , a n d thus have C 2 v s y m m e t r y , one observes v e r y s i m p l e spectra c o n s i s t i n g o f a sharp s inglet f o r the s i l y l m e t h y l p r o t o n s , a v i r t u a l t r iplet f o r the m e t h y l e n e s (due to c o u p l i n g to the trans d i s p o s e d p h o s p h i n e d o n o r s ) , a n d p h e n y l resonances o f the d i p h e n y l p h o s p h i n o groups i n w h i c h the or tho protons appear as one set. T h i s can be seen i n T a b l e 2-1 f o r the d i m e t h y l (2), d i p h e n y l (6) a n d d i b e n z y l (9) c o m p l e x e s i n w h i c h there are e q u i v a l e n t e n v i r o n m e n t s above a n d b e l o w the p l a n e o c c u p i e d b y the m e t a l a n d the tr identate l i g a n d . A s f o r the rest o f the c o m p l e x e s (where R * R ' ) h a v i n g o n l y C s s y m m e t r y , t w o s inglets are o b s e r v e d f o r the s i l y l m e t h y l p r o t o n s as w e l l as an A B quartet o f v i r t u a l tr iplets for the methylenes and t w o sets o f or tho p h e n y l resonances , a n d this i s i l lus tra ted i n F i g u r e 2-1 f o r the m e t h y l neopenty l c o m p l e x (3). T h e a - p r o t o n s o f the a l k y l substituents o n i r i d i u m have c h e m i c a l shif ts i n the range o f 0.51 p p m to 3.42 p p m , w i t h the m e t h y l and t r i m e t h y l s i l y l m e t h y l a - p r o t o n s 21 Table 2-1. * H N M R Data for Iridium Bis(hydrocarbyl) Complexes2 1 lr(R)R'[N(SIMe2CH2PPh2)2] Si(CH 3)2 P C H 2 S i b P(C6Hs)2 Other 2: R = R' = CH 3 0.15 (s) 1.86 (t, Ja p p=5.0) 7.06 7.61 (m, meta/para) (m, ortho) l r -CH 3 , 0.94 (t, 3Jp H =6.0) 3: R = CH 3 ; R' = CH2CMG3 0.12 (s) 0.54 (s) 1.80 (dt, Ja p p=5.0, Jgem=13-2) 1.99 (dt, Japp=5.0) 7.11 7.61 7.82 (m, meta/para) (m, ortho) (m, ortho) l r -CH 3 , lr-CH 2C(CH 3) 3, lr-CH 2C(CH 3) 3, 1.24 (t, 3JP H=5.4) 1.65 (t, 3JP H=7.8) 0.82 (S) 4: R = CH 3 ; R" = C 6 H 5 0.17 (s) 0.35 (s) 1.83 (t, Japp=5.0) 7.06 7.39 (m, meta/para) (m, ortho) l r -CH 3 , l r - C 6 H 5 , 1.48 (t, 3JpH=6.0) 6.11 (t, meta, 3JHH=7.0) 6.17 (t, para, 3 j H H = 7.o) 6.94 (m, ortho, obscured) 5: R = CH 3 ; R' = CH 2SiMe 3 0.15 (s) 0.54 (s) 1.87 (dt, Japp=6, Jgem=13) 2.05 (dt, Japp=4) 7.18 7.63 7.89 (m, meta/para) (m, ortho) (m, ortho) l r -CH 3 , lr-CH 2Si(CH 3) 3, lr-CH 2Si(CH 3) 3, 1.51 (t, 3JP H=6) 0.51 (t, 3JPH=8) 0.0 (S) 6: R = R' = C 6 H 5 0.23 (s) 1.85 (t, Japp=5.0) 6.92 7.31 (m, meta/para) (m, ortho) lr-(C6H 5)2, 6.71 (t, meta, 3 J H H = 8 .0 ) 6.79 (t, para, 3JHH=8.0) 7.31 (m, ortho, obscured) 7: R = C 6 H 5 ; R' = CH^Me* 8: R = CH 2Ph; R' = C H 3 9: R = R1 = CH2Ph 10: R = CH 2Ph; R' = CH 2SiMe 3 11: R = CH 2Ph;R , = C 6 H 5 0.40 (s) 0.62 (s) -0.02 (s) 0.20 (s) 1.74 (dt, Japp=5.1, =13.5) Jgerrv 0.42 (S) 0.45 (s) 0.23 0.27 (S) (S) 2.07 (dt, Japp=5.1) 1.68 (dt, Ja p p=4.9, Jgom=12.9) 1.79 (dt, Japp=4.9) 0.24 (s) 1.72 (t, J a p p=5) 1.98 (dt, Japp=4.7, Jgom=13.0) 1.84 (dt, Japp=4.7) 1.55 (dt, Ja p p=5.0, Jgem=13-0) 1.76 (dt, Japp=5.0) 7.01 (m, meta/para) 7.22 (m, ortho) 7.45 (m, ortho) 7.23 (m, meta/para) 7.55 (m, ortho) 7.80 (m, ortho) 7.02 (m, meta/para) 7.53 (m, ortho) 7.21 (m, meta/para) 7.63 (m, ortho) 7.77 (m, ortho) 6.95 (m, 7.31 (m, 7.51 (m, meta/para) ortho) ortho) lr-CH 2C(CH 3) 3, lr-CH 2C(CH 3) 3, l r - C 6 H 5 , l r - C H 3 , lr-CH 2 C6H 5 , lr-CH2C6Hs, l r - C H 2 C 6 H 5 , l r -CH 2 C 6 H 5 , l r -CH 2 C 6 H 5 , l r -CH 2 C 6 H 5 , lr-CH 2Si(CH 3) 3, lr-CH 2Si(CH 3) 3, l r -CH 2 C 6 H 5 , l r -CH 2 C 6 H 5 , l r - C 6 H 5 , 2.24 (t, 3 J P H = 8 ) 0.88 (s) 6.81 (br, meta) 6.87 (t, para, 3 j H H = 8 ) 7.01 (m, ortho, obscured) 1.50 (t, 3J P H = 5 .5) 2.71 (t, 3J P H =6 .9 ) 7.23 (m, obscured) 3.38 (t, 3 J P H = 6 ) 6.76 (t, meta, 3 J H H = 8 ) 6.92 (t, para, 3 J HH=8) 6.97 (d, ortho, 3 J H H = 8 ) 3.40 (t, 3J P H = 5.6) 6.88 (t, meta, 3 J H H = 7 . 5 ) 7.07 (m, para, obscured) 7.11 (m, ortho, obscured) 0.80 (t, 3 J P H = 7 . 5 ) -0.05 (s) 3.42 (t, 3J P H =6 .6 ) 6.95 (m, obscured) 6.95 (m, obscured) 8 All spectra were recorded at 25°C in C6D6 at 300 MHz or 400 MHz. Chemical shifts (in ppm) are referenced to residual solvent proton! (C6H5// at 7.15 ppm). All coupling constants (J) are given in Hz. b Japp is defined as half the distance between the outer two lines of the virtual triplet 22 Table 2-II. 1 3 C { 1 H } N M R Data for Iridium Bis(hydrocarbyl) CompIexesa lr(R)FnN(SIMe2CH2PPh2)2] SI(CH3)2 PCH2SI»> P(C S H 5 ) 2 Other 2: R=Fr=CH3 5.09 (s) 24.90 (t, Ci, 134.42 (t, Japp=48.7) Ir-C H 3 , -27.71 (t, 2JCp=4.7) Japp-6.7) C2.Ce, 134.16 (t, Japp=5.8) C3.Cs, 128.06 (obscured) c 4, 129.69 (s) 3: R=CH3; R'-CHaCMea 4.74 (s) 24.98 (t, Ci. 138.45 (t, Japp=25.2) Ir-C H 3 , -28.45 (t, 2JCP=6.8) 6.36 (t, Japp=6.4) 131.70 (t, Japp=20.2) Ir-C H 2C(CH3) 3 , 16.34 (t, 2JCP=3.1) Japp=4.4) (hCe, 135.47 (t, Japp=6.1) lr-CH2C (CH3)3, 34.95 (s) 132.91 (t, Japp=5.0) lr-CH2C(C H 3) 3, 31.94(s) Ca.Cs, 128.15 (obscured) C 4 , 129.57 (s) 129.78 (s) 4: R=CH3; R=C 6H 5 5.28 (S) 23.10 (t, Ci. Ir-C H 3 , -22.06 (t, 2JCP=4.6) 5.36 (s) Japp=7.1) C2.C6, 134.43 (t, Japp=5.3) l r - C 6 H 5 , Ci, 127.15 (t, 2JCP=6.8) 133.91 (t, Japp=5.6) C2,C 6, 137.35 (t, 3JCP=3.3) Cs.Cs. 127.95 (obscured) Cs.Cs, 126.25 (s) c 4. 129.69 (s) c 4, 120.84 (s) 129.87 (s) 5: R=CH3; R'=CH2SiMe3 4.81 (8) 24.76 (t, Ci. 137.38 (t, Japp=24.7) Ir-C H 3 , -27.93 (t, 2JCP=6.1) 6.16 (t, Japp=6.4) 131.71 (t, Japp=18.4) Ir-C H 2Si(CH 3) 3, -14.37 (s) Japp=4.1) C2.Cs, 135.53 (t, Japp=6.1) lr-CH2Si(C H 3) 3, 2.24 (s) 133.08 (t, Japp=4.8) Cs.Cs, 127.70 (s) 128.34 (s) c 4, 129.70 (s) 129.94 (s) 6: R=R,=C6H5 5.01 (S) 22.84 (t, Ci. 133.59 (t, Japp=23.9) l r - C 6 H 5 , Ci. 125.64 (t, 2J C P = 7.0) Japp-8.1) Ca.Ce, 134.41 (t, Japp=5.6) C2,C 6, 138.80 (t, 3JcP=3.5) C3.Cs. 127.60 (obscured) C3.C5, 126.13 (s) C4, 129.77 (s) c 4, 121.39 (s) 7: R=C6H5; R'=CH2CMe3 6.03 (s) 23.87 (t, C|. 129.95 (t, Japp=21.1) Ir-C 6 H 5 , Ci 6.60 (t, Japp-7.1) 137.48 (t, Japp=25.6) Ca.Cs Japp=3.6) Ca.Cs, 134.09 (t, Japp=6.0) Cs.Cs, 125.26 (s) 133.42 (t, Japp=4.9) c 4. 121.61 (s) Cs.CS, 127.93 (obscured) Ir-C H 2C(CH 3) 3, 20.45(s) c 4, 129.47 (s) lr-CH2C (CH3)3, 35.64 (s) 129.77(s) lr-CH2C(C H 3) 3, 31.49 (s) 8: R=CH2Ph; R'=CH3 4.67 (s) 24.29(t, Ci. 132.82 (t, Japp=20.7) Ir-C H 2C 6H5, 2.60 (s) 5.59 (t, Japp=6.7) 136.77 (t, Japp=24.5) lr-CH2C eHs.Ci •Japp=3.9) Cz.Cs, 133.06 (t, Japp=4.8) C2,C6, 133.46 (t, 3JCP=4.9) 135.51 (t, Japp=6.2) C3,Cs, 127.64 (s) Cs.Cs, 128.2 (obscured) c 4, 124.25 (s) c 4 , Ir-C H 3 , -31.60 (t, 2jC P=5.3) 9: R=R'=CH2Ph 4.74 (s) 21.88 (t, Ci, 134.12 (t, Japp=22.0) Ir-C H 2C 6Hs, -4.22 (t, 2JCP=3.6) Japp-7.7) Cz.Cs, 133.59 (t, Japp=5.4) lr-CH2CsH5,C1, 151.86 (s) C3.Cs, 128.10 (obscured) C2,Ce, c 4, C3.Cs. c 4, 123.78 (s) 10: R=CH2Ph; R'=CH2SiMe3 6.03 (S) 22.14 (t, Ci Ir-C rfeCsHs, -1.46 (t, 2JCP=3.1) 4.82 (s) Japp=7.3) lr-CH 2C 6H5,Ci, 151.40 (s) C2.Cs. 133.65 (t, Japp=5.5) C2.Ce 134.25 (t, Japp=5.6) C3.Cs C3.Cs. 128.60 (obscured) C 4 c 4 Ir-C H 2Si(CH 3) 3, -24.22 (t, 2JC P=4.1) lr-CH2Si(C H3)3, 2.57 (s) 11: R=CH2Ph; R'=C6H5 5.53 (s) 23.17 (t, Ci, 131.76 (t, Japp=22.6) Ir-C l-bCsHs, 4.13 (s) Japp=7.7) 135.57 (t, Japp=24.4) Ir-C^CsHs.CL 151.77 (s) C2,Cs, 133.75 (t, Japp=5.2) Ca.Cs 134.45 (t, Japp=5.8) Cs.Cs C3.Cs, 127.91 (obscured) c 4 l r - C 6 H 5 , Ci, 120.76 (t, 2JCP=7.7) c 4 C2.Cs Cs.Cs c 4 a All spectra were recorded at 25°C in C6D6 at 75.43 MHz. All chemical shifts (in ppm) are referenced to Cs 1 3CD6 at 128.00 ppm. All coupling constants (J) are given in Hz. b Japp is defined as half the distance between the outer two lines of the virtual triplet. P(C 6 H 5 ) 2 meta/para ortho ph2 Me 2 Si s I ^..CHg N lr.%* Me2Si | ^ C H 2 C M e 3 •P Ph2 I i i i i i i i i i I i i i i i i i i i | i 8.0 7.0 6.0 lr-CH 2C(CH 3) 3 lr-CW2CMe3 PCH 2Si lr-Ctf3 ArJUJ Si(CH 3) 2 i i i i I i i i i | i i i i I i i i i | i i i i I i i i i | 'i i i i 1 i i i i | i I ' ' | i ' ' t I ' ' ' ' | 1 1 5.0 4.0 3.0 2.0 1.0 0.0 PPM F i g u r e 2-1. ! H N M R spectrum for c o m p l e x 3 (300 M H z , C6D 6 ) 24 resonat ing further u p f i e l d than those o f the n e o p e n t y l a n d b e n z y l groups as w o u l d be expected . A l l s h o w c o u p l i n g to the p h o s p h i n e l i g a n d s w i t h 3 J p r a n g i n g between 5.4 a n d 8 H z . A s c a n be seen i n the ^ C p H } N M R data l i s t e d i n T a b l e 2-I I , the m e t h y l c a r b o n b o n d e d to i r i d i u m resonates a n y w h e r e b e t w e e n - 3 1 . 6 0 a n d - 2 2 . 0 6 p p m d e p e n d i n g o n the s e c o n d h y d r o c a r b o n subst i tuent . T h e m e t h y l e n e c a r b o n o f the t r i m e t h y l s i l y l m e t h y l l i g a n d is a lso f o u n d u p f i e l d be tween -24 .22 a n d -14 .37 p p m . A s f o r those o f the b e n z y l a n d n e o p e n t y l g r o u p s , the r e s o n a n c e s are f o u n d f u r t h e r d o w n f i e l d be tween -4 .22 to 4.13 p p m and 16.34 to 20 .45 p p m , respec t ive ly . A l t h o u g h 1 3 C { ! H } N M R data f o r i r i d i u m a l k y l s are s o m e w h a t l i m i t e d i n the l i terature , there does s e e m to be s o m e p r e c e d e n c e f o r h i g h f i e l d shi f ts f o r m e t h y l c a r b o n s . F o r e x a m p l e , i n the c o m p l e x e s (T| 5-C5Me5)Ir(PMe3)(CH3)X ( X = C I , CH3, H ) the m e t h y l c a r b o n r e s o n a n c e appears b e t w e e n -18 .09 p p m and -37 .96 p p m d e p e n d i n g o n the nature o f X . 5 J In the b i s ( h y d r o c a r b y l ) d e r i v a t i v e s , 2 - 1 1 , t w o b o n d c o u p l i n g to p h o s p h o r u s ( 2 Jp ) w i t h va lues between 3.1 and 7.0 H z can be o b s e r v e d f o r most o f the carbon atoms b o n d e d d i rec t ly to i r i d i u m . 2.4.2 Solution Structure A s d e s c r i b e d i n a p r e v i o u s c o m m u n i c a t i o n 8 f o r the m e t h y l a l k y l c o m p l e x e s I r ( C H 3 ) R , [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (R ' = CH3 , C H 2 C M e 3 , C H 2 S i M e 3 , C H 2 P h ) , the f i v e - c o o r d i n a t e i r i d i u m b i s ( h y d r o c a r b y l ) c o m p l e x e s h a v e a t r i g o n a l b i p y r a m i d a l g e o m e t r y i n b o t h the s o l u t i o n a n d s o l i d states o n the bas is o f * H N M R , n u c l e a r O v e r h a u s e r ef fect d i f f e rence ( N O E D I F F 1 1 ) exper iments and X - r a y d i f f r a c t i o n studies. I n p a r t i c u l a r , the N O E D I F F resul ts c l e a r l y suppor t this s t e r e o c h e m i s t r y e s p e c i a l l y w h e n cont ras ted to those resul ts o b t a i n e d f o r the s q u a r e - p y r a m i d a l m e t h y l h a l i d e c o m p l e x e s . I n the latter s i tuat ion , i r r a d i a t i o n o f one o f the sets o f m e t h y l e n e protons o f the l i g a n d b a c k b o n e g ives r ise to a p o s i t i v e N O E for the i r i d i u m m e t h y l (k-CH^) 25 resonance o f the c o m p l e x I r ( C H 3 ) B r [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , i n d i c a t i n g that the m e t h y l i s a p i c a l a n d c i s to the a m i d e d o n o r . T h e ana logous N O E D I F F e x p e r i m e n t f o r the m e t h y l i o d i d e c o m p l e x , la, w a s c o m p l i c a t e d b y a m o r e c o m p l e x m u l t i p l e t f o r the m e t h y l e n e ( P C / / 2 S i ) resonance c lose i n c h e m i c a l shif t to the i r i d i u m m e t h y l (h-CH^) resonance , thus o b s c u r i n g any observable N O E . T h e b e n z y l b r o m i d e (lb) and p h e n y l i o d i d e (lc) c o m p l e x e s w e r e a l so f o u n d to s h o w the expec ted enhancement i n the Ir-CH^Ph a n d the o r t h o p r o t o n s o f the i r i d i u m - p h e n y l g r o u p w h e n the a p p r o p r i a t e , r e s p e c t i v e m e t h y l e n e resonances w e r e i r r a d i a t e d as s h o w n i n F i g u r e s 2 -2 a n d 2-3 . H o w e v e r , the ana logous N O E results are not o b s e r v e d u p o n i r r a d i a t i o n o f the l i g a n d m e t h y l e n e protons o f the b i s ( h y d r o c a r b y l ) c o m p l e x e s . F o r e x a m p l e , the N O E D I F F spec t rum f o r c o m p o u n d 10 does not s h o w any enhancement for the I r - C / / 2 P h n o r f o r the I r - C 7 / 2 S i M e 3 o n i r r a d i a t i o n o f either set o f methy lene protons o n the b a c k b o n e o f the a n c i l l a r y l i g a n d ( F i g u r e 2-4) . T h e d i p h e n y l (6) and the d i b e n z y l (9) c o m p l e x e s ( F i g u r e 2-5) a l s o s h o w n o e n h a n c e m e n t o f the a p p r o p r i a t e r e s o n a n c e s o f the h y d r o c a r b y l g r o u p w h e n the l i g a n d m e t h y l e n e p r o t o n s are p u l s e d i n a N O E D I F F e x p e r i m e n t . I n d e e d , a l l o f the c o m p l e x e s 2 - 1 1 g i v e a n a l o g o u s resul t s a n d are therefore c o n s i d e r e d to h a v e a geometry d i f fe rent to that o f the h y d r o c a r b y l h a l i d e c o m p l e x e s 1. G i v e n that b o t h sets o f c o m p l e x e s are f i v e - c o o r d i n a t e w i t h the latter c o m p l e x e s h a v i n g a square p y r a m i d a l structure, the inescapable c o n c l u s i o n is that the b i s ( h y d r o c a r b y l ) d e r i v a t i v e s are t r i g o n a l b i p y r a m i d a l . T h i s i s cons i s tent w i t h the accepted o r i g i n o f the N O E 1 1 as a through-space transfer o f m a g n e t i z a t i o n that var ies as 1/r 6 ; thus, i n the square p y r a m i d a l geometry , the a p i c a l h y d r o c a r b y l l i g a n d is c loser to the m e t h y l e n e p r o t o n s o f the l i g a n d b a c k b o n e than i n the t r i g o n a l b i p y r a m i d a l g e o m e t r y w h e r e the h y d r o c a r b y l g r o u p s are i n the e q u a t o r i a l p l a n e . A d d i t i o n a l e v i d e n c e s u p p o r t i n g th is c o n c l u s i o n are the X - r a y c r y s t a l s tructures w h i c h w e r e repor ted for the m e t h y l neopenty l c o m p l e x ( 3 ) 8 a n d the d i b e n z y l der iva t ive ( 9 ) . 