Syntheses of polyaluminium compounds by hydroalumination reactions, chelating Lewis acids possessing two and four coordinately unsaturated aluminium atoms

Article abstract of DOI:10.1016/S0022-328X(02)01970-8

Hydroalumination of C≡C triple bonds was achieved by treatment of the tetraalkynylbenzene derivative the starting compounds multifunctional Lewis acids were obtained with two or four coordinatively unsaturated aluminium atoms. Alkenyl derivatives resulted

Full text of DOI:10.1016/S0022-328X(02)01970-8

Journal of Organometallic Chemistry 664 (2002) 110ꢃ115
/
www.elsevier.com/locate/jorganchem
Syntheses of polyaluminium compounds by hydroalumination
reactions, chelating Lewis acids possessing two and four
coordinatively unsaturated aluminium atoms
Werner Uhl ꢀ, Madhat Matar
Fachbereich Chemie der Philipps-Universitat, Hans-Meerwein-Straße, D-35032 Marburg, Germany
¨
Received 26 April 2002; accepted 11 September 2002
Abstract
Hydroalumination of Cꢀ
/
C triple bonds was achieved by treatment of the tetraalkynylbenzene derivative 1,2,4,5-(Me3Siꢁ
/
Cꢀ
/
C)4C6H2 with di(tert-butyl)aluminium hydride. Depending on the stoichiometric ratio of the starting compounds multifunctional
Lewis acids were obtained with two or four coordinatively unsaturated aluminium atoms. Alkenyl derivatives resulted which have
the Al and H atoms in cis positions and the di(tert-butyl)aluminium and trimethylsilyl groups attached to the terminal carbon atoms
of the Cꢂ/C double bonds.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Aluminium; Hydroalumination
1. Introduction
methylene bridged tetraalkyldialanes are stable only
when they are effectively shielded by bulky substituents.
Insufficient steric shielding by smaller ligands resulted in
dismutation reactions [5,7]. One related compound
Chelating Lewis acids possessing two or more co-
ordinatively unsaturated atoms of the third main-group
elements boron [1], aluminium [2], gallium [3] and
indium [4] found considerable interest in current re-
search, because they may find some application in phase
transfer processes or in anion recognition, for instance.
About 10 years ago we obtained a stable tetraalkyldia-
luminium derivative which contained a methylene
bridge between both its tricoordinate aluminium atoms
bearing smaller substituents [Li2(R3AlCH2AlR3); Rꢁ
/
CH2SiMe3] was stabilized by coordinative saturation
of its aluminum atoms [8]. In some recent investigations,
we found that the hydroalumination [9] of polyalkynes
is a facile method for the synthesis of a broad variety of
polyaluminium compounds in high yield, and we
obtained dialuminium derivatives by the reaction of
di(tert-butyl)aluminium hydride with 1,4-bis(trimethyl-
silyl)butadiyne or 1,4-bis(trimethylsilylethynyl)benzene
[10]. We hoped to isolate even aluminium richer
compounds by the employment of tetraalkynylbenzene
derivatives.
[R2Alꢁ
nium compound was synthesized by the treatment of
Cl2AlꢁCH2ꢁAlCl2 with four equivalents of the lithium
/
CH2ꢁ
/
AlR2, RꢁCH(SiMe3)2]. That dialumi-
/
/
/
compound LiCH(SiMe3)2 [5], and it is a potential
acceptor of up to two donor atoms. Indeed, it proved
to be a very effective chelating Lewis acid, which gave
stable adducts with hydrido (1, Scheme 1), nitrato (2,
Scheme 1), nitrito, diphosphanylmethanido, methylthio-
lato, acetato and azido ligands [6]. However, those
2. Results and discussion
Treatment
of
1,2,4,5-tetrakis(trimethylsilylethy-
nyl)benzene with two equivalents of di(tert-butyl)alu-
minium hydride in boiling n-hexane for 3 days and
recrystallization of the rough product of the reaction
from the same solvent afforded the colourless product 3
ꢀ Corresponding author. Tel.: ꢂ
2825653
E-mail address: uhl@chemie.uni-marburg.de (W. Uhl).
