Silicon(IV) chelates of an (ONN′)-tridentate pyrrole-2-carbaldimine ligand: Syntheses, structures and UV/Vis properties

Article abstract of DOI:10.1515/znb-2009-11-1242

The tridentate (ONN′)-chelator properties of the pyrrole-2-(o- hydroxyphenyl)carbaldimine dian-ion (L^2-) were explored for the neutral penta-coordinate diorganosilicon complexes LSiRR′(R,R′ = Ph,Ph; Ph,Me; Ph, tBu) where the ligand L occupies t

Full text of DOI:10.1515/znb-2009-11-1242

Silicon(IV) Chelates of an (ONNꢀ)-Tridentate Pyrrole-2-Carbaldimine
Ligand: Syntheses, Structures and UV/Vis Properties
Daniela Gerlacha, Andreas W. Ehlersb, Koop Lammertsmab, and Jo¨rg Waglera
a Institut fu¨r Anorganische Chemie, Technische Universita¨t Bergakademie Freiberg,
Leipziger Straße 29, 09596 Freiberg, Germany
b Department of Chemistry, Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083,
1081 HV Amsterdam, The Netherlands
Reprint requests to Dr. Jo¨rg Wagler. Fax: (+49) 3731 39 4058.
E-mail: joerg.wagler@chemie.tu-freiberg.de
Z. Naturforsch. 2009, 64b, 1571 – 1579; received September 14, 2009
Dedicated to Professor Hubert Schmidbaur on the occasion of his 75th birthday
The tridentate (ONNꢀ)-chelator properties of the pyrrole-2-(o-hydroxyphenyl)carbaldimine dian-
ion (L2−) were explored for the neutral penta-coordinate diorganosilicon complexes LSiRRꢀ (R,Rꢀ =
Ph, Ph; Ph, Me; Ph, tBu) where the ligand L occupies the ax-eq-ax sites in a distorted trigonal-
bipyramidal arrangement arround the silicon atom, and for the neutral hexa-coordinate L2Si, that
has a mer-coordination. Single-crystal X-ray diffraction analyses show an almost planar ligand back-
bone with a Si–N bond to the imine group that is shorter in hexa-coordinate L2Si than in penta-
coordinate LSiRRꢀ. In sharp contrast to the almost colorless neutral ligand LH2, both complexes
show pronounced UV/Vis absorptions in the red-brown region that originate from HOMO - LUMO
and HOMO-1 - LUMO transitions, and that are due to intra-ligand π-π∗ transitions from the N-o-
oxyphenylimine towards the imine moiety.
Key words: Chelate, Time-dependent DFT, Hypercoordination, Pyrrole, Schiff Base, UV/Vis
Introduction
Relatively little is known about the coordinative
abilities of the L2− ligand [8], except in transition
metal complexes of copper, nickel, rhodium, iridium
and rhenium [6], some of which have found use as
catalysts in the polymerization of ethylene and α-
olefins [7]. In the present study we focus on the intrigu-
ing flexibility of this ligand in the coordination sphere
of silicon.
Silicon compounds with a silicon coordination num-
ber of five or six [1, 2] are of interest for their enhanced
reactivity [3] and electronic properties [4]. Of the many
ligands that are explored for their coordination behav-
ior to silicon, our focus is on the tridentate ONNꢀ-
chelators and in particular on the doubly deprotonated
2-(N-2-hydroxyphenyl)pyrrolcarbaldimine (LH2) [5].
This tridentate chelator can in principle occupy differ-
ent coordination sites of the trigonal-bipyramidal sili-
con coordination sphere, as shown for the neutral com-
pounds LSi(CH2)3 and LSiPhMe (Scheme 1) [5d].
Results and Discussion
The 2-(N-2-hydroxyphenyl)pyrrolcarbaldimine di-
anion acts as a tridentate (ONNꢀ)-chelator in the neu-
tral penta-coordinate LSiPhMe that carries two addi-
tional C substituents [5d]. The imine group gives an
unexpectedly short N–Si bond whereas that resulting
from the deprotonated pyrrole is slightly longer. To ex-
plore whether this behavior relates to steric conges-
tion around the silicon atom, novel penta-coordinate
Si complexes were synthesized from the neutral lig-
and LH2 and the diorganodichlorosilanes Cl2SiRRꢀ
(R,Rꢀ = Me, Me; Cy, Me; Ph, tBu; Ph, Cy; Ph, Ph)
(Scheme 2).
