Models for homogeneous deep hydrodesulfurization. Intramolecular CO substitution by the sulfur in [(η6-2-methylbenzothiophene)Mn(CO)3]+ and [(η6-dibenzothiophene)Mn(CO)3]+ after regiospecific insertion of platinum into a C-S bond

Article abstract of DOI:10.1021/om000100d

Coordination of Mn(CO)₃⁺ to a carbocyclic ring of sterically congested thiophenes activates a C-S bond to regiospecific insertion of platinum. The resulting metallathiacycles contain a nucleophilic sulfur atom that undergoes spontaneous intramolecular CO substitution at the manganese center.

Full text of DOI:10.1021/om000100d

Organometallics 2000, 19, 1823-1825
1823
Mod els for Hom ogen eou s Deep Hyd r od esu lfu r iza tion .
In tr a m olecu la r CO Su bstitu tion by th e Su lfu r in
[(η6-2-m eth ylben zoth iop h en e)Mn (CO)3]+ a n d
[(η6-d iben zoth iop h en e)Mn (CO)3]+ a fter Regiosp ecific
In ser tion of P la tin u m in to a C-S Bon d
Huazhi Li, Gene B. Carpenter, and Dwight A. Sweigart*
Department of Chemistry, Brown University, Providence, Rhode Island 02912
Received February 4, 2000
+
Summary: Coordination of Mn(CO)3 to a carbocyclic
ring of sterically congested thiophenes activates a C-S
bond to regiospecific insertion of platinum. The resulting
metallathiacycles contain a nucleophilic sulfur atom that
undergoes spontaneous intramolecular CO substitution
at the manganese center.
seconds at room temperature but do not proceed at all
in the absence of the Mn(CO)3+ precoordination.4 Of the
The removal of sulfur as H2S from petroleum feed-
stocks is a major industrial process known as hydrode-
sulfurization (HDS).1 Unsaturated heterocycles contain-
ing the thiophene nucleus are resistant to HDS and, as
a consequence, comprise most of the sulfur contamina-
tion in fossil fuels. Desulfurization requires cleavage of
the C-S bonds by insertion of a metal catalyst, followed
by hydrogenolysis of the M-C bonds. Thiophenes are
relatively unreactive because the conjugated sulfur atom
is only very weakly nucleophilic toward a metal. In
addition, steric factors play a major role, as evidenced
by the fact that benzothiophenes (BT’s) and diben-
zothiophenes (DBT’s) with alkyl substituents near the
sulfur are especially difficult to treat.2 Successful pro-
cessing of these species is termed “deep hydrodesulfu-
rization”.
two C-S bonds in BT, C(aryl)-S and C(vinyl)-S, we
reasoned that precoordination selectively activates
C(aryl)-S, thus accounting for the regiospecificity in-
dicated in eq 1. That the C(vinyl)-S bond is broken in
eq 2 is thought to be due to greater steric congestion at
the C(aryl)-S bond that is manifest with the bulky Pt-
(PPh3)2 nucleophile. To test this hypothesis and, more
importantly, to investigate the influence of steric factors
on C-S bond cleavage reactions that model deep hy-
drodesulfurization, we examined the reactions of η6-
coordinated 2-MeBT and DBT with the weak nucleo-
phile Pt(PPh3)2(C2H4). As is documented below, the C-S
We recently demonstrated that η6 coordination of an
electrophilic metal fragment to the carbocyclic ring in
BT or DBT activates the C-S bonds in the adjacent
heterocyclic ring to cleavage upon reduction or upon
attack by metal nucleophiles.3 Equations 1 and 2
illustrate specific reactions with BT that occur within
(1) (a) Topsøe, H.; Clausen, B. S.; Massoth, F. E. Hydrotreating
Catalysis; Springer: Berlin, 1996. (b) Petroleum Chemistry and Refin-
ing; Speight, J . G., Ed.; Taylor & Francis: Washington, DC, 1998. (c)
Startsev, A. N. Catal. Rev.-Sci. Eng. 1995, 37, 353. (d) Sanchez-
Delgado, R. A. J . Mol. Catal. 1994, 86, 287. (e) Angelici, R. J .
