A chelating β-diketonate/phenoxide ligand and its coordination behavior toward titanium and scandium

Article abstract of DOI:10.1039/b511915d

Dibenzoylmethane derivatives with one (L¹H₂) or both (L²H₃, L³H₃) benzenes linked at their ortho positions to 4,6-di-tert-butylphenol moieties by two-carbon linkers have been synthesized. The mono-β-diketone-monophenol ligand L ¹H₂ is metalated by titanium alkoxides to form the homoleptic complex (L¹)₂Ti and heteroleptic complexes (L¹)Ti([OCH₂CH₂]₂NR) (R = H, CH ₃), and reacts with Cp₃Sc to form CpSc(L¹). These are the first examples of complexes of a β-diketonate ligand which is further chelating to a single metal center. Crystallographic analysis of (L¹)₂Ti indicates that the 10-membered ring allows chelation of the phenoxide with little strain, and both fac and mer geometries are accessible in solution. Protonolysis of the second cyclopentadienyl ring of Cp₃Sc appears to take place by an indirect, Cp₃Sc- catalyzed pathway. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b511915d

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www.rsc.org/dalton | Dalton Transactions
A chelating b-diketonate/phenoxide ligand and its coordination
behavior toward titanium and scandium
Tobias Schroeder, Vesela Ugrinova, Bruce C. Noll and Seth N. Brown*
Received 24th August 2005, Accepted 17th October 2005
First published as an Advance Article on the web 17th November 2005
DOI: 10.1039/b511915d
Dibenzoylmethane derivatives with one (L1H2) or both (L2H3, L3H3) benzenes linked at their ortho
positions to 4,6-di-tert-butylphenol moieties by two-carbon linkers have been synthesized. The
mono-b-diketone-monophenol ligand L1H2 is metalated by titanium alkoxides to form the homoleptic
complex (L1)2Ti and heteroleptic complexes (L1)Ti([OCH2CH2]2NR) (R = H, CH3), and reacts with
Cp3Sc to form CpSc(L1). These are the first examples of complexes of a b-diketonate ligand which is
further chelating to a single metal center. Crystallographic analysis of (L1)2Ti indicates that the
10-membered ring allows chelation of the phenoxide with little strain, and both fac and mer geometries
are accessible in solution. Protonolysis of the second cyclopentadienyl ring of Cp3Sc appears to take
place by an indirect, Cp3Sc-catalyzed pathway.
The ethylene-bridged diketone-monophenol L1H2 in particular
readily forms chelates with early transition metals such as titanium
and scandium, yielding stable and apparently largely unstrained
complexes.
Introduction
b-Diketonates have been used as ligands for almost 120 years.1,2
They form homo- or heteroleptic complexes with virtually every
transition metal, p-block metal, and lanthanide. The great chem-
ical stability and covalency of many of their complexes has led
to them being particularly useful sources of volatile precursors
for applications such as chemical vapor deposition.3 A wide
variety of b-diketonates with different substituents have been
prepared, allowing one to tune properties of their complexes such
as volatility, Lewis acidity, or aggregation state, and in the case
of chiral b-diketonates, to achieve chiral recognition (as in chiral
shift reagents4) or enantioselective catalysis.5 The robustness of
the complexes, and in particular the ability to chemically modify
the diketonate ligand without destroying the metal complexes,
has even earned these ligands an important place in chemical
education.6
However, one important limitation of the b-diketonate ligand is
that it can bind in no more than two sites; b-diketonates that are
further chelating to a single metal center are unknown. In contrast
to b-ketoiminates or b-diketiminates, where the nitrogen atom has
a substituent which can easily link to another chelating group (as
in the well-known tetradentate acacen ligand), the only sites for
further elaboration on a diketone are pointed away from the site
where the oxygen atoms bind to a metal. Thus, while polyketones7
and bis(b-diketone) ligands,8 as well as mixed diketone/phosphine
ligands,9 are known, their complexes are always bi- or polymetallic.
Based on our earlier observations of good hydrolytic stability
of chelating polyphenoxide complexes of titanium(IV),10 we antic-
ipated that b-diketonate ligands containing dangling phenoxides
would also allow the preparation of water-stable derivatives of
the early transition metals. Here we report the preparation of
dibenzoylmethane derivatives where one or both aryl groups are
linked by two-carbon tethers to 4,6-di-tert-butylphenol groups.
Results and discussion
Synthesis of b-diketones with dangling phenols
Because the substituents on the carbonyl carbons and the a-
carbon of a b-diketone are directed away from the metal, any
polydentate diketonate will require that the pendant groups form a
rather large ring to allow chelation. Inspection of simple molecular
models suggested that a dibenzoylmethane derivative joined to a
phenoxide in the ortho position with a two-carbon tether would
form a relatively unstrained 10-membered chelate ring, with the
two-carbon linker in a fully extended conformation. A ring of this
size would allow a nearly linear M–O–C angle at the phenoxide,
as is typically observed in unconstrained early metal aryloxides.11
Indeed, compatibility with such large angles and the consequent
p-bonding has been adduced as a reason for the favorability of
forming large-ring titanium aryloxide chelates.12
Synthesis of the ligand begins with construction of the phe-
noxide “arm” (Scheme 1). Horner–Wadsworth–Emmons conden-
sation of dimethyl 2-bromobenzylphosphonate (1, prepared by
an Arbuzov reaction of 2-bromobenzyl bromide) with 3,5-di-
tert-butyl-2-hydroxybenzaldehyde gives the 2ꢀ-bromostyrylphenol
2 in good yield and with complete E-selectivity. (The di-tert-
butyl substitution pattern was chosen to give a bulky substituent
ortho to the phenol and because of the commercial availability
and moderate price of the appropriate salicylaldehyde.) The
phenol group was protected as a tert-butyldimethylsilyl ether using
TBSCl–DBU to give 3, followed by lithium–halogen exchange and
carboxylation to give the unsaturated carboxylic acid 4. Protection
of the phenol as a trimethylsilyl ether was tried, but the TMS group
proved labile under the conditions used to prepare and isolate
the carboxylic acid. The two-carbon linker could be reduced by
diimide at this stage to provide the saturated acid 5.
Department of Chemistry and Biochemistry, 251 Nieuwland Science Hall,
University of Notre Dame, Notre Dame, Indiana, 46556-5670, USA. E-mail:
Seth.N.Brown.114@nd.edu; Fax: 01 574 631 6652; Tel: 01 574 631 4659
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Scheme 1 Preparation of phenol “arms”.
Formation of the carboxylic acid sets up the protected phenol
for formation of the diketone by Claisen condensation.13 To
prepare a diketone-monophenol ligand (Scheme 2), the saturated
acid 5 was converted to the acyl chloride and condensed with
the lithium enolate of 4ꢀ-methylacetophenone in the presence of
excess lithium bis(trimethylsilyl)amide. O-acylation is seen as a
side product in this reaction at short reaction times,14 but the O-
acylated product is converted to the thermodynamic C-acylated
product 6 upon heating or prolonged reaction at room temperature
(preferably in the presence of excess lithium enolate). Desilylation
with ice-cold tetrabutylammonium fluoride in THF furnishes
the tridentate diketone-monophenol L1H2. Both unsaturated and
saturated versions of bis(phenol)-diketone ligands were prepared
by analogous routes (Scheme 3). In this case the unsaturated
acid 4 was taken on to make both the acyl chloride 7 and,
through treatment with methyllithium,15 the protected phenol-
bearing methyl ketone 8, which were then coupled under basic
conditions to form the unsaturated diketone 9. Deprotection of 9
furnished the trans-alkene-bridged ligand L2H3, while the alkane-
bridged analogue L3H3 was prepared by diimide reduction of the
stilbenes either before or after desilylation of 9.
Scheme 3 Preparation of diketone-bis(phenol)s L2H3 and L3H3.
The structure of the b-diketone-bis(styrylphenol) ligand L2H3
was confirmed by X-ray crystallography (Table 1). The compound
crystallizes as the cis-enol tautomer (Fig. 1), which also appears to
predominate in solution, as judged from the downfield C–H proton
at d 6.33 and enol O–H proton at d 17.01 (in C6D6). The structural
details of the enolized dibenzoylmethane core, such as the presence
of a strong intramolecular hydrogen bond, are very similar to
those of other structurally characterized dibenzoylmethanes.16
Fig. 1 Thermal ellipsoid plot of L2H3, with methyl hydrogens and
minor disordered components omitted for clarity. Selected bond distances
˚
(A) and angles: C1–O1, 1.269(3); C3–O2, 1.311(3); C1–C2, 1.411(3);
C2–C3, 1.381(3);C4–C5, 1.338(3);C6–C7, 1.333(3);O1–C1–C2, 122.1(2)◦;
C1–C2–C3, 121.2(2)◦; O2–C3–C2, 120.01(19)◦.
Scheme 2 Preparation of diketone-monophenol L1H2.
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Table 1 X-ray crystallographic details for L2H3 and (L1)2Ti·4CH2Cl2
L2H3
(L1)2Ti·4CH2Cl2
Molecular formula
Formula weight
T/K
C47H56O4
684.92
100(2)
C68H80Cl8O6Ti
1324.82
100(2)
Crystal system
Triclinic
Triclinic
¯
¯
Space group
P1
P1
Total data collected
No. of ind. reflns
Rint
41961
65373
9525
0.0438
7190
16402
0.0279
12632
Obs. reflns [I >2r(I)]
˚
a/A
9.1032(4)
11.9561(5)
18.4632(8)
104.741(2)
96.902(3)
92.611(2)
1923.21(14)
2
13.1693(5)
14.4819(6)
18.8272(8)
69.077(1)
88.780(2)
89.507(2)
3353.1(2)
2
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
l/mm−1
0.073
0.496
No. refined param.
R1, wR2 [I>2r(I)]
562
1068
0.0365, 0.0930
Fig. 2 Thermal ellipsoid plot of (L1)2Ti·4CH2Cl2, with solvent molecules
0.0696, 0.1880
and hydrogen atoms omitted for clarity.
178.5 and 174.3◦ for the two bridges. The bond distances and
Both alkenes are trans, but the conformation implies substantial
flexibility in the structure, with the aryl groups twisted out of
the plane of the diketone moiety by substantial but widely varying
amounts (89.0 and 31.5◦ for C11–C16 and C21–C26, respectively).
Similarly, the alkenes are not coplanar with the arenes to which
they are bonded, with angles of 37.7 and 52.4◦ between the C4–C5
olefin and the arene planes and 31.0 and 7.4◦ for the C6–C7 olefin.
