Synthesis of 1,1'-ferrocenediyl salicylaldimine ligands and their application in titanium-initiated lactide polymerization

Article abstract of DOI:10.1021/om0607144

The synthesis of bidentate N/O 1,1'-ferrocenediyl analogues of N-aryl-salicylaldimines has been accomplished from the previously unreported 1'-hydroxyferrocenecarbaldehyde, 3. Thus, the reaction of 3 with 2,6-diisopropylaniline and with aniline leads to the isolation of N-(2,6-diisopropylphenyl)-(1'(hydroxy)ferrocenyl)aldimine, 5, and N-phenyl-(1'-(hydroxy)ferrocenyl)aldimine, 6, respectively. However, attempts to synthesize analogues of bis(iminophenoxide) (salen) ligands by treatment of 3 with 1,2-ethylenediamine and with trans-(+/-)-1,2-diaminocyclohexane led to intractable product mixtures, while reaction with 1,2-phenylenediamine resulted in formation of a substituted benzimidazole. Titanium bis(isopropoxide) complexes of 5,6, and, for comparative purposes, 1'-(diphenylphosphino) hydroxyferrocene have been synthesized, and in a preliminary study all three complexes were found to initiate the ring-opening polymerization of rac-lactide in a well-controlled manner.

Full text of DOI:10.1021/om0607144

316
Organometallics 2007, 26, 316-320
Synthesis of 1,1′-Ferrocenediyl Salicylaldimine Ligands and Their
Application in Titanium-Initiated Lactide Polymerization
Robert C. J. Atkinson, Kathryn Gerry, Vernon C. Gibson,* Nicholas J. Long,*
Edward L. Marshall, and Lara J. West
Department of Chemistry, Imperial College London, London, SW7 2AZ, United Kingdom
ReceiVed August 7, 2006
The synthesis of bidentate N/O 1,1′-ferrocenediyl analogues of N-aryl-salicylaldimines has been
accomplished from the previously unreported 1′-hydroxyferrocenecarbaldehyde, 3. Thus, the reaction of
3 with 2,6-diisopropylaniline and with aniline leads to the isolation of N-(2,6-diisopropylphenyl)-(1′-
(hydroxy)ferrocenyl)aldimine, 5, and N-phenyl-(1′-(hydroxy)ferrocenyl)aldimine, 6, respectively. However,
attempts to synthesize analogues of bis(iminophenoxide) (salen) ligands by treatment of 3 with 1,2-
ethylenediamine and with trans-(+/-)-1,2-diaminocyclohexane led to intractable product mixtures, while
reaction with 1,2-phenylenediamine resulted in formation of a substituted benzimidazole. Titanium bis-
(isopropoxide) complexes of 5, 6, and, for comparative purposes, 1′-(diphenylphosphino)hydroxyferrocene
have been synthesized, and in a preliminary study all three complexes were found to initiate the ring-
opening polymerization of rac-lactide in a well-controlled manner.
Scheme 1. Single-Site Ti-Based Lactide Polymerization
Inititator Supported by a Ferrocenyl-Derivatized Salen
Ligand, a Redox-Switchable Molecular Catalyst
Introduction
Monoanionic, bidentate salicylaldiminates (iminophenoxides)1
and their closely related tetradentate, dianionic relations bis-
(iminophenoxides) (“salen”)2 are two of the most widely studied
ligand classes in contemporary coordination chemistry, finding
particularly widespread usage as supports for catalytic systems.
This is in part a repercussion of their ease of synthesis (typically
from inexpensive starting materials) and the simplicity with
which steric and electronic properties may accordingly be varied,
thereby allowing catalytic performance to be fine-tuned. As part
of an ongoing research program within our laboratories, we have
exploited such versatility to incorporate redox-active centers into
these and other related ligand families, with the ultimate aim
of synthesizing redox-switchable molecular catalysts.3 For
example, in a proof of concept study we have recently
demonstrated how rac-lactide polymerization activity could be
modulated according to the oxidation state of even remote redox
centers (I being ca. 30 times more active than its oxidized
derivative, II, Scheme 1).4
Scheme 2. Recent Examples of “Salen”-Type Compounds
with Ferrocene Units Appended
In addition, recent improvements to the synthesis of 1,1′-
bis(amino)ferrocene5 has led to its incorporation into the
backbone of salen ligands (III, Scheme 2) and the coordination
* Corresponding
v.gibson@imperial.ac.uk.
authors.
