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Bonding Electron Density Distribution in Tetra-tert-butylcyclobutadieneЧ A Molecule with an Obviously Non-Square Four-Membered ring.

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ward to support a square structure for 2 are in no way sufficient or convincing.
Received: December 16, 1982;
revised: February 7, 1983 [Z 225 1El
German version: Angew. Chem. 95 (1983) 414
CAS Registry number:
2, 66809-05-0.
[l] T. Bally, S Masamune, Tetrahedron 36 (1980) 343, and literature cited
[2] X-ray structure analysis of a) 2 (room temperature), 3: H. Irngartinger,
N. Riegler, K.-D. Malsch, K.-A. Schneider, G. Maier, Angew. Chem. 92
(1980) 214; Angew. Chem. Inr. Ed. Engl. 19 (1980) 211; b) 2 (low temperature): H. Irngartinger, M. Nixdorf, ibid. 95 (1983) 415; 22 (1983) 403; c)
5 : H. Irngartinger, H. Rodewald, ibid. 86 (1974) 783; 13 (1974) 740; d) 6 :
L. T. J. Delbaere, M. N. G. James, N. Nakamura, S . Masamune, J. Am.
Chem. SOC.97 (1975) 1973.
[31 W. T. Borden, E. R. Davidson, J. Am. Chem. SOC. 102 (1980) 7958.
141 PE spectra of a) 2, 3: E. Heilbronner, T. B. Jones, A. Krebs, G. Maier,
K.-D. Malsch, J. Pocklington, A. Schmelzer, J. Am. Chem. SOC.102 (1980)
564; b) 4 : G. Lauer, C. Muller, K.-W. Schulte, A. Schweig, G. Maier, A.
Alzerreca, Angew. Chem 87 (1975) 194; Angew. Chem. Int. Ed. Engl. 14
(1975) 172; c) 5 : G. Lauer, C. Miiller, K.-W. Schulte, A. Schweig, A.
Krebs, ibid 86 (1974) 597; 13 (1974) 544; d) 6 : R. S. Brown, S . Masamune, Can. J. Chem. 53 (1975) 972; e) E. Heilbronner, J. P. Maier in C. R.
Brundle, A. D. Baker: Electron Spectroscopy. T h e o y . Techniques. and Applicarions, Vol. I , Academic Press, London 1917.
151 0. Ermer, S . Lifson, J. Am. Chem. SOC.95 (1973) 4121.
2, X = S; 3 , X = C H Z
in the crystal at room temperature, due to static or dynamic disorder. Since the bond lengths in the ring differ
significantly at room temperature the molecular arrangement in which the double bond is almost parallel to the
twofold rotation axis must be more populated than the arrangement perpendicular to it but with otherwise the same
orientation of the molecule. This unequal distribution of
the disordered molecules is even more pronounced at
- 150 "C. Whether a completely ordered structure is
achieved. is still unclear.
Bonding Electron Density Distribution in
Tetra-ferf-butylcyclobutadiene-A Molecule with an
Obviously Non-Square Four-Membered ring**
By Hermann Irngartinger* and Matthias Nixdorf
We have found by X-ray structure analysis that the sides
of the non-planar four-membered ring in tetra-tert-butylcyclobutadiene 1 are almost equal (1.464 and 1.483 A) at
room temperature""]. Although the actual differences in
length are still significant-being of the order of ten times
the standard deviation-markedly greater differences of
0.14-0.26A occur in the cyclobutadiene derivatives 2 to
4"l. In order to explain this discrepancy, we have carried
out low-temperature measurements at - 30 and - 150 "C
on 1 and repeated the room temperature measurement
with a second crystal on another diffractometer. The repeat measurement yielded, within the limit of error, the
same results as earlier. The values at - 30 "C (1.466(2) and
1.491(2), 1.493(2)A) do not seriously differ from the room
temperature data. However, measurements of the bond
lengths in the four-membered ring at - I5OS0Cyielded the
values 1.441(2) and 1.526(1) and 01.527(2)A, respectively,
with a greater difference of 0.086 A compared to the room
temperature data (Fig. 1). Force field calculations and
spectroscopic findings likewise clearly indicate a nonsquare structure for the four-membered ringc2].The conformation of 1 in the crystal remains almost unchanged at
low temperature; within the error of measurement, the angle at which the four-membered ring is folded remains
about the same (169.9").
