Synthesis of d2 tungsten arene complexes and their reaction with diphenylacetylene

Article abstract of DOI:10.1021/om0004390

The synthesis of the d² arene complexes [W(NPh)(η⁶-arene)(o-Me₃SiN)₂C₆H₄)] (arene = C₆H₆Et (3), C₆H₅Pr (4) by the room-temperature hydrogenolysis

Full text of DOI:10.1021/om0004390

Organometallics 2000, 19, 2953-2955
2953
Syn th esis of d 2 Tu n gsten Ar en e Com p lexes a n d Th eir
Rea ction w ith Dip h en yla cetylen e
R. C. Mills, K. A. Abboud, and J . M. Boncella*
Department of Chemistry and Center for Catalysis, University of Florida,
Gainesville, Florida 32611-7200
Received May 24, 2000
Summary: The synthesis of the d2 arene complexes
Sch em e 1
[W(NPh)(η6-arene)(o-(Me3SiN)2C6H4)] (arene ) C6H5Et
(3), C6H5Pr (4)) by the room-temperature hydrogenolysis
of the dialkyl complexes [W(NPh)(o-(Me3SiN)2C6H4)(R)2]
(R ) CH2CH2Ph (1), CH2CH2CH2Ph (2)) is described.
The ethylbenzene complex 3 reacts with diphenylacety-
lene, giving the metallacyclopent-3-ene complex 5.
The chemistry of metal complexes containing six-
membered π-arene ligands has been thoroughly devel-
oped since Fischer and Hafner first characterized Cr(η6-
benzene)2.1 Stable arene complexes have now been
characterized for virtually all of the transition metals.2
Although most early examples were limited to com-
pounds containing metals in low oxidation states,3 more
recently d0 metal arenes have become more common.4
Surprisingly, examples of d2 arene complexes have been
limited to [Zr(η6-C6H5Me)(PMe3)2Cl2]5 and [Ti(η6-C6H6)-
(AlCl3)2Cl2],6 formed from the reduction of the appropri-
ate metal halide in the presence of an arene, and [Ta-
(η6-C6Me6)(OAr)2Cl],7 formed from the metal-mediated
cyclotrimerization of 2-butyne. Following earlier work
from our group on the reactivity of â-hydrogen-contain-
ing W(VI) dialkyl complexes of the type [W(NPh)(o-(Me3-
SiN)2C6H4)R2] (where R ) CH2CH3, CH2CMe3)8 with
H2,9 we report the synthesis of d2 tungsten arene com-
plexes with the general formula [W(NPh)(η6-arene)-
(1) (a) Fischer, E. O.; Hafner, W. Z. Naturforsch. 1955, 10B, 665.
(b) Marr, G.; Rockett, B. W. In The Chemistry of the Metal-Carbon
Bond; Hartle, F. R., Patai, S., Eds.; Wiley: New York, 1982. (c)
Calderazo, F.; Pampaloni, G. J . Organomet. Chem. 1992, 423, 307. (d)
J olly, P. W. Acc. Chem. Res. 1996, 26, 544.
(2) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
(3) (a) Maslowsky, E. J . J . Chem. Educ. 1992, 70, 980. (b) Green,
M. L. H. J . Organomet. Chem. 1980, 200, 119. (c) Yoon, M.; Lin, J .;
Young, V. G.; Miller, G. J . J . Organomet. Chem. 1996, 507, 31. (d)
Lockwood, M. A.; Fanwick, P. E.; Eisenstein, O.; Rothwell, I. P. J . Am.
Chem. Soc. 1996, 118, 2762. (e) Maseras, F.; Lockwood, M. A.;
Eisenstein, O.; Rothwell, I. P. J . Am. Chem. Soc. 1998, 120, 6598. (f)
Ashmore, J .; Green, J . C.; Green, M. L. H.; Smith, M. L.; Menhert, C.
D.; Wucherer, E. J . J . Chem. Soc., Dalton Trans. 1995, 1873. (g)
Menhert, C. D.; Chenega, A. N.; Green, M. L. H. J . Organomet. Chem.
1996, 513, 247. (h) Lockwood, M. A.; Fanwick, P. E.; Rothwell, I. P.