/
49-6421-2825751; fax: ꢂ49-6421-
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 2 ) 0 1 9 7 0 - 8

W. Uhl, M. Matar / Journal of Organometallic Chemistry 664 (2002) 110ꢃ
/115
111
ð1Þ
Scheme 1.
in 37% yield (Eq. (1)). In the 1H-NMR spectrum,
compound 3 shows two resonances of trimethylsilyl
groups and a singlet for the tert-butyl substituents in an
intensity ratio of 1:1:2. Two signals of equal intensity
were observed at low field (dꢁ7.88 and 8.05). They
/
were assigned to both protons attached to the benzene
ring and to two alkene protons resulting from the
addition of Alꢁ/H groups to two alkyne moieties of the
tetraalkyne starting compound. In accordance with the
result of the crystal structure determination (see below),
a centrosymmetric product had formed in which two Cꢀ
/
C triple bonds in a trans position were hydroalumi-
nated. Two Cꢀ
/
C triple bonds remained unchanged. An
absorption at 2152 cmꢄ1 was observed for these bonds
in the IR spectrum, the vibrations of the alkene and
benzene groups were detected at 1590 and 1547 cmꢄ1
respectively.
,
Fig. 1 shows the molecular structure of 3. The
molecules are located on crystallographic inversion
atoms of the tert-butyl groups (198.1 pm). The Siꢁ
distances of the alkynyl SiMe3 groups (C7ꢁSi2 183.7(2)
pm; Si2ꢁMe 184.7(3)ꢃ185.8(3) pm) are shorter than
those of the alkenyl SiMe3 group (C5ꢁSi1 187.2(2) pm;
Si1ꢁMe 185.7(3)ꢃ188.3(3) pm). The lengths of the Cꢂ
double and CꢀC triple bonds (C4ꢁC5 134.7(3) pm; C6ꢁ
C7 119.2(3) pm) correspond to standard values [12]. The
atoms C6, C7 and Si2 of the linear alkyne groups (angles
at C6 and C7 176.6(2) and 177.0(2)8, respectively) are
located almost ideally in the plane formed by the
benzene carbon atoms (maximum deviation 10 pm of
Si2). In contrast, the alkenyl groups are tilted, and the
atoms Al and Si1 lie 73 and 171 pm above and below the
benzene plane. Torsion angles relevant for the descrip-
tion of that tilting are given in the legend of Fig. 1. The
Al atoms have a planar surrounding (sum of the angles
359.58). The normals of the planes (C5, Al, Ct1, Ct2)
and (C1, C2, C3, C1?, C2?, C3?) (benzene) include an
/
C
/
centers. Two Alꢁ
/
H groups were added to two alkyne
/
/
substituents of the tetraalkynyl starting compound in
trans positions, and we observe the alternating arrange-
ment of hydrogen atoms, alkenyl and alkynyl substitu-
ents attached to the central benzene ring. The
aluminium and silicon atoms are bonded in geminal
positions to the b-carbon atoms of the alkene groups.
Negative hyperconjugation [11] with the trimethylsilyl
groups may help to stabilize the negative charge of these
carbon atoms, which results from the high electronega-
tivity difference between carbon and aluminium, and
may thus favour this particular arrangement. The
hydroalumination gave a stereoselective cis addition,
and the hydrogen and aluminium atoms are located on
/
/
/
/C
/
/
/
the same sides of the Cꢂ
the AlꢁC distances to the alkenyl carbon atoms are a
little shorter (195.5 pm) than those to the inner carbon
/C double bonds. As expected,
/

112
W. Uhl, M. Matar / Journal of Organometallic Chemistry 664 (2002) 110ꢃ115
/
Its 1H-NMR spectrum showed two singlets of tert-butyl
and trimethylsilyl groups in an intensity ratio of 2:1, and
in the same ratio the resonances of the alkene and
benzene protons were observed at low field (dꢁ
and 7.39, respectively). Absorptions at 1589 and 1538
cmꢄ1 were recorded in the IR spectrum for the Cꢂ
double bonds and the benzene ring.
/8.09
/C
The molecular structure of 4 is depicted in Fig. 2. All
alkynyl substituents were transformed to alkenyl groups
by the addition of Alꢁ/H bonds. Once again a selective
cis addition was observed. The four coordinatively
unsaturated aluminium atoms are attached to the b-
carbon atoms of the alkenyl groups, and they are in a
geminal position with the trimethylsilyl substituents.
