Cyclometalated products of [(COE)2RhCl]2 and 1,3-(RSCH2)2C6H4 (R = tBu, iPr) are dimeric. Synthesis, molecular structures, and solution dynamics of [μ-ClRh(H)(RSCH2)2C6H3 -2,6]2

Article abstract of DOI:10.1021/ic011189y

Two tridentate thioether pincer ligands, 1,3-(RSCH₂)₂C₆H₄ (R = ^tBu, 1a; R = ⁱPr, 1b) underwent cyclometalation using [(COE)₂RhCl]₂ in air/moisture-free benzene at room temperature. The resultant complexes, [μ-CIRh(H)-(RSCH₂)₂C₆H₃ -2,6]₂ (R = ^tBu, 2a; R = ⁱPr, 2b) are dimeric both in the solid state and in solution. A battery of variable-temperature one- and two-dimensional ¹H NMR experiments showed conclusively that both complexes undergo dynamic exchange in solution. Exchange between two dimeric diastereomers of 2a in solution occurred via rotation about the Rh-C_ipso bond. The dynamic exchange of 2b was significantly more complex as an additional exchange mechanism, sulfur inversion, occurred, which resulted in the exchange between several diastereomers in solution.

Full text of DOI:10.1021/ic011189y

Inorg. Chem. 2002, 41, 2633−2641
Cyclometalated Products of [(COE)2RhCl]2 and 1,3-(RSCH ) C H (R )
2 2 6 4
tBu, iPr) Are Dimeric. Synthesis, Molecular Structures, and Solution
Dynamics of [µ-ClRh(H)(RSCH ) C H -2,6]2
2 2 6 3
,†
Daniel R. Evans,* Mingsheng Huang,† W. Michael Seganish,† Esther W. Chege,† Yiu-Fai Lam,†
James C. Fettinger,† and Tracie L. Williams‡
Department of Chemistry and Biochemistry, UniVersity of Maryland,
College Park, Maryland 20742, and Center for Food Safety and Nutrition,
5100 Paint Branch Parkway, College Park, Maryland 20740
Received November 21, 2001
t
i
Two tridentate thioether pincer ligands, 1,3-(RSCH ) C H (R ) Bu, 1a; R ) Pr, 1b) underwent cyclometalation
2 2
6 4
using [(COE)2RhCl]2 in air/moisture-free benzene at room temperature. The resultant complexes, [µ-ClRh(H)-
t
i
(RSCH ) C H -2,6]2 (R ) Bu, 2a; R ) Pr, 2b) are dimeric both in the solid state and in solution. A battery of
2 2
6 3
1
variable-temperature one- and two-dimensional H NMR experiments showed conclusively that both complexes
undergo dynamic exchange in solution. Exchange between two dimeric diastereomers of 2a in solution occurred
via rotation about the Rh−Cipso bond. The dynamic exchange of 2b was significantly more complex as an additional
exchange mechanism, sulfur inversion, occurred, which resulted in the exchange between several diastereomers
in solution.
Introduction
This bonding arrangement is ideal in many respects as it
provides stable chelates and exploits the strong trans effect
of Cipso to provide very active homogeneous catalysts.
Another attractive feature of these systems is that a wide
array of chelating auxiliaries is possible with a multitude of
properties. For example, amino- and phosphino-containing
pincer ligands (L ) NR2, PR2) chelate metals spanning the
entire periodic table.2 Examination of pincer complexes (L
) NR2 (M ) Pt), PR2 (M ) Rh)) provided important clues
as to the nature of cyclometalation.3 A pincer ligand (L )
NR2) presented an opportunity to study the elusive silyl
cation,4 while another system (L ) P(O)R2) afforded a
glimpse into the reactivity of penta- and hexacoordinate
Sn(IV) adducts.5 Other pincer-metal complexes exhibit
extraordinary thermal stability and catalyze alkane dehydro-
genation,6a,b Kharasch,6c and Suzuki reactions,2k while
palladium-pincers,6d-h (L ) PR2, SR) are extremely active
Heck catalysts. Several examples exist in which the introduc-
tion of chiral elements provided pincer-metal complexes
capable of enantioselective catalysis.7 Finally, thioether-based
pincer complexes, when ligated with Pd(II), either function
as unique small molecule receptors8 or serve as templates
for supramolecular assemblies.9 Our own contribution showed
that incorporation of the rarely studied sulfoxide within this
framework provided stable chelates of Pd(II).10
Initial reports that utilized the anionic tridentate “pincer”
ligand (LCL-) appeared some time ago.1 This ligand frame-
work received further attention due to its ability to chelate a
wide array of transition metals. Unlike other spectator ligands
commonly encountered in organometallic chemistry (Cp-,
Tp-, TACN, etc.) that coordinate metals facially, the pincer
ligands coordinate metals meridonally in which the two
pendant ligands are situated trans to each other.
* Corresponding author. Telephone: (301) 405-8436. Fax: (301) 314-
9121. E-mail: de44@umail.umd.edu.
† University of Maryland.
‡ CFSAN/FDA.
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10.1021/ic011189y CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/19/2002
Inorganic Chemistry, Vol. 41, No. 10, 2002 2633

Evans et al.
Scheme 1
To date, the only known examples of thioether-based
pincer ligand complexes involve chelation to the heavier
metals of group 10.8,9,11 Our research program comprises
the examination of new ligand systems as applied to
homogeneous catalysis.10 Considering the utility of R(LCL)M
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H.; Van Koten, G.; Vrieze, K. Acta Crystallogr., Sect. C: Cryst. Struct.
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Grove, D. M.; Jastrzebski, J.; Kooijman, H.; Vandersluis, P.; Smeets,
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R.; Manojlovicmuir, L.; Muir, K. W. J. Organomet. Chem. 1995, 493,
243-249. (f) Sutter, J. P.; James, S. L.; Steenwinkel, P.; Karlen, T.;
Grove, D. M.; Veldman, N.; Smeets, W. J. J.; Spek, A. L.; van Koten,
G. Organometallics 1996, 15, 941-948. (g) Hogerheide, M. P.;
Boersma, J.; Spek, A. L.; van Koten, G. Organometallics 1996, 15,
1505-1507. (h) Bonnardel, P. A.; Parish, R. V.; Pritchard, R. G. J.
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E.; Kraatz, H.-B.; Hassner, L.; Ben-David, Y.; Milstein, D. Organo-
metallics 1999, 18, 3873-3884. (j) Brandts, J. A. M.; Kruiswijk, E.;
Boersma, J.; Spek, A. L.; van Koten, G. J. Organomet. Chem. 1999,
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P.; Williamson, A.; Incarvito, C. D.; Rheingold, A. L. Organometallics
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systems examined thus far, and the importance of group 9
metals as catalytically active metals, our desire is to explore
the chemistry of R(SCHS) in conjunction with Rh and Ir.
Herein, we wish to report the first example of R(SCS)
ligation to Rh(III).
Results and Discussion
Synthesis of Ligands and Complexes. Several reports
adequately describe the synthesis of the requisite starting
material, 1,3-(RSCH2)2C6H4, R(SCHS) (1a, R ) tBu; 1b, R
i
) Pr);8,9,11 however, the availability of reagents prompted
an alternative formulation. Preparation of 1 proceeded in one
step upon reaction of a stoichiometric amount of RSNa with
1,3-(ClCH2)2C6H4 in DMF at 100 °C (eq 1). The procedure
(3) (a) Terheijden, J.; Van Koten, G.; Vinke, I. C.; Spek, A. L. J. Am.
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Shimon, L. J. W.; Ben-David, Y.; Martin, J. M. L.; Milstein, D. J.
