Models for deep hydrodesulfurization (HDS). Remote activation of C-S bonds in alkylated benzothiophenes and dibenzothiophenes by metal coordination to a carbocyclic ring

Article abstract of DOI:10.1021/om0102448

A series of alkylated benzothiophene and dibenzothiophene complexes containing a manganese tricarbonyl moiety coordinated to a carbocyclic ring have been synthesized. Reaction of these with the mild nucleophile Pt(PPh₃)₂(C₂H₄) leads to rapid room-temperature insertion of Pt(PPh₃)₂ into a C-S bond to afford metallathiacyclic complexes. With benzothiophene complexes bearing no substituent at the 2- or at the 3-position, it is shown that initial rapid coordination of the platinum to the C=C bond in the heterocyclic ring takes place prior to insertion into the C(vinyl)-S bond. When a substituent is present at the benzothiophene 2- and/or 3-position, formation of the η²-(C=C) intermediate is blocked, the reaction rate slows, and insertion into the C(aryl)-S bond becomes possible or even dominant. An η¹-S intermediate is suggested in these cases. Insertion into the C-S bond nearer the coordinated ring in dibenzothiophene complexes, even ones alkylated at the 4-and/or 6-positions, occurs rapidly at rates similar to those found for alkylated benzothiphene complexes. Even the normally intractable 4,6-Me₂DBT is remotely activated to rapid C-S bond cleavage by Pt(PPh₃)₂ when precoordinated to the Mn(CO)₃⁺ moiety. On the basis of observed regioselectivities, low-temperature infrared studies, and room-temperature stopped-flow kinetics, a mechanism is proposed for the insertion of platinum into precoordinated benzothiophenes and dibenzothiophenes. The palladium complex Pd(PPh₃)₂(C₂H₄) is capable of inserting into C-C, C-S, and C-Se bonds in coordinated biphenylene, thiophenes, and selenophenes. The X-ray structure of the biphenylene insertion product is reported. It is concluded that the metallacycles formed from Pd(PPh₃)₂(C₂H₄) are in general not as rapidly formed or as stable as those obtained with Pt(PPh₃)₂(C₂H₄). X-ray structures are reported for (η⁵-selenophene)Mn(CO)₃⁺ and its Pt(PPh₃)₂ insertion product.

Full text of DOI:10.1021/om0102448

3550
Organometallics 2001, 20, 3550-3559
Mod els for Deep Hyd r od esu lfu r iza tion (HDS). Rem ote
Activa tion of C-S Bon d s in Alk yla ted Ben zoth iop h en es
a n d Diben zoth iop h en es by Meta l Coor d in a tion to a
Ca r bocyclic Rin g
Kunquan Yu, Huazhi Li, Eric J . Watson, Kurtis L. Virkaitis,
Gene B. Carpenter, and D. A. Sweigart*
Department of Chemistry, Brown University, Providence, Rhode Island 02912
Received March 26, 2001
A series of alkylated benzothiophene and dibenzothiophene complexes containing a
manganese tricarbonyl moiety coordinated to a carbocyclic ring have been synthesized.
Reaction of these with the mild nucleophile Pt(PPh3)2(C2H4) leads to rapid room-temperature
insertion of Pt(PPh3)2 into a C-S bond to afford metallathiacyclic complexes. With
benzothiophene complexes bearing no substitutent at the 2- or at the 3-position, it is shown
that initial rapid coordination of the platinum to the CdC bond in the heterocyclic ring
takes place prior to insertion into the C(vinyl)-S bond. When a substituent is present at
the benzothiophene 2- and/or 3-position, formation of the η2-(CdC) intermediate is blocked,
the reaction rate slows, and insertion into the C(aryl)-S bond becomes possible or even
dominant. An η1-S intermediate is suggested in these cases. Insertion into the C-S bond
nearer the coordinated ring in dibenzothiophene complexes, even ones alkylated at the 4-
and/or 6-positions, occurs rapidly at rates similar to those found for alkylated benzothiphene
complexes. Even the normally intractable 4,6-Me2DBT is “remotely activated” to rapid C-S
+
bond cleavage by Pt(PPh3)2 when precoordinated to the Mn(CO)3 moiety. On the basis of
observed regioselectivities, low-temperature infrared studies, and room-temperature stopped-
flow kinetics, a mechanism is proposed for the insertion of platinum into precoordinated
benzothiophenes and dibenzothiophenes. The palladium complex Pd(PPh3)2(C2H4) is capable
of inserting into C-C, C-S, and C-Se bonds in coordinated biphenylene, thiophenes, and
selenophenes. The X-ray structure of the biphenylene insertion product is reported. It is
concluded that the metallacycles formed from Pd(PPh3)2(C2H4) are in general not as rapidly
formed or as stable as those obtained with Pt(PPh3)2(C2H4). X-ray structures are reported
+
for (η5-selenophene)Mn(CO)3 and its Pt(PPh3)2 insertion product.
In tr od u ction
contamination in fossil fuels can be traced to these
species. For this reason, the successful processing of
such thiophenic materials is termed “deep hydrodes-
ulfurization”.
The hydrodesulfurization (HDS) of petroleum feed-
stocks is a heterogeneous reaction of major industrial
importance that is practiced on a massive scale.1
Removal of sulfur from organosulfur molecules occur-
ring in petroleum is essential for both industrial and
environmental reasons, and recent federal regulations
aim to severely limit sulfur oxide emissions from
gasoline and diesel fuels. The sulfur-containing mol-
A variety of organometallic systems have been studied
as models for the homogeneous HDS of thiophenes.3 The
key steps include cleavage of a C-S bond by metal
insertion, hydrogenolysis of the M-C bonds, and elimi-
nation of RSH or H2S. Thiophenes are relatively unre-
active because the sulfur atom is a very weak donor,
and they become even less reactive when there are
substitutents near the sulfur that offer steric interfer-
ence. A few studies of C-S bond cleavage and/or
desulfurization of alkylated DBTs with nucleophilic
metal species have appeared.4-6 With the most intrac-
table substrate, 4,6-Me2DBT, some success has been
noted with reactive nickel and platinum reagents.5,6
ecules benzothiophene (BT) and dibenzothiophene (DBT)
are of special interest because their alkylated deriva-
tives are difficult to desulfurize.1,2 This is particularly
true of DBTs, and consequently, much of the sulfur
(2) (a) Shih, S. S.; Mizahi, S.; Green, L. A.; Sarli, M. S. Ind. Eng.
Chem. Res. 1992, 31, 1232. (b) Topsøe, H.; Gates, B. C. Polyhedron
1997, 16, 3212.
(3) (a) Sanchez-Delgado, R. A. J . Mol. Catal. 1994, 86, 287. (b)
Angelici, R. J . Polyhedron 1997, 16, 3073. (c) Angelici, R. J . Organo-
metallics 2001, 20, 1259. (d) Bianchini, C.; Meli. J . Chem. Soc., Dalton
Trans. 1996, 801. (e) Bianchini, C.; Meli, A. Acc. Chem. Res. 1998, 31,
109. (f) Rauchfuss, T. B. Prog. Inorg. Chem. 1991, 39, 259.
(1) (a) Topsøe, H.; Clausen, B. A.; Massoth, F. E. Hydrotreating
Catalysis; Springer: Berlin, 1996. (b) Petroleum Chemistry and Refin-
ing; Speight, J . G., Ed.; Taylor & Francis: Washington, DC, 1998.
10.1021/om0102448 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 07/07/2001

Models for Deep HDS Remote Activation of C-S Bonds
Sch em e 1
Organometallics, Vol. 20, No. 16, 2001 3551
However, other reagents that normally cleave C-S
bonds do not do so with 4,6-Me2DBT and lead instead
to C-H activation or simple η1-S binding.4a,b
this “remote activation” of the thiophene ring in 4 can
be achieved with a number of electrophilic MLn moi-
eties: Mn(CO)3+, FeCp+, RuCp+, Ru(C6Me6)2+, and Cr-
(CO)3.8 As a result, the C-S bonds in 4 become far more
A considerable amount of research has been directed
at C-S bond cleavage reactions of benzothiophenes.
