Modeling the Claus Reaction: Preparation of trans-Pt(PPh3)2(phthalimido)S(O)2SR

Full text of DOI:10.1021/ic960617a

6356
Inorg. Chem. 1996, 35, 6356-6357
Modeling the Claus Reaction: Preparation of trans-Pt(PPh3)2(phthalimido)S(O)2SR
Alan Shaver,* He´le`ne Boily, and Anne-Marie Lebuis
Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada H3A 2K6
ReceiVed May 24, 1996
The removal of sulfur from crude oil is accomplished by
hydrodesulfurization (HDS)1 followed by the Claus process,2
which converts the H2S produced by HDS to sulfur and water
(eq 1). Natural gas contaminated by H2S is purified by direct
Treatment of Pt(PPh3)3SO2 with RSphth7 gave pale yellow
complexes of the type trans-Pt(PPh3)2(phth)S(O)2SR, 1a-f,
where phth ) phthalimido (eq 2). The IR and NMR (1H and
2H2S + SO2 catalyst8 3/8S8 + 2H2O
(1)
(2)
application of the Claus process. The Claus reaction is
conducted at 300 °C using alumina as a catalyst although other
materials also catalyze the reaction. The mechanism is un-
known, but the reaction must involve the formation of sulfur-
sulfur bonds and oxygen transfer, a suite of reactions with few
precedents in homogeneous catalysis. Three simple conceptual
models of the Claus reaction can be described. Model A depicts
31P) spectra of 1a-f are consistent with their formulation,8 and
the structure of 1f, shown in Figure 1, confirms the presence of
the PtS(O)2SCH2Ph moiety.9 Interestingly, while organic thio-
sulfonates (RS(O)2SR′) are known,10 few structures have been
-
reported;11 complexes 1a-f are the first to contain an RSS(O)2
ligand.12 Sulfito groups are the parent ligands of this new
class.3k,13
attack by H2S on adsorbed SO2, model B represents attack by
SO2 on adsorbed H2S,3 and in C both the H2S and the SO2 are
adsorbed before reaction.4 Studies of the sequential adsorption
and reactions of SO2 and H2S on alumina5 are for the most part
inconclusive; however, preadsorbed SO2 is reactive toward
H2S.5d Therefore, the complex Pt(PPh3)3SO2,6 chosen as an
example of preadsorbed SO2, was treated with a source of RS+
as a simulation of model A.
Attachment of the RS+ residue to the SO2 ligand of Pt(PPh3)3-
SO2 and oxidation of the metal center result in a much shorter
Pt-S distance (2.261(3) Å) in 1f than in the precursor (2.368-
(3) Å).14 The Pt-S distance in 1f is also shorter than those in
cis-Pt(PPh3)2(phth)SSCHMe2 (2.353(3) Å),15 [Pt(PPh3)2(S(O)-
(7) (a) Behforouz, M.; Kerwood, J. E. J. Org. Chem. 1969, 34, 51. (b)
Buchel, K. H.; Conte, A. Chem. Ber. 1967, 100, 1248. (c) Harpp, D.
N.; Ash, D. K.; Back, T. G.; Gleason, J. G.; Orwig, B. A.; van Horn,
W. F.; Snyder, J. P. Tetrahedron Lett. 1970, 3551.
(8) Preparative procedures and characterization data are given in the
Supporting Information.
(9) Crystal data for trans-Pt(PPh3)2(phth)S(O)2SCH2Ph‚0.75CH2Cl2 1f:
monoclinic P21/c (No. 14), a ) 21.212(4) Å, b ) 13.996(2) Å, c )
17.789(3) Å, V ) 4868.9(14) Å3, â ) 112.79(1)°, Z ) 4, Dc ) 1.524
g/cm3, µ(Mo KR) ) 3.190 mm-1, λ(Mo KR) ) 0.709 30 Å (graphite
monochromated); 2θmax ) 50°, 32 688 measured reflections (8585
unique, R(int) ) 0.133); R ) 0.063, Rw ) 0.108, GOF ) 0.887 (4409
reflections with I > 2.00σ(I)). A complete structural report is included
in the Supporting Information.