This structural variability suggested that the styryl- (or phenethyl-)
phenol arms would have the flexibility required to chelate to a
transition metal.
angles of cis-mer-(L1)2Ti are generally extremely similar to those
of unconstrained (acac)2Ti(O-2,6-iPr2C6H3)2 (Table 2), though
18
◦
1
˚
Table 2 Selected bond distances (A) and angles ( ) in (L )2Ti·4 CH2Cl2
and for comparison, analogous distances and angles in (acac)2Ti(O-2,6-
iPr2C6H3)2
a
a
(L1)2Ti·4CH2Cl2
(acac)2Ti(O-2,6-iPr2C6H3)2
Ti–O1
Ti–O4
Ti–O2
Ti–O5
Ti–O3
Ti–O6
O1–C1
O4–C6
C1–C2
C6–C7
C2–C3
C7–C8
O2–C3
O5–C8
C4–C5
C9–C10
2.0831(12)
2.0599(11)
1.9459(11)
1.9429(11)
1.8284(12)
1.8322(11)
1.2805(19)
1.2778(19)
1.413(2)
1.410(2)
1.382(2)
1.393(2)
1.2948(19)
1.2882(19)
1.544(2)
2.046(5)
1.985(5)
1.834(5)
1.28(1)
1.41(1)
1.38(1)
1.28(1)
n/a
Titanium(IV) complexes of diketonate-phenoxide ligands
The diketone-monophenol ligand L1H2 reacts immediately at
room temperature in a 2 : 1 molar ratio with titanium(IV)
isopropoxide to form the air- and moisture-stable red complex
(L1)2Ti (eqn 1). 1H NMR spectra of the reaction mixture in
benzene-d6 show a large number of sharp peaks, suggestive
of formation of a monometallic complex that exists as several
geometric isomers. The formulation of the complex as a monomer
is supported by mass spectrometry, which shows peaks at the
expected mass of 984 amu, and no sign of higher oligomers.
Upon heating, the NMR spectrum changes, with some peaks
disappearing and◦others growing, forming an equilibrium mixture
within 16 h at 70 C. 1H and 13C NMR spectra of the equilibrium
mixture show three different L1 environments, consistent with the
presence of three symmetric isomers, or one symmetric and one
unsymmetric isomer.
1.546(2)
O1–Ti–O2
O4–Ti–O5
O1–Ti–O4
O2–Ti–O5
O3–Ti–O6
O1–Ti–O5
O2–Ti–O4
O1–Ti–O3
O4–Ti–O6
O1–Ti–O6
O4–Ti–O3
O5–Ti–O3
O2–Ti–O3
O5–Ti–O6
Ti–O3–C31
Ti–O6–C61
81.27(5)
81.16(5)
80.87(5)
160.81(5)
101.15(5)
84.39(5)
84.03(4)
168.83(5)
168.46(5)
89.37(5)
89.05(5)
98.88(5)
92.98(5)
91.84(5)
165.86(10)
163.25(11)
82.8(2)
83.1(2)
161.7(3)
97.3(2)
83.5(2)
172.1(2)
89.9(2)
2 L1H2 + Ti(OiPr)4 → (L1)2Ti + 4 iPrOH
(1)
The ability of the linked phenoxide to chelate to the titanium is
confirmed by the crystallization of the dichloromethane solvate of
cis-mer-(L1)2Ti (Fig. 2). The molecule possesses an approximate
(non-crystallographic) twofold axis relating the two ligands and
adopts the cis arrangement of diketonates that is universally
observed in the alkoxide complexes (dike)2Ti(OR)2.17 In order
to accommodate the large Ti–O–C angles typical of titanium
aryloxides,12 the ethylene bridge in the 10-membered chelate ring
adopts a fully extended conformation, with dihedral angles of
92.9(2)
162.2(4)
a Ref. 18. The complex (acac)2Ti(O-2,6-iPr2C6H3)2 has crystallographic C2
symmetry, so its bond distances and angles are listed next to the first of the
pair of analogous distances or angles in (L1)2Ti. The numbering scheme is
that of (L1)2Ti.
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there are small distortions suggestive of increasing constraints
in the chelated compound. One rather perceptible distortion in
cis-mer-(L1)2Ti is the folding of the b-diketonate rings out of
the plane defined by the titanium and the two bound oxygens.
Both rings are markedly bent inwards, towards the molecular
twofold axis, with “fold angles” between the diketonate planes and
TiO2 planes of 21.1 and 17.2◦. This distortion is not significant
in (acac)2Ti(O-2,6-iPr2C6H3)2,18 but it is quite common in other
(dike)2Ti complexes. For example, the six diketonates in the oxo
cluster [(dbm)2Ti]3(Cp*Ti)2(O)6 (Hdbm = dibenzoylmethane)19
show fold angles ranging from 2.7–24.1◦ with an average of 16◦,
emphasizing the low energetic cost of such moderate deviations
from planarity. Thus, the structural data, in conjunction with the
observation that monomers are strongly favored over oligomers,
support the notion that the chelate ring linking the diketonate to
the phenoxide is relatively unstrained.
When pure crystalline cis-mer-(L1)2Ti is redissolved in C6D6
at room temperature, it immediately equilibrates to the same
mixture of isomers it contained before crystallization. This rapid
isomerization is in contrast to the much slower isomerization
rate displayed by the kinetic mixture of (L1)2Ti isomers, which
requires hours of heating at 70◦ to effect complete isomerization to
the thermodynamic mixture. Diketonatotitanium(IV) complexes
are well known to undergo facile isomerizations via a trigonal twist
mechanism.20 Since there is only one possible isomer of (L1)2Ti
with a meridional arrangement of the diketonate-phenoxide, the
presence of multiple geometric isomers suggests that the intrinsic
geometric preference of the ligand is rather small. In fact, a
fac isomer would be expected to be somewhat more compact
than the mer, with a distance from the (equatorial) carbonyl
carbon to the phenoxide ipso carbon estimated from the crystal
amine presumed to be trans to the phenoxide on the basis of
the trans influence. The fluxional process presumably corresponds
to an interconversion between the two enantiomers of the chiral
complex, which results in a time-averaged mirror plane. If this
interconversion takes place by a trigonal twist mechanism, then
it must proceed through the intermediacy of the unobserved mer
isomer (Scheme 4), once again demonstrating the flexibility of
the L1 framework.
Scheme 4 Fluxionality of (L1)Ti([OCH2CH2]2NR).
In contrast to the straightforward preparative chemistry
of L1H2, reaction of neither L2H3 nor L3H3 with titanium(IV)
alkoxides has resulted in isolable complexes. Reactions carried out
with comparable quantities of the ligand and titanium alkoxide
appear to result in complex mixtures of bis(diketonato)titanium
1
complexes, as judged by H NMR and mass spectrometry. This
result is consistent with the higher kinetic reactivity of b-diketones
compared to phenols with titanium alkoxides.20a Reactions using
a large excess of titanium also give ill-defined mixtures which
decompose upon attempted removal of the excess titanium
alkoxide by precipitation with water or vacuum distillation.
Cyclopentadienylscandium complexes of a
b-diketonate-monophenoxide
˚
˚
structure of only 4.57 A, compared to 4.77 A in the observed mer
isomer (the corresponding distances in (acac)2Ti(O-2,6-iPr2C6H3)2
18
Tricyclopentadienylscandium reacts readily with one equivalent
of L1H2 to eliminate cyclopentadiene and form Cp2Sc(L1H), where
the scandium is coordinated to the b-diketonate (Scheme 5). The
regioselectivity is confirmed by the loss of the enol proton in the
1H NMR, while the signal for the phenolic O–H is still observed
at d 4.99 in C6D6. The reaction of Cp2Sc(L1H) with a second
equivalent of Cp3Sc, or the direct reaction of L1H2 with two
equivalents of Cp3Sc, results in metalation of the phenol with
˚
are 4.38 and 4.87 A, respectively ). Presumably chelation is
sufficiently unstrained, and the backbone sufficiently flexible, that
the energetic cost of increasing the chelate span from the fac to the
mer isomer is small.
(2)
The reaction of Ti(OiPr)4 with diethanolamine or N-methyl-
diethanolamine, followed by an addition of L1H2, results in the
formation of the heteroleptic complexes (L1)Ti([OCH2CH2]2NR)
(R = H, CH3) (eqn 2). In both cases, yields of monometallic com-
plexes are high, with no sign of formation of either polymetallic or
homoleptic by-products. 1H NMR spectra of the two compounds
at room temperature show the presence of a mirror plane, but the
broadness of many of the resonances suggests that this is due to a
fluxional process. This has been confirmed for the diethanolamine
complex by a variable-temperature NMR study, which shows that
the static structure of the complex has no symmetry, as judged by
the observation of twelve inequivalent protons due to the CH2CH2
hydrogens in diethanolamine and L1 at temperatures below about
−30 ◦C. Since the mer complex would have a mirror plane, the
complexes apparently adopt a fac geometry, with the tertiary
Scheme 5 Proposed pathway for metalation of L1H2 by Cp3Sc.
Dalton Trans., 2006, 1030–1040 | 1033
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a second Cp2Sc group, forming (Cp2Sc)2L1. The presence of two
independent Cp2Sc units is clearly indicated by the observation
of two 10H cyclopentadienyl peaks in the 1H NMR. Both
Cp2Sc(L1H) and (Cp2Sc)2L1 maintain a mirror plane, as confirmed
by the equivalence of the geminal protons in the CH2CH2 group
of the ethylene linker.
Experimental
General procedures
Unless otherwise noted, procedures were carried out on the
benchtop without precautions to exclude air or moisture. When
dry THF was required, it was vacuum transferred from sodium
benzophenone ketyl. Benzene and toluene were dried over sodium.
Dry DMF was purchased from Aldrich and stored in a drybox.
Protonolysis of a second cyclopentadienyl group by the pendant
phenol in Cp2Sc(L1H) is extremely slow. The monoscandium
complex can be heated in benzene at 70 ◦C for several days and only
undergoes slow decomposition without any sign of metalation to
form CpSc(L1). This chelated complex can be prepared, but only
when Cp2Sc(L1H) is heated in the presence of excess Cp3Sc (or
equivalently, with (Cp2Sc)2L1, which forms rapidly under these
conditions). Thus, Cp3Sc effectively catalyzes the metalation of
Cp2Sc(L1H). This preparative route results in the contamination
of CpSc(L1) with (Cp2Sc)2L1, which has prevented isolation of
CpSc(L1) in its pure form, but in situ characterization by NMR
clearly indicates that chelation has taken place. Cyclopentadiene
is lost from the precursor Cp2Sc(L1H) and can be observed by
NMR, leaving a single cyclopentadienyl peak due to the complex
that integrates as 5H and is shifted substantially downfield of the
usual Cp2Sc moieties. Furthermore, the mirror plane characteristic
of either scandocene complex is lost, with the ethylene bridge
appearing as a CHHꢀCHꢀꢀHꢀꢀꢀ pattern.
