Binucleating ligands: Synthesis of acyclic achiral and chiral Schiff base-pyridine and Schiff base-phosphine ligands

Article abstract of DOI:10.1021/jo961020f

5-tert-Butyl-3-(2′-pyridyl)salicyaldehyde and 5-tert-butyl-3-(diphenylphosphino)salicyaldehyde were synthesized from 4-tert-butylphenol in good overall yields. Condensation of the salicyaldehydes with 2,3-diamino-2,3-dimethylbutane afforded the desired dinucleating Schiff base-pyridine and Schiff base-phosphine ligands, respectively. 5-tert-Butyl-3-(2′-pyridyl)salicyaldehyde reacted with optically active 1,2-diaminocyclohexanes to give chiral dinucleating Schiff base-pyridine ligands.

Full text of DOI:10.1021/jo961020f

8414
J . Org. Chem. 1996, 61, 8414-8418
Bin u clea tin g Liga n d s: Syn th esis of Acyclic Ach ir a l a n d Ch ir a l
Sch iff Ba se-P yr id in e a n d Sch iff Ba se-P h osp h in e Liga n d s
Fung Lam, J ia Xi Xu, and Kin Shing Chan*
Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong
Received May 31, 1996X
5-tert-Butyl-3-(2′-pyridyl)salicyaldehyde and 5-tert-butyl-3-(diphenylphosphino)salicyaldehyde were
synthesized from 4-tert-butylphenol in good overall yields. Condensation of the salicyaldehydes
with 2,3-diamino-2,3-dimethylbutane afforded the desired dinucleating Schiff base-pyridine and
Schiff base-phosphine ligands, respectively. 5-tert-Butyl-3-(2′-pyridyl)salicyaldehyde reacted with
optically active 1,2-diaminocyclohexanes to give chiral dinucleating Schiff base-pyridine ligands.
In tr od u ction
The synthesis of dinucleating ligands capable of bind-
ing metal ions in close proximity has continued to arouse
interest among chemists. Since 1970,1,2 the preparation
of dinucleating ligands plays a central role in bimetallic
chemistry which is currently the area of extensive
investigation due to its importance in the fields of
bioinorganic chemistry, homogeneous catalysis, and mag-
netic exchange processes.3 The design of dinucleating
system determines the nature of metal ions to be incor-
porated, coordination environment, and metal-metal
separation of the bimetallic complexes. Several kinds of
dinucleating ligands have been reported1,2 to afford
binuclear complexes. Previous efforts have been focused
on the synthesis and complexation of a vast array of
symmetrical dinucleating macrocycles due to the relative
ease of their synthesis.4 However, this kind of ligand is
usually more useful in the preparation of homobimetallic
complexes while the synthesis of heterobimetallic com-
plexes is better accomplished by using the heteroditopic
ligands.5 An important category of the heteroditopic
ligands is the Schiff base-crown ether macrocyclic com-
pounds.6 The Schiff base-crown ether ligands have been
demonstrated to complex soft and hard metal ions in
their soft (Schiff base) and hard (crown ether) cavities.
F igu r e 1.
Another type is the acyclic Schiff base-carboxylic acids
which were reported to complex soft and hard metal ions
selectively.7 While the aforementioned heteroditopic
ligands bear hard binding sites coupled to the Schiff base
moieties, here we report the synthesis of achiral and
chiral acyclic side-off Schiff base-pyridine and Schiff
base-phosphine ligands containing the relatively softer
pyridyl and phosphino groups which may allow complex-
ation of low valent transition metal ions.8 The general
structure of the dinucleating ligands is shown in Figure
1.
As shown in Figure 1, in these phenolic bridged
dinucleating ligands, the Schiff base moieties provide the
internal salen type N2O2 cavity while the functional
groups X serve as the extra binding ends to constitute
the external O2X2 donor set. Schiff base ligands are well
known to afford stable transition metal complexes,9 and
their monometallic chemistry has been extensively stud-
ied.10 The dinucleating properties of our Schiff base
system are attributed to the donor groups X (X )
2-pyridyl or diphenylphosphino) at 3′-positions giving rise
to the external O2X2 binding sites. While the O2N2 sites
of the pyridyl derivative are expected to bind first row
transition metal ions, the O2P2 system of the Schiff base-
phosphine ligand can complex the softer second and third
row transition metal ions as well.11 In order to enhance
the solubility of the ligands and their bimetallic com-
plexes in organic solvents, the lipophilic tert-butyl groups
and the tetramethylethylene bridge are introduced in our
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) (a) Casellato, U.; Vigato, P. A.; Vidali, M. Coord. Chem. Rev.
1977, 23, 31. (b) Casellato, U.; Vigato, P. A.; Fenton, D. E.; Vidali, M.