Most studies have utilized highly reactive coordinatively
unsaturated nucleophilic metal fragments, which gener-
ally insert into the C(vinyl)-S bond in 1 to afford the
metallathiacycle 2. Insertion into the stronger C(aryl)-S
bond in free benzothiophene to afford 3 has not been
observed. However, there are several reported cases of
susceptible to nucleophilic cleavage than in the corre-
sponding free BTs. For example, even the mild nucleo-
phile Pt(PPh3)2, generated from Pt(PPh3)3 or Pt(PPh3)2-
(C2H4), reacts rapidly at room temperature with 4 (MLn
) Mn(CO)3+) to give the corresponding metallathiacycle,
as depicted in Scheme 1. In comparison, Pt(PPh3)2(C2H4)
does not react with free BT, and the far more nucleo-
philic Pt(PEt3)3, which does react with free BT and DBT,
reaches equilibrium only after several hours at 80 °C.9
As can be seen in Scheme 1, (η6-BT)Mn(CO)3+ reacts
with Pt(PPh3)2 to give the C(vinyl)-S insertion product,
while both the 2-MeBT and DBT analogues lead initially
to fission of the C-S bond nearer the coordinated
carbocyclic ring. In solution, these initial products
undergo a subsequent very slow spontaneous decarbo-
nylation as the sulfur in the metallathiacyclic ring
attacks the manganese center.10 This CO substitution
reaction can be made “instantaneous” by using the
decarbonylating agent Me3NO.
In the present study, we examine more closely the
effect of alkylation on the insertion of Pt(PPh3)2 into
C-S bonds in coordinated BT and DBT complexes. It
is shown, for example, that even 4,6-Me2DBT reacts
rapidly in this manner. The regiochemistry that is
obtained in these reactions is discussed with reference
to possible mechanisms of C-S bond cleavage. A key
mechanistic question concerns the presence of platinum-
C(aryl)-S bond insertions in 2-MeBT. Thus, Cp*Rh-
(PMe3) reacts to give 2 as the kinetic product, which
then undergoes an intramolecular isomerization to a
mixture of 2 and 3.7 Similarly, Pt(PEt3)2 is reported6 to
give 2 as an initial product, which subsequently rear-
ranges to 3 and then dimerizes with loss of a PEt3 ligand
to give a complex whose X-ray structure proves that the
C(aryl)-S bond was broken. In the latter case, however,
the complex formulated as 2 was not proven to have this
structure and in our view could quite possibly have
been, in fact, the isomer 3. Whether the reasons are
thermodynamically or kinetically based, the conclusion
from these two studies is that the 2-methyl substituent
provides the steric environment responsible for the
eventual formation of a C(aryl)-M-S linkage.
An alternative to the use of highly reactive transition
metal fragments to cleave C-S bonds in BT and DBT
systems is to activate the heterocyclic ring by precoor-
dination of a metal to a carbocyclic ring. For example,
(4) (a) Myers, A. W.; J ones, W. D. Organometallics 1996, 15, 2905.
(b) Bianchini, C.; Casares, J . A.; Masi, D.; Meli, A.; Pohl, W.; Vizza, F.
J . Organomet. Chem. 1997, 541, 143. (c) Vicic, D. A.; J ones, W. D. J .
Am. Chem. Soc. 1999, 121, 7606.
(5) Vicic, D. A.; J ones, W. D. Organometallics 1998, 17, 3411.
(6) Are´valo, A.; Berne`s, S.; Garc´ıa, J . J .; Maitlis, P. M. Organome-
tallics 1999, 18, 1680.
(8) Dullaghan, C. A.; Zhang, X.; Greene, D. L.; Carpenter, G. B.;
Sweigart, D. A.; Camiletti, C.; Rajaseelan, E. Organometallics 1998,
17, 3316.
(9) Garcia, J . J .; Mann, B. E.; Adams, H.; Bailey, N. A.; Maitlis, P.
M. J . Am. Chem. Soc. 1995, 117, 2179.
(7) Myers, A. W.; J ones, W. D.; McClements, S. M. J . Am. Chem.
Soc. 1995, 117, 11704.
(10) Li, H.; Carpenter, G. B.; Sweigart, D. A. Organometallics 2000,
19, 1823.

3552 Organometallics, Vol. 20, No. 16, 2001
Yu et al.
Ch a r t 1
converted the aryl species into a dicarbonyl product, in
analogy with that shown in Scheme 1 for 5b, while the
vinyl species decomposed. The formation of a 1:1 aryl:
vinyl mixture from 5c suggests that steric congestion
in the vicinity of the sulfur atom, as in 2-MeBT, is not
necessarily required to access C(aryl)-S insertion. This
matter is discussed further below. Interestingly, reac-
tion of Pt(PPh3)2(C2H4) with (η6-3-MeBT)Mn(CO)2-
[P(OEt)3]+ gave only vinyl insertion, possibly because
the phosphite ligand sterically limits access to the
C(aryl)-S bond.
Reaction of the 2,3-Me2BT complex 5f gave conversion
to the anticipated aryl product only, along with a trace
amount of the bimetallic 7f (νCO ) 1985, 1775 cm-1).
The bimetallic, which cannot be isolated because it
readily reverts to reactants upon attempted precipita-
tion, arises from nucleophilic attack of the platinum on
a carbonyl ligand. This type of reaction is, in fact, the
bonded η1-S and/or η2-(CdC) intermediates. These
generic types of species are thought to occur prior to
insertion and prior to hydrogenation, respectively, under
HDS conditions. Low-temperature IR and room-tem-
perature stopped-flow kinetics were used to investigate
the probable role of such intermediates in the insertion
reaction. We also report results concerning the use of a
palladium(0) nucleophile to effect C-S fission and the
use of both Pt(0) and Pd(0) in related C-Se cleavage
reactions.
normal one seen when Pt(PPh3)2(C2H4) reacts with
(arene)Mn(CO)3+ complexes.11 It is only when an alter-
native binding site or reaction pathway is available for
the platinum that the bimetallic is not formed. Platinum
insertion into the 3,7-Me2BT complex 5g was found to
cleanly form the vinyl product only, thus demonstrating
that a 7-Me group can influence the regioselectivity. A
trace amount of bimetallic 7g was also formed from the
reaction of 5g. Since a substituent at the 7-position
favors the vinyl product while a substituent at the
2-position favors the aryl product, it was not clear what
to expect from the 2,7-Me2BT complex 5h . In situ IR
spectra showed that Pt(PPh3)2(C2H4) does indeed insert
into 5h . 31P NMR spectra indicated that the primary
product is the aryl metallathiacycle, along with much
smaller amounts of the vinyl isomer and the bimetallic
7h . As expected, treatment of the reaction mixture with
Me3NO converted the aryl product to a dicarbonyl
species (see Scheme 1). Attempted precipitation of the
aryl product by addition of diethyl ether to the reaction
mixture gave only starting complex 5h , which demon-
strates that the insertion/deinsertion is reversible and
rapid in both directions in this case.
Resu lts a n d Discu ssion
P la t in u m In ser t ion in t o Coor d in a t ed Ben zo-
th iop h en es. The BT complexes 5c,d ,f-h , which have
not been previously reported, were easily synthesized
by a standard procedure (see Chart 1 and Experimental
Section). The addition of Pt(PPh3)2(C2H4) to 5a -h at
room temperature in dichloromethane results in rapid
insertion of Pt(PPh3)2 into the C(vinyl)-S bond or the
C(aryl)-S bond, or both. The regiochemistry of platinum
insertion into 5a , 5b, and 5e was shown previously to
occur at C(vinyl)-S, C(aryl)-S, and C(vinyl)-S, respec-
tively, to afford metallathiacycles that were isolated and
characterized by single-crystal X-ray diffraction.8,10
Chart 1 lists the results obtained with these, along with
the previously unreported methylated BT complexes
5c,d ,f-h . The assignment of the C-S cleavage as vinyl
or aryl was based on (1) a distinctive difference between
the 31P NMR chemical shifts and the J P-Pt coupling
constants for vinyl versus aryl insertions with 5a ,b,e
and (2) the observation, shown in Scheme 1, that the
C(aryl) metallathiacycle from 5b undergoes rapid de-
carbonylation with Me3NO to give a stable isolable
product, whereas the C(vinyl) analogue from 5a decom-
poses upon treatment with Me3NO.10
P la tin u m In ser tion in to Coor d in a ted Diben -
zoth iop h en es. Chart 2 lists the DBT complexes stud-
ied, all of which are new except 6a . During the synthesis
+
of 6b and 6c, the Mn(CO)3 moiety was found to
coordinate to both arene rings, but separation of the two
isomers was possible by fractionalization crystallization.