1
All other reagents were used without further purification. H-
1
and 13C{ H}-spectra were recorded on a Varian UnityPlus 300
FT-NMR or a Varian UnityPlus 600 FT-NMR spectrometer and
are reported in ppm downfield of TMS. Infrared spectra were
measured as evaporated films on KBr plates on a Perkin–Elmer
Paragon 1000 FT-IR spectrometer and are reported in wavenum-
bers (cm−1). Fast atom bombardment (FAB) mass spectra were
measured in positive ion mode on a JEOL JMS-AX505HA mass
spectrometer using 3-nitrobenzyl alcohol (NBA) or nitrophenyl
octyl ether (NPOE) as the matrix. Elemental analyses were carried
out by M–H–W laboratories (Phoenix, AZ, USA). In some cases,
the sensitivity of compounds, or their immediate use as synthetic
intermediates, prevented us from obtaining satisfactory analyses.
Preparation of ligands
The preference for the scandium-catalyzed reaction over direct
protonolysis in the formation of CpSc(L1) is remarkable. It
is reasonable that proton transfer takes place only within the
coordination sphere of scandium, as we have observed in reactions
of titanium alkoxides.21 If so, direct protonolysis of Cp2Sc(L1H)
would require coordination of the bulky phenol to the scandium,
which would be strongly disfavored by the bidentate coordination
of the diketonate. In contrast, the phenoxide-ligated scandium in
(Cp2Sc)2L1 is still Lewis acidic and could potentially coordinate
to one of the diketonate oxygens to form a bridging diketonate
(Scheme 5). Cyclopentadienyl transfer between scandium atoms
would then give Cp3Sc and CpSc(L1). This must be an equilibrium
process, with the expulsion of Cp3Sc thermodynamically uphill,
since the addition of Cp3Sc to CpSc(L1) converts it into the
discandium complex (Cp2Sc)2L1. In the presence of the phenolic
proton on Cp2Sc(L1H), however, the Cp3Sc reacts irreversibly to
release cyclopentadiene and complete the catalytic cycle. This
metal-catalyzed reaction represents a very unusual pathway for
achieving the “proton-coupled ligand substitution”22 required to
chelate the L1 ligand.
Dimethyl 2-bromobenzylphosphonate (1). Into a 250 mL round
bottom flask were placed 36.62 g of 2-bromobenzyl bromide
(Aldrich, 0.147 mol), 38 mL of trimethyl phosphite (0.322 mol,
2.2 equiv.), and a stir bar. The flask was placed on a heating
mantle on a stirring plate and capped with a condenser with an
N2 tee vented to a mineral oil bubbler. The colorless solution was
stirred and purged for 30 min at room temperature. While purging,
the solution was heated for 15 min using the heating mantle, at
which point it started to effervesce vigorously as CH3Br gas was
released. The heating was switched off for about 15–20 min, during
which time the solution was heated by the exothermic reaction.
Heating was then resumed for another 45–50 min. The N2 flow
was stopped and the reaction mixture was allowed to cool to
room temperature. The flask was detached from the condenser
and connected to a distilling adapter affixed to a vacuum take-off
adapter. The mixture was distilled under vacuum to remove the
dimethyl methylphosphonate which forms as a side product, and
the colorless residual liquid yielded 38.22 g (93%) of dimethyl (2-
bromobenzyl)phosphonate. Spectroscopic data were in agreement
with those reported in the literature.23
trans-2-Bromo-3ꢀ,5ꢀ-di-tert-butyl-2ꢀ-hydroxystilbene (2). In a
round bottom flask in the drybox, 13.40 g of 3,5-di-tert-butyl-
2-hydroxybenzaldehyde (Aldrich, 57.2 mmol) was dissolved in
150 mL dry DMF. To this stirred solution was added 9.23 g of
solid sodium methoxide (Aldrich, 173 mmol, 3 equiv.). Dimethyl
2-bromobenzylphosphonate (19.15 g, 68.6 mmol, 1.2 equiv.) was
dissolved in 20 ml DMF and the solution added in portions to
the stirred reaction mixture over the course of 20 min. The flask
was capped with a rubber septum and the solution stirred at RT
under nitrogen for 16 h. After neutralizing the reaction mixture
with 400 mL saturated aqueous NH4Cl and 150 mL 1 M HCl, the
aqueous phase was separated and extracted with 5 × 100 mL of
Et2O. The combined organic phases were dried with MgSO4 and
the solvent removed under reduced pressure. The crude product
Conclusions
Dibenzoylmethane derivatives with one or two sterically hindered
pendant phenols have been prepared. The linkage employed,
consisting of a two-carbon bridge between the ortho positions
of the phenol and the benzoyl group, allows for the first time an
additional chelation from a b-diketone to a single metal center.
The crystal structure of (L1)2Ti indicates that the chelation is not
accompanied by any significant distortions in bond distances and
angles, and the relatively unstrained nature of the 10-membered
chelate ring is further supported by its ability to form monomeric
complexes with both fac and mer geometries of the three oxygen
atoms.
1034 | Dalton Trans., 2006, 1030–1040
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was purified by column chromatography on silica gel, eluting with
hexanes to give a crystalline material, which was washed with
hexanes to yield 16.61 g of pure bromostyrylphenol (75%). H
by a hose adapter vented to a mineral oil bubbler. The reaction
mixture was warmed to 0 ◦C and the rubber septum removed
for short periods of time while dry ice was added to the reaction
mixture. The bright yellow solution was poured into a separatory
funnel and 70 mL of 1 M HCl was added. The aqueous phase was
separated and extracted with 3 × 30 mL of Et2O. The combined
organic phases were dried with MgSO4 and the solvents removed
under reduced pressure. After standing uncapped in the hood
overnight, a slightly yellow solid was obtained, which was washed
with hexanes to give 4.70 g (86%) of the carboxylic acid. 1H NMR
(CDCl3): d 8.08 (dd, 8.0, 1.5 Hz, 1H, H-3), 7.86 (d, 16.0 Hz, 1H,
alkene CH), 7.69 (dd, 8.0, 1.5 Hz, 1H, H-6), 7.56 (td, 8.0, 1.5 Hz,
1H, H-4 or -5), 7.45 (d, 3.0 Hz, 1H, meta to silyloxy), 7.34 (td, 8.0,
1.5 Hz, 1H, H-4 or -5), 7.34 (d, 3.0 Hz, 1H, meta to silyloxy), 7.26
(d, 16.0 Hz, 1H, alkene CH), 1.43, 1.33 (s, 9H each, ArC(CH3)3),
1
NMR (CDCl3): d 7.68 (dd, 8.0, 1.5 Hz, 1H, H-3 or -6), 7.60 (dd,
8.0, 1.5 Hz, 1H, H-3 or -6), 7.37 (d, 16.5 Hz, 1H, alkene CH), 7.34
(td, 8.0, 1.5 Hz, 1H, H-4 or -5), 7.31 (s, 2H, meta to OH), 7.20
(d, 16.5 Hz, 1H, alkene CH), 7.15 (td, 8.0, 1.5 Hz, 1H, H-4 or
1
-5), 5.21 (s, 1H, OH), 1.47, 1.35 (s, 9H each, C(CH3)3). 13C{ H}
NMR (CDCl3): d 150.00 (COH), 142.93, 137.54, 136.01, 133.25,
130.72, 129.16, 127.83, 127.38, 127.12, 124.65, 124.50, 124.20,
122.87, 35.03 (C(CH3)3), 34.58 (C(CH3)3), 31.79 (C(CH3)3), 30.15
(C(CH3)3). IR: 3538 (w, mOH), 3400 (w), 2959 (s), 2904 (m), 2868
(m), 1627 (w), 1470 (m), 1441 (m), 1392 (m), 1362 (m), 1250 (m),
1235 (m), 1215 (m), 1189 (m), 1151 (m), 1117 (m), 1021 (m), 966
(w), 881 (w), 745 (m). FAB-MS: m/z = 386 (M+, 79Br), 388 (M+,
81Br). Anal.: Calcd for C22H27BrO: C, 68.22; H, 7.03; found C,
68.57; H, 6.70.
1
0.97 (s, 9H, SiC(CH3)3), 0.20 (s, 6H, Si(CH3)2). 13C{ H} NMR
(CDCl3): d 172.56 (COOH), 150.64 (C–OSi), 143.29, 140.94,
139.66, 133.16, 131.81, 131.33, 129.13, 127.51, 127.23, 127.00,
126.45, 125.59, 122.32, 35.64 (ArC(CH3)3), 34.54 (ArC(CH3)3),
31.73 (ArC(CH3)3), 31.61 (ArC(CH3)3), 27.20 (SiC(CH3)3), 19.54
(SiC(CH3)3), −0.50 (Si(CH3)2). IR: 3061 (m), 2958 (s), 2926 (s),
2901 (m), 2862 (m), 2636 (w), 2532 (w), 1689 (s, mCO), 1625 (w),
1597 (w), 1566 (w), 1475 (m), 1464 (m), 1436 (m), 1409 (m), 1360
(m), 1299 (m), 1260 (m), 1255 (m), 1237 (m), 1200 (w), 1164 (w),
1127 (w), 1079 (w), 976 (w), 925 (m), 885 (m), 839 (m), 805 (m),
780 (m), 746 (m). FAB-MS: m/z = 466 (M+). Anal.: Calcd for
C29H42O3Si: C, 74.63; H, 9.07; found C, 74.70; H, 9.22.