(10) (a) Block, E. Angew. Chem., Int. Ed. Engl. 1992, 31, 1135. (b)
Freeman, F. Chem. ReV. 1984, 84, 117. (c) Oae, S. Organic Chemistry
of Sulfur; Plenum Press: New York, 1977. (d) Reid, E. E. Organic
Chemistry of BiValent Chemistry; Chemical Publishing Co.: New
York, 1958; Vol. 1.
* Author to whom correspondence should be addressed.
(1) (a) Satterfield, C. N. Heterogeneous Catalysis in Industrial Practice,
2nd ed.; McGraw-Hill: New York, 1991; pp 378-383. (b) Gates, B.
C.; Katzer, J. R.; Schuit, G. C. A. Chemistry of Catalytic Processes;
McGraw Hill: New York, 1979; pp 390-445.
(2) (a) Grancher, P. Hydrocarbon Process. 1978, 57, 155. (b) Grancher,
P. Hydrocarbon Process. 1978, 57, 257. (c) George, Z. M.; Tower,
R. W. Can. J. Chem. Eng. 1985, 63, 618 and references therein.
(3) For examples of model B involving soluble metal thiolates and sulfides
see: (a) Eller, P. G.; Kubas, G. J. J. Am. Chem. Soc. 1977, 99, 4346.
(b) Shaver, A.; Plouffe, P.-Y. Inorg. Chem. 1992, 31, 1823. (c) Schenk,
W. A.; Dombrowski, E.; Reuther, I.; Stur, T. Z. Naturforsch., B: Chem.
Sci. 1992, 47B, 732. (d) Darensbourg, M. Y.; Tuntulani, T.; Reiben-
spies, J. H. Inorg. Chem. 1994, 33, 611. (e) Kubas, G. J.; Ryan, R. R.
J. Am. Chem. Soc. 1985, 107, 6138. (f) Kubas, G. J.; Wasserman, H.
J.; Ryan, R. R. Organometallics 1985, 4, 419. (g) Brunner, H.;
Klement, U.; Pfauntsch, J.; Wachter, J. Angew. Chem., Int. Ed. Engl.
1987, 26, 230. (h) Kubas, G. J.; Ryan, R. R. Inorg. Chem. 1984, 23,
3181. (i) Toupadakis, A.; Kubas, G. J.; Burns, C. J. Inorg. Chem.
1992, 31, 3810. (j) Kubas, G. J.; Ryan, R. R.; Kubat-Martin, K. A. J.
Am. Chem. Soc. 1989, 111, 7823. (k) Kubat-Martin, K. A.; Kubas, G.
J.; Ryan, R. R. Organometallics 1989, 8, 1910. (l) Yamanari, K.; Mori,
M.; Dogi, S.; Fuyuhiro, A. Inorg. Chem. 1994, 33, 4807. (m) Heyke,
O.; Neher, A.; Lorenz, I.-P. Z. Anorg. Allg. Chem. 1992, 608, 23.
(4) For examples of model C involving soluble complexes containing both
thiolato and SO2 ligands see refs 3b and 3c and: Kubas, G. J. Inorg.
Chem. 1979, 18, 182.
(11) (a) Wahl, G. H.; Bordner, J.; Harpp, D. N.; Gleason, J. G. Acta
Crystallogr., Sect. B 1973, B29, 2272. (b) Noordik, J. H.; Vos, A.
Recl. TraV. Chim. Pays-Bas 1967, 86, 156. (c) Block, E.; O’Connor,
J. J. Am. Chem. Soc. 1974, 96, 3921.
-
(12) The RSS(O)2 ligands in 1a-f are isomeric with those in (a) CpRu-
(PPh3)(CO)SS(O)2-4-C6H4Me (Shaver, A.; Plouffe, P. Y. J. Am. Chem.
Soc. 1991, 113, 7780) and (b) CpRu(CO)2SS(O)2Ph (Trojansek, D.
Ph.D. Thesis, McGill University, 1995).
(13) (a) Michelin, R. A.; Napoli, M.; Ros, R. J. Organomet. Chem. 1979,
175, 239. (b) Barlex, D. M.; Kemmitt, R. D. W. J. Chem. Soc., Dalton
Trans. 1972, 1437. (c) Graziani, M.; Ros, R.; Carturna, G. J.