Am. Chem. Soc. 1998, 120, 12539-12544. (d) Gossage, R. A.; Ryabov,
A. D.; Spek, A. L.; Stufkens, D. J.; van Beek, J. A. M.; van Eldik, R.;
van Koten, G. J. Am. Chem. Soc. 1999, 121, 2488-2497. (e)
Gandelman, M.; Vigalok, A.; Konstantinovski, L.; Milstein, D. J. Am.
Chem. Soc. 2000, 122, 9848-9849. (f) Albrecht, M.; Spek, A. L.;
van Koten, G. J. Am. Chem. Soc. 2001, 123, 7233-7246. (g) Albrecht,
M.; Spek, A. L.; van Koten, G. J. Am. Chem. Soc. 2001, 123, 7233-
7246.
resulted in the isolation of 1a as fine off-white needles and
1b as a colorless liquid in isolated yields of 82% and 87%,
respectively. H NMR and HR-FAB-MS yielded data that
1
were consistent with the formulated species.
Two general procedures exist for the preparation of Rh-
pincer complexes; both depend on the presence of Rh(I),
Scheme 1. The first method generates Rh(I) in situ in
refluxing isopropyl alcohol/water solution starting with
RhCl3‚3H2O with subsequent addition of an excess of
R(LCHL).1a All attempts to utilize this method for the
metalation of 1 repeatedly failed. Indeed, addition of ligand
to the reaction solution always resulted in the formation of
an orange-yellow solid that was insoluble in most organic
solvents. The solid dissolved upon heating in d6-DMSO, but
(4) Chauhan, M.; Chuit, C.; Corriu, R. J. P.; Mehdi, A.; Reye, C.
Organometallics 1996, 15, 4326-4333.
(5) Mehring, M.; Schurmann, M.; Jurkschat, K. Organometallics 1998,
17, 1227-1236.
(6) (a) Liu, F.; Pak, E. B.; Singh, B.; Jensen, C. M.; Goldman, A. S. J.
Am. Chem. Soc. 1999, 121, 4086-4087. (b) Jensen, C. M. Chem.
Commun. 1999, 2443-2449, and references therein. (c) Gossage, R.
A.; Van De Kuil, L. A.; Van Koten, G. Acc. Chem. Res. 1998, 31,
423-431. (d) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D.
J. Am. Chem. Soc. 1997, 119, 11687-11688. (e) Morales-Morales,
D.; Redon, R.; Yung, C.; Jensen, C. M. Chem. Commun. 2000, 1619-
1620. (f) Morales-Morales, D.; Grause, C.; Kasaoka, K.; Redon, R.;
Cramer, R. E.; Jensen, C. M. Inorg. Chim. Acta 2000, 300-302, 958-
963. (g) Bergbreiter, D. E.; Osburn, P. L.; Liu, Y.-S. J. Am. Chem.
Soc. 1999, 121, 9531-9538. (h) Gruber, A. S.; Zim, D.; Ebeling, G.;
Monteiro, A. L.; Dupont, J. Org. Lett. 2000, 2, 1287-1290.
(7) (a) Gorla, F.; Venanzi, L. M.; Albinati, A. Organometallics 1994, 13,
43-54. (b) Stark, M. A.; Richards, C. J. Tetrahedron Lett. 1997, 38,
5881-5884. (c) Longmire, J. M.; Zhang, X. M.; Shang, M. Y.
Organometallics 1998, 17, 7, 4374-4379. (d) Stark, M. A.; Jones,
G.; Richards, C. J. Organometallics 2000, 19, 1282-1291. (e)
Albrecht, M.; Kocks, B. M.; Spek, A. L.; van Koten, G. J. Organomet.
Chem. 2001, 624, 271-286.
1
inspection of the H NMR spectrum revealed 1 as the only
species in solution. Previous work noted that oligomeric
adducts, or “large ring systems”, of arene-free pincer ligands
form under these conditions rather than the desired cyclo-
metalated species.12 Therefore, under these reaction condi-
tions, the process of oligomerization is apparently favored
rather than cyclometalation.
(8) (a) Kickham, J. E.; Loeb, S. J. Inorg. Chem. 1994, 33, 4351-4359.
(b) Kickham, J. E.; Loeb, S. J. Inorg. Chem. 1995, 34, 5656-5665.
(c) Cameron, B. R.; Loeb, S. J.; Yap, G. P. A. Inorg. Chem. 1997,
36, 5498-5504. (d) Kickham, J. E.; Loeb, S. J.; Murphy, S. L. Chem.
Eur. J. 1997, 3, 1203-1213.
(11) (a) Errington, J.; McDonald, W. S.; Shaw, B. L. J. Chem. Soc., Dalton
Trans. 1980, 2312-2314. (b) Dupont, J.; Beydoun, N.; Pfeffer, M. J.
Chem. Soc., Dalton Trans. 1989, 1715-1720. (c) Lucena, N.; Casabo,
J.; Escriche, L.; Sanchez-Castello, G.; Teixidor, F.; Kivekas, R.;
Sillanpaa, R. Polyhedron 1996, 15, 3009-3018. (d) Loeb, S. J.;
Shimizu, G. K. H.; Wisner, J. A. Organometallics 1998, 17, 2324-
2327. (e) van Manen, H. J.; Nakashima, K.; Shinkai, S.; Kooijman,
H.; Spek, A. L.; van Veggel, F.; Reinhoudt, D. N. Eur. J. Inorg. Chem.
2000, 2533-2540.
(12) (a) Crocker, C.; Empsall, H. D.; Errington, R. J.; Hyde, E. M.;
McDonald, W. S.; Markham, R.; Norton, M. C.; Shaw, B. L.; Weeks,
B. J. Chem. Soc., Dalton Trans. 1982, 1217-1224. (b) Briggs, J. R.;
Constable, A. G.; McDonald, W. S.; Shaw, B. L. J. Chem. Soc., Dalton
Trans. 1982, 1225-1230.
(9) (a) Loeb, S. J.; Shimizu, G. K. H. Chem. Commun. 1993, 1395-
1397. (b) Huck, W. T. S.; van Veggel, F. C. J. M.; Kropman, B. L.;
Blank, D. H. A.; Keim, E. G.; Smithers, M. M. A.; Reinhoudt, D. N.
J. Am. Chem. Soc. 1995, 117, 8293-8294. (c) Huck, W. T. S.;
Snellink-Ruel, B.; van Veggel, F.; Reinhoudt, D. N. Organometallics
1997, 16, 4287-4291. (d) Huck, W. T. S.; Prins, L. J.; Fokkens, R.
H.; Nibbering, N. M. M.; van Veggel, F.; Reinhoudt, D. N. J. Am.
Chem. Soc. 1998, 120, 6240-6246.
(10) Evans, D. R.; Huang, M.; Seganish, W. M.; Fettinger, J. C.; Williams,
T. L. Organometallics, 2002, 21, 893-900.
2634 Inorganic Chemistry, Vol. 41, No. 10, 2002

Synthesis of [µ-ClRh(H)RSCH2)2C6H3-2,6]2
A recently developed method for the metalation of
R(PCHP) using [(L)2RhCl]2 (L ) COE, ethylene) seemed
like an attractive alternative as it occurs under much milder
conditions.13 The reaction of 1 with [(COE)2RhCl]2 in
benzene at room temperature for a period of 18 h, Scheme
1, provided the desired cyclometalation products, which
resulted in isolated yields of 95% and 83% for 2a and 2b,
respectively. Infrared analysis of both complexes confirmed
the presence of the hydride ligand, as strong Rh-H stretches
1
were present at 2108 (2a) and 2120 cm-1 (2b). H NMR
analysis of 2a in C6D6 solution showed two hydride
resonances, approximately 20 ppm upfield of TMS (average
1JRhH ) 24 Hz) in a ratio of 2.2 to 1. The hydride region of
2b was significantly more complex as at least 11 resonances
appeared in the -19 to -22 ppm region. Two resonances
observed at -19.93 (1JRhH ) 25.6 Hz) and -20.16 (1JRhH
)
Figure 1. ORTEP representation of 2a. Thermal ellipsoids are drawn at
the 50% probability level. Benzene solvate and C-H hydrogens have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): Rh(1)-
C(1), 1.992(3), Rh(1)-S(1), 2.2981(8); Rh(1)-S(2), 2.3087(8); Rh(1)-
Cl(1), 2.5045(8); Rh(1)-Cl(1A), 2.5821(8); Rh(1)-H(1), 1.50(3); C(1)-
Rh(1)-S(1), 84.42(9); C(1)-Rh(1)-S(2), 86.00(9); C(1)-Rh(1)-H(1),
87.1(12).
