Synthesis and characterization of bifunctional compounds: Templates for metal crown ether assemblies

Article abstract of DOI:10.1021/om050639h

(dppe)Pd-salicylimine cations and (dppe)Pd-catecholate complexes with dangling primary ammonium ions are excellent donors for 18-crown-6 (18-c-G) and benzo-18-c-6 receptors. The self-assembly of these host-guest complexes from their constituent components is efficient, and two X-ray-generated structures showing atom connectivity are reported. A discussion of N-imine isomers of the Schiff base-derived 4-aminobenzylamine is also included.

Full text of DOI:10.1021/om050639h

Organometallics 2005, 24, 5479-5483
5479
Synthesis and Characterization of Bifunctional
Compounds: Templates for Metal Crown Ether
Assemblies
D. Luke Nelsen, Peter S. White,‡ and Michel R. Gagne´*
Department of Chemistry, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599
Received July 27, 2005
(dppe)Pd-salicylimine cations and (dppe)Pd-catecholate complexes with dangling primary
ammonium ions are excellent donors for 18-crown-6 (18-c-6) and benzo-18-c-6 receptors. The
self-assembly of these host-guest complexes from their constituent components is efficient,
and two X-ray-generated structures showing atom connectivity are reported. A discussion
of N-imine isomers of the Schiff base-derived 4-aminobenzylamine is also included.
Scheme 1
Introduction
Following the inspiration that enzyme active sites are
typically multifunctional (acids, bases, H-bond donors,
acceptors, metals, etc.), synthetic chemists have labored
to gain access to similarly multifunctional transition
metal catalysts. The most common approach to this end
is the synthesis of complex multifunctional ligands that
coordinate to the metal in question. One of the most
elegant applications of this notion is the work of
Hayashi and Ito on chiral ferrocenyl diphosphines
derivatized with polyols or crown ether appendages,1
wherein the functional group was proposed to utilize
secondary binding interactions (ion pairing, H-bonding,
etc.) to guide the nucleophile into the electrophilic P2-
Pd(π-allyl)+ fragment (e.g., A). The most reactive cata-
lysts also tended to be the most enantioselective,
suggesting that an optimum arrangement of metal and
receptor could also stabilize the transition state. Many
conceptually similar approaches have been reviewed.2
construction of synthetic active sites within porous
polymers.6 Often termed molecular imprinting, the
method involves the copolymerization of premade (or
preorganized) templates into highly rigid, but porous,
polymers.7 Postpolymerization modification of the tem-
plate can reveal new synthetic active sites capable of
reactions not possible or with selectivities not available
to solution analogues.8 In one recent application of this
methodology we attempted to build an active site that
might mimic the transition state proposed by Ito, i.e., a
P2Pd(II) fragment associated with a crown ether (Scheme
1).9,10 While the crown and catalyst were clearly associ-
ated in the polymeric active site (from reactivity stud-
ies), the solution characterization of 1 revealed that the
ion-pair that served to associate the crown to the
(4) (a) Polborn, K.; Severin, K. Eur. J. Inorg. Chem. 2000, 1687-
1692. (b) Polborn, K.; Severin, K. Chem. Eur. J. 2000, 6, 4604-4611.
(c) Polborn, K.; Severin, K. Chem. Commun. 1999, 2481-2482.
(5) The broader field of catalysis in imprinted polymers has been
reviewed: (a) Tada, M.; Iwasawa, Y. J. Mol. Catal. A: Chem. 2003,
3953, 1-23. (b) Alexander, C.; Davidson, L.; Hayes, W. Tetrahedron
2003, 59, 2025-2057. (c) Wulff, G. Chem. Rev. 2002, 102, 1-28. (d)
Davis, M. E.; Katz, A.; Ahmad, W. R. Chem. Mater. 1996, 8, 1820-
1839.
We3 (and others)4,5 have taken a different tack in the
synthesis of selective catalysts, namely, the de novo
* To whom correspondence should be addressed. E-mail: mgagne@
unc.edu.
‡ To whom correspondence regarding X-ray crystallography should
be directed. E-mail: pwhite@unc.edu.
(6) (a) Santora, B. P.; Gagne´, M. R.; Moloy, K. G.; Radu, N. S.
