Synthesis and characterization of the monomeric molybdenum trithiolate Mo(η7-dmpt)(η1-dmpt)2 (dmpt = 2,6-dimesitylphenylthiolate)

Article abstract of DOI:10.1039/a803064b

Treatment of MoCl₃(THF)₃ with 3 equiv. of LiSC₆H₃Mes₂-2,6 (Mes = C₆H₂Me₃-2,4,6) (Lidmpt) affords the monomeric molybdenum trithiolate Mo(η⁷-dmpt)(η¹

Full text of DOI:10.1039/a803064b

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Synthesis and characterization of the monomeric molybdenum trithiolate
7
1
Mo(h -dmpt)(h -dmpt)2 (dmpt = 2,6-dimesitylphenylthiolate)
Birsen S. Buyuktas, Marilyn M. Olmstead and Philip P. Power*†
Department of Chemistry, University of California, Davis, California 95616, USA
Treatment of MoCl3(THF)3 with 3 equiv. of LiSC6H3Mes2-
2,6 (Mes = C6H2Me3-2,4,6) (Lidmpt) affords the monomeric
a consequence of the large size of the SC6H3Mes2-2,6 ligand
and the p-interaction between one of the mesityl groups on the
ligand and the metal. The metal–ligand p-interaction may arise
in part from the unique reactivity of the trigonal MoIII fragment4
which in the case of the Mo[N{C(CD3)2CH3}C6H3Me2-3,5]3
complex is capable of activating N23b,9 to afford, inter alia, the
nitride N°Mo[N{C(CD3)2CH3}C6H3Me2-3,5]3. In the case of
1, the strong interaction between the metal and a p-ring system
apparently prevents the dinitrogen activation observed for the
amide complexes. Note that the synthesis and manipulation of 1
were conducted under an N2 atmosphere. Furthermore, hexane
solutions of purified 1 show no sign of reaction with N2 upon
standing for 3 days at room temperature. Although the structure
of 1 is unique it may be compared to that described for the MoII
7
1
molybdenum trithiolate Mo(h -dmpt)(h -dmpt)2, 1, which is
spectroscopically and structurally characterized; the MoS3
array has distorted trigonal pyramidal geometry which is
caused by strong p-interactions between molybdenum and
an ortho-mesityl group from one of the thiolate sub-
stituents.
Stable, well characterized examples of monomeric, three-
coordinate MoIII complexes are rare. In general, such com-
pounds are dimerized to form triply bonded species of formula
L3Mo°MoL3 (L = uninegative ligand) which have been
extensively studied.1 Although it is probable that the in-
completely characterized, sterically encumbered derivatives
Mo{N(Pri)2}3 and Mo{N(SiMe3)2}3 are monomers,2 the
first well established three-coordinate MoIII compound was
7
1
species [Mo(h -dpt)(h -dpt)(CO)], 2 (dpt = SC6H3Ph2-2,6)10a
6
which also possesses a Mo–h -Ph ring interaction involving a
thiolate ligand.10b However, the h -coordination of the ortho-
6
3
Mo[N{C(CD3)2CH3}C6H3Me2-3,5]3 which, like the related
phenyl ring may be displaced by the addition of CO or bidentate
neutral ligands such as 2,2A-bipyridyl. The Mo–S distances in 2
[2.239(4) and 2.358(3) Å] are quite similar to those in 1.
molybdenum triamidoamine derivative [Mo(OTf)({C6F5N-
(CH2)2}3N)],4 activates dinitrogen at room temperature to form
a variety of complexes, including imines and nitrides. The
stabilization of these unusual and interesting complexes by
bulky aryl amido substituents suggested that it should be