27.6 Hz) corresponded to 23% and 45% of the total
1
integrated intensity of the hydride region. H NMR spectra
recorded at 88 °C showed a broad coalesced hydride
resonance, and suggested that the multiple resonances
observed at room temperature exchanged at a rate that was
slow relative to the NMR time scale of 400.132 MHz.
Crystals suitable for X-ray diffraction showed that 2 was
dimeric in the solid state; see below. The immediate question
to answer was whether 2 was dimeric in solution. This is
1
important as the dynamic exchange observed by H NMR
could be a result of a monomer-dimer equilibrium. Evidence
to support the formulation of 2 as a dimer in solution came
from electrospray mass spectroscopy, ESI-MS. Experiments
performed under a variety of conditions failed to reveal the
presence of any monomer in solution. Indeed, the predomi-
nant ion present in CH2Cl2 solution for 2 was [2-Cl]+.
ExclusiVe obserVation of the dimeric species proVides
unambiguous eVidence that these complexes are dimeric in
solution.
This is an extraordinary outcome, as previous reports that
used phosphine-based pincer ligands, 1,3-(R2PCH2)-2-R′-
C6H3 (R ) tBu, R′ ) H, Me),1c,13 showed conclusively that
the metalated adducts (R(PCP)Rh(R′)Cl) were monomeric.
In these examples, the rhodium resides within a square
pyramidal coordination environment in which Cipso is trans
to Cl, and R′ occupies the apical site. In the case where R′
Figure 2. ORTEP representation of 2b. Thermal ellipsoids are drawn at
the 50% probability level. Benzene solvate and C-H hydrogens have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): Rh(1)-
C(1), 1.979(3); Rh(1)-S(1), 2.3286(8); Rh(1)-S(2), 2.2975(7); Rh(1)-
Cl(1), 2.5838(7); Rh(1)-Cl(1A), 2.5089(7); Rh(1)-H(1), 1.44(4); C(1)-
Rh(1)-S(1), 84.58(8); C(1)-Rh(1)-S(2), 83.54(8); C(1)-Rh(1)-H(1),
85.4(14).
1
) H, JRhH was a diagnostic reporter of the coordination
respectively, while Tables 1 and 2 provide selected metrical
parameters and crystallographic data for both complexes.
(During the course of manuscript revision, an additional
structure of 2a was determined (see Supporting Information).)
The average bond distances reported herein reflect the
averages of the values listed in Tables 1 and S8). The
centrosymmetric dimers crystallized in either the triclinic (2a)
or monoclinic (2b) crystal systems with the monomeric
species being crystallographically unique. The center of
symmetry for both molecules lies at the centroid of the
Rh(1)-Cl(1)-Rh(1A)-Cl(1A) four-membered ring. Either
benzene or methylene chloride solvates exist in both
structures, depending on the solvent of crystallization.
geometry as large coupling to rhodium was observed (ca.
50 Hz).1a,c Further evidence to demonstrate that 2 is dimeric
in solution occurred upon inspection of the observed Rh-H
coupling constants. Indeed, the coupling observed in these
two complexes (2a and 2b) was reduced by a factor of 2,
when compared to R(PCP)Rh(H)Cl, and is similar to that
observed for H2RhL2(µ-Cl)2RhL2 (L ) PPh3).14 Thus, unlike
the related chemistry with PCP ligands, the SCS ligands
result in dimeric complexes. Further corroboration of this
fundamental difference resulted upon the determination of
the dimeric molecular structures of both 2a and 2b.
Molecular Structures. ORTEP representations (50%
probability) of 2a and 2b appear in Figures 1 and 2,
(13) Rybtchinski, B.; Vigalok, A.; Ben-David, Y.; Milstein, D. J. Am. Chem.
Soc. 1996, 118, 12406-12415.
(14) Duckett, S. B.; Newell, C. L.; Eisenberg, R. J. Am. Chem. Soc. 1994,
116, 10548-10556.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2635

Evans et al.
Two structures, tBu(PCP)Rh(H)Cl1c and tBu (PCP)Rh(CH3)-
Cl,13 possess square pyramidal coordination geometries, and
three structures trans-Cy(PCP)RhCl2(L) (L ) H2O, MeOH,
EtOH) are octahedral.2e The average Rh-Cipso observed here,
1.985(7) Å, is slightly shorter than either of the two
R(PCP)Rh complexes (average 2.007(11) Å), but is within
the average observed for the octahedral complexes (1.999(13)
Å). The observed Rh-Cleq (chloride trans to Cipso) distance
is 2.508(3) Å and is significantly longer than the average
Table 1. Selected Bond Distances and Bond, Torsional (ω), and
Interplanar (Ω) Angles for 2a and 2b
2a
2b
Bond Distances, Å
1.992(3)
Rh(1)-C(1)
Rh(1)-S(1)
Rh(1)-S(2)
Rh(1)-Cl(1)
Rh(1)-Cl(1A)
Rh(1)-H(1)
1.979(3)
2.3286(8)
2.2975(7)
2.5838(7)
2.5089(7)
1.44(4)
2.2981(8)
2.3087(8)
2.5045(8)
2.5821(8)
1.50(3)
Bond Angles, deg
84.42(9)
t
Rh-Cl distance of 2.448(33) Å for the two Bu(PCP)Rh-
C(1)-Rh(1)-S(1)
C(1)-Rh(1)-S(2)
S(1)-Rh(1)-S(2)
C(1)-Rh(1)-H(1)
S(1)-Rh(1)-H(1)
S(2)-Rh(1)-H(1)
Cl(1)-Rh(1)-H(1)
Cl(1A)-Rh(1)-H(1)
Rh(1)-Cl(1)-Rh(1A)
84.58(8)
83.54(8)
167.74(3)
85.4(14)
91.4(14)
84.6(14)
178.6(14)
95.0(14)
94.32(2)
(R′)Cl structures. This comes as no surprise considering that
the chlorides for 2 bridge the two rhodium centers. The
average rhodium-hydride distance of 1.45(5) Å is in
agreement with the average Rh-H distance (1.5(1) Å)
observed from other crystallographically determined rhodium-
hydride complexes.15 Finally, the average Rh-S distance
observed for 2a and 2b, 2.308(15) Å, is slightly shorter than
other Rh(III) complexes containing trans-ligated thioethers
(2.346(19) Å, N ) 13).16 This reduced distance is a
consequence of the confined pendant ligands within the
pincer framework.
86.00(9)
170.41(3)
87.1(12)
91.2(12)
88.7(12)
96.7(12)
176.6(12)
94.73(3)
Torsional Angles, ω,a deg
b
c
H(1)-Rh-S-Ceq
H(1)-Rh-S-Cax
39.7
-42.0
-10.1
-1.8
Interplanar Angle, Ω,d deg
13.7
16.1
a For a torsion angle defined by i-j-k-l, sign conventions are (+) if a
clockwise and (-) if a counterclockwise rotation of the i-j bond vector is
required to bring it inline with the k-l vector as one views along the j-k
vector. Ceq ) C(9) (2a) and C(12) (2b). Cax ) C(13) (2a) and C(9) (2b).
d Angle between the least-squares planes of the arene and the coordination
plane.
