Effects of the heterocycle and its substituents on structure and fluxionality in rhodium(I) and iridium(I) complexes with the hindered thiolates 6-tert-butylpyridine-2-thiolate and 1-alkyl-4-tert-butylimidazole-2-thiolate (alkyl = methyl and tert-butyl)

Article abstract of DOI:10.1021/om060317t

Three new sterically hindered heterocyclic thiolate ligands are studied (HetS = 6-tert-butylpyridine-2-thiolate, ^tBu-PyS; 1-methyl-4-tert-butylimidazole-2-thiolate, Me-^tBu-ImS; 1,4-di-tert-butylimidazole-2-thiolate, ^tBu₂-ImS). Related Rh(I) and Ir(I) metal complexes with molecular formulas [M(HetS)(COD)] _n, [M(HetS)(CO)₂]_n, and [M(HetS)(CO)(PPh ₃)]_n (where n = 1 or 2) were made to assess the steric and electronic effects of heterocycle (pyridine vs imidazole) and bulky substituents on the ring. A combination of solution-phase molecular weight determination, infrared spectroscopy, variable-temperature NMR, and solid-state X-ray diffraction studies were used to determine the molecularity of the complexes (value of n) and the coordination modes of the ligands. In the pyridine series, no evidence was found for nitrogen coordination; the presence of the tert-butyl group makes the heterocyclic thiolate behave like a nonheterocyclic derivative. In the imidazole series, three coordination modes were found, all of them including complexation through both the thiolate sulfur and the basic ring nitrogen. Evidence for fluxional and dimer-monomer interconversions was found for several of the imidazole derivatives, and the size of the 1-alkyl group played a significant role in determining the structures of the complexes.

Full text of DOI:10.1021/om060317t

4374
Organometallics 2006, 25, 4374-4390
Effects of the Heterocycle and Its Substituents on Structure and
Fluxionality in Rhodium(I) and Iridium(I) Complexes with the
Hindered Thiolates 6-tert-Butylpyridine-2-thiolate and
1-Alkyl-4-tert-butylimidazole-2-thiolate (alkyl ) methyl and
tert-butyl)
Valent´ın Miranda-Soto,‡ Jesu´s J. Pe´rez-Torrente,† Luis A. Oro,† Fernando J. Lahoz,†
M. Luisa Mart´ın,† Miguel Parra-Hake,‡ and Douglas B. Grotjahn*,‡,§
Centro de Graduados e InVestigacio´n, Instituto Tecnolo´gico de Tijuana, Apartado Postal 1166, 22000
Tijuana, Baja California, Me´xico, and Departamento de Qu´ımica Inorga´nica, Instituto UniVersitario de
Cata´lisis Homoge´nea, Instituto de Ciencia de Materiales de Arago´n, UniVersidad de Zaragoza-Consejo
Superior de InVestigaciones Cient´ıficas, 50009 Zaragoza, Spain, and Department of Chemistry and
Biochemistry, San Diego State UniVersity, 5500 Campanile DriVe, San Diego, California 92182-1030
ReceiVed April 9, 2006
Three new sterically hindered heterocyclic thiolate ligands are studied (HetS ) 6-tert-butylpyridine-
t
2-thiolate, Bu-PyS; 1-methyl-4-tert-butylimidazole-2-thiolate, Me-tBu-ImS; 1,4-di-tert-butylimidazole-
2-thiolate, tBu2-ImS). Related Rh(I) and Ir(I) metal complexes with molecular formulas [M(HetS)(COD)]n,
[M(HetS)(CO)2]n, and [M(HetS)(CO)(PPh3)]n (where n ) 1 or 2) were made to assess the steric and
electronic effects of heterocycle (pyridine vs imidazole) and bulky substituents on the ring. A combination
of solution-phase molecular weight determination, infrared spectroscopy, variable-temperature NMR,
and solid-state X-ray diffraction studies were used to determine the molecularity of the complexes (value
of n) and the coordination modes of the ligands. In the pyridine series, no evidence was found for nitrogen
coordination; the presence of the tert-butyl group makes the heterocyclic thiolate behave like a
nonheterocyclic derivative. In the imidazole series, three coordination modes were found, all of them
including complexation through both the thiolate sulfur and the basic ring nitrogen. Evidence for fluxional
and dimer-monomer interconversions was found for several of the imidazole derivatives, and the size
of the 1-alkyl group played a significant role in determining the structures of the complexes.
thiolates include not only those displayed by nonheterocyclic
thiolates (e.g., B in Chart 1) but also head-to-head and head-
to-tail bridging (e.g., D and E). Less common coordination
modes are mixed forms such as C, and in mononuclear species
(A) as a chelating ligand.
Part of our interest in heterocyclic thiolates stems from results
using related phosphines in bifunctional catalysis.6 Heterocyclic
phosphines are responsible for dramatic enhancements in
catalysis of alkyne anti-Markovnikov hydration,7 alkyne alkoxy-
carbonylation,8 nitrile hydration,9 and certain H/D exchange
reactions.10 Various roles have been discussed for these
bifunctional ligands. Recent structural and stoichiometric reac-
tivity studies by the Grotjahn group on pyrid-2-yl and imidazol-
Introduction
In the evolution of organometallic chemistry, phosphines
rapidly became a privileged class of ligands because one can
modulate the structure and reactivity of metal complexes and
their reactivity through extensive electronic and steric variation
of all three phosphorus substituents.1,2 In comparison, thiolate
ligands3 are less utilized, although they are of particular interest
for their roles in metalloenzymes, metallopharmaceuticals, and
other areas.4 Thiolates show a strong tendency to form bridging
polynuclear species, control of which can be achieved in some
measure by use of steric or electronic factors. Heterocyclic
thiolates present an interesting and useful subclass, because the
heterocyclic nitrogen is an additional site for coordination.5
Taken together, common coordination modes for heterocyclic
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S. Coord. Chem. ReV. 1997, 165, 475. (c) Raper, E. S. Coord. Chem. ReV.
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191. (e) Garnovskii, A. D.; Sadimenko, A. P.; Sadimenko, M. I.; Garnovskii,
D. A. Coord. Chem. ReV. 1998, 173, 31.
* Corresponding author. E-mail: grotjahn@chemistry.sdsu.edu.
‡ Instituto Tecnolo´gico de Tijuana.
† Universidad de Zaragoza-CSIC.
§ San Diego State University.
(6) Grotjahn, D. B. Chem. Eur. J. 2005, 11, 7146.
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Metals, 3rd ed.; Wiley: New York, 2000.
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Int. Ed. 2001, 40, 3884. (b) Grotjahn, D. B.; Lev, D. A. J. Am. Chem. Soc.
2004, 126, 12232. (c) Lev, D. A.; Grotjahn, D. B. Catal. Org. React. 2005,
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10.1021/om060317t CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/02/2006

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4375
Chart 1. Relevant Coordination Modes of Pyridine- and
Imidazole-2-thiolates
Scheme 1. Syntheses of New Thiols
studying the effect of the steric environment of the thiolate sulfur
was accomplished in the imidazole series by making 1-methyl
and 1-tert-butyl derivatives.
Results
Ligand Synthesis. 6-tert-Butylpyridine-2-one is a known
compound18 that could be readily converted to the novel thio
analogue 6-tert-butylpyridine-2-thiol (tBu-PySH) using Lawes-
son’s reagent (Scheme 1). In the imidazole series, the 1,4-di-
tert-butyl derivative was new, made as had been recently the
1-methyl-4-tert-butyl analogue19 using a method patterned after
that for the 1-isopropyl-4-tert-butyl analogue.20
Complexes Derived from 6-tert-Butylpyridine-2-thiol (tBu-
PySH). The direct protonation of the methoxide bridging ligands
in the complexes [M(µ-OMe)(COD)]2 (M ) Rh, Ir) by 6-tert-
butylpyridine-2-thiol (tBu-PySH) in dichloromethane resulted
in the formation of the dinuclear complexes [Rh(µ-tBu-PyS)-
(COD)]2 (1, Scheme 2) and [Ir(µ-tBu-PyS)(COD)]2 (2), which
were isolated as yellow and red microcrystalline solids in good
yield. The determination of the molecular weight in chloroform
supports the dinuclear formulation of the complexes. In addition,
the FAB+ spectra showed the dinuclear ions at m/z 755 and
933, respectively.
2-yl phosphines have begun to show intriguing differences
between the two heterocyclic substituents11 as well as the role
of not only the imidazole but also the phosphorus substituents
on the propensity for forming monodentate κ1-P or chelating
κ2-P,N species.12 In the work presented here, one larger goal is
to examine similar factors in heterocyclic thiolate complexes,
because the sulfur atom bears only the heterocycle and not two
additional groups. Hence, one might be able to focus solely on
the steric and electronic contribution of the heterocycle and its
substituents.
Coordination of pyridine-2-thiolate (PyS) to Rh(I) and Ir(I)
species as in M2(PyS)2L1L2, where L1 and L2 are CO, alkenes,
or CO and phosphine, has established that doubly bridged
species of types C and E could be formed and may interconvert
in solution.13 The closely related species 1-alkylimidazole-2-
thiolate has to our knowledge not been examined on Rh(I) or
Ir(I), although it has shown a variety of coordination modes in
other systems.14-17 In the work reported here, we chose to
increase steric hindrance at the basic heterocyclic nitrogen by
using derivatives with an adjacent tert-butyl group. In addition,
1
The H NMR spectrum of compound 1 in CD2Cl2 at RT
showed three resonances at δ 7.38 (t), 7.16 (d), and 7.04 (d),
for the aromatic protons of the equivalent 6-tert-butylpyridine-
2-thiolate (tBu-PyS-) ligands, and a singlet at δ 1.32 ppm for
t
the Bu groups. The diolefin region of the spectrum showed
broad resonances and evidenced a fluxional behavior on the
NMR time scale. Thus, at 25 °C, the dCH and >CH2 protons
(15) (a) Shu, M.; Walz, R.; Wu, B.; Seebacher, J.; Vahrenkamp, H. Eur.
J. Inorg. Chem. 2003, 2502. (b) Bell, N. A.; Clegg, W.; Creighton, J. R.;
Raper, E. S. Inorg. Chim. Acta 2000, 303, 12. (c) Ruiz, J.; Florenciano, G.;
Lo´pez, G.; Chaloner, P. A.; Hitchcock, P. B. Inorg. Chim. Acta 1998, 281,
165. (d) Yap, G. P. A.; Jensen, C. M. Inorg. Chem. 1992, 31, 4823. (e)
Wilton-Ely, J. D. E. T.; Honarkhah, S. J.; Wang, M.; Tocher, D. A.; Slawin,
A. M. Z. Dalton Trans. 2005, 1930.
(11) Grotjahn, D. B.; Hoerter, J. M.; Lev, D. A.; Dwyer, T. J.
Unpublished results.
(12) Grotjahn, D. B.; Gong, Y.; Zakharov, L. N.; Golen, J. A.; Rheingold,
A. L. J. Am. Chem. Soc. 2006, 128, 438.
(13) (a) Oro, L. A.; Ciriano, M. A.; Pe´rez-Torrente, J. J.; Villarroya, B.
E. Coord. Chem. ReV. 1999, 1. (b) Ciriano, M. A.; Viguri, F.; Pe´rez-Torrente,
J. J.; Lahoz, F. J.; Oro, L. A.; Tiripicchio, A.; Tiripicchio-Camellini, M. J.
Chem. Soc., Dalton Trans. 1989, 25. (c) Dahlenburg, L. Ku¨hnlein, M. Eur.
J. Inorg. Chem. 2000, 2117. (d) Oro, L. A.; Ciriano, M. A.; Viguri, F.;
Tiripicchio, A.; Tiripicchio-Camellini, M.; Lahoz, F. J. NouV. J. Chim. 1986,
10, 75.
(16) (a) Allan, R. A.; Bashall, A.; Palmer, J. S.; McPartlin, M.; Mosquera,
M. E. G.; Rawson, J. M.; Weathley, A. E. H.; Wright, D. S. Chem. Commun.
1997, 1975. (b) Raper, E. S.; Creighton, J. R.; Clegg, W. Inorg. Chim.
Acta 1991, 183, 179. (c) Cooper, D. A.; Rettig, S. J.; Storr, A.; Trotter, J.
Can. J. Chem. 1986, 64, 1643.
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(b) Landgrafe, C.; Sheldrick, W. S.; Sudfeld, M. Eur. J. Inorg. Chem. 1998,
407. (c) Lowe, G.; Ross, S. A.; Probert, M.; Cowley, A. Chem. Commun.
2001, 1288.
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L. Eur. J. Inorg. Chem. 2000, 1411.
(14) (a) Azam, K. A.; Hanif, K. M.; Ghosh, A. C.; Kabier, S. E.;
Karmakar, S. R.; Malik, K. M. A.; Parvin, S.; Rosemberg, E. Polyhedron
2002, 21, 885. (b) Bonati, F.; Burini, A.; Pietroni, B. R.; Giorgini, E.; Bovio,
B. J. Organomet. Chem. 1988, 344, 119.
(19) Miranda-Soto, V.; Parra-Hake, M.; Morales-Morales, D.; Toscano,
R. A.; Boldt, G.; Koch, A.; Grotjahn, D. B. Organometallics 2005, 24,
5569.
(20) Corey, E. J.; Brunelle, D. J. Tetrahedron Lett. 1976, 3409.

4376 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
t
Scheme 2. Syntheses of Bu-PyS Complexes
Figure 1. Molecular structure of compound [Ir(µ-tBu-PyS)(COD)]2
(2).
structure confirms the thiolate coordination µ-(1:2κ2S) of the
6-tert-butylpyridine-2-thiolate ligands that adopt a relative syn-
endo disposition.
The reaction of the mononuclear complexes [M(acac)(CO)2]
(M ) Rh, Ir) with 6-tert-butylpyridine-2-thiol (tBu-PySH) in
dichloromethane (1:1 molar ratio) gave deeply colored solutions
from which the dinuclear compounds [Rh(µ-tBu-PyS)(CO)2]2
(3, Scheme 2) and [Ir(µ-tBu-PyS)(CO)2]2 (4) were isolated as
red and green microcrystalline solids, respectively, in good yield.
It is noticeable that solutions of compounds 3 and 4 can also
be prepared by direct carbonylation of compounds 1 and 2 in
dichloromethane. However, the presence of free 1,5-cyclooc-
tadiene in the reaction media makes the isolation of the
complexes difficult.
The dinuclear formulation of the complexes relies on the
FAB+ spectra, which showed the molecular ions at m/z 650
and 829 and the sequential losses of several carbonyl ligands.
Moreover, the IR spectra indicate that the coordination mode
t
of the bridging Bu-PyS- ligands (1:2κ2S) remains unchanged
upon carbonylation. Thus, the IR spectra of both compounds
in dichloromethane showed three ν(CO) bands for the terminal
carbonyl groups at 2082 (m), 2064 (s), and 2016 (s) cm-1
(compound 3) and 2073 (m), 2053 (s), and 2002 (s) cm-1
(compound 4). This pattern of intensities (m, s, s) is typical for
tetracarbonyl dinuclear complexes having thiolato ligands as
bridges24 and is distinct from that seen for cis-HT dimers of
type E.13
were observed as one resonance at δ 4.84 ppm and two
resonances at δ 2.42 and 1.96 ppm, respectively. However, on
cooling at -70 °C the dCH protons were observed as two
resonances at δ 4.98 and 4.43 ppm. This dynamic behavior can
also be detected in the 13C{1H} NMR spectrum, where the d
CH carbons were observed as two broad resonances at δ 81.3
and 77.9 ppm at -70 °C and as a doublet at δ 80.3 ppm (JRh-C
) 11.9 Hz) at room temperature. The spectroscopic information
obtained from the variable-temperature NMR analysis suggests
an open-book structure resulting from the thiolate µ-(1:2κ2S)
The 1H NMR spectra at RT of both complexes showed
t
equivalent Bu-PyS- ligands. The only observed temperature
t
coordination mode of both Bu-PyS- ligands with a syn
effect was the slight broadening of the resonances for both
complexes at -50 °C in CDCl3. The equivalent carbonyl ligands
were observed as a doublet at δ 184.4 ppm (JRh-C ) 71.9 Hz)
and a singlet at δ 173.4 ppm in the 13C{1H} NMR spectra of 3
and 4, respectively, in agreement with a C2V symmetry structure
resulting from a syn disposition of the bridging thiolato ligands
(Scheme 2).
disposition. In fact, the inversion of the nonplanar Rh2S2
ring21,22a-d would account for the equivalence of all the olefinic
dCH protons and carbons at room temperature.
The behavior in solution of compound [Ir(µ-tBu-PyS)(COD)]2
(2) is identical to that of compound 1, which strongly supports
1
a similar structure with a C2V symmetry. In particular, the H
The tetracarbonyl compound [Rh(µ-tBu-PyS)(CO)2]2 (3),
obtained in situ by carbonylation of diolefin complex [Rh(µ-t-
Bu-PyS)(COD)]2 (1) in dichloromethane, was reacted with 2
molar equiv of triphenylphosphine to give the complex [Rh(µ-
tBu-PyS)(CO)(PPh3)]2 (5, Scheme 2) after evolution of carbon
monoxide. However, the related iridium complex [Ir(µ-tBu-
PyS)(CO)(PPh3)]2 (6) was better obtained from the reaction of
[Ir(acac)(CO)(PPh3)] with tBu-PySH in dichloromethane. Com-
pound 5 was isolated as a moderately stable yellow solid, but
NMR spectrum in CDCl3 at -55 °C showed the expected two
broad resonances for the dCH protons and four sharp multiplets
for the >CH2 protons as a consequence of the differentiation
between the two groups of exo and endo protons.23 The
molecular structure of 2 was determined by an X-ray diffraction
analysis (discussed below) and is shown in Figure 1. The
(21) Abel, E. W.; Orrell, K. G. Prog. Inorg. Chem. 1984, 32, 1.
(22) (a) Brunner, H.; Bu¨gler, J.; Nuber, B. Tetrahedron Asymmetry 1996,
7, 3095. (b) Ferna´ndez, E.; Ruiz, A.; Castillo´n, S.; Claver, C.; Piniella, J.
F.; Alvarez-Larena, A.; Germani, G. J. Chem. Soc., Dalton Trans. 1995,
2137. (c) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Lahoz, F. J.; Oro, L. A. J.
Chem. Soc., Dalton Trans. 1992, 1831. (d) Cotton, F. A.; Lahuerta, P.;
Latorre, J.; Sanau, M.; Solana, I.; Schowtzer, W. Inorg. Chem. 1988, 27,
2131. (e) Fonseca, I.; Hernandez, E.; Sanz-Aparicio, J.; Terreros, P.; Torrens,
H. J. Chem. Soc., Dalton Trans. 1994, 781.
(24) (a) Kiriakidou-Kazemifar, N. K.; Auca, M.; Pakkanen, T. A.; Tunik,
S. P.; Nordlander, E. J. Organomet. Chem. 2001, 623, 65. (b) Polo, A.;
Claver, C.; Castillo´n, S.; Ruiz, A.; Bayo´n, J. C.; Real, J.; Meali, C.; Masi,
D. Organometallics 1992, 11, 3525. (c) Bayo´n, J. C.; Esteban, P.; Real, J.;
Claver, C.; Polo, A.; Ruiz, A.; Castillo´n, S. J. Organomet. Chem. 1991,
403, 393. (d) Bonet, J. J.; Thorez, A.; Maisonnat, A.; Galy, J.; Poilblanc,
R. J. Am. Chem. Soc. 1979, 101, 5940.
(23) Rodman. G. S.; Mann, K. R. Inorg. Chem. 1988, 27, 3338.