E-mail:
n.long@imperial.ac.uk;
chemistry of this3d and substituted phenoxy analogues6 (termed
“salfen” ligands) has been described for a range of metals
including Al, Mg, Ti, and Zr. Ferrocenylamine has also been
employed to synthesize N-ferrocenylsalicylaldimine, IV,7 which
was shown to support moderate ethylene polymerization activity
when complexed to group 4 metals.
To date, the only reported example of a salen-type ligand to
be derived from a hydroxyferrocene was reported by Ito and
co-workers,8 who synthesized enantiopure 2-hydroxyferrocene-
carbaldehyde via the reduction of the corresponding carboxylic
(1) Calligarir, M.; Randaccio, L. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Gillard, R. D. McCleverty, J., Eds.; Pergamon
Press Ltd: Oxford, 1987; Vol. 2, pp 723-726.
(2) Cozzi, P. G. Chem. Soc. ReV. 2004, 410-421.
(3) (a) Gibson, V. C.; Long, N. J.; Oxford, P. J.; White, A. J. P.; Williams,
D. J. Organometallics 2006, 25, 1932-1939. (b) Gibson, V. C.; Gregson,
C. K. A.; Halliwell, C. M.; Long, N. J.; Oxford, P. J.; White, A. J. P.;
Williams, D. J. J. Organomet. Chem. 2005, 690, 6271-6283. (c) Gibson,
V. C.; Halliwell, C. M.; Long, N. J.; Oxford, P. J.; Smith, A. M.; White,
A. J. P.; Williams, D. J. Dalton Trans. 2003, 918-926. (d) Gibson, V. C.;
Long, N. J.; Marshall, E. L.; Oxford, P. J.; White, A. J. P.; Williams, D. J.
Dalton Trans. 2001, 1162-1164.
(4) Gregson, C. K. A.; Gibson, V. C.; Long, N. J.; Marshall, E. L.;
Oxford, P. J.; White, A. J. P. J. Am. Chem. Soc. 2006, 128, 7410-7411.
(5) Shafir, A.; Power, M. P.; Whitener, G. D.; Arnold, J. Organometallics
2000, 19, 3978-3982.
(7) Bott, R. K. J.; Schormann, M.; Hughes, D. L.; Lancaster, S. J.;
Bochmann, M. Polyhedron 2006, 25, 387-396.
(8) Sawamura, M.; Sasaki, H.; Nakata, T.; Ito, Y. Bull. Chem. Soc. Jpn.
1993, 66, 2725-2729.
(6) Shafir, A.; Fiedler, D.; Arnold, J. Dalton Trans. 2002, 555-560.
10.1021/om0607144 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/14/2006

Synthesis of 1,1′-Ferrocenediyl Salicylaldimine Ligands
Scheme 3. Synthesis of Compounds 3-6a
Organometallics, Vol. 26, No. 2, 2007 317
Scheme 4. Synthesis of Compounds 8 and 9
Scheme 5. Synthesis of Compound 10
The 1H NMR spectrum of 3 in CD2Cl2 contains four
multiplets (pseudotriplets) at 3.87, 4.26, 4.66, and 4.86 ppm. A
broad signal observed at 5.66 ppm arises from the OH proton
(resonance sharpens in d6-DMSO; δ 8.39), and a singlet at 9.80
ppm is attributable to the aldehydic proton. The 13C{1H} NMR
spectrum features six signals arising from the cyclopentadienyl
carbons and a signal at 186.4 ppm corresponding to the carbonyl
carbon. The IR spectrum also exhibits diagnostic stretches at
a
Reagents and conditions: (i) n-butyllithium, THF, -78 °C, 10
min; (ii) N,N-dimethylformamide, THF, rt, 20 h; (iii) Cu2O, acetic acid,
MeCN, reflux, 15 h; (iv) 10% aq KOH, MeOH, 40 °C, 10 min; CO2
(s); (v) 0.5 equiv of 1,2-phenylenediamine, H+, EtOH, 80 °C, 1.5 h;
(vi) 5: 2,6-diisopropylaniline, H+, EtOH, 80 °C, 3 h; 6: aniline, H+,
EtOH, 80 °C, 3 h.
1683 (νCdO) and 3500 (νO-H) cm-1
.
