[2+2] Photodimerization in the solid state aided by molecular templates of rectangular macrocycles bearing oxamidato ligands

Article abstract of DOI:10.1021/om901125r

A series of binuclear half-sandwich iridium and rhodium complexes bearing oxamidato ligands [Cp^*₂M₂(μ-N,N'- bis(aryl)oxamidato)Cl₂] (1a, M = Ir, aryl = Ph; 1b, M = Ir, aryl = C₆H₄-p-Me; 2a, M = Rh, aryl = Ph; 2b, M = Rh, aryl = C₆H₄-p-Me) functioned as potential organometallic clip linear templates were synthesized by the reactions of the lithium salts of oxamide with [Cp^*MCl₂]₂ (M = Ir or Rh), respectively. Treatment of the binuclear complexes (1a-2b) with trans-1,2-bis(4-pyridyl)ethylene (4,4'-bpe) in the presence of AgOTf (OTf = CF₃SO₃) gave the corresponding tetranuclear complexes of general formula [Cp^*₄M₄(μ-N,N'- bis(aryl)oxamidato)2(μ-4,4'-bpe)₂]-(OTf)₄ (3a, M = Ir, aryl = Ph; 3b, M = Ir, aryl = C6H₄-p-Me; 4a, M = Rh, aryl = Ph; 4b, M = Rh, aryl = C₆H₄-p-Me) in high yields. Confirmed by the single-crystal X-ray analysis, the molecular structures of tetranuclear complexes 3a and 4a showed that two binuclear fragments as building blocks were connected by μ-4,4'-bpe to construct a rectangular cavity with the dimensions 5.58 × 13.59 A (3a) and 5.55 ×13.65A (4a). The two μ-4,4'-bpe ligands in 3a and 4a are close to each other within 4.2 A to allow the [2+2] photoreaction in the solid state, which was proved by ¹H NMR of the resulting products (5a-6b') and single-crystal X-ray analysis.

Full text of DOI:10.1021/om901125r

2842 Organometallics 2010, 29, 2842–2849
DOI: 10.1021/om901125r
[2þ2] Photodimerization in the Solid State Aided by Molecular Templates
of Rectangular Macrocycles Bearing Oxamidato Ligands
Wan-Zheng Zhang, Ying-Feng Han, Yue-Jian Lin, and Guo-Xin Jin*
Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, Department of Chemistry,
Advanced Materials Laboratory, Fudan University, Shanghai, 200433, People’s Republic of China
Received December 28, 2009
A series of binuclear half-sandwich iridium and rhodium complexes bearing oxamidato ligands
[Cp*2M2(μ-N,N0-bis(aryl)oxamidato)Cl2] (1a, M=Ir, aryl=Ph; 1b, M=Ir, aryl=C6H4-p-Me; 2a,
M=Rh, aryl=Ph; 2b, M=Rh, aryl=C6H4-p-Me) functioned as potential ‘‘organometallic clip’’
linear templates were synthesized by the reactions of the lithium salts of oxamide with [Cp*MCl2]2
(M = Ir or Rh), respectively. Treatment of the binuclear complexes (1a-2b) with trans-1,2-bis(4-
pyridyl)ethylene (4,40-bpe) in the presence of AgOTf (OTf = CF3SO3) gave the corresponding
tetranuclear complexes of general formula [Cp*4M4(μ-N,N0-bis(aryl)oxamidato)2(μ-4,40-bpe)2]-
(OTf)4 (3a, M = Ir, aryl = Ph; 3b, M = Ir, aryl = C6H4-p-Me; 4a, M = Rh, aryl = Ph; 4b, M =
Rh, aryl=C6H4-p-Me) in high yields. Confirmed by the single-crystal X-ray analysis, the molecular
structures of tetranuclear complexes 3a and 4a showed that two binuclear fragments as building
blocks were connected by μ-4,40-bpe to construct a rectangular cavity with the dimensions 5.58 ꢀ
0
˚
˚
13.59 A (3a) and 5.55ꢀ13.65 A (4a). The two μ-4,4 -bpe ligands in 3a and 4a are close to each other
1
˚
within 4.2 A to allow the [2þ2] photoreaction in the solid state, which was proved by H NMR of the
resulting products (5a-6b0) and single-crystal X-ray analysis.
Introduction
by employing noncovalent bonds such as hydrogen bonds,
coordination bonds, π π stacking, and halogen-halogen
forces, and it has still been a challenge to organize the two
double bonds in the solid state.6,7
By using the strength and directionality of hydrogen bonds
and coordination-driven self-assembly to functionalize mo-
lecules as linear templates, MacGillivray and co-workers
have assembled olefinic compounds within discrete molecu-
lar assemblies in the solid state for the [2þ2] photoreaction.8
We9 and others10 have reported the synthesis of a series
of tetranuclear complexes with half-sandwich Ir, Rh, and
Ru fragments by the combination of binuclear complexes
3 3 3
To rationally design a molecule that adopts suitable geo-
metric criteria that is not easy to achieve in the liquid phase
for reaction in the solid state is currently attracting signifi-
cant attention.1 That ecologically harmful organic solvents
are not required in the solid state means not only the
development of simple, more environmentally friendly syn-
thetic method2 but also access in high efficiency and selec-
tivity to a product that is less available or unavailable in
solution.3 The foundation of the solid-state bimolecular
reaction was based on the pioneering work of Schmidt and
co-workers.4 Ever since Schmidt postulated conditions for
the photochemical dimerization of CdC bonds in the solid
state,5 extensive studies have been made on the template-
controlled solid-state photochemical [2þ2] cycloadditions
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Ziller, J. W.; Lobkovsky, E. B.; Grubbs, R. H. J. Am. Chem. Soc. 1998, 120,
3641–3649. (e) Maekawa, Y.; Kato, S.; Hasegawa, M. J. Am. Chem. Soc.
1991, 113, 3867–3872. (f) Sharma, C. V. K.; Panneerselvam, K.; Shimoni, L.;
Katz, H.; Carrell, H. L.; Desiraju, G. R. Chem. Mater. 1994, 6, 1282–1292.
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*Correspondingauthor. Tel: þ86-21-65643776. Fax: þ86-21-65641740.
E-mail: gxjin@fudan.edu.cn.
(1) (a) MacGillivray, L. R.; Papaefstathiou, G. S.; Friscic, T.; Varsh-
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(b) Holman, K. T.; Pivovar, A. M.; Swift, J. A.; Ward, M. D. Acc. Chem. Res.
2001, 34, 107–118.
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metallics 2004, 23, 5813–5817. (f) Lee, J. Y.; Hong, S. J.; Kim, C.; Kim, Y.