The structure of complex [6c]BF4 was examined by
X-ray crystallography and the atom connectivity was
unequivocally established, although the small size of the
crystal, resulting in very low intensities, and disorder
Complex 5d was included in the study because of a
favorable low-temperature solubility compared to 5a
(vide infra). As expected, the reaction of 5d with Pt-
(PPh3)2(C2H4) resulted in exclusive formation of the
“vinyl” product. It was anticipated that the 3-MeBT
complex 5c would lead to vinyl insertion, but 31P NMR
spectra of the reaction mixture showed a 1:1 mixture
of vinyl and aryl products. This conclusion was con-
firmed by subsequent treatment with Me3NO, which
-
in the BF4 anion combined to limit the refinement to
R1 ) 0.115 and wR2 ) 0.169.
It was shown previously that the parent complex 6a
reacts with Pt(PPh3)2(C2H4) to insert platinum into the
(11) Zhang, X.; Watson, E. J .; Dullaghan, C. A.; Gorun, S. M.;
Sweigart, D. A. Angew. Chem., Int. Ed. 1999, 38, 2206.

Models for Deep HDS Remote Activation of C-S Bonds
Organometallics, Vol. 20, No. 16, 2001 3553
Ch a r t 2
were performed. In the infrared, the relevant species
that may be detected, other than the starting material
and the insertion product, are (1) a platinum-bonded
η2-(CdC) intermediate with the BT systems and (2) the
bimetallic 7. A possible η1-S intermediate may be
important mechanistically, but would likely not be
detected spectroscopically because the sulfur is too weak
a donor. This assumption is supported by the observa-
tion that free benzothiophene does not react with Pt-
(PPh3)2(C2H4). Complexation to Mn(CO)3+ would make
the sulfur an even weaker donor.12 Complexes contain-
ing a thiophenic η1-S bond are known, but generally only
with highly reactive unsaturated systems such as
Cp*Re(CO)2, Cr(CO)5, CpMn(CO)2, etc.12,13
The background information available with which to
compare data obtained with the thiophenic complexes
includes platinum insertion into coordinated benzofuran
and platinum binding to the CdC bond in coordinated
styrenes. Scheme 2 gives the mechanism observed for
insertion into the C-O bond in the benzofuran complex
9.11 In this case there is very rapid coordination of the
platinum to the CdC double bond to give the observable
η2-intermediate 10 prior to slow insertion (t1/2 ≈ 2 h).
The probable role of an η2-intermediate was further
probed in the benzofuran system by studying the
reactions of the 2-methylbenzofuran and 2,3-dihydroben-
zofuran complexes. The former presents steric hin-
drance to η2-coordination at the CdC bond, while the
latter does not possess a CdC bond in the heterocyclic
ring. Neither complex reacted with Pt(PPh3)2(C2H4) to
give C-O bond fission, but rather gave bimetallics
analogous to 7, e.g., [(η6-2-methylbenzofuran)Mn(CO)-
(µ-CO)2Pt(PPh3)2]+. Furthermore, in neither case were
any reaction intermediates detectable by IR.11 These
observations support the mechanism indicated in Scheme
2, in which an η2-intermediate is on the lowest energy
reaction pathway to C-O fission. If access to this
intermediate is blocked, the kinetically favored product
becomes the bimetallic (7).
C-S bond nearer the coordinated ring and that the
resulting metallathiacycle can be converted with Me3-
NO to the dicarbonyl, as outlined in Scheme 1.10 With
the alkylated complexes in Chart 2, we were interested
in seeing if they would insert platinum at all and, if so,
at what rate and with what regiochemistry. With 6b
and 6c the insertion reaction occurred rapidly at room
temperature and in good yield. The regiochemistry was
established by reacting the product from 6c with Me3-
NO according to eq 1. The dicarbonyl thus formed (8c)
was fully characterized spectroscopically and by MS and
EA. For steric reasons, formation of a dicarbonyl product
is consistent only with the platinum having inserted into
the C-S bond indicated.10
Binding of Pt(PPh3)2 to the exocyclic CdC bond in the
styrene complexes 11a -d was recently reported.14 As
In view of the results with 6b,c, one would expect that
the 4,6-dialkylated DBT complexes 6d -e would undergo
cleavage of the C-S bond nearer the coordinated ring.
In the case of 6d , solution IR spectra taken after the
addition of Pt(PPh3)2(C2H4) indicated that rapid inser-
tion had taken place. However, attempted precipitation
with diethyl ether yielded only starting cation, 6d . As
with the 2,7-Me2BT analogue discussed above, it is
concluded that the insertion/deinsertion steps are re-
versible and relatively rapid. Proof that insertion into
6d had taken place was obtained by treatment of the
reaction mixture with Me3NO, which produced a good
yield of dicarbonyl complex 8d , which was fully char-
acterized. The 4,6-Et2DBT complex 6e reacted with Pt-
(PPh3)2(C2H4) to give a mixture of insertion and bime-
tallic products in a ratio of ca. 2:1, the latter (7e) arising
from attack on a CO ligand by the platinum.
expected, it was found that precoordination of the Mn-
+
(CO)3 moiety greatly facilitates the platinum η2-(Cd
C) binding. In the insertion reaction with (η6-BT)Mn-
+
(CO)3 (5a ), the environment in the vicinity of the Cd
C bond that is available to the platinum for possible
initial coordination is most closely approximated by the
cis-â-methylstyrene complex 11b. It is relevant to note,
therefore, that free cis-â-methylstyrene does not react
with Pt(PPh3)2(C2H4), but 11b reacts rapidly and com-
pletely under ordinary experimental conditions. Com-
plex 11c behaves likewise. The most sterically encum-
bered system, 11d , fails to give a detectable η2-(CdC)
(12) Rudd, J . A.; Angelici, R. J . Inorg. Chim. Acta 1995, 240, 393.
(13) (a) Choi, M.-G.; Angelici, R. J . Organometallics 1992, 11, 3328.
(b) Reynolds, M. A.; Guzei, I. A.; Logsdon, B. C.; Thomas, L. M.;
J acobson, R. A.; Angelici, R. J . Organometallics 1999, 18, 4075.
(14) Zhang, X.; Yu, K.; Carpenter, G. B.; Sweigart, D. A.; Czech, P.
T.; D’Acchioli, J . S. Organometallics 2000, 19, 1201.
In ter m ed ia tes a n d th e Rea ction Mech a n ism . To
probe the mechanism of platinum insertion into the BT
and DBT complexes, a series of low-temperature infra-
red and room-temperature stopped-flow experiments

3554 Organometallics, Vol. 20, No. 16, 2001
Yu et al.
Sch em e 2
that η2-(CdC) coordination is not on the insertion
reaction pathway for these hindered complexes. Looking
at the hindered BTs, it is striking that mono- and
dialkylation cause about the same rate reduction, with
barely a factor of 2 separating the six hindered BTs
listed! To us, the only conclusion is that any alkylation
at the 2- and/or 3-position shuts down the possibility of
η2-(CdC) bonding. If there is any intermediate in the
insertion reactions of these hindered systems, it is
probably of the η1-S type. The similarity in rate of
2-MeBT and 3-MeBT complexes could be taken as
evidence for the absence of an η1-S intermediate due to
anticipated differential steric hindrance. However, X-ray
structures of simple η1-S-M thiophenic complexes
generally show the metal “M” moiety to be well out of
the thiophene plane, so that the effects of methyl
substituents at the 2- and 3-positions need not be either
large or much different. The same reasoning applies to
any η1-S intermediate occurring with the dibenzo-
thiophenes. As Table 1 shows, there is, incredibly, only
a factor of about 2 separating the rates of insertion into
the DBT and 4,6-Me2DBT complexes.
We suggest that the most likely mechanism for all
DBT and hindered BT complexes involves an η1-S
intermediate. The unhindered complexes (BT, 5-MeBT,
7-MeBT) must have available a different lower energy
pathway. This follows because the mechanism obeyed
by the former must also be available to the latter. That
the latter react so much more rapidly means that they
follow a pathway unavailable to the hindered com-
plexes.15 Results with benzofuran and styrene com-
plexes mentioned above lead one to predict confidently16
that an η2-(CdC) intermediate should be rapidly formed
when the unhindered complexes and Pt(PPh3)2(C2H4)
are mixed. In turn, it follows that the η2-(CdC) complex
must be a true intermediate and not represent a dead-
end; otherwise the unhindered complexes would be the
slowest to react, not the fastest. The vinyl insertion
obtained with unhindered systems (BT, 5-MeBT, 7-MeBT)
has the regiochemistry expected from an η2-intermedi-
ate that converts directly to insertion product. If the
intermediate is of the η1-S type, however, it appears that
either vinyl or aryl insertion is kinetically viable.
