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Gas-Phase Reactions of M+ and [CpM]+ (M = Fe Co Ni) with 1 3 5-Trisilacyclohexane First Evidence for the Formation of 1 3 5-Trisilabenzene.

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1111 When starting with racemates, OY,,,,, =
sample ofcomposition (tl, I ) OY,,, = j([jd
+ I ) , while for a
+ 1) - 2(/k/41'2)!tl(/1- 1). The
optical yield can be related to the thermodynamic chirdl recognition.
AAG = - RT1nl.i. as /j = [(I + OY)/(l - OY]' when d = l = I = 0.5
( 0 s OY < 1).
[12] This exprcssion was obtained from J = (PDjFD)
( k P / k " by
) applying the
distribution constant (K,)-Hildebrand solubility (= polarity) parameter
(6)relationship [12a.b] to both diastereomeric salts. a ) H. Freiser. Solvent
E.viruciion in An Introduction io Sepurarioil Science (Eds.: B. L. Karger,
S. R . Snyder. C. Horvath), Wiley, New York, 1973, Chapter 9, pp. 248250. b) P. J. Schoenmakers, H . A . H . Billiet. L. de Galan, Chroniurogruphiu, 1982. 1 5 ( 3 ) , 205-214. c) For a description of optical yield
related to the Taft's u* parameters of the interacting groups in the
diastereomeric salts. see: ref. [2 b]. d) For the role of chiral discrimination
in the energetics of salt formation. see: S . P. Zingg. E. M. Arnett. A. T.
McPhail. A . A. Bothner-By. W. R. Gilkerson, J. A m . Chem. Soc., 1988,
110. 1565- 15x0.
[I 31 J. H. Hildebrand. R. L. Scott, Regular Solurion.!, Prentice-Hall, Englewood ClilTs. NJ, 1962.: A. F. M. Barton, CRC Hundbook of Soluhilif?
.T urui Orher Cohesion Purunwirrs, C R C Press Inc.. Boca Raton.
Florida. 1983.
[I41 Tbc total resolution of carboxylic acid 1 was effected by selective solubilization with dioxane. The enantiomeric excess of the sample is soluble in
this solvent. while the racemic part forms a stable and insoluble solvate
[ ( * ) - I 'dioxane] [4b].
Gas-Phase Reactions of M + and [CpM]+
(M = Fe, Co, Ni) with 1,3,5-Trisilacyclohexane:
First Evidence for the Formation of
By Asgrir Bjarnason* and Ingvar Arnason
The chemistry of carbosilanes has recently been reviewed."' and a number of silicon-substituted cyclohexane
derivatives have been reported including C,H,,Si 1,[']
C,H,,Si, 2a,I3]and Si,H,, 3.14]Metal-catalyzed triple dehydrogenation of the all-carbon analogue to form cyclohexatriene (benzene) is well known, and its mono- and disila
analogues, C,H,Si 4 and C4H,Si, 5, have been isolated and
characterized at low temperature in an argon matrix.15]To
our knowledge, however, neither C,H,Si, 6 nor Si,H, have
yet been observed. We report here on C,H,Si,, C,H,Si,, and
C,H,,Si, as ligands produced in the reactions of Fe', C o + ,
Ni'. [CpFe]+,[CpCo]', and [CpNi]' with 2a. The formulas
2a: X = H
2b: X = D
sit ?iH2
2c: x = CI
Dr. A. Bjarnason."' Prof. Dr. I. Arnason Science Institute,
University of Iceland
Dunhaga 3. IS-I07 Reykjavik. (Iceland)
A. Bjarnason is also Adjunct Associate Professor in the Department of
Chemistry University of Delaware, Newark, D E (USA).
This research was funded in part through grants from the University of
Iceland Research Fund and the Icelandic Science Foundation. We thank
Prof. D. P. Ridge for providing instrument access and for helpful discussions.
Ang6'11,.Clfwv. Inr. Ed. E n d . 1992, 31, No. 12
for the ligdnds were unambiguosly determined, but the structures, especially that of C,H,Si,, can only be speculated o n ;
nevertheless, these appear to be the first observations of the
trisilabenzene 6.