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Published on Web 06/08/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 13, 2010 2843
Scheme 1. Photodimerization of [Cp*4M4(μ-4,40-bpe)2(μ-C2O4)2](OTf)4
Scheme 2. Synthesis of Binuclear and Tetranuclear Complexes
bridged by oxalato or chloranilate and pyridyl-based sub-
units. In these complexes, the distances between two pyridyl-
based ligands are close to each other because of the presence
of π π interactions and fall within the ranges for [2þ2]
3 3 3
photoreaction.5
By taking into account the dimensions of the tetranuclear
rectangle macrocycles and using the μ-oxalato binuclear
iridium and rhodium complexes as ‘‘organometallic clip’’
linear templates, [2þ2] photodimerization has been inves-
tigated (Scheme 1), which was based on ‘‘organometallic
macrocycles’’ through single-crystal to single-crystal trans-
formation.9f UV irradiation of [Cp*2Ir4(μ-η4-C2O4)2(μ-4,40-
bpe)2](OTf)4 and [Cp*2Rh4(μ-η4-C2O4)2(μ-4,40-bpe)2](OTf)4
produced the expected rctt-tetrakis(4-pyridyl)cyclobutane
(rctt-tpcb) in high yields after a period of 25 or 50 h (Scheme 1).
Therrien’s group reported the formation of [Ru4(η6-p-
cymene)4(μ-oxalato)2(μ-rctt-tpcb)](OTf)4 by [2þ2] cycload-
dition of the olefinic double bonds in the supramolecular
rectangle [Ru4(η6-p-cymene)4(μ-oxalato)2(μ-4,40-bpe)2](OTf)4.10d
Compared with μ-oxalato binuclear iridium and rhodium com-
plexes, we anticipate that μ-oxamidato binuclear iridium
and rhodium complexes could also play a role as potential
‘‘organometallic clip’’ linear templates to assemble 4,40-bpe
in tetranuclear rectangle macrocycles with ordered geome-
try, which would be suitable for exploring [2þ2] photodi-
merization in the solid state. Herein we report the stepwise
formation of bi- and tetranuclear half-sandwich iridium and
rhodium complexes bearing oxamidato bridges, based on
4,40-bpe subunits. A new series of bi- and tetranuclear
iridium and rhodium complexes were synthesized and
characterized, and the solid-state photochemical [2þ2] cyclo-
addition activity of [Cp*4M4(μ-N,N0-bis(aryl)oxamidato)2-
(μ-4,40-bpe)2](OTf)4 (M=Ir, 3a, aryl=Ph; 3b, aryl=C6H4-
p-Me; M = Rh; 4a, aryl = Ph; 4b, aryl = C6H4-p-Me) was
explored. The structures of binuclear complex [Cp*2Rh2(μ-
N,N0-bis(4-methylphenyl)oxamidato)Cl2] (2b) and tetranuc-
lear complexes 3a, 4a, and irradiated product [Cp*4Ir4(μ-N,
N0-diphenyloxamidato)2(μ-rctt-tetrakis(4-pyridyl)cyclobut-
ane)](OTf)4 were confirmed by X-ray analysis.
ꢀꢀ ꢁ
(8) (a) Gao, X.; Friscic, T.; MacGillivray, L. R. Angew. Chem., Int.
ꢀꢀ ꢁ
Ed. 2002, 41, 2070–2073. (b) Friscic, T.; MacGillivray, L. R. Chem.
Commun. 2003, 1306–1307. (c) Dushyant, B.; Papaefstathiou, G. S.;
MacGillivray, L. R. Chem. Commun. 2002, 1964–1965. (d) Papaefstathiou,
G. S.; Zhong, Z. M.; Geng, L.; MacGillivray, L. R. J. Am. Chem. Soc. 2004,
126, 9158–9159. (e) MacGillivray, L. R.; Reid, J. L.; Ripmeester, J. A. J. Am.
Chem. Soc. 2000, 122, 7817–7818. (f) Hamilton, T. D.; Papaefstathiou,
G. S.; MacGillivray, L. R. J. Am. Chem. Soc. 2002, 124, 11606–11607.
(9) (a) Wang, J.-Q.; Ren, C.-X.; Jin, G.-X. Organometallics 2006, 25,
74–81. (b) Wang, J.-Q.; Zhang, Z.; Weng, L.-H.; Jin, G.-X. Chin. Sci. Bull.
2004, 49, 735–738. (c) Han, Y.-F.; Lin, Y.-J.; Jia, W.-G.; Weng, L.-H.; Jin,
G.-X. Organometallics 2007, 26, 5848–5853. (d) Han, Y.-F.; Lin, Y.-J.; Jia,
W.-G.; Jin, G.-X. Organometallics 2008, 27, 4088–4097. (e) Han, Y.-F.; Jia,
W.-G.; Lin, Y.-J.; Jin, G.-X. Organometallics 2008, 27, 5002–5008. (f) Han,
Y.-F.; Lin, Y.-J.; Jia, W.-G.; Wang, G.-L.; Jin, G.-X. Chem. Commun. 2008,
1807–1809. (g) Han, Y.-F.; Lin, Y.-J.; Jia, W.-G.; Jin, G.-X. Angew. Chem.,
Int. Ed. 2009, 48, 6234–6238. (h) Jia, W.-G.; Han, Y.-F.; Lin, Y.-J.; Weng,
L.-H.; Jin, G.-X. Organometallics 2009, 28, 3459–3464. (i) Zhang, W.-Z.;
Han, Y.-F.; Lin, Y.-J.; Jin, G.-X. Dalton. Trans. 2009, 8426–8431.
Result and Discussion
As shown in Scheme 2, when oxamide compounds were
treated successively with 2 equiv of n-BuLi in THF at -78 °C
and 1 equiv of [Cp*IrCl2]2 or [Cp*RhCl2]2 at 50 °C, the
binuclear complexes [Cp*2M2(μ-N,N0-bis(aryl)oxamidato)-
Cl2] (1a, M = Ir, aryl = Ph; 1b, M = Ir, aryl = C6H4-p-Me;
2a, M=Rh, aryl=Ph; 2b, M=Rh, aryl=C6H4-p-Me) were
formed in about 70% yields. The 1H NMR spectra showed a
sharp singlet at δ=1.34 for 1a and 1.33 for 1b due to the Cp*
protons, and the signals of N-H were absent. For 2a and 2b,
(10) (a) Yamamoto, Y.; Suzuki, H.; Tajima, N.; Tatsumi, K. Chem.-
Eur. J. 2002, 8, 372–379. (b) Suzuki, H.; Tajima, N.; Tatsumi, K.; Yama-
moto, Y. Chem. Commun. 2000, 1801–1802. (c) Yan, H.; S€uss-Fink, G.;
Neels, A.; Evans, H. S. J. Chem. Soc., Dalton Trans. 1997, 4345–4350.
(d) Barry, N. P. E.; Therrien, B. Inorg. Chem. Commun. 2009, 12, 465–468.

2844 Organometallics, Vol. 29, No. 13, 2010
Zhang et al.