trans-2-Bromo-3ꢀ,5ꢀ-di-tert-butyl-2ꢀ-(tert-butyldimethylsilyloxy)-
stilbene (3). Into a round bottom flask were weighed 16.59 g
(42.8 mmol) of bromostyrylphenol 2 and 13.02 g (86.4 mmol,
2 equiv.) of tert-butyldimethylsilylchloride. Dichloromethane
(130 mL) and a stir bar were added and the flask was capped
with a rubber septum. To the stirred solution 13.0 mL (13.3 g,
84 mmol, 2 equiv.) of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)
was added dropwise via a syringe over the course of 5 min. After
stirring for 4 h the orange reaction mixture was poured into a
separatory funnel and 80 mL of 1 M HCl was added. The aqueous
layer was separated and extracted with 3 × 50 mL of Et2O. The
combined organic phases were dried with MgSO4 and the solvent
evaporated at reduced pressure. The residue was purified by
column chromatography on silica gel, eluting with 1 : 1 mixture of
hexanes : EtOAc to give 19.45 g of 3 (91%) as a colorless oil. 1H
NMR (CDCl3): d 7.60 (dd, 8.0, 1.5 Hz, 1H, H-3 or -6), 7.59 (dd,
8.0, 1.5 Hz, 1H, H-3 or -6), 7.43 (d, 2.5 Hz, 1H, meta to silyloxy),
7.35 (d, 2.5 Hz, 1H, meta to silyloxy), 7.31 (td, 8.0, 1.5 Hz, 1H,
H-4 or -5), 7.26 (s, 2H, alkene CH), 7.11 (td, 8.0, 1.5 Hz, 1H, H-4
or -5), 1.43, 1.35 (s, 9H each, ArC(CH3)3), 0.98 (s, 9H, SiC(CH3)3),
2-(3ꢀ,5ꢀ -Di-tert-butyl-2ꢀ -(tert-butyldimethylsilyloxy)phenethyl)-
benzoic acid (5). In a two-neck round-bottom flask 0.893 g
(1.91 mmol) of stilbenecarboxylic acid 4 was dissolved in 15 mL
of methoxyethanol. One neck of the flask was capped with
a rubber septum, the other with a reflux condenser capped
with a hose adapter vented through a mineral oil bubbler. The
apparatus was flushed with nitrogen (using a needle through the
septum) for 15 min. The solution was heated to reflux and a
solution of 0.891 g (4.78 mmol, 2.5 equiv.) of tosylhydrazide
in 15 mL of methoxyethanol was added over the course of
45 min using a syringe. After heating the reaction mixture at
reflux for 16 h under N2, the solution was allowed to cool to
room temperature and poured into a separatory funnel. 50 mL
of saturated NaHCO3 solution and 30 mL of Et2O were added,
and the aqueous phase was separated and extracted with 3 ×
20 mL of Et2O. The combined organic phases were dried with
MgSO4 and the solvents evaporated in vacuo. The residue was
purified by column chromatography using silica gel, eluting first
with hexanes, followed by a mixture of 10% EtOAc–hexanes.
Evaporation of the eluate gave the product as a white crystalline
1
0.21 (s, 6H, Si(CH3)2). 13C{ H} NMR (CDCl3): d 150.66 (C–OSi),
143.36, 139.74, 137.93, 133.24, 131.05, 128.85, 128.56, 127.71,
126.96, 126.64, 125.68, 124.12, 122.12, 35.65 (ArC(CH3)3), 34.55
(ArC(CH3)3), 31.75 (ArC(CH3)3), 31.59 (ArC(CH3)3), 27.22
(SiC(CH3)3), 19.53 (SiC(CH3)3), −0.49 (Si(CH3)2). IR: 2958 (s),
2930 (s), 2903 (m), 2860 (m), 1625 (w), 1586 (w), 1467 (s), 1438
(s), 1412 (w), 1392 (w), 1362 (m), 1291 (w), 1255 (s), 1232 (m),
1202 (w), 1163 (w), 1126 (w), 1024 (w), 977 (w), 924 (m), 887 (m),
839 (m), 822 (m), 805 (m), 780 (m), 747 (m), 682 (w). FAB-MS:
m/z = 500 (M+, 79Br), 502 (M+, 81Br).
trans-3ꢀ,5ꢀ-Di-tert-butyl-2ꢀ-(tert-butyldimethylsilyloxy)-stilbene-
2-carboxylic acid (4). Protected bromostilbene 3 (5.86 g,
11.7 mmol) was weighed into a three-neck round bottom flask.
One neck was capped with a rubber septum and another with
a glass stopper, and the flask was attached to the vacuum line
through a needle valve inserted in the third neck. Dry THF
(70 mL) was vacuum transferred into the flask and the solution
chilled to −78 ◦C. To the stirred solution 15 mL (24 mmol,
2 equiv.) of a solution of n-butyllithium in hexanes (Strem,
1.59 M) was added over 15 min using a syringe. After stirring the
solution for 1 h at −78 ◦C, the stopper was replaced under N2 flow
solid (0.333 g, 37%). H NMR (CDCl3): d 8.09 (dd, 7.5, 1.5 Hz,
1
1H, H-6), 7.37 (td, 7.5, 1.5 Hz, 1H, H-4 or -5), 7.28 (td, 7.5,
1.5 Hz, 1H, H-4 or -5), 7.17 (d, 2.5 Hz, 1H, meta to silyloxy), 7.02
(dd, 7.5, 1.5 Hz, 1H, H-3), 6.93 (d, 2.5 Hz, 1H, meta to silyloxy),
3.27 (t, 8.0 Hz, 2H, CH2CH2), 2.98 (t, 8.0 Hz, 2H, CH2CH2),
1.41, 1.25 (s, 9H each, ArC(CH3)3), 0.95 (s, 9H, SiC(CH3)3), 0.30
1
(s, 6H, Si(CH3)2). 13C{ H} NMR (CDCl3): d 173.39 (COOH),
149.73 (C–OSi), 145.30, 142.67, 138.66, 132.89, 131.92, 131.87,
130.96, 128.18, 126.14, 125.25, 122.79, 36.17, 35.63, 34.30, 33.53,
31.74 (ArC(CH3)3), 31.58 (ArC(CH3)3), 27.42 (SiC(CH3)3), 19.92
(SiC(CH3)3), −0.44 (Si(CH3)2). IR: 3072 (m), 2958 (s), 2900 (m),
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2862 (m), 2636 (w), 2654 (w), 2553 (w), 1694 (s, mCO), 1603 (w),
1576 (w), 1472 (m), 1440 (m), 1408 (m), 1392 (m), 1362 (m), 1300
(m), 1264 (s), 1234 (m), 1203 (w), 1167 (w), 1142 (w), 1123 (w),
1080 (w), 926 (m), 911 (m), 891 (m), 840 (m), 823 (m), 808 (m),
780 (m), 735 (m). FAB-MS: m/z = 468 (M+).
1391 (m), 1361 (m), 1298 (m), 1263 (m), 1255 (m), 1232 (m), 1204
(w), 1184 (w), 1166(w), 1130 (w), 925 (w), 886 (w), 838 (w), 822
(w), 810 (w), 778 (w). FAB-MS: m/z = 584 (M+), 527 ([M-tBu]+).
1-(2ꢀ -(3ꢀꢀ,5ꢀꢀ -Di-tert-butyl-2ꢀꢀ -hydroxyphenethyl)phenyl)-3-p-
tolylpropane-1,3-dione (L1H2). Into a two-neck round bottom
flask was placed 1.587 g (2.71 mmol) of the silylated diketone 6.
One neck was capped with a rubber septum and 200 mL of dry
THF was vacuum transferred into the flask. The solution was
chilled to 0 ◦C and 5.5 mL (5.5 mmol, 2 equiv.) of 1 M Bu4NF in
THF was added to the stirred solution via syringe. After stirring
the reaction mixture at RT for 15 min, the solution was poured
into a separatory funnel. Ether (40 mL) and 0.5 M aqueous HCl
(100 mL) were added and the phases separated. The aqueous phase
was extracted with 3 × 40 mL of Et2O and the combined organic
phases were dried over MgSO4. The solvent was evaporated and
the slightly yellow solid washed with hexanes. The hexane wash
was chromatographed (7.5% EtOAc–hexanes, silica gel) and the
purified fractions combined with the hexane-insoluble material to
yield 1.057 g (83%) of L1H2 as a crystalline white solid. 1H NMR
(CD3COCD3): d 16.91 (br s, 1H, enol OH), 7.99 (d, 8.0 Hz, 2H,
tolyl-H meta to CH3), 7.76 (dd, 7.5, 1.5 Hz, 1H, H-6ꢀ), 7.49 (td,
7.5, 1.5 Hz, 1H, H-4ꢀ), 7.44 (dd, 7.5, 1.5 Hz, 1H, H-3ꢀ), 7.37 (td,
8.0, 1.5 Hz, 1H, H-5ꢀ), 7.37 (d, 8.0 Hz, 2H, tolyl-H ortho to CH3),
7.15 (d, 2.5 Hz, 1H, meta to OH), 6.98 (d, 2.5 Hz, 1H, meta to
OH), 6.81 (s, 1H, COCHCO), 3.13 (m, 2H, CH2CH2), 2.99 (m,
2H, CH2CH2), 2.42 (s, 3H, tolyl CH3), 1.41, 1.24 (s, 9H each,
2-(3ꢀ,5ꢀ -Di-tert-butyl-2ꢀ-(tert-butyldimethylsilyloxy)phenethyl)-
benzoyl chloride. Into a round bottom flask was weighed 1.418 g
of phenethylbenzoic acid 5 (3.04 mmol). 50 mL of dry toluene was
vacuum transferred into the flask and the solution was taken into
the drybox. In the drybox 0.633 g of phosphorus pentachloride
(Aldrich, 3.04 mmol) was added and the reaction mixture stirred
at RT for 4 h. The solvent was evaporated on the vacuum line
1
and the crude product was used without further purification. H
NMR (CDCl3): d 8.18 (dd, 7.5, 1.5 Hz, 1H, H-6), 7.38 (td, 7.5,
1.5 Hz, 1H, H-4 or -5), 7.31 (td, 7.5, 1.5 Hz, 1H, H-4 or -5),
7.14 (d, 3.0 Hz, 1H, meta to silyloxy), 6.94 (dd, 7.5, 1.5 Hz, 1H,
H-3), 6.74 (d, 3.0 Hz, 1H, meta to silyloxy), 3.11 (t, 7.5 Hz, 2H,
CH2CH2), 2.91 (t, 7.5 Hz, 2H, CH2CH2), 1.39, 1.20 (s, 9H each,
ArC(CH3)3), 0.93 (s, 9H, SiC(CH3)3), 0.28 (s, 6H, Si(CH3)2). IR:
2960 (s), 2861 (m), 1777 (s, mCO), 1644 (w), 1600 (w), 1569 (w),
1474 (m), 1440 (m), 1361 (m), 1256 (m), 1234 (m), 1203 (w), 1186
(w), 1129 (w), 927 (m), 884 (m), 868 (m), 840 (m), 780 (m).
1-(2ꢀ -(3ꢀꢀ,5ꢀꢀ -Di-tert-butyl-2ꢀꢀ -(tert-butyldimethylsilyloxy)phen-
ethyl)phenyl)-3-p-tolylpropane-1,3-dione (6). In the drybox,
1.485 g of LiN(SiMe3)2 (Aldrich, 7.6 mmol, 2.5 equiv.) and
20 ml of dry THF were placed into a glass bomb. A solution of
0.489 g 4ꢀ-methylacetophenone (3.65 mmol, 1.2 equiv.) in 15 ml
of dry THF was added and the mixture stirred at RT for 15 min.