1 2 26 Ph 2 P Me 2Si v CHgPh N -Me2Si I-Ir Br I •P Ph 2 X^y*—* JL l r -CH 2 C 6 H 5 PCH 2 Si jA—* jk. 8 7 6 5 2 1 0 ppm F i g u r e 2-2. l¥L N M R s p e c t r u m ( b o t t o m ) and N O E D I F F s p e c t r u m ( top) f o r c o m p l e x l b (400 M H z , C6D6); i r r a d i a t i o n o f the m e t h y l e n e p r o t o n s o f the l i g a n d b a c k b o n e results i n a p o s i t i v e N O E f o r the methylene protons o f the b e n z y l l i g a n d 27 irradiate here Ph2 P rv^Si^ Me2Si Ir •P Ph2 l r -C 6 H 5 (ortho) 8 ^ 4 -PCH 2 Si 1 0 ppm Figure 2-3. lH N M R s p e c t r u m (bot tom) a n d N O E D I F F spectra (top) f o r c o m p l e x l c (400 M H z , C7D8); i r r a d i a t i o n o f the d o w n f i e l d m e t h y l e n e protons o f the l i g a n d b a c k b o n e resul ts i n a p o s i t i v e N O E f o r the or tho protons o f the p h e n y l l i g a n d , but there i s n o enhancement u p o n i r rad ia t ion o f the u p f i e l d methylene protons * denotes r e s i d u a l so lvent resonances 28 - T 1 —i — — r • 1 1 8 7 3 2 1 0 ppm Figure 2-4. * H N M R s p e c t r u m (bot tom) a n d N O E D I F F spectra f o r c o m p l e x 10 (400 M H z , C 6 D 6 ) ; i r radia t ion o f either set o f methylene protons o f the l i g a n d backbone r e s u l t s i n n o p o s i t i v e N O E f o r the m e t h y l e n e p r o t o n s o f the b e n z y l a n d t r i m e t h y l s i l y l m e t h y l l i g a n d s * denotes r e s i d u a l so lvent resonances 29 M e 2 S i s Me?Si Ph 2 - P Ir CH2Ph CHgPh •P Ph 2 8 A lr-CH2Ph KL irradiate here PCH 2 Si _A A 1 Figure 2-5. * H N M R s p e c t r u m ( b o t t o m ) a n d N O E D I F F s p e c t r u m ( top) f o r c o m p l e x 9 ( 400 M H z , C^Dq); i r r a d i a t i o n o f the m e t h y l e n e p r o t o n s o f the l i g a n d b a c k b o n e resul t s i n n o o b s e r v a b l e N O E f o r the m e t h y l e n e p r o t o n s o n the b e n z y l l i g a n d s * denotes r e s i d u a l so lvent resonances 30 2 .4 .3 Solid State Structure F i g u r e s 2 -6 a n d 2-7 s h o w the m e t h y l n e o p e n t y l (3 ) a n d d i b e n z y l (9 ) d e r i v a t i v e s i n c l u d i n g per t inent b o n d lengths a n d angles as taken f r o m the X - r a y c r y s t a l l o g r a p h i c a n a l y s e s . 8 ' 1 2 B o t h m o l e c u l e s are best d e s c r i b e d as h a v i n g a t r i g o n a l b i p y r a m i d a l c o n f i g u r a t i o n w i t h the largest d i s t o r t i o n f r o m the i d e a l b e i n g the angle subtended b y the t w o a l k y l l i g a n d s . C o n s i d e r a b l y less than the 1 2 0 ° e x p e c t e d , the ang le m e a s u r e s o n l y 7 7 . 6 ( 1 ) ° and 7 6 . 0 ( 4 ) ° f o r the d i b e n z y l a n d m e t h y l n e o p e n t y l c o m p o u n d s , r e s p e c t i v e l y . T h e c l o s i n g d o w n o f th i s e q u a t o r i a l a n g l e has been p r e d i c t e d 1 3 b y a theoret ical c a l c u l a t i o n for d 6 f ive -coordinate c o m p l e x e s . O n the basis o f extended H i i c k e l ca l cu la t ions , i t was c o n c l u d e d that a t r igona l b i p y r a m i d a l geometry w o u l d a c t u a l l y be s t a b i l i z e d b y an angular d e f o r m a t i o n i n the equator ia l p l a n e i n the f o r m o f a decrease i n one o f the angles f r o m 1 2 0 ° to 9 0 ° . T h e further decrease o f the angle f r o m the predic ted 9 0 ° to ~ 7 6 ° is not f u l l y understood but m a y be steric i n o r i g i n . M o r e o v e r , i t was p o i n t e d out that strong a - d o n o r l i g a n d s subtending this angle w o u l d further s tab i l ize the t r igona l b i p y r a m i d a l f o r m , as w o u l d the presence o f a s ingle faced 7t-donor s u c h as an a m i d o l i g a n d . T h e c o m b i n a t i o n o f these f a c t o r s i n the b i s ( h y d r o c a r b y l ) c o m p l e x e s 2-11 results i n a dis tor ted t r i g o n a l b i p y r a m i d a l geometry b e i n g m o r e stable than the square p y r a m i d a l f o r m . . . . 31 F i g u r e 2 - 6 . M o l e c u l a r s t r u c t u r e o f the m e t h y l - n e o p e n t y l d e r i v a t i v e (3 ) as d e t e r m i n e d b y X - r a y c r y s t a l l o g r a p h i c a n a l y s i s . 8 Se lec ted b o n d lengths and angles ( A a n d d e g ) ; I r - P l 2 . 3 0 8 ( 2 ) , I r - P 2 2 . 3 0 3 ( 2 ) , I r - N 2 . 1 0 9 ( 7 ) , I r C l 2 . 1 3 1 ( 9 ) , I r - C 2 2 . 0 8 9 ( 9 ) ; N - I r - C l 1 5 2 . 5 ( 3 ) , N - I r - C 2 1 3 1 . 5 ( 3 ) , C l - I r - C 2 7 6 . 0 ( 4 ) , P l - I r - P 2 168.45(9) , N - I r - P l 88 .2(2) , N - I r - P 2 85.9(2) . Figure 2-7. M o l e c u l a r structure o f the d i b e n z y l d e r i v a t i v e (9) as d e t e r m i n e d b y X -r a y c r y s t a l l o g r a p h i c a n a l y s i s . 1 2 Se lected b o n d lengths and angles ( A and deg) ; I r - P l 2 .3148(8 ) , I r - P 2 2 .3125(8) , I r - N 2 .113(3) , I r - C 3 1 2 .102(3) , I r - C 3 8 2 .125(3) ; N - I r -C 3 1 141 .6(1) , N - I r - C 3 8 140.8(1) , C 3 1 - I r - C 3 8 77 .6 (1 ) , P l - I r - P 2 170 .25 , N - I r - P l 85 .31(8) , N - I r - P 2 84 .93(8) . 32 2.5 Experimental T h e G e n e r a l I n f o r m a t i o n sect ion o f this chapter appl ies to a l l the w o r k done f o r this thesis . Chapters 3 a n d 4 w i l l conta in a d d i t i o n a l i n f o r m a t i o n pert inent to the w o r k d e s c r i b e d i n those chapters . 2.5.1 General Information. A l l m a n i p u l a t i o n s w e r e p e r f o r m e d u n d e r p r e p u r i f i e d n i t r o g e n i n a V a c u u m A t m o s p h e r e s H E - 5 5 3 - 2 g l o v e b o x e q u i p p e d w i t h a M O - 4 0 - 2 H p u r i f i e r o r i n standard S c h l e n k - t y p e g lassware o n a v a c u u m l i n e . I r C l 3 * x H 2 0 w a s o b t a i n e d f r o m J o h n s o n -M a t t h e y a n d w a s u s e d as r e c e i v e d to prepare I r ( r i 2 - C 8 H i 4 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] a n d I r ( C H 3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] as o u t l i n e d i n a p r e v i o u s p u b l i c a t i o n 1 0 . T o l u e n e a n d d i e t h y l ether were p u r i f i e d b y r e f l u x i n g o v e r d a r k b l u e o r p u r p l e s o l u t i o n s o f s o d i u m - b e n z o p h e n o n e k e t y l (Na - P h 2 C O ) f o l l o w e d b y d i s t i l l a t i o n under a r g o n . H e x a n e s a n d t e t r a h y d r o f u r a n w e r e p r e d r i e d b y r e f l u x i n g o v e r C a H 2 a n d d i s t i l l e d f r o m N a - P h 2 C O u n d e r a r g o n . Deutera ted benzene (C^D^) w a s p u r c h a s e d f r o m A l d r i c h , d r i e d o v e r a c t i v a t e d 4 A m o l e c u l a r s ieves , v a c u u m - t r a n s f e r r e d , and d e o x y g e n a t e d through several f r e e z e - p u m p - t h a w c y c l e s p r i o r to use. C a r b o n , h y d r o g e n , a n d n i t r o g e n analyses o f these air a n d m o i s t u r e sens i t ive c o m p o u n d s w e r e exper t ly p e r f o r m e d b y M r . Peter B o r d a o f this department . F o r the c o m p o u n d s i n w h i c h 1/2 o r 1/4 m o l e o f toluene i s i n c l u d e d i n the e lementa l analys is c a l c u l a t i o n , J H N M R w a s used to c o n f i r m i ts presence . * H N M R spectra w e r e r e c o r d e d o n e i ther a V a r i a n X L - 3 0 0 spectrometer (300 M H z ) o r a B r u k e r W H - 4 0 0 spectrometer (400 M H z ) . 1 3 C { 1 H } and 3 1 P { ! H } N M R spectra w e r e r e c o r d e d o n a V a r i a n X L - 3 0 0 spec t rometer (75 .43 M H z a n d 121 .421 M H z r e s p e c t i v e l y ) . T h e 3 1 P { 1 H } N M R spectra w e r e r e f e r e n c e d to e x t e r n a l P ( O M e ) 3 set at +141.0 p p m re la t ive to 8 5 % H3PO4. A s s i g n m e n t o f resonances for the ^ C p H } N M R spectra was a i d e d b y the use o f A t t a c h e d P r o t o n Tes t e x p e r i m e n t s d o n e f o r s e v e r a l o f the 33 c o m p l e x e s o n a V a r i a n X L - 3 0 0 s p e c t r o m e t e r u s i n g s t a n d a r d p u l s e sequences . N O E D I F F e x p e r i m e n t s w e r e c a r r i e d out o n a B r u k e r W H - 4 0 0 spec t rometer (400 M H z ) u s i n g s tandard p u l s e sequences. A l l reagents w e r e o b t a i n e d i n the highest p u r i t y p o s s i b l e . T h e o r g a n o l i t h i u m reagents w e r e p r e p a r e d as d e s c r i b e d i n the l i tera ture ( L i C H 2 C M e 3 1 4 , L i C g H s 1 5 , L i C H 2 S i M e 3 1 6 , L i C H 2 P h 1 7 ) or used as r e c e i v e d f r o m A l d r i c h (IJCH3,1.4 M so lut ion i n E t 2 0 ) . 2.5.2 Synthesis of Iridium Bis(hydrocarbyl) Complexes Ir(CH3)R'[N(SiMe2CH2PPh2)2] , R' = CH3, CH2CMe3, C6H5, CH2SiMe3. U n d e r an inert a tmosphere , a 5 m L toluene (or t o l u e n e / E t 2 0 f o r R ' = C6H5, o r E t 2 0 f o r R ' = C H 3 ) s o l u t i o n o f 1.1 equivalents o f the appropriate o r g a n o l i t h i u m reagent (30 m m o l ) w a s added to 2 0 0 m g o f I r ( C H 3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] i n 30 m L o f toluene at 2 0 ° C , resu l t ing i n i m m e d i a t e c o l o u r changes o f the so lut ion f r o m green to r e d o r p u r p l e . A f t e r s t i r r i n g f o r 3 0 m i n u t e s , the so lvent w a s r e m o v e d in vacuo a n d the res idue extrac ted w i t h hexanes , f i l t e r e d t h r o u g h C e l i t e a n d r e d u c e d to dryness . R e c r y s t a l l i z a t i o n f r o m toluene/hexanes or neat hexanes at r o o m temperature (or b y c o o l i n g to - 3 0 o C ) , f o l l o w e d b y decantat ion a n d d r y i n g in vacuo gave products i n i so la ted y i e l d s r a n g i n g f r o m 60-80%. Ir(CH3)2[N(SiMe2CH2PPh2)2]: 3 1 P { 1 H } N M R ( C 6 D 6 ) : 19.67 p p m (s). A n a l . C a l c d f o r C 3 2 H 4 2 l r P 2 S i 2 N : C , 51.18; H , 5 .64; N , 1.86. F o u n d : C , 51.24; H , 5.80; N , 1.86. Ir(CH3)CH2CMe3[N(SiMe2CH2PPh2)2]:3lP{1H} N M R ( C 6 D 6 ) : 11.53 p p m (s). A n a l . C a l c d f o r C 3 6 H 5 o I r P 2 S i 2 N : C , 53.57; H , 6.24; N , 1.74. F o u n d : C , 53 .71 ; H , 6 .26; N , 1.59. Ir(CH3)C6H5[N(SiMe2CH2PPh2)2]: 3 1 P { ! H } N M R ( C 6 D 6 ) : 16.56 p p m (s). A n a l . C a l c d f o r C 3 7 H 4 4 N I r P 2 S i 2 « l / 4 C 7 H 8 : C , 55.66; H , 5 .54; N , 1.68. F o u n d : C , 34 55 .54 ; H , 5.50; N , 1.60. Ir(CH3)CH2SiMe3[N(SiMe2CH2PPfi2)2]:3lP{lH} N M R ( C 6 D 6 ) : 13.51 p p m (s). A n a l . C a l c d f o r C 3 5 H 5 o I r P 2 S i 3 N : C , 51.07; H , 6.12; N , 1.70. F o u n d C , 51.00; H , 6.00; N , 1.67. Ir(C6H5)I[N(SiMe2CH2PPh2)2] 3 0 0 m g o f I r ( C H 3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] i n 4 0 m L o f benzene w a s heated to 8 0 ° C o v e r n i g h t w i t h s t i r r i n g , f o l l o w e d b y s o l v e n t r e m o v a l in vacuo a n d r e c r y s t a l l i z a t i o n f r o m toluene/hexanes to g i v e o l i v e green crysta ls i n 7 0 % y i e l d . 3 1 p { l H } N M R ( C 6 D 6 ) : 10.66 ppm(s ) ; * H N M R ( C 6 D 6 ) : S i ( C / / 3 ) 2 , -0.11 (s), 0 .52 (s); P C / / 2 S i , 1.57 (dt, J a p p = 5 . 4 H z , J g e m = 1 3 . 4 H z ) , 1.77 (dt, J a p p = 5 . 6 H z ) ; lT-CeH5, 6 .29 (t, meta , J H = 7 . 7 H Z ) , 6 .54 (t, para , J H = 7 . 1 ) , 6.84 (d , or tho , J R = 9 H z ) ; P(CeHs)2, 7.01 ( m , meta/para) , 7 .55 ( m , or tho) , 7 .84 ( m , or tho) . A n a l . C a l c d f o r C 3 6 H 4 i N I r P 2 S i 2 « l / 4 C 7 H 8 : C , 47 .83 ; H , 4 .57 ; N , 1.48. F o u n d : C , 47 .80 ; H , 4.74; N , 1.36. Ir(C6H5)R'[N(SiMe2CH2PPh2)2], R' = CeHs, CH2CMe3 T h e syntheses o f these c o m p l e x e s w e r e c a r r i e d out as d e s c r i b e d f o r the I r ( C H 3 ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] analogues above . Ir(C6H5)2[N(SiMe2CH2PPh2)2]:3lP{lll} N M R ( C 6 D 6 ) : 11.22 p p m (s). A n a l . C a l c d f o r C 4 2 H 4 6 l r P 2 S i 2 N : C , 57 .64 ; H , 5 .30; N , 1.60. F o u n d C , 57 .66 ; H , 5.40; N , 1.53. Ir(C6H5)CH2CMe3[N(SiMe2CH2PPh2)2]:31P{1H) N M R ( C 6 D 6 ) : 11.77 p p m (s). A n a l . C a l c d for C 4 i H 5 2 N I r P 2 S i 2 » l / 2 C 7 H 8 : C , 58.40; H , 6.17; N , 1.53. F o u n d : C , 58 .18 ; H , 5.88; N , 1.55. 35 Ir(CH2Ph)Br[N(SiMe2CH2PPh2 hi 1.1 equivalents of P h C H 2 B r ( 40 mmol) was added to 3 0 0 mg of Ir(COE)[N(SiMe2CH2PPh.2)2] in 50 m L of toluene, and the mixture was then stirred in the dark for 24 h. Solvent removal followed by recrystallization from toluene/hexanes gave bright green crystals in 8 0 % yield. 3 lp{ l r l } N M R ( C 6 D 6 ) : 0 .10 ppm (s). lH N M R ( C 6 D 6 ) : S i ( C / / 3 ) 2 , -0 .23 (s), 0 .46 (s); P C / / 2 S i , 1.55 (q o f t , J g e m = 1 5 H z , J a p p = 5 Hz) ; I r - C / / 2 C 6 H 5 , 4 .95 (t, 3 J P = 5 . 0 Hz) ; I r - C H 2 C 6 / / 5 , 6.65 (t, meta, J H = 8 Hz) , 6 .95 (t, para, J H = 7 . 5 H Z ) , 7.28 (d, ortho, J H = 8 H Z ) ; P(C6#5) 2 , 7 .04 (m, meta/para), 7.91 (m, ortho). Anal . Calcd for C 3 7H43BrIrNP 2 Si2: C , 49 .82; H , 4 .86; N , 1.57. Found: C , 49 .58 ; H , 5.00; N , 1.53. Ir(CH2Ph)R'[N(SiMe2CH2PPh2)2], R' = CH3, CH2Ph, CH2SiMe3, Ctfls The syntheses of these complexes were carried out as described for the Ir (CH 3 )R' [N(SiMe2CH 2 PPh2)2] analogues above . 1 8 Ir(CH2Ph)CH3[N(SiMe2CH2PPh2)2]: 3 1 P { 1 H } N M R ( C 6 D 6 ) : 12.87 ppm (s). A n a l . Calcd for C 3 8 H 4 6 l r N P 2 S i 2 : C , 55.18; H , 5 .61 ; N , 1.69. Found: C , 55 .40; H , 5.50; N , 1.65. Ir(CH2Ph)2[N(SiMe2CH2PPh2)2]: 3 1 P { 1 H } N M R ( C 6 D 6 ) : 4 . 96 ppm (s). A n a l . Calcd for C4 4 H5oIrNP 2 Si2 : C , 58 .51 ; H , 5 .58; N , 1.55. Found: C , 58 .70 ; H , 5.50; N , 1.52. Ir(CH2Ph)CH2SiMe3[N(SiMe2CH2PPh2)2]: 3 1 P { 1 H } N M R ( C 6 D 6 ) : 7 .43 ppm (s). Anal . Calcd for C 4 i H 5 4 I r N P 2 S i 3 : C , 56 .54; H , 6.18; N , 1.48. Found: C , 56.30; H , 6.26; N , 1.20. Ir(CH2Ph)C6H5[N(SiMe2CH2PPh2)2]: 3 1 P { 1 H } N M R ( C 6 D 6 ) : 11.68 ppm (s). Anal . Calcd for C 4 5 H 4 8 I r N P 2 S i 2 : C , 59.19; H , 5 .30; N , 1.53. Found: C , 58 .87; H , 5.64; N , 1.57. 36 2.6 References 1. M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , J . A m . C h e m . S o c , 107 (1985) 6708. 2 . (a) L . V a s k a and J . W . D i L u z i o , J . A m . C h e m . S o c , 84 (1962) 679 . (b) J . Chat t a n d A . E . U n d e r h i l l , J . C h e m . S o c , (1963) 2088 . (c) R . F . H e c k , J . A m . C h e m . 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(n) B . E . M a n n , B . L . S h a w and R . E . S t a i n b a n k , J . C h e m . S o c , C h e m . C o m m u n . , (1972) 151 . (o) M . A . Bennet t , R . C h a r l e s a n d T . R . B . M i t c h e l l , J . A m . C h e m . S o c , 100 (1978) 2737 . (p) M . A . Bennet t and J . C . Je f fery , I n o r g . C h e m . , 19 (1980) 3 7 6 3 . (q) T . H . T u l i p a n d D . L . T h o r n , J . A m . C h e m . S o c , 103 (1981) 2448. (r) D . L . T h o r n and T . H . T u l i p , J . A m . C h e m . S o c , 103 (1981) 5986 . (s) N . L . Jones and J . A . Ibers , O r g a n o m e t a l l i c s , 2 (1983) 4 9 0 . (t) K . A . B e r n a r d a n d J . D . A t w o o d , O r g a n o m e t a l l i c s , 6 (1987) 1133 . (u) M . K u b o t a , T . M . M c C l e s k y , R . K . H a y a s h i and C . G . W e b b , J . A m . C h e m . S o c , 109 (1987), 7569 . 3 . J . D . A t w o o d , C o o r d . C h e m . R e v . , 83 (1988) 93 . 4. ' R . H . Crabtree , C h e m . R e v . , 85 (1985) 245 . 