The regiochemical and infrared data presented above
suggest, very simply, that BT complexes 5 that are
unsubstituted at the CdC bond react with Pt(PPh3)2-
(C2H4) via initial rapid formation of an η2-(CdC) inter-
mediate that subsequently converts directly to product.
This intermediate cannot form with DBT or appropri-
Ta ble 1. Ap p r oxim a te Ha lf-Lives in Min u tes a t
-20 °C for In ser tion of P la tin u m in to a C-S Bon d
+
in (η6-Th iop h en e)Mn (CO)3 Com p lexesa
thiophene
half-life
thiophene
half-life
5-MeBT
7-MeBT
2-MeBT
3-MeBT
2,3-Me2BT
2,3-Et2BT
fastb
fastb
41/2
6
6
6
2,7-Me2BT
3,7-Me2BT
DBT
4,6-Me2DBT
4,6-Et2DBT
10
51/2
11/2
31/2
7
a
Measured by IR in dichloromethane solvent with 2 equiv of
-
Pt(PPh3)2(C2H4) per equivalent of manganese complex (as the BF4
b
salt). Half-life , 30 s.
species, reacting instead via attack at a CO to afford
the bimetallic [(η6-â-dimethylstyrene)Mn(CO)(µ-CO)2Pt-
(PPh3)2]+.
In view of the results noted above for the benzofuran
and styrene reactions, and in view of the demonstrated
existence of η2-(CdC) complexes with benzothiophene,3,12
it is reasonable to speculate that the mechanism in
Scheme 2 may be applicable to the platinum C-S
insertion reaction with (η6-BT)Mn(CO)3+ (5a ). In other
words, oxidative addition into the C-S bond is preceded
by η2-coordination to the CdC bond. It must be noted,
however, that the benzofuran and benzothiophene sys-
tems differ sharply in that methyl substituents at the
benzothiophene 2- and/or 3-positions do not prevent the
insertion reaction. This could be interpreted to mean
that η2-(CdC) coordination is not required for C-S
insertion in BT complexes. Obviously, the fact that the
reaction occurs with DBT analogues also argues for an
accessible pathway not incorporating η2-binding.
The platinum insertion reactions were followed in the
infrared at -20 °C using a fiber optic probe. The results
are presented in Table 1. At higher temperatures, the
reactions were too rapid to be conveniently tracked, and
at lower temperatures the reactions were either too slow
or solubility problems arose. The “half-life” values listed
in Table 1 refer to the time for half of the reactant (5 or
6) to be converted to product. The conditions were not
strictly pseudo-first-order, so that the half-lives are only
semiquantitative absolutely, but in a relative sense they
are highly meaningful. It may be seen that the BT
complexes unhindered to η2-(CdC) coordination (5-
MeBT, 7-MeBT) react very rapidly, with only final
product being observed as fast as the first IR spectrum
collection could be completed (ca. 30 s). For all of the
other reactions listed in Table 1, it was possible to follow
the time evolution of the products, and in no case were
any intermediate species observed. The lack of any
detectable η2-(CdC) intermediate in any of the systems
slow enough to be followed is entirely consistent with
the benzofuran and styrene results given above.
From a first glance at the data one would not conclude
very much mechanistically about the unhindered sys-
tems, 5-MeBT and 7-MeBT (but see below). However,
the results for the other thiophenes suggest strongly
(15) Inherent is the assumption that the hindered and unhindered
complexes would not differ greatly in the rate of formation of any η1-S
intermediate or in its conversion to insertion product. This assumption
is supported by the observed small effect that multiple alkylation has
on the insertion rate of the hindered BT systems.
(16) IR spectra obtained at -20 °C under conditions identical to that
in Table 1 showed that Pt(PPh3)2(C2H4) coordinates to (η6-benzofuran)-
Mn(CO)3+ in an η2-(CdC) fashion at a rate too large to measure by IR
(t1/2 , 30 s). Subsequent stopped-flow experiments were performed at
room temperature (vide supra).

Models for Deep HDS Remote Activation of C-S Bonds
Organometallics, Vol. 20, No. 16, 2001 3555
ately substituted (hindered) BT complexes, and accord-
ingly, these are forced to follow a different reaction
pathway, possibly one containing an η1-S intermediate.
To further test these conclusions, we performed room-
temperature stopped-flow experiments with a variety
of (arene)Mn(CO)3+ complexes reacting with Pt(PPh3)2-
(C2H4). These were conducted in dichloromethane under
nitrogen, with the manganese complex at about 1.0 mM
and with a slightly higher concentration (ca. 1.1 mM)
of Pt(PPh3)2(C2H4). The purpose of these experiments
was to search for intermediates and obtain a semiquan-
titative relative reactivity order and not to determine
accurate rate constants, which would have been difficult
in any case due to the sensitivity of the solutions.
F igu r e 1. Crystal structure of the cation in [12]BF4.
Selected bond lengths (Å) and angles (deg): Se-C(2) 1.877-
(4), Se-C(5) 1.883(4), Mn-Se 2.4298(6), Mn-C(2) 2.160-
(3), Mn-C(3) 2.161(3), Mn-C(4) 2.157(3), Mn-C(5) 2.159-
(3), O(1)-C(6)-Mn 178.3(3), O(2)-C(7)-Mn 177.8(3), O3-
C(8)-Mn 176.6(4).
Complexes 11a ,b,d gave a clean single-step optical
density change when mixed with Pt(PPh3)2(C2H4). The
times required for half of the reactant to be consumed
(t1/2) were as follows: 11a (5 ms), 11b (40 ms), 11d (1.2
s). The first two reactions involve only coordination to
the CdC bond, and the stopped-flow results prove that
this is very rapid, as previously thought. The somewhat
slower reaction of 11b compared to 11a is due to the
â-methyl substituent. The much slower reaction of 11d
reflects the fact that this complex is sterically prevented
from forming a η2-(CdC) product and forms instead the
bimetallic [(η6-â-dimethylstyrene)Mn(CO)(µ-CO)2Pt-
results corroborated the IR results with direct spectral
evidence for this intermediate when predicted to be
present, as well as for its absence when so predicted. It
is concluded that C-S bond cleavage occurs substan-
tially more rapidly when initial η2-coordination to the
platinum is possible, but such coordination is not
required for insertion.
P la tin u m In ser tion in to C-Se Bon d s. Angelici
has shown17 that selenophene and thiophene act simi-
larly with respect to metal coordination to the π-system.
Likewise, the insertion of a metal into a C-Se bond in
selenophene occurs similarly to C-S bond insertion in
thiophene.17,18 We thought it worthwhile to examine the
effect of metal coordination to the π-system on the ease
of C-Se fission in selenophene and benzoselenophene.
It was found that the nucleophile Pt(PPh3)2(C2H4)
inserts rapidly and cleanly into 12 and 13 to afford the
metallaselenacycles 14 and 15, respectively. Complex
(PPh3)2]+. The same type of bimetallic complex forma-
+
tion occurs in the reaction with (mesitylene)Mn(CO)3
,
which gave a t1/2 of 3 s. The benzofuran complex 9 is
known11 to initially form a mixture of η2-(CdC) and
bimetallic species that ultimately convert to insertion
product. In accordance with this, the kinetics showed
two hard-to-separate steps, with the slower one having
a t1/2 of 1.3 s and the faster one roughly estimated as
ca. a factor of 10 shorter. With (η6-dihydrobenzofuran)-
Mn(CO)3+, which has no CdC bond, only bimetallic (7)
formation was observed with t1/2 ) 1.5 s.
The results with the styrene and benzofuran com-
plexes establish the kind of rate to expect for η2-(CdC)
formation and for formation of the bimetallic 7. The
eight thiophene complexes, 5b,c,f-h and 6a ,d ,e, all of
which can be classified as “hindered” with respect to η2-
(CdC) formation, gave a single optical density change
with t1/2 values in the 1.5-4 s range. IR spectra of
product solutions verified that insertion had occurred
in each case. With the two “unhindered” complexes
studied by the stopped-flow method, namely, (η6-5-
+
+
MeBT)Mn(CO)3 (5d ) and (η6-7-MeBT)Mn(CO)3 (5e),
the kinetic behavior was quite different. Instead of a
single “slow” step, the reaction of 5d and of 5e produced
a two-step optical density change in each case. For both
complexes the t1/2 was estimated as ca. 70 ms for the
first step and 280 ms for the second step. On the basis
of the results given above for the styrene complex 11b,
the 70 ms time is nicely in the range of what would be
expected for the postulated η2-(CdC) coordination to
platinum. We suggest that the second (280 ms) step is
due to the insertion into the C(vinyl)-S bond, which is
accelerated by about a factor of 10 over that found for
the hindered complexes under our experimental condi-
tions.
