904 Organometallics, Vol. 23, No. 4, 2004
Wrobel et al.
Ta ble 4. Cr ysta llogr a p h ic a n d Exp er im en ta l Da ta a
for Com p lex 6
in the form of colorless crystals. 1H NMR (250 MHz, CDCl3,
7.24 ppm, 300 K): δ 6.77 (s, 6H, Ph), 2.24 (s, 9H, para-Me),
2.15 (s, 18H, ortho-Me), 2.08 (s, 1H, Si-OH). 1H NMR (250
MHz, C6D6, 7.15 ppm, 300 K): δ 6.73 (s, 6H, Ph), 2.31 (s, 18H,
ortho-Me), 2.10 (s, 9H, para-Me), 1.90 (s, 1H, Si-OH).13C NMR
(250 MHz, C6D6, 128.0 ppm, 300 K): δ 144.6 (Ph, ortho-C),
139.2 (Ph, para-C), 135.4 (Ph, ipso-C), 130.0 (Ph, meta-C), 24.6
(ortho-Me), 21.1 (para-Me). EI-MS: 401 (M+), 282, 267, 264,
235, 163. Anal. Calcd for C27H34OSi: C, 80.54; H, 8.51.
Found: C, 80.27; H, 8.30.
B is [t r is (2,4,6-t r im e t h y lp h e n y l)s ilo x y ]a lu m in u m -
m eth yl (2). To a stirred solution of 0.054 g (0.375 mmol)
of Al2Me6 in 15 mL of toluene was added dropwise 0.50 g (1.24
mmol) of tris(2,4,6-trimethylphenyl)silanol 1 in 5 mL of toluene
during 5 min at room temperature. After the evolution of
methane had ceased, the solution was stirred for another 30
min and the solvent then removed under vacuo. The remaining
white powder was heated to 140 °C for 18 h in vacuo to remove
any residual Al2Me6. In this manner 0.42 g (0.50 mmol, 81%
yield) of pure 2 was obtained in the form of a colorless powder.
1H NMR (250 MHz, C6D6, 7.15 ppm, 300 K): δ 6.71 (s, 12H,
Ph), 2.29 (s, 36H, ortho-Me), 2.11 (s, 18H, para-Me), -0.55 (s,
3H, Al-Me). 1H NMR (250 MHz, C6D5CH3, 7.17/7.09/7.00 ppm,
213 K): δ 6.70 and 6.61 (two br s, together 12H, Ph), 2.51 und
2.42 (two br s, together 18H, ortho-Me), 2.16 (s, 18H, para-
Me), 2.14 (overlapping with the signals at 2.05) and 2.05 (two
br s, together 18H, ortho-Me), -0.45 ppm (s, 3H, Al-Me). 13C
NMR (250 MHz, C6D6, 128.0 ppm, 300 K): δ 144.1 (Ph, ortho-
C), 138.6 (Ph, para-C), 137.2 (Ph, ipso-C), 130.0 (Ph, meta-C),
25.0 (ortho-Me), 21.1 (para-Me), -10.9 (Al-Me). 27Al NMR (400
MHz, C6H5F, 358 K): no resolved signal detectable. EI-MS:
844 (M+), 829 (M+ - Me), 710, 605, 589, 485, 282, 265, 163,
133, 120, 105.
formula
C42H28AlBF20N2
cryst color and form
cryst syst, space group
a [Å]
b [Å]
c [Å]
colorless prisms
triclinic, P1h
12.4159(14)
13.6012(14)
14.6254(19)
66.390(8)
R [deg]
â [deg]
65.179(9)
84.685(8)
γ [deg]
Z; V [Å3]
2; 2045.5(4)
0.65 × 0.3 × 0.25
173; 1.589
0.177; 984
ω, 1.6-27°
9826
8724 (Rint ) 2.04%)
6969
595; 1.015
3.98%; 9.84%
5.39%; 10.7%
0.363
cryst size [mm]
T [K]; dcalcd, [g/cm3]
µ [mm-1], F(000)
scan mode; θ range [deg]
no. of reflns collected
no. of ind reflns
no. of obsd reflns (I > 2σ(I))
no. of params; GOF
R(F), Rw(F2)a (obsd data)
R(F), Rw(F2)a (all data)
largest diff peak [e/Å3]
Weighting scheme: w-1 ) σ2(Fo2) + (0.049P)2 + 0.9727P, with
a
P ) (F0 + 2Fc2)/3.
2
for X-ray structure determination were isolated from a con-
centrated solution of 6 in chlorobenzene into which pentane
1
was slowly allowed to diffuse at room temperature. H NMR
(250 MHz, C6D6 7.15 ppm, 300 K): δ 6.87 (m, 6H, Ph), 6.35
(m, 4H, Ph), 1.65 (s, 12H, N-Me), -0.92 (s, 6H, Al-Me).
Rea ctivity Stu d ies on th e NMR Sca le. Since all com-
pounds studied were stable in C6D6, reactivity studies were
performed in that solvent. NMR tubes were dried prior to use
at 200 °C in vacuo for 48 h. Stock solutions of the individual
compounds were prepared in a glovebox and mixed at room
temperature at various ratios of the reactants. NMR tubes
were sealed and kept at -80 °C until the first measurement.
Reactions were followed by 1H NMR spectroscopy at room
temperature.