The structures of 3a and 4a have also been confirmed by
X-ray analyses at 293 K. The yellow single crystal 3a was
obtained by slow diffusion of Et2O into CH2Cl2 solutions of
3a, while red single crystal 4a was obtained by slow diffusion
of hexane into CH2Cl2 solutions of 4a. Perspective drawings
of 3a and 4a with the atomic numbering scheme are given in
Figures 2a and 3, respectively. The crystal units of 3a and 4a
are composed of [Cp*2M4(μ-N,N0-diphenyloxamidato)2-
(μ-4,40-bpe)2]4þ (3a, M=Ir; 4a, M=Rh) cations and OTf-
counteranions in the solid. Assuming that the Cp* ligand
occupies three coordination sites, each Ir or Rh center adopts
a three-legged piano-stool conformation, which has six-co-
ordinate geometry and is coordinated by one nitrogen atom
and one oxygen atom from the oxamidato ligand and one
nitrogen atom from 4,40-bpe. The complex cations have a
rectangular cavity bridged by oxamidato ligands and 4,40-
˚
bpe molecules with the dimensions 5.58ꢀ13.59 A for 3a and
˚
5.55 ꢀ 13.65 A for 4a, respectively. The complex cations of
Figure 1. Complex cation of 2b with thermal ellipsoids drawn at
the 30% level. All hydrogen atoms are omitted for clarity.
Selected distances (A) and angles (deg): Rh(1)-N(1) 2.097(3),
Rh(1)-O(1) 2.127(2), Rh(1)-Cl(1) 2.4012(13), N(1)-C(1A)
1.301(4), N(1)-C(2) 1.429(4), O(1)-C(1) 1.275(4), C(1)-C(1A)
1.500(6), N(1)-Rh(1)-O(1) 77.63(9),N(1)-Rh(1)-Cl(1) 87.48(9),
O(1)-Rh(1)-Cl(1) 87.37(8), C(1A)-N(1)-Rh(1) 115.6(2), C(1)-
O(1)-Rh(1) 113.41(19),O(1)-C(1)-N(1A) 127.0(3),O(1)-C(1)-
C(1A) 118.4(3), N(1A)-C(1)-C(1A) 114.6(3).
[Cp*2Ir4(μ-η4-C2O4)2(μ-4,40-bpe)2]4þ are known to consist of
a cavity with the dimension 5.56ꢀ13.25 A,9f which is similar
˚
˚
to that of 3a and 4a.
As anticipated, the structure of 3a showed that the two
4,40-bpe ligands are close to each other. Unlike the double
bonds of the two 4,40-bpe ligands in [Cp*2Ir4(μ-η4-C2O4)2(μ-
4,40-bpe)2](OTf)4, which lie parallel to each other with a
distance of 3.23 A,9f the double bonds are criss-crossed with
˚
a torsion angle of 75.3° and the center-to-center distance
the 1H NMR showed similar spectra compared with 1a and 1b.
These spectroscopic data indicate a dimeric structure in which
the Ir or Rh centers are connected by an oxamidato ligand.
The structure of 2b was confirmed by X-ray crystal
analysis at 293 K. The red crystal was obtained by slowly
evaporating a CHCl3 solution of 2b. A perspective drawing
of 2b with the atomic numbering scheme is given in Figure 1.
The crystal structure of 2b consists of binuclear units, con-
nected by an oxamidato ligand, and each rhodium atom is
surrounded by one oxygen atom and one nitrogen atom from
the oxamidato ligand and one chlorine atom. All of the rhod-
ium centers have six-coordinate geometry, assuming that the
Cp* ligand occupies three coordination sites. The two rho-
˚
3.79 A, as shown in Figure 2b. The C25 C26 and C25-
3 3 3
˚
(A) C26(A) distances are 3.87 A. The contacts between
3 3 3
˚
CdC bonds of adjacent assemblies are 10.33 and 8.65 A, as
shown in Figure 2c,d. Consequently, [2þ2] photodimeriza-
tion is unlikely to occur between adjacent assemblies accord-
ing to the distance criterion of Schmidt for [2þ2] photo-
reactions.5 As a result, the double bonds of the assembly are
the sole olefins of the solids that conform to the criterion of
photodimerization in a solid.
As shown in Scheme 3, a powdered crystalline sample of 3a
was subjected to UV irradiation using an Hg lamp for a
period of approximately 30 h to investigate its photoreaction
activity. The cycloaddition was accompanied by a color
change from yellow to pale yellow. The dimerization of 4,40-
bpe gave two stereoisomers of cyclobutane rings 5a and 5a0 in
100% photochemical conversion, of which 64.5% is due to
rctt-tpcb (5a) (where rctt-tpcb = rctt-tetrakis(4-pyridyl)cyclo-
butane) and 35.5% is due to the rtct-tpcb isomer (5a0) (where
rtct-tpcb = rtct-tetrakis(4-pyridyl)cyclobutane) (Table 1), as
˚
dium atoms are separated by 5.5917(17) A, similar to the
4
8c
˚
Rh Rh distance (5.548 A) of [Cp*2Rh2(μ-η -C2O4)Cl2].
The Rh-N and Rh-O bond distances are 2.097(3) and
2.127(2) A, respectively. The bond distance of Rh-Cl is
2.4012(13) A, and the two chlorine atoms are oriented in a
3 3 3
˚
˚
trans manner.
1
1
Tetranuclear complexes bearing 4,40-bpe ligands, which
are formulated as [Cp*4Ir4(μ-N,N0-bis(aryl)oxamidato)2(μ-
4,40-bpe)2](OTf)4 (3a, aryl = Ph; 3b, aryl = C6H4-p-Me),
were prepared by direct reaction of 1a or 1b with 4,40-bpe in
evident by H NMR spectroscopy in CDCl3. The H NMR
spectrum showed complete disappearance of the singlet for the
pyridyl protons at δ = 7.89 and 8.14 ppm, the appearance of
signals at δ=5.70 and 4.98 ppm due to rctt-tpcb protons, and
signals at δ = 5.62 and 5.24 ppm due to rtct-tpcb protons, as
shown in Figure 4.
1
the presence of AgOTf (Scheme 2) in high yields. The H
NMR spectrum of 3a showed resonances at approximately
δ=7.89 (d) and 8.14 (d) ppm, which are assigned to dipyridyl
protons. Similarly, in the 1H NMR spectrum, the CHdCH
protons appear at 7.63 ppm for 3b as a singlet, while the
resonances for the pyridyl unit appear at approximately δ=
7.86 (d) and 8.12 (d). A sharp singlet at δ=1.25 is observed
due to the protons of Cp* of 3a and 3b.