Scheme 1.
c
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
Table 1. Selected 29Si NMR chem-
ical shifts δ (in ppm relative to
SiMe4) of penta-coordinate silicon
complexes LSiRRꢀ.
˚
Rꢀ
Me
Me
tBu
Me
Cy
Ph
δ
Table 2. Selected bond lengths (A) for LSiPhtBu, LSiPhMe,
R
Me
Cy
Ph
Ph
Ph
Ph
and LSiPh2 with estimated standard deviations in paren-
−62.2
−62.3
−72.2
−74.1
−75.7
−85.5
theses.
LSiPhtBu
LSiPhMe
LSiPh2
Si1–O1
Si1–N1
Si1–N2
Si1–C18
Si1–C12 (Ph)
1.791(2)
1.926(2)
1.883(2)
1.906(2)
1.890(2)
1.776(2)
1.923(2)
1.897(2)
1.867(2)
1.885(2)
1.781(2)
1.905(2)
1.890(2)
1.885(2)
1.892(2)
Scheme 2.
Scheme 3.
Scheme 4.
pyrrole ring (Scheme 3, right) [6d]. The three com-
plexes LSiPhtBu, LSiPhMe, and LSiPh2 further re-
veal that their respective C5–N2 imine bond length
Fig. 1. Molecular structure of LSiPhtBu (left; only one of
the two independent molecules in the asymmetric unit is
shown) and LSiPh2 (right). (ORTEP; displacement ellipsoids
at the 20 % probability level; hydrogen atoms omitted for
clarity).
˚
of 1.309(2), 1.306(2), and 1.310(2) A, is longer than
˚
in LH2 (1.283(2) A). This elongation of the imine
bond suggests relevant contributions from the canon-
ical forms depicted in Scheme 4 or – in other words –
the tridentate ligand acts as an extended π system.
All complexes LSiRRꢀ were analyzed by 29Si NMR
spectroscopy (Table 1). The observed chemical
shift depends on the nature of the two carbon
substituents and is at higher field in the order
alkyl/alkyl< alkyl/aryl< aryl/aryl. Within each of the
three sets, the chemical shifts are very similar, thereby
suggesting also a similar coordination for the ONNꢀ-
ligand. This was confirmed by single crystal X-ray
diffraction analyses for the complexes LSiPhtBu and
LSiPh2 (Fig. 1) that compare well with the earlier re-
ported structure for LSiPhMe (Table 2) [5d].
Steric factors underlie the differences in the Si–C
bond lengths. For example, the Si–C bond to the tBu
group in LSiPhtBu is much longer than that to the
phenyl and methyl groups in LSiPhMe and LSiPh2.
The three distorted trigonal-bipyramidal systems with
the oxygen and pyrrole nitrogen atoms in axial posi-
tions also show a remarkable flexibility of the ONNꢀ
ligand in the silicon coordination sphere, as is partic-
ularly evident from the differences in the equatorial
The molecular structures of the three complexes all A–Si–B angles (especially in case of the two crystallo-
show the Si1–N1 bond to the pyrrole to be slightly graphically independent molecules for LSiPhtBu, Ta-
longer than the Si1–N2 bond to the imine. This dif- ble 3). The equatorial N2–Si1–C12 angle differs by up
ference might be due to the axial versus equatorial co- to 5.6◦ in the two independent molecules of LSiPhtBu
ordination of the penta-coordinate silicon, but Schilde and by up to 23.2◦ in the three different complexes,
et al., who reported on a comparable Re(V) complex, possibly due to the lower steric demand of the methyl
attributed the difference to electron pushing of the group in LSiPhMe. In contrast, the axial O1–Si1–N1
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
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˚
Table 3. Selected bond angles (deg) for LSiPhtBu, LSiPhMe
and LSiPh2 with estimated standard deviations in parenthe-
ses.
Table 4. Selected bond lengths (A)
LSiPh2 L2Si
of LSiPh2 and L2Si (average of all
four molecules for L2Si); (NP = ni-
trogen atom in the pyrrolic system,
NI = imine nitrogen atom).