12 was reported previously.17 Herein a higher yield
synthesis is presented, along with the X-ray structure
of [12]BF4, shown in Figure 1 and tabulated in Table 2.
The structure of 12 is analogous to that reported17 for
(η5-2,5-dimethylselenophene)Cr(CO)3, with the selenium
atom slightly (0.13 Å) out of the plane of the ring carbon
atoms. The C-Se bond lengths are longer by about
0.025 Å than that found in free selenophene. The X-ray
structure of [14]BF4, the product of platinum insertion
into a C-Se bond in 12, is shown in Figure 2. In 14,
the C(2)-C(3)-C(4)-C(5)-Se atoms are nearly planar
(mean deviation 0.039 Å), with the platinum atom
displaced 0.88 Å from this plane. This contrasts with
(17) White, C. J .; Angelici, R. J .; Choi, M.-G. Organometallics 1995,
14, 332.
(18) Vicic, D. A.; Myers, A. W.; J ones, W. D. Organometallics 1997,
16, 2751.
The low-temperature infrared studies provided strong
evidence for the existence of an η2-intermediate in some
cases and for its absence in others. The stopped-flow

3556 Organometallics, Vol. 20, No. 16, 2001
Ta ble 2. Cr ysta llogr a p h ic Da ta for [12]BF 4, [14]BF 4‚CH2Cl2, a n d [16]BF 4‚CH2Cl2
Yu et al.
[12]BF4
[14]BF4‚CH2Cl2
[16]BF4‚CH2Cl2
formula
fw
C7H4BF4MnO3Se
356.81
C44H36Cl2BF4MnO3P2PtSe
1161.37
C52H40Cl2BF4MnO3P2Pd
1093.83
temp
298
298
298
wavelength
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
0.71073
monoclinic
P21/n
12.0723(13)
7.3028(8)
12.7774(14)
90
103.618(2)
90
1094.8(2)
4
2.165
4.575
680
0.71073
triclinic
P1
0.71073
monoclinic
P21/n
15.2761(18)
10.7032(12)
30.097(4)
90
100.903(2)
90
4832.2(10)
4
1.504
0.868
2208
10.9840(9)
13.7558(12)
16.0753(14)
74.4470(10)
75.1980(10)
79.6590(10)
2246.2(3)
2
Z
d
calcd, g cm-3
1.717
4.447
1132
µ, mm-1
F(000)
cryst dimens, mm
θ range, deg
no. of reflns collected
no. of indept reflns
no. of data/restraints/params
GOF on F2
0.36 × 0.34 × 0.26
2.09-28.28
16 039
2629 (Rint ) 0.0521)
2629/0/154
1.071
0.25 × 0.24 × 0.21
1.80-28.36
35 923
10 768 (Rint ) 0.0515)
10 768/4/522
1.087
0.26 × 0.20 × 0.15
2.02-26.55
64 982
10 014 (Rint ) 0.0654)
10 014/0/595
1.191
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
0.0384, 0.1031
0.0436, 0.1085
0.0535, 0.1434
0.0708, 0.1612
0.0571, 0.1206
0.0806, 0.1324
BT analogue, and as would be expected, complex 13
rapidly inserted Pt(PPh3)2 into a C-Se bond to give a
high yield of the metallaselenacycle 15.
P a lla d iu m In ser tion in to C-C, C-S, a n d C-Se
Bon d s. The palladium analogue19 of the platinum
nucleophile utilized in the reactions described above, Pd-
(PPh3)2(C2H4), was briefly investigated in order to
compare the chemical behavior and relative usefulness
of these two systems. The strained C-C bond in
biphenylene becomes especially susceptible to cleavage
when precoodinated by the manganese tricarbonyl frag-
ment.20 It was found that Pd(PPh3)2(C2H4) inserts into
(η6-BP)Mn(CO)3+ to afford a good yield of the insertion
product 16. Interestingly, monitoring the reaction in
dichloromethane by IR spectroscopy showed that the
dimetallic 17 formed initially (νCO ) 1996, 1818 cm-1
)
and then converted over an hour at room temperature
to 16. The formation of 17 is reversible, and the reaction
F igu r e 2. Crystal structure of the cation in [14]BF4.
Selected bond lengths (Å) and angles (deg): Se-C(5) 1.869-
(11), Pt-Se 2.4219(10), Pt-C(2) 2.256(5), Pt-P(1) 2.3477-
(19), Pt-P(2) 2.2927(18), Mn-Se 2.4840(17), Mn-C(2)
2.430(6), Mn-C(3) 2.214(13), Mn-C(4) 2.167(10), Mn-C(5)
2.108(11), C(2)-Pt-Se 85.55(14), Se-Pt-P(1) 86.82(5),
P(1)-Pt-P(2) 96.79(7), C(2)-Pt-P(2) 90.92(15), C(2)-Pt-
P(1) 171.61(15), Se-Pt-P(2) 176.14(5).
the structure of the product of Cp*Rh(PMe3) insertion
into selenophene, in which the six-membered metalla-
selenacyclic ring is planar.18 The coordination geometry
about the platinum in 14 is planar (mean deviation
0.042 Å). The chemical shifts for the 77Se NMR spectra
of 12 and 14 occur at 276 and -246 ppm relative to
selenophene, which is assigned at 605 ppm.17 This
upfield shift of 522 ppm upon platinum insertion is
consistent with the loss of conjugation in the nonplanar
heterocyclic ring present in 14.
system eventually transforms to the thermodynamically
favored product, 16. The bimetallic 17 is analogous to
7 in the case of platinum and arises from nucleophilic
attack at a carbonyl. The palladium nucleophile seems
to be considerably more prone generally than is the
(19) Visser, A.; van der Linde, R.; de J ongh, R. O. Inorg. Synth. 1976,
16, 127.
(20) Zhang, X.; Carpenter, G. B.; Sweigart, D. A. Organometallics
1999, 18, 4887.
J ust as with benzothiophene, precoordination of Mn-
+
(CO)3 to the carbocyclic ring in benzoselenophene to
afford 13 was easily achieved. Also in analogy with the

Models for Deep HDS Remote Activation of C-S Bonds
Organometallics, Vol. 20, No. 16, 2001 3557
F igu r e 3. Crystal structure of the cation in [16]BF4. The phenyl groups are omitted in (B) for clarity. Selected bond
lengths (Å) and angles (deg): Pd-C(1) 2.078(4), Pd-C(12) 2.089(4), Pd-P(1) 2.3892(12), Pd-P(2) 2.3601(11), C(6)-C(7)
1.463(6), C(1)-C(6) 1.425(6), C(12)-C(7) 1.412(6), Mn-C(1) 2.308(4), Mn-C(2) 2.186(5), Mn-C(3) 2.179(5), Mn-C(4) 2.182-
(5), Mn-C(5) 2.190(5), Mn-C(6) 2.242(5), C(1)-Pd-C(12) 80.15(17), C(1)-Pd-P(1) 90.48(13), P(1)-Pd-P(2) 97.10(4), C(12)-
Pd-P(2) 95.41(12), P(1)-Pd-C(12) 158.59(12), P(2)-Pd-C(1) 168.45(12).
platinum to form the bimetallic species with (arene)-
Con clu sion s
+
Mn(CO)3 complexes. For example, Pt(PPh3)2(C2H4)
On the basis of substituent effects on regioselectivity
and on rate studies, it is concluded that C-S bond
cleavage in (η6-BT)Mn(CO)3+ proceeds via initial rapid
coordination of the Pt(PPh3)2 nucleophile to the CdC
bond in the heterocyclic ring, followed by rapid insertion
into the C(vinyl)-S bond. When a substituent is present
at the benzothiophene 2- and/or 3-position, formation
of the η2-(CdC) intermediate is blocked, the reaction
rate slows, and insertion into the C(aryl)-S bond
becomes possible or even dominant. An η1-S intermedi-
ate is suggested in these cases. Insertion into the C-S
bond nearer the coordinated ring in dibenzothiophene
complexes, even ones alkylated at the 4- and/or 6-posi-
tions, occurs rapidly at rates similar to those found for
alkylated benzothiphene complexes. Thus, even the
normally intractable 4,6-Me2DBT is “remotely acti-
vated” to rapid C-S bond cleavage by Pt(PPh3)2 when
reacts completely with (η6-BP)Mn(CO)3 to give 18 as
+
the sole product within 1 min at room temperature,
without any evidence of bimetallic formation.20
Platinum and palladium also differ in that a solution
of the insertion product 18 slowly (weeks) eliminates
PPh3 to give 19. It was postulated that formation of 19,
which was characterized by X-ray diffraction, may be
sterically driven. With palladium, it was possible to
obtain good crystals of the bis-phosphine insertion
product, and the X-ray structure of 16 is shown in
Figure 3. The five-membered metallacyclic ring C1-
C6-C7-C12-Pd is fairly planar (mean deviation 0.058
Å). The most interesting feature of the structure of 16
is the large deviation from planar coordination around
the palladium. This is especially apparent in Figure 3B,
which shows a P(1) phosphorus that is 1.0 Å out of the
plane of the metallacyclic ring. It is presumed that this
large deviation from the expected planarity is attribut-
able to steric congestion in 16.