X-ray crystallographic analysis of [Cp*4Ir4(μ-N,N0-dip-
henyloxamidato)2(μ-rctt-tpcb](OTf)4 (5a) at 293 K confir-
med the formation of new bonds, as shown in Figure 5. The
pyridyl rings are bent toward each other. Similarly to 3a,
each Ir atom is coordinated by one nitrogen atom from
rctt-tpcb and one oxygen atom and one nitrogen atom of
4a and 4b were obtained from 2a or 2b, AgOTf, and 4,40-
bpe by a similar procedure to that described for 3a and 3b in
bridging oxamidato ligands with Ir Ir separations of 5.6
3 3 3
˚
and 13.45 A, as defined by the iridium centers. For the
complex [Cp*2Ir4(μ-η4-C2O4)2(μ-4,40-tpcb)2](OTf)4,9f each
Ir atom is coordinated by one nitrogen atom from rctt-tpcb
and two oxygen atoms of bridging oxalato ligands with
1
about 70% yields. The H NMR spectrum of 4a showed
singlets at δ = 1.29, 7.55, 7.80, and 8.04 ppm due to Cp*,
olefinic, and the pyridyl protons, respectively. A similar 1H
NMR spectrum of 4b was also observed.
˚
Ir Ir separations of 5.56 and 13.12 A, as defined by the
3 3 3

Article
Organometallics, Vol. 29, No. 13, 2010 2845
Figure 2. (a) Complex cation of 3a with thermal ellipsoids drawn at the 30% level. All hydrogen atoms, anions, and solvent molecules
are omitted for clarity. (b) The double bonds are criss-crossed with a torsion angle of 75.3°. (c) Stacking of the molecules in crystals of 3a
viewed along the c-axis. (d) Stacking of the molecules in crystals of 3a viewed along the a-axis. d1 (3.79 A) represents the center-to-center
˚
0
˚
˚
distance between double bonds of the two 4,4 -bpe ligands in the organometallic macrocycles, while d2 (=10.33 A) and d3 (=8.65 A)
represent the distance of CdC bonds between adjacent assemblies. Ir, N, O, and C atoms are represented by green, blue, red, and gray,
˚
respectively. Selected distances (A) and angles (deg): Ir(1)-O(1) 2.116(5), Ir(1)-N(1) 2.119(6), Ir(1)-N(3) 2.127(7), Ir(2)-N(2)
2.100(6), Ir(2)-O(2) 2.122(5), Ir(2)-N(4) 2.144(9), O(1)-Ir(1)-N(1) 77.4(2), O(1)-Ir(1)-N(3) 83.4(2), N(1)-Ir(1)-N(3) 87.0(2),
C(1)-N(1)-Ir(1) 115.5(5), C(3)-N(1)-Ir(1) 127.2(5), C(2)-O(1)-Ir(1) 115.5(5), N(1)-C(1)-C(2) 115.8(7), O(1)-C(2)-C(1)
115.3(7).
iridium centers, which are similar to that of the corre-
sponding distances for [Cp*4Ir4(μ-N,N0-diphenyloxamid-
ato)2(μ-rctt-tpcb](OTf)4. As a result, the carbon-carbon
[Cp*2Ir4(μ-η4-C2O4)2(μ-4,40-tpcb)2](OTf)4 are 1.45 and
˚
1.87 A.
UV irradiation of a powdered crystalline sample of 3b
similarly also gave the products as a mixture of rctt-tpcb
(5b) and rtct-tpcb (5b0) in 100% photochemical conversion
˚
bond lengths of rctt-tpcb are 1.53, 1.54, 1.56, and 1.61 A,
while the carbon-carbon bond lengths of rctt-tpcb of

2846 Organometallics, Vol. 29, No. 13, 2010
Zhang et al.
(rctt-tpcb, 75.2%; rtct-tpcb, 24.8%) after a period of
30 h (Table 1), as evident by 1H NMR spectroscopy in
CDCl3 (Figure 6). The cycloaddition was also accompanied
by a color change from yellow to pale yellow. The formation
of products was characterized by a complete disappearance
of the olefinic singlet at δ = 7.63 ppm; in addition, the
appearance of singlets at δ=5.66 and 4.99 ppm due to rctt-
tpcb protons and δ = 5.55 and 5.20 ppm due to rtct-tpcb
protons also evidenced the transformation.
Building on the orientation of the criss-crossed double
bonds of 3a, either the cycloaddition of C25, C26 and
C25(A), C26(A) or C25, C26(A) and C25(A), C26 will lead
to rtct-tpcb. The formation of rctt-tpcb requires both the
reactive olefins to be aligned in a parallel fashion. Therefore,
a conversion of the criss-crossed olefins to a parallel align-
ment must have occurred prior to dimer formation. This
could be interpreted by the double bonds of the 4,40-bpe
ligands undergoing pedal-like motion prior to photodimer-
ization. Such dynamic behavior of double bonds (CdC,
NdN, CdN) has been studied by Ogawa and co-workers.11
Some recent examples of solid-state [2þ2] photoreactions
that gave regiospecific cyclobutane isomers can also be
rationalized on the assumption of pedal motion.12 UV
irradiation of 3b, which gave the products as a mixture,
could also be explained by the assumption of pedal motion.
The incomplete pedal-like motion of 4,40-bpe observed here
is reflected in the residual formation of rtct-tpcb during
photodimerization.
Figure 3. Complex cation of 4a with thermal ellipsoids drawn at
the 30% level. All hydrogen atoms, anions, and solvent mole-
˚
cules are omitted for clarity. Selected distances (A) and angles
(deg): Rh(1)-N(1) 2.112(4), Rh(1)-O(1) 2.124(3), Rh(1)-N(3)
2.140(4), Rh(2)-N(2) 2.112(4), Rh(2)-O(2) 2.111(3), Rh(2)-
N(4) 2.147(4), N(1)-Rh(1)-O(1) 78.06(14), N(1)-Rh(1)-N(3)
87.98(16), O(1)-Rh(1)-N(3) 85.82(16), C(1)-N(1)-Rh(1)
114.3(3), C(3)-N(1)-Rh(1) 127.2(3), C(2)-O(1)-Rh(1) 113.3(3),
O(1)-C(2)-C(1) 118.6(4), N(1)-C(1)-C(2) 115.1(4).
Scheme 3. Photodimerization of 3a-4b
Table 1. Formation of rctt-tpcb and rtct-tpcb on Photolysis of Complexes 3a-4b
starting
material
yield of
rctt-tpcb (%)
yield of
rtct-tpcb (%)
a
d (A)
˚
cavity (A)
˚
metal
time (h)
conversion (%)
3a
3b
4a
4b
Ir
Ir
Rh
Rh
5.58 ꢀ 13.59
5.55 ꢀ 13.65
3.79
30
30
260
260
100
100
41.7
35.9
64.5
75.2
29.2
25.6
35.5
24.8
12.5
10.3
4.05
ad represents the center-to-center distance of the reactive carbon-carbon double bond.