The acyl chloride prepared from 1.418 g of carboxylic acid 5
(3.04 mmol, assuming quantitative yield) was dissolved in 5 ml of
dry THF and the solution was dropped into the reaction mixture,
with stirring, over 10 min using a syringe. The bomb was closed
1
C(CH3)3). 13C{ H} NMR (CD3COCD3): d 194.74 (carbonyl),
184.39 (carbonyl), 152.23 (ArC–OH), 145.05, 142.76, 142.68,
138.02, 136.81, 133.01, 132.60 (2 overlapped resonances), 130.85,
130.43, 128.68, 128.24, 127.65, 126.19, 122.98, 98.05 (COCHCO),
36.10, 36.08, 35.19, 35.02, 32.51 (C(CH3)3), 30.76 (C(CH3)3), 22.10
(tolyl CH3). IR: 3470 (s, phenol mOH), 2958 (s), 2869 (m), 1605 (s),
1579 (m), 1564 (m), 1510 (m), 1480 (m), 1445 (m), 1415 (m), 1391
(m), 1362 (m), 1308 (m), 1281 (m), 1214 (m), 1200 (m), 1186 (m),
1153 (w), 1122 (w), 1087 (w), 949 (w), 878 (w), 805 (w), 768 (w),
738 (w). FAB-MS: Exact mass for C32H38O3 calcd 470.2805, obsd
470.2800. Anal.: Calcd for C32H38O3: C, 81.66; H, 8.14; found C,
79.84; H, 8.49.
◦
and the reaction mixture stirred in a 65 C oil bath for 4 h. The
solution was cooled to room temperature, opened to the air, and
poured into a separatory funnel. 40 mL of 1 M HCl and 20 mL
of Et2O were added, the phases separated, and the aqueous
phase extracted with 3 × 20 mL of Et2O. The combined organic
phases were dried with MgSO4 and the solvents evaporated
under reduced pressure. The oily residue was chromatographed
on silica gel with 2.5% EtOAc–hexanes to give diketone 6 as a
pale red oil (1.587 g, 89%). NMR spectroscopy in acetone-d6
indicates that the compound exists predominantly as the enol.
1H NMR (CD3COCD3): d 7.97 (d, 8.0 Hz, 2H, tolyl-H meta to
CH3), 7.66 (dd, 7.5, 1.5 Hz, 1H, H-6ꢀ), 7.39 (td, 7.5, 1.5 Hz, 1H,
H-4ꢀ or -5ꢀ), 7.36 (d, 8.0 Hz, 2H, tolyl-H ortho to CH3), 7.32 (td,
7.5, 1.5 Hz, 1H, H-4ꢀ or -5ꢀ), 7.19 (dd, 7.5, 1.5 Hz, 1H, H-3ꢀ),
7.18 (d, 2.5 Hz, 1H, meta to silyloxy), 6.90 (d, 2.5 Hz, 1H, meta
to silyloxy), 6.74 (s, 1H, COCHCO), 3.13 (m, 2H, CH2CH2),
2.99 (m, 2H, CH2CH2), 2.42 (s, 3H, tolyl CH3), 1.37, 1.19 (s,
9H each, ArC(CH3)3), 0.92 (s, 9H, SiC(CH3)3), 0.30 (s, 6H,
trans-3ꢀ,5ꢀ-Di-tert-butyl-2ꢀ-(tert-butyldimethylsilyloxy)-stilbene-
2-carbonyl chloride (7). Into a 100 mL round bottom flask was
measured 6.925 g (14.8 mmol) of carboxylic acid 4. In the drybox,
3.142 g of PCl5 (15.1 mmol), 50 mL of dry benzene, and a stir
bar were added to the flask. The flask was capped with a rubber
septum and taken outside of the drybox. The yellow solution was
stirred for 4 h at RT, while vented to a mineral oil bubbler to allow
HCl to escape. The flask was opened and the solvent removed
on a rotary evaporator to leave a thick yellow oil, which was
evacuated on a vacuum line for 2 h to ensure complete removal of
POCl3 (as verified by the absence of a signal in the 31P NMR). The
viscous acyl chloride 7 (7.174 g, 100%) was stored in the drybox.
1H NMR (CDCl3): d 8.08 (d, 8.0 Hz, 1H, H-3), 7.97 (d, 16.0 Hz,
1H, alkene CH), 7.84 (d, 2.4 Hz, 1H, meta to silyloxy), 7.67 (d,
2.4 Hz, 1H, meta to silyloxy), 7.56 (d, 8.0 Hz, 1H, H-6), 7.53 (d,
16.0 Hz, 1H, alkene CH), 7.14 (t, 7.5 Hz, 1H, H-4 or -5), 6.90
(t, 7.5 Hz, 1H, H-4 or -5), 1.65, 1.42 (s, 9H each, ArC(CH3)3),
1
Si(CH3)2). 13C{ H} NMR (CD3COCD3): d 188.95 (carbonyl),
185.77 (carbonyl), 150.93 (COSi), 144.93, 143.85, 142.30, 139.71,
138.11, 133.62, 132.23, 132.19, 132.04, 130.82, 130.11, 128.68,
127.46, 126.22, 123.90, 98.11 (COCHCO), 36.50, 36.06, 35.16,
35.03, 32.36 (ArC(CH3)3), 32.22 (ArC(CH3)3), 28.17 (SiC(CH3)3),
22.08 (ArCH3), 20.86 (SiC(CH3)3), 0.14 (SiCH3). IR: 3060 (w),
3028 (w), 2954 (s), 2930 (s), 2903 (m), 2860 (m), 1604 (m), 1584
(m), 1562 (m), 1535 (m), 1501 (m), 1464 (m), 1439 (m), 1411 (m),
1
1.07 (s, 9H, SiC(CH3)3), 0.24 (s, 6H, Si(CH3)2). 13C{ H} NMR
(CDCl3): d 167.74 (COCl), 150.84 (COSi), 143.47, 140.73, 139.83,
134.33, 133.81, 133.16, 131.43, 128.64, 127.53, 127.29, 126.13,
1036 | Dalton Trans., 2006, 1030–1040
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1
124.87, 122.09, 35.67 (ArC(CH3)3), 34.57 (ArC(CH3)3), 31.74
(ArC(CH3)3), 31.64 (ArC(CH3)3), 27.17 (SiC(CH3)3), 19.49
(SiC(CH3)3), −0.59 (Si(CH3)2). IR: 3061 (w), 3020 (w), 2959 (s),
2904 (s), 2861 (s), 1774 (s, mCO), 1623 (m), 1595 (m), 1561 (w),
1471 (s), 1437 (s), 1412 (m), 1392 (m), 1362 (m), 1292 (m), 1256
(s), 1234 (s), 1203 (m), 1185 (m), 1166 (m), 1126 (m), 1104 (m),
1051 (w), 1006 (w), 975 (m), 924 (m), 882 (m), 869 (m), 839 (m),
801 (m), 780 (m). FAB-MS: 484 (M+).
combined yield 1.7545 g, 31%. H NMR (CDCl3): d 16.46 (br s,
1H, enol OH) 7.67 (d, 7.0 Hz, 2H, H-3ꢀ or -6ꢀ), 7.59 (d, 8.0 Hz,
2H, H-3ꢀ or -6ꢀ), 7.47 (d, 16.0 Hz, 2H, alkene CH), 7.44 (t, 2H,
7.0 Hz, H-4ꢀ or -5ꢀ), 7.40 (d, 2.4 Hz, 2H, meta to silyloxy), 7.31
(d, 3.0 Hz, 2H, meta to silyloxy), 7.28 (d, 16.5 Hz, 2H, alkene
CH), 7.22 (t, 8.0 Hz, 2H, H-4ꢀ or -5ꢀ), 6.33 (s, 1H, COCHCO),
1.41, 1.28 (s, 18H each, ArC(CH3)3), 0.95 (s, 18H, SiC(CH3)3),
1
0.18 (s, 12H, Si(CH3)2). 13C{ H} NMR (CDCl3): d 188.60
=
(C O), 150.57 (COSi), 143.37, 139.74, 137.55, 135.55, 131.25,
trans-2-Acetyl-3ꢀ,5ꢀ-di-tert-butyl-2ꢀ-(tert-butyldimethylsilyloxy)-
stilbene (8). In a 100 mL round bottom flask 3.1845 g of
carboxylic acid 4 (6.82 mmol) was dissolved in 40 mL of dry
THF. In the drybox, 9.4 mL of methyllithium in Et2O (Acros,
1.6 M, 2.2 equiv.) was syringed into the stirred solution. During
the first 30 s, a gas evolves and the solution turns tan. After
stirring for 2 h under N2, the reaction was quenched with 20 mL
of 1 M HCl and the cloudy light yellow mixture was transferred
into a separatory funnel. The organic layer was separated and
washed with 50 mL of saturated aqueous NH4Cl. The aqueous
layers were combined and extracted with 2 × 20 mL of ether. The
combined organic layers were dried over MgSO4, and the solvent
was removed on a rotary evaporator to give a thick light yellow
oil, which was dried in vacuo for 2 h to give 3.1391 g of the ketone
130.33, 129.17, 128.90, 127.17, 126.90, 125.63, 125.61, 121.76,
103.37 (COCHCO), 35.66 (ArC(CH3)3), 34.51 (ArC(CH3)3),
31.74 (ArC(CH3)3), 31.64 (ArC(CH3)3), 27.20 (SiC(CH3)3), 19.55
(SiC(CH3)3), −0.55 (Si(CH3)2). IR: 3066 (w), 3015 (w), 2956 (s),
2905 (m), 2862 (m), 1599 (m), 1578 (m), 1552 (w), 1472 (m), 1463
(m), 1434 (m), 1412 (w), 1392 (w), 1361 (m), 1294 (w), 1255 (s),
1233 (s), 1203 (w), 1163 (w), 1126 (w), 1075 (w), 1056 (w), 1031
(w), 1005 (w), 978 (w), 924 (m), 884 (m), 840 (m), 823 (w), 806
(w), 780 (m). FAB-MS: 913 (M+). Anal.: Calcd for C59H84O4Si2:
C, 77.58; H, 9.27; found C, 77.58; H, 9.32.