Chem. Soc. Rev. 1979, 8, 199. (c) Lehn, J . M. Pure Appl. Chem. 1980,
52, 2441.
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Coord. Chem. Rev. 1987, 77, 165. (b) Vigato, P. A.; Tamburini, S.;
Fenton, D. E. Coord. Chem. Rev. 1990, 106, 25. (c) Fraser, C.; J ohnston,
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van Staveren, C. J .; Gerritsma, G. J .; Reinhoudt, D. N. Inorg. Chem.
1989, 28, 1133. (b) van Staveren, C. J .; van Eerden, J .; van Veggel, F.
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Reinhoudt, D. N. Angew. Chem., Int. Ed. Engl. 1989, 28, 746.
S0022-3263(96)01020-1 CCC: $12.00 © 1996 American Chemical Society

Binucleating Ligands
J . Org. Chem., Vol. 61, No. 24, 1996 8415
Sch em e 1
Sch em e 2
ligand design. 1,2-Diaminocyclohexanes, readliy avail-
able chiral diamines, are employed for the synthesis of
chiral ligands.
The class of chiral dinucleating ligands is especially
interesting since the asymmetric induction coupled with
bimetallic cooperativity in a multiple redox reaction for
these heterobimetallic complexes would be promising
biomimetics as well as potential asymmetric catalysts
such as aerobic oxidation catalysts.12 We now disclose
our full results in the synthesis of acyclic achiral and
chiral Schiff base-pyridine and achiral Schiff base-
phosphine ligands.13
as shown in Scheme 2. Bromination of 4-tert-butylphenol
(1) gave a 96% yield of the dibromophenol 8 which was
then methylated with Me2SO4 to afford the dibromo-
anisole 9 in 94% yield. Lithiation of 7 with n-BuLi in
Et2O at -78 °C followed by quenching with PPh2Cl
produced (3-bromo-5-tert-butyl-2-anisyl)diphenylphos-
phine (10) in 75% yield. 9 was lithiated with n-BuLi/
TMEDA in Et2O at -78 °C and was subsequently
quenched with anhydrous DMF to afford the o-methoxy-
benzaldehyde 11 in 70% yield. Without the addition of
TMEDA, no aldehyde 11 was formed even though the
lithiation was succcessful as evidenced by the formation
of deuteriated arene upon trapping reaction with D2O.
Demethylation of 11 with BBr3 yielded the salicyaldehyde
11 in 80% yield which was then condensed with 2,3-
diamino-2,3-dimethylbutane to afford ligand 13 in 70%
yield.
Resu lts a n d Discu ssion
The dinucleating ligands 7 and 13 were prepared by
the condensation of 2,3-diamino-2,3-dimethylbutane and
optically active 1,2-diaminocyclohexanes with 5-tert-
butyl-3-(2′-pyridyl)salicyaldehyde and 5-tert-butyl-3-
(diphenylphosphino)salicyaldehyde which were synthe-
sized according to Schemes 1 and 2.
As shown in Scheme 1, the ligand 7 was synthesized
from 4-tert-butylphenol in four steps in 50% overall yield.
Formylation of 4-tert-butylphenol with formaldehyde14 in
the presence of SnCl4 afforded the salicyaldehyde 2 which
was then brominated with Br2/AcOH15 to give 3-bromo-
5-tert-butylsalicyaldehyde (3) in 95% yield. Stille type
palladium-catalyzed cross coupling16 of 3 with 2-(tri-n-
butylstannyl)pyridine17 in THF produced 5-tert-butyl-3-
(2′-pyridyl)salicyaldehyde (5) in 93% yield. Condensation
of 5 with 2,3-diamino-2,3-dimethylbutane18 afforded the
desired dinucleating ligand 7 in 76% yield.
The enantiomeric pair of chiral acyclic pyridine ligands
was prepared via the condensation of 5-tert-butyl-3-(2′-
pyridyl)salicyaldehyde (5) with either (R,R)- and (S,S)-
1,2-diaminocyclohexanes in the form of mono(+)-tar-
trates19 in 85 and 86% yield, respectively (Scheme 3). 16
and 17 showed equal but opposite sign of optical rotation
confirming their enantiomeric relationship.
The characteristic functionalities of Schiff base ligands
include the hydrogen bonded hydroxyl groups and the
azomethine groups (-CdN-). These functional groups
were identified in 7, 13, 16, and 17 by comparing the
spectroscopic data with literature values of similar
systems.1a,6 Broad peaks were observed in the range
3600-2400 cm-1 in their IR spectra which strongly
suggested the presence of hydrogen bonded OH groups.
