This dissertation has been 65—9339 microfilmed exactly as received BODDEKER, Karl Wilhelm, 1934- SYNTHESIS AND CHARACTERIZATION OF A NEW CLASS OF CYCLOBORAZANES. The Ohio State University, Ph.D., 1965 Chemistry, inorganic University Microfilms, Inc., Ann Arbor, Michigan SYNTHESIS AND CHARACTERIZATION OF A NEW CLASS OF CYCLOBORAZANES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Karl Vilhelm BSddeker, cand.chem., H.Sc. The Ohio State University - 1965 Approved by Department of Chemistry ACKNOWLEDGMENTS This work was supported financially by a grant from the National Science Foundation. I would like to thank Professor Sheldon G. Shore for sug­ gesting this problem and for his guidance throughout the inves­ tigation. I am indebted to my student colleagues, Dr. C. W. Hickam, Jr. and Dr. G. E. McAchran for their willingly sharing experience and equipment. My wife, Helga, has made it possible for me to study in the United States; I gratefully acknowledge her moral support and patience. ii VITA July 12, 193^ . Born in Berlin,Germany 1955 .......... Reifeprufung in Dtisseldorf, Germany 1939 ■ ........ Diplomvorexamen in Chemistry, University of Gottingen, Germany 1962 ........ .. M.Sc., The Ohio State University, Columbus, Ohio 1962-1963 ........ Teaching Assistant, Dept, of Chemistry, The Ohio State University, Columbus, Ohio iii CONTENTS Page Acknowledgments .................................... ii V i t a ................................................ ill Tables.............................................. v± Illustrations ....... .................... •• vii I. INTRODUCTION .................................... 1 A. Background ..... ................ ..... 1 1. Introduction........................... 2 2. Nomenclature ............................ 3 3. The boron-nitrogen system ........ 7 B. Statement of the problem .......... 10 II. EXPERIMENTAL .................................. 12 A. Apparatus .............. 12 B. Reagents and s o l v e n t s ...................... 20 C. Generation of diborane ........... 23 D. Analytical procedure ........................ 26 E. Diammoniate of diborane and ammohia-borane . • 27 1. Synthesis .............................. 27 2. Properties ................ 29 F. Cycloborazanes ................ 30 1. Synthesis ........... 30 2. Separation of products................... 37 3. Characterization .................... ^1 iv CONTENTS (contd.) Page G. Pyrolysis of cyclopentaborazane .............. 55 1. Procedure ........................ 55 2. Products .......................... 53 H. Pyrolysis of cyclodiborazane .................. 6l III. D I S C USSION.............. 66 A. Cleavage of diborane ............................................................... 66 B. The reaction of sodium amide with diammoniate of diborane ............ ......... 69 C. Cyclic versus open aminoboranes .............. 73 Bibliography.............. 76 v TABLES Table Page 1. The boron-nitrogen s y s t e m ........ • .............. 4 2. Analysis of (BH^NHg)^ ^ 3 . X-ray powder diffraction pattern of ( B ^ N ^ ^ • • • ^2 4. Infrared spectrum of (BH^NB^)^ ^ 5« X-ray powder diffraction pattern of (BH^NH^)^ . 46 6 . Infrared spectrum of ( B H ^ H ^ ) ^ .................... 48 7. Analysis of (BH^NH^)^ 49 8 . X-ray posder diffraction pattern of (BH^NHg)^ 50 9. Infrared spectrum of (BH^NH^)^ .................... 50 1 0 . Mass spectra of pyrolysis products of (BI^NI^)^ • • 64 11. Infrared spectrum of open-chain aminoboranes . 75 vi ILLUSTRATIONS Figure Page 1. Reaction station and large volume trap of the auxiliary reaction train ........ 13 2. Reaction apparatus . • . • ................... 13 3 . Apparatus for fractional micro-sublimation . 17 4. Apparatus for the synthesis of cycloborazanes . 32 5. Infrared spectrum of (BELjRHg^................. 44 6 . Infrared spectrum of (BI^NH^)^................. 47 7. Infrared spectrum of (BI^NH^)^ . ............. 31 8 . Comparison of X-ray powder diffraction patterns 54 9* Pyrolysis apparatus ................... 56 10. Pyrolysis a p p a r a t u s ..................... 56 11. Pyrolysis apparatus ..................... 