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4377
Table 1. Selected Bond Distances (Å) and Angles (deg) for 2
and 13
compound 2
compound 13
Ir(1)-S(1)
Ir(1)-S(2)
Ir(2)-S(1)
Ir(2)-S(2)
Ir(1)-C(1)
Ir(1)-C(2)
Ir(1)-C(5)
Ir(1)-C(6)
Ir(2)-C(9)
2.357(2) Rh(1)-S(1)
2.363(2) Rh(1)-S(2)
2.358(2) Rh(2)-S(1)
2.369(2) Rh(2)-S(2)
2.119(8) Rh(1)-C(1)
2.093(8) Rh(1)-C(2)
2.138(9) Rh(1)-C(5)
2.112(8) Rh(1)-C(6)
2.115(8) Rh(2)-C(9)
2.120(8) Rh(2)-C(12)
2.096(8) Rh(2)-C(13)
2.121(9) Rh(2)-C(16)
1.795(8) S(1)-C(17)
1.798(9) S(2)-C(28)
2.3651(9)
2.3696(9)
2.3617(10)
2.3699(9)
2.144(4)
2.141(4)
2.147(4)
2.150(4)
2.118(5)
2.126(4)
2.143(4)
Ir(2)-C(12)
Ir(2)-C(13)
Ir(2)-C(16)
2.144(5)
1.768(4)
1.767(4)
77.09(3)
S(1)-C(17)
S(2)-C(26)
S(1)-Ir(1)-S(2)
S(1)-Ir(1)-Ct(1)a
S(1)-Ir(1)-Ct(2)a
S(2)-Ir(1)-Ct(1)a
S(2)-Ir(1)-Ct(2)a
Ct(1)-Ir(1)-Ct(2)a
S(1)-Ir(2)-S(2)
S(1)-Ir(2)-Ct(3)a
S(1)-Ir(2)-Ct(4)a
S(2)-Ir(2)-Ct(3)a
S(2)-Ir(2)-Ct(4)a
Ct(3)-Ir(2)-Ct(4)a
Ir(1)-S(1)-Ir(2)
Ir(1)-S(1)-C(17)
Ir(2)-S(1)-C(17)
Ir(1)-S(2)-Ir(2)
Ir(1)-S(2)-C(26)
Ir(2)-S(2)-C(26)
74.73(7)
97.6(2)
171.0(2)
170.8(2)
101.2(2)
87.2(3)
74.59(8)
101.5(2)
170.6(2)
170.1(2)
97.7(2)
S(1)-Rh(1)-S(2)
S(1)-Rh(1)-Ct(1)a
S(1)-Rh(1)-Ct(2)a
S(2)-Rh(1)-Ct(1)a
S(2)-Rh(1)-Ct(2)a
Ct(1)-Rh(1)-Ct(2)a
S(1)-Rh(2)-S(2)
S(1)-Rh(2)-Ct(3)a
S(1)-Rh(2)-Ct(4)a
S(2)-Rh(2)-Ct(3)a
S(2)-Rh(2)-Ct(4)a
Ct(3)-Rh(2)-Ct(4)a
Rh(1)-S(1)-Rh(2)
Rh(1)-S(1)-C(17)
Rh(2)-S(1)-C(17)
Rh(1)-S(2)-Rh(2)
Rh(1)-S(2)-C(28)
Rh(2)-S(2)-C(28)
97.48(10)
174.17(7)
172.68(9)
97.69(8)
87.49(12)
77.15(3)
173.91(11)
96.91(11)
98.61(12)
173.74(9)
87.16(16)
92.67(3)
113.74(12)
110.85(13)
92.35(3)
Figure 2. Molecular structure of compound [Rh(µ-tBu-PyS)(CO)-
(PPh3)]2 (5).
compound 6 is an air-sensitive orange solid. Both complexes
have been fully characterized by elemental analysis, FAB+ mass
spectra, and NMR. In addition, the molecular structure of
compound 5 has been determined by X-ray diffraction methods
and is shown in Figure 2, which will be discussed in greater
detail below. As in the previous four complexes 1-4, the
dinuclear structure is maintained by two 6-tert-butylpyridine-
2-thiolate ligands with a thiolate coordination mode µ-(1:2κ2S);
however unlike the previously discussed complexes the two
thiolates adopt a relative anti disposition, and a cis disposition
of the triphenylphosphine ligands is seen. The spectroscopic
data obtained from solutions of the compounds 5 and 6 in C6D6
are in accordance with the structure found in the solid state for
compound 5 with a Cs symmetry. Thus, two sharp singlets were
86.9(3)
76.08(6)
115.6(3)
124.4(3)
75.75(7)
122.7(3)
117.3(3)
113.75(12)
112.03(12)
a Midpoints of the cyclooctadiene olefinic bonds: Ct(1) for C(1)dC(2),
Ct(2) for C(5)dC(6), Ct(3) for C(9)dC(16), and Ct(4) for C(12)dC(13).
Table 2. Selected Bond Distances (Å) and Angles (deg) for 5
Rh(1)-S(1)
Rh(1)-S(2)
Rh(1)-P(1)
Rh(1)-C(28)
S(1)-C(1)
2.3910(6)
2.3809(6)
2.2598(6)
1.825(2)
1.793(2)
1.152(3)
Rh(2)-S(1)
Rh(2)-S(2)
Rh(2)-P(2)
Rh(2)-C(38)
S(2)-C(29)
C(38)-O(2)
2.3914(6)
2.3646(6)
2.2514(6)
1.837(2)
1.793(2)
1.140(3)
t
t
observed for the Bu groups of the two inequivalent Bu-PyS-
1
ligands in the H NMR of both compounds. In addition, the
C(28)-O(1)
two equivalent triphenylphosphine ligands were observed as a
doublet at δ 38.9 ppm (JRh-P ) 158.7 Hz) (compound 5) and
a sharp singlet at δ 20.5 ppm (compound 6) in the 31P{1H}
NMR spectra of both compounds. Finally, the equivalent
carbonyl ligands of compound 5 were observed as a ddd at δ
S(1)-Rh(1)-S(2)
S(1)-Rh(1)-P(1)
81.81(2)
90.63(2)
S(1)-Rh(1)-C(28) 169.60(8)
S(1)-Rh(2)-S(2)
S(1)-Rh(2)-P(2)
82.136(19)
92.71(2)
S(1)-Rh(2)-C(38) 175.81(8)
S(2)-Rh(1)-P(1)
S(2)-Rh(1)-C(28)
P(1)-Rh(1)-C(28)
Rh(1)-S(1)-Rh(2)
Rh(1)-S(1)-C(1)
Rh(2)-S(1)-C(1)
172.42(2)
93.82(7)
93.73(7)
80.779(19) Rh(2)-S(2)-Rh(1)
106.39(7)
103.68(7)
S(2)-Rh(2)-P(2)
S(2)-Rh(2)-C(38)
P(2)-Rh(2)-C(38)
173.60(2)
95.16(7)
90.20(7)
2
190.2 ppm (1JRh-C ) 75.3 Hz, JP-C ) 17.1 Hz, and another
81.538(18)
coupling J ) 2.9 Hz) in the 13C{1H} NMR spectrum. Further
evidence for a cis arrangement of the two carbonyls in solution
comes from the appearance of two IR bands at 1989 and 1976
cm-1, whereas if the two carbonyls were trans, a single IR band
would be seen (e.g., ref 24b).
Rh(2)-S(2)-C(29) 112.42(8)
Rh(1)-S(2)-C(29) 105.91(7)
Rh(2)-C(38)-O(2) 175.0(2)
Rh(1)-C(28)-O(1) 176.6(2)
and the Ir- - -Ir separation 2.9055(8) Å. Among related Ir
complexes, this metal-metal separation is rather small. The
closest analogue to 2 characterized by X-ray diffraction is [Ir-
Molecular Structures of Compounds [Ir(µ-tBu-PyS)-
(COD)]2 (2) and [Rh(µ-tBu-PyS)(CO)(PPh3)]2 (5). Good-
quality crystals for X-ray diffraction of compound 2 were
obtained by diffusion of pentane into a concentrated solution
of the complex in dichloromethane. Key bond lengths and angles
are shown in Table 1, whereas collection and refinement data
for all complexes in this paper are in Table 5. The structure of
2 (Figure 1) shows the syn-endo disposition of the two thiolates
with respect to the folded Ir2S2 core. Coordination geometry at
both Ir centers is distorted square planar, with similar acute Ir-
S-Ir [76.08(6)° and 75.75(7)°] and S-Ir-S angles [74.73(7)°
and 74.59(8)°], whereas the S-Ir-C angles are between 95.6-
(3)° and 101.4(2)°. The values for trans-angles S-Ir-Ct (Ct
) centroid of CdC bond) are close to 180° [range 170.1(2)-
174.17(7)°], but also reflect the distortion of the square-planar
metal environment. The fold of the Ir2S2 core is 101.02(6)°,
(µ-PhS)(COD)] ,22d in which the Ir- - -Ir distance is 3.181(1) Å.
2
The two complexes are similar in their Ir-S bond distances:
for 2 the range is 2.357-2.369(2) Å, average 2.362(1) Å,
whereas in [Ir(µ-PhS)(COD)]2,22d the average value is 2.345(7)
Å. In the related complex [Ir(µ-SCH2CH2CH2NMe2)(COD)]2,22b
Ir-S distances were very similar [average 2.340(2) Å], whereas
the metal-metal distance [2.946(1) Å] was not quite as short
as that in 2. Finally, in [Ir(µ-SC6F5)(COD)]2,22e even though
thiolates are very electron-withdrawing, the Ir-S distances
[range 2.375(2)-2.402(3) Å, average 2.390(2) Å] and Ir- - -Ir
distance (3.066(1) Å) are more similar to those in the SPh
analogue.
Suitable crystals for X-ray diffraction of compound 5 were
grown by diffusion of methanol into a concentrated solution of