Polyhedron 1997, 16, 3073. (f) Bianchini, C.; Meli, A. J . Chem. Soc.,
Dalton Trans. 1996, 801. (g) Angelici, R. J . Acc. Chem. Res. 1988, 21,
387. (h) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259. (i) Angelici,
R. J . Bull. Soc. Chim. Belg. 1995, 104, 265. (j) Bianchini, C.; Meli, A.
Acc. Chem. Res. 1998, 31, 109.
(2) (a) Shih, S. S.; Mizrahi, S.; Green, L. A.; Sarli, M. S. Ind. Eng.
Chem. Res. 1992, 31, 1232. (b) Vasudevan, P. T.; Fierro, J . L. G. Catal.
Rev.-Sci. Eng. 1996, 38, 161. (c) Kabe, T.; Akamatsu, K.; Ishihara, A.;
Otsuki, S.; Godo, M.; Zhang, Q.; Qian, W. Ind. Eng. Chem. Res. 1997,
36, 5146. (d) Vicic, D. A.; J ones, W. D. Organometallics 1998, 17, 3411.
(e) Vicic, D. A.; J ones, W. D. J . Am. Chem. Soc. 1999, 121, 7606. (f)
Gates, B. C.; Topsøe, H. Polyhedron 1997, 16, 3213. (g) Myers, A. W.;
J ones, W. D.; McClements, S. M. J . Am. Chem. Soc. 1995, 117, 11704.
(h) Bianchini, C.; Casares, J . A.; J imenez, M. V.; Meli, A.; Moneti, S.;
Vizza, F.; Herrera, V.; Sanchez-Delgado, R. Organometallics 1995, 14,
4850. (i) Bianchini, C.; J imenez, M. V.; Meli, A.; Moneti, S.; Vizza, F.;
Herrera, V.; Sanchez-Delgado, R. A. Organometallics 1995, 14, 2342.
(j) Meyers, A. W.; J ones, W. D. Organometallics 1996, 15, 2905. (k)
Bianchini, C.; Casares, J . A.; Masi, D.; Meli, A.; Pohl, W.; Vizza, F. J .
Organomet. Chem. 1997, 541, 143.
+
bond nearer the Mn(CO)3 moiety is preferentially
cleaved in these sterically congested systems and, in a
surprising development, it was found that the nucleo-
(3) (a) Dullaghan, C. A.; Sun, S.; Carpenter, G. B.; Weldon, B.;
Sweigart, D. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 212. (b) Sun,
S.; Dullaghan, C. A.; Sweigart, D. A. J . Chem. Soc., Dalton Trans. 1996,
4493. (c) Dullaghan, C. A.; Zhang, X.; Walther, D.; Carpenter, G. B.;
Sweigart, D. A. Organometallics 1997, 16, 5604. (d) Zhang, X.;
Dullaghan, C. A.; Watson, E. J .; Carpenter, G. B.; Sweigart, D. A.
Organometallics 1998, 17, 2067. (e) Dullaghan, C. A.; Zhang, X.;
Greene, D. L.; Carpenter, G. B.; Sweigart, D. A.; Camiletti, C.;
Rajaseelan, E. Organometallics 1998, 17, 3316. (f) Zhang, X.; Dul-
laghan, C. A.; Carpenter, G. B.; Sweigart, D. A.; Meng, Q. Chem.
Commun. 1998, 93. (g) Dullaghan, C. A.; Carpenter, G. B.; Sweigart,
D. A.; Choi, D. S.; Lee, S. S.; Chung, Y. K. Organometallics 1997, 16,
5688. (h) Zhang, X.; Watson, E. J .; Dullaghan, C. A.; Gorun, S. G.;
Sweigart, D. A. Angew. Chem., Int. Ed. Engl. 1999, 38, 2206.
(4) In the original report of eq 23e the nucleophile used was Pt(PPh3)3
instead of Pt(PPh3)2C2H4. The latter nucleophile, which gives the same
product as the former, was subsequently found to be more generally
useful in reactions of thiophenic complexes.
