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Methylation of fluorocyclophosphonitriles Ranganathan, T.N 1971

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THE METHYLATION OF FLUOROCYCLOPHOSPHONITRILES by • T.N. RANGANATHAN M.Sc, U n i v e r s i t y o f Madras ( I n d i a ) , 1960. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of ' Chemistry We accept t h i s t h e s i s as conforming to the '. r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1971. In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r re ference and study . I f u r t h e r agree t h a t pe rmiss ion f o r e x t e n s i v e copy ing o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department o r by h i s r e p r e s e n t a t i v e s . I t i s understood that copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed wi thout my w r i t t e n p e r m i s s i o n . Department of The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada Date ABSTRACT The main part of t h i s t h e s i s i s concerned with the study of the r e a c t i o n s of f l u o r o c y c l o p h o s p h o n i t r i l e s , (NPF2)3_r>> w i t h methyl-l i t h i u m , which e x h i b i t a new o r i e n t a t i o n p a t t e r n , and which appear to i n v o l v e i n d u c t i v e i n t e r a c t i o n s of the s u b s t i t u e n t (the CH^ group) with a homomorphic TT-system. Nuclear magnetic resonance spectroscopy has been the p r i n c i p a l t o o l f o r deducing the s t r u c t u r e s of the isomers i s o l a t e d by gas l i q u i d chromatography from r e a c t i o n s of the fluorocyclophospho-5 4 n i t r i l e s w i t h m e t h y l - l i t h i u m . J„.. _ and J„„ have been observed f o r the f i r s t time i n p h o s p h o n i t r i l i c d e r i v a t i v e s . Although the assignments of the frequencies i n the i n f r a r e d s p e c t r a of the m e t h y l f l u o r o - and m e t h y l c y c l o p h o s p h o n i t r i l e s are inadequate f o r a complete v i b r a t i o n a l a n a l y s i s , the p a t t e r n of frequencies found f o r trans-1^-N^P^F^Me,, shows that i t i s not centrb-symmetrical and n e i t h e r i s the d e r i v a t i v e 1,1,5,5-N^P^F^Me^. In the c r y s t a l the l a t t e r compound has a saddle shape, and i t i s l i k e l y that the f l e x i b i l i t y i s caused by the i n t e r c o n v e r s i o n of the tub to saddle forms, which can take place by bond t o r s i o n a l movements onl y , without angular deformation. The most important aspect of the work i s the f r e s h evidence which i s provided on the nature and extent of d e l o c a l i s a t i o n w i t h i n the p h o s p h o n i t r i l i c r i n g . S t r u c t u r a l l y , the t r a n s m i s s i o n of the e f f e c t o f the s u b s t i t u e n t s i s seen i n the s i g n i f i c a n t a l t e r n a t i o n of bond lengths i n 1, l-N^P^F^N^- Since the molecular framework i s n e a r l y p l a n a r , the c o n d i t i o n s f o r the a p p l i c a t i o n o f simple Huckel theory are s a t i s f i e d , and the e f f e c t o f a T T - i n d u c t i v e p e r t u r b a t i o n at P has t h e r e f o r e been estimated through the c a l c u l a t i o n of bond-atom p o l a r i s a b i l i t i e s IT.- = ^ r s f o r a d e l o c a l i s e d ir-system based on an 8-membered r i n g . The c l o s e correspondence i n p a t t e r n of the observed d e v i a t i o n s i n the i n d i v i d u a l bond lengths from the mean and the bond-atom p o l a r i s a b i l i t i e s seems very d i r e c t evidence f o r e l e c t r o n i c d e l o c a l i s a t i o n i n p h o s p h o n i t r i l i c molecules, and suggests that simple Huckel methods can provide a u s e f u l guide to t h e i r chemistry. The predominantly geminal s u b s t i t u t i o n observed i n the r e a c t i o n of (NPF2)^ with LiMe has been w e l l explained by an i n d u c t i v e e f f e c t o f the methyl s u b s t i t u e n t on the TT-system of the p h o s p h o n i t r i l i c r i n g . The atom-atom p o l a r i s a b i l i t i e s f o r the three r i n g systems i n v e s t i g a t e d have been c a l c u l a t e d u s i n g simple Huckel theory, which show t h a t , from t h i s cause alone, a second n u c l e o p h i l i c s u b s t i t u t i o n should take place p r i n c i p a l l y at P^, as found. Also the atom-atom p o l a r i s a b i l i t i e s e x p l a i n the observed geminal and a n t i p o d a l sub-s t i t u t i o n , an o r i e n t a t i o n p a t t e r n which has not been recognised p r e v i o u s l y . This i s the f i r s t case i n which c y c l i c d e l o c a l i s a t i o n has been shown to have a d e c i s i v e e f f e c t on p h o s p h o n i t r i l i c chemistry. ACKNOWLEDGMENTS I am s i n c e r e l y g r a t e f u l to Professor N.L. Paddock f o r h i s i n v a l u a b l e h e l p , encouragement and guidance throughout t h i s research. I am indebted to Dr. L.D. H a l l and Mr. R.B. Malcolm f o r the heteronuclear double resonance experiments and f o r many u s e f u l d i s c u s s i o n s on the i n t e r p r e t a t i o n o f the n.m.r. s p e c t r a ; and to Dr. R.E. Pincock f o r p r o v i d i n g the gas chromatograph and the carbowax.column. I would l i k e to thank the f o l l o w i n g people f o r t h e i r co-operation and encouragement: Dr. J . Serreq'i,\ Mr. E. B i c h l e r , Mr. R.T. Oakley, Mr. R.W. Har r i s o n and Mr. C.J. Stewart, I would a l s o l i k e to thank Miss V. Ormerod f o r t y p i n g the o r i g i n a l manuscript. F i n a l l y , the f i n a n c i a l support from the U n i v e r s i t y of B r i t i s h Columbia i s g r a t e f u l l y acknowledged. - i v -Page ABSTRACT • ... , .'.1: ACKNOWLEDGMENTS . ............ .. .... . . i i i TABLE OF CONTENTS • - • >.. i v LIST OF TABLES • .... v i i l LIST OF FIGURES - ........ • • . i x CHAPTER 1. GENERAL INTRODUCTION ' 1 CHAPTER 2. PHENYLCYCLOPHOSPHONITRILES • .. 20 2.1'. I n t r o d u c t i o n ....< 20 2.2. i Preparation of F l u o r o c y c l o p h o s p h o n i t r i l e s 21 2.2.1. H e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e (NPF 2)g 2 2 2.2.2. O c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (NPF 2)4 24 2.2.3. Deca f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e (NPF2)^ 2 5 2.2.4. • Dodecafluorocyclohexaphosphonitrile 25 t N P V 6  2.3.1. O c t a p h e n y l c y c l o t e t r a p h o s p h o n i t r i l e (NPPh 2) 4 .................................. 26 2.3.2. Dodecaphenylcyclohexaphosphonitrile CNPPh 2) 6 . 26 2.4. Reactions o f Phenylphosphonitriles 27 2.4.1. Reaction of Decaphenylcyclopentaphospho-n i t r i l e w i t h M e t h y l - l i t h i u m . . . 27 2.5. I n f r a r e d S p e c t r a l Data . 28 CHAPTER 3. METHYLATION OF OCTAFLUOROCYCLOTETRAPHOSPHONITRILE.. 38 3.1. I n t r o d u c t i o n 38 3.2. Pre p a r a t i o n o f M e t h y l - l i t h i u m 39 3.3. Reactions o f ^ Eluorophosphonitriles w i t h M e t h y l - l i t h i u m ... 41 3.3.1. Reaction of Octafluorocyclotetraphospho-n i t r i l e (NPF 9). with M e t h y l - l i t h i u m • 43 - V -Page 3.3.1.1. Experiment 1 .... 1 43 3.3.1.2. Experiment 2 ............< 44 3.3.1.3. Experiment 3 • ' 46 3.3.1.4. • Experiment 4 • ...... . . 48 3.3.1.5. Experiment 5 ............................ 49 3.4. Nuclear Magnetic Resonance Spectroscopy.. 51 3.4.1. Monomethylheptafluorocyclotetraphospho-n i t r i l e ............................. 53 3.4.2. 1,1-Dimethylhexafluorocyclotetraphospho-n i t r i l e .......................... 55 3.4.3. tra n s - 1 , 5 - D i m e t h y l h e x a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e 58 3.4.4. D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (mixture o f two isomers) . .... 60 3.4.5. 1,1 , 3 - T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e 62 3.4.6. 1,1,5 - T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e ............ 66 3.4.7. 1 , 1 , 5 , 5 - T e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e .................... 71 3.4.8. O c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e 74 3.4.9. ^ Conclusion • • ' 74 3.5. • C r y s t a l S t r u c t u r e of M e t h y l f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e s 76 CHAPTER 4. METHYLATION OF HEXAFLUOROCYCLOTRIPHOSPHONITRILE AND DECAFLUOROCYCLOPENTAPHOSPHONITRILE ...... 80 4.1. I n t r o d u c t i o n . 80 4.2. Reaction of Decafluorocyclopentaphospho-n i t r i l e w i t h M e t h y l - l i t h i u m 80 4.2.1. Experiment 1 82 4.2.2. Experiment 2 4.2.3. Experiment 3 ... • ... . 84 4.2.4. - Reaction of N ^ F ^ with Hg(CH 3) 2 85 4.2.5. Reaction o f Ng,P 5F 1 Q with S n ( C H 3 ) 4 . 86 4.2.6. Reaction o f L P F n w i t h MeMgCJl • 86 - v i -Page 4.3.1. Reaction of Hexafluorocyclotriphospho-n i t r i l e w i t h M e t h y l - l i t h i u m -Experiment 1 • ............... 87 4.3.2. Experiment 2 88 4.3.3. Experiment 3 ........... 89 4.4. The Nuclear Magnetic Resonance Spectra o f Monomethylnonafluorocyclopentaphosphonitrile (NfPf-FgMe), Dimethyloctaf luorocyclopenta-p h o s p h o n i t r i l e (N^P^FgMe2> mixture o f isomers), and Decamethylcyclopentaphospho-n i t r i l e ( N ^ M e ^ ) .. . . - 90 4.4.1. Monomethylnonafluorocyclopentaphospho-n i t r i l e ................... 90 4.4.2. D i m e t h y l o c t a f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e (mixture o f isomers) •. 92 4.4.3. Decamethylcyclopentaphosphonitrile 92 4.5. The Nuclear Magnetic Resonance Spectra of Mon o m e t h y l p e n t a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , D i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , and H e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e 93 4.5.1. Mo n o m e t h y l p e n t a f l u o r o c y c l o t r i p h o s p h o n i t r i l e 93 4.5.2. 1,1-Dimethyltetrafluorocyclotriphospho-n i t r i l e • 96 4.5.3. H e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e 97 CHAPTER 5. BASE PROPERTIES . .• 99 5.1. I n t r o d u c t i o n • • ...... . 99 5.2. The Base Strengths of Methylcyclophospho-n i t r i l e s • • • • 1 l ^ 2 5.3. N-Methylphosphonitrilium Iodides 1^8 5.3.1. Pre p a r a t i o n o f Undecamethylcyclopenta-p h o s p h o n i t r i l i u m Iodide (N 5P^Me^ 1) +I~ .... 108 5.4. The Nuclear Magnetic Resonance Spectra o f N-Methylcyclophosphonitrilium Iodides .... HO 5.4.1. H e p t a m e t h y l c y c l o t r i p h o s p h o n i t r i l i u m Iodide ( N 3 P 3 M e 7 ) + l " • , HO 5.4.2. Nonamethylcyclotetraphosphonitrilium Iodide" (N 4P 4Me 9) + l " • ..... 112 5.4.3. Undecamethylcyclopentaphosphonitrilium Iodide (N 5P 5Me 1 1) + I ~ •. _ H 4 - v i i -Page 5.5. Reactions o f N-Methylcyclophospho-n i t r i l i u m Iodides ............ 115 5.5.1. P y r o l y s i s .. 115 5.5.2. Hoffman E l i m i n a t i o n ........ 118 5.5.3. Sodium Borohydride Reduction ............ 118 CHAPTER 6. VIBRATIONAL SPECTRA OF METHYLFLUOROCYCLOPHOSPHO-NITRILES AND METHYLCYCLOPHOSPHONITRILES ...... . 120 6.1. I n t r o d u c t i o n ............................ 120 6.2. Monomethylfluorocyclophosphonitriles, N P F„ ,Me where n = 3-5 . . • .134) n n 2n-l 6.3. • 1,1, - D i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o -n i t r i l e N 3P 3F 4Me 2 •. .( 139 :• 6.4. 1,1-Dimethylhexafluorocyclotetraphospho-n i t r i l e and trans-1,5-Dimethylhexafluoro- ^ c y c l o t e t r a p h o s p h o n i t r i l e . 142 6.5. l j l j S - T j r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o -n i t r i l e and 1,1,5-Trimethylpentafluorocyclo-t e t r a p h o s p h o n i t r i l e -144/ 6.6. 1 , 1 , 5 , 5 - T e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e /146_y 6.7. M e t h y l c y c l o p h o s p h o n i t r i l e s (NPMe 2) 3_ 5 ... 147 6.8. Conelusion . i'4,8-CHAPTER 7. DISCUSSION 150 7.1. S t r u c t u r a l E f f e c t s ... ......... 150 7.2. O r i e n t a t i o n a l E f f e c t s ,159/ APPENDIX 1. .... • .... ' 170 APPENDIX 2 _..«....• ...... :175.> REFERENCES • .... • • • 1 7 7 " - v i ' i i -LIST OF TABLES Page 1) Symmetry Species of s, p, and d - o r b i t a l s C C 2 v s i t e symmetry) 7 2) F i r s t I o n i z a t i o n P o t e n t i a l s of P h o s p h o n i t r i l i c F l u o r i d e s ... 14 3) Geometry o f the E x o c y c l i c Groups i n N.P.(NMe ?) s and N 6 P 6 ^ 1 2 v i - * . . , , . ; . , . . - . . . . 1 5 19 4) The F Chemical S h i f t s o f the Pe n t a f l u o r o p h e n y l f l u o r o -p h o s p h o n i t r i l e s .... .......... 18 5) P h y s i c a l P r o p e r t i e s o f the P h o s p h o n i t r i l i c F l u o r i d e s 23 6) Phenyl V i b r a t i o n s (vC-C and 3C-H) i n Monosubstituted Benzenes ............................ '. .. 33 7) . Phenyl V i b r a t i o n s i n ( N P P h 2 ) 3 _ 6 and i n PPh 5 • 34 8) V a s(PNP) f o r P h o s p h o n i t r i l i c D e r i v a t i v e s , ( N P X 2 ) n (n = 3-6). 35 9) N.m.r. Parameters o f M e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s . . 75 10) N.m.r. Parameters of M e t h y l f l u o r o c y c l o t r i p h o s p h o n i t r i l e s and Methylf l u o r o c y c l o p e n t a p h o s p h o n i t r i l e ••.. . / 98 11) Base Strengths o f T r i m e r i c and Tetrameric P h o s p h o n i t r i l i c D e r i v a t i v e s . . ................... 100 12) Base Strength.of N 3P 3Me 6 ....<.... . 104 13) Base Strength of N ^ M e g . . . •. . . 105 14) Base Strength o f N rP rMe 1 ( ) •. 106 15) S e l e c t i o n Rules f o r C 2 y Point Group i n N 3P 3F 4Me 2 .. . .• 140 16) Bond-atom P o l a r i s a b i l i t i e s . . • 156 17) Atom-atom P o l a r i s a b i l i t i e s 167 18) Tr-Electron Density per Nitrogen Atom f o r the Ring Systems « 3 - 6 173 - i x -LIST OF FIGURES Figure Page_ 1) T y p i c a l p h o s p h o n i t r i l i c d e r i v a t i v e s • 2 2) St r u c t u r e of N^P^CJl^ - a) S i n g l y bonded s t r u c t u r e w i t h formal charges, b) Tr-bonded s t r u c t u r e ........... 6 3) A x i s system ........ . 8 4) T T - o r b i t a l s at N and P p r o j e c t e d on the l o c a l PNP plane .. 10 5) Schematic arrangement o f T T-electron l e v e l s a) homomorphic i n t e r a c t i o n • 12 b) heteromorphic i n t e r a c t i o n • ........ 13 6) The St r u c t u r e o f N 3P 3 (NHPr 1) 4CJi 2H + •. , 16 7) I . r . s p e c t r a of p h e n y l c y c l o p h o s p h o n i t r i l e s - a) N_P_Ph, 29 b) N 4 P 4 P h 8 .c) N 5 P 5 P h 1 ( ) d ) N 6 P 6 P h 1 2 30 8) N.m.r. sp e c t r a of monomethylheptafluorocyclotetraphospho-n i t r i l e ............ 54 9) P o s s i b l e f i v e isomers o f d i m e t h y l h e x a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e ......... 56 10) N.m.r. spect r a o f 1,1-dimethylhexafluorocyclotetraphospho-n i t r i l e ................. . .. 57 11) N.m.r. sp e c t r a o f t r a n s - 1 , 5 - d i m e t h y l h e x a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e >. ................. 59 12) P o s s i b l e f i v e isomers o f t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e .......v 62 13) ''"H n.m.r. spectrum o f 1 , 1 , 3 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e 63 14) "*"H n.m.r. spectrum o f 1 , 1 , 5 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e 67 19 15) F n.m.r. spectrum o f 1 , 1 , 5 - t r i m e t h y l p e n t a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e 69 16) N.m.r. sp e c t r a of 1 , 1 , 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e 72 17) P o s s i b l e two geminal isomers of t e t r a m e t h y l t e t r a f l u o r o -c y c l o t e t r a p h o s p h o n i t r i l e ' • 71 18) a) The s t r u c t u r e 1,1-dimethylhexafluorocyclotetraphospho-n i t r i l e b) The s t r u c t u r e 1 , 1 , 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e 79 - X -Figure Page 19) N.m.r. spec t r a o f monomethylpentafluorocyclotriphospho-n i t r i l e ....-............>............ 94 31 20) P n.m.r. spectrum of monomethylpentafluorocyclotri-p h o s p h o n i t r i l e • 95 21) P o s s i b l e three isomers o f d i m e t h y l t e t r a f l u o r o c y c l o t r i -p h o s p h o n i t r i l e ...... ......................... 96 22) Po t e n t i o m e t r i c t i t r a t i o n curves A. N_PJVIe, B. N.P.Me0 = • N 5 P 5 M e 1 0 • . • • • • • • • • • • • • • ' » 23) "''H n.m.r. spectrum o f nonamethylcyclotetraphosphonitrilium i o d i d e .• • ............ • ... . < 113 24) n.m.r. sp e c t r a o f h e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e and o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e . .• 117 25) I . r . and Raman s p e c t r a o f monomethylpentafluorocyclotri-p h o s p h o n i t r i l e . ... ......... . ... 123 26) I . r . and Raman sp e c t r a o f monomethylheptafluorocyclotetra-p h o s p h o n i t r i l e ................................ 124 27) I . r . and Raman sp e c t r a o f monomethylnonafluorocyclopenta-p h o s p h o n i t r i l e ••• 125 28) I . r . and Raman spec t r a of 1 , 1 - d i m e t h y l t e t r a f l u o r o c y c l o t r i -p h o s p h o n i t r i l e 126 29) I . r . s p e c t r a o f 1,1-dimethylhexafluorocyclotetraphospho-n i t r i l e and trans-1,5-dimethylhexafluorocyclotetraphospho-• n i t r i l e • 127 30) I . r . s p e c t r a o f 1,1,3-trimethylpentafluorocyclotetraphospho-n i t r i l e and 1 , 1 , 5 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e 128 31) I . r . and Raman spec t r a o f 1,1, 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o -c y c l o t e t f a p h o s p h o n i t r i l e 129 32) I . r . and Raman spectra o f h e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e . 130 33) I . r . and Raman spec t r a of o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e 131 34) I . r . spectrum o f decamethylcyclopentaphosphonitrile -. 132 35) The approximate atomic motions i n each normal mode f o r the methyl groups and f o r a t r i m e r i c d e r i v a t i v e N^P^X^ 133 36) The s t r u c t u r e s o f p h e n y l c h l o r o c y c l o t r i p h o s p h o n i t r i l e s 152 - x i -Figure Page 37) The s t r u c t u r e o f 1 , 1 - d i p h e n y l t e t r a f l u o r o c y c l o t r i p h o s p h o -n i t r i l e ..................... ................... 153 38) The s t r u c t u r e s o f the ca t i o n s i n (N^MegH*) 2CoZl^~ 155 39) The s t r u c t u r e s of m e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s .. 157 40) Comparison of (1) d e v i a t i o n s of i n d i v i d u a l P-N bond lengths from the mean i n N^P^Me,, a n c^ ^ Bond-atom p o l a r -i s a b i l i t i e s , HMO, = a p + g • ............. 158 41) A c t i v a t i o n energies f o r the r e a c t i o n it ic Cl~ + (NPC£ 2) n -+ (NPC£ 2) n + C£~ 1 163 42) C a l c u l a t e d charge d e n s i t y at s u b s t i t u t e d phosphorus atom as a f u n c t i o n o f r i n g s i z e ; HMO c a l c u l a t i o n s , OL. = a p {+. 23, a p = a p + 0.53 ........... ........................ 165 43) The o r i e n t a t i o n p a t t e r n i n the methylation o f (NPF2)4 and the f l u o r i n a t i o n and the dimethylamination o f (NPClL) .., 169 - 1 -CHAPTER 1 GENERAL INTRODUCTION P h o s p h o n i t r i l i c compounds, c h a r a c t e r i z e d by the f o r m a l l y unsaturated repeating u n i t -N=X, , e x i s t i n a s e r i e s of c y c l i c and l i n e a r polymers. The c y c l i c molecules (NPX2) n, with a s t a b l e s t r u c -t u r a l core, undergo s u b s t i t u t i o n r e a c t i o n s to give a v a r i e t y of d e r i v a t i v e s . The lower members (n = 3 and 4) i n the c y c l i c s e r i e s have an e l a b o r a t e l y developed chemistry, which i s of great t h e o r e t i c a l s i g n i f i c a n c e . Though the p i o n e e r i n g work was i n i t i a t e d by Stokes i n 1895,* a c l e a r understanding of the chemistry of these compounds has been a t t a i n e d only i n the l a s t decade. Numerous p u b l i c a t i o n s , d e l i n e a t i n g the s y n t h e t i c and t h e o r e t i c a l s i g n i f i c a n c e , have appeared 2-7 i n recent years. There are s e v e r a l review a r t i c l e s , which describe both the general background and the recent advances i n t h i s f i e l d . Very many d e r i v a t i v e s have been synt h e s i s e d , e i t h e r by ammonolysis of halogen d e r i v a t i v e s of pentavalent phosphorus X 0PC£- + NH.Cl + - (NPXJ + 4HC£ (1.1) 2 3 4 n 2 n or by s u b s t i t u t i o n r e a c t i o n s , u s u a l l y of the c h l o r i d e s , w i t h organic and i n o r g a n i c n u c l e o p h i l e s . Some of them are i l l u s t r a t e d i n F i g . 1. 8 9 The c h l o r i d e s , known from t r i m e r to octamer, ' t h e r e f o r e occupy a - 2 -CD o z V y •Of z / A _ LL U_ Y II l L LL" \ u 1 0 ; /\ LL LL V ^ u. o= -z V 7 V a . — z or / ^ z v z ^ ^ LL O_ Z ^ - 3 -c e n t r a l p o s i t i o n i n p h o s p h o n i t r i l i c chemistry, and considerable a t t e n t i o n has been d i r e c t e d to t h e i r s y n t h e s i s and chemistry. They are commonly prepared by the r e a c t i o n s of phosphorus penta c h l o r i d e w i t h ammonium c h l o r i d e i n an i n e r t solvent such as tetrachloroethane. The simple equation PCA C + NH.C£ -> - (NPC£_) + 4HC£ .. (1.2) 5 4 n 2 n J conceals some complexity. According to co n d i t i o n s e i t h e r c y c l i c or l i n e a r products can predominate. The r e a c t i o n proceeds through the formation o f l i n e a r d e r i v a t i v e s PC£ 4 (NPCJi^CJl and H(NPCJ£2)nC£, the l a t t e r compounds f i n a l l y c y c l i s i n g by i n t r a m o l e c u l a r e l i m i n a t i o n of 9 11 HC£. Both types of the above l i n e a r d e r i v a t i v e s have been i s o l a t e d . ' A l k y l and a r y l p h o s p h o n i t r i l e s have been prepared i n a s i m i l a r way by the ammonolysis o f Me 2PC£ 3, 1 2 Et 2PC£ 3, 1 3 Ph 2PCJ> 3, 1 4' 1 5 PhPCJ^ 1 6 and 17 PhPBr^. C y c l i s a t i o n of l i n e a r a l k y l p h o s p h o n i t r i l e s r e q u i r e s e i t h e r 13 18 heat or ( l i k e N - t r i a l k y l B - t r i c h l o r o b o r a z i n e ) the use of a t e r t i a r y 12 amine. The bromophosphonitriles are prepared by an improved ammonolysis technique i n which PBr^ i s replaced by P B r 3 , and bromine 19 i s added i n p o r t i o n s at d e f i n i t e i n t e r v a l s . Analogous methods cannot, however, be used f o r the p r e p a r a t i o n of the p h o s p h o n i t r i l i c f l u o r i d e s . Ammonolysis o f PC£j- and NH^F gives mainly ammonium hexa-fluorophosphate together w i t h n e g l i g i b l e amounts of p a r t i a l c h l o r o f l u o r o -20 p h o s p h o n i t r i l e s . A d e t a i l e d account of the synth e s i s o f f l u o r o -- 4 -p h o s p h o n i t r i l e s (by a s u b s t i t u t i o n r e a c t i o n ) i s given i n S e c t i o n 2.2. Aminolysis forms an important part o f ) p h o s p h o n i t r i l i c chemistry because the products i l l u s t r a t e some of the p o s s i b l e o r i e n t a t i o n p a t t e r n s . The r e a c t i o n s of c h l o r o t r i - a n d t e t r a -p h o s p h o n i t r i l e s w i t h dimethylamine have been i n v e s t i g a t e d i n great 21-24 d e t a i l . Becke-Goehring suggested that the base stre n g t h of the amines i s dominant i n governing the s u b s t i t u t i o n . Strong bases such as alkylamines give predominantly non-geminally s u b s t i t u t e d d e r i v a t i v e s whereas weak bases such as arylamines give mainly the geminally * 25 26 s u b s t i t u t e d d e r i v a t i v e s . ' This g e n e r a l i s a t i o n , however, seems to be o v e r s i m p l i f i e d , as the course of s u b s t i t u t i o n by t-butylamine 27 (pKa = 10.45) i s e x c l u s i v e l y geminal, and that by a n i l i n e (pKa = 4.58) 28 i s e x c l u s i v e l y non-geminal. The p a t t e r n of s u b s t i t u t i o n i s not e x p l i c a b l e simply i n terms of e l e c t r o s t a t i c e f f e c t s ; conjugative and s t e r i c i n t e r a c t i o n s a l s o p l a y an important r o l e i n these s u b s t i t u t i o n r e a c t i o n s . I t has been reported that as the amine molecule becomes l a r g e r , the s u b s t i t u t i o n becomes more and more d i f f i c u l t and d r a s t i c experimental c o n d i t i o n s are r e q u i r e d to push the r e a c t i o n to comple-29 t i o n . The work described l a t e r i n t h i s t h e s i s b r ings out.the importance of u - e l e c t r o n e f f e c t s i n i n f l u e n c i n g the mode of s u b s t i t u -t i o n . O r i e n t a t i o n a l e f f e c t s can be c o r r e l a t e d much as they are i n the chemistry of benzene, and the same t h e o r e t i c a l b a s i s i s r e l e v a n t . Though aminolysis of c h l o r o p h o s p h o n i t r i l e s has been explored i n the greatest d e t a i l , many other n u c l e o p h i l i c s u b s t i t u t i o n r e a c t i o n s - 5 -30 have a l s o been reported i n the l i t e r a t u r e . A large number of alkoxy, 31 32 33 34 35 a r y l o x y , ' i s o t h i o c y a n a t o ' and a l k y l t h i o p h o s p h o n i t r i l i c d e r i v a t i v e s have been synthesised and c h a r a c t e r i z e d . There i s a s t r i k i n g d i f f e r e n c e between the s u b s t i t u t i o n of c h l o r i n e i n N^P^Ci^ by phenoxy and ./by e t h y l t h i o groups, the former s u b s t i t u t i o n being 31 35 predominantly non-geminal,.and the l a t t e r e x c l u s i v e l y geminal. In order to understand the d i f f e r e n t types of s u b s t i t u t i o n behaviour, i t i s necessary.to consider bonding i n p h o s p h o n i t r i l i c molecules i n more d e t a i l . A simple p i c t u r e of the bonding, shown i n F i g . 2a w i t h formal charges at phosphorus and n i t r o g e n , i s compatible 36 w i t h the high molecular f l e x i b i l i t y and e q u a l i t y of r i n g bonds i n molecules which vary.only i n r i n g s i z e . The P-N bonds should be p o l a r , and s i n c e most p h o s p h o n i t r i l i c r e a c t i o n s are n u c l e o p h i l i c displacements at phosphorus, i t seems l i k e l y that the phosphorus atoms c a r r y a p a r t i a l p o s i t i v e charge. However, t h i s simple p i c t u r e of bonding i s r u l e d out, not only because i t would r e q u i r e a small angle (about 109°) at n i t r o g e n , but a l s o because both bond angles and bond lengths depend on r i n g s i z e , the angle at n i t r o g e n v a r y i n g over the range 120 - 150°, o and the r i n g bond lengths between 1.50 and 1.60 A. I t i s t h e r e f o r e necessary to consider Tr-bonding i n p h o s p h o n i t r i l i c molecules, as i n F i g . 2b, which suggests the occurrence of d e l o c a l i s a t i o n . Though the occurrence of a TT-system i n p h o s p h o n i t r i l i c molecules i s analogous to benzene i n some r e s p e c t s , there i s a d i s t i n c t d i f f e r e n c e between the two. In benzene, a l l the normally a v a i l a b l e (2s + 2p) o r b i t a l s are - 6 -ci . CL CI CI i N • p + j «... \/ N N" CL CL CI-CL' CI CI / P . I v. \/ N. V N s p •N / C I CL F i g . 2. Str u c t u r e o f N_P_fX. •i 5 o a) singly-bonded s t r u c t u r e w i t h formal charges b) TT-bonded s t r u c t u r e - 7 -used f o r e i t h e r a- or T r-bonding, whereas i n p h o s p h o n i t r i l e s , i n which the simplest assumptions i n v o l v e the use of d - o r b i t a l s at phosphorus, f i v e o r b i t a l s are a v a i l a b l e to accommodate one e l e c t r o n and a l l must be considered, i n p a r t i c u l a r 3d , 3d , 3d and 3d o ? i n the axes r xz yz xy x -y^ of F i g . 3. Nitrogen uses a 2p and a h y b r i d 2s-2p o r b i t a l . There z y are two p o s s i b l e types of d e l o c a l i s a t i o n : i n one the p a r t i c i p a t i n g o r b i t a l s are. antisymmetric to r e f l e c t i o n i n the molecular plane (TT system),. and i n the other they are symmetric (TT system). In a a • • s TT -system both the 3d and 3d o r b i t a l s o f phosphorus are expected a J • X Z yz tr tr tr to take p a r t , together w i t h the 2p z o r b i t a l of n i t r o g e n . For a TT system the 3 d ^ , 3d^ 2 a r e allowed to p a r t i c i p a t e , together w i t h s and Py n i t r o g e n o r b i t a l s . Table 1 Symmetry Species of s, p, and d-orbitals.f;(C,, s i t e symmetry). E C_ a, a 2 h v s, p , d 2 2 A T 1 1 1 1 ' r y x - y z 1 d x y A 2 1 1 - 1 - 1 V % i - i i - i Pz* d y z B2 1 - 1 - 1 1 I t i s necessary to d i s t i n g u i s h between two types of T T - i n t e r a c t i o n s , 37-39 these being r e f e r r e d to as homomorphic and heteromorphic r e s p e c t i v e l y . The i n t e r a c t i o n i s homomorphic i f the p a r t i c i p a t i n g o r b i t a l s are of F i g . 3. Axi s system the same symmetry species and heteromprphic i f they are of d i f f e r e n t 37 species i n the l o c a l molecular s i t e group. The e l e c t r o n s of each of the r i n g atoms are i n a p o t e n t i a l f i e l d imposed by a l l atoms of the molecule. Where the r i n g i s planar the l o c a l f i e l d belongs to the symmetry group C^, and each atomic o r b i t a l can be c l a s s i f i e d according to a r e p r e s e n t a t i o n of t h i s group. A c l a s s i f i c a t i o n i s shown i n Table 1 f o r planar r i n g s . In a non-planar r i n g the f i e l d imposed on an atom by nearest neighbour remains C^, and a c l a s s i f i c a t i o n under t h i s ' s i t e ' group r e t a i n s an approximate s i g n i f i c a n c e . Thus i n the T r a and the TT systems both d and d are heteromorphic, and d and s xz xy r yz d x2_ v2 a r e homomorphic. The model chosen to describe the e l e c t r o n wave fun c t i o n s i n p h o s p h o n i t r i l i c molecules assumes the T T-electrons f r e e to c i r c u l a t e over the r i n g system as i n the case of benzenoid aromatics."