Polyhedron 1995, 14, 3363. (i) Wexler, P. A.; Wigley, D. E.; Koerner,
J . B.; Albright, T. A. Organometallics 1991, 10, 2319.
(4) (a) Horton, A. D.; de With, J . Organometallics 1997, 16, 5424.
(b) Thorn, M. G.; Etheridge, Z. C.; Fanwick, P. E.; Rothwell, I. P.
Organometallics 1998, 17, 3636. (c) Muso, F.; Solari, E.; Floriani, C.;
Schenk, K. Organometallics 1997, 16, 4889. (d) Calderazo, F.; Ferri,
I.; Pampaloni, G.; Troyanov, S. J . Organomet. Chem. 1996, 518, 187.
(e) Lancaster, S. J .; Robinson, G. B.; Bochman, M.; Coles, S. J .;
Hursthouse, M. B. Organometallics 1995, 14, 2456. (f) Pellechia, C.;
Grassi, A.; Immirzi, A. J . Am. Chem. Soc. 1993, 115, 1160.
(5) Diamond, G. M.; Green, M. L. H.; Walker, N. M.; Howard, J . A.
K.; Mason, S. A. J . Chem. Soc., Dalton Trans. 1992, 2641.
(6) Troyanov, S. J . Organomet. Chem. 1994, 475, 139.
(o-(Me3SiN)2C6H4)] (arene ) CH3CH2C6H5, CH3CH2-
CH2C6H5) and their reaction with diphenylacetylene.
Room-temperature hydrogenolysis (34 psi, H2) of a
toluene solution of [W(NPh)(o-(Me3SiN)2C6H4)(CH2-
CH2C6H5)2] (1) or [W(NPh)(o-(Me3SiN)2C6H4)(CH2CH2-
CH2C6H5)2] (2) (Scheme 1) results in a slow color change
from orange to dark purple over several days. From this
solution, the d2 arene complexes [W(NPh)(η6-ethylben-
zene)(o-(Me3SiN)2C6H4)] (3) and [W(NPh)(η6-propylben-
zene)(o-(Me3SiN)2C6H4)] (4) (Scheme 1) can be isolated
as dark purple solids. Compounds 3 and 4 are indefi-
(8) (a) Wang, S. Y. S.; Abboud, K. A.; Boncella, J . M. J . Am. Chem.
Soc. 1997, 119, 11990. (b) Vanderlende, D. D.; Wang, S. Y. S.; Boncella,
J . M. J . Organomet. Chem. 1997, 530, 59.
(7) Bruck, M. A.; Copenhaver, A. S.; Wigley, D. E. J . Am. Chem.
Soc. 1987, 109, 6525.
(9) Boncella, J . M.; Vanderlende, D. D.; Wang, S. Y. S. J . Organomet.
Chem. 1999, 591, 8.
10.1021/om0004390 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 07/14/2000

2954 Organometallics, Vol. 19, No. 16, 2000
Communications
F igu r e 1. Molecular structure of W(NPh)(η4-propylben-
zene)(o-(Me3SiN)2C6H4) (4), showing 40% thermal ellipsoids
and the atom-labeling scheme. The silylmethyl hydrogen
atoms have been removed for clarity. Selected bond dis-
tances (Å): W-N(1), 1.762(4); W-N(2), 2.057(4); W-N(3),
2.056(4); W-C(1), 2.533(5); W-C(2), 2.503(5); W-C(3),
2.251(5); W-C(4), 2.363(5); W-C(5), 2.382(5); W-C(6),
2.267(5); C(1)-C(2), 1.371(6); C(2)-C(3), 1.459(7); C(3)-
C(4), 1.416(7); C(4)-C(5), 1.372(7); C(5)-C(6), 1.434(7);
C(6)-C(1), 1.459(7). Selected bond angles (deg): W-N(1)-
C(7), 155.2(6); N(1)-W-N(2), 102.50(16), N(1)-W-N(3),
103.44(16); N(3)-W-N(2), 77.66(14).
F igu r e 2. Molecular structure of the W metallacyclopent-
3-ene complex 5, showing 40% thermal ellipsoids and the
atom-labeling scheme. All hydrogen atoms have been
removed for clarity, except those of the metallacycle.