On the basis of these results we assume that equilibrating effects are operating in the four-membered ring of 1
[*I Prof. Dr. H. Irngartinger, M. Nixdorf
Organisch-chemisches lnstitut der Universitat
Im Neuenheimer Feld 270, D-6900 Heidelberg I (Germany)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. We thank Prof. G. Maier, Dr. K.D. Malsch, and Dr. K. A. Schneider (Universitat Giessen) for supplying
Angew. Chem. Inr. Ed. Engl. 22 (1983) No. 5
Fig. 1. Bond lengths
and anglesJ"] of the four-membered ring of 1 at
- 150 "C; standard deviations 0.002 A and 0.1 respectively; vibration ellipsoids for 50% probability: Crystallographic data ( - 150 "C): a = 17.530(3),
b=9.150(1), c = 11.769(2)A, b= 106.56(2)", monoclinic space group C2/c,
Z=4. The centric space group derives from statistical tests. Tentative refinement with room temperature data in the space group Cc led to trapezoidal
distortion of the four-membered ring. Up to sin6/A= I.l5A-' (Mo,,-radiation) 4813 independent reflections (3184 observed, I > 30(0); refinement of
the C atoms with 953 reflections of higher order (0.75<sin8/1< I L I S k ' ) ,
1 1 reflections per variable; R =0.048 IS].
If the low-temperature geometry of the four-membered
ring is transferred to the structure at room temperature and
an equal population of the two disorder orientations is assumed, then the thermal vibration of 0.051 l(5) A' vertical
to the bisector of the four-membered ring angle and within
the ring plane contains a contribution A U of only
0.0009 A2 (1.8%), thus explaining why no effects of equilibration on the thermal parameters of the four-membered
ring atoms were to be observed at room temperature. This
value is smaller than that calculated (0.0083 A2) on the basis of the data for 3[la1.The value for 1 has to be set at a
higher rate if an incompletely ordered structure is present
at low temperatures.
We have experimentally determined the bonding electron density distribution in 1 according to the "X-X"
method[31using the low temperature data ( - 150 "C) (Fig.
2). The density maxima of the four-membered ring bonds
are shifted outwards from the bond axes, so that bent
bonds are present, similarly a: in the case of Zc4]. The single bond (with a shift of 0.20 A) is more strongly bent than
the double bond (0.10 A). Unlike the bond angle of 89.8"
(Fig. I), the angle between the density maxima is 1 1 1 (Fig.
Q Verlag Chemie GmbH, 6940 Weinheim, 1983
0570-0833/83/0505-0403 $02.50/0
2). The maxima of electron densities on the singlesand
double bonds have different values (0.37 and 0.57 e/A3).
R = C(CH,),, K' = Si(CH,),
Fig. 2. Deformation densities in the four-membered ring of 1 (223 I A F values from the range sinO/A 10.75 k').
The contour intervals are 0.05 e/A3.
Although we cannot rule out equilibration effects also
still being effective at low temperatures the differences in
the two bond types of the cyclobutadiene system emerge
just as clearly in the electron density distribution as in the
bond lengths.
2 forms colorless, air-sensitive crystals [m. p. > 130 "C
(decomp.)] which are readily soluble in dichloromethane,
benzene, and toluene and moderately soluble in ether and
pentane. According to the crystal structure analysis, 2 has
a planar P2NZfour-membered ring, which is bridged by a
symmetrical NSbN bridge (Fig. 1). The lone pair of electrons of N3 bond coordinatively to antimony; the considerably larger distances 1.771(4) and 1.772(6) A for P1-N3
and P2-N3, respectively, can therefore be considered as
an ideal model for PN single-bond lengths in molecules
with trivalent phosphorus.
Received: December 28, 1982;
revised: February 25, 1983 [ Z 233 IE]
German version: Angew Chem 95 (1983) 415
CAS Registry number:
1, 66809-05-0.
[ I ] a) H. Irngartinger, N. Riegler, K.-D. Malsch, K.-A. Schneider, G. Maier;
Angew. Chem. 92 (1980) 214; Angew. Chem. In?. Ed Engl. 19 (1980) 21 1 ;
b) H. Irngartinger, H. Rodewald, ibid. 86 (1974) 783 and 13 (1974) 740; c)
L. T. J. Delbaere, M. N. G. James, N. Nakamura, S. Masamune, J . Am.
Chem. SOC.97 (1975) 1973; d) Review: T. Bally, S. Masamune, Tetrahedron 36 (1980) 343.
121 0. Ermer, E . Heilbronner, Angew. Chem. 95 (1983) 414; Angew. Chem.
