Dinuclear oxidative addition of N-H and S-H bonds at chromium. Reaction of ?Cr(CO)3(C5Me5) with {o-(HA)C6H4S-Cr(CO)3 (C5Me5)} (A = S, NH) yielding [η2-o-(μ-A)C6H4S-Cr (C5Me5)]2 and H-Cr(CO)3(C5Me5)

Article abstract of DOI:10.1021/ic0204934

Reaction of the 17-electron radical ?Cr(CO)₃Cp* (Cp* = C₅Me₅) with 0.5 equiv of 2-aminophenyl disulfide [(o-H₂-NC₆H₄)₂S₂] results in rapid oxidative addition to form the initial product (o-H₂N)C₆H₄S-Cr(CO)₃Cp*. Addition of a second equivalent of ?Cr(CO)₃Cp* to this solution results in the formation of H-Cr(CO)₃Cp* as well as 1/2[{η²-o-(μ-NH)C₆H₄S} CrCp*]₂. Spectroscopic data show that (o-H₂N)C₆H₄S-Cr(CO)₃Cp* loses CO to form {η²-(o-H₂N)-C₆H₄S} Cr(CO)₂Cp*. Attack on the N-H bond of the coordinated amine by ?Cr(CO)₃Cp* provides a reasonable mechanism consistent with the observation that both chelate formation and oxidative addition of the N-H bond are faster under argon than under CO atmosphere. The N-H bonds of uncoordinated aniline do not react with ?Cr-(CO)₃Cp*. Reaction of the 2 mol of ?Cr(CO)₃Cp* with 1,2-benzene dithiol [1,2-C₆H₄(SH)₂] yields the initial product (o-HS)C₆H₄S-Cr(CO)₃Cp* and 1 mol of H-Cr(CO)₃Cp*. Addition of 1 equiv more of ?Cr(CO)₃Cp* to this solution also results in the formation of 1 equiv of H-Cr(CO)₃Cp*, as well as the dimeric product 1/2[{η²-o-(μ-S)C₆H₄S}- CrCp*]₂. This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination of the second thiol group prior to oxidative addition. The crystal structures of [{η²-o-(μ-NH)C₆H₄S} CrCp*]₂ and [{η²-o-(μ-S)C₆H₄S} CrCp*]₂ are reported.

Full text of DOI:10.1021/ic0204934

Inorg. Chem. 2002, 41, 6769−6774
Dinuclear Oxidative Addition of N−H and S−H Bonds at Chromium.
•
Reaction of Cr(CO)3(C Me5) with {o-(HA)C H S−Cr(CO)3(C Me5)} (A ) S,
5
6 4
5
NH) Yielding [η2-o-(µ-A)C H S−Cr(C Me5)]2 and H−Cr(CO)3(C Me5)
6 4
5
5
,†
Kengkaj Sukcharoenphon,† Telvin D. Ju,† Khalil A. Abboud,‡ and Carl D. Hoff*
Department of Chemistry, UniVersity of Miami, Coral Gables, Florida 33124, and
Department of Chemistry, UniVersity of Florida, GainesVille, Florida 32611
Received August 5, 2002
Reaction of the 17-electron radical •Cr(CO)3Cp* (Cp* ) C Me5) with 0.5 equiv of 2-aminophenyl disulfide [(o-H -
5
2
NC H ) S ] results in rapid oxidative addition to form the initial product (o-H N)C H S−Cr(CO)3Cp*. Addition of a
6
4 2
2
2
6 4
second equivalent of •Cr(CO)3Cp* to this solution results in the formation of H−Cr(CO)3Cp* as well as 1/2[{η2-o-
(µ-NH)C H S}CrCp*]2. Spectroscopic data show that (o-H N)C H S−Cr(CO)3Cp* loses CO to form {η2-(o-H N)-
6
4
2
6
4
2
C H S}Cr(CO)2Cp*. Attack on the N−H bond of the coordinated amine by •Cr(CO)3Cp* provides a reasonable
6
4
mechanism consistent with the observation that both chelate formation and oxidative addition of the N−H bond are
faster under argon than under CO atmosphere. The N−H bonds of uncoordinated aniline do not react with •Cr-
(CO)3Cp*. Reaction of the 2 mol of •Cr(CO)3Cp* with 1,2-benzene dithiol [1,2-C H (SH)2] yields the initial product
6
4
(o-HS)C H S−Cr(CO)3Cp* and 1 mol of H−Cr(CO)3Cp*. Addition of 1 equiv more of •Cr(CO)3Cp* to this solution
6
4
also results in the formation of 1 equiv of H−Cr(CO)3Cp*, as well as the dimeric product 1/2[{η2-o-(µ-S)C H S}-
6
4
CrCp*]2. This reaction also occurs more rapidly under Ar than under CO, consistent with intramolecular coordination
of the second thiol group prior to oxidative addition. The crystal structures of [{η2-o-(µ-NH)C H S}CrCp*]2 and
6
4
[{η2-o-(µ-S)C H S}CrCp*]2 are reported.