10.1021/om000100d CCC: $19.00 © 2000 American Chemical Society
Publication on Web 04/18/2000

1824 Organometallics, Vol. 19, No. 10, 2000
Communications
Sch em e 1. Regiosp ecific In ser tion of P t in to a
C(a r yl)-S Bon d a n d Su bsequ en t CO Su bstitu tion
by th e Su lfu r
philicity of the sulfur atom in the resulting metallathia-
cyclic ring is so great that it spontaneously attacks the
manganese and displaces a CO ligand.
+
We previously reported3e that (η6-2-MeBT)Mn(CO)3
(1) reacts rapidly with Pt(PPh3)3 to give a complex that
was postulated on the basis of 31P NMR data to be the
product of C(aryl)-S insertion, as shown in the first
reaction in Scheme 1. In the present work, attempts to
grow crystals of 2 suitable for X-ray diffraction were
unsuccessful; therefore, it was decided to synthesize the
corresponding Mn(CO)2P(OEt)3 complex in the hope of
obtaining adequate crystals. Thus, stirring [2]BF4 under
N2 at room temperature in CH2Cl2 containing 2 equiv
of P(OEt)3 led to a slow transformation (t1/2 ≈ 10 h) to
a dicarbonyl species that, surprisingly, did not contain
P(OEt)3. The same complex could be obtained within
minutes by treating 2 with 1 equiv of Me3NO or by
simply allowing a solution of 2 to sit (without P(OEt)3)
overnight.5 An X-ray structure6 of the product showed
it to be 3, in which the sulfur in the metallathiacyclic
ring of 2 had displaced a CO ligand from Mn(CO)3.
Figure 1 gives the structure of the cation in [3]BF4.
These results are significant for several reasons. (1)
They show that insertion into the C(aryl)-S bond in
BT’s is possible even with bulky nucleophiles, provided
a metal is precoordinated to the carbocyclic ring and
there is a substituent in the 2-position. (2) The sulfur
F igu r e 1. Structure of the cation in [3]BF4. Selected bond
lengths (Å) and angles (deg): Pt(1)-P(1) ) 2.3182(11), Pt-
(1)-P(2) ) 2.2806(10), Pt(1)-C(8) ) 2.092(4), Pt(1)-S(1)
) 2.3945(11), S(1)-C(2) ) 1.817(5), S(1)-Mn(1) ) 2.3487-
(14), C(2)-C(3) ) 1.312(7), C(3)-C(9) ) 1.492(6), C(8)-
C(9) ) 1.470(6), C(2)-C(10) ) 1.504(7); P(1)-Pt(1)-P(2)
) 100.40(4), P(1)-Pt(1)-S(1) ) 92.01(4), P(2)-Pt(1)-C(8)
) 91.89(12), C(8)-Pt(1)-S(1) ) 76.15(12), Pt(1)-S(1)-Mn-
(1) ) 90.81(4), Pt(1)-S(1)-C(2) ) 90.77(15), S(1)-C(2)-
C(3) ) 116.4(4), C(2)-C(3)-C(9) ) 116.3(4), C(3)-C(9)-
C(8) ) 119.7(4), Pt(1)-C(8)-C(9) ) 119.1(3).
atom in the metallathiacyclic ring in 2 possesses a
greatly enhanced nucleophilicity compared to that in
free BT. The sulfur’s nucleophilic character is so pro-
nounced that external tertiary phosphite cannot com-
pete with the intramolecular ring closure in the CO
substitution reaction shown in Scheme 1. Preliminary
work7 suggests that the sulfur atom is more nucleophilic
in general when the metal, whether Pt or Mn, is
inserted into the C(aryl)-S as opposed to the C(vinyl)-S
bond.
Interestingly, it was found that a solution of [3]BF4
in a mixture of CH2Cl2 and Et2O under N2 for 2 months
deposits crystals of the dimer [(PPh3)2PtS]2, which was
determined by X-ray crystallography to have the ex-
pected bridging sulfide structure.8 This shows that
2-MeBT can be desulfurized via the cooperative interac-
tions of manganese and platinum.