Selected bond distances (Å): W-N(1), 1.745(3); W-N(2),
2.034(3); W-N(3), 2.037(3); W-C(1), 2.162(4); W-C(2),
2.589(4); W-C(3), 2.582(3); W-C(4), 2.204(4); C(1)-C(2),
1.497(5); C(2)-C(3), 1.364(5); C(3)-C(4), 1.495(5). Selected
bond angles (deg): W-N(1)-C(24), 176.2(3); C(1)-W-C(4),
76.97(15); N(2)-W-N(3), 79.43(12).
Sch em e 2
are significantly shorter than those for ring carbons 1
(2.533 Å) and 2 (2.503 Å) (Figure 1). As a result, a
considerable distortion from planarity of the coordinated
arene ring is observed (the angle between the planes
formed by C2-C1-C6-C5 and C2-C3-C4-C5 is 20.4°).
Furthermore, the short ring C-C distances for C4-C5
(1.372 Å) and C1-C2 (1.371 Å), consistent with C-C
double bonds, coupled with the fold of the arene ring
indicate that there is a significant disruption of aroma-
ticity upon coordination. Overall, the interaction of the
arene ring with the tungsten center in 4 is similar to
the (σ2π) bonding extreme of a 1,3-butadiene-metal
interaction.12 Despite the inherent stability of the
coordinated arene ring in 3 and 4, compound 3 was
found to undergo a unique coupling reaction with
diphenylacetylene.
nitely stable at room temperature in the solid state
when stored under an inert atmosphere. In addition,
solutions of both 3 and 4 display surprising stability
toward arene-arene exchange reactions which have
been observed to readily occur for analogous molybde-
num arene complexes,10 suggesting a more robust
interaction between tungsten and the arene ring. The
Thermolysis (60 °C) for 12 h of a toluene solution
containing equimolar amounts of 3 and PhCtCPh
afforded the W(VI) metallacyclopent-3-ene species [o-
(Me3SiN)2C6H4)(NPh)WCH2C(Ph)dC(Ph)CHPh] (5) in
1
54% yield (Scheme 2). The H NMR of 5 displays two
2
doublet resonances (2.58 and 2.81 ppm, J ) 10.8 Hz)
and a singlet resonance (4.77 ppm, 2J (W-H) ) 4.8 Hz),
for the R-CH2 and R-CH protons of the metallacycle,
respectively. In the 13C{1H} NMR spectrum the two
carbons bonded to the metal center resonate at δ 57.74
1
new π-bound arene ring is clearly indicated in the H
NMR spectra of 3 and 4. The aromatic resonances of
the coordinated ring display typical upfield chemical
shifts (δ 4.27 (t), 4.65 (d), 4.73 (t) for 3 and δ 4.29 (t),
4.68 (d), 4.74 (t) for 4) associated with arene complexes
due to the depletion of π-electron density from the ring
upon coordination to the metal center.2
Single crystals of 4 suitable for an X-ray diffraction
study were obtained through slow evaporation of a
concentrated C6D6 solution of 4.11 The crystal structure
of 4 shows that the arene ring is coordinated in an η4
fashion. The W-C distances of four of the ring carbons,
3 (2.251 Å), 4 (2.363 Å), 5 (2.382 Å), and 6 (2.267 Å),
1
ppm as a triplet with J (13C-1H) ) 143.0 Hz and 73.72
ppm as a doublet with 1J (13C-1H) ) 137.36 Hz.13 An
X-ray diffraction study of a single crystal of 5 grown by
slow evaporation of a pentane solution of 5 (Figure 2)
confirmed the metallacyclopent-3-ene structure which
was deduced from the spectroscopic data.14
(11) Crystal data for 4: C27H39N3Si2W, Mr ) 645.64, monoclinic, P21/
n, dark red-purple, a ) 12.1874(5) Å, b ) 15.6037(7) Å, c ) 14.5968(6)
Å, R ) 90°, â ) 94.317(1)°, γ ) 90°, 173(2) K, Z ) 4, R ) 0.0371 with
GOF ) 0.961 on F2.
(10) Ortiz, C. G.; Boncella, J . M. Unpublished results.
(12) Maslowsky, E. J . Chem. Educ. 1992, 70, 980.