Low field broad singlets appeared at δ 14.76, 14.37, 14.14,
Similarly, ligand 13 was prepared by the condensation
reaction with 5-tert-butyl-3-(diphenylphosphino)salicy-
aldehyde (11) in six steps starting from 4-tert-butylphenol
(12) For leading references: Larrow, J . F.; J acobsen, E. N. J . Am.
Chem. Soc. 1994, 116, 12919.
(13) Lam, F.; Chan, K. S. Tetrahedron Lett. 1996, 35, 2439.
(14) Casiraghi, G.; Casnati, G.; Puglia, G.; Sartori, G.; Terenghi, G.
J . Chem. Soc. Perkin Trans. 1 1980, 1862.
(15) Wriede, U.; Fernandez, M.; West, K. F.; Harcourt, D.; Moore,
H. W. J . Org. Chem. 1987, 52, 4485.
1
and 14.14 in the H NMR spectra of 7, 13, 16, and 17
respectively, and supported hydrogen bonded phenolic
protons. In the IR spectra of these compounds, strong
(16) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(17) J utzi, P.; Gilge, U. J . Organomet. Chem. 1983, 246, 163.
(18) Sayre, R. J . Am. Chem. Soc. 1955, 77, 6899.
(19) Larrow, J . F.; J acobsen, E. N. Gao, Y.; Hong, Y.; Nie, X.; Zepp,
C. M. J . Org. Chem. 1994, 59, 1939.

8416 J . Org. Chem., Vol. 61, No. 24, 1996
Lam et al.
Sch em e 3
Sch em e 4
at 250 MHz. Chemical shifts (δ) were reported in ppm
downfield from internal standard tetramethylsilane, and
coupling constants (J ) were reported in hertz. 13C Spectra
were obtained at 62.9 or 125 MHz. Mass spectra (EI) were
obtained at 70 eV, and FABMS was recorded using m-
nitrobenzyl alcohol (NBA) as the matrix at National Tsing Hua
University, Taiwan. Elemental analyses were performed by
the Medac Ltd, Department of Chemistry, Brunel University,
United Kingdom. Specific rotation were determined on a
polarimeter.
Unless otherwise noted, all materials were obtained from
commercial suppliers and used without further purification.
2-(Tributylstannyl)pyridine (4),17 2,3-diamino-2,3-dimethyl-
butane (6),18 2,6-dibromo-4-tert-butylphenol (8),23 2,6-dibromo-
4-tert-butylanisole (9),24 (R,R)-1,2-diammoniocyclohexane mono-
(+)-tartrate,19 and (S,S)-1,2-diammoniocyclohexane mono-
(-)-tartrate salt (5)19 were prepared according to the literature
methods. Tetrahydrofuran (THF) and diethyl ether were
distilled from sodium benzophenone ketyl immediately prior
to use. Hexane was distilled over calcium chloride, and toluene
was distilled from sodium. Silica gel (70-230 mesh) was used
for column chromatography. Thin layer chromatography was
performed on Merck precoated silica gel 60 F254 plates. All
melting points were uncorrected.
signals at 1620-1630 cm-1 were observed and likely
arose from the CdN stretch of the imine linkage. The
singlets at δ 8.3-8.4 in their NMR spectra, indicating
the presence of azomethine protons,20 substantiated the
IR assignment.
Compounds 7 and 13 also exhibited characteristic UV-
vis spectra of Schiff base ligands. Schiff base ligands
exhibit two absorption peaks at a lower energy region
(>300 nm). Bosnich21 has made general assignments of
the electronic transitions. The stronger, higher energy
peak is attributed to the π f π* transition of the
azomethine chromophore while the weaker and less
energetic peak is assigned to the n f π* transition
involving the promotion of the lone pair electron of
azomethine nitrogen atom to the antibonding π orbital
associated with the azomethine group. Both 7 and 13
exhibited a pair of absorption bands in their electronic
spectra. The strong peak at 340-350 nm and the less
intense peak at 430-440 nm corresponded well to the
expected π f π* and n f π* transitions of Schiff base
derivatives.
3-Br om o-5-ter t-bu tyl-2-h yd r oxyben za ld eh yd e (3). To
a solution of 219 (0.52 g, 2.93 mmol) and sodium acetate (0.44
g, 5.37 mmol) in glacial acetic acid (13 mL), was added bromine
(0.47 g, 2.93 mmol) in acetic acid (5 mL) dropwise within 0.5
h. The mixture was heated at 50 °C for 12 h. The solvent
was removed in vacuo, and the residue was poured into water
and then extracted with dichloromethane. The organic layer
was washed with Na2S2O5 and NaHCO3 solution and dried
(MgSO4). The solvent was removed, and the crude product
was purified by column chromatography using hexane/ethyl
acetate (5:1) as the eluent (Rf ) 0.70) to give pale yellow solids
Preliminary studies showed that both ligands 16 and
17 formed mononuclear metal complexes with copper and
nickel ions in high yields (Scheme 4). Both homo and
hetero binuclear complexes were prepared, and the full
characterization by X ray crystallography as well as their
catalytic activity are in progress.