1,3-Bis(2ꢀ-(3ꢀꢀ,5ꢀꢀ-di-tert-butyl-2ꢀꢀ-hydroxystyryl)phenyl)propane-
1,3-dione (L2H3). In the drybox, 0.3385 g of protected diketone
9 (0.371 mmol) was dissolved in 15 mL of THF in a 50 mL round
bottom flask to give a dark orange solution. The flask was capped
with a rubber septum and taken out of the drybox. After stirring
the solution for 30 min at 0 ◦C, Bu4NF (3.7 mL, 1 M solution in
THF, 3.7 mmol, 10 equiv.) was added with a syringe. The solution
1
8 (99%). H NMR (CDCl3): d 7.66 (dd, 7.5, 1.0 Hz, 1H, H-3 or
-6), 7.65 (dd, 8.0, 1.0 Hz, 1H, H-3 or -6), 7.49 (td, 7.5, 1.0 Hz,
1H, H-4 or -5), 7.47 (d, 16.0 Hz, 1H, alkene CH), 7.40 (d, 2.4 Hz,
1H, meta to silyloxy), 7.34 (d, 2.7 Hz, 1H, meta to silyloxy),
7.33 (td, 7.5, 1.0 Hz, 1H, H-4 or -5), 7.24 (d, 16 Hz, 1H, alkene
CH), 2.62 (s, 3H, CH3CO) 1.43, 1.35 (s, 9H each, ArC(CH3)3),
◦
turned a very dark brown. It was stirred for 15 min at 0 C and
quenched with 15 mL of 1 M HCl. The organic layer of the orange
mixture was separated and the aqueous layer extracted with 2 ×
20 mL of ether. The combined organic layers were dried over
MgSO4, filtered, and the solvent removed on a rotary evaporator,
leaving a thick dark orange oil. A few mL of hexane were added
to it, swirled well and the mixture allowed to stand overnight to
ensure complete precipitation of the light yellow product, which
was filtered and air-dried for 1 h to give 0.1826 g of L2H3 (72%).
1H NMR (C6D6): d 17.01 (br s, 1H, enol OH), 7.65 (d, 16.0 Hz,
2H, alkene CH), 7.45 (d, 2.5 Hz, 2H, meta to OH), 7.44 (dd,
7.0, 1.0 Hz, 2H, H-3ꢀ or -6ꢀ), 7.37 (d, 2.5 Hz, 2H, meta to OH),
7.33 (d, 7.0 Hz, 2H, H-3ꢀ or -6ꢀ), 7.07 (td, 7.5, 1.0 Hz, 2H, H-4ꢀ
or -5ꢀ), 6.94 (td, 7.0, 1.0 Hz, 2H, H-4ꢀ or -5ꢀ), 6.90 (d, 16.0 Hz,
2H, alkene CH), 6.33 (s, 1H, COCHCO), 5.38 (br s, 2H, phenol
1
0.97 (s, 9H, SiC(CH3)3), 0.21 (s, 6H, Si(CH3)2). 13C{ H} NMR
(CDCl3): d 202.57 (COCH3), 150.60 (COSi), 143.27, 139.64,
137.89, 137.85, 131.63, 131.20, 129.04, 128.99, 127.46, 126.96,
126.03, 125.55, 122.03, 35.63 (ArC(CH3)3), 34.53 (ArC(CH3)3),
31.74 (ArC(CH3)3), 31.59 (ArC(CH3)3), 30.36 (COCH3), 27.21
(SiC(CH3)3), 19.53 (SiC(CH3)3), −0.55 (Si(CH3)2). IR: 3062 (w),
3021 (w), 2958 (s), 2904 (s), 2861 (s), 1686 (s, mCO), 1624 (w), 1595
(m), 1562 (m), 1474 (s), 1464 (s), 1438 (s), 1412 (m), 1392 (m),
1362 (s), 1296 (s), 1259 (s), 1237 (s), 1203 (m), 1164 (m), 1126 (m),
1070 (w), 1042 (w), 1007 (w), 975 (m), 954 (m), 924 (m), 889 (s),
839 (s), 823 (m), 806 (m), 781 (s), 756 (s). FAB-MS: 465 (M + H+).
1,3-Bis(2ꢀ -(3ꢀꢀ,5ꢀꢀ -di-tert-butyl-2ꢀꢀ -(tert-butyldimethylsilyloxy)-
styryl)phenyl)-propane-1,3-dione (9). Into a 100 mL round
OH), 1.55, 1.26 (s, 18H each, C(CH3)3). 13C{ H} NMR (CDCl3):
1
bottom flask was measured 3.1931
g of acetylstilbene 8
=
d 188.40 (C O), 150.15 (C–OH), 142.63, 137.60, 136.06, 135.17,
(6.75 mmol). In the drybox, 2.2600 g of LiN(SiMe3)2 (13.5 mmol,
2 equiv.) and 15 mL of THF were added to the ketone. The very
dark orange-brown solution was stirred for 15 min, then 2.9360 g
of acyl chloride 7 (6.05 mmol, 0.90 equiv.) dissolved in 15 mL
of THF was added, causing the solution to turn darker brown.
The reaction mixture was stirred under N2 for 3 d, then poured
into a separatory funnel with 50 mL of 1 M HCl. The cloudy
yellow organic layer was separated and washed with 50 mL of
saturated aqueous NH4Cl, and the combined aqueous layers
were extracted with 2 × 20 mL of ether. The combined organic
layers were dried over MgSO4, filtered, and the solvent was
removed on a rotary evaporator, giving a thick orange oil which
solidified after a few minutes. The crude material was triturated
with 20 mL of hexane and the precipitated product was filtered
on a glass frit and air-dried for 1 h. Reduction of the volume of
the filtrate and further addition of hexane yielded a second crop;
131.71, 130.80, 129.13, 127.85, 127.50, 127.34, 124.58, 124.27,
122.87, 102.65 (COCHCO), 35.10 (C(CH3)3), 34.51 (C(CH3)3),
31.77 (C(CH3)3), 30.14 (C(CH3)3). IR: 3498 (br, mOH), 3397 (br,
mOH), 3066 (w), 2960 (s), 2905 (m), 2870 (m), 1601 (s), 1580 (s),
1557 (m), 1476 (s), 1444 (s), 1416 (w), 1391 (w), 1362 (m), 1296
(w), 1276 (w), 1250 (w), 1217 (s), 1190 (m), 1153 (w), 1119 (w),
1090 (w), 1076 (w), 1029 (w), 969 (w), 879 (w), 845 (w), 823 (w),
772 (w). FAB-MS: 685 (M + H+) Anal.: Calcd for C47H56O4: C,
82.42; H, 8.24; found C, 82.27; H, 7.93.
1,3-Bis(2ꢀ -(3ꢀꢀ,5ꢀꢀ -di-tert-butyl-2ꢀꢀ -(tert-butyldimethylsilyloxy)-
phenethyl)phenyl)propane-1,3-dione (10). In a two-neck round
bottom flask 200 mg (0.219 mmol) of the unsaturated and
protected diketone 9 was reduced with TsNHNH2 (204 mg,
1.09 mmol, 5 equiv.) as described for the reduction of 4 to 5. After
workup, the residue was chromatographed on a short column of
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 1030–1040 | 1037
©

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silica gel, eluting with hexanes. The saturated, protected diketone
10 was isolated as a pale yellow oil; yield 87 mg (43%). 1H NMR
(acetone-d6): d 16.88 (s, 1H, enol OH), 7.64 (dd, 7.5, 1.5 Hz, 2H,
H-6ꢀ), 7.36 (td, 7.5, 1.5 Hz, 2H, H-4ꢀ or -5ꢀ), 7.29 (td, 7.5, 1.5 Hz,
2H, H-4ꢀ or -5ꢀ), 7.20 (d, 2.5 Hz, 2H, meta to silyloxy), 7.12 (dd,
7.5, 1.5 Hz, 2H, H-3ꢀ), 6.92 (d, 2.5 Hz, 2H, meta to silyloxy),
6.41 (s, 1H, COCHCO), 3.14 (m, 4H, CH2CHꢀ2), 3.02 (m, 4H,
CH2CHꢀ2), 1.40, 1.20 (s, 18H each, ArC(CH3)3), 0.93 (s, 18H,
101.51 (COCHCO), 101.09 (COCHCO), 99.76 (COCHCO),
42.91, 40.38, 39.91, 39.73, 36.51, 36.16, 36.12, 36.07, 34.91, 34.87,
34.85, 34.79, 32.32 (C(CH3)3), 32.28 (C(CH3)3), 32.22 (C(CH3)3),
31.59 (C(CH3)3), 31.19 (C(CH3)3), 31.10 (C(CH3)3), 23.08 (tolyl
CH3), 21.54 (tolyl CH3). IR: 2956 (s), 2925 (s), 2867 (m), 1601
(m), 1588 (s), 1551 (s), 1523 (s), 1495 (s), 1473 (m), 1447 (m), 1434
(m), 1410 (w), 1360 (s), 1322 (m), 1300 (m), 1283 (m), 1231 (s),
1202 (m), 1184 (w), 1165 (m), 1125 (m), 1093 (w), 1064 (w), 1047
(w), 1018 (w), 944 (w), 914 (w), 866 (m), 799 (w), 765 (m), 763
(w). FAB-MS: 984 (M+). Anal.: Calcd for C64H72O6Ti: C, 78.03;
H, 7.37; found C, 77.84; H, 7.44.
1
SiC(CH3)3), 0.31 (s, 12H, Si(CH3)2). 13C{ H} NMR (CDCl3): d
=
190.32 (C O), 149.82 (COSi), 142.65, 141.57, 138.68, 136.32,
131.16, 130.89, 130.78, 128.80, 126.04, 125.03, 122.78, 101.38
(COCHCO), 35.60, 34.99, 34.32, 33.67, 31.75 (ArC(CH3)3),
31.50 (ArC(CH3)3), 27.49 (SiC(CH3)3), 20.01 (SiC(CH3)3), −0.36
(Si(CH3)2).
