Scheme 2
[(C5Me5)Co]2(m-C4H4S)8 and [(dippe)Ni]2(m-C8H6S)9}, or the
migration of a CO group from one Re to the other.
The reaction of isomer 1A with 2 equiv. of PMe3 would lead
to product 2 in which the olefin is displaced and the Re–Re bond
is cleaved, leaving the terminal vinyl carbon coordinated to the
Re(CO)3 unit. On the other hand, the reaction of isomer 1 with
3 equiv. of PMe3 would lead to product 3 with the vinyl carbon
bonded to the Re(CO)4 moiety while undergoing Re–olefin,
Re–S and Re–Re bond cleavages. An attempt to detect the two
isomers of 1 by low temperature (250 °C, CD2Cl2 solvent) 1H
NMR spectroscopy showed only the same isomer that is present
in the room temperature spectrum.‡ However, variable tem-
perature 13C NMR spectra of 1 (250 °C to +20 °C) showed that
the CO ligands are fluxional. Thus, while the two isomers are
not detected by the NMR studies, a low concentration of the
highly reactive 1A would reasonably account for the formation of
2.
The reactions in Scheme 1 are of special interest because they
indicate the variety of ways that a bridging, C,S-cleaved BT
ligand can bind to two metal centers. Were C–S cleavage to
occur on a HDS catalyst, all three forms of BT represented in
compounds 1–3 would be potential modes of BT adsorption on
the catalyst surface.
Fig. 2 Molecular structure of 2 in the solid state. Selected bond lengths (Å)
and angles (°): Re(1)···Re(2) 4.2874(3), Re(1)–S 2.5027(9), Re(2)–S
2.5320(9), C(8)–S 1.796(3), Re(1)–C(1) 2.169(3), C(1)–C(2) 1.343(5),
Re(1)–S–Re(2) 116.76(3), C(1)–Re(1)–S 86.51(10), Re(1)–S–C(8)
109.94(12), Re(2)–S–C(8) 105.40(12), P(1)–Re(1)–S 87.24(3), P(2)–
Re(2)–S 88.04(3).
The X-ray structure of 2 (Fig. 2) shows that the C(1)–C(2)
2
double bond is no longer h -coordinated and the Re–Re bond
has been cleaved. Both Re atoms are pseudo-octahedral and
each contains a PMe3 ligand. The S bridges both Re atoms
almost symmetrically with distances of 2.5027(9) Å for Re(1)–
S and 2.5320(9) Å for Re(2)–S.
A single crystal X-ray analysis of 3 (Fig. 3) shows that there
are no single atom bridges between the two Re centers nor is
there a metal–metal bond. The Re centers are pseudo-octahedral
with respect to the C–Re–C angles between Re and adjacent CO
ligands. The Re(1)–C(1) distance is 2.205(3) Å which is longer
than that in either 1 or 2. The Re(2)–S distance is 2.5086(9) Å
which is similar to those in both 1 and 2.
The authors thank the U.S. Department of Energy, Office of
Science, Office of Basic Energy Sciences, Chemical Sciences
Division, under contract W-7405-Eng-82 with Iowa State
University for financial support.
Notes and references
† Satisfactory elemental analyses were obtained for 1–3.