Macromolecules 2001, 34, 658-661. (b) Sherrington, D. C. Chem.
Commun. 1998, 2275-2286.
(1) (a) Hayashi, T.; Kanehira, K.; Hagihara, T.; Kumada, M. J. Org.
Chem. 1988, 53, 113-120. (b) Sawamura, M.; Nagata, H.; Sakamoto,
H.; Ito, Y. J. Am. Chem. Soc. 1992, 114, 2586-2592. (c) Sawamura,
M.; Nakayama, Y.; Tang, W.-M.; Ito, Y. J. Org. Chem. 1996, 61, 9090-
9096.
(7) (a) Wulff, G. Angew. Chem., Int. Ed. Engl. 1995, 34, 1812-1832.
(b) Molecularly Imprinted Polymers Man-made Mimics of Antibodies
and Their Applications in Analytical Chemistry; Sellergren, B., Ed.;
Elsevier: Amsterdam, 2001. (c) Molecularly Imprinted Materials-
Sensors and Other Devices; Shea, K. J., Yan, M., Roberts, J. M., Eds.;
Materials Research Society: Warrendale, PA, 2002; Vol. 723.
(8) Santora, B. P.; Gagne´, M. R. Chem. Innov. 2000, 23-29.
(9) Viton, F.; White, P. S.; Gagne´, M. R. Chem. Commun. 2003,
3040-3041.
(2) (a) Sawamura, M.; Ito, Y. Chem. Rev. 1992, 92, 857-871. (b)
Ma, J.-A.; Cahard, D. Angew. Chem., Int. Ed. 2004, 43, 4566-4583.
(c) Shibasaki, M.; Sasai, H.; Arai, T. Angew. Chem., Int. Ed. Engl. 1997,
36, 1236-1256.
(3) Becker, J. J.; Gagne´, M. R. Acc. Chem. Res. 2004, 37, 798-804.
10.1021/om050639h CCC: $30.25 © 2005 American Chemical Society
Publication on Web 09/20/2005

5480 Organometallics, Vol. 24, No. 22, 2005
Nelsen et al.
catalysts was sufficiently weak (and presumably omni-
directional as well) that broad featureless NMR spectra
were observed at ambient temperature. Thus, the
molecule used to create the active site was itself
dynamic and poorly structured, even though a beneficial
imprinting effect was observed.
Presuming that a more well defined template would
lead to even better imprinting results, we designed
several second-generation templates that physically
attached the ammonium linker to the ligand, the goal
being a spatially precise assembly of catalyst and crown
ether. This article reports on the synthesis and struc-
tural characterization of compounds that lend them-
selves to future molecular imprinting experiments while
also providing a molecular visualization of the crown/
catalyst assembly that may be relevant to the Hayashi-
Ito allylation reactions.
Figure 1. Plot of 3 showing the atom connectivity and
extensive disorder in the crown ether.
Results and Discussions
c-6, a relatively stable monoprotonated adduct, 3, was
obtained. Repeated washings with ether and/or crystal-
lizations from MeOH/tBuOMe did not dislodge the single
equivalent of the crown from 3. Most diagnostic in the
1H NMR was the broadened resonance at 9.0 ppm (3H),
characteristic of a PhNH3+‚18-c-6 host-guest complex.13
In contrast, the NH of PhCH2NH3+‚18-c-6 resonates at
∼7.4 ppm, suggesting that 3 resulted from aniline
protonation and subsequent trapping with the crown
ether. 1H NMR analysis of 3 indicates that even to -56
°C the crown ether decomplexes and recomplexes faster
than the NMR time scale, as only a single resonance is
observed for the two faces of the crown. Standing CD2-
Cl2 or CDCl3 solutions of 3 begin to decompose at
extended times (>12 h), although X-ray quality crystals
could be obtained by the overnight vapor diffusion of
tBuOMe into a saturated MeOH solution.