Si–NP 1.905(1) 1.894
Si–NI 1.890(1) 1.867
Si–O 1.781(1) 1.768
N=C 1.310(2) 1.309
LSiPhtBu
LSiPhMe
LSiPh2
N2–Si1–C18 108.7(1) / 111.5(1) 135.2(1) / 136.6(1) 111.1(1)
N2–Si1–C12 133.9(1) / 128.3(1) 111.2(1) / 110.2(1) 134.4(1)
C18–Si1–C12 117.4(1) / 120.2(1) 113.6(1) / 113.2(1) 114.5(1)
O1–Si1–N1
158.1(1) / 160.1(1) 160.8(1) / 159.8(1) 161.2(1)
Scheme 6.
Fig. 2. Molecular structure of (LH)PhtBuSi-O-SiPhtBu(LH).
(ORTEP; displacement ellipsoids at the 20 % probability
level; C-bound hydrogen atoms omitted for clarity.)
Scheme 5.
Fig. 3. Molecular structure of one of the four crystallo-
graphically independent molecules of L2Si (ORTEP; dis-
placement ellipsoids at the 50 % probability level; hydro-
angle is essentially the same for all three complexes,
probably due to the almost planar arrangement of the
tridentate ligand. This then seems to suggest that the
radius of the silicon atom determines the depth of
SiRRꢀ insertion into the ligand clamp.
˚
gen atoms omitted for clarity). Selected bond lengths (A):
Si1–O1 1.768(5), Si1–O2 1.776(5), Si1–N2 1.886(6), Si1–
N4 1.864(6), Si1–N1 1.887(6), Si1–N3 1.905(6), N2–C5
1.280(8), N4–C16 1.325 (8).
The synthesis of LSiPhtBu also gave a small amount
of (LH)PhtBuSi-O-SiPhtBu(LH) as by-product. Its [135.0(1)◦, (Scheme 5; middle)] and Liu et al. [11]
molecular structure (Fig. 2), obtained by a single [151.2(1)◦, (Scheme 5, right)] and than that observed
crystal X-ray diffraction analysis, reveals a disilox- in (LH)PhtBuSi-O-SiPhtBu(LH) (156.1(1)◦).
ane with singly deprotonated ligands (LH−) that are
The synthesis of LSiCl2 was attempted to expand
attached to the Si atom only by the phenoxy oxy- the series of penta-coordinate LSiRRꢀ complexes with
gen atoms. This suggests that double deprotonation is halogen substituents. However, the reaction of the tri-
needed for the ligand to coordinate its imine nitrogen dentate ligand L2− with SiCl4 resulted in the formation
to the diorganosilicon moiety. The two crystallograph- of the hexa-coordinate silicon chelate L2Si (Scheme 6)
ically independent molecules exhibit an arrangement that has a characteristic 29Si NMR chemical shift at
comparable to that of the copper complexes reported −160.4 ppm. Brown crystals of L2Si could be obtained
by Castro et al. [6a]. Molecular structures of simi- that were suitable for a single crystal X-ray diffraction
lar disiloxanes with a [C2(ArO)]-Si-O-Si-[(O-Ar)C2] analysis (Fig. 3).
backbone have been described of which the open-
A comparison of the bond lengths of L2Si with those
chain disiloxane by Jiang et al. (Scheme 5, left) [9] of LSiPh2 (Table 4) surprisingly shows that despite
shows a notably wider Si–O–Si angle (160.7(1)◦) than its higher silicon coordination number, all Si–N and
the cyclic siloxanes reported by Hanson et al. [10] Si–O bonds in L2Si are shorter than those in penta-
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
coordinate LSiPh2. Apparently, replacement of the two is expected to be only small on replacing a phenoxy
phenyl substituents by a ligand with three electroneg- proton by a “Si+” ion, while that for the imine group
ative binding sites enhances the Lewis acidity of the is substantial on coordination of the nitrogen lone pair,
Si atom. The largest difference is found for the Si–NI but there are also indications that this interpretation is
˚
bond (0.023A). This behavior is in accord with re- flawed.
cent findings by Seiler et al. [12]. Because of the pla-
The comparable UV/Vis characteristics of LSiRRꢀ
narity of the tridentate ligand L2− the ax-eq-ax posi- and the salop Sn(IV) complexes can be considered
tions of the distorted trigonal bipyramid are occupied as a result of both the similar donor-atom situation
in LSiPh2, while a mer arrangement results for L2Si.