^'^O This c y c l i c d e l o c a l i s a t i o n p i c t u r e considers the overlap of 3d^ z of phosphorus with neighbouring 2p z or n i t r o g e n to predominate over that of the 3d o r b i t a l . However, there i s another model of d e l o c a l i s a -yz t i o n which considers the overlap of 3d and 3d of phosphorus with c xz • yz r r 41 2p z of n i t r o g e n to be e q u a l l y important. This a l t e r n a t i v e d e s c r i p -t i o n leads to l i m i t e d d e l o c a l i s a t i o n over sets or " i s l a n d s " o f three adjacent centres as shown i n F i g . 4. The r e l a t i o n between the two 42 models i s considered i n d e t a i l by C r a i g and M i t c h e l l . Experimentally i t i s hard to d i s t i n g u i s h between the two models p u r e l y on the b a s i s of the s t r u c t u r e s of homogeneously s u b s t i t u t e d p h o s p h o n i t r i l e s . Although geometric features of homo-F i g . 4. 7 r - o r b i t a l s at N and P p r o j e c t e d on the l o c a l PNP plane. A] dTT- o r b i t a l s i n the d x z and d y Z scheme. B] O r b i t a l s r o t a t e d by 45° f o r " i s l a n d " d e l o c a l i s a t i o n . Shaded atomic o r b i t a l s are • combined i n molecular o r b i t a l s . : - 11 -geneously s u b s t i t u t e d compounds are compatible w i t h d e l o c a l i s a t i o n , more s u b t l e experiments are r e q u i r e d not only to d i s t i n g u i s h c y c l i c d e l o c a l i s a t i o n from " i s l a n d " d e l o c a l i s a t i o n , but a l s o the type (TT or TT ) i n v o l v e d . I o n i s a t i o n p o t e n t i a l s of p h o s p h o n i t r i l i c mole-43 cules give important i n f o r m a t i o n about the d e l o c a l i s e d Tr-bonding. They d i s c r i m i n a t e more c l e a r l y between the symmetry types (homomorphic or heteromorphic) and between the TT and TT systems. The arrangement cL S of Tr-electron l e v e l s f o r the two types of i n t e r a c t i o n i s shown i n F i g . 5. The f i r s t i o n i s a t i o n p o t e n t i a l s of p h o s p h o n i t r i l i c f l u o r i d e s are given i n Table 2. They depend markedly on the r i n g s i z e , a pro-nounced a l t e r n a t i o n being found f o r the smaller r i n g s . This p o s i t i v e l y excludes i o n i s a t i o n e i t h e r from a l o c a l i s e d T T s non-bonding p a i r or from a Tr " i s l a n d " , and shows a l s o that the d - o r b i t a l s are used Sft ' unequally; the d e t a i l e d form of the v a r i a t i o n defines the symmetry type of the uppermost molecular o r b i t a l s . The observed a l t e r n a t i o n i s good evidence that the uppermost u-system i s of the homomorphic type. F u r t h e r , the s t r u c t u r e s of heterogeneously s u b s t i t u t e d d e r i v a t i v e s , '67 the r e l a t i v e r a t e s of f l u o r i n a t i o n of N_P„C£^ and N.P.C£ 0, and the J O o 4 4 o s u b s t i t u t i o n behaviour and t r a n s m i s s i o n of e l e c t r o n i c e f f e c t discussed l a t e r i n t h i s t h e s i s , provide strong experimental evidence f o r c y c l i c d e l o c a l i s a t i o n . I t i s evident from previous pages that s u b s t i t u t i o n i s not completely e x p l i c a b l e i n terms of e l e c t r o s t a t i c and s t e r i c e f f e c t s . Conjugative i n t e r a c t i o n s , though weak i n nature, seem to p l a y an - 2 / 3 F i g . 5. Schematic arrangement of i r - e l e c t r o n l e v e l s , a) homomorphic i n t e r a c t i o n F i g . 5. Schematic arrangement of tr-electron l e v e l s b) heteromorphic i n t e r a c t i o n - 14 -Table 2 a F i r s t I o n i z a t i o n P o t e n t i a l s o f P h o s p h o n i t r i l i c F l u o r i d e s (eV) n 3 4 5 6 7 8 ( N P F 2 ) n 11.4 10.7 11.4 10.9 11.3 10.9 a G.R. Branton, C E . B r i o n , D.C. F r o s t , K.A.R. M i t c h e l l , and N.L. Paddock, J . Chem. Soc. A, 151 (1970). k By photoelectron spectroscopy; estimated u n c e r t a i n t y ± 0.01 eV. important r o l e i n s u b s t i t u t i o n r e a c t i o n s . The p h o s p h o n i t r i l i c d e r i v a -t i v e s which show s t r u c t u r a l evidence o f e x o c y c l i c T r-bonding are those which r e l e a s e e l e c t r o n s to phosphorus by l o n e - p a i r d e l o c a l i s a t i o n , v i z . , alkoxy and a l k y l a m i n o - d e r i v a t i v e s . The d - o r b i t a l s on phosphorus that p a r t i c i p a t e i n conjugation are the d ^ - , the d ^ y2~> a n d the d 2 - o r b i t a l s ; the f i r s t one belonging to the TT -system and the l a t t e r two to the T T s-system (the d e f i n i n g plane f o r the e x o c y c l i c T r-system being the XPX plane, assumed perpendicular to the NPN pl a n e ) . A c l e a r i n d i c a t i o n of the o r b i t a l s i n v o l v e d i s given by the s t r u c t u r e s o f the dimethylamides 44 45 N 4P 4(NMe 2)g and N^ P^ . (NMe2) ^ . Information about the geometry o f the e x o c y c l i c groups i s given i n Table 3. E l e c t r o n r e l e a s e to phosphorus i s i n d i c a t e d both by the large angles around the e x o c y c l i c n i t r o g e n atoms and by the shortness of the P-N bonds. I t i s confirmed f u r t h e r by t h e i r c o n t r a c t i o n to - 15 -Table 3 Geometry of the E x o c y c l i c Groups i n (N M e 2 ) s a and N ^ j N M e ^ ^ N 4 P 4 ( N M e 2 ) 8 C N 6 P 6 ( N M e 2 ) 1 2 C P-N bond length (A): Bond (1) 1.671(358.5°) 1.663(357.5°) Bond (2) 1.686(345.5°) 1.675(348.7°) Average 1.678(352.0°) 1.669(353.1°) NPN angle 103.8° 102.9° a G.J. B u l l e n , J . Chem. S o c , 3193 (1962). b A.J. Wagner and A. Vos, Acta C r y s t . , B24, 1423 (1968). The f i g s , i n parentheses are the sums of angles round the e x o c y c l i c n i t r o g e n atoms. - 16 -F i g . 6. The s t r u c t u r e of N P(NHPr^CJ^H" 1". - 17 -1.61 A, when the r i n g i s p r o t o n a t e d 4 ^ ( F i g . 6 ). In the n e u t r a l molecules, the two dimethylamine groups attached to the same phosphorus atoms d i f f e r i n d e t a i l . For s t e r i c reasons, they are d i f f e r e n t l y a l i g n e d , and the r e f o r e i n t e r a c t t h r o u g h . d i f f e r e n t d - o r b i t a l s . In both molecules, that group which i s the b e t t e r o r i e n t e d f o r T r - i n t e r a c t i o n w i t h the TT - o r b i t a l s d 9 ? and d o i s the more s t r o n g l y bound, as s x -y , z^ 6 1 ' judged by the ,sum of the angles round the n i t r o g e n atom. These s t r u c t u r e s show that TT - andTr - o r b i t a l s are used unequally i n exo-ci S c y c l i c Tr-bonding and s t r o n g l y suggest that d 2 2 a n d d 2 o r b i t a l s are y Z more important. This c o n c l u s i o n i s i n agreement w i t h the s t r u c t u r e of 47 N^P^F4?h2> i n which the phenyl groups, u n r e s t r i c t e d s t e r i c a l l y by neighbouring P F 2 groups, are both o p t i m a l l y a l i g n e d f o r Tr-bonding with the T T s - o r b i t a l s . Thus s t r u c t u r a l i n v e s t i g a t i o n s sharpen the con-c l u s i o n s a r r i v e d at from the study of s u b s t i t u t i o n behaviour. The f l u o r o p h o s p h o n i t r i l e s are shown to be strong T r-acceptors 19 through F n.m.r. spec t r a o f flu o r o p h e n y l groups attached to the 48 19 p h o s p h o n i t r i l i c r i n g . . The F chemical s h i f t s of the pe n t a f l u o r o -p h e n y l f l u o r o p h o s p h o n i t r i l e s are shown i n Table 4. The la r g e d e s h i e l d -f ing o f the p - f l u o r i n e atom, r e l a t i v e to the m-fluorine atom, i s an i n d i c a t i o n of a conjugative e f f e c t , the d i f f e r e n c e 6" -6 being much 49 greater than f o r CH 3 (5.0 p.p.m. ) or CZ, Br, I (5.3, 6.0, 7.1 49 p.p.m. )', which i n t e r a c t mainly i n d u c t i v e l y . The v a r i a t i o n of,-.6 with r i n g s i z e (except f o r the l a r g e s t r i n g s ) shows that the conjuga-t i v e i n t e r a c t i o n i s of the homomorphic type (the homomorphic TT-system - 18 -The 19 F Chemical Table 4 S h i f t s of the P e n t a f l u o r o -3. p h e n y l f l u o r o p h o s p h o n i t r i l e s . 6 6 6 -6 P m m p WWF5 143.8 159.1 15.3 WWF7 144.6 159.3 14.7 143.3 159.4 16.1 WWF11 144.4 159.4 15.0 N 7 P 7 ^ C 6 F 5 ) F 1 3 144.4 159.4 15.0 WWF15 144.4 159.4 15.0 a T. Chivers and N.L. Paddock, Chem. Comm., 704 (1968) of the benzene r i n g i n t e r a c t i n g w i t h the homomorphic fr-system o f the p h o s p h o n i t r i l i c r i n g ) , and t h i s i s i n agreement w i t h the s t r u c t u r a l 44 45 47 work on the dimethylamides ' and on N^P^F^Pl^. The predominantly non-geminal pathway observed i n the s u b s t i t u t i o n r e a c t i o n s of p h o s p h o n i t r i l i c c h l o r i d e s w i t h alkylamines can be explained by conjugative i n t e r a c t i o n s i n so f a r as the s u b s t i t u e n t r e l a y s negative charge to the phosphorus atom to which i t i s attached. The r e a c t i o n of p h e n y l - l i t h i u m w i t h f l u o r o p h o s p h o n i t r i l e s , (liPF^)^ ^, i s predominantly non-geminal.^ S t e r i c i n t e r a c t i o n s are b e l i e v e d to be l a r g e l y r e s p o n s i b l e f o r t h i s non-geminal course, t h e i r i n f l u e n c e being r e i n f o r c e d by conjugative i n t e r a c t i o n s . - 19 -There has p r e v i o u s l y been no systematic attempt e i t h e r to d i s t i n g u i s h the various types of e l e c t r o n i c i n f l u e n c e on r e a c t i v i t y , or to c o r r e l a t e the chemical e f f e c t s with the occurrence o f a d e l o c a l i s e d iT-system which these molecules e v i d e n t l y c o n t a i n . The methylation of the p h o s p h o n i t r i l i c r i n g i s i n p r i n c i p l e a simple r e a c t i o n , because the methyl group i s not expected to i n t e r a c t con-j u g a t i v e l y . In the next Chapter, d e t a i l s are given of the i n f r a r e d s p e c t r a o f the p h e n y l p h o s p h o n i t r i l e s , which confirm the occurrence of conjugative i n t e r a c t i o n between the r i n g s , but which do not r e l i a b l y i n d i c a t e i t s extent. I t i s t h e r e f o r e important to separate the various e l e c t r o n i c e f f e c t s as f a r as p o s s i b l e , and a study of the m e t h y l p h o s p h o n i t r i l e s , which are not expected to show conjugative e f f e c t s , seemed appropriate. The main part of t h i s t h e s i s i s t h e r e f o r e concerned with the study of the r e a c t i o n s of the f l u o r o p h o s p h o n i t r i l e s , (NPF2)3_r )> w i t h m e t h y l - l i t h i u m , which e x h i b i t a new o r i e n t a t i o n p a t t e r n , and which appear to i n v o l v e i n d u c t i v e i n t e r a c t i o n s of the s u b s t i t u e n t w i t h a homomorphic Tr-system. - 20 -CHAPTER 2 PHENYLCYCLOPHOSPHONITRILES 2.1. I n t r o d u c t i o n A v a r i e t y of p h e n y l - s u b s t i t u t e d t r i - and t e t r a p h o s p h o n i t r i l e s 4 7 has been reported i n the l i t e r a t u r e . ' These are commonly prepared e i t h e r a) by ammonolysis of phenylhalophosphorane and ammonium ui -.14,16 c h l o r i d e X 0PC£_ + NH.C£ -* - (NPXJ + 4HC£. 2 3 4 n 2 n (X = Ph.) or b) by F r i e d f e l - C r a f t s r e a c t i o n of h e x a c h l o r o c y c l o t r i p h o s p h o n i t r i l e , 51 52 (NPC^)^- ' N u c l e o p h i l i c s u b s t i t u t i o n r e a c t i o n s of (NPCl^)^ 4 w i t h 53-55 phenylmagnesium bromide have r e c e i v e d c o n s i d e r a b l e a t t e n t i o n . In p a r t i c u l a r , the r e a c t i o n of phenylmagnesium bromide with hexachloro-c y c l o t r i p h o s p h o n i t r i l e r e s u l t s i n l i n e a r products and low y i e l d s of 54 the hexaphenyl d e r i v a t i v e , N^P^Ph^. On the other hand f l u o r o c y c l o -p h o s p h o n i t r i l e s , (NPF2) 3 4 , undergo s u b s t i t u t i o n r e a c t i o n s with p h e n y l - l i t h i u m , the r e a c t i o n s having been explored i n some d e t a i l ^ _0'36\>57 I t was pointed out i n the I n t r o d u c t i o n that the r e a c t i o n s of f l u o r o -c y c l o p h o s p h o n i t r i l e s w i t h p h e n y l - l i t h i u m f o l l o w predominantly a non-geminal course which could be a t t r i b u t e d to the existence of s t e r i c and conjugative i n t e r a c t i o n s . The i n f l u e n c e o f these e f f e c t s on the - 21 -course of, s u b s t i t u t i o n has been supported by the observation that the r e a c t i o n i s retarded by the phenyl groups already p r e s e n t . ^ The only p h e n y l p h o s p h o n i t r i l e s so f a r known are of the 6-and 8-membered r i n g s . This Chapter describes the p r e p a r a t i o n of o c t a -p h e n y l c y c l o t e t r a p h o s p h o n i t r i l e , (NPPh,,)^, and dodecaphenylcyclohexa-p h o s p h o n i t r i l e , (NPPh,,)^, and a l s o gives an account o f t h e i r r e a c t i o n s w i t h a) m e t h y l - l i t h i u m and b) methyl i o d i d e . While t h i s work was i n progress, a sample o f decaphenylcyclopentaphosphonitrile was prepared and k i n d l y s u p p l i e d by Mr.S.M. Todd. Although v (PNP) i n CNPPh,) . -r13) has. been reported" - there has been no f u r t h e r d e t a i l about the i n f r a -red spectra of these phenyl d e r i v a t i v e s . In t h i s Chapter, the i n f r a -red s p e c t r a of the p h e n y l c y c l o p h o s p h o n i t r i l e s , (NPPh 2) n where n = 3-6 are i l l u s t r a t e d and t h e i r p o s s i b l e assignments are, discussed:. 2.2. P r e p a r a t i o n o f Fluor.ocyclophosphonitriles The c y c l i c p h o s p h o n i t r i l i c f l u o r i d e s , CNPF 2) n, are known f o r n = 3-17.^ Since the lower members of the s e r i e s are the s t a r t i n g m a t e r i a l s ' f o r the r e a c t i o n s w i t h p h e n y l - l i t h i u m and with methyl-l i t h i u m (described i n the next Chapter), i t has been necessary to evolve a simple and e f f i c i e n t method of preparing them. They are made by f l u o r i n a t i n g the corresponding c h l o r i d e s , ^ - ^ ^ s i n c e the r e a c t i o n of NH^F w i t h PC£c-. which might have been expected to give these com-pounds, r e s u l t s i n the formation o f ammonium hexafluorophosphate. The p r e p a r a t i o n o f the t r i m e r i c and t e t r a m e r i c f l u o r i d e s , (NPF,,)^ ^, was f i r s t reported by Seel and L a n g e r , ^ i n which KS0 2F was used as - 22 -the f l u o r i n a t i n g agent. In a l a t e r p r e p a r a t i o n reported by Chapman et. a l . , KSC>2F was replaced by KF and S0 2, and the r e a c t i o n was c a r r i e d out f o r s e v e r a l days i n an a u t o c l a v e . ^ F l u o r i d e s of l a r g e r r i n g s i z e s were i s o l a t e d f o r the f i r s t time, and t h e i r c y c l i c nature was e s t a b l i s h e d by spectroscopic techniques. The use of sodium f l u o r i d e as a f l u o r i n a t i n g agent was explored by M o e l l e r and o t h e r s . A 3 ' ^ 4 Small amounts o f water or aqueous HF were found to c a t a l y s e the r e a c t i o n . The p h y s i c a l p r o p e r t i e s of the lower members of the f l u o r i d e s e r i e s are given i n Table 5. For the work described i n t h i s t h e s i s , the p r e p a r a t i v e method 62 of Seel and Langer was f o l l o w e d , p a r a f f i n o i l being used as solvent i n place o f nitrobenzene. Potassium f l u o r o s u l p h i t e was made i n b u l k y by shaking, f o r s i x days, a mixture o f f i n e l y ground potassium f l u o r i d e and sulphur d i o x i d e . In a t y p i c a l p r e p a r a t i o n about 4 Kg. were made i n one batch. An a n a l y s i s by iodimetry showed that the weight of S0 2 absorbed corresponded to 98% of that r e q u i r e d f o r the r e a c t i o n KF + SQ 2 + KS0 2F. ..... (2.1) 2.2.1. H e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e (NPF,,)^ The experimental arrangement c o n s i s t e d of a three-necked f l a s k of 500 ml. c a p a c i t y , f i t t e d w i t h a stopcock, a mercury sealed s t i r r e r and a condenser. The f l a s k was charged with hexachloro-Table 5 P h y s i c a l P r o p e r t i e s of the P h o s p h o n i t r i l i c F l u o r i d e s 5 n i n ( N P F ^ P-N s t r e t c h i n g frequency (cm? ) 1297 1419 1438 1439 1408 1400 1386 m.p. 27.1° 30.4 C -50c -45.5C -61< -16.9C b.p. d (g.ml ) 51.0° 89.7° 120.1' 2.237 2.239 1.8259 147.2' 1.8410 170.7' 1.8496 192.8 C 1.8567 AH (Kcal.mole ) v a p v J AS y ap ( c a l .mole ^deg. "*•) 7.65 23.6 8.91 24.6 9.8 24.9 11.6 26.2 12.0 25.8 A.C. Chapman, N.L. Paddock, D.H. Paine, H.T. Searle, and D.R. Smith, J . Chem. S o c , 3608 (1960). - 24 -c y c l o t r i p h o s p h o n i t r i l e , (NPC£ 2) 3 (46.9 g„, 0.135 moles), potassium-f l u o r o s u l p h i t e (141 g., 1.16 moles) and p a r a f f i n o i l (300 ml.). The stopcock end of the f l a s k was connected to a dry nit r o g e n l i n e and the condenser end was connected to a r e c e i v e r - t r a p . A slow stream o f nit r o g e n was maintained through the system. The f l a s k was heated i n an o i l bath, the r e a c t i o n mixture being continuously s t i r r e d . The r e a c t i o n , N 7P„C£, + 6KS0-F + N 7P„F, + 6KC£ + 6S0A (2.2) 3 3 6 2 3 3 6 2 s t a r t e d at 110-115°C and was complete i n about s i x hours. During the r e a c t i o n the temperature was maintained at 110-115°; higher temperatures caused the r e a c t i o n to become v i o l e n t and the product to decompose. A f t e r the completion of the r e a c t i o n , the bath temperature was r a i s e d to 140-150° and maintained f o r about two hours. Care was taken to see that the r e c e i v e r - t r a p was cooled w e l l throughout the r e a c t i o n . The h e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , ( N P F 2 ) 3 , c o l l e c t e d i n the r e c e i v e r , was separated from S0 2 by f r a c t i o n a t i o n i n vacuo. The pure product, N^P^Fg (23.7 g., 70% of t h e o r y ) , was i d e n t i f i e d by 3 6 comparison of i t s i . r . spectrum with that reported i n the l i t e r a t u r e . 2.2.2. O c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e . (NPF,,)^ The p r e p a r a t i o n was s i m i l a r to that o f N^P^F^. The i n t e r -mediate c h l o r i d e - f l u o r i d e s . N.P.F C£_ are much more r e a c t i v e than 4 4 x 8-x - 25 -the corresponding t r i m e r i c d e r i v a t i v e s , so the condenser was unnecessary. The r e a c t i o n s t a r t e d at a lower temperature (100-105°) than that r e q u i r e d f o r N^P^F^ (110-115°) and was complete i n about 4 hours. The product, N.P.F. (19.2 g.., 89% of t h e o r y ) , obtained from 4 4 o a t y p i c a l r e a c t i o n o f o c t a c h l o r o c y c l o t e t r a p h o s p h o n i t r i l e , N^P^Cilg (30 g , 0.065 moles), with KS0 2F (80 g., 0.655 moles) i n p a r a f f i n o i l (200 ml.), was i d e n t i f i e d by comparison o f i t s i . r . spectrum with that 36 reported i n the l i t e r a t u r e . 2.2.3. Decafluorocyclopentaphosphonitrile (NPF^)^ The experimental procedure was s i m i l a r to that of N^P^F^ except that a l a r g e r excess o f KSO^F, a 21. (rather that 500 ml.) f l a s k , and two r e c e i v e r - t r a p s i n s e r i e s , were used. In contrast to the pre p a r a t i o n of N^P^F^ and N^P^Fg, most of the pentameric f l u o r i d e was recovered from the r e a c t i o n mixture by batch d i s t i l l a t i o n under reduced pressure. The y i e l d obtained, from a r e a c t i o n of decachloro-c y c l o p e n t a p h o s p h o n i t r i l e , N 5 P 5 C J l 1 0 (200 g., 0.351 moles), with p o t a s s i u m f l u o r o s u l p h i t e , KS0 2F (840 g., 6.89 moles), i n p a r a f f i n o i l (1£.), was 83.8 g.. (60% theory ) . The product, N ^ F ^ , was cha r a c t e r -i z e d by comparison of i t s i . r . spectrum with that reported i n the 36 l i t e r a t u r e . 2.2.4. Dodecafluorocyclohexaphosphonitrile (NPF^)^ A sample of t h i s compound, re q u i r e d f o r the p r e p a r a t i o n of the phenyl d e r i v a t i v e , was a v a i l a b l e from a previous p r e p a r a t i o n . - 26 -2.3.1. O c t a p h e n y l c y c l o t e t r a p h o s p h o n i t r i l e 0 (NPPh,,)4 P h e n y l - l i t h i u m • (72.5 mmole) i n ether (45 ml.) was added drop-wise at room temperature to a w e l l s t i r r e d s o l u t i o n of o c t a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e (2.00 g., 6 mmole) i n 25 ml. ether, under n i t r o g e n . The t u r b i d i t y , which appeared f i r s t a f t e r adding the f i r s t few drops of L i P h , increased to a brownish white p r e c i p i t a t e on f u r t h e r a d d i t i o n . A f t e r the complete a d d i t i o n o f L i P h , the r e a c t i o n mixture was heated under r e f l u x f o r 4 days. Removal o f solvent by d i s t i l l a t i o n and subsequent e x t r a c t i o n of the s o l i d residue w i t h CHCi^ gave a brownish white product which was d e c o l o r i z e d to give a white c r y s t a l l i n e powder of N 4 P 4 P h g (1.8 g.,.37.5% o f t h e o r y ) , m.p. 320°, l i t . v a l u e 1 4 319.5-321°. CFound: C, 71.96; H, 4.96; N, 7.06; N 4 P 4 ( C 6 H 5 ) g r e q u i r e s C, 72.36; H, 5.03; N, 7.04%). 2.3.2. Dodecaphenylcyclohexaphosphonitrile. - (NPPh^)^ P h e n y l - l i t h i u m (115.5 mmole) ether (55 ml.) was added dropwise at room temperature to a w e l l s t i r r e d s o l u t i o n of dodecafluorocyclo-hexaphosphonitrile (3.70 g., 8.92 mmole) i n 25 ml. ether, under n i t r o g e n . The r e s t o f the procedure was s i m i l a r to that described f o r the pr e p a r a t i o n of N 4P 4Phg, except that the r e a c t i o n time was reduced to 2 days. The impure product on d e c o l o r i z a t i o n y i e l d e d a white c r y s t a l l i n e powder o f N^ p^ P a^2 ( 4- 7^ g-> 52.8% of theory ) . [Found: C, 72.01; H, 4.98; N, 7.02; N ^ P h ^ r e q u i r e s C, 72.36; H, 5.03; N, 7.04%]. - 27 -2.4. Reactions of P h e n y l p h o s p h o n i t r i l e s . P h e n y l c y c l o p h o s p h o n i t r i l e s are weak bases compared to the corresponding e t h y l and dimethylamino d e r i v a t i v e s . I t has been reported that m e t h y l c y c l o p h o s p h o n i t r i l e s react smoothly and q u a n t i t a t i v e l y w i t h a l k y l i o d i d e s , R l (R •= C H 3 , C^H^.), to give the corresponding quaternary 68 i o d i d e s . A l s o , l i t h i u m a l k y l s are known to p a r t i c i p a t e i n a d d i t i o n 69 r e a c t i o n s . With a view to f i n d i n g out whether phenylcyclophospho-n i t r i l e s are b a s i c enough to give quaternary i o d i d e s and whether such a d d i t i o n r e a c t i o n s , known i n organic chemistry, do take place i n p h o s p h o n i t r i l i c chemistry, the r e a c t i o n s of decaphenylcyclopenta-p h o s p h o n i t r i l e , (NPPl^)^-, w i t h CH^I and LiCH^ were c a r r i e d out. 2.4.1. Reaction of Decaphenylcyclopentaphosphonitrile w i t h M e t h y l - l i t h i u m . M e t h y l - l i t h i u m (commercial grade, 2.5 mmoles) i n diethyl<Tether (5 ml.) was added dropwise to the decaphenylcyclopentaphosphonitrile (0.46 g., 0.46 mmoles) i n t e t r a h y d r o f u r a n (10 ml.). A f t e r the complete a d d i t i o n o f m e t h y l - l i t h i u m , the r e a c t i o n mixture was heated to 60-70°3 f o r about 16 hours. The solvent was then removed by d i s t i l l a t i o n and the r e s i d u a l s o l i d was covered w i t h excess methyl-iodide and r e f l u x e d f o r 12 hours. Removal of methyl-iodide and subsequent e x t r a c t i o n o f the s o l i d m a t e r i a l with iCHC£ <gave unreacted decaphenylcyclopentaphospho-n i t r i l e (0.40 g.V:, i d e n t i f i e d by comparison of i t s i . r . spectrum w i t h that of ah .authentic sample). - 28 -2-8 Two conclusions could be reached from t h i s experiment: 1) There i s no a d d i t i o n i n t h i s r e a c t i o n , which may p o s s i b l y be hindered by the s t e r i c requirements of the two phenyl groups on the phosphorus. 2) P h e n y l c y c l o p h o s p h o n i t r i l e s are not b a s i c enough to form quaternary i o d i d e s since N^P^Ph^p was recovered a f t e r methyl i o d i d e treatment. The second p o i n t was confirmed by r e f l u x i n g decaphenylcyclopenta-p h o s p h o n i t r i l e , (NPPl^)^ (0.20 g.j), with excess methyl-iodide f o r about 15 hours. Removal of methyl i o d i d e gave the unreacted phenylphospho-n i t r i l e (0.18 g^, i d e n t i f i e d by comparison of i t s i . r . spectrum with that of an authentic sample). 2.5. I n f r a r e d S p e c t r a l Data I t was pointed out i n the I n t r o d u c t i o n that the p e n t a f l u o r o -phenyl group p a r t i c i p a t e s i n conjugative i n t e r a c t i o n w i t h the phospho-48 n i t r i l i c r i n g . G e n e r a l l y , i f e l e c t r o n i c i n t e r a c t i o n s are strong, t h e i r e f f e c t i s r e f l e c t e d i n the s h i f t s of i n f r a r e d frequencies (e.g., of the >C=0 group) and i t becomes p o s s i b l e to assess these e l e c t r o n i c 70 71 e f f e c t s . ' Conjugative i n t e r a c t i o n s i n p h o s p h o n i t r i l i c r i n g s are weak and t h e i r i n f l u e n c e on v i b r a t i o n a l frequencies i s not known. In t h i s s e c t i o n , the i n f r a r e d s p e c t r a (recorded on a P e r k i n Elmer Gr a t i n g Spectrometer 457), covering the range 400-1600 cm \ of the p h e n y l c y c l o p h o s p h o n i t r i l e s , (NPPh-), are i l l u s t r a t e d i n F i g . 7(A-D>. \IS10 ii i no l/9o l3lo ikSS l a l3oo 695 me. 7/Z. 103o I01O 7SS, looo 8io. Ss-o a _ 665" S+8 Sio 5'0 4-27 ISoo noo tooo 9oo goo loo 6oo 1 Soo two /Z2.2. 1309 6fo tee 1175 libo 74-3 888 1030 lo70 fooo 75a. f /Sbo lti-oo ISOO ISOO noo IOOO *?oo F i g . 7. I . r . s p e c t r a o f p h e n y l c y c l o p h o s p h o n i t r i l e s , 6(,o 4-(>o B A. N_P,Ph, TOO 6oo Soo 4oo B. N 4 P 4 P h 8 l&5 I4-/L0 5~6o IIZO //go H60 730 745 1030 lo7o fooo 76o 660 6'S Sal c r ISOQ lif-OO I300 /SOO 1100 to 00 9oo 800 7oO 600 Soo 4oo ISIo 12.60 1X19 1310 If-tl-O S6S 612, HIS IIWO I/60 7Zo 7*5 755-10Z0 laoo '07! 970 8$5 860 660 D l5oo frequencies given i n cm. u n i t s 14-00 1300 1&00 1100 i°oo ^00 F i g . 7. I . r . s p e c t r a of p h e n y l c y c l o p h o s p h o n i t r i l e s . -1 2oo 700 600 Soo 4-00 C . N 5 P 5 P h 1 ( ) D. N 6 P 6 P h 1 2 - 31 -The phenyl v i b r a t i o n s i n phosphorus-phenyl compounds and i n mono-73 74 s u b s t i t u t e d benzenes ' are w e l l e s t a b l i s h e d . The d i s c u s s i o n o f i n f r a r e d s p e c t r a l data, i n t h i s s e c t i o n , i s d i v i d e d i n t o two p a r t s : 1) The p r i n c i p a l v i b r a t i o n s o f the phenyl group (vC-C and 6C-H), which are l i k e l y to be s e n s i t i v e to conjugation. 2) The v i b r a t i o n s o f the p h o s p h o n i t r i l i c r i n g i n c l u d i n g those of P-C bonds. V i b r a t i o n s o f the Phenyl Ring The s t r e t c h i n g modes vC-G f o r benzene are shown i n F i g . 8. A l g a A.R. K a t r i t z k y , Quart. Rev. (London), 13, 353 (1959). In p h e n y l c y c l o p h o s p h o n i t r i l e s and i n monosubstituted benzenes, the s i t e * symmetry operating on the phenyl group i s C^v and th e r e f o r e the degenerate modes i n benzene are s p l i t i n these molecules. The s p e c t r a l p o s i t i o n s of these v i b r a t i o n s , - which f a l l i n the region 1600-900 cm are or of lower symmetry - 32 -r e l a t i v e l y constant. The in-plane C-H deformation frequencies ($C-H) -1 74 i n monosubstituted benzenes f a l l i n the r e g i o n 1350-1070 cm . I t 75 i s known from l i t e r a t u r e that the frequencies of these v i b r a t i o n s are not s e n s i t i v e to the nature o f the s u b s t i t u e n t s on the phenyl r i n g . However, the i n t e n s i t i e s o f these v i b r a t i o n s show some v a r i a t i o n which could be c o r r e l a t e d w i t h the e l e c t r o n i c nature (electron-donating or 75 e l e c t r o n - a t t r a c t i n g ) of the s u b s t i t u e n t s . These v i b r a t i o n s f o r some monosubstituted benzenes are shown i n Table 6. I t i s seen from Table 6 that the band near 1600 cm * i s i n s e n s i t i v e to the nature of the s u b s t i t u e n t , but. i t s i n t e n s i t y shows a s i g n i f i c a n t v a r i a t i o n . This band, however, v a r i e s from 1647 cm * to 1609 cm *, i n 4 - s u b s t i t u t e d py r i d i n e ' 1-oxides/'as-the s u b s t i t u e n t changes' from .strongly e l e c t r o n -76 donating to s t r o n g l y e l e c t r o n - a t t r a c t i n g . The p r i n c i p a l phenyl v i b r a t i o n s i n a l l p h e n y l c y c l o p h o s p h o n i t r i l e s and i n pentaphenyl-p h o s p h o r a n e ^ ^ are s i m i l a r and are shown i n Table 7. I t i s evident from Table 7 that the phenyl v i b r a t i o n s i n p h e n y l c y c l o p h o s p h o n i t r i l e s are s i m i l a r to other phenyl d e r i v a t i v e s and so these are not i n any case s e n s i t i v e to e l e c t r o n i c i n t e r a c t i o n s . However, the band near 1600 cm * i n monosubstituted benzenes i s lowered (1590 cm i n phenylcyclo-p h o s p h o n i t r i l e s and i s a l s o weak. Further the band near 1580 cm * i n the former compounds does not appear i n those of the l a t t e r . This suggests that the conjugative i n t e r a c t i o n of the p h o s p h o n i t r i l i c r i n g may be comparable w i t h that o f the cyano group w i t h the phenyl r i n g . Table 6 Phenyl V i b r a t i o n s (vC-C and gC-H) i n Monosubstituted Benzenes. Substituent A l B l A l B l B l A l VC-C (cm:1) £A VC-C (cm: 1) £A v C " ? l (cm: ) £A VC-C (cm: 1) £A 3C-H (cm: 1) £A 3C-H (cm: 1) £A NMe2 1605 250 1577* 40 1500 140 - - 1030 35 OMe 1601 140 1591 85 1494 135 1453 40 1077 45 1018 35 CA 1587 40 1562* 10 1479 110 1447 30 1084 1066* 80 20 1023 65 CN 1604 15 1585* 5 1495 45 1452 40 1068 10 1025 20 a A.R. K a t r i t z k y and J.H. Lagowski, J . Chem. S o c , 4155 (1958). * denotes shoulder e. i s apparent e x t i n c t i o n c o e f f i c i e n t Table 7 Phenyl V i b r a t i o n s i n (NPPhQ a and i n PPh A l A l B l B l A l B l A i B 2 B x A l VC-C VC-C VC-C VC-C VC-C 3C-H 3C-H 6C-H 3C-H $C-H (cm: ) (cm: 1) (cm:.1) (cm:,1) (cm: 1) (cm:1) (cm: 1) (cm: 1) (cm: 1) (cm: 1) 1590 1480 1440 1305-1315 1000 1285-1295 1170-1180 1160 1070 1030 (1582) (1480) (1435) (1320) (997) (1257) (1185) (1160) (1066) (1028) a „ Present i n v e s t i g a t i o n C. Degani, M. Halmann, I. L a u l i c h t , and S. Pinchas, Spectrochim. Acta., 20, 1289 (1964). 