Thus, compound 4 has four Lewis acidic centers in one
molecule. The alkenyl groups are tilted with respect to
the plane of the benzene ring similar as described before
for compound 3 and alternately adopt positions above
and below the molecular plane. The molecular symme-
try approaches D2. The structural parameters corre-
spond well to those of the alkenyl groups in 3 and do not
need a further discussion.
Fig. 1. Molecular structure and numbering scheme of compound 3;
the thermal ellipsoids are drawn at the 40% probability level; methyl
groups are omitted for clarity; hydrogen atoms with arbitrary radius.
Selected bond lengths (pm) and angles (8): Alꢁ
198.2(3), AlꢁCT2 198.0(3), Si1ꢁC5 187.2(2), Si2ꢁ
147.4(3), C4ꢁC5 134.7(3), C2ꢁC6 144.3(3), C6ꢁC7 119.2(3), C1ꢁ
C5 128.7(2), C4ꢁC5ꢁAl 114.4(2), C4ꢁC5ꢁSi1 130.1(2), C2ꢁC6ꢁ
176.6(2), C6ꢁC7ꢁSi2 177.0(2). Torsion angles (8): C3?ꢁC1ꢁC4ꢁ
29.7(3), C1ꢁC4ꢁC5ꢁSi1 6.1(4), C1ꢁC4ꢁC5ꢁAl 171.9(2), C4ꢁC5ꢁ
AlꢁCT1 110.7(2), C4ꢁC5ꢁAlꢁCT2 ꢄ61.8(2).
/
C5 195.5(2), Alꢁ
C7 183.7(2), C1ꢁ
C4ꢁ
C7
C5
/
CT1
/
/
/
/
C4
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
angle of 34.58 so that overall a rather flat molecule
results.
A second product was determined by NMR spectro-
scopy in the rough product of a reaction mixture which
was stored at room temperature only. Its concentration
was larger than or at least equal to that of 3. However, it
could not be isolated in a pure form or even be enriched
by recrystallization of the residue of the mother liquor
1
which remained after isolation of 3. It showed an H-
NMR spectrum quite similar to that of 3 with two
resonances of trimethylsilyl groups (dꢁ
and one signal of tert-butyl groups at dꢁ
intensity ratio of 1:1:2. The alkene and benzene protons
resonate at dꢁ8.06 and 7.46. We suppose that a
/0.26 and 0.09)
/
1.22 in an
/
compound had formed in which the hydroalumination
occurred on neighbouring alkyne groups. Most of the
second product rearranged upon heating of a solution of
the mixture in hexane to 60 8C to give the sterically less
stressed, centrosymmetric compound 3. This process
probably proceeds via elimination of the alane and re-
Fig. 2. Molecular structure and numbering scheme of compound 4;
the thermal ellipsoids are drawn at the 40% probability level; methyl
groups are omitted for clarity; hydrogen atoms with arbitrary radius.
Selected bond lengths (pm) and angles (8): C1ꢁ
135.5(4), C02ꢁAl1 195.8(3), C02ꢁSi1 187.7(3), C2ꢁ
C03ꢁC04 135.2(4), C04ꢁAl2 196.0(3), C04ꢁSi2 187.6(3), C4ꢁ
148.0(4), C05ꢁC06 135.5(4), C06ꢁAl3 194.7(3), C06ꢁSi3 187.5(3),
C5ꢁC07 148.3(4), C07ꢁC08 134.9(4), C08ꢁAl4 195.7(3), C08ꢁSi4
187.9(3), C1ꢁC01ꢁC02 126.4(3), C01ꢁC02ꢁAl1 124.9(2), C01ꢁC02ꢁ
Si1 124.7(2), C2ꢁC03ꢁC04 128.0(3), C03ꢁC04ꢁAl2 120.4(2), C03ꢁ
C04ꢁSi2 128.0(3), C4ꢁC05ꢁC06 126.9(3), C05ꢁC06ꢁAl3 121.7(2),
C05ꢁC06ꢁSi3 126.9(2), C5ꢁC07ꢁC08 125.7(3), C07ꢁC08ꢁAl4
122.7(2), C07ꢁC08ꢁSi4 124.0(2). Torsion angles (8, average values):
(H)CꢁCꢁCꢂC ꢄ46.8, CꢁCꢂCꢁSi ꢄ12.7, CꢁCꢂCꢁAl 178.4, CꢂCꢁ
AlꢁCT 70.1 and ꢄ101.9.