N-(o-oxyphenylimine) and a planar arrangement of
the tridentate ligand, which gives rise to an extended
π system. That the red shift of band 1 is related to
the planarity of the ligand was earlier demonstrated
by one of us for salop silicon complexes. For ex-
ample, structure A (R, R = Me, Silyl) in Scheme 8
has a planar ONOꢀ-ligand and absorbs at 464 nm,
while B (R, R = Ph, Ph) with a twisted ligand ab-
sorbs at 386 nm [14]. Although the planarity of the
ONNꢀ-ligand would suggest an influence of the pyr-
role ring on the extended π system and hence on
the optical properties of LSiRRꢀ, its definite role re-
mains unclear. Interaction of the pyrrole ring with the
imine group is expected to cause an intramolecular
charge transfer. However, the influence of different sol-
vents on the second absorption band of LSiPh2 was
found to be marginal, i. e., 458.0 nm in acetonitrile,
463.0 nm in THF, 468.7 nm in toluene, and 470.4 nm in
chloroform (Fig. 5), which indicates that polar effects
do not contribute significantly and raises the concern
whether this absorption band is properly attributed to
the π → π∗ transition of the conjugated C=N-bridged
system.
All penta-coordinate complexes are intensely red,
and the origin of the color was examined by analy-
sis of the UV/Vis spectra of LSiPhtBu, LSiPhMe and
LSiPh2. Upon complex formation with a diorganosil-
icon moiety both bands of the pale-yellow lig-
and LH2 (λmax1 = 307, λmax2 = 357 nm) undergo
large bathochromic shifts, particularly the second
one, as is shown in Fig. 4 for LSiPh2 (λmax1
=
352, λmax2 = 470 nm), while the molar extinc-
tion decreases significantly only for the first band
(LH2: ε1 = 12700, ε2 = 24600; LSiPh2: ε1 = 4690,
ε2 = 19700 L mol−1 · cm−1). If the same interpreta-
tion applies that Pettinari et al. used to explain the
UV/Vis spectra for the related salop Sn(IV) complexes
(Scheme 7) [13], then the absorption at 352 nm should
be attributed to a π → π∗ transition of the benzenoid
system and the band at 470 nm to a π → π∗ transi-
tion of the imine-bridged conjugated π system. At first
sight this interpretation seems reasonable as the change
for the benzenoid system on going from LH2 to LSiPh2
Scheme 8.
Fig. 4. UV/Vis spectra of LH2 (dashed line; 1 mmol L−1
and 1 mm) and LSiPh2 (dotted line; 1 mmol L−1 and quartz
cuvettes d = 1 mm); E = log(I0/I).
Fig. 5. UV/Vis spectra of LSiPh2 in (left to right) acetonitrile,
THF, toluene, chloroform; c = 1 mmol L−1; d = 1 mm; E =
log(I0/I).
Scheme 7.
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
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Table 5. Singlet transitions calculated for LH2 and LSiPh2
using TD DFT B3LYP/6-311+G(d,p).a
Excited Transition
state
cb
E
λ
fc
(eV) (nm)
LH2
1
HOMO → LUMO
0.61738 3.3612 368.9 0.5031
HOMO-1 → LUMO −0.19011
2
HOMO → LUMO
HOMO-1 → LUMO
HOMO-2 → LUMO
0.13735 3.9760 311.8 0.2668
0.63669
0.10671
LSiPh2
1
HOMO → LUMO
HOMO-1 → LUMO
HOMO-1 → LUMO
0.63031 2.6908 460.8 0.2463
0.14950
0.64472 3.4087 363.7 0.1811
2
a
The energies of the HOMO-1, HOMO and LUMO (a. u.) are,
respectively, −0.238, −0.210, and −0.074 for LH2, and −0.225,
−0.197, and −0.080 for LSiPh2; b c = coefficient of the wave func-
c
tion for each excitation; f = oscillator strength.
Fig. 7. From top: LUMO, HOMO and HOMO-1 of LH2 (left)
and LSiPh2 (right), isosurface: 0.04.
HOMO-1 energies of LSiPh2, i. e., 0.013 a. u. relative
to the LH2. Fig. 7 shows the three noted MOs for both
LH2 and LSiPh2. All functional groups contribute to
these orbitals except the phenolic group in the LUMOs.