Having successfully isolated 3, we next attempted to convert
it into salen-like proligands. However, the condensation of 3
with either 1,2-ethylenediamine or trans-(+/-)-1,2-diaminocy-
clohexane (0.5 equiv) led to intractable product mixtures
(spectroscopic analysis of which provided no evidence for
formation of the bis(imino alcohol)s). The analogous reaction
with 1,2-phenylenediamine also failed to produce the bis(imine),
instead generating the disubstituted benzimidazole 4 as an
orange precipitate in 60% yield (Scheme 3). The isolation of 4
is consistent with the reported formation of N-ferrocenylmethyl-
2-ferrocenylbenzimidazole from the reaction of ferrocenecar-
baldehyde with 1,2-phenylenediamine.12
acid. Condensation with ethylenediamine gave the potentially
tetradentate C2-symmetric proligand V. However, this compound
is extremely air and moisture sensitive and no coordination
chemistry or catalysis was therefore attempted. More recently,
variants of V featuring a carbon spacer between the cyclopen-
tadienyl ring and the hydroxyl substituent have been reported
by Bildstein and co-workers: this modification renders the
ligands far more stable to air oxidation (although at the time of
writing complexation studies have not been described).9
Prompted by the report of Bildstein,9 here we disclose our
investigations into the synthesis of ferrocenediylaldimines
derived from a new 1,1′-ferrocenediyl analogue of salicylalde-
hyde, namely, 1′-hydroxyferrocenediylcarbaldehyde. In addition,
titanium bis(isopropoxide) complexes with these proligands have
been synthesized. Preliminary data concerning their ability to
initiate the ring-opening polymerization of rac-lactide (rac-LA)
are also presented.
The synthesis of bidentate salicylaldimine ligands proceeds
in a more straightforward manner. Hence, N-(2,6-diisopropyl-
phenyl)-{1′-(hydroxy)ferrocenyl}aldimine, 5, was synthesized
in 85% yield by heating equimolar amounts of 3 with 2,6-
diisopropylaniline in ethanol at 80°C. N-(Phenyl)-{1′-(hydroxy)-
ferrocenyl}aldimine, 6, was prepared in an analogous fashion
(82%). Both 5 and 6 were found to be air stable and could be
stored in air for several days with no noticeable decomposition.
Complexation Studies. The early transition metal coordina-
tion chemistry of 5 and 6 has been investigated by treatment
with Ti(OiPr)4. For comparison, the corresponding complexation
of a recently reported 1-phosphino-1′-hydroxyferrocene ligand
(7)11 is also described here. Thus CH2Cl2 solutions of 5, 6, or
7 (2.0 equiv) were added to Ti(OiPr)4 and stirred at room
temperature overnight to afford compounds 8, 9, and 10,
respectively (Schemes 4 and 5).
Results and Discussion
Ligand Syntheses. The synthesis of the 1,1′-ferrocenediyl
analogue of salicylaldehyde, 1′-hydroxyferrocenediylcarbalde-
hyde, 3, was successfully achieved via the route shown in
Scheme 3. Hence, 1′-(bromo)ferrocenecarbaldehyde, 1,10 was
refluxed with 1.3 equiv of acetic acid and 0.7 equiv of copper-
(I) oxide in acetonitrile for 15 h to yield 2 as a brown oil that
crystallized on standing in ca. 50% yield. Hydrolysis of the
acetate moiety was achieved by dissolving 2 in a 1:1 mixture
of 10% aqueous potassium hydroxide solution and methanol
and stirring at 40 °C for 70 min. The solution was then cooled
to room temperature and solid CO2 added slowly to lower the
pH until a red precipitate was observed. This precipitate was
isolated to yield 3 as a red powder in 95% yield. In common
with other 1′-substituted hydroxyferrocenes,11 3 can be stored
in air for some days with no noticeable decomposition.
The 1H NMR spectrum of 8 features broad resonances
consistent with a fluxional solution state structure. Nevertheless,
the hydroxyferrocene aldiminate signals are clearly discernible
i
including the Pr methyl groups (a doublet at 1.15 ppm), the
associated methine resonance (δ 3.01), and four multiplets for
the ring protons (3.98, 4.27, 4.55, and 4.81 ppm). Only one
imine resonance is observed (7.99 ppm), consistent with a trans
planar or an R-cis ligand conformation. Although the OiPr
methine resonance is obscured by the cyclopentadienyl protons,
the methyl doublet is observed, overlapping with the aryl-iPr
(9) Wo¨lfle, H.; Kopacka, H.; Wurst, K.; Ongania, K.-H.; Go¨rtz, H.-H.;
Preishuber-Pflu¨gl, P.; Bildstein, B. J. Organomet. Chem. 2006, 691, 1197-
1215.
