Synthetic and mechanistic studies of the four-electron reduction of dioxygen, N=N, and N=O double bonds by tungsten(II) aryloxide compounds

Article abstract of DOI:10.1021/om030604m

Reduction of the cyclometalation-resistant aryloxide compounds [W(OC₆HPh₂-2,6-R₂-3,5)₂- fCl₄] (1, R = Ph; 2, R = Me; 3, R = Bu^t) in the presence of a variety of phosphine ligands generates the W(II) species [W(OC₆HR₂Ph-η⁶-C₆H₄) (OC₆HPh₂-2,6- R₂-3,5)(L)] (4-6) in moderate yield. Compounds 4-6 contain a three-legged piano-stool geometry with one of the aryloxide ligands chelated to the tungsten via an ortho phenyl ring. Solid-state structural parameters for the PMe₃, PEt₃, and PBuⁿ₃ adducts 4b-d indicate a shortening of the W-C(ipso) and W-C(para) distances consistent with a tungstanorbornadiene resonance contribution. Solution studies of 4b show that exchange on the NMR time scale of ortho and meta protons occurs at elevated temperatures via phosphine dissociation and not π-arene dissociation. Reaction of 4b with O₂ or the trans-diazines PhN=NPh, TolN=NTol, and PhN=NTol (Tol = 4-methylphenyl) led to the corresponding bis(oxo) and bis(arylimido) derivatives [W(OC₆HPh₄-2,3,5,6)₂(X)₂ (PMe₃)] (X = O, NPh, Ntol; 7-10, respectively). Structural studies show a trigonal-bipyramidal geometry for 7 and 10 with equatorial O or NAr groups and an axial PMe₃. Formation of the mixed-imido species [W(OC₆HPh₄-2,3,5,6)₂(NPh)(NTol)(PMe₃ )] (10) did not involve generation of any 8 or 9. Cleavage of nitrosobenzene by 4b led to [W(OC₆-HPh₄-2,3,5,6)₂ (NPh)(O)(OPMe₃)] (11) containing terminal oxo and phenylimido groups and a phosphine oxide donor ligand. Compound 4b was also found to ring-open the substrates pyridazine, benzo[c]cinnoline, and phthalazine to produce the three new seven-membered diaza metallacycles 12-14. Structural studies show 12 and 14 to contain planar rings, whereas the two backbone phenyl rings in 13 are twisted by 33° with respect to each other. Structural parameters are more consistent with a formulation as a d⁰-W(VI) metal center with a 2,7-diazatungstahepta-1,3,5,7-tetraene ring and two tungsten-imido bonds for 12 and 14, although there is some evidence for a 2,7-diazatungstahepta-2,4,6-triene (d²-W(IV) metal center) resonance contribution for 14. A kinetic study of the reaction of 4b with trans-4,4′-dimethylazobenzene (TolN=NTol) to produce 9 was carried out. The rate of disappearance of 4b was monitored using ¹H NMR and shown to have a first-order dependence on both [4b] and [TolN=NTol] and inverse first-order dependence on [PMe₃]. The kinetic data was fit to a mechanistic model involving fast exchange of azobenzene with PMe₃ followed by a rate-determining product formation. The concentration of free PMe₃ (strong inhibition) is controlled by the position of the fast coordination equilibrium of the product [W(OC₆HPh₄-2,3,5,6)₂ (NTol)₂(PMe₃)] (9). Reaction of trans-MesN=NMes (NMes = NC₆H₃Me₃-2,4,6) with 4b was slow even at 100°C. However, photolysis to produce cis-MesN=NMes led to rapid room-temperature formation of [W(OC₆HPh₄-2,3,5,6)₂(NMes)₂] (15). The many orders of magnitude rate acceleration for cis-diazines over their trans counterparts combined with all the other mechanistic work makes a compelling argument that these cleavage reactions (four-electron reductions) are taking place at a single metal center.