Thus, both observed transitions in which the LUMO
plays an important role must be interpreted as π-π∗
transitions that show only a very modest electron den-
sity transfer from the o-iminophenol towards the imine
moiety.
Fig. 6. UV/Vis spectra simulated for LH2 (dashed line)
and LSiPh2 (dotted line) using TD DFT on the B3LYP/6-
311+G(d,p) level.
This MO-based analysis which is in sharp contrast
to the interpretation advocated by Pettinari that sep-
arates the π-π∗ transition of the imine-linked conju-
gated system (band 2) from the π-π∗ transition of the
benzenoid system (band 1) may therefore also be ap-
plicable to the N-(o-oxyphenyl)imine-containing Sn
complexes [13] and the Si-salop complexes [14].
The same UV/Vis absorptions that are attributable to
the pyrrole-2-carbaldimine ligand in LSiPh2 are also
found in hexa-coordinate L2Si, as shown in Fig. 8.
Thus, the presence of a second tridentate ligand, and
the absence of the carbon substituents, has hardly any
effect on the UV/Vis spectrum, thereby underscoring
In oder to analyze the origin of both observed ab-
sorption bands in more detail time-dependent DFT cal-
culations were performed. The molecular structures of
LH2 [5d] and LSiPh2 were optimized with B3LYP/6-
31G(d) and subsequently analyzed by TDDFT for sin-
glet transitions at B3LYP/6-311G+(d,p)using eight ex-
cited states. These computations predict indeed two
strong absorption bands for both LH2 and LSiPh2,
as summarized in Table 5. The simulated spectra dis-
played in Fig. 6 agree remarkably well with the experi-
mentally obtained spectra shown in Fig. 4 with a ∆λmax
of only 12 nm, and also the relative intensities compare
well, although only qualitatively.
The UV/Vis absorption bands for the two com- the intra-ligand character of the transition. The very
pounds appear to have the same origin. The HOMO – modest blue shift of the high-energy band from 470 nm
LUMO transition is the predominant contributor for for LSiPh2 to 464 nm for L2Si is responsible for the
the lowest energy band and the HOMO-1 – LUMO small difference in colors, i. e. dark-red for LSiPh2
transition for the other band. The surprisingly strong and brownish-orange for L2Si. The corresponding blue
red shift observed on going from LH2 to LSiPh2 shift of the low-energy band from 352 to 338 nm for
is mainly due to the elevation of the HOMO and L2Si is more pronounced and is attributed to the short-
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
(0.29 g, 2.9 mmol) in THF (2.5 mL). The red mixture was
◦
stirred at ambient temperature for 0.5 h and stored at 4 C
overnight. The precipitate (Et3NHCl) was filtered off and
washed with THF (8 mL). From the filtrate the solvent was
removed in vacuo, and the residue was dissolved in CDCl3
for 29Si NMR spectroscopic analysis. (Attempts to crystal-
lize LSiMe2, e. g., from diethyl ether or pentane or mixtures
1
thereof, failed so far). – 29Si{ H} NMR: δ = −62.2.
LSiCyMe
LSiCyMe was obtained following the procedure de-
scribed for LSiMe2. Starting materials: Ligand LH2 (0.36 g,
Fig. 8. UV/Vis spectra of LSiPh2 (dotted line, 0.5 mmol L−1
)
1.9 mmol) in THF (5 mL); cyclohexylmethyldichlorosilane
(0.40 g, 2.0 mmol) and triethylamine (0.59 g, 5.8 mmol) in
THF (5 mL). (Attempts to crystallize LSiCyMe, e. g., from
diethyl ether or pentane or mixtures thereof, failed so far). –
and L2Si (dashed line, 0.25 mmol L−1) in chloroform; d =
1 mm; E = log(I0/I).
1
29Si{ H} NMR: δ = −62.3.
ening (i. e., strengthening) of the Si–N and Si–O bonds
that is expected to cause a lowering of the HOMO and
HOMO-1 levels.
