Thermochemistry of Sulfur Atom Transfer. Enthalpies of Reaction of Phosphines with Sulfur, Selenium, and Tellurium, and of Desulfurization of Triphenylarsenic Sulfide, Triphenylantimony Sulfide, and Benzyl Trisulfide

Article abstract of DOI:10.1021/ic9715862

The enthalpies of reaction of neat PBu₃ with solid sulfur (-27.1 ± 0.5 kcal/mol), selenium (-20.0 ± 0.6 kcal/ mol), and tellurium (-4.9 ± 0.6 kcal/mol) have been measured by solution calorimetry. The enthalpies of reaction of a series of phosphines with sulfur in toluene solution have been measured as follows (values in kcal/mol): PCy₃ = -30.9 ± 1.9, PBu₃ = -28.9 ± 0.3, PMe₃ = -27.1 ± 0.4, PMe₂Ph = -26.0 ± 0.5, PMePh₂ = -23.8 ± 0.3. PPh₃ = -21.5 ± 0.3. These values correlate with literature data for enthalpies of protonation and indicate that P to S σ donation is probably the dominant factor in determining the R₃P=S bond strength, estimates for which range from 88 to 98 kcal/mol. The enthalpies of S atom transfer to PPh₃ by S=AsPPh₃ and S=SbPh₃ in toluene solution are -17.7 ± 1.2 and -21.5 ± 1.0 kcal/mol, respectively. The enthalpy of removal of the central S atom from BzSSSBz by PCy₃, yielding BzSSBz and S=PCy₃, is -29.0 ± 1.8 kcal/mol. These data are used to establish a range of enthalpies of S atom transfer in these compounds which spans 31 kcal/mol from S=SbPPh₃ to S=PCy₃.

Full text of DOI:10.1021/ic9715862

Inorg. Chem. 1998, 37, 2861-2864
2861
Ar ticles
Thermochemistry of Sulfur Atom Transfer. Enthalpies of Reaction of Phosphines with
Sulfur, Selenium, and Tellurium, and of Desulfurization of Triphenylarsenic Sulfide,
Triphenylantimony Sulfide, and Benzyl Trisulfide
Kenneth B. Capps, Bodo Wixmerten, Andreas Bauer, and Carl D. Hoff*
Department of Chemistry, University of Miami, Coral Gables, Florida 33124
ReceiVed December 17, 1997
The enthalpies of reaction of neat PBu3 with solid sulfur (-27.1 ( 0.5 kcal/mol), selenium (-20.0 ( 0.6 kcal/
mol), and tellurium (-4.9 ( 0.6 kcal/mol) have been measured by solution calorimetry. The enthalpies of reaction
of a series of phosphines with sulfur in toluene solution have been measured as follows (values in kcal/mol):
PCy3 ) -30.9 ( 1.9, PBu3 ) -28.9 ( 0.3, PMe3 ) -27.1 ( 0.4, PMe2Ph ) -26.0 ( 0.5, PMePh2 ) -23.8
( 0.3, PPh3 ) -21.5 ( 0.3. These values correlate with literature data for enthalpies of protonation and indicate
that P to S σ donation is probably the dominant factor in determining the R3PdS bond strength, estimates for
which range from 88 to 98 kcal/mol. The enthalpies of S atom transfer to PPh3 by SdAsPPh3 and SdSbPh3 in
toluene solution are -17.7 ( 1.2 and - 21.5 ( 1.0 kcal/mol, respectively. The enthalpy of removal of the
central S atom from BzSSSBz by PCy3, yielding BzSSBz and SdPCy3, is - 29.0 ( 1.8 kcal/mol. These data
are used to establish a range of enthalpies of S atom transfer in these compounds which spans 31 kcal/mol from
SdSbPPh3 to SdPCy3.
Introduction
Sulfur atom transfer and the energetics associated with it are
important to understanding transition metal-sulfur chemistry.1
Despite that, there is relatively little reliable data available for
the energetics of reactions of sulfur with metal complexes aside
from that for formation of simple metal sulfides. As part of
our interest in the thermochemistry of complexes of chromium,
molybdenum, and tungsten,2 we have recently reported kinetic
and thermodynamic studies of reactions of group VI metal
complexes with thiols and disulfides.3-6
Extension of that work into the MdS area has prompted our
investigation of the thermochemistry of sources and sinks for
sulfur and heavier chalcogen atoms. Such data is not only of
intrinsic interest, but provides needed ancillary data for develop-
ing metal/chalcogen thermochemistry since the complexes
EdYR3 (E ) S, Se, Te; Y ) P, As, Sb) are frequently used as
transfer agents. Reactions such as that shown in eq 1 below
can readily remove “excess” sulfur from metal complexes7-9
in favorable cases:
R3P(l) + 1/8S8(s) f R3PdS (soln in PR3)
(2)
R ) n-Pr, ∆H ) -27.6 kcal/mol
R ) n-Bu, ∆H ) -27.5
R ) OEt, ∆H ) -26.6
The nearly constant values obtained in this work were in contrast
to work on phosphine oxides.11
The mechanisms of addition and subtraction of sulfur atoms
in particular is a relatively unexplored but important area.
