Advances in Organometallic Chemistry, 7

337 Pages·1969·14.709 MB·English

by  F G A Stone, Robert West

T
H. J. EMELEUS HENRY GILMAN
CONTRIBUTORS TO THIS VOLUME
A. G. Brook
James P. Collman
Henry Gilman
W. P. Grifith
K. Kuhlein
J. J. Mrowca
W. P. Neumann
G. W. Parshall
Warren R. Roper
Advunces in
ORGANOM€TALLIC
CH E MIS TR Y
EDITED BY
F. G. A. STONE ROBERT WEST
DEPARTMENT OF INORGANIC CHEMISTRY DEPARTMENT OF CHEMISTRY
SCHOOL OF CHEMISTRY UNIVERSITY OF WISCONSIN
THE UNIVERSITY MADISON, WISCONSIN
BRISTOL, ENGLAND
VOLUME 7
1968
ACADEMIC PRESS New York London
0
COPYRIGH@T 1 968, BY ACADEMIPCR ESSI, NC.
ALL RIGHTS RESERVED.
NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM,
BY PHOTOSTAT, MICROFILM, OR ANY OTHER MEANS, WITHOUT
WRITTEN PERMISSION FROM THE PUBLISHERS.
ACADEMIC PRESS, INC.
111 Fifth Avenue, New York, New York 10003
United Kingdom Edition published by
ACADEMIC PRESS, INC. (LONDON) LTD.
Berkeley Square House, London, W.l
LIBRAROYF C ONGRESCS ATALOCGA RDN UMBE6R4-:1 6030
PRINTED IN THE UNITED STATES OF AMERICA
List of Contributors
Numbers in parentheses indicate the pages on which the authors’ contributions begin.
A. G. BROOK(9 5), Department of Chemistry, University of Toronto, Toronto,
Canada
JAMES P. COLLMAN(5 3), Department of Chemistry, University of North
Carolina, Chapel Hill, North Carolina
HENRYG ILMAN(l ), Department of Chemistry, Iowa State University, Ames,
Iowa
W.P . GRIFFIT(H21 l), Department of Inorganic Chemistry, Imperial College,
University of London, London, England
K. KUHLEIN(2 41), Institute of Organic Chemistry, Justus Liebig University,
Giessen, Germany
J. J. MROWC(A15 7), Central Research Department, E. I. du Pont de Nemours
and Company, Wilmington, Delaware
W.P . NEUMAN(2N4 1), Institute of Organic Chemistry, Justus Liebk Univer-
sity, Giessen, Germany
G. W. PARSHAL(L15 7), Central Research Department E. I. du Pont de
Nemours and Company, Wilmington, Delaware
WARRENR. ROPER( 53), Department of Chemistry, University of Auckland,
Auckland, New Zealand
1 Present address: Department of Chemistry, Stanford University, Palo Alto, California
2 Present address: Farbwerke Hoechst A. G., Frankfurt/Main, Germany
V
Some Personal Notes on More
Than One-Half Century of
Organometallic Chemistry
H EN RY GI LMAN
Deportment of Chemistry
lowa State University
Ames, lowo
I. Grignard Reagents : Some General Procedures and Techniques . 4
11. Organolithium Compounds. . 7
111. Relative Reactivities . 11
-
IV. Metalation . . 15
V. Halogen-Metal Exchange . 19
VI. Metal-Metal Exchange . 21
VII. Catenation . 25
VIII. Some Free-Radical Studies . 28
IX. Solvent Coordination Effects . 30
X. Physiological Action and Chemical Constitution . 30
XI. Some World War I1 Studies . 33
XII. Some Recent and Current Studies . 34
A. Mass Spectroscopy . 34
B. d?r-d?rBonding . 35
C. Concerning Dissociation of Dimetallic and Dimetalloidal Species. 36
.
D. Asymmetrical Silicon in Organosilicon Compounds 38
E. Noncatalyzed Disproportionation of Diphenylsilane . 39
.
F. Silenes 39
.
G. Small-Ring Organosilicon Compounds 40
H. Ultraviolet Spectra Studies . 41
I. Silylmetallics . 43
J. Organometallic Compounds of Copper, Silver, and Gold; Thermal
Stabilities . 44
K. Reactions with Perhalogenated Types . 46
XIII. What Constitutes Discovery ? . 47
XIV. Epilogue . 49
.