(10) Dong, T. Y.; Lai, L.-L. J. Organomet. Chem. 1996, 509, 131-134.
(11) Atkinson, R. C. J.; Gibson, V. C.; Long, N. J.; White, A. J. P.;
Williams, D. J. Dalton Trans. 2004, 1823-1826.
(12) Benito, A.; Martinez-Manez, R.; Paya, J.; Soto, J.; Tendero, M. J.
L.; Sinn, E. J. Organomet. Chem. 1995, 503, 259-263.

318 Organometallics, Vol. 26, No. 2, 2007
Atkinson et al.
Table 1. Polymerization Data for the Ring-Opening of
rac-LA Using 8-10a
% conversionb
c
c
d
initiator
6 h
24 h
Mn
Mw/Mn
Pr
kapp/h-1
8
9
10
63
58
95
96
94
96
9290
10 960
8970
1.17
1.27
1.17
0.50
0.50
0.67
0.14
0.12
0.53
b
1
a Toluene, 70 °C, [LA]0/[Ti] ) 100. Determined by H NMR spectro-
c
scopy (CDCl3). Determined by GPC (CHCl3 versus polystyrene calibrants).
dPr ) probability of racemic enchainment, determined by homonuclear
1
decoupled H NMR.
methyl doublet at δ 1.15. Elemental analysis results were also
consistent with the proposed formulation.
Figure 1. Plot of Mn vs monomer conversion for the polymerization
of rac-LA using 10 (toluene, 70 °C, [LA]0:[10] ) 100) (polydis-
persities shown in parentheses).
The 1H NMR spectrum of 9 is less readily assigned with even
broader resonances, consistent with increased mobility due to
the smaller N-substituent. The OiPr methyls are observed at 1.22
ppm (the methine proton is hidden by the ferrocenyl multiplet
resonances at 3.70, 4.04, 4.35, and 4.82 ppm). The presence of
the isopropoxide ligands is confirmed by 13C NMR (δ 25.6,
CH(CH3)3; 81.5, CHMe2). The imine protons give rise to a
single broad signal at 8.37 ppm. Despite the overall similarity
1
to the H and 13C spectra of 8, satisfactory elemental analysis
could not be obtained for this product, even after repeated
attempts at purification. Although we acknowledge that the
smaller steric bulk of 6 relative to 5 may lead to complications
such as tris(chelation), the similar lactide polymerization
behavior exhibited by both 8 and 9 (Vide infra) is further
evidence that the two titanium complexes share a common
structural motif.
Finally, the titanium bis-isopropoxide complex of 1′-(diphe-
nylphosphino)hydroxyferrocene, 7, was also synthesized by
stirring 2 equiv of the ligand with titanium(IV) isopropoxide in
CH2Cl2 at 30 °C for 15 h to afford complex 10 as a red powder
in 45% yield. 1H NMR spectral data (in toluene-d8) fully
supports the proposed four-coordinate structure (Scheme 5)
including multiplets at δ 3.67, 4.15, 4.21, and 4.35 (cyclopen-
tadienyl protons), a septet at δ 4.57, and a doublet at δ 1.22
(both due to the isopropoxide groups). 31P NMR also indicates
that the phosphine units are not bound to the titanium, giving
rise to a single resonance at -16.5 ppm (cf. corresponding
resonance for 7 in C6D6: -18.0 ppm), although the possibility
of hemilabile coordination in solution cannot be entirely
dismissed.
Figure 2. Plots of ln{[LA]0/[LA]t} vs time for initiators 8-10
(toluene, 70 °C, [LA]0:[Ti] ) 100).
unlike related (salen)Ti(OiPr)2 initiators, which in some cases
exhibit induction delays of up to 8 h under comparable
conditions.4
Furthermore, initiators 8-10 differ fundamentally from their
salen-supported analogues4 by generating two polyester chains
from every titanium center. Thus, Mn values reported in Table
1 are approximately half those recorded with (salen)Ti(OiPr)2
under comparable conditions (e.g., with salen ) (CH2NdCH-
3-tBu-2-O-C6H3)2, Mn ) 17 850 at 90% conversion).