Article
Organometallics, Vol. 29, No. 13, 2010 2847
Figure 4. 1H NMR spectra of 3a (400 MHz, CDCl3) before UV
irradiation (a) and after 30 h of UV irradiation (b). The red circle
represents the signal of rctt-tpcb (5a), while the blue circle repre-
sents the signal of rtct-tpcb (5a0), and the green circle represents the
signal of CH2Cl2.
Figure 6. 1H NMR spectra of 3b (400 MHz, CDCl3) before UV
irradiation (a) and after 30 h of UV irradiation (b). The red circle
represents the signal of rctt-tpcb (5b), while the blue circle repre-
sents the signal of rtct-tpcb (5b0), and the green circle represents the
signal of CH2Cl2.
were re-collected at 100 K, we found that the double bonds of
the two 4,40-bpe ligands in 4a adopt two conformations in the
structure: parallel and antiparallel. This type of phenomenon
that the occupancy factor of the misoriented conformer
decreases as the temperature decreases could well compare
with the conclusions drawn by Ogawa and co-workers.11 The
˚
distances of C20 C26 and C20(A) 26(A) are 4.14 A,
3 3 3
3 3 3
which is longer than that of 3a. UV irradiation of powdered
crystalline samples of 4a for a period of approximately 260 h
also gave the products as a mixture of rctt-tpcb (6a) and rtct-
tpcb (6a0) in 29.2% and 12.5% yields, respectively, which was
evidenced by the 1H NMR (Table 1). Similarly, the mixture
of products rctt-tpcb (6b) and rtct-tpcb (6b0) in 25.6% and
10.3% yields was also obtained by UV irradiation of pow-
dered crystalline samples of 4b for a period of approximately
260 h.
Figure 5. Complex cation of 5a with thermal ellipsoids drawn at
the 30% level. All hydrogen atoms, anions, and solvent mole-
˚
cules are omitted for clarity. Selected distances (A) and angles
(deg): Ir(1)-N(5) 2.117(9), Ir(1)-N(1) 2.122(9), Ir(1)-O(1)
2.130(8), Ir(2)-O(2), 2.090(9), Ir(2)-N(2) 2.120(9), Ir(2)-N(7)
2.146(12), C(29)-C(35) 1.522(15), C(29)-C(30) 1.527(16), C-
(29)-C(32) 1.610(18), C(30)-C(40) 1.499(17), C(30)-C(31)
1.543(18), C(31)-C(32) 1.563(16), N(5)-Ir(1)-N(1) 87.2(4),
N(5)-Ir(1)-O(1) 84.3(4), N(1)-Ir(1)-O(1) 77.1(4), O(2)-Ir-
(2)-N(2) 78.3(4), O(2)-Ir(2)-N(7) 83.0(4), N(2)-Ir(2)-N(7)
86.3(4), C(2)-N(1)-Ir(1) 115.7(9), C(1)-N(2)-Ir(2) 113.3(8),
C(1)-O(1)-Ir(1) 114.7(8), C(2)-O(2)-Ir(2) 113.8(8), N(2)-
C(1)-O(1) 126.8(11), N(2)-C(1)-C(2) 115.9(12), O(1)-C(1)-
C(2) 117.3(12), O(2)-C(2)-N(1) 128.2(12), O(2)-C(2)-C(1)
117.7(12), N(1)-C(2)-C(1) 114.1(13).
Conclusion
We have presented the synthesis and characterization of a
series of bi- and tetranuclear half-sandwich iridium and rho-
dium complexes. All the binuclear complexes have been
shown to function as linear templates and to organize the
double bonds in criss-cross conformation in the solid state.
Prior to photodimerization, the conformation of these CdC
bonds of 4,40-bpe ligands was changed from antiparallel to
parallel through pedal-like motion. Hence the 4,40-bpe lig-
ands gave quantitative conversion to the cyclobutane deri-
vative with exclusively rctt stereochemistry on UV irradia-
tion of the powdered crystalline sample. The incomplete
pedal-like motion of 4,40-bpe resulted in the residual forma-
tion of rtct-tpcb during photodimerization. This is again an
example that proved that the olefinic bonds do not need to be
The double bonds of the two 4,40-bpe ligands in 4a are
also criss-crossed with a torsion angle of 84.8° and the center-
to-center distance 4.05 A. It is of interest that when the data
˚
(11) (a) Harada, J.; Ogawa, K. J. Am. Chem. Soc. 2001, 123, 10884–
10888. (b) Harada, J.; Ogawa, K.; Tomoda, S. J. Am. Chem. Soc. 1995, 117,
4476–4478. (c) Ogawa, K.; Sano, T.; Yoshimura, S.; Takeuchi, Y.; Toriumi,
K. J. Am. Chem. Soc. 1992, 114, 1041–1051. (d) Harada, J.; Ogawa, K.;
Tamoda, S. Acta Crystallogr. Sect. B 1997, 53, 662–672. (e) Harada, J.;
Harakawa, M.; Ogawa, K. Acta Crystallogr. Sect. B 2004, 60, 589–597.
(12) (a) Furukawa, D.; Kobatake, S.; Matsumoto, A. Chem. Com-
mun. 2008, 55–57. (b) Ohba, S.; Hosomi, H.; Ito, Y. J. Am. Chem. Soc. 2001,
123, 6349–6352. (c) Ito, Y.; Hosomi, H.; Ohba, S. Tetrahedron 2000, 56,
6833–6844. (d) Natarajan, A.; Mague, J. T.; Venkatesan, K.; Ramamurthy, V.
Org. Lett. 2005, 7, 1895–1898. (e) Peedikakkal, A. M. P.; Vittal, J. J.
Chem.-Eur. J. 2008, 14, 5329–5334.
˚
parallel (within 4.2 A) to one another in the solid state for
photoreaction. It is noticed that different half-sandwich
complex templates result in different geometries of the
organized CHdCH in the solid state compared with our
previous templates of μ-oxalato binuclear iridium and rho-
dium complexes. As a result, new products were obtained.
The interesting reactions provided in this report also cause us
to explore this kind of reaction by modifying the metal

2848 Organometallics, Vol. 29, No. 13, 2010
Zhang et al.
templates and olefinic compounds. Work is still in progress
following this pursuit.
and [Cp*RhCl2]2 (123.6 mg, 0.2 mmol). IR (KBr): ν/cm-1 3448.1,
2916.9, 1569.7, 1507.8, 1347.5, 1188.4, 1026.1, 803.6, 727.8, 527.9,
504.1. H NMR (400 MHz, CDCl3): δ (ppm) 7.56 (d, 4H; CH,
1
oxamidato), 7.08 (d, 4H; CH, oxamidato), 2.33 (s, 6H; CH3,
oxamidato), 1.33 (s, 30H; Cp*). Anal. Calcd for C36H44N2Cl2O2Rh2:
C, 53.15; H, 5.45; N, 3.44. Found: C, 53.05; H, 5.42; N, 3.31.
