MECHANISTIC STUDY ON THE IRRADIATION OF IMINOPHOSPHORANES by ANDREW SUET-WAI YIM B. SC., University of Oregon, 1968. A THESIS SUEMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF' SCIENCE in the Department of Chemi.s t ry @ ANDREW SUET-WAI YIM 1977 SIMON FRASER UNIVERSITY December 1977 All rights reserved. This thesis may not be reproduced in whole or in part, by photocopy or other means, without permission of the author. APPROVAL Name: Andrew Suet-Wai Yim Degree: Master of Science Title of Thesis: Mechanistic Study on the Irradiation of Iminophosphorane s Examining Committee : A. C. hehlschlager Senior Supervisor E. Kiehlmann Examining Committee L. K. Peterson Examining Committee \ K.. N. leiso or EFamining Committee . , Date Approved: Dec . 28th, 1977. PARTIAL COPYRIGHT LICENSE I hereby grant to Simon Fraser University the right to lend my thesis, project or extended essay (the title of which is shown below) to users of the Simon Fraser University Library, and to make partial or single copies only for such users or in response to a request from the library of any other university, or other educational institution, on its own behalf or for one of its users. I further agree that permission for multiple copying of this work for scholarly purposes may be granted by me or the Dean of Graduate Studies. It is understood that copying or publication of this work for financial gain shall not be allowed without my written permission. Title of Thesis/Project/Extended Essay Author: (signature) ABSTRACT The photodissociation of N-aryl- and N-alkyl- t riphenyliminophosphoranes ( ylids ) lead to t riphenylphosphine and products which could be considered to be derived from monovalent nitrogen (nitrene) intermediates. Only one case of the irradiation of a triphenylimin6phosphorane has been reported (~.~immerand M. Jayawant, Tetra. Letters, 5061 (1966)). Like the irradiation of methylenetriphenylphosphoranes, the irradiation of N-subst ituted t riphenyliminophosphoranes is also wavelength-dependent, resulting in different modes of photodecomposit ion. Ylids with resonance-stabiliztng subst ituent s on the nitrogen are stable to irradiation with a pyrex filter (~300nm) but liberate benzene when irradiated in a quartz cell (>200 nm) . N-aryl ylids afford photoexcited ylids upon irradiation, resulting in azobenzene derivatives and t riphenylphosphine . Pry1 nitrenes are unlikely intermediates. Tn the presence of oxygen, photooxidation takes place to produce triphenylphos- phine oxide and secondary products. Aryl nitrenes are apparently involved via deoxygenation of nitrosobenzene derivatives by triphenylphosphine . Both of the latter are products of the irradiation. N-alkyl ylids may generate alkyl nitrenes upon irradiat ion, although more concrete evidence is necessary to clarify this. iii A proposal is made for further research in this study. TO MY WIFE AND CHILDREN ACKNOWLEDGMENT The author wishes to express his sincere thanks to his Research Supervisor, Dr. A. C. Oehlsc hlager, for guidance and advice during the course of this work. Thanks is also extended to: Mrs. C. Emery for the initial study of this work; The faculty, staff and students of the chemistry department of Simon Fraser University for providing comradeship, encouragement and helpful discussions; Mrs. L. Y. Yim for typing the manuscript of this dissertation; And the National Research Council of Canada for providing generou support for this work. TABLE OF CONTENTS Page Abstract i List of Tables viii List of Figures x Introduction 1 Results and Discussion 20 Work with P-chloroiminophcsphoranes 20 Preparation of Triaryliminophosphoranes 21 Irradiation of Iminophosphoranes 22 A) W Spectra of Iminophospho- ranes 22 B) General Irradiation Conditions 23 c ) Photochemically Stable Ylids 23 D) N-Aryl-triphenyliminophos- phoranes 24 a) Trapping of Aryl Nitrene by a Photostable Ylid 40 b) Trapping of Aryl Nitrene by a Photolabile Ylid 40 E) N-Alkyl -t riphenyliminophos- phoranes 44 F) Wavelength Dependence of Irradiation of Triphenylimino- phosphoranes 48 Experiment a1 53 References 64 vii LIST OF TABLES Page TABLE I Solvent effect on the product distribution of the irradiation of diphenyltriphenylphosphinazine (1-26) and diphenyldiazomethane (1-27) TABLE I1 Wavelength dependence of the irradiation of diphenylmethylene- t riphenylphosphorane (1-21) in cyclohexene TABLE 111 Irradiation of dimethylmethylene- t riphenylphosphorane (1-29) TABLE IV Formation of azobenzene in the irradiation of phenyl and substituted phenyl azides TABLE V Irradiation of N-phenyltriphenyl- iminophosphorane ( 1-36) TABLE VI Irradiation of ortho-substituted N-phenylt riphenyliminophosphoranes in benzene 31 TABLE VII Solvent ef feet on product distribution of the irradiation of