Organomet. Chem. 1971, 27, C19. (d) Schenk, W. A.; Karl, U. Z.
Naturforsch., B: Chem. Sci. 1989, 44B, 993. (e) Schenk, W. A.; Urban,
P.; Stahrfeldt, T.; Dombroswki, E. A. Z. Naturforsch., B: Chem. Sci.
1992, 47B, 1493.
(14) Ellen, P. G.; Ryan, R. R.; Moody, D. C. Inorg. Chem. 1976, 15, 2442.
(15) Shaver, A.; Hartgerink, J.; Lai, R. D.; Bird, P. Organometallics 1983,
2, 938.
(5) (a) Datta, A.; Cavell, R. G.; Tower, T. W.; George, Z. M. J. Phys.
Chem. 1985, 89, 443. (b) Datta, A.; Cavell, R. G. J. Phys. Chem.
1985, 89, 450. (c) Datta, A.; Cavell, R. G. J. Phys. Chem. 1985, 89,
454. (d) Karge, H. G.; Dalla Lana, I. G. J. Phys. Chem. 1984, 88,
1958.
(6) Levison, J. J.; Robinson, S. D. J. Chem. Soc., Dalton Trans. 1972,
2013.
S0020-1669(96)00617-9 CCC: $12.00 © 1996 American Chemical Society

Communications
Inorganic Chemistry, Vol. 35, No. 22, 1996 6357
Complex 1f reacted with ROH in CHCl3 to give quantitatively
the sulfito complexes trans-Pt(PPh3)2(phth)S(O)2OR8 (R ) H,
C2H5, CHMe2). These are resistant to loss of SO2 up to 200
°C. Exchange of 1f with RSH is very slow, whereas treatment
of 1f with H2S gave Pt(PPh3)2(H)(SH)22 and (PhCH2S)2 as the
1
major products as determined by H NMR.
Treatment of Pt(PPh3)3SO2 with the oxidized sulfur transfer
reagent RS(O)phth23 was expected to produce complexes
containing the PtS(O)2S(O)R moiety; however, complexes 1d-f
and PPh3O were isolated and there was no evidence of the
expected products. Since RS(O)phth is deoxygenated only very
slowly by PPh3, complexes 1d-f are probably the products of
deoxygenation of trans-Pt(PPh3)2(phth)S(O)2S(O)R by free PPh3
released from Pt(PPh3)3SO2. The apparent activation of the
Figure 1. ORTEP drawing of trans-Pt(PPh3)2(phth)SO2SCH2Ph, 1f.
Selected bond lengths (Å) and angles (deg): Pt-S, 2.261(3); Pt-P(1),
2.341(3); Pt-P(2), 2.360(2); Pt-N, 2.061(7); S(1)-S(2), 2.154(4);
S(1)-O(1), 1.446(7); S(1)-O(2), 1.451(7); Pt-S(1)-O(1), 114.4(3);
Pt-S(1)-O(2), 112.5(3); Pt-S(1)-S(2), 102.3(1); O(1)-S(1)-O(2),
114.2(5); P(1)-Pt-P(2), 171.1(1); S(1)-Pt-N, 177.2(2).
-
oxygen atom on the â-sulfur atom of the RS(O)S(O)2 ligand
is noteworthy. The complexes CpRu(PPh3)(CO)SS(O)R also
undergo facile oxygen exchange to give CpRu(PPh3(CO)SSR
and CpRu(PPh3)(CO)SS(O)2R.12 Kubas and co-workers have
observed similar chemistry.3h-k,24 On the other hand, complexes
1a-f, which have oxygen atoms on the R-sulfur atom, are inert
toward PPh3. This observation may be useful in developing
Claus-like chemistry with soluble metal complexes.