+
precoordinated to the Mn(CO)3 moiety. These results
suggest that η6-coordination of BTs and DBTs on a Mo/
Co sulfide heterogeneous HDS catalyst constitutes a
viable mechanism for C-S activation prior to insertion
and subsequent hydrogenolysis.
The palladium complex Pd(PPh3)2(C2H4) is capable of
inserting into C-C, C-S, and C-Se bonds in coordi-
nated biphenylene, thiophenes, and selenophenes. How-
ever, it is concluded that the resulting matallacyclic
products are in general not as rapidly formed or as
stable as those obtained with Pt(PPh3)2(C2H4).
Pd(PPh3)2(C2H4) reacted with the styrene complexes
11b,c by coordinating to the CdC bond, but upon
attempted isolation, the products reverted back to
reactants 11b,c. With (η5-thiophene)Mn(CO)3+ and (η6-
benzothiophene)Mn(CO)3+, Pd(PPh3)2(C2H4) did react to
give C-S insertion, but again attempted precipitation
of products with diethyl ether merely reversed the
insertion. With 2-MeBT, 3-MeBT, and DBT systems (5b,
5c, 6a ), the only observable product was the bimetallic
analogue of 17. Pd(PPh3)2(C2H4) was found to insert
Exp er im en ta l Section
Gen er a l P r oced u r es. Standard materials were purchased
from commercial sources and used without further purification.
Solvents were HPLC grade and opened under nitrogen.
Literature methods were used to synthesize Pt(PPh3)2(C2H4),21
Pd(PPh3)2(C2H4),19 [η6-biphenylene)Mn(CO)3]BF4,22 complexes
5a -c,e and 6a ,23 7-MeBT,24 3,7-Me2BT,25 2,3-Me2BT,26 2,7-Me2-
BT,27 and dibenzothiophenes 4-MeDBT, 4-EtDBT, and 4,6-Et2-
DBT.28 31P NMR chemical shifts are relative to a 85%
phosphoric acid external reference. 77Se chemical shifts are
relative to selenophene external reference, assigned a value
cleanly into a C-Se bond in (η5-selenophene)Mn(CO)3
+
to give the palladium analogue of 14, which was isolated
and characterized (see Experimental Section).

3558 Organometallics, Vol. 20, No. 16, 2001
Yu et al.
of 605 ppm.17 Low-temperature IR experiments were per-
formed using a Remspec IR fiber optic immersion probe.
Syn th esis of Ben zoth iop h en e Com p lexes 5d ,f-h . These
complexes were easily made by a procedure essentially identi-
cal to that used for 5a -c.23 For [5d ]BF4: Yield 90%. IR (CH2-
Cl2): νCO 2074 (s), 2016 (s, br) cm-1. 1H NMR (CD2Cl2): δ 8.29
(d, J ) 5.5, 1H), 7.67-7.58 (m, 2H), 7.22 (s, H4), 6.36 (d, J )
6.9, 1H), 2.57 (s, Me). Anal. Calcd for C12H8SMnO3BF4: C,
38.54; H, 2.16. Found: C, 38.95; H, 2.17. For [5f]BF4: Yield
done at room temperature under nitrogen, typically with about
50 mg of thiophene complex and a slight molar excess of Pt-
(PPh3)2(C2H4). In ser tion in to 5c: In situ 31P NMR showed a
1:1 mixture of vinyl and aryl insertion products IR (CH2Cl2):
νCO 2058 (s), 2004 (s, br) cm-1 31P NMR (CD2Cl2) for vinyl
.
product: δ 27.35 (dd J P-P ) 22, J Pt-P ) 3485), 20.27 (dd, J P-P
) 22, J Pt-P ) 1890). 31P NMR (CD2Cl2) for aryl product: δ 25.55
(dd J P-P ) 20, J Pt-P ) 3160), 15.28 (dd, J P-P ) 20, J Pt-P
)
2130). The addition of Me3NO to a mixture of the isomers was
found to convert the aryl product only to a dicarbonyl species
[IR (CH2Cl2): νCO 1989 (s), 1943 (m) cm-1] in analogy to the
chemistry shown in Scheme 1. In ser tion in to 5d : Yield 75%.
85%. IR (CH2Cl2): νCO 2074 (s), 2016 (s, br) cm-1
(CD3COCD3): δ 7.47 (d, J ) 7.4, H7), 7.12 (d, J ) 7.6, H4),
6.50 (m, H5,6), 2.62 (s, Me), 2.43 (s, Me). Anal. Calcd for C13H10
.
1H NMR
-
SMnO3BF4: C, 40.24; H, 2.60. Found: C, 40.08; H, 2.27. For
IR (CH2Cl2): νCO 2057 (s), 1999 (s, br) cm-1 1H NMR (CD2-
.
[5g]BF4: Yield 85%. IR (CH2Cl2): νCO 2070 (s), 2012 (s, br)
Cl2): δ 7.32-7.16 (m, 32H), 6.54 (d, J ) 6.7, 1H), 6.23 (s, H4),
1
cm-1. H NMR (CD3COCD3): δ 8.33 (s, H2), 7.52 (dd, J ) 6.9,
5.94 (d, J ) 5.5, 1H), 2.31 (s, Me). 31P NMR (CD2Cl2): δ 25.49
0.8, H6), 6.90 (dd, J ) 6.2, 0.8, H5), 6.81 (d, J ) 6.2, H4), 3.06
(s, Me), 2.68 (s, Me). Anal. Calcd for C13H10SMnO3BF4: C,
40.24; H, 2.60. Found: C, 40.15; H, 2.54. For [5h ]BF4: Yield
(dd J P-P ) 23, J Pt-P ) 3410), 21.14 (dd, J P-P ) 23, J Pt-P )
1900). HR MS: M+ (m/z) calcd 1006.1046, obsd 1006.1015.
Anal. Calcd for C48H38SMnO3PtP2BF4: C, 52.72; H, 3.50.
Found: C, 52.80; H, 3.65. In ser tion in to 5f: Yield 70%. IR
(CH2Cl2): νCO 2055 (s), 2003 (s, br) cm-1. 1H NMR (CD2Cl2): δ
7.65-7.03 (m, 30H), 6.58 (d, J ) 7.0, H7), 6.36 (d, J ) 7.0,
H4), 5.78 (t, J ) 5.9, H6), 5.68 (t, J ) 5.9, H5), 2.53 (s, Me),
2.32 (s, Me). 31P NMR (CD2Cl2): δ 25.29 (dd J P-P ) 20, J Pt-P
) 3140), 16.57 (dd, J P-P ) 20, J Pt-P ) 2130). In ser tion in to
85%. IR (CH2Cl2): νCO 2069 (s), 2010 (s, br) cm-1 1H NMR
.
(CD2Cl2): δ 7.28 (s, H3), 7.1 (d, J ) 7.3, H4), 6.52 (t, J ) 7.3,
H5), 6.22 (d, J ) 6.7, H4), 2.86 (s, Me), 2.75 (s, Me). Anal. Calcd
for C13H10SMnO3BF4: C, 40.24; H, 2.60. Found: C, 39.74; H,
2.69.
Syn th esis of Diben zoth ioph en e Com plexes 6b-e. These
complexes were easily made by a procedure essentially identi-
cal to that used for 6a .23 For [6b]BF4: The overall yield was
60%, which consisted of a 3:1 mixture of complexes containing
the metal coordinated to the methylated ring (isomer A) and
the unmethylated ring (isomer B). Isomer A was separated
from the mixture by fractional crystallization from acetone/
5g: Yield 60%. IR (CH2Cl2): νCO 2055 (s), 1996 (s, br) cm-1
.