1
As determined by homonuclear decoupled H NMR spec-
troscopy, complex 10 exhibits moderate heteroselectivity (Pr
) 0.67). Tellingly, the microstructure of the PLA samples using
8 is identical to that obtained from 9 (i.e., atactic, Pr ) Pm )
0.5014), and this testifies to the isostructural nature of these two
compounds. The similar chain lengths generated by these
initiators further support this conclusion, with the slightly
broader molecular weight distribution observed with 9 consistent
with increased transesterification possibly promoted by thes-
maller steric demands of its N-phenyl-substituted ancillary
ligands.
Repeated attempts to gain structural information on the
ligands and, more importantly, the titanium complexes unfor-
tunately failed largely due to decomposition of the samples in
solution over prolonged periods of time. We have, however,
reported the structural determination of ligand 7.11
Polymerization Studies. The ring-opening polymerization
of rac-LA has been investigated using 8, 9, and 10 as initiators
in toluene at 70 °C ([LA]0:[Ti] ) 100; see Table 1). All three
complexes initiate well-controlled polymerizations, characterized
by relatively narrow molecular weight distributions. This
behavior is exemplified in Figure 1, which shows a linear
increase in chain length with monomer conversion recorded with
initiator 10. Linear plots of ln{[LA]0/[LA]t} versus time (shown
in Figure 2) further indicate that the polymerizations are all first-
order in monomer and show that 10 is far more active than
either 8 or 9. Indeed, complex 10 required just 6 h to attain
high conversion and is therefore one of the most active known
titanium-based initiators for this process4,13 (possibly a repercus-
sion of the relatively low coordination number of the metal
center in this complex). In addition, no significant induction
period is observed prior to propagation for the three initiators,
(13) (a) Kim, Y.; Jnaneshwara, G. K.; Verkade, J. G. Inorg. Chem. 2003,
42, 1437-1447. (b) Kim, Y.; Verkade, J. G. Macromol. Rapid Commun.
2002, 23, 917-921. (c) Kim, Y.; Verkade, J. G. Organometallics 2002,
21, 2395-2399. (d) Russell, S. K.; Gamble, C. L.; Gibbins, K. J.; Juhl, K.
C. S.; Mitchell, W. S.; Tumas, A. J.; Hofmeister, G. E. Macromolecules
2005, 38, 10336-10340. (e) Davidson, M. G.; Jones, M. D.; Lunn, M. D.;
Mahon, M. F. Inorg. Chem. 2006, 45, 2282-2287. (f) Chmura, A. J.;
Davidson, M. G.; Jones, M. D.; Lunn, M. D.; Mahon, M. F. Dalton Trans.
2006, 887-889. (g) Gendler, S.; Segal, S.; Goldberg, I.; Goldschmidt, Z.;
Kol, M. Inorg. Chem. 2006, 45, 4783-4790. (h) Patel, D.; Liddle, S. T.;
Mungur, S. A.; Rodden, M.; Blake, A. J.; Arnold, P. L. Chem. Commun.
2006, 1124-1126.
(14) Pr and Pm are the probabilities of racemic and meso dyad formation.

Synthesis of 1,1′-Ferrocenediyl Salicylaldimine Ligands
Organometallics, Vol. 26, No. 2, 2007 319
Synthesis of N-{(CH2C5H4)Fe(C5H4OH)}-2-{(C5H4)Fe(C5H4-
OH)}-C7H4N2 (4). Compound 3 (0.57 g, 2.49 mmol) and 1,2-
phenylenediamine (0.13 g, 1.24 mmol, 0.5 equiv) were dissolved
in EtOH (20 cm3), and two drops of HCO2H were added. The
mixture was stirred at 80 °C for 1.5 h, after which time an orange
precipitate was visible. The solvent was removed in vacuo, and
the residue was washed with cold EtOH (5 cm3) to yield 4 as an
orange solid (0.40 g, 0.75 mmol, 60%).
Conclusion
The previously unreported 1′-hydroxyferrocenecarbaldehyde,
3, has been employed to prepare bidentate monoanionic sali-
cyaldiminate ligands, which, when complexed to Ti(IV) centers,
support well-behaved polymerization of rac-lactide. Further
studies into the coordination behavior of these ligands and their
redox chemistries are currently being pursued in our laboratories.
Anal. Calc for C28H24Fe2N2O2: C 63.19, H 4.55, N 5.26.