LSiPhtBu and (LH)PhtBuSi-O-SiPhtBu(LH)
A solution of LH2 (0.35 g, 1.9 mmol) THF (5 mL) was
added dropwise to a solution of tbutylphenyldichlorosilane
(0.46 g, 2.0 mmol) and triethylamine (0.40 g, 4.0 mmol)
in THF (5 mL). Then the mixture was stirred under re-
flux for 15 h. After storage at room temperature overnight
the Et3NHCl precipitate was filtered off and washed with
THF (6 mL). From the filtrate the solvent was removed in
vacuo, and the residue was dissolved in CDCl3 for an ini-
tial NMR analysis. Thereafter the solvent was removed in
vacuo, and the red residue was dissolved in diethyl ether
(1 mL) and pentane (1 mL). This solution was stored at 4 ◦C
Conclusion
The di-anionic ONNꢀ-tridentate ligand L2− prefers
the ax-eq-ax positions in a distorted trigonal-
bipyramidal arrangement at silicon in the neutral
penta-coordinate complexes LSiRRꢀ (R,Rꢀ = Ph,Ph;
Ph,Me; Ph,tBu) and a mer-coordination in the neu-
tral hexa-coordinate L2Si. The UV/Vis characteristics
of these compounds are dominated by ligand-based
HOMO – LUMO and HOMO-1 – LUMO transitions.
Binding of the ligand to silicon causes a significant for several days, whereupon a first fraction of crystals had
formed. X-Ray diffraction analysis confirmed their iden-
tity as disiloxane (LH)PhtBuSi-O-SiPhtBu(LH). The super-
natant was transferred into a new Schlenk tube and stored
at 4 ◦C for further 3 weeks to yield red crystals of LSiPhtBu,
which were separated from the solution by decantation and
dried in vacuo. Yield: 0.075 g (0.22 mmol, 11.5 %). M. p. >
230 ◦C (decomposition). – UV/Vis (CHCl3): λmax (lg εmax) =
359.8 nm (3.72), 472.9 nm (4.32). – 1H NMR (400 MHz,
CDCl3): δ = 0.93 (s, 9 H, (CH3)3C), 6.53 – 6.55 (m, 1 H,
ar), 6.76 (t, J = 7.6 Hz, 1 H, ar), 6.91 (d, J = 8.4 Hz,
1 H, ar), 7.07 – 7.10 (mm, 2 H, ar), 7.26 – 7.30 (mm, 5 H,
ar), 7.54 – 7.56 (mm, 2 H, ar), 8.60 (s, 1 H, N=C-H). –
bathochromic shift of the two observed absorption
bands (LSiPh2 versus LH2) due to elevated HOMO
and HOMO-1. The time-dependent DFT calculations
further show that the observed excitations are accom-
panied by an electron density transfer from the N-(o-
oxyphenyl)imine towards the imine C=N moiety of the
planar ligand.
Experimental Section
All syntheses were carried out in anhydrous solvents un-
der an inert atmosphere of dry argon using standard Schlenk
techniques. UV/Vis and NMR spectroscopic analyses were
also performed using anhydrous solvents, on a Specord
S100 UV/Vis spectrometer and a Bruker DPX 400 NMR
spectrometer, respectively. Computational analyses were
done with the GAUSSIAN03 software [15].
1
13C{ H} NMR (100 MHz, CDCl3): δ = 21.7 ((CH3)3C),
28.3 ((CH3)3C), 111.5, 114.5, 117.3, 117.4, 120.4, 127.3,
127.8, 128.7, 128.9, 135.0, 135.6, 140.9, 144.2 (ar), 154.4
1
(C=N). – 29Si{ H} NMR (79.5 MHz, CDCl3): δ = −72.2. –
C21H22N2OSi (346.5): calcd. C 72.79, H 6.40, N 8.08; found
C 72.38, H 6.52, N 7.80.
LSiMe
2
LSiPhCy
A solution of ligand LH2 (0.25 g, 1.34 mmol) in THF
(2.5 mL) was added dropwise to a stirred solution of
LSiPhCy was obtained following the procedure de-
dimethyldichlorosilane (0.18 g, 1.4 mmol) and triethylamine scribed for LSiMe2. Starting materials: Ligand LH2 (0.33 g,
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D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
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Table 6. Crystal structure data for LSiPhtBu, (LH)PhtBuSi-O-SiPhtBu(LH), LSiPh2 and L2Si.