6
4
Introduction
was shown to result in the formation of an initial tricarbonyl
complex that readily lost CO to form a chelated complex
Recent work in our laboratory has investigated the
mechanism of reaction of the 17-electron organometallic
•
radical Cr(CO)3Cp* (Cp* ) C5Me5) with the thiols1 and
disulfides2 as shown in eqs 1 and 2, where R ) methyl,
phenyl
2•Cr(CO)3Cp* + H-SR f
H-Cr(CO)3Cp* + RS-Cr(CO)3Cp* (1)
2•Cr(CO)3Cp* + RS-SR f 2RS-Cr(CO)3Cp* (2)
More recently,3 reaction of pyridine thione with •Cr(CO)3Cp*
Reaction 3 proceeds not by direct attack on the N-H bond3
but by addition of the chromium radical to the CdS bond
of the thione to form an initial activated adduct.4
* To whom correspondence should be addressed. E-mail: choff@
jaguar.ir.miami.edu.
† University of Miami.
‡ University of Florida.
(1) Ju, T. D.; Lang, R. F.; Roper, G. C.; Hoff, C. D. J. Am. Chem. Soc.
1996, 118, 5328.
(2) Ju, T. D.; Capps, K. B.; Lang, R. F.; Roper, G. C.; Hoff, C. D. Inorg.
Chem. 1997, 36, 614.
Oxidative addition of the N-H bond at metals has been
reported but is relatively rare for first-row transition metal
(3) Sukcharoenphon, K.; Moran, D.; Abboud, K. A.; Schaefer, H. F., III.;
Schleyer, P. v. R.; Hoff, C. D., manuscript in preparation.
(4) Crich, D.; Quintero, L. Chem. ReV. 1989, 89, 1413 and references
therein.
10.1021/ic0204934 CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/19/2002
Inorganic Chemistry, Vol. 41, No. 25, 2002 6769

Sukcharoenphon et al.
complexes. Milstein5 has investigated N-H activation reac-
tions such as the following
of reaction (∼20 min), FTIR data showed only ν(CO) for the
hydride. The reaction mixture was filtered and then concentrated
by evaporation in vacuo. With the addition of 35 mL of heptane,
cooling at -20 °C over a period of roughly 72 h afforded fine
black crystals that were isolated, washed with heptane, and vacuum-
dried. Storage of the filtrate in the freezer yielded a second crop of
crystals for a total of 0.168 g (50%) of air-stable dimer product.
Repeating the procedure in CH2Cl2 gave an 80% yield. FAB mass
spectroscopic data of an aliquot of a toluene solution of the dimer
showed an intense signal for the parent ion (m/e): M+ ) 654, M+-
Cp* ) 519, 1/2M+ ) 327 (100%). Elemental analysis. Found (calcd)
(%): C 58.6 (58.7), H 5.9 (5.9). Qualitative observation of the rate
of reaction under either argon or carbon monoxide showed the decay
of infrared bands assigned to (o-HS)C6H4S-Cr(CO)3Cp* (∼2008,
1955, 1920 cm-1) to proceed more rapidly under an argon
atmosphere.