References 50
It was in 1912 that I carried out my first organometallic reaction. This
was done as part of laboratory work in an elementary course in organic
chemistry. The reaction was between acetone and methylmagnesium
I
2 HENRY GILMAN
iodide to give tert-butyl alcohol. This experiment was a bit of a disappoint-
ment, even though some of the tert-butyl alcohol was obtained. From the
lectures we had learned how versatile was the Grignard reagent for obtaining
the widest variety of compounds ; and there was an extra bit of pleasure and
a challenge in writing out paper syntheses on some assigned work and in
“ ”
examinations. Perhaps very few less satisfactory syntheses could have been
selected for beginners in laboratory work because of the low yield of product
obtained. I vowed that if I ever taught beginners, I would select a Grignard
reaction which gave good yields of a solid which could be conveniently
isolated ;a nd this was done several years later, as part of a beginning labora-
tory course I taught, with a reaction between ethyl benzoate and phenyl-
magnesium bromide to give triphenylcarbinol.
My subsequent academic training through my Ph.D. work did not include
any laboratory experiments involving organometallic chemistry. For a
one-year period after my bachelor’s degree, I went to Europe; and of this
time spent more than one-half year with Professor Staudinger in Zurich,
where I did a little work on diazo compounds. At that time Staudinger was
interested in both azo compounds and in ketenes. It was not surprising,
therefore, that he mentioned in a general discussion the possibility of
preparing diazoketene, N=N=C=C=O. I observed that this might be a
rather unstable compound, having four units of unsaturation in a com-
pound containing only five atoms. He agreed, but suggested we visit a room
in the basement of the Chemistry building at the ETH (Eidgenossische
Technische Hochschule) which had one rather small incandescent red bulb
to reduce risks that might be involved in photochemical activation. Shortly
thereafter, I completed the work on which I was engaged and the time had
come for me to move on to Oxford with Professor W. H. Perkin. Therefore,
I did not make use of that unusual laboratory and I do not know what was
subsequently done with the exciting diazoketene problem.
On returning to Harvard, I completed my graduate work with Professor
E. P. Kohler, who was not only an excellent and polished lecturer, but also
a superb laboratory worker. While at Bryn Mawr College and later at
Cambridge, he did classic work which laid a firm foundation for the under-
standing of conjugated systems, and particularly for 1,4-additions of
Grignard reagents to alpha,beta- unsaturated carbonyl systems.
After some war work, instructing at Cambridge, and then at the Uni-
versity of Illinois (where Roger Adams had gone a few years earlier, and
with whom I had done some research work as a senior), I went on to Iowa
More Than One-Half Century of Organometrlllc Chemistry 3
State at Ames (Zu). Here I did my first research work on organometallic
chemistry. The problem was one involving the mode of addition of phenyl-
magnesium bromide to diphenylketene. The idea for it came from some
regular class lectures given by Kohler. I had not done research prior to that
time either with the Grignard reagent or with ketenes.
Two possible modes of addition could be involved primarily in this
reaction. First, there might be addition to the olefinic linkage.
+
PhzC=C=O PhMgBr + PhzC-C=O
I I
BrMg Ph
(1)
Second, there might be addition to the carbonyl group.
+
PhzC=C=O PhMgBr + PhzC=C-OMgBr
I
Ph
(11)
The product isolated, triphenylvinyl alcohol (or its ketone), would be
expected to result by either mode of addition. In a sense, these involved a
sort of impossible reaction because ketene additions were then inter-
" "
preted as additions to the olefinic linkage, and at that time there was no
known addition of the Grignard reagent to an olefinic linkage. One way of
throwing light on the course of the reaction was to treat the intermediate
compound with benzoyl chloride to see whether the -MgBr was on carbon
or oxygen. The product isolated was the benzoate of triphenylvinyl alcohol.
This supported structure (11) and established the general hypothesis that
additions to ketenes involved initially the carbonyl group rather than the
olefinic linkage.
This work, with Heckert, was our first publication in the area of organo-
metallic chemistry (24). It was not only a pleasant beginning, but gave as
much satisfaction as any subsequent work.
The finding that the Grignard reagent did not add to diphenylketene in
a manner like that generally accepted then for addition reactions to ketenes,
led logically to a study of some other related terminal cumulated unsaturated
systems :
RzC=C=O
RN=C=O
RN=C=S
RN=S=O
4 HENRY GILMAN
The results with all of these types proved or indicated that phenylmagnesium
bromide added initially to the terminal unsaturated linkage. It was in
connection with these studies that we observed a highly unusual trans-
formation.
In the reaction of each of these terminal cumulated unsaturated systems
with phenylmagnesium bromide in ether, the reaction stops at the terminal
unsaturated group even with a liberal excess of phenylmagnesium bromide
and extended refluxing in ether. This was hardly unexpected with ketenes
inasmuch as subsequent addition to an ethylenic linkage was unlikely on
the basis of information then available on the nonaddition of RMgX to
isolated olefinic linkages. The situation, however, was different with types
like phenyl isocyanate and phenyl isothiocyanate, because it was known that
organomagnesium halides add to the -N=C- group. Accordingly, it was
expected that when phenyl isocyanate (or phenyl isothiocyanate) was
refluxed for an extended time and at elevated temperatures with an excess
of PhMgBr, a second molecule of the Grignard reagent should add to the
-N=C- linkage. The chief product isolated contained neither oxygen
nor sulfur and was shown to be N-(o-phenylbenzhydry1)aniline (111).