At the outset we desired a ligand framework that
would be modular and amenable to a variety of deriva-
tization techniques. A salicylimine seemed to provide
both the scaffold for attaching multiple donor acceptor-
type functionalities and the means for a convergent
synthesis. Concurrent work in our laboratory had
demonstrated that salicylimines were stable on P2Pt-
(II) and P2Pd(II) fragments,11 and so we were confident
that this ligand set would be amenable to functional-
ization and derivatization.12
Salicylimine/Crown Ether Complexes. Following
a procedure developed for unfunctionalized derivatives,
a combination of 4-aminobenzylamine, 5-Cl-salicylalde-
hyde, Cs2CO3, NaBF4, and (dppe)PdCl2 in a 1:1 mixture
of CH2Cl2/MeOH for 2 h cleanly provided a new product,
2, in good yield (84%) after aqueous workup (eq 1). The
pair of doublets in the 31P NMR (JP-P ) 28 Hz) was
consistent with the formulation of the product as a
salicylimine. Of course, two isomers are possible, an
N-benzylimine and an N-arylimine. On the basis of the
key CH2N resonance in the 1H NMR, and model
compounds (N-phenyl and N-benzyl), the N-benzylimine
isomer was obtained, consistent with previous experi-
ments showing a strong preference for an electron-
donating imine substituent.11 Compound 2 was air and
moisture stable.
As with many crown ether structures, disorder in the
crown was extensive and a structural refinement lead-
ing to reliable metrical parameters was not possible,
despite significant effort. Nevertheless, the structure
was sufficient to unambiguously establish the atom
connectivity shown in Figure 1.
The gross features of the solid-state structure’s con-
nectivity are maintained in the solution state as judged
by the NOESY spectrum. As shown in Scheme 2, the
key cross-peaks are indicative of crown ether coordina-
tion to the anilinium ion at the terminus of the ligand.
Cross-peaks between the P-Ph and NCH2 and the
P-Ph and OCH2 (weak) resonances were also observed.
In toto, the solution and solid-state structures of 3 are
adequately represented by the two-dimensional picture
in eq 2.
Attempts to protonate 2 with ethereal HBF4 led to
extensive decomposition; however, in the presence of 18-
(10) Metal ammine and aquo complexes are known to bind crown
ethers. See for example: (a) Colquhoun, H. M.; Lewis, D. F.; Stoddart,
J. F.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1983, 607-613. (b)
Vance, T. B., Jr.; Holt, E. M.; Varie, D. L.; Holt, S. L. Acta Crystallogr.
1980, B36, 153-155.
(11) Kerber, W. D.; Nelsen, D. L.; White, P. S.; Gagne´, M. R. J.
Chem. Soc., Dalton Trans. 2005, 1948-1951.
(12) Electron-withdrawing groups on the salicylaldehyde were found
to provide enhanced stabilization to the complexes in their protonated
state so the 5-Cl derivative was utilized throughout (see footnote 9).
(13) Gokel, G. W.; Abel, E. In Comprehensive Supramolecular
Chemistry; Gokel, G. W., Ed.; Elsevier: New York, 1996; Vol. 1, pp
511-535.

Templates for Metal Crown Ether Assemblies
Organometallics, Vol. 24, No. 22, 2005 5481
Scheme 2. Key NOE Cross Peaks in the NOESY
Protonation of 2 with HBF4 in the presence of benzo-
18-c-6 led to an analogous product, 4, which also
contained the distinctive resonance at 9.0 ppm for the
ArNH3+‚crown. Adduct 4 was considerably more sensi-
tive than 3 to polar solvents (e.g., MeOH), and attempts
to crystallize the product invariably led to decomposi-
tion. Most of the decomposition products were unidenti-
fied, but one crown ether-containing compound proved
to be exceptionally crystalline and was subjected to
X-ray analysis. Unfortunately, like compound 3, 5 was
disordered and only atom connectivity information was
obtained at a confidence level sufficient for publication
(Figure 2). Surprisingly, this compound proved to be an
isomer of 4 wherein the two nitrogen positions were
exchanged, i.e., N-arylimine/ArCH2NH3+‚crown complex
5.
Spectrum of 3 (CDCl3, -56 °C)
ions toward an otherwise acid-sensitive metal fragment.