4^ Values i n parentheses belong to PPh - 35 -V i b r a t i o n s o f the P h o s p h o n i t r i l i c Ring The spectra o f the p h e n y l c y c l o p h o s p h o n i t r i l e s , ( N P P l ^ ) . ^ , are a l l s i m i l a r to one another. The main v a r i a t i o n i s i n the p o s i t i o n of v (PNP). Frequencies o f t h i s antisymmetric v i b r a t i o n f o r some p h o s p h o n i t r i l i c d e r i v a t i v e s are given i n Table 8. Table 8 V a_(PNP) (cnu 1) f o r P h o s p h o n i t r i l i c D e r i v a t i v e s , (NPX^)^ (n = 3-6) N 3 P 3 X 6 N 4 P 4 X 8 N 5 P 5 X 1 0 Me a Pk b ClC F d > e 0CH 3 f N 6 P 6 X 1 2 1185 (1180) 1202,1190 (1190,1168) 1218 1297 1235 1222 (1220) 1222 (1213,1170) 1310 1419,1438 1337 1255 1270 1355 1439 1340 1260 1325 1408 1335 present i n v e s t i g a t i o n (Chapter 6) values i n parentheses are abstracted from H.T. S e a r l e , Proc. Chem. S o c , 7 (1959). k present i n v e s t i g a t i o n values i n parentheses are abstracted.from A.J. B i l b o , Z. N a t u r f o r s c h . , 15B, 330 (1960). ° L.G. Lund, N.L. Paddock, J.E. P r o c t o r , and H.T. S e a r l e , J . Chem. S o c , 3608 (1960). d A.C. Chapman, N.L. Paddock, D.H. Paine, H.T. S e a r l e , and D.R. Smith, J . Chem. S o c , 3608 (1960). ./continued - 36 -A.C. Chapman and N.L. Paddock, J . Chem. S o c , 635 (1962). f F. R a l l o , R i c . S c i . , 8, 1134 (1965). I t i s seen from Table 8 that v (PNP), f o r a p a r t i c u l a r r i n g s i z e , depends 3.S on the e l e c t r o n e g a t i v i t y (on Pauling's s c a l e ) of the s u b s t i t u e n t s attached to phosphorus. Since methyl and phenyl groups do not d i f f e r much i n e l e c t r o n e g a t i v i t y , the values of v (PNP) f o r methyl- and phenylcyclo-clS p h o s p h o n i t r i l e s are almost p a r a l l e l . The bands i n the region 850-890 and 750-760 cm. 1 i n p h e n y l c y c l o p h o s p h o n i t r i l e s are t e n t a t i v e l y assigned to P-N r i n g e l o n g a t i o n and P-N r i n g b r e athing v i b r a t i o n s . The c o r r e s -ponding bands i n N^P^Ph^ and N 4P 4Phg have been reported to be at 850 cm.-'1' ( N 3 P 3 P h 6 ) , 882 cm. - 1 ( N ^ P h g ) ; and 753 cm. - 1 ( N ^ P h ^ . 1 3 The bands i n the region 660-745 cm. 1 are assigned to v(P-C) v i b r a t i o n s , except the one at 690-695 cm. 1 which belongs to phenyl r i n g deformation. In the absence of Raman data these assignments are u n c e r t a i n . The f o l l o w i n g general observations r e s u l t from i . r . s p e c t r a of the p h e n y l p h o s p h o n i t r i l e s . 1) The frequencies of the phenyl v i b r a t i o n s are s i m i l a r to those of other phenyl d e r i v a t i v e s . Their i n t e n s i t i e s suggest that the con-j u g a t i v e i n t e r a c t i o n between the two r i n g s i s s i m i l a r to that of a cyano-group w i t h a benzene r i n g . 2) The s p e c t r a o f a l l the p h e n y l p h o s p h o n i t r i l e s are s i m i l a r to one another. The main v a r i a t i o n i s i n V (PNP) as observed i n other as p h o s p h o n i t r i l i c d e r i v a t i v e s . There i s , t h e r e f o r e , no other v i b r a t i o n which i s s e n s i t i v e to p h o s p h o n i t r i l i c r i n g s i z e . - 37 -3) The i n t e r a c t i o n of the phenyl group w i t h the phospho-n i t r i l i c r i n g , while probably not strong, i s s u f f i c i e n t to s p l i t the degenerate modes but i s not s u f f i c i e n t enough to give a whole range o f frequencies as i n (NPF2) n-Conclusion Although the course of the r e a c t i o n of h e x a f l u o r o c y c l o t r i -p h o s p h o n i t r i l e , (NPF2) 3, with p h e n y l - l i t h i u m i s b e l i e v e d to be l a r g e l y c o n t r o l l e d by s t e r i c e f f e c t s , ^ ( a ) the r e s u l t s of the i n f r a r e d spectra of p h e n y l c y c l o p h o s p h o n i t r i l e s , (NPPl^)^ g, suggest that conjugative i n t e r a c t i o n s seem e q u a l l y important. Since i t i s d i f f i c u l t to i s o l a t e these e f f e c t s i n the above r e a c t i o n , we have i n v e s t i g a t e d the r e a c t i o n s of f l u o r o c y c l o p h o s p h o n i t r i l e s , (NPF,,).^, w i t h m e t h y l - l i t h i u m (described i n Chapter 3 and 4) i n which these e f f e c t s are avoided. The s u b s t i t u t i o n p a t t e r n i n the l a t t e r r e a c t i o n s i s l a r g e l y expected t o be c o n t r o l l e d by an i n d u c t i v e e f f e c t of the s u b s t i t u e n t (GH^ group) on a d e l o c a l i s e d TT-system. - 38 -CHAPTER 3 METHYLATION OF OCTAFLUOROCYCLOTETRAPHOSPHONITRILE 3.1. I n t r o d u c t i o n 7 7 78 I t has been reported ' that r e a c t i o n s o f l i t h i u m - a l k y I s w i t h c h l o r o c y c l o p h o s p h o n i t r i l e s are u s u a l l y complex and do not give any s u b s t i t u t e d products. On the other hand, M o e l l e r and co-workers i n v e s t i g a t e d the r e a c t i o n s of f l u o r o c y c l o p h o s p h o n i t r i l e s , 0 ^ ^ 2 ) 3 4 with n - b u t y l - l i t h i u m and i s o l a t e d only the mono- and d i - s u b s t i t u t e d 79 products. According to these authors, complete s u b s t i t u t i o n was not p o s s i b l e and they d i d not rep o r t anything about the course o f the s u b s t i t u t i o n . The only methyl d e r i v a t i v e sp f a r obtained through d i r e c t s u b s t i t u t i o n i s 1 , 3 , 5 - t r i m e t h y l t r i c h l o r o c y c l o t r i p h o s p h o n i t r i l e , 77 N^P^C^Me^. The course of the r e a c t i o n i s • NMe^ci N M e 2 ^ M e c ^ M e N' !<?? • _HM^2 I ^ N M ^ - Q J I Cl a ' N i ' ^ C i M - f X N / N M e M ^ P \ N / P ^ M e NMe, The i s o l a t i o n of 1 , 1 - d i m e t h y l t e t r a c h l o r o c y c l o t r i p h o s p h o n i t r i l e , N^P^CH^Ae^. as a by-product i n the r e a c t i o n of dimethyldiaminophosphonium c h l o r i d e 80 w i t h phosphorus pe n t a c h l o r i d e was reported by F r a z i e r and S i s l e r . Also these authors reported the i s o l a t i o n of methyl- and e t h y l -c y c l o p h o s p h o n i t r i l e s , CNPX 2) 3 4 (X = Me and E t ) , from the r e a c t i o n s - 39 -of dimethyl- and diethyl-chlorophosphines w i t h gaseous chloramine and . 81 ammonia. We have chosen to i n v e s t i g a t e o r i e n t a t i o n a l e f f e c t s i n phospho-n i t r i l i c r i n g s by studying the r e a c t i o n s o f m e t h y l - l i t h i u m w i t h f l u o r o -c y c l o p h o s p h o n i t r i l e s , CI^PF2-'n ^ n = ^ t n e I n t r o d u c t i o n , i t was pointed out that conjugative e f f e c t s might occur as w e l l as e l e c t r o -s t a t i c , s t e r i c , and T T-inductive i n t e r a c t i o n s , and these are avoided i f the methyl group i s used as the s u b s t i t u e n t . Further since the e l e c t r o -n e g a t i v i t i e s of carbon and f l u o r i n e d i f f e r w i dely, p o l a r e f f e c t s should be e a s i l y apparent. The r e a c t i o n o f o c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e , ( 1 ^ 2 ) 4 , with an excess o f m e t h y l - l i t h i u m gives a good y i e l d o f o c t a -m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e , (NPlVk^^, the best method so f a r found f o r the pr e p a r a t i o n o f t h i s compound, and de c a f l u o r o c y e l o p e n t a p h o s p h o n i t r i l e , ( 1 ^ ^ 2 ) 5 , s i m i l a r l y gives a (smaller) y i e l d o f decamethylcyclopenta-p h o s p h o n i t r i l e , (NPNk^)^, which i s otherwise i n a c c e s s i b l e . P a r t i a l l y s u b s t i t u t e d d e r i v a t i v e s o f a l l the three r i n g s i z e s have been obtained, and f o r the tetramer i n p a r t i c u l a r , a new o r i e n t a t i o n p a t t e r n i s found, which has not been recognized so f a r . We have c o r r e l a t e d t h i s sub-s t i t u t i o n p a t t e r n w i t h a i r - i n d u c t i v e e f f e c t , a d e t a i l e d d i s c u s s i o n of which appears l a t e r i n t h i s t h e s i s . 3.2. Preparation o f M e t h y l - l i t h i u m Organo-lithium reagents are very s e n s i t i v e to moisture and oxygen and t h e r e f o r e i t i s necessary to take s p e c i a l precautions f o r t h e i r p r e p a r a t i o n and handling. They are commonly prepared e i t h e r by - 40 -t r a n s - m e t a l a t i o n r e a c t i o n s of organo-mercury compounds with l i t h i u m or 8 2 -by the r e a c t i o n of an a l k y l h a l i d e with,.lithium. In the l a t t e r p r e p a r a t i o n the organo- l i t h i u m reagent i s contaminated with l i t h i u m h a l i d e , the presence o f which does not s e r i o u s l y i n t e r f e r e with the subsequent n u c l e o p h i l i c r e a c t i o n s . Donor solv e n t s such as THF and ( e s p e c i a l l y ) d i e t h y l ether, are very s u i t a b l e f o r many n u c l e o p h i l i c r e a c t i o n s w i t h o r g a n o - l i t h i u m reagents. The s t a b i l i t y o f some of these reagents i n donor solv e n t s i s not high and i t i s necessary to^make them immediately p r i o r to the r e a c t i o n . Though m e t h y l - l i t h i u m i s r e l a t i v e l y s t a b l e i n ether and a v a i l a b l e commercially, i t was d e s i r a b l e to prepare i t f r e s h l y before s t a r t i n g the r e a c t i o n w i t h p h o s p h o n i t r i l i c f l u o r i d e s . In p r e l i m i n a r y experiments,it was a l s o found that accurate c o n t r o l of the amount of m e t h y l - l i t h i u m was r e q u i r e d , i f s i d e - r e a c t i o n s were to be avoided. L i t h i u m ribbon o f very high p u r i t y (obtained from A l f a Inorganics) was used. The appropriate weighed amount of l i t h i u m was introduced i n t o a three necked f l a s k o f 250 ml. c a p a c i t y , the f l a s k being f i t t e d w i t h a stop-cock (connected to a dry n i t r o g e n l i n e ) , a dry i c e condenser and a p r e s s u r e - e q u a l i s i n g j a c k e t t e d graduated se p a r a t i n g f u n n e l . The f l a s k was f l u s h e d w e l l w i t h n i t r o g e n before i n t r o d u c i n g the l i t h i u m . The flow o f n i t r o g e n was reduced and dry ether (50-150 ml., d i s t i l l e d from LiA£H. i n a dry n i t r o g e n atmosphere p r i o r to the r e a c t i o n ) was i n t r o -duced i n t o the f l a s k . Methyl bromide, u s u a l l y 30-50% i n excess of theory, was t r a n s f e r r e d to the separating funnel c o n t a i n i n g about 15-20 ml. of dry - 41 -ether, and added at room temperature to the s t i r r e d r e a c t i o n mixture i n p o r t i o n s o f 5 ml. at a time. The r e a c t i o n , which was s l u g g i s h i n the beginning, became vigorous a f t e r 15 minutes. A f t e r the completion of the r e a c t i o n i n about 2 h. (when a l l the l i t h i u m had disappeared), the s o l u t i o n was r e f l u x e d g e n t l y f o r about h a l f an hour to remove excess methyl bromide. [In a t y p i c a l p r e p a r a t i o n an a n a l y s i s of the LiCH, s o l u t i o n showed that the conversion o f L i to LiCHg was about 98% of theory.] The flow of n i t r o g e n was then stopped, and the dry i c e condenser and the separating funnel were replaced by stoppers. 3.3. Reaction o f F l u o r o p h o s p h o n i t r i l e s w i t h M e t h y l - l i t h i u m , < The general r e a c t i o n scheme was the same as that described f o r the p r e p a r a t i o n o f m e t h y l - l i t h i u m . A three-necked f l a s k o f 250 ml. c a p a c i t y , f i t t e d w i t h a constant a d d i t i o n dropping f u n n e l , a stop-cock (connected to a dry n i t r o g e n l i n e ) and a condenser, was charged with the p h o s p h o n i t r i l i c f l u o r i d e and a t e f l o n s t i r r i n g bar. Dry d i e t h y l ether was then introduced i n t o the f l a s k which was cooled to -20°, and a moderate flow o f dry n i t r o g e n was maintained through the system. M e t h y l - l i t h i u m was t r a n s f e r r e d to the dropping funnel by n i t r o g e n pressure. I t s l o s s during t r a n s f e r and a d d i t i o n to the p h o s p h o n i t r i l i c f l u o r i d e was estimated through h y d r o l y s i s and subsequent t i t r a t i o n o f the r e s u l t i n g LiOH w i t h standard H^SO^. The n i t r o g e n flow was reduced and the m e t h y l - l i t h i u m s o l u t i o n was added dropwise to the f l u o r i d e s o l u t i o n which was s t i r r e d v i g o r o u s l y u s i n g a magnetic s t i r r e r . The - 42 -t u r b i d i t y , which appeared i n i t i a l l y a f t e r adding the f i r s t few drops o f m e t h y l - l i t h i u m , g r a d u a l l y turned to a white p r e c i p i t a t e on f u r t h e r a d d i t i o n o f m e t h y l - l i t h i u m . The a d d i t i o n was complete i n about 2-3 h., during which time the r e a c t i o n temperature was maintained around -20°. The f l a s k was then allowed to warm up to room temperature and the r e a c t i o n was continued f o r another 10-12 h. The s o l u t i o n was f i l t e r e d , under n i t r o g e n pressure, to remove i n s o l u b l e l i t h i u m s a l t s . The product (a mixture o f p a r t i a l l y methylated d e r i v a t i v e s ) recovered from the f i l t r a t e a f t e r removing ether, was f r a c t i o n a l l y d i s t i l l e d under reduced pressure. P r e l i m i n a r y attempts to p u r i f y these p a r t i a l l y methylated d e r i v a t i v e s by t h i n l a y e r chromatography and by f r a c t i o n a l d i s t i l l a t i o n u s i n g a spinning band column were unsuccessful because, a) the m e t h y l - f l u o r o -p h o s p h o n i t r i l e s are very s e n s i t i v e to h y d r o l y s i s , thus rendering t h i n l a y e r chromatography u n s u i t a b l e f o r t h e i r p u r i f i c a t i o n and b) the '''H and 19 F n.m.r. spec t r a o f the v a r i o u s f r a c t i o n s obtained by f r a c t i o n a l d i s t i l l a t i o n u s i n g a spinning band column showed the presence o f isomers, and t h i s d i s t i l l a t i o n technique was not e f f i c i e n t enough f o r the separation of these isomers. I t was th e r e f o r e necessary to i n v e s t i g a t e the p u r i f i c a t i o n and the sep a r a t i o n of the va r i o u s isomers o f the methylated d e r i v a t i v e s by g a s - l i q u i d chromatography. The chromatograph used was the Varian Aerograph instrument (Model A 90P). A t r i a l o f d i f f e r e n t l i q u i d phases showed that the most s u i t a b l e one f o r these compounds was Carbowax 20M. The column used was a 1/4" x 10' - 20% carbowax 20M supported on HMDS t r e a t e d chromosorb W (60-80 mesh). The c a r r i e r gas used was helium. The temperatures o f - 43 -the detector and the i n j e c t o r were kept at 240° and 250° r e s p e c t i v e l y i n a l l g . l . c . i n v e s t i g a t i o n s . 3.3.1. Reaction o f O c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (NPF,,)^ with  M e t h y l - l i t h i u m By v a r y i n g the p r o p o r t i o n of m e t h y l - l i t h i u m to o c t a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e , (NPF2) 4, s e v e r a l new, and i n some cases i s o m e r i c , methyl f l u o r o p h o s p h o n i t r i l e s were prepared. Furt h e r , by usin g a small excess o f m e t h y l - l i t h i u m (over that r e q u i r e d f o r N^P^Fg- + 8LiCH 3 N^P^Meg + 8 L i F ) , a good y i e l d of o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e , N.P.Me„, was obtained. The i s o l a t i o n of these methyl d e r i v a t i v e s i s 4 4 8' J described i n the f o l l o w i n g 5 experiments. 3.3.1.1. Experiment 1 M e t h y l - l i t h i u m (25.60 mmole) i n ether (50 ml.) was added drop-wise to o c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e , ^ P ^ F g (7.68'g., 23.15 mmole) i n ether (60 ml.) at -20°, under n i t r o g e n . The r e s t of the procedure was the same as that described i n Sectio n 3.3. Unreacted N 4 P 4 F g (1.8 g.) was recovered from ether. The crude product (3.68 g.) on f r a c t i o n a l d i s t i l l a t i o n gave two f r a c t i o n s : a) The main f r a c t i o n (3.06 g.), was a c l e a r l i q u i d b o i l i n g at 130-135° (752 mm.). I t was f u r t h e r f r a c t i o n a t e d by g . l . c . (column temperature 100°, He flow 40 ml. min. 1 ) , which showed the main sharp peak ( r e t e n t i o n time 2.17 min.) to be as s o c i a t e d w i t h a small one of sh o r t e r r e t e n t i o n time. The p r i n c i p a l component (recovery - 44 -82%) was found to be N^P^Me, b.p. 130.7° (.756 nun.) (Found: C, 3.67; H, 0.92; N, 17.08; F, 40.55; N 4P 4F 7Me r e q u i r e s C, 3.89, H, 1.01; N, 16.88; F, 40.63%). High r e s o l u t i o n mass measured 327.918; C a l c . f o r N 4P 4F yMe 327.919. b) The smaller f r a c t i o n (0.42 g.) was a c l e a r l i q u i d b o i l i n g at 100-110° (100 mm.). F r a c t i o n a t i o n b y . g . l . c . showed the presence o f 5 components, t h e i r r e t e n t i o n times (min.) being 2.17, 11.15, 12.7, 15.84 and 18.76. Peak 1 corresponded to N j P ^ M e , and the remainder (2-5) probably to four o f the f i v e p o s s i b l e isomers of N P F Me Since these were produced i n only small q u a n t i t i e s , the second experiment was designed to increase t h e i r p r o p o r t i o n . 3.3.1.2. Experiment 2 In t h i s r e a c t i o n of N 4P 4Fg (8.54 g., 25.6 mmole) i n ether (50 ml.) with m e t h y l - l i t h i u m (69.9 mmole) i n ether (75 ml.), the crude product (6.4 g.) on f r a c t i o n a l d i s t i l l a t i o n gave two f r a c t i o n s . The f i r s t one (1.9 g.) was a c l e a r l i q u i d b o i l i n g at 101-105° (300 mm.). This on f r a c t i o n a t i o n by g . l . c . (column temperature 150°, He flow 50 ml. min. !) showed a sharp peak ( r e t e n t i o n time 0r,9 min.), which vwas i d e n t i c a l to that o f an authentic sample of N^F^Me. The second f r a c t i o n (3.8 g.) was a c l e a r l i q u i d b o i l i n g at 85-95° (30 mm.). This on f u r t h e r f r a c t i o n a t i o n by g . l . c . showed the presence o f f i v e components, the r e t e n t i o n times and r e l a t i v e y i e l d s ' h e i n g : - 45 -Component Retention time (min.) R e l a t i v e Y i e l d (%) 1 2 3 4 5 0.9 2.1 3.1. 7.3 9.2 1 72.0 8.3 10.7 8.2 Peaks 2 and 3 had shoulders on them suggesting the presence o f isomers. Components 2 and 3 were incompletely separated, and were t h e r e f o r e mixed f o r l a t e r f r a c t i o n a t i o n ; the mixture i s r e f e r r e d to l a t e r as f r a c t i o n 11(a). I t was a c l e a r l i q u i d (recovery 85%) and i t s a n a l y s i s corresponded to N 4P 4F 6Me 2 (Found: C, 7.42; H, 1.96; N 4P 4F 6Me 2 r e q u i r e s C, 7.41; H, 1.86%). Since components 4 and 5 were i n small amounts, these were mixed and the mixture was a low melti n g s o l i d . I t s a n a l y s i s corresponded to N 4P 4F 5Me 3 [Found: C, 11.38; H, 2.95; N 4P 4F 5Me 3 r e q u i r e s C, 11.25; H, 2.81%]. The y i e l d o f d i f f e r e n t d e r i v a t i v e s based on the N 4P 4Fg used, and estimated from g . l . c , i s given below Compound Y i e l d (%) 32.8 26.2 8.8 The chromatographic r e s u l t s thus p o s i t i v e l y show the occurrence o f isomers and i t i s , t h e r e f o r e , d e s i r a b l e to i s o l a t e and c h a r a c t e r i z e them, as t h e i r nature w i l l throw some l i g h t on the course - 46 -of s u b s t i t u t i o n . The next experiment was designed to increase the p r o p o r t i o n of the t r i s u b s t i t u t e d isomers. 3.3.1.3. Experiment 3 The crude product (6.8 g.), obtained from the r e a c t i o n of N 4 P 4 F 8 (- 1 0  g'' 3 0 ' 1 m m o l e ) i n e t h e r ( 6 0 m 1 - ) w i t h m e t h y l - l i t h i u m (100.1 mmole) i n ether (100 ml.), on f r a c t i o n a l d i s t i l l a t i o n gave a) a c l e a r l i q u i d (0.5 g.) b o i l i n g at 100-105° (300 mm.), b) a c l e a r l i q u i d (4.9 g.) b o i l i n g at 110-115° (40 mm.) and c) the r e s i d u a l l i q u i d (0.8 g.) from which a s o l i d (0.2 g.) separated. G a s - l i q u i d chromato-graphy o f f r a c t i o n (a) (column temperature 130°, He flow 140 ml. min. 1 ) , showed a sharp peak ( r e t e n t i o n time 0.5 min.), which was i d e n t i c a l to that of N 4P 4F 7Me. F r a c t i o n (b) was f u r t h e r f r a c t i o n a t e d by g . l . c , which showed 4 components, t h e i r r e t e n t i o n times and r e l a t i v e y i e l d s being given below. Component Retention Time (min.) R e l a t i v e Y i e l d (%) \ 2' .S8 ) 3 7.92 30.8 4 10.07 40.6 The a n a l y s i s o f components 1 and 2, c o l l e c t e d as I I I ( a ) (recovery 80%),' N corresponded to N 4P 4F 6Me 2. (Found: C, 7.62; H, 1.90; N 4P 4F 6Me 2 r e q u i r e s C, 7.41; H, 1.86%). - 47 -Component 3 (recovery 85%) was a low m e l t i n g s o l i d and i t s a n a l y s i s corresponded tp N ^ F Me 3, m.p. 29.5° [Found: C, 11.38, H, 2.95; N, 17.42; F, 29.43;- N 4P 4F 5Me 3 r e q u i r e s C, 11.25; H, 2.81; N, 17.50; F, 29,69%). High r e s o l u t i o n mass measured 319.970; Cal c . f o r N 4P 4F 5Me 3 319.969. Component 4 (recovery 83%) was a s o l i d and i t s a n a l y s i s corresponded to N 4P 4F 5Me 3, m.p. 70.2°. [Found: C, 11.34; H, 2.93; N, 17.38; F, 29.50; N ^ F ^ e - . - r e q u i r e s C, 11.25; H, 2.81; N, 17.50; F, 29.69%]. .High r e s o l u t i o n mass measured 319.970; Calc. f o r N 4P 4F 5Me 3 319.969. F r a c t i o n s I I I (a) and 11(a) (Section 3.3.1.2.) were mixed together to give a new f r a c t i o n 111(A). This f r a c t i o n I I I (A) was f u r t h e r f r a c t i o n -ated by g . l . c . (column temperature 90°, He flow 30 ml. min. 1 ) , which showed 4 components, t h e i r r e t e n t i o n times and r e l a t i v e y i e l d s being given below. Component Retention Time (min.) R e l a t i v e Y i e l d (%) 1 13.4 40.7 2 15.3 11.2 3 19.4 16.3 4 (v. broad) 22-2 31.8 Peak 4 was r e s o l v e d p a r t i a l l y when a 20' column was used i n place of a 10' one. Since f r a c t i o n 111(A) corresponded to N4P4F^Me2» g . l . c . r e s u l t s , thus, c l e a r l y i n d i c a t e the formation o f a l l p o s s i b l e 5 isomers (see Sectio n 3.4.2.) i n the r e a c t i o n of N 4P 4Fg with m e t h y l - l i t h i u m . The separation o f these isomers was t r i e d by g . l . c . (using la 10' column)..^ - 48 -Component 1 was a s o l i d and i t s a n a l y s i s corresponded to I^P^^Me,,, m.p. 49.5°., [Found: C, 7.37; H, 1.72; N, 17.08; N 4 P 4 F 6 ( C H 3 ) 2 r e q u i r e s C, 7.41; H, 1.86; N, 17.28%]. High r e s o l u t i o n mass measured 323.942; Calc. f o r N.P,F,Me0 323.944. 4 4 O Z Component 2 was hydrolysed and could not be c h a r a c t e r i z e d . Component 3 was a s o l i d and i t s a n a l y s i s corresponded to N 4P 4F^Me 2 J m.p. 70-71°.. [Found: C, 7.19; H, 1.85; N 4P 4F 6Me 2 r e q u i r e s C, 7.41; H, 1.86%]. High r e s o l u t i o n mass measured 323.945; C a l c . f o r N ^ F ^ f r ^ 323.944. Component 4 was a l i q u i d ( c o n t a i n i n g 2 isomers) with an a n a l y s i s corresponding to N 4P 4F 6Me 2 [Found: C, 7.21; H/2.00; N, 17.10; N 4 P 4 F 6 M e 2 r e c l u i r e s c> 7.41; H, 1.86; N, 17.28%]. G a s - l i q u i d chromatography (column temperature 165°, He flow 60 ml. min. *) of the s o l i d ( i n CHCZ^) separated from the r e s i d u a l l i q u i d (c) showed a sharp peak ( r e t e n t i o n time 8.4 min.). The a n a l y s i s of t h i s s o l i d compound corresponded to w 4 P 4 F 4 M e 4 [Found: C, 15.3; H, 3.67; N, 17.88; N 4P 4F 4Me 4 r e q u i r e s C, 15.2; H, 3.80; N, 17.79%). Since the t e t r a - s u b s t i t u t e d compound was formed i n small amounts the next experiment was designed to increase i t s amount. 3.3.1.4. Experiment 4 M e t h y l - l i t h i u m (81.6 mmole) i n ether (100 ml.) was added dropwise to N 4 P 4 F g (7.2 g., 21.6 mmole) i n ether (50 ml.) at -20°, under n i t r o g e n . A f t e r completion o f the r e a c t i o n (12 h.) the solvent - 49 -was removed by d i s t i l l a t i o n and the r e s i d u a l s o l i d was ex t r a c t e d w i t h l i g h t p e t r o l (30-60°). The crude product (5.1 g.), obtained from p e t r o l e x t r a c t , was a mixture o f s o l i d and l i q u i d . The s o l i d ( i n s o l u b l e i n p e t r o l ) was p u r i f i e d by s u b l i m a t i o n i n vacuo (0.1 mm.> bath tempera-ture 90°). The a n a l y s i s o f the c r y s t a l l i n e sublimate (1.6 g.) corresponded to N 4P 4F 4Me 4, m.p. 171-172°. (Found: C, 15.45; H, 3.91; N, 17.95; F, 25.00; N 4P 4F 4Me 4 r e q u i r e s C, 15.20; H, 3.80; N, 17.79; F, 24.05%). High r e s o l u t i o n mass measured 315.994; Cal c . f o r N 4P 4F 4Me 4 315.994. G a s - l i q u i d chromatography (column temperature 165°, He flow 60 ml. min. "*") of the sublimate ( i n CHCic^) showed a sharp peak ( r e t e n t i o n time 8.4 min.), which showed the compound to be s i n g l e and not a mixture of isomers. An understanding o f the o r i e n t a t i o n p a t t e r n i s most l i k e l y to be a t t a i n e d by a study o f those members of the s e r i e s N 4P 4F xMeg_ x which c o n t a i n few methyl groups, and no attempt was t h e r e f o r e made to prepare the more h e a v i l y s u b s t i t u t e d d e r i v a t i v e s , x < 4. However, there has been np d i r e c t method, so f a r , . o f p r eparing the f u l l y methylated compound (N 4P 4Meg). The next experiment describes the p r e p a r a t i o n o f octamethyl-c y c l o t e t r a p h o s p h o n i t r i l e , (NPMe2) 4 > i n good y i e l d . 3.3.1.5. Experiment 5 As i n the previous experiments m e t h y l - l i t h i u m (242.5 mmole) i n ether (150 ml.) was added dropwise to o c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e , ( N P F 2 ) 4 (9.1 g., 27.5 mmole) at -20°C, under n i t r o g e n . A f t e r the completion o f the r e a c t i o n (16 h.) ether was removed and the r e s i d u a l - 50 -s o l i d was e x t r a c t e d twice w i t h CHCil^ under r e f l u x . The crude product (7.0 g.) obtained from the CHCJi^ e x t r a c t was p u r i f i e d by vacuum sub l i m a t i o n [0.1 mm., bath temperature 170°). The sublimate was r e c r y s t a l l i s e d from dry p e t r o l (30-60°) i n a dry n i t r o g e n atmosphere. The a n a l y s i s o f the c r y s t a l s (5.2 g., 63.2% of theory) corresponded to N 4P 4Me g, m.p. 162-163 ( l i t . 1 2 163-164°), [Found: C, 31.83; H, 8.07; N, 18.72; N 4P 4Me g r e q u i r e s C, 32.00; H, 8.00; N, 18.67%]. High r e s o l u t i o n mass measured, 300.095; Cal c . f o r N.P.Mes, 300.095. - 51 -3.4- Nuclear Magnetic Resonance Spectroscopy Nuclear magnetic resonance spectroscopy has been the p r i n c i p a l t o o l f o r e s t a b l i s h i n g the s t r u c t u r e of the compounds i s o l a t e d from the various r e a c t i o n s of f l u o r o c y c l o p h o s p h o n i t r i l e s , (NPF^n ( n = 3-5), with m e t h y l - l i t h i u m . In t h i s s e c t i o n the n.m.r. spec t r a of compounds i n the s e r i e s N.P.Me F„ where x = 1-4 are discussed,and those o f the 4 4 x 8-x ' t r i m e r i c and pentameric d e r i v a t i v e s are discussed i n Chapter 4. The 1 19 31 H, F and P n.m.r. s p e c t r a were recorded on a Var i a n HA-100 Spectro-19 meter, w i t h the probe operating at 94.1 MHz. and 40.48 MHz. f o r F and 31 P r e s p e c t i v e l y . Magnetic double resonance experiments were c a r r i e d out i n some cases, using the heteronuclear decoupler designed by 83 R. Burton and L.D. H a l l . Since the chemical s h i f t (6) and the c o u p l i n g constant (J) values are of the same magnitude, there are second order 19 31 e f f e c t s i n a l l the F and P s p e c t r a ; these are most pronounced i n the monosubstituted d e r i v a t i v e s N 4P 4F^Me, N^P^F^Me and N^P^F^Me. However, t h i s e f f e c t i s reduced i n the spec t r a o f d i - , t r i - and t e t r a s u b s t i t u t e d d e r i v a t i v e s and, t h e r e f o r e , i t i s p o s s i b l e to evaluate the approximate c o u p l i n g constants and chemical s h i f t s from a simple f i r s t order a n a l y s i s . A l l the ^ H n.m.r. spec t r a examined are simple 19 31 i n c o n t r a s t to those o f F and P and t h e i r i n t e r p r e t a t i o n i s based on a simple f i r s t order a n a l y s i s . The use of ^H n.m.r. measurements i n c o n f i g u r a t i o n a l a n a l y s i s of N,P_fNMe„) X, , where X = C£ or Ph and n =2-4, has been p r e v i o u s l y 3 3 V 2'n 6-n' r . 