Int. Ed. Engl. 22 (1983) 402.
[3] P. Coppens, Angew. Chem. 89 (1977) 33; Angew. Chem. Inr. Ed. Engl. 16
(1977) 32.
141 H. Irngartinger, H.-L. Hase, K.-W. Schulte, A. Schweig, Angew. Chem. 89
(1977) 194; Angew. Chem. Int. Ed. engl. 16 (1977) 187.
[5] Further details of the crystal structure investigation can be obtained on
request from the Fachinformationszentrum Energie Physik Mathematik,
D-7514 Eggenstein-Leopoldshafen on quoting the number CSD 50369,
the names of the authors, and complete citation of the journal.
Fig. 1. Molecular structure of 2 (molecule 1) in the crystal. Selected bond angles ["]: CII-Sbl-Ne 147.2(1), CII-SblLN4 95.1(2), C1I-Sbl-NI 94.5(2), S b l NI-PI 107.3(2), Sbl-N4-P2 107.2(2), NI-Sbl-N4 103.5(2), N2-P2-N4
107.3(3), N3-P2-N4 91.8(3), NI-Pl-N3 91.6(2), NI-PI-N2 i08.0(3), Sbl-N3P2 92.4(3), Sbl-N3-PI 92.1(2).-Crystal structure data: space group: triclinic
P i : a=9.5564(9), b=9.613$1), c=31.229(2)
a=79.731(6), @=80.065(6),
y=60.450(8)"; V=2444.0 A', 2 = 4 (two independent molecules, which d o
not significantly differ in their individual distances and angles):
g . cm-3: 7872 independent reflections, R =0.044, R,=0.050. Further details
of the crystal structure investigation can be obtained from the Fachinformationszentrum Energie, Physik, Mathematik, D-7514 Eggenstein-Leopoldshafen by quoting the depository number CSD 50338, the names of the authors, and the journal citation.
Synthesis and Structure of a
Bicyclic SbNP Compound with
Intramolecular Donor-Acceptor Bonding**
By Otto J. Scherer*, Gotthelf Wolmershuuser, and
Herbert Conrad
Amino(imin0)phosphanes having at least one (CH,),Si
group on the amino nitrogen atom are suitable, among
other things, for the preparation of various phosphorus-nitrogen-element heterocyclesr']. Treatment of lert-butylimino(tert-butyltrimethylsilylamino)phosphane I with SbC13
represents a new variant of this reaction; the four-membered ring compound ClSb(NR)PClNR, which is the product expected by analogy to the reaction with AsCI,~*],is not
formed, and the reaction yields the SbNP bicycle 213].
[*] Prof. Dr. 0. J. Scherer, Dr. G. Wolmershauser, H. Conrad
Fachbereich Chemie der Universitat
Erwin-Schrodinger-Strasse,D-6750 Kaiserslautern (Germany)
This work was supported by the Fonds der Chemischen Industrie. Prof.
Dr. C. Kriiger, Max-Planck-Institut fur Kohlenforschung, Mulheim, is
thanked for the X-ray intensity measurements.
0 Verlag Chemie GmbH. 6940 Weinheim. 1983
The distorted trigonal-bipyramidal environment at antimony is comparable with that in CI3Sb. H2NC6HS(A)(A:
Sb-CI,,,, 2.52, Sb-N 2.53 A, Cl-Sb-N 166.3°[41).As expected, the greatest difference occurs in the NSbCl axial
angle (147.2' in 2 ) . The 'H-NMR spectrum (200 MHz, solvent, C,Ds, TMS int.) exhibits three signal groups at room
temperature: 6= 1.52 ("t", A,XX'A; system, 18H (SbN),
l4Jp~+'JpHl=1.9 Hz); 1.25 ( s , 9 H (PN)). "P('H)-NMR
(C,Ds, 85% H3P04 ext.): 6 = 159.8 (s). Temperature dependent 'H-NMR studies of a 30% toluene solution of 2
indicate that the different (CH3)3C signals of the P2N2
four-membered ring coalesce at ca. 80°C, whereas in a
20% solution this occurs at ca. 120 "C (extrapolated). This
result indicates that the inversion of configuration at anti-
0570-0833/83/0505-0404 $02.50/0
Angew. Chem. Inl. Ed. Engl. 22 (1983) No. 5
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bonding, butylcyclobutadieneч, obviously, distributions, molecules, non, ring, tetra, electro, tert, density, squares, four, membered
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