[1-(2ꢀ-(3ꢀꢀ,5ꢀꢀ-Di-tert-butyl-2ꢀꢀ-oxyphenethyl)phenyl)-3-p-tolylpropane-
1,3-dionato](di(2-oxyethyl)amine)titanium(IV), (L1)Ti[(OCH2CH2)2-
NH]. In the drybox, 4.5 mg (43 lmol) diethanolamine was
weighed into a round bottom flask. A stir bar, 12.5 lL (12.1 mg,
43 lmol) of titanium(IV) isopropoxide and 3 mL of dry benzene
were added. The reaction mixture was stirred for 20 min at RT. A
solution of 20.0 mg (42 lmol) of L1H2 in 2 mL of benzene was
then added dropwise to the stirred mixture over the course of
1 min using a syringe. The reaction mixture was stirred for 10 min
at RT, and the solvent removed on the vacuum line. The orange
residue was transferred into a vial, suspended in a small amount
of hexanes and the vial placed in a freezer at −40 ◦C. After
16 h the solvent was removed using a syringe and the orange
residue dried in vacuum. Yield 26 mg (98%). 1H NMR (CD2Cl2,
1,3-Bis(2ꢀ -(3ꢀꢀ,5ꢀꢀ -di-tert-butyl-2ꢀꢀ -hydroxyphenethyl)phenyl)-
propane-1,3-dione (L3H3). The silylated compound 10 (87 mg,
0.095 mmol) was deprotected using Bu4NF (0.3 mL, 0.3 mmol,
3 equiv.) as described for L2H3. Washing the crude product with
0.5 mL of ethanol and 1 mL of 10% EtOAc in hexanes gave 55 mg
(83%) L3H3 as a slightly yellow solid. 1H NMR (C6D6): d 16.94 (s,
1H, enol O–H), 7.45 (d, 2.5 Hz, 2H, meta to OH), 7.19 (d, 7.5 Hz,
2H, H-3ꢀ or -6ꢀ), 7.13 (d, 2.5 Hz, 2H, meta to OH), 7.04 (t, 7.5 Hz,
2H, H-4ꢀ or -5ꢀ), 6.92 (t, 7.5 Hz, 2H, H-4ꢀ or -5ꢀ), 6.87 (d, 7.5 Hz,
2H, H-3ꢀ or -6ꢀ), 6.11 (s, 2H, phenol OH), 6.04 (s, 1H, COCHCO),
3.07 (m, 4H, CH2CHꢀ2), 2.92 (m, 4H, CH2CHꢀ2), 1.64, 1.38 (s, 18H
13
1
◦
=
each, C(CH3)3). C{ H} NMR (C6D6): d 190.80 (C O), 151.85
(Ar C–OH), 142.45, 142.25, 136.32, 135.86, 132.10, 132.02, 129.96,
126.84, 126.73, 125.56, 122.90, 101.86 (COCHCO), 36.13, 35.75,
35.27, 34.77, 32.35 (C(CH3)3), 30.62 (C(CH3)3). IR: 3492 (m, mOH),
2956 (s), 2870 (m), 1673 (m, mC=O), 1602 (m), 1480 (s), 1462 (m),
1415 (m), 1391 (m), 1362 (m), 1274 (m), 1214 (s), 1198 (s), 1222
(s), 877 (w), 820 (w), 752 (w). FAB-MS: Exact mass for C47H60O4
calcd 688.4466, obsd 688.4470.
−60 C, assignments by selective decoupling): d 7.95 (d, 8.5 Hz,
2H, tolyl-H meta to -CH3), 7.63 (d, 7.0 Hz, 1H, H-3ꢀ or -6ꢀ), 7.40
(t, 7.0 Hz, 1H, H-4ꢀ or -5ꢀ), 7.33 (d, 7.0 Hz, 1H, H-3ꢀ or -6ꢀ), 7.32
(t, 7.0 Hz, 1H, H-4ꢀ or -5ꢀ), 7.28 (d, 8.5 Hz, 2H, tolyl-H ortho to
–CH3), 7.12 (d, 2.5 Hz, 1H, meta to OTi), 6.97 (d, 2.5 Hz, 1H,
meta to OTi), 6.83 (s, 1H, COCHCO), 4.68 (dt, 11.0, 5.5 Hz, 1H,
CHHꢀO–Ti), 4.45 (dt, 11.0, 5.5 Hz, CHHꢀO–Ti), 4.41 (dt, 11.0,
5.5 Hz, 1H, CHHꢀO–Ti), 4.30 (dt, 11.0, 5.5 Hz, CHHꢀO–Ti),
3.68 (td, 12.5, 2.5 Hz, 1H, CHHꢀAr), 3.39 (ddt, 11.5, 6.0, 5.5 Hz,
1H, NHCHHꢀ), 3.28 (ddt, 12.0, 6.0, 5.5 Hz, 1H, NHCHHꢀ), 3.17
(tt, 6.0, 5.5 Hz, 1H, NH), 3.10 (dq, 11.5, 5.5 Hz, NHCHHꢀ),
2.93 (dq, 12.0, 5.5 Hz, 1H, NHCHHꢀ), 2.62 (td, 12.5 Hz, 2.5 Hz,
1H, ArCHHꢀ), 2.51 (td, 12.5, 5.5 Hz, 1H, ArCHHꢀ), 2.38 (s,
3H, tolyl CH3), 2.11 (td, 12.5, 5.5 Hz, 1H, ArCHHꢀ), 1.55,
Preparation of metal complexes
Bis{1-[2ꢀ -(3ꢀꢀ,5ꢀꢀ -di-tert-butyl-2ꢀꢀ -oxyphenethyl)phenyl]-3-p-
tolylpropane-1,3-dionato}titanium(IV), (L1)2Ti. 100 mg L1H2
(0.213 mmol) was weighed into a glass bomb, a stir bar was
added and 20 mL of dry benzene was added by vacuum transfer.
In the drybox, 31.5 lL of titanium(IV) isopropoxide (Aldrich,
30.6 mg, 0.107 mmol) was added. The reaction mixture was
1
1.23 (s, 9H each, C(CH3)3). 13C{ H} NMR (C6D6): d 190.83
(carbonyl), 185.21 (carbonyl), 163.10 (phenoxide ipso C), 143.62,
142.95 (sl br), 142.79, 140.55 (v br), 139.57, 135.29, 134.04,
131.72, 130.63, 129.96, 128.83, 126.42 (2 overlapping resonances),
125.90, 122.18, 100.04 (COCHCO), 72.23 (N(CH2CH2O)2), 53.18
(N(CH2CH2O)2), 38.70, 36.41, 35.21, 34.88, 32.38 (C(CH3)3),
30.57 (C(CH3)3), 21.82 (tolyl CH3). IR: 3312 (w, mNH), 3176 (w),
2957 (s), 2920 (s), 2853 (s), 1602 (s), 1584 (s), 1547 (s), 1524 (s),
1499 (s), 1472 (s), 1446 (s), 1410 (s), 1361 (s), 1327 (s), 1304 (s),
1252 (s), 1237 (s), 1208 (m), 1185 (m), 1167 (m), 1101 (s), 1087 (s),
1061 (s), 1017 (w), 957 (m), 914 (m), 870 (s), 796 (m), 767 (s), 748
(m). FAB-MS: m/z = 619 (M+).
◦
stirred at 70 C for 17 h. The solvent was evaporated to give the
1
product in quantitative yield as a mixture of isomers. H NMR
(C6D6): d 7.93 (d, 8.0 Hz), 7.64 to 7.50 (m), 7.44 to 7.01 (m),
6.77 (d, 7.0 Hz), 6.57 (s, COCHCO), 6.54 (s, COCHCO), 6.51
(s, COCHCO), 5.28 to 5.13 (m, ethylene-H), 4.80 to 4.62 (m,
ethylene-H), 3.10 to 2.89 (m, ethylene-H), 1.79 (s, Me or tBu),
1.70 (s, Me or tBu), 1.63 (s, Me or tBu), 1.61 (s, Me or tBu), 1.38
1
(s, Me or tBu), 1.37 (s, Me or tBu), 1.30 (s, Me or tBu). 13C{ H}
NMR (C6D6): d 187.79 (carbonyl), 187.60 (carbonyl), 187.24 (car-
bonyl), 184.85 (carbonyl), 184.70 (carbonyl), 184.06 (carbonyl),
165.69 (phenoxide-C–O–Ti), 165.23 (phenoxide-C–O–Ti), 164.86
(phenoxide-C–O–Ti), 147.51, 145.27, 145.19, 143.49, 143.41,
143.31, 143.19, 143.15, 139.22, 139.19, 139.14, 137.76, 137.69,
135.57, 135.51, 135.16, 134.66, 134.32, 134.26, 133.31, 132.77,
132.20, 132.12, 130.22, 129.95, 129.71, 129.64, 129.22, 128.98,
128.87, 128.81, 128.57, 128.50, 128.25, 128.18, 127.86, 127.56,
127.17, 126.83, 126.77, 126.68, 126.38, 122.30, 122.27, 122.21,
[1-(2ꢀ -(3ꢀꢀ,5ꢀꢀ -Di-tert-butyl-2ꢀꢀ -oxyphenethyl)phenyl)-3-p-tolyl-
propane-1,3-dionato](N-methyldi(2-oxyethyl)amine)titanium(IV),
(L1)Ti[(OCH2CH2)2NCH3]. This complex was prepared using
the procedure described for the diethanolamine derivative, using
5.1 mg (43 lmol) of N-methyldiethanolamine in place of the di-
ethanolamine, to give 22 mg (81%) of (L1)Ti[(OCH2CH2)2NCH3]
as a yellow powder. 1H NMR (C6D6): d 7.96 (d, 8.0 Hz, 2H, tolyl-H,
1038 | Dalton Trans., 2006, 1030–1040
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meta to CH3), 7.52 (d, 2.0 Hz, 1H, meta to aryl-O–Ti), 7.41 to 7.38
(m, 1H, H-4ꢀ or -5ꢀ), 7.21 (d, 2.0 Hz, 1H, meta to aryl-O–Ti), 7.11
to 7.02 (m, 3H, H-3ꢀ, -6ꢀ, and -4ꢀ or -5ꢀ), 6.95 (d, 8.0 Hz, 2H, tolyl-
H, ortho to CH3), 6.65 (s, 1H, COCHCO), 4.89 (br, 1H), 4.30 (br,
4H), 3.13 (br, 1H), 2.80 (br, 2H), 2.47 (br, 2H), 2.36 (br, 2H), 2.05
(s, 9H, C(CH3)3), 2.03 (s, 3H, tolyl- or N–CH3), 1.99 (s, 3H, tolyl-
a small vial. The crude product was suspended in some hexane
and the vial was allowed to stand overnight at −40 ◦C. The
solution was decanted from the residue and the yellow solid dried
1
in vacuo to give 7.5 mg (37%) of (L1)[ScCp2]2. H NMR (C6D6):
d 7.83 (d, 8.0 Hz, 2H, tolyl-H meta to CH3), 7.46 (s, 1H, meta to
aryl-O–Sc), 7.45 (d, 7.0 Hz, 1H, H-3ꢀ or -6ꢀ), 7.27 (s, 1H, meta to
aryl-O–Sc), 7.19 (t, 7.0 Hz, 1H, H-4ꢀ or 5ꢀ), 7.09 (t, 7.0 Hz, 1H,
H-4ꢀ or -5ꢀ), 7.08 (d, 7.0 Hz, 1H, H-3ꢀ or -6ꢀ), 6.99 (d, 8.0 Hz,
2H, tolyl-H ortho to CH3), 6.65 (s, 1H, COCHCO), 6.16 (s, 10H,
CpH), 6.12 (s, 10H, CpH), 3.41 (t, 7.5 Hz, 2H, CH2), 2.79 (t,
7.5 Hz, 2H, CH2), 2.06 (s, 3H, tolyl-CH3), 1.53, 1.40 (s, 9H each,
1
or N–CH3), 1.41 (s, 9H, C(CH3)3). 13C{ H} NMR (C6D6): 191.03
(carbonyl), 185.82 (carbonyl), 163.44 (phenoxide ipso C), 143.75,
142.93, 142.62 (sl br), 140.75 (v br), 139.47, 135.16, 134.14, 131.42,
130.50, 129.93, 128.92, 126.35 (2 overlapping resonances), 125.87,
122.14, 100.06 (COCHCO), 71.19 (CH2O), 70.78 (CH2O), 62.05
(NCH2), 44.92, 38.54, 36.39, 35.32 (C(CH3)3), 34.89 (C(CH3)3),
32.37 (C(CH3)3), 31.56 (C(CH3)3), 21.79 (tolyl CH3). IR: 2952 (m),
2861 (m), 1602 (m), 1583 (m), 1544 (s), 1526 (s), 1500 (s), 1473 (m),
1448 (m), 1410 (m), 1360 (s), 1328 (m), 1303 (m), 1252 (w), 1236
(m), 1206 (w), 1183 (w), 1167 (w), 1146 (w), 1113 (w), 1088 (s),
1070 (m), 1031 (w), 1017 (w), 989 (w), 916 (w), 871 (m). FAB-MS:
634 (M + H)+.