4378 Organometallics, Vol. 25, No. 18, 2006
Table 3. Selected Bond Distances (Å) and Angles (deg) for 7a
Miranda-Soto et al.
Rh(1)-S(1)
Rh(1)-S(2)
Rh(1)-C(1)
Rh(1)-C(2)
Rh(1)-C(5)
Rh(1)-C(6)
S(1)-C(17)
N(1)-C(17)
N(2)-C(17)
C(1)-C(2)
C(5)-C(6)
2.4024(12)
2.3715(12)
2.136(5)
2.156(5)
2.125(5)
2.137(5)
1.763(4)
1.309(5)
1.366(5)
1.386(8)
1.371(8)
2.3969(11)
2.3727(12)
2.143(5)
2.126(5)
2.135(5)
2.126(5)
1.752(4)
1.318(6)
1.364(6)
1.384(8)
1.392(9)
Rh(2)-S(1)
Rh(2)-N(3)
Rh(2)-C(9)
Rh(2)-C(10)
Rh(2)-C(13)
Rh(2)-C(14)
S(2)-C(25)
N(3)-C(25)
N(4)-C(25)
C(9)-C(10)
C13)-C(14)
2.3535(12)
2.125(5)
2.147(6)
2.126(5)
2.168(8)b
2.182((8)b
1.729(5)
1.325(6)
1.352(6)
1.378(9)
1.404(12)b
2.3500(12)
2.138(4)
2.148(5)
2.105(5)
2.125(5)
2.137(5)
1.726(5)
1.331(6)
1.354(6)
1.400(8)
1.389(9)
S(1)-Rh(1)-S(2)
S(1)-Rh(1)-Ct(1)c
S(1)-Rh(1)-Ct(2)c
S(2)-Rh(1)-Ct(1)c
S(2)-Rh(1)-Ct(2)c
Ct(1)-Rh(1)-Ct(2)c
Rh(1)-S(1)-Rh(2)
Rh(1)-S(1)-C(17)
Rh(2)-S(1)-C(17)
S(1)-C(17)-N(1)
S(1)-C(17)-N(2)
N(1)-C(17)-N(2)
96.19(4)
95.71(4)
94.69(11)
177.77(13)
169.53(12)
82.95(14)
86.61(17)
87.60(4)
111.69(17)
116.33(17)
127.4(4)
S(1)-Rh(2)-N(3)
S(1)-Rh(2)-Ct(3)c
S(1)-Rh(2)-Ct(4)b,c
N(3)-Rh(2)-Ct(3)c
N(3)-Rh(2)-Ct(4)b,c
Ct(3)-Rh(2)-Ct(4)b,c
Rh(1)-S(2)-C(25)
Rh(2)-N(3)-C(25)
Rh(2)-N(3)-C(26)
S(2)-C(25)-N(3)
S(2)-C(25)-N(4)
N(3)-C(25)-N(4)
81.48(13)
80.85(12)
100.55(10)
165.97(14)
165.41(16)
93.97(18)
87.76(17)
111.71(17)
115.7(3)
137.4(4)
126.1(4)
123.7(4)
110.1(4)
94.30(11)
178.24(12)
168.70(12)
83.42(12)
86.21(16)
88.50(4)
110.92(16)
117.06(16)
128.1(4)
100.44(13)
165.8(2)
173.18(17)
93.4(3)
86.2(3)
112.39(17)
115.5(4)
138.5(4)
126.6(4)
123.3(4)
110.1(4)
120.3(4)
111.6(4)
121.5(4)
111.1(4)
a Two crystallographically independent molecules were observed in the crystal. b Olefinic atoms C(13) and C(14) exhibited static disorder; mean values
for the two disordered moieties are stated in the table. c Midpoints of the cyclooctadiene olefinic bonds: Ct(1), C(1)dC(2); Ct(2), C(5)dC(6); Ct(3), C(9)dC(10);
and Ct(4), C(13)dC(14).
(µ-Me-tBu-ImS)(COD)]2 (8) were obtained from the reaction
Table 4. Selected Bond Distances (Å) and Angles (deg) for
18
of the dinuclear compounds [M(µ-OMe)(COD)]2 with 1-methyl-
4-tert-butylimidazole-2-thiol (Me-tBu-ImSH) in dichloromethane.
Ir-P
2.2342(12)
2.125(3)
1.749(4)
1.163(5)
Ir-S
2.4095(13)
1.816(5)
1.324(5)
1.350(5)
Ir-N(1)
S-C(2)
C(1)-O(1)
Ir-C(1)
N(1)-C(2)
N(2)-C(2)
The compounds were isolated as orange and red microcrystalline
solids in good yield and have been characterized by elemental
analysis, FAB+ spectra, and spectroscopic methods. The FAB+
spectra of both compounds showed the dinuclear ions at m/z
760 and 939, respectively. The 1H NMR spectrum in CDCl3 or
CD2Cl2 at RT for compound 7 showed broadened resonances
for every type of proton, which suggested fluxional behavior.
Thus, the dCH and >CH2 protons of the COD ligands were
observed in CD2Cl2 as a resonance at δ 4.59 ppm and two
resonances at δ 2.47 and 1.93 ppm, respectively. Moreover, three
resonances at δ 6.50, 3.45, and 1.28 ppm were observed for
the Me-tBu-ImS- ligands, which correspond to the dCH,
P-Ir-S
97.67(4)
166.37(9)
90.08(14)
68.83(9)
169.70(14)
103.54(16)
78.22(13)
Ir-N(1)-C(2)
Ir-N(1)-C(4)
C(2)-N(1)-C(4)
Ir-C(1)-O
S-C(2)-N(1)
S-C(2)-N(2)
N(1)-C(2)-N(2)
99.0(2)
152.4(3)
107.5(3)
176.2(5)
113.0(3)
135.3(3)
111.7(3)
P-Ir-N(1)
P-Ir-C(1)
S-Ir-N(1)
S-Ir-C(1)
N(1)-Ir(1)-C(1)
Ir-S-C(2)
the complex in dichloromethane. Key bond lengths and angles
are shown in Table 2. Like 2, 5 (Figure 2) shows a folded Rh2S2
core, with both Rh atoms in distorted square-planar coordination
geometry, and the thiolate cis to both small CO ligands [bonded
through S(2)] is endo to the Rh2S2 core. The sums of the four
bond angles between pairs of cis ligands around each metal add
up to 360.0°, within experimental uncertainty. In contrast to 2,
5 shows an anti disposition of the two thiolates, with the thiolate
flanked by the large PPh3 ligands occupying the exo position
with respect to the Rh2S2 core. The greatest distortions from
square-planar geometry consist of the small S-Rh-S angles
[81.81(2)° and 82.136(19)°]. In addition, the S-Rh-CO angles
involving S(2) are the largest [95.16(7)° and 93.82(7)°], followed
by the other intraligand cis angles. As for Rh-S bond distances,
those trans to the CO ligands [Rh(1)-S(1) 2.3910(6) Å and
Rh(2)-S(1) 2.3914(6) Å] are slightly longer than those trans
to the phosphines [Rh(1)-S(2) 2.3809(6) Å and Rh(2)-S(2)
2.3646(6) Å], a phenomenon seen in the analogous complex
with PhS- ligands.25d The shape of the complex, including the
relative cis disposition of the phosphines and the anti disposition
of thiolates, as well as its metrical parameters, are very similar
to those of literature complexes that have been structurally
characterized.25a-d
t
N-CH3, and Bu protons, respectively.
To establish the coordination mode of the bridging 1-methyl-
4-tert-butylimidazole-2-thiolate ligands in the dinuclear com-
1
pounds, variable-temperature H analysis was carried out on
1
both complexes. The H NMR spectrum of compound [Ir(µ-
Me-tBu-ImS)(COD)]2 (8) in toluene-d8 at RT consisted of
featureless resonances except for the dCH resonance of the Me-
tBu-ImS- ligands, which was observed as a sharp singlet at δ
5.99 ppm. On warming, well-defined resonances resulted, and
at 70 °C the spectrum closely resembled that of compound 7 at
RT (Figure 3a). More conclusive results came from the 1H NMR
spectrum of 8 at -60 °C that evidence the lack of symmetry in
the molecule (Figure 3b). Thus, six distinct singlets were
observed at δ 5.75 and 5.62 ppm, 2.92 and 2.54 ppm, and 1.64
and 1.32 ppm for the dCH, N-Me, and tBu protons, respectively,
of the inequivalent Me-tBu-ImS- ligands. In addition, eight
different resonances were observed for the dCH protons of the
inequivalent COD ligands that could be grouped in four sets,
corresponding to the four HCdCH olefin fragments, with the
(25) References to structures of complexes like 5: (a) Dilworth, J. R.;
Morales, D.; Zheng, Y. J. Chem. Soc., Dalton Trans. 2000, 3017. (b)
Schumann, H.; Hemling, N.; Goren, N.; Blue, J. J. Organomet. Chem. 1995,
485, 209. (c) Jones, R. A.; Schwab, S. T. J. Crystallogr. Spectrosc. 1986,
16, 577. (d) Bonet, J. J.; Kalck, P.; Poilblanc, R. Inorg. Chem. 1977, 16,
1514. (e) Osakada, K.; Matsumoto, K.; Yamamoto, T.; Yamamoto, A.
Organometallics 1985, 4, 857.
Complexes Derived from 1-Methyl-4-tert-butylimidazole-
2-thiol (Me-tBu-ImSH) and Molecular Structure of 7. The
complexes [Rh(µ-Me-tBu-ImS)(COD)]2 (7, Scheme 3) and [Ir-

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4379
Table 5. Data Collection and Refinement for Structures of 2, 5, 7, 13, and 18
2
5
7
13
18
mol. formula
MW
C34H48Ir2N2S2
933.26
C56H54N2O2P2Rh2S2
1118.89
C32H50N4Rh2S2
760.7
C39H66N4ORh2S2
876.90
C30H34IrN2OPS
693.82
cryst dimens (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
0.29×0.05×0.05
monoclinic
P21/c
11.665(3)
28.630(7)
11.170(3)
90.00
117.252(5)
90.00
3316.4(14)
4
0.31×0.17×0.10
0.21×0.12×0.05
0.12×0.11×0.03
monoclinic
P21/n
10.4217(7)
20.8686(14)
18.8799(12)
90.00
96.6200(10)
90.00
4078.7(5)
4
0.16×0.13×0.05
triclinic
triclinic
triclinic
P1h
P1h
P1h
12.0428(14)
12.7050(14)
18.720(2)
81.561(2)
72.552(2)
69.439(2)
2555.7(5)
2
11.2689(9)
16.9773(14)
18.2119(15)
101.9520(10)
105.6020(10)
90.2450(10)
3276.4(5)
4
9.243(5)
9.618(5)
16.901(5)
99.912(5)
94.141(5)
104.632(5)
1421.5(11)
2
Z
D
calc (g cm-3
)
1.869
8.168
0.312, 0.667
1.454
0.833
0.779, 0.921
1.542
1.162
0.790, 0.941
1.428
0.946
0.896, 0.975
1.621
4.851
0.495, 0.784
µ (mm-1
)
min. max. transmn
factor
2θmax (deg)
no. of measd reflns
no. of indep reflns
57.52
22228
7937 [R(int) )
0.0652]
5605
57.68
31989
12 188 [R(int) )
0.0309]
57.52
40642
15 513 [R(int) )
0.0271]
57.70
27234
9767 [R(int) )
0.0346]
8056
57.42
17587
6712 [R(int) )
0.0368]
5954
no. of intense reflns
with I > 2σ(I)
no. of params
10417
12855
378
776
724
615
429
R(F) intense, all (%)
wR(F2) intense, all (%)
GOF
5.32, 8.72
8.90, 9.89
1.025
3.15, 3.97
7.12, 7.45
1.024
5.20, 6.52
11.92, 12.58
1.063
4.44, 5.77
10.33, 11.03
1.037
3.18, 3.92
6.27, 6.50
1.046
help of the 1H-1H COSY spectrum. In experiments of this kind,
generally toluene-d8 led to greater chemical shift differences
for the dCH protons of coordinated COD ligands than did CD2-
Cl2, but there was no obvious solvent dependence on equilibria
at the same temperature.
Scheme 3. Syntheses of Me-tBu-ImS Complexes
Compound 7 undergoes a similar dynamic behavior, although
the coalescence temperature was lower than that found for
complex 8, as might be expected for a second-row congener.
Interestingly, the 1H NMR spectrum of compound 7 in CD2Cl2
at -95 °C was similar to that of 8 at -60 °C: for the two
inequivalent Me-tBu-ImS- ligands, a total of six singlets were
seen, and for the dCH protons of the COD ligands, seven broad
resonances (two overlapping) were identified with the help of
1
the H-1H COSY spectrum.
Suitable crystals for X-ray diffraction of compound 7 were
obtained by cooling a concentrated solution of the complex in
n-hexane. The ORTEP diagram of one of the two crystallo-
graphically independentsbut chemically analogoussmolecules
is shown in Figure 4, and key bond lengths and angles are
collected in Table 3. Although 7 is dinuclear with the two metal
centers bridged by two thiolate ligands, one ligand is in
µ-(1κS,2κN) coordination mode, which makes the complex
unsymmetrical (cf. C, Chart 1). Both Rh centers feature distorted
square-planar geometry. Looking at the bonding of the six-
membered Rh-S-Rh-SCN ring at the core of the complex,
the angle Rh(1)-S(1)-Rh(2) of the thiolate in µ-(1:2κ2S)
coordination mode is 88.05(4)°, about 12° more open than the
corresponding angles in 2 (Table 1), presumably a consequence
of the presence of the second thiolate in µ-(1κS,2κN) coordina-
tion and the larger size of the central ring. The intraligand cis
angles at each Rh center, S(1)-Rh(1)-S(2) [mean 95.95(3)°]
and S(1)-Rh(2)-N(3) [mean 81.17(9)°], are also significantly
larger than the corresponding 74.59(8)° and 74.73(7)° angles
in the Ir2S2 core of 2. Looking at bond distances, the Rh(1)-
S(1) distance [2.3997(8) Å] is approximatively 0.05 Å longer
than the Rh(2)-S(1) one [2.3518(9) Å], and Rh(1)-S(2) is
between both of these [2.3721(9) Å]. A survey of the literature
highlights complex [Rh(µ-PyS)(tfbb)]2,13b for which a crystal
structure revealed µ-(1κS,2κN) and µ-(1:2κ2S) coordination, with
similar key angles in the six-membered core ring and similar
bond distances. To our knowledge, there is no other structurally
characterized dinuclear complex of pyridine- or imidazole-
thiolates or their benzo or saturated derivatives with such a
structure, so further comparisons are impossible.

4380 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
Figure 4. Molecular structure of compound [Rh(µ-Me-tBu-ImS)-
(COD)]2 (7).
Scheme 4. Possible Pathways Responsible for the Fluxional
Behavior of Complexes [M(µ-Me-tBu-ImS)(COD)]2
(M ) Rh, 7; Ir, 8): bis-µ-(1:2K2S) (B) S
µ-(1KS,2KN)-µ-(1:2K2S) (C) S HT-bis-µ-(1KS,2KN) (E)
Figure 3. 1H NMR spectra of compound [Ir(µ-Me-tBu-ImS)(cod)]2
(8) in toluene-d8 at (a) 70 °C and (b) -60 °C.
The NMR spectroscopic data for both 7 and 8 at low
temperature are compatible with the unsymmetrical dinuclear
structure revealed by solid-state data in Figure 4. On the other
hand, the data at higher temperatures can be explained by
switching of the coordination modes of the bridging ligands.
Possible pathways in this dynamic equilibrium (Scheme 4) could
include symmetrical dinuclear species having bis-µ-(1:2κ2S) or
bis-µ-(1κS,2κN) (either a cis head-to-tail or head-to-head isomer)
coordinated bridging ligands.13b
The direct protonation of the acetylacetonate ligands in the
mononuclear complexes [M(acac)(CO)2] (M ) Rh, Ir) with
1-methyl-4-tert-butylimidazole-2-thiol (Me-tBu-ImSH) resulted
in the formation of the dinuclear complexes [Rh(µ-Me-tBu-ImS)-
(CO)2]2 (9, Scheme 3) and [Ir(µ-Me-tBu-ImS)(CO)2]2 (10),
which were isolated as orange and dark purple microcrystalline
solids in high yield. The dinuclear formulation of the compounds
is sustained by the IR and the FAB+ spectra, which showed
several dinuclear ions. In particular, the IR spectra of both
compounds in dichloromethane showed three ν(CO) bands for
the terminal carbonyl groups at 2077 (s), 2057 (m), and 2005
(s) cm-1 (9) and 2068 (s), 2041 (m), and 1990 (s) cm-1 (10).
This pattern and their relative intensities (s, m, s) are charac-
teristic of dinuclear complexes with an approximately face-to-
face disposition of both metal coordination planes resulting from
a µ-(1κS,2κN) coordination mode of both Me-tBu-ImS- bridging
ligands located in a relative cis position.26
The compound [Ir(µ-Me-tBu-ImS)(CO)2]2 (10) is apparently
1
rigid since no changes were observed in the H and 13C{1H}
NMR spectra between -50 and 25 °C. The spectroscopic
information evidenced equivalent Me-tBu-ImS- bridging ligands,
and interestingly, two distinct resonances for the carbonyl
ligands were observed in the 13C{1H} NMR spectrum at δ 173.5
and 172.2 ppm. These data would be consistent with either a
head-to-head (cis-HH) or head-to-tail (cis-HT) structure with
Cs and C2 symmetry, respectively. In sharp contrast, the
compound [Rh(µ-Me-tBu-ImS)(CO)2]2 (9) is dynamic, as can
(26) (a) Connelly, N. G.; Finn, C. J.; Freeman, M. K.; Orpen, G. A.;
Stirling, J. J. Chem. Soc., Chem. Commun. 1984, 1025. (b) Mannotti-
Lanfredi, A.; Tiripicchio, A.; Uson, R.; Oro, L. A.; Ciriano, M. A.;
Villarroya, B. E. Inorg. Chim. Acta 1984, 88, L9.

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4381
1
be observed in the 13C{1H} NMR spectrum, but not in the H
NMR spectrum, which remains unchanged in the range of
temperatures under study and shows equivalent bridging ligands.
It is noticeable that the carbonyl ligands were not observed in
the 13C{1H} NMR spectrum in chloroform at room temperature.
However, on cooling to -50 °C, two doublets at δ 186.7 (d,
JC-Rh ) 64.8 Hz) and 182.8 (d, JC-Rh ) 68.7 Hz), corresponding
to two sets of equivalent carbonyl ligands, were observed. On
Scheme 5. Possible Structures for 11 and 12
warming, a broad doublet resonance at δ 185.10 (d, JRh-C
)
68.7 Hz) was observed in toluene-d8 at 80 °C as a consequence
of the scrambling of the carbonyl ligands that became equivalent
at high temperature. This dynamic behavior is not involving
the fragmentation of the dinuclear framework, as the molecular
weight determined in chloroform at RT is in agreement with
that expected for a dinuclear formulation. Thus, the more
reasonable explanation for the observed scrambling is the
interconversion, from µ-(1κS,2κN) to µ-(1:2κ2S), of the coor-
dination mode of both Me-tBu-ImS- bridging ligands.13b
The spectroscopic data for both compounds showing the
equivalence of the bridging thiolates are compatible with both
a syn-bis-µ-(1:2κ2S) and a bis-µ-(1κS,2κN) (cis-HT) structure
(Scheme 5). As far as the relative disposition of the bulky
triphenylphosphine ligands is concerned, only the trans (C2)
arrangement is possible in the bis-thiolate structure, whereas in
the head-to-tail case, either of two trans isomers (C2 symmetry)
are possible. Despite the dynamic behavior, which could be
associated with the restricted rotation of the phenyl rings in the
PPh3 ligands at low temperature, both complexes seem to have
rigid structures since no changes in the coordination mode of
the bridging ligands have been observed (31P NMR evidence).
Dinuclear compounds containing benzothiazole-2-thiolate
(bzta-) or 2-mercaptothiazolinate (tzdt-) ligands such as [Rh-
It is noteworthy that compounds 9 and 10 exist as a single
isomer. The spectroscopic data of both compounds at low
temperature are identical and should have the same cis-HH or
cis-HT structure. However, the cis-HT structure is preferred over
t
the cis-HH because of the steric repulsion between the Bu
groups in the latter structure.
The reaction of [M(acac)(CO)(PPh3)] (M ) Rh, Ir) with
1-methyl-4-tert-butylimidazole-2-thiol (Me-tBu-ImSH) in dichlo-
romethane gave orange solutions of the complexes [Rh(µ-Me-
tBu-ImS)(CO)(PPh3)]2 (11, Scheme 3) and [Ir(µ-Me-tBu-ImS)-
(CO)(PPh3)]2 (12), which were isolated as orange solids, after
recrystallization from dichloromethane/methanol, in moderate
yield. Both complexes are air-sensitive solids that slowly
decompose in solution, which precluded a reliable determination
of the molecular weight in solution. Nevertheless, the FAB+
spectra of both complexes showed the molecular ions as well
as other dinuclear ions that resulted from the sequential loss of
carbonyl and triphenylphosphine ligands. The IR spectra of both
compounds consisted of a strong ν(CO) band for the terminal
carbonyl groups at 1974 and 1973 cm-1, respectively.
27
(µ-bzta)(CO)(PPh3)]2 or [Rh(µ-tzdt)(CO)(PR3)]2 (R ) Me,
Ph)28a show rigid structures derived from a cis-HT arrangement
of the bridging ligands with a trans disposition of the PR3
ligands, which are located trans to the sulfur donor atoms. It is
noticeable that the cis isomer was not observed in solution, in
contrast with the chemistry of related dinuclear thiolate-bridged
species [Rh(µ-SR)(CO)(PR3)]2 where both isomers are usually
observed in solution.25d,e However, it is worth mentioning that
the compound [Rh(µ-SPy)(CO)(PPh3)]2, with an analogous
structure in the solid state, is dynamic in solution and several
species coexist in equilibrium that are solvent and temperature
dependent.13c Having in mind the above considerations we
believe that complexes 11 and 12 have a cis-HT structures with
C2 symmetry. In addition, the observed coupling constant JRh-P
for complex 11 is in good agreement with trans Ph3P-Rh-S
bonds (JRh-P ≈ 160-162 Hz).28
Compound 12 exists at -60 °C as a single isomer with
equivalent triphenylphosphine ligands, as evidenced by the 31P-
{1H} NMR spectrum in toluene-d8, which showed a single
resonance at δ 22.13 ppm. The 1H NMR at the same temperature
showed three resonances at δ 5.33, 2.54, and 1.43 for the
equivalent Me-tBu-ImS- ligands. On warning, a second negli-
gible isomer is observed in the 31P{1H} NMR spectrum at δ
17.95 ppm. However, the main difference was observed in the
aromatic region of the spectrum: at room temperature, two
averaged resonances for the triphenylphosphine protons were
seen, which at -60 °C resolved into a set of nine well-defined
multiplets that spread out between 9 and 7.1 ppm. On the other
hand, no significant change in the chemical shift of the
phosphorus resonance was observed at low temperature. The
31P{1H} NMR spectrum of compound 11 in toluene-d8 at RT
Complexes Derived from 1,4-Di-tert-butylimidazole-2-thiol
(tBu2-ImSH). The deprotonation of 1,4-di-tert-butylimidazole-
2-thiol (tBu2-ImSH) by the methoxo bridges of the complexes
[M(µ-OMe)(COD)]2 (M ) Rh, Ir) resulted in the formation of
the complexes [Rh(µ-tBu2-ImS)(COD)]n (13, Scheme 6) and [Ir-
(µ-tBu2-ImS)(COD)]2 (14), which were isolated as yellow and
red microcrystalline solids in good yield.
showed the presence of a main isomer at δ 38.7 ppm (JRh-P
)
The molecular structure of compound [Rh(µ-tBu2-ImS)-
(COD)]2 (13) has been determined by X-ray diffraction methods
and is shown in Figure 5, which will be discussed further below.
Compound 13 is dinuclear in the solid state and exhibits a
thiolate µ-(1:2κ2S) coordination mode of both tBu2-ImS- ligands
161.4 Hz) together with a minor isomer (ca. 10%) at δ 40.6
ppm (JRh-P ) 165.0 Hz). Although the ratio between the two
isomers is approximately the same at -60 °C (≈10:1), the signal
for the minor isomer is shifted to higher frequency and was
found at δ 49.9 ppm with a similar coupling constant (JRh-P
)
(27) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Lahoz, F. J.; Oro, L. A. J.
Organomet. Chem. 1993, 455, 225.
(28) (a) Cowie, M.; Sielisch, T. J. Organomet. Chem. 1988, 348, 241.
(b) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Casado, M. A.; Lahoz, F. J.; Oro,
L. A. Inorg. Chem. 1996, 35, 1782.
163.7 Hz). Interestingly, the same temperature effect on the
triphenylphosphine protons described above for the iridium
compound was observed at -60 °C for compound 11, pointing
to similar structures and fluxionality for 11 and 12.