(LH)PhtBuSi-
LSiPhtBu
O-SiPhtBu(LH)
LSiPh2
L2Si
Formula
Mr
C21H22N2OSi
346.50
C42H46N4O3Si2
711.01
C23H18N2OSi
366.48
C22H16N4O2Si
396.48
T, K
296(2)
296(2)
296(2)
90(2)
Crystal size, mm3
Crystal system
Space group
0.60×0.20×0.05
0.26×0.12×0.04
0.45×0.24×0.22
orthorhombic
Pbca
9.5504(2)
16.9266(4)
22.7329(5)
90
0.14×0.12×0.07
tetragonal
P41
10.9255(3)
10.9255(3)
62.141(4)
90
90
90
7417.6(6)
16
1.42
triclinic
triclinic
¯
¯
P1
P1
˚
a, A
9.0899(14)
12.067(2)
17.595(3)
85.207(8)
86.712(9)
88.912(8)
1919.9(5)
4
1.20
0.1
736
−11 ≤ h ≤ +11
−15 ≤ k ≤ +13
−22 ≤ l ≤ +22
27.5 / 0.65
44727 / 8707
0.0372
9.9444(3)
11.2545(3)
19.4439(8)
92.260(2)
91.666(2)
111.796(2)
2016.76(12)
2
1.17
0.1
756
−11 ≤ h ≤ +11
−13 ≤ k ≤ +13
−22 ≤ l ≤ +23
25.0 / 0.59
17886 / 7094
0.0372
˚
b, A
˚
c, A
α, deg
β, deg
90
90
γ, deg
3
˚
V, A
3674.91(14)
8
1.33
0.1
1536
−12 ≤ h ≤ +11
−21 ≤ k ≤ +21
−25 ≤ l ≤ +29
27.5 / 0.65
22159 / 4176
0.0261
Z
Dcalcd, g cm−3
µ (MoKα ), cm−1
F(000), e
hkl range
0.2
3296
−13 ≤ h ≤ +6
−11 ≤ k ≤ +12
−52 ≤ l ≤ +73
25.0 / 0.59
22936 / 11661
0.0560
−1
˚
max, deg / (sinθ/λ)max, A
θ
Refl. measured / unique
Rint
Param. refined
451
460
244
1046
R(F)/wR(F2)a [I ≥ 2σ(I)]
R(F)/wR(F2)a (all data)
x (Flack)
0.0422 / 0.1094
0.0732 / 0.1203
–
1.048
0.300 / −0.251
0.0471 / 0.0979
0.1112 / 0.1127
–
0.940
0.201 / −0.178
0.0372 / 0.1044
0.0561 / 0.1123
–
1.077
0.298 / −0.235
0.0545 / 0.1065
0.0708 / 0.1140
−0.03(16)
0.999
GoF (F2)a
∆ρfin (max/min), e A
−3
˚
0.321 / −0.269
a Definition of R values and GoF, as well as information on weighting scheme applied: R(F) = Σ(|Fo|−|Fc|)/Σ|Fo| for the observed reflections
[F2 ≥ 2σ(F2)]. wR(F2) = {Σ[w(Fo − Fc2)2]/Σw(Fo2)2}1/2; GoF(F2) = {Σ[w(Fo − Fc2)2]/(n− p)}1/2, (n = number of reflections, p =
number of parameters) with w = 1/[s2(Fo2)+(AP)2 +BP] where P = (Fo2 +2Fc2)/3.
2
2
1.8 mmol) in THF (5 mL); cyclohexylphenyldichlorosilane CDCl3): δ = 6.56 (s, 1 H, ar), 6.77 (t, J = 7.6 Hz, 1 H,
(0.48 g, 1.9 mmol) and triethylamine (0.54 g, 5.4 mmol) in ar), 7.02 (d, J = 7.6 Hz, 2 H, ar), 7.09 – 7.12 (m, 2 H,
THF (5 mL). (Attempts to crystallize LSiPhCy, e. g., from ar), 7.23 – 7.32 (m, 7 H, ar), 7.49 (d, J = 7.6 Hz, 4 H,
1
diethyl ether or pentane or mixtures thereof, failed so far). – ar), 8.54 (s, 1 H, N=C-H). – 13C{ H} NMR (100 MHz,
1
29Si{ H} NMR (79.5 MHz, CDCl3): δ = −75.7.
