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Elimination and Addition at the Phosphorus-Carbon p-p Bond.

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Elimination and Addition
at the Phosphorus-Carbon pn-pa Bond""'
By Rolf Appel, Giinther Maier, Hans Peter Reisenauer,
and Axel Westerhaus['l
The existence of three phosphaalkynes has so far been reported: Besides the parent compound, phosphaacetylene
HCP, which was first obtained as long ago as 1961 on passage of PHI through an electric arc generated between
the fluoro- and the methyl-derivative (1-phosphapropyne) could later also be prepared and
characterized, in particular by microwave and photoelectron
spectroscopy["]. In both cases the method employed for the
synthesis was the elimination of hydrogen halide, from trifluoromethylphosphane and dichloro(ethyl)phosphane, respectively. The pyrolysis of dichloro(ethyl)phosphane, however, does not proceed uniformly; ethylene, PCl, , ethane and
acetylene are formed as well as HCl, and the l-phosphapropyne obtained in only low yield is contaminated with difficultly separable byproducts.
We have now found that when chloro[phenyl(trimethylsilyl)methylene]phosphane (I)[" is heated to 700 "C under
vacuum (Hg-diffusion pump), chlorotrimethylsilane is selectively cleaved and phenylmethylidynephosphane (2-phenylphosphaacetylene) (2) is formed in almost quantitative yield.
The elimination process was optimized by means of a mass
spectrometer coupled directly to the pyrolysis apparatus and
(2) was collected in a cold trap cooled to - 196 "C.
c, -P-c 1
- Me3S>Cl
+ l B
(2) exists in the monomeric state only at low temperatures;
slow decomposition sets in above - 50 "C. According to I'PNMR spectroscopic measurements its half-life at 0°C is 7
min. The silyl compound Me,SiCP'41 is much more stable.
Experimen f aI
A quartz tube (25 mm diameter) packed with quartz wool
in the hot zone is preheated in a controllable 10 cm-long ring
oven at 750°C. Approximately 0.5 g of an excess supply of
( I ) (room temperature) is thermolyzed under vacuum (Hgdiffusion pump) for 12 h and the condensate collected in
cold-trap at - 196 "C. The condensate is taken up in a small
amount of CD2ClZand rapidly filtered at - 78 "C; the filtrate
contains only (CH,) Sic1 and (2).
(3) is thermolyzed analogously at 800°C. According to
,'P-NMR measurements the condensate consists mainly of
unreacted (3) together with small amounts of (2) and a series
of unidentified by-products.
Received: July 28. 1980 [ Z 642 IE]
German version: Angew. Chem. 93. 215 (19x1)
CAS Registry numbers:
(IJ.74483-17-3; (2). 76684-21-4 (31. 4545-85-1; ( l a ) , 76684-22-5; (4b).76684-236.
[ I ] a) T. E. Gier, J. Am. Chem. SOC.83. 1769 ( 1961); b) S. P. Andenon. H . Goldwhite, D. KO. A. Letsou, J. Chem. SOC.Chem Commun 1975. 744; c) H. W.
Kroto, J. F. Nixon, N. P. C. Simmons, N. P. C. Westwood. J . Am. Chem. SOC.
100, 446 (1978); M . J. Hopkinson. H. W. Kroto. J. f. Nixon. N. P. C. Simmons. Chem. Phys. Lett. 42, 460 (1976).
[Z] R. Appel. A. Westerhous. Angew. Chem. 92, 578 (1980); Angew. Chem Inr.
Ed. Engl. / 9 , 556 (1980).
[3] "CI'HI-NMR (CDIC12. 22.6 MHz, TMS int.): 6= 164.9 [d,J(PC)=48.3 Hz,
PC]; " P / ' H : - N M R (32.2 MHz. H,PO, ext.): 6= -32.0. cf. also [Ib].
(41 R. Appel, A. Westerhaus, Tetrahedron Lett.. in press.
Ba4SiAs4 and Ba4GeAs4, Zintl Phases
with Isolated SiAs2- and GeAst- anions[**'
By Brigitte Eisenmann, Hanna Jordan,
and Herbert SchuJer[*I
The k C triple-bond structural element in (2) is detectable by the characteristic I3C- and 31P-NMRdataP1 and is
confirmed by stepwise HC1-addition; initially the phosphaalkene (4a) is formed, which reacts with a second equivalent of
HC1 to give the benzyldichlorophoshane (3). It can be shown
by )'P-NMR spectroscopic measurements that (3) can also
be dehydrochlorinated with tertiary amines (B), with reversal
of this formation reaction"]. However, the Z-isomer (46) is
formed concomitantly besides (42). Owing to a stereospecific
cis-addition at the triple bond, (46)is not obtained on addition of HCl to (2).
In contrast to the halosilane-elimination, direct vacuum
pyrolysis of (3) affords numerous unidentified by-products
and only very small amounts of (2).
Zintl phases are intermetallic compounds which display a
pronounced heteropolar bonding contribution and whose
anionic partial lattices, in agreement with an ionic formulation, obey the (8 - N) rule. A classification according to this
Zintl-Klemm concepti1] embraces the majority of compounds of the alkali and alkaline-earth metals which contain, in particular, the semimetals of the 4th and 5th main
group as anionic partners. Only such compounds have so far
been systematically characterized whose anionic partial lattice is made up of merely one element. No comprehensive investigations have been carried out on compounds with binary anions which may also be interpreted as Zintl phases and
which represent bridging members between ternary intermet a l k compounds and salts with complex anions.
Particularly impressive examples for such an extension of
the Zintl-Klemm concept are the isotypic compounds
Ba4SiAs4 and Ba4GeAs4 reported here for the first time,
which contain "isolated" SiAs4- and GeAs4-tetrahedra, i. e.
('1 Prof. Dr. R Appel, DiplLChem. A. Westerhaus
Anorganisch-chemisches Institut der Universitat
Gerhard-Domagk-Strasse 1. D-5300 Bonn I (Germany)
Prof. Dr. G. Maier, Dr. H. P. Reisenauer
Institut fur Organische Chemie der Universitat
Heinrich-Buff-Ring 58. D-6300 Giessen 1 (Germany)
I**] Phosphorus-Carbon-Halogen Compounds, Part 26.-Part
Peters, R. Schmitz, 2. Anorg. Allg. Chem., in press.
Angew. Chem Inr. Ed. Engl 20 ( / 9 8 / )No. 2
25: R. Appel, J.
Prof. Dr H. Schafer. Dr B Eisenrnann. DiplLIng. H. Jordan
Abterlung 11 fur Anorganische Chemie im
Eduard-Zintl-Institut der Technischen Hochschule
Hochschulstrasse 4, D-6100 Darmstadt (Germany)
1'1 This work was supported by the Deutsche Forschungsgemeinschafl and the
Fonds der Chemischen Industrie.
0 Verlag Chemie, GmbH, 6940 Weinheim, IY81
S 02.50/0
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elimination, bond, additional, carbon, phosphorus
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