Functionalized macrocyclic ligands: Big building blocks for metal coordination

Article abstract of DOI:10.1021/om020738k

A report on the synthesis of two conjugated macrocyclic ligands, 5a and 5b is presented. Both macrocycles incorporate a 3,5-diethynylpyridine subunit, making them suitable for further elaboration. Ligands 5a and 5b are both quite robust, surviving indefinitely under ambient conditions. Thermally, 5a decomposes at 104 °C, whereas platinacycle 5b is substantially more stable, melting at 248 °C.

Full text of DOI:10.1021/om020738k

Organometallics 2003, 22, 1353-1355
1353
F u n ction a lized Ma cr ocyclic Liga n d s: Big Bu ild in g
Block s for Meta l Coor d in a tion
Katie Campbell, Robert McDonald,† Michael J . Ferguson,† and
Rik R. Tykwinski*
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada
Received September 6, 2002
Summary: Two large, conjugated, macrocyclic ligands,
5a and 5b, have been efficiently prepared from easily
accessible precursors. Both macrocycles incorporate a
3,5-diethynylpyridine subunit, making them suitable for
further elaboration, as demonstrated via their coordina-
tion to give Pt complexes 6a and 6b.
tion of appropriate functionality, led to their adaptation
for use as sensors7 and in host-guest chemistry.8
Particularly interesting are the recent reports of func-
tionalized macrocycles that form well-ordered layers on
metal surfaces directed by secondary bonding interac-
tions.6a,9
Herein, we report the synthesis of two new macrocy-
clic ligands, 5a and 5b. Macrocycle 5a is prepared using
a series of Pd-catalyzed cross-coupling and Cu-catalyzed
oxidative homocoupling reactions. A common precursor,
oligomeric 4, is readily elaborated into the larger ligand,
platinacycle 5b, through incorporating a transition-
metal-σ-acetylide linkage.10 The presence of Pt within
the macrocyclic core is expected to facilitate further
elaboration via displacement of the phosphine ligands.11
Complex 6a and the interesting bimetallic species 6b
have been prepared and demonstrate the coordinative
ability of these large, macrocyclic ligands. Crucial to the
employment of any supramolecular building block is a
fundamental knowledge of its structural attributes, and
therefore a thorough discussion of the solid-state char-
acteristics of these molecules is presented.
The synthesis of the diphenylvinylidene-functional-
ized macrocycle 5a is outlined in Scheme 1. Oligomer 3
was prepared by the Pd-catalyzed cross-coupling of 3,5-
diethynylpyridine with 2 equiv of vinyl triflate 2, as
previously reported.5b Protiodesilylation of oligomer 3,
followed by a second iteration of the cross-coupling step
with 2, led to the formation of extended oligomer 4.12
After desilylation with TBAF, divergent elaboration
of deprotected 4 provides macrocycles 5a and 5b.
Treatment of the deprotected polyyne with CuI and
TMEDA in CH2Cl2 in the presence of air leads to the
The predictable and directional bonding of organic
ligands allows for the engineering of supramolecular
coordination complexes with extraordinary structures
and functional properties.1 Using both rigid and flexible
molecular spacers, well-ordered architectures such as
molecular squares,2 cages,3 and tubular structures4 have
been constructed, utilizing a range of transition metals
as the vertexes. Nearly all of these examples, however,
exploit linear, aromatic ligands such as pyridine or
bipyridine and their derivatives.
We have been intrigued with the synthesis of conju-
gated macrocycles that function in a manner analogous
to that of linear, pyridine-derived ligands. Specifically,
our efforts have focused on the incorporation of pyridyl
groups into the framework of cross-conjugated macro-
cycles such that the orientation of the pyridine nitrogen
outward from the core allows for the preparation of a
variety of hybrid metal-organic structures and orga-
nized materials.5 Indeed, macrocycles with shape-
persistent cores6 display unique physical properties and
association behavior that have, through the incorpora-
* To whom correspondence should be addressed. E-mail:
rik.tykwinski@ualberta.ca.
† X-ray Crystallography Laboratory, Department of Chemistry,
University of Alberta.
(1) (a) Leininger, S.; Olenyuk, B.; Stang, P. J . Chem. Rev. 2000, 100,
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40, 2022-2043. (c) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita,
N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001, 509-518. (d)
Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34, 759-
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1997, 119, 11611-11619. (b) Whiteford, J . A.; Lu, C. V.; Stang, P. J .
J . Am. Chem. Soc. 1997, 119, 2524-2533. (c) Aoyagi, M.; Biradha, K.;
Fujita, M. Bull. Chem. Soc. J pn. 1999, 72, 2603-2606. (d) Sun, S.-S.;
Lees, A. J . J . Am. Chem. Soc. 2000, 122, 8956-8967.