5 . (a) K . Isobe, P . M . B a i l e y and P . M . M a i t l i s , J . C h e m . S o c , C h e m . C o m m u n . , (1981) 808 . (b) A . H . J a n o w i c z a n d R . G . B e r g m a n , J . A m . C h e m . S o c , 104 37 (1982) 352 . (c) J . K . H o y a n o and W . A . G . G r a h a m , J . A m . C h e m . S o c . , 104 (1982) 3723 . (d) A . H . J a n o w i c z a n d R . G . B e r g m a n , J . A m . C h e m . Soc . , 105 (1983) 3929 . (e) J . K . H o y a n o , A . D . M c M a s t e r and W . A . G . G r a h a m , J . A m . C h e m . Soc . , 105 (1983) 7190 . (f) M . G o m e z , D . J . R o b i n s o n , a n d P . M . M a i d i s , J . C h e m . S o c . , C h e m . C o m m u n . , (1983) 825. (g) A . J . Res t , I. W h i t w e l l , W . A . G . G r a h a m , J . K . H o y a n o a n d A . D . M c M a s t e r , J . C h e m . Soc . , C h e m . C o m m u n . , (1984) 624. (h) M . J . W a x , J . M . S t ryker , J . M . B u c h a n a n , C . A . K o v a c a n d R . G . B e r g m a n , J . A m . C h e m . S o c , 106 (1984) 1121 . (i) A . H . J a n o w i c z , R . A . P e r i a n a , J . M . B u c h a n a n , C . A . K o v a c , J . M . S t r y k e r , M . J . W a x a n d R . G . B e r g m a n , P u r e A p p l . C h e m . , 56 (1984) 13. (j) J- M - B u c h a n a n , J . M . S t r y k e r and R . G . B e r g m a n , J . A m . C h e m . S o c , 108 (1986) 1537. 00 S. P . N o l a n , C . D . H o f f , P . O . S t o u d a n d , L . J . N e w m a n , J . M . B u c h a n a n , R . G . B e r g m a n , G . K . Y a n g a n d K . S. Peters , J . A m . C h e m . S o c , 109 (1987) 3 1 4 3 . (1) A . J . Res t , I. W h i t w e l l , W . A . G . G r a h a m , J . K . H o y a n o and A . D . M c M a s t e r , J . C h e m . S o c , D a l t o n T r a n s . , (1987) 1181 . 6. (a) M . D . R a u s c h a n d G . A . M o s e r , I n o r g . C h e m . , 13 (1974) 11 . (b) L . D a h l e n b u r g , F . M i r z a e i , A . Y a r d i m c i o g l u and R . N a s t , Z . N a t u r f o r s c h , T e i l B , 37 (1982) 310 . (c) L . D a h l e n b u r g a n d R . N a s t , J . O r g a n o m e t . C h e m . , 110 (1976) 3 9 5 . (d) L . D a h l e n b u r g a n d F . M i r z a e i , J . O r g a n o m e t . C h e m . , 251 (1983) 11 . (e) L . D a h l e n b u r g , J . O r g a n o m e t . C h e m . , 251 (1983) 347 . (f) E . A r p a c a n d L . D a h l e n b u r g , J . O r g a n o m e t . C h e m . , 251 (1983) 3 6 1 . (g) L . D a h l e n b u r g a n d C . P r e n g e l , O r g a n o m e t a l l i c s , 3 (1984) 934 . (h) W . M . Rees , M . R . C h u r c h i l l , Y . J . L i and J . D . A t w o o d , O r g a n o m e t a l l i c s , 4 (1985) 1162. (i) L . D a h l e n b u r g , F . M i r z a e i and B . P i e t s c h , Inorg . C h i m . A c t a . , 97 (1985) L 5 . (j) B . J . R a p p o l i , M . R . C h u r c h i l l , T . S. Jan ik , W . M . Rees and J . D . A t w o o d , J . A m . C h e m . S o c , 109 (1987) 5145 . (k) A . A . D e l P a g g i o , R . A . A n d e r s e n a n d E . L . M u e t t e r t i e s , O r g a n o m e t a l l i c s , 6 (1987) 1260. 38 7. (a) J . R . S h a p l e y and J . A . O s b o r n , J . A m . C h e m . S o c . , 92 (1970) 6976 . (b) G . Y a g u p s k y a n d C . K . B r o w n , J . C h e m . S o c . ( A ) , (1970) 1392. (c) M . R . C h u r c h i l l and S. A . B e z m a n , I n o r g . C h e m . , 12 (1973) 5 3 1 . (d) L . D a h l e n b u r g a n d F . M i r z a e i , J . O r g a n o m e t . C h e m . , 251 (1983) 123. (e) L . D a h l e n b u r g and F . M i r z a e i , I n o r g . C h i m . A c t a . , 97 (1985) L I . (f) L . D a h l e n b u r g a n d A . Y a r d i m c i o g l u , J . O r g a n o m e t . C h e m . , 299 (1986) 149. (g) W . M . R e e s , M . R . C h u r c h i l l , J . C . Fet t inger a n d J . D . A t w o o d , J . O r g a n o m e t . C h e m . , 319 (1987) 4 1 1 . 8. M . D . F r y z u k , P . A . M a c N e i l and R . G . B a l l , J . A m . C h e m . S o c . , 108 (1986) 6414. 9. M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , O r g a n o m e t a l l i c s , 5 (1986) 2469 . 10. M . D . F r y z u k , P . A . M a c N e i l and N . T . M c M a n u s , O r g a n o m e t a l l i c s , 6 (1987) 882. 11. J . K . Saunders and J . W . E a s t o n , i n " T h e D e t e r m i n a t i o n o f O r g a n i c Structures b y P h y s i c a l M e t h o d s " ; E d s . , F . C . N a c h o d , J . J . Z u c k e r m a n and E . W . R a n d a l l ; A c a d e m i c Press : N e w Y o r k , 1976; V o l . 6, p . 2 7 1 . 12. M . D . F r y z u k , P . A . M a c N e i l , R . L . M a s s e y a n d R . G . B a l l , J . O r g a n o m e t . C h e m . , (1989), accepted for p u b l i c a t i o n . 13. D . L . T h o r n and R . H o f f m a n n , N o u v . J . C h i m . , 3 (1979) 39. 14. R . R . S c h r o c k and J . D . F e l l m a n n , J . A m . C h e m . S o c , 100 (1978) 3359. 15. M . Sch losser and V . Ladenberger , J . Organomet . C h e m . , 8 (1967) 193. 16. M . R . C o l l i e r , M . F . L a p p e r t a n d R . P e a r c e , J . C h e m . S o c , D a l t o n T r a n s . , (1973) 4 4 5 . 17. G . G . Eberhart a n d W . A . But te , J . O r g . C h e m . , 29 (1964) 2928 . 18. A n alternate synthet ic m e t h o d f o r c o m p o u n d s w h e r e R ^ C H j P h i n v o l v e d u s i n g K C H 2 P h d i s s o l v e d i n T H F . S y n t h e s i s o f K C H 2 P h : M . S c h l o s s e r a n d J . H a r t m a n n , A n g e w . C h e m . , Int. E d . E n g l . , 12 (1973) 508. 39 C H A P T E R 3. P H O T O R E A C T I V I T Y O F I R I D I U M B I S ( H Y D R O C A R B Y L ) C O M P L E X E S I r ( R ) R , [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 3.1 Photochemical Versus Thermal Reaction Conditions A l t h o u g h p h o t o c h e m i s t r y i s a f a i r l y large s u b d i s c i p l i n e o f o r g a n i c c h e m i s t r y , o n l y r e c e n t l y has i t been ex tended to o r g a n o m e t a l l i c c o m p l e x e s , a n d a l ready there h a v e b e e n d i s c o v e r i e s o f c a t a l y t i c a l l y a n d s y n t h e t i c a l l y u s e f u l t r a n s f o r m a t i o n s access ib le t h r o u g h the use o f l i g h t as an energy s o u r c e . 1 A n e x a m p l e o f h o w v a s t l y d i f f e r e n t the resul ts c a n be w h e n p h o t o c h e m i c a l rather than t h e r m a l c o n d i t i o n s are used is s h o w n i n the reac t ion o f substituted i m i n e s w i t h a c h r o m i u m carbene c o m p l e x ( S c h e m e 3 - 1 ) . 2 H e a t i n g the reactants to 5 0 ° C resul ts i n the i m i n e abs t rac t ing a p r o t o n f r o m the pVcarbon o f the carbene, f o l l o w e d b y a l k y l a t i o n o f the f o r m e d i m i n i u m species a n d the eventual f o r m a t i o n o f a n e w carbene c o m p l e x . H o w e v e r , i r r a d i a t i o n o f the same reactants w i t h v i s i b l e l i g h t p r o d u c e s ^ - l a c t a m s s t e r e o s p e c i f i c a l l y a n d i n exce l lent y i e l d . Scheme 3-1 (CO) 5 Cr=c: .OMe \ . H (CO) 5 Cr=cT + N = < CH3 Ph v u v MeO Ph C H 3 - * TT" U R T h e products f r o m a p h o t o c h e m i c a l react ion c a n d i f f e r so dras t i ca l ly f r o m those o f a t h e r m a l process because o f the d i f fe rent p o s s i b l e react ions o f an e l e c t r o n i c a l l y e x c i t e d m o l e c u l e as c o m p a r e d to a t h e r m a l l y e x c i t e d m o l e c u l e . N o t m u c h i s yet u n d e r s t o o d at the e l e c t r o n i c l e v e l to e x p l a i n the p h o t o l y s i s processes o b s e r v e d i n 40 many transition metal complexes, but the investigations on these systems are continuing.3 3.2 Thermal Stability When benzene solutions of the bis(hydrocarbyl) complexes Ir(R)R'[N(SiMe2CH2PPh2)2] (2-11) were heated to temperatures above 80°C for extended periods of time, very little or no decomposition was observed by *H and 3 1P{ 1H} NMR spectroscopy. The thermal stability of these compounds can be attributed to the unique tridentate ancillary ligand system [N(SiMe2CH2PPh2)2]" which appears to hinder decomposition reactions even though the iridium centre is coordinatively unsaturated. This is consistent with the proposal4 that thermal decomposition can be inhibited for metal o-hydrocarbyl complexes by the use of bulky and chelating ligands. However, in contrast to their thermal stability, many of the bis(hydrocarbyl) complexes were found to react upon exposure to sunlight. 3.3 Photochemical Reactivity The first discovery of the photoreactivity of the iridium bis(hydrocarbyl) complexes was for the methyl neopentyl derivative 3 as was described in equation 1-19. The reaction required 10 hours of photolysis under a sunlamp to go to completion as monitored by NMR spectroscopy. The major iridium species produced, Ir(H)2[N(SiMe2CH2PPh2)2l> can also be synthesized by the reaction of Ir(COE)[N(SiMe2CH2PPh2)2l with dihydrogen.5 The more interesting methylidene complex formed, Ir(=CH2)[N(SiMe2CH2PPh2)2L has been previously characterized by X-ray crystallographic analysis and by ! H , ^ C ^ H ) and 31P{1H} NMR. 6 The rest of the series of bis(hydrocarbyl) complexes were also individually studied under photolytic conditions, and the results are summarized in Table 3-1. As can be seen, photolysis of several of the derivatives resulted in a complex mixture of products. In 41 contrast , those c o m p l e x e s c o n t a i n i n g p h e n y l der iva t ives w e r e f o u n d to be unreact ive to l i g h t as w e l l as heat, and d i d not g ive rise to the expected i r i d i u m b e n z y n e c o m p l e x . T h e m o s t i n t e r e s t i n g resul ts w e r e o b t a i n e d f r o m the p h o t o l y s i s o f the c o m p l e x e s I r ( R ) R ' [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] w h e r e R = R ' = C H 3 (2), R = C H 2 P h and R ' = C H 3 (8) , R = R ' = C H 2 P h (9) . Table 3-1. Photolysis Results for Iridium Bis(hydrocarbyl) Complexes IrfRJR'lNKSiMezCHaPPha)^ hv time iHand3ip{iH} NMR Observations Ratio of Iridium Species Produced* lrt(=CH2) lrt(H)2 lrt(C2H4) lrt(=CHPh) 2: R = R' = C H 3 20 hours still some unreacted starting material 2 2 3 3: R = CH 3 ; R' = CH2CMe3 10 hours no unreacted starting material 2 3 -4: R = CH 3 ; R' = C 6 H 5 8 hours no change - -5: R = CH 3 ; R' = CH2SiMe 3 20 hours very complex; multiple peaks 6: R = R' = CeHs 20 hours no change - -7: R = C6H5; R' = ChfeCMes 8 hours no change - -8: R = CH 2Ph; R' = CH 3 2 hours no unreacted starting material 1 5 -9: R = R' = CH 2Ph 6 days very little unreacted starting material 1 2 10: R = CH 2Ph; R'= CH2SiMe 3 55 hours very complex; multiple peaks V 11:R = CH 2Ph;R'= C6H 5 55 hours no change - -* Based on integrals in ' H NMR spectra Irt= IrtN(SiMe2CH2PPh2)2] V indicates the presence of the iridium species was noted; however, the complexity of the spectra prevented accurate integration of the peaks to determine relative amounts 4 2 3.3.1 Photolysis of I r ( C H 3 ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (2) W i t h i n 2 0 h o u r s o f e x p o s u r e to the s u n l a m p , the presence o f the d i m e t h y l d e r i v a t i v e decreased s i g n i f i c a n t l y i n the 1 H a n d 3 1 P { 1 H } N M R spectra , and three i r i d i u m species w e r e i d e n t i f i e d as s h o w n i n equat ion 3 - 1 . A g a i n , the d i h y d r i d e and m e t h y l i d e n e species w e r e p r o d u c e d , as w e l l as an i r i d i u m (I) e thylene adduct w h i c h c a n be o b t a i n e d i n d e p e n d e n t l y u p o n r e a c t i o n o f I r ( C O E ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] w i t h e t h y l e n e . 5 T h e r e s o n a n c e s o f the e x p e c t e d s i d e p r o d u c t s ( C 2 H 4 , C H 4 a n d H2) c o r r e s p o n d i n g to the o b s e r v e d i r i d i u m species p r o d u c e d c o u l d not be detected i n the ! H N M R spec t rum. 3.3.2 P h o t o l y s i s o f I r ( C H 2 P h ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (9) I n the case o f the d i b e n z y l d e r i v a t i v e , the d i h y d r i d e species w a s o b s e r v e d to be the m i n o r p r o d u c t w i t h the m a j o r species b e i n g a n e w i r i d i u m c o m p l e x (equation 3 -2 ) . O n the b a s i s o f lK a n d ^ C f 1 ! ! } N M R d a t a , t h i s n e w c o m p l e x i s (3-1) + N — l r = = C H 2 43 i d e n t i f i e d as an i r i d i u m b e n z y l i d e n e c o m p l e x , I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , w h i c h w i l l be d i scussed i n m o r e deta i l i n sect ion 4 . 1 . A l t h o u g h the f o r m a t i o n o f the products w a s d e f i n i t e l y ev ident w i t h i n the f irst 12 hours , the reac t ion r e q u i r e d a p p r o x i m a t e l y 6 d a y s o f exposure to the s u n l a m p before the m a j o r i t y o f the start ing m a t e r i a l h a d been deple ted , a n d yet there appeared to be v e r y l i t t le d e c o m p o s i t i o n o c c u r r i n g d u r i n g this ex tended t i m e o f p h o t o l y s i s . 3.3.3 Photolysis of I r ( C H 2 P h ) ( C H 3 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] (8) S i n c e the p h o t o l y s i s o f the d i m e t h y l d e r i v a t i v e gave rise to some m e t h y l i d e n e , a n d the d i b e n z y l to m o s t l y b e n z y l i d e n e , i t w a s thought the b e n z y l m e t h y l c o m p l e x m i g h t p r o d u c e a m i x t u r e o f both a l k y l i d e n e s . H o w e v e r , the results o b t a i n e d i l lustrate the u n p r e d i c t a b i l i t y o f the i r i d i u m b i s ( h y d r o c a r b y l ) sys tem under p h o t o l y t i c c o n d i t i o n s at this stage o f the research. T h e d i h y d r i d e c o m p l e x was f o r m e d a lmos t e x c l u s i v e l y a l o n g w i t h a s m a l l a m o u n t o f the m e t h y l i d e n e , w i t h i n a v e r y short p h o t o l y s i s t i m e p e r i o d o f less than 2 hours (equat ion 3-3) . A l s o v e r y c l e a r l y i d e n t i f i a b l e i n the lH N M R s p e c t r u m w e r e the resonances due to styrene as w e l l as s m a l l a m o u n t s o f t o l u e n e . U p o n p r o l o n g e d e x p o s u r e o f the r e a c t i o n m i x t u r e to the s u n l a m p , the c o r r e s p o n d i n g spect ra b e c a m e m o r e c o m p l e x a n d d i f f i c u l t to in terpret , the e x t r a resonances p r e s u m a b l y due to d e c o m p o s i t i o n products o f the c o m p l e x e s . N — I r = C H 2 + r * N — Ir ( 3 - 3 ) | ^ C H 3 -(CH3Ph) -P -(CHj^CHPh) Ph 2 8a 44 3.4 D e u t e r i u m L a b e l l i n g Studies I n an attempt to g a i n some unders tanding about the p r o d u c t f o r m a t i o n i n the p h o t o l y s i s react ions , the m e t h y l b e n z y l c o m p l e x w a s synthes ized a l o n g w i t h the three d i f f e r e n t c o m b i n a t i o n s o f d e u t e r i u m l a b e l l e d h y d r o c a r b y l l i g a n d s , a n d e a c h w a s p h o t o l y z e d i n d i v i d u a l l y and m o n i t o r e d b y N M R spectroscopy to determine the fate o f the d e u t e r i u m l a b e l s . T h e results are d e p i c t e d i n equat ions 3-4, 3-5 a n d 3-6. T h e p r o d u c t s o b t a i n e d f r o m p h o t o l y s i s o f 8b a n d 8c c o n f i r m that the m e t h y l i d e n e uni t o r i g i n a t e s f r o m the m e t h y l l i g a n d , a n d that the d i h y d r i d e cons i s t s o f o n e h y d r o g e n a t o m f r o m e a c h o f the t w o h y d r o c a r b y l groups . T h e p h o t o l y s i s o f 8 d s h o w e d the i n c o r p o r a t i o n o f d e u t e r i u m in to both products . These results p a r a l l e l those f o u n d f o r the l a b e l l i n g s tudy p e r f o r m e d o n the m e t h y l n e o p e n t y l d e r i v a t i v e (3) i n w h i c h the m e t h y l l i g a n d w a s l a b e l l e d (CD3) and the l a b e l w a s traced i n the m e t h y l i d e n e uni t ( = C D 2 ) a f t e r p h o t o l y s i s . 