Thermochemical data is needed to help understand the driving
forces in the seemingly complex reactivity displayed in metal-
sulfur chemistry.
(5) Ju, T. D.; Lang, R. F.; Roper, G. C.; Hoff, C. D. J. Am. Chem. Soc.
1996, 118, 5328.
(6) Mukerjee, S. L.; Gonzalez, A. A.; Nolan, S. P.; Ju, T. D.; Lang, R.
F.; Hoff, C. D. Inorg. Chim. Acta 1995, 240, 175.
(7) Goh, L. Y.; Hambley, T. W.; Robertson, G. B. Organometallics 1987,
6, 1051.
Skinner and co-workers10 have reported the enthalpies of
reaction of neat PR3 with sulfur as shown in eq 2:
(8) Hermann, W. A.; Rohrmann, J.; Schafer, A. J. Organomet. Chem.
1984, 265, C1.
(1) Transiton Metal-Sulfur Chemistry. ACS Symp. Ser. 1996, 653.
(2) Hoff, C. D. Prog. Inorg. Chem. 1992, 40, 503 and references therein.
(3) Ju, T. D.; Capps, K. B.; Lang, R. F.; Roper, G. C.; Hoff, C. D. Inorg.
Chem. 1997, 36, 614.
(4) Lang, R. F.; Ju, T. D.; Bryan, J. C.; Kubas, G. J.; Hoff, C. D. Inorg.
Chim. Acta 1997, 259, 317.
(9) The enthalpy of reaction 1 and related metal desulfurization reactions
are under active investigation: Capps, K. B.; Bauer, A.; Wong, R. C.
S.; Hoff, C. D. Work in progress.
(10) Chernick, C. L.; Pedley, J. B.; Skinner, H. A. J. Chem. Soc. 1957,
1851.
(11) Chernick, C. L.; Skinner, H. A. J. Chem. Soc. 1956, 1401.
S0020-1669(97)01586-3 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/15/1998

2862 Inorganic Chemistry, Vol. 37, No. 12, 1998
Capps et al.
Bartlett and co-workers12 have investigated the kinetics and
mechanism of reaction of PPh3 with sulfur:
E
neat PBu3
E
toluene soln
-28.9 ( 0.6
-20.5 ( 1.3
-5.1 ( 0.8
S(solid)
Se(solid)
Te(solid)
-27.1 ( 0.6
-20.0 ( 1.5
-4.9 ( 1.0
S(soln)
Se(solid)
Te(solid)
Ph3P + 1/8S8 f Ph3PdS
(3)
25% SdPBu3 dissolved in PBu3. Reaction of solid sulfur was
rapid, occurring essentially at the rate of dissolution. Reaction
of selenium and tellurium was much slower and took hours to
reach completion. The value obtained for sulfur with the neat
PBu3 is in agreement with the earlier value of Skinner and co-
workers of -27.5 ( 0.5 kcal/mol under similar conditions.
Enthalpies of reaction in solution refer to reaction of a 1.5 M
toluene solution of the phosphine and the solid chalcogen (Se,
Te) or a toluene solution of it (S). The values for Se and Te
appear to be slightly more exothermic (0.5) and (0.2) kcal/mol,
respectively. These measurements were performed to determine
if enthalpies of solution and dilution play a role in the
thermochemistry of the relatively polar compounds involved.
Any effect of this type appears to be small (less than 1 kcal/
mol) and close to experimental errors.
To the authors’ knowledge, the enthalpy of reaction 3 has
not been reported. It is important because PPh3 is a much milder
reagent than PBu3 and is also a much weaker ligand,2 less likely
to displace other ligands from a metal center.