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84, 778-785. (c) Collins, S. K.; Yap, G. P. A.; Fallis, A. G. Org. Lett.
2000, 2, 3189-3192. (d) Zhao, D.; Moore, J . S. J . Org. Chem. 2002,
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3075-3098.
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(3) (a) Olenyuk, B.; Whiteford, J . A.; Fechtenko¨tter, A.; Stang, P. J .
Nature 1999, 398, 796-799. (b) Hiraoka, S.; Fujita, M. J . Am. Chem.
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F. Chem. Eur. J . 2001, 7, 1333-1341. (b) Bosch, E.; Barnes, C. L.
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J .; Chai, M.; Ray, D. G., III; Rinaldi, P. L.; Tessier, C. A., Youngs, W.
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(11) See, for example: Espinet, P.; Soulantica, K.; Charmant, J . P.
H.; Orpen, A. G. Chem. Commun. 2000, 915-916.
(12) Full details of the synthesis and characterization of compounds
4-6 are provided as Supporting Information.
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121, 7457-7458. (b) Cotton, F. A.; Lin, C.; Murillo, C. A. Chem.
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Tykwinski, R. R. J . Am. Chem. Soc. 2002, 124, 7266-7267. (b)
Campbell, K.; McDonald, R.; Tykwinski, R. R. J . Org. Chem. 2002,
67, 1133-1140. (c) Campbell, K.; McDonald, R.; Branda, N. R.;
Tykwinski, R. R. Org. Lett. 2001, 3, 1045-1048.
10.1021/om020738k CCC: $25.00 © 2003 American Chemical Society
Publication on Web 03/06/2003

1354 Organometallics, Vol. 22, No. 7, 2003
Communications
Sch em e 1a
a
Reaction conditions: (a) TBAF, THF; (b) 2 (2 equiv), Pd(PPh3)4, CuI, Et2NH, THF, 60 °C; (c) CuI, TMEDA, CH2Cl2, O2, 25 °C;
(d) trans-PtCl2(PPh3)2, CuI, Et2NH, 40 °C; (e) trans-PtCl2(SEt2)2, CH2Cl2, 25 °C.
formation of macrocyclic ligand 5a . Treatment of the
deprotected intermediate with trans-PtCl2(PPh3)2 at
high dilution in Et2NH, in the presence of a catalytic
amount of CuI,14 leads to the formation of platinacycle
5b. Ligands 5a and 5b are both quite robust, surviving
indefinitely under ambient conditions. Thermally, 5a
decomposes at 104 °C, whereas platinacycle 5b is
substantially more stable, melting at 248 °C.
Single crystals of 5a and 5b, suitable for X-ray
crystallographic analysis, were grown from CH2Cl2/
acetone solutions at 4 °C.15 The ORTEP diagram of 5a
(Figure 1, top) reveals the dimensions of this macrocyclic
ligand, which spans 5.3 Å (C(3A) to C(20)) by 9.0 Å
(C(13) to C(27)). The pentagon-shaped macrocycle has
adopted a psuedo-envelope conformation in the solid
state, one in which the vinylidene carbon C(13) rests
1.52 Å outside of a plane defined by the remaining four
vertexes of the pentagon that includes C(17), C(23),
C(27), and the centroid of the pyridine ring (Pycent). As
a result of this puckering, the dihedral angle between
the C(17)-C(23)-C(27)-Pycent and C(17)-C(13)-Pycent
planes is 31°. The macrocycle is relatively free from
strain, as reflected in the mean alkyne bond angle of
F igu r e 1. (top) ORTEP drawing of 5a (20% probability
level), showing the psuedo-envelope conformation. (bottom)
(13) (a) Hay, A. S. J . Org. Chem. 1962, 27, 3320-3321. (b) Siemsen,
ORTEP drawing of 5b (20% probability level). Only the ipso
carbons of the triphenylphosphine ligands are shown, for
clarity. Selected bond lengths (Å): Pt-P(1) ) 2.3059(17),
Pt-P(2) ) 2.2958(17), Pt-C(20) ) 1.994(6), Pt-C(21) )
1.993(6), C(19)-C(20) ) 1.215(8), C(21)-C(22) ) 1.203(8).
The cocrystallized solvent is not shown in either case.
P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int. Ed. 2000, 39,
2633-2657.
(14) Sonagashira, K.; Ohga, K.; Takahashi, S.; Hagihara, N. J .
Organomet. Chem. 1980, 188, 237-243.