/
C01 148.0(4), C01ꢁ
C03 147.9(4),
C05
/
C02
/
/
/
/
/
/
/
addition of the released Alꢁ/H groups to yield the
/
/
/
thermodynamically more favored product. The com-
plete consumption of the by-product was not observed
even upon elongated heating.
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
A much more specific reaction was observed when we
treated the tetraalkyne with four equivalents of di(tert-
butyl)aluminium hydride, and the product (4) of the
fourfold hydroalumination was isolated in 76% yield (1).
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/

W. Uhl, M. Matar / Journal of Organometallic Chemistry 664 (2002) 110ꢃ
/115
113
3. Experimental
3.3. Treatment of C6H2(Cꢀ
/
Cꢁ
/
SiMe3)4 with four
equivalents of HAl(CMe3)2
All procedures were carried out under purified Ar in
dried solvents (C6H5CH3 over Naꢃbenzophenone; n-
/
C6H14 over LiAlH4). The starting compounds di(tert-
butyl)aluminium hydride [13] and 1,2,4,5-tetrakis(tri-
methylsilylethynyl)benzene [14] were synthesized ac-
cording to literature procedures.
3.3.1. Compound 4
A solution of 0.71 g (1.54 mmol) of C6H2(Cꢀ
SiMe3)4 in 50 ml of n-C6H14 was slowly added to a
solution of 0.88 g (6.18 mmol) of di(tert-butyl)alumi-
nium hydride in 20 ml of n-C6H14 at r.t. The colour
changed to yellow. The mixture was stirred for 2 h at r.t.
All volatile components were removed in vacuo. The
/
Cꢁ
/
3.1. Treatment of C6H2(Cꢀ
/
Cꢁ
/
SiMe3)4 with two
residue was dissolved in 2ꢃ
crystals of 4 precipitated from that solution upon
cooling to ꢄ15 8C. Yield: 1.20 g (76%). M.p. (Ar,
sealed capillary): 135 8C (dec.). Molar mass (in C6H6 by
cryoscopy): Found 1075. Calc. 1031.8 g molꢄ1 1H-
NMR (C6D6, 400 MHz, 298 K): dꢁ8.07 (4H, s, Cꢂ
/
3 ml of n-C6H14. Colourless
equivalents of HAl(CMe3)2
/
3.1.1. Compound 3
A solution of HAl(CMe3)2 (0.80 g, 5.63 mmol) in 20
ml of n-C6H14 was slowly added to a solution of
.
/
/
CH), 7.36 (2H, s, C6H2), 1.23 (72H, s, CMe3), 0.19
(36H, s, SiMe3). 13C-NMR (C6D6, 100.6 MHz, 298 K):
C6H2(Cꢀ
/
Cꢁ/SiMe3)4 (1.30 g, 2.82 mmol) in 50 ml of n-
C6H14 at room temperature (r.t.). The colour of the
mixture changed to yellow. The solution was heated
under reflux for 3 days. The solvent was removed in
vacuo, and the residue was recrystallized twice from n-
dꢁ
154.0 (Cꢂ
/
160.9 (Cꢂ
/
C, carbon atoms attached to Al and Si),
C, carbon atoms attached to phenyl), 140.8
/
(phenyl, carbon atoms attached to alkenyl), 129.8
(phenyl, carbon atoms attached to hydrogen), 29.9
(CMe3), 19.1 (AlCMe3), 2.0 (SiMe3). IR (CsBr, paraffin,
cmꢄ1): 1589 w, 1538 s phenyl, nCꢂ
paraffin; 1307 w, 1246 vs dCH3; 1176 m, 1153 w, 1072
m, 1035 m, 1006 m nCC; 940 s, 916 m, 837 vs, 807 s, 784
m, 753 m nCC, dCH3; 651 m nSiC; 595 m, 552 w, 530 w,
457 m, 427 m, 417 m, 399 w nAlC, dCC.