Data on the enthalpies of formation of phosphine selenides
and tellurides are scarce. The chemistry of inorganic selenide
and telluride complexes was recently reviewed by Roof and
Kolis.13 Zingaro14 has reported the preparation of Bu3PdTe
and the fact that, on standing, it has a tendency to eliminate
elemental tellurium. In addition to varying the chalcogen in
R3PdE, the pnicogen can also be varied in the series R3YdS.
Jason15,16 recently reported the facile S atom transfer ability of
Ph3SbdS and Ph3AsdS. Baechler and his students17 have also
reported a series of kinetic and equilibrium studies on atom
transfer and exchange for several complexes R3YdE (Y ) P,
As, Sb; E ) O, S, Se, Te):
1
Reaction of a solution of /8S8 dissolved in toluene with a
solution of PBu3 was exothermic by 28.9 ( 0.6 kcal/mol
1
compared to reaction of the neat PBu3 and solid /8S8 which
R3YdE + R′3Y h R3Y + R′3YdE
(4)
was exothermic by -27.1 ( 0.6. The observed difference is
attributed to enthalpies of solvation of reactants and products.
The enthalpy of solution of 1/8S8 in benzene solution, as shown
in eq 6, has been reported.19 Assuming the enthalpy of solution
The thermochemistry of organosulfur compounds was developed
largely by a few groups18 that used rotating combustion bomb
calorimetrysa little used technique in recent times. This work
reports the first in a series of measurements aimed at expanding
the thermochemistry of sulfur and establishing a scale of SAT
(sulfur atom transfer) thermochemistry.
1/8S8 (solid) f 1/8S8 (C6H6 soln), ∆H ) +0.7 kcal/mol
(6)
is the same in toluene, leads to a calculated enthalpy of reaction
of -28.2 ( 0.6 kcal/mol for reaction of solid sulfur with a
toluene solution of the phosphine. The reaction is thus 1.1 (
1.2 kcal/mol more exothermic in toluene solution versus neat
phosphine. This is in keeping with the small solvation effect
observed for Se and Te. A number of enthalpies of reaction
were measured in methylene chloride solution as well. Irre-
producible results were obtained in a number of cases, presum-
ably due to side reactions with solvent occurring during
chalcogenation of phosphine.20
Experimental Section
Orthorhombic sulfur (99.9995%) was obtained from Johnson Mathey.
It was further recrystallized from carbon disulfide and stored and
handled in the glovebox under an argon atmosphere. Selenium
(99.999%) and tellurium (99.999%) were obtained from Aldrich
chemical and used as obtained. Triphenylphosphine and tricyclohexy-
lphosphine were recrystallized from methylene chloride/heptane. Or-
ganophosphines used were all of the highest purity commercially
available and degassed prior to use. Triphenylantimony sulfide was
obtained from Strem chemical. A pure sample of triphenylarsenic
sulfide was provided by Dr. Mark Jason of Monsanto Chemical
Company (St. Louis, MO). Benzene, deuterobenzene, and toluene were
purified by reflux followed by distillation from sodium benzophenone
ketyl under argon. Methylene chloride was distilled from P2O5 under
argon atmosphere. Calorimetric measurements were made using a
Setaram C-80 Calvet calorimeter at 30 °C as described elsewhere.3-6
Reported data are all based on an average of at least five measurements.
Experimental errors are the standard deviation. Infrared measurements
were made using a Perkin-Elmer 2000 FTIR; NMR data were obtained
on a Varian VXR 400 Spectrometer.
Enhalpies of Reaction of Phosphines with 1/8S8. The
enthalpies of reaction 7 were measured with all species in
solution:
PR3 + 1/8S8 f SdPR3,
∆H (kcal/mol)
PCy3, -30.9 ( 1.9
PBu3, -28.9 ( 0.3
PMe3, -27.1 ( 0.4
PMe2Ph, -26.0 ( 0.5
PMePh2, -23.8 ( 0.3
PPh3, -21.5 ( 0.3
Results
Some of the calorimetric measurements were performed in
toluene, benzene, and deuterobenzene to confirm the reaction
products by NMR under actual calorimetric conditions. All
Enthalpies of Reaction of PBu3 with S, Se, and Te. The
enthalpies of reaction (kcal/mol) of PBu3 and S, Se, and Te
were measured as summarized in eq 5:
(16) Jason, M. E.; Ngo, T.; Rahman, S. Inorg. Chem. 1997, 36, 2633.
(17) Baechler, R. D.; Stack, M.; Stevenson, K.; Vanvalkenburgh, V.
Phosphorous, Sulfur, Silicon 1990, 48, 49.