6 T h i s suggests that the m e c h a n i s m s f o r the t w o p h o t o r e a c t i o n s are re la ted . A n o t h e r s i m i l a r i t y i s that i n b o t h cases the d i h y d r i d e c o m p l e x i s f o u n d to be the m a j o r product f o r m e d . Ph 2 Me,Si | CH2Ph C e D ( N |r / Me 2 Si' | ^ C D 3 "(CH2DPh) Me2Si | \ _ ^ P -(CD2=CHPh) ^V-^P Ph 2 Ph 2 8b hv 2gD6 Ph 2 - P Me 2Si s J Me 2Si s N — I r = C D 2 + N • Me2Si ^ Ph 2 / v P „ h 2 , / ^ P hv / Me 2Si N I . .CD 2 C 6 D 5 C D Me 2Si s | Me 2SiN N | r ' * * - N — | r = C H 2 + N • Ph 2 - P I r - P Ph 2 Ph 2 - P Me2Si / | ^ C H 3 -<CHD2C6D5) M e V | \ p -{CHzSsCDCeDs) \ ^ - P Ph 2 P "2 8c Me,Si Ph 2 - P hv Me 2Si s I Me 2 Si y J ^ .CD 2 C 6 D 5 c < j D ( N Ir* Me2 p -(CD2 = CDC6D5) \^-P Ph 2 Ph2 8d 2 S i ' | ^ C D 3 -(CD3C6DS) Me2Si^ | v -(CD2 = CDC6D5) Me 2Si s N — I r = C D 2 + N • • Ir ! ' P Ph 2 Pha P Ir Me2Si «-P Ph 2 . H ..D ( 3 - 4 ) ( 3 - 5 ) ( 3 - 6 ) 45 3.5 Ultraviolet/Visible Spectroscopy I n o r d e r to d e t e r m i n e the nature o f the a b s o r p t i o n s r e s p o n s i b l e f o r the o b s e r v e d p h o t o r e a c t i v i t y , the b i s ( h y d r o c a r b y l ) c o m p l e x e s w e r e a l so charac ter ized by U V / V I S spec t roscopy and the results are l i s t e d i n T a b l e 3 - U . A l l o f the c o m p l e x e s w e r e f o u n d to e x h i b i t absorpt ions i n the v i s i b l e r e g i o n be tween A.=370 a n d 521 n m , w i t h e x t i n c t i o n coef f i c ients r a n g i n g f r o m 2 0 0 to 1000 ( L m o H c n r 1 ) . These values are cons is tent w i t h d - d t rans i t ions w h i c h appear to be charac ter i s t i c o f f i v e - c o o r d i n a t e m o l e c u l e s w i t h d 6 c o n f i g u r a t i o n , 7 ' 8 a n d w h i c h a lso account f o r the intense c o l o u r s o b s e r v e d that range f r o m deep r e d to dark p u r p l e d e p e n d i n g o n the substituents R and R ' . Table 3-II. U V / V I S Spectral Data for Iridium Bis(hydrocarbyl) CompIexes a l r (R)R , [N(SiMe 2 CH 2 PPh 2 )2] e ( X 102)c,d 2: R = R' = C H 3 4 8 3 2.7 3 7 0 5.3 (shoulder) 3: R = C H 3 ; R' = C H ^ M e s 4 9 3 4.3 3 7 8 7.8 (shoulder) 4: R = C H 3 ; R' = C 6 H 5 4 6 0 2.0 5: R = C H 3 ; R' •= C H 2 S i M e 3 5 1 4 7.5 3 8 3 10 (shoulder) 6: R = R' = C 6 H 5 4 6 4 3.5 5 6 5 2.9 7: R = C 6 H 5 ; R' = C H 2 C M e 3 521 7.9 8: R = C H 2 P h ; R' = C H 3 5 0 0 5.9 9: R = R' = C H 2 P h 4 9 4 8.3 10: R = C H 2 P h ; R' = C H 2 S i M e 3 5 1 9 2.6 11: R = C H 2 P h ; R'= C 6 H 5 4 8 3 5.6 a A l l spectra recorded at 25"C in hexanes from 200 to 900 nm, backcorrected with hexanes ''Wavelength of maximum absorption (nm) c£=molar extinction coefficient, calculated from A=ebc, where A=absorption at Xoux, b=l cm, c=concentration (mol/L) dThe entries corresponding to "shoulder" refer to an absorption partially obscured by the intense band (probably due to a charge transfer transition) which typically cut off at -330 nm 46 S i n c e the p h o t o l y s i s o f the b i s ( h y d r o c a r b y l ) c o m p l e x e s w e r e p e r f o r m e d b y p l a c i n g the samples w i t h i n a w a t e r - c o o l e d p y r e x j a c k e t i n f r o n t o f a s u n l a m p , i t i s a s s u m e d that most o f the r a d i a t i o n o f w a v e l e n g t h shorter than 315 n m was f i l tered out before r e a c h i n g the s a m p l e s . 9 There fore , the absorpt ion o f r a d i a t i o n c o r r e s p o n d i n g to the d - d t r a n s i t i o n s (as o p p o s e d to the c h a r g e t r a n s f e r b a n d ) a p p e a r s to be respons ib le f o r the p h o t o c h e m i s t r y o f these c o m p l e x e s . It i s not p r e s e n d y unders tood h o w the i n t e r a c t i o n o f l i g h t w i t h these c o m p l e x e s resul ts i n the o b s e r v e d products . H o w e v e r , a v e r y s i m p l i f i e d v i e w o f the m e t a l d orbi ta ls i n v o l v e d and the p o s s i b l e d - d t rans i t ions c a n be i n f e r r e d f r o m c r y s t a l f i e l d theory f o r a f i v e - c o o r d i n a t e d 6 m e t a l c o m p l e x . F i g u r e 3 - l a s h o w s the o r b i t a l sp l i t t ing d i a g r a m f o r a t r i g o n a l b i p y r a m i d a l c o m p l e x 1 0 w h i c h i s the g e o m e t r y a s s i g n e d to the b i s ( h y d r o c a r b y l ) c o m p l e x e s i n S e c t i o n 2 . 4 . 2 . A s m e n t i o n e d b r i e f l y t h e n , these c o m p l e x e s e x h i b i t a d z2 d22 d x y - 4 - — \ — d x y dx2-y2 d x 2. y 2 d x z , d y z d x 2 , d y z (a) (b) Figure 3-1. O r b i t a l s p l i t t i n g d i a g r a m s f o r a d 6 m e t a l c o m p l e x w i t h (a) i d e a l t r i g o n a l b i p y r a m i d a l g e o m e t r y ; a n d (b) d i s t o r t e d t r i g o n a l b i p y r a m i d a l g e o m e t r y due to presence o f s t rong a - d o n o r l i g a n d s i n e q u a t o r i a l p o s i t i o n s . d i s tor t ion f r o m the i d e a l a n d this w a s predic ted b y a theoret ical c a l c u l a t i o n f o r d 6 f i v e -c o o r d i n a t e c o m p l e x e s that h a v e a - d o n o r l i g a n d s i n the e q u a t o r i a l p l a n e . 1 1 T h e presence o f s t rong a -donor l i g a n d s (such as h y d r o c a r b y l s ) is b e l i e v e d to break the degeneracy o f the d x y and d x 2 . y 2 set ( F i g u r e 3 - l b ) , a n d this corresponds s t ructura l ly to a decrease i n the angles s u b t e n d i n g the l i g a n d s . W i t h the g i v e n n e w o r b i t a l 47 s p l i t t i n g d i a g r a m , the e x c i t a t i o n o f an e lec t ron u p o n the absorpt ion o f r a d i a t i o n to an e m p t y d o r b i t a l w o u l d have a d e s t a b i l i z i n g effect towards the l i g a n d s b o u n d to i r i d i u m . T h i s c o u l d result i n the w e a k e n i n g o r e v e n b r e a k i n g o f a meta l l i g a n d b o n d as s h o w n i n F i g u r e 3-2a f o l l o w e d b y an H - a b s t r a c t i o n b y the r e s u l t i n g r a d i c a l l i g a n d f r o m another l i g a n d . A l t e r n a t i v e l y , the d - d t rans i t ion c o u l d l ead to a p o l a r i z a t i o n o f the M - L b o n d i n w h i c h the l i g a n d bears a m o r e negat ive charge (F igure 3-2b) . T h i s , too , c o u l d then result i n H - a b s t r a c t i o n f r o m a n e i g h b o u r i n g l i g a n d . A l t h o u g h w h a t is o c c u r r i n g at the e l e c t r o n i c l e v e l c a n o n l y be p o s t u l a t e d , s u c h r a t i o n a l i z a t i o n s are b a s e d o n the o b s e r v e d products o f the p h o t o l y s i s exper iments , and appear to be consis tent w i t h an i n t r a m o l e c u l a r H - a b s t r a c t i o n m e c h a n i s m . hv M r L„lr -R •R' hv 5+ •R *R' 6--R (a) (b) Figure 3 - 2 . P o s s i b l e ef fects o n the m e t a l - h y d r o c a r b y l b o n d s due to the absorpt ion o f v i s i b l e rad ia t ion . 3.6 Possible Mechanism for the Photoreactions A p o s s i b l e m e c h a n i s m f o r the p h o t o l y s i s o f the m e t h y l b e n z y l c o m p l e x (8) w h i c h accounts f o r the products o b s e r v e d a n d i s consistent w i t h the l a b e l l i n g studies i s s h o w n i n S c h e m e 3 -2 . T h e s i m p l e s t w a y to e x p l a i n the f o r m a t i o n o f the m e t h y l i d e n e c o m p l e x is b y cc-hydrogen (deuterium) abstract ion f r o m the m e t h y l l i g a n d b y the b e n z y l l i g a n d , r e s u l t i n g i n the e l i m i n a t i o n o f to luene. T h i s i s a l so consistent w i t h the a b o v e pos tu la te that the r o l e o f the l i g h t i n the r e a c t i o n i s to cause the p o p u l a t i o n o f o r b i t a l s w h i c h are a n t i b o n d i n g i n nature w i t h respect to the m e t a l -48 h y d r o c a r b y l b o n d , thus r e s u l t i n g i n e i ther a c o o r d i n a t e d b e n z y l r a d i c a l l i g a n d , o r an i r i d i u m - b e n z y l b o n d p o l a r i z e d w i t h most o f the e lectron densi ty r e s i d i n g o n the b e n z y l l i g a n d . H o w e v e r , the f o r m a t i o n o f the d i h y d r i d e c o m p l e x requi res a m o r e elaborate p a t h w a y . P r e v i o u s w o r k i n our laboratory has suggested the i n v o l v e m e n t o f the a m i d o g r o u p o f the tridentate l i g a n d as a basic site w h i c h can be protonated to an a m i n e . 1 2 T h e r e f o r e , the a m i d e m a y be i n v o l v e d i n abstract ing a h y d r o g e n (deuter ium) f r o m the m e t h y l l i g a n d , l e a v i n g a m e t h y l i d e n e b e n z y l a m i n e c o m p l e x as s h o w n i n S c h e m e 3-2. T h e n i n s e r t i o n o f the m e t h y l i d e n e unit in to the i r i d i u m b e n z y l b o n d , f o l l o w e d b y a (3-h y d r o g e n e l i m i n a t i o n r e a c t i o n w i t h the loss o f s tyrene w o u l d g i v e a m o n o h y d r i d e a m i n e c o m p l e x . A f i n a l rearrangement i s necessary to g i v e the o b s e r v e d deuter io -h y d r i d o i r i d i u m c o m p l e x as s h o w n . A g a i n , this is consis tent w i t h the postulate that the l i g h t causes a rupture o r p o l a r i z a t i o n o f the I r - N b o n d , thus c a u s i n g the a m i d e to abstract a p r o t o n f r o m the n e i g h b o u r i n g m e t h y l l i g a n d . T h e same g e n e r a l m e c h a n i s t i c p a t h w a y s c a n a l s o be u s e d to e x p l a i n the p r o d u c t s o b t a i n e d o n p h o t o l y s i s o f the d i m e t h y l a n d d i b e n z y l c o m p l e x e s , w i t h the e x c e p t i o n o f the f o r m a t i o n o f the i r i d i u m ( I ) e thylene adduct for the f o r m e r reac t ion . T h e o r i g i n o f this c o m p l e x is not presently understood. 4 9 Scheme 3-2 Ph 2 •P M e 2 S i s | , . CD 3 Me 2Si :N CH 2Ph •P P h 2 P h 2 - P M e 2 S i s .CD, :N Me 2Si t Ph 2 M e 2 S i s i D " | ( 7 C D 2 M e 2 S i ' | ^ C H 2 P h •P P h 2 Abstraction of D + by amide CH 2Ph •P Ph 2 Ph 2 Me 2 Si^ :N I r = C D ? Me 2Si •P Ph 2 + CH 2DPh Ph 2 M e 2 S i s ,.D | ^ : C D 2 N — I r ^ M e 2 S i / | ^ C H 2 P h •P Ph 2 Insertion of methylidene into Ir-alkyl bond P h 2 ' P Me 2Si. .D I Ph 2 - P ,N I r—CD 2CH2Ph M e 2 S i v % . D N ° — I r — H Me 2Si | - ( C D 2 = C H P h ) M e 2 S / | Ph 2 M e 2 S i s :N — Me 2 Si H 5 0 3.5 Experimental 3.5.1 Thermolysis Studies A C 6 D 6 so lut ion (1 m L ) o f the des i red c o m p o u n d (30 m g ) w a s sealed under N 2 i n an N M R tube . T h e tube w a s heated to 8 0 ° C i n an o i l bath a n d m o n i t o r e d p e r i o d i c a l l y b y * H N M R spectroscopy. 3.5.2 Photolysis Studies A C 6 D 6 s o l u t i o n (1 m L ) o f the des i red c o m p o u n d (30 m g ) w a s sealed under N 2 i n an N M R tube. T h e tube w a s p l a c e d w i t h i n a w a t e r - c o o l e d P y r e x j acke t i n front o f a 275 W a t t s u n l a m p and the react ion was m o n i t o r e d b y and 3 1 P N M R . 3.5.3 U V / V I S Spectrophotometry A n exac t a m o u n t ( a p p r o x i m a t e l y 30 m g ) o f the c r y s t a l l i n e c o m p o u n d w a s w e i g h e d out i n the N 2 f i l l e d g l o v e b o x a n d d i s s o l v e d i n a k n o w n v o l u m e o f spectra l -grade h e x a n e ( w h i c h h a d been d r i e d o v e r a c t i v a t e d 4 A m o l e c u l a r s ieves , v a c u u m -t r a n s f e r r e d , a n d d e o x y g e n a t e d t h r o u g h s e v e r a l f r e e z e - p u m p - t h a w c y c l e s p r i o r to use) . T h e s o l u t i o n w a s then t ransferred i n t o a 1 c m q u a r t z c e l l e q u i p p e d w i t h a K o n t e s T e f l o n needle v a l v e . Spectra were obta ined o n a P e r k i n - E l m e r 5 5 2 3 A U V / V I S s p e c t r o p h o t o m e t e r . 3.5.4 Synthesis of Deuterium Labelled Samples [ N o t e : refer to S e c t i o n 2.5 f o r syntheses o f analogous c o m p o u n d s . ] KCD2(C6D5) T h e synthesis w a s carr ied out as f o r K C H 2 P h , u s i n g C7D8 instead o f C7H8. Ir(CD3)I[N(SiMe2CH2PPh2)2] T h e s y n t h e s i s w a s c a r r i e d o u t as d e s c r i b e d f o r t h e I r ( C H 3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] ana logue , u s i n g C D 3 I (98 a t o m % D , A l d r i c h ) 51 instead o f CH3I . Ir(CD3)R'[N(SiMe2CH2PPh2)2], Ir(CH3)R'[N(SiMe2CH2PPh2)2] , R'=CD2Ph, CH2Ph T h e syntheses o f these c o m p l e x e s w e r e c a r r i e d out as d e s c r i b e d f o r the Ir(CH3)(CH2Ph)[N(SiMe2CH2PPh2)2] a n a l o g u e , u s i n g the a p p r o p r i a t e p o t a s s i u m salt ( K C H ^ P h o r K C D 2 ( C 6 D s ) ) . 3.6 References 1. G . L . G e o f f r o y a n d M . S . W r i g h t o n , " O r g a n o m e t a l l i c P h o t o c h e m i s t r y " , A c a d e m i c Press , N e w Y o r k (1979) ; p . l . 2 . L . S. H e g e d u s , M . A . M c G u i r e , L . M . Schul tze , C . Y i j u n and O . P . A n d e r s o n , J . A m . C h e m . Soc . , 106 (1984) 2680. 3. D . B . P o u r r e a u and G . L . G e o f f r o y , A d v . Organomet . C h e m . , 24 (1985) 249 . 4. J . D a v i d s o n , M . F . L a p p e r t and R . Pearce, C h e m . R e v . 7 6 (1976) 219 . 5. M . D . F r y z u k and P . A . M a c N e i l , O r g a n o m e t a l l i c s 2 (1983) 682 . 6. M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , J . A m . C h e m . S o c , 107 (1985) 6708. 7. M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , O r g a n o m e t a l l i c s , 5 (1986) 2469. 8. (a) A . R . S i e d l e , R . A . N e w m a r k and L . H . P i g n o l e t , O r g a n o m e t a l l i c s , 3 (1984) 855. (b) P . R . H o f f m a n and K . G . C a u l t o n , J . A m . C h e m . S o c , 97 (1975) 4 2 2 1 . 9. J . G . C a l v e r t and J . N . P i t t s , " P h o t o c h e m i s t r y " , J o h n W i l e y a n d Sons Inc . , N e w Y o r k (1966); p .748 . 