Ir(PR3)3Cl + H2N-(C6H5) f H-Ir(PR3)3(Cl)[N(H)(C6H5)]
(4)
Relatively few examples of N-H oxidative addition to
mononuclear complexes have been reported,6,7 and those
published have been primarily for third-row as opposed to
first-row metals. Activation of the N-H bond of ammonia
with formation of an NH2 bridged dimer has also been
reported by Milstein.8
For polynuclear complexes, prior coordination of an amine
might activate the N-H bond to oxidative addition. As part
of studies of oxidative addition of the S-H bond, it has been
shown that binding to low-valent metals might decrease the
thermochemical barrier to oxidative addition of the RS-H
bond by as much as ∼25-30 kcal/mol.1,9 This work reports
reactions yielding chromium thiolates of the forms (o-HS)-
C6H4S-Cr(CO)3Cp* and (o-H2N)C6H4S-Cr(CO)3Cp* in
which, unlike the chelating 2-mercaptopyridine ligand shown
in eq 3, the potentially chelating ligand is capable of further
oxidative addition of S-H and N-H bonds.
Reaction •Cr(CO)3Cp* and 2-Aminophenyl Disulfide. a.
Cr/S ) 2/1. To a Schlenk tube containing [Cr(CO)3Cp*]2 (0.587
g, 1.08 mmol) and (2-H2NC6H4)2S2 (0.138 g, 0.556 mmol) was
added 30 mL of toluene under argon. The reaction mixture was
periodically monitored by FTIR spectroscopy. Following rapid
initial reaction of •
Cr(CO)3Cp*, IR peaks indicative of the formation
of (o-H2N)C6H4S-Cr(CO)3Cp* were found (2005, 1946, 1921
cm-1), as well as those assigned to H-Cr(CO)3Cp* (1996, 1911
cm-1). Careful analysis of the spectroscopic data revealed small
bands at 1934 and 1855 cm-1 present as an intermediate complex.
The bands were tentatively assigned to the chelate complex
{η2-(o-H2N)C6H4S}Cr(CO)2Cp* on the basis of studies performed
at a 1/1 Cr/S ratio described below. After approximately 7.5 h, the
reaction was judged complete because of full formation of the
hydride. Heptane (43 mL) was added, and the sample was stored
in a freezer at -20 °C. Over a 3-day period, brown crystals
precipitated and were collected and rinsed with heptane. Storage
of the filtrate in the freezer yielded a second crop of crystals for a
total yield of 0.184 g (55%) of the [{η2-o-(µ-NH)C6H4S}CrCp*]2
product. MS in toluene (m/e): M+ ) 620 (100%), M+-Cp* )
485, 1/2M+ ) 310. Elemental analysis. Found (calcd) (%): C 61.4
(61.9), H 6.6 (6.3), N 4.6 (4.5).
Experimental Section
General. Reactions were performed under an argon or carbon
monoxide atmosphere using standard glovebox and Schlenk tube
techniques. Toluene and heptane were purified by distillation from
sodium benzophenone ketyl under argon; methylene chloride by
refluxing and subsequent distillation from phosphorus pentoxide.
Research-grade carbon monoxide was purchased from Matheson
and was used without further purification. FTIR spectra were
obtained on a Perkin-Elmer 2000 instrument equipped with
microscope/reactor that has been previously described.1,2 NMR data
were obtained on a Bruker AVANCE 300 MHz NMR spectrometer.
Mass spectral data utilizing FAB were acquired on a VG MASS-
LAB TRIO-2 spectrometer. Elemental analyses were performed by
Galbraith Laboratories, Inc. 2-Aminophenyl disulfide [(2-H2-
NC6H4)2S2] (recrystallized from slow cooling of a toluene/heptane
mixture) and 1,2-benzene dithiol [1,2-C6H4(SH)2] (96%, used as
purchased) were obtained from Aldrich Chemical.