Full text of DOI:10.1021/om030604m

Organometallics 2004, 23, 329-343
329
Articles
Syn th etic a n d Mech a n istic Stu d ies of th e F ou r -Electr on
Red u ction of Dioxygen , NdN, a n d NdO Dou ble Bon d s by
Tu n gsten (II) Ar yloxid e Com p ou n d s
Margaret R. Lentz, J onathan S. Vilardo, Mark A. Lockwood,
Phillip E. Fanwick, and Ian P. Rothwell*
Department of Chemistry, Purdue University, 560 Oval Drive,
West Lafayette, Indiana 47907-2038
Received September 16, 2003
Reduction of the cyclometalation-resistant aryloxide compounds [W(OC6HPh2-2,6-R2-3,5)2-
Cl4] (1, R ) Ph; 2, R ) Me; 3, R ) But) in the presence of a variety of phosphine ligands
generates the W(II) species [W(OC6HR2Ph-η6-C6H4)(OC6HPh2-2,6-R2-3,5)(L)] (4-6) in moder-
ate yield. Compounds 4-6 contain a three-legged piano-stool geometry with one of the
aryloxide ligands chelated to the tungsten via an ortho phenyl ring. Solid-state structural
parameters for the PMe3, PEt3, and PBun adducts 4b-d indicate a shortening of the
3
W-C(ipso) and W-C(para) distances consistent with a tungstanorbornadiene resonance
contribution. Solution studies of 4b show that exchange on the NMR time scale of ortho
and meta protons occurs at elevated temperatures via phosphine dissociation and not π-arene
dissociation. Reaction of 4b with O2 or the trans-diazines PhNdNPh, TolNdNTol, and PhNd
NTol (Tol ) 4-methylphenyl) led to the corresponding bis(oxo) and bis(arylimido) derivatives
[W(OC6HPh4-2,3,5,6)2(X)2(PMe3)] (X ) O, NPh, Ntol; 7-10, respectively). Structural studies
show a trigonal-bipyramidal geometry for 7 and 10 with equatorial O or NAr groups and an
axial PMe3. Formation of the mixed-imido species [W(OC6HPh4-2,3,5,6)2(NPh)(NTol)(PMe3)]
(10) did not involve generation of any 8 or 9. Cleavage of nitrosobenzene by 4b led to [W(OC6-
HPh4-2,3,5,6)2(NPh)(O)(OPMe3)] (11) containing terminal oxo and phenylimido groups and
a phosphine oxide donor ligand. Compound 4b was also found to ring-open the substrates
pyridazine, benzo[c]cinnoline, and phthalazine to produce the three new seven-membered
diaza metallacycles 12-14. Structural studies show 12 and 14 to contain planar rings,
whereas the two backbone phenyl rings in 13 are twisted by 33° with respect to each other.
Structural parameters are more consistent with a formulation as a d0-W(VI) metal center
with a 2,7-diazatungstahepta-1,3,5,7-tetraene ring and two tungsten-imido bonds for 12
and 14, although there is some evidence for a 2,7-diazatungstahepta-2,4,6-triene (d2-W(IV)
metal center) resonance contribution for 14. A kinetic study of the reaction of 4b with trans-
4,4′-dimethylazobenzene (TolNdNTol) to produce 9 was carried out. The rate of disappear-
1
ance of 4b was monitored using H NMR and shown to have a first-order dependence on
both [4b] and [TolNdNTol] and inverse first-order dependence on [PMe3]. The kinetic data
was fit to a mechanistic model involving fast exchange of azobenzene with PMe3 followed by
a rate-determining product formation. The concentration of free PMe3 (strong inhibition) is
controlled by the position of the fast coordination equilibrium of the product [W(OC6HPh4-
2,3,5,6)2(NTol)2(PMe3)] (9). Reaction of trans-MesNdNMes (NMes ) NC6H3Me3-2,4,6) with
4b was slow even at 100 °C. However, photolysis to produce cis-MesNdNMes led to rapid
room-temperature formation of [W(OC6HPh4-2,3,5,6)2(NMes)2] (15). The many orders of
magnitude rate acceleration for cis-diazines over their trans counterparts combined with
all the other mechanistic work makes a compelling argument that these cleavage reactions
(four-electron reductions) are taking place at a single metal center.
In tr od u ction
ligands have a tendency to stabilize the metals in their
highest formal oxidation states (d0 electron configura-
There continues to be a great deal of interest in the
inorganic and organometallic chemistry associated with
monoanionic alkoxide,1,2 aryloxide, siloxide,2 and amido3
ligation. With the group 4-6 metals, these π-donating
(1) Bradley, D. C.; Mehrotra, R. C.; Rothwell, I. P.; Singh, A. Alkoxo
and Aryloxo Derivatives of Metals; Academic Press: San Diego, CA,
2001.