Con clu sion
In conclusion, we have synthesized acyclic chiral and
achiral dinucleating ligands of Schiff bases of pyridine
and phosphine groups. Preliminary complexation studies
show that these ligands formed heterobimetallic com-
plexes with Ni and Cu.22 Further studies of the bi-
metallic chemistry of these ligands are in progress.
1
of 15 (0.71 g, 95%): mp 81-83 °C (CH2Cl2/hexane); H NMR
(CDCl3, 250 MHz) δ 1.30 (s, 9 H), 7.48 (d, 1 H, J ) 2.2 Hz),
7.79 (d, 1 H, J ) 2.2 Hz), 9.82 (s, 1 H), 11.39 (s, 1 H); mass
spectrum m/ e (% relative intensity) 258 (M+ + 2, 35), 256 (M+,
35), 243 (100), 241 (100); IR (film) 3600-3200, 2958, 1656,
1456, 736, 724 cm-1. Anal. Calcd for C11H13BrO2: C, 51.38;
H, 5.10. Found: C, 51.20; H, 5.08.
3-(2′-P yr id yl)-5-ter t-bu tyl-2-h yd r oxyben za ld eh yd e (5).
Salicyaldehyde 3 (0.040 g, 0.156 mmol), 2-(tri-n-butylstannyl)-
pyridine (0.17 g, 0.468 mmol), and Pd(PPh3)4 (0.018 g, 0.0156
mmol) were dissolved in anhydrous THF (5 mL). The mixture
was degassed by the freeze-thaw-pump method (three cycles)
Exp er im en ta l Section
UV-vis spectra were recorded using CH2Cl2 as the solvent.
IR spectra were recorded on a FT-IR spectrophotometer as
neat film on KBr plates. 1H NMR spectra were recorded either
(20) Alyea, E. C.; Malek, A. Can. J . Chem. 1975, 53, 939.
(21) Bosnich, B. J . Am. Chem. Soc. 1968, 90, 627.
(22) Lam, F.; Wang, R.-J .; Mak, T. C. W.; Chan, K. S. J . Chem. Soc.,
Chem. Commun. 1994, 2439.
(23) Kajigaeshi, S.; Kakinimi, T.; Tokiyama, H.; Hirakawa, T.;
Okamoto, T. Chem. Lett. 1987, 627.
(24) Koike, K.; Murata, K.; Kosugi, K. Chem. Abstr. 1991, 114,
101336s.

Binucleating Ligands
J . Org. Chem., Vol. 61, No. 24, 1996 8417
IR (film) 2963, 1687, 1586, 1247 cm-1
and then heated at 100 °C under nitrogen for 72 h. The
solvent was removed at reduced pressure, and the residue was
purified by column chromatography using hexane/ethyl acetate
(10:1) as the eluent to give yellow solids (Rf ) 0.20) as the
product (0.037 g, 93%): mp 89-91 °C (CH2Cl2/hexane); 1H
NMR (CDCl3, 250 MHz) δ 1.37 (s, 9 H), 7.30 (m, 1 H), 7.89
(td, 1 H, J ) 1.8, 8.3 Hz), 7.90 (d, 1 H, J ) 2.5 Hz), 7.99 (d, 1
H, J ) 8.3 Hz), 8.09 (d, 1 H, J ) 2.5 Hz), 8.56 (d, 1 H, J ) 4.3
Hz), 10.60 (s, 1 H) 15.09 (bs, 1 H); 13C NMR (CDCl3, 62.9 MHz)
δ 31.30, 34.24, 119.57, 120.10, 122.01, 124.25, 127.13, 129.75,
137.93, 140.05, 145.89, 157.00, 161.20, 190.80; mass spectrum
m/ e (% relative intensity) 255 (M+, 8), 240 (22), 227 (100), 212
(56); IR (film) 3600-2400, 1680, 1597, 1480, 1255 cm-1. Anal.
Calcd for C16H17NO2: C, 75.27; H, 6.71; N, 5.49. Found: C,
74.89; H, 6.60; N, 5.42.
. Anal. Calcd for
C24H25O2P: C, 76.58; H, 6.69. Found: C, 76.61; H, 6.73.