C6H14 (20/ꢄ
solid. M.p. (sealed capillary, Ar): 57 8C. Molar mass (in
C6H6 by cryoscopy): Found: 700. Calc. 747.4 g molꢄ1
1H-NMR (C6D6, 400 MHz, 298 K): dꢁ
8.05 (2H, s, Cꢂ
CH), 7.88 (2H, s, C6H2), 1.20 (36H, s, CMe3), 0.27 (18H,
s, SiMe3 of alkynyl), 0.21 (18H, s, SiMe3 attached to Cꢂ
C double bond). 13C-NMR (C6D6, 100.6 MHz, 298 K):
dꢁ161.9 (CꢂC, carbon atoms attached to Al and Si),
151.8 (CꢂC, carbon atoms attached to phenyl), 143.5
/
15 8C). Yield: 0.78 g (37%), colourless
/C; 1463 vs, 1377 vs
.
/
/
/
/
/
/
3.4. Crystal structure determinations
(phenyl, carbon atoms attached to alkenyl), 133.0
(phenyl, carbon atoms attached to hydrogen), 122.1
Single crystals of compound 3 were obtained by
(phenyl, carbon atoms attached to alkynyl), 104.0 (Cꢀ
carbon atoms attached to phenyl), 101.0 (CꢀC, carbon
atoms attached to SiMe3), 29.9 (CMe3), 19.3 (AlCMe3),
1.7 (SiMe3 attached to CꢂC), 0.1 (SiMe3 attached to Cꢀ
C). IR (CsBr, paraffin, cmꢄ1): 2153 m nCꢀ
C; 1590 w,
1547 w nCꢂC, aryl; 1464 vs, 1377 vs paraffin; 1249 vs
/C,
recrystallization from C6H5CH3 (20/ꢄ
/
15 8C), single
/
crystals of 4 from n-C6H14 (20/ꢄ15 8C). Crystal data
/
and structure refinement parameters are given in Table
1. Some tert-butyl groups of 4 showed a disorder (CT2,
/
/
/
CT4ꢃCT7). Their methyl groups were refined on split
/
/
positions, with the exception of the group at CT7 (0.63
and 0.37) the occupation factors were near 0.5.
dCH3; 1176 w, 1048 m nCC; 843 vs, 760 s nCC,
d,rCH3(Si); 698 w nsSiC; 638 m nasSiC; 596 w, 468
vw, 451 w, 414 w nAlC.
4. Supplementary material
3.2. NMR data of the by-product of the synthesis of 3
The NMR spectra were recorded in a mixture with 3.
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
1H-NMR (C6D6, 300 MHz, 298 K): dꢁ
CH), 7.46 (2H, s, C6H2), 1.22 (36H, s, CMe3), 0.26 and
/
8.06 (2H, s, Cꢂ
/
Data Centre, CCDC nos. 184180ꢃ184181 for com-
/
pounds 4 and 3. Copies of this information may be
obtained free of charge from The Director, CCDC, 12
0.09 (each 18H, s, SiMe3). 13C-NMR (C6D6, 75 MHz,
298 K): dꢁ
103.4 and 99.9 (phenyl, Cꢂ
(AlCMe3), 1.7 and 0.2 (SiMe3).
/
162.2, 153.0, 145.1, 137.9, 128.7, 121.3,
Union Road, Cambridge CB1 1EZ, UK (Fax: ꢂ44-
1233-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
/
/
C, CꢀC), 29.9 (CMe3), 19.3
/

114
W. Uhl, M. Matar / Journal of Organometallic Chemistry 664 (2002) 110ꢃ115
/
(j) V.C. Williams, W.E. Piers, W. Clegg, M.R.J. Elsegood, S.
Collins, T.B. Marder, J. Am. Chem. Soc. 121 (1999) 3244;
(k) V.C. Williams, C. Dai, Z. Li, S. Collins, W.E. Piers, W. Clegg,
M.R.J. Elsegood, T.B. Marder, Angew. Chem. 111 (1999) 3922;
Angew. Chem. Int. Ed. 38 (1999) 3695;
Table 1
Crystal data, data collection parameters and structure refinement for 3
a
and 4
3
4
(l) V.C. Williams, G.J. Irvine, W.E. Piers, Z. Li, S. Collins, W.