Reaction of •Cr(CO)3Cp* and 1,2-Benzene Dithiol. To a stirred
solution of [Cr(CO)3Cp*]2 (0.829 g, 1.53 mmol) in 40 mL of toluene
under argon was injected 120 µL (1.04 mmol) of 1,2-C6H4(SH)2,
and the progress of the reaction was periodically monitored by FTIR
spectroscopy. Bands attributed to •Cr(CO)3Cp* rapidly decreased,
as new bands assigned to (o-HS)C6H4S-Cr(CO)3Cp* (∼2008,
1955, 1920 cm-1) and H-Cr(CO)3Cp* (1996, 1911 cm-1) grew
within minutes of addition. Subsequently, there was a steady
increase in bands due to H-Cr(CO)3Cp* and decrease in bands
assigned to (o-HS)C6H4S-Cr(CO)3Cp*. No other ν(CO) bands in
the infrared region were detected during reaction, in particular none
indicative of the chelate {η2-(o-HS)C6H4S}Cr(CO)2Cp*. At the end
b. Cr/S ) 1/1. Studies by both IR and NMR (C6D6) spec-
troscopies were performed on this reaction in an identical manner
but at a 1/1 Cr/S ratio designed to maximize the formation of (o-
H2N)C6H4S-Cr(CO)3Cp*. Under a CO atmosphere, bands (2005,
1946, 1921 cm-1) assigned to this complex were present for a period
of days. 1H NMR data (C6D6) were readily collected for (o-H2N)-
C6H4S-Cr(CO)3Cp* under these conditions to give δ (ppm) 7.68
(d, 1 H, -SPh), 6.92 (t, 1 H, -SPh), 6.66 (t, 1 H, -SPh), 6.44 (d,
1 H, -SPh), 4.20 (s, 2 H, -NH2), 1.39 (s, 15 H, -Cp*) (see Figure
1 of the Supporting Information). Evacuation of CO and purging
with argon resulted in the appearance of new bands at 1934 and
1855 cm-1 that were assigned to {η2-(o-H2N)C6H4S}Cr(CO)2Cp*.
Addition of CO rapidly regenerated (o-H2N)C6H4S-Cr(CO)3Cp*.
This process can be repeated several times, but the proposed
complex {η2-(o-H2N)C6H4S}Cr(CO)2Cp* appears to be unstable
and to decomposes slowly in solution. Attempts to obtain NMR
data for {η2-(o-H2N)C6H4S}Cr(CO)2Cp* were frustrated by the
presence of paramagnetic materials generated during this slow
decomposition, which releases CO, thereby converting {η2-(o-H2N)-
C6H4S}Cr(CO)2Cp* to {η1-(o-H2N)C6H4S}Cr(CO)3Cp* as de-
scribed in relation to FTIR experiments below.
(5) Casalnuovo, A. L.; Calabrese, J. C.; Milstein, D. J. Am. Chem. Soc.
1988, 110, 6738.
(6) Kubas, G. J. Metal Dihydrogen and σ-Bonded Complexes; Kluwer
Academic: New York, 2001.
(7) Fulton. J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc. Chem.
Res. 2002, 35, 44 and references therein.
(8) Schultz, M.; Milstein, D. J. Chem. Soc., Chem. Commun. 1993, 318.
(9) Lang, R. F.; Ju, T. D.; Kiss, G.; Hoff, C. D.; Bryan, J. C.; Kubas, G.
J. Inorg. Chim. Acta 1997, 259, 317.
c. Cr/S ) 1/1 Followed by Additional Cr. To a 100-mL Schlenk
tube containing solid [Cr(CO)3Cp*]2 (0.0618 g, 0.114 mmol) and
(2-H2NC6H4)2S2 (0.0348 g, 0.140 mmol, ∼20% excess) was added
20 mL of toluene under an atmosphere of argon. The flask was
6770 Inorganic Chemistry, Vol. 41, No. 25, 2002

OxidatiWe Addition of N-H and S-H Bonds at Cr
Table 1. Crystallographic Data and Structure Refinement for [{η2-o-(µ-NH)C6H4S)CrCp*]2 and [{η2-o-(µ-S)C6H4S}CrCp*]2
[{η2-o-(µ-NH)C6H4S}CrCp*]2
[{η2-o-(µ-S)C6H4S}CrCp*]2
Crystal Data
C32H40Cr2N2S2
620.78
chemical formula
formula weight
C32H38Cr2S4
654.86
crystal system
space group
a, Å
b, Å
c, Å
monoclinic
P2(1)/n
11.3847(6)
9.6404(5)
13.3979(7)
90
95.782(2)
90
1462.98(13)
2
triclinic
P1h
8.0712(3)
10.3454(4)
10.7893(5)
62.673(2)
70.209(2)
80.978(2)
753.09(5)
1
R, °
â, °
γ, °
V, Å3
Z
F
calcd, mg/m3
1.409
0.910
1.444
1.020
µ, mm-1
crystal size, mm
color
0.19 × 0.17 × 0.15
0.19 × 0.17 × 0.14
brown
black
Data Collection
T, K
193
193
λ, Å
0.710 73
2.24-27.50
12 738
3356
integration
0.710 73
2.22-27.48
6589
3335
integration
theta range, °
no. of reflections
independ. reflections
absorption correction
Solution and Refinement
solution
refinement
direct methods
direct methods
full-matrix least-squares on F2
full-matrix least-squares on F2
data/restraints/param
GOF
3356/0/181
1.069
0.0255
0.0677
0.353
3335/0/178
1.079
0.0232
0.0646
0.378
R1a
wR2b [I > 2 σ(I)]
largest diff peak, e Å-3
largest diff hole, e Å-3
-0.270
-0.372
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
closed and evacuated briefly; then the mixture was stirred vigorously
for 30 min. During that time, periodic brief evacuation (to remove
any CO present) was performed. An infrared spectrum at that time
showed bands consistent with a mixture of (o-H2N)C6H4S-
Cr(CO)3Cp* and {η2-(o-H2N)C6H4S}Cr(CO)2Cp*, with no signs
of unreacted starting material [Cr(CO)3Cp*]2 or of H-Cr(CO)3Cp*.