Reactions of metal ions with organic molecules in the gas
phase have been extensively studied in recent years by several
research groups.16] Dehydrogenation of cyclohexane by
Fe [ 7 - 91 Co [ 8 101 Ni ,[8. 91 [CpCo] + ,[I 11 and [CpNi] + [I21
have been reported, and in all cases, save Ni', elimination of
up to three hydrogen molecules was observed to form the
benzene ligand. Reactions of metal ions with silicon compounds in the gas phase have not been studied extensively.
Of particular interest for us was the study of Beauchamp
et al. on methylsilanes,[131in which elimination of molecular
hydrogen from a single silicon atom was observed and a
product with a metal-silicon double bond proposed. The
formation of the coordinated benzene from cyclohexane in
the reactions with metal ions and ionic metal complex fragments prompted us to investigate reactions of such ions with
2 a in the gas phase, since efforts to produce 6 have been
unsuccessful so far.
The product distribution in the dehydrogenation reactions
of M' and [CpM]' with 2a is shown in Table 1. Interestingf
Table I. Product distribution [ "/.] in dehydrogenation reactions of 1.3.5-trisiIdcyclohexane with M + and [CpM]'.
Reactant ion
Elimination of
3 H,
ly, [CpM]' ions are more reactive than the bare metal ions
and cleave more than one H, molecule from 2 a . [CpNi]' is
the most efficient, which is somewhat surprising: if the structure and bonding in [CpMC,H,Si,]+ were analogous to that
in [CpMC,H,]+, then in the case of M = Ni it would be a
20electron, in the case of M = Co a 19electron, and in the
case of M = Fe an 18electron species. From this point of
view one would have expected the Fe complex to be formed
more favorably than the Ni complex.
To test if H, is cleaved only from the carbosilane and
whether the Cp ligand participates in that process, isotopically labeled [[D,JCpFe]+ was allowed to react with 2a. Although minor products (< 5 %) from loss of deuterium were
observed, the main elimination reactions left the Cp ligand
Another question that arises in light of the results of
Beauchamp et al.['31is whether hydrogen is eliminated only
from Si, and if the metal than possibly forms a double bond
to Si. The dissociation energies of the Si-H and C-H bonds
are 314 and 414 kJmol-', respectively.['] As less energy is
required to break the Si-H bond and in addition, backbonding may exist in the bond between the metal ion and Si, it was
essential to establish which hydrogen atoms are eliminated in
the reactions.
For this purpose, a sample of 2 b was prepared and allowed to react with M + and [CpM]+. The results indicate
that Ni' eliminates only D, (1 and 2 equiv). Fe' eliminates
H,, HD, and D, in the ratio 0.2:0.6:1.0, but only a minor
amount of double dehydrogenation is observed (see
'~cVCH Verlu~.s~esellschu~i
m h H , W-6Y40 Weinheim, 1992
OS70-0833/Y2/f212-1633 S 3.50+ ,2510
Table 1); in the case of C o t , the cleavage of one equivalent
of molecular hydrogen from 2 a is a minor reaction, but in
the reaction with 2 b two equivalents of molecular hydrogen
are formed as H,, HD, or H, + D,, HD + D,, and D, in the
ratio 0.05:0.1:0.8: 1 .O. These results suggest that Nit eliminates hydrogen only from SI and, thus, may form bonds only
to silicon atoms in the ring. Fe+ and Co' show less preference for elimination from the silicon atoms, and elimination
of H D points to the formation of a double bond between C
and Si. Triple dehydrogenation in the reactions of [CpM]'
with 2b was shown to involve mostly elimination of 3 H D
and to a lesser extent 2 HD + D,. Only traces of the product
of the elimination of 3 equivalents of D, was observed, which
supports the hypothesis that the main product in the triple
dehydrogenation reaction requires the formation of three
carbon-silicon double bonds and that the 1,3,5-trisilabenzene 6 ligand is produced.