Preparation of Tetranuclear Complexes. [Cp*4Ir4(μ-N,N0-dip-
henyloxamidato)2(μ-4,40-bpe)2](OTf)4 (3a). Two equivalents of
AgOTf (36 mg, 0.14 mmol) was added to a suspension of bi-
nuclear complex 1a (48 mg, 0.05 mmol) in CH3OH (15 mL) at
room temperature, and the mixture was stirred for 4 h, followed
by filtration. One equivalent of 4,40-bpe (9 mg, 0.05 mmol) was
added to the filtrate, and the mixture was stirred for 15 h before
being filtered. The solvent was removed and the residue was
extracted with CH2Cl2. Yellow powders were obtained after
evaporation of the solvent under reduced pressure, washed with
diethyl ether, and dried in vacuo. Yield: 52 mg, 75.7%. IR (KBr):
ν/cm-1 3494.1, 3061.2, 2921.3, 1605.1, 1578.4, 1488.6, 1451.2,
1345.8, 1260.1, 1156.8, 1030.2, 748.3, 638.6, 574.2, 517.8. 1H
NMR (400 Hz, CDCl3): δ (ppm) 8.14 (d, 8H; CH, Py-H), 7.89
(d, 8H; CH, Py-H), 7.65(m, 12H; CH, oxamidato (8H); HCdCH,
4,40-bpe (4H)), 7.40 (m, 12H; CH, oxamidato), 1.25 (s, 60H; Cp*).
Anal. Calcdfor C96H100N8F12S4O16Ir4: C, 41.98; H, 3.67;N, 4.08.
Found: C, 41.96 ; H, 4.06; N, 4.06.
[Cp*4Ir4(μ-N,N0-bis(4-methylphenyl)oxamidato)2(μ-4,40-bpe)2]-
(OTf)4 (3b). This complex (yellow, 62.4 mg, 89%) was obtained
from 1b (50 mg, 0.05 mmol), AgOTf (36 mg, 0.14 mmol), and
4,40-bpe (10 mg, 0.05 mmol) by a similar procedure to that des-
cribed for 3a. IR (KBr): ν/cm-1 3506.2, 2922.6, 1613.3, 1585.1,
1507.3, 1343.9, 1260.1, 1158.2, 1031.4, 839, 639.5, 515.3. 1H
NMR (400 Hz, CD3OD): δ (ppm) 8.12 (d, 8H; CH, Py-H), 7.86
(d, 8H; CH, Py-H), 7.63 (s, 4H; HCdCH, 4,40-bpe), 7.46 (d, 8H;
CH, oxamidato), 7.25 (d, 8H; CH, oxamidato), 2.49 (s, 12H;
Experiment Section
All manipulations were performed using standard Schlenk
techniques under an atmosphere of nitrogen. CH2Cl2 was dried
over CaH2, and CH3OH was distilled over Mg/I2. THF, diethyl
ether, and hexane were dried over Na and then distilled under
1
nitrogen immediately prior to use. The H NMR spectra were
measured on a VAVCE-DMX 400 spectrometer in CDCl3 or
CD3OD. Elemental analysis was performed on an Elementar
Vario EL III analyzer. IR (KBr) spectra were recorded on a
Nicolet FT-IR spectrophotometer.
The oxamide compounds13 and [Cp*IrCl2]214 and [Cp*RhCl2]2
14
were prepared according to the reported procedures, while other
chemical reagents were purchased from commercial sources and
used without further purification.
Preparation of Binuclear Complexes. [Cp*2Ir2(μ-N,N0-diph-
enyloxamidato)Cl2] (1a). Two equivalents of n-BuLi (0.30 mL,
0.48 mmol) was added to a solution of N,N0-diphenyloxamide
(48 mg, 0.2 mmol) in 15 mL of THF at -78 °C. The reaction
mixture was allowed to reach room temperature gradually with
stirring in about 2 h. Then the mixture was added to a suspen-
sion of [Cp*IrCl2]2 (159.2 mg, 0.2 mmol) in 5 mL of THF and
stirred overnight at 50 °C. The solvent was evaporated in vacuo,
and the residue was extracted with CH2Cl2. The extract was
evaporated to dryness and washed with diethyl ether to give the
products (yellow, 148 mg, 76.8%). IR (KBr): ν/cm-1 3441.7,
2984.2, 2916, 1604.3, 1579.8, 1488.1, 1448.6, 1382.5, 1352,
1031.1, 944.6, 755.1, 697.8. 1H NMR (400 MHz, CDCl3):
δ (ppm) 7.60 (d, 4H; CH, oxamidato), 7.11-7.31 (m, 6H; CH,
oxamidato), 1.34 (s, 30H; Cp*). Anal. Calcd for C34H40N2-
Cl2O2Ir2: C, 42.36; H, 4.18; N, 2.91. Found: C, 42.03; H, 4.20;
N, 2.64.
CH3, oxamidato), 1.25 (s, 60H; Cp*). Anal. Calcd for C100H108
-
N8F12S4O16Ir4: C, 42.85; H, 3.88; N, 4.00. Found: C, 42.78; H,
4.06; N, 3.50.
[Cp*2Ir2(μ-N,N0-bis(4-methylphenyl)oxamidato)Cl2] (1b). This
complex (yellow, 150 mg, 75.6%) was prepared in a way analo-
gous to that for complex 1a using N,N0-bis(4-methylphenyl)-
oxamide (53.6 mg, 0.2 mmol), n-BuLi (0.30 mL, 0.48 mmol),
and [Cp*IrCl2]2 (159.2 mg, 0.2 mmol). IR (KBr): ν/cm-1 3458.2,
3024.4, 2989, 2914.6, 1586.3, 1507.4, 1449.7, 1382.7, 1352.4,
1190.6, 1032.4, 803.1, 729.7, 536.2. 1H NMR(400 MHz, CDCl3):
δ (ppm) 7.48 (d, 4H; CH, oxamidato), 7.07 (d, 4H; CH, oxa-
midato), 2.34 (s, 6H; CH3, oxamidato), 1.33 (s, 30H; Cp*). Anal.
CalcdforC36H44N2Cl2O2Ir2: C, 43.58; H, 4.47; N, 2.82. Found: C,
43.17; H, 4.58; N, 2.54.
[Cp*2Rh2(μ-N,N0-diphenyloxamidato)Cl2] (2a). Two equiva-
lents of n-BuLi (0.30 mL, 0.48 mmol) was added to a solution of
N,N0-diphenyloxamide (48 mg, 0.2 mmol) in 15 mL of THF at
-78 °C. The reaction mixture was allowed to reach room tem-
perature gradually with stirring in about 2 h. Then the mixture
was added to a suspension of [Cp*RhCl2]2 (123.6 mg, 0.2 mmol)
in 5 mL of THF and stirred overnight at 50 °C. The solvent was
evaporated in vacuo, and the residue was extracted with CH2Cl2.