5-ter t-Bu tyl-3-(d ip h en ylp h osp h in o)-2-h yd r oxyben za l-
d eh yd e (12). To a solution of 11 (0.83 g, 2.2 mmol) in
anhydrous CH2Cl2 (20 mL) at -78 °C under nitrogen, was
added slowly BBr3 (2.8 g, 11 mmol) in anhydrous CH2Cl2 (20
mL) via a syringe. The yellow solution was stirred at -78 °C
under nitrogen for 2 h and allowed to stir for further 10 h at
room temperature. The mixture was added to ice-water and
extracted with CH2Cl2. The aqueous layer was neutralized
by saturated NaHCO3 and extracted with CH2Cl2. The dichlo-
romethane extract was dried over Na2SO4 to give a yellow oil
which was purified by column chromatography (hexane-ethyl
acetate 10:1) to afford a pale yellow solid (0.63 g, 80%): Rf )
1
0.60; mp 110-112 °C (CH2Cl2/hexane); H NMR (CDCl3, 250
MHz) δ 1.28 (s, 9 H), 7.06 (dd, 1 H, J ) 2.5, 4.8 Hz), 7.37 (m,
10 H), 7.54 (d, 1 H, J ) 2.5 Hz), 9.90 (s, 1 H), 11.43 (d, 1 H, J
) 2.8 Hz); 13C NMR (CDCl3, 62.9 MHz) δ 30.87, 33.99, 119.34,
122.47, 125.62 (d, J CP ) 25.2 Hz), 127.53, 128.48 (d, J CP ) 6.9
Hz), 128.72 (d, J CP ) 22.0 Hz), 130.72 (d, J CP ) 14.5 Hz), 133.81
(d, J CP ) 20.8 Hz), 135.79 (d, J CP ) 11.3 Hz), 138.94, 172.77,
161.13 (d, J CP) 17.0 Hz), 199.80; mass spectrum m/ e (relative
intensity) 362 (M+, 36), 334 (100); calcd for C23H23O2P: 362.1436;
Bis[5′-ter t-bu tyl-3′-(2′′-p yr id yl)sa licylid en e]-1,1,2,2-tet-
r a m eth yleth ylen ed ia m in e (7). To a solution of 5 (0.042 g,
0.165 mmol) in refluxing absolute ethanol (5 mL) was added
slowly in 20 min 2,3-diamino-2,3-dimethylbutane (6) (0.0096
g, 0.083 mmol) in absolute ethanol (5 mL) to yield a yellow
solution. The solution was refluxed for 1 h. After cooling,
yellow crystals were collected by filtration. The rest of product
was obtained by cooling the filtrate at 0 °C for several hours
followed by filtration to afford totally 0.037 g of bright yellow
solids as the product (76%): mp 218-220 °C (ethanol); 1H
NMR (CDCl3, 250 MHz) δ 1.35 (s, 18 H), 1.41 (s, 12 H), 7.15-
7.20 (m, 2 H), 7.33 (d, 2 H, J ) 2.5 Hz), 7.69 (td, 2 H, J ) 1.9,
7.5 Hz), 7.96 (d, 2 H, J ) 2.5 Hz), 8.05 (d, 2 H, J ) 8.3 Hz),
8.44 (s, 2 H), 8.68 (d, 2 H, J ) 4.3 Hz), 14.76 (bs, 2 H); 13C
NMR (CDCl3, 62.9 MHz) δ 23.63, 32.14, 34.77, 65.82, 119.67,
122.15, 125.31, 127.66, 129.86, 131.51, 136.45, 141.57, 149.81,
156.65, 158.57, 162.48; mass spectrum m/ e (% relative inten-
sity) 590 (M+, 11); IR (film) 3600-2400, 2962, 1628, 1598,
1469, 1257 cm-1; UV-vis [λmax, nm (ꢀ, L mol-1 cm-1)] 342 (21.5
× 103), 434 (1.65 × 103). Anal. Calcd for C38H46N4O2‚1/2 H2O:
C, 76.09; H, 7.90; N, 9.34. Found: C, 76.13; H, 7.85; N, 9.35.
(3-Br om o-5-ter t-bu tyl-2-m eth oxyph en yl)diph en ylph os-
p h in e (10). To a solution of 924 (5.01 g, 15.6 mmol) in
anhydrous ether (20 mL) under nitrogen -78 °C was added
n-BuLi (1.6 M, 10 mL, 16.0 mmol) dropwise. The mixture was
stirred for 0.5 h at -78 °C to give a yellow solution to which
PPh2Cl (3.44 g, 15.6 mol) in anhydrous ether (10 mL) was
added dropwise at -78 °C under nitrogen. The solution was
allowed to warm up to room temperature and stirred for 2 h.