Clegg, M.R.J. Elsegood, T.B. Marder, Organometallics 19 (2000)
1619;
Formula
Temperature (K)
Crystal system
Space group [15]
a (pm)
C42H76Al2Si4
193(2)
Triclinic
C58H114Al4Si4
193(2)
Monoclinic
P21/n; No. 14
1467.21(9)
3353.5(2)
1542.3(1)
90
(m) W.E. Piers, G.J. Irvine, V.C. Williams, Eur. J. Inorg. Chem.
(2000) 2131 (Microreview);
¯
P1; No. 2
/
680.18(8)
1310.1(1)
1562.0(2)
110.789(8)
95.723(9)
92.092(9)
1290.9(2)
1
(n) L.D. Henderson, W.E. Piers, G.J. Irvine, R. McDonald,
Organometallics 21 (2002) 340;
b (pm)
c (pm)
(o) B. Schilling, V. Kaiser, D.E. Kaufmann, Chem. Ber./Recueil
130 (1997) 923;
a (8)
b (8)
g (8)
104.094(8)
90
(p) M. Reilly, T. Oh, Tetrahedron Lett. 36 (1995) 221;
(q) M. Reilly, T. Oh, Tetrahedron Lett. 36 (1995) 217;
(r) K. Nozaki, M. Yoshida, H. Takaya, Bull. Chem. Soc. Jpn. 69
(1996) 2043;
V (10ꢄ30 m3)
Z
7360.1(8)
4
0.931
Dcalc (g cmꢄ3
)
0.961
0.173
(s) K. Nozaki, T. Tsutsumi, H. Takaya, J. Org. Chem. 60 (1995)
6668;
(t) J.D. Hoefelmeyer, F.P. Gabbaı, Organometallics 21 (2002)
¨
m (mmꢄ1
)
0.157
0.3ꢅ0.3ꢅ0.1
STOE IPDS
Crystal size (mm)
Diffractometer
Radiation
0.5ꢅ0.2ꢅ0.1
STOE IPDS
982.
[2] (a) H. Hoberg, V. Gotor, A. Milchereit, C. Kruger, J.C.
¨
Moꢃ/Ka
Moꢃ
2.10ꢃ
/
Ka
25.93
Theta range for data collec- 1.40ꢃ
tion (8)
Index ranges
/25.97
/
Sekutowski, Angew. Chem. 89 (1977) 563; Angew. Chem. Int.
Ed. Engl. 16 (1977) 539;
ꢄ85h 58,
ꢄ165k 516,
ꢄ195l 519
3622
ꢄ185h 517,
ꢄ365k 541,
ꢄ185l 518
8508
¨
(b) C. .Uffing, A. Ecker, R. Koppe, K. Merzweiler, H. Schnockel,
¨
¨
Chem. Eur. J. 4 (1998) 2142;
(c) H. Martin, H. Bretinger, Z. Naturforsch. Teil B: Chem. Sci. 46
Reflections observed
[I ꢀ2s(I)]
Independent reflections
(1991) 615;
(d) O. Saied, M. Simard, J.D. Wuest, Inorg. Chem. 37 (1998)
2620;
5014
14136
[Rintꢁ0.0894]
229
0.0507
[Rintꢁ0.0403]
680
0.0647
(e) O. Saied, M. Simard, J.D. Wuest, Organometallics 17 (1998)
1128;
Parameters
Rꢁa ½½Fojꢄ½Fc½j/
a ½Foj[(I ꢀ2s(I)]
(f) F.A.R. Kaul, M. Tschinkl, F.P. Gabbaı, J. Organomet. Chem.
¨
539 (1997) 187;
2
2 2
wR2ꢁ{Sw(jFoj ꢄjFcj ) /
0.1473
0.1069
(g) M. Tschinkl, R.E. Bachman, F.P. Gabbaı, Chem. Commun.
¨
(1999) 1367;
S(F2o)2}1/2 (all data)
Max./min. residual electron 0.395/ꢄ0.272
0.496/ꢄ0.287
(h) M. Tschinkl, T.M. Cocker, R.E. Bachman, R.E. Taylor, F.P.
density (1030 e mꢄ3
)
Gabbaı, J. Organomet. Chem. 604 (2000) 132;
¨
(i) J.J. Eisch, K. Mackenzie, H. Windisch, C. Kruger, Eur. J.
¨
a
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