10. F . A . C o t t o n a n d G . W i l k i n s o n , " A d v a n c e d Inorganic C h e m i s t r y " , 4th E d . , John W i l e y and Sons , N e w Y o r k (1980); p . 642 . 11. D . L . T h o r n a n d R . H o f f m a n n , N o u v . J . C h i m . , 3 (1979) 39. 12. ' M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , J . A m . C h e m . S o c , 109 (1987) 2 8 0 3 . 52 C H A P T E R 4. I R I D I U M A L K Y L I D E N E C O M P L E X E S I r ( = C H R ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , R = H , Ph 4.1 Iridium Benzylidene Complex I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 4.1.1 Synthesis and Characterization T h e s y n t h e s i s of t h e i r i d i u m a l k y l i d e n e c o m p l e x e s I r ( C H R ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] ( R = H , P h ) b y p h o t o - i n d u c e d a - H e l i m i n a t i o n f r o m a b i s ( h y d r o c a r b y l ) c o m p l e x has been s h o w n to be a u n i q u e m e t h o d o f g e n e r a t i n g a l k y l i d e n e s f o r a late t ransi t ion m e t a l . T h e synthesis o f the b e n z y l i d e n e c o m p l e x ( R = P h ) w a s c a r r i e d o u t b y p h o t o l y z i n g a b e n z e n e s o l u t i o n o f the d i b e n z y l c o m p l e x I r ( C H 2 P h ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] for 1 w e e k . A l t h o u g h the m e t h y l i d e n e c o m p l e x ( R = H ) h a d been p r e v i o u s l y i s o l a t e d 1 b y se lect ive c r y s t a l l i z a t i o n , attempts at i s o l a t i n g the b e n z y l i d e n e c o m p l e x f r o m s o l u t i o n have been unsuccess fu l so far . E v e n t h o u g h i t is the ma jor i r i d i u m species p r o d u c e d i n the reac t ion , w i t h a product ra t io o f 2:1 to the d i h y d r i d e c o m p l e x I r ( H ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , i t appears that the b e n z y l i d e n e c o m p l e x i s m u c h t o o s o l u b l e i n the c r y s t a l l i z a t i o n s o l v e n t s (hexanes , t o l u e n e , pentane) t r ied . Se lec t ive c r y s t a l l i z a t i o n o f the d i h y d r i d e f r o m the react ion m i x t u r e was a lso u n s u c c e s s f u l . H o w e v e r , the b e n z y l i d e n e c o m p l e x has b e e n c h a r a c t e r i z e d s p e c t r o s c o p i c a l l y , a n d T a b l e 4-1 shows a c o m p a r i s o n o f the N M R data w i t h that o f the m e t h y l i d e n e c o m p l e x . T h e l a r g e c h e m i c a l sh i f t d o w n f i e l d f o r the a l k y l i d e n e C a resonance i s i n d i c a t i v e o f a carbon a t o m w h i c h is m u l t i p l y b o n d e d to a transi t ion meta l , a n d b o t h v a l u e s f a l l w i t h i n the repor ted range o f 2 0 0 - 3 0 0 p p m (re la t ive to S i M e 4 ) t y p i c a l o f a l k y l i d e n e c o m p l e x e s . 2 T h e ^ C p H } N M R s p e c t r u m o f the b e n z y l i d e n e c o m p l e x s h o w s a (broad) tr iplet due to the t w o b o n d c o u p l i n g to the trans d i s p o s e d p h o s p h i n e d o n o r s ( 2 J C P = 10 H z ) , a n d the resonance i s fur ther s p l i t i n t o t w o i n the gated d e c o u p l e d spectrum w i t h the c o u p l i n g to the a - p r o t o n m e a s u r i n g 133 H z . 53 Table 4-1. Spectroscopic Data for Iridium Alkylidene Complexes 3 lr(CHPh)[N(SiMe2CH2PPh2)2] lr(CH2)[N(SiMe2CH2PPh2)2] 31P{1H}NMR 11.5 (s) 17.4 (s) 1 H N M R : \r=ChR 18.65 (t, 3 J H P = 1 3 ) 16.3 (t, 3 J H P = 1 4.5) Si(CW)2 0.14 (s) 0.15 (s) PCH 2Si 2.06 (t, J a p p = 5 ) 2.11 (t, J a p p = 6 ) P(C6H5)2 7.0 (m, meta/para) 7.04 (m, meta/para) 7.78 (m, ortho) 7.84 (m, ortho) 13C{1H}NMR 211.1 (br t, 2J C P = 1 0 ) 200.1 (t, 2J C P =11) 1 3 C N M R 211.1 (d of m, 1 J C H = 1 3 3 ) b 200.1 (tt, 1 J C H = 1 3 6 ) C a A l l spectra recorded at 25° in C6D6I all chemical shifts in ppm; all coupling constants (J) in Hz. ^Gated decoupled spectrum. cProton coupled spectrum. A l s o c h a r a c t e r i s t i c o f an i n d i u m - b o u n d a l k y l i d e n e u n i t i s the l o w f i e l d resonance f o r the a - p r o t o n i n the lK N M R s p e c t r u m . 3 . 4 F o r the b e n z y l i d e n e c o m p l e x , the presence o f one singlet f o r the s i l y l m e t h y l protons and o f one v i r t u a l t r iplet f o r the m e t h y l e n e p r o t o n s o f the l i g a n d b a c k b o n e suggests that the b e n z y l i d e n e u n i t i s r o t a t i n g a b o u t the I r = C d o u b l e b o n d o n the lH N M R t i m e sca le . I n o r d e r to i n v e s t i g a t e the m a g n i t u d e o f the r o t a t i o n a l barr ie r , a l o w temperature s tudy w a s p e r f o r m e d . 4.1.2 Determination of I r = C Rotational Barrier F i g u r e 4-1 s h o w s the c h a n g e s o b s e r v e d i n the ! H N M R spec t ra o f the b e n z y l i d e n e c o m p l e x as the t e m p e r a t u r e i s l o w e r e d b e l o w 2 5 ° C . A t r o o m temperature , the s inglet at 0 .14 p p m represents the s i l y l m e t h y l protons o f the l i g a n d b a c k b o n e , a n d at - 8 0 ° C (the temperature o f coa lescence) the s ingle t broadens a n d e v e n t u a l l y spl i ts i n t o t w o singlets as c a n be seen at - 9 0 ° C and - 9 5 ° C . B a s e d o n this l o w temperature N M R study, the free energy o f rotat ion w a s ca l cu la ted to be A G ^ r o t = 9.3 k c a l / m o l (see e x p e r i m e n t a l sect ion) . 178 K I r = C # P h 18.65 8 7 2 1 ppm 0 Figure 4-1. ! H N M R s p e c t r u m o f J j ( C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] i n C 7 D 8 at 298 K (bottom), and the peaks due to the s i l y l m e t h y l protons ( in the r e g i o n 0 . 0 - 0 . 5 p p m ) as the temperature i s l o w e r e d to 178 K ( s h o w n above) , t denotes resonance peaks due to I r (H )2 [N (S iMe2CH2PPh2)2] * denotes r e s i d u a l so lvent peaks 55 A l t h o u g h there h a v e b e e n s e v e r a l t h e o r e t i c a l s t u d i e s 5 o n m o d e l carbene c o m p l e x e s i n w h i c h the barr ier to ro ta t ion i s p r e d i c t e d , there are v e r y f e w reported v a l u e s o f c a l c u l a t e d A G $ r o t o f c o m p l e x e s w h i c h have been s y n t h e s i z e d a n d i so la ted . S c h r o c k ' s g r o u p r e p o r t e d A G * r o t v a l u e s d e t e r m i n e d b y N M R studies o n a series o f t a n t a l u m a n d n i o b i u m a l k y l i d e n e c o m p l e x e s , a n d the v a l u e s r a n g e d f r o m 15.6 to a p r e d i c t e d £ 2 3 k c a l / m o l . 6 S i m i l a r l y , barr ier o f rotat ion va lues o f 12.3 to 15.7 k c a l / m o l w e r e ca l cu la ted for a f a m i l y o f tungsten a l k y l i d e n e c o m p l e x e s . 7 A t the other end o f the s c a l e , the p r e d i c t e d v a l u e s f o r F i s c h e r - t y p e carbene c o m p l e x e s are m u c h l o w e r , c a l c u l a t e d at 0.41 to 3 .60 k c a l / m o l f o r the m o d e l c o m p o u n d s ( C O ) s C r = C H ( O H ) a n d ( C O ) 5 F e = C H ( O H ) . 5 b T h e A G * r o t = 9 . 3 k c a l / m o l f o r I r ( C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] f a l l s i n be tween the va lues f o r the t w o extreme types o f carbene c o m p l e x e s , c loser to those repor ted f o r the S c h r o c k - t y p e a l k y l i d e n e s . T h i s m i g h t be expected based o n the nature o f the C a substituents a lone as both the b e n z y l i d e n e c o m p l e x a n d the S c h r o c k -t y p e a l k y l i d e n e s l a c k h e t e r o a t o m subst i tuents . T h e p r e s e n c e o f o n e o r m o r e heteroatoms X o n the carbene c a r b o n s h o u l d result i n a decrease i n the M = C a d o u b l e b o n d character due to m u l t i p l e b o n d i n g b e t w e e n C a a n d X , a n d therefore , a l o w e r barr ier to ro ta t ion . 4.2 Iridium Methylidene Complex I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 4.2.1 Other Isolated Transition-Metal Methylidene Complexes A l t h o u g h b r i d g i n g m e t h y l e n e c o m p l e x e s are b e c o m i n g w e l l k n o w n , 8 t e r m i n a l m e t h y l e n e (or m e t h y l i d e n e ) c o m p l e x e s ( L n M = C H 2 ) are not as c o m m o n . T h e r e have been severa l repor ted cases i n w h i c h a m e t h y l i d e n e species w a s i n f e r r e d as a react ion i n t e r m e d i a t e , observed i n s o l u t i o n , o r e v e n c h a r a c t e r i z e d by s p e c t r o s c o p i c t e c h n i q u e s , 9 but there are v e r y f e w e x a m p l e s i n w h i c h the m e t h y l i d e n e c o m p l e x w a s a c t u a l l y i s o l a t e d . T a b l e 4-IJ l i s ts those e x a m p l e s f r o m the l i terature a l o n g w i t h the reported i n f o r m a t i o n o f their character izat ion. 56 Table 4-II. Other Reported Isolated Methylidene Complexes Complex Characterization (of methylene ligand) 1 H N M F P 1 3 C N M R 8 X-ray Structure" Reference Cp2(CH3)Ta=CH2 - 0 . 2 2 (s)c 2 2 8 (t)c.j J C H = 1 3 2 2 . 0 2 6 ( 1 0 ) 1 0 [(PMe3)4(CI)W=CH2]+ C F 3 S 0 3 - - 0 . 1 6 d ( J H W = 5 1 ) 2 2 0 J C H = 1 2 0 1 1 [Cp(NO)(PPh3)Re=CH2]+ X" X- - B F 4 - 1 5 . 6 5 (t), J H - T = J H P = 4 1 5 . 4 8 (d)d.« «JHH"=4, J K P < 1 2 9 0 . 3 (t), J C H = 1 5 1 1 0 0 . 5 (d)d.'.i J C H = 1 9 0 1 2 X- = P F 6 " 1 5 . 6 7 (t), J H H , = J H P = 4 1 5 . 4 2 (br d)d.g Jm-r=4, J H ' P ^ I [Cp*(NO)(L)Re=CH2]+PF6-L = P P h 3 1 5 . 2 7 (d), j H i - r = 6 1 4 . 3 5 (d)d 2 8 7 . 7 (br, s)e 2 . 1 4 5 ( 2 2 ) , 2 . 1 5 2 (32)k 1 3 L = P(OPh) 3 1 4 . 4 9 (d), J H H - = 5 1 4 . 1 4 (d)d 2 9 3 . 3 (d)d J C p = 1 2 1 . 8 9 8 ( 1 8 ) (CI) (NO)(PPh 3 ) 2 Os=CH 2 1 3 . 8 (t)» J H P = 1 9 . 2 1 . 9 2 ( 1 ) 1 5 ( l ) (CO)(PPh 3 ) l r=CH 2 1 2 . 8 8 (t)d.h J H P = 1 9 1 7 Chemical shifts in ppm, coupling constants in Hz, °M=C bond distance, in A. GC^De- dCD2Cl2- ^ D C l s . fat -33°C. gat 10°C. nat -50°C. »at -70°C. JGated decoupled spectrum. kDisordered. T h e f irst entry i n the table is the w e l l - k n o w n c o m p l e x synthes ized b y S c h r o c k , a n d represents the v e r y f i rs t i s o l a b l e t r a n s i t i o n - m e t a l m e t h y l i d e n e c o m p l e x . 1 0 T h e r e a c t i v i t y o f this c o m p o u n d i s i n d i c a t i v e o f a n u c l e o p h i l i c c a r b o n a t o m . T h e next repor ted i so la ted m e t h y l i d e n e c o m p l e x came f r o m the same labora tory , this time w i t h a t u n g s t e n m e t a l c e n t r e . 1 1 B a s e d o n N M R s t u d i e s , the m e t h y l i d e n e m o i e t y i s b e l i e v e d to be T - s h a p e d i n w h i c h one H a i s c lose to the m e t a l centre, a n d the other m a k e s u p a H a - C a - W b o n d angle a p p r o a c h i n g 180° . 57 A l l o f the c a t i o n i c r h e n i u m m e t h y l i d e n e c o m p l e x e s l i s t e d i n T a b l e 4- I I were g e n e r a t e d b y a b s t r a c t i n g a p r o t o n f r o m a c o o r d i n a t e d m e t h y l l i g a n d u s i n g P h 3 C + X \ 1 2 ' 1 3 T h e m o r e react ive c y c l o p e n t a d i e n y l der ivat ives a lso represent the f irst i so la ted e lec t rophi l i c m e t h y l i d e n e c o m p l e x e s , and for L = P P I 1 3 , the c o m p l e x was f o u n d to c o u p l e to generate the e thylene c o m p l e x [(Cp)Re(NO)(PPh3)(H2C=CH2)]+PF6" w i t h a large degree o f enant iomer s e l f - r e c o g n i t i o n . 1 4 T h e o s m i u m c o m p l e x represents the f i r s t r e p o r t e d e x a m p l e o f a n e u t r a l m e t h y l i d e n e o f the later t r a n s i t i o n m e t a l s , p r e p a r e d b y the a d d i t i o n o f CH2N2 to OsCl(NO)(PPh3)3. 1 5 T h e m e t h y l i d e n e l i g a n d w a s f o u n d not to be e l e c t r o p h i l i c , and neither i s i t as n u c l e o p h i l i c as i n S c h r o c k ' s tanta lum c o m p l e x . !6 Instead, the authors be l i eve that i t is the electron r i c h O s = CH2 d o u b l e b o n d w h i c h interacts w i t h v a r i o u s e lec t rophi les , a n d that the b o n d is ac tua l ly n o n - p o l a r . T h e o n l y other i r i d i u m m e t h y l i d e n e c o m p l e x w h i c h has been i so la ted is ac tual ly t h e r m a l l y unstable a n d w a s charac ter ized o n l y at - 5 0 ° C . 1 7 A t r o o m temperature, the c o m p l e x rearranges to a p h o s p h o r o u s y l i d e in termediate w h i c h undergoes o x i d a t i v e a d d i t i o n to f o r m an ortho-metal la ted h y d r i d e c o m p l e x s h o w n i n equat ion 4 - 1 . 0 - ! P P h , • P P h 2 CH2 I r ^ C H . C D z C ' 2 > C ( 4 - D RT O C ' I OCT I P P h 3 P P h 3 4.2.2 R e a c t i v i t y o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] A p r e l i m i n a r y inves t iga t ion o f the p o l a r i t y a n d nature o f the I r = C d o u b l e b o n d w a s under taken b y s u r v e y i n g the r e a c t i v i t y o f the m e t h y l i d e n e c o m p l e x w i t h v a r i o u s reagents a n d s m a l l m o l e c u l e s . S i n c e m o s t o f the e x p e r i m e n t s w e r e p e r f o r m e d as N M R tube reac t ions , the results are s t i l l qui te specula t ive . H o w e v e r , severa l o f the react ions s h o w p o t e n t i a l f o r s o m e e x t r e m e l y interes t ing c h e m i s t r y , and i t is ev ident 58 e v e n at this ear ly stage o f the study that the m e t h y l i d e n e c o m p l e x is a h i g h l y react ive species a n d behaves u n l i k e the p r e v i o u s l y s tudied m e t h y l i d e n e c o m p l e x e s . 4.2.2.1. R e a c t i o n w i t h M e t h y l I o d i d e T h e i r i d i u m m e t h y l i d e n e c o m p l e x reacted c l e a n l y w i t h CH3I w i t h i n 30 minutes at r o o m temperature to g i v e a s ingle p r o d u c t b y 3 1 P { 1 H } N M R (4.8 p p m (s)), w i t h a c o r r e s p o n d i n g c o l o u r change f r o m p u r p l e to y e l l o w to green . O n the basis o f the * H N M R s p e c t r u m ( F i g u r e 4 - 2 ) , the n e w c o m p l e x appears to be a s i x c o o r d i n a t e i r i d i u m ( I I I ) c o m p o u n d , w i t h a h y d r i d e l i g a n d , i o d i d e l i g a n d a n d J t - b o u n d e t h y l e n e o c c u p y i n g the a v a i l a b l e c o o r d i n a t i o n sites o n the metal- tr identate l i g a n d uni t . W h e n the a n a l o g o u s r e a c t i o n w a s c a r r i e d o u t u s i n g CD3I, the t r i p l e t at 2 .2 p p m ( c o r r e s p o n d i n g to the c o o r d i n a t e d e thylene protons) decreased i n in tens i ty b y a fac tor o f t w o . In a d d i t i o n , the h y d r i d e resonance at -13.2 p p m w a s s i g n i f i c a n t l y r e d u c e d and n o l o n g e r integrated as one p r o t o n , i n d i c a t i n g a deuter ide l i g a n d (the presence o f the h y d r i d e s i g n a l at a l l i s p r o b a b l y due to h y d r o g e n i m p u r i t i e s i n the CD3I). P h 2 ^ P h 2 / ^ p X ^ p Me 2Si s I Me 2Si s | y - (4-2) N lr = CH2 + CH3I ^ § ^ N |r» 1 / I 30 min. RT / S1 Me2Si I Me2Si yf \ P h 2 P h 2 E q u a t i o n 4 - 2 s h o w s the s tereochemis t ry o f the p r o d u c t as i t i s b e l i e v e d to ex is t i n s o l u t i o n , w i t h the i o d o l i g a n d trans to the a m i d e o f the a n c i l l a r y l i g a n d . T h i s ass ignment was a r r i v e d at by c o m p a r i s o n o f the h y d r i d e resonance at -13 .2 p p m w i t h those o f re lated h y d r i d e c o m p l e x e s f o r w h i c h the structure i s k n o w n . T y p i c a l l y w i t h the tridentate l i g a n d [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] " o n i r i d i u m , a h y d r i d e situated trans to the n i t r o g e n m o i e t y o r to a ha l ide group has a resonance f r e q u e n c y m u c h further u p f i e l d , b e t w e e n - 1 9 a n d - 2 5 p p m . 