4382 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
t
Scheme 6. Syntheses of Bu2-ImS Complexes
Figure 5. Molecular structure of compound [Rh(µ-tBu2-ImS)-
(COD)]2 (13).
Scheme 7. Proposed Dimer-Monomer Equilibrium
Involving 13-16
with a syn-endo disposition. The 1H NMR spectrum in toluene-
d8 at -60 °C is in agreement with the structure found in the
solid state, since a single resonance for the H5 protons of the
t
equivalent Bu2-ImS- bridging ligands and two resonances of
the same intensity for the dCH protons of the COD ligands
Cl2. The inequivalence of the bridging ligands suggests a
dinuclear structure having two thiolate-coordinated (1:2κ2S)-
tBu2-ImS- ligands with an anti disposition. Moreover, the
inversion of the Ir2S2 ring (ring-flipping) easily explains the
number of resonances observed for the olefinic protons of the
COD ligands.29 It is worth mentioning that the 1H NMR
spectrum also shows minor resonances at δ 6.67 and 6.05 ppm,
which correspond to other unidentified isomers (<10%).
The reaction of [M(acac)(CO)2] (M ) Rh, Ir) with 1,4-di-
tert-butylimidazole-2-thiol in dichloromethane gave deep red
and purple solutions of the complexes [Rh(µ-tBu2-ImS)(CO)2]n
(15) and [Ir(µ-tBu2-ImS)(CO)2]n (16), which were isolated as
orange and purple microcrystalline solids in good yield. The
carbonyl compounds gave satisfactory elemental analysis, and
their FAB+ spectra showed the presence of the dinuclear ions.
However, the IR spectra in cyclohexane (Figure 6) showed more
ν(CO) bands for the terminal carbonyl groups than expected
for a single dinuclear isomer.
were observed. However, the compound is fluxional, as
1
evidenced by the H NMR in CD2Cl2 at RT, which showed
mainly featureless resonances probably due to a dynamic process
involving the inversion of the Rh2S2 ring. Interestingly, a new
static species was observed showing sharp resonances at δ 6.21,
t
1.56, and 1.08 for the Bu2-ImS- protons. Taking into account
that the molecular weight measured in chloroform is lower than
that expected for a dinuclear formulation (508 vs 844), we
suggest that the dinuclear species is in equilibrium with
approximately 15% of the mononuclear compound [Rh(tBu2-
ImS)(COD)] (Scheme 7) at RT, as deduced from the relative
1
integrals in the H NMR spectrum. This proposal is supported
by the FAB+ mass spectrum, which, in addition to the dinuclear
ion [Rh(µ-tBu2-ImS)(COD)]2 at m/z 844 (11%), also shows
+
the mononuclear ion [Rh(tBu2-ImS)(COD)]+ at m/z 422 (100%).
Further support comes from the 13C{1H} NMR spectrum in CD2-
Cl2 at RT, where the resonances of [Rh(tBu2-ImS)(COD)] are
observed at chemical shifts comparable to that found for related
mononuclear complexes (see below).
1
The H NMR spectrum of compound 16 in CDCl3 at RT
showed the presence of two main species having equivalent
tBu2-ImS- ligands. In addition, both species are dynamic and
no carbonyl ligands were observed in the 13C{1H} NMR
spectrum as a consequence of scrambling processes involving
the carbonyl ligands. The available spectroscopic information
suggests that in solution compound 16 exists as an equilibrium
(Scheme 7) between the dinuclear [Ir(µ-tBu2-ImS)(CO)2]2 (n )
2) and mononuclear [Ir(tBu2-ImS)(CO)2] (n ) 1) species, the
The 1H NMR spectra of compound [Ir(µ-tBu2-ImS)(COD)]2
(14) in CD2Cl2 at -95 °C or in toluene-d8 at -80 °C are
comparable to that observed for compound 8 and are in
accordance with a dinuclear structure having two bridging
ligands with µ-(1κS,2κN) and µ-(1:2κ2S) coordination modes,
1
respectively. However, the H NMR spectrum at RT is not
compatible with the expected dynamic behavior of this type of
complexes. On the contrary, two broad singlets for the H5
protons of the tBu2-ImS- ligands and two broad resonances for
the dCH protons of the COD ligands were observed in CD2-
(29) Hill, R.; Kelly, B. A.; Kennedy, F. G.; Knox, S. A. R.; Woodward,
P. J. Chem. Soc., Chem. Commun. 1977, 434.

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4383
Figure 6. Partial IR spectra of compounds [M(µ-tBu2-ImS)(CO)2]2 in cyclohexane: (a) M ) Rh, 15; (b) M ) Ir, 16.
1
former being more abundant (≈75%) at room temperature. Thus,
the absorptions at ν(CO) 2072 (s), 2041 (m), and 1998 (s) cm-1
in the IR spectrum in cyclohexane (Figure 6b) correspond to
the dinuclear species, whereas the bands at ν(CO) 2059 and
1986 cm-1 could be assigned to the mononuclear species. The
difference between the last two absorptions (73 cm-1) is typical
of mononuclear complexes having two carbonyl ligands in cis
disposition.30,31 The dinuclear species showed the characteristic
resonance for the H5 protons of the tBu2-ImS- ligands at δ 6.51
and isochronous tBu groups at 1.48 ppm, whereas the resonances
at δ 6.04, 1.58, and 1.23 ppm were assigned to the mononuclear
species.
On cooling to -50 °C in CDCl3 the equilibrium is shifted
toward the dinuclear species to the extent of 95%, as deduced
from the integrals of the H5 resonances. Interestingly, two sets
of equivalent carbonyl ligands were observed in the 13C{1H}
NMR at -50 °C, at δ 173.5 and 173.1 ppm, suggesting that
the most probable structure of the dinuclear species results from
the µ-(1κS,2κN) coordination of the bridging ligands with a cis-
HT disposition (dimer shown in Scheme 7).
The molecular weight of compound [Rh(µ-tBu2-ImS)(CO)2]n
(15) measured in chloroform (534 vs 740) suggests that an
equilibrium similar to that described for compound 16 could
be operative. This fact has been corroborated by the spectro-
scopic data obtained from the IR and NMR, which indicate that
the mononuclear species predominates over the dinuclear one.
The IR spectrum in cyclohexane (Figure 6a) shows two strong
ν(CO) absorptions at 2069 and 2000 cm-1, which have been
assigned to the mononuclear species [Rh(tBu2-ImS)(CO)2], and
three weaker absorptions at ν(CO) 2079 (s), 2059 (m), and 2012
(s) cm-1, with the usual intensity pattern for a dinuclear [Rh-
(µ-tBu2-ImS)(CO)2]2 (cis-HT isomer, Scheme 7) having a face-
to-face disposition of both rhodium coordination planes.
The H NMR spectrum of compound 15 is not structurally
informative. However, the carbonyl region of the 13C{1H} NMR
spectrum in CDCl3 at RT showed a doublet at δ 183.9 ppm
(JRh-C ) 73.4 Hz) for the mononuclear species [Rh(tBu2-ImS)-
(CO)2]. As above, the equilibrium is shifted toward the dinuclear
species when decreasing the temperature, as indicated by the
13C{1H} NMR spectrum at -50 °C. The spectrum showed the
expected two doublet resonances for the cis-HT isomer of the
dinuclear species at δ 187.0 (d, JRh-C ) 64.0 Hz) and 183.3 (d,
JRh-C ) 70.3 Hz) and also a little amount of the mononuclear
species. The equivalence of the carbonyl ligands in the mono-
nuclear species results from a dynamic behavior that probably
involves the opening and re-forming of the four-membered
strained metallaheterocycle via the Rh-N bond. Similar dy-
namic behavior has been observed in the compounds [Rh-
(SPymMe2)(COD)]31 and [Rh(SPymMe2)(CO)(PPh3)]13c con-
taining 4,6-dimethylpyrimidine-2-thiolate ligands.
The carbonylation of the diolefin complexes [M(µ-tBu2-ImS)-
(COD)]2 in dichloromethane gave deep colored solutions of the
carbonyl complexes [M(µ-tBu2-ImS)(CO)2]n (where n ) 1 or
2). Further reaction with 2 molar equiv of triphenylphosphine
resulted in the evolution of carbon monoxide and the formation
of the mononuclear complexes [Rh(tBu2-ImS)(CO)(PPh3)] (17,
Scheme 6) and [Ir(tBu2-ImS)(CO)(PPh3)] (18), which were
isolated as yellow solids in moderate yield. The molecular
structure of compound 18 has been determined by an X-ray
diffraction analysis and shows a chelating coordination mode
(κ2S,N) of the Bu2-ImS- ligand (Figure 7, discussed below).
t
The spectroscopic data showed that both compounds exist
in solution as a single isomer and are compatible with the
structure found in the solid state. In particular, the determination
of the molecular weights in chloroform indicates that the
molecular structure is maintained in solution. The FAB+ spectra
of both complexes showed the mononuclear ions [M(tBu2-ImS)-
(CO)(PPh3)]+ at m/z 605 and 694, respectively, although some
dinuclear ions were also observed in the spectrum of compound
18. The 31P{1H} NMR spectrum of compound 17 in toluene-d8
shows a slightly broad doublet at δ 49.83 ppm (JRh-P ) 156.3
Hz), which became sharper at -60 °C. However, no changes
(30) (a) Teuma, E.; Loy, M.; Le Berre, C.; Etienne, M., Daran, J.-C.;
Kalck, P. Organometallics 2003, 22, 5661. (b) Elgafi, S.; Field, L. D.;
Mecerle, B. A.; Turner, P.; Hambley, T. W. J. Organomet. Chem. 1999,
588, 69. (c) Crotti, C.; Cenini, S.; Rindone, B.; Tollari, S.; Demartin, F.
Chem. Commun. 1986, 784.
(31) Rojas, S.; Fierro, J. L. G.; Fandos, R.; Rodr´ıguez, A.; Terreros, P.
J. Chem. Soc., Dalton Trans. 2001, 2316.

4384 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
complex is mononuclear. The sum of the four cis intraligand
angles is equal to 360.0° within experimental uncertainty, but
the individual angles are distorted from idealized values: first,
the chelated imidazolethiolate enforces a small S-Ir-N angle
[68.83(9)°], as expected for such species. In contrast, the largest
angle [103.54(16)°] is between the Ir-CO bond and the adjacent
Ir-N bond, whereas the S-Ir-P angle is rather large [97.67-
(4)°] and the remaining P-Ir-CO angle ideal within experi-
mental uncertainty. The closest analogues for such a species
are those derived from Rh(CO)(PPh3) and Rh(CO)2 fragments
and 4,6-dimethylpyrimidine-2-thiolate,13c,31 which show very
similar distortions in bond angles within a square-planar
arrangement.
Discussion
t
Pyridinethiolate Complexes of Bu-PyS. The dinuclear
complexes [M(µ-tBu-PyS)(L2)]2 (M ) Rh, Ir) display an open-
book structure resulting from the thiolate µ-(1:2κ2S) coordination
Figure 7. Molecular structure of compound [Ir(µ-tBu2-ImS)(CO)-
(PPh3)] (18).
t
mode of the Bu-PyS- ligands irrespective of the steric and
electronic properties of the auxiliary ligands. The only influence
of the terminal ligands appears to be related with the spatial
disposition of the thiolate bridges. Ab initio theoretical studies
on edge-sharing dinuclear d8 complexes with thiolate ligands33
indicate that the bent structure is more favorable for rhodium
and iridium complexes as a consequence of the tendency of
the metals to form M- - -M contacts. The possible conformations
of the bridging ligands (syn-exo, syn-endo, and anti) seem to
be determined by the interplay of several factors including the
existence of weak metal-metal bonding, the increased steric
repulsion between terminal ligands upon bending, the steric
repulsion between the substituents at the bridging atoms, and
the hydrogen-bonding interactions involving the terminal ligands
and the substituents at the bridges.
1
were observed in the H NMR spectrum between -60 °C and
room temperature. The triphenylphosphine ligand in compound
18 was observed as a sharp singlet at δ 19.9 ppm in the 31P-
{1H} NMR spectrum in C6D6 at RT. Finally, the carbonyl ligand
carbon was observed as the expected doublet of doublets at δ
189.8 ppm (JRh-C ) 75.3 Hz, JP-C ) 19.7 Hz) (17) and as a
singlet at δ 176.6 ppm (18) in the 13C{1H} NMR spectra in
C6D6 at RT. A diagnostic for the κ2S,N coordination mode of
the tBu2-ImS- ligand is the chemical shift of the CS resonance
in the 13C{1H} NMR, which is observed at higher frequency
(≈158 ppm) than in the dinuclear complexes (≈147 ppm). The
IR spectra of both compounds in dichloromethane showed a
strong ν(CO) band for the terminal carbonyl ligand at 1968 and
1953 cm-1, respectively.
The complexes [M(µ-tBu-PyS)(COD)]2 (M ) Rh, 1; Ir, 2)
present a syn-endo conformation of the thiolato ligands. Interest-
ingly, a number of dinuclear rhodium and iridium complexes
containing cyclooctadiene as bidentate terminal ligands and
terminal thiolate ligands as bridges display the syn-endo
conformation in the solid state22a,24b,32c,d and have a dynamic
behavior similar to that found in complexes 1 and 2.32c,d
Similarly, the syn disposition is also the preferred conformation
for thiolate-bridged complexes with four terminal carbonyl
ligands and the endo conformer is usually found in the solid
state (in accordance with the theoretical calculations).34 It is
noticeable that the spectroscopic data for the tetracarbonyl
complexes [M(µ-tBu-PyS)(CO)2]2 (M ) Rh, 3; Ir, 4) are also
in agreement with a syn conformation of the tBu-PyS- ligands.
In contrast, the complexes [M(µ-tBu-PyS)(CO)(PPh3)]2 (M )
Rh, 5; Ir, 6), containing two bulky triphenylphosphine ligands
arranged in a cis disposition, display an anti conformation with
the endo substituent at the side of the molecule with the small
carbonyl ligands, as is generally found in related complexes
containing both monodentate25a-c and bridging diphosphine35
ligands.
Molecular Structure of [Rh(µ-tBu2-ImS)(COD)]2 (13)
and [Ir(µ-tBu2-ImS)(CO)(PPh3)] (18). Good-quality crystals
for X-ray diffraction of compound 13 were obtained by slow
diffusion of n-hexane into a solution of the complex in
dichloromethane. The molecular structure is shown in Figure
5, and key bond distances and angles are shown in Table 1.
The structure of 13 shows the syn-endo disposition of the two
thiolates with respect to the folded Rh2S2 core. Coordination
geometry at both Rh centers is distorted square planar, with
clearly acute S-Rh-S angles [77.09(3)° and 77.15(3)°]. In
comparison with the structure of 2, the M-S-M angles
are significantly larger [92.67(3)° and 92.35(3)°], a reflec-
tion of the fact that the M- - -M bond distance is about 0.5 Å
larger [3.4194(4) Å in 13 and 2.9055(8) Å in 2] and that
the M2S2 core is more open [139.06(5)° fold angle in 13
and 101.02(6)° in 2]. Among related Rh2S2 complexes, the
metal-metal distance is between extremes, such as the 3.52 Å
22a
value cited for [Rh(µ-S-C(R)dNR)(COD)]2 and 2.960(1)
24b
or 2.955 Å in [Rh(µ-SCH2CH2CH2NMe2)(COD)]2
and
[Rh(µ-SC6F5)(COD)]2.32a
Suitable crystals for X-ray diffraction of compound 18 were
obtained by slow diffusion of methanol into a solution of the
complex in dichloromethane at -15 °C. Key bond distances
and angles are shown in Table 4; Figure 7 confirms that the
The results described above contrast with the ability of the
related parent compound pyridine-2-thiolate to bridge rhodium
or iridium centers in dinuclear complexes through the N and S
atoms. For example, the complexes [Rh(µ-SPy)(COD)]2, [Rh-
(µ-SPy)(CO)2]2, and [Rh(µ-SPy)(CO)(PPh3)]213b-d all have a cis-
(32) (a) Cruz-Garritz, D.; Rodriguez, B.; Torrens, H.; Leal, J. Transition
Met. Chem. (Dordrecht) 1984, 9, 284. (b) Cruz-Garritz, D.; Garcia-
Alejandre, J.; Torrens, H.; Alvarez, C.; Toscano, R. A.; Poilblanc, R.;
Thorez, A. Transition Met. Chem. (Dordrecht) 1991, 16, 130. (c) Fandos,
R.; Mart´ınez-Ripoll, M.; Otero, A.; Ruiz, M. J.; Rodr´ıguez, A.; Terreros,
P. Organometallics 1998, 17, 1465. (d) Wark, T. A.; Stephan, D. W. Can.
J. Chem. 1990, 68, 565.
(33) Aullo´n, G.; Ujaque, G.; Lledo´s, A.; Alvarez, S. Chem. Eur. J. 1999,
5, 1391.
(34) (a) Pursiainen, J.; Teppana, T.; Rossi, S.; Pakkanen, T. A. Acta
Chem. Scand. 1993, 47, 416. (b) Bonet, J. J.; de Mountazon, D.; Poilblanc,
R.; Galy, J. Acta Crystallogr. Sect. B 1979, 35, 832.