(2) (a) Wolczanski, P. T. Polyhedron 1995, 14, 3335. (b) Marciniec,
B.; Maciejewski, H. Coord. Chem. Rev. 2001, 223 301. (c) Chisholm,
M. H. Chemtracts: Inorg. Chem. 1992, 4, 273.
* To whom correspondence should be addressed. E-mail: rothwell@
purdue.edu.
10.1021/om030604m CCC: $27.50 © 2004 American Chemical Society
Publication on Web 01/07/2004

330 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
Sch em e 1
tion). With small ligation the lower redox states tend
to be dominated by dinuclear compounds containing
metal-metal bonds of various bond orders.4 Mono-
nuclear species can be stabilized either by electronically
saturating the coordination sphere or by the use of bulky
ligation.5 In the latter case the resulting low-coordinate
compounds can exhibit reactivity involving the binding
and reduction of important substrates, including dini-
trogen.
In the case of early d-block metal aryloxide chemistry,
our group and others have found that 2,6-disubstituted
phenoxides have a nagging tendency to undergo facile
intramolecular CH bond activation at low-valent metal
centers.6,7 Recently we have demonstrated the inhibition
of cyclometalation processes with 2,6-diphenylphenoxide
ligands by the introduction of meta substituents onto
the phenoxide nucleus.8 In this paper we report on the
use of these “cyclometalation resistant” ligands to
stabilize low-valent, mononuclear derivatives of tung-
sten. The exploitation of these species for the four-
electron reduction of important substrates such as
dioxygen, organic diazo, and nitroso compounds is
reported.9,10 Particular emphasis is placed on the mecha-
nistic aspects of the cleavage of the NdN bond in cis/
trans diazo compounds and the possible reaction path-
ways. We have previously communicated some aspects
of this work as well as a thorough theoretical analysis
of the reactivity of cis-diazines with these tungsten
reagents.11,12 A very recent publication has dealt with
related low-valent tungsten aryloxides containing py-
ridine ligation.13
Resu lts a n d Discu ssion
Syn th esis a n d Solid -Sta te Str u ctu r e of W(II)
Ar yloxid es. Previous studies have shown that the
sodium amalgam reduction of the tetrachloride species
[W(OC6H3Ph2-2,6)2Cl4], in the presence of phosphine
ligands (L), typically leads to the bis-cyclometalated
compounds [W(OC6H3Ph-η1-C6H4)2(L)2] (I). With the
choice of a suitable phosphine, the deep green compound
[W(OC6H3Ph-η6-C6H5)(OC6H3Ph2-2,6)(L)] (II) can also
be isolated and shown to thermally convert to the
cyclometalated species and H2.12b
(3) (a) Gade, L. H. Acc. Chem. Res. 2002, 35, 575. (b) Fryzuk, M. D.
In Modern Coordination Chemistry; Leigh, G. J ., Winterton, N., Eds.;
Royal Society of Chemistry: Cambridge, U.K., 2002; pp 187-207. (c)
Kempe, R.; Noss, H.; Irrgang, T. J . Organomet. Chem. 2002, 647, 12.
(d) Holland, P. L.; Andersen, R. A.; Bergman, R. G. Comments Inorg.
Chem. 1999, 21, 115. (e) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9. (f)
Beswick, M. A.; Wright, D. S. Coord. Chem. Rev. 1998, 176, 373.
(4) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms,
2nd ed.; Wiley: New York, 1998.
(5) Cummins, C. C. Prog. Inorg. Chem. 1998, 47, 685.