The alkyl groups of both 2a and 2b occupy either axial
(ax) or equatorial (eq) positions. An adequate measure of
the positioning of the alkyl groups is the torsional angle (ω,
H-Rh-S-C) between the hydride and the tertiary carbon
(2a) or the secondary carbon (2b) of the alkyl substituent.
The torsional angles for the equatorial substituents are
approximately 40° (depending upon the view), but those of
the axial substituents are quite different. The measured values
of ω for the axial substituents of 2a and 2b are -1.8° and
-10.1°, respectively. Since there was no detectable disorder
present in the alkyl substituents, this difference must be
attributable to conformational differences between the two
five-membered rings. The conformation of the bicyclic
system and the thioether substituents deserves mentioning.
Common to all pincer complexes, there exists a twist about
the Cipso-M bond such that one-third of the arene resides
above the coordination plane and the other third lies below
(Figure 1). Estimation of the extent of puckering is possible
b
c
Table 2. Crystal Data and Structure Refinement Parameters for 2a and
2b
2a
2b
empirical formula
formula weight
crystal system
space group
a, Å
C22H32S2ClRh
498.96
triclinic
C17H25S2ClRh
431.85
monoclinic
P2(1)/c
13.7742(5)
14.5168(5)
9.3963(3)
90
101.5540(10)
90
1840.79(11)
4
1.558
1.291
884
0.407 × 0.204 × 0.046
2.06-27.53
28 251
4227 [R(int) ) 0.0425]
99.7
empirical
F2
1.138
R1 ) 0.0306
wR2 ) 0.0694
P-1
9.7415(4)
10.7597(4)
11.4033(4)
104.7330(10)
92.8090(10)
93.9840(10)
1150.40(8)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
Dcalcd, Mg/m3
abs coeff, mm-1
F(000)
1.440
1.044
516
(15) (a) Crocker, C.; Errington, R. J.; McDonald, W. S.; Odell, K. J.; Shaw,
B. L.; Goodfellow, R. J. J. Chem. Soc., Chem. Commun. 1979, 498-
499. (b) Kovalev, I. P.; Erdakov, K. V.; Vinogradov, M. G.; Yanovskii,
A. I.; Struchkov, Y. T. Metalloorg. Khim. 1989, 2, 673-676. (c)
Rappert, T.; Nurnberg, O.; Mahr, N.; Wolf, J.; Werner, H. Organo-
metallics 1992, 11, 4156-4164. (d) Wang, K.; Emge, T. J.; Goldman,
A. S.; Li, C. B.; Nolan, S. P. Organometallics 1995, 14, 4929-4936.
(e) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Gozin, M.;
Milstein, D. J. Am. Chem. Soc. 1998, 120, 13415-13421. (f) Hahn,
C.; Spiegler, M.; Herdtweck, E.; Taube, R. Eur. J. Inorg. Chem. 1998,
1425-1432.
(16) (a) McCrindle, R.; Ferguson, G.; McAlees, A. J.; Parvez, M.; Ruhl,
B. L.; Stephenson, D. K.; Wieckowski, T. J. Chem. Soc., Dalton Trans.
1986, 2351-2359. (b) Ferguson, G.; Matthes, K. E.; Parker, D. Angew.
Chem., Int. Ed. Engl. 1987, 26, 1162-1163. (c) Clark, P. D.; Machin,
J. H.; Richardson, J. F.; Dowling, N. I.; Hyne, J. B. Inorg. Chem.
1988, 27, 3526-3529. (d) Helps, I. M.; Matthes, K. E.; Parker, D.;
Ferguson, G. J. Chem. Soc., Dalton Trans. 1989, 915-920. (e) Blake,
A. J.; Reid, G.; Schroder, M. J. Chem. Soc., Dalton Trans. 1989,
1675-1680. (f) Cooper, S. R.; Rawle, S. C.; Yagbasan, R.; Watkin,
D. J. J. Am. Chem. Soc. 1991, 113, 1600-1604. (g) Parvez, M.; Fait,
J. F.; Clark, P. D.; Jones, C. G. Acta Crystallogr., Sect. C: Cryst.
Struct. Commun. 1993, 49, 383-385. (h) Gaswami, N.; Alberto, R.;
Barnes, C. L.; S., J. Inorg. Chem. 1996, 35, 7546-7555. (i) Blake,
A. J.; Li, W. S.; Lippolis, V.; Schroder, M. Acta Crystallogr., Sect.
C: Cryst. Struct. Commun. 1998, 54, 1410-1413.
cryst size, mm3
theta range, deg
reflns collect.
ind reflns
0.200 × 0.073 × 0.055
1.85-27.5
18 095
5279 [R(int) ) 0.0626]
99.5
empirical
F2
1.002
R1 ) 0.0376
wR2 ) 0.0751
completeness, %
abs correct.
refine. method
GOF on F2
final R indices
[I > 2σ(I)]
Both rhodium atoms possess octahedral geometries in
which the coordination sphere is composed of the mer-
R(SCS) ligand, an axially coordinated hydride, and two
bridging chloride ligands. These are the only reported
crystallographic structures of (SCS)Rh-pincer complexes to
date; thus, direct comparison of bond distances and bond
angles to previously reported structures is not possible.
Fortunately, several structures of R(PCP)Rh are presently
available for comparison with the structures obtained herein.
2636 Inorganic Chemistry, Vol. 41, No. 10, 2002

Synthesis of [µ-ClRh(H)RSCH2)2C6H3-2,6]2
them prevented a complete determination of the exchange
system. Thus, these experiments substantiate the existence
of chemical exchange in solution. The question left remaining
is the nature of the exchange process.
Metalated pincer complexes are known to undergo ex-
change in solution upon rotation about the M-Cipso
bond;11b,18a-c another exchange process possible for these
particular systems is atomic inversion.11b,18d,f Since the dimer
does not dissociate in solution, the only other conceivable
exchange process would be due to pendant thioether dis-
sociation. This is highly unlikely considering the nature of
the chelate. Furthermore, experimental evidence, found in
the guise of 13C NMR, suggested that this does not occur as
both 2a and 2b show two-bond Rh-C coupling to the
benzylic and S-tethered carbons within the ligand framework.
Thus, the problem at hand is to determine which process is
operative for 2, i.e., either Rh-Cipso rotation or sulfur
inversion.
Figure 3. Two-dimensional 1H-1H EXSY (500 MHz, -14 °C, CD2Cl2)
spectrum of the hydride resonances of diastereomers A and B of 2a recorded
using a mixing time of 275 ms.