6l vii I . INTRODUCTION A* Background 1. Introduction It is well known that the "renaissance of inorganic chem­ istry" is due to no small degree to the pioneering work of Alfred Stock and his school in the field of boron chemistry. The unique character from the standpoint of normal valendy relationships of many boron—containing substances prepared and identified by Stock has stimulated ewer increasing research activity in both exper­ imental and theoretical chemistry. The development by Stock's group of new apparatus and techniques was of equally far-reaching importance; in particular, the chemical vacuum line has made pos­ sible the investigation of substances not capable of existence outside the thermally and atmospherically controlled environment of the vacuum system. The chemistry of the element boron is distinguished not only by the unique series of boron—hydrides, but also by the sys­ tem of boron—nitrogen compounds. It was one of Stock’s pupils, Egon Wiberg* who began the systematic investigation of these compounds. He introduced the concept of isosterism to interpret similarities in physical properties between molecules or atom groupings having the same number of atoms and electrons and the sane total nuclear charge* The groups B-N and C-C represent such an IsoBteric pair andt indeed, many boron—nitrogen compounds are known which are isosteric analogs of hydrocarbons. The fact that Stock discovered the perhaps most striking example for this simil- arity, borazine, "inorganic benzene" (l), resulted for a time in an overemphasis of the existing analogies and in misappraisal of the differences, as well as difficulties, involved* Deceptive, too, was the early belief that boron, being a neighbor of carbon in the periodic table, should have an extensive chemistry re­ sembling organic chemistry* Even today, almost forty years after the first synthesis of borazine, the number of boron—nitrogen compounds containing only the elements boron, nitrogen, and hydro­ gen is small, although many organic derivatives are known. The present investigation represents a contribution to the chemistry of unsubstituted isosteric analogs of hydrocarbons in the boron- nitrogen system. 2• Nomenclature At present, no generally accepted system for the nomen­ clature of boron-containing substances exists* In 1955* an "Advisory Committee on the Nomenclature of Organic Boron Com­ pounds" was established within the American Chemical Society which, in 1957 and 1958, produced a "Preliminary Beport" (2) containing recommendations approved by the Chemical Abstracts Service* These recommendations are followed in this dissertation, except that the well-known designation "diammoniate of diborane" for the compound is used, rather than "diaramine— dihydroboron(l )hydroboraten as recommended. The other de­ signations are as follows: Amine-boranes are addition compounds of amines with borane, BH^, or substituted boranes. Aminoboranes are compounds which have a normal covalent bond between boron and nitrogen atoms and in which the free elec­ tron pair of the nitrogen can participate in the B-N bond. Cycloborazanes are cyclic aminoboranes containing alter­ nating B-N bonds. If it is not known whether a compound has a cyclic or chain-like structure, the compound is referred to as an aminoborane, and the degree of polymerization is noted. Borazines (formerly called borazoles) are the isosteric analogs of cyclic aromatic hydrocarbons. 3* The boron—nitrogen system Modern boron-nitrogen chemistry may be said tc' begin with the first synthesis of the diammoniate of diborane by Stockand Kuss in 1923 (3)• Much of the subsequent work was done by Wiberg, — t who developed the basic concepts of the more modern approaches to this system. He classified the boron-nitrogen derivatives into the three major groups of amine-boranes, aminoboranes, and borazines, according to the nature of the bond and in reference to the principal classes of aliphatic hydrocarbons (*0 • The diammoniate of diborane itself, the true nature of which was not recognized until 1958 (5)1 has no place in this classification, as have a number of other boron-nitrogen compounds discovered since* Nevertheless, it must be considered the parent compound for most any of the unsubstituted boron-nitrogen species known, not only historically, but also by way of definite synthetic relationships, as outlined below* In the following table are summarized the boron-nitrogen species under consideration, including some which have recently been identified in this laboratory* Not included are the hydra- zinoboranes and the amine-substituted derivatives of some of the species, which also consist of the elements boron, nitrogen, and hydrogen only* TABLE 1 THE BORON-NITROGEN SYSTEM I II III IV BEjNHj BH2NH2 [bh2 (nh5)23 [bh^] B3N5H6 (-bh2nh2-) (BH2NH2)2 BH^NH^ EjNBH2NH2 (?) (bh2nh2)3 VA* b2h3nh2 (7) ( B H ^ H ^ H^NB^HBHj (?) B3N3H6 (bh2nh2 )5 b5n5h8 VAo Compounds followed by a question mark have not been identified; however, their existence under certain conditions appears to be possible* The species in the first three columns of Table 1 can be identified with Wiberg'B classes of boron-nitrogen compounds, i.e. are analogs of hydrocarbons. A survey of the table indicates that the B-N unit apparently does not possess the ability for catenation which characterizes the isosteric