To this solution was added an additional amount of solid [Cr-
(CO)3Cp*]2 (0.0550 g, 0.101 mmol). The flask was again sealed
and evacuated. Over a 2-h period, aliquots of this solution were
removed at approximately 15-min intervals. Each aliquot removed
was placed in the sealed FTIR cell and scanned three times at
approximately 5-min intervals. The course of the reaction in the
evacuated Schlenk tube showed smooth decreases in the bands
assigned to both (o-H2N)C6H4S-Cr(CO)3Cp* and {η2-(o-H2N)-
C6H4S}Cr(CO)2Cp* (both species remained present during the
graphite monochromator utilizing Mo KR radiation (λ ) 0.710 73
Å). Cell parameters were refined using up to 8192 reflections. A
full sphere of data (1850 frames) was collected using the ω-scan
method (0.3° frame width). The first 50 frames were remeasured
at the end of data collection to monitor instrument and crystal
stability (maximum correction on I was <1%). Absorption correc-
tions by integration were applied on the basis of measured indexed
crystal faces.
The structure was solved by the direct methods in SHELXTL6
and refined using full-matrix least squares. The non-H atoms were
treated anisotropically, whereas the hydrogen atoms were calculated
in ideal positions riding on their respective carbon atoms. Crystal-
lographic data and structural refinement for both dimeric structures
are summarized in Table 1.
[(η2-o-(µ-NH)C6H4S)CrCp*]2. From a reaction of 4 equiv of
•Cr(CO)3Cp* with (2-H2NC6H4)2S2 in toluene, a filtered aliquot
containing both the chromium hydride and dimer products was
layered with 2-3 equiv of heptane by volume in a sealed ampule.
No separation of the hydride was needed because of its high
solubility in heptane. After a period of 11 days at room temperature,
dark crystalline blocks separated from a light-brown solution of
the hydride and were isolated, washed with heptane, and stored in
degassed mineral oil.
The crystal structure determined is shown in Figure 1, and
selected bond lengths and angles are listed in Table 2. The NH
proton was located from a difference Fourier map and refined freely.
The geometry around the Cr atom is a three-sided pyramid with
the Cp* occupying the axial position. A total of 181 parameters
were refined in the final cycle of refinement using 3005 reflections
with I > 2σ(I) to yield R1 and wR2 values of 2.55 and 6.77%,
respectively. Refinement was done using F 2.
•
reaction), as well as decreases in the bands due to Cr(CO)3Cp*.
The concentration of H-Cr(CO)3Cp* increased in parallel with the
decrease in starting material. Individual aliquots in the sealed cell
(from which released CO cannot escape) showed an increase in
(o-H2N)C6H4S-Cr(CO)3Cp* and H-Cr(CO)3Cp*, along with a
•
decrease in {η2-(o-H2N)C6H4S}Cr(CO)2Cp* and Cr(CO)3Cp*. A
mass spectrum of an aliquot of the solution at the end of the reaction
confirmed the presence of [{η2-o-(µ-NH)C6H4S}CrCp*]2. Reactions
performed under similar conditions but under a CO atmosphere
were qualitatively observed to proceed on a much slower time scale
with no detectable amounts of {η2-(o-H2N)C6H4S}Cr(CO)2Cp*
present in solution.