In the case of the two crown ether types, 18-c-6 is known
to bind ammonium ions ∼60 times more strongly than
benzo-18-c-6 (log KA ) 5.9 vs 4.1 (MeOH)).16,17 Similarly,
strong solvent effects are known to be operative in
ammonium-crown binding, with polar protic solvents
being significantly less stabilizing than nonprotic and
nonpolar solvents (acetone > CH3CN > MeOH >
H2O).13,18 Thus, factors tending to increase the strength
of the ammonium-crown interaction (and concomi-
tantly decreasing the concentration of the uncomplexed
anilinium ion) serve to increase the stability of the
metal-crown aggregate toward decomposition. For
example, even the relatively sensitive complex 4 is
stable to 60 °C overnight in a nonpolar solvent like
o-Cl2C6H4 (cf. MeOH).
A priori assessment of their comparative thermody-
namic stability was not obvious since two key factors,
ArNH3+‚crown vs ArCH2NH3+‚crown and Pd-N-CH2-
Ar vs Pd-N-Ar, ran counter to one another; that is,
Pd prefers the more basic N-alkyl substituent14 while
Nitrodopamine/Crown Ether Complexes. An-
other ligand class that was examined for attaching
functional groups was the catechols. In particular,
5-nitrodopamine proved to be particularly well behaved,
the crown prefers to bind ArCH2NH3
that are primarily steric in nature, 18-c-6 binds to a
primary alkylammonium ion slightly better (log KA
.
+ 15 For arguments
)
3.99; MeOH) than the more acidic anilinium ion (log KA
) 3.80; MeOH).15 To determine the magnitude of the
bias for N-benzyl- over N-phenylimine, 1 equiv of
benzylamine was added to 6, and the solution heated
to promote imine interchange (CH3NO2, eq 4). As
expected, the N-benzylsalicylate complex 7 was favored
by >20:1 at 60 °C, suggesting that 5 likely results from
a crystallization-induced process and not by being
significantly favored on thermodynamic grounds.
The lack of stability of protonated complexes in the
absence of crown ether, the enhanced stability of the
18-c-6 complex (3) over the benzo-18-c-6 (4), and the
stability of the adducts in nonpolar solvents (e.g.,
o-Cl2C6H4) coupled with their instability in polar sol-
vents are consistent with a scenario wherein the crown
ether attenuates the effective acidity of the ammonium
(14) No trace of the alternative form of 3 was observed in the crude
reaction mixture during its synthesis (eq 1).
(15) Izatt, R. M.; Lamb, J. D.; Izatt, N. E.; Rossiter Jr., B. E.;
Christensen, J. J.; Haymore, B. L. J. Am. Chem. Soc. 1979, 101, 6273-
6276.
Figure 2. Two views of a Chem 3D representation of 5.
Extensive disorder in the counterions did not provide a
quality structure (see Supporting Information).

5482 Organometallics, Vol. 24, No. 22, 2005
Nelsen et al.
distilled from sodium methoxide prior to use. (dppe)PdCl2,20
5-nitrodopamine,21 and (dppe)Pd(2-(N-phenylimininomethyl)-
phenolate)(BF4)11 were prepared according to the literature
procedures. All other materials were purchased from Aldrich.
NMR solvents (CDCl3 and CD3NO2) were purchased from
Cambridge Isotope Labs. All 1H, 31P, and 13C NMR spectra
were recorded on a Bruker AMX 400 or AMX 300 spectrometer,
and chemical shifts were referenced to the residual solvent
peaks (1H, 13C) or 85% H3PO4 external standard (31P). Com-
plexes that were unstable in solution at long times were cooled
to acquire carbon NMR. Elemental analysis was performed
by Complete Analysis Laboratories, Inc., Parsippany, NJ
both toward formation of the free base metal complex
(8, eq 5) and to the protonated 18-c-6 adduct (9, eq 6).
Perhaps reflecting the poor nucleophilicity of the nitro-
catecholate, reaction of (dppe)PdCl2 with 1 equiv of the
anion in a biphasic mixture of CH2Cl2 and H2O was
sluggish, but proceeded quicker and cleaner with 2 equiv
of the ligand to generate blood red solutions of the Pd-
catecholate (eq 5). The excess ligand and salts were
conveniently removed in the aqueous workup.
