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Methoxytetramethylarsorane (CH3)4AsOCH3.

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both (Sa) and ( 5 6 ) ; alkyne is inserted, yielding three new
types of complexes, which in the case of diphenylacetylene
can be converted into tricarbonyl(tetraphenylcyc1obutadiene)iron"'l.
Experimental:
( 2 b ) : ( 1 b ) (6g, 0.063mol) and Fe2(C0)9(6g, 0.016mol) are
stirred in n-hexane (120ml) until all the Fe2(C0)9is consumed.
Column chromatography at - 10°C (silica gel Serva 100200 nm; n-hexaneltoluene) and crystallization from etherlnhexane afford analytically pure (2b) (1.4 g, 32%), m.p.
384O0C.--(6b): Analogous to the preparation"] of ( 5 b ) ;
chromatographic separation (neutral A1,03 ; n-hexanebenzene) affords ( 5 b ) , and further elution with benzene affords
(6b) in 20% yield; sublimes at 130°C in a closed tube.
Received: September 30, 1974 [Z 152 IE]
German version: Angew. Chem. 87, 206 (1975)
CAS Registry numbers:
( 2 a ) , 54515-75-2; ( 2 b ) . 54517-20-3; ( S b ) , 32507-01-0; ( 6 b ) , 54575-93-8;
Fe,(CO),, 15321-51-4
[l] Transition-metal Complexes of Azo Compounds, Part 3.-Part 2 : H.
Kisch. J . Organometal. Chem. 38, C 19 (1972).
[2] R. P. Bennerr, Inorg. Chem. 9, 2184 (1970).
[3] M . Herberhold and W Golla, J. Organometal. Chem. 26, C27 (1971).
R. G. Little and R. J . Doedens, Inorg. Chem. 1 1 , 1392 (1972).
X-ray structure analysis (C.Kriiger) not yet complete.
C. Kriiyer, Chem. Ber. 106, 3230 (1973).
We thank Dr. K . Hildenbrand for measurement of the I3C-NMR spectra,
Dr. F. W Greuels for valuable discussions.
[8] This appears to be a general property of complexes of type (2).
[9l M . Hrrberholdand K . Leonhard, J. Organometal. Chem. 1974. We thank
these authors for communicating results prior to publication.
[lo] H . Kisch, Roc. XVI. Int. Conf. Coord. Chem., Dublin 1974, Abstr.
3.21.
[ i l l Note added in proof (March 11, 1975): In the meantime complexes
of type (3) have been prepared from diazirines and Fe,(CO),; A. Albini and
H. Kisch, J. Organometal. Chem. 1975, in press.
[4]
[S]
[6]
[7]
and
Methoxytetramethylarsorane,(CH3)&sOCH3
By Hubert Schmidbaur and Wolfgang Richter"]
Compounds of formula R A s X are usually arsonium salts
of strictly ionic structure, RAs+X-[']. Methoxytetramethylarsorane ( 4 ) , however, has now been found to be one of the
few compounds of five-coordinate arsenic with covalent bonding, and thus the gap between methoxyfetramethyl-phosphoranel'], (CH3)4POCH3, and -stiboranel3], (CH3)6bOCH3, is
closed.
For the synthesisrto1we used the method of desilylati~n[~]
of the corresponding silyl-substituted arsenic ylide (2)[51 with
(CH&As
+ C1CH2Si(CH3),
[(CH3)3AsCH2Si(CH3),]C1
(1)
"-Cd19Llj- LICI, - < , l l , o
(CH3)3As=CH-Si (CH,),
(2)
YH3,.CH3
H3 C-.4s'
'CH3
6
C I 1 3 V H ~ (Ctl
~,hlVCI1,
CI I @€I
t
-
(CH3)3As=CH,
(3)
H3 C'
(4)
[*] Prof. Dr. H. Schmidbaur and DipLChem. W. Richter
Anorganisch-chemisches Laboratorium der Technischen Universitat
8 Miinchen 2, Arcisstr. 21 (Germany)
Angew. Chem. internat. Edit.
Vol. 14 (1975) f No. 3
subsequent addition of methanol to the free trimethylmethylenearsorane (3)"J.
As in the corresponding phosphorus system[2*41 the reactions
(2) + (3) + ( 4 ) can be carried out either stepwise or as a
"single pot" reaction, in both cases at -20°C in diethyl ether
as a solvent. ( 4 ) is formed as a colorless distillable liquid
(b. p. 38 "C/17 torr) of high chemical reactivity. The compound
fumes in air and, when finely divided, is self-inflammable.
Its aqueous and alcoholic solutions react strongly alkaline
since tetramethylarsonium hydroxide is immediately
formed['!
The 'H- and ' 3C-NMR spectra of toluene (or benzene) solutions of ( 4 ) at room temperature show virtual structural
equivalence of the four methyl groups bound to arsenic. Only
at very low temperatures, however, as with phosphorus analogs, is a splitting of the corresponding lines into two singlet
signals (area ratio 3 : 1) observed. This proves also that ( 4 )
has a fluctuating trigonal-pyramidal structure[81 (Table 1).
Here, for the first time with arsenic, it is possible to distinguish
alkyl groups bound axially (a) and equatorially (e) in the
samemolecule; this has not yet been found for the homologous
antimony
Table 1. 'H- and "C-NMR data for (CH3)4AsOCH3 ( 4 ) in [D.]-toluene,
measured against TMS int. [ppm].
'H
35
- 100
I
3c
0
- 105
3.49
3.50
51.6
52.4
1.27
1.45 (e)
0.00 (a)
20.9
17.0 (e)
26.0 (a)
As with (CH3)4POCH3, there is the surprising discovery that
the resonance of the axial C atoms lies at lower field than
that of the three equatorial C atoms, whereas the H atoms
show the reverse relation. This phenomenon is presumably
based on the trans-influence of the methoxy group.
The 13C resonances of the ylidic C atoms of (2) and (3)
are, however, as expected, recorded at high field and confirm
the carbanionic nature of this structural unit[91.
Received: November 4, 1974;
revised: November 29, 1974 [Z 153 IE]
German version: Angew. Chem. 87,204 (1975)
[l] G . 0.Doak and L. D. Freedman: Organometallic Compounds of Arsenic,
Antimony and Bismuth. Wiley-Interscience, New York 1970.
[2] H. Schmidbaur, H. Sriihler, and W Buchner, Chem. Ber. 106, 1238 (1973);
107, 1420 (1974); Z. Anorg. Allg. Chem. 405, 202 (1974).
[3] H. Schmidbaur, J. Weidlein, and K . H . Mitschke, Chem. Ber. 102, 4136
( 1969).
[4] H. Schmidbaur and W Tronich, Chem. Ber. 101. 595 ( 1 968).
[5] N . E . Miller, Inorg. Chem. 4, 1458 (1965).
[6] H. Schmidbaur and W Tronich, Inorg. Chem. 7, 168 (1968).
[7] X. H. Mitschke and H. Schmidbaur, Chem. Ber. 106, 3645 (1973).
[8] H . Schmidbaur, W Buchner, and F. H . Kohler, J. Amer. Chem. SOC.
96,6208 (1974). We thank Dr. Kiihler also for the I3C-NMR measurements
recorded here.
[9] H. Schmidbaur, W Buchner. and D. Scheutzow, Chem. Ber. 106. 1251
(1973); H. Schmidbaur, W Richter, W Wolf,and F. H . Kiihler, Chem. Ber.,
in press.
[lo] Note: ( 4 ) hasmeanwhilebeenobtainedalsofrom (CH3)5Asand MeOH:
J . Weidlein, personal communication.
183
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