possible to isolate further examples of monomeric, low
coordinate trivalent complexes with other ligands. Here it is
shown that the use of the thiolate ligand SC6H3Mes2-2,6
(dmpt)5 enables the isolation of the first monomeric homoleptic
6
However, the distortions in the geometry of the h -interacting
6
Mes ring in 1 are not observed in the h -Ph ring of 2 although
in the latter the ipso-carbon is displaced slightly (by ca. 0.14 Å)
from the averaged plane of the other five ring carbon atoms.
The structural distortion observed in the mesityl ring which
interacts with Mo has similarities to those observed in a variety
of transition metal complexes.11 In many instances this results
in a 1,4-diene type of localization of multiple bond character
within the aromatic ring. In 1, however, the localization does not
show a regular pattern. Thus, although the C(8)–C(9) distance,
1.360(9) Å, is short, the C(11)–C(12) distance, 1.420(10) Å, is
7
1
molybdenum trithiolate complex Mo(h -dmpt)(h -dmpt)2, 1.
Complex 1 was synthesized in moderate yield‡ by the
reaction of 3 equiv. of LiSC6H3Mes2-2,6 with MoCl3(THF)3.6
The dark red, almost black, crystalline product, 1, has good
solubility in hydrocarbon solvents. The electronic absorption
spectrum is almost featureless with a rapid rise in absorption at
< 400 nm and a very weak shoulder at 490 nm (e = 4600) is
apparent. Magnetic studies confirm the paramagnetic character
with mB = 3.6 (T = 293 K). The monomeric structure of 1 was
established by a single crystal X-ray crystal study of its pentane
solvate, 1·0.25pentane.§ The Mo atom is bound to three thiolate
sulfurs and two of the Mo–S distances have almost equal values
of 2.393(2) and 2.394(2) Å, whereas the other is slightly
shortened to 2.314(2) Å. The MoS3 array is grossly distorted
from planarity as indicated in the three S–Mo–S angles, which
have the values 88.68(6), 105.59(7), and 91.67(7)°. The Mo–
S–C angles also are different with an angle of 102.3(2)° being
observed at S(1) (which bears the mesityl ring that interacts with
Mo, vide infra) which is 14–16° narrower than the correspond-
ing angles at S(2) and S(3). The coordination sphere of Mo is
completed by a strong interaction with the C(11) ortho-mesityl
ring. This ring is bent along the C(7)···C(10) axis (fold angle =
159.4°) such that these two atoms are closest to Mo [Mo–C
distances = 2.220(6) and 2.248(7) Å] while the Mo–C distances
to the remaining ring carbons are in the range 2.295(6)–2.502(6)
Å.
Fig. 1 Thermal ellipsoid plot of 1. Important bond distances (Å) and angles
(°) are as follows: Mo–S(1) 2.393(2), Mo–S(2) 2.394(2), Mo–S(3) 2.314(2),
Mo–C(7) 2.220(6), Mo–C(8) 2.502(6), Mo–C(9) 2.433(6), Mo–C(10)
2.248(7), Mo–C(11) 2.295(6), Mo–C(12) 2.389(8), S(1)–Mo–S(2)
88.68(6), S(1)–Mo–S(3) 105.59(7), S(2)–Mo–S(3) 91.67(7), Mo–
S(1)–C(1) 102.3(2), Mo–S(2)–C(25) 116.1(2), Mo–S(3)–C(49) 118.6(2)°.
Previous examples of related MoIII thiolates [e.g.
7
Mo2(SMes)6
or the heteroleptic species Mo2{S-
8
(But)}2(NMe2)4 ] have been shown to be dimeric with Mo–Mo
triple bonds. The monomeric structure observed for 1 (Fig. 1) is
Chem. Commun., 1998
1689