(dppe)Pd(chlorosalicylimine), 2. To a suspension of
NaBF4 (225 mg, 2.05 mmol), (dppe)PdCl2 (492 mg, 0.854
mmol), 4-aminobenzylamine (80 mg, 0.854 mmol), and 5-chloro-
2-hydroxybenzaldehyde (134 mg, 0.854 mmol) in a mixture of
48 mL 1:1 CH2Cl2/MeOH was added Cs2CO3 (306 mg, 0.940
mmol). The reaction was stirred at room temperature and
monitored periodically by 31P NMR until complete (4 h). To
the solution was added 25 mL of H2O, the layers were
separated, and the aqueous phase was back extracted three
times with 5 mL of CH2Cl2. The organics were combined, dried
over MgSO4, and filtered, and the solvent was removed in
vacuo, yielding a solid, which was dissolved in hot MeOH and
cooled to afford orange crystals in 84% yield. 1H{31P} NMR
(400 MHz, CDCl3): δ 7.97 (d, J ) 7.6 Hz, 4H), 7.91 (d, J ) 8.0
Hz, 4H), 7.76 (m, 12H), 7.12 (dd, J ) 10.8, 2 Hz, 1H), 7.16 (d,
J ) 2.8, 1H), 6.65 (d, J ) 8.0 Hz, 2H), 6.57 (d, J ) 8.8 Hz,
3H), 4.42 (s, 2H), 3.92 (s, 2H), 3.02 (br, 2H), 2.77 (br, 2H). 31P-
{1H} NMR (162 MHz, CDCl3): δ 63.5 (d, JP-P ) 27.8 Hz), 59.2
(d, JP-P ) 27.8 Hz); 13C{1H}{31P} NMR (75 MHz, CDCl3): δ
164.5, 162.6, 146.9, 135.6, 133.4, 133.2, 132.8, 130.1, 129.5,
129.2, 126.1, 125.2, 124.5, 122.7, 120.7, 120.0, 115.2, 67.3, 32.0,
24.6. Anal. Calcd for C40H36BClF4N2OP2Pd: C, 56.43; H, 4.26;
N, 3.29. Found: C, 56.29; H, 4.12; N, 3.35.
As before, protonation with ethereal HBF4 in the
presence of 1.1 equiv of 18-c-6 provided the ammonium
ion-crown ether host-guest complex 9, which persisted
even after several washings with ether and recrystal-
lization. On the basis of the spectroscopic data (broad
ammonium signal at 7.3 ppm), we suggest the solution
structure shown in eq 6.
The stability of 9 was initially surprising since previ-
ous experiments19 had shown that the protonated par-
ent dopamine complex was prone to decomposition (data
not shown). As before,12 an electron-withdrawing group
(NO2) appeared to resolve this sensitivity, and the
resulting complexes were stable and well-behaved. In
fact, 9 was indefinitely stable even in the presence of
protic solvents such as methanol (cf. 3-5), suggesting
that for stability reasons it may be the best candidate
for imprinting experiments.
2‚HBF4‚18-c-6, 3. To a solution of 2 (90 mg, 0.106 mmol)
and 18-C-6 (31 mg, 0.117 mmol) in 5 mL of CH2Cl2 was added
54% HBF4 in diethyl ether (14.6 µL, 0.106 mmol). The solution
was stirred for 5 min, and then 10 mL of diethyl ether was
added to precipitate a yellow solid. The solid was filtered and
washed three times with 5 mL portions of diethyl ether and
then dried under vacuum (<10 mTorr) for 12 h. The solid was
crystallized from MeOH/tBuOMe to afford yellow crystals in
1
92% yield. H{31P} NMR (400 MHz, CDCl3): δ 8.96 (br, 3H),
In summary, we report a series of complexes wherein
dangling primary amine groups can be protonated to
noncovalently bind crown ethers. In general, the sali-
cylimines and the catecholates are moderately acid
sensitive; however, binding of the crown ether to the
primary ammonium ion serves to make the desired
supramolecular aggregate and attenuate the ion’s acid-
ity, which stabilizes the metal-ligand complex. Molec-
ular imprinting experiments with these second-genera-
tion metal templates have been initiated.