Dilute HCl (10 mL) was added to the solution at 5 °C. The
mixture was extracted with ether, and the organic layer was
collected and dried over MgSO4. After removal of solvent, a
pale yellow oil was obtained. White crystals were collected
by crystallization from ethanol, and the crude product from
the mother liquor was purified by column chromatography
using hexane/ethyl acetate (10:1) as the eluent (Rf ) 0.70) to
give totally 5.0 g of 10 (75%): mp 101-103 °C (CH2C2/hexane);
1H NMR (CDCl3, 250 MHz) δ 1.08 (s, 9 H), 3,77 (s, 3 H), 6.64
(dd, 1 H, J ) 2.5, 4.2 Hz), 7.20-7.36 (m, 10 H), 7.50 (d, 1 H,
J ) 2.5 Hz); mass spectrum m/ e (% relative intensity) 428
(M+ + 2, 98), 426 (M+, 100). IR (film) 3069, 2962, 1474, 1267
found: 362.1410; IR (film) 3600-3200, 2963, 1651 cm-1
.
Bis[5′-ter t-bu tyl-3′-(d ip h en ylp h osp h in o)sa licylid en e]-
1,1,2,2-tetr a m eth yleth ylen ed ia m in e (13). To a solution of
12 (0.20 g, 0.55 mmol) in refluxing absolute ethanol (10 mL),
was added slowly in 20 min 2,3-diamino-2,3-dimethylbutane
(6) (0.033 g, 0.28 mmol) in absolute ethanol (10 mL) to yield a
yellow solution. The ethanolic solution was refluxed for 4 h.
After cooling, yellow crystals were collected after filtration to
1
afford 13 (0.155 g, 70%): mp 186-189 °C (ethanol); H NMR
(CDCl3, 250 MHz) δ 1.07 (s, 18 H), 1.34 (s, 12 H), 6.76 (dd, 2
H, J ) 2.5, 4.5 Hz), 7.19 (d, 2 H, J ) 2.0 Hz), 7.32 (m, 20 H),
8.31 (s, 2 H), 14.37 (bs, 2 H); 13C NMR (CDCl3, 62.9 MHz) δ
23.19, 31.17, 33.98, 65.21, 117.16, 124.20 (d, J CP ) 13.2 Hz),
128.32 (m), 129.25, 133.83 (d, J CP ) 19.5 Hz), 134.60, 136.99
(d, J CP ) 11.3 Hz), 140.81, 162.11 (m); FABMS m/ e (% relative
intensity) 805 (M+1+, 85); IR (film) 3600-2400, 2962, 1625,
1598, 1435 cm-1; UV-vis [λmax, nm (ꢀ, L mol-1 cm-1)] 340 (7.77
× 103), 436 (1.15 × 103). Anal. Calcd for C52H58N2O2P2.3/
2H2O: C, 75.07; H, 7.39; N, 3.37. Found: C, 75.06; H, 7.31;
N, 3.25.
Bis[5′-ter t-bu tyl-3′-(2′′-p yr id yl)sa licylid en e]-(R,R)-1,2-
cycloh exa n ed ia m in e (16). (R,R)-1,2-Diammoniocyclohexane
mono-(+)-tartrate19 (0.132 g, 0.5 mmol), K2CO3 (0.138 g, 1.0
mmol), and distilled water (0.7 mL) were stirred together to
form a solution, and then ethanol (2.7 mL) was added. The
resulting mixture was heated to reflux, and a solution of
aldehyde 5 (0.132 g, 0.5 mmol) in ethanol (1.3 mL) was added
dropwise. The funnel was rinsed with ethanol (0.2 mL), and
the yellow solution was stirred at refluxed for 4 h. Water (0.7
mL) was added, and the stirred mixture was cooled to rt. The
mixture was extracted with CH2
Cl2. The extracted mixture
was washed with water (2 × 1.5 mL) and brine (1.5 mL). After
drying over Na2SO4, the solvent was removed under vaccum,
and the residue was recrystallized from hexane to give yellow
solids (0.25 g, 85% yield): mp 170-1 °C, (phase change 118-
119 °C). Rf ) 0.32 (hexane/ethyl acetate ) 5:1); 1H NMR
(CDCl3, 250 MHz) δ 1.29 (s, 18 H), 1.40-2.10 (m, 8 H), 3.33
(m, 2 H), 7.22 (dd, 2 H, J ) 5.2, 7.0 Hz), 7.26 (d, 2 H, J ) 2.5
Hz), 7.73 (ddd, 2 H, J ) 1.8, 7.0, and 7.8 Hz), 7.85 (d, 2 H, J
) 2.5 Hz), 7.96 (d, 2 H, J ) 7.8 Hz), 8.38 (s, 2 H), 8.71 (d, 2 H,
J ) 5.2 Hz), 14.14 (bs, 2 H); 13C NMR (125 MHz, CDCl3), 24.19,
31.38, 33.13, 34.05, 72.59, 118.91, 121.56, 124.44, 126.60,
128.97, 130.59, 135.82, 141.13, 149.21, 156.10, 156.93, 164.87;
mass spectrum, m/ e (% relative intensity), 588 (M+, 32), 334
(70), 294 (5), 254 (100), 212 (9), IR (neat film), 733, 796, 1256,
1451, 1565, 1596, 1629, 1633, 2862, 2936, 2960, 2400-3600
cm-1
.
