Air-stable crystalline primary phosphines and germanes: Synthesis and crystal structures of dibenzobarellenephosphine and tribenzobarellenegermane

Article abstract of DOI:10.1039/a901083a

The syntheses of dibenzobarellenephosphine and tribenzobarellenegermane are described; at room temperature these primary phosphines and germanes form air-stable crystals whose structures are reported together with that of tribenzobarellenemethane.

Full text of DOI:10.1039/a901083a

Air-stable crystalline primary phosphines and germanes: synthesis and crystal
structures of dibenzobarellenephosphine and tribenzobarellenegermane
Marcin Brynda,a Michel Geoffroy*a and Ge´rald Bernardinellib
a De´partement de Chimie Physique, 30 Quai Ernest Ansermet, 1211 Gene`ve, Switzerland
b Laboratoire de Cristallographie, 24 Quai Ernest Ansermet, 1211 Gene`ve, Switzerland.
E-mail: geoffroy@sc2a.unige.ch
Received (in Basel, Switzerland) 9th February 1999, Accepted 13th April 1999
The syntheses of dibenzobarellenephosphine and tribenzo-
barellenegermane are described; at room temperature these
primary phosphines and germanes form air-stable crystals
whose structures are reported together with that of tri-
benzobarellenemethane.
Primary phosphines are generally air-sensitive liquid com-
pounds. Most of the reported crystal structures with an RPH2
moiety have therefore been determined on molecules where the
phosphorus atom is coordinated to a metal atom.1 The crystal
structure of free primary phosphines could be obtained in only
a very limited number of cases: (1) when the phosphorus atom
is bound to a cumbersome protective aryl group (But3C6H2),2 to
an iron dicyclopentadienyl group3 or to a triptycyl moiety;4 (2)
after dimerisation of anthracenephosphine;5 (3) after N-qua-
ternisation of aminoalkylphosphines.6 Recent results7 indicated
Fig. 1 Perspective view of 1. Ellipsoids are represented with 40%
probability. Selected bond distances (Å) and angles (°): P1–C7 1.859(4);
that benzo derivatives of barrelene were likely to lead to stable
crystalline RPH2 compounds; we have therefore taken ad-
C1–C6 1.402(4); C1–C7 1.536(4); C6–C10 1.522(4); C7–C8 1.539(6); C8–
vantage of this to attempt the synthesis of a primary phosphine
C9 1.314(7); C9–C10 1.520(6); P–H01 1.36(3); C1–C7–C8 105.5(2); C1–
which contains a double bond in the vicinity of the phosphorus
atom. We report below the synthesis and the structure of the
remarkably air-stable primary phosphine 1. The synthesis of
dibenzobarellenephosphine† is shown in Scheme 1.
C7–C1A 103.3(3); C1–C7–P1 113.2(2); C7–C8–C9 115.2(4); C8–C9–C10
114.1(4); C6–C10–C6A 104.5(3); C6–C10–C9 106.1(2); H01–P–H01A
93(2).
In the context of this study, we envisaged using benzobar-
ellene derivatives to form a crystalline primary germane.
Although less reactive than their silicon homologues, primary
germanes are generally air-sensitive liquid (or gaseous) com-
pounds at room temperature. As far as we know, the only crystal
structure reported for RGeH3 was obtained at 160 K on
cyclopentadienyl germane, which melts at 200 K.8 We report
below the synthesis† (Scheme 2) and the crystal structure‡ of
tribenzobarrelenegermane 2 which forms air-stable crystals
with a melting point of 232 °C.
In the solid state the dibenzobarellenephosphine 1‡ is located
on a mirror plane perpendicular to the b axis with P1, C7, C8,
C9, C10, H8, H9 and H10 in special positions 4c. All hydrogen
atoms have been observed and refined without constraint. No
significant electronic density corresponding to a hydrogen site
located in the trans position relative to the C7–C8 bond was
observed, meaning that only one rotamer is present and that no
free rotation of the phosphine around the C–P bond occurs at
180 K. The dihedral angle between the mean planes of the
phenyl moieties is 113.8° (angle between the central ethylene
bridge and a phenyl moiety = 123.1°).
This compound is isostructural with tribenzobarellene-
methane 3,9 whose structure,‡ to the best of our knowledge, has
never been published. Both 2 and 3 show disordered structures.
The molecules are located on 3-fold axes with C1, C8, Ge (resp.
¯
C9) and H8 atoms in special positions 6c of the space group R3.
The disorder consists of an inversion of the molecule approx-
imately maintaining the position of the tribenzobarrelene
skeleton and mainly affecting the germanium (resp. C9) atom.
The refinement of such models fixing the sum of the
occupations of the Ge (resp. C9) sites to 1 shows disorder ratios
of 60.0(4)/40.0(4)% and 61.5(7)/38.5(7)% for 2 and 3 re-
spectively. The relatively high values of the R factors and
uncertainties obtained for 2 show that this compound is more
affected than 3 by the disorder. Indeed, in the crystal packing,
Scheme 1
Scheme 2
Chem. Commun., 1999, 961–962
961