8.05 (s, 2H), 7.78 (m, 4H), 7.57 (m, 16H), 7.28, (s, 1H), 7.13 (d,
J ) 9.2 Hz, 2H), 6.96 (m, 2H), 6.38 (d, J ) 9.2 Hz, 2H), 4.72
(s, 2H), 3.67 (s, 24H), 2.76 (br, 2H), 2.58 (br, 2H). 13C{1H,31P}
NMR (75 MHz, -40 °C, CDCl3): δ 167.9, 167.8, 162.5, 138.3,
135.9, 134.0, 132.9, 129.9, 129.5, 129.3, 127.8, 125.3, 124.4,
122.9, 122.3, 120.7, 120.1, 69.8, 66.4, 30.9, 24.5. 31P{1H} NMR
(162 MHz, CDCl3): δ 66.6 (d, JP-P ) 29.9 Hz), 60.1 (d, JP-P
)
29.8 Hz). Anal. Calcd for C52H61B2ClF8N2O7P2Pd: C, 51.90; H,
5.11; N, 2.33. Found: C, 51.63; H, 5.04; N, 2.34.
2‚HBF4‚Benzo-18-c-6, 4. To a solution of 2 (90 mg, 0.106
mmol) and benzo-18-c-6 (36 mg, 0.117 mmol) in 5 mL of CH2-
Cl2 was added 54% HBF4 in diethyl ether (14.6 mg, 0.106
mmol). The solution was stirred for 5 min, and the solvent
was removed in vacuo. The yellow solid was washed three
times with 5 mL portions of diethyl ether and dried under
vacuum (<10 mTorr) for 12 h. The solid was obtained in
quantitative yield. 1H{31P} NMR (400 MHz, CDCl3): δ 9.31
(br, 3H), 7.97 (br, 1H), 7.75 (m, 4H), 7.62 (m, 12H), 7.39 (br,
6H), 7.15, (m, 2H), 6.93 (br, 4H), 6.78 (m, 2H), 6.36 (m, 1H),
4.64, (br, 2H), 4.23 (br, 4H), 3.92 (br, 4H), 3.74 (m, 12H), 2.69
(br, 2H), 2.53 (br, 2H). 13C {1H,31P} NMR (75 MHz, -40 °C,
CDCl3): δ 167.7, 167.6, 162.5, 147.8, 145.7, 135.9, 133.9, 133.3,
Experimental Section
General Methods. All reactions were performed under
nitrogen using standard Schlenk techniques unless otherwise
mentioned. Dichloromethane and ether were passed through
a column of activated alumina before use. Methanol was
(16) Timko, J. M.; Moore, S. S.; Walba, D. M.; Hiberty, P. C.; Cram,
D. J. J. Am. Chem. Soc. 1977, 99, 4207-4219.
(17) This proved to also be the case with the metal complexes, as
the addition of 1 equiv of 18-c-6 to 4 led to quantitative displacement
of benzo-18-c-6 as judged by the collapse of the pair of multiplets in
the aromatic portion of the benzo-18-c-6; the free crown exhibits a broad
singlet in the aromatic region.
(18) De Boer, J. A. A.; Reinhoudt, D. N. J. Am. Chem. Soc. 1985,
107, 5347-5351.
(19) Kerber, W. D.; Viton, F., unpublished results.
(20) Gugger, P.; Limmer, S. O.; Watson, A. A.; Willis A. C.; Wild S.
B. Inorg. Chem. 1993, 32, 5692-5696.
(21) Napolitano, A.; d’Ischia, M.; Costantini, C.; Prota, G. Tetrahe-
dron 1992, 48, 8515-8522.

Templates for Metal Crown Ether Assemblies
Organometallics, Vol. 24, No. 22, 2005 5483
133.0, 132.8, 129.8, 129.5, 128.9, 127.7, 125.2, 124.2, 122.5,
122.0, 120.5, 120.0, 111.4, 70.2, 70.0, 69.6, 68.7, 67.0, 66.6, 66.4,
53.6, 30.8, 24.4. 31P{1H} NMR (162 MHz, CDCl3): δ 64.8 (d,
JP-P ) 27.9 Hz), 58.1 (d, JP-P ) 27.6 Hz). Anal. Calcd for
C52H61B2ClF8N2O7P2Pd: C, 53.74; H, 4.91; N, 2.24. Found: C,
53.52; H, 4.82; N, 1.99.
was added. The solvent was then removed in vacuo, and the
solid was dried for 12 h under vacuum (<10 mTorr) to afford
8 (147 mg, 84% yield) as a red crystalline solid. 1H{31P} NMR
(400 MHz, CDCl3): δ 8.00-7.95 (m, 8H), 7.56 (m, 12H), 7.38
(s, 1H), 6.40 (s, 1H), 2.9 (m, 4H), 2.59 (s, 4H), 1.51 (br, 2H).