Incidental to an examination of the course of the reaction it was postulated
that benzophenone-anil, Ph2C=NPh, was an intermediate, and it was then
established that this anil as well as PhN=C=O and PhN=C=S gave (111)
under forcing conditions. What apparently happens in these cases is an
unlocking of the benzene ring’’ or the highly unusual type of 1,4-addition
to a conjugated system that is part aliphatic and part aromatic ; the following
transformations were depicted to account for the formation of (111) :
No reaction of this kind had been described at that time. Shortly thereafter
this type of reaction was found to be rather general, particularly as the
result of the splendid studies by E. P. Kohler, and by Fuson [who wrote an
excellent review article on it (22)].
I
GRIGNARD REAGENTS: SOME GENERAL PROCEDURES
AND TECHNIQUES
Quite early in our studies we became aware of the desirability and the
necessity of developing new and improved laboratory procedures for
operations involving Grignard reagents. Methods for quantitative analysis
were paramount, and in this as well as many other studies we were fortunate
More Than One-Half Century of Organometallic Chemistry 5
in having a background of prior studies by others. Within the obvious
limitations of a personal account of this kind, it is out of the question to make
appropriately adequate references to the work of others, just as it is not
possible to include adequate mention and references to our own work.
MgBr
HC, c‘/C H
H H
This presentation carries with it an inordinately high degree of selectivity.
Actually, because of our numerous publications we have been compelled,
to our deep regret, to make some almost random selections and thereby to
commit gross omissions of some equally worthy and interest;-? work.
To offset this in part we have included in a series of general referel.. (I, 2,
4, 9-11, 13-23,26-35,37,43-46) citations to review articles, chapters, etc.,
on some aspects of part of our work which contain, in turn, appropriate
references to pertinent work by others.
In the several procedures examined for the quantitative determination of
RMgX compounds, the one which we found most convenient was the
simple acid-titration method. In their classic book on the Grignard reagent,
Kharasch and Reinmuth (36)e valuate the several procedures and conclude :
Organic chemists appear to have accepted the acidimetric method rather
“
generally, possibly because of the extreme simplicity of its technique and
the consistency of its results. Incidentally, smaller aliquot portions of
Grignard solution and lower concentrations of standard acid and base than
those originally proposed by Gilman et al., have been found entirely
satisfactory.”
6 HEN RY GI LM AN
Another important tool developed was a qualitative test, namely, the
Michler’s ketone Color Test I. This we found to be uncommonly helpful
over the years, and we looked upon it as one of the most useful and important
reactions in organometallic chemistry. As our studies extended into other
areas such as those involving organolithium compounds, other color tests
were developed to differentiate RMgX from RLi compounds, and also to
differentiate between types of RLi compounds.
With suitable procedures for the qualitative and for the quantitative
estimation of such classes of organometallic compounds, we were provided
with the essential means for examining a series of significant factors. Among
these were such aspects as (1) optimal conditions for the preparation of
important types of organometallic compounds ;( 2) catalysts for the prepara-
tion of some RM compounds, otherwise preparable with difficulty; (3)
effects of a wide variety of solvents; (4) stability of some RM compounds or
their solutions; and (5) relative reactivities of some RM compounds.
We might mention first that it was our practice whenever exploring a new
group of organometallic compounds to try to devise useful qualitative and
quantitative procedures. This applied not only to the more conventional,
synthetically useful types such as RMgX and RLi, but also to species such
as R3SiM, R3GeM, R3SnM, and R3PbM.
The determination of optimal conditions for the preparation of some
moderately reactive organometallic types provided certain unexpected
dividends, described elsewhere, such as the benzhydryl radical (Ph,CH-)
formed incidental to the preparation of Ph,CHMgX (then an inaccessible
type). Also, the development of satisfactory conditions for the synthesis of
allylmagnesium halide types (prior to which time they were unavailable and
used indirectly by their formation in situ in the presence of reactants by the
Barbier technique) was of particular significance in some relative reactivity
and analytical studies. In connection with the benzyl and related Grignard
types, mention should be made of the extensive studies with J. E. Kirby on
the rearrangement reactions of benzylmagnesium halides and their
congeners.
An anecdote may be in order relative to an aspect of catalysts for the
preparation of some Grignard reagents. After a series of experiments
revolving around the known catalytic effects of copper and some of its
compounds, we found that an alloy of magnesium with 12;5-% of copper
was highly effective when used in a fine state and activated by iodine. The
required amount of this catalyst was extremely small. At the request of a