Collision-induced dissociation (CID) experiments can
give valuable information about the structure of ions
trapped in the cell of an FT mass spectrometer; Jacobson
and Freiser successfully employed this technique to study
products from the reactions of [CpCo] with cyclohexane.1' 'I They found, for example, that [Co(Cp)(benzene)]+
lost benzene upon CID, consistent with a stronger bond
between Co-Cp than between Co-benzene. CID studies on
[CpNiC,H,Si,]+ (accelerated to 90 eV) were performed with
Ar as the collision gas. Aside from losses of one, two, and
three molecules of hydrogen, three other fragment ions were
observed at mjz 123 (45 YO),58 (35 YO),and 93 (20 YO),corresponding to [CpNi]', Ni +,and C,H ,Si+, respectively. The
last ion is probably formed by rearrangements, since under
multiple-collision conditions (higher pressure of Ar) it was
the dominant fragment ion, but at conditions approaching
the single-collision regime this ion became less intense with
respect to the signal corresponding to [CpNi] , which became the dominant fragment ion. These observations are in
accord with the proposed structure of [CpNiC,H,Si,]+.
The results from the CID experiments and the deuterium
labeling studies lead us to the conclusion that the trisilabenzene 6 was formed as a ligand in these experiments. Further
studies of reactions of metal ions and ionic metal complex
fragments with other silicon-containing compounds are in
progress in light of these promising results.
CAS Registry numbers:
2a. 291-27-0; 2b, 144436-83-9; 6, 143587-15-9; F e + , 14067-02-8; Co', 16610-
75-6; Ni'. 14903-34-5; [CpFe]', 61827-27-8; [CpCo]+. 79075-58-4; [CpNi]',
[I] G . Fritz, E. Matern, Carbo.ri1anes. Synthe.res and ReactJonr, Springer,
Berlin, 1986.
[2] R. West, J. Am. Cliem. Soc. 1954, 76, 6012.
[3] G. Fritz. H. Frohlich, Z. Anorg. ANg. Chem. 1971. 382, 9.
[4] a) E. Hengge, D. Kovar, Angew. Chem. 1977, 89, 417; Angen. Cheni. Int.
Ed. Engl. 1977, 16, 403; b) Z. Anorg. Allg. Chern. 1979, 459, 123.
[S] a) G. Maier. G. Mihm. H. P. Reisenauer. Anrew. Chem. 1980. 92. 58:
Angew'. Chem. In/. Ed. Engl. 1980.15, 52; b) G. Meier, G. Mihm, R. 0. W.
Baumgdrtner, H . P. Reisenauer. Cheni. Ber. 1984, 117. 2337; c) G. Maier,
K. Schottler, H. P. Reisenauer, Tetrahedron Lett. 1985, 26, 4079.
For representative work in this field see, for example: a) P. B. Armentrout,
J. L. Beauchamp, J. A m . Chem. Soc. 1981, 103, 784; b) J. Wronka, D. P.
Ridge, ibid 1984, 106, 67; c) S. K. Huang, J. Allison, Organomezalhcs
1983,2.883:d) Y Huang, B. S. Freiser, J. Am. Chrm. Soc. 1988,110,387;
e) A. K. Chowdhury, C . L. Wilkins, ihid. 1987, 105, 5336; f) N. Aristov.
P. B. Armentrout, J. Phj,s. Chem. 1987, Yf, 6178, g ) H . Schwarz, Acr.
Chem. R e s 1989, 22, 282; h) A. Bjarnason, J. W Taylor, Organomerallics
1989.8.2020;i) A. Bjarnason, ihid. 1991,lO. 1244; For a recent review see:
j) K . Eller. H. Schwarz, Chem. Rev. 1991, 91. 1121.
G. D. Byrd. R. C. Burnier, B. S. Freiser. J. Am. Chem. Soc. 1982, 104,
D. B. Jacobson, B. S. Freiser. J. Am. Chem. Soc. 1983, f05, 7492.
D. B. Jacobson, B. S. Freiser. Organometallics 1984, 3, 513.
P. B. Armentrout, J. L. Beauchamp, J. Am. Cheni. SOC.1981, 103, 6628
D. B. Jacobson, B. S. Freiser, J. Ain. Chem. Soc. 1985. 107, 7399.
a) J. Miiller, W. Goll. Cheni. Ber. 1973, 106, 1129; b) R. R. Corderman,
Dissertation, California Institute of Technology, Pasadena, CA, USA,
H. Kang, D . B. Jacobson, S. K. Shin, J. L. Beauchamp, M. T. Bowers, J.
Am. CAern. Soc. 1986, 108, 5668.
a ) A . Bjarnason, J. W Taylor, J. A. Kinsinger, R. B. Cody, D. A. Weil,
Anal. Chem. 1989.61.1889;b) A. Bjarnason. 3. W Tdylor, Organometalfics
1990. 9, 1493.