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Tribenzobarellenegermane: 2 g (6.0 mmol) of bromotriptycene were
dissolved in 30 ml of dry THF. Then 4.1 ml of BuLi (1.6 M hexane) were
introduced very slowly into the solution during a few minutes at 278 °C.
After 10 min the temperature was slowly raised up to 0 °C and then cooled
quickly to 280 °C. 1.93 g of GeCl4 (9.0 mmol) was added all at once and
the solution was vigorously stirred. After 30 min a gentle reflux was applied
during 1.5 h. The solution was cooled in an ice bath and 0.4 g (10.6 mmol)
of LiAlH4 was carefully added. After refluxing for 2 h the reaction was
quenched with a few drops of HCl/H2O and the residual germane was
extracted with Et2O (3 3 30 ml). The final product was purified via silica
gel chromatography using hexane–Et2O (9:1) as eluant. Small transparent
crystals were obtained directly from this solution (35%), mp 232 °C;
dH(CDCl3, 200 MHz) 2.37 (s, 3H), 4.44 (s, 1H), 6.96–7.04 (m, 6H),
7.33–7.42 (m, 6H); m/z 330 (M+), 253, 226, 176, 126.
‡ Crystal data for 1: C16H31P, M = 236.3; orthorhombic, Pnma, Z = 4, a
= 11.7836(5), b = 14.3232(7), c = 7.2002(5) Å, V = 1215.2(1) Å3, T =
180 K, m = 1.753 mm21 for Cu-Ka radiation (A* min., max. = 1.174,
1.585), F000 = 496, Dc = 1.291 g cm23, 1560 measured reflections, 780
unique reflections of which 665 were observable [|Fo| > 4s(Fo)]. Full-
matrix least-squares refinement based on F using weight of 1/[s2(Fo) +
0.0001(Fo2)] gave final values R = 0.038, wR = 0.037 for 115 variables
and 665 contributing reflections. Hydrogen atoms were observed and
¯
Fig. 2 Perspective view of 2. Ellipsoids are represented with 40%
probability. Selected bond distances (Å) and angles (°): C1–Ge 1.861(8);
C1–GeA 1.77(1); Cl–C2 1.513(8); C7–C8 1.541(5); C2–C1–Ge 111.8(3);
C7–C8–GeA 114.0(3); C2–C1–C2A 107.1(5); C7–C8–C7A 104.6(5) [for the
isostructural 3 (Ge)C9): C1–C2 1.529(2); C1–C9 1.546(5); C1–C9A
1.546(6), C7–C8 1.524(2); C2–C1–C2A 105.0(1); C2–C1–C9 113.62(9);
C7–C8–C9A 113.07(8); C7–C8–C7A 105.6(1)].
refined. For 2: C20H16Ge, M = 328.9; trigonal, R3, Z = 6, a = 11.8154(7),
c = 17.7571(7) Å, V = 2146.8(3) Å3, T = 200 K, m = 2.794 mm21 for Cu-
Ka radiation (A* min., max. = 1.661, 2.898), F000 = 1008, Dc = 1.527 g
cm23, 1872 measured reflections, 593 unique reflections of which 563 were
observables [|Fo| > 4s(Fo)]. Full-matrix least-squares refinement based on
F using weight of 1/s2(Fo) gave final values R = 0.086, wR = 0.060 for 69
variables and 563 contributing reflections. Hydrogen atoms were calcu-
¯
lated. For 3: C21H16, M = 268.4; trigonal, R3, Z = 6, a = 11.7919(7), c =
17.5871(8) Å, V = 2117.8(2) Å3, T = 170 K, m = 0.538 mm21 for Cu-Ka
the shortest distances between two disordered sites of the Ge
(resp. C9) atoms located along c axis (on both sides of a centre
of inversion) are 1.557(7) and 2.065(8) Å for 2 and 3
respectively. It should be noted that a refinement of 2 in the
noncentrosymmetric space group R3 leads to a final value of the