84 reported. The non-equivalence of -NMe2 groups attached to the same - 52 -84 phosphorus atom i n 1,1,3,5-N^P^(NMe2)4C£2 and to d i f f e r e n t phosphorus 85 atoms i n l,3,5,7-N 4P 4Ph 4(NMe 2) 4, a r i s i n g from d i f f e r e n t chemical environments, has a l s o been p r e v i o u s l y demonstrated by "''H n.m.r. spectroscopy. The *H n.m.r. s p e c t r a of dimethylaminocyclophosphonitriles c o n s i s t o f a doublet a r i s i n g from c o u p l i n g of NMe2 protons with d i r e c t l y bonded phosphorus, the c e n t r a l area of the doublet being occupied by a 86—88 complex s t r u c t u r e . Although chemical non-equivalence pf s u b s t i t u e n t s has been observed i n some cases, conformational non-equivalence has. not been encountered so f a r . The s t r u c t u r a l deduction of c i s - t r a n s isomerism i I K « - A u A 3 1r> * 50(a),89,90 has a l s o been e f f e c t e d by F and P n.m.r. measurements. The complete a n a l y s i s o f the n.m.r. spec t r a has been reported only f o r 91 1,1-N 3P 3F 2C£ 4 and the s e r i e s N ^ C i ^ X where X = F, 0CH 3, 0CH 2'CH 3, 92 0CH 2-CF 3, 0CH(GH 3) 2 or N(CH 3) 2. In the present i n v e s t i g a t i o n , the *H n.m.r. s p e c t r a o f compounds, N 4P 4Me xFg_^ where x = 1-4, have been extremely u s e f u l i n d i f f e r e n t i a t i n g geminal from non-geminal isomers. The c o u p l i n g constant o f CH 3 protons with a F atom when both are bonded to the same phosphorus atom, i s s i z a b l e (6.5 Hz.) and, t h e r e f o r e , the occurrence o f t h i s c o upling i n the n.m.r. s p e c t r a i n d i c a t e s the presence of a EPFMe group i n the compound 19 31 under i n v e s t i g a t i o n . The usefulness o f F and P n.m.r. measurements i n deducing the s t r u c t u r e s o f some isomers i s i l l u s t r a t e d i n the 1 19 31 s p e c i f i c examples shown l a t e r i n t h i s s e c t i o n . The H, F, and P chemical s h i f t s reported i n t h i s s e c t i o n are r e l a t i v e to i n t e r n a l TMS, i n t e r n a l CFC£ 3 and e x t e r n a l P^^ r e s p e c t i v e l y . Though the =PFMe 19 31 reg i o n i s r e l a t i v e l y simple i n the F and P n.m.r. s p e c t r a o f the - 53 -monosubstituted d e r i v a t i v e s (N^PgFj-Me, N^P^^Me and N,-P5FgMe), the =PF 2 region i s observed as a complex p a t t e r n due to long range couplings. Because of t h i s complexity, the chemical s h i f t s 6 and 6ri, and the r r c o u p l i n g constant Jpp of the P F 2 group i n these compounds are obtained as average values. The heteronuclear double resonance technique has been very u s e f u l i n deducing the s t r u c t u r e s of the two isomers of N^P^^Me^ which would, otherwise, be d i f f i c u l t to s o l v e . 3.4.1. Monomethylheptafluorocyclotetraphosphonitrile N^P^F^Me ( p r i n c i p a l component of f r a c t i o n (a) - 3.3.1.1.). The "*"H n.m.r. spectrum of t h i s compound (neat sample) i s shown i n F i g . 8A. I t c o n s i s t s of twelve l i n e s , the main doublet (centred at 6 = 1.70 p.p.m.) a r i s i n g from c o u p l i n g of methyl protons w i t h d i r e c t l y bonded phosphorus atom P. ( J r H D = 18.7 Hz.). Coupling w i t h f l u o r i n e A L H 3 F A atom F f u r t h e r s p l i t s the doublet i n t o doublets ( J c r u = 6.5 Hz.). 93 I t i s reported that J p ^ i s about 2 Hz. i n dimethylaminofluorocyclo-p h o s p h o n i t r i l e s . There i s long range c o u p l i n g w i t h v i c i n a l phosphorus atom P ( J ^ H p = 1.5 Hz.) which f u r t h e r s p l i t s each component i n t o a t r i p l e t o f r e l a t i v e areas 1:2:1. The t r i p l e t s t r u c t u r e i s not symmetrical and i s not w e l l r e s o l v e d , which could probably be due to unresolved long range couplings. In dimethylamino d e r i v a t i v e s p 7? 84 c/i 3 i s about 17 Hz. ' i n =PC£(NMe 2), about 12.8 Hz. i n .=Ph(NMe 2) 8 4 and 93 ... about 12.4 Hz. i n =:PF(NMe2). We can now add to t h i s s e r i e s p about 18.7 Hz. i n =PFMe. 75.1 9E2103.9 125.2 K 6 4 52.6 62.6 " i ^ 74.3P.p.m. F i g . 8. N.m.r. s p e c t r a o f monomethylheptafluorocyclotetraphosphonitrile. A. *H n.m.r. Spectrum. 19 ^ i B. F n.m.r. spectrum. C. P n.m.r. spectrum. - 55 -19 The F n.m.r. spectrum (Fig- 8B) of N^P^F^Me (neat sample) c o n s i s t s of two doublets o f r e l a t i v e area 6:1, the doublets being centred at 69.7 p.p.m. ( J F p = 866 Hz.) and at 57.6 p.p.m. (J = A 942 Hz.). The high f i e l d doublet w i t h m u l t i p l e t s t r u c t u r e and the low f i e l d doublet w i t h unresolved f i n e s t r u c t u r e a r i s e from =PF 2 and =PFMe groups. The =PF 2 p o r t i o n of the spectrum has a complicated AB p a t t e r n and so i t i s d i f f i c u l t to get the J and 6 values simply and e x a c t l y . The =PFMe p o r t i o n o f the spectrum i s r e l a t i v e l y simple and, t h e r e f o r e , J and 6 could be c l o s e r to the f i r s t order values. 31 The P spectrum ( F i g . 8C) of N^P^F^Me (neat sample), obtained by the extended o f f ^ s e t f i e l d sweep (10,000 Hz. sweep width) technique b a s i c a l l y c o n s i s t s of a high f i e l d t r i p l e t ( r e l a t i v e areas 1:2:1) and a low f i e l d doublet, both being of r e l a t i v e areas 3:1. The t r i p l e t and the doublet are centred at 125.2 p.p.m. ( J p p =861 Hz.) and at 86.7 p.p.m. (J = 939 Hz.). A 3.4.2. D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N / [P 4F 6Me 2 (component 1 of f r a c t i o n I I I (A) - 3.3.1.3.) This compound must be one of the 5 isomers i l l u s t r a t e d i n F i g . 9.a-^e. 1 The H n.m.r; spectrum ( F i g . 10A) of t h i s compound ( s o l u t i o n i n CCl^) c o n s i s t s o f s i x l i n e s . The main doublet, being centred at 5 = 1.64 p.p.m. ( J r =14.6 Hz.), r e s u l t s from c o u p l i n g o f methyl protons w i t h 3 A 84 d i r e c t l y bonded phosphorus atom P^. I t i s reported that i n dimethyl-aminochlorophosphonitriles p i s about 11.6 Hz. i n =P(NMe 2) 2-d e F i g . 9. P o s s i b l e f i v e isomers of d i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e . a) l , l - N 4 P 4 F 6 M e 2 b) cls-1,3 - N 4P 1 +F 6Me 2 c) trans_-l ,3 -N 1 + Pi +F 6Me 2 d) c i _ s - l ,5-Ni +P 1 +F eMe 2 e) trans_-l ,5-N l tP t tF 6Me 2 Further c o u p l i n g o f methyl protons with v i c i n a l phosphorus atoms s p l i t s each component i n t o a t r i p l e t ( J r u D = 1.4 Hz.). The absence of F.CH, 3 B 6 s p l i t t i n g i n the spectrum shows unambiguously the presence of the geminal group SPN^- The spectrum has signs o f unresolved s t r u c t u r e which could p o s s i b l y be due to long range c o u p l i n g o f the methyl protons with remote f l u o r i n e atoms. The i n t e r p r e t a t i o n o f the n.m.r. spectrum of N^P^F^Me^ i s , t h e r e f o r e c o n s i s t e n t w i t h a geminal s t r u c t u r e ( F i g . 9a) 94 which i s confirmed by an X-ray c r y s t a l s t r u c t u r e determination. - 57 -Fig. 10. N.m.r. spectra of 1,1-dimethylhexafluorocyclotetraphosphonitrile. 1 ig A. H n.m.r. spectrum. B. F n.m.r. spectrum. - 58 -19 I t s geminal s t r u c t u r e i s f u r t h e r confirmed by the F n.m.r. spectrum ( F i g . 10B) i n which the doublet due to =PFMe (being centred at 57.7 p.p.m. i n N^P^F^Me) i s absent. The spectrum c o n s i s t s of two doublets of r e l a t i v e areas 1:2, both being centred at 69.2 p.p.m. (J = 845 Hz.) and 68.5 p.p.m. (J = 846 Hz.). Both the doublets b C B have unresolved f i n e s t r u c t u r e r e s u l t i n g from lone range co u p l i n g . 31 The P spectrum, c o n s i s t i n g o f a t r i p l e t and a s i n g l e t of r e l a t i v e areas 3:1, i s compatible w i t h the geminal s t r u c t u r e e s t a b l i s h e d 1 19 by H and F n.m.r. sp e c t r a . The t r i p l e t i s centred at 126.5 p.p.m. (Jpp = 870 Hz.) and the s i n g l e t resonance occurs at 93.02 p.p.m. 3.4.3. D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N^P^Me,, (component 5 of f r a c t i o n I I I ( A ) - 3.3.1.3.) The "*"H n.m.r. spectrum ( F i g . 11A) of t h i s compound ( s o l u t i o n i n CC£ 4) c o n s i s t s o f twelve l i n e s . The main doublet, a r i s i n g from c o u p l i n g o f methyl protons with d i r e c t l y bonded phosphorus atom P. ( J r u D = A CH 3F A 18.8 Hz.), i s centred at & = 1.73 p.p.m. • Further s p l i t t i n g by the f l u o r i n e atom bonded to the same phosphorus atom P^ ( J ^ p, = 6.3 Hz.) and by the v i c i n a l phosphorus atoms P R ( J r H D = 1.7 Hz.) causes the a 3 B twelve l i n e spectrum. Although the spectrum shows the presence o f a =PFMe group, i t i s not p o s s i b l e to determine which of the four p o s s i b l e isomers ( F i g . 9t>-e) i t i s . I f the two methyl groups were on an t i p o d a l phosphorus atoms ( F i g . 9d-e.) a t r i p l e t s t r u c t u r e would be expected, as found, but v i c i n a l s u b s t i t u t i o n cannot be r u l e d out on t h i s b a s i s , - 59 -51.5P-prn. 6l6PP-m. ' 64.9Pp.m. 74.2 P.p.m. F i g . 11. N.m.r. spec t r a o f trans- 1,5-dimethylhexafluorocvclotetra-p h o s p h o n i t r i l e . A. 1H n.m.r. spectrum. B. 1 9 F n.m.r. spectrum. - 60 -because the cou p l i n g constants to che m i c a l l y d i s t i n c t phosphorus atoms are s m a l l , and might appear i d e n t i c a l . 19 The F n.m.r. spectrum o f t h i s compound, N^P^F^Me^ i s very i n f o r m a t i v e and i t shows beyond doubt that the s u b s t i t u t i o n i s i n f a c t a n t i p o d a l , and that the isomer i s trans 1,5-dimethyl 1,3,3,5,7,7 hexa-f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e CFig. 9e). The spectrum ( F i g . 11B) c o n s i s t s of two doublets of r e l a t i v e areas 2:1, the doublets being centred r e s p e c t i v e l y at 69.6 p.p.m. (J = 872 Hz.) and at 56.6 p.p.m. ( J p , = 946 Hz.). I f the compound had one of the s t r u c t u r e s b-d i n A F i g . 9 then the F-atoms i n the two =PF 2 groups would be ma g n e t i c a l l y non-equivalent, and the high f i e l d doublets (belonging to the two chem i c a l l y s h i f t e d F atoms) should be s p l i t f u r t h e r i n t o doublets by the m a g n e t i c a l l y non-equivalent f l u o r i n e atoms. I t i s reported, i n p h e n y l f l u o r o c y c l o t r i p h o s p h o n i t r i l e s , 1,3, N 3 P 3 F 4 P h 2 5 0 / a n d 1,1,3 N 3 P 3 F 3 P h 3 , 5 7 that Jpp i s about 70 Hz. i n =PF2- The geminal F-F cou p l i n g i s not observed i n the a c t u a l spectrum which demonstrates the t r a n s - a n t i p o d a l s t r u c t u r e o f the compound. Each component of the doublets has unresolved f i n e s t r u c t u r e a r i s i n g from long range co u p l i n g . 3.4.4. D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N^P^F^Me2 (mixture of two isomers, component f : 4 of f r a c t i o n ( I I I ( A ) - 3.3.1.3.) . The ^H n.m.r. spectrum o f t h i s mixture (neat sample) has a doublet of doublets w i t h c o u p l i n g constants 18.2 Hz. and 5.8 Hz. The observed - 61 -spectrum i s , t h e r e f o r e , c o n s i s t e n t w i t h the presence of a =PFMe group. In c ontrast to the a n t i p o d a l - t r a n s isomer, the t r i p l e t s t r u c t u r e a r i s i n g from c o u p l i n g o f methyl protons with the v i c i n a l phosphorus atoms i s not w e l l r e s o l v e d . The main doublet (J„LI n = 18.2 Hz.) i s CH 3P centred at 6 = 1.72 p.p.m. This i s f u r t h e r s p l i t by the f l u o r i n e atom (J _ = 5.8 Hz.) i n t o doublets. Even a heteronuclear double resonance CH 3F experiment i s not inf o r m a t i v e about the stereochemical nature o f the 31 isomers. I r r a d i a t i o n at the P resonance frequency (40.481600 MHz.) 19 leaves the F coupling and the spectrum c o n s i s t s of a s i n g l e doublet. 19 I r r a d i a t i o n at the F resonance frequency (94.089400 MHz.) leaves the 31 P co u p l i n g and the spectrum again c o n s i s t s of a s i n g l e doublet. The double resonance experiment shows that both the isomers have the same n.m.r. parameters. 19 The F n.m.r. spectrum shows the presence o f two isomers i n the mixture, but t h e i r stereochemical nature i s s t i l l undecided. In the act u a l spectrum there are two low f i e l d doublets, both being centred at 55.8 p.p.m. ( J p p = 962 Hz.) and at 56.9 p.p.m. ( J p p = 946 Hz.). I t i s seen i n N^P^^Me that Sp i n =PFMe i s 57.7 p.p.m. and, t h e r e f o r e , the two low f i e l d doublets must a r i s e from two SPFMe groups. The =PF 2 p o r t i o n of the spectrum i s complicated and, t h e r e f o r e , could not be i n t e r p r e t e d . - 62 -3.4.5. T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N^P 4F 5Me 5 (component 3 of f r a c t i o n (b) - 3.3.1.3.) This compound must be one of the f i v e p o s s i b l e isomers shown i n F i g . 12a-e. F i g . 12. P o s s i b l e f i v e isomers o f tri m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o -n i t r i l e . a) 1,1 J3 - N 1 +P 4F 5Me 3 b) l.ljS - N^P^FsMea c) 1,3,5-1^^51^3 d) l,trans-3,5 - N i tP l tF 5Me 3 e ) l ,cis-3,5 -N i tP l tF 5Me 3 I t s *H n.m.r. spectrum i n CCi^ ( F i g . 13A) i s very complex and i s d i f f i -c u l t to i n t e r p r e t , though i t suggests the presence of =PMe2 and EPFMe groups. But a heteronuclear double resonance experiment has been very u s e f u l i n deducing the s t r u c t u r e o f the compound. The spectrum 19 (Fig . 13B), obtained on i r r a d i a t i n g at the F resonance frequency (94.089650 MHz.), c o n s i s t s o f three doublets with c o u p l i n g constants - 63 -F i g . 13. H n.m.r. spectrum of 1 , 1 , 3 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e . A. Normal spectrum. B. Spectrum obtained by i r r a d i a t i o n 19 at the F resonance frequency. C. Spectrum obtained by 31 i r r a d i a t i o n at the P resonance frequency. I - 64 -14.7 Hz., 14.6 Hz., and 18.8 Hz. I t i s seen that J i s 14.6 Hz. 3 i n =PMe2 ( s e c t i o n 3.4.2.) and 18.7 Hz. i n =PFMe ( s e c t i o n 3.4.1.). 19 Thus, the F decoupled spectrum i s compatible w i t h the presence of =PMe2 and =PFMe groups, the non-geminal s t r u c t u r e s c-e i n F i g . 12 being r u l e d out. The occurrence of two doublets with coupling constants 14.6 Hz. and 14.7 Hz. c l e a r l y shows th a t the two methyl groups i n the =PMe2 group are non-equivalent. The a n t i p o d a l s t r u c t u r e ( F i g . 12b) i s r u l e d out a l s o , s i n c e the two methyl groups i n the PMe 2 group are d i s t i n c t l y non-equivalent ( F i g . 13B). These r e s u l t s are uniquely con-s i s t e n t w i t h the s t r u c t u r e (a) i n F i g . 12 f o r t h i s compound. I r r a d i a -31 t i o n at the P resonance frequency (40.481330 MHz.), shown i n F i g . 13C, 19 leaves only the F cou p l i n g (6.1 Hz.). The three methyl environments 31 i n the compound are, thus;, evident from the P decoupled spectrum. Of the two methyl groups i n =PMe2 i t i s d i f f i c u l t to f i n d out which one i s the more s h i e l d e d . The chemical s h i f t s and coupling constants are given below. 6(p.p.m.) J(Hz.) CH 3 ; 1.55 C H 3 P A 14.7 CH 3 1.60 CH 3P A 14.6 C H 3 1.62 ^ H > B 18.8 CH 3F 6.1 The F n.m.r. spectrum i s again compatible with the s t r u c t u r e deduced from the *H n.m.r. spectrum. The non-equivalence of the two - 65 -f l u o r i n e atoms on P^ ( F i g . 12a) i s seen i n the a c t u a l spectrum. The f l u o r i n e atoms on P^ would be expected to be s l i g h t l y non-equivalent, but t h i s i s not observed i n the a c t u a l spectrum. The =PF 2 p o r t i o n i n the observed spectrum i s : The observed spectrum i s i n good agreement w i t h that expected from a f i r s t order a n a l y s i s . Of the two f l u o r i n e atoms F" and F'", i t i s d i f f i c u l t to f i n d out which one i s the more s h i e l d e d . The 6 and J values are: - 66 -6(p.p.m.) F 68.9 F" or F*"; 69.1' F" or F'" 66.9 F' • 55.3 J(Hz.) FP 844 pm'p o r pt.p 8 3 6 F*"r;P or F"P 844 F'P 961 F"F"" 70 50,5-7 I t i s reported that J _ i n =PF„ i s about 70 Hz. r r Z 31 The P n.m.r. spectrum of N^P^F^Me^ b a s i c a l l y c o n s i s t s of a high f i e l d t r i p l e t ( 6 p = 126.1 p.p.m., J p p = 850 Hz.), a s i n g l e t ( 6 p = 95.2 p.p.m.), and a low f i e l d doublet ( 6 p = 90.0 p.p.m.; J p p = 951 Hz.). The t r i p l e t , s i n g l e t and the doublet a r i s e r e s p e c t i v e l y from =PF2> =PMe2 and =PFMe groups. Since the r e s o l u t i o n of the spectrum was poor P-P coupling constants could not be obtained. 3.4.6. T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N 4 P 4 F 5 M e 3 ( c o m P o n e n t 4 of f r a c t i o n (b) - 3.3.1.3.) The normal '''H n.m.r. spectrum o f this-compound, ( s o l u t i o n i n CCA^) shown i n F i g . 14A, c o n s i s t s of a doublet and a more complex region of r e l a t i v e areas 2:1. Although the a c t u a l spectrum i s compatible with the presence of a =PFMe group and a =PMe2 group i n the compound ( F i g . 12b). a heteronuclear double resonance experiment has been necessary to deduce 19 the a c t u a l s t r u c t u r e . I r r a d i a t i o n at the F resonance frequency 31 (94.088880 MHz.), shown i n F i g . 14B, leaves the P cou p l i n g (14.8 Hz., - 67 -1.40 g F i g . 14. H n.m.r. spectrum o f 1 , 1 , 5 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e . A. Normal spectrum. B. Spectrum obtained by i r r a d i a t i o n 19 at the F resonance frequency. C. Spectrum obtained by 31 i r r a d i a t i o n at the P resonance frequency. - 68 -31 18.8 Hz. and 1.7 Hz.). I r r a d i a t i o n at the P resonance frequency (40.481,330 MHz.), shown i n F i g . 14C, leaves the 1 9 F coupling (6.2 Hz.). The resonance s i g n a l s of the methyl protons i n =PMe2 are broad (decoupled spectra) suggesting t h e i r s l i g h t non-equivalence. The 19 chemical s h i f t s determined from F decoupled spectrum are: 6-7 , 1.60 p.p.m.; I S ^ I , 1.67 p.p.m. 3 19 3 The F n.m.r. spectrum ( F i g . 15) i s i n t e r e s t i n g i n that the P F 2 p o r t i o n i s simple i n co n t r a s t to that observed i n other compounds reported e a r l i e r i n t h i s chapter, and f i t s i n w e l l w i t h a f i r s t order assignment. The f l u o r i n e atoms F 1 and F" on P^ ( F i g . 15) are non-equivalent and t h i s i s observed i n the a c t u a l spectrum. The complete assignment o f the spectrum i s shown i n F i g . 15. I t i s known i n c y c l o -4 FF 4 FF 95 hexane and carbohydrate chemistry that J . i s greater than J J J c i s to trans I t i s l i k e l y to be tru e i n p h o s p h o n i t r i l i c chemistry a l s o , but w i t h the a v a i l a b l e n.m.r. data o f p h o s p h o n i t r i l i c d e r i v a t i v e s i t i s d i f f i c u l t to 4 FF draw any d e f i n i t e c o n c l u s i o n at t h i s stage. I f cou p l i n g J a r e indeed 4 FF l a r g e r than J t r a n s ^ n p h o s p h o n i t r i l i c compounds then F' i s more 4 FF sh i e l d e d than F" ( F i g . 15B). This coupling «?cj_s h a s not been observed, so f a r , among p h o s p h o n i t r i l i c compounds. Although the spectrum i s simple and could be i n t e r p r e t e d on a f i r s t order b a s i s , there are some second order e f f e c t s which are evident from the d i f f e r e n c e i n the i n t e n s i t i e s of the s i g n a l s i n the =PF 2 p o r t i o n of the spectrum. These e f f e c t s a l s o cause the two halves of the spectrum i n =PF 2 ( F i g . 15A) to be s l i g h t l y d i f f e r e n t . In view o f t h i s complexity, a complete a n a l y s i s of the spectrum w i l l be i n order. . - 69 -F i g . 15. F n.m.r. spectrum o f 1 , 1 , 5 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e . A. Spectrum obtained at a sweep width o f 1000 Hz. B. Part of the spectrum obtained at a sweep width of 500 Hz. - 70 -The 6 and J values are given below. 6 (p. p. m.) J (Hz .) F 55.9 FP 944 F' 68.8 F'P A 876 F" 67.7 F"P. 884 A F'F" 65 F'P 11 F"P 12 F'F 13.5 It i s reported that J p p i s 14.0 Hz. i n 1,1 N 3P 3C£ 4F 2 and that the s i g n 3 of J„_, i s opposite to that of J _ „ and J ™ . FP P-P FP 31 The P n.m.r. spectrum (obtained at a sweep width of 1000 Hz.) of N 4P 4FgMe 3 ( s o l u t i o n i n CC£ 4) c o n s i s t s of a low f i e l d doublet, a broad s i n g l e t , and a 1:2:1 t r i p l e t , a r i s i n g from PFMe, PMe 2 and PF 2 groups. The doublet and s i n g l e t are complex, owing to long range coupling. The t r i p l e t i s r e l a t i v e l y simple, each component of i t being s p l i t by P. and P R i n t o a doublet of doublets (compound s t r u c t u r e given below). - 71 -Since the l i n e width i s about 30 Hz., f u r t h e r long range co u p l i n g o f P^ , 3 with f l u o r i n e atom ( J p p ) i s not observed. J p p and J p p are 41 Hz. C A C B and 70 Hz., the values observed f o r N 4P 4F 4Me 4 (3.4.7.) and I ^ P ^ M e (4.5.1.). The 6 and J values are given below. 6(p.p.m.) J (Hz.) 93.7 89.9 125.8 P F B P F P P C B P P C A 962 872 70 41 3.4.7. T e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e N / |P 4F / |Me 1 (sublimate - 3.3.1.4.). The *H n.m.r. of t h i s compound ( s o l u t i o n i n C H C i i ^ i s shown i n F i g . 16B. I t c o n s i s t s o f s i x l i n e s . This r u l e s out the presence o f a =PFMe group i n the compound. The compound must have one of the two geminal s t r u c t u r e s shown i n F i g . 17a-b. 1/ N Me I Me Me N^Me F - atoms not shown F i g . 17. P o s s i b l e two geminal isomers o f t e t r a m e t h y l t e t r a f l u o r o -c y c l o t e t r a p h o s p h o n i t r i l e . a) 1,1,3,3-N^PjtFi+Mei, b) 1 , 1 , 5 , 5 - ^ ? ^ ! ^ 92.8 99.0 120.8 ~ " 141.8 143.6 P.P.m. 16. N.m.r. spec t r a o f 1 , 1 , 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e . 19 i 3 i A. F n.m.r. spectrum. B. H n.m.r. spectrum. C. P n.m.r. spectrum. - 73 -m. Although the a c t u a l spectrum i s c o n s i s t e n t w i t h s t r u c t u r e b i n F i g . 17, i t i s d i f f i c u l t to draw a d e f i n i t e c o n c l u s i o n , since the d i f f e r e n c e between J r„ D and J _ i n s t r u c t u r e c a ) i s not expected to be much; L H 3 F A L H 3 F B the overlapping doublet of doublets w i l l give a good approximation to a t r i p l e t . The main doublet ( J r H „ = 14.7 Hz.) a r i s e s from coupling ^ t t3 FA of methyl protons with phosphorus atom and i s centred at 6 = 1.61 p.p. I t i s f u r t h e r s p l i t i n t o a 1:2:1 t r i p l e t by c o u p l i n g w i t h v i c i n a l phos-phorus a t o m s ( J r H „ = 1.5 Hz.). 19 The F n.m.r. spectrum ( F i g . 16A) of the compound ( s o l u t i o n i n CHC&g) shows that the compound i s a geminal d e r i v a t i v e (absence o f a low f i e l d doublet as observed i n Is^P^F^Me and N^P^F^Me^) ; but as i n the ~^H n.m.r. spectrum i t i s d i f f i c u l t to d i s t i n g u i s h between s t r u c t u r e s a and b i n F i g . 17, since the c o u p l i n g of f l u o r i n e atoms w i t h chemically 3 d i s t i n c t phosphorus atoms ( Jpp> F i g - 17a) would not be expected to d i f f e r 3 3 much. However, i f J and J p p are d i s t i n c t l y d i f f e r e n t , then each h F A B component of the main doublet w i l l be s p l i t i n t o a doublet of doublets (four l i n e s ) i n s t e a d o f a t r i p l e t . Only i n these circumstances can ' 19 the two p o s s i b l e s t r u c t u r e s be d i s t i n g u i s h e d through'the" F n.m.r. spectrum. The main doublet i s centred at 66.4 p.p.m. ( J c r ) = 882 Hz., F P B J = 10.7 Hz.). A 31 The P n.m.r. spectrum ( F i g . 16C) of the compound ( s o l u t i o n i n CHCJl^) i s uniquely c o n s i s t e n t w i t h s t r u c t u r e b of F i g . 17. I t c o n s i s t s of a t r i p l e t o f t r i p l e t s (9 l i n e s ) and a broad s i n g l e t j ' f o r s t r u c t u r e (a) ( F i g . 17) a t r i p l e t o f doublets'" (6 l i n e s ) would be expected. ) The compound i s t h e r e f o r e both geminal and a n t i p o d a l . This s t r u c t u r e and a broad s i n g l e t - 74 -has been confirmed by an X-ray c r y s t a l s t r u c t u r e determination. The 6 and J values are given below. 6(p.p.m.) J(Hz.) P. 92.8 PJF 885 A D P B 120.8 P A P B 37 3.4.8. O c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e N^P^Meg (3.3.1.5.) The ^H n.m.r. spectrum of t h i s compound ( s o l u t i o n i n CC£^) c o n s i s t s of a doublet w i t h an unsymmetrical shoulder attached to each component ( F i g . :24B). Since t h i s i s an &^24 s y s t e m > such an unsymmetrical s t r u c t u r e i s not unexpected. The coupling of methyl protons with v i c i n a l phosphorus atoms i s not r e s o l v e d . The doublet i s centred at 6 = 1.34 p.p.m. (J = 12.0 Hz.). 31 The P n.m.r. spectrum of t h i s compound i n CCJl^ and D^O have been determined, the 6 values being 98.7 p.p.m. and 86.2 p.p.m. The long range co u p l i n g w i t h methyl protons i s not r e s o l v e d . The n.m.r. parameters of m e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s ar,e'-.gij#en i n •Tab;l;e'i9. "> 3.4.9. Conclusion 1) The p h o s p h o n i t r i l i c r i n g i n a l l the d e r i v a t i v e s i n v e s t i g a t e d 94 i s s t a t i s t i c a l l y planar and i n f a c t the molecule N^P^F^Me^ deviates only s l i g h t l y from p l a n a r i t y i n the c r y s t a l . I f there i s s u f f i c i e n t puckering of the r i n g which could freeze the molecule to a p a r t i c u l a r r i g i d conformation then the s u b s t i t u e n t s attached to the phosphorus atoms would be expected to be c h e m i c a l l y non-equivalent. This would Table 9 N.m.r. Parameters of M e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s (6 i n p.p.m., J i n Hz.) PFMe PMe„ P F 2 Compound 2. z 6 P 6 F J P F 6Me J Me JFMe;- • 6P 6Me JPMe 4 j PMe 6 P J P F 2JPP 2 j JPP N 4P 4F yMe 86.7 57.6 939(942) 1.70 18.7 6.5 •->- - - 1.5 125.2 69.27 861(866) - -gem 1,1N.P F Me ? - - - - - - 93 0 1.64 14.6 1.4 126.5 69.2, 870(846) - -*+ H- O Z 68.5 (845) trans 1,5N.P.F^Me„ 4 4 6 z - 56.6 (946) 1.73 18.8 6.3 - - - 1.7 - 69.6 (872) - -l,l,3N 4P 4F 5Me 3 90.0 55.3 951(961) 1.62 18.8 6.1 95 2 1.61 1.55 14.7 14.6 126.1 69.1, 68.9, 66.9 850(844) (836) (844) 70 — l , l , 5 N 4 P 4 F 5 M e 3 89.9 55.9 962(944) 1.67 18.9 6.2 93 7 1.60 14.8 1.7 125.8 68.8, 67.7 872(884) (876) 65 70,41 l , l , 5 , 5 N 4 P 4 F 4 M e 4 - - - - - - 92 8 1.61 14.7 1.5 120.8 66.4 885(882) - 37 N P Me IN4 4 8 - - - - - - 98 86 7 a  2b 1.34 12.0 - - - - - -a i n CC£. 4 b i n D 20 J obtained from P n.m.r. sp e c t r a , values i n parentheses from F n.m.r. sp e c t r a . - 76 -r e s u l t i n complicated n.m.r. spec t r a and t h e i r i n t e r p r e t a t i o n would be d i f f i c u l t . Since a l l the n.m.r. spec t r a examined, i n p a r t i c u l a r those of the d i - , t r i - and t e t r a s u b s t i t u t e d d e r i v a t i v e s are f a i r l y simple and could be i n t e r p r e t e d on a f i r s t order b a s i s , p o s s i b l e conformational e f f e c t s are b e l i e v e d to be absent. „ 2) Although there are second order e f f e c t s i n a l l the n.m.r. s p e c t r a , they do not s e r i o u s l y a f f e c t the i n t e r p r e t a t i o n on a f i r s t order b a s i s i n many cases. I t was t h e r e f o r e p o s s i b l e to deduce the s t r u c t u r e s of the compounds through t h e i r n.m.r'. spe c t r a . The c o n f i r m a t i o n of such s t r u c t u r e s f o r the compounds N^P^F^J^ and N^P^F ^Me^f through X-ray c r y s t a l s t r u c t u r e determination s t r o n g l y suggests that the s t r u c t u r a l conclusions drawn i n other cases are l i k e l y to be c o r r e c t . : 3.5. C r y s t a l S t r u c t u r e of M e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s o The geminal and the a n t i p o d a l s t r u c t u r e s of I v ^ P ^ ^ l S ^ and 94 96 N 4 P 4 F 4 M e 4 have been confirmed c r y s t a l l o g r a p h i c a l l y . ' Both mole-cules have a c r y s t a l l o g r a p h i c C^ symmetry a x i s , passing through the PMe^ group i n the f i r s t molecule and through the PF 2 groups i n the second, so that the phosphorus atoms i n each molecule l i e i n a plane. The con-40 formation of both molecules i s of the l i m i t i n g "saddle" type, though, sin c e the r i n g angles at n i t r o g e n are large i n N^P^^Me^ the n i t r o g e n atoms deviate only s l i g h t l y (± 0.15 A.) from the phosphorus plane. I t 97 i s u s e f u l to compare the r i n g conformations f o r the s e r i e s I^P^Meg, - 77 -N 4P 4Me 4F 4, NjjP^F^IV^ and N^P^Fg. The octaraethyl compound adopts the 'tub' conformation p r i m a r i l y f o r s t e r i c reasons. The tetr a m e t h y l -t e t r a f l u o r o compound has the 'saddle' conformation w i t h the nitrogens o being an average of 0.48 A o f f the phosphorus plane. This displacement o i s reduced to 0.15 A i n N.P.F,Me_, and the o c t a f l u o r o compound i s 4 4 o i. planar. Thus there i s a d i r e c t c o r r e l a t i o n between the number of f l u o r i n e s and the tendency towards p l a n a r i t y , t h i s being a t t r i b u t a b l e to the large i n d u c t i v e e f f e c t s o f the f l u o r i n e s u b s t i t u e n t s . The d e t a i l e d geometry of the two s t r u c t u r e s i s shown i n F i g . 18. The s i g n i f i c a n c e of the s t r u c t u r e s i n r e l a t i o n to s u b s t i t u t i o n a l behaviour i s discussed i n Chapter 7. N R and N 2 off P-plane by ± 0.15 A oc cr ( P - N ) = 0.006 A cr ( P — F ) = 0.005-0.008A cr ( P - C ) = 0.01 A O" (ang les ) = 0.5° F i g . 18(a). Structure of 1,1-dimethylhexafluorocyclotetraphosphonitrile ( 1 , i - N ^ P ^ M e ) . N1 and N 2 off P-plane by ± 0 . 4 8 A a~ ( P - N ) = 0 . 0 1 A ^(angles) =1.0° F i g . 