The extract was evaporated to dryness and washed with diethyl
ether to give the products (orange, 115.6 mg, 73.6%). IR (KBr):
ν/cm-1 3445.8, 2914.3, 1599.4, 1576.4, 1487.2, 1350, 1076.3,
1026.4, 756.1, 698.9. 1H NMR (400 MHz, CDCl3): δ (ppm) 7.69
(d, 4H; CH, oxamidato), 7.10-7.32 (m, 6H; CH, oxami-
dato), 1.34 (s, 30H; Cp*). Anal. Calcd for C34H40N2Cl2O2Rh2:
C, 51.99; H, 5.13; N, 3.57. Found: C, 51.69; H, 5.49; N, 3.57.
[Cp*2Rh2(μ-N,N0-bis(4-methylphenyl)oxamidato)Cl2] (2b). This
complex (orange, 129.2 mg, 79.3%) was prepared in a way
analogous to that for complex 2a using N,N0-bis(4-methylphe-
nyl)oxamide (53.6 mg, 0.2 mmol), n-BuLi (0.30 mL, 0.48 mmol),
[Cp*4Rh4(μ-N,N0-diphenyloxamide)oxamidato)2(μ-4,40-bpe)2]-
(OTf)4 (4a). This complex (orange, 40 mg, 67%) was obtained
from 2a (40 mg, 0.05 mmol), AgOTf (36 mg, 0.14 mmol), and
4,40-bpe (10 mg, 0.05 mmol) by a similar procedure to that
described for 3a. IR (KBr): ν/cm-1: 3494.6, 3062.2, 2919.9,
1601.8, 1576.1, 1488.1, 1429.8, 1261.6, 1224.1, 1157.9, 1029.5,
750, 639.1, 567.2, 518.5. N. 1H NMR (400 Hz, CDCl3): δ (ppm)
8.04 (d, 8H; CH, Py-H), 7.80 (d, 8H; CH, Py-H), 7.66 (m, 8H;
CH, oxamidato), 7.55 (s, 4H; HCdCH, 4,40-bpe), 7.40 (m, 12H;
CH, oxamidato), 1.29 (s, 60H; Cp*). Anal. Calcd for
C96H100N8F12S4O16Rh4: C, 48.25; H, 4.22; N, 4.69. Found: C,
48.14; H, 4.42; N, 4.42.
[Cp*4Rh4(μ-N,N0-bis(4-methylphenyl)oxamide)2(μ-4,40-bpe)2]-
(OTf)4 (4b). This complex (orange, 46.5 mg, 76%) was obtained
from 2b (41 mg, 0.05 mmol), AgOTf (36 mg, 0.14 mmol), and
4,40-bpe (10 mg, 0.05 mmol) by a similar procedure to that
described for 3a. IR (KBr): ν/cm-1 3495.2, 2921.6, 1610.5,
1577.3, 1505.6, 1429.6, 1341.4, 1260.6, 1223.8, 1157.3, 1029.4,
837.9, 639, 512.8. 1H NMR (400 Hz, CDCl3): δ (ppm) 8.02 (d,
8H; CH, Py-H), 7.77 (d, 8H; CH, Py-H), 7.53 (s, 4H; HCdCH,
4,40-bpe), 7.43 (d, 8H; CH, oxamidato), 7.18 (d, 8H; CH,
oxamidato), 2.47 (s, 12H; CH3, oxamidato), 1.28 (s, 60H;
Cp*). Anal. Calcd for C100H108N8F12S4O16Rh4: C, 49.11; H,
4.45; N, 4.58. Found: C, 49.01; H, 4.65; N, 4.33.
UV Irradiation of 3a. A powdered sample of 3a was placed
between two glass slides and irradiated using a broad Hg lamp
(300 W) for approximately 40 h. Yellow crystals of 5a suitable
for X-ray diffraction study were obtained by slow diffusion of
diethyl ether into a concentrated solution of the complexes in
CH3OH. Conversion: 100% (rctt-tpcb: 64.5%; rtct-tpcb:
35.5%). 1H NMR (400 Hz, CDCl3): δ (ppm) rctt-tpcb: 8.86
(d, 2H; CH, Py-H), 8.66 (m, 2H; CH, Py-H), 8.52 (d, 2H; CH,
Py-H), 8.08 (m, 2H; CH, Py-H), 7.32 - 7.68 (m, 6H; CH, Py-H),
6.94 (m, 2H; CH, Py-H), 5.70, (d, 2H; CH, cyclobutane), 4.98,
(13) Stylianides, N.; Danopoulos, A. A.; Pugh, D.; Hancock, F.;
Zanotti-Gerosa, A. Organometallics 2007, 26, 5627–5635.
(14) White, C.; Yates, A.; Maitles, P. M. Inorg. Synth. 1992, 29, 228–
234.

Article
Organometallics, Vol. 29, No. 13, 2010 2849
Table 2. Crystallographic Data and Structure Refinement Parameters for 2b, 3a, 4a, and 5a
2b 2CHCl3
3
3a
4a(1)
4a(2) 2CH2Cl2 2H2O
3
5a
3
formula
fw
T, K
C36H44Cl2N2O2Rh2
1052.19
293(2)
C96H100F12N8O16S4Ir4
2746.88
293(2)
C96H100F12N8O16S4Rh4
2389.72
293(2)
C96H100F12 N8O16Rh4S4
2595.60
100(2)
C96H100F12N8O16S4Ir4
2746.88
293(2)
cryst syst
space group
triclinic
P1
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
triclinic
P1
˚
a (A)
8.577(3)
11.861(4)
11.888(4)
98.828(4)
102.200(4)
107.769(4)
1094.3(7)
1
43.871(14)
15.719(4)
16.759(5)
90
44.077(15)
15.603(5)
16.711(6)
90
43.839(4)
15.3993(15)
16.7973(16)
90
15.272(6)
16.769(7)
22.522(10)
101.900(6)
95.976(6)
94.781(6)
5581(4)
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
97.747(7)
90
98.426(5)
90
97.9470(10)
90
3
˚
V (A )
Z
11452(6)
4
1.593
11368(7)
4
1.396
11230.7(19)
4
1.535
2
1.635
F
calcd (g/cm3)
1.597
cryst size (mm3)
0.10 ꢀ 0.10 ꢀ 0.08
1.277
4970
0.30 ꢀ 0.20 ꢀ 0.10
4.785
25 587
0.17 ꢀ 0.11 ꢀ 0.08
0.723
25 485
0.18 ꢀ 0.17 ꢀ 0.10
0.832
29 753
0.12 ꢀ 0.10 ꢀ 0.08
4.909
25 399
μ(Mo KR) (mm-1
)
no. collected reflns
no. unique reflns
no. of params
4189
241
11 208
606
11 111
631
11 008
721
21 291
1165
no. of obsd data
GOF
83.8%
0.995
50.4%
0.812
52.7%
0.835
79.5%
1.087
43.1%
0.833
R1, wR2 [I > 2σ(I)]a
R1, wR2 (all data)a
largest diff peak and
0.0366, 0.0878
0.0453, 0.0914
0.580/-0.414
0.0457, 0.0925
0.0904, 0.0988
1.144/-0.612
0.0515, 0.1196
0.0940, 0.1288
0.663/-0.470
0.0476, 0.1445
0.0605, 0.1548
1.072/ -1.116
0.0654, 0.1551
0.1287, 0.1699
1.149/-0.605
-3
˚
hole (e/A
)
P
P
P
aR1 =
Fo| - |Fc (based on reflections with Fo2 > 2σF2).2 wR2 = [ [w(Fo2 - Fc ) ]/ [w(Fo2)2]]1/2; w = 1/[σ2(Fo2) þ (0.095P)2]; P = [max(Fo2, 0) þ
2 2
2Fc ]/3 (also with Fo2 > 2σF2).