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under reduced pressure to ca. 15 ml and storage of the solution in a 220 °C
near normal for an aromatic ring, whereas the C(7)–C(8) bond
is lengthened to 1.494(9) Å. Perhaps the most structurally
freezer gave black crystals of 1·0.25pentane, which were suitable for X-ray
structure determination. Total yield: 1.08 g, 51%, mp 112–115 °C. Anal.
Calc. for 1, C72H75S3Mo: C, 76.36; H, 6.68. Found C, 75.94; H, 6.81%.
UV–VIS (lmax, e): 490 nm (sh), 4600 dm3 mol21 cm21. IR (Nujol,
n/cm21): 3040sh, 2950s, 2920s, 2850s, 2720w, 1720w, 1610m, 1560w,
1460s, 1450s, 1370s, 1255m, 1090w, 1020w, 845, 800m, 740w, 730w,
710w. Magnetic moment mB = 3.6 (T = 293 K).
related Mo environment to that seen in
1
is in
[{(h -PhMe)Mo(µ-SMe)2}2][PF6]2.12 In this case, the oxidation
state of Mo is also 3+; however, the Mo–S distances
[2.451(1)–2.462(1) Å] are, of course, considerably longer
owing to their bridging nature. Nonetheless, the range of Mo–C
distances [2.287(3)–2.416(3) Å] is similar to the
2.220(6)–2.502(6) Å range observed in 1. In essence, the Mo–
ring p-interaction in 1 is as strong as that seen for other Mo
species with neutral 6p-electron ring donors. Furthermore, the
6
§ Crystal data for 1 at T = 130 K with Mo-Ka (l = 0.71073 Å) radiation:
M = 1150.48, a = 27.927(6), b = 19.974(4), c = 23.346(5) Å, b =
103.82(3)°, V = 12646(4) Å3, m = 0.347 mm21, monoclinic, space group
C2/c, Z = 8, R1 = 0.062 for 6177 [I > 2s(I)] data. CCDC 182/922.
7
Mo–S distances are similar to those observed in Mo2(SMes)6
but longer than the 2.262(1) Å in the Mo4+ species Mo(SC6H2-
Pri3-2,4,6)4.13
1 F. A. Cotton and R. A. Walton, Multiple Bonds between Metal Atoms,
Clarendon, Oxford, 2nd edn., 1993.
2 M. H. Chisholm, Acc. Chem. Res., 1990, 23, 419; M. H. Chisholm and
W. Reichert, Adv. Chem. Ser., 1976, 150, 273; D. C. Bradley and M. H.
Chisholm, Acc. Chem. Res., 1976, 9, 273.
3 (a) C. E. Laplaza, A. L. Odom, W. M. Davis, C. C. Cummins and J. D.
Protasiewicz, J. Am. Chem. Soc., 1995, 117, 4999; (b) C. E. Laplaza,
M. J. A. Johnson, J. Peters, A. L. Odom, E. Kim, C. C. Cummins, G. N.
George and I. J. Pickering, J. Am. Chem. Soc., 1996, 118, 8623; (c) C. C.
Cummins, Prog. Inorg. Chem., 1998, 47, 685.
4 R. R. Schrock, Acc. Chem. Res., 1997, 30, 9 and references therein.
5 J. J. Ellison, K. Ruhlandt-Senge and P. P. Power, Angew. Chem., Int. Ed.
Engl., 1994, 33, 1178.
6 J. R. Dilworth and J. Zubieta, Inorg. Synth., 1986, 24, 193.
7 M. H. Chisholm, J. F. Corning and J. C. Huffman, J. Am. Chem. Soc.,
1983, 105, 5924.
8 M. H. Chisholm, J. F. Corning and J. C. Huffman, Inorg. Chem., 1983,
22, 38; M. H. Chisholm, J. F. Corning, K. Folting and J. C. Huffman,
Polyhedron, 1985, 4, 383.
9 C. E. Laplaza and C. C. Cummins, Science, 1995, 268, 861.
10 (a) P. T. Bishop, J. R. Dilworth, T. Nicholson and J. Zubieta, J. Chem.
Soc., Dalton Trans., 1991, 385; (b) for ortho-aryl phenoxide–group 6
metal interactions see: M. A. Lockwood, P. E. Farwick, O. Eisenstein
and I. P. Rothwell, J. Am. Chem. Soc., 1996, 118, 2762.
11 D. J. Arney, P. A. Wexler and D. E. Wigley, Organometallics, 1990, 9,
1282.
In summary, the SC6H3Mes2-2,6 ligand permits the isolation
of the first monomeric complex of formula Mo(SR)3 (R = alkyl
or aryl group). However, intramolecular interactions between
the Mo atom and a ligand Mes ring prevent the molecule from
displaying significant reactivity toward N2 under ambient
conditions.
We thank the National Science Foundation and the Donors of
the Petroleum Research Fund administered by the American
Chemical Society for financial support and TUBITAK (Turkish
Scientific and Technical Research Institution) for fellowship
support for B. B.
Notes and References
† E-mail: pppower@uc.davis.edu
‡ All manipulations were carried out under anaerobic and anhydrous
conditions. The thiol HSC6H3Mes2-2,6 was synthesized as described in the
literature.5 1·0.25pentane: HSC6H3Mes2-2,65 (1.91 g, 5.5 mmol) was
dissolved in diethyl ether (25 ml) and treated slowly with BunLi (3.6 ml of
a 1.6
M solution in hexane; 5.5 mmol) with cooling in an ice bath. The
mixture was stirred for 30 min at 0 °C and allowed to warm to room
temperature with continuous stirring for a further 1 h. The solution was then
6
added slowly to a suspension of MoCl3(THF)3 (0.767 g, 1.83 mmol) in
12 W. E. Silverthorn, C. Couldwell and K. Prout, J. Chem. Soc., Chem.
Commun., 1978, 1009.
13 E. Roland, E. C. Walborsky, J. C. Dewan and R. R. Schrock, J. Am.
Chem. Soc., 1985, 107, 5795.
diethyl ether (25 ml) at ca. 0 °C. The mixture became deep red and stirring
was continued for 18 h at room temperature. The precipitate was allowed to
settle and the supernatant, deep red solution was decanted to another
Schlenk tube via a cannula. The ether was evaporated under reduced
pressure and hexane (40 ml) was added to the dark red residue. Filtration
through Celite gave a clear, dark red solution. Reduction of the volume
Received in Bloomington, IN, USA, 24th April 1998; 8/03064B
1690
Chem. Commun., 1998