R. B. Cody, Jr., J. A. Kinsinger, S . Ghaderi, I. J. Amster, F. W. McLafferty.
C. E. Brown. Anal. Chim. Acta 1985, 178,43.
a) M. B. Comisarow, V. Grassi. G . Parisod, Chem. Phys. Lert. 1978, 57,
413; h) A. G. Marshall, M. B. Comisarow. G. Parisod, J. Chem. P h y ~ .
1979, 71.4434.
Experimental Procedure
The experimental method has been described in detail elsewhere [14], but it IS
summarized briefly here: The experiments were conducted with an EXTREL
FTMS-2000 Fourier-transform mass spectrometer with dual-cell configuration [15]. Fe' and [CpFe]' were generated from [CpFe(CO),I], which was
introduced into the mass spectrometer in a sample vial on the direct insertion
probe. The ions were produced by electron impact in the source side of the dual
cell and transfered to the analyzer side. The ion of interest was isolated with
double-resonance techniques [I 61 and allowed to react with 2a or 2 b. which was
introduced to the analyzer side through two pulsed valves from the batch inlet
system. Co' and (CpCoI'were produced in the same manner from [Cp,Co],
and N i t and [CpNi]+ from [CpNiCO],. I t should be noted, that only [CpNl]+
containing the 58Ni isotope was isolated and allowed to react with the carbosilane. The course of the reaction could be monitored by collecting mass spectra
after a variable delay time andlor by varying the pressure of the sample in the
expansion volume of the batch inlet system. For ClD studies a second set of
pulsed valves was used to introduce the Ar collision gas on the analyzer side
after isolation of the ion of interest. This ion was then excited to kinetic energies
sufficient for its dissociation upon collision with the Ar atoms.
2a was prepared from 2c according to a published procedure [ 3 ] . 2b was
prepared in an analogous manner using LiAID, instead of LiAIH, and chardcterized by N M R spectroscopy.
Received: May 14, 1992
Revised: August 22, 1992 [Z 53461El
German version: Angew. Chrni. 1992, 104, 1654
Verluysgesellschaf~mbH, W-6940 Weinheim, 1992
A 1 :1 Adduct of 2-Aminobenzothiazole and a Urea
Derivative, and Its Spatial Arrangement**
By David R. Armstrong, Matthew G. Davidson,
Avelino Murtin, Paul R. Raithby, Ronald Snaith.*
and Dietmar Stalke
We reported recently the fortuitous isolation and structural characterization of the unique 1:l adduct of 2aminobenzothiazole OxNH, (1) and hexamethylphosphoramide (HMPA 2), which is stable even in boiling water."] In
view of the similarity between 1 and certain of the natural
bases found in DNA (A, G, and C have exo-NH, groups as
well as N atoms and/or NH units in their ring systems; T has
ring NH units), this adduct (1 2) was suggested as a model
to help explain the carcinogenicity of 2. The carcinogenicity
[*] Dr. R. Snaith, M. G . Davidson, A. Martin, Dr. P. R. Raithby
University Chemical Laboratory
Lensfield Road, GB-Cambridge, CB2 1EW (UK)
Dr. D . R. Armstrong
Department of Pure and Applied Chemistry
University of Strathclyde, GB-Glasgow, GI 1XL (UK)
Dr. D. Stalke
Institute for Inorganic Chemistry
Tammannstrasse 4, D-W-3400 Cottingen (FRG)
[**I We thank the Science and Engineering Research Council (SERC) and the
Associated Octel Co. Ltd. (CASE award to M. G. D.) for financial support.
Angew. Chem. Int. Ed. Engl. 1992, 31. N o . 12
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trisilabenzene, trisilacyclohexane, reaction, first, evidence, formation, gas, phase, cpm
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