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Tris(trimethylplumbyl)heptaphosphanortricyclene P7(PbMe3)3.

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(-20 'C) for 30 s with 150 mL of an aqueous solution of 20 g KzCO,
cooled to 0°C and subsequent drying over K2C03,Filtration, and evaporation of the solution to dryness at ca. 10 torr. The last traces of solvent
and rBuOH were removed in a high vacuum (bath temperature <3O"C).
Attempts to distill the compounds resulted in polymerization.
Tris(trimethylplumby1)heptaphosphanortricyclene
P7(PbMe& 1'1
By Dieter Weber, Carlos Mujica, and
Hans Georg von Schnering*
Molecular compounds containing phosphorus-lead
bonds are still a rarity. The few known examples include
the substituted phosphanes P(PbR3)3and R-P(PbR3)' described by Schumann et al.'']. Entry to these P-Pb systems, however, is essentially thwarted by the lability of the
P-Pb bond. It is well known that no binary lead phosphides exist, and that molten lead is even used for the crystallization of Hittorf s phosphorus. As regards ternary
compounds, the only known examples are the polyphosphides of the type HgPbP,, discovered by Krebs et al.['].
We have now been able to prepare P7(PbMe3)3 3 from
and CIPbMe3 in a facile reaction. The reacP7(SiMe3)3lf6]
tion proceeds (presumably according to an SN2 mechanism) practically quantitatively in monoglyme at - 50 "C
with cleavage of C1SiMe3. In complete contrast to the very
sensitive Si-compound 1, the colorless crystals of the Pbcompound 3 can be stored for days in air without any notable change, until finally decomposition with darkening in
color (precipitation of lead) takes place. The analogous
Sn-compound P7(SnMe3)32 can be obtained in the same
way by reaction with CISnMe3['I. Finally, the analogous
Ge-compound can also be synthesized, directly, in a heterogeneous reaction from Na3P7 and C1GeMe3.
Mass spectroscopically, only fragment ions are detectable above 298 K, a clear indication of the thermal lability
of the P-Pb bond. Thus, it is understandable that 3, unlike 1, cannot be sublimed. The formation of 3 is favored
by its relatively sparing solubility and by the volatility of
C1SiMe3. The IR spectra of all four P7(MMe3)3compounds
with M = Si, Ge, Sn, Pb are characterized on the one hand
by the intense M-C
vibrations, dependent upon the
atomic weight, and on the other by two groups of almost
invariant skeletal vibrations of the central nortricyclene
system.
P
Fig. 2/3. Structure of P,(PbMe,)3 3. Average bond lengths: A=221.2,
B=217.6, C=217.8, D=261.1 pm ((i(Pb-C)=219 pm). Crystal structure:
P2, (No. 14); a=990.8(2),b=1819.1(3),~=697.0(1) pm; 0=99.66(2)";2=2;
2348 hkl; MoKnradiation: R=0.052.
[*I Prof. Dr. H. G. von Schnering, Dr. D. Weber, C. Mujica
Max-Planck-Institut fur Festkorperforschung
Heisenbergstrasse 1, D-7000 Stuttgart 80 (Germany)
Angew. Chem. Inr. Ed. Engl. 21 (1982) No. I 1
The X-ray structure analysis (Fig. 2/3) reveals 3 as being isotypic with l [ l o l . The bond lengths d(P-Pb) average
261.1 pm (CR,,,=258 pm). The bond lengths and angles in
the nortricyclene framework closely resemble those in the
other compoundsI'oI. The twisting of the P-skeleton about
the threefold axis in 1, determined by the steric interaction
of the substituents with the free electron pairs on the
bridge atoms, is also observed once again. The P7(MMe3)3
molecules are chiral; in each case only one enantiomer is
present in the crystal (P2,). In the case of the Pb compound we were able to determine the absolute configuration. Since the crystals are relatively easy to handle there is
the possibility of being able to separate the enantiomers.
Received: July 5, 1982 [Z 83 IE]
German version: Angew. Chem. 94 (1982) 869
The complete manuscript of this communication appears in:
Angew. Chem. Suppi. 1982, 1801-1812
CAS Registry number:
3, 83417-29-2.
111 Chemistry and Structural Chemistry of the Phosphides and Polyphosphides, Part 30.-Part 29: W. Klemm, H. G. von Schnering, Z. Anorg.
Allg. Chem.. in press.
[2] H. Schumann, A. Roth, 0. Stelzer, M. Schmidt, Inorg. Nucl. Cbern. Lell.
1966, 311.
151 H. Krebs, T. Ludwig, Z . Anorg. Allg. Chem. 294 (1958) 257.
[6] G. Fritz, W. Holderich, Narunvissenschafren 62 (1975) 573.
[7] D. Weber, C. Mujica, K. D. Hoppe, H. G. von Schnering, G. Fritz, unpublished results.
[lo] W. Honle, H. G. von Schnering, Z . Anorg. ANg. Chem. 440 (1978) 171.
Control of the Conformation of Transition States
in Intramolecular Diels-Alder Reactions
with Inverse Electron Demand**
By Lutz-F. Tietze*, Hartmut Stegelmeier, Klaus Harms,
and Thomas Brumby
In memoriam, Otto Bayer
Intramolecular Diels-Alder reactions permit the stereocontrolled synthesis of several chiral centers in one step""];
in this connection the configuration of at least two of the
newly formed chiral centers is determined by the conformation of the chain linking the reacting n systems. We
were able to demonstrate that 2-alkylidene-1,3-dicarbonyl
compounds of type 1 lead exclusively, within a few minutes at 20 "C, to trans-annelated products 2 via an intramolecular Diels-Alder reaction with inverse electron demand[Ib1.The chiral center in the chain of this system enables a stereoinduction with de-value >98% to be
achieved['].
Exclusively cis-annelated products are formed from arylidene compounds of type 3, in which two C atoms are
part of an aromatic ring. In this case the endo-transition
state 3 B is energetically more favorable than the exo-transition state 3 A[3a1.The 2-benzylidene- I ,3-dicarbonyl compounds 3 can be obtained by condensation of aldehydes 4
with 1,3-dicarbonyl compounds, e.g. 5 or 7,in presence of
[*I Prof. Dr. L.-F. Tietze, K. Harms, T. Brumby
lnstitut fur Organische Chemie der Universitat
Tammannstrasse 2, D-3400 Gottingen (Germany)
Dr. H. Stegelmeier
Chemisch-Wissenschaftliches Labor Pharma, Bayer AG
Postfach 10 1709, D-5600 Wuppertal 1 (Germany)
I**] Intramolecular Cycloadditions, Part 5. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. Dr. J. Kurz (Bayer AG, Wuppertal) is thanked for NMR spectra.-Part 4: [2a].
0 Verlag Chemie GmbH, 6940 Weinheim, 1982
0570-0833/82/1111-0863 $02.50/0
863
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pbme3, trish, heptaphosphanortricyclene, trimethylplumbyl
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