X-ray Crystallographic Experiments
Data Collection. Data were collected at 173 K on a Siemens
SMART PLATFORM equipped with a CCD area detector and a
Inorganic Chemistry, Vol. 41, No. 25, 2002 6771

Sukcharoenphon et al.
Figure 2. ORTEP diagram of [{η2-o-(µ-S)C6H4S}CrCp*]2.
Table 2. Selected Bond Lengths (Å) and Angles (°) for
[{η2-o-(µ-NH)C6H4S}CrCp*]2
Figure 1. ORTEP diagram of [{η2-o-(µ-NH)C6H4S}CrCp*]2.
Cr-CrA
Cr-N1
Cr-N1A
Cr-S1
2.8381(4)
2.0457(13)
2.0688(13)
2.3729(4)
0.795(17)
Cr-Cp* (centroid)
CrA-N1
1.909(3)
2.0688(12)
1.4202(19)
1.7605(16)
[(η2-o-(µ-S)C6H4S)CrCp*]2. In a fashion similar to that de-
N1-C1
S1-C2
scribed in the previous section, a filtered aliquot of the toluene
N1-H1
•
solution from reaction of 3 equiv of Cr(CO)3Cp* with 1,2-C6H4-
(SH)2 was layered with 1 equiv of heptane by volume into a sealed
glass ampule. The solvent diffusion over a period of 4 days at room
temperature yielded dark blocks that were isolated, washed with
heptane, and stored in degassed mineral oil.
The crystal structure determined is shown in Figure 2, and
selected bond lengths and angles are listed in Table 3. The
asymmetric unit consists of a half-dimer located on a center of
inversion. A total of 178 parameters were refined in the final cycle
of refinement using 3149 reflections with I > 2σ(I) to yield R1
and wR2 of 2.32 and 6.46%, respectively. Refinement was done
using F 2.
Cr-N1-CrA
S1-Cr-N1
S1-Cr-N1A
C1-N1-H1
Cr-N1-H1
CrA-N1-H1
N1-Cr-N1A
87.22(5)
Cr-N1-C1
Cr-S1-C2
CrA-N1-C1
S1-C2-C1
S1-C2-C3
N1-C1-C2
N1-C1-C6
112.42(9)
93.50(5)
83.01(4)
90.76(4)
107.1(12)
118.8(12)
107.5(12)
92.78(5)
123.63(10)
119.04(11)
122.40(13)
117.77(13)
122.09(14)
IR, NMR, and MS spectroscopies. Under an atmosphere of
argon, the bands at 2005, 1946, and 1921 cm-1 (toluene) of
the tricarbonyl were replaced by bands at 1934 and 1855
cm-1 assigned to the chelating dicarbonyl, as shown in eq 6
Results and Discussion
•
Reaction of Cr(CO)3Cp* with 2-aminophenyl disulfide
occurs rapidly to form an initial tricarbonyl complex, as
shown in eq 5
Changing the atmosphere from Ar back to CO regenerated
the tricarbonyl complex, indicating that KeqpCO in atm , 1 for
reaction 6 because, at 1 atm CO pressure, conversion of
formed dicarbonyl to tricarbonyl is quantitative. That is in
contrast to the analogous decarbonylation in reaction 3 which
Under a CO atmosphere, the aniline thiolate derivative was
stable for short periods of time, and it was characterized by
6772 Inorganic Chemistry, Vol. 41, No. 25, 2002

OxidatiWe Addition of N-H and S-H Bonds at Cr
Table 3. Selected Bond Lengths (Å) and Angles (°) for
[{η2-o-(µ-S)C6H4S}CrCp*]2
rate were found to be essentially the same as those of
thiophenol; however, reaction was found to proceed further
to generate additional products. Following an investigation
of reaction 7, we reinvestigated the reaction of 1,2-C6H4(SH)2
Cr-CrA
Cr-S1
Cr-S2
S1-C1
3.04
Cr-Cp* (centroid)
CrA-S1
1.898(2)
2.3638 (4)
2.3549 (4)
1.7806 (14)
2.3816 (4)
2.3816 (4)
1.7561 (14)
Cr-S1A
•
with Cr(CO)3Cp* and found that it proceeded with the net
S2-C2
stoichiometry shown in eq 9
S1-Cr-S1A
S1-Cr-S2
Cr-S1-CrA
Cr-S2-C2
CrA-S1-C1
Cr-S1-C1
99.964(12)
S1A-Cr-S2
S1-C2-C1
S2-C2-C3
S1-C1-C2
S1-C1-C6
87.664(14)
121.89(10)
119.68(11)
120.37(10)
119.20(11)
86.504(13)
80.036(12)
101.81(5)
111.02(5)
101.72(5)
shows no signs of reversibility even under 25 atm CO.