(15) Crystallographic data are as follows. Compound 5a : C73H43N‚
0.5CH2Cl2 (formula weight 976.55) crystallized in the triclinic space
group P1h (No. 2) with a ) 10.4978(8) Å, b ) 17.2773(14) Å, c ) 17.4207-
(14) Å, R ) 116.6701(14)°, â ) 95.7338(16)°, γ ) 91.9950(18)°, V )
2798.1(4) Å3, Z ) 2, Fcalcd ) 1.159 g cm-3, µ(Mo KR) ) 0.112 mm-1
,
2
T ) -80 °C, R1(F) ) 0.0866 (5429 reflections with Fo g 2σ(Fo2)), and
175.3°. Furthermore, the vinylidene bond angles C(12)-
C(13)-C(15) ) 111.1(4)°, C(16)-C(17)-C(19) ) 113.3-
(3)° C(22)-C(23)-C(25) ) 113.1(3)°, and C(26)-C(27)-
C(29) ) 113.0(3)° are only slightly less than those of
the acyclic oligomer 4.16
wR2(F2) ) 0.2980 for all 11 265 unique data. Compound 5b: C109H73
-
NP2Pt‚0.5CH2Cl2‚acetone (formula weight 1754.25) crystallized in the
triclinic group P1h (No. 2) with a ) 14.6025(13) Å, b ) 17.2169(15) Å,
c ) 20.0200(17), R ) 107.5427(17)°, â ) 109.1503(16)°, γ ) 94.3186-
(16)°, V ) 4448.0(7) Å3, Z ) 2, Fcalcd ) 1.310 g cm-3, µ(Mo KR) ) 1.695
mm-1, T ) -80 °C, R1(F) ) 0.0571 (13 339 reflections with Fo
g
2
2σ(Fo2)), and wR2(F2) ) 0.1520 for all 18 125 unique data. Compound
6a : C77H53Cl2NPtS‚1/3CHCl3 (formula weight 1330.03) crystallized in
the monoclinic group P21/n (an alternate setting of P21/c (No. 14)) with
a ) 19.9238(15) Å, b ) 17.3126(13) Å, c ) 20.0804(15) Å, â ) 106.9222-
(13)°, V ) 6626.5(9) Å3, Z ) 4; Fcalcd ) 1.333 g cm-3, µ(Mo KR) ) 2.312
mm-1, T ) -80 °C, R1(F) ) 0.0802 (9989 reflections with Fo2 g 2σ(Fo2)),
and wR2(F2) ) 0.2327 for all 13 527 unique data. Compound 6b:
C113H83Cl2NP2Pt2S‚3CH2Cl2 (formula weight 2264.66) crystallized in
the triclinic group P1h (No. 2) with a ) 15.0241(11) Å, b ) 18.4070(13)
Å, c ) 20.9726(15) Å, R ) 64.8410(10)°, â ) 88.1120(10)°, γ ) 72.132-
Crystallographic analysis of 5b shows that the mac-
rocyclic core is slightly wider than that of 5a , spanning
4.9 by 10.2 Å (Figure 1, bottom). The conjugated
skeleton is nearly planar with a maximum deviation
from planarity of 0.07 Å, and the P(1)-Pt and Pt-P(2)
bonds are almost exactly perpendicular to the plane of
the macrocycle. Unexpectedly, the Pt-acetylide linkage
(2)°, V ) 4964.4(6) Å3, Z ) 2, Fcalcd ) 1.515 g cm-3, µ(Mo KR) ) 3.134
mm-1, T ) -80 °C, R1(F) ) 0.0382 (15 112 reflections with Fo
2σ(Fo2)), and wR2(F2) ) 0.0950 for all 19877 unique data.
g
(16) Campbell, K.; McDonald, R.; Tykwinski, R. R. Unpublished
results.
2

Communications
Organometallics, Vol. 22, No. 7, 2003 1355
spectively, are consistent with those observed in un-
strained Pt acetylides.10e Thus, the strain that is
imparted as a result of increasing planarity is accom-
modated primarily by a distortion of the acetylenic
π-system, rather than in the metal-acetylide linkage.
To examine the coordinative ability of these large,
macrocyclic ligands and the associated changes in
structure, complexes 6a and 6b were prepared (Scheme
1). Addition of trans-PtCl2(SEt2)2 to a CH2Cl2 solution
of 5a or 5b and stirring at room temperature for 1-2
days gave 6a and 6b as robust, orange crystalline solids.
Interestingly, the thermal stability of 6a is substantially
greater than that of the uncoordinated ligand 5a , with
6a decomposing only at 238 °C.
X-ray crystallographic analysis was performed on
single crystals of 6a and 6b grown by slow evaporation
of a CHCl3 and CH2Cl2/acetone solution, respectively.