Tr is(2,4,6-t r im et h ylp h en yl)siloxyd ia lu m in u m p en t a -
m eth yl (3). To a stirred solution of 0.12 g (1.66 mmol)
of Al2Me6 in 15 mL of toluene was added dropwise 0.30 g (0.75
mmol) of tris(2,4,6-trimethylphenyl)silanol 1 in 5 mL of toluene
during 5 min at room temperature. After the evolution of
methane had ceased, the solution was stirred for another 15
min and the solvent then removed in vacuo. Residual toluene
and excess Al2Me6 were removed from the resulting colorless
foam by coevaporation with 10 mL of pentane to yield 0.38 g
(0.72 mmol, 97% yield) of 3 in the form of a colorless powder.
Although rapid methyl exchange between 3 and Al2Me6 leads
to coalescence of their respective 1H NMR signals, the absence
Meth yl/Ch lor id e Exch a n ge w ith Zir con ocen e Dich lo-
r id e Com p lexes. To study reactions of siloxalane 3 with the
zirconocene dichlorides listed in Table 2, 500 µL of a 5 mM
stock solution of the respective zirconocene dichloride was
mixed with 50-200 µL of a 50 mM stock solution of 3, directly
in a NMR tube, so as to obtain initial, nominal [3]init:[Zr]tot
ratios I in the range of 1:1 to 4:1. The solutions were stored
1
of significant amounts of Al2Me6 is indicated by the H NMR
1
1
for 24 h at room temperature, after which their H NMR were
integral ratios obtained for this product. H NMR (250 MHz,
taken on a 250 MHz NMR spectrometer. Concentration ratios
Q ) [Cp2ZrMeCl]:[Cp2ZrCl2] were obtained from the respective
signal intensities of these species. Initial concentration ratios
I ) [3]init:[Zr]tot were experimentally determined by comparing
1/15 of the total signal intensities of all Al- and Zr-bound
methyl groups with 1/10 (for (C5H5)2ZrCl2) or 1/8 (for (n-
BuC5H4)2ZrCl2 and Me2Si(C5H4)2ZrCl2) of the total signal
intensities of all Cp protons. From the data thus obtained
(Supporting Information), the equilibrium constants listed in
Table 2 were evaluated by use of the relationship KEXC ) Q/[I(1
+ 1/Q) - 1].17
Nominal equilibrium constants for the heterogeneous reac-
tion systems containing Al2Me6-treated silica gel were evalu-
ated from the data reported in ref 4 by assuming that the Al
content of the samples used (4.3%) would be entirely due to
the presence of a surface species analogous to 3.18 If other,
less reactive Al-containing surface species were also present
in addition to a singly siloxy-bridged species, apparent KEXC
values would be underestimated by a factor corresponding to
the proportion of the latter.
C6D6, 7.15 ppm, 300 K): δ 6.67 (s, 6H, Ph), 2.59 (br s, 9H,
ortho-Me), 2.18 (br s, 9H, ortho-Me), 2.05 (s, 9H, para-Me),
1
-0.39 (br s, 15H, Al-Me). H NMR (250 MHz, C6D5CH3, 7.17/
7.09/7.00 ppm, 213 K): δ 6.57 (s, 3H, Ph), 6.50 (s, 3H, Ph),
2.59 (s, 9H, ortho-Me), 2.13 (s, 9H, ortho-Me), 2.06 (s, 9H, para-
Me), 0.36 (s, 3H, Al-µ-Me), -0.49 (s, 6H, terminal Al-Me),
-0.54 (s, 6H, terminal Al-Me). 13C NMR (250 MHz, C6D6, 128.0
ppm, 300 K): δ 144.8 (Ph, ortho-C), 139.9 (Ph, para-C), 134.6
(Ph, ipso-C), 130.4 (Ph, meta-C), 26.7 (ortho-Me) 25.0-24.7
(ortho-Me), 20.9 (para-Me), -2.6 to -4.1 (Al-Me). 27Al NMR
(400 MHz, C6H5F, 358 K): δ 158.0 (w1/2 ca. 2500 Hz).
[AlMe2(NP h Me2)2]+[B(C6F 5)4]- (6). To a stirred solution
of 0.40 g (0.99 mmol) of tris(2,4,6-trimethylphenyl)silanol 1
in 40 mL of toluene was added dropwise 0.16 g (1.12 mmol) of
Al2Me6 in 20 mL of toluene during 5 min. To the resulting
solution of tris(2,4,6-trimethylphenyl)siloxydialuminumpenta-
methyl 3 was added 0.40 g (0.5 mmol) of solid [PhMe2NH]+-
[B(C6F5)4]-, and the suspension was stirred for 48 h at ambient
temperature. The solvent and all volatile components were
removed in vacuo, and the resulting powder was washed
several times with 20 mL portions of pentane. Addition of 10
mL of toluene, filtration, and drying of the collected residue
in vacuo provided 0.05 g (0.05 mmol, 20% yield) of 6 in NMR-
pure quality as a sligthly brownish powder. Crystals suitable
Sem iem p ir ica l Ca lcu la tion s of Dim er iza tion En er gies.
Energy differences between the dinuclear complexes and their
two mononuclear halves, each with optimized geometries, were
calculated for the siloxalanes and alkoxalanes listed in Table