1
C(CH3)3). 13C{ H} NMR (C6D6): d 190.57 (carbonyl), 184.73
(carbonyl), 161.84 (phenoxide-C–OSc), 143.03, 141.64, 141.23,
139.08, 135.88, 134.71, 133.54, 132.95, 130.45, 130.17, 129.85,
128.49, 126.64, 124.09, 122.07, 115.86 (Cp), 113.12 (Cp), 100.63
(COCHCO), 42.08, 35.67, 34.82, 34.32, 32.54 (C(CH3)3), 31.57
(C(CH3)3), 21.76 (tolyl CH3). IR (nujol mull): 1601 (m), 1584 (s),
1542 (s), 1523 (s), 1498 (s), 1411 (m), 1303 (s), 1272 (s), 1234 (m),
1185 (w), 1126 (w), 1015 (s), 855 (m), 789 (s).
[1-(2ꢀ -(3ꢀꢀ,5ꢀꢀ -Di-tert -butyl-2ꢀꢀ-hydroxyphenethyl)phenyl)-3-p-
tolylpropane - 1,3 - dionato ] di ( g5 - cyclopentadienyl ) scandium(III),
(L1H)ScCp2. Into an NMR tube 40.0 mg (85 lmol) of L1H2
was weighed. In the drybox 20.4 mg (85 lmol) of tricyclopentadi-
enylscandium(III) and some benzene-d6 were added. After shaking
the reaction mixture vigorously for 10 min, the tube was allowed to
stand in the drybox at room temperature for 30 min. The reaction
mixture was poured into a flask, a stir bar was added and the
flask was attached to a needle valve. The solvent was evaporated
on the vacuum line and inside the drybox the yellow residue was
suspended in hexanes. The supernatant was removed using a pipet
and transferred into a flask and the solvents evaporated in vacuo
1-(2ꢀ -(3ꢀꢀ,5ꢀꢀ -Di-tert-butyl-2ꢀꢀ -oxyphenethyl)phenyl)-3-p-tolyl-
propane-1,3-dionato-(g5-cyclopentadienyl)scandium(III), L1ScCp.
Into an NMR tube were weighed 30 mg (64 lmol) of L1H2.
The tube was taken into the drybox and 20 mg (83 lmol) of
Cp3Sc and benzene-d6 (0.5 mL) were added. The reaction mixture
was shaken vigorously for 10 min and the tube was placed in an
oil bath at 73 ◦C. After 5.5 h the heating was stopped and the
1
tube was allowed to stand in the drybox overnight at RT. By H
NMR, the solution contained equimolar amounts of L1(ScCp2)2
and L1ScCp. Attempts to raise the yield of the monoscandium
complex by adding more ligand or further heating of the reaction
mixture led to decomposition of the product, which could thus be
1
to give 41 mg (75%) of (L1H)ScCp2 as a yellow solid. H NMR
1
characterized only in situ by NMR. H NMR (C6D6): d 7.71 (d,
(C6D6): d 7.81 (d, 8.0 Hz, 2H, tolyl-H, meta to CH3), 7.34 (d,
2.5 Hz, 1H, meta to OH), 7.32 (dd, 7.0, 2.0 Hz, 1H, H-3ꢀ or -6ꢀ),
7.07 (d, 2.5 Hz, 1H, meta to OH), 7.02 (d, 8.0 Hz, 2H, tolyl-H, ortho
to CH3), 7.00 to 6.93 (m, 2H, H-4ꢀ and -5ꢀ), 6.75 (dd, 7.0, 2.0 Hz,
1H, H-3ꢀ or -6ꢀ), 6.48 (s, 1H, COCHCO), 6.20 (s, 10H, CpH),
4.99 (s, 1H, OH), 3.09 (t, 7.0 Hz, 2H, CH2), 2.92 (t, 7.0 Hz, 2H,
CH2), 2.08 (s, 3H, tolyl CH3), 1.47, 1.35 (s, 9H each, C(CH3)3).
8.0 Hz, 2H, tolyl-H, meta to CH3), 7.43 (d, 2.5 Hz, 1H, meta to
aryl-O–Sc), 7.23 (d, 2.5 Hz, 1H, meta to aryl-O–Sc), 7.05 (m, 4H,
H-3ꢀ,4ꢀ,5ꢀ,6ꢀ), 6.90 (d, 8.0 Hz, 2H, tolyl-H, ortho to CH3), 6.64 (s,
5H, Cp–H), 6.41 (s, 1H, COCHCO), 3.12 to 2.91 (m, 2H, CHHꢀ),
2.85 to 2.71 (m, 2H, CHꢀꢀ Hꢀꢀꢀ ), 1.99 (s, 3H, tolyl CH3), 1.69, 1.43
(s, 9H each, C(CH3)3).
1
13C{ H} NMR (C6D6): d 190.47 (carbonyl), 185.23 (carbonyl),
X-Ray crystallography
151.57 (phenol-C–OH), 143.27, 142.56, 141.48, 139.41, 135.92,
135.72, 132.04, 130.12, 129.85, 128.93, 128.58, 126.82, 126.43,
125.37, 122.43, 113.27 (Cp), 100.37 (COCHCO), 35.49, 35.16,
33.13, 32.52, 32.31 (C(CH3)3), 30.43 (C(CH3)3), 21.77 (tolyl CH3).
IR: 3549 (w, mOH), 2952 (s), 2926 (m), 2863 (m), 1601 (w), 1584 (m),
1542 (s), 1536 (s), 1522 (s), 1499 (s), 1477 (s), 1445, 1410 (m), 1373
(s), 1361 (s), 1316 (m), 1301 (m), 1273 (m), 1232 (w), 1211 (w),
1185 (m), 1058 (w), 1042 (w), 1017 (m), 785 (s), 752 (m). FAB-MS:
645 (M + H)+, 579 (M–Cp)+.
Crystals of L2H2 were grown as yellow blocks when the oily
material formed after desilylation of 10 was allowed to stand
overnight in hexane solution. Crystals of the mer isomer of (L1)2Ti
were grown by allowing a concentrated solution of the complex
(as a mixture of isomers) in dichloromethane–methanol to stand
for two weeks at −20 ◦C. The crystals were placed in inert oil
and transferred to the tip of a glass fiber in the cold N2 stream
of a Bruker Apex CCD diffractometer (T = 100 K). Data were
reduced, correcting for absorption and decay, using the program
SADABS.24 The structures were solved using direct methods, with
remaining non-hydrogen atoms found on difference Fourier maps.
All heavy atoms were refined anisotropically. The OH groups
in L2H3 were disordered unequally over the two ortho positions
in each of the phenol rings, and one tert-butyl group in L2H3
was disordered over two orientations. All hydrogen atoms were
located on difference maps and refined isotropically, except the
hydrogens on the minor O–H groups and the tert-butyl hydrogens
in L2H3. Calculations used SHELXTL (Bruker Analytical X-ray
[1-(2ꢀ-(3ꢀꢀ,5ꢀꢀ-Di-tert-butyl-2ꢀꢀ-(oxydi-g5-cyclopentadienylscandium-
(III))phenethyl)phenyl)-3-p-tolylpropane-1,3-dionato]di(g5 -cyclo-
pentadienyl)scandium(III),
(L1)[ScCp2]2. In
the
drybox
16 mg (25 lmol) of (L1H)ScCp2 and 6 mg (25 lmol) of
tricyclopentadienylscandium(III) were weighed into a NMR
tube. Benzene-d6 was added and the reaction mixture shaken
vigorously. After standing at room temperature for 30 min, the
reaction mixture was poured into a flask. A stir bar was added
and the flask was attached to a needle valve. The solvents were
evaporated on the vacuum line and the residue transferred into
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Systems), with scattering factors and anomalous dispersion terms
taken from the literature.25 Further details about the individual
structures are in Table 1. CCDC reference numbers 281977 and
281978. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b511915d
G. G. Stanley, J. Am. Chem. Soc., 1986, 108, 7430–7431; (d) A. W.
Maverick, D. P. Martone, J. R. Bradbury and J. E. Nelson, Polyhedron,
1989, 8, 1549–1556; (e) A. W. Maverick, M. L. Ivie, J. H. Waggenspack
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10 V. Ugrinova, G. A. Ellis and S. N. Brown, Chem. Commun., 2004,
468–469.
Acknowledgements
11 G. D. Smith, P. E. Fanwick and I. P. Rothwell, Inorg. Chem., 1990, 29,
3221–3226.
T. S. thanks the ISAP program of the DAAD for fellowship
support, and V. U. thanks Procter & Gamble for a summer research
fellowship. Financial support of this work by the Faculty Research
Program of the University of Notre Dame and by BLURP is
gratefully acknowledged.
12 A. G. Maestri and S. N. Brown, Inorg. Chem., 2004, 43, 6995–7004.
13 C. R. Hauser, F. W. Swamer and J. T. Adams, Org. React., 1954, 8,
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14 C. Wiles, P. Watts, S. J. Haswell and E. Pombo-Villar, Tetrahedron Lett.,
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16 V. Bertolasi, P. Gilli, V. Ferretti and G. Gilli, J. Am. Chem. Soc., 1991,
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