Found: C 63.27, H 4.54, N 5.17. 1H NMR δ (d8-THF) ppm: 3.66
(t, 2H, C5H4), 3.84 (t, 2H, C5H4), 3.94 (t, 2H, C5H4), 3.97 (t, 2H,
C5H4), 4.09 (m, 4H, C5H4), 4.42 (t, 2H, C5H4), 4.71 (t, 2H, C5H4),
5.16 (s, 2H, CH2), 7.21 (m, 2H, C6H4), 7.59 (m, 2H, C6H4), 9.60
(br s, 2H, OH). 13C{1H} NMR δ (d8-THF) ppm: 43.9 (CH2), 57.9,
62.9, 63.1, 64.3, 69.4, 70.2, 70.5, 72.3, 83.7, 122.0 (C5H4), 111.1,
119.3, 123.0, 124.2, 135.8, 142.6 (C6H4), 153.5 (CHN). IR(CH2-
Cl2) ν cm-1: 3265 (br s, O-H), 1459 (CdN). m/z: 532 (M+),
451 (M+ - C5H4OH), 319 (M+ - FcCH2OH).
Synthesis of N-(2,6-Diisopropylphenyl)-{1′-(hydroxy)ferro-
cenyl}aldimine, (C5H4OH)(C5H4CHdN-2,6-iPr2C6H3)Fe (5). Com-
pound 3 (0.270 g, 1.18 mmol) and 2,6-diisopropylaniline (0.22 cm3,
1.2 mmol) were dissolved in EtOH (10 mL), and 1 drop of HCO2H
was added. The solution was stirred at 80 °C for 3 h and then at
room temperature overnight. The solvent was removed in vacuo,
and the resulting solid was washed with hexane (7 cm3) to yield 5
as a brown powder (0.390 g, 1.01 mmol, 85%).
Experimental Section
General Procedures. All preparations were carried out using
standard Schlenk techniques. All solvents were distilled over
standard drying agents under nitrogen directly before use, and all
reactions were carried out under an atmosphere of nitrogen.
Chromatographic separations were carried out on silica gel (Kie-
selgel 60, 70-230 mesh) unless otherwise stated. 1H NMR spectra
were recorded using a Delta upgrade on a JEOL EX270 MHz
spectrometer operating at 270.1 MHz (1H). 13C{1H} NMR spectra
were obtained on either a Bruker DRX-400 or AM-500 spectrom-
eter. Chemical shifts (δ) are reported in ppm using the residual
proton impurities in the NMR solvent as an internal reference.
Infrared spectra were recorded as solutions in CH2Cl2 using a
Perkin-Elmer 983 spectrometer. Mass spectra were recorded using
EI or positive FAB methods, on an Autospec Q mass spectrometer.
GPC measurements were performed in HPLC grade CHCl3 at 1.0
mL min-1 using a Polymer Laboratories LC1220 HPLC pump and
a Spark Midas autosampler connected to two 5 µm columns (300
× 7.5 mm) and a Shodex RI-101 differential refractometer. The
columns were calibrated with polystyrene standards ranging in
molecular weight from 2.9 × 103 to 3.2 × 106 amu, and
chromatograms were analyzed using Cirrus software (Polymer
Laboratories) in order to establish molecular weights and polydis-
persities.
Synthesis of 1′-(Acetoxy)ferrocenecarbaldehyde, (C5H4OCO-
CH3)(C5H4CHO)Fe (2). A mixture of 110 (1.00 g, 3.42 mmol),
acetic acid (0.25 cm3, 4.4 mmol, 1.3 equiv, previously dried over
molecular sieves), and Cu2O (0.34 g, 2.4 mmol, 0.7 equiv) was
heated to reflux in MeCN (60 cm3) for 15 h under nitrogen. After
cooling, CH2Cl2 was added (100 cm3) and the mixture was filtered.
The residue was then washed with an additional 30 cm3 CH2Cl2.
The filtrate and washings were combined, extracted with water (70
cm3), and dried over MgSO4. The solvent was removed in vacuo,
and the resultant crude oil was purified by column chromatography
(silica, hexane/EtOAc, 2:1) to yield 2 as an orange oil (0.47 g, 1.7
mmol, 51%).
Anal. Calc for C13H12FeO3: C 57.39, H 4.45. Found: C 57.41,
H 4.63. 1H NMR δ (CDCl3) ppm: 2.13 (s, 3H, CH3), 4.04 (t, 2H,
C5H4), 4.57 (t, 2H, C5H4), 4.63 (t, 2H, C5H4), 4.86 (t, 2H, C5H4),
9.92 (s, 1H, CHO). 13C{1H} NMR δ (CDCl3) ppm: 21.1 (CH3),
62.1, 64.7, 70.7, 74.2, 80.4, 116.4 (C5H4), 168.7 (OCdCH3), 193.3
(CHO). IR (CH2Cl2) ν cm-1: 1722 (CdO), 1682 (CdO). m/z: 272
(M+), 230 (M+ - OAc), 202 (M+ - OAc - CHO).