31P{1H} NMR (162 MHz, CDCl3): δ 55.0 (qAB, ∆νAB, 66.6 Hz,
JAB 32.4 Hz). 13C{1H}{31P} NMR (75 MHz, CDCl3): δ 171.8,
161.9, 136.7, 132.9, 132.2, 129.4, 128.2, 127.2, 117.9, 111.9,
43.2, 39.2, 25.9. Anal. Calcd for C34H32N2O4P2Pd: C, 58.25;
H, 4.60; N, 4.00. Found: C, 58.05; H, 4.36; N, 4.39.
8‚HBF4‚18-c-6, 9. To a solution of 7 (39 mg, 0 0.055 mmol)
and 18-c-6 (16 mg, 0.060 mmol) in 5 mL of CH2Cl2 was added
54% HBF4 in diethyl ether (7.6 µL, 0.055 mmol). The solution
was stirred for 5 min, and a light orange solid was precipitated
by the addition of 20 mL of diethyl ether. The solid was filtered
and washed twice with 5 mL portions of diethyl ether, yielding
compound 9 (56 mg, 93% yield). 1H{31P} NMR (400 MHz,
CDCl3): δ 7.95 (br, 8H), 7.58 (s, 1H), 7.41 (br, 12H), 7.22 (br,
3H), 6.42 (s, 1H), 3.62 (br, 24H), 3.03 (br, 4H), 2.67 (br, 4H).
31P{1H} (162 MHz, CDCl3) δ 56.0 (qAB, ∆νAB, 44.7 Hz, JAB 23.6
Hz). 13C{1H}{31P} (75 MHz, CDCl3): δ 172.8, 163.1, 136.0,
133.0, 132.1, 129.4, 128.3, 128.2, 123.2, 117.8, 112.0, 70.1, 40.3,
34.0, 26.0, 25.9. Anal. Calcd for C46H57BF4N2O10P2Pd: C, 52.46;
H, 5.46; N, 2.66. Found: C, 52.53; H, 5.58; N, 2.81.
2‚HBF4‚Benzo-18-c-6 (isomer), 5. To a solution of (dppe)-
Pd(chlorosalicylimine) (90 mg, 0.106 mmol) and 18-c-6 (36 mg,
0.117 mmol) in 5 mL of CH2Cl2 was added 54% HBF4 in diethyl
ether (14.6 µL, 0.106 mmol). The solution was stirred for 5
min and then precipitated by addition of 10 mL of diethyl
ether. The solid was filtered and washed three times with 5
mL portions of diethyl ether. The solid was dissolved in MeOH
t
and crystallized by slow diffusion of BuOMe to afford yellow
crystals in low yield. 1H{31P} NMR (400 MHz, CDCl3): δ 7.93
(br, 1H), 7.75 (m, 3H), 7.62 (m, 12H), 7.51 (m, 8H), 7.40, (s,
1H), 7.21 (s, 1H), 7.10 (m, 2H), 6.73 (s, 4H), 6.40 (br, 1H), 6.34,
(m, 2H), 4.59 (s, 2H), 4.32 (br, 4H), 3.95 (br, 4H), 3.81 (m, 12H),
2.76 (br, 2H), 2.58 (br, 2H); 31P{1H} NMR (162 MHz, CDCl3):
δ 66.4 (d, Jp-p ) 28.9 Hz), 60.0 (d, Jp-p ) 28.7 Hz).