1H NMR (CD2Cl2): δ 7.36-7.05 (m, 32H), 6.41 (br, 1H), 6.20
(br, 1H), 2.54 (s, Me), 2.49 (s, Me). 31P NMR (CD2Cl2): δ 25.97
(dd J P-P ) 22, J Pt-P ) 3475), 21.02 (dd, J P-P ) 22, J Pt-P
)
1880). In ser tion in to 5h . The reaction mixture was probed
in situ, as attempted precipitation with diethyl ether led to
formation of starting material. IR (CH2Cl2): νCO 2054 (s), 1987
1
diethyl ether. IR (CH2Cl2): νCO 2074 (s), 2016 (s, br) cm-1. H
NMR (CD2Cl2): δ 8.46 (d, J ) 7.5, H9), 8.08 (d, J ) 8.0, H6),
7.86 (m, H7,8), 7.55 (d, J ) 6.4, H1), 6.69 (t, J ) 6.6, H2), 6.50
(d, J ) 6.3, H3), 2.92 (s, Me). Anal. Calcd for C16H10SMnO3-
BF4: C, 45.32; H, 2.38. Found: C, 45.23; H, 2.87. For [6c]BF4:
The overall yield was 67%, which also consisted of a 3:1
mixture of isomers A and B. Isomer A was separated from the
mixture by fractional crystallization from acetone/diethyl
(s, br) cm-1 31P NMR (CD2Cl2): δ 18.46 (dd J P-P ) 20, J Pt-P
. )
3220), 15.00 (dd, J P-P ) 20, J Pt-P ) 2120). Treatment with
Me3NO converted the product to the dicarbonyl 7, thus proving
that the insertion was into C(aryl)-S. In ser tion in to 6b:
Yield 75%. IR (CH2Cl2): νCO 2058 (s), 2007 (s), 1993 (s) cm-1
.
1H NMR (CD2Cl2): δ 7.53-7.06 (m, 34H), 6.02 (d, J ) 6.8, 1H),
5.74 (t, J ) 6.4, 1H), 5.48 (t, J ) 5.8, 1H), 2.29 (s, Me). 31P
NMR (CD2Cl2): δ 16.41 (dd J P-P ) 19, J Pt-P ) 3170), 13.70
(dd, J P-P ) 19, J Pt-P ) 2150).). MS FAB: 1056 (M+). Anal.
Calcd for C52H40SMnO3PtP2BF4: C, 54.61; H, 3.53. Found: C,
54.75; H, 3.64. In ser tion in to 6c: Yield 70%. IR (CH2Cl2):
ether. IR (CH2Cl2): νCO 2074 (s), 2016 (s, br) cm-1 1H NMR
.
(CD2Cl2): δ 8.48 (d, J ) 7.4, H9), 8.07 (d, J ) 7.6, H6), 7.85
(m, H7,8), 7.64 (d, J ) 7.6, H1), 6.72 (t, J ) 6.6, H2), 6.51 (d,
J ) 6.4, H3), 3.20 (q, J ) 8.3, CH2), 1.59 (t, J ) 7.5, Me). Anal.
Calcd for C17H12SMnO3BF4: C, 46.61; H, 2.76. Found: C,
46.59; H, 2.97. For [6d ]BF4: Yield 65%. IR (CH2Cl2): νCO 2073
ν
CO 2058 (s), 2004 (s), 1993 (s) cm-1. 1H NMR (CD2Cl2): δ 7.7-
6.8 (m, 34H), 6.11 (d, J ) 6.3, 1H), 5.80 (t, J ) 6.5, 1H), 5.49
(s), 2017 (s, br) cm-1 1H NMR (CD2Cl2): δ 8.29 (d, J ) 7.2,
.
(t, J ) 6.3, 1H), 3.3-3.0 (m, CH2), 1.40 (m, Me). 31P NMR (CD2-
H9), 7.70 (m, H7,8), 7.52 (d, J ) 6.9, H1), 6.71 (t, J ) 6.5, H2),
6.50 (d, J ) 6.0, H3), 2.93 (s, Me), 2.66 (s, Me). Anal. Calcd for
Cl2): δ 16.28 (dd J P-P ) 20, J Pt-P ) 3730), 13.97 (dd, J P-P
)
-
20, J Pt-P ) 1730). MS FAB: 1070 (M+). Anal. Calcd for C53H42
C
17H12SMnO3BF4: C, 46.61; H, 2.76. Found: C, 46.55; H, 2.80.
SMnO3PtP2BF4: C, 54.98; H, 3.66. Found: C, 55.28; H, 3.72.
The reaction of the insertion product of 6c with 1.1 equiv of
Me3NO in CH2Cl2 gave the dicarbonyl complex 8c: Yield 60%.
For [6e]BF4: Yield 50%. IR (CH2Cl2): νCO 2072 (s), 2012 (s,
1
br) cm-1. H NMR (CD2Cl2): δ 8.31 (d, J ) 7.5, H9), 7.74 (m,
1
IR (CH2Cl2): νCO 1986 (s), 1940 (m) cm-1. H NMR (CD2Cl2):
H7,8), 7.60 (d, J ) 6.5, H1), 6.73 (t, J ) 6.1, H2), 6.53 (d, J )
5.5, H3), 3.23 (m, CH2), 2.99 (q, J ) 7.3, CH2)1.60 (t, J ) 7.2,
Me), 1.43 (t, J ) 7.2, Me). Anal. Calcd for C19H16SMnO3BF4:
C, 48.96; H, 3.46. Found: C, 49.09; H, 3.36.
δ 7.5-7.1 (m, 34H), 6.64 (d, J ) 5.8, 1H), 6.04 (d, J ) 7.6,
1H), 4.78 (t, J ) 6.2, 1H), 3.43 (q, J ) 7.0, CH2), 1.71 (t, J )
7.0, Me). 31P NMR (CD2Cl2): δ 13.04 (dd J P-P ) 14, J Pt-P
)
2280), 12.15 (dd, J P-P ) 14, J Pt-P ) 3500). MS FAB: 1042 (M+).
Anal. Calcd for C52H42SMnO2PtP2BF4: C, 55.28; H, 3.75.
Found: C, 55.39; H, 3.64. In ser tion in to 6d : In situ IR
spectra indicated clean insertion: [νCO 2057 (s), 1992 (s), 1993
(s) cm-1], but attempted precipitation with diethyl ether
afforded starting material 6d . To prove that insertion had
occurred at the C-S bond nearer the coordinated carbocyclic
ring, 1.1 equiv of Me3NO was added to the reaction mixture
to afford dicarbonyl 8d : Yield 75%. IR (CH2Cl2): νCO 1986 (s),
P la tin u m In ser tion in to Ben zoth iop h en e a n d Diben -
zoth iop h en e Com p lexes. In general, the insertion reactions
were performed as described previously.8,10 All reactions were
(21) Nagel, U. Chem. Ber. 1982, 115, 1998.
(22) Dullaghan, C. A.; Carpenter, G. B.; Sweigart, D. A. Chem. Eur.
J . 1997, 3, 75.
(23) (a) Sun, S.; Yeung, L. K.; Sweigart, D. A.; Lee, T.-Y.; Lee, S. S.;
Chung, Y. K.; Switzer, S. R.; Pike, R. D. Organometallics 1995, 14,
2613. (b) Zhang, X.; Dullaghan, C. A.; Watson, E. J .; Carpenter, G. B.;
Sweigart, D. A. Organometallics 1998, 17, 2067.
(24) Loozen, H. J . J . J . Org. Chem. 1974, 38, 1036.
(25) (a) Buchwald, S. L.; Fang, Q. J . Org. Chem. 1989, 54, 2793. (b)
Barr, K. J .; Watson, B. T.; Buchwald, S. L. Tetrahedron Lett. 1991,
32, 5465.
(26) Lee, C. C.; Igbal, M.; Gill, U. S.; Sutherland, R. G. J . Organomet.
Chem. 1985, 288, 89.
(27) Loozen, H. J . J .; Godefroi, E. F. J . Org. Chem. 1973, 38, 1057.
(28) Kuehm-Caube`re, C.; Adach-Becker, S.; Fort, Y.; Caube`re, P.
Tetrahedron 1996, 52, 9087.
1941 (m) cm-1 1H NMR (CD2Cl2): δ 7.5-7.0 (m, 33H), 6.44
.