Flack parameter10 of x = 0.47(28), large values of D/s, non-
positive values of ∑Uij∑ and a value of R of about 13%. These
observations lead us to exclude the presence of a non-
centrosymmetric, twinned and disordered structure as observed
for the analogous tribenzobarrelenephosphine compound.4
EPR experiments on the dynamics of radicals produced from
1 and 2 are currently in progress.
radiation (A* min., max. = 1.083, 1.165), F000 = 852, Dc = 1.263 g cm23
,
1985 measured reflections, 634 unique reflections of which 629 were
observables [|Fo| > 4s(Fo)]. Full-matrix least-squares refinement based on
F using weight of 1/s2(Fo) gave final values R = 0.038, wR = 0.036 for 95
variables and 629 contributing reflections. Hydrogen atoms were observed
and refined. CCDC 182/1228. See http://www.rsc.org/suppdata/cc/
1999/961/ for crystallographic files in .cif format.
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We thank the Swiss National Science Foundation for
financial support.
Notes and references
† Syntheses: All experiments were performed under dry N2.
Bromodibenzobarellene was synthesized following a slight modification
of the method reported by Mori et al. (ref. 11): 3.57 g (14 mmol) of
9-bromoanthracene and 3.48 g (17 mmol) of the furan–acetylene adduct in
20 ml of triglyme were sealed in a glass tube and placed in an autoclave.
Very vigorous stirring was applied and the mixture was heated at 120 °C for
48 h and then at 200 °C for 24 h. The oily brown solution was washed with
water (3 3 30 ml) to remove the solvent. After the usual work-up
bromodibenzobarellene was separated by chromatography on silica gel
using hexane–Et2O (10:1) as eluant. The yellow powder was recrystallised
from CH2Cl2–EtOH (68%): transparent crystals, mp 105 °C; dH(CDCl3,
200 MHz) 5.13 (dd, 1H), 7.05 (m, 6H), 7.26 (d, 2H), 7.71 (d, 2H); m/z (M+),
282, 256, 203, 176, 150, 101, 75.
Dibenzobarellenephosphine: 4.9 ml of BuLi (1.6 M, hexane) were very
slowly introduced, at 280 °C, into a solution containing 2 g (7.1 mmol) of
bromodibenzobarellene dissolved in 30 ml of dry THF. After 10 min the
temperature was slowly raised up to 260 °C. Then the solution was quickly
cooled to 2100 °C and 1.1 ml of PCl3 (12.5 mmol) was added all at once;
the solution was vigorously stirred for 30 min and gently refluxed for 1 h.
The solution was then cooled in an ice bath and 0.53 g (14 mmol) of LiAlH4
were carefully added. After refluxing for 2 h, the reaction was quenched
with a few drops of HCl/H2O and the residual phosphine was extracted with
Et2O (3 3 30 ml). The final product was purified by chromatography on
silica gel using hexane–Et2O (9:1) as eluant. Small, thin crystals were
obtained directly from this solution (42%): mp 108 °C; dP(CDCl3, 80 MHz)
143.6 (t, JPH 199); dH(CDCl3, 200 MHz) 3.55 (d, JPH 200, 1H, PH), 5.13
(dd, 2H), 6.76 (ddd, 1H), 7.05 (m, 6H), 7.32 (m, 2H), 7.50 (m, 2H).
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Chem. Commun., 1999, 961–962