2
(d, 2H; CH, cyclobutane); rtct-tpcb: 8.72 (d, 2H; CH, Py-H),
8.58 (d, 2H; CH, Py-H), 8.33 (m, 2H; CH, Py-H), 7.98 (m, 2H;
CH, Py-H), 7.32-7.68 (m, 6H; CH, Py-H), 7.06 (m, 2H; CH, Py-
H), 5.62, (m, 2H; CH, cyclobutane), 5.24, (m, 2H; CH, cyclo-
butane); 7.32-7.68 (m, 40H; CH, oxamidato), 1.31, (s, 60H;
Cp*), 1.26, (s, 60H; Cp*). Anal. Calcd for C96H100N8F12S4O16-
Ir4: C, 41.98; H, 3.67; N, 4.08. Found: C, 41.97 ; H, 3.58; N, 4.16.
UV Irradiation of 3b. A powdered sample of 3b was placed
between two glass slides and was irradiated using a broad Hg
lamp (300 W) for approximately 40 h. Conversion: 100% (rctt-
tpcb: 75.2%; rtct-tpcb: 24.8%). 1H NMR (400 Hz, CDCl3):
δ (ppm) rctt-tpcb: 8.83 (d, 2H; CH, Py-H), 8.62 (m, 2H; CH, Py-
H), 8.50 (d, 2H; CH, Py-H), 8.04 (m, 2H; CH, Py-H), 7.58 (d,
2H; CH, Py-H), 6.95 (d, 2H; CH, Py-H), 7.14-7.48 (m, 4H; CH,
Py-H), 5.66, (d, 2H; CH, cyclobutane), 4.99, (d, 2H; CH,
cyclobutane); rtct-tpcb: 8.70 (d, 4H; CH, Py-H), 8.55 (d, 2H;
CH, Py-H), 8.28 (m, 2H; CH, Py-H), 7.94 (d, 2H; CH, Py-H),
7.63 (m, 2H; CH, Py-H), 7.05 (m, 2H; CH, Py-H), 7.14-7.48 (m,
4H; CH, Py-H), 5.55, (m, 2H; CH, cyclobutane), 5.20, (m, 2H;
CH, cyclobutane); 7.14-7.48 (m, 32H; CH, oxamidato), 2.46 (d,
24H; CH3), 1.30 (s, 60H; Cp*), 1.27 (s, 60H; Cp*). Anal. Calcd
for C100H108N8F12S4O16Ir4: C, 42.85; H, 3.88; N, 4.00. Found:
C, 42.67; H, 3.84; N, 3.85.
of unit cell and intensity data were performed with graphite-
˚
monochromated Mo KR radiation (λ=0.71073 A). All the data
were collected at room temperature or 100 K using the ω-scan
technique. These structures were solved by direct methods, using
Fourier techniques, and refined on F2 by a full-matrix least-
squares method. All the calculations were carried out with the
SHELXTL-97 program.15 In all complexes, hydrogen atoms
were placed in geometrically calculated positions with fixed
isotropic thermal parameters. In complex 2b, all non-hydrogen
atoms were refined anisotropically. There were disordered
solvent molecules in the crystal structures of 3a, 4a, and 5a,
which cannot be refined properly. New data sets corresponding
to omission of them were generated with the SQUEEZE
algorithm,16 and then the structures were refined to conver-
gence. In complexes 3a and 4a, all non-hydrogen atoms were
refined anisotropically except one anion, while in 5a all non-
hydrogen atoms were refined anisotropically except for one
anion. Bond lengths restraints were applied to one of the refined
OTf- anions in 3a and 4a to avoid unreasonable distortion of its
molecular geometry. Bond distances C26-C26(A) (3a), C20-
C20(A) (4a), and C(26)-C(26A) (4a) were also restrained by
DFIX instructions. Two of four pentamethylcyclopentadienyl
ligands in the cation of 5a were disordered because of rotation at
room temperature. They were refined to two idealized positions
(56:44), and their carbon atoms were refined with ISOR instruc-
tions. For 5a, bond lengths were applied to model the disorder of
two OTf- anions. A summary of the crystallographic data and
structure refinement parameters is listed in Table 2.
UV Irradiation of 4a. A powdered sample of 4a was placed
between two glass slides and was irradiated using a broad Hg lamp
(300 W) for approximately 260 h. Conversion: 41.7% (rctt-tpcb:
1
29.2%; rtct-tpcb: 12.5%). H NMR (400 Hz, CDCl3): δ (ppm)
rctt-tpcb: 5.60 (m, 2H; cyclobutane), 4.92 (m, 2H; cyclobutane);
rtct-tpcb: 5.51 (m, 2H; cyclobutane), 5.07 (m, 2H; cyclobutane).
UV Irradiation of 4b. A powdered sample of 4b was placed
between two glass slides and was irradiated using a broad Hg lamp
(300 W) for approximately 260 h. Conversion: 35.9% (rctt-tpcb:
Acknowledgment. This work was supported by the Na-
tional Science Foundation of China (20531020, 20721063,
20771028), Shanghai Science and Technology Committee
(08DZ2270500, 08DJ1400103), Shanghai Leading Aca-
demic Discipline Project (B108), and the National Basic
Research Program of China (2009CB825300).
1
25.6%; rtct-tpcb: 10.3%). H NMR (400 Hz, CDCl3): δ (ppm)
rctt-tpcb: 5.56 (m, 2H; cyclobutane), 4.92 (m, 2H; cyclobutane);
rtct-tpcb: 5.50 (m, 2H; cyclobutane), 5.06 (m, 2H; cyclobutane).
X-ray Structure Determination. Data were collected on a
CCD-Bruker SMART APEX system. All the determinations
Supporting Information Available: 1H NMR data for photo-
dimerization reaction of complexes 3a-4b and the crystallo-
graphic data for 2b, 3a, 4a, and 5a are available free of charge via
the Internet at http://pubs.acs.org.
€
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(15) Sheldrick, G. M. SHELXL-97; Universitat Gottingen: Germany, 1997.
(16) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.