Many reports exist that describe the dynamic exchange
that occurs in these pincer-metal complexes11b,18a-d as well
as the fluxional behavior attributable to sulfur inversion.11b,18,19
In the complex Me(SCS)PdCl,11b the authors concluded from
by calculating the interplanar angle (Ω) that exists between
the least-squares planes of the arene ring, Parene, and that of
the coordination plane, Pcoord. The values of Ω calculated
for 2a and 2b are 13.7° and 16.1°, respectively. Thus, the
complex with the smaller substituent (iPr vs tBu) shows the
largest degree of bicyclic distortion. This may seem to
contradict initial expectations as a number of R(SCS)PdCl
complexes do indeed show that an increase in the steric bulk
of the S substituent results in an increase in Ω.10,11a,c
However, unlike the R(SCS)PdCl systems, the Rh complexes
are dimeric, and as such, the substituent interacts not only
with the cyclic ring system, but also with other elements
present within the dimer. This is important as the interactions
that exist between monomeric pairs control the type of
exchange that occurs in solution.
t
the X-ray structure of Bu(SCS)PdCl11a that the hydrogens
R to the point of chelation should be diastereotopic. Indeed,
at room temperature, Me(SCS)PdCl displays a single reso-
nance for the benzylic hydrogens, but upon cooling to -40
°C two sets of AB quartets were observed for the benzylic
hydrogens, which was attributed to the existence of two
diastereomers in solution. The authors reasoned that, in this
particular system, the source of exchange was due to either
sulfur inversion or rotation about the Pd-Cipso bond, but they
were unable to unambiguously determine which pathway was
operative. In the case of R(NCN)NiBr, the source of
exchange was due solely to M-Cipso bond rotation and was
strongly dependent upon the nature of R. For example, in
Me(NCN)NiBr,18a the benzylic hydrogens appeared as sin-
glets even at -83 °C, but when the two opposing nitrogen
substituents were tethered to one another via a poly-
(methylene) chain, the rate of rotation slowed enough to be
a measurable phenomenon.18b In addition, the introduction
of sterically bulky ligands served to increase the barrier to
rotation, thereby permitting measurement of this process.18c
The presence of two AB quartets of unequal intensity, for
the benzylic hydrogens in the 1H NMR spectrum (C6D6) of
Dynamic Exchange in Solution. Observation of multiple
1
resonances at room temperature in the H NMR spectrum
that coalesce at higher temperatures suggested that some type
of dynamic exchange was operating in solution. Further
evidence to support this notion came upon acquisition of two-
1
dimensional (2D) H-1H EXSY spectra for 2 in CD2Cl2.
1
Figure 3 shows the 2D phase-sensitive H EXSY spectrum
of 2a in CD2Cl2 at -14 °C.17 The off-diagonal peaks are of
the same phase as the diagonal peaks, indicating that the
observed correlation is attributable to chemical exchange and
not an NOE (NOE ≡ nuclear Overhauser effect). Careful
optimization of the mixing time allowed accurate integration
of the relative intensities of the two signals and yielded
observed rates of exchange of 0.6 s-1 at -14 °C and 12.6
s-1 at 24 °C. A similar experiment performed on a sample
of 2b at -30 °C showed that there is a minimum of two
exchange networks between different diastereomers in solu-
tion, all of which exchange at higher temperatures. Unfor-
tunately, the number of peaks and lack of resolution between
(18) M-C rotation. (a) Grove, D. M.; van Koten, G.; Ubbels, H. J. C.;
Zoet, R. Organometallics 1984, 3, 1003-1009 and references therein.
(b) Terheijden, J.; van Koten, G.; van Beek, J. A. M.; Vriesema, B.
K.; Kellogg, R. M.; Zoutberg, M. C.; Stam, C. H. Organometallics
1987, 6, 89-93. (c) van Beek, J. A. M.; van Koten, G.; Dekker: G.
P. C. M.; Wissing, E.; Zoutberg, M. C.; Stam, C. H. J. Organomet.
Chem. 1990, 394, 659-678. (d) van Beek, J. A. M.; van Koten, G.;
Ramp, M. J.; Coenjaarts, N. C.; Grove, D. M.; Goubitz, K.; Zoutberg,
M. C.; Stam, C. H.; Smeets, W. J. J.; Spek, A. L. Inorg. Chem. 1991,
30, 3059-3068. Sulfur inversion. (e) Orrell, K. G. Coord. Chem. ReV.
1989, 96, 1-48. (f) Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog.
Inorg. Chem. 1984, 32, 1-118.
(19) (a) Abel, E. W.; Moss, I.; Orrell, K. G.; Sik, V. J. Organomet. Chem.
1987, 326, 187-200. (b) Abel, E. W.; Budgen, D. E.; Moss, I.; Orrell,
K. G.; Sik, V. J. Organomet. Chem. 1989, 362, 105-115. (c) Ascenso,
J. R.; Carvalho, M. D.; Dias, A. R.; Romao, C. C.; Calhorda, M. J.;
Veiros, L. F. J. Organomet. Chem. 1994, 470, 147-152.
(17) (a) Perrin, C. L.; Gipe, R. K. J. Am. Chem. Soc. 1984, 106, 4036-
4038. (b) Perrin, C. L.; Dwyer, T. J. Chem. ReV. 1990, 90, 935-967.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2637

Evans et al.
Scheme 2
2a, showed that two diastereomers existed in solution and
the rate of exchange was slow relative to the NMR time scale.
Scheme 2 represents the two possible equilibria, rotation
about the Rh-Cipso bond and sulfur inversion, that are
possible for these complexes. The starting point is the
Newman projection (A) of the observed solid-state structure
for 2a (cf. Figure 1). A clockwise rotation about the Rh(1)-
C(1) bond (monomer on top) would result in the formation
of a complex B that is a diastereomer of A. This dimer is C2
symmetric where the 2-fold axis is perpendicular to and
passes through the centroid of the Cl-Rh-Cl′-Rh′ four-
membered ring. The alkyl groups remain syn relative to each
other, but simply change orientations relative to the two
meridonal ligands. The inherent symmetry of both A and B
suggests that both hydrides are magnetically equivalent, and
thus this exchange process would yield only two signals.
Assuming that sulfur inversion occurs without a concomitant
change in the conformation of the ring system,11b then
inversion at S1 would result in a species, C, which is C1
symmetric. This process situates one alkyl group anti, relative
to the hydride, and produces a complex that exhibits two
anisochronous hydrides. Since the data do not support the
presence of species C, the only observable exchange process
in 2a must be due to rotation about the Rh-Cipso bond.
In the event that both of the processes occur in tandem,
then a scheme that includes both sulfur inversion and Rh-
Figure 4. 1H NMR spectrum (hydride region) of 2b in d8-toluene at 21
°C.
Scheme 3
depicting the dimers as Newman projections, a matrix is
sufficient to describe the inherent stereochemical properties
of each species. The positions of the alkyl groups are denoted
as either axial (ax) or equatorial (eq), relative to the
metallocycle, and either syn or anti, relative to the hydride.
The starting point for the scheme is the centrosymmetric
diastereomer A′ (cf. Figure 2 and Scheme 2) in which the
iPr groups are either ax or eq, and syn relative to the hydride.
Rotation about the Rh-Cipso bond (A′fB′) simply changes
the relative orientations of the alkyl substituents and accounts
for the presence of the two predominant signals (2 and 5)
shown in Figure 4. Sulfur inversion at S(1) (A′fC′) and
S(2) (A′fD′) results in the placement of one iPr group anti
relative to the hydride. These two complexes are diastereo-
meric, and both would provide two anisochronous hydride
signals in the 1H NMR spectrum. (The scheme is simplified
by recognition of the fact that inversion of sulfur at either
S(1) or S(1A), and either S(2) or S(2A) yields species that
are enantiomeric.) Conversely, starting from the C2-sym-
metric diastereomer, B′, sulfur inversion at either S(1) or
S(2) would result in two diastereomeric complexes, E′ and
F′. This scheme suggests that at least 10 hydride resonances
are possible (one signal each for A′ and B′, two signals each
for C′, D′, E′, and F′). Obviously, a more complex scheme
could easily account for additional resonances as rotation
about the Rh-Cipso bond could occur for C′, B′, E′, and F′.
Schematic accuracy aside, rationalization of the additional
hydride resonances observed for 2b must include both
dynamic processes.