Synthesis of 1′-(Hydroxy)ferrocenecarbaldehyde, (C5H4OH)-
(C5H4CHO)Fe (3). Compound 2 (0.470 g, 1.73 mmol) was
dissolved in a mixture of 10% aqueous KOH (10 cm3) and MeOH
(10 cm3) and stirred at 40 °C for 70 min. The solution was cooled,
and solid CO2 was added slowly until a red precipitate was
observed. The reaction mixture was extracted with Et2O (3 × 10
cm3) and the organic layer separated and dried over Na2SO4. The
solvent was then removed in vacuo to yield 3 as a red powder (0.36
g, 1.6 mmol, 95%).
Anal. Calc for C23H27FeNO: C 70.96, H 6.99, N 3.60. Found:
1
C 70.98, H 7.10, N 3.57. H NMR δ (C6D6) ppm: 1.22 (d, 12H,
CH3), 3.28 (t, 2H, CHMe2), 4.04 (br t, 2H, C5H4), 4.30 (br t, 2H,
C5H4), 4.40 (br t, 2H, C5H4), 4.87 (br t, 2H, C5H4), 6.99 (m, 1H,
C6H3), 7.31 (m, 2H, C6H3), 7.89 (s, 1H, CHN). 13C{1H} NMR δ
(C6D6) ppm: 23.9 (CH3), 28.1 (CHMe2), 58.5, 63.1, 70.3, 72.8
(C5H4), 123.5, 124.8, 138.7, 149.5 (C6H3), 164.8 (CHN). IR (CH2-
Cl2) ν cm-1: 3575 (s, O-H), 1633 (CdN). m/z: 389 (M+), 372
(M+ - OH), 202 (M+ - CHdNAr).
Synthesis of N-(Phenyl)-{1′-(hydroxy)ferrocenyl}aldimine,
(C5H4OH)(C5H4CHdNPh)Fe (6). Compound 3 (0.18 g, 0.78
mmol) and aniline (0.07 cm3, 0.8 mmol) were dissolved in EtOH
(10 mL), and 1 drop of HCO2H was added. The solution was stirred
at 80 °C for 3 h and then at room temperature overnight. The solvent
was removed in vacuo, and the resulting solid was washed with
hexane (7 cm3) to yield 6 as a red-brown powder (0.19 g, 0.63
mmol, 82%).
Anal. Calc for C17H15FeNO: C 66.91, H 4.95, N 4.59. Found:
1
C 66.82, H 4.95, N 4.47. H NMR δ (d8-THF) ppm: 3.75 (t, 2H,
C5H4), 4.04 (t, 2H, C5H4), 4.38 (t, 2H, C5H4), 4.75 (t, 2H, C5H4),
7.08 (d, 3H, C6H5), 7.27 (t, 2H, C6H5), 8.28 (s, 1H, CHN). 13C-
{1H} NMR δ (d8-THF) ppm: 58.1, 63.3, 70.4, 72.1, 82.5, 114.9
(C5H4), 121.4, 125.3, 129.5, 154.6 (C6H5), 161.6 (CHN). IR (CH2-
Cl2) ν cm-1: 3570 (br s, O-H), 1624 (CdN). m/z: 305 (M+).
Synthesis of [(C5H4O)(C5H4CHdN-2,6-iPr2C6H3)Fe]2Ti(OiPr)2
(8). Compound 5 (0.080 g, 0.21 mmol) was dissolved in CH2Cl2
(10 cm3) and added via cannula to a solution of Ti(OiPr)4 (0.030
g, 0.10 mmol) in CH2Cl2 (10 cm3). The reaction mixture was stirred
at room temperature for 15 h. The resulting dark red solution was
evaporated to dryness and the residue coevaporated with pentane
(2 × 10 cm3) to yield 8 as a dark red powder (0.055 g, 0.058 mmol,
58%).
Anal. Calc for C52H66Fe2N2O4Ti: C 66.26, H 7.06, N 2.97.