1 8 F o r e x a m p l e , i n t h e c o m p l e x I r ( H ) 2 I [ N H ( S i M e 2 C H 2 P P h 2 ) 2 ] , the h y d r i d e s are p o s i t i o n e d c i s to each other, w i t h the 59 S i ( C / / 3 ) l l | i l l l | l i l l | I M I j I I I I | I 1 -•3. 0 -13. 2 -13. 4 Ir-C2#4 meta/para .1 i { ; i ; , I | I l I • | i I I l | l I I l | l l l I | i I l l | l l l l | l l I l | l l l I | • I I I i 8 7 3 2 1 0 PPM Figure 4-2. l H N M R s p e c t r u m o f I r ( C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + C H 3 I i n C 7 D 8 after 9 0 minutes at r o o m temperature. Inset i s en larged 4 times as c o m p a r e d to the rest o f the spectrum. * denotes r e s i d u a l so lvent peaks 60 one trans to the i o d i d e r e s o n a t i n g at -19 .39 p p m a n d the other (trans to the a m i n e , N H ) at -23 .10 p p m . H y d r i d e c h e m i c a l shi f t v a l u e s h a v e been re la ted to the trans-i n f l u e n c e o f the l i g a n d p o s i t i o n e d trans to the h y d r i d e . 1 9 In oc tahedra l c o m p l e x e s , l i g a n d s w i t h h i g h t r a n s - i n f l u e n c e have been o b s e r v e d to cause l o w - f i e l d shi f ts f o r h y d r i d e s trans to t h e m . T h e r e f o r e , s ince C2H4 i s g e n e r a l l y h i g h e r i n the trans-i n f l u e n c e ser ies than r o r R 2 N - (or R 2 N H ) , 1 9 the a s s i g n m e n t o f the e thy lene a n d h y d r i d e l i g a n d s m u t u a l l y trans i n the n e w c o m p l e x seems reasonable . S c h e m e 4-1 s h o w s a p o s t u l a t e d m e c h a n i s m f o r the p r o d u c t i o n o f the n e w c o m p l e x I r ( T | 2 - C 2 H 4 ) I ( H ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , a s s u m i n g i t e x i s t s w i t h the a s s i g n e d s tereochemistry . T h e f i rs t step i n v o l v e s trans o x i d a t i v e a d d i t i o n o f m e t h y l i o d i d e to the square planar i r i d i u m c o m p l e x , f o l l o w e d by inser t ion o f the methylene unit i n t o the m e t a l - m e t h y l b o n d . Inser t ion react ions i n v o l v i n g carbenes are k n o w n , and they h a v e been c o n s i d e r e d to be a n a l o g o u s to the m i g r a t o r y i n s e r t i o n reac t ions o f c a r b o n y l c o m p o u n d s . 2 0 In fact , there are several e x a m p l e s o f apparent a l k y l - c a r b e n e i n s e r t i o n s ( for e x a m p l e , see S c h e m e 1 - 6 ) . 2 1 T h e e t h y l i o d i d e in termedia te w h i c h w o u l d resul t f r o m the i n s e r t i o n r e a c t i o n i s b e l i e v e d to ex i s t i n a square p y r a m i d a l c o n f i g u r a t i o n w i t h the e t h y l g r o u p a p i c a l , cons i s tent w i t h the s t ructures o f the ana logous m e t h y l , b e n z y l and p h e n y l ha l ide c o m p l e x e s f o r w h i c h this s tereochemistry has been c o n f i r m e d (see sect ion 2.4.2) . A t this po in t , P -hydride e l i m i n a t i o n f r o m the e t h y l group w o u l d appear to g i v e the des i red p r o d u c t except f o r the fact that the e thylene and h y d r i d e l i g a n d s w o u l d be c i s ins tead o f trans to each other. M o r e o v e r , w i t h the g i v e n a s s u m e d stereochemistry o f the e t h y l i o d i d e intermediate , there i s n o a v a i l a b l e c o o r d i n a t i o n site c i s to the e t h y l l i g a n d f o r this to o c c u r . T h u s i t i s necessary to i n v o k e the i n v o l v e m e n t o f the a m i d o g r o u p o f the " a n c i l l a r y " l i g a n d . In p r e v i o u s w o r k w i t h this tridentate l i g a n d sys tem, there have been severa l e x a m p l e s i n w h i c h the a m i d o g r o u p b e c o m e s i n v o l v e d i n a r e a c t i o n b y b e c o m i n g hydrogenated to an a m i n e f u n c t i o n a l i t y . 1 8 There fore , i t i s not 61 P h 2 M e 2 S i s N l r = : C H , M e , S i P h 2 P h , Scheme 4-1 C H 3 I Oxidat ive Addi t ion M e 2 S i / ^ H ~ | " C I > C H 2 •N Ir — I M e 2 S i - P P h 2 P h 2 P M e 2 S i . N -/ M e 2 S i H S Ir 1 - P P h 2 P-H A b s t r a c t i o n _ By Amide Inversion at N Centre M e 2 S i N I r " = = C H 2 M e ^ i ' \f I P h 2 C H 2 Migratory Insert ion P h 2 - P Me 2 Si , , CH2CH3 N-M e , S i - P P h 2 P h 2 » P M e 2 S i s J M e 2 S i N Ir-~ P P h 2 Migration of H to Iridium " P h 2 M e 2 S i N — I r -M e 2 S i H I \ P P h 2 unreasonable to propose an a -hydrogen abstract ion f r o m the e t h y l l i g a n d b y the a m i d e to g i v e an i r i d i u m ( I ) e thylene i o d i d e a m i n e c o m p l e x . I n v e r s i o n at the n i t rogen centre w o u l d then p l a c e the h y d r o g e n a t o m adjacent to the e m p t y c o o r d i n a t i o n site a n d transfer o f this group to the metal centre w o u l d g i v e the des i red n e w c o m p l e x w i t h the p r o p o s e d s te reochemis t ry . 62 T h e p r o p o s e d e t h y l i o d i d e in termedia te I r (CH2CH3 ) I [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] c o u l d p r e s u m a b l y be accessed i n the same m a n n e r as the other h y d r o c a r b y l h a l i d e c o m p l e x e s w e r e p r e p a r e d . A s a m p l e o f J x ( C O E ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 l w a s reacted w i t h E t I o n a s m a l l scale and m o n i t o r e d b y N M R spectroscopy. A l t h o u g h the react ion g a v e a f a i r l y c o m p l e x m i x t u r e o f products ( p r o b a b l y due to the presence o f excess E t I ) , resonances due to the I r ( r | 2 - C 2 H 4 ) I ( H ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] spec ies w e r e i d e n t i f i e d i n the * H N M R s p e c t r u m . T h i s r e s u l t g i v e s f u r t h e r s u p p o r t to the m e c h a n i s m p r o p o s e d f o r the react ion o f the methyl idene c o m p l e x w i t h CH3I. 4 . 2 . 2 . 2 R e a c t i o n w i t h E t h y l e n e T h e r e a c t i o n o f the m e t h y l i d e n e c o m p l e x w i t h C2H4 w a s m u c h s l o w e r , t a k i n g t w o days at r o o m temperature to g o to c o m p l e t i o n . T h e f i n a l * H a n d 3 1 P { 1 H } N M R spec t ra af ter the d i s a p p e a r a n c e o f a l l o f the s tar t ing m a t e r i a l c l e a r l y s h o w the presence o f t w o i r i d i u m p r o d u c t s : the i r i d i u m ( I ) i t - b o u n d e t h y l e n e c o m p l e x I r ( T | 2 -C 2 H 4 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 L 2 2 and a n e w species w h i c h appears to be an i r id ium(I I I ) a l l y l h y d r i d e c o m p l e x (equat ion 4-3) . T h i s n e w c o m p l e x corresponds to a s inglet at P h 2 PUZ P / ^ - P I M e 2 S i s I I r ^ y v + N — l r ( 4 - 3 ) •P ' \ ^ - P P h 2 P h 2 2 1 6.5 p p m i n the 3 1 P { 1 H ) N M R spectrum, a n d has a 1 H N M R spec t rum c o n s i s t i n g o f an u p f i e l d t r iplet at -21.1 p p m (2jp=13 Hz) f o r the h y d r i d e , resonances character is t ic o f an r i 3 - b o u n d a l l y l at 2.8 p p m ( m , 2 H), 3.0 p p m ( m , 2 H), a n d 4.1 p p m ( m , 1 H), and a n c i l l a r y l i g a n d resonances i n d i c a t i v e o f inequiva lent environments f o r the t w o faces o f the meta l - t r identa te p l a n e : S i ( C / / 3 ) 2 0.11 p p m (s) and 0.58 p p m (s), P C / / 2 S i 1.76 p p m (m) , P(Cf3//5)2 7.1 p p m (m) a n d 7.7 p p m (m). A l l y l meta l h y d r i d e c o m p l e x e s are P h 2 M e 2 S i v j M e 2 S i s N lr = CH2 + H2C-CH2 N / I 2 dsvs f M e Z S ' \ ^ - M e 2 S i ^ P h 2 63 not u n c o m m o n and , i n fact, several have been reported f o r i r i d i u m a l o n e . 2 3 - 2 4 W h e n the reac t ion w a s m o n i t o r e d every f e w hours b y N M R spectroscopy, the spectra obta ined w e r e f o u n d to be m o r e c o m p l e x and d i f f i c u l t to interpret . A l t h o u g h there i s n o c o n c l u s i v e e v i d e n c e as yet about the nature o f any intermediates i n v o l v e d , a m e c h a n i s m f o r the f o r m a t i o n o f the a l l y l h y d r i d e product has been p r o p o s e d based o n c o m p a r i s o n to s i m i l a r reac t ions i n the l i tera ture . T h e r e i s p r e c e d e n c e f o r a lkene r e a c t i o n w i t h a l k y l i d e n e species v i a i n i t i a l c o o r d i n a t i o n to the m e t a l centre as s h o w n i n S c h e m e 4 - 2 . 2 5 T h e next step i n v o l v e s m e t a l l a c y c l o b u t a n e f o r m a t i o n , w h i c h i s one o f the k e y steps p r o p o s e d i n the c u r r e n t l y f a v o u r e d m e c h a n i s m f o r the o l e f i n metathes is r e a c t i o n i n v o l v i n g t r a n s i t i o n - m e t a l carbene c o m p l e x e s . 2 6 T h e o b s e r v e d a l l y l m e t a l h y d r i d e c o m p l e x i s o b t a i n e d after p%hydrogen e l i m i n a t i o n f r o m the m e t a l l a c y c l e . A v e r y s i m i l a r react ion m e c h a n i s m has been p r o p o s e d f o r the f o r m a t i o n o f another i r i d i u m a l l y l h y d r i d e species , th is t i m e f r o m a m e t h o x y m e t h y l e thylene s tar t ing c o m p l e x w h i c h i s thought to be c o n v e r t e d f i r s t to a m e t h y l i d e n e e thylene species (see S c h e m e 1 - 5 ) . 2 4 Scheme 4-2 P h 2 P h 2 Metal lacyclobutane Formation t P h 2 P h 2 64 I n t e r e s t i n g l y , w h e n t h e r e a c t i o n w a s r e p e a t e d u s i n g I r(=CD2 ) [N(SiMe2CH2PPh2 )2L there w a s n o d e u t e r i u m l a b e l o b s e r v e d i n the a l l y l l i g a n d . Instead, the exact same e n d resul ts w e r e o b t a i n e d as w i t h the undeuterated m e t h y l i d e n e c o m p l e x . T h i s suggests that some sort o f exchange process is o c c u r r i n g d u r i n g the course o f the r e a c t i o n , and a p o s s i b i l i t y w h i c h ties i n w i t h the p r o p o s e d m e c h a n i s m i s s h o w n i n S c h e m e 4 - 3 . S i n c e m e t a l l a c y c l o b u t a n e f o r m a t i o n c a n be r e v e r s i b l e , 2 6 a m e t h y l i d e n e - e t h y l e n e in termedia te c o u l d f o r m w h e r e the d e u t e r i u m l a b e l i s i n c o r p o r a t e d i n t o the 7C-bound e t h y l e n e (D2C=CH2>. T h i s c o u l d then be d i s p l a c e d b y free ethylene s ince the react ions were p e r f o r m e d under a s l ight excess o f C2H4. I f the exchange process o f the c o o r d i n a t e d ethylene w i t h free e thylene i s faster than the P - e l i m i n a t i o n step, the f i n a l a l l y l h y d r i d e p r o d u c t w o u l d not be expected to c o n t a i n any d e u t e r i u m l a b e l . S c h e m e 4-3 P h , M e 2 S i s N Ir ' ; C D , M e 2 S i "P CH, P h , M e 2 S i s M e 2 S i M e 2 S i M e 2 S i P h 2 7 A* "as?2 ~ C H 2 M e 2 S i -P \ P h 2 P h 2 - P I I r ' ZCHZ D 2 IN P h , P h 2 - P I r C D 2 . . X . -P P h 2 C H 2 C H 2 65 4.2.2.3 R e a c t i o n w i t h A c e t y l e n e W i t h i n 2 h o u r s at r o o m temperature, the r e a c t i o n o f the m e t h y l i d e n e w i t h an excess o f C2H2 resul ted i n a c o l o u r change f r o m p u r p l e to y e l l o w w i t h the f o r m a t i o n o f one p r o d u c t b y 3 1 P { J H } N M R (-15.2 p p m (s)). T h e * H N M R s p e c t r u m i s not f u l l y unders tood because o f the c o m p l e x i t y o f the methylene and p h e n y l reg ions . H o w e v e r , the m o s t o b v i o u s features are the presence o f resonances t y p i c a l o f an a l l y l l i g a n d (sets o f peaks at 3.1 p p m , 3.9 p p m , a n d 4 .4 p p m , in tegrat ing as 2 : 2 : 1 , r e s p e c t i v e l y ) , a n d t w o singlets f o r the s i l y l m e t h y l protons . E q u a t i o n 4-4 s h o w s a p o s s i b l e product f o r m a t i o n w h i c h w o u l d i n v o l v e 2 e q u i v a l e n t s o f a c e t y l e n e a n d a f a i r l y i n v o l v e d m e c h a n i s m ( S c h e m e 4 -4 ) , and at this stage appears to be a reasonable e x p l a n a t i o n based o n the o b s e r v e d N M R data. y — P h z ^ P h 2 M e * S i v I C D M e 2 S i s I N lr = C H 2 + 2HC^CH 6 6 - N I / v ( 4 " 4 ) c / I 2 hours RT / M e 2 S i | M e 2 S i P h 2 P h 2 T h e f i r s t step i n the p r o p o s e d r e a c t i o n m e c h a n i s m is c o o r d i n a t i o n o f the acetylene f o l l o w e d b y p r o t o n abstract ion b y the a m i d e to g i v e an ace ty l ide c o m p l e x . A n o t h e r acetylene m o l e c u l e c o u l d coordinate to the e m p t y site o n i r i d i u m and interact w i t h the m e t h y l i d e n e l i g a n d as s h o w n . A c e t y l e n e s have been repor ted to react w i t h m e t a l m e t h y l e n e s p e c i e s , 2 7 and a r e s u l t i n g m e t a l l a c y c l o b u t e n e f r o m s u c h a reac t ion has been i s o l a t e d and s tructural ly c h a r a c t e r i z e d . 2 8 In order to f o r m an a l l y l l i g a n d , the a m i n e f u n c t i o n a l i t y w o u l d have to inver t a n d transfer the p r o t o n to the nearest c a r b o n o f the m e t a l l a c y c l e . 66 Ph2 -P M e 2 S i s N | r = C H 2 S c h e m e 4-4 + C 2 H 2 M e 2 S i - P P h 2 P h 2 P M e 2 S i v . - H I .ti* ~ \ | R = = = C H 2 M e 2 S i H C s ^ C H P h 2 Metal lacyclobutene Format ion M e 2 S i H P h 2 P Inversion M e 2 S i N l r C H 2 ' A / H C = = = C H - - - P P h 2 at N Centre M e 2 S I. P h 2 ' H C = = C H :CHo M e 2 S i - P P h 2 Abstraction of H + by Amide P h 2 •P N I r , = CHp M e , S i P h , P h 2 - P M e 2 S i s L — ^ N I r - — £ H 2 Me H C = i = C H - P P h 2 Migration of H* and Allyl Formation P h 2 - P Me 2Si s N l r Me2Si P h , 4.2.2.4 R e a c t i o n w i t h C a r b o n M o n o x i d e U n d e r 1 atmosphere o f C O , a benzene (or toluene) s o l u t i o n o f the m e t h y l i d e n e c o m p l e x w a s e v e n t u a l l y a l l c o n v e r t e d to the i r i d i u m ( I ) c a r b o n y l a d d u c t I r ( C O ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] 2 2 w h e n le f t at r o o m temperature ( e q u a t i o n 4 -5 ) . H o w e v e r , the *H N M R spec t rum o f the sample r u n w i t h i n the f i rs t f e w m i n u t e s o f the r e a c t i o n at r o o m temperature s h o w e d the presence o f a m o r e c o m p l e x species . 