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4385
HT dinuclear structure resulting from the thionate coordination
mode µ-(1κS,2κN) of both SPy- ligands. Thus, the presence of
a bulky tert-butyl substituent at position 6 of the pyridine-2-
thionate structure reduces the ability of the pyridine nitrogen
atom to coordinate, and as a consequence, the tBu-PyS- ligand
behaves as a normal thiolate ligand. It would be of interest to
determine the minimum size of a substituent needed to give
this result. However, we note that in related systems neither a
methyl nor a chloro substituent is sufficient, because the related
pyridonate dinuclear complexes [M(µ-OPy)(CO)2]2,36 [M(µ-
complexes of the related ligands imidazole-2-thiolate and
1-methylimidazole-2-thiolate have been structurally character-
ized.
It is worthy of notice that dinuclear complexes are usually
obtained with the 1-methyl-4-tert-butylimidazole-2-thiolate
ligand, although the interplay between the bulky tert-butyl group
at the 4 position and the steric properties of the auxiliary ligands
determines the coordination mode and the relative disposition
of the bridging ligands. However, the second tert-butyl group
at the N atom of the heterocycle in the ligand 1,4-di-tert-
butylimidazole-2-thiolate changes both the coordination mode
of the ligands and the nuclearity of the complexes.
When the auxiliary ligands are 1,5-cyclooctadiene, the
dinuclear complexes are dynamic, displaying at the stopped-
exchange limit a µ-(1:2κ2S)(1κS,2κN) coordination of the
bridging ligands as in the complexes [M(µ-Me-tBu-ImS)(COD)]2
(M ) Rh, 7; Ir, 8) and [Ir(µ-tBu2-ImS)(COD)]2 (14). Moreover,
the change in the coordination mode of the ligands from
µ-(1κS,2κN) to µ-(1:2κ2S) appears to be responsible for the
fluxional behavior in solution. Interestingly, as the bulkiness
of the bridging ligand is increased, the difficulties for the
µ-(1κS,2κN) coordination result in the µ-(1:2κ2S) coordination
of both thiolates, as in the dinuclear complexes 13 and 14 (at
room temperature), which display a typical bis-thiolate dinuclear
structure with relative dispositions syn-endo and anti, respec-
tively. Moreover, the dinuclear complex [Rh(µ-tBu2-ImS)-
(COD)]2 (13) appears to be in equilibrium with the mononuclear
compound [Rh(tBu2-ImS)(COD)] at room temperature, a con-
version perhaps driven by release of strain.
37
OMePy)(COD)]2 (M ) Rh, Ir)23 and [Rh(µ-OClPy)(nbd)]2
(OPy- ) 2-pyridonate, OMePy- ) 6-methyl-2-pyridonate,
OClPy- ) 6-chloro-2-pyridonate) all display structures with
staggered face-to-face d8-ML2 environments derived from the
µ-(1κO,2κN) coordination mode of the pyridonate ligands,
irrespective of the substitution at the position ortho to the
pyridine nitrogen.
Imidazolethiolate Complexes from Me-tBu-ImS and tBu2-
ImS. In contrast to what was seen using the 6-tert-butylpyridine-
2-thiolate ligand, the imidazole-2-thiolate derivatives can act
as bidentate bridges through the N and S heteroatoms even in
the presence of bulky substituents on the heterocycle. In fact,
from literature structures of 1-methyl-imidazole-2-thiolate com-
plexes, coordination through only the sulfur atom appears to
be rare, whether in mononuclear complexes or in dinuclear
species as bridging [µ-(1:2κ2S)] ligands.14 Instead, the more
usual coordination modes of this ligand are µ-(1κS,2κN),15
µ-(1κN,1:2κS),16 and (κ2S,N).17 In general, three factors may
explain the higher propensity of the imidazole derivatives to
act as bidentate ligands. First, imidazoles are more basic than
pyridines, by about 2 pKa units.38 Second, in the smaller, five-
membered ring, the steric influence of the tert-butyl group on
the adjacent N-heterocyclic donor atom should be reduced.
Finally, a five-membered heterocycle ring results in significantly
larger N-C-S bond angles that can produce more open
dinuclear structures, resulting in less steric interference between
the bridging and terminal ligands. In this context, we note that
the rhodium and iridium coordination chemistry of the five-
membered heterocyclic ligands benzothiazole-2-thiolate,13b,27,39
2-mercaptothiazolinate,28a,40 and benzimidazole-2-thiolate41 have
been studied in detail. However, neither rhodium nor iridium
The smaller carbonyl ligands facilitate the µ-(1κS,2κN)
coordination mode of the bridging ligands, as demonstrated in
the dinuclear complexes [M(µ-Me-tBu-ImS)(CO)2]2 (M ) Rh,
9; Ir, 10). Interestingly, the complexes are obtained exclusively
as the cis-HT isomer since with this disposition the tert-butyl
groups are placed further apart in the dinuclear structure. Related
tetracarbonyl complexes such as [M(µ-OPy)(CO)2]2 (M ) Rh,
13b
Ir),36 [Ir(µ-SPy)(CO)2]2,42 and [Rh(µ-bzta)(CO)2]2 exist in
solution as the cis-HH and cis-HT isomers, generally in
equilibrium, although only one isomer has been found in the
solid state. However, the complexes [Rh(µ-SPy)(CO)2]213d and
[Ir(µ-bzta)(CO)2]243 are dynamic but exist as a single isomer in
solution at low temperature.
In contrast, the complexes [M(µ-tBu2-ImS)(CO)2]n (M ) Rh,
15; Ir, 16), containing the bulkier 1,4-di-tert-butylimidazole-2-
thiolate bridging ligands, exist in solution as an equilibrium
between dinuclear (n ) 2) and mononuclear (n ) 1) complexes,
whose composition depends on the metal center (Rh or Ir) and
the temperature. Thus, the mononuclear [Rh(tBu2-ImS)(CO)2]
and the dinuclear [Ir(µ-tBu2-ImS)(CO)2]2 species are predomi-
nant at room temperature; however, in both cases the equilibrium
is shifted to the dinuclear species as the temperature decreased.
An analogous equilibrium between di- and mononuclear com-
plexes in palladium chemistry has been observed by Jensen et
al. in the dynamic dinuclear complexes [Pd(µ-PyS)Cl(PMe3)]2,44
[Pd(µ-Spym)Cl(PMe3)]2 (SPym- ) pyrimidine-2-thiolate), and
[Pd(µ-SPymMe)Cl(PMe3)]2 (SPymMe- ) 4-methylpyrimidine-
(35) (a) Choukroun, R.; Dahan, F.; Gervais, D.; Rifai, C. Organometallics
1990, 9, 1982. (b) Kalck, P.; Randrianalimanana, C.; Ridmy, M.; Thorez,
A.; tom Dieck, H.; Ehlers, J. New J. Chem. 1988, 12, 679.
(36) (a) Tejel, C.; Ciriano, M. A.; Villarroya, B. E.; Gelpi, R.; Lo´pez, J.
A.; Lahoz, F. J.; Oro, L. A. Angew. Chem. Int. Ed. 2001, 40, 4084. (b)
Ciriano, M. A.; Villarroya, B. E.; Oro, L. A.; Apreda, C.; Foces-Foces, F.
H.; Cano, J. J. Organomet. Chem. 1989, 366, 377.
(37) Boyd, D. C.; Szalapski, R.; Mann, K. R. Organometallics 1989, 8,
790.
(38) Perrin, D. D. Dissociation Constants of Organic Bases in Aqueous
Solution; Butterworth: London, 1965.
(39) (a) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Oro, L. A.; Tiripicchio,
A.; Tiripicchio-Camellini, M.; Lo´pez, J. A.; Lanfranchi, M. Organometallics
1995, 14, 4764. (b) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Oro, L. A.;
Tiripichio, A. J. Organomet. Chem. 1994, 469, C31. (c) Ciriano, M. A.;
Pe´rez-Torrente, J. J.; Oro, L. A.; Lahoz, F. J. Inorg. Chem. 1992, 31, 969.
(d) Ciriano, M. A.; Pe´rez-Torrente, J. J.; Oro, L. A.; Tiripicchio, A.;
Tiripicchio-Camellini, M.; J. Chem. Soc., Dalton Trans. 1991, 255. (e)
Ciriano, M. A.; Pe´rez-Torrente, J. J.; Oro, L. A.; Viguri, F.; Tiripicchio,
A.; Tiripicchio-Camellini, M.; Lahoz. F. J. J. Chem. Soc., Dalton Trans.
1990, 1493. (f) Ciriano, M. A.; Oro, L. A.; Pe´rez-Torrente, J. J.; Tiripicchio,
A.; Tiripicchio-Camellini, M. J. Chem. Soc., Chem. Commun. 1986, 1737.
(40) Sielisch, T.; Cowie, M. Organometallics 1988, 7, 707.
(41) (a) Tejel, C. Villarroya, B. E.; Ciriano, M. A.; Edwards, A. J.; Lahoz,
F. J.; Oro, L. A.; Lanfranchi, M.; Tiripicchio, A.; Tiripicchio-Camellini,
M. Inorg. Chem. 1998, 37, 3954. (b) Tejel, C. Villarroya, B. E.; Ciriano,
M. A.; Oro, L. A.; Lanfranchi, M.; Tiripicchio, A.; Tiripicchio-Camellini,
M. Inorg. Chem. 1996, 35, 4360.
2-thiolate) but not in [Pd(µ-MeImS)Cl(PMe3)]2 (MeImS-
)
1-methylimidazole-2-thiolate), which is dinuclear and static in
solution.15d
(42) Ciriano, M. A.; Viguri, F.; Oro. L. A.; Tiripicchio, A.; Tiripicchio-
Camellini, M. Angew. Chem., Int. Ed. Engl. 1988, 28, 444.
(43) Ciriano, M. A.; Sebastia´n, S.; Oro. L. A.; Tiripicchio, A.; Tiripicchio-
Camellini, M. Angew. Chem., Int. Ed. Engl. 1987, 27, 402.
(44) Yamamoto, J. H.; Yoshida, W.; Jensen, C. M. Inorg. Chem. 1991,
30, 1353.