PBu3 + E f EdPBu3
(5)
(18) For reference to original work in rotating bomb calorimetry of
organosulfur compounds, see: Stull, D. R.; Westrum, E. F.; Sinke,
G. C. The Chemical Thermodynamics of Organic Compounds;
Wiley: New York, 1969; p 70.
(19) Wagman, D. D.; Evans, W. H.; Parker, V. B.; Schumm, R. H.; Halow,
I.; Bailey, S. M.; Churney, K. L.; Nuttall, R. L. J. Phys. Chem. Ref.
Data 1982, 11 (Suppl. 2).
The “neat” reactions under eq 5 refer to reaction of pure PBu3
with the solid chalcogen. The product is a solution of 10-
(12) Bartlett, P. D.; Meguerian, G. J. Am. Chem. Soc. 1956, 78, 3710.
(13) Roof, L. C.; Kolis, J. W. Chem. ReV. 1993, 93, 1037.
(14) Zingaro, R. A.; Steeves, B. H.; Irgolic, K. J. Organomet. Chem. 1965,
4, 320.
(20) Capps, K. B.; Bauer, A.; Wixmerten B.; Hoff, C. D. Unpublished
results.
(15) Jason, M. E. Inorg. Chem. 1997, 36, 2641.

Thermochemistry of Sulfur Atom Transfer
Inorganic Chemistry, Vol. 37, No. 12, 1998 2863
BzSSSBz + PCy3 f BzSSBz + SdPCy3 (11)
were found to go to completion as described. There was no
apparent difference in enthalpies of reaction when done in
toluene or benzene.
The experimental value of -29.0 ( 2.0 kcal/mol has a relatively
large error since the desulfurization reaction is relatively slow
and takes over 3 h to go to completion.
The products in reaction 11 were confirmed by NMR analysis
of authentic samples.
Enthalpy of Reaction of PPh3 and PCy3 with Selenium.
Extension of the studies shown in reaction 7 with solid selenium
and toluene solutions of PCy3 and PPh3 were performed to see
if the order of stability extended on to selenium. The enthalpy
of reaction of PCy3 was found to be -20.2 ( 1.6 kcal/
molsessentially the same as that of PBu3. The enthalpy of
reaction of PPh3 was -13.0 ( 1.2 kcal/mol, showing a
significant decrease in bond strength similar to that observed
in analogous reactions of sulfur. The high experimental errors
reported are due to the very slow rate of reaction of PPh3 with
selenium. Extension of this work to additional tellurium
derivatives was not attempted due to the marginal stability14 of
the R3PdTe complexes.
Discussion
The goal of this work was to provide background data for
reactions in which sulfur is either removed from or added to a
metal complex as part of an overall program in metal/sulfur
thermochemistry. The main area investigated is a series of
phosphine sulfides, but this is also extended to heavier
elementssarsine and stibine sulfides as well as phosphine
selenides and tellurides. These data provide a basis for
expanding sulfur atom transfer thermochemistry. This is
illustrated by measuring the enthalpy of removing the central
atom of BzSSSBz.
Enthalpy of Reaction of SdSbPh3 and SdAsPh3 with
PPh3. As discussed by Baechler,17 reactions 8 and 9 were found
to proceed rapidly to completion as shown:
Enthalpies of S Atom Transfer. The range of enthalpies
of S atom transfer (SAT) are summarized in Table 1 for all the
complexes studied. Elemental sulfur in either benzene or
toluene solution is taken as the reference point. The sulfur atom
transfer enthalpies reported in Table 1 can be compared to some
of the equilibrium and kinetic studies reported by Baechler.17
For many of these reactions, the kinetic data is of principal
importance since the equilibrium constants were too large to
be estimated beyond the fact that they were greater than 500.
A value of Keq ) 12 was reported for reaction 12 at 130 °C in
bromobenzene:
SdAsPh3 + Ph3P f AsPh3 + Ph3PdS
SdSbPh3 + Ph3P f SbPh3 + Ph3PdS
(8)
(9)
The enthalpy of reaction 8 could be measured with all species
in solution because SdAsPh3 shows no tendency to eliminate
sulfur on the time scale of the calorimetric measurements. The
experimental value for this reaction, -17.7 ( 0.8 kcal/mol,
corresponds directly to the difference in bond strengths between
Ph3PdS and Ph3AsdS.