CDCl3): δ = 112.1, 115.1, 118.1 (2x), 121.0, 127.7, 128.1,
128.6, 129.0, 134.4, 135.0, 139.7, 139.8, 144.3 (ar), 153.7
1
(C=N). – 29Si{ H} NMR (79.5 MHz, CDCl3): δ = −85.5. –
LSiPh
2
C23H18N2OSi (366.5): calcd. C 75.37, H 4.95, N 7.63; found
C 75.16, H 5.20, N 7.80.
A solution of LH2 (0.31 g, 1.7 mmol) in THF (5 mL)
was added dropwise to a solution of diphenyldichlorosilane
(0.44 g, 1.8 mmol) and triethylamine (0.34 g, 3.4 mmol) in
THF (5 mL). After stirring the mixture at r. t. for 1 h the pre-
cipitate was filtered off and washed with THF (6 mL). From
L Si
2
0.56 g (3.03 mmol) LH2 was dissolved in chloroform
the orange filtrate the solvent was removed in vacuo, and (6.5 mL) and added dropwise to a solution of silicon tetra-
the residue was dissolved in chloroform (1.5 mL), where- chloride (0.27 g, 1.59 mmol) and triethylamine (0.64 g,
upon crystallization of LSiPh2 commenced. The mixture was 6.36 mmol) in chloroform (5 mL). The mixture was stored
◦
stored at 4 C overnight. Then the crystals of LSiPh2 were at r. t. for 8 weeks. The brown precipitate, which had formed
isolated by decantation and washed with a mixture of chlo- within this time, was filtered off and washed with small
roform (1 mL) and hexane (1 mL). Yield: 0.26 g (0.71 mmol, amounts of chloroform and dried in vacuo. Yield: L2Si
◦
◦
42.6 %). M. p. 154 C. – UV/Vis (CHCl3): λmax(lgεmax) = 0.24 g, 40 %. M. p. > 320 C (decomposition). – UV/Vis
352.3 nm (3.67), 470.4 nm (4.29). – 1H NMR (400 MHz, (CHCl3): λmax(lgεmax) = 338 nm (4.12), 464 nm (4.60). –
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1578
D. Gerlach et al. · Silicon(IV) Chelates of an (ONN’)-Tridentate Pyrrole-2-Carbaldimine Ligand
1H NMR (400 MHz, CDCl3): δ = 6.15 – 6.17 (m, 2 H, the non-hydrogen atoms. The hydrogen atoms on carbon
arPyrrol), 6.64 (s, 2 H, arPyrrol), 6.78 (d, J = 8.0 Hz, 2 H, were refined isotropically in idealized positions. The hydro-
ar), 6.83 (m, 2 H, ar), 6.88 – 6.89 (m, 2 H, arPyrrol), 7.09 gen atoms bound to the nitrogen atoms were found by analy-
(m, 2 H, ar), 7.40 (dd, 3J = 7.8, 4J = 1.0 Hz, 2 H, ar). –
sis of the residual electron density and were refined isotrop-
ically without bond length restraints. Selected parameters of
data collection and structure refinement are summarized in
Table 6.
CCDC 744885 (LSiPhtBu), CCDC 744883 (LSiPh2),
CCDC 744884 ((LH)PhtBuSi-O-SiPhtBu(LH)) and CCDC
744882 (L2Si) contain the supplementary crystallographic
data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif.
1
13C{ H} NMR (100 MHz, CDCl3): δ = 112.7, 116.1, 116.6,
118.3, 119.9, 128.4, 128.8, 131.7, 133.0, 141.7 (ar), 152.5
1
(C=N). – 29Si{ H} NMR (79.5 MHz, CDCl3): δ = −160.3. –
C22H16N4O2Si (396.5): calcd. C 66.65, H 4.07, N 14.13;
found C 66.63, H 4.05, N 13.66.
Crystal structure determinations
Data were collected on Bruker Apex II diffractome-
ter equipped with a CCD area detector using graphite-
˚
monochromated MoKα radiation (λ = 0.71073 A). The
Acknowledgement
structures were solved by Direct Methods (SHELXS [16])
and refined by full-matrix least-squares methods on F2
(SHELXL [17]) with anisotropic displacement parameters for
D. G. is grateful to Deutscher Akademischer Austausch
Dienst (DAAD) for the award of a scholarship.
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