Anal. Calcd for C23H24BrOP: C, 64.65; H, 5.66.
Found: C, 64.95; H, 5.69.
5-ter t-Bu tyl-3-(d ip h en ylp h osp h in o)-2-m eth oxyben za l-
d eh yd e (11). To a well-stirred solution of 10 (2.94 g, 6.9
mmol) and TMEDA (1.04 g, 9.0 mmol) in anhydrous ether (10
mL) at -78 °C was added n-BuLi (1.6 M, 4.4 mL, 7.0 mmol)
dropwise under nitrogen. The orange solution was stirred at
-78 °C for 1 h. Distilled DMF (2.52 g, 34.5 mmol) was added
to the solution via a syringe at -78 °C under nitrogen. The
mixture was allowed to warm up to room temperature and
stirred for 2 h. Dilute HCl was slowly added to the reaction
mixture until pH ) 2. After stirring for 1-2 h, the mixture
was extracted with dichloromethane, and the organic layer was
dried (Na2SO4) to afford yellow oil after removal of solvent.
The crude product was purified by column chromatography
(hexane/ethyl acetate ) 10:1) to give white solids of 22 (1.82
g, 70%): Rf ) 0.55; mp 125-126 °C (CH2Cl2/hexane); 1H NMR
(CDCl3, 250 MHz) δ 1.10 (s, 9 H), 3.86 (s, 3 H), 7.01 (m, 1 H),
7.24-7.35 (m, 10 H), 7.82 (d, 1 H, J ) 2.3 Hz), 10.35 (s, 1 H);
MS m/ e (relative intensity) 376 (M+, 88), 348 (97), 185 (14);
cm-1. [R]20 ) -518° (c ) 1.0, CH2Cl2 ); UV-vis [λmax, nm (L
D
mol-1 cm-1)] 342 (16.6 × 103). Anal. Calcd for C38H44N4O2:
C, 77.52; H, 7.53; N, 9.52. Found: C, 77.38, H, 7.56; N, 9.46.
Bis[5′-ter t-b u t yl-3′-(2′′-p yr id yl)sa licylid en e]-(S,S)-1,2-
cycloh exa n ed ia m in e (17). (S,S)-1,2-Diammoniocyclohexane
mono-(-)-tartrate19 (0.132 g, 0.5 mmol), K2CO3 (0.138 g, 1.0
mmol), and distilled water (0.7 mL) were stirred until dissolu-

8418 J . Org. Chem., Vol. 61, No. 24, 1996
Lam et al.
tion was achieved, and then ethanol (2.7 mL) was added. The
resulting mixture was heated to reflux, and a solution of
aldehyde 5 (0.132 g, 0.5 mmol) in ethanol (1.1 mL) was added
dropwise. The funnel was rinsed with ethanol (0.2 mL), and
the yellow solution was stirred at reflux for 4 h before heating
was discontinued. Water (0.7 mL) was added, and the stirred
mixture was cooled to rt. The mixture was extracted with
CH2Cl2. Then the extracted mixture was washed with water
(2 × 1.5 mL) and brine (1.5 mL) and dried over Na2SO4. The
solvent was removed under vaccum, and the residue was
recrystallized in hexane to give the yellow solid (0.253 g, 86%
yield): mp 169-70 °C (phase change 118-119 °C); Rf ) 0.32
(hexane/ethyl acetate: 5:1); 1H NMR (CDCl3, 250 MHz): 1.29
(s, 18 H), 1.40-2.10 (m, 8 H), 3.33 (m, 2 H), 7.22 (d, 2 H, J )
5.2, 7.0 Hz), 7.26 (d, 2 H, J )2.5 Hz), 7.73 (ddd, 2 H, J ) 1.8,
7.0, and 7.8 Hz), 7.85 (d, 2 H, J ) 2.5 Hz), 7.96 (d, 2 H, J )
7.8 Hz), 8.38 (s, 2 H), 8.71 (d, 2 H, J ) 5.2 Hz),14.14 (bs, 2 H);
13C NMR (125 MHz, CDCl3), 24.20, 31.38, 33.14, 34.05, 72.59,
118.91, 121.57, 124.44, 126.60, 128.97, 130.60, 135.83, 141.14,
149.21, 156.10, 156.93, 164.88; mass spectrum, m/ e (% relative
intensity), 588 (M+, 22), 334 (73), 294 (9), 254 (100), 212 (11);
IR (neat film) 734, 796, 1256, 1451, 1565, 1596, 1630, 1634,
2935, 2960, 2400-3600 cm-1; [R]20D ) +517° (c ) 1.0, CH2Cl2);
UV-vis [λmax, nm (L mol-1 cm-1)] 342 (16.1 × 103). Anal. Calcd
for C38H44N4O2: C, 77.52; H, 7.53; N, 9.52. Found: C, 76.04,
H, 7.64; N, 9.22.