18(b). S t r u c t u r e of 1 , 1 , 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e ( l , l , 5 , 5 - N 4 P 4 F 4 M e 4 ) . - 80 -CHAPTER 4 METHYLATION OF HEXAFLUOROCYCLOTRIPHOSPHONITRILE  AND DECAFLUOROCYCLOPENTAPHOSPHONITRILE 4.1. I n t r o d u c t i o n I t i s seen from the r e a c t i o n s o f o c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e , (NPF2) 4, that the course o f the s u b s t i t u t i o n i s predominantly geminal, a p r e v i o u s l y unrecognised o r i e n t a t i o n p a t t e r n . Since a simple e l e c t r o -s t a t i c e f f e c t can not account f o r t h i s , the i n f l u e n c e of a d e l o c a l i s e d 7T-system seems apparent. I f a TT-effect i s the c o n t r o l l i n g f a c t o r i n the o r i e n t a t i o n then the p a t t e r n and r e l a t i v e r a t e s might be expected-to be dependent on r i n g s i z e . The r e a c t i o n s of he x a f l u o r o c y c l o t r i p h o s p h o -n i t r i l e , ( W ^ ) ^ and d e c a f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e , (^^2)5 with m e t h y l - l i t h i u m c l e a r l y demonstrate that the three r i n g systems N^P^ and N^P^ behave d i f f e r e n t l y towards m e t h y l - l i t h i u m . An explanation f o r t h i s d i f f e r e n c e appears l a t e r i n t h i s t h e s i s . 4.2. Reaction o f Decaflu o r o c y c l o p e n t a p h o s p h o n i t r i l e w i t h M e t h y l - l i t h i u m The experimental procedure was s i m i l a r to that described f o r the r e a c t i o n o f N^P^Fg with LiCH^ 1 ( s e c t i o n 3.3). M e t h y l - l i t h i u m (34.4 mmole) i n ether (60 ml.) was added dropwise to decafluorocyclopentaphospho-n i t r i l e (7.4 g., 17.78 mmole) i n ether (50 ml.) atc~/20°, under n i t r o g e n . The crude product (5.5 g.) on f r a c t i o n a l d i s t i l l a t i o n gave two f r a c t i o n s . F r a c t i o n (a) (3.4 g.) was a c l e a r l i q u i d b o i l i n g at 99-105° (100 mm.). - 81 -This was f u r t h e r f r a c t i o n a t e d by g . l . c . (column temperature 90°, He flow 70 ml. min. 1 ) , which showed the main sharp peak ( r e t e n t i o n time 3.3 min.) to be as s o c i a t e d w i t h a smaller one of s h o r t e r r e t e n t i o n time. The *H n.m.r. spectrum of t h i s f r a c t i o n before p u r i f i c a t i o n by g . l . c . was taken and i s discussed i n s e c t i o n 4.4.1. The a n a l y s i s of the p r i n c i p a l component (recovery 85%) corresponded to N^P^F^Mey: b.p. 156.6° (748 mm.). [Found: C, 3.07; H, 0:78, N, 17.11; F, 41.36; N 5P FgMer r e q u i r e s C, 2.92; H, 0.73; N, 17.04; F, 41.61%]. High r e s o l u t i o n mass measured, 410.890; Calc. f o r NgP F gMe, 410.893. F r a c t i o n (b) (1.6 g.) was a c l e a r v i scous l i q u i d b o i l i n g at 125-132° (100 mm.). Further f r a c t i o n a t i o n by g . l . c . showed 4 components with r e t e n t i o n times, (min.) 1.6, 6.1, 7.7, 12.8 (broad with shoulders .-on e i t h e r s i d e ) . Component 1 corresponded to N^P^FgCH^, since the r e t e n t i o n time o f an authentic sample was 1.6 min. While component 2 was decomposed and could not be c h a r a c t e r i z e d , component 3 could not be c o l l e c t e d i n c h a r a c t e r i z a b l e amount. Component 4, which i s l i k e l y to be a s s o c i a t e d w i t h two more isomers, was c o l l e c t e d as a c l e a r l i q u i d w i t h an a n a l y s i s corresponding to N^P^Fg(CH^)^. [Found: C, 5.73; H, 1.31; N, 17.39; N 5 P 5 F g ( C H 3 ) 2 r e q u i r e s C, 5.90; H, 1.47; N, 17.20%]. I t i s very l i k e l y t hat component 2 and 3 are al s o isomers o f N^Pj-Fg ( C H 3 ) 2 , i n which case a l l the p o s s i b l e f i v e isomers of N^-P^Fg (CH 3) were formed i n the r e a c t i o n as i n that o f N 4P 4Fg with L i C H 3 > In view of the i n c r e a s i n g d i f f i c u l t i e s of se p a r a t i o n of the isomers f u r t h e r experiments to get p a r t i a l l y methylated d e r i v a t i v e s were not undertaken. - 82 -However, t h e . p r e v i o u s l y unknown decamethylcyclopentaphosphonitrile, Nj-P,. (CH.J)^Q, was obtained i n a r e a c t i o n of the corresponding f l u o r i d e w i t h a small excess of m e t h y l - l i t h i u m . The i s o l a t i o n o f N.-P,-(CH^) ^ i s described i n the f o l l o w i n g three experiments? 4.2.1. Experiment 1 1) The experimental procedure was s i m i l a r to that used f o r the p r e p a r a t i o n of o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e , N 4 P 4 ( C H 3 ) g ( 3 . 3 . 1 . 5 . ) . M e t h y l - l i t h i u m (554.2 mmole) i n ether (400 ml.) was added dropwise to d e c a f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e , N^P^F^^ (20.1 g., 48.74 mmole) at - 2 0 ° , under n i t r o g e n . A f t e r the completion of the r e a c t i o n (14 h . ) , the solvent was removed and the r e s i d u a l s o l i d was e x t r a c t e d twice w i t h l i g h t p e t r o l to give p e t r o l s o l u b l e and p e t r o l i n s o l u b l e p o r t i o n s . The p e t r o l i n s o l u b l e p o r t i o n was e x t r a c t e d w i t h CHCJl^ under r e f l u x , to give a pasty mass (7 g.). This could not be c h a r a c t e r i z e d by elemental a n a l y s i s and by n.m.r. and i V r . spectroscopy. Though there was a broad absorption around 1300-1200 cm 1 region i n the i . r . spectrum, the whole spectrum was complicated and i t s i n t e r p r e t a t i o n i n c o n c l u s i v e . The p e t r o l 1 " . 1 9 s o l u b l e product contained p a r t i a l l y methylated d e r i v a t i v e s (from the 7 F n.m.r. spectrum) and i t showed f i v e c l o s e l y spaced spots on examination by t h i n l a y e r chromatography on an alumina p l a t e . As g . l . c . was not p r a c t i c a b l e due to the l a c k of a column which could be used at high temperatures without appreciable decomposition of the component, i t was thought d e s i r a b l e to separate the compounds by s o l i d - l i q u i d chromato-graphy . - 83 -S o l i d - l i q u i d Chromatography: Column length : 75 cm.; O.D. = 3 cm. S o l i d phase : Alumina, Woelm n e u t r a l grade IV Sample : 4 g. The column was. eluted i n i t i a l l y w i t h e t h y l a c e t a t e , 5 ml. p o r t i o n s of eluate being c o l l e c t e d every 10 mins. The s e p a r a t i o n was f o l l o w e d by t h i n l a y e r chromatography. The p o l a r i t y of the eluent was r a i s e d using methanol. F i n a l l y f i v e major f r a c t i o n s were c o l l e c t e d . Though a p r e l i m i n a r y s e p a r a t i o n was thus r e a l i s e d , the recovery (45%) was poor. Further, the f i r s t 4 f r a c t i o n s showed d i f f e r e n t r f values on an alumina p l a t e from those found f o r the mixture, and t h e i r *H n.m.r. spec t r a d i d not correspond to any p a r t i a l l y s u b s t i t u t e d d e r i v a t i v e . I t i s very l i k e l y t hat these p a r t i a l l y methylated d e r i v a t i v e s were hydrolysed i n the column. However, f r a c t i o n 5 gave a s o l i d m a t e r i a l (0.5 g.) which was f u r t h e r p u r i f i e d by s u b l i m a t i o n i n vacuo. The a n a l y s i s of the sublimate corresponded to ^P,-(CH^)^, m.p. 64-65°, [Found: C, 31.86; H, 8.15; N, 18.64; N 5 P 5 ( C H 3 ) 1 0 r e q u i r e s C, 32.00; H, 8.00; N, 18.67%]. High r e s o l u t i o n mass measured, 375.119; Cal c . f o r Nj-Pj-Me^, 375.118. In c o n t r a s t to the r e a c t i o n of N^P^Fg with LiCH^ the s i m i l a r r e a c t i o n w i t h N^P^-F^ gives only a small, y i e l d of the f u l l y methylated j d e r i v a t i v e . This could be a t t r i b u t e d to the occurrence of a competitive side r e a c t i o n ( p o s s i b l y of an a d d i t i o n type) le a d i n g to r i n g opening. The pasty mass (7 g.) recovered from the CHCJl^ e x t r a c t could be the product of t h i s side r e a c t i o n . In order to increase the amount of - 84 -Nj-Pj-Me^Q the r e a c t i o n was repeated using a longer r e a c t i o n p e r i o d . 4.2.2. Experiment 2 The p e t r o l s o l u b l e product (1.00 g.), obtained from a r e a c t i o n of N 5 p 5 F 1 o '•5'6 1 3 - 6 J™ 1 0 1 6) i n ether (60 ml.) and m e t h y l - l i t h i u m (153.5 mmole) i n ether (100 ml.), showed 3 spots on examination by t h i n l a y e r chromatography on an alumina p l a t e , the spot due to N^P^Me^Q being very intense (by comparison with pure N^P^-Me.^). Since s o l i d - l i q u i d chromatography was not s u i t a b l e f o r the p u r i f i c a t i o n o f the product a chemical method was attempted through formation of the p e r c h l o r a t e . Impure N^P^Me^ CO-2 g.) i n g l a c i a l a c e t i c a c i d was t r e a t e d wit h p e r c h l o r i c a c i d to give the s o l i d p e r c h l o r a t e . This was d i s s o l v e d i n minimum water and the pH was brought to 7 using KOH. The s o l u t i o n was c h i l l e d and then f i l t e r e d to remove most of the i n s o l u b l e KCilO^ and the f i l t r a t e was evaporated to n e a r l y dryness. E x t r a c t i o n o f the s o l i d w i t h p e t r o l gave a product (0.08 g.) which showed three spots on an alumina p l a t e . Thus t h i s method was not s u i t a b l e f o r the p u r i f i c a t i o n of t h i s compound. 4.2.3. •• Experiment 3 Since the y i e l d of N^P^Me^Q was s t i l l l e s s , the r e a c t i o n c o n d i t i o n s were modified w i t h a view to improve i t . N^P^F^^ (11.8 g., 35.55 mmole) i n ether (50 ml.), cooled to -20°, was added dropwise to me t h y l - l i t h i u m (324.6 mmole) i n dry ether C200 ml.) at -35°, under - 85 -n i t r o g e n . The temperature was maintained at -35° throughout the r e a c t i o n . A f t e r the completion of the r e a c t i o n (40 h.) the solvent was removed and the r e s i d u a l s o l i d was e x t r a c t e d w i t h l i g h t p e t r o l . The p e t r o l s o l u b l e product (2.8 g.) showed three spots on an alumina p l a t e , the spot due to N^P^Me^p being very intense (by comparison w i t h an authentic sample). The product was p u r i f i e d by a combination of repeated r e c r y s t a l l i s a t i o n from l i g h t p e t r o l (35°C) at -10°C and repeated vacuum s u b l i m a t i o n . The a n a l y s i s of the p u r i f i e d sample corresponded to N^Me.^, m.p. 64-65° [Found: C, 32.08; H, 8.12; N, 18.52; N 5P 5Me 1 Q r e q u i r e s C, 32.00; H, 8.0; N, 18.67%]. No great improvement i n y i e l d was obtained. The smaller y i e l d of N^P^Me^Q, as compared with that of N^P^eg from N 4P 4Fg when excess of LiCH^ was used, i s suggestive of a competitive side r e a c t i o n . Since l i t h i u m a l k y l s are powerful n u c l e o p h i l e s and are 69 known to take p a r t i n a d d i t i o n r e a c t i o n s , t h i s side r e a c t i o n seems very l i k e l y t o be of an a d d i t i o n type. In order to avoid t h i s a d d i t i o n r e a c t i o n , we have i n v e s t i g a t e d the use of HgfCH^^, Sn ( C H 3 ) 4 and MeMgCJl ( i n THF) as methylating agents i n these r e a c t i o n s . I t i s found from the f o l l o w i n g three experiments that there was no r e a c t i o n when Hg(CH 3) 2 and Sn (CFLp 4 were used and no product could be i s o l a t e d when MeMgCJl was used. 4.2.4. Reaction of N ^ F ^ with Hg(CH 3) 2 ' Dimethyl mercury, : Hg (CH^),, (2.4 g.), was added to decafluoro-c y c l o p e n t a p h o s p h o n i t r i l e , (NPF,,),. (0.8 g.), and the mixture was heated - 86 -.under r e f l u x . There was no v i s i b l e r e a c t i o n . A f t e r 24 h. the HgCCHg^ was removed by d i s t i l l a t i o n and the r e s i d u a l l i q u i d was i d e n ^ t i f i e d as unreacted N^P^F^p by comparison of i t s i . r . spectrum w i t h that o f an authentic sample. 4.2.5. Reaction of N r P r F 1 Q w i t h SnCCH^)^ Tetramethyl t i n j Sn(CH 3) 4 (.1.3 g.) was added to N 5 P 5 F 1 Q (0.7 g.) and the mixture was heated under r e f l u x . -There was no v i s i b l e r e a c t i o n The contents were then t r a n s f e r r e d to a Carius tube. The tube was sealed o f f i n vacuo and was heated at 150° f o r 30 h. The s o l u t i o n was c l e a r i n d i c a t i n g the absence of any r e a c t i o n . Tetramethyl t i n , SnCCH^)^, was removed and the r e s i d u a l l i q u i d was i d e n t i f i e d as unreacted Nj-P^F^Q by comparison of i t s i . r . spectrum with that o f an authe n t i c sample. 4.2.(6/. Reaction o f N C P R F 1 A w i t h MeMgC£ ^ 5—5—10 : — — . Methyl magnesium c h l o r i d e , MeMgC£ (79.65 mmole) i n THF (30 ml.) was added dropwise to decaf l u o r o c y c l o p e n t a p h o s p h o n i t r i l e , (NPF2)r ) (2.8 g., 6.75 mmole) at room temperature, under n i t r o g e n . A f t e r the a d d i t i o n of the Grignard reagent, the r e a c t i o n mixture was heated under r e f l u x f o r 12 h. The solvent was then removed and the r e s i d u a l s o l i d was e x t r a c t e d , f i r s t w ith l i g h t p e t r o l and then with CHCJl^. There was no s o l u b l e m a t e r i a l . I t i s c l e a r from the foregoing r e a c t i o n s of I^P^Fg and N^PCJF-^Q with m e t h y l - l i t h i u m that there i s a d i f f e r e n c e i n the r e a c t i v i t y although - 87 -the general p a t t e r n i s l i k e l y to be the same f o r both r i n g systems. The r e l a t i v e y i e l d s o f the f u l l y methylated d e r i v a t i v e s , N.P.Me0 and 4 4 o Nj-P^-Me^Q, seem to suggest that the main s u b s t i t u t i o n i s associated w i t h a competitive s i d e r e a c t i o n ( p o s s i b l y o f the additon t y p e ) . The s i m i l a r r e a c t i o n s o f N^P^F^ with m e t h y l - l i t h i u m were i n v e s t i g a t e d , as the r e s u l t s of such r e a c t i o n s were expected to throw some l i g h t on the extent of p a r t i c i p a t i o n o f a d e l o c a l i z e d TT-system, contained i n these phospho-n i t r i l i c molecules, i n chemical r e a c t i o n s . A c t u a l l y a d i f f e r e n c e i n behaviour i n the r e a c t i o n s of N^P^F^. with m e t h y l - l i t h i u m from those of N 4P 4Fg and N^P^F^^ was observed, i n that i t was not p o s s i b l e to detect any d e r i v a t i v e c o n t a i n i n g more than two methyl groups. The r e a c t i o n s are described i n the f o l l o w i n g three experiments. 4 . 3 . 1 . Reaction of H e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e with M e t h y l - i / L t h i u m - Experiment 1 The experimental procedure was s i m i l a r to that used f o r N^P^Fg and NJ-PI-FJQ. M e t h y l - l i t h i u m ( 6 8 . 0 0 mmole) i n ether ( 7 5 ml.) was added dropwise to h e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , N^P^F^ ( 9 . 8 9 g., 35 . 6 mmole) i n ether (75 ml.) at - 2 0 ° , under n i t r o g e n . In. c o n t r a s t to the r e a c t i o n s of N 4 P 4 F g and N^P^F^Q described e a r l i e r , the f i r s t few drops of methyl-l i t h i u m produced a white p r e c i p i t a t e which increased on f u r t h e r a d d i t i o n . The crude product ( 3 . 5 g.) gave on d i s t i l l a t i o n a) a c l e a r l i q u i d ( 1 . 4 4 g.) b o i l i n g at 1 0 0 ° ( 7 5 3 mm.) and b) a n o n - d i s t i l l a b l e h i g h l y viscous l i q u i d which l a t e r s o l i d i f i e d ( 1 . 5 g.). Further f r a c t i o n a t i o n o f (a) by g,.T.c. (column temperature 8 0 ° , He flow 55 ml. min. ^ ) showed a main sharp peak - 88 -( r e t e n t i o n time 3.4 min.) to be as s o c i a t e d w i t h a smaller i m p u r i t y peak of s h o r t e r r e t e n t i o n time (2.8 min.). The p r i n c i p a l component (recovery 80%) was a c l e a r l i q u i d %.p. 105.7° (752 mm.) with an a n a l y s i s corresponding to I ^ P ^ M e , [Found: C, 5.00; H, 1.30; N, 16.94; F, 38.50; N 3P 3F 5Me r e q u i r e s C, 4.90; H, 1.22; N, 17.14; F, 38.77%]. High r e s o l u t i o n mass measured, 244.943; Cal c . f o r N 3P 3F 5Me, 244.945. The n o n - d i s t i l l a b l e m a t e r i a l (b) could not be c h a r a c t e r i z e d . 4.3.2. Experiment 2 As there was no i n d i c a t i o n of any higher s u b s t i t u t e d d e r i v a -t i v e s being formed i n the above r e a c t i o n (4.3.1.), i t was repeated w i t h a d i f f e r e n t p r o p o r t i o n of m e t h y l - l i t h i u m to h e x a f l u o r o c y c l o t r i p h o s p h o -n i t r i l e . The crude product (a viscous l i q u i d , 2.3 g.), obtained from a r e a c t i o n of h e x a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , N 3P 3F^ (5.86 g., 23.5 mmole) i n ether (50 ml.) w i t h m e t h y l - l i t h i u m (66.4 mmole) i n ether (75 ml.) at -20°, gave on d i s t i l l a t i o n a) a c l e a r l i q u i d (0.42 g.) b o i l i n g at 100° (756 mm.), b) a n o n - d i s t i l l a b l e m a t e r i a l (1.7 g.) and c) a c r y s t a l l i n e s o l i d (0.17 g.) recovered from the condenser. F r a c t i o n a t i o n o f (a) showed a main sharp peak ( r e t e n t i o n time 2.9 min.) to be associated w i t h a smaller peak of s h o r t e r r e t e n t i o n time. • The main component was i d e n t i f i e d as N3P3F,-Me by comparison o f i t s r e t e n t i o n time with that of an a u t h e n t i c sample. The n o n - d i s t i l l a b l e m a t e r i a l , as before (4.3.1.), could not be c h a r a c t e r i z e d . The c r y s t a l l i n e compound was p u r i f i e d by r e c r y s t a l l i s a t i o n from a CHC&--CC&. mixture (1:2). The a n a l y s i s of the - 8 9 -p u r i f i e d compound corresponded to H^P^F^Qie)^, m.p. 1 2 7 . 5 - 1 2 8 ° [Found: C, 10.19;- H, 2.48; N, 1 7 . 4 0 ; N 3 P 3 F 4 ( C H 3 ) 2 r e q u i r e s C, 9.93; H, 2.30; N, 1 7 . 1 7 % ] . High r e s o l u t i o n mass measured, 2 4 0 . 9 7 0 ; C a l c . f o r N 3 P 3 F 4 M e 2 , 2 4 0 . 9 7 1 . There was no s i g n o f more h i g h l y methylated compounds. The above two r e a c t i o n s s t r o n g l y suggest that the competitive s i d e r e a c t i o n predominates over the main s u b s t i t u t i o n process because a) no d e r i v a t i v e c o n t a i n i n g more than two methyl groups could be i s o l a t e d b) the d i s u b s t i t u t e d d e r i v a t i v e was i s o l a t e d only i n small amount. In c o n t r a s t to the r e a c t i o n s of N 4 P 4 F g and NJ-PJ-F^Q with excess of methyl-l i t h i u m to give N 4P 4Meg and N^P^Me^^, s i m i l a r r e a c t i o n o f N 3 P 3 F g d i d not produce any f u l l y methylated d e r i v a t i v e . In f a c t no i s o l a b l e product could be obtained from such r e a c t i o n . This seems to suggest that the r e l a t i v e importance of s u b s t i t u t i o n i n the three r i n g systems (N 3P 3, N 4 P 4 and N,-P,.), l i e s i n the i n c r e a s i n g order N 4 P 4 > N^P^ > N 3 P 3 - The r e a c t i o n o f N3P3'F/^ with an excess o f m e t h y l - l i t h i u m i s described i n the next experiment, with the object of i n v e s t i g a t i n g p o s s i b l e a d d i t i o n products. 4 . 3 . 3 . Experiment 3 M e t h y l - l i t h i u m ( 2 4 0 . 5 mmole) i n ether ( 1 0 0 ml.) was added drop-wise to N 3 P 3 F 6 ( 5 . 9 0 g., 23.74 mmole) at 0 ° , under n i t r o g e n . A f t e r the r e a c t i o n was complete ( 1 0 h.), the solvent was removed and the r e s i d u a l s o l i d was d i v i d e d i n t o two p a r t s . An excess o f methyl i o d i d e (to re a c t w i t h N - l i t h i o compounds and give s o l u b l e N-methyl d e r i v a t i v e s ) was added to one par t i n a small autoclave, which was then heated at 15 0 ° f o r 3 - ,90 -days. The excess o f methyl i o d i d e was then removed. The s o l i d gave no e x t r a c t a b l e m a t e r i a l w i t h l i g h t p e t r o l , benzene or chloroform. E t h y l a l c o h o l (25 ml.) and h y d r o c h l o r i c a c i d (2N, 25 ml.) were added to the other p a r t i n a Carius tube, the tube was sealed o f f and heated at 150° f o r 4 days. The s o l u t i o n was then made a l k a l i n e w i t h KOH and was e x t r a c t e d w i t h benzene to i s o l a t e any Me^PO which had been formed; none was found. The occurrence of an a d d i t i o n r e a c t i o n i s the r e f o r e not yet proved, and the nature of the s o l i d product formed on methylat-i n g N^P^F^ i s s t i l l i n doubt. 4.4. The Nuclear Magnetic Resonance Spectra o f Monomethylnonafluoro-c y c l o p e n t a p h o s p h o n i t r i l e ( N c . P r F g M e ) > Dimethyloctafluorocyclopenta- p h o s p h o n i t r i l e (N^P^FgMe^, mixture of isomers), and Decamethyl- c y c l o p e n t a p h o s p h o n i t r i l e (N^P^Me^^)_. 4.4.1. Monomethylnonafluorocyclopentaphosphonitrile N^P^FgMe (main  component of f r a c t i o n (a) - 4.2.) The "''H n.m.r. spectrum of t h i s compound (neat sample) i s s i m i l a r to that o f N^P^^Me (3.4.1.), except that the coupling o f methyl protons w i t h v i c i n a l phosphorus atoms i s not r e s o l v e d . I f the lack o f r e s o l u t i o n o f the v i c i n a l c o upling i s due to r a p i d molecular tumbling, then t h i s would be expected to be r e s o l v e d i n the spectrum observed at low tempera-ture . On the contrary there was a general broadening of the s i g n a l s i n the a c t u a l spectrum obtained at a low temperature which could presumably be due to an increase i n the v i s c o s i t y of the sample. The spectrum at - :91--room temperature c o n s i s t s of four l i n e s . The main doublet, being centred at 6 = 1.73 p.p.m. ( J Q ^ p = 18.4 Hz.), a r i s e s from c o u p l i n g o f the methyl protons w i t h the d i r e c t l y bonded phosphorus atom. 19 The F n.m.r. spectrum of N^P^F^Me (neat sample) i s again s i m i l a r to that o f N 4P 4F 7Me (3.4.1.). The EPF 2 region i s observed as a complex p a t t e r n due to long range couplings, the EPFMe p o r t i o n being r e l a t i v e l y simple. The a c t u a l spectrum c o n s i s t s o f two doublets, both being centred at 56.8 p.p.m. ( J „ N = 984 Hz.).and 67.3 p.p.m. ( J C N = rr rr 853 Hz.) r e s p e c t i v e l y . They a r i s e from HPFMe and =PF 2 groups r e s p e c t i v e l y . 31 The P n.m.r. spectrum of N^P^FgMe b a s i c a l l y c o n s i s t s o f a high f i e l d t r i p l e t (centred at 130.0 p.p.m.; J P P = 866 Hz.) and a low f i e l d doublet (centred at 89.1 p.p.m.; J P P = 938 Hz.), both being of r e l a t i v e areas 4:1. The ^H n.m.r. spectrum of N^P^F^Me before p u r i f i c a t i o n s by gas-l i q u i d chromatography ( f r a c t i o n (a) - 4.2.) shows al s o a low f i e l d doublet (centred at 6 = 3.87 p.p.m.; p = 13.3 Hz.) i n a d d i t i o n to that p o r t i o n due to pure N^P^FgMe. This low f i e l d doublet i s absent i n the spectrum of the p u r i f i e d sample and c o l l a p s e s to a s i n g l e t on i r r a d i a t i n g 31 at the P resonance frequency (40.479 MHz.). This suggests that the impurity contains a EPMe2 or a =PMe group. Although i t was present i n small amounts (~5%) i n a l l the monosubstituted d e r i v a t i v e s of the three r i n g s i z e s i n v e s t i g a t e d , i t could not be recovered i n c h a r a c t e r i z a b l e amount. - 92 -4.4.2. D i m e t h y l o c t a f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e N^ -P^ FoMe^  (component 4 of f r a c t i o n (b) - 4.2.) The '''H n.m.r. spectrum of t h i s mixture (neat sample) c o n s i s t s of four l i n e s ; t h i s being c o n s i s t e n t w i t h the presence of a EPFMe group. 31 I r r a d i a t i o n at the P resonance frequency (40.481700 MHz.) leaves the 19 F c o u p l i n g (6.0 Hz. and 6.3 Hz.). Two doublets are observed i n the 31 P decoupled spectrum, both being centred at 6 = 1.71 p.p.m. (J„ u c = CH 3F 6.3 Hz.) and.at 6= 1.67 p.p.m. • ( J ^ p = 6.0 Hz.). Since only two doublets are observed, the 6 and J values of two isomers must be 19 i d e n t i c a l . I r r a d i a t i o n at the F resonance frequency (94.089100 MHz.) 31 leaves the P c o u p l i n g (18.0 Hz.). Since the resonance s i g n a l s are 19 broad, only a s i n g l e doublet i s observed i n the F decoupled spectrum. The heteronuclear decoupling experiment i s , t h e r e f o r e , i n c o n c l u s i v e about the stereochemical nature of the isomers. 4.4.3. Decamethylcyclopentaphosphonitrile N^P^Me^Q The ^H n.mr. spectrum of N^P^Me^^ ( s o l u t i o n i n CC& 4) i s s i m i l a r to that of N.P.MeQ ( F i g . 24B). I t c o n s i s t s of a doublet (5 r, u = 4 4 o 3 1.38 p.p.m., p = 12.4 Hz.). There i s no long range c o u p l i n g of methyl protons w i t h v i c i n a l phosphorus atom. 31 -~ The P spectrum (obtained at a sweep width of 250 H z . ) i n D^OJJshows-a s i n g l e broad band ( 5 p = 92.9 p.p.m.). Long range coupling of the phos-phorus atom with methyl protons ijsi not r e s o l v e d i n the a c t u a l spectrum. - 93 -4.5. The Nuclear Magnetic Resonance Spectra o f Monomethyipentafluoro- c y c l o t r i p h o s p h o n i t r i l e , D i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , and H e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e . 4.5.1. Mo n o m e t h y l p e n t a f l u o r o c y c l o t r i p h o s p h o n i t r i l e N^P^F^Me (4.2.3) The n.m.r. spectrum of t h i s compound (neat sample), shown i n F i g . 19A, c o n s i s t s of 36 l i n e s . The complete assignment of the couplings i s shown i n F i g . 19A. ^JriJ n has been observed f o r the f i r s t 3 time i n p h o s p h o n i t r i l i c compounds. The second order e f f e c t s , which are 19 31 so pronounced i n the F ( F i g . 19B) and i n the P ( F i g . 20) n.m.r. sp e c t r a , are b e l i e v e d to cause the\unsymmetrical shape of the t r i p l e t s i n the observed spectrum. 19 The F n.m.r. spectrum of N^P^F^Me i s shown i n F i g . 19B. The =PF 2 region o f the spectrum i s observed as a complex p a t t e r n , the =PFMe p o r t i o n being r e l a t i v e l y simple. The low f i e l d doublet., a r i s i n g from ,the)=PFMe group, i s centred at 53.1 p.p.m. (Jpp = 992 Hz.). In view of the high complexity o f the =PF 2 p o r t i o n of the spectrum, i t s complete a n a l y s i s w i l l be i n order. 31 The P n.m.r. spectrum of N^P^F^Me (neat sample), as shown i n F i g . 20, c o n s i s t s b a s i c a l l y of a high f i e l d t r i p l e t and a low f i e l d doublet, both being centred at 104.7 p.p.m. ( J p = 1007 Hz.) and 65.9 p.p.m. B (J p = 892 Hz.) r e s p e c t i v e l y . The middle and outer components of the A t r i p l e t are not i d e n t i c a l , because. o f - t h e pronounced second order e f f e c t s i n the. spectrum. The expanded spectrum was obtained at a sweep width o f IBI ll J i VV" V 48.1 58-5 64.3 74.1 p. p.m. F i g . 19. N.m.r. spectra of monomethylpentafluorocyclotriphosphonitrile. 1 1 Q A. H n.m.r. spectrum. B. F n.m.r. spectrum. P n.m.r. spectrum of monomethylpentafluorocyclotriphosphonitrile - 96 -1000 Hz. The EPFMe p o r t i o n of the spectrum i s simple and an assignment of the couplings i s shown i n F i g . 20. The 6 and J values are given below. 6 (p.p.m.) J(Hz.) P A 65.9 P AF 1007 P D 104.7 P_F 892 D D P A P B 7 0 P A C H 3 1 9 4.5.2. D i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e N^P^F^Me,, The compound must be one of the three isomers shown i n F i g . 21. F i g . 21. P o s s i b l e three isomers of d i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e . a) l , l - N 3 P 3 F 1 + M e 2 b) cis_-l,3-N 3P 3F i +Me 2 c) trans-1,3-N 3P 3F 4Me ? F atoms not shown The "^H n.m.r. spectrum of t h i s compound Csolution i n CHCJl^) c o n s i s t s of s i x l i n e s . The main doublet a r i s e s from co u p l i n g o f methyl protons with d i r e c t l y bonded phosphorus atom ( J ^ p = 14.6 Hz.) and i s centred at 6 = 1.65 p.p.m. Further coupling of the methyl protons with v i c i n a l - 97 -phosphorus atoms s p l i t s the doublet i n t o t r i p l e t s ( J ^ p = 1.9 Hz.). The absence of CH^-F cou p l i n g i s c o n c l u s i v e evidence f o r a geminal s t r u c t u r e as shown i n F i g . 21a. Each component of the t r i p l e t s has unresolved f i n e s t r u c t u r e which could p o s s i b l y be due to long range cou p l i n g o f the methyl protons w i t h remote f l u o r i n e atoms. 19 The F spectrum of N^P^F^Me^ c o n s i s t s of a doublet with m u l t i p l e t s t r u c t u r e which i s centred at 68.8 p.p.m. (Jpp = 927 Hz.). This i s again c o n s i s t e n t w i t h a geminal s t r u c t u r e ( F i g . 21a) as 6 i n SPFMe i s observed to be below 58.0 p.p.m. (3.4.1.). 4.5.3. H e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e , N^P^Me^. The ^H n.m.r. spectrum ( F i g . 24A-5.5.1.) of t h i s compound ( k i n d l y s u p p l i e d by Mr. S.M. Todd) i n CCi^ c o n s i s t s of s i x l i n e s . The main doublet, a r i s i n g from c o u p l i n g o f the methyl protons w i t h the d i r e c t l y bonded phosphorus atom, i s centred at 6 = 1.30 p.p.m. (J„ = 14.0 Hz.). Further c o u p l i n g of the methyl protons w i t h OH3F the v i c i n a l phosphorus atoms s p l i t s the main doublet i n t o t r i p l e t s , 4 J C H p being 1.2 Hz. 3 31 The P spectrum of N^P^Me^ i n D^ O (obtained at a sweep width of 250 Hz.) c o n s i s t s of a s i n g l e broad band, 6p being 80.6 p.p.m. The n.m.r. parameters o f ; t h e m e t h y l f l u o r o c y c l o t r i p h b s p h o n i f r i l e s ' and the met h y l f l u o r o c y c l o p e n t a ^ ^ i n Table 10. Table 10 N.m.r. Parameters of M e t h y l f l u o r o c y c l o t r i p h o s p h o n i t r i l e s and M e t h y l f l u o r o c y c l o p e n t a p h o s p h o n i t r i l e ( 6 i n p.p.m., J i n Hz.) PFMe PMe 2 P F 2 Compound V J P F 6Me JPMe JFMe 6 P 6Me JPMe PMe 6 P 6 F J P F N 3P 3F 5Me 65.9 53.1 1007(992) 1.78 18.8 (19.0) a 6.9 • - • 2.00 104.7 - 892 70 gem l , l N 3 P 3 F 4 M e 2 - - - - - - 1.65 14.6 1.90 - 68.8 (927) -N 3P 3Me 6 - - - - - 80.6* 1.30 14.0 . 