Anion directed synthesis of paddlane and trisilver tweezer complexes based upon silver coordination chemistry

Article abstract of DOI:10.1021/ja050154k

Addition of AgBF₄ or Ag(O₃SCF₃) to the tripodal ligand, ^Me₃tacnRh(CCPh)₃, yields a paddlane complex as well as a novel trinuclear silver "tweezer" complex based upon silver acetylene coordination chemistry. The paddlane is composed of two ^Me₃tacnRh(CCPh)₃ moieties held together by silver acetylene interactions. The tweezer complex is composed of one tripodal moiety with three silver atoms coordinated to each acetylene-Rh-acetylene face. The tweezer complex is stabilized by additional interactions, including a triflate anion which serves to cap the complex. Copyright

Full text of DOI:10.1021/ja050154k

Published on Web 03/30/2005
Anion Directed Synthesis of Paddlane and Trisilver Tweezer Complexes
Based upon Silver Coordination Chemistry
Paul D. Custer, Jered C. Garrison, Claire A. Tessier,* and Wiley J. Youngs*
Department of Chemistry, The UniVersity of Akron, Akron, Ohio 44325
Received January 10, 2005; E-mail: youngs@uakron.edu
Scheme 1
The self-assembly of supramolecular species is a major area of
research interest.1 Many self-assembly motifs have been based upon
metal coordination chemistry and labile σ donors. The advantages
of these metal-labile donor systems are that the metals provide a
fixed geometry, making it easier to design complex architectures.
The coordination of transition metals to alkyne-containing moieties
is well-known.2
Our group has been interested in alkyne-containing cyclophanes
(cyclynes),2b,h,k as well as heterocyclynes, such as platinum-alkyne-
based molecular squares, for some time.3 We have previously used
silver coordination chemistry to self-assemble supramolecular
complexes of cyclynes.4 Anions have been shown to play a directing
role in the coordination chemistry of silver alkynes.5 Herein, we
report the synthesis of the rhodium tripodal acetylide 2 (Scheme
1) and the study of the coordination chemistry of 2 with AgBF4
and Ag(O3SCF3). The silver tetrafluoroborate complex of 2 self-
assembles to form a novel paddlane 3 based upon silver alkyne
coordination chemistry. With silver triflate, 2 forms a unique
trinuclear silver alkyne tweezer complex 4.
Me3
The combination of Me tacnRhCl3 ( tacn ) N,N′,N′′-trimethyl-
2.627(6) Å. The alkyne bonds lengthen, compared to 2, by an
3
1,4,7-triazacyclononane), 1,6 with an excess of PhCCLi results in
the formation of the tripodal rhodium phenylacetylide, Me tacnRh-
(CCPh)3, 2, as a white solid (65%). Combining 2 with excess AgBF4
in acetonitrile gives 3 (97%) as off-white crystals. Interestingly,
the combination of excess Ag(O3SCF3) and 2 in acetonitrile does
not produce the triflate salt of 3, but instead yields the trinuclear
silver tweezer complex 4 as light-brown crystals (88%).
average of 0.048(7) Å upon coordination to the silver cations.
Crystals of 4, suitable for X-ray diffraction, were grown from a
concentrated acetonitrile solution. The molecular structure of
complex 4 is depicted in Figure 3. Complex 4 is a novel trinuclear
silver alkyne complex with a silver cation bonding to each alkyne-
rhodium-alkyne tweezer. The Ag-alkyne bond distances range
from 2.378(5) to 2.662(5) Å, with an overall average of 2.517(5)
Å. The silver cations are also stabilized by three triflate anions, as
well as a coordinating acetonitrile. The axial triflate is coordinated
to all three silver atoms with Ag(1)-O(1), Ag(2)-O(2), and Ag-
(3)-O(3) distances of 2.482(7), 2.397(5), and 2.424(5) Å, respec-
3
IR spectra of the tripodal alkyne ligand 2 show an alkyne
stretching frequency of 2103 cm-1. The alkyne stretching frequency
of 3 is 2047 cm-1; the frequency shift is consistent with coordination
of a metal to the alkyne. ES-MS of crystalline 3, in acetone, reveals
that the silver complex exists as the monomer and dimer in the gas
phase. The H and 13C NMR spectra of the cationic portions of 3
1
and 4 were indistinguishable.
Crystals of 2 and 3, suitable for X-ray diffraction studies, were
grown from a concentrated acetonitrile solution. The structures of