Cipso rotation would easily account for the additional hydride
resonances observed in 2b. Evidence to support that the
sulfur-inversion pathway is operative in 2b appears in Figure
1
4, which corresponds to the H NMR spectrum (hydride
region) of 2b in d8-toluene at 21 °C. The figure identifies
11 unique hydride signals, but careful examination shows
several others whose presence is either partially obscured
by larger signals or difficult to discriminate from noise. The
two predominant peaks (2 and 5) presumably represent the
two diastereomers that interconvert via Rh-Cipso bond
rotation, as their relative intensities are nearly identical with
that observed for 2a in d8-toluene (see below). As mentioned
above, increasing the temperature of the sample to 88 °C
results in the coalescence of all hydride signals (see Sup-
porting Information), and suggests that all of the minor
hydride signals represent unique diastereomeric species that
readily interconvert on the NMR time scale (400.132 MHz).
The discussion involving Scheme 2 suggested that at least
four hydride signals would be possible for the three species
present in solution (one each for A and B and two for C). A
scheme that accounts for all of the possible diastereomers
for 2b in solution would be prohibitively expansive, and so
an abbreviated version appears in Scheme 3. Rather than
Suppression of the atomic inversion pathway in 2a must
t
be a consequence of the increase in steric bulk of the Bu
substituent. Scheme 4 depicts the Newman projections of
the undetected intermediates that would occur in 2 for either
Rh-Cipso rotation (I) or sulfur inversion (II). Rotation around
the metal-carbon bond situates both alkyl groups in pseudo-
equatorial positions (peq) while the sulfur atoms retain
2638 Inorganic Chemistry, Vol. 41, No. 10, 2002

Synthesis of [µ-ClRh(H)RSCH2)2C6H3-2,6]2
Scheme 4
tetrahedral geometry. A two-point estimation of the activation
parameters, as provided by the determined rate constants via
EXSY experiments, for the process (A f I f B; Schemes
2 and 4) observed for 2a yielded ∆Hq and ∆Sq values of 12
kcal mol-1 and -13 cal mol-1 K-1, respectively. These
values provide some insight into the nature of this process,
which is an inherent characteristic of all pincer-metal
chelates. The enthalpic penalty of about 12 kcal mol-1 is in
agreement with expectations when one considers that rotation
about the Rh-Cipso bond results in a reduction of Ω, and
would naturally lead to a lengthening of this bond length.
The observed value of -13 eu for ∆Sq is presumably a
baseline measure of the eclipsing interactions that exist
Figure 5. Hydride region of [tBu(SCS)Rh(H)Cl]2 at 24 °C in (a) CD2Cl2,
(b) d4-1,2-dichlorobenzene, (c) d8-toluene, and (d) d6-benzene.
t
for the A-B equilibrium: ∆H ) -1.0 ( 0.1 kcal mol-1
and ∆S ) -3.3 ( 0.6 cal mol-1 K-1. The preference of B
with respect to A at lower temperatures in CD2Cl2 is a
consequence of the reduced contribution of the T∆S term,
and is perhaps suggestive of the ability of the solvent to
stabilize the dipole moment of the former in solution.
between the Bu substituents and the benzylic hydrogens.
The intermediate formed upon inversion at S(1), II, is very
similar to I with the exception that the sulfur becomes
trigonal planar and the alkyl group resides within the
coordination plane. Considering that the distance between
the two opposing sulfurs is only ca. 4.1 Å, it becomes
apparent why this process does not occur in 2a as there must
Conclusions
t
be prohibitive steric interactions that exist between the Bu
and either the equatorially coordinated chloride or the
opposing sulfur lone pair or both. Apparently, the iPr group
is capable of overcoming these geometrical restrictions by
accessing a rotamer that directs the methyl groups away from
the sterically congested environment.
Pincer complexes containing pendant thioether linkages
form stable adducts with Rh(III). Unlike the phosphine-
pincer complexes, the R(SCS) complexes are dimeric both
1
in the solid state and in solution. The H NMR spectra are
somewhat complex due to the dynamic exchange, but
variable-temperature one-dimensional and EXCSY 1H NMR
experiments established that dynamic exchange was operative
for both 2a and 2b. Literature precedent indicated that the
source of this exchange was either due to rotation about the
Rh-Cipso bond or brought about by inversion at sulfur. The
steric bulk of the tert-butyl substituents of 2a prohibited
sulfur inversion, which provided a single source of exchange,
Rh-Cipso rotation. The isopropyl substituents present in 2b
apparently are small enough to allow for the existence of
both dynamic processes. The presence of these dynamic
exchange processes provides a rationale for the absence of
literature reports describing the chemistry of the thioether
pincer ligands with either Rh or Ir. One should expect to
encounter similarly complex solution behavior for these
complexes with smaller alkyl groups. Since the solution
Considering that 2a exhibits only a single dynamic
exchange process, is it possible to assign the two hydride
resonances? The symmetry differences of both A and B
suggest that the latter would possess a dipole moment and
that perturbation of the equilibrium would occur upon
variation of the dielectric of the solvent. Figure 5 contains
the hydride region of 2a in four different solvents (CD2Cl2,
o-Cl2C6D4, d8-toluene, and d6-benzene) where A denotes the
upfield hydride resonance. There exists a strong solvent de-
pendence, as the ratio between the two (A/B) increases upon
a decrease in the dielectric constant of the solvent. The inte-
grated intensities of the two hydride signals are nearly equal
in CD2Cl2, but become unequal upon a decrease in the sol-
vent polarity. Based on these observations, the upfield reso-
nance is attributable to the low-polarity diastereomer, A.
Finally, a system undergoing a two-site exchange provides
an opportunity to determine the apparent equilibrium constant
t
behavior of the Bu(SCS)-pincer adducts are readily inter-
pretable, our focus in this area will concentrate on this ligand
framework. Indeed, preliminary results demonstrate that 2a
participates in anion methathesis reactions with either AgOTf
or AgBF4 to provide dimeric complexes as well.20 These
complexes show extraordinary reactivity with alkyl and aryl
silanes. Experiments are currently in progress to map out
the complete reactivity and solution behavior of these
interesting molecules.
1
between the two species. Variable-temperature H NMR in
CD2Cl2 from -82 to 24 °C showed that the downfield
resonance is nearly 3 times more abundant than that of A at
-82 °C. Careful integration of the hydride signals afforded
an apparent equilibrium constant (Kapp ) B/A) at each
temperature and provided an opportunity to subject these data
to a van’t Hoff analysis. This resulted in the following values,
Inorganic Chemistry, Vol. 41, No. 10, 2002 2639

Evans et al.
4 × 30 cm column). The desired product eluted as a pale yellow
band, and removal of the hexane/CHCl3 solution resulted in the
isolation of a pale yellow liquid. The crude yield (>97% purity)
for a 57.1 mmol reaction was 92.7%. Further purification occurred
upon distillation (bp ) 185-187 °C (5 mTorr)) to yield a colorless
liquid. Spectroscopic Data: 1H NMR (C6D6) δ (TMS): 7.326 (s,
1H, ArH), 7.093 (m, 3H, ArH), 3.502 (s, 4H, ArCH2SiPr), 2.597
Experimental Section
All materials, unless otherwise specified, were obtained from
Acros or Aldrich and were used without purification. [(COE)2RhCl]2
was prepared according to a literature procedure.21 When necessary,
work was performed in a Vacuum Atmospheres drybox or using
Schlenk techniques under a nitrogen atmosphere. 1H and 13C NMR
spectra were recorded using a Bruker DRX 400 spectrometer with
an operating frequency of 400.132 and 100.625 MHz, respectively.