4386 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
to use.47 The complexes [Rh(µ-Cl)(COD)]2,48 [Ir(µ-Cl)(COD)]2,48
[Ir(µ-OMe)(COD)]2,49 [Rh(µ-OMe)(COD)]2,49 [Rh(acac)(CO)2],50
[Rh(acac)(CO)(PPh3)],50 [Ir(acac)(CO)2],51 [Ir(acac)(CO)(PPh3)],51
and precursor 6-tert-butyl-2-pyridinone18 were prepared by known
procedures. 1-Methyl-tert-butylimidazole-2-thiol was made as
recently reported.19 NMR spectra were recorded at 300, 400, or
500 MHz with Varian and Bruker spectrometers at variable
temperature. 1H and 13C{1H} NMR chemical shifts are reported in
ppm downfield from tetramethylsilane and referenced to residual
solvent resonances [1H NMR: 7.25 for CHCl3 in CDCl3, 5.32 for
CHDCl2 in CD2Cl2, 2.09 for C6D5CHD2 in toluene-d8, and 7.15
for C6HD5 in C6D6. 13C{1H} NMR: 77.23 for CDCl3, 54.00 for
The combination of the bulky 1,4-di-tert-butylimidazole-2-
thiolate and triphenylphosphine ligands results in the formation
of the mononuclear complexes [M(tBu2-ImS)(CO)(PPh3)] (M
) Rh, 17; Ir, 18), which exhibit a chelating coordination mode
(κ2S,N) of the tBu2-ImS- ligand. Interestingly, the structure may
also be determined by steric factors, as the PPh3 ligand is
coordinated trans to the N atom in the four-membered metal-
lacycle in order to avoid steric repulsions with the tBu at position
4. It is worth noting that the mononuclear complexes [Rh(tBu2-
ImS)(COD)] and [M(tBu2-ImS)(CO)(PPh3)] (M ) Rh, Ir) are
static, but the carbonyl complexes [M(tBu2-ImS)(CO)2] are
dynamic. It may be that the equivalence of the carbonyl ligands
is attained through the intermediary three-coordinated species
resulting from the decoordination of the nitrogen, which is
facilitated by both the strong labilizing effect of the strong
π-acceptor carbonyl ligands and the strain of the four-membered
metallacycle.
Therefore, the introduction of two t-Bu groups on the
imidazole-2-thiolate framework induces the formation of mono-
nuclear compounds by destabilization of the dinuclear structure
by steric and electronic means. In sharp contrast, the cis-HT
dinuclear structure of the complexes [M(µ-Me-tBu-ImS)(CO)-
(PPh3)]2 (M ) Rh, 11; Ir, 12) results from the µ-(1κS,2κN)
coordination of both 1-methyl-4-tert-butylimidazole-2-thiolate
ligands. These results point out that the steric influence of the
N-tBu substituent is greater than that of the N-Me, which, in
turn, seems to be responsible for the nuclearity of the complexes.
The steric influence of the bridging ligands on their coordina-
tion mode has been observed in dinuclear cis-HT complexes
with tridentate 1,8-naphthyridin-2-onate ligands. Thus, the
coordination of the ligands in the complex [Rh(µ-Onapy)(CO)2]2
is µ-(1κN,2κN) but µ-(1κN,2κO) in the complex [Rh(µ-
OMePhnapy)(CO)2]2 (OMePhnapy- ) 5-methyl-7-phenyl-1,8-
naphthyridin-2-onate) as an effect of the bulky phenyl rings.45
On the other hand, the structural influence of the terminal ligands
has been observed in the complexes [Rh(µ-OMe2napy)(COD)]2
and [Rh2(µ-OMe2napy)2(CO)2(COD)], which have µ-(1κN,2κO)-
coordinated bridging ligands and display cis-HT and cis-HH
structures, respectively.46
1
CD2Cl2, and 128.39 for C6D6], where H NMR signals are given
followed by multiplicity, coupling constants J in hertz, and
integration in parentheses. For complex coupling patterns listed,
e.g., for (dt, J ) 3.2, 7.9, 1H), the doublet exhibits a 3.2 Hz coupling
constant. 31P{1H} NMR chemical shifts were measured relative to
H3PO4 (85%). Molecular weights were determined in chloroform
solutions on a Knauer vapor pressure osmometer (isopiestic
method). Carbon, hydrogen, nitrogen, and sulfur analyses were
carried out in a Perkin-Elmer 2400 CHNS/O analyzer. IR spectra
were obtained in solution held in NaCl cells using an FT-IR
spectrophotometer (either Bruker Equinox 55 or Perkin-Elmer
Spectrum One). MS data were recorded on a VG Autospec double-
focusing mass spectrometer operating in the positive mode. Ions
were produced with a Cs+ gun at ca. 30 kV, and 3-nitrobenzyl
alcohol (NBA) was used as the matrix.
Synthesis of 1,4-Di-tert-butylimidazole-2-thiol. To a solution
of 1-bromo-3,3-dimethyl-2-butanone (20.0 g, 112 mmol) in THF
(250 mL) was added tert-butylamine (24.5 g, 335 mmol) in one
portion, and the mixture was heated under reflux for 1 day. After
workup with water and diethyl ether, crude 1-(tert-butylamino)-
3,3-dimethylbutan-2-one (15.2 g) remained. 1H NMR (CDCl3,
199.97 MHz, 25 °C): δ 3.64 (s, 2 H, CH2), 1.17 (s, 9 H, CH3,
t
N-tBu), 1.10 ppm (s, 9 H, CH3, Bu). Crude 1-(tert-butylamino)-
3,3-dimethylbutan-2-one in ethanol (100 mL) and a solution of
KSCN (9.95 g, 103 mmol) in 2 N HCl (3.5 g) were heated under
reflux overnight. The room-temperature mixture was diluted with
water (250 mL) and placed in the freezer to complete precipita-
tion of 1,4-di-tert-butylimidazole-2-thiol (9.58 g, 51%). Mp:
286.7-292.3 °C (dec), raised to 288.0-291.0 °C by rinsing of
crystals with ethyl acetate and subsequent recrystallization from
THF and hexanes. 1H NMR (CDCl3, 300.08 MHz, 30 °C): δ 10.4
(br s, 1 H), 6.42 (d, J ) 1.8 Hz, 1 H), 1.81 (s, 9 H), 1.25 ppm
(s, 9 H). 13C{1H} NMR (CDCl3, 50.2 MHz, 30 °C): δ 158.4,
137.0, 109.2, 58.3, 30.2, 29.3, 28.2. Anal. Calcd for C11H20N2S
(212.35): C, 62.22; H, 9.49; N, 13.19. Found: C, 62.24; H, 9.35;
N, 13.24.
Synthesis of 6-tert-Butylpyridine-2-thiol. Argon was bubbled
through a solution of 6-tert-butyl-2-pyridinone (4.00 g, 26.5 mmol)
in toluene (100 mL) for 10 min. Lawesson’s reagent (5.350 g, 3.22
mol) was then added, and the reaction mixture was heated to reflux
for 22 h. The mixture was cooled at room temperature, and water
(100 mL) was added. After 1 h of stirring, phases were separated
and the aqueous phase was extracted with diethyl ether (4 × 30
mL). The organic fractions were combined, washed with water (4
× 50 mL), dried over magnesium sulfate, and filtered. After
removing the solvent under vacuum, the yellow crude solid was
Conclusions
The profound steric effect of a bulky tert-butyl group adjacent
to nitrogen in tBu-PyS makes it coordinate like a normal thiolate
such as PhS: no evidence for metal-nitrogen interaction was
seen. In contrast, despite the presence of a tert-butyl group in
a similar position on the two imidazole ligands, complexes with
metal-nitrogen coordination were isolated. This shows a
stronger coordination ability of imidazole, as evidenced not only
in two bridging coordination modes [µ-(1κS,2κN) and µ-(1:2κ2S)
in 7] but also in a mononuclear species as a chelating ligand
[κ2S,N in 18]. Among imidazolethiolate complexes, changing
the steric demand of the nonbasic ring nitrogen (Me-tBu-ImS
t
vs Bu2-ImS) partially controls access to the sulfur atom and
hence modifies the capacity of the thiolate to bridge metals.
Experimental Section
(47) (a) Shriver, D. F. The Manipulation of Air-sensitiVe Compounds;
McGraw-Hill: New York, 1969. (b) Armarego, W. L. F.; Perrin, D. D.
Purification of Laboratory Chemicals, 4th ed.; Butterworth-Heinmann:
Oxford, 1996.
(48) Giordano, G.; Crabtree, R. H. Inorg. Synth. 1979, 19, 218.
(49) Uso´n, R.; Oro, L. A.; Cabeza, J. Inorg. Synth. 1985, 23, 126.
(50) (a) Herna´ndez-Gruel, M. A. F.; Pe´rez-Torrente, J. J.; Ciriano, M.
A.; Oro, L. A. Inorg. Synth. 2004, 34, 127. (b) Bonati, F.; Wilkinson, G. J.
Chem. Soc. 1964, 3156.
General Procedures. All manipulations were performed under
dry argon atmosphere using Schlenk techniques. Solvents were dried
by standard methods and distilled under argon immediately prior
(45) Minteert, M.; Sheldrick, W. S. Inorg. Chim. Acta 1997, 254, 93.
(46) Villarroya, B. E.; Oro, L. A.; Lahoz, F. J.; Edwards, A. J.; Ciriano,
M. A.; Alonso, P. J.; Tiripicchio, A.; Tiripicchio-Camellini, M. Inorg. Chim.
Acta 1996, 250, 241.
(51) Pitt, C. G.; Monteith, L. K.; Ballard, L. F.; Collman, J. P.; Morrow,
J. C.; Roper, W. R.; Ulk, D. J. Am. Chem. Soc. 1996, 88, 4286.

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4387
purified by column chromatography on silica gel by using CH2-
Cl2/petroleum ether (1:1) and CH2Cl2/MeOH (99:1) solvent systems
to yield pure 6-tert-butylpyridine-2-thiol (3.938 g, 89%). 1H NMR
(CDCl3, 300.08 MHz, 30 °C): δ 10.54 (br s, 1 H), 7.38 (d, J )
8.7 Hz, 1 H), 7.27 (t, J ) 7.2 Hz, 1 H), 6.57 (d, J ) 7.2 Hz, 2 H),
1.33 (s, 9 H). 13C{1H} NMR (CDCl3, 125.7 MHz, 30 °C): δ 158.9,
138.1, 131.1, 109.3, 35.2, 29.3. Anal. Calcd for C9H13NS
(167.27): C, 64.62; H, 7.83; N, 8.37. Found: C, 65.02; H, 7.87;
N, 8.01.
CH, COD), 3.83 (br s, 1 H, dCH, COD), 3.58 (br m, 1 H, dCH,
COD), 3.29 (s, 3 H, N-CH3), 3.27 (s, 3 H, N-CH3), 3.06 (br s, 1
H, dCH, COD), 2.74 (br s, 2 H, >CH2, COD), 2.49 (br s, 1 H,
>CH2, COD), 2.17-1.88 (br m, 7 H, >CH2, COD), 1.51 (br s, 11
H, CH2, COD, and CH3, tBu), 1.04 (br s, 9 H, CH3, tBu). 13C{1H}
NMR (CD2Cl2, 75.46 MHz, 25 °C): δ 151.2 (SC), 142.6 (C4), 116.2
(C5), 81.2 (d, JC-Rh ) 11.92 Hz, dCH, COD), 33.9 (N-CH3), 32.3
t
t
(C, Bu), 31.6 (CH2, COD), 30.4 (CH3, Bu). 13C{1H} APT NMR
(CD2Cl2, 75.47 MHz, -95 °C): δ 149.6 (SC), 149.3 (SC), 146.5
(C4), 140.3 (C4), 33.9 (N-CH3), 33.1 (N-CH3), 31.6 (CH2, COD)
Representative Procedure for the Synthesis of [M(HetS)-
(COD)]n Complexes. Synthesis of [Rh(µ-tBu-PyS)(COD)]2 (1).
[Rh(µ-OMe)(COD)]2 (0.200 g, 0.413 mmol) and 6-tert-butylpyri-
dine-2-thiol (0.138 g, 0.826 mmol) were dissolved in dry CH2Cl2
(4 mL) to give immediately an orange solution. The mixture was
stirred 3.5 h at room temperature and concentrated under vacuum
to 1-2 mL. Addition of cold MeOH (3 mL) to the concentrated
solution gave the product as a yellow microcrystalline solid, which
was filtered off, washed with cold MeOH (2 × 5 mL), and vacuum-
t
t
t
31.0 (C, Bu), 30.5 (CH3, Bu), 28.6 (CH3, Bu). MS [FAB+ m/z
(%)]: 760 (20) [M+], 652 (31) [M+ - COD]. Anal. Calcd for
C32H50N4S2Rh2 (760.71): C, 50.52; H, 6.63; N, 7.37; S, 8.43.
Found: C, 50.25; H, 6.53; N, 7.32; S, 8.66.
Synthesis of [Ir(µ-Me-tBu-ImS)(COD)]2 (8). Following the
general procedure, [Ir(µ-OMe)(COD)]2 (0.273 g, 0.413 mmol) and
1-methyl-4-tert-butylimidazole-2-thiol (0.140 g, 0.826 mmol) were
1
used to prepare 8 (0.352 g, 91%). H NMR (toluene-d8, 300.12
1
dried (0.261 g, 84%). H NMR (CD2Cl2, 300.13 MHz, 25 °C): δ
MHz, 70 °C): δ 6.06 (s, 2 H, H5), 4.46 (br s, 8 H, dCH, COD),
2.94 (br s, 6 H, N-CH3), 2.36 (br s, 8 H, CH2, COD), 1.66 (br s,
8 H, CH2, COD), 1.40 (br s, 24 H, CH3, tBu).1H NMR (toluene-d8,
300.12 MHz, 25 °C), selected resonances: δ 5.99 (s, 2 H, H5),
7.38 (t, J ) 7.7 Hz, 2 H, H4), 7.16 (d, J ) 7.5 Hz, 2 H, H3), 7.04
(d, J ) 7.6 Hz, 2 H, H5), 4.84 (br s, 8 H, dCH, COD), 2.42 (br m,
8 H, CH2, COD), 1.96 (br m, 8 H, CH2, COD), 1.32 (s, 18 H, CH3,
tBu). 1H NMR (CD2Cl2, 300.13 MHz, -70 °C): δ 7.34 (t, J ) 7.7
Hz, 2 H, H4), 7.06 (d, J ) 7.6 Hz, 2 H, H3), 6.99 (d, J ) 7.7 Hz,
2 H, H5), 4.98 (br s, 4 H, dCH, COD), 4.43 (br s, 4 H, dCH,
COD), 2.33 (br m, 8 H, CH2, COD), 1.87 (br m, 8 H, CH2, COD),
1
4.63 (br s, 8 H, dCH, COD). H NMR (toluene-d8, 300.12 MHz,
-60 °C): δ 5.88 (br s, 1 H, dCH, COD), 5.75 (s, 1 H, H5), 5.62
(s, 1 H, H5), 5.58 (br s, 1 H, dCH, COD), 5.40 (br s, 1 H, dCH,
COD), 4.74 (br s, 1 H, dCH, COD), 4.23 (br s, 1 H, dCH, COD),
4.11 (br s, 1 H, dCH, COD), 3.60 (br s, 1 H, dCH, COD), 3.40
(br s, 1 H, dCH, COD), 2.92 (br s, 5 H, N-CH3 and CH2, COD),
2.72 (br s, 1 H, CH2, COD), 2.54 (s, 3 H, N-CH3), 2.44 (br m, 5
H, CH2, COD), 1.89 (br m, 2 H, CH2, COD), 1.64 (br s, 9 H, CH3,
tBu), 1.32 (br s, 15 H, CH2, COD and CH3, tBu). 1H NMR (CDCl3,
400.16 MHz, 25 °C), selected resonances: δ 6.42 (s, 2 H, H5),
t
1.20 (s, 18 H, CH3, Bu). 13C{1H} NMR (CD2Cl2, 75.46 MHz, 25
°C): δ 169.9 (SC), 158.9(C6), 136.3 (C5), 126.9 (C4), 116.4 (C3),
80.3 (d, JC-Rh ) 11.9 Hz, dCH, COD), 38.2 (C, tBu), 31.6 (CH2,
COD) 30.2 (CH3, tBu). 13C{1H} APT NMR (CD2Cl2, 75.47 MHz,
-70 °C): δ 168.7 (SC), 157.3 (C6), 135.6 (C5), 125.7 (C4), 115.5
(C3), 81.3 (br s, dCH, COD), 77.9 (br s, dCH, COD), 37.3 (C,
tBu), 30.8 (CH2, COD), 29.2 (CH3, tBu). MW: found 717.6 (calcd
1
4.47 (br s, 8 H, dCH, COD), 3.42 (s, 6 H, N-CH3). H NMR
754.69). MS [FAB+ m/z (%)]: 755 (55) [MH]+, 646 (100) [M+
COD]. Anal. Calcd for C34H48N2S2Rh2 (754.69): C, 54.11; H, 6.41;
-
(CDCl3, 300.12 MHz, -55 °C): δ 6.47 (s, 1 H, H5), 6.42 (s, 1 H,
H5), 4.82 (br m, 2 H, dCH, COD), 4.68 (br m, 1 H, dCH, COD),
4.13 (br m, 2 H, dCH, COD), 3.51 (br m, 1 H, dCH, COD), 3.40
(s, 3 H, N-CH3), 3.37 (s, 3 H, N-CH3), 3.12 (br s, 1 H, dCH,
COD), 3.04 (br m, 1 H, dCH, COD), 2.48 (br m, 2 H, CH2, COD),
2.31 (br m, 2 H, CH2, COD), 2.01 (br m, 4 H, CH2, COD), 1.86
(br m, 4 H, CH2, COD), 1.75 (br s, 10 H, CH2, COD and CH3,
N, 3.71; S, 8.50. Found: C, 54.01; H, 5.92; N, 3.42; S, 8.60.
Synthesis of [Ir(µ-tBu-PyS)(COD)]2 (2). Following the general
procedure, [Ir(µ-OMe)(COD)]2 (0.273 g, 0.413 mmol) and 6-tert-
butylpyridine-2-thiol (0.138 g, 0.826 mmol) were used to prepare
2 (0.328 g, 86%). 1H NMR (CDCl3, 300.13 MHz, 22 °C): δ 7.41
(t, J ) 7.8 Hz, 2 H, H4), 7.20 (d, J ) 7.7 Hz, 2 H, H3), 7.06 (d, J
) 7.8 Hz, 2 H, H5), 4.56 (br s, 8 H, dCH, COD), 2.17 (br m, 8 H,
CH2, COD), 1.70 (br m, 8 H, CH2, COD), 1.30 (s, 18 H, CH3,
tBu). 1H NMR (CDCl3, 300.13 MHz, -55 °C): δ 7.43 (t, J ) 7.8
Hz, 2 H, H4), 7.17 (d, J ) 7.7 Hz, 2 H, H3), 7.05 (d, J ) 7.7 Hz,
2 H, H5), 4.74 (br s, 4 H, dCH, COD), 4.26 (br s, 4 H, dCH,
COD), 2.21 (br s, 4 H, CH2, COD), 2.06 (br s, 4 H, CH2, COD),
1.81 (br m, 4 H, CH2, COD), 1.54 (br m, 4 H, CH2, COD), 1.26 (s,
t
tBu), 1.14 (br s, 13 H, CH2, COD and CH3, Bu). MS [FAB+ m/z
(%)]: 939 (73) [M+], 830 (9) [M+ - COD]. Anal. Calcd for
C32H50N4S2Ir2 (939.33): C, 40.92; H, 5.37; N, 5.96; S, 6.83.
Found: C, 40.81; H, 4.98; N, 5.90; S, 6.81.
Synthesis of [Rh(µ-tBu2-ImS)(COD)]2 (13). Following the
general procedure, [Rh(µ-OMe)(COD)]2 (0.116 g, 0.239 mmol) and
1,4-di-tert-butylimidazole-2-thiol (0.102 g, 0.479 mmol) were used
to prepare 13 (0.169 g, 84%). Two main species are observed by
NMR at RT in CD2Cl2: A (dinuclear) and B (mononuclear), in a
t
18 H, CH3, Bu). 13C{1H} APT NMR (CDCl3, 100.63 MHz, 25
°C): δ 169.6 (SC), 153.4 (C6), 136.2 (C5), 126.6 (C4), 117.0 (C3),
ratio of 85% to 15%. H NMR (CD2Cl2, 400.16 MHz, 25 °C),
1
t
65.1 (dCH, COD), 38.0 (C, Bu), 32.1 (CH2, COD), 30.1 (CH3,
selected resonances: δ 6.61 (br s, 2 H, H5, A), 6.21 (s, 1 H, H5,
B), 4.00-4.56 (br m, 8 H, dCH, COD, A), 1.56 (s, 9 H, N-tBu,
B), 1.08 (s, 9 H, tBu, B). 1H NMR (toluene-d8, 300.13 MHz, -60
°C): δ 6.63 (br m, 2 H, H5), 5.70 (br s, 4 H, dCH, COD), 4.42 (br
s, 4 H, dCH, COD), 3.71 (br s, 3 H, CH2, COD), 2.94 (br s, 3 H,
CH2, COD), 2.24 (br m, 5 H, CH2, COD), 1.80 (br m, 5 H, CH2,
COD), 1.54 (br s, 18 H, CH3, N-tBu), 1.37 (br s, 18 H, CH3, tBu).
MW: found 508 (calcd 844.8). MS [FAB+ m/z (%)]: 844 (11)
tBu). 13C{1H} APT NMR (CDCl3, 75.47 MHz, -55 °C): δ 169.2
(SC), 152.7 (C6), 136.2 (C5), 126.2 (C4), 116.8 (C3), 66.5 (dCH,
t
COD), 64.2 (dCH, COD), 37.8 (C, Bu), 32.1 (CH2, COD), 31.8
t
(CH2, COD), 29.8 (CH3, Bu). MW: found 934.4 (calcd 933.3).
MS [FAB+ m/z (%)]: 933 (36) [M]+, 824 (18) [M+ - COD]. Anal.
Calcd for C34H48N2S2Ir2 (933.32): C, 43.75; H, 5.18; N, 3.00; S,
6.87. Found: C, 43.45; H, 4.95; N, 2.92; S, 6.33.
t
[M+], 736 (47) [M+ - COD], 633 (63) [M+ - Bu2-ImS], 422
Synthesis of [Rh(µ-Me-tBu-ImS)(COD)]2 (7). Following the
general procedure, [Rh(µ-OMe)(COD)]2 (0.200 g, 0.413 mmol) and
1-methyl-4-tert-butylimidazole-2-thiol (0.140 g, 0.826 mmol) were
used to prepare 7 (0.258 g, 82%). 1H NMR (CD2Cl2, 400.16 MHz,
25 °C): δ 6.50 (s, 2 H, H5), 4.59 (br s, 8 H, dCH, COD), 3.45 (s,
6 H, N-CH3), 2.47 (br m, 8 H, CH2, COD), 1.93 (br m, 8 H, CH2,
(100) [M+ - Rh(tBu2-ImS)(COD)]. Anal. Calcd for C38H62N4S2-
Rh2 (844.86): C, 54.02; H, 7.40; N, 6.63; S, 7.59. Found: C, 53.94;
H, 7.00; N, 6.38; S, 7.41.
Synthesis of [Ir(µ-tBu2-ImS)(COD)]2 (14). Following the
general procedure, [Ir(µ-OMe)(COD)]2 (0.175 g, 0.264 mmol) and
1,4-di-tert-butylimidazole-2-thiol (0.112 g, 0.528 mmol) were used
to prepare 14 (0.249 g, 92%). 1H NMR (CD2Cl2, 400.16 MHz, 25
°C), selected resonances: δ 6.67 (s, unidentified isomer), 6.61 (s,
t
1
COD), 1.28 (s, 18 H, CH3, Bu). H NMR (CD2Cl2, 300.13 MHz,
-95 °C): δ 6.51 (s, 1 H, H5), 6.45 (s, 1 H, H5), 5.12 (br s, 1 H,
dCH, COD), 4.74 (br m, 3 H, dCH, COD), 4.09 (br m, 1 H, d