The enthalpy of reaction 9 was measured using solid Ph3-
SbdS due to the instability of this compound in solution.15 The
experimental measurement yielded a value of -16.2 ( 0.9 kcal/
mol, however this had to be corrected by addition of the enthalpy
of solution of Ph3SbdS. The enthalpy of solution of Ph3SbdS
in toluene was found to be +5.3 ( 0.5 kcal/mol. Elimination
of sulfur is slow relative to the rate of solution. Adding the
enthalpy of solution to the enthalpy of reaction gives a value
of -21.5 kcal/mol for the enthalpy of reaction 9. This is the
same as the value of reaction of PPh3 with sulfur in solution as
shown in eq 7 and implies that the enthalpy of reaction of Ph3-
SdPPh3 + PPh2Me h PPh3 + SdPPh2Me
(12)
Despite a difference in solvent polarity (benzene versus bro-
mobenzene) and temperature (100 °C), there is reasonable
agreement between the equilibrium constant of Baechler17 and
the enthalpy of reaction measured here. The ∆H°30 ) -2.3
kcal/mol enthalpy difference in Table 1 compares favorably with
the ∆G°303 ) -2.0 kcal/mol calculated from the equilibrium
data.17 Together this implies, as might be expected, a near zero
entropy change for reaction 12.
1
Sb and /8S8 is essentially thermoneutral. Thus, even as the
Bond Strength Estimates. The data in Table 1 summarizes
bond strength estimates for these complexes. The enthalpies
of formation of the gas-phase atoms S, Se, and Te are known19
[S ) +66.7, Se ) +54.3, Te ) +47.1 kcal/mol]. Reasonable
bond strength estimates can be obtained by simply adding these
values to the observed enthalpies of reaction. This assumption
would be strictly correct if the transfer enthalpies of, for
example, PR3 (toluene solution) and SdPR3 (toluene solution)
to the gas phase would cancel each other. This assumption is
probably reasonable and is commonly made. An alternative
view is to consider that the enthalpies of solution of the gas
phase chalcogen atoms in benzene or toluene would be
essentially zero.
solution of Ph3SbdS is observed to yield slow decomposition
to Ph3Sb and sulfur15 little heat is absorbed or evolved during
this process. Close examination of the thermograms for the
enthalpy of solution of Ph3SbdS indicated that, following the
endothermic enthalpy of solution, the reaction never became
exothermic, sindicating that while elimination of sulfur from
Ph3SbdS is near zero it is endothermic and not exothermic.
We estimate the enthalpy of elimination of sulfur to be in the
range 0-0.5 kcal/mol.
As a check on the thermochemistry of reactions 8 and 9 we
measured the enthalpy of reaction 10.
SdSbPh3 + AsPh3 f SbPh3 + SdAsPh3
(10)
Despite experimental agreement with the data of Skinner, the
bond strength estimate we make for SdPBu3 is 96 kcal/mol
versus the earlier value of 92 kcal/mol.10 This reflects only
the uncertainty in extrapolating data from solution to gas phase.
The work of Skinner was done in neat phosphine versus our
solution studies. In addition, Skinner assumed a difference in
enthalpy of transfer to the gas phase of PBu3 and SdPBu3. This
highlights the fact that “absolute” bond dissociation energies
for all but the simplest molecules are seldom known to better
than (3 kcal/mol. The more important relative bond strengths,
The experimental enthalpy of reaction taking into account the
enthalpy of solution of Ph3SbdS was -4.1 kcal/mol. This
agrees with the value calculated by subtracting eq 8 from eq 9
(-21.5 - 17.7 ) -3.8 kcal/mol). Such checks on data are
important in systems such as these were trace species in solution
can led to spurious results.
Enthalpy of Reaction of BzSSSBz with PCy3. The enthalpy
of reaction 11 was measured with both limiting PCy3 and
BzSSSBz in solution:

2864 Inorganic Chemistry, Vol. 37, No. 12, 1998
Capps et al.
Table 1. Combined Enthalpies of Chalcogen Atom Transfer in
Benzene/Toluene Solution and Bond Stength Estimates
compound
-∆H SAT (kcal/mol)
BDE (kcal/mol)
Sulfur:
SdPCy3
SdPBu3
30.9
28.9
27.1
26.0
23.8
21.5
3.8
98
96
94
93
91
88
70
SdPMe3
SdPMe2Ph
SdPMePh2
SdPPh3
SdAsPh3
BzSSSBz
SdSbPh3
Selenium:
SedPBu3
SedPCy3
SedPPh3
Tellurium:
TedPBu3
1.9
0
67
20.5
20.2
13.0
75
75
67
4.9
52
and enthalpies of reaction in solution, are known to better than
(1 kcal/mol for most of the reactions in Table 1. An average
estimate of 94 ( 3 kcal/mol seems reasonable for the absolute
value of the SdPBu3 bond strength.