Compound 7. To a suspension of NaBF4 (37 mg, 0.38
mmol), (dppe)PdCl2 (81 mg, 0.141 mmol), benzylamine (16 µL,
0.141 mmol), and 2-hydroxybenzaldehyde (12 µL, 0.141 mmol)
in 12 mL of a 1:1 mixture of CH2Cl2/MeOH was added Cs2-
CO3 (46 mg, 0.141 mmol). The reaction was stirred at room
temperature and was monitored by 31P NMR until complete
(4 h). The solution was added to 6 mL of water and separated.
The aqueous layer was extracted three times with 5 mL
portions of CH2Cl2. The organics were combined and dried over
MgSO4. The solvent was removed in vacuo, and the solid was
crystallized by vapor diffusion of tBuOMe into CH2Cl2 to afford
yellow crystals in 96% yield (97 mg). 1H{31P} NMR (400 MHz,
CDCl3): δ 7.85 (m, 5H), 7.55 (m 16H), 7.16 (m, 5H), 6.66 (d, J
) 7.2 Hz, 2H), 6.60 (t, J ) 7.2 Hz, 1H), 6.46 (d, J ) 8.4, 1H),
4.48 (s, 2H), 2.80 (br, 2H), 2.58 (br, 2H). 31P{1H} (162 MHz,
CDCl3): 63.03 (d, JP-P ) 28.5 Hz), 58.29 (d, JP-P ) 28.6). 13C-
{31P}{1H} (75 MHz, CDCl3): δ 167.1, 167.0, 164.2, 136.6, 136.2,
135.5, 133.2, 132.7, 130.0, 129.5, 128.7, 127.8, 126.8, 126.7,
125.2, 125.0, 121.2, 119.9, 116.2, 67.4, 31.7, 24.5.
(dppe)Pd(5-nitrodopamine), 8. To a suspension of (dppe)-
PdCl2 (144 mg, 0.25 mmol) and NaBF4 (65 mg, 0.60 mmol) in
15 mL of CH2Cl2 in air was added 5 mL of a red water solution
containing 5-nitrodopamine (99 mg, 0.50 mmol) and KOH (56
mg, 1.00 mmol). The reaction was complete after stirring in
air for 1 h (31P NMR). After addition of 10 mL of CH2Cl2, the
deep red organic layer was separated. The aqueous layer was
twice extracted with 5 mL portions of CH2Cl2. The combined
organic fractions were back-extracted with 5 mL of H2O, dried
over MgSO4, and filtered, and the solvent was then removed
to a calculated volume of 15 mL, whereupon 7 mL of MeOH
Equilibrium Measurements (typical procedure). To a
solution of 7 (17.9 mg, 0.025 mmol) in 1.0 mL of CDCl3 was
added 2.3 µL of aniline (0.025 mmol). The solution was placed
and sealed in a J-Young NMR tube and heated at 60 °C. The
reaction was monitored by 31P NMR. Equilibrium concentra-
tions were calculated from the molar ratio of the two P2Pd-
(N,O) complexes.
Crystallographic Data. Compound 3: empirical formula
) C54H61B2ClF8N2O7P2Pd; fw (g mol-1) ) 1227.49; space group
) P21/n (a ) 9.2636(3) Å, b ) 20.5121(7) Å, c ) 29.0311(10)
Å, â ) 91.5850(20)°); V ) 5514.3(3) Å3; Z ) 4; T ) -100 °C;
Dc ) 1.479 g cm-3; λ ) 0.70930 Å; µ ) 0.52 mm-1; Rf ) 0.074;
Rw ) 0.080. Compound 5: empirical formula ) C56H57B2-
ClF8N2O7P2Pd; fw (g mol-1) ) 1247.48; space group ) P21/c (a
) 12.7519(4) Å, b ) 14.7900(4) Å, c ) 34.4644(10) Å; â )
92.8791(12)°); V ) 6491.8(3) Å3; Z ) 4; T ) -100 °C; Dc )
1.276 g cm-3; λ ) 0.70930 Å; µ ) 0.45 mm-1; Rf ) 0.082; Rw
0.103.
)
Acknowledgment. We gratefully thank the Na-
tional Science Foundation (CHE-0315203) and the
Department of Energy, Office of Basic Energy Sciences,
each for partial support of this work. D.L.N. is a UNC
Venable Fellow.
OM050639H