1.2 - - - -N 5P 5F 9Me 56.8 938(984) 1.73 18.4 6.5 - - - - 130.0 67.3 866(853) -N 5P 5Me 1 0 - - - - - - 92.9* 1.38 12.4 - - - - -* i n D 20 31 19 J obtained from P n.m.r. sp e c t r a , values i n parentheses from F n.m.r. spec t r a . - 99 -CHAPTER 5 BASE PROPERTIES 5.1. I n t r o d u c t i o n The b e h a v i o u r o f p h o s p h o n i t r i l i c compounds as L e w i s bases i s 99 100 /^ "^^  2 w e l l known. ' A number o f complexes such as [NPfN^Lpj ' ^ I g X 99 ^ (X = 3AgN0 3, 2CuS0 4 o r 2ZnC£2) have been p r e p a r e d . M e t h y l c y c l o -p h o s p h o n i t r i l e s , (NPMe2) x (x = 3-4) have been r e p o r t e d t o r e a c t s m o o t h l y 68 and c o m p l e t e l y w i t h m e t h y l and e t h y l i o d i d e s t o f o r m q u a t e r n a r y s a l t s . The base s t r e n g t h s o f s e v e r a l p h o s p h o n i t r i l i c d e r i v a t i v e s have been r e p o r t e d , some o f them b e i n g g i v e n i n T a b l e 11, f r o m w h i c h i t can be seen t h a t t h e e f f e c t o f l i g a n d v a r i a t i o n i s f a r g r e a t e r t h a n t h a t o f v a r i a t i o n i n r i n g s i z e . I t i s now w e l l e s t a b l i s h e d t h a t p r o t o n a t i o n t a k e s p l a c e a t t h e r i n g n i t r o g e n atom, and a p o s s i b l e c o r r e l a t i o n o f base s t r e n g t h and s t r u c t u r e has been s u g g e s t e d ; ^ 1 ' 1 0 2 t h e e f f e c t o f a p a r t i c u l a r s u b s t i t u e n t on the base s t r e n g t h depends on b o t h " m u l t i p l e bond" and i n d u c t i v e e f f e c t s . The i n d u c t i v e e f f e c t s a r e a p p a r e n t i n t h e l a r g e d i f f e r e n c e i n pK„ between N^P^Et^ and N^P^Cit^, (Tab l e 1 1 ) , and s u c h e l e c t r o n - r e l e a s i n g s u b s t i t u e n t s as t h e d i m i n o group i n c r e a s e t h e base s t r e n g t h t h r o u g h i T - c o n j u g a t i v e i n t e r a c t i o n s . The c r y s t a l and m o l e c u l a r s t r u c t u r e s o f 44 45 N 4P 4(NMe2)g and N^P^. ( h f l ^ ) - ^ show t h a t e x o c y c l i c n i t r o g e n forms Tr-bonds w i t h p h o s p h o r u s , and t h e e l e c t r o n r e l e a s e i s s u f f i c i e n t t o make th e r i n g i a - 100 -Table 11 Base Strengths o f Trimerie and Tetrameric a b P h o s p h o n i t r i l i c D e r i v a t i v e s . 5 NHEt C Et Ph OEt SEt OPh SPh C£ 8.2 6.4 1.5 -0.2 -2.8 -5.8 -4.8 <-6.0 (8.67) (5.85) 8.1 7.6 2.2 +0.6 - -6.0 - -6.0 (8.70) (6.45) NMe, N 7P„X. 7.6 3 3 6 N 4P 4X g 8.3 3. ' pK determined i n nitrobenzene, except values i n parentheses (pK , determined i n water ) 3. b Results from D. Feakins, W.A. Last, N. Nemuchwala, and R.A. Shaw, J . Chem. Soc.,. '28404 (1965), except where s t a t e d . C D. Feakins, W.A. L a s t , and R.A. Shaw, J . Chem. Soc., 4464 (1964). - 101 -ni t r o g e n a stronger base than e x o c y c l i c n i t r o g e n . The geometry of N^P^CNft^^ a l s o suggests that the T r system i s c h i e f l y i n v o l v e d . The main f a c t o r s which a f f e c t the base strength.of a phospho-n i t r i l i c d e r i v a t i v e are: 1) the h y b r i d i s a t i o n s t a t e of the n i t r o g e n atom, 2) the extent to which the n i t r o g e n lone p a i r p a r t i c i p a t e s i n T T-bonding, and 3) the d i f f e r e n c e s i n the degree of s o l v a t i o n of the protona-ted species. The t h i r d e f f e c t i s a s p e c i f i c one, and i n the absence of d e t a i l e d i n f o r m a t i o n on p a r t i c u l a r cases i t i s d i f f i c u l t to draw any d e f i n i t e c o n c l u s i o n . The base strengths o f i n d i v i d u a l molecules are expected to depend i n par t on the h y b r i d i s a t i o n s t a t e of the lone p a i r . As the r i n g s i z e increases from N^P^ to N^P^, the angle at n i t r o g e n i n v a r i a b l y i n c r e a s e s , and, i n so f a r as t h i s i n d i c a t e s a change i n a - h y b r i d i s a -t i o n , the base strengths of the eight-membered r i n g s are, from t h i s cause alone, expected to be the h i g h e r . 1 ^ 1 Such a change i s o f f s e t by the d e l o c a l i s a t i o n of the lone p a i r i n t o the T T - o r b i t a l s of phosphorus, but the r e l a t i v e e f f e c t s i n the 6-, 8- and the 10-membered r i n g s depend on the symmetry type of the T i ^ - i n t e r a c t i o n s . I f heteromorphic, N^P^ r i n g s would be more s t r o n g l y b a s i c than N 4P 4 r i n g s , which i n tu r n are more b a s i c than N..P,- r i n g s ( r e f e r Appendix). That i s , there w i l l be a steady decrease i n the base stre n g t h w i t h increase i n r i n g s i z e . On the co n t r a r y , i f the TT - i n t e r a c t i o n i s homomorphic, an a l t e r n a t i o n - 102 -i n the base strength, with, r i n g s i z e i s expected. S o l u b i l i t y measure-ments of hydrogen c h l o r i d e i n s o l u t i o n s of the p h o s p h o n i t r i l i c c h l o r i d e s show t h a t , while the t r i m e r i s the strongest base, the pentamer i s weaker than e i t h e r the tetramer or hexamer, and these r e s u l t s are borne out by measurements of the p a r t i t i o n o f the c h l o r i d e s between s u l p h u r i c 3 a c i d and n-hexane. 5.2. The Base Strengths of M e t h y l c y c l o p h o s p h o n i t r i l e s The base strengths of m e t h y l c y c l o p h o s p h o n i t r i l e s , (NPMe 2) x (x = 3,4 and 5 ) , i n water, were determined p o t e n t i o m e t r i c a l l y using the standard procedure described i n " I o n i z a t i o n Constants of Acids and Bases" by A l b e r t and Serjeant. The pK values-were c a l c u l a t e d using a TBH +1-TH +1 the equation pK = pH + l o g - — - — — . Hexamethylcyclotriphospho-[B + ] + [ H + J n i t r i l e was k i n d l y s u p p l i e d by Mr. S.M. Todd and o c t a m e t h y l c y c l o t e t r a -p h o s p h o n i t r i l e and decamethylcyclopentaphosphonitrile were synthesized i n t h i s l a b . The samples were sublimed i n vacuo before use. pH was measured w i t h a Radiometer pH meter (model 25 w i t h expanded scale) u s i n g a Radiometer glass electrode (Type G202C) and a calomel e l e c t r o d e . The t y p i c a l t i t r a t i o n curves are shown i n F i g . 22. Only i n the case of decamethylcyclopentaphosphonitrile i s the pK value large enough to a2 be measured. The pK & values f o r N^P^Me^ l^P^Meg, and N 5 p 5 M e 1 0 a r e given i n Tables 12-14. The average pK values (from Tables 12-14) f o r N„P_Me,, N.P.Me0 and NcP.-Me,„ are 5.03 ± 0.01, 5.72 ± 0.01 3 3 6 4 4 o o o i U and 6.69 ± 0.01. For NLP-Me , pK = 3.97 ± 0.01. The steady increase - 104 -Table 12 Base Strength of N 3P 5Me 6 Concentration of N^P^Me^ at h a l f n e u t r a l i s a t i o n = 0.004M (0.0450 g. d i s s o l v e d i n 49 ml. of CO^ f r e e d i s t i l l e d water). 1 2 3 4 5 T i t r a n t 0.1 W O (ml.) pH S t o i c h i o m e t r i c Concentrations P K a a i [B] [BH +] 0 7.19 0.004 0 0.1 6.26 0.0038 0.00.02 4.98 0.2 5.97 0.0036 0.0004 5.02 0.3 5.78 0.0034 0.0006 5.03 0.4 5.62 0.0032 0.0008 5.02 0.5 5.50 0.0030 0.0010 5.02 0.6 5.40 0.0028 0.0012 5.03 0.7 5.30 0.0026 0.0014 5.03 0.8 5.21 0.0024 0.0016 5.03 0.9 5.12 0.0022 0.0018 5.03 1.0 5.03 0.0020 0.0020 5.03 1.1 4.95 0.0018 0.0022 5.03 1.2 4.86 0.0016 0.0024 5.03 1.3 4.78 0.0014 0.0026 5.04 1.4 4.68 0.0012 0.0028 5.04 1.5 4.59 0.0010 0.0030 5.05 1.6 4.48 0.0008 0.0032 5.06 1.7 4.35 0.0006 0.0034 5.06 1.8 4.21 0.0004 0.0036 5.09 1.9 4.02 0.0002 0.0038 5.12 pK = 5.03 ± 0.01 at 0.004M (using values 2-13) a l - 105 -Table 15  Base Strength of N.P,Me Concentration of N ^ M e g at h a l f n e u t r a l i s a t i o n = 0.004M (0.0600 g. d i s s o l v e d i n 49 ml. o f C0_ fr e e d i s t i l l e d water). 1 2 3 4 5 T i t r a n t 0.1 NHC£ (ml.) PH. S t o i c h i o m e t r i c concentrations P K a a l [B] [BH +] 0 7.87 0. 004 0 5.67 0.1 6.95 0. 0038 0 .0002 5.71 0.3 6.47 0 0034 0 0006 5.72 0.4 6.33 0. 0032 0 0008 5.73 0.5 6.20 0. 0030 0 .0010 5.72 0.6 6.09 0. 0028 0 .0012 5.72 0.7 6.00 0. 0026 0 .0014 5.73 0.8 5.90 0. 0024 0 .0016 5.72 0.9 5.80 0. 0022 0 .0018 5.71 1.0 5.72 0. 0020 0 .0020 5.72 1.1 5.62 0 0018 0 .0022 5.71 1.2 5.53 0. 0016 0 .0024 5.71 1.3 5.43 0 0014 0 .0026 5.70 1.4 5.31 0 0012 0 .0028 5.68 1.5 5.20 0 0010 0 .0030 5.67 1.6 5.05 0 0008 0 .0032 5.65 1.7 4.88 0 0006 0 . 0034 5.62 1.8 4.65 0 0004 0 .0036 5.58 1.9 4.34 0 0002 0 .0038 5.52 pK = 5.72 ± 0.01 at 0.004M (using values 2-12) a l - 106 -Table 14  Base Strength of N rP rMe Concentration o f N P Me 1 Q throughout = 0.004M. (0.0750 g. d i s s o l v e d i n 50 ml. of CO f r e e d i s t i l l e d water). 1 2 3 4 5 T i t r a n t S t o i c h i o m e t r i c 0.1 NHCJl pH. concentrations p K a (ml.) [BH +] :: a l [B] 0 8.60 0 0040 0 6.58 0.1 7.86 0 .0038 0 .0002 6.66 0.2 7.61 0 0036 0 .0004 6.66 0.3 7.42 0 .0034 0 .0006 6.67 0.4 7.28 0 0032 0 .0008 6.68 0.5 7.17 . 0 0030 0 .0010 6.69 0.6 7.05 0 0028 0 .0012 6.68 0.7 6.96 0 0026 0 .0014 6.69 0.8 6.87 0 0024 0 .0016 6.69 0.9 6.78 0 0022 0 .0018 6.69 1.0 6.69 0 0020 0 .0020 6.69 . 1.1 6.61 0 0018 0 .0022 6.70 1.2 6.51 0 0016 : 0 .0024 6.69 1.3 6.42 0 0014 0 .0026 6.69 1.4 6.32 0 0012 0 .0028 6.69 1.5 6.22 0 0010 0 .0030 6.70 1.6 6.09 0 0008 0 .0032 6.69 1.7 5.95 0 0006 0 .0034' 6.70 1.8 5.77 0 0004 0 0036 6.72 1.9 5.56 0 0002 0 .0038 6.84 2.0 5.30 0 0 .004 pH [BH +] (BH 2 +] .2.1/ . 5.05 ''.0 0038 •10 .0002: 3.75 2.2 4.86 0 0036 0 .0004 3.89 2.3 4.70 0 0034 0 .0006 3.93 2.4 4.57 0 0032 0 0008 3.96 2.5 4.45 0. 0030 0 0010 3.95 2.6 4.35 0 0028 0 0012 3.96 ./continued -107 -Table 14 (continued). pH [BH +] [BH 2 +] p K a 2.7 4.26 0.0026 0 0014 3.97 2.8 4.17 0.0024 0 0016 3.96 2.9 4.09 0.0022 0 0018 3.97 3.0 4.02 0.0020 0 0020 3.98 3.1 3.93 0.0018 0 0022 3.97 3.2 3.86 0.0016 0 0024 3.98 3.3 3.78 0.0014 0 0026 3.97 3.4 3.71 0.001'2: 0 0028 3.98 3.5 3.63 0.0010 0 0030 3.98 3.6 3.55 0.0008 0 0032 3.98 3.7 3.47 0.0006 0 0034 3.98 3.8 3.38 0.0004 0 0036 3.97 3.9 3.30 0.0002 0 0038 3.97 = 6.69 ± 0.01 at 0.004M (using values 3-17) = 3.97 ± 0.01 (using values 4-19) - 108 -i n the base stre n g t h w i t h r i n g s i z e may be a r e s u l t of the dominating h y b r i d i s a t i o n e f f e c t over the lone p a i r d e l o c a l i s a t i o n e f f e c t . I t i s very l i k e l y t hat the angle at n i t r o g e n i n N^P^Me^Q i s l a r g e r than that 97 i n N^P^Meg (132°), and t h i s i n t u r n confers more p-character on the lone p a i r o r b i t a l at n i t r o g e n . I f the base strength depends only on the two opposing e f f e c t s , namely the h y b r i d i s a t i o n s t a t e of the n i t r o g e n atom and the lone p a i r d e l o c a l i s a t i o n i n t o phosphorus d - o r b i t a l s , then the r e s u l t s o f the present i n v e s t i g a t i o n are compatible with a dominance of the f i r s t e f f e c t . An i n v e s t i g a t i o n of the base strengths of more b a s i c d e r i v a t i v e s i n the l a r g e r r i n g s i z e s , i n combination w i t h s t r u c t u r a l i n f o r m a t i o n , i s h i g h l y d e s i r a b l e i n e v a l u a t i n g the importance of the two e f f e c t s . 5.3. N-Methylcyclophosphonitrilium Iodides The p r e p a r a t i o n o f me t h y l c y c l o p h o s p h o n i t r i l i u m i o d i d e s , + — +-— • " 68 (N^P^Me^) I and (N^P^Me^). j ,- has been reported p r e v i o u s l y . In t h i s s e c t i o n we report the p r e p a r a t i o n of undecamethylcyclopentaphospho-n i t r i l i u m i o d i d e , (N^P^Me^^) +I by the method described i n reference 68. 1 3 1 The H n.m.r. and P n.m.r. spec t r a o f the p h o s p h o n i t r i l i u m i o d i d e s are discussed i n the next s e c t i o n . 5.3.1. P r e p a r a t i o n of Undecamethylcyclopentaphosphonitrilium '-Iodide, An excess of methyl i o d i d e was added to decamethylcyclopenta-p h o s p h o n i t r i l i c (1.00 g., 2.67 mmoles) and the mixture was heated under - 109 -r e f l u x f o r 2 hr. The excess of methyl i o d i d e was removed and the c r y s t a l l i n e s o l i d product was washed s e v e r a l times with dry ether under n i t r o g e n . The a n a l y s i s o f the c r y s t a l l i n e product (1.10 g.), m.p. ~ 200°(d), corresponded to N 5 P 5 M e n I . (Found: C, 25.52; H, 6.52; N, 13.71; I , 24.44; N^Me.^1 re q u i r e s C, 25.53; H, 6.38; N, 13.54; I , 24.60%). The i o n i c nature of i o d i n e i n the compound was demonstrated by p r e c i p i t a t i n g Agl q u a n t i t a t i v e l y from an aqueous s o l u t i o n . Although i t i s i n t e r e s t i n g to note that methylcyclophospho-n i t r i l e s are analogous to p y r i d i n e i n forming the p h o s p h o n i t r i l i u m i o d i d e s w i t h CH^I and 0 2 ^ 1 , they do not form, u n l i k e p y r i d i n e , the corresponding phenacyl s a l t s . Since the base s t r e n g t h of N^P^Meg pK & 5.72) i s greater than that of p y r i d i n e (pK 5.23) lack o f formation of phenacylphosphonitrilium s a l t s can probably be a t t r i b u t e d t o s t e r i c f a c t o r s . The attempted r e a c t i o n to prepare the phenacyl d e r i v a t i v e s i s described i n the f o l l o w i n g experiment. To N^P^Meg (0.1 g.) i n ether (10 ml.) phenacyl bromide (0.3 g.) was added and the mixture was heated under r e f l u x f o r 2 h. The solvent was removed and the r e s i d u a l s o l i d was found t o co n t a i n no phospho- ; n i t r i l i u m bromide since the water s o l u b l e p o r t i o n d i d not p r e c i p i t a t e AgBr. The water s o l u b l e m a t e r i a l was found to be N^P^Meg by comparison of i t s i . r . spectrum with that of an authe n t i c sample. - 110 -5.4. The Nuclear Magnetic Resonance Spectra of N-methylcyclophospho- n i t r i l i u m Iodides. 5.4.1. H e p t a m e t h y l c y c l o t r i p h o s p h o n i t r i l i u m Iodide, (N^P^Me.,)*!". The ~^H n.m.r. spectrum o f (N,jP3Me7) + I i n D^ O c o n s i s t s o f a low f i e l d 1:2:1 t r i p l e t and two high f i e l d doublets of r e l a t i v e areas 1:4:2. The CH^ resonance (6 = 2.92 p.p.m.) i s s p l i t by coupling with P^ i n t o a 1:2:1 t r i p l e t ( J = 10.9 Hz.). The 3 A low f i e l d doublet, a r i s i n g from c o u p l i n g o f CH^ protons w i t h P^, i s centred at 6 = 1.92 p.p.m. ( J r H i p = 13.3 Hz.). Furth e r , each com-L H 3 FA ponent of the doublet seems to be s p l i t i n t o a doublet ( s i m i l a r to the + — u p f i e l d doublet o f (N^P^Me^) I shown i n F i g . 23). As a p r e f e r e n t i a l c o upling of CH^' protons with Pg and not with P^ seems q u i t e u n l i k e l y , each component of the low f i e l d doublet may p o s s i b l y c o n t a i n four t r a n s i t i o n s which are not completely r e s o l v e d . The high f i e l d doublet (centred at 6 = 1.68 p.p.m., J r H n p = 14.2 Hz.) i s s p l i t i n t o a 1:2:1 L H 3 PB t r i p l e t ( J ^ Hp = 1.3 Hz.) due to coupling o f CH, with P^. I r r a d i a -3 A t i o n at the phosphorus resonance frequency (40.482, 800 MHz.) leaves the high f i e l d doublet unchanged and causes the t r i p l e t and the low f i e l d doublet to c o l l a p s e to a s i n g l e t . F u r t h e r , a l l the f i n e s p l i t t i n g s disappear. I r r a d i a t i o n at the phosphorus resonance frequency - I l l -(40.482, 320 MHz.) leaves the t r i p l e t and the low f i e l d doublet unchanged and causes the high f i e l d doublet to c o l l a p s e to a s i n g l e t . Again, a l l the f i n e s p l i t t i n g s disappear. This shows p o s i t i v e l y that the f i n e s p l i t t i n g observed i n the low f i e l d doublet i s a r e s u l t o f lone range c o u p l i n g and not a chemical s h i f t d i f f e r e n c e . The CH^ group must t h e r e f o r e e i t h e r l i e i n the PNP plane or be f l i p p i n g so f a s t that the four CH^' protons have an averaged i d e n t i c a l environment. The-former suggestion i s supported by the c r y s t a l s t r u c t u r e s o f c o b a l t 1 ^ 3 and c o p p e r 1 ^ h a l i d e complexes of N^P^Meg and that of i 46 N 3P 3C£ 2(NHPr )HC£ ( F i g . 6) i n which the adduct atom l i e s i n the NPN plane. The occurrence of two d i f f e r e n t r i n g conformations i n the same 104 c r y s t a l shows that t h e i r energies d i f f e r only s l i g h t l y , and that deformation i s easy. The 6 and J values are given below. 5(p.p.m.) J(Hz.) CH 3 2.92 C H 3 P A 10.9; C H 3 ' 1.92 C H 3 , P A 13.3 CH 3" 1.68 C H 3 " P B C H 3 " P A 14.2 1.3 31 The r e l a t i v e P chemical s h i f t (from the decoupling frequencies) S p -S p i s 11.9 p.p.m. B A 31 The P spectrum o f (N^P^Mej) I i n D^ O (obtained at a sweep width o f 1000 Hz.) c o n s i s t s of two broad s i n g l e t s o f r e l a t i v e areas - 112 -2:1; 6 p A and 6 p B being 64.2 p.p.m. and 76.6 p.p.m. r e s p e c t i v e l y . 5.4.2. Nonamethylcyclotetraphosphonitrilium Iodide, ( N ^ M e g ) * ' l ~ . The 1H n.m.r. spectrum o f ( N 4 P 4 M e g ) + I ~ ( s o l u t i o n i n CHC£ 3) i s shown i n F i g . 23. I t i s s i m i l a r to that o f ( N 3 P 3 M e 7 ) + I ~ , except that the r e l a t i v e areas o f the three kinds of bands are i n the r a t i o 1:4:4. The low f i e l d doublet shows unresolved s t r u c t u r e , and the apparent doublet s p l i t t i n g i n the high f i e l d doublet p o s s i b l y contains four t r a n s i t i o n s f o r reasons given e a r l i e r . The sp e c t r a 31 obtained by i r r a d i a t i o n at the P resonance frequencies (40.481, 650 MHz. and 40.482, 280 MHz.) are shown i n F i g . 23, and make c l e a r that the low and high f i e l d doublets r e s u l t from c o u p l i n g o f CH^' protons w i t h P^ and that o f CH^" protons w i t h P . Since a l l the f i n e s p l i t t i n g s disappear on i r r a d i a t i o n , they a r i s e from long range couplings and not from chemical s h i f t d i f f e r e n c e s . The 6 and J values are given below. <5(p.p.m.) CH 3 3.14 CH 3' 2.05 CH 3" 1.55 J(Hz.) C H 3 P A 11.2 C H 3 , P A 13.5 C H 3 " P B 12.6 V CH, j 3 ll —•!>-i i \ r H3 :'/ PJ CH 3 CH, \ . 3 CH3 / 328 3.03 2.78 2.53 2.03 1.78 El 153 1.28 § 2.50 2.25 2.00 1.75 § 1.50 1.30 3.25 3.00 2.75 2.50 2.25 2.00 1.75 31. H n.m.r. spectrum of nonamethylcyclotetraphosphonitrilium i o d i d e . A. Normal spectrum. B and C. Spectra obtained by i r r a d i a t i o n at the " i P resonance frequencies. 1-50 § 125 - 114 -31 The r e l a t i v e P chemical s h i f t (from the decoupling frequencies) 6 p -6 p i s 15.6 p.p.m. B FA 3 The P spectrum of N^P^Meg I - i n D 20 (obtained at a sweep width of 1000 Hz.) c o n s i s t s of two broad s i n g l e t s o f r e l a t i v e areas 1:1, 6 p and 6 being 70.0 p.p.m. and 83.5 p.p.m. r e s p e c t i v e l y . A FB + -5.4.3. Undecamethylcyclopentaphosphonitrilium Iodide, (N^P^Me^) I 1 The H n.m.r. spectrum of CH*" ^ // CH~ (N rP rMe 1 1) + I i n CHC£_ c o n s i s t s o f -••-vv. < \ ^^ i '~> 5 5 1 1 3 a low f i e l d 1:2:1 t r i p l e t , and *' v N , 3 three high f i e l d doublets, t h e i r ^^3\l + I /^^3 r e l a t i v e areas being i n the r a t i o * ^ B V ' 1:4:4:2. The i n t e r p r e t a t i o n o f M \ D ^ — ' ' M 1 / \ the H n.m.r. spectrum of CH* CH* ( N 4 P 4 M e g ) + l " (5.4.2.) suggests that these bands should a r i s e r e s p e c t i v e l y from the c o u p l i n g o f CH^ protons with P^, CH^' protons w i t h P^, CH^" protons w i t h Pfi, and CH^" protons with P^ ,, and that the s h i e l d i n g of the methyl protons should be i n the i n c r e a s i n g order CH^"' > CH^ '' > CH^' > CH^. In f a c t , the s p e c t r a 31 obtained by i r r a d i a t i o n at the P resonance frequencies (40.482, 100 MHz. and 40.481, 256 MHz.) unambiguously show the above assignment to be c o r r e c t . The 6 and J values are: - 115 -6 (p.p.m.) J(Hz.) 3.05 11.5 2.04 13.5 1.54 12.4 mi 1.43 11.5 31 The r e l a t i v e P chemical s h i f t (from the decoupling frequencies) width of 1000 Hz.) c o n s i s t s o f two broad s i n g l e t s of r e l a t i v e areas 3:2; 6 and 6 (P = P and P„) being 74.1 p.p.m. and 90.4 p.p.m. 5.5. Reactions of N-Methylcyclophosphonitrilium Iodides Although m e t h y l c y c l o p h o s p h o n i t r i l e s are analogous to p y r i d i n e i n forming the quaternary i o d i d e s , the r e a c t i o n s o f p h o s p h o n i t r i l i u m and p y r i d i n i u m s a l t s are d i f f e r e n t . In t h i s s e c t i o n some r e a c t i o n s o f ph o s p h o n i t r i l i u m i o d i d e s are described. 5.5.1. P y r o l y s i s The a c t i o n of heat on 1 - a l k y l p y r i d i n i u m s a l t s may lead to a rearrangement of the 1-substituent to the 2 and 4 p o s i t i o n s . 1 ^ 3 This change i s known as the Ladenburg rearrangement. Sometimes the 3-isomer i s formed i n very small amount. A l l the methylphosphonitrilium i o d i d e s decompose around 200°. I t i s of i n t e r e s t to i s o l a t e and c h a r a c t e r i z e , i f p o s s i b l e , the products r e s u l t i n g from such decomposition on heating. = 20.8 p.p.m. The "^P spectrum of (N,.P<-Me^) + I i n D 20 (obtained at a sweep - 116 -106—108 I t has been reported p r e v i o u s l y that bigger p h o s p h o n i t r i l i c r i n g s break down to smaller ones i n a mass spectrometer. This k i n d of behaviour has a l s o been observed p r e v i o u s l y i n other experiments, f o r instance a small amount of N^P^Fg was obtained i n the p r e p a r a t i o n of 109 N 6 P ^ F 1 2 by the r e a c t i o n of N^PgCil^ w i t h KSG^F. Such a r i n g contrac-t i o n has been p r e v i o u s l y r e p o r t e d " * ^ to occur i n the r e a c t i o n of PhMgBr with N 4P 4CJlg. S i m i l a r r i n g c o n t r a c t i o n has a l s o been observed i n the rearrangement of N - l i t h i o c y c l o s i l o x a z a n e s . I n the present i n v e s t i g a -t i o n , we have obtained small amounts of N-P-Me.. and N„P.Me0 from the o o 6 4 4 o decomposition of undecamethylcyclopentaphosphonitrilium i o d i d e . A small sample of (Nj-Pc.Me^) + I (0.8 g.) was decomposed at 350-400° to give a dark mass, which on e x t r a c t i o n w i t h l i g h t p e t r o l gave a white s o l i d (0.17 g.). This product showed three spots on examination by t h i n l a y e r chromatography on an alumina p l a t e . Pre-p a r a t i v e t h i n l a y e r chromatography of t h i s s o l i d product (0.15 g.) gave two components. a) 0.076 g., b) 0.014 g. The mass spectrum of (a) showed a medium peak at m/e 225 and an intense one at m/e 210. This component was i d e n t i f i e d as N^P^Me^, but i t showed a l s o an impurity peak at m/e 289. I t s i d e n t i t y was confirmed by comparison of the n.m.r. sp e c t r a ( F i g . 24A and C) and i . r . s p e c t r a w i t h those of an authentic sample. [Found: C, 33.05; H, 8.02; N^P^Me^ re q u i r e s C, 32.00; H, 8.00%;];. Component (b) was s i m i l a r l y i d e n t i f i e d as N 4P 4Meg by comparison of the mass, i . r . , and *H n.m.r. ( F i g . 24B and D) spectra w i t h those of an a u t h e n t i c sample. [Found: C, 31.68; H, 7.99; $ r u = 1.30 p.p.m. 3 JCH 3P = 14.0 Hz. J-3P 1.2 Hz. 1.44 1.39 1.29 CH, I 3 ^ = 1.30 p.p.m. CH 3P C H 7 S n _ . ( / CH.P 7 3  C H3 = 14.0 Hz, = 1.2 Hz. 1.16 g CH 6 C H 3 = 2 - 3 4 P'P-m-J - 12.0 Hz. 1.42 1.37 1.32 V w \ | H 3 ' 1.34 p.p.m. JCH P = 1 2 , 0 H z < 1.27 1.22 § 1.40 1.35 1.30 1.25 1.20 § F i g . 24. H n.m.r. s p e c t r a o f h e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e and o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e . A. Spectrum o f N ^ M e ^ B. Spectrum of N ^ M e g . C. Spectrum of Component a (.5.5.1.) D. Spectrum of component b (5.5.1.) - 118 -N 4P 4Me g r e q u i r e s C, 32.00; H, 8.00%). 5.5.2. Hoffman E l i m i n a t i o n I t i s known that quaternary ammonium hydroxide, R^I^ROH-, on p y r o l y s i s gives NR^ and an o l e f i n i f the group R has a '3>hydrogen atom. We have observed that the quaternary hydroxide (N.P.Me oEt) +0H~' on heating gives N 4P 4Meg. The N-ethyl quaternary i o d i d e (N 4P 4MegEt) + I~* (0-25 g.) d i s s o l v e d i n water was t r e a t e d w i t h &g2®' The s o l u t i o n was ' f i l t e r e d from Ag s a l t s and the f i l t r a t e was evaporated to dryness. The s o l i d residue was sublimed i n vacuo to give a c r y s t a l l i n e sublimate (0.13 g.), which was i d e n t i f i e d as, N 4P 4Meg by comparison o f i t s i . r . spectrum with that of 12 an a u t h e n t i c sample, m.p. 162° ( l i t . 162-163°). 5.5.3. Sodium Borohydride Reduction Metal hydride r e d u c t i o n of p y r i d i n i u m s a l t s to give dihydro-p y r i d i n e i s w e l l k n o w n 1 1 2 / S i m i l a r r e d u c t i o n of (N.P.Me„) + I w i t h 4 4 y NaBH 4 was found to cleave the p h o s p h o n i t r i l i c r i n g . Sodium borohydride (0.3 g.) and methanolic sodium hydroxide (1 ml.) were added to nonamethylcyclotetraphosphonitrilium i o d i d e (0.3 g.) d i s s o l v e d i n a c e t o n i t r i l e (15 ml.). The r e a c t i o n mixture was s t i r r e d f o r 24 h. The solvent was then removed and the residue was ext r a c t e d w i t h p e t r o l . There was no p e t r o l s o l u b l e product. However, e x t r a c t i o n w i t h CHCZ^ gave a h i g h l y viscous l i q u i d w i t h a smell of ammonia. I t i s very l i k e l y - 119 -that the p h o s p h o n i t r i l i c r i n g had cleaved i n the r e a c t i o n . Although the i . r . spectrum of the CHCZ^ s o l u b l e product showed a strong absorp-t i o n around 1200 cm 1 , the complete spectrum was complicated and the i n t e r p r e t a t i o n i n c o n c l u s i v e . - 120 -CHAPTER 6 VIBRATIONAL SPECTRA OF METHYLFLUOROCYCLOPHOSPHONITRILES AND METHYLCYCLOPHOSPHONITRILES 6.1. I n t r o d u c t i o n Although the v i b r a t i o n a l s p e c t r a o f the p h o s p h o n i t r i l i c u ,.A »S6}, 113-117 . . ., r x m r o . :36;, 118-124 h a l i d e s , i n p a r t i c u l a r the c h l o r i d e s , (NPCJ^)^ 4> have re c e i v e d considerable a t t e n t i o n i n recent years, much l e s s i s known about the v i b r a t i o n a l s p e c t r a of p a r t i a l l y s u b s t i t u t e d d e r i v a t i v e s . An i n v e s t i g a t i o n of the v i b r a t i o n a l s p e c t r a , i n some d e t a i l , o f the 125 126 127 t r i p h o s p h o n i t r i l i c c h l o r i d e bromides, ' c h l o r i d e f l u o r i d e s and 128 dimethylamino c h l o r i d e s and bromides, has been reported r e c e n t l y , and assignments of the fundamental v i b r a t i o n s have been proposed. There i s pronounced v i b r a t i o n a l c o u p l i n g , p a r t i c u l a r l y i n the p h o s p h o n i t r i l i c f l u o r i d e s , which tends to spread the frequencies over a wide range. The s p e c t r a of m e t h y l f l u o r o c y c l o p h o s p h o n i t r i l e s show many of the same features as those of the other d e r i v a t i v e s , and some assignments can be made w i t h f a i r assurance. The methyl groups do, however, introduce d i f f i c u l t i e s , i n that f o r instance the CH^ r o c k i n g modes are expected i n the same region (900-1000 cm ^) as the P F 2 antisymmetric s t r e t c h i n g modes, and, as i n the hydrocarbon f i e l d , i t may take some time before the assignments o f t h i s type o f v i b r a t i o n are c e r t a i n . Although s e v e r a l authors have reported assignments o f p h o s p h o n i t r i l i c r i n g v i b r a t i o n s , they o f t e n d i f f e r a p p r e c i a b l y . The wide frequency range covered does - 121 -however suggest the existence of a s t r o n g l y coupled e l e c t r o n i c system i n the molecules. The t e n t a t i v e assignments o f f e r e d i n the f o l l o w i n g pages do not, t h e r e f o r e , a l l have the same s t a t u s . Some are s u f f i c i e n t l y c e r t a i n to be h e l p f u l i n confirming the o r i e n t a t i o n o f s u b s t i t u e n t s and deducing molecular symmetry, but there i s s t i l l i n s u f f i c i e n t d e t a i l e d knowledge to discuss p r o f i t a b l y the mutual e l e c t r o n i c i n f l u e n c e s of the r i n g and e x o c y c l i c groups, as was done f o r the phenyl d e r i v a t i v e s . In t h i s Chapter, the i . r . s p e c t r a (covering the region 250-1500 cm. "*•) of the m e t h y l f l u o r o c y c l o p h o s p h o n i t r i l e s and methylcyclo-p h o s p h o n i t r i l e s are discussed; they are i l l u s t r a t e d i n F i g s . 25-34. In some cases Raman s p e c t r a are in c l u d e d . The i . r . s p e c t r a were recorded on a P e r k i n Elmer Gr a t i n g Spectrophotometer 457. The l i q u i d samples were examined as t h i n f i l m s and the s o l i d s as n u j o l m u l l s . 1 In a d d i t i o n , a l l the samples were examined as d i l u t e s o l u t i o n s i n CS^ and CCZ^. The Raman sp e c t r a were taken on a Cary 81 Spectrometer equipped w i t h a Spectra-Physics 125 l a s e r source. The l i q u i d s were st u d i e d as neat samples and the s o l i d s as powder or s o l u t i o n s i n CHCZ^, C^H^ or CCZ^. The fundamentals are d i v i d e d f o r convenience of d i s c u s s i o n - i n t o two types o f v i b r a t i o n . 1) Those i n which the methyl groups are considered as p o i n t masses and which are c a l l e d the s k e l e t a l v i b r a t i o n s and 2) those i n which the v i b r a t i n g motion i s l a r g e l y confined to the methyl groups and which are c a l l e d the methyl v i b r a t i o n s . The d i v i s i o n i s j u s t i f i e d because the i n t e r a c t i o n between the s k e l e t a l and methyl v i b r a t i o n s i s sm a l l . The s k e l e t a l v i b r a t i o n s are f u r t h e r subdivided i n t o 1) those belonging to the p h o s p h o n i t r i l i c r i n g , 2) those belonging to the PF„ and - 122 -PF groups and 3) those belonging t o the P-C and PC groups. The approx-imate atomic motions i n each normal mode are shown i n F i g . 