‡ Selected spectroscopic data: for 1: 1H NMR (CD2Cl2, 300 MHz) d 8.63
(d, 1 H, J = 11.4 Hz), 7.11 (m, 2 H), 7.05 (dt, 1 H, J1 7.5, J2 1.5 Hz), 7.00
(d, 1 H, J 11.4 Hz), 6.93 (dt, 1 H, J1 7.2, J2 1.5 Hz). IR (hexanes) nCO
:
2099m, 2043s, 2027s, 1981s, 1977s, 1957m, 1947s cm21. For 2: 1H NMR
(CD2Cl2, 300 MHz): d 8.06 (dd, 1 H, J1 14.1, J2 2.4 Hz), 7.44 (dd, 1 H, J1
14.1, J2 3.6 Hz), 7.26 (d, 1 H, J 7.8 Hz), 7.00 (m, 2 H), 6.87 (m, 1 H), 1.87
(d, 9 H, PMe3, J 9.3 Hz), 1.19 (d, 9 H, PMe3, J 8.4 Hz). IR (CH2Cl2) nCO
:
2100w, 2003s, 1953m, br, 1896m, br, 1873m, br cm21. For 3: 1H NMR
(CD2Cl2, 300 MHz): d 7.89 (dd, 1 H, J1 13.5, J2 3.9 Hz), 7.43 (dd, 1 H, J1
7.8, J2 1.2 Hz), 7.21 (d, 1 H, J 7.2 Hz), 6.99 (dt, 1 H, J1 7.5, J2 1.5 Hz), 6.92
(m, 2 H), 1.62 (m, 27 H, 3PMe3). IR(CH2Cl2) nCO 2079w, 2018s, 1978s(sh),
1972s, 1933s, 1893s cm21
.
crystallographic files in .cif format.
1 H. Topsø´e, B. S. Clausen and F. E. Massoth, Hydrotreating Catalysts in
Catalysis: Science and Technology, ed. J. R. Anderson and M. Boudart,
Springer-Verlag, Berlin, Heidelberg, 1996, vol. 11.
2 R. J. Angelici, in Encyclopedia of Inorganic Chemistry, ed. R. B. King,
Wiley, New York, 1994, vol. 3, pp 1433–1443.
3 B. C. Gates, J. R. Katzer and G. C. A. Schuit, Chemistry of Catalytic
Processes, MacGraw Hill, New York, 1979, pp. 390–447; G. D. Galpern,
in The Chemistry of Heterocyclic Compounds, ed. S. Gronowitz, John
Wiley and Sons, Inc., New York, 1985, vol. 44, Part 1, pp. 325–351.
4 N. Flitcroft, D. K. Huggins and H. D. Kaesz, Inorg. Chem., 1964, 3,
1123.
5 M. R. Churchill, K. N. Amoh and H. J. Wasserman, Inorg. Chem., 1981,
20, 1609.
6 A. E. Ogilvy, M. Draganjac, T. B. Rauchfuss and S. R. Wilson,
Organometallics, 1988, 7, 1171.
7 W. D. Jones, D. A. Vicic, R. M. Chin, J. H. Roache and A. W. Myers,
Polyhedron, 1997, 16, 3115.
8 W. D. Jones and R. M. Chin, Organometallics, 1992, 11, 2698.
9 D. A. Vicic and W. D. Jones, J. Am. Chem. Soc., 1999, 121, 7606.
Fig. 3 Molecular structure of 3 in the solid state. Selected bond lengths (Å)
and angles (°). Re(1)–C(1) 2.205(3), Re(2)–S 2.5086(9), C(1)–C(2)
1.327(4), S–C(8) 1.769(3), C(2)–C(3) 1.479(4), Re(1)–C(1)–C(2) 134.8(3),
C(8)–S–Re(2) 113.18(12), P(2)–Re(2)–S 84.54(3), C(1)–C(2)–C(3)
129.8(3), C(1)–Re(1)–P(1) 82.44(8).
In the reaction (Scheme 1) of 1 with PMe3, the relative
amounts of 2 and 3 formed are the same whether 1 or 5 equiv.
of PMe3 are used. This means that the tri-phosphine product 3
is not formed from the bis-phosphine product 2 even in the
presence of an excess of PMe3. Therefore 2 and 3 must form by
independent pathways. The structures of 2 and 3 are also
fundamentally different from each other because the terminal
vinyl carbon is bound to the Re(CO)3 unit in 2 whereas in 3 it
is coordinated to the Re(CO)4 group. The formation of these
products may be understood in terms of a mechanism that
involves two forms of 1 resulting (Scheme 2) either from a “flip-
flop” of the vinyl group from one Re to the other, as proposed
for related bridging thiophene complexes {Fe2(CO)6(C8H6S),6
Communication a909161k
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Chem. Commun., 2000, 513–514