Because of its reactivity, {η2-(o-H2N)C6H4S}Cr(CO)2Cp*
could not be purified.
Solutions containing a mixture of (o-H2N)C6H4S-Cr(CO)3-
Cp* and {η2-(o-H2N)C6H4S}Cr(CO)2Cp* react further with
•Cr(CO)3Cp*. The fact that this reaction is much faster under
argon than under carbon monoxide is consistent with attack
on the chelating dicarbonyl in the overall scheme shown in
eq 7
The crystal structure of [{η2-o-(µ-S)C6H4S}CrCp*]2 is shown
in Figure 2 and discussed below. Reaction 9 might follow a
mechanism similar to that shown in eq 7. However, because
of the more reactive nature of the S-H bond in this system,
prior coordination of the S-H bond might not be needed
for reaction, and other more complex reaction mechanisms
cannot be ruled out.
The structures of [{η2-o-(µ-NH)C6H4S}CrCp*]2 and [{η2-
o-(µ-S)C6H4S}CrCp*]2, (Figures 1 and 2, Tables 1-3) are
roughly similar. The four-membered Cr-N-Cr-N and Cr-
S-Cr-S ring systems are both essentially planar with
dihedral angles of 0; however, the Cr-Cr distances (2.84
and 3.05 Å, respectively) are significantly longer for the
S-bridged dimer. The Cr-N-Cr-N unit is nearly a square
(angles of 87.22° and 92.78°), whereas the Cr-S-Cr-S
complex shows considerable distortion (angles of 99.964°
and 80.036°). It is of interest to note that [{η2-o-(µ-NH)-
C6H4S}CrCp*]2, which is bridged through N, could have
adopted a S-bridged structure with terminal amido and
bridging sulfide groups. The reasons for preference of the
NH-bridged over the S-bridged form are not known, and the
authors could not find literature data for comparable com-
plexes to provide insight. Several mononuclear and dinuclear
structures containing these ligands but with different metals
have been reported recently, including [(Cp*Rh)2(µ(S)-1,2-
C6H4S2-S,S′)2],12 [PPN]Fe(CO)2(CN)(S,NH-C6H4) and
[PPN]2[(CN)(CO)2Fe(µ-S,S-C6H4]2,13 [CpV(η2,µ-S2Ph)]2,14
and [PPN]2[W(CO)3(NH,S-C6H4)] and [PPN]2[W(CO)4-
(S,S-C6H4)].15 The authors are not aware of comparable
dinuclear Cr structures in the literature containing these
ligands; however, a number of dinuclear complexes of the
formula [(η5-C5R5)(Y)Cr(µ-X)]2 have been reported.16 Such
complexes show Cr-Cr bond distances in the range of 2.6-
3.6 Å and, in some cases, antiferromagnetic coupling. The
two dimeric complexes discussed here also show antiferro-
The crystal structure of [{η2-o-(µ-NH)C6H4S}CrCp*]2 is
shown in Figure 1 and discussed later. The key step in
reaction 8 is proposed attack of the Cr radical on the
complexed N-H bond. The fact that the oxidative addition
reaction is slow under CO atmosphere supports the conclu-
sion that it is the complexed (through the NH2 group)
dicarbonyl and not the uncomplexed tricarbonyl that is
reactive. In addition, the chromium radical does not react
with the uncomplexed N-H bond of aniline10
2•Cr(CO)3Cp* + H2N-C6H5 -X f
(12) Xi, R.; Abe, M.; Suzuki, T.; Nishioka, T.; Isobe, K. J. Organomet.