(5) Synthesis of [3]BF4: Me3NO (0.055 mmol) was added to a
solution of [2]BF4 (0.055 g, 0.050 mmol) in CH2Cl2 (5 mL) under N2 at
room temperature. There was an immediate color change from yellow
to red. After 10 min, the solution was concentrated and the product
precipitated with diethyl ether. Purification was effected by reprecipi-
tation from diethyl ether. Yield: 60%. IR (CH2Cl2): νCO 1989 (s), 1944
(m) cm-1 1H NMR (CD2Cl2): δ 7.51-7.27 (m, 30H), 7.07 (s, H3), 6.58
.
(d, J ) 6 Hz, H4), 5.18 (t, J ) 5.5 Hz, H7), 4.87 (t, J ) 6 Hz, H6), 4.71
(t, J ) 6 Hz, H5), 1.41 (s, Me). 31P NMR (CD2Cl2): δ 22.28 (dd, J P-P
)
(7) Watson, E. J .; Li, H.; Sweigart, D. A. Unpublished results.
(8) The crystal structure of [(PPh3)2PtS]2 was determined as de-
scribed in ref 6 for [3]BF4. The structure was determined by direct
methods and refined on F2 using the SHELXTL version 5 package.
Only a few of the 30 expected hydrogen atoms appeared in a difference
map, because the scattering was dominated by the heavier atoms. Each
hydrogen was introduced in an ideal position, riding on the atom to
which it is bonded, and refined with isotropic temperature factors 20%
greater than that of the ridden atom. All other atoms were refined
with anisotropic displacement parameters, except for the disordered
solvent molecules. The molecule is located on a 2-fold rotation axis, so
that only half is independent. There was clear evidence for some
disordered solvent in the crystal; however, no discrete solvent molecules
could be recognized. The solvent was modeled by two clusters of six
carbon atoms, which fit neatly into gaps between the [(PPh3)2PtS]2
molecules. Crystal data: 25 °C, Mo KR radiation, crystal dimensions
0.46 × 0.26 × 0.15 mm, monoclinic crystal system, space group C2/c,
a ) 17.2348(13) Å, b ) 18.2934(15) Å, c ) 20.4947(16) Å, â ) 91.325-
(3)°, V ) 6459.9(9) Å3, Z ) 8, Fcalcd ) 1.694 g cm-3, µ ) 4.539 mm-1, θ
range 1.62-26.45°, 385 variables refined with 6636 independent
reflections to final R indices (I > 2σ(I)) of R1 ) 0.0590 and wR2 )
0.1500, and GOF ) 1.117.
13 Hz, J P-Pt ) 3420 Hz), 16.73 (dd, J P-P ) 13 Hz, J P-Pt ) 2310 Hz).
Anal. Calcd for C47H38O2SP2MnPtBF4: C, 52.97; H, 3.56. Found: C,
52.70; H, 3.63.
(6) The crystal structure of [3]BF4 was determined with a Siemens
P4 diffractometer equipped with a CCD area detector and controlled
by SMART version 5 software. Data reduction was carried out by
SAINT version 5 and by SADABS and included profile analysis and
an empirical absorption correction. The structure was determined by
direct methods and refined on F2 using the SHELXTL version 5
package. Thirty-one of the 38 expected hydrogen atoms appeared in a
difference map. Each hydrogen was introduced in an ideal position,
riding on the atom to which it is bonded, and refined with isotropic
temperature factors 20% greater than that of the ridden atom. All other
atoms were refined with anisotropic displacement parameters. Crystal
data: 25 °C, Mo KR radiation, crystal dimensions 0.28 × 0.24 × 0.20
mm, triclinic crystal system, space group P1h, a ) 10.9549(5) Å, b )
13.2328(7) Å, c ) 15.4405(9) Å, R ) 80.429(2)°, â ) 88.043(2)°, γ )
81.572(2)°, V ) 2183.2(2) Å3, Z ) 2, Fcalcd ) 1.621 g cm-3, µ ) 3.666
mm-1, θ range 1.88-27.88°, 533 variables refined with 10 243 inde-
pendent reflections to final R indices (I > 2σ(I)) of R1 ) 0.0392 and
wR2 ) 0.0922, and GOF ) 1.080.