67 C 6 D 6 \ — u — c o < 4- 5) N lr = CH2 + CO 1 week RT Me2Si Me2Si P Ph 2 I n order to g a i n m o r e i n f o r m a t i o n about the course o f this r e a c t i o n , a v a r i a b l e l o w temperature N M R study w a s p e r f o r m e d . A t - 6 0 ° C , the m a j o r species i d e n t i f i e d i n b o t h the 3 1 P { 1 H } and lH N M R w a s the m e t h y l i d e n e c o m p l e x , w i t h the 3 1 P { ! H } N M R c h e m i c a l shi f t o f 17.4 p p m , and the characterist ic t r iplet resonance at 16.3 p p m i n the * H N M R spec t rum. A l s o o b s e r v e d was the presence o f a n e w c o m p l e x , appear ing as a s inglet at 11.4 p p m i n the 3 1 P { 1 H ) N M R spec t rum, and h a v i n g a t r iplet i n the lH N M R spec t rum at 12.05 p p m . T h i s i s consistent w i t h a C O adduct o f the m e t h y l i d e n e c o m p l e x as s h o w n i n the f irst step o f S c h e m e 4-5 . A t - 2 0 ° C , the m a j o r species present w a s this n e w c o m p l e x a l o n g w i t h a s m a l l amount o f the i r i d i u m ( I ) C O adduct , w h i c h c o n t i n u e d to increase i n concent ra t ion as the r e a c t i o n m i x t u r e w a s a l l o w e d to w a r m u p . A s e c o n d n e w c o m p l e x w a s f i r s t de tec ted at 0 e C , a n d h a d a m a x i m u m c o n c e n t r a t i o n w i t h i n a f e w m i n u t e s at r o o m temperature at w h i c h p o i n t the m a j o r p r o d u c t w a s the i r i d i u m ( I ) C O adduct , a n d the m e t h y l i d e n e - C O c o m p l e x w a s n o w present i n a v e r y s m a l l quant i ty ( F i g u r e 4-3) . T h e second n e w c o m p l e x corresponds to t w o sets o f double ts i n the 3 J p p H } N M R , i n d i c a t i n g that the p h o s p h i n e donors o f the l i g a n d b a c k b o n e are i n e q u i v a l e n t (20.8 p p m (d) a n d 25 .2 p p m (d), Jpj> = 8.2 H z ) . A l o n g w i t h t w o singlets at 0.01 a n d 0.35 f o r the s i l y l m e t h y l protons i n the * H N M R w e r e t w o sets o f doublets at 1.39 p p m (J = 16.1 H z ) a n d 1.65 p p m (J = 12.1 H z ) , and a double t o f doublets at 2.33 p p m (J = 7.3 H z ; J = 12.4 H z ) . T h e structure o f the second n e w c o m p l e x i s not o b v i o u s f r o m the i n f o r m a t i o n o b t a i n e d thus f a r . It i s c o n c e i v a b l e that the i n s e r t i o n o f the C H 2 u n i t o f the m e t h y l i d e n e - C O adduct i n t o one o f the i r i d i u m - p h o s p h o r u s b o n d s o f the tridentate l i g a n d w o u l d g i v e a p r o d u c t consis tent w i t h the N M R data (see S c h e m e 4 .5) . T h i s 68 X Ph, CH 2 Me2Si | N lr CO / Me2Si^ P Ph2 meta/para I r - C / / 2 - P P h 2 S i ( C / / 3 ) + ) P C / / 2 S i A . J L S i ( C / / 3 ) i i i—I—i—i—I—i—I—i—I—i—i—i—i—i—i—i—i—i—i—r l i l I | i i—r-0 PPM F i g u r e 4-3. * H N M R s p e c t r u m o f I r ( C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] u n d e r 1 atmosphere o f C O i n C7D8 after a f e w minutes at r o o m temperature. t denotes resonance peaks due to product o f Ir(H)2 [N(SiMe2CH2PPh2)2] + C O X denotes resonance peaks due to I r ( C O ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] * denotes r e s i d u a l so lvent peaks 69 w o u l d break the e q u i v a l e n c y o f the p h o s p h i n e d o n o r s (thus t w o d o u b l e t s i n the 3 1 P { 1 H } N M R spectrum) and a lso reduce the c o u p l i n g o f the methy lene protons o f the l i g a n d b a c k b o n e f r o m an A B quartet o f v i r t u a l tr iplets to t w o doublets . T h e r e m a i n i n g d o u b l e t o f d o u b l e t s i n the * H N M R s p e c t r u m c a n be a t t r ibuted to the i n s e r t e d methy lene protons w h i c h w o u l d c o u p l e to both o f the inequiva lent phosphines . Indeed, t h i s a s s i g n m e n t i s a l s o c o n s i s t e n t w i t h the b r o a d b a n d d e c o u p l i n g * H N M R e x p e r i m e n t p e r f o r m e d (where the phosphorus n u c l e i are d e c o u p l e d ) , i n w h i c h the three sets o f m e t h y l e n e resonances at 1.39 p p m , 1.65 p p m a n d 2 .33 p p m c o l l a p s e to three s i n g l e t s . S c h e m e 4-5 Me 2 Si s | + c Q M e 2 S i s | ^ Me 2Si^ N I r = CH 2 • N l r ^ • N lr CO Me 2Si v | Me 2Si | CO M e 2 S i ' P \ P \^-^-P Ph2 Ph2 Ph2 Ph2 Me 2Si^ | 2 N lr CO Me2Si | Ph 2 T h e r e i s p r e c e d e n c e f o r i n s e r t i o n r e a c t i o n s o f a CH.2 u n i t i n t o a m e t a l -p h o s p h i n e b o n d a n d this w a s p r e v i o u s l y s h o w n i n e q u a t i o n 4-1 f o r the t h e r m a l l y uns tab le i r i d i u m m e t h y l i d e n e c o m p l e x r e p o r t e d b y R o p e r et a l . 1 7 H o w e v e r , i t i s d i f f i c u l t to r a t i o n a l i z e the r e s u l t i n g i n s e r t i o n p r o d u c t as a r e a c t i o n i n t e r m e d i a t e t o w a r d s the f o r m a t i o n o f the f i n a l p r o d u c t , I r ( C O ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] - A m o r e p l a u s i b l e r e a c t i o n in termediate w o u l d be a c o m p l e x w i t h a c o o r d i n a t e d ketene s ince there i s l i t e ra ture p r e c e d e n c e f o r ketene f o r m a t i o n f r o m m e t a l carbene c a r b o n y l 7 0 c o m p l e x e s , 2 9 but the N M R data are not consistent w i t h such a f o r m u l a t i o n . Perhaps the p r o p o s e d i n s e r t i o n p r o d u c t i s f o r m e d r e v e r s i b l y f r o m an in termedia te c o m p l e x ( p o s s i b l y t h e m e t h y l i d e n e C O a d d u c t ) w h i c h a l s o l e a d s t o the m o r e t h e r m o d y n a m i c a l l y s table i r i d i u m (I) C O c o m p l e x ( S c h e m e 4 -5 ) , o r the i n s e r t i o n p r o d u c t m i g h t lose C H 2 d i r e c t l y to g i v e the f i n a l product . Free ethylene w a s observed i n v e r y s m a l l quant i ty i n the * H N M R spec t rum and c o u l d account f o r the fate o f the m e t h y l i d e n e m o i e t y . 4 .2 .2 .5 R e a c t i o n w i t h T r i m e t h y l p h o s p h i n e W h e n PMe3 w a s a d d e d to a b e n z e n e s o l u t i o n o f the i r i d i u m m e t h y l i d e n e c o m p l e x at r o o m temperature, the s o l u t i o n i m m e d i a t e l y c h a n g e d c o l o u r to y e l l o w to g i v e o n l y the k n o w n i r i d i u m ( I ) PMe3 adduct Ir(PMe3)[N(SiMe2CH2PPh2)2] 2 2 and free e t h y l e n e (equat ion 4-6) . T o g a i n s o m e u n d e r s t a n d i n g o f the m e c h a n i s m , this P h 2 P I Ir PMe 3 + C 2 H 4 ( 4 - 6 ) I •P P h 2 r e a c t i o n w a s a l s o inves t iga ted b y N M R at l o w temperatures. A t - 6 0 ° C , the reac t ion h a d a l ready b e g u n to take p l a c e as there were n o resonances due to the m e t h y l i d e n e c o m p l e x . Instead, there w a s a b r o a d p e a k at 11.35 p p m w h i c h sharpened u p to a d o u b l e t o f tr iplets at - 2 0 ° C ( 3 J H P = 1 7 . 1 H Z , 3 J H P = 1 2 . 0 Hz). Cons i s tent w i t h this and the set o f l i g a n d b a c k b o n e resonances i n d i c a t i n g i n e q u i v a l e n t e n v i r o n m e n t s f o r the t w o faces o f the tridentate l i g a n d i s a m e t h y l i d e n e c o m p l e x w i t h a c o o r d i n a t e d PMe3 l i g a n d ( F i g u r e 4-4) . A t 0 ° C , this intermediate c o m p l e x disappears c o m p l e t e l y , g i v i n g the f i n a l products Ir(PMe 3 ) [N (SiMe2CH 2 PPh2 )2] and free C2H4. P h 2 - P M e 2 S i y N I r CHg + P M e 3 M e 2 S i C 6 D 6 RT M e 2 S i > v M e 2 S i - P P h 2 71 Ph 2 M e 2 S i s N Ir" :CH 9 Me 2Si PMe, •P Ph 2 Ir=C#2 I i i i i I i i i—i | i i i i 1 2 1 1 P ( C 6 H 5 ) meta/para ortho n—ill 1 — i—r-r—i—I i i | I i i P C t f 2 S i P (C * f t )3 l r -P(CH 3 ) 3 S i ( C / / 3 ) 8 "i—i i i | i i i . i i i—i i i | i i i i i i i i—i | i i i 2 1 0 P P M F i g u r e 4-4. lH N M R s p e c t r u m o f I r ( C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + P M e 3 i n C7D8 at - 2 0 ° C . Inset i s en larged 4 t imes as c o m p a r e d to the rest o f the spectrum. * denotes r e s i d u a l so lvent peaks 7 2 I t i s p o s s i b l e t h a t t h e i n t e r m e d i a t e c o m p l e x Ir(=CH2)(PMe3)[N(SiMe2CH2PPh2)2] a l so undergoes a m e t h y l i d e n e i n s e r t i o n in to an I r - P b o n d as w a s m e n t i o n e d f o r the C O r e a c t i o n , but this t i m e i n v o l v i n g the Ir-PMe3 b o n d ( S c h e m e 4-6). D i s s o c i a t i o n o f the r e s u l t i n g c o m p l e x w o u l d g i v e a " I r [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] " f ragment (captured b y excess P M e 3 ) a n d free C H 2 P M e 3 y l i d e . A t t a c k b y t h i s r e a c t i v e y l i d e o n another m o l e c u l e o f the i n t e r m e d i a t e I r ( = C H 2 ) ( P M e 3 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 l w o u l d resul t i n the o b s e r v e d free e thylene and another I r ( P M e 3 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] . S c h e m e 4-6 P n z ^ P h 2 * ^ P M e 2 S i v I + P M e 3 M e 2 S i s N l r = C H 2 • M | R M e 2 S i | M e 2 S i / I ^ X C H 2 P M e 3 P \ P P h 2 Ph 2 P h 2 -P M e 2 S i y N l r M e 2 S i -P P h 2 C H 2 P M e 3 Me2Si Ph2 * P PMe, , P Phj M e 2 S i s N M e 2 S i P h 2 - P I r C H 2 - P M e 3 P h , P h , M e 2 S i s 2 N M e 2 S i l r PMea + H 2 C = C H 2 -P P h 2 73 At this point in the study, there is no direct evidence for the generation of the free (or coordinated) CH2PMe3 ylide, which may be difficult to observe by NMR spectroscopy if that step of the reaction is too fast. It is thought that the synthesis of CH2PMe3 (or CR2PMe3) and its addition to the methylidene would shed some light on the course of the reaction. 4.2.2.6 Reaction with Dihydrogen The reaction of the iridium methylidene complex with H2 within 30 minutes at room temperature gave the trihydride amine complex Ir(H)3[NH(SiMe2CH2PPh2)2], which had been previously synthesized by placing the dihydride Ir(H)2[N(SiMe2CH2PPh2)2] under 1 atmosphere of H 2 . 1 8 The only other iridium compounds detected at any time during the reaction, even at low temperatures, were the original methylidene complex and the dihydride complex which presumably forms first (equation 4-7). The reaction most likely proceeds by successive additions of H2 to the iridium complex, and leads to the conversion of the methylidene to a methyl ligand and the eventual loss of methane from the metal. 4.2.2.7 Other Reactions Attempted Small scale reactions of the methylidene complex were also attempted with 1,3-butadiene and with phenylacetylene, but in both cases the reaction mixtures appeared very complex by * H and 3 1 P{ 1 H} NMR spectroscopy and, therefore, were not pursued any further. N — I r = CH 2 (4-7) Ph 2 Ph2 7 4 A s l i g h t l y l a r g e r s ca le r e a c t i o n w i t h t r i m e t h y l a l u m i n u m r e s u l t e d i n an i m m e d i a t e c o l o u r change f r o m p u r p l e to b r i g h t orange e v e n at - 7 8 ° C , but b o t h the 3 1 P { 1 H } a n d * H N M R spectra w e r e e x t r e m e l y c o m p l e x a n d i n d i c a t e d that several products h a d been f o r m e d . H o w e v e r , a f e w y e l l o w - o r a n g e crystals were i so la ted f r o m a to luene-hexane s o l u t i o n o f the reac t ion m i x t u r e a n d F i g u r e 4-5 s h o w s the * H N M R spec t rum o f these crysta ls i n C 6 D 6 - T h i s c o m p o u n d also g i v e s r i se to a s inglet at 11.3 p p m i n the 3 1 P { 1 H } N M R s p e c t r u m . S i n c e t h e d i h y d r i d e c o m p l e x I r ( H ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] is of ten an i m p u r i t y present i n these react ions due to the d i f f i c u l t y i n separat ing i t c o m p l e t e l y f r o m the m e t h y l i d e n e c o m p l e x , a sample o f the d i h y d r i d e a lone w a s also reacted w i t h A l M e 3 . T h e exact same * H N M R w a s obta ined as that s h o w n i n F i g u r e 4 - 5 , a n d therefore, the c rys ta l s o b t a i n e d f r o m the o r i g i n a l r e a c t i o n m i x t u r e apparent ly w e r e , i n fact , due to the d i h y d r i d e i m p u r i t y reac t ing w i t h A l M e 3 . B a s e d o n the N M R data , i t appears that the p r o d u c t w h i c h has f o r m e d has t w o c i s h y d r i d e s o n i r i d i u m , w i t h one o f the m e t h y l groups f r o m the a l u m i n u m b r i d g i n g the t w o metals ( corresponding to the tr iplet at -0.08 p p m ) as d r a w n i n equat ion 4 -8 . + A IMe 3 RT ,N—--j T . M e 2 A I ^ C H 3 I Me?Si ' I H ( 4 - 8 ) 75 M e 2 S i s M — M e 2 A i y C H 3 ' * Me 2Si Ph 2 .H y I r- H Ph. I I I I I I 1 I I I I I I I I I 1 1 ) I I I I I I IM I | I I I I I I I I I | I I I I I I I I I | 1 1 1 I I I I I I [ I I I I 1 I I I I I I M I I | I I I I | I I I I | I III I | I I I I | I I I I | I I I I | I - 1 5 - 1 6 - 1 7 - 1 8 -20 PPM meta/para P C / / 2 S i * P C / / 2 S i S i ( C / / 3 ) A l ( C / / 3 ) 2 I r - C / / 3 I I I I I I I I I I I I I I I 1—1 I I I I I I I I I I I I I I I I I I I I I I I I ' ' I I ' I 1 I 1 1 1 1 8 7 3 2 1 0 P P M F i g u r e 4-5. * H N M R s p e c t r u m o f I r ( H ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] + A l M e 3 i n C 6 D 6 . Inset i s en larged 5 t imes as c o m p a r e d to the rest o f the spectrum. * denotes r e s i d u a l so lvent peaks 76 4 .2.3 S u m m a r y o f R e a c t i v i t y o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] A l t h o u g h this p r e l i m i n a r y survey o f the react iv i ty o f the m e t h y l i d e n e c o m p l e x is s t i l l far f r o m c o n c l u s i v e f o r m a n y o f the react ions at tempted, i t has been v a l u a b l e i n de terrn in ing w h i c h react ions w i l l g i v e the m o s t interest ing o r p r o m i s i n g results w h e n d o n e o n a l a rger scale . T h e react ions w i t h CH3I, C2H4 a n d C2H2 are p a r t i c u l a r l y notable because they a l l appear to g i v e r ise to products r e s u l t i n g f r o m c a r b o n - c a r b o n b o n d f o r m a t i o n o f the m e t h y l i d e n e C H 2 uni t w i t h the a d d e d reagent. A l t h o u g h it i s d i f f i c u l t at this p o i n t to say too m u c h about the p o l a r i t y o f the i r i d i u m - c a r b o n d o u b l e b o n d , the c a r b o n a t o m does not seem to be e l e c t r o p h i l i c i n nature o n the basis o f the resul t s o b t a i n e d f r o m the a d d i t i o n o f e l e c t r o n - r i c h substrates . F o r e x a m p l e , the react ions w i t h P M e 3 , C O , C2H4 and C2H2 (both w i t h Tt-electrons) appear to i n v o l v e c o o r d i n a t i o n f i r s t to i r i d i u m , i m p l y i n g that the m e t a l i s the m o r e e l e c t r o n d e f i c i e n t centre. H o w e v e r , the c o m p l e x reac t ion m i x t u r e obta ined o n the a d d i t i o n o f the L e w i s a c i d A l M e 3 suggests that this i r i d i u m m e t h y l i d e n e i s not b e h a v i n g i n the same m a n n e r as S c h r o c k ' s n u c l e o p h i l i c tanta lum m e t h y l i d e n e c o m p l e x (see equat ion 1-8). Perhaps , as w a s c o n c l u d e d about the o s m i u m m e t h y l i d e n e c o m p l e x , the i r i d i u m m e t h y l i d e n e I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] cannot be p l a c e d in to either category o f the F i s c h e r -type carbenes o r the S c h r o c k - t y p e a l k y l i d e n e s , but rather has u n i q u e character is t ics . 