35"for the methyl groups and f o r a t r i m e r i c d e r i v a t i v e N^P^X^. The bands i n the region 400-200 cm. ^ normally a r i s e from wagging, t o r s i o n a l and out-of-plane r i n g deformation modes and t h e i r assignments are u n c e r t a i n . In t h i s Chapter, t h e r e f o r e , no attempt i s made to propose any assignments f o r these bands. The PF 2 antisymmetric s t r e t c h i n g region 900-1000 cm.""1', as mentioned e a r l i e r , contains more l i n e s than expected. In view of t h i s complexity and i n the absence of s p e c t r a l data o f deuterated d e r i v a t i v e s i t i s very d i f f i c u l t to make a reasonable choice. The methyl v i b r a t i o n s , on the other hand, are s i g n i f i c a n t l y i n s e n s i t i v e to v i b r a -t i o n a l c o u p l i n g ; t h e i r assignments seem to be w e l l e s t a b l i s h e d . However, even here an i n v e s t i g a t i o n o f the i . r . s p e c t r a o f the deuterated d e r i v a t i v e s would be necessary to e s t a b l i s h the CH^ r o c k i n g and t w i s t i n g modes. V (PNP) i s w e l l e s t a b l i s h e d i n a l l the p h o s p h o n i t r i l i c d e r i v a -as t i v e s and i s observed i n the region 1290-1410 cm. ^ i n (NPF,,)^ ^- This frequency i s found to be very dependent on the e l e c t r o n e g a t i v i t y of the su b s t i t u e n t attached to phosphorus f o r a p a r t i c u l a r r i n g s i z e (Table 8; 2.5.). The other r i n g frequencies reported i n t h i s Chapter are i n agreement with those reported p r e v i o u s l y . A l l frequencies are given i n cm. u n i t s . fih/4-13ZZ. IS7S-JI9Z /C62 1— IIOO • %5 %0 S08 710 I Oil 960 729 5o5 550 U-3S b-oo - l . r . 338 1 l4-oo l3oo /SOO looo 9oo 80O 700 600 $00 4-00 3oo 7 2 7 , / S k w j l j y . 93(/.9oo? 860& 78(J T 46S; 670,? 4> Raman 3oi 323, /4-00 I3oo 1&00 noo looo 9po Soo loo &00 Soo F i g . 25. I.R. and Raman spec t r a of mo n o m e t h y l p e n t a f l u o r o c y c l o t r i p h o s p h o n i t r i l e (N^P^Fc-Me). 3oo A l l f requencies are given i n cm. ^ u n i t s VtrlO i.r. 9s» 735T l4-oo 13/5 13.90 i3oo IRoo 1078 //OO 973 ??8 IOOO 880 8S7 9/o 9oo 835 76/s*. BOO &60 700 Sip 55S 6oo 4-Oo 34-S S9Z 3oo Raman 556,p 2.99, df, f4-3,0, df3 9% 54^. 3— 7oO /4-oo l3oo i&oo t noo looo ^qo Soo 7oo Goo 5oo *+oo F i g . 26. I . r . and Raman s p e c t r a o f monomethylheptafluorocyclotetraphosphonitrile (N^P^F^Me). f4-Z5~ i.r. 13/5 /&8S~ 10IS 966 9*5", 998 937S6 889 839 253 808 loo 60S 5/0 315 l4-oo l3oo /Soo J/00 1000 9oo 800 loo 1 600 1)00 4-00 3oo 999, p <t3*,*t> 253,? g ' ° ' ^ T 3— loo Raman 3,69, df, l^-OO F i g . l3oo 1 £00 //oo looo .^po Soo loo Goo Soo ^00 • '. . • ' . • sT -2.7. I . r . and Raman sp e c t r a o f monomethylnonafluorocyclopentaphosphonitrile (N^P^FgMe). 3 00 l4-oo IS7/ /3oo i3oo /Soo l loo 930 lOO * * J lL looo 878 S60 9oo 778 758 7iO 80O 700 4-6S 54-$ 4-S.o i.r. •335-600 $00 4-00 3oo 1 L 14-28 14-03 9 6 3 - r U 7/o?p«„ca^) 423 Raman \S79 3/p 338 t*hOO 1300 I l&OO II0O I looo <?oo Soo 7oo Goo SoO ^00 Zoo F i g . 28.. I . r . and' Raman s p e c t r a o f 1 , 1 - d i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e (1,l-N 3P 3F 4Me 2) 1390 !3o$ r l4-oo /S75•5^ i3oo I //oo /380j /3 9^ ; /4-C70 l3oo I l&OO I too * ^33 ( ruyd) 1,1-N P F Me 4 4 6-2 9.6/ g 7 ? llO 98S So,/; ' 7 6 a S<?5" 6 5"-6 looo 9oo 398 330 Soo 700 600 $00 4-oo 3oo t r a n s - l , 5 - N 4 P 4 F 6 M e 2 IZo 940 975-r looo 8s<? 8 0 3 S05 650 foo 800 loo Goo Soo 4-oo 3 00 F i g . 29. I . r cyc . s p e c t r a o f 1 , 1 - d i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (1,1-N.P.F,MeJ and tra n s - 1 , 5 - d i m e t h y l h e x a f l l o t e t r a p h o s p h o n i t r i l e (1,5-N 4P 4F 6Me 2>. 1 4 4 b 1  uoro-13 75" 1.1.3-N 4P 4F 5Me 935 87{ 878 69-8 96c 8/0 975 832, \?56 776 4-n 1302. 99o 9/8 75"? 12)1, &7/SA. S39 375" I4-oo l3oo /SOO //OO IOOO 9oo Soo 700 6oo Soo 4-oo 3oo /37o l , l , 5 - N 4 P 4 F 5 M e 3 89o 9& /3/Z , / 3 ° 5 " 9-ro 975\ 14-00 1300 t&oo I IIOO 7oo 278SK 8SO 773 7so 4-89 6 fosz SA. 4-4-0 IOOO 9oo 8oo 7oo r _ Goo Soo 4-00 3oo F i g . 30. I . r . s p e c t r a o f 1 , 1 , 3 - t r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (1,1,3-N.P.F Me ) and 1,1,5-trimethyl-p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (1, l^S-N'P F^Me^) . 4 4 5 3 879 _ L _ 763 7*7 Raman £66 34-& I4-00 F i g . 3-1. !3oo i Zoo I 1 IOOO 9oo Soo i loo Goo Soo U-OO 3oo I . r . and Raman sp e c t r a o f 1 , 1 , 5 , 5 - t e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e ("1,1.5 5-N P F Me T j v . , J , - 4 4 4 4 l/2§~ 1 i . r . 1238 IS 90 i ; r 14-00 i3oo ISoo 1100 V30 toio 1000 &62 ... On r\MJjoL ) 898 9oo 6 8 0 747 79,5 77/ &?0 74LO 7/5" 600 372. 4-3/ 4 % 4so 56/ 3o£. _1 3oo I4-4& /<28S Raman 95-7 79o 866 Si 6 J J 7 m 76S 373 36 3 1 I'hOO 13 00 \ 12,00 1100 1 looo r 9oo . Soo r 7oo Goo Soo U-oo 3 00 F i g . 32. I . r . and Raman s p e c t r a o f h e x a m e t h y l c y c l o t r i p h o s p h o n i t r i l e (N_P_Me,) 3 3 6 mo | / 4 2 2 /4-/S-I /4-oo 1^/if.^f, /4-Z6 df, noo as a. i MO 9Z0 995" lOU-o i3oo /Soo //oo looo %7o 2e>o 9oo 860 ~7bO 736 787. 7oO 80O ~700 76W 761 i.r. 4-33 .630 &18 &60 SA 390 600 Soo 4-oo Soi^cccl^.) $88, f> A33 R80 3oo Raman 3sv 36/ i'4-oo l3oo t&Oo _ _ 1 — 1100 1 looo 9oo Soo 3 7oo Goo Soo 4-oo 3 00 F i g . 33,. I . r . and Raman s p e c t r a of o c t a m e t h y l c y c l o t e t r a p h o s p h o n i t r i l e fN P Me 1 I25S '3oo U90 1430 iWlSt, 10^8 1400 1300 /SOO 9/8 980 93o //OO — r IOOO 87°C8S7, 7 6 / 739 loo 79o 6ti Ab3 6 9 o 494 4-SZ. 4-38 3?4-U3-0 3 6 ? 333 Boo loo 6oo 5 0 o 4-oo F i g . 34. I . r . spectrum o f decamethylcyclopentaphosphonitrile (N-Pj-Me^). Methyl V i b r a t i o n s Ring V i b r a t i o n s (assumed molecular symmetry D,, ) PX~ V i b r a t i o n s A S Y M M E T R I C S T R E T C H S Y M M E T R I C S T R E T C H A S Y M M E T R I C D E F O R M A T I O N S Y M M E T R I C D E F O R M A T I O N TORSION Those CH bonds which are s t r e t c h i n g are la b e l e d S and those c o n t r a c t i n g C. Those HCH angles which become s m a l l e r are l a b e l e d B f o r bend, and those which become l a r g e r , 0 f o r open. A dash means no change. r i n g b r e a t h i n g r i n g e l o n g a t i o n -*—«-V V t r i g o n a l s t r e t c h i n g P=N s t r e t c h i n g v (PNP) t r i g o n a l deformation asymmetric deformation P< X X symmetric s t r e t c h i n g A s c i s s o r s bending Crt ) P / x-wagging X X antisymmetric s t r e t c h i n g A P \ x x r o c k i n g \ ) P X' t o r s i o n Co) A, out o f plane deformation out of plane deformation F i g . 35 . The approximation atomic motions i n each normal mode f o r the methyl groups and f o r a t r i m e r i c d e r i v a t i v e N 3P 3X 6. - 134 -6.2. Monomethylfluorocyclophosphonitriles, N n p n F 2 n l M e w n e r e n = 5~ 5-R i.r. 3014,dp.;. 3018w 2939,s,p 2940m 1416,dp 1418m 1322 808* Methyl V i b r a t i o n s R i.r. 3020w,dp 3018vw 2941ms,p 2938w 1420,dp merged with v a s(PNP) 1315 857 f N 6P 5F f lMe R i.r. 3013w,dp 2940ms,p 2940vw 1419,dp merged wi t h v a s(PNP) 1315 v a s(CH) v s(CH) 6 a s ^ 6 S(CH 3) probably CH 3 r o c k i n g v i b r a t i o n absent i n other monosubstituted d e r i v a t i v e s N 3 P 3 F 5 X ^ X = C £ j B r ' N M e 2 a n d N C S'- ) t absent i n other monosubstituted d e r i v a t i v e s N 4P 4F 7X. S k e l e t a l V i b r a t i o n s : Many of the assignments i n t h i s s e c t i o n are p o s s i b l e because the sp e c t r a of the monosubstituted d e r i v a t i v e s N3P3F,.X, where X = NMe2, C£, Br or NCS, have many bands i n common, which are th e r e f o r e a t t r i b u t e d to the N 3 P 3 F 3 group. A s i m i l a r statement a p p l i e s to compounds N 4P 4F^X and N[-Pj-FgX. Frequencies depending on the attachment of the methyl group can t h e r e f o r e o f t e n be picked out e a s i l y -P-C frequencies R i . r . 785 p 790 v(P-C) - absent i n other monosubstituted d e r i v a t i v e s . - 135 -R i . r . 436(p?) 438 : p(P-C) - absent i n other monosubstituted d e r i v a -t i v e s . v(P-C) - absent i n other monosubstituted d e r i v a -t i v e s . I t i s very l i k e l y that the weak Raman band i s p o l a r i z e d . p(P-C) - P o s s i b l e a l t e r n a t i v e assignment w i t h P(PF 2) i . p . v(P-C) - absent i n other monosubstituted d e r i v a -t i v e s . p(P-C) probably PF,, and P-F frequencies Comparison o f the spe c t r a o f the monosubstituted d e r i v a t i v e s among themselves and with those of N^P^F^ confirms some e a r l i e r a s s i g n -ments and suggests a l t e r a t i o n s to others. V(PF), v ( P F 2 ) i i In N^P^F^ (assumed symmetry D,^) these have species + E ; + I I i t A„ + E (primed sym., double primed asym.). In the monosubstituted N^P^Me R i . r . 733 (?) 735 475 p 472 R i . r . 700 482 dp? 488 - 136 -d e r i v a t i v e s the degenerate l e v e l s are s p l i t , one A i n each becoming V ( P - F ) , v ( P - X ) , so that the species now are . A~ v (P-X) + A* V ( P F 2 ) s , i . p . + A" V ( P F 2 ) s , o.p. + A' v ( P F 2 ) A S , i . p . + A" v ( P F 2 ) A S , o.p. + A* v ( P F ) . ' 1 'VA "> -1 In N 3 P 3 F 6 , A and E v i b r a t i o n s are e s t a b l i s h e d 0 0 ' a t 741, 860 cm. , and from t h e i r p o s i t i o n s , i n t e n s i t i e s and p o l a r i z a t i o n ^ P F ^ s ' i - P -and o.p. are l o c a t e d at 727(p) (729 i . r . ) cm. - 1 and 860 (dp) (860 i . r . ) cm."1 i n N 3P 3F 5Me. V(P-C) i s at 790 cm. - 1. The choice of a n t i -symmetric v i b r a t i o n s i s not obvious, because there are too many l i n e s i n the appropriate r e g i o n . The most l i k e l y assignments seem to be f o r " -1 " -1 ^3^3^6' ^ ' C m ' (Raman a c t i v e o n l y , dp) and A 2 , 960 cm. ( i . r . o n l y ) . In N,P„FJV[e these correspond to V (PF,,), i . p . (931 cm. 1 , dp) O O *D cLS Z. and V ( P F 9 ) , o.p. (971, dp; 972 cm.'1, i . r . ) , and v(P-F) at 945 cm."1 ( i . r . o n l y ) . This assignment and correspondence i s supported by the absence of the f i r s t , the weakness of the second and the strength o f the t h i r d i n N-^P^Me. 6(P-F), 6(PF 2) p(P-F) seems c e r t a i n l y assignable at 400 cm. 1 i n N 3P 3F 3Me; i t i s absent i n ^ 3 P 3 F ^ (and other evenly j s u b s t i t u t e d d e r i v a t i v e s except N 3 P 3 F 4 M e 2 ) , and present i n N 3P 3F 5C£ (400 cm. - 1) and N ^ F ^ r (398 cm. - 1). 6 ( P F 2 ) , i . p . seems e s t a b l i s h e d at 566 cm. 1 i n Ji ^ P . ^ ^ , and i s _1 ' assigned at 550-551 cm. i n N 3P 3F 3Me. A d e f i n i t e E v i b r a t i o n at - 137 -464-465 cm. - 1 i n ^ P , ^ becomes 6 ( P F 2 ) , o.p. at 465 cm. 1 i n N 3P 3F 5Me. " -1 The p o s s i b l e choice of p ( P F 2 ) , i . p . (A 2 ) f o r N 3 P 3 F 6 i s 512 cm. -the corresponding band i n N 3P 3F 3Me i s at (510 R) 505 cm.-"''. N,P 4F yMe V(PF), V(PF 2) The symmetry species of the P F 2 s t r e t c h i n g v i b r a t i o n s should be t I I _2 3A + 3A . The intense p o l a r i z e d Raman l i n e at 605 cm. i n N.P.F 0 i s 4 4 o assigned to v g ( P F 2 ) , i . p . The corresponding band i n N^P^F^Me i s at 609 (p) cm. ^; t h i s i s absent i n the i . r . spectrum. The degenerate —1 '36~ symmetric s t r e t c h i n g v i b r a t i o n i s at 770 cm. i n N.P.F . This s p l i t s 4 4 8 to give v(P-C) at 735 cm"1 and ^ C P F ^ , o.p. at 835 cm. - 1. The other V g ( P F 2 ) , o.p. i s at 910 cm. 1 ( t h i s i s weakly present i n the i . r . spectrum o f N^P^Fg at 895 cm. 1 and i n other monosubstituted d e r i v a t i v e s at 905-910 cm." 1). v(P-F) i s assigned at 950 cm. - 1, V (PF,,), i . p . i s assigned at 960 cm. - 1 and v (PF ), o.p. at 973, 998 cm. - 1. 6(P-F) and 6,(P-F2) 6(PF 2) i . p . i s assigned at 555 (556, p) cm. 1 , 6 ( P F 2 ) , o.p. at 485 cm. - 1 p ( P F 2 ) , i . p . i s assigned at 510 cm. - 1 and p(PF) at 412 ' (414, p) cm. 1 . — 5 — 5 ^ 9 — v(PF> and v ( P F 2 ) The symmetry species o f the P F 2 s t r e t c h i n g v i b r a t i o n s should be ' " -1 4A + 4A . V S ( P F 2 ) , i . p . i n n 5 P 5 F I ; Q i s a s s i S n e d a t 6 0 9 W C 6 1 5 S>P) c m - •• - 138 -and the corresponding band i n N^P^FgMe i s at 608 (611, p) cm. V s ( P F 2 ) (degenerate) occurs at 717 cm. i n N ^ F ^ Q . -y This s p l i t s to give v ( P - C ) at 700 cm. - 1 and V g ( P F 2 ) , o.p. at 808 cm. - 1. The second —1 36 ^  degenerate ^ C P f ^ ) D a n c ^ occurs at 866 cm. i n NJ-PJ-F^Q. This s p l i t s to give v g ( P F 2 ) , o.p. at 853 cm. - 1 and ^ S C P F 2 ) , o.p. at 889 cm. - 1. v ( P F ) i n Nr-Pr-FgMe i s assigned at 945 cm. 1. This i s probably a c c i d e n t a l l y degenerate w i t h v ( P F - ) o.p.; v ( P F , , ) , i . p . i s assigned at 927 sh. The cLS z cLS z other two V ( P F „ ) , o.p. v i b r a t i o n s are assigned at 966 and 998 cm. 1 cLS z 1 r e s p e c t i v e l y . 6(PF) and r6(PF 2) 6 ( P F 2 ) , o.p. i s assigned at (482,dp) 488 cm."1 and p(PF 2) i . p . at 510 cm. 1 p(P-F) i s assigned at 445 cm. 1. Ring V i b r a t i o n s TO ' _1 v & s(PNP) (E i n N 3 P 3 F 6 ) i n N ^ F g C J l i s assigned at 1280 (vs) cm. ,': a corresponding band occurs at 1275 cm. 1 i n N3P3F,-Me. The r i n g elonga-1 127 125 t i o n v i b r a t i o n (E i n N ^ F g ) i n N 3 P 3 F 5 C i l and N ^ C J ^ B r i s assigned at 845(s) cm. 1 and 870(m) cm. 1 r e s p e c t i v e l y . The corresponding band occurs at 900 cm. 1 i n N^P^F^Me. The other r i n g v i b r a t i o n s are u n c e r t a i n . N^F^Me v (PNP) i s assigned at 1410 cm. 1 and the r i n g elongation cLS . . . . v i b r a t i o n i s assigned at 880 cm. 1. The r i n g b r e athing mode i s assigned at 761 cm. 1 ; the weak band at 660 cm. 1 could p o s s i b l y be assigned to - 139 -r i n g deformation. 6.3. 1 , 1 - D i m e t h y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e , ^ P ^ F ^ i M ^ This molecule belongs to the po i n t group C^, the s e l e c t i o n r u l e s of which are shown i n Table 15. Methyl V i b r a t i o n s R i . r . 3008 w 3000 vw 2929 m,p 2932 w 1438 1427 1403 1411 1318 1300 982 975 V a s(CH) v s (CH) 6 a s t C H 3 > ycH3) r e s o l v e d degenerate CH^ rocking S k e l e t a l V i b r a t i o n s  P-C frequencies R i . r . 710, p 710 752 758 420 423 V s ( P C 2 ) , a c c i d e n t a l l y degenerate w i t h ^ ( P F ^ ' i-p> V a s C P C V p o s s i b l y 6 (PC^) PF,, V i b r a t i o n s 710, p 710 860 V s ( P F 2 ) , i . p . V s ( P F 2 ) , o.p., the corresponding band i n N^P^F^Me occurs at 860. Table 15 S e l e c t i o n Rules f o r Point Group Ring V i b r a t i o n s PF 2 V i b r a t i o n s PC^ V i b r a t i o n s T o t a l A c t i v i t y number of S t r e t c h Deformation S t r e t c h Deformation St r e t c h Deformation v i b r a t i o n R i . r . 3 A 1 2 A 1 A l 2 A 1 A l A l 10A 1 / / A2 A 2 2A 2 A 2 5A 2 / X 3 B 1 2 B 1 B l 2 B 1 h B l 10B / / B2 B2 2B 2 B2 5B 2 / / -,141- -R i . r . 930 v a s C P F 2 ) , i . p . 963,dp? - : v a s C P F 2 ) , o.p. 5(PF 2) modes 549, p 548 : 6 ( P F 2 ) , i . p . 492 : probably p ( P F 2 ) , i . p . ; the corresponding band i n N 3P 3F 5Me occurs at 510. 465 468 : SPF 2 > o.p. Ring V i b r a t i o n s 1260,1271 : v (PNP); degenerate i n N_P,F,. 3.S J O O 879,894 878,900 : r i n g e l o ngation v i b r a t i o n (E* i n L P F , ) . These 127 -5 3 6 bands occur i n N 3 P 3 F 4 C ^ 2 at 835, 855 cm. ; i n c i s N P CI.(NMe„) 1 2 8 at 880, 901 cm"1; i n 3 3 l v 2 ;2 gem N 3 P 3 B r 4 ( N M e 2 ) 2 1 2 8 at 835, 851" cm 764 778 : p o s s i b l y A r i n g b r e a thing v i b r a t i o n . The 125 corresponding v i b r a t i o n i n N_P_C£.Br_ occurs -1 .5 3 4 2 at 773 cm. , i n N.P C£,F, at 785 cm. , i n 117 _ f i28 N 3 P 3 ( N C S ) 6 at 790 cm. , i n gem N 3P 3Br^(NMe 2) 2 at 776 cm. 1. The assignment o f the fundamental v i b r a t i o n s i s c o n s i s t e n t w i t h a symmetry f o r the molecule. This i s supported by the s p l i t t i n g of the V (PNP) v i b r a t i o n and the r i n g e l o ngation vibration,,which are otherwise as degenerate i n N_P,F A. Furth e r , the v (PF„), o.p. v i b r a t i o n i s i . r . i n a c t i v e as would be expected f o r a symmetry. - 1-42 .-6.4. 1,1-D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e and t r a n s -1 , 5 ^ D i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e Methyl v i b r a t i o n s ( i - r - only) l.S.N^P^Me -2 3004 w 2938 w 2922 (Vw) obscured by v (PNP) 1308 1312 P-C V i b r a t i o n s at 762 cm. . In trans-1,5-N^P^FgMe,,, c o u p l i n g of the v i b r a t i o n s of the two PFC u n i t s occurs g i v i n g in-phase and out-of-phase components f o r both the PF and PC v i b r a t i o n s . v(PC), i . p . i s assigned at 700 cm. - 1 and v(PC), o.p. at 720 cm. 1 . The cou p l i n g i n the trans isomer i s not as strong as in . t h e geminal d e r i v a t i v e . The frequency d i f f e r e n c e s between V (PC„) and V (PC„) i s 52 cm. 1 i n the. geminal d e r i v a t i v e S Z. cLS Z ( c f . 48 cm. 1 f o r 1, l-N^V ^  . Coupling of 52 cm. 1 i s not unexpected f o r the geminal d e r i v a t i v e , but i s expected 'to be much l e s s f o r the trans isomer (trans and an t i p o d a l s u b s t i t u t i o n having been e s t a b l i s h e d by 19 F n.m.r.) i n which the PFC u n i t s are separated by r i n g bonds. ' The frequency d i f f e r e n c e , of 20 cm. 1 between vPC, .i. p . and v(PC), o.p. v i b r a t i o n s suggests s t r o n g l y e l e c t r o n i c c o u p l i n g i n the r i n g . - 143 -PF and PF,, V i b r a t i o n s V(PF) and v C P F j Since V s C P F 2 ) , i . p . i n N^P^F^Me i s assigned t o a strong p o l a r i z e d Raman band at 609 cm. 1 ( i . r . i n a c t i v e ) , t h i s band i s expected to be i n a c t i v e i n the i . r . s p e c t r a of N^P^F^Me,, isomers. The other two V s ( P F 2 ) , o.p. v i b r a t i o n s i n 1,l-N^P^F^Me,, are assigned at 860 and 921 cm. 1. The v (PF,,), i . p . i s assigned at 938 cm. 1 . The molecule i s 3.S 2. assumed to have a symmetry and th e r e f o r e one of the two v & s ( P F 2 ) , o.p. modes would be expected to be i . r . i n a c t i v e . The band at 961 cm. 1 i s assigned to v ( P F 7 ) , o.p. and that at 988 cm. 1 to CH r o c k i n g v i b r a t i o n . 3.S JL o I t i s necessary to i n v e s t i g a t e the Raman spectrum of t h i s compound before drawing any conc l u s i o n about the molecular symmetry. In trans-1,5-N 4 P 4 F 6 M e 2 J ' V s ^ P F 2 ^ ' i - P ' i s i , r * i n a c t i v e a n d V S ( P F 2 - ' ' i s a t 920 cm. - 1. V C ( P F 0 ) , i . p . i s at 942 cm. - 1 and V (PF-) i s at 975 cm. - 1. 3.J L. 3.S Z v ( P F ) , i . p . i s at 850 cm. - 1 and v ( P F ) , o.p. at 860 cm. - 1. The small d i f f e r e n c e i n frequency between v ( P F ) , i . p . and v ( P F ) , o.p. modes shows that although c o u p l i n g around the r i n g i s s m a l l , i t i s c e r t a i n l y present. 5(PF) and 6 ( P F J  l , l - N 1 P / l F 6 M e 2 i . r . 551 503 488 462 trans-1,5-N^P^FgMe,, i . r . 505" 482 (probably a c c i d e n t a l l y degenerate w i t h P(PC). 415 <5(PF2), i . p . p ( P F 2 ) , i . p . < S ( P F 2 ) , o.p. p ( P F 2 ) , o.p. p(PF) - 144 -Ring V i b r a t i o n s V a s(PNP) i n 1,l-N 4P 4F 6Me 2 i s assigned at 1390 cm. - 1 and i n trans-1,5-N^F^Me,, at 1386 cm. - 1 (shows s i g n of s p l i t t i n g 1380, 1392 cm. 1 ) . The r i n g e l o n g a t i o n mode i n 1, l-I^P^^Me,, seems to be at 878 cm. 1 and i n trans-1,5-N / ]P 4F 6Me 2 at 895 cm. - 1. The r i n g breathing mode i n 1,l-N 4P 4F 6Me 2 i s assigned at 801 cm. - 1 and i n trans_-l ,5-N 4P 4F 6Me 2 at 803 cm."1-. The i n t e n s i t y d i f f e r e n c e ( F i g . 29) i s pronounced and i s a f u r t h e r c o n f i r m a t i o n of the t r a n s - a n t i p o d a l s t r u c t u r e of the non-geminal isomer. The band at 650-656 cm. 1 i n both the isomers can be assigned to the r i n g deformation mode. 6.5. 1 , 1 , 3 - T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e and  1,1 , 5 - T r i m e t h y l p e n t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e Since the symmetry i s so low and the l i n e s are so numerous, the assignments i n these molecules are l e s s c e r t a i n than i n other compounds discussed e a r l i e r . ( i . r . only) l,l,5-N 4P^F 5Me 5 3000 v.w v (CH) clS 2938 " : v s(CH) 1313 } : o (CH ) 1305 Methyl V i b r a t i o n s 1 1 3-N P F Me 3000 w 2935 w 1311 1302 - 145"-^ P-C frequencies 692 758 776 700 760 773 V ( P - C ) V C P C 2 ) S V t P C A s v(PF) and v ( P F 2 ) 925 950 911 949 : v ( P F 2 ) s , o.p. : V(PF) The l a r g e number of bands i n the r e g i o n 900-1000 cm. makes the assignment o f the V CPFo) v i b r a t i o n s extremely d i f f i c u l t • . The as deformation frequencies seem much c l e a r e r ; 539 498 462 418 508 489 440 6 ( P F 2 ) , i . p . p ( P F 2 ) , i . p . 6 ( P F 2 ) , o.p. p ( P F 2 ) , o.p. P ( P - F ) Ring V i b r a t i o n s 1375 890,878 1370 890,87£ V a s(PNP) s p l i t t i n g of degenerate r i n g s t r e t c h i n g mode - 146 -6.6. 1 , 1 , 5 , 5 - T e t r a m e t h y l t e t r a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e Methyl V i b r a t i o n s R 3002 i.r. 3000 2927 (P) 2930 1430 1425. 1412 1415. 1310 1300 V a s(CH) Vs (CH) } : 6 a s(CH 3) 1 : 6 SCCH 3) P-C frequencies 685 747 763 720 761 423 4v(PC 2) v i b r a t i o n s 6 (PC ) probably V(PF 2) 600 (p) 879 590 883 959 971 6(PF) and 6(PF 2) 543 (P) 487 472 v ( P F 2 ) s , i . p . • v ( P F 2 ) s , o.p.; probably a c c i d e n t a l l y degenerate with r i n g e l ongation mode. v ( P F 2 ) a s ; i . P . v ( P F 2 ) a s , o.p. 6 ( P F 2 ) , i . p . 6 ( P F 2 ) , o.p. p ( P F 2 ) , o.p. - .147 -Ring V i b r a t i o n s 879 763 i.r. 1350 (broad) 883 761 V a s (PNP) probably r i n g e l o n g a t i o n mode a c c i d e n t a l l y degenerate w i t h v ( P F 2 ) s , o.p. r i n g breathing probably a c c i d e n t a l l y degenerate w i t h v ( P C 2 ) . The p a t t e r n of frequencies observed c l e a r l y shows that the molecule i s not centrosymmetrical as would be expected f o r a symmetry. 6.7. Mejthylcyclophosphonitriles (NPMe 2) 3 ^ Methyl V i b r a t i o n s NJ^Me, —6—o o N P Me N P Me -5-5^10 R -2994 p 2995 dp 1426 i.r. R i.r. 1412 }dp 2925(w) 2922 p 2920(mw) 2994(m) 2991 dp 2995(m) 1424 1413 1426 1430 } }dp 1422} 1416 1415 1286 1298 } } 1306 1290 1300 1290 i.r. 2922 m 2996(ms) 1430 1423 sh} 1415 1300 } 1290 v s(C-H) V a s(C-H) 6as< C H3> 6 S(CH 3) Although the assignments o f the methyl v i b r a t i o n s seem to be w e l l e s t a b l i s h e d , the s k e l e t a l v i b r a t i o n s introduce considerable d i f f i c u l t i e s . I t i s , t h e r e f o r e , necessary to i n v e s t i g a t e i n d e t a i l the s p e c t r a o f the deuterated d e r i v a t i v e s before a reasonable assignment can be made. However, the v (PNP) v i b r a t i o n could be picked out e a s i l y 3.S i n the i . r . s p e c t r a of a l l the m e t h y l c y c l o p h o s p h o n i t r i l e s . As i n the case of other p h o s p h o n i t r i l i c d e r i v a t i v e s V (PNP) increases w i t h r i n g ciS s i z e . 6.8. Conclusion , Although the assignments given above are inadequate f o r a complete v i b r a t i o n a l a n a l y s i s , s e v e r a l p a r t i a l conclusions are p o s s i b l e . 1) The geminally s u b s t i t u t e d d e r i v a t i v e N ^ P ^ F ^ a s t* i e symmetry C-2v> a s expected, the lowering i n symmetry from being accompanied by marked s p l i t t i n g o f V (PNP). 2) Although a s i m i l a r , but l e s s c e r t a i n , c onclusion could be drawn f o r gem-N^P^^Me^, there i s no s p l i t t i n g of V a s ( P N P ) . The same contrast between the t r i m e r i c and t e t r a m e r i c d e r i v a t i v e s i s found f o r the f l u o r i d e -c h l o r i d e s N^P^F^C^, N^P^FyCl, and has been a t t r i b u t e d to r i n g f l e x i b i l i t y i n the 8-membered r i n g s . 3) The p a t t e r n o f frequencies found f o r the non-geminal-antipodal ^4 P4^6^ e2 ^ s o m e r show that i t i s not centro-symmetrical, and n e i t h e r i s the a n t i p o d a l d e r i v a t i v e N^P^F^Me^. In the c r y s t a l , the l a t t e r compound has a saddle shape, and i t i s l i k e l y t hat the f l e x i b i l i t y i n s o l u t i o n i s caused by the i n t e r c o n v e r s i o n of the tub to saddle forms, which can take place by bond t o r s i o n a l movements o n l y , without angular deformation. 4) The numerical values of the CH^ deformation frequencies, i n 129 comparison w i t h those of other d e r i v a t i v e s , suggest that there i s no - 149 -conjugative i n t e r a c t i o n between the methyl groups and the. r i n g ; t h i s c o n c l u s i o n agrees with the r e s u l t s o f c r y s t a l s t r u c t u r e determinations. 5) v (PNP) decreases s t e a d i l y as methyl groups are introduced as i n t o the r i n g . This frequency i s otherwise known.to decrease w i t h the e l e c t r o n e g a t i v i t y of the attached groups, and the e f f e c t has been 40 a t t r i b u t e d to d - o r b i t a l expansion by the l e s s e l e c t r o n e g a t i v e groups. This explanation forms a b a s i s f o r the c o n s i d e r a t i o n of s t r u c t u r e and r e a c t i v i t y given i n the f o l l o w i n g Chapter. - 1.50 -CHAPTER 7  DISCUSSION The most important aspect o f the work described i n t h i s t h e s i s i s the f r e s h evidence which i s provided on the nature and extent o f e l e c t r o n i c d e l o c a l i s a t i o n w i t h i n the p h o s p h o n i t r i l i c r i n g . 1) S t r u c t u r a l l y , the tr a n s m i s s i o n of the e f f e c t o f s u b s t i t u e n t s i s seen p a r t i c u l a r l y c l e a r l y i n the a l t e r n a t i o n o f bond lengths i n 1,1-dimethyl--h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e , so g i v i n g a d i r e c t demonstration of e l e c t r o n i c d e l o c a l i s a t i o n . 2) The o r i e n t a t i o n p a t t e r n observed i n the r e a c t i o n of f l u o r o c y c l o -p h o s p h o n i t r i l e s , (NPF^)^ wit h m e t h y l - l i t h i u m , and the behaviour o f the three r i n g systems i n these r e a c t i o n s s t r o n g l y suggest that the uppermost Tr-system, which p a r t i c i p a t e s i n chemical r e a c t i o n s , i s of the homomorphic type. 7.1. S t r u c t u r a l E f f e c t s In homogeneously-substituted p h o s p h o n i t r i l e s , the r i n g bond lengths i n a p a r t i c u l a r molecule are a l l c l o s e l y equal. I n e q u a l i t i e s i n bond le n g t h are found e i t h e r a) when the s u b s t i t u e n t s on one phosphorus atom are d i f f e r e n t from those on the othe r s , or b) when one ni t r o g e n atom i n the r i n g i s protonated. We can expect two general - 151 -r e s u l t s from a change i n l i g a n d e l e c t r o n e g a t i v i t y at one centre. As a consequence of the change i n o r b i t a l s i z e , and the r e s u l t i n g changes i n Tr-bond (and to a smaller extent, cr-bond) str e n g t h s , the mean r i n g bond length w i l l change, and we can expect the greatest change to occur i n the two bonds, which meet at the perturbed atom. 130-13 The s t r u c t u r e s of a s e r i e s of p h e n y l c h l o r o t r i p h o s p h o n i t r i l e s 47 and of 1 , 1 - d i p h e n y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e give evidence that the mean bond lengths i n the s e r i e s N 3P 3C£ 6, N 3P 3C£ 4Ph 2, N ^ C J ^ P h ^ (F i g . 36) tend to increase with decreasing l i g a n d e l e c t r o n e g a t i v i t y . The 133 values are: P-N (a-d) 1.580 (mean of three determinations ), 1.583, 1.581, 1.597 A and 1.572 A i n N 3 P 3 F 4 P h 2 ( F i g . 37); P-Cl ( a - c ) , 1.986, 1.998, 2.017 A ; P-C (b-d) , 1.788, 1.792, 1.804 A ; 1.795 A i n N ^ F g P l ^ . Because a l l the bonds meeting at a given atom vary together i n the same sense, changes i n a - h y b r i d i s a t i o n are not now of major importance. The bond length i n e q u a l i t i e s , shown i n F i g . 36 and F i g . 37, are t h e r e f o r e a t t r i b u t a b l e to changes i n the Tr-bonds. The importance of the l a t t e r i s shown by the a l t e r n a t i o n of the bond lengths; f o r a pure a - i n d u c t i v e e f f e c t a steady change away from the perturbed atom would be expected. A l l the three inhomogeneously-substituted molecules show the same type of v a r i a t i o n , i n that only the four r i n g bonds nearest to the perturbed atom are a f f e c t e d , the remote p a i r being c l o s e to the average length. The bonds to the more e l e c t r o n e g a t i v e phosphorus atom are o shortened and the adjacent p a i r i s lengthened, the d i f f e r e n c e (0.06 A i n N_P_C£.Ph?) being s i g n i f i c a n t l y greater than that expected from a . C! \ / . 9 S S Ph Ph \ y i . 7 3 3 30 iM f t I i N CI Ci \ /z.O\7 N (o) 102.1 crt^ci x u — ci c i—p N \ / ci S.O ( N i 2 0 , i \ ci CI •CI CI—R ( b ) 1 0 4 . 4 Ph! Ph jl.555 11.993 ] ..P-^-Cl Ph-—P x \ / 555 1.609 1.792 N CI Ph 1.573 R-^-Ph P h —R Ph (c) 9 8 . 5 Cit Ct 1 2 4 . 9 t P x - j P h Ph Y . 0 4 . 4 Ph Ph Ph \ y^.804 [ .597 (d) F i g . 36. Structures of p h e n y l c h l o r o c y c l o t r i p h o s p h o n i t r i l e s . - 153 -P h Ph L l 0 7 . 9 ° ( 3 y / 1 . 7 9 5 ( 9 ) N \ 1 . 6 1 8 ( 5 ) ^ ) I I 5 . 5 ° ( 3 ) I 2 0 . 7 ° ( 2 ) N /'V I 2 0 . 7 ° ( 3 ) 1 . 5 3 9 ( 5 ) 2 0 . 0 ° ( 2 ) p. l . 5 3 2 ( ) N 1 . 5 5 8 ( 4 ) F i g . 