(d, J ) 5.9, 1H), 5.02 (d, J ) 6.2, 1H), 4.70 (t, J ) 6.2, 1H),
2.67 (s, Me), 1.71 (s, Me). 31P NMR (CD2Cl2): δ 17.30 (dd J P-P
) 14, J Pt-P ) 2290), 11.92 (dd, J P-P ) 14, J Pt-P ) 3425). MS
FAB: 1042 (M+). Anal. Calcd for C52H42SMnO2PtP2BF4: C,
55.28; H, 3.75. Found: C, 55.09; H, 3.72. In ser tion in to 6e:
In situ IR spectra indicated formation of a 2:1 mixture of
insertion product and bimetallic 7e, but attempted precipita-

Models for Deep HDS Remote Activation of C-S Bonds
Organometallics, Vol. 20, No. 16, 2001 3559
tion with diethyl ether afforded only starting material 6e. For
the insertion product formed in situ: IR (CH2Cl2): νCO 2056
(s), 1989 (br, s) cm-1. 1H NMR (CD2Cl2): δ 2.99-2.92 (m, 2H),
2.62-2.55 (m, 2H), 1.13 (t, J ) 6.8, Me), 0.87 (t, J ) 7.7, Me).
31P NMR (CD2Cl2): δ 15.45 (dd J P-P ) 18, J Pt-P ) 3150), 14.57
(dd, J P-P ) 18, J Pt-P ) 2160).
Stop p ed -F low Kin etics. All stopped-flow measurements
were made at room temperature in HPLC grade CH2Cl2 under
nitrogen, using a Dionex apparatus. Manganese complex
concentrations were about 1.0 × 10-3 M, and the platinum
nucleophile was typically in slight excess. Due to the sensitivity
of solutions of Pt(PPh3)2(C2H4) to oxygen, it was not deemed
worthwhile to attempt pseudo-first-order conditions. Rather,
semiquantitative reactivity comparisons and the detection of
intermediates were the goal. To this end, a wavelength
between 405 and 475 nm was used to follow optical density
changes after mixing. It was possible to record output within
5 ms of mixing of the solutions. Data were stored on a digital
oscilloscope for subsequent plotting.
SeMnO3PdP2BF4: C, 52.28; H, 3.47. Found: C, 52.21; H, 3.62.
Syn th esis of [13]BF 4. This benzoselenophene complex was
prepared as described for the benzothiophene analogue.23 For
[13]BF 4: Yield 75%. IR (CH2Cl2): νCO 2072 (s), 2014 (s, br)
1
cm-1. H NMR (CD3COCD3): δ 9.19 (d, J ) 5.9, H2), 8.14 (d,
J ) 6.0, H7), 8.03 (d, J ) 5.9, H3), 7.75, (d, J ) 5.0, H4), 6.84
(m, H5,6). 77Se NMR (CD3COCD3): δ 617. MS FAB: 321 (M+).
In ser tion of P t in to 13: It was found that Pt(PPh3)2(C2H4)
rapidly inserts into a C-Se bond in 13 to afford 15. The
procedure used was the same as that for insertions into 5 and
6. For [15]BF4: Yield 93%. IR (CH2Cl2): νCO 2061 (s), 2004 (s)
cm-1. 1H NMR (CD2Cl2): δ 7.43-7.19 (m, 32H, Ph, H2,3), 6.83
(br, 1H), 6.38 (br, 1H), 6.12 (br, 1H), 6.04 (br, 1H). 31P NMR
(CD3COCD3): δ 24.98 (dd J P-P ) 20, J Pt-P ) 3440), 20.43 (dd,
J P-P ) 20, J Pt-P ) 1920). 77Se NMR (CD3COCD3): δ 361 (dd,
J Se-P ) 74, 70). MS FAB: 1040 (M+). Anal. Calcd for C47H36
-
SeMnO3PtP2BF4: C, 50.11; H, 3.22. Found: C, 50.70; H, 3.44.
P a lla d iu m In ser tion in to [(η6-Bip h en ylen e)Mn (CO)3]-
BF 4. Pd(PPh3)2(C2H4) (140 mg, 0.21 mmol) was added to a
suspension of [(η6-biphenylene)Mn(CO)3]BF4 (76 mg, 0.20
mmol) in CH2Cl2 (10 mL) at room tempertaure under nitrogen.
An IR spectrum within a few minutes indicated that the
reactant had been converted to bimetallic 17. After stirring
the solution for 1 h in the dark, IR indicated complete
conversion to insertion product 16. The volume was reduced
to a few milliliters, and the product precipitated with diethyl
ether as a yellow powder. Reprecipitation from acetone af-
forded a pure material. For [16]BF4: Yield 81%. IR (CH2Cl2):
In ser t ion in t o Selen op h en e a n d Ben zoselen op h en e
Com p lexes. The selenophene complex 12 has been reported
previously.17 We found that the manganese tricarbonyl trans-
fer method23a using (η6-acenaphthene)Mn(CO)3 gives an
+
improved yield. For [12]BF4: Yield 92%. IR (CH2Cl2): νCO 2071
1
(s), 2008 (s, br) cm-1. H NMR (CD3COCD3): δ 7.62 (s, H2,5),
7.28 (s, H3,4). 77Se NMR (CD3COCD3): δ 276. MS FAB: 271
(M+). Anal. Calcd for C7H4SeMnO3BF4: C, 23.56; H, 1.13.
Found: C, 23.91; H, 1.25. A golden yellow crystal of [12]BF4
suitable for X-ray diffraction was grown by vapor diffusion of
diethyl ether into an acetone solution at -15 °C over several
days. In ser tion of P t in to 12: It was found that Pt(PPh3)2-
(C2H4) rapidly inserts into a C-Se bond in 12 to afford 14.
The procedure used was the same as that for insertions into 5
and 6. For [14]BF4: Yield 88%. IR (CH2Cl2): νCO 2045 (s), 1987
(s), 1971 (s) cm-1. 1H NMR (CD3COCD3): δ 7.58-7.47 (m, 12H,
Ph), 7.45-7.21 (m, 19H), 7.26 (m, 1H), 5.74 (m, 1H), 4.82 (m,
1H). 31P NMR (CD2Cl2): δ 20.30 (dd J P-P ) 20, J Pt-P ) 3560),
18.23 (dd, J P-P ) 20, J Pt-P ) 2120). 77Se NMR (CD2Cl2): δ -246
(dd, J Se-P ) 73, 40). Anal. Calcd for C43H34SeMnO3PtP2BF4:
C, 47.98; H, 3.18. Found: C, 47.56; H, 3.03. A yellow crystal
of [14]BF4 suitable for X-ray diffraction was grown by vapor
diffusion of diethyl ether into a CH2Cl2 solution at -15 °C over
several days. In ser tion of P d in to 12: The use of Pd(PPh3)2-
(C2H4) leads to the palladium analogue of 14: Yield 78%. IR
(CH2Cl2): νCO 2045 (s), 1988 (s), 1970 (s) cm-1. 1H NMR (CD2-
Cl2): δ 7.45-7.21 (m, 30H, Ph), 7.70 (d, J ) 6.2, 1H), 6.62 (t,
J ) 7.5, 1H), 5.54 (m, 1H), 4.11 (t, J ) 7.5, 1H). 31P NMR (CD2-
Cl2): δ 34.21 (d J P-P ) 39.5), 22.95 (d, J P-P ) 39.4). 77Se NMR
νCO 2059 (s), 2002 (s) cm-1 1H NMR (CD2Cl2): δ 7.44-7.19
.
(m, 30H, Ph), 7.17 (1H), 7.03 (t, J ) 7.5, 1H), 6.92 (d, J ) 4.9,
1H), 6.56 (m, 2H), 6.18 (t, J ) 6.4, 1H), 5.62 (d, J ) 5.5, 1H),
5.28 (d, J ) 6.4, 1H). 31P NMR (CD2Cl2): δ 33.95 (d J P-P
)
31.5), 25.60 (d, J P-P ) 31.5). MS FAB: 922 (M+). Anal. Calcd
for C51H38MnO3PdP2BF4‚CH2Cl2: C, 57.10; H, 3.69. Found: C,
57.12; H, 3.76. A crystal of [16]BF4‚CH2Cl2 suitable for X-ray
diffraction was grown by vapor diffusion of diethyl ether into
a CH2Cl2 solution at -20 °C over several days.
Ack n ow led gm en t. This work was supported by
grant CHE-9705121 from the National Science Founda-
tion.
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 [12]BF4, [14]BF4,
and [16]BF4. This material is available free of charge via the
Internet at http://pubs.acs.org.
(CD2Cl2): δ -267 (dd, J Se-P ) 33, 39). Anal. Calcd for C43H34
-
OM0102448