Comparison of Enthalpies of Reaction of PR3 and Sulfur
to Enthalpies of Protonation. The relative SdPR3 bond
strength data shown in Table 1 shows a reasonably strong
dependence on the nature of R. The trend is the same one that
has been seen for a number of studies of the enthalpies of
binding of the phosphine ligands to metal complexes.2 In
addition, Angilici and co-workers21 recently reported enthalpies
of protonation of phosphine ligands. A plot of the enthalpies
of reaction of PR3 ligands with sulfur versus protonation is
shown in Figure 1. There is a good correlation. Since bonding
of H+ to PR3 involves only donation of lone pair electrons from
the phosphine to the proton, the correlation in Figure 1 is
suggestive that the dominant component in the bond between
PR3 and sulfur is similarly σ donation. The ability of PR3 to
act as a π acceptor of electron density from lone pairs on S
would be expected to be most important for PPh3. In terms of
bond strengths at least, the correlation with enthalpies of
protonation appears to imply that it is sigma donation which
dominates the SdPR3 bond strength.
Figure 1. Enthalpy of protonation of phosphine ligands (data taken
from ref 21) versus enthalpy of reaction with sulfur.
at negligible rate. The reactivity of TedPBu3 is probably
associative and not dissociative in nature.
There is a less dramatic decrease in bond strength in going
from SdPPh3 to SdAsPPh3 to SdSbPPh3 of 88 to 70 to 67
kcal/mol. Surprisingly, the drop from As to Sb is relatively
small. Keeping the chalcogen (sulfur) constant and changing
the pnicogen from P to As to Sb appears to have less influence
on the bond strength than changing the chalcogen from S to Se
to Te while keeping the pnicogen fixed (phosphorus).
It was surprising to the authors to find that benzyl trisulfide
is thermochemically very close to benzyl disulfide and sulfur.
It has been reported that under certain conditions trisulfides and
tetrasulfides decompose to disulfides and elemental sulfur,22 in
keeping with a low enthalpy of desulfurization. The thermo-
chemical abilities to add a single S atom in terms of 1/8S8, Ph3-
SbdS, BzSSSBz, and Ph3AsdS are all lowsin the range 0-4
kcal/mol. The mechanisms by which sulfur is transferred by
each of them may be expected to differ, despite their similar
thermochemical values. Extension of this work to other main
group and transition metal sulfur complexes is under active
investigation.
Conclusion
The data in Table 1 provides good entry to determining a
wider range of sulfur atom transfer energies. For the phosphines
studied, the approximate 10 kcal/mol range measured may prove
useful in choosing which phosphine to use to desulfurize other
organic and inorganic complexes. That basis is strictly ther-
modynamic, since the reaction mechanisms of sulfur addition
and elimination, as pointed out by Jason,15,16 remain largely
unexplored.
The trends in bond strength among the phosphines are similar
to those observed for metal complexes2 and also correlate well
with enthalpies of protonation.21 This may imply that R3P f
S σ donation is the principal factor determining the PdS bond
strength. There is a dramatic drop in bond strength in the series
SdPBu3 to SedPBu3 to TedPBu3 of 96 to 75 to 52 kcal/mol.
EVen for TedPBu3, howeVer, this bond strength is large enough
that simple dissociation to PBu3 and a Te atom should occur
Acknowledgment. Support of this work by the National
Science Foundation and the Petroleum Research Fund, admin-
istered by the American Chemical Society, is gratefully
acknowledged. A.B. also acknowledges support by the Deutsche
Forschungsgemeinschaft through a postdoctoral fellowship. The
authors give special thanks to Dr. Mark Jason, Monsanto, for
helpful discussions and gift of triphenylarsenic sulfide.
(21) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51. Note that data used for
the enthalpies of protonation is taken from this article. The enthalpy
of protonation of PnBu3 was not reported but is expected to be quite
similar to the value reported for PEt3. In Figure 1 the enthalpy of
sulfurization of PBu3 is matched to this value for enthalpy of
protonation.
IC9715862
(22) Voronkov, M. G.; Vyazankin, N. S.; Deryagina, E. N.; Deryagina, E.
N.; Nakhmanovich, A. S.; Usov, V. A. Reactions of Sulfur with
Organic Compounds; Consultants Bureau: New York, 1987.