Chem. 1997, 549, 117.
H-Cr(CO)3Cp* + (C6H5)(H)N-Cr(CO)3Cp* (8)
(13) Liaw, W. F.; Lee, N. H.; Chen, C. H.; Lee, C. M.; Lee, G. H.; Peng,
S. M.; J. Am. Chem. Soc. 2000, 122, 488.
(14) Stephan, D. W. Inorg. Chem. 1992, 31, 4218.
(15) Darensbourg, D. J.; Draper, J. D.; Frost, B. J.; Reibenspies, J. H. Inorg.
Chem. 1999, 38, 4705.
Reaction of •Cr(CO)3Cp* with 1,2-C6H4(SH)2 was inves-
tigated11 several years ago to compare it to reactions of
thiophenol as shown in reaction 2. The initial products and
(16) (a) Pariya, C.; Theopold, K. H. Curr. Sci. 2000, 28, 1345 and references
therein. (b) Hutton, M. A.; Durham, J. C.; Grady, R. W.; Harris, B.
E.; Jarrell, C. S.; Mooney, J. M.; Castellani, M. P.; Rheingold, A. L.;
Kolle, U.; Korte, B. J.; Sommer, R. D.; Yee, G. T.; Boggess, J. M.;
Czernuszewicz, R. S. Organometallics 2001, 20, 734 and references
therein.
(10) Sukcharoenphon, K.; McDonough, J. E.; Hoff, C. D. University of
Miami, Coral Gables, FL. Unpublished results.
(11) Ju, T. D. Thermodynamic and Kinetic Studies of Oxidative Addition
of Thiols and Disulfides to Cr(CO)3C5Me5 and W(phen)(CO)3(EtCN).
Ph.D. Thesis, University of Miami, Coral Gables, FL, 1996.
Inorganic Chemistry, Vol. 41, No. 25, 2002 6773

Sukcharoenphon et al.
magnetic coupling, in addition to a well-resolved ESR spectra
in solution. More detailed investigations of the magnetic and
spectroscopic properties17 of these complexes might yield
additional insights into the nature of the metal-metal
interactions in these dimers.
occur faster than that of the amino thiol, in keeping with the
lower H-S versus H-N bond strength.17 More detailed
kinetic and thermodynamic investigation of these reactions
is in progress, but this report (to the authors’ knowledge) is
the first showing oxidative addition of the N-H bond with
•Cr(CO)3Cp*. This illustrates again, as is well-known in the
literature, the powerful role chelation can play in coordinative
activation of even strong bonds.
Conclusion
The H-N(H)(C6H5) bond strength (88 kcal/mol18) is
considerably stronger than the H-Cr(CO)3Cp* bond strength
(62 kcal/mol). Free aniline does not react with •Cr(CO)3Cp*
under conditions in which aniline disulfide does react to yield
[{η2-o-(µ-NH)C6H4S}CrCp*]2. Spectrosopic data support the
mechanism shown in eq 7 in which coordination of the
pendant NH2 group serves to activate it to attack by
•Cr(CO)3Cp*. Similar observations were made for related
reactions of 1,2-C6H4(SH)2 leading to [{η2-o-(µ-S)C6H4S}-
CrCp*]2. Reaction of the chelating bis thiol is observed to
Acknowledgment. Support of this work by the Petroleum
Research Fund, administered by the American Chemical
Society, is gratefully acknowledged. K.A.A. acknowledges
the National Science Foundation and the University of
Florida for funding of the purchase of the X-ray equipment.
Supporting Information Available: Tables containing full
crystallographic data including bond lengths and angles, thermal
parameters, atomic coordinates, and hydrogen-atom parameters for
both crystal structures are given (CIF). Figure of NMR spectrum
of {η1-(o-H2N)C6H4S}Cr(CO)3Cp*. This material is available free
of charge via the Internet at http://pubs.acs.org.
(17) Walker, L.; Angerhofer, A.; Sukcharoenphon, K.; McDonough, E. J.;
Hoff, C. D. University of Miami, Coral Gables, FL. Work in progress.
(18) Lide, D. R., Ed. Handbook of Chemistry and Physics, 81st ed.; CRC
Press: Boca Raton, FL, 2000.
IC0204934
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