Proton decoupled spectra were recorded and both short- (1JCH) and
3
3
(sept, JHH ) 6.7 Hz, 2H, SCH(CH3)2), 1.084 (d, JHH ) 6.7 Hz,
12H, SCH(CH3)2). 13C {1H} NMR (100.625 MHz, CD2Cl2) δ
1
(1JCH): 139.2 (s, C1,3), 129.2 (d, C5, JCH ) 156.2 Hz), 128.4 (d,
long-range (3JCH) coupling were observed; however, only JCH
1
1
1
C2, JCH ) 160.1 Hz), 127.2 (d, C4,6, JCH ) 159.3 Hz), 34.9 (t,
ArCH2S-, 1JCH ) 139.1 Hz), 34.3 (q, -SCH(CH3)2, 1JCH ) 139.2
values were reported. All chemical shifts were reported relative to
internal TMS (CDCl3) or relative to solvent residual. FT-IR data
were collected using a Nicolet Magna-IR 560 spectrometer employ-
ing 1 cm-1 resolution. Fast atom bombardment (FAB) mass
spectrometry was performed on a VG7070E magnetic sector mass
spectrometer. Elemental analyses were performed by Desert Ana-
lytics (Tucson, AZ). Electrospray mass spectrometry was operated
in the positive-ion mode using a Micromass QTOF II (Beverly,
MA). Samples, in methylene chloride, were directly infused using
a syringe pump operating at 5 mL/min. High-resolution spectra were
recorded with poly-D-alanine as an internal molecular weight
standard. X-ray analyses were performed using a Bruker SMART
CCD system operating at -80 °C (vide infra).
Hz), 23.0 (-SCH(CH3)2, JCH ) 126.9 Hz). HR FAB-MS (MH+)
1
obsd (theor): 255.1252 (255.1241) (4.3 ppm).
Preparation of [µ-ClRh(H)(tBuSCH2)2C6H3-2,6]2, 2a. To a
solution of a 1.435 g (2.00 mmol) of [Rh(COE)2Cl]2 in 75 mL of
dry benzene at 25 °C was added 1.187 g (4.20 mmol) of tBu(SCHS)
ligand in 5 mL of dry benzene. The solution was stirred for 18 h
at 25 °C. The resultant pale yellow solid was filtered, washed with
5 × 5 mL of hexanes, and dried in a vacuum for 24 h. This yielded
1.44 g (85.5%) of 2a. The combined filtrate and washing solution
was evaporated to dryness in vacuo. The residue was washed with
5 × 5 mL of hexanes and dried under vacuum for 24 h. This yielded
0.15 g of the same product. IR (νRhH, cm-1): KBr 2108, CH2Cl2
Preparation of 1,3-(tBuSCH2)2C6H4, 1a. To a flask containing
25 mL of anhydrous DMF, 1.4437 g of NaH (95%; 57.2 mmol)
was added. The suspension was stirred thoroughly and then cooled
to 0 °C where 6.44 mL of 2-methyl-2-propanethiol (57.2 mmol)
was added slowly via a syringe yielding a dark brown solution.
The solution was stirred an additional 20 min until gas evolution
ceased. 1,3-(ClCH2)2C6H4 (5.00 g, 28.5 mmol/25 mL DMF) was
added dropwise to the sodium tert-butylthiolate solution. Upon
complete addition of dichloro-m-xylene, the solution turned cloudy
white. The ice bath was removed and the solution heated at 100
°C, with stirring, for 3 h. The reaction was allowed to cool to room
temperature and was quenched with 100 mL of H2O, and an
additional 50 mL of CHCl3 was added with mixing. The mixture
was separated and the aqueous layer washed twice more with 25
mL portions of CHCl3. The collected CHCl3 solution was then
washed with water (5 × 50 mL) to remove DMF. Evaporation of
the solvent yielded a yellow oil which was recrystallized using
CH3OH/H2O (2:1) in a refrigerator. White needles were collected
by filtration and dried at 30 °C for 3 days at 5 mTorr. The final
isolated yield was 6.61 g (23.4 mmol, 82%). A second crystalliza-
tion yielded an additional 0.243 g of material, but was slightly
1
1
(NaCl plate) 2113. H NMR: except in the arene H region, two
distinct sets of resonances were observed for A and B (δ, ppm,
A/B ) 2.33, C6D6): 6.88-6.69 (m, 6H, ArH), A: 4.26 and 3.65
(d, 2JHH ) 14.5 Hz, 8H, ArCH2S), 1.41 (s, 36H, t-Bu), -20.04 (d,
1JRhH ) 25.7 Hz, 2H, RhH); B: 4.16 and 3.67 (d, 2JHH ) 14.5 Hz,
1
8H, ArCH2S), 1.42 (s, 36H, t-Bu), -19.44 (d, JRhH ) 23.2 Hz,
2H, RhH). (δ, ppm, A/B ) 1.72, C7D8): 6.18-6.65 (m, 6H, ArH),
A: 4.12 and 3.65 (d, 2JHH ) 14.8 Hz, 8H, ArCH2S), 1.42 (s, 36H,
1
t-Bu), -20.16 (d, JRhH ) 25.2 Hz, 2H, RhH); B: 4.20 and 3.63
(d, 2JHH ) 14.4 Hz, 8H ArCH2S), 1.41 (s, 36H, t-Bu), -19.55 (d,
1JRhH ) 24.0 Hz, 2H, RhH). (δ, ppm, A/B ) 1.28, 1,2-Cl2C6D4
(o-DCB)): 7.01-6.92 (m, 6H, ArH), A: 4.43 and 4.08 (d, 2JHH
)
)
1
15.6 Hz, 8H, ArCH2S), 1.72 (s, 36H, t-Bu), -20.02 (d, JRhH
2
25.2 Hz, 2H, RhH); B: 4.48 and 4.07 (d, JHH ) 15.3 Hz, 8H,
1
ArCH2S), 1.71 (s, 36H, t-Bu), -19.51 (d, JRhH ) 24.4 Hz, 2H,
RhH). (δ, ppm, A/B ) 1.02, CD2Cl2): 6.80-6.69 (m, 6H, ArH),
A: 4.27 and 3.88 (d, 2JHH ) 14.8 Hz, 8H, ArCH2S), 1.47 (s, 36H,
1
t-Bu), -20.48 (d, JRhH ) 25.6 Hz, 2H, RhH); B: 4.20 and 3.88
2
(d, JHH ) 15.2 Hz, 8H, ArCH2S), 1.466 (s, 36H, t-Bu), -20.07
1
(d, JRhH ) 24.4 Hz, 2H, RhH). One set of signals observed for
13C NMR spectrum. 13C {1H} NMR (100.625 MHz, CD2Cl2) δ:
1
3
yellow in color. H NMR (δ, CDCl3): 7.329 (t, JHH ) 7.4 Hz,
1H, ArH), 7.219 (s, 1H, ArH), 7.209 (d, 3JHH ) 7.4 Hz, 2H, ArH),
3.746 (s, 4H, ArCH2S), 1.350 (s, 18H, SC(CH3)3). 13C {1H} NMR
1
2
165.27 (d, Cipso, JRhC ) 33.0 Hz), 146.40 (d, Cortho, JRhC ) 21.2
1
1
Hz), 125.56 (d, Cpara, JCH ) 160.3 Hz), 120.91 (d, Cmeta, JCH
156.5 Hz), 48.51 (d, SC(CH3)3, JRhC ) 24.4 Hz), 43.38 (td,
)
2
(100.625 MHz, CD2Cl2) δ (1JCH): 139.3 (s, C1,3), 129.97 (d, C5,
2
1
ArCH2S, JRhC ) 3.5 Hz, JCH ) 139.2 Hz), 29.86 (q, SC(CH3)3,
1JCH ) 127.7 Hz). Elemental analysis for 2a‚C6H6 obsd (theor):
C, 49.81 (49.62); H, 6.37 (6.36). Crystals of 2a suitable for X-ray
were obtained from slow evaporation of solvent from a benzene
solution or a 1:3 benzene/CH2Cl2 solution. High-resolution ESI-
MS (CH2Cl2) for 2a (C32H52S4Cl2Rh2tM) gave as the predominant
ion [M - Cl]+. Calculated isotopic mass for [C32H52S4ClRh2]+
805.0750 amu, observed 805.0723 amu (3.4 ppm).