37. St r u c t u r e o f 1 , 1 - d i p h e n y l t e t r a f l u o r o c y c l o t r i p h o s p h o n i t r i l e . — 154 -comparison of the s t r u c t u r e s of N^^CfL^ and'N^Phg (-0.02 A). S i m i l a r v a r i a t i o n s i n N 3 P 3 F 4 P h 2 have been i n t e r p r e t e d i n terms of greater donation of lone p a i r e l e c t r o n s to the bond to the more e l e c t r o n e g a t i v e 47 phosphorus atom. I t i s c o n c l u s i v e that the p a t t e r n o f bond length i n e q u a l i t i e s i s a d i r e c t r e s u l t o f T T-electron i n t e r a c t i o n s . I t i s not, however, p o s s i b l e to d i s t i n g u i s h between an " i s l a n d " model and those models i n v o l v i n g more extensive d e l o c a l i s a t i o n , the expected length of the t h i r d bond from the perturbed phosphorus atom being about the same i n a l l cases. P e r t u r b a t i o n at n i t r o g e n by pr o t o n a t i o n produces s t r u c t u r a l e f f e c t s comparable to those r e s u l t i n g from a change i n l i g a n d e l e c t r o -n e g a t i v i t y at phosphorus, as i l l u s t r a t e d by the s t r u c t u r e of N 3P 3CNHP r 1)4C£ 2H tC£~ ( F i g . 6; Chapter 1) and of (Me 2) g• 2H;CoCJt 4r^ 3 ^ The l a t t e r s t r u c t u r e i s p a r t i c u l a r l y i n f o r m a t i v e , i n that two pro-tonated 8-membered r i n g s with d i f f e r e n t conformations occur i n the same 2-c r y s t a l a s s o c i a t e d w i t h the CoCJl^ i o n ( F i g . 38) . The average bond lengths o f the two ca t i o n s are: 1.697, 1.540, 1.614, 1.582 (lengths of successive bonds from N + (X)) and each length being the average of the four bonds e q u i d i s t a n t from N + ( F i g . 38). The behaviour shown by the p h e n y l c h l o r o p h o s p h o n i t r i l e s , i n which the bond lengths a l t e r n a t e w i t h i i n c r e a s i n g d i s t a n c e from the perturbed centre, i s here continued to a f u r t h e r bond, and we can again a t t r i b u t e the bond length changes to v a r i a t i o n s i n the T r - i n t e r a c t i o n s . As i n the case of p h e n y l c h l o r o c y c l o t r i p h o s p h o n i t r i l e s , the s t r u c t u r e s of a s e r i e s o f m e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s give F i g . 38. Structures of the cations i n ( N ^ M e g H ^ C o C ^ 2 " . The protonated n i t r o g e n atoms are marked with a s t e r i s k s . - 156 -evidence that the mean bond lengths i n the s e r i e s N . P . F 9 8 N.P.F.Me 9 4 4 4 o 4 4 6 2 96 97 N4^4 F4^ e4 a n d ^ 4 P 4 M e 8 39) tend to increase w i t h decreasing l i g a n d e l e c t r o n e g a t i v i t y . The values o f the mean lengths o f the r i n g bonds (and, i n parentheses, the mean r i n g angles at nitrogen) are: 1.51 A (147°); 1.518 (145°); 1.560 (135°); 1.596 (132°). As i n the 130-132 p h e n y l c y c l o t r i p h o s p h o n i t r i l e s , the longer bonds i n 1,1,5,5-tetra-m e t h y l t e t r a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (N^P^F^Me^) meet i n the phosphorus atom c a r r y i n g the l e s s e l e c t r o n e g a t i v e s u b s t i t u e n t . The bonds i n 1, 1 - d i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (N^P^F^Me^) show the f u r t h e r f e a t u r e that a h i g h l y s i g n i f i c a n t a l t e r n a t i o n o f bond length occurs away from the p e r t u r b i n g methyl groups, the second bond (1.47 A) being the sh o r t e s t so f a r found i n a p h o s p h o n i t r i l i c molecule. The large v a r i a t i o n i n the i n d i v i d u a l values, as of the mean va l u e s , i s to be a t t r i b u t e d to the p o l a r i s a b i l i t y o f the bonding system, and shows that s t r u c t u r a l i n f l u e n c e s are propagated through the whole molecule. Since the molecular framework i s ne a r l y p l a n a r , the co n d i t i o n s f o r the a p p l i c a t i o n o f simple Hiickel theory are s a t i s f i e d , and the e f f e c t of a T r-inductive p e r t u r b a t i o n at phosphorus has th e r e f o r e been estimated through the c a l c u l a t i o n o f bond-atom p o l a r i s a b i l i t i e s 1 3 4 - - IT = ^ r s r s , t g ctt f o r a d e l o c a l i s e d T r-system based on an 8-membered r i n g (see Appendix 1). The bond-atom p o l a r i s a b i l i t i e s are given i n Table 16. r s 01 12 23 34 TT +0.T04 -0.056 +0.016 -0.020 rs,o Table 16 - Bond-atom p o l a r i s a b i l i t i e s F i g . 39. Structures of m e t h y l f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e s . - 158 --0.05-1 I — "I 1 1 a b e d Bond F i g . 40. Comparison of ( i ) d e v i a t i o n s of i n d i v i d u a l P-N bond lengths from the mean i n N^P^gMe,, and ( i i ) Bond-atom p o l a r i s a p i l i t i e s , HMO, a M = a D + 3-They are shown i n F i g . 40, i n comparison w i t h the observed d e v i a t i o n s of i n d i v i d u a l bond lengths from the mean, f o r the four successive d i s t i n c t bonds i n N^P^F^I^. The c l o s e correspondence i n p a t t e r n , l i k e 43 the p a t t e r n of i o n i s a t i o n p o t e n t i a l s i n (NPF2) , seems very d i r e c t evidence f o r e l e c t r o n i c d e l o c a l i s a t i o n i n p h o s p h o n i t r i l i c molecules, and suggests that simple Huckel methods can provide a u s e f u l guide to the chemistry of p h o s p h o n i t r i l i c d e r i v a t i v e s . 7.2. O r i e n t a t i o n a l E f f e c t s The predominantly geminal s u b s t i t u t i o n observed i n the r e a c t i o n of o c t a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e (N^P^Fg), can not be explained by a simple e l e c t r o s t a t i c e f f e c t . In view of the high e l e c t r o n e g a t i v i t y of f l u o r i n e , e l e c t r o s t a t i c c o n s i d e r a t i o n s alone would r e q u i r e successive s u b s t i t u t i o n to occur non-geminally, whatever the s u b s t i t u e n t . The geminal s u b s t i t u t i o n f r e q u e n t l y encountered i n aminolysis r e a c t i o n s of c h l o r o c y c l o p h o s p h o n i t r i l e s w i t h primary amines has been explained by a proton a b s t r a c t i o n mechanism, as suggested f o r the h y d r o l y s i s of 135s-phosphoryl compounds." - Reactions of h e x a c h l o r o c y c l o t r i p h o s p h o n i t r i l e , 136' 27 (NPCi!^)3, w i t h ammonia and t e r t i a r y butylamine give e x c l u s i v e l y 13fe ^ geminally s u b s t i t u t e d d e r i v a t i v e s . I t has been repor t e d , ' t h a t , although geminal s u b s t i t u t i o n i n these r e a c t i o n s i s discouraged by d e l o c a l i s a t i o n of lone p a i r e l e c t r o n s on n i t r o g e n i n t o phosphorus d - o r b i t a l s , a competitive proton a b s t r a c t i o n of r e l a t i v e l y greater importance occurs simultaneously. I t has been suggested that the course of the r e a c t i o n of (NPCJ^D-j with NH^ i s as f o l l o w s : NT Gl C C l / N H 2 N N' NH-C l C l N' N X I CJ C l N ^ 2 / N H 2 N N N' • PC .C l <-, NH N N C l N Cl A s i m i l a r mechanism has been suggested f o r the r e a c t i o n of (NPCH^)^ with 27 t-butylamine. The r e a c t i o n o f (NPF,,)^ with NHMe^ gives about 12% '93 ' gem-N^P^F^ (N)Me2) 2 • ^ The course o f phenylation of hexaf l u o r o c y c l o t r i -p h o s p h o n i t r i l e CN^P^F^) with p h e n y l - l i t h i u m i s predominantly non-57 geminal. The preference f o r non-geminal s u b s t i t u t i o n i s a t t r i b u t e d to the greater s t e r i c requirements of the phenyl group, which may be f u r t h e r r e i n f o r c e d by m i l d conjugative i n t e r a c t i o n s . On the c o n t r a r y , PhMgBr i n THF has been reported to react with ( N P F 2 ) 3 i n THF to give 1 37'' only the mono- and the geminal d i - s u b s t i t u t e d d e r i v a t i v e s . - I t i s 13 7s suggested that the monomeric nature of PhMgBr i n THF, i n co n t r a s t to the dimeric nature of PhLi i n d i e t h y l ether and THF, could be a p o s s i b l e reason f o r the geminal s u b s t i t u t i o n . F u r t h e r , the increased Lewis a c i d i t y o f magnesium compared to l i t h i u m i n these compounds may favour - 161 -a f l u o r i d e a b s t r a c t i o n mechanism as the f i r s t step, thus f o l l o w i n g a pathway s i m i l a r to the F r i e d e l - C r a f t s r e a c t i o n . An SN 2 mechanism i s 79 however proposed f o r the r e a c t i o n of (NPF,,).^ 4 with n - b u t y l - l i t h i u m . In the absence of k i n e t i c i n f o r m a t i o n i t i s r a t h e r d i f f i c u l t to suggest a d e t a i l e d mechanism f o r the r e a c t i o n of fluorocyclophospho-n i t r i l e s , (NPF,,)^ with m e t h y l - l i t h i u m . I t i s , however, q u i t e l i k e l y that the s u b s t i t u t i o n proceeds through a carbanion a t t a c k . Methyl-138 l i t h i u m , which i s t e t r a m e r i c i n d i e t h y l ether, - can d i s s o c i a t e i n t o dimers [ L i 4 ( C H 3 ) 4 ^ 2 L i 2 ( C H 3 ) 2 ] or a l t e r n a t i v e l y i n t o L i 4 ( C H 3 ) 3 + + _ 139 + CH_ .'• -'" Ions of the form L i R , p a r t i c u l a r l y when n = 4, are the 3 n n-1 r ' most important species seen i n the mass spec t r a of a l k y l - l i t h i u m com-101 141 140 pounds. O p t i c a l l y a c t i v e s e c - a l k y l - l i t h i u m compounds racemize more r a p i d l y i n an e t h e r - c o n t a i n i n g medium than i n hydrocarbon solvents. Since racemization very probably proceeds through a carbanion i n t e r -mediate, there i s a strong support f o r the argument that the i o n i c "14.0 , d i s s o c i a t i o n proceeds r e a d i l y i n e t h e r r Further the s o l v a t e d dimer i n e q u i l i b r i u m w i t h i t s monomer acts as a source of carbanion. Although more, extensive i n f o r m a t i o n on the e q u i l i b r i a and k i n e t i c s o f m e t h y l - l i t h i u m i n e t h e r e a l s o l u t i o n s would be d e s i r a b l e , the o r i e n t a t i o n p a t t e r n and r e l a t i v e y i e l d s of the various products found i n the r e a c t i o n of m e t h y l - l i t h i u m w i t h the p h o s p h o n i t r i l i c f l u o r i d e s can nevertheless be understood on a simple b a s i s , lyiZ)., a T T-inductive e f f e c t of the e n t e r i n g methyl group on a homomorphic 7T-system w i t h i n the r i n g . A s i m i l a r e f f e c t has been suggested by - 162 -67 Emsley and Paddock to e x p l a i n the r e l a t i v e r a t e s of successive r e a c t i o n steps i n the f l u o r i n a t i o n of (NPCJ^)^ 4 w i t h potassium f l u o r o s u l p h i t e . In the f l u o r i n a t i o n r e a c t i o n there are three important r e s u l t s : 1) geminal s u b s t i t u t i o n occurs as f a r as p o s s i b l e , 2) the PFC£ group i s more r e a c t i v e to a n i o n i c f l u o r i n a t i n g agents than i s the PC&2 group and 3) the second f l u o r i n a t i o n step i s f a s t e r , r e l a t i v e to the f i r s t , i n the t e t r a m e r i c than i n the t r i m e r i c s e r i e s . The f i r s t two r e s u l t s can be explained by the e l e c t r o n withdrawing power of the f l u o r i n e atom attached to the phosphorus atom - an e l e c t r o s t a t i c , or " d i r e c t - f i e l d " e f f e c t . A simple e l e c t r o s t a t i c e f f e c t i s inadequate to account f o r the t h i r d r e s u l t , although r i n g f l e x i b i l i t y could e x p l a i n the greater r e a c t i v i t y of the 8-membered r i n g s i n general. The inadequacy of a simple e l e c t r o s t a t i c e f f e c t i s f u r t h e r shown experimentally by the 142-r e s u l t s of Sbwerby on the r a t e of exchange of c h l o r i d e ion w i t h a s e r i e s of c h l o r o c y c l o p h o s p h o n i t r i l e s , (NPCJl^Dg The a c t i v a t i o n energy f o r t h i s exchange r e a c t i o n i s an o s c i l l a t i n g f u n c t i o n of r i n g s i z e , being high f o r the 6-membered r i n g and low f o r the 8-membered r i n g . In F i g . 41 the r e s u l t s are shown, i n comparison with a model c a l c u l a t i o n of TT-electron d e n s i t i e s , the ir-system being assumed to be of the homomorphic Tr s-type i n v o l v i n g the d^2_ 2 o r b i t a l at phosphorus, and an ,143 spy. o r b i t a l at n i t r o g e n . These exchange experiments show that the r e a c t i v i t y of a p h o s p h o n i t r i l e to a n u c l e o p h i l e v a r i e s i n the opposite sense to the TT-charge d e n s i t y at the phosphorus atom, the ir-system being homomorphic r a t h e r than heteromorphic; the r e l a t i v e r a t e s of the - 163 -I 6 J ( ] _ 1 [ 3 4 5 6 n in ( NPCAJ F i g . 41. A c t i v a t i o n energies f o r the r e a c t i o n * * Cl~ + (NPC£ 2) n (NPC£ 2) n + C£" The upper curves show c a l c u l a t e d (HMO) T T-electron d e n s i t i e s at phosphorus, assuming a = a + 3-successive steps i n tke f l u o r i n a t i o n of (NPCZ^)^ 4 are i n agreement with the T r - i n d u c t i v e e f f e c t of the s u b s t i t u e n t on these ir-charge d e n s i t i e s . The e f f e c t i s c a l c u l a t e d , u s i n g Hiickel molecular o r b i t a l s , by applying a p e r t u r b a t i o n 6p,^ to one phosphorus atom, to simulate the e f f e c t of the increased e l e c t r o n e g a t i v i t y of the phosphorus o r b i t a l s , as a con-sequence of s u b s t i t u t i o n of c h l o r i n e by f l u o r i n e . The general e f f e c t of the i n c rease i n e l e c t r o n e g a t i v i t y i s to concentrate T r-electron d e n s i t y on the perturbed atom. That such a c o n c e n t r a t i o n a c t u a l l y occurs i s 92 shown by the work of Heatley and Todd. The T T-inductive e f f e c t , causing an accumulation of charge at phosphorus, i s important because i t d i f f e r s , according to whether the Tr-system i s homomorphic or hetero-morphic. The charge d e n s i t i e s at a phosphorus atom perturbed by an 143 e l e c t r o n e g a t i v e s u b s t i t u e n t (<5or = 0.58) are shown i n F i g . 42. I t can be seen t h a t , i n so f a r as r e a c t i v i t i e s are determined by T T-electron d e n s i t y at phosphorus, we can expect the r e l a t i v e r a t e s of the second f l u o r i n a t i o n step to be greater i n the t r i m e r than i n the tetramer, i f the higher l e v e l s are of the heteromorphic type, and l e s s i f they are homomorphic. The l a t t e r type i s observed, i n agreement with the more 144 d e t a i l e d k i n e t i c i n f o r m a t i o n on c h l o r i d e i o n exchange and w i t h the 43 measurements of i o n i s a t i o n p o t e n t i a l s . I f the energy l e v e l s i n v o l v e d are of the homomorphic type, then n u c l e o p h i l i c s u b s t i t u t i o n r a t e s i n the Nj-P,. s e r i e s should be slower than f o r N 4P 4- This has been found to be 144 so q u a l i t a t i v e l y . -In the f l u o r i n a t i o n r e a c t i o n , e l e c t r o s t a t i c e f f e c t s are dominant, and determine the o r i e n t a t i o n p a t t e r n ; T T-electron e f f e c t s 'control only - 165 -F i g . 42. C a l c u l a t e d charge de n s i t y at s u b s t i t u t e d phosphorus atom as a f u n c t i o n of r i n g s i z e ; HMO c a l c u l a t i o n s , = ap + 23, a ' = a p + 0.53. The f u l l l i n e r e f e r s to homomorphic, the dotted l i n e to heteromorphic i n t e r a c t i o n s . - 166 -the r e l a t i v e rates of formation of the successive c h l o r i d e - f l u o r i d e s . E x p e r i m e n t a l l y , i t i s observed that methylation of o c t a f l u o r o c y c l o -t e t r a p h o s p h o n i t r i l e (N^P^Fg) with m e t h y l - l i t h i u m i s predominantly geminal, thus suggesting the dominance of the :T T-inductive e f f e c t over the e l e c t r o s t a t i c e f f e c t i n the above r e a c t i o n . The consequences o f T T - i n d u c t i v e i n t e r a c t i o n s f o r atomic TT-charges are embodied i n Table 17 f o r 6-, 8- and 10-membered r i n g s (see Appendix 1). This Table gives values of the atom-atom p o l a r i s a -b i l i t i e s of p h o s p h o n i t r i l i c systems f o r two values of the r e l a t i v e e l e c t r o n e g a t i v i t y of P and N. The t a b u l a t e d numbers give the change i n T T - e l e c t r o n d e n s i t y at atom S f o r a u n i t increase i n the Coulomb parameter of atom 1, and so simulate-the e f f e c t of the s u b s t i t u t i o n of a more e l e c t r o n e g a t i v e f o r a l e s s e l e c t r o n e g a t i v e l i g a n d on the T T-charg d e n s i t i e s . I t w i l l be seen that such a s u b s t i t u t i o n concentrates T T - e l e c t r o n d e n s i t y at atom 1, so that-geminal s u b s t i t u t i o n i s discourag Conversely, a l e s s e l e c t r o n e g a t i v e s u b s t i t u e n t (as methyl i s ) would concentrate T T - e l e c t r o n d e n s i t y elsewhere i n the molecule. The Table shows t h a t , provided the TT-system i s d e l o c a l i s e d and the e l e c t r o -n e g a t i v i t y d i f f e r e n c e of P and N i s great enough, t h i s c oncentration may not be i n the most remote p o s i t i o n , but may be c l o s e r t o the perturbed atom. Since 6a (the p e r t u r b a t i o n of the Coulomb i n t e g r a l at P^ by the s u b s t i t u t i o n of a methyl group f o r f l u o r i n e ) i s negative, the induced charges have the same s i g n as the t a b u l a t e d values, and from t h i s cause alone, a second n u c l e o p h i l i c s u b s t i t u t i o n should take place p r i n c i p a l l y at P,, as found. The s u b s t i t u t i o n of the t h i r d and Table 17 Atom-Atom P o l a r i s a b i l i t i e s TT s, Atom (s) 2CN :) 3 ( P 2 ) 4(N 2) 5 ( P 3 ) 6(N 3) N 3 P 3 N 4 P 4 Homomorphic P = 1 P = 2 +0.309 +0.182 -0.126 -0.078 +0.003 -0.002 -0.063 -0.022 Heteromprphic P = 1 p = 2 +0.252 +0.158 -0.085 -0.063 -0.041 -0.016 0 0 Horn, and Het. P = 1 P = 2 +0.273 +0.166 -0.096 -0.068 -0.023 -0.010 -0.006 -0.003 -0.023 -0.004 . Homomorphic P =. 1 +0.305 -0.112 • +0.001 -0.031 -0.020 -0.020 ; N 5 P 5 Heteromorphic p = 1 +0.283 -0.102 -0.015 -0.012 -0.013 0 HMO c a l c u l a t i o n s , a^ = ap + p8. P o l a r i s a b i l i t i e s c a l c u l a t e d according to C A . Coulson and H.C. Longuet-Higgins, Proc. Roy. Soc. A191, 39 (1947).' 9a, f o u r t h groups can be expected to occur where the TT-induced negative charge i s l e a s t , and Table 17 shows t h a t , provided the e l e c t r o -n e g a t i v i t y d i f f e r e n c e between the T r - o r b i t a l s at P and N i s great enough, t h i s i s at P^ i n the N4P4 r i n g . In agreement, i t i s found t h a t , although some attack takes place at P2> entry of the t h i r d and f o u r t h groups i n t o the 8-membered r i n g takes place to a major extent both geminally and i n the a n t i p o d a l p o s i t i o n . This o r i e n t a t i o n p a t t e r n has not been observed p r e v i o u s l y , and, s i n c e i t i s a d i r e c t consequence of the assumptions made above about r e a c t i v i t y , i s e q u a l l y a d i r e c t demonstration of t h e i r v a l i d i t y . There has been no previous case i n which c y c l i c d e l o c a l i s a t i o n has been shown to have a d e c i s i v e e f f e c t on p h o s p h o n i t r i l i c chemistry. The course of methylation of (NPF2)4 l s shown i n F i g . 43 i n comparison with that of f l u o r i n a t i o n and dimethyl-amination of (NPCJ^^- The c o n t r a s t i n p a t t e r n s , and the correspondence of the methylation p a t t e r n w i t h the expectation from simple d e l o c a l i s a -t i o n theory i s very s a t i s f a c t o r y . Since we are d e a l i n g with a d e l o c a l i s e d system, a d d i t i o n r e a c t i o n s are expected to be less.important than s u b s t i t u t i o n r e a c t i o n s . Nevertheless, and perhaps e s p e c i a l l y because d e l o c a l i s a t i o n i s q u a n t i t a t i v e l y l e s s important than i n benzene and i t s d e r i v a t i v e s , a d d i t i o n r e a c t i o n s occur c o m p e t i t i v e l y with the s u b s t i t u t i o n r e a c t i o n , and the c a l c u l a t i o n s again provide some guide to the r e l a t i v e behaviour of the three r i n g s i z e s i n v e s t i g a t e d , at l e a s t as f a r as the y i e l d s of f u l l y - m e t h y l a t e d compounds are concerned. No simple N^P^ d e r i v a t i v e s c o n t a i n i n g more than two methyl groups could be i s o l a t e d . The s e l f -N p ' p „ N P / \ IVi A Me Me N W Me Mo \ / N hi' A 4-D \ M^ Me 7C (a) N N' \ yMa v / P + P P P X / Me V N N p • p Me Me Me {2 I N \ / P Me Me F - atoms not shown N NI N N \ A — A A ,p ^ - P / \ / \ / s / \ P N hi N N / \ / F N / \ F P P • P p A \ / C£ - atoms not shown B \ / A / y\ A - A A N / / \ NMe<, .p p IV Me, I Ci - atoms not shown c F i g . 43. The o r i e n t a t i o n p a t t e r n i n the methylation o f ( N P F 2 ) 4 ; and i n the f l u o r i n a t i o n and the dimethylamination of (NPC£ 2) 4. (A) r e a c t i o n of ( N P F 2 ) 4 w i t h LiCH^ (B) r e a c t i o n of (NPC£ 2) 4 with KS0 2F (C) r e a c t i o n of (NPC£ 2) 4 with NHMe2 p o l a r i s a b i l i t i e s shown i n the f i r s t column of Table 17 show t h a t , i r r e s p e c t i v e of r e l a t i v e e l e c t r o n e g a t i v i t y , the p o s i t i v e charge on induced by the two methyl groups i s highest i n the 6-membered r i n g and f o r homomorphic i n t e r a c t i o n s , and the a d d i t i o n of a t h i r d methyl group to P^ i s t h e r e f o r e most, l i k e l y i n t h i s case. The s e l f - p o l a r i s a b i l i t i e s T T^ ^ f o r N^P^, N^P^ and N^P^ r i n g s (Table 17) show, t h a t , provided chemical behaviour depends mainly on the homomorphicTT-system, the importance of the s u b s t i t u t i o n r e a c t i o n r e l a t i v e to the a d d i t i o n r e a c t i o n should increase i n the order N^P^ < N^ P,. < N^P^. Although an a d d i t i o n +• - 145 compound Cs N^P^F^ has been i s o l a t e d i n other experiments no such products were found here; i t i s probable that the i n i t i a l a d d i t i o n was followed by breakdown of the r i n g . The best i n d i c a t i o n at present i s i n d i r e c t , i n the y i e l d s of the f u l l y methylated d e r i v a t i v e s , N^P^Me^ (0), N 4P 4Me g (63%), N 5P 5Me 1 0 (20-25%). T h e . p o s i t i v e charge on phosphorus induced by a p a i r of methyl groups i s l e a s t f o r the 8-membered r i n g , and the s u b s t i t u t i o n r e a c t i o n i s th e r e f o r e dominant i n t h i s case. Simple TT - e l e c t r o n theory t h e r e f o r e forms a good b a s i s f o r understanding the s t r u c t u r a l features of the m e t h y l - f l u o r o c y c l o p h o s p h o n i t r i l e s , and the o r i e n t a t i o n behaviour i n the s u b s t i t u t i o n r e a c t i o n . I t may als o provide some guidance i n i n t e r p r e t i n g the s i d e - r e a c t i o n s which at present l i m i t the scope of the s u b s t i t u t i o n r e a c t i o n , but are not understood. - .171 -APPENDIX 1 The atom-atom p o l a r i s a b i l i t i e s f o r the three r i n g systems (N^P^, N^P^ and Nj-Pc-) are determined using the formula j = l k=m+l s,r C .C -C ,C . r j s j rk sk E. - E, J k 134 derived from simple f i r s t order p e r t u r b a t i o n theory. I t i s evident from the above formula that the a t o m i c - o r b i t a l c o e f f i c i e n t s and the energies of the m.o.'s are to be known f o r c a l c u l a t i n g . t h e mutual atom p o l a r i s a b i l i t i e s . These are determined from the unperturbed molecules u s i n g a simple Hiickel treatment. The formulae used f o r such c a l c u l a -t i o n s are given i n the f o l l o w i n g pages. The s e c u l a r equations to be used f o r planar (AB) n r i n g systems are a^-E 23cosic.Tr/n 28cos£Tr/n a p-E = 0 ( f o r homomorphic i n t e r a c t i o n ) and a^-E 2i8sin&Tr/n -2i8sin£ir/n a p-E 0 ( f o r heteromorphic i n t e r a c t i o n ) Using these equations and t a k i n g = a p + p$ (to account f o r the e l e c t r o n e g a t i v i t y d i f f e r e n c e between the n i t r o g e n and the phosphorus atoms) the equation f o r the energy of; the m o l e c u l a r - o r b i t a l s i s derived as a p + aN F — :  E„ = a ± 3x where a = — ' x/2 = / t 2 + p 2/16 I ay av ^ J ( t 2 = cos 2 £ T r/n f o r homomorphic and sin 2 £ T r / n f o r heteromorphic i n t e r a c t i o n s ) , 8 = resonance i n t e g r a l H_^s and a = Coulomb i n t e g r a l H • In the present c a l c u l a t i o n s values o f 1 and 2 f o r p are used. The c o e f f i c i e n t s (a) and (b) i n the equation afp + b$^; where f p and are symmetry-adapted'.sets of atomic o r b i t a l s , are then c a l c u l a t e d u s i n g the formulae a 2 = (x-p/2)/2x and b 2 = (x + p/2)/2x. From the values o f b 2 the TT-electron d e n s i t y per n i t r o g e n atom i s c a l c u l a t e d f o r (NP) where n = 3-6 f o r homomorphic and heteromorphic i n t e r a c t i o n s using the general formula V = • J" n.C... ; r v -j i r 1 where C. i s the c o e f f i c i e n t of atom r i n the i t h m.o., which i s occupied by n_. e l e c t r o n s . The values are shown i n Table 18 f o r p = 1, Table 18 Tr-E'lectron Density per Nitrogen /A/tom ,fbr the /Ring 'Systems (NP) Ring s i z e Homomorphic I n t e r a c t i o n s Heteromorphic -Interactions n Tr-charge on N 7T-charge on N 3 1.379 1.518 4 1.477 1.477 5 1.418 1.458 6 1.449 1.449 For the p e r t u r b a t i o n c a l c u l a t i o n i t i s necessary to have the molecular o r b i t a l s i n r e a l form. The intermediate o r b i t a l s ¥p are found as f o l l o w s . The complex form i s n-1 n-1 A = I exp(2TTUk/n)\ = I cos (2Tr£k/n)\ k=0 k k=0 K n-1 + i I sin(2Tr£k/n)\ k=0 k I f the ^  are symmetric w i t h respect to the molecular plane o f symmetry which remains a f t e r p e r t u r b a t i o n ( p z , d x2_y2> d z2> dy Z)» then the two sums on the r i g h t hand s i d e are r e s p e c t i v e l y symmetric and a n t i -symmetric with respect to i t . That i s , f o r sym. i n t e r a c t i o n s , the A' combinations are: and the A" combinations are: n-1 I cos ( 2 7 T i i k/n ) T ' k=0 * n-1 I sin^ T r J c . k/n) 1!' k=0 * f o r antisymmetric i n t e r a c t i o n s , (d x z»d ) the A' combinations are: and the A" combinations are: n-1 I sin(27T£k/n),i'l k=0 * n-1 I'J cos(2TT£k/n)T' k=0 * For the n i t r o g e n o r b i t a l s $ (p£) the A' combinations are: n-1 I cos[2Tr£(k + | ) ] * k + 1 k=0 the A" combinations are: n-1. I sin[ ,2Tr£(k + 1 k=0 1 k 2 The complete m.o.'s are obtained from these intermediate o r b i t a l s and the c o e f f i c i e n t s a,b. Knowing the energies o f the m.o.'s and a l s o the complete m.o.'s the mutual atom p o l a r i s a b i l i t i e s are c a l c u l a t e d using the formula m n C ,C ,C ,C . TT = 4 t y r j sj rk sk 6 ' j = l k=m+l E. - E, J i k the sum being taken over the j occupied and k unoccupied levels. The atom-bond p o l a r i s a b i l i t i e s are calculated s i m i l a r l y using the formula m st ,r 2 I I j=l k=m+l C .C . (C .CL, + C .C . ) r j r k v sj tk t j sk E. - E. J k APPENDIX 2 Nomenclature There has been no unique system of naming the P-N rin g compounds The names phosphonitrile and phosphazene are i n frequent use. The names such as phosphorus chloronitride, phosphonitridic dichloride, and chloro-phosphinic n i t r i d e are seldom used i n the l i t e r a t u r e . The name phospho-)* n i t r i l e i s used i n th i s thesis. Thus, the compounds N^ P^ F^ . and N^P^F^ are named hexafluorocyclotriphosphonitrile and dodecafluorocyclohexa-phosphonitrile or simply trimeric and hexameric phosphonitrilic fluorides In the case of inhomogeneously substituted derivatives, the problem of isomerism arises when more than two substituents are present i n the ring. The phosphonitrilic r i n g i s assumed to be planar s t a t i s t i c a l l y with the exocyclic groups projecting above and below the plane. Disregarding conformational and op t i c a l isomerism one encounters positional and geometrical isomerism. For a d i s u D s t i t u t i o n i n cyclotetraphosphonitrile, the substitution i s geminal or v i c i n a l or antipodal i f the substituents are respectively attached to the same phosphorus atom or adjacent phosphorus atoms or opposite -176 r phosphorus atoms. C i s - t r a n s isomerism a r i s e s i f the s u b s t i t u e n t s are on d i f f e r e n t phosphorus atoms and the nomenclature i s s i m i l a r to that used i n the organic chemistry. The naming o f d i f f e r e n t isomers of N ^ P ^ M e 2 (3.4.2.) i s discussed below. 1) Geminal isomer o f N,P.F,Me,, 4 4 6 2 This compound i s named e i t h e r gem-dimethylhexafluorocyclotetra-p h o s p h o n i t r i l e (gem-N^P^F^Me^) or 1,1-dimethylhexafluorocyclotetra-p h o s p h o n i t r i l e ( 1 , l - N ^ P ^ F ^ l V ^ ) • 2) V i c i n a l isomer a) v i c i n a l c i s - or v i c i n a l t r a n s - d i m e t h y l h e x a f l u o r o c y c l o t e t r a -p h o s p h o n i t r i l e ( v i c . ; c i s - ^P^F^Me^ or vic.-trans-N^P^F^Me^). b) c i s - 1 , 3 - or t r a n s - 1 , 3 - d i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e . 3) A n t i p o d a l isomer a) a n t i p o d a l - c i s - or a n t i p o d a l - t r a n s - d i m e t h y l h e x a f l u o r o c y c l o t e t r a -phosphoni'trile ( a n t i c i s - , 1 , 5 - or a n t i . - t r a n s ~ l ,5-N^P^F^Me,,. ) b) c i s - 1 , 5 - or t r a n s - 1 , 5 - d i m e t h y l h e x a f l u o r o c y c l o t e t r a p h o s p h o n i t r i l e ( c i s - 1 , 5 - or trans-1,5-N^P^FgMe,,). - -177 -REFERENCES 1) H.N. 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Although 36 l i n e s would be expected only 34 l i n e were observed due to o v e r l a p p i n g , ige 9 9 . 5 . 1 . diamino i n s t e a d of dimino Page 147. 6.7. The Raman band at 2994cmT 1'in.N,P 7Me^- i s 3 3 o at 2920cm':1 " • Note:. The proton chemical shifts((5 ) reported, i n t h i s t h e s i s are . d o w n f i e l d t o TKS. 

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