Communications
Organometallics, Vol. 19, No. 16, 2000 2955
followed by rearrangement16 to generate 5. Support for
the proposed formation of the η2-styrene intermediate
through loss of H2 comes from reactions of the mixed-
dialkyl tungsten complex [W(NPh)(o-(Me3SiN)2C6H6)-
(CH2CH2C6H5)(Me)] with PhCtCPh, in which 5 is
formed in high yield.17
Sch em e 3
We are currently investigating the scope of this type
of chemistry with several different mixed-dialkyl sys-
tems and a variety of unsaturated substrates. Our
interest in the initial coupling of coordinated ethylben-
zene with PhCtCPh focuses on the observed loss of H2.
Further studies into the mechanism for this process and
the possible generality of the dehydrogenation of the
arene side chain are currently in progress.
Ack n ow led gm en t. We wish to acknowledge the
National Science Foundation (Grant No. CHE-9523279)
for the support of this work. K.A.A. wishes to acknowl-
edge the National Science Foundation and the Univer-
sity of Florida for funding of the purchase of the X-ray
equipment.
It has been shown that early-transition-metal com-
plexes facilitate the metal-mediated [2 + 2] cycloaddi-
tion of alkynes and olefins to generate metallacyclo-
pentenes.15 The formation of 5 appears to proceed by
initial C-H bond activation of the coordinated ethyl-
benzene in 3, followed by reductive elimination of H2
(Scheme 3). The intermediate η2-styrene complex then
undergoes the expected cycloaddition with PhCtCPh
Su p p or tin g In for m a tion Ava ila ble: Figures giving 300
MHz 1H NMR spectra of 2-5 and tables of crystal data,
structure solution and refinement, atomic coordinates, bond
lengths and angles, and anisotropic thermal parameters for 4
and 5. This material is available free of charge via the Internet
at http://pubs.acs.org.
(13) The 1J (13C-1H) coupling constants measured for the R-carbons
of 5 (143 and 137 Hz) are similar to those for strongly σ2π-bound group
4 and 5 butadiene complexes (138-150 Hz):13a-c (a) Yasuda, H.;
Tatsumi, K.; Nakamura, A. Acc. Chem. Res. 1985, 18, 120. (b) Kruger,
C.; Muller, G.; Erker, G.; Dorf, U.; Engel, K. Organometallics 1985, 4,
215. (c) Yasuda, H.; Tatsumi, K.; Okamoto, T.; Mashima, K.; Lee, K.;
Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1985, 107, 2410.
(14) Crystal data for 5: C40H46N3Si2W, Mr ) 808.83, monoclinic, P21/
n, dark red-brown, a ) 18.4684(8) Å, b ) 20.4038(9) Å, c ) 20.9892(9)
Å, R ) 90°, â ) 109.780(1)°, γ ) 90°, 173(2) K, Z ) 8, R ) 0.0328 with
GOF ) 1.072 on F2.
(15) (a) Erker, G.; Kropp, K. J . Am. Chem. Soc. 1979, 101, 3659. (b)
Erker, G.; Dorf, U.; Rheingold, A. L. Organometallics 1988, 7, 138. (c)
Takahasi, T.; Xi, Z.; Rousset, C. J .; Suzuki, N. Chem. Lett. 1993, 1001.
(d) Mansel, S.; Thomas, D.; Lefeber, C.; Heller, D.; Kempe, R.;
Baumann, W.; Rosenthal, U. Organometallics 1997, 16, 2886.
OM0004390
(16) Reaction of an analogous Mo styrene complex with PhCtCPh
at room temperature initially (after 2 h) yields a metallacyclopent-2-
ene. Over a period of 2 days this product is slowly converted to a
metallacyclopent-3-ene analogous to 5, suggesting the final step in the
formation of 5 is rearrangement of the metallacyclopent-2-ene.
(17) Thermolysis (70 °C) of a toluene solution of the mixed-dialkyl
complex [W(NPh)(o-(Me3SiN)2C6H6)(CH2CH2C6H5)(Me)] yields an η2-
styrene complex with the liberation of CH4. In agreement with the
proposed mechanism for the formation of 5, thermolysis of [W(NPh)-
(o-(Me3SiN)2C6H6)(CH2CH2C6H5)(Me)] in the presence of 1 equiv of
PhCtCPh produces 5 in good yield.