N-2-biphenyl- t riphenyliminophosphorane (1-39) 34 viii Page TABLE VIII Effect of purge gas on product distribution of the irradiation of ylid 1-39 in benzene 35 TABLE IX Effect of oxygen on product distribution of the irradiation of ylid 1-36 38 TABLE X Irradiation of N-alkyt riphenyl- iminophosphoranes 45 TABLE XI Migratory aptitudes of pyrolysis of trityl azides 51 TABU3 XI1 List of iminot riphenylphosphoranes prepared 56 LIST OF FIGURES Page FIGURE 1 Irradiation of dimethylmethylene- t riphenylphosphorane ( 1-29) 11 FIGURE 2 Irradiation of N-t -butylt riphenyl- iminophosphorane (1-30) 13 FIGURE 3 Mechanistic scheme of organic azide reaction with olefin 16 FIGURE 4 Irradiation of N-2-biphenyltriphenyl- iminophosphorane (1-39) in the presence of oxygen 37 FIGRUE 5 Irradiation of N-aryltriphenylimino- phosphorane in the presence of aryl azides 41 FIGURE 6 Irradiation of N-benzyltriphenyl- iminophosphorane (1-48) 46 FIGURE 7 Irradiation of N-cyclohexyltri?henyl- iminophosphorane (1-54) 47 FIGURE 8 Mechanistic scheme of N-aryltriphenyl- iminophosphorane irradiation 49 INTRODUCTION Molecules possessing double bonds between pentavalent phosphorus and carbon (methylenephosphoranes) or nitrogen (iminophosphoranes, monophosphazenes, or phosphinimines) ( 1-1 ) 1 are classified as ylids . Depending on the phosphorus, carbon and nitrogen substi- tuents, some of these ylids are susceptible to photolytic fragmentation. Radiation induced homolytic dissociation of the heteromultiple bonds of these ylids may lead to a phosphine (I-2), and a reactive carbene or nitrene (1-3) (equation 1 ) . Amino nitrenes have been invoked in a number of nitro- gen-sulfur ylid photodissociations. Anderson and co-workers 2 irradiated a number of dimethylsulfoximines in the presence of olefins, and found that aziridines were formed along with dimethylsulfoxide (equation 2). Since the same aziridines were formed when the analogous cyclic N-amino compound was oxidized by lead t3traacetate in the presence of olefins, the amino nitrene was considered the most likely intermediate in both reactions. Strength is lent to this suggestion by several additional reports of the trapping of presumed amino- nitrenes with olefins to form aziridines3 . All of the reactions reported to date that appear to involve trappable amino nitrenes are those where the amino nitrogen is substituted with electron-withdrawing groups. 0 Carbenes have been invoked in a number of carbon sulfur photodissociation react ions. Corey and Chaykovsky 4 first reported the results of irradiation of dimethylsulfoxonium phenacylide (1-4). Upon irradiation in alcohol, the ylid was transformed smoothly to dimethylsulfoxide and the corres- ponding ester 1-5 by a reaction that was envisioned to involve the ket ocarbene (1-6) and ketene (1-7)intermediates (equation ROH - PhCH=C=O -> PhCH2C02R 1-7 1-5 3 It was not determined if the formation of the ketene was concerted or involved the ketocarbene intermediate (equation 4). Trost has irradiated dimethylsulfonium phenacylide (1-8) in chloroform and benzene 5 , and obtained nearly quanti- tative yields of trans-1,2,3-tribenzoylcyclopropane (1-9). The cyclopropane (1-9) was envisioned as arising from the reactions of a carbene (1-6) with a second mole of ylid (1-8) to produce dibenzoylethylene (1-10) which subsequently combined either with ylid or carbene to form cyclopropane 1-9 (equation 5). Ph CMe I I 0 R'OH 1 (1-11) In ethanol a 48% yield of acetophenone (1-11), propiophenone (1-12, and ethylphenyl acetate (1-13, Rf = ~t) were formed and the yield of cyclopropane 1-9 was lowered to 40-50%. A reasonable mechanistic pathway for the formation of propiophenone involves a Stevens rearrangement of the ylid followed by the photolytic decomposition of the resultant 6 &-methylthiopropiophenone . The ylid does not undergo the Stevens rearrangement thermally under these conditions. This formation of propiophenone was thus taken by the author as an example for the first photolytic induced Stevens rearrange- ment (equation 6). Using 2-propanol caused significant increase in the ratio of acetophenone to phenylacetic ester. This was considered to indicate that the ketone arose via a carbene intermediate, since an increase in the reactivity of the solvent toward hydrogen abstract ion should increase the relative amount of ketone by this route. The formation of benzoylnorcarane (1-14) when the reaction was carried out in the presence of cyclohexene was considered to be another indication of a carbene . Although the course of reaction can be explained by other mechanisms, they were considered less likely. The ylid 1-6 could give a diradical which dimerized to form dibenzoylethylene (1-10) and then underwent further reaction with the irradiated ylid to yield