4.3 E x p e r i m e n t a l 4.3.1 G e n e r a l C O , C2H4 a n d 1,3-butadiene w e r e u s e d as r e c e i v e d f r o m M a t h e s o n . H2 w a s p u r i f i e d b y p a s s i n g i t through a c o l u m n o f ac t ivated 4 A m o l e c u l a r s ieves a n d M n O . C D 3 I (98 a t o m % D ) was obta ined f r o m M S D , CH3I f r o m A l d r i c h , a n d P M e 3 f r o m S t r e m , a n d a l l were t ransferred to suitable conta iners a n d degassed t h r o u g h severa l f r e e z e / p u m p / t h a w c y c l e s b e f o r e use . A l M e 3 w a s p u r c h a s e d as a to luene s o l u t i o n ( 2 M ) f r o m A l d r i c h and used as r e c e i v e d . 77 V a r i a b l e temperature N M R s tudies , ^ C p H } a n d G a t e d D e c o u p l e d N M R e x p e r i m e n t s w e r e a l l p e r f o r m e d o n a V a r i a n X L - 3 0 0 s p e c t r o m e t e r (300 M H z ) a c c o r d i n g to s tandard p r o c e d u r e s , e x c e p t f o r the l o w t e m p e r a t u r e s t u d y o f the b e n z y l i d e n e c o m p l e x ( for the b a r r i e r o f r o t a t i o n c a l c u l a t i o n ) a n d the b r o a d b a n d d e c o u p l i n g e x p e r i m e n t , b o t h o f w h i c h w e r e p e r f o r m e d o n a B r u k e r W H - 4 0 0 spectrometer (400 M H z ) . 4 .3 .2 Attempted Isolation of I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] A t h i c k - w a l l e d P y r e x v e s s e l f i t ted w i t h a K o n t e s needle v a l v e ( " b o m b " ) w a s l o a d e d w i t h 3 0 0 m g o f I r ( C H 2 P h ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] i n 2 0 m L benzene a n d e x p o s e d to the s u n l a m p f o r 1 w e e k o v e r w h i c h t i m e the s o l u t i o n t u r n e d f r o m a deep c o p p e r r e d c o l o u r to dark b r o w n . T h e s o l u t i o n was p u m p e d to dryness , extracted w i t h t o l u e n e , f i l t e r e d t h r o u g h C e l i t e a n d le f t to c r y s t a l l i z e at - 3 0 ° C . U n f o r t u n a t e l y , n o crysta ls w e r e obta ined e v e n t h o u g h v a r i o u s v o l u m e s o f so lvent w e r e t r i e d . H e x a n e s a n d pentane w e r e a l so t r i e d as c r y s t a l l i z a t i o n so lvents , as w e r e l o n g e r and shorter p h o t o l y s i s t ime per iods , a l l to n o a v a i l . 4 . 3 . 3 . C a l c u l a t i o n of R o t a t i o n a l B a r r i e r f o r I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] T h e A G ^ r o t w & s c a l c u l a t e d f r o m the E y r i n g equat ion w h e r e the rate c o n s t a n t 3 0 i s g i v e n b y kc = T C A V c / V I . Therefore , A G * = - R T C In [(7tAv c h)(\2~ k T c ) - ! ] where R is the gas constant , T c i s the temperature o f coalescence , h i s P l a n c k ' s constant , k is the B o l t z m a n n constant , a n d A v c i s the p e a k separat ion at coa lescence . F r o m the l o w t e m p e r a t u r e lK N M R study o f the c o m p l e x I r ( = C H P h ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , the v a l u e s o f T c = 193 K a n d A v c = 5 8 H z ( taken as the p e a k s e p a r a t i o n at l o w temperature) w e r e obta ined , g i v i n g A G * r o t = 9.3 k c a l / m o l . 78 4.3.4 R e a c t i o n o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2)2] w i t h V a r i o u s S u b s t r a t e s D u e to the l i m i t e d quanti t ies o f i r i d i u m start ing mater ia l s a n d because o f the d i f f i c u l t y i n i s o l a t i n g large y i e l d s o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 L a l l r e a c t i v i t y exper iments w e r e p e r f o r m e d as N M R tube react ions . I n the g l o v e b o x , an N M R tube f i t t e d w i t h a B 1 4 j o i n t w a s c h a r g e d w i t h a p p r o x i m a t e l y 2 0 m g o f c r y s t a l l i n e I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , and then attached to a K o n t e s t e f l o n needle v a l v e a lso w i t h a B 1 4 j o i n t . T h e N M R tube c o u l d then be r e m o v e d f r o m the g l o v e b o x a n d attached to a v a c u u m l i n e . F o r most o f the substrates u s e d , a s l ight excess o f the substrate was either s y r i n g e d i n t o the N M R tube under a strong argon f l o w , o r condensed o r vacuum-trans fer red into the c o o l e d ( - 1 9 6 ° C ) N M R tube. I n the case o f H2 and C O , one atmosphere o f the gas substrate w a s added. T h e N M R tube was then sealed and the reac t ion w a s s tudied b y N M R spect roscopy. S i n c e the A l M e 3 w a s a v a i l a b l e as a t o l u e n e s o l u t i o n , a p p r o x i m a t e l y 1 e q u i v a l e n t w a s s y r i n g e d i n t o a 4 0 m L t o l u e n e s o l u t i o n o f 3 0 m g o f I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 l i n a b o m b , w h i c h was c o o l e d to - 7 8 ° C . T h e react ion m i x t u r e w a s w a r m e d to r o o m temperature , r e d u c e d to d r y n e s s , a n d a s a m p l e w a s c h e c k e d b y N M R . T h e rest w a s extracted w i t h to luene , f i l t e r e d t h r o u g h C e l i t e and a l l o w e d to c r y s t a l l i z e i n the g l o v e b o x ( c r y s t a l l i z a t i o n w a s i n d u c e d b y the a d d i t i o n o f h e x a n e ) . T h e exac t same p r o c e d u r e as d e s c r i b e d above w a s u s e d f o r the r e a c t i o n o f I r ( H ) 2 [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] w i t h A l M e 3 . 4.4 R e f e r e n c e s 1. M . D . F r y z u k , P . A . M a c N e i l and S. J . 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K i e l , V . K . W o n g a n d J . A . G l a d y s z , J . A m . C h e m . Soc . , 104 (1982) 141. 13. A . T . P a t t o n , C . E . S trouse , C . B . K n o b l e r and J . A . G l a d y s z , J . A m . C h e m . S o c . , 105 (1983) 5804. 14. J . H . M e r r i f i e l d , G . - Y . L i n , W . A . K i e l and J . A . G l a d y s z , J . A m . C h e m . Soc . , 105 (1983) 5 8 1 1 . 15. A . F . H i l l , W . R . R o p e r , J . M . W a t e r s a n d A . H . W r i g h t , J . A m . C h e m . S o c , 105 (1983) 5939. 16. R . R . S c h r o c k and P . R . Sharp, J . A m . C h e m . S o c , 100 (1978) 2389 . 17. G . R . C l a r k , W . R . R o p e r and A . H . W r i g h t , J . O r g a n o m e t . C h e m . , 273 (1984) C 1 7 . 18. M . D . F r y z u k , P . A . M a c N e i l a n d S. J . R e t t i g , J . A m . C h e m . S o c , 109 (1987) 2803 . 19. T . G . A p p l e t o n , H . C . C l a r k and L . E . M a n z e r , C o o r d . C h e m . R e v . 10 (1973) 335 . 20 . J . P . C o l l m a n , L . S . H e g e d u s , J . R . N o r t o n a n d R . G . F i n k e , " P r i n c i p l e s and A p p l i c a t i o n s o f O r g a n o t r a n s i t i o n M e t a l C h e m i s t r y " , U n i v e r s i t y Sc ience B o o k s , M i l l V a l l e y , C a . , (1987); p p . 379-380. 2 1 . (a) D . L . T h o r n a n d T . H . T u l i p , J . A m . C h e m . S o c , 103 (1981) 5984 (b) H . K l e i t z e i n , H . W e r n e r , P . S e r h a d l i a n d M . L . Z i e g l e r , A n g e w . C h e m . , Int. E d . E n g l . , 22 (1983) 46 . (c) P . J e rnakof f and N . J . C o o p e r , J . A m . C h e m . S o c , 106 (1984) 3026 . 22 . M . D . F r y z u k , P . A . M a c N e i l and S. J . R e t t i g , O r g a n o m e t a l l i c s , 5 (1986) 2469 . 2 3 . (a) T . H . T u l i p and J . A . Ibers, J . A m . C h e m . S o c , 101 (1979) 4 2 0 1 . (b) W . D . 81 M c G h e e and R . G . B e r g m a n , J . A m . C h e m . Soc . , 110 (1988) 4246 . 24. D . L . T h o r n , O r g a n o m e t a l l i c s , 1 (1982) 879. 25 . A . J . S c h u l t z , R . K . B r o w n , J . M . W i l l i a m s and R . R . S c h r o c k , J . A m . C h e m . S o c . , 103 (1981) 169. 26 . re f 2 0 , p p . 475-485 . 27 . R . J . M c K i n n e y , T . H . T u l i p , D . L . T h o r n , T . S . C o o l b a u g h and F . N . T e b b e , J . A m . C h e m . S o c . , 103 (1981) 5584 . 28 . J . C . C a l a b r e s e , D . C . R o e , D . L . T h o r n and T . H . T u l i p , O r g a n o m e t a l l i c s , 3 (1984) 1223. 29 . (a) W . A . H e r r m a n n and J . P l a n k , A n g e w . C h e m . Int. E d . E n g l . , 17 (1978) 525 . (b) T . W . B o d n a r and A . R . C u t l e r , J . A m . C h e m . Soc . , 105 (1983) 5926. (c) P . T . B a r g e r , B . D . Santars iero , J . A r m a n t r o u t a n d J . E . B e r c a w , J . A m . C h e m . S o c . , 106 (1984) 5178. 30. W . A . T h o m a s , A n n . R e v . N M R Spectrosc . , 1 (1968) 43 . 82 C H A P T E R 5. C O N C L U S I O N S T h e i r i d i u m ( U I ) b i s ( h y d r o c a r b y l ) c o m p l e x e s Ir(R)R'[N(SiMe2CH2PPh2)2] f o r R = C H 3 , C6H5, C H 2 P h , and R ' = C H 3 , C6H5, C H 2 P h , C H 2 C M e 3 , C H 2 S i M e 3 w e r e s y n t h e s i z e d i n h i g h y i e l d s f r o m the h y d r o c a r b y l h a l i d e p r e c u r s o r s I r ( R ) X [N(SiMe2CH2PPh2>2]» w h e r e X = I o r B r , b y r e a c t i o n w i t h the a p p r o p r i a t e o r g a n o l i t h i u m salt L i R ' . A l l ten o f the h i g h l y c o l o u r e d b i s ( h y d r o c a r b y l ) c o m p l e x e s w e r e f u l l y c h a r a c t e r i z e d b y e lementa l a n a l y s i s a n d b y * H , 1 3 C { 1 H } a n d 3 1 P N M R s p e c t r o s c o p y . T h e g e o m e t r y o f these f i v e - c o o r d i n a t e c o m p l e x e s w a s d e t e r m i n e d to be t r i g o n a l b i p y r a m i d a l both i n s o l u t i o n , o n the basis o f N O E D I F F exper iments , and i n the s o l i d state b y c o m p a r i s o n to the X - r a y structures o f the m e t h y l n e o p e n t y l and d i b e n z y l d e r i v a t i v e s . A l l o f these a i r and mois ture sensi t ive b i s ( h y d r o c a r b y l ) c o m p l e x e s w e r e f o u n d to be t h e r m a l l y stable. H o w e v e r , the m e t h y l n e o p e n t y l c o m p l e x h a d been p r e v i o u s l y f o u n d to g i v e r ise to an i r i d i u m m e t h y l i d e n e c o m p l e x Ir(=CH2)[N(SiMe2CH2PPh2)2] w h e n e x p o s e d to s u n l i g h t . B e c a u s e o f the interest i n s u c h c o m p l e x e s i n w h i c h a c a r b e n e u n i t i s s t a b i l i z e d b y a t r a n s i t i o n m e t a l , the rest o f the ser ies o f b i s ( h y d r o c a r b y l ) c o m p l e x e s w e r e a l s o sub jec ted to p h o t o l y s i s w i t h the h o p e o f p r o d u c i n g o t h e r a l k y l i d e n e s p e c i e s . A s a r e s u l t , a b e n z y l i d e n e c o m p l e x Ir(=CHPh)[N(SiMe2CH2PPh2)2] was d i s c o v e r e d and charac ter ized s p e c t r o s c o p i c a l l y , a l t h o u g h i t has not yet been i s o l a t e d i n a pure state. O n the basis o f the o b s e r v e d N M R data , the b e n z y l i d e n e uni t appeared to be rotat ing about the I r = C b o n d , and the rotat ional barr ier f o r this c o m p l e x w a s ca lcula ted to be 9.3 k c a l / m o l . T h e f o r m a t i o n o f the i r i d i u m a l k y l i d e n e c o m p l e x e s b y p h o t o - i n d u c e d H -abstract ion f r o m a h y d r o c a r b y l l i g a n d i s a unique m e t h o d f o r the synthesis o f a carbene c o m p l e x f o r a late t r a n s i t i o n m e t a l . T h i s r e a c t i o n w a s i n v e s t i g a t e d f u r t h e r b y d e u t e r i u m l a b e l l i n g studies and character izat ion o f the b i s ( h y d r o c a r b y l ) c o m p l e x e s b y U V / V I S s p e c t r o s c o p y . A l t h o u g h the m e c h a n i s m s f o r the o b s e r v e d p h o t o c h e m i c a l 83 processes o f the b i s ( h y d r o c a r b y l ) c o m p l e x e s r e m a i n qui te specula t ive , i t appears that the absorpt ion o f v i s i b l e l i g h t i s due to d - d transi t ions w h i c h g i v e rise to the exc i ted states r e s p o n s i b l e f o r the o b s e r v e d c h e m i s t r y . F i n a l l y , t h e r e a c t i v i t y o f t h e i r i d i u m m e t h y l i d e n e c o m p l e x I r ( = C H 2 ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] w a s a lso b r i e f l y e x p l o r e d w i t h severa l reagents and s m a l l m o l e c u l e s . T h e r e a c t i o n s w i t h CH3I, C2H4 a n d C 2 H 2 a l l s e e m to i n v o l v e c a r b o n - c a r b o n b o n d f o r m a t i o n w i t h the m e t h y l i d e n e C H 2 u n i t to g i v e e i ther c o o r d i n a t e d e thy lene o r a l l y l p r o d u c t s . I n the reac t ions w i t h P M e 3 a n d C O , both reagents were o b s e r v e d to coordinate to the meta l centre o f the m e t h y l i d e n e c o m p l e x f i r s t , before reac t ing to g i v e the f i n a l i r i d i u m ( I ) adducts I r ( L ) [ N ( S i M e 2 C H 2 P P h 2 ) 2 ] , L = P M e 3 , C O . T h i s i m p l i e s that the m e t a l i s m o r e e l e c t r o n d e f i c i e n t than the m e t h y l i d e n e u n i t , a n d that the m e t h y l i d e n e i s p r o b a b l y n u c l e o p h i l i c ra ther than e l e c t r o p h i l i c i n nature. H o w e v e r , further studies w i t h a v a r i e t y o f e l ec t rophi les and n u c l e o p h i l e s are needed to c o n f i r m this interpretat ion. T h e m a i n p r o b l e m i n s t u d y i n g the reac t iv i ty o f the i r i d i u m m e t h y l i d e n e c o m p l e x w a s the d i f f i c u l t y i n o b t a i n i n g large amounts o f the pure c o m p l e x i n order to p e r f o r m the react ions o n a reasonably s i z e d sca le . B e f o r e fur ther s tudy o n this c o m p l e x i s d o n e , a h i g h e r y i e l d i n g m e t h o d o f p r e p a r i n g o r i s o l a t i n g the i r i d i u m methyl idene c o m p l e x s h o u l d be d e v e l o p e d . 

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