Communications
Organometallics, Vol. 19, No. 10, 2000 1825
Sch em e 2. Regiosp ecific In ser tion of P t in to a
C-S Bon d in DBT a n d Su bsequ en t CO
Su bstitu tion by th e Su lfu r
tivities were established unequivocally. As can be seen,
the platinum inserts into the C-S bond nearer the
FeCp+ moiety, and it is probable that the same regi-
oselectivity obtains with 5. Another strong indication
of the regiochemistry in 5 and 6 is provided by the
observation that 2 readily converts to 3, but the isomer
of 2 (sans the 2-Me group) having the platinum inserted
into the C(vinyl)-S bond (eq 2) decomposes rather than
undergoing CO substitution by the sulfur upon treat-
ment with Me3NO. From molecular models, it appears
that a sulfur bonded to the carbocyclic ring containing
the Mn(CO)3+ fragment is ill-positioned to form a bond
to the manganese. The conclusion is that 6 indeed has
the platinum situated as indicated.
Con clu sion . The conclusion from this work is that
remote activation by precoordination to the carbocy-
clic ring of 2-substituted benzothiophenes and diben-
zothiophenes selectively activates the C-S bond nearer
the coordinated metal to cleavage by nucleophilic re-
agents. That this methodology works with such steri-
cally congested thiophenic systems renders it a reason-
able model for deep hydrodesulfurization. The metalla-
thiacyclic complexes formed in this manner contain a
highly nucleophilic sulfur atom.
Dibenzothiophenes are even more resistant to hy-
drodesulfurization than are benzothiophenes. We previ-
ously reported3e that (η6-DBT)Mn(CO)3+ readily inserts
Pt(PPh3)2 into a C-S bond. It was thought likely that
the C-S bond broken was the one farther removed from
the coordinated carbocyclic ring. We now report that this
conclusion was incorrect. The chemistry that applies to
(η6-DBT)Mn(CO)3+ is remarkably similar to that found
for (η6-2-MeBT)Mn(CO)3+ and is summarized in Scheme
2. Thus, a CH2Cl2 solution of the insertion product 5
was found to convert slowly (t1/2 ≈ 3.5 days) to 6, which
could also be generated rapidly by adding Me3NO to
induce the CO substitution.9
Although crystals of 6 suitable for X-ray diffraction
could not be grown, the regiochemistry was established
by reacting (η6-DBT)FeCp+ with Pt(PPh3)2(C2H4) and
examining crystals of the resulting insertion product 7.
The crystals of 7 were of poor quality and produced
broad reflections, so that it was not possible to get good
integrated intensities. Nevertheless, the atom connec-
Ack n ow led gm en t. This work was supported by
Grant No. CHE-9705121 from the National Science
Foundation.
(9) Synthesis of [6]BF4: the procedure was identical with that
described above for [3]BF4. Yield: 50%. IR (CH2Cl2): νCO 1991 (s), 1947
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, bond lengths and angles, anisotropic displacement
parameters, and hydrogen coordinates for [3]BF4 and [(PPh3)2-
PtS]2. This material is available free of charge via the Internet
at http://pubs.acs.org.
(m) cm-1 1H NMR (CD2Cl2): δ 7.57-7.06 (m, Ph, H6-8), 6.71 (d, J )
.
5 Hz, H5), 6.10 (d, J ) 8 Hz, H4), 5.49 (t, J ) 8 Hz, H1), 5.04 (t, J )
6 Hz, H2), 4.70 (t, J ) 6 Hz, H3). 31P NMR (CD2Cl2): δ 16.54 (dd, J P-P
) 12 Hz, J P-Pt ) 3410 Hz), 15.60 (dd, J P-P ) 12 Hz, J P-Pt ) 2300 Hz).
Anal. Calcd for C50H38O2SP2MnPtBF4: C, 54.51; H, 3.45. Found: C,
54.29; H, 3.58. MS FAB: 1014 (M+).
OM000100D