Found: C 66.23, H 6.99, N 2.95. 1H NMR δ (CD2Cl2) ppm: 1.15
(2 × d, 36H, CH3), 3.01 (sept, 4H, ArCHMe2), 3.98 (br t, 4H, C5H4),
4.27 (br t, 4H, C5H4), 4.55 (br t, 4H, C5H4), 4.81 (br t, 4H, C5H4),
7.06 (m, 6H, C6H3), 7.99 (s, 2H, CHN). 13C{1H} NMR δ (CD2-
Cl2) ppm: 23.8, 25.9 (CH3), 28.0, 80.2 (CHMe2), 60.5, 63.5, 69.6,
73.5 (C5H4), 123.2, 123.9, 138.2, 150.1 (C6H3), 163.0 (CHN). m/z:
389 (L+).
Anal. Calc for C11H10FeO2: C 57.43, H 4.38. Found: C 57.52,
H 4.52. 1H NMR δ (CD2Cl2) ppm: 3.87 (t, 2H, C5H4), 4.26 (t, 2H,
C5H4), 4.66 (t, 2H, C5H4), 4.86 (t, 2H, C5H4), 5.66 (br s, 1H, OH),
9.80 (s, 1H, CHO). 13C{1H} NMR δ (CDCl3) ppm: 58.7, 63.8,
70.9, 74.3, 79.8, 123.8 (C5H4), 186.4 (CHO). IR (THF) ν cm-1
3500 (OH), 1683 (CdO). m/z: 230 (M+), 202 (M+ - CHO).
:

320 Organometallics, Vol. 26, No. 2, 2007
Atkinson et al.
Synthesis of [(C5H4O)(C5H4CHdPh)Fe]2Ti(OiPr)2 (9). Com-
pound 6 (0.080 g, 0.26 mmol) was dissolved in CH2Cl2 (10 cm3)
and added via cannula to a solution of Ti(OiPr)4 (0.038 g, 0.13
mmol) in CH2Cl2 (10 cm3). The reaction mixture was stirred at
room temperature for 15 h. The resulting dark red solution was
evaporated to dryness and the residue coevaporated with pentane
(2 × 10 cm3) to yield 9 as a brown powder (0.040 g, 0.052 mmol,
40%).
1H NMR δ (CD2Cl2) ppm: 1.22 (CH3), 3.70 (br, 4H, C5H4),
4.04 (br, 4H, C5H4), 4.35 (br, 4H, C5H4), 4.82 (br, 4H, C5H4), 7.12
(m, 3H, C6H5), 7.33 (m, 2H, C6H5), 8.37 (s, 2H, CHN). 13C{1H}
NMR δ (CD2Cl2) ppm: 25.6 (CH3), 81.5 (CHMe2), 60.6, 63.7, 70.2,
73.9 (C5H4), 121.0, 125.5, 129.4, 154.4 (C6H5), 162.0 (CHN). m/z:
307 (L+).
Synthesis of [(C5H4O)(C5H4PPh2)Fe]2Ti(OiPr)2 (10). 1′-
(Diphenylphosphino)hydroxyferrocene11 (7) (0.100 g, 0.26 mmol)
was dissolved in CH2Cl2 (10 cm3) and added via cannula to a
solution of Ti(OiPr)4 (0.037 g, 0.13 mmol) in CH2Cl2 (10 cm3).
The reaction mixture was stirred at 30 °C for 15 h. The resulting
deep red solution was evaporated to dryness and the residue washed
with pentane (20 cm3). The mixture was filtered and the residue
dried under vacuum to yield 10 as a deep red powder (0.055 g,
0.059 mmol, 45%).
Anal. Calc for C50H50Fe2O4P2Ti‚(CH2Cl2)0.75: C 60.95, H 5.19.
1
Found: C 60.81, H 5.39. H NMR δ (C6D5CD3) ppm: 1.22 (d,
6H, -OCH(CH3)2), 3.67 (t, 2H, C5H4), 4.15 (t, 2H, C5H4), 4.21 (t,
2H, C5H4), 4.35 (t, 2H, C5H4), 4.57 (m, 1H, -OCH(CH3)2), 7.10
(m, 6H, PC6H5), 7.55 (m, 4H, PC6H5). 13C{1H} NMR δ (CD2Cl2)
ppm: 25.5 (CH3), 60.3, 63.7, 64.0, 73.0, 73.9 (C5H4), 128.4, 129.1,
135.0 (C6H5). 31P{1H} NMR δ (C6D5CD3) ppm: -16.5. m/z: 386
(L+).
Acknowledgment. We acknowledge financial support from
the Department of Chemistry, Imperial College London.
OM0607144