4388 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
1 H, H5), 6.56 (s, 1 H, H5), 6.05 (s, unidentified isomer), 4.21 (br
s, 4 H, dCH, COD), 3.96 (br s, 4 H, dCH, COD), 2.41 (br m, 4
H, CH2, COD), 2.21 (br m, 1 H, >CH2, COD), 2.01 (br m, 4 H,
CH2, COD), 1.87 (br m, 4 H, CH2, COD). 1H NMR (CD2Cl2, 300.12
MHz, -95 °C), selected resonances: δ 6.60 (s, 1 H, H5), 6.56 (s,
1 H, H5), 4.99 (br s, 1 H, dCH, COD), 4.78 (br s, 1 H, dCH,
COD), 4.63 (br s, 1 H, dCH, COD), 4.03 (br s, 1 H, dCH, COD),
3.63 (br s, 1 H, dCH, COD), 3.27 (br s, 1 H, dCH, COD), 2.89-
2.96 (br m, 2 H, dCH, COD). 13C{1H} APT NMR (CD2Cl2, 75.47
MHz, -95 °C): δ 150.0 (SC), 147.3 (SC), 143.8 (C4), 135.6 (C4),
56.4 (dCH, COD), 55.9 (dCH, COD), 31.9 (C, N-tBu), 31.0 (C,
used to prepare 10 (0.216 g, 90%). 1H NMR (CDCl3, 300.12 MHz,
25 °C): δ 6.31 (s, 2 H, H5), 3.41 (s, 6 H, N-CH3), 1.46 (s, 18 H,
t
CH3, Bu). 13C{1H} NMR APT (CDCl3, 100.63 MHz, 25 °C): δ
173.5 (CO), 172.2 (CO), 151.8 (SC), 149.0 (C4), 117.5 (C5), 34.9
(N-CH3), 32.6 (C, tBu), 31.5 (CH3, tBu). IR (CH2Cl2, cm-1): 2068
(s), 2041 (m), 1990 (s). MS [FAB+ m/z (%)]: 836 (42) [M+], 808
(94) [M+ - CO]. Anal. Calcd for C20H26N4O4S2Ir2 (836.06): C,
28.77; H, 3.14; N, 6.71; S, 7.68. Found: C, 28.61; H, 2.96; N,
6.70; S, 7.73.
Synthesis of [Rh(µ-tBu2-ImS)(CO)2]n (15). Following the
general procedure, [Rh(acac)(CO)2] (0.250 g, 0.968 mmol) and 1,4-
di-tert-butylimidazole-2-thiol (0.192 g, 0.905 mmol) were used to
prepare 15 (0.288 g, 86%). Two main species are observed:
dinuclear (A) and mononuclear (B). 13C{1H} APT NMR (CDCl3,
75.47 MHz, 25 °C), selected resonances: δ 183.9 (d, JC-Rh ) 73.4
Hz, CO, B), 114.0 (C,5 A), 101.8 (C,5 B). 13C{1H} APT NMR
(CDCl3, 75.47 MHz, -50 °C), the dinuclear species prevails: δ
187.0 (d, JC-Rh ) 64.0 Hz, CO, A), 183.3 (d, JC-Rh ) 70.3 Hz,
CO, A), 146.9 (SC, A), 146.6 (C4, A), 114.0 (C5, A), 102.1 (C5,
tBu). MS [FAB+ m/z (%)]: 1023 (14) [M+], 811 (25) [M+
-
tBu-ImS], 512 (100) [M+ - Ir(tBu-ImS)(COD)]. Anal. Calcd for
C38H62N4S2Ir2 (1023.48): C, 44.59; H, 6.11; N, 5.47; S, 6.27.
Found: C, 44.39; H, 5.96; N, 5.32; S, 6.24.
Representative Procedure for the Synthesis of [M(HetS)-
(CO)2]n Complexes (n ) 1 or 2). Synthesis of [Rh(µ-tBu-PyS)-
(CO)2]2 (3). [Rh(acac)(CO)2] (0.250 g, 0.968 mmol) and 6-tert-
butylpyridine-2-thiol (0.170 g, 1.02 mmol) were dissolved in dry
CH2Cl2 (4 mL) to give immediately a dark brown solution. The
mixture was stirred overnight at room temperature and concentrated
under vacuum to 1 mL. Addition of cold deoxygenated MeOH (4
mL) to the concentrated solution gave the product as a dark red
microcrystalline solid, which was filtered, washed with cold MeOH
(3 × 8 mL), and vacuum-dried (0.266 g, 85%). 1H NMR (CDCl3,
400.16 MHz, 25 °C): δ 7.56 (d, J ) 7.5 Hz, 2 H, H3), 7.47 (t, J
) 7.5 Hz, 2 H, H4), 7.21 (d, J ) 7.3 Hz, 2 H, H5), 1.38 (s, 18 H,
t
B), 57.3 (C, N-tBu, A), 32.2 (C, Bu, A), 31.6 (CH3, N-tBu, A),
t
29.5 (CH3, Bu, A). IR (cyclohexane, cm-1): 2079 (s), 2069 (s),
2059 (m), 2012 (s), 2000 (s). MW: found 534 (calcd 740.54). MS
[FAB+ m/z (%)]: 713 (18) [M+ - CO], 685 (9) [M+ - 2CO], 656
(100) [M+ - 3CO]. Anal. Calcd for C26H38N4S2O4 Rh2 (740.54):
C, 42.17; H, 5.17; N, 7.57; S, 8.66. Found: C, 41.73; H, 4.48; N,
7.25; S, 8.32.
Synthesis of [Ir(µ-tBu2-ImS)(CO)2]n (16). Following the general
procedure, [Ir(acac)(CO)2] (0.200 g, 0.575 mmol) and 1,4-di-tert-
butylimidazole-2-thiol (0.114 g, 0.538 mmol) were used to prepare
16 (0.193 g, 78%). Two main species are observed by NMR: A
(dinuclear) and B (mononuclear). 1H NMR (CDCl3, 300.12 MHz,
25 °C), dinuclear species (75%): δ 6.51 (s, 2 H, H5), 1.48 (s, 18
t
CH3, Bu). 13C{1H} NMR APT (CDCl3, 75.46 MHz, 25 °C): δ
184.4 (d, JC-Rh ) 71.9 Hz, CO), 170.6 (SC), 156.2 (C6), 136.7
t
t
(C3), 124.2 (C4), 118.3 (C5), 37.9 (C, Bu), 30.2 (CH3, Bu). IR
(CH2Cl2, cm-1): 2082 (m), 2064 (s), 2016 (s). MS [FAB+ m/z (%)]:
650 (9) [M+], 623 (23) [M+ - CO], 594 (32) [M+ - 2CO], 566
(27) [M+ - 3CO], 538 (37) [M+ - 4CO]. Anal. Calcd for
C22H24N2S2O4Rh2 (650.37): C, 40.63; H, 3.72; N, 4.31; S, 9.86.
Found: C, 40.41; H, 3.35; N, 4.10; S, 9.69.
t
H, CH3, N-tBu and Bu), [Ir(µ-tBu2-ImS)(CO)2]2; mononuclear
species (25%): δ 6.04 (s, 1 H, H5), 1.58 (s, 9 H, CH3, N-tBu),
1.23 (s, 9 H, CH3, N-tBu), [Ir(tBu2-ImS)(CO)2]. 13C{1H} APT
NMR (CDCl3, 75.47 MHz, 25 °C): δ 114.6 (C5, A), 108.4 (C5, B),
Synthesis of [Ir(µ-tBu-PyS)(CO)2]2 (4). Following the general
procedure, [Ir(acac)(CO)2] (0.200 g, 0.575 mmol) and 6-tert-
butylpyridine-2-thiol (0.101 g, 0.606 mmol) were used to prepare
4 (0.182 g, 77%). 1H NMR (CDCl3, 300.12 MHz, 25 °C): δ 7.53
(d, J ) 4.5 Hz, 4 H, H3 and H5), 7.22 (t, J ) 4.2 Hz, 2 H, H4),
1.35 (s, 18 H, CH3, tBu). 13C{1H} NMR APT (CDCl3, 75.47 MHz,
25 °C): δ 173.4 (CO), 170.9 (SC), 153.5 (C6), 137.2 (C3), 124.3
(C4), 119.3 (C5), 38.1 (C, tBu), 30.2 (CH3, tBu). IR (CH2Cl2, cm-1):
2073 (m), 2053 (s), 2002 (s). MS [FAB+ m/z (%)]: 829 (25) [M+],
800 (50) [M+ - CO], 772 (57) [M+ - 2CO]. Anal. Calcd for
C22H24N2S2O4Ir2 (829.00): C, 31.87; H, 2.92; N, 3.38; S, 7.74.
Found: C, 31.46; H, 2.34; N, 3.07; S, 7.12.
t
58.2 (C, N-tBu, A), 32.9 (C, Bu, A), 32.5 (CH3, N-N-tBu, A),
31.4 (C, tBu, B), 30.0 (CH3, tBu, B), 29.7 (CH3, tBu, A). 1H NMR
(CDCl3, 300.12 MHz, -50 °C), dinuclear species (95%): δ 6.47
(s, 2 H, H5), 1.42 (s, 18 H, CH3, N-tBu and tBu), [Ir(µ-tBu2-ImS)-
(CO)2]2; mononuclear species (5%): δ 6.01 (s, 1 H, H5), 1.56 (s,
t
9 H, CH3, N-tBu), 1.18 (s, 9 H, CH3, Bu), [Ir(tBu2-ImS)(CO)2].
13C{1H} APT NMR (CDCl3, 75.47 MHz, -50 °C): δ 173.5 (CO),
173.1 (CO), 146.8 (SC), 145.9 (C4), 114.6 (C5), 57.9 (C, N-tBu),
32.7 (C, tBu), 32.3 (CH3, N-tBu), 29.6 (CH3, tBu), [Ir(µ-tBu2-ImS)-
(CO)2]2. IR (cyclohexane, cm-1): 2072 (s), 2059 (m), 2041 (m),
1998 (s), 1986 (m). MS [FAB+ m/z (%)]: 919 (9) [M+], 890 (25)
[M+ - CO], 460 (17) [M+ - Ir(tBu2-ImS)(CO)2]. Anal. Calcd for
C26H38N4S2O4 Ir2 (919.26): C, 33.97; H, 4.17; N, 6.10; S, 6.98.
Found: C, 33.23; H, 3.93; N, 6.01; S, 6.63.
Synthesis of [Rh(µ-Me-tBu-ImS)(CO)2]2 (9). Following the
general procedure, [Rh(acac)(CO)2] (0.250 g, 0.968 mmol) and
1-methyl-4-tert-butylimidazole-2-thiol (0.164 g, 0.968 mmol) were
used to prepare 9 (0.266 g, 84%). 1H NMR (CDCl3, 300.08 MHz,
25 °C): δ 6.30 (s, 2 H, H5), 3.40 (s, 6 H, N-CH3), 1.42 (s, 18 H,
Synthesis of [M(HetS)(CO)(PPh3)]n Complexes (n ) 1 or 2).
Synthesis of [Rh(µ-tBu-PyS)(CO)(PPh3)]2 (5). Carbon monoxide
was bubbled through an orange solution of complex 1 (0.0754 g,
0.100 mmol) in CH2Cl2 (4 mL) for 10 min. The solution color
changed to red-orange. Solid triphenylphosphine (0.0524 g, 0.200
mmol) was then added to give an orange solution with evolution
of carbon monoxide. The reaction mixture was stirred for 0.5 h at
room temperature. Evaporation of this solution to 1 mL and addition
of cold MeOH (4 mL) gave the complex as a yellow solid, which
was filtered with a cannula, washed with cold MeOH (4 × 2.5
t
1
CH3, Bu). H NMR (CDCl3, 300.12 MHz, -50 °C): δ 6.31 (s, 2
t
H, H5), 3.40 (s, 6 H, N-CH3), 1.39 (s, 18 H, CH3, Bu). 13C{1H}
APT NMR (CDCl3, 75.46 MHz, 25 °C): δ 152.0 (SC), 149.4 (C4),
116.9 (C5), 34.9 (N-CH3), 32.1 (C, tBu), 31.1 (CH3, tBu). 13C{1H}
APT NMR (CDCl3, 75.47 MHz, -50 °C): δ 186.7 (d, JC-Rh
)
64.8 Hz, CO), 182.8 (d, JC-Rh ) 68.7 Hz, CO), 151.0 (SC), 148.5
(C4), 116.9 (C5), 35.0 (N-CH3), 31.9 (C, tBu), 30.6 (CH3, tBu). IR
(CH2Cl2, cm-1): 2077 (s), 2057 (m), 2005 (s). MW: found 656.2
(calc 656.3). MS [FAB+ m/z (%)]: 628 (22) [M+ - CO], 572 (71)
[M+ - 3CO]. Anal. Calcd for C20H26N4O4S2Rh2 (656.38): C, 36.60;
H, 3.99; N, 8.54; S, 9.77. Found: C, 36.78; H, 3.83; N, 8.44; S,
9.85.
1
mL), and vacuum-dried (0.1062 g, 95%). H NMR (C6D6, 400.16
MHz, 25 °C): δ 7.81-7.84 (m, 12 H, o-CHPh, PPh3), 7.12 (d, J )
7.8 Hz, 1 H, H3), 6.97-6.98 (m, 19 H, p-CHPh and m-CHPh of
PPh3, H3), 6.90 (t, J ) 7.5 Hz, 1 H, H4), 6.82 (t, J ) 7.8 Hz, 1 H,
t
Synthesis of [Ir(µ-Me-tBu-ImS)(CO)2]2 (10). Following the
general procedure, [Ir(acac)(CO)2] (0.200 g, 0.575 mmol) and
1-methyl-4-tert-butylimidazole-2-thiol (0.098 g, 0.575 mmol) were
H4), 6.72 (t, J ) 9.3, 8.0 Hz, 2 H, H5), 1.47 (s, 9 H, CH3, Bu),
t
1.35 (s, 9 H, CH3, Bu). 31P{1H} NMR (C6D6, 161.99 MHz, 25
°C): δ 38.9 (d, JP-Rh ) 158.7 Hz). 13C{1H} APT NMR (C6D6,