1JCH ) 156.9 Hz), 128.7 (d, C2, JCH ) 160.8 Hz), 127.7 (d, C4,6
,
1
1JCH ) 159.2 Hz), 43.0 (s, -SC(CH3)3), 33.5 (t, ArCH2S-, JCH
1
1
) 139.7 Hz), 31.0 (q, -SC(CH3)3, JCH ) 127.0 Hz). Elemental
analysis for C16H26S2 obsd (theor): C, 68.24 (68.02); H, 9.32 (9.28).
Melting point (uncorrected): 38.1-38.4 °C.
Preparation of 1,3-(iPrSCH2)2C6H4, 1b. Synthesis of this
compound occurred using a procedure similar to that for 1a with
the exception that purification of 1b proceeded by column chro-
matography (slurried 60-200 mesh SiO2; hexane/CHCl3 (70:30);
Preparation of [µ-ClRh(H)(iPrSCH2)2C6H3-2,6]2, 2b. Per-
formed in a manner identical to that for 2a. Isolated yield for a 4.2
mmol reaction of 1b with 2.0 mmol of [(COE)2RhCl]2 was 1.304
g, 83.0%. 1H NMR (d8-toluene, 90 °C, ppm): 6.690 (br s, 6H, ArH),
(20) Evans, D. R.; Huang, M., Chege, E. W. Abstracts of Papers, 221st
National Meeting of the American Chemical Society, San Diego, CA,
Apr 1-5, 2001; American Chemical Society: Washington, DC, 2001;
INOR 699.
2
4.180 (br s, 4H, ArCH2S), 3.665 (d, JHH ) 14.4 Hz, ArCH2S),
3.044 (br s, 4H, SCH(CH3)2), 1.362, 1.313 (2 broad singlets, 24H,
SCH(CH3)2). FT-IR (KBr, cm-1): 2120 (s, Rh-H). Consistent with
(21) Bennett, M. A.; Saxby, J. D. Inorg. Chem. 1968, 7, 321-325.
2640 Inorganic Chemistry, Vol. 41, No. 10, 2002

Synthesis of [µ-ClRh(H)RSCH2)2C6H3-2,6]2
the EXSY data, some diastereomers do not readily exchange at
ambient temperature, but undergo exchange at elevated tempera-
tures. The following reported signals are those of the major signal
observed in the spectrum. 13C {1H} NMR (100.625 MHz, CD2Cl2)
δ: 166.03 (d, Cipso, 1JRhC ) 31.8 Hz), 145.73 (s, Cortho), 128.72 (d,
P2(1)/c (no. 14) for 2b. The structure was determined by direct
methods with the successful location of nearly all atoms using the
program XS.24 The structure was refined with XL.25
After the initial refinement difference Fourier cycle, additional
atoms were located and included within the connectivity table. After
several of these refinement difference Fourier cycles, all of the
atoms were refined isotropically and then anisotropically. Except
for the hydride ligands, all hydrogen atoms were placed in calcu-
lated positions. The final structure (2a) was refined to convergence
[∆/σ e 0.001] with R(F) ) 5.93%, wR(F2) ) 8.12%, GOF ) 1.002
for all 5279 unique reflections [R(F) ) 3.76%, wR(F2) ) 7.51%
for those 3906 data with Fo > 4σ(Fo)]. The final structure (2b)
was refined to convergence [∆/σ e 0.001] with R(F) ) 4.45%,
wR(F2) ) 7.88%, and GOF ) 1.138 for all 4227 unique reflections
[R(F) ) 3.06%, wR(F2) ) 6.94% for those 3128 data with Fo >
4σ(Fo)]. A final difference Fourier map was featureless, indicating
that the structure is therefore both correct and complete.
C
para, 1JCH ) 158.0 Hz), 121.79 (d, Cmeta, 1JCH ) 157.2 Hz), 43.43
(d, SCH(CH3)2, 1JCH ) 140.4 Hz), 41.51 (t, ArCH2S, 1JCH ) 142.1
1
Hz), 22.25 (q, SC(CH3)3, JCH ) 127.9 Hz). Elemental analysis
for 2b‚C6H6 obsd (theor): C, 47.47 (47.28); H, 5.86 (5.83). Crystals
of 2b suitable for X-ray were obtained from slow evaporation of
solvent from a benzene solution. High-resolution ESI-MS (CH2Cl2)
for 2b (C28H44S4Cl2Rh2/M) gave as the predominant ion [M - Cl]+.
Calculated isotopic mass for [C28H44S4ClRh2]+ 782.0124 amu,
observed 749.0015 amu (0.9 ppm).
X-ray Analysis. Colorless block crystals with dimensions 0.200
× 0.073 × 0.055 mm3 (2a) and 0.407 × 0.204 × 0.046 mm3 (2b)
were placed and optically centered on the Bruker SMART CCD
system at -80 °C. The initial unit cell was indexed using a least-
squares analysis of a random set of reflections collected from three
series of 0.3° wide ω scans (25 frames/series) that were well
distributed in reciprocal space. Data frames were collected [Μï
ΚR] with 0.2° wide ω scans for 10 s. Five complete ω-scan series,
909 frames, were collected with an additional 200 frames a repeat
of the first series for redundancy and decay purposes. The crystal-
to-detector distance was 4.973 cm, thus providing a complete sphere
of data to 2θmax ) 55°. A total of 18 095 (2a) or 28 251 (2b)
reflections were collected and corrected for Lorentz and polarization
effects and absorption using Blessing’s method as incorporated into
the program SADABS22 with 5279 unique [R(int) ) 0.0626] (2a)
and 4227 unique [R(int) ) 0.0425] (2b).
Structural Determination and Refinement. All crystallographic
calculations were performed on a personal computer (PC) with dual
Pentium 450 MHz processors and 384 MB of extended memory.
The SHELXTL23 program package, XPREP, was now implemented
to determine the probable space group and to set up the initial files.
System symmetry indicated the unique centrosymmetric triclinic
space group P-1 (no. 2) for 2a and the monoclinic space group
The function minimized during the full-matrix least-squares
2
2
refinement was ∑w(Fo - Fc2), where w ) 1/[σ2(Fo ) + (RP)2 +
2
âP] and P ) (max(Fo ,0) + 2Fc2)/3 (2a: R ) 0.0314, â ) 0.00;
2b: R ) 0.0337, â ) 1.65). An empirical correction for extinction
was attempted but was found to be negative and therefore was not
applied.
Acknowledgment. Acknowledgment is made for the
financial support provided through the Petroleum Research
Fund as administered by the American Chemical Society.
Supporting Information Available: Stacked plots of the
1
variable-temperature H NMR of 2b recorded in d8-toluene, and
figures containing the low-resolution ESI-MS of 2a and 2b in
CH2Cl2. Crystal structure data for 2a (additional molecular structure
of 2a‚2CH2Cl2) and 2b including tables of atomic parameters,
anisotropic thermal parameters bond distances and bond angles.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC011189Y
(22) (a) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-38. (b) Sheldrick,
G. M. SADABS ‘Siemens Area Detector Absorption Correction’;
University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(23) Sheldrick, G. M. SHELXTL/PC, version 5.03; Siemens Analytical
X-ray Instruments, Inc.: Madison, WI, 1994.
(24) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, A46, 467-473.
(25) Sheldrick, G. M. Shelxl93 Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
Inorganic Chemistry, Vol. 41, No. 10, 2002 2641