(CH2)4S] (Pt-S(O) ) 2.333(2) Å, Pt-S ) 2.334(3) Å).16 The
S-O bond lengths are within the normal range,17 while the S-S
bond distance (2.154(4) Å) is longer11c than that in 4-C6H4BrS-
(O)2S-4-C6H4Br (2.091(6) Å)11b and those in cis-Pt(PPh3)2(phth)-
SSCHMe2 (2.037(4) Å)15 and in other metal-coordinated
polysulfur oxide ligands of the type RS(O)S- and RS(O)2S-.18
Complex 1f lost SO2 at 110 °C under vacuum to give trans-
Pt(PPh3)2(phth)SCH2Ph, which does not react in solution with
SO2 to regenerate 1f. This leads one to suggest that the 1,2-
oxidative addition19 of RSphth to the Pt-SO2 bond in Pt(PPh3)3-
SO2 occurs via direct attachment of the RS+ group to the
pyramidal (nucleophilic)17 SO2 ligand rather than by attack at
the platinum metal atom followed by insertion of SO2 into the
Pt-SR bond thus formed. While insertion reactions of SO2
into metal-carbon bonds are well-known,20 similar insertion
reactions of SO2 into other metal-atom bonds are rare3fk,13ac,21
and are unknown for M-SR bonds even in complexes contain-
ing both the RS- and SO2 groups as ligands4 (i.e., model C).
Acknowledgment. We thank the Natural Sciences and
Engineering Council of Canada and the Quebec Department of
Education for financial support and postgraduate scholarships
to H.B.
Supporting Information Available: Text giving preparative
methods, spectroscopic data, and X-ray analysis and tables of crystal
data, atomic coordinates, anisotropic thermal parameters, bond lengths
and angles, and calculated hydrogen atom coordinates for 1f (16 pages).
See any current masthead page for ordering information.
IC960617A
(21) (a) Kubat-Martin, K. A.; Kubas, G. J.; Ryan, R. R. Organometallics
1988, 7, 1657. (b) Green, L. M.; Meek, D. W. Organometallics 1989,
8, 659. (c) Alcock, N. W.; Platt, A. W.; Powell, H. H.; Pringle, P. G.
J. Organomet. Chem. 1989, 361, 409. (d) Bryndza, H. E.; Dretchmor,
S. A.; Tulip, T. H. J. Am. Chem. Soc. 1986, 108, 4805. (e) Randall,
S. L.; Miller, C. A.; Janik, T. S.; Rowen-Churchill, M.; Atwood, J.
D. Organometallics 1994, 13, 141.
(22) (a) Blacklaws, I. M.; Ebsworth, E. A. V.; Rankin, D. W. H.; Robertson,
H. E. J. Chem. Soc., Dalton Trans. 1978, 753. (b) Ugo, R.; La Monica,
G.; Cenini, S. J. Chem. Soc. A 1971, 522. (c) Morelli, D.; Segre, A.;
Ugo, R.; LaMonica, G.; Cenini, S.; Conti, F.; Bonati, F. J. Chem.
Soc., Chem. Commun. 1967, 524.
(16) Weigand, W.; Bosl, G.; Robl, C.; Amrein, W. Chem. Ber. 1992, 125,
1047.
(17) Mingos, D. M. P. Transition Met. Chem. 1978, 3, 1.
(18) S-S bond distances are as follows. (a) CpRu(PPh3)(CO)E:12a E )
SS(O)CHMe2, 2.076(3) Å; E ) SS(O)2-4-C6H4Me, 2.023(3) Å. (b)
CpRu(CO)2E:12b E ) SS(O)Ph, 2.050(4) Å; E ) SS(O)2Ph, 2.037(2)
Å. (c) CpRu(PPh3)2E: E ) SS(O)CH2Ph, 2.086(3) Å (Weigand, W.;
Bosl, G.; Robl, C.; Kroner, J. Z. Naturforsch., B:; Chem. Sci. 1993,
48B, 627.
(19) Other examples of 1,2-oxidative addition to a metal-ligand bond: (a)
Casey, C. P.; Vosejpka, P. C.; Askham, F. R. J. Am. Chem. Soc. 1990,
112, 3713. (b) Reed, C. A.; Roper, W. R. J. Chem. Soc. A 1970, 3054.
(20) Wojcicki, A. AdV. Organomet. Chem. 1974, 12, 31.
(23) Harpp, D. N.; Back, T. G. J. Org. Chem. 1973, 38, 4328.
(24) Kubas, G. J. Acc. Chem. Res. 1994, 7, 183.