Rh(I) and Ir(I) Complexes with Hindered Thiolates
Organometallics, Vol. 25, No. 18, 2006 4389
1
2
100.63 MHz, 25 °C): δ 190.2 (ddd, JC-Rh ) 75.3 Hz, JC-P
)
solid precipitated. The mixture was cooled in an iPrOH/CO2 bath,
and additional cold diethyl ether (2 mL) was added. The orange
solid was filtered with a cannula, washed with cold diethyl ether
(3 × 2 mL), and vacuum-dried (0.153 g, 68%). This compound is
4
3
17.1 Hz, JC-P or JC-Rh ) 2.9 Hz, CO), 168.8 (SC), 168.4 (SC),
164.2 (C6), 162.1 (C6), 135.9 (d, JC-P ) 44.6 Hz, Cipso-P), 135.5
(C3), 135.3 (d, JC-P ) 12.4 Hz, o-CHPh, PPh3), 135.1 (C3), 130.1
(p-CHPh, PPh3), 128.5 (d, JC-P ) 10.24 Hz, m-CHPh, PPh3), 127.5
1
not stable in solution and is air sensitive. H NMR (C6D6, 400.16
(C4), 125.0 (C4), 116.4 (C5), 115.6 (C5), 38.2 (C, Bu), 38.0 (C,
MHz, 25 °C): δ 7.93 (br s, CHPh, PPh3), 7.81 (m, CHPh, PPh3),
7.00 (br m, CHPh, PPh3), 5.54 (s, 2 H, H5), 2.66 (s, 6 H, N-CH3),
1.41 (s, 18 H, CH3, tBu). 1H NMR (toluene-d8, 300.12 MHz, -60
°C): δ 8.95 (m, CHPh, PPh3), 8.03 (m, CHPh, PPh3), 7.77 (m, CHPh,
PPh3), 7.42 (m, CHPh, PPh3), 7.15 (br m, CHPh, PPh3), 7.07 (br m,
CHPh, PPh3), 6.98 (br m, CHPh, PPh3), 6.82 (m, CHPh, PPh3), 6.66
(m, CHPh, PPh3), 5.33 (s, 2 H, H5), 2.54 (s, 6 H, N-CH3), 1.43 (br
s, CH3, tBu). 31P{1H} NMR (C6D6, 121.49 MHz, 25 °C): δ 22.25,
17.95 (second isomer). 31P{1H} NMR (toluene-d8, 121.49 MHz,
-60 °C): δ 22.13. IR (cyclohexane, cm-1): 1973 (s). MS [FAB+
t
tBu), 30.8 (CH3, tBu). IR (toluene, cm-1): 1989 (s), 1976 (m). MS
[FAB+ m/z (%)]: 1120 (8) [MH]+, 1091 (11) [M+ - CO], 800
(69) [M+ - PPh3 - 2CO]. Anal. Calcd for C56H54N2O2P2S2Rh2
(1118.92): C, 60.11; H, 4.86; N, 2.50; S, 5.73. Found: C, 60.01;
H, 4.56; N, 2.47; S, 5.61.
Synthesis of [Ir(µ-tBu-PyS)(CO)(PPh3)]2 (6). [Ir(acac)(CO)-
(PPh3)]2 (0.174 g, 0.300 mmol) and 6-tert-butylpyridine-2-thiol
(0.0501 g, 0.300 mmol) were dissolved in dry CH2Cl2 (2 mL) to
obtain a red solution. The reaction mixture was stirred 0.5 h at
room temperature and concentrated to 1 mL. The reaction mixture
m/z (%)]: 1303 (7) [M+], 1042 (20) [M+ - PPh3], 984 (9) [M+
-
i
PPh3 - 2CO]. Anal. Calcd for C54H56N4O2P2S2Ir2 (1303.55): C,
49.75; H, 4.33; N, 4.30; S, 4.92. Found: C, 49.63; H, 4.15; N,
4.40; S, 4.81.
was cooled in an PrOH/CO2 bath, and cold MeOH (3 mL) was
added to obtain a gummy product. The solvent was removed under
vacuum and the residue dissolved in CH2Cl2 (1 mL). Hexane was
added, but no precipitate was observed. The solvent was removed
under vacuum and the residue dissolved in CH2Cl2 (1 mL). Diethyl
ether (3 mL) was added and an orange solid precipitated. Filtration
and washing with cold diethyl ether (2 × 2 mL) followed by drying
under vacuum gave product (0.144 g, 74%). This compound is not
stable in solution and is air sensitive. 1H NMR (C6D6, 400.16 MHz,
25 °C): δ 8.04 (d, J ) 7.5 Hz, 1H, H3), 7.90-7.94 (m, 1H, H3),
7.82-7.85 (m, 12H, o-CHPh, PPh3), 7.19 (d, J ) 7.6 Hz, 1H, H4),
6.96-7.00 (m, 18H, p-CHPh and m-CHPh of PPh3), 6.82 (t, J ) 7.8
Hz, 1H, H4), 6.71 (d, J ) 7.6 Hz, 1H, H5), 6.66 (d, J ) 7.8 Hz,
Synthesis of [Rh(µ-tBu2-ImS)(CO)(PPh3)] (17). Carbon mon-
oxide was bubbled through an orange solution of complex 13 (0.101
g, 0.120 mmol) in CH2Cl2 (10 mL) for 10 min, and the solution
color changed to red. Solid triphenylphosphine (0.063 g, 0.240
mmol) was then added to give a yellow solution with evolution of
carbon monoxide. The reaction mixture was stirred for 1 h at room
temperature. Workup as described in the synthesis of compound 5
gave the complex as a yellow solid (0.106 g, 73%). 1H NMR (C6D6,
400.16 MHz, 25 °C): δ 7.83-7.85 (m, 6 H, o-CHPh, PPh3), 6.98-
7.02 (m, 9 H, p-CHPh and m-CHPh of PPh3), 6.20 (s, 1 H, H5), 1.47
1H, H5), 1.41 (s, 9H, CH3, Bu), 1.26 (s, 9H, CH3, Bu). 31P{1H}
NMR (C6D6, 161.99 MHz, 25 °C): δ 20.5. MS [FAB+ m/z (%)]:
1298 (68) [MH]+, 1038 (30) [M+ - PPh3], 1008 (32) [M+ - PPh3
- CO]. Anal. Calcd for C56H54N2O2P2S2Ir2 (1297.55): C, 51.84;
H, 4.19; N, 2.16; S, 4.94. Found: C, 51.51; H, 4.08; N, 1.99; S,
4.90.
Synthesis of [Rh(µ-Me-tBu-ImS)(CO)(PPh3)]2 (11). [Rh(acac)-
(CO)(PPh3)]2 (0.200 g, 0.406 mmol) and 1-methyl-4-tert-butyl-
imidazole-2-thiol (0.0691 g, 0.406 mmol) were dissolved in dry
CH2Cl2 (4 mL) to obtain a red solution. The reaction mixture was
stirred 1 h at room temperature and concentrated to 1 mL. Cold
MeOH (5 mL) was added and the mixture concentrated until an
(s, 9 H, CH3, N-tBu), 1.25 (s, 9 H, CH3, Bu). 31P{1H} NMR
t
t
t
(toluene-d8, 121.49 MHz, 25 °C): δ 49.83 (br d, JP-Rh ) 156.3
Hz). 31P{1H} NMR (toluene-d8, 121.49 MHz, -60 °C): δ 49.84
(d, JP-Rh ) 162.0 Hz). 13C{1H} APT NMR (C6D6, 100.63 MHz,
25 °C): δ 189.8 (dd, JC-Rh ) 75.3 Hz, JC-P ) 19.7 Hz, CO), 157.9
(SC), 146.1 (C4), 135.2 (d, JC-P ) 49.7 Hz, Cipso-P), 134.9 (d, JC-P
) 11.7 Hz, o-CHPh, PPh3), 130.5 (d, JC-P ) 2.1 Hz, p-CHPh, PPh3),
128.7 (d, JC-P ) 10.2 Hz, m-CHPh, PPh3), 107.2 (C5), 56.4 (C,
t
t
N-tBu), 32.0 (C, Bu), 30.5 (CH3, N-tBu), 29.5 (CH3, Bu). IR
(CH2Cl2, cm-1): 1968 (s). MW: found 605.8 (calcd 604.5). MS
[FAB+ m/z (%)]: 605 (20) [MH]+, 577 (87) [M+ - CO]. Anal.
Calcd for C30H34N2OPSRh (604.54): C, 59.60; H, 5.67; N, 4.63;
S, 5.30. Found: C, 59.72; H, 5.51; N, 4.45; S, 5.23.
i
orange solid precipitated. The mixture was cooled in an PrOH/
CO2 bath, leading to further precipitation. The orange solid was
filtered using a cannula, washed with cold MeOH (2 × 2 mL), and
vacuum-dried (0.179 g, 78%). 1H NMR (toluene-d8, 300.12 MHz,
25 °C): δ 7.90 (br m, CHPh, PPh3), 7.70 (m, CHPh, PPh3), 7.03
(br m, CHPh, PPh3), 5.64 (s, 2 H, H5), 2.73 (s, 6 H, N-CH3), 1.37
(s, 18 H, CH3, tBu). 1H NMR (toluene-d8, 300.12 MHz, -60 °C):
δ 8.94 (br m, CHPh, PPh3), 8.00 (br m, CHPh, PPh3), 7.82 (br m,
CHPh, PPh3), 7.69 (m, CHPh, PPh3), 7.36 (br m, CHPh, PPh3), 7.11
(br m, CHPh, PPh3), 6.94 (br m, CHPh, PPh3), 6.84 (br m, CHPh,
PPh3), 6.67 (br m, CHPh, PPh3), 5.51 (s, 2 H, H5), 2.63 (s, 6 H,
Synthesis of [Ir(µ-tBu2-ImS)(CO)(PPh3)] (18). Carbon mon-
oxide was bubbled through a dark red solution of the complex [Ir-
(µ-tBu2-ImS)(COD)]2 (14) (0.153 g, 0.150 mmol) in CH2Cl2 (8 mL)
for 15 min, and the solution color changed to dark purple. Solid
triphenylphosphine (0.063 g, 0.240 mmol) was then added and the
mixture stirred for 0.5 h at room temperature under slight negative
pressure to give an orange-yellow solution. Workup as described
in the synthesis of compound 5 gave the complex as a yellow solid
1
(0.135 g, 65%). H NMR (C6D6, 400.16 MHz, 25 °C): δ 7.87-
7.92 (m, 6 H, o-CHPh, PPh3), 6.97-7.04 (m, 9 H, p-CHPh and
NCH3), 1.41 (br s, 18 H, CH3, Bu). 31P{1H} NMR (toluene-d8,
m-CHPh of PPh3), 5.98 (s, 1 H, H5), 1.46 (s, 9 H, CH3, N-tBu),
t
t
121.49 MHz, 25 °C): δ 40.6 (d, JP-Rh ) 165.0 Hz, minor isomer),
38.7 (d, JP-Rh ) 161.4 Hz). 31P{1H} NMR (toluene-d8, 121.49 MHz,
-60 °C): δ 49.9 (d, JP-Rh ) 163.7 Hz, minor isomer), 39.2 (d,
JP-Rh ) 160.1 Hz). IR (cyclohexane, cm-1): 1974 (s). MS [FAB+
m/z (%)]: 1125 (10) [M+], 1096 (46) [M+ - CO], 955 (35) [M+
- Me-tBu-ImS]. Anal. Calcd for C54H56N4O2P2S2 (1124.93): C,
57.65; H, 5.02; N, 4.98; S, 5.70. Found: C, 57.33; H, 4.98; N,
4.93; S, 5.30.
Synthesis of [Ir(µ-Me-tBu-ImS)(CO)(PPh3)]2 (12). [Ir(acac)-
(CO)(PPh3)]2 (0.1152 g, 0.198 mmol) and 1-methyl-4-tert-butyl-
imidazole-2-thiol (0.0337 g, 0.198 mmol) were dissolved in dry
CH2Cl2 (2 mL) to obtain a red solution. The reaction mixture was
stirred 0.5 h at room temperature and concentrated to 1 mL. Diethyl
ether (3 mL) was added and the mixture concentrated until orange
1.14 (s, 9 H, CH3, Bu). 31P{1H} NMR (C6D6, 161.99 MHz, 25
°C): δ 19.9. 13C{1H} APT NMR (C6D6, 100.63 MHz, 25 °C): δ
176.6 (CO), 158.1 (SC), 145.6 (C4), 134.9 (d, JC-P ) 10.9 Hz,
o-CHPh, PPh3), 134.4 (presumably the upfield peak of a doublet
for Cipso-P, with the downfield peak obscured by the larger doublet
centered at 134.9), 130.6 (d, JC-P ) 2.1 Hz, p-CHPh, PPh3), 128.6
(d, JC-P ) 10.2 Hz, m-CHPh, PPh3), 107.5 (C5), 56.4 (C, N-tBu),
t
t
32.1 (C, Bu), 30.3 (CH3, N-tBu), 29.5 (CH3, Bu). IR (CH2Cl2,
cm-1): 1953 (s). MW: found 648.1 (calcd 693.8). MS [FAB+ m/z
(%)]: 694 (100) [M+]. Anal. Calcd for C30H34N2OPIrS (693.85):
C, 51.93; H, 4.94; N, 4.04; S, 4.62. Found: C, 51.62; H, 4.99; N,
3.97; S, 4.40.
Crystal Structure Determination of Complexes 2, 5, 7, 13,
and 18. X-ray data were collected for all complexes at low

4390 Organometallics, Vol. 25, No. 18, 2006
Miranda-Soto et al.
temperature [223(2) K for 2, 173(2) K for 5, and 100(2) K for 7,
13, and 18] on a Bruker SMART APEX CCD diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Data
were corrected for absorption using a multiscan method applied
with the SADABS program.52 The structures were solved by direct
methods with SHELXS-86.53 Refinement, by full-matrix least
squares on F2 with SHELXL97,53 was similar for all complexes,
including isotropic and subsequently anisotropic displacement
parameters for all non-hydrogen nondisordered atoms. Particular
details concerning the existence of static disorder and hydrogen
refinement are listed below. All the highest electronic residuals were
observed in close proximity to the metals (or in the disorder region)
and have no chemical sense.
gens, except those of the tBu moiety, were included from observed
positions and refined as isotropic atoms. Details for 7: Two
independent, but chemically analogous, molecules were observed
in the crystal structure. High thermal parameters revealed the
existence of static disorder in three different spatial regions: two
tBu groups and part of a cyclooctadiene molecule [atoms C(12)-
C(15)]; a model based on two moieties was used in each case.
Hydrogens were included in calculated positions for all nondisor-
dered atoms; riding refinement was used. Details for 13:
A
methanol solvent molecule was present in the crystal structure.
Hydrogens were in calculated positions; riding model was used.
Refinement for 18: Hydrogens were included in observed positions;
refinement was performed as free isotropic atoms.
Refinement details for 2: One of the tert-butyl substituents was
observed disordered, and a model with two complementary positions
was included. Hydrogens were included in calculated positions, and
riding refinement was used. Details for 5: One Bu substituent
exhibited high thermal parameters; no clear model of disorder could
be established; eventually dynamic disorder was assumed. Hydro-
Acknowledgment. The financial support of Consejo Na-
cional de Ciencia y Tecnolog´ıa (CONACyT, Mexico) (grant
38829-E), Ministerio de Ciencia y Tecnolog´ıa (MCyT, Spain)
(grant BQU2002-1729), a graduate scholarship (CONACyT) for
V.M.S., and Fundacio´n Carolina (support for V.M.S.) are
acknowledged.
t
(52) SAINT+ Software for CCD difractometers; Bruker AXS: Madison,
WI, 2000. Sheldrick, G. M. SADABS, Program for Correction of Area
Detector Data; University of Go¨ttingen: Go¨ttingen, Germany, 1999.
(53) SHELXTL Package v. 6.10; Bruker AXS: Madison, WI, 2000.
Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go¨ttingen:
Go¨ttingen, Germany, 1997.
Supporting Information Available: CIF files for all crystal
structures. This information is available free of charge via the
Internet at http://pubs.acs.org.
OM060317T