Copper (II) Bis[5′-ter t-bu tyl-3′-(2′′-pyr idyl)salicyliden e]-
(S,S)-1,2-cycloh exa n ed ia m in e (19). To a refluxing solution
of (S,S) Schiff base 17 (50 mg, 0.085 mmol) in ethanol (10 mL)
was added dropwise Cu(OAc)2‚H2O (17 mg, 0.085 mmol),
dissolved in hot ethanol (10 mL), within 20 min. The resulting
brown suspension was refluxed for 1 h. After the mixture was
cooled, the precipitate was filtered and recrystallized in CHCl3/
EtOH to give 90 mg of brown solid (yield 81%): mp 352-353
°C; IR (neat film) 2949, 2927, 1622, 1536, 1444, 1429, 1249,
1226, 798 cm-1. [R]20D ) 1.1 × 103o (c ) 0.02, CH2Cl2), UV-vis
[λmax, nm (ꢀ, L mol-1 cm-1)] 388 (20.4 × 103). Anal. Calcd for
C38H42N4O2Cu: C, 70.23; H, 6.52; N, 8.63. Found: C, 70.29,
H, 6.52; N, 8.63. HRMS calcd 650.2682, found 650.2705.
Nick el(II) Bis[5′-ter t-bu tyl-3′-(2′′-p yr id yl)sa licylid en e]-
(S,S)-1,2-cycloh exa n ed ia m in e (20). To a refluxing solution
of (S,S) Schiff base 17 (50 mg, 0.085 mmol) in ethanol (10 mL)
was added dropwise Ni(OAc)2‚4H2O (21 mg, 0.085 mmol),
dissolved in hot ethanol (10 mL), within 20 min. The yellow
precipitate appeared, and the mixture was refluxed for 1 h.
After cooling, the precipitate was filtered and recrystallized
in CHCl3/EtOH to give 53.4 mg of a muddy yellow solid (yield
97%): mp 380-381 °C; 1H NMR (CDCl3, 250 MHz) 1.32 (s, 18
H), 1.62 (br, 2 H), 1.76 (br, 4 H), 2.36 (br, 2 H), 3.24 (br, 2 H),
6.94 (dd, 2 H, J ) 7.6, 7.8 Hz), 7.01 (dd, 2 H, J ) 6.9, 7.6 Hz),
7.09 (s, 2 H), 7.46 (s, 2 H), 8.17 (d, 2 H, J ) 2.2 Hz), 8.21 (d,
2H, J ) 7.8 Hz), 8.57 (d, 2H, J ) 2.2 Hz); IR (neat film) 2949,
Copper (II) Bis[5′-ter t-bu tyl-3′-(2′′-pyr idyl)salicyliden e]-
(R,R)-1,2-cycloh exa n ed ia m in e (18). To a refluxing solution
of (R,R) Schiff base 16 (50 mg, 0.085 mmol) in ethanol (10 mL)
was added dropwise Cu(OAc)2‚H2O (17 mg, 0.085 mmol),
dissolved in hot ethanol (10 mL), within 20 min. The resulting
brown suspension was refluxed for 1 h. After the mixture was
cooled, the precipitate was filtered and recrystallized in CHCl3/
EtOH to give 90 mg of brown solid (yield 81%): mp 352-353
°C; IR (neat film) 2949, 2927, 1622, 1536, 1444, 1429, 1249,
2927, 1622, 1537, 1445, 1251, 797 cm-1; [R]20 ) 1.1 × 103o (c
D
) 0.05, CH2Cl2); UV-vis [λmax, nm (ꢀ, L mol-1 cm-1)] 425 (13.6
× 103), 329 (16.3 × 103). Calcd for C38H42N4O2Ni: HRMS calcd
645.2739, found 645.2743.
Ack n ow led gm en t. We thank the Croucher Foun-
dation for the award of a studentship to F. L. and the
Dow Chemical Co. for financial support.
1226, 797 cm-1; [R]20 ) -1.1 × 103° (c ) 0.02, CH2Cl2), UV-
D
vis [λmax, nm (ꢀ, L mol-1 cm-1)] 387 (21.0 × 103). Anal. Calcd
for C38H42N4O2Cu: C, 70.23; H, 6.52; N, 8.63. Found: C, 69.96,
H, 6.66; N, 8.50. HRMS calcd 650.2682, found 650.2745.
J O961020F