The ORTEP diagram of 6a (Figure 2, top) shows that
the coordinated macrocycle adopts a more planar con-
formation in comparison to the unbound ligand 5a ;
C(23) is only 0.56 Å from the plane defined by the other
four vertexes of the pentagon C(17)-C(13)-Pycent
-
C(27), and the dihedral angle between the C(17)-
C(13)-Pycent-C(27) and C(17)-C(23)-C(27) planes is
10.9°. Surprisingly, the increased planarity does not
coincide with an increase in strain. The four vinylidene
bond angles of 6a are comparable to those of the
uncoordinated ligand, 5a . The alkyne bond angles are
similarly unaffected, with an average bond angle of
175.4°. The geometry about Pt is square planar, with
an angle between the N-C(1)-C(2)-C(3)-C(4)-C(5)
and N-Pt-Cl(1)-Cl(2)-S planes of 47.4°.
In contrast, the ORTEP diagram of complex 6b
(Figure 2, bottom) reveals that the macrocyclic portion
of this complex is planar and almost completely un-
changed upon coordination to the Pt center. All alkyne
and vinylidene bond angles are consistent with those
observed in the unbound ligand 5b. All Pt-carbon, Pt-
phosphorus, and Pt-nitrogen bond lengths and related
bond angles are similarly unaffected.
We have described a synthetic route to highly func-
tionalized macrocyclic ligands and demonstrated their
ability to bind to transition metals via the preparation
of 6a and 6b. Solid-state structural characterization of
this series of compounds outlines skeletal changes as a
function of metal coordination. Future efforts will focus
on elaboration of these macrocyclic systems to afford
higher order transition-metal complexes.
F igu r e 2. (top) ORTEP drawing of 6a (20% probability
level). Selected bond lengths (Å) and angles (deg): Pt-N
) 2.062(7), Pt-S ) 2.271(3), Pt-Cl(1) ) 2.285(3), Pt-Cl-
(2) ) 2.304(3); C(12)-C(13)-C(15) ) 112.2(8), C(16)-
C(17)-C(19) ) 114.2(7), C(22)-C(23)-C(25) ) 112.4(8),
C(26)-C(27)-C(29) ) 113.0(8), N-Pt-S ) 177.4(2), Cl(1)-
Pt-Cl(2) ) 178.41(10). (bottom) ORTEP drawing of 6b
(20% probability level). Only the ipso carbons of the
triphenylphosphine ligands are shown, for clarity. Selected
bond lengths (Å) and angles (deg): Pt(2)-N ) 2.051(4),
Pt(2)-S ) 2.2665(14), Pt(2)-Cl(1) ) 2.3029(14), Pt(2)-Cl-
(2) ) 2.2909(14), Pt(1)-P(1) ) 2.3076(12), Pt(1)-P(2) )
2.3037(12), Pt(1)-C(20) ) 2.004(4), Pt(1)-C(21) ) 1.998-
(4), C(19)-C(20) ) 1.201(6), C(21)-C(22) ) 1.209(6);
C(12)-C(13)-C(15) ) 112.8(4), C(16)-C(17)-C(19) )
111.1(4), C(22)-C(23)-C(25) ) 113.6(4), C(26)-C(27)-
C(29) ) 112.6(4), P(1)-Pt(1)-P(2) ) 177.28(4), C(20)-
Pt(1)-C(21) ) 176.36(19), N-Pt(2)-S ) 176.04(12), Cl(1)-
Pt(2)-Cl(2) ) 178.87(5). The cocrystallized solvent is not
shown in either case.
Ack n ow led gm en t. We are grateful for financial
support provided by the University of Alberta and the
Natural Sciences and Engineering Research Council of
Canada (NSERC). K.C. thanks NSERC for a graduate
scholarship.
and the increased planarity slightly add to the strain
present in the conjugated framework of the ligand. The
mean alkyne bond angle is 173.8° with a minimum
angle of 169.4(8)° (C(4)-C(30)-C(29)). The vinylidene
bond angles C(16)-C(17)-C(19) ) 112.1(5)°, C(12)-
C(13)-C(15) ) 112.7(6)°, C(26)-C(27)-C(29) ) 114.1-
(6)°, and C(22)-C(23)-C(25) ) 111.4(6)° are on average
the same as found in 5a . The P(1)-Pt-P(2) and C(20)-
Pt-C(21) bond angles at 177.77(6) and 179.6(3)°, re-
Su p p or tin g In for m a tion Ava ila ble: Text and figures
giving synthetic and spectral details for 4, 5a ,b, and 6a ,b and
tables and figures giving X-ray crystallographic details for 5a ,b
and 6a ,b. This material is available free of charge via the
Internet at http://pubs.acs.org.
OM020738K