2 and 3 are depicted in Figures 1 and 2, respectively. Complex 2
is an octahedral complex with rhodium acetylide distances ranging
from 1.977(5) to 2.010(5) Å. In the solid state, 3 exists as a dimer
Me3
with two silver cations bridging two tacnRh(CCPh)3 moieties.
The tetrafluoroborate anions are noncoordinating. Each silver cation
is coordinated to two alkynes of one tripodal ligand [C(18)-C(19)
and C(26)-C(27)] and one alkyne of the other [C(10A)-C(11A)],
as well as to the other silver cation. The Ag(1)-Ag(1A) distance
is 2.9439(8) Å, which is slightly longer than silver-silver distances
of 2.89 Å in metallic silver.7 The shortest Ag-alkyne interaction
is the acetylene C(10A)-C(11A) (2.363(4) and 2.377(5) Å,
respectively). The remaining two alkynes, C(18)-C(19) and C(26)-
C(27), have bonding distances to Ag(1) ranging from 2.387(5) to
Figure 1. Molecular structure of 2. Selected bond distances (Å) and angles
(deg): Rh-C(10) ) 1.995(4), Rh-C(18) ) 2.010(5), Rh-C(26) ) 1.977-
(5), C(10)-C(11) ) 1.181(6), C(18)-C(19) ) 1.135(7), C(26)-C(27) )
1.197(6), C(10)-Rh-C(18) ) 91.16(18), C(18)-Rh-C(26) ) 91.94(17),
C(10)-Rh-C(26) ) 90.00(17), Rh-C(10)-C(11) ) 174.4(4), Rh-C(18)-
C(19) ) 167.1(4), Rh-C(26)-C(27) ) 174.1(4).
9
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J. AM. CHEM. SOC. 2005, 127, 5738-5739
10.1021/ja050154k CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
Figure 3. Detailed view of the acetylene coordination chemistry of 4. All
of the phenyl carbons except the meso ones have been removed for clarity.
Exterior triflate anions and the acetonitrile molecule have been removed,
except for the donor atoms. Selected bond distances (Å) and angles (deg):
Ag(1)-C(10) ) 2.443(5), Ag(1)-C(11) ) 2.468(6), Ag(1)-C(26) ) 2.551-
(5), Ag(1)-C(27) ) 2.565(5), Ag(1)-O(1) ) 2.482(7), Ag(1)-N(4) )
2.220(6), Ag(2)-C(10) ) 2.378(5), Ag(2)-C(11) ) 2.619(6), Ag(2)-C(18)
) 2.467(5), Ag(2)-C(19) ) 2.662(5), Ag(2)-O(2) ) 2.397(5), Ag(2)-
O(4) ) 2.279(4), Ag(3)-C(18) ) 2.418(5), Ag(3)-C(19) ) 2.617(5), Ag-
(3)-C(26) ) 2.409(5), Ag(3)-C(27) ) 2.605(5), Ag(3)-O(3) ) 2.424(5),
Ag(3)-O(7) ) 2.337(4), C(10)-C(11) ) 1.233(8), C(18)-C(19) ) 1.234-
(7), C(26)-C(27) ) 1.227(8), Rh(1)-C(10)-C(11) ) 172.7(5), Rh(1)-
C(18)-C(19) ) 176.0(4), Rh(1)-C(26)-C(27) ) 176.0(5).
Figure 2. (a) Cationic portion of 3 showing the paddlane arrangements.
(b) Emphasizing the coordination about the silver cations. All of the phenyl
carbon atoms except the meso ones have been removed for clarity. Selected
bond distances (Å) and angles (deg): Ag(1)-Ag(1A) ) 2.9439(8), Ag-
(1)-C(10) ) 2.363(4), Ag(1)-C(11) ) 2.377(5), Ag(1)-C(18) ) 2.387-
(5), Ag(1)-C(19) ) 2.466(5), Ag(1)-C(26) ) 2.515(5), Ag(1)-C(27) )
2.627(6), C(10)-C(11) ) 1.218(8), C(18)-C(19) ) 1.221(7), C(26)-C(27)
) 1.219(8), Rh(1)-C(10)-C(11) ) 168.9(4), Rh(1)-C(18)-C(19) )
174.0(5), Rh(1)-C(26)-C(27) ) 175.0(5).
Supporting Information Available: Crystallographic data and
detailed experimental preparations of 2, 3, and 4. ES-MS and IR spectra
of 2 and 3. This material is available free of charge via the Internet at
http://pubs.acs.org.
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silver each, but with shorter silver-oxygen bond distances [Ag-
(2)-O(4) ) 2.279(4) Å and Ag(3)-O(7) ) 2.337(4) Å]. The
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In conclusion, we have synthesized a rhodium tripodal acetylide
complex 2. We reported the synthesis and structural characterization
of a novel silver-alkyne paddlane complex, as well as a unique
trinuclear silver alkyne complex of 2. The two complexes appear
to be formed by the directing effects of the anions upon the silver
alkyne coordination chemistry. Our future work will explore the
dynamic behavior of 3 and 4, as well as explore the coordination
chemistry of these novel rhodium tripodal acetylide ligands with
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Acknowledgment. We thank the National Science Foundation
(CHE-0315980) for the financial support of this research. We also
gratefully acknowledge The University of Akron and the Ohio
Board of Regents for financial support.
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