(6) (a) Rothwell, I. P. Acc. Chem. Res. 1988, 21, 153. (b) Lefebvre,
F.; Leconte, M.; Pagano, S.; Mutch, A.; Basset, J .-M. Polyhedron 1995,
14, 3209. (c) Chesnut, R. W.; Durfee, L. D.; Fanwick, P. E.; Rothwell,
I. P.; Folting, K.; Huffman, J . C. Polyhedron 1987, 6, 2019.
(7) The cyclometalation of a variety of aryloxide ligands by low-
valent Mo, W systems has been demonstrated; see: (a) Hascall, T.;
Murphy, V. J .; J anak, K. E.; Parkin, G, J . Organomet. Chem. 2002,
652, 37. (b) Hascall, T.; Baik, M. H.; Bridgewater, B. A.; Shin, J . H.;
Churchill, D. G.; Friesner, R. A.; Parkin, G. Chem. Commun. 2002,
2644. (c) Rabinovich, D.; Zelman, R.; Parkin, G. J . Am. Chem. Soc.
1990, 112, 9632. (d) Rabinovich, D.; Zelman, R.; Parkin, G. J . Am.
Chem. Soc. 1992, 114, 4611.
(8) (a) Vilardo, J . S.; Lockwood, M. A.; Hanson, L. G.; Clark, J . R.;
Parking, B. C.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton
Trans. 1997, 3353. (b) Lockwood, M. A.; Clark, J . R.; Parkin, B. C.;
Rothwell, I. P. J . Chem. Soc., Chem. Commun. 1996, 1973. (c)
Lockwood, M. A.; Potyen, M. C.; Steffey, B. D.; Fanwick, P. E.;
Rothwell, I. P. Polyhedron 1995, 14, 3293.
(9) For the pioneering use of W(II) halides for the cleavage of CdN
and CdO bonds see: Bryan, J . C.; Mayer, J . M. J . Am. Chem. Soc.
1990, 112, 2298.
(10) For cleavage of ketones by ditungsten systems see: (a)
Chisholm, M. H.; Folting, K.; Klang, J . A. Organometallics 1990, 9,
602. (b) Chisholm, M. H.; Folting, K.; Klang, J . A. Organometallics
1990, 9, 607.
(11) Maseras, F.; Lockwood, M. A.; Eisenstein, O.; Rothwell, I. P.
J . Am. Chem. Soc. 1998, 120, 6598.

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 331
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(L)]
Figu r e 1. Molecular structure of[W(OC6HPh3-η6-C6H5)(OC6-
HPh4-2,3,5,6)(PMe3)] (4b).
L
PMe3 (4b) PEt3 (4c) PBun3 (4d ) PMe2Ph (4e)
W-O(1)
2.028(3) 2.014(3)
1.990(3) 1.985(3)
2.171(4) 2.189(5)
2.335(4) 2.332(5)
2.267(4) 2.281(5)
2.201(4) 2.228(5)
2.277(4) 2.284(5)
2.277(4) 2.291(5)
2.474(1) 2.495(1)
2.025(4)
1.987(4)
2.164(6)
2.343(7)
2.285(6)
2.212(7)
2.272(7)
2.256(7)
2.492(2)
1.455(9)
1.365(9)
1.446(9)
1.417(9)
1.398(9)
1.433(8)
2.022(9)
1.966(9)
2.16(1)
2.35(1)
2.25(1)
2.18(1)
2.27(1)
2.24(2)
2.478(4)
1.41(2)
1.39(2)
1.43(2)
1.44(2)
1.36(2)
1.46(2)
In contrast, reduction of the meta-substituted com-
pounds [W(OC6HPh2-2,6-R2-3,5)2Cl4] (1, R ) Ph; 2, R
) Me; 3, R ) But) in the presence of a variety of
phosphine ligands generates the W(II) species [W(OC6-
HR2Ph-η6-C6H5)(OC6HPh2-2,6-R2-3,5)(L)] (4-6) in mod-
erate yield (Scheme 1). Solutions of these deep green
compounds in C6D6 are unchanged (NMR) after being
heated at 100 °C for hours. The molecular structures of
these compounds are of particular interest. A related
pyridine adduct has also been recently reported.13 Four
derivatives, 4b-e, have been subjected to single-crystal
X-ray diffraction analysis. An ORTEP view of the PMe3
derivative 4b is shown in Figure 1, and a comparison
of key structural parameters is given in Table 1. The
compounds all adopt a three-legged piano-stool geom-
etry with one of the aryloxide ligands chelated to the
tungsten via an η6-arene interaction through an ortho
phenyl ring. The chelated aryloxide has a W-O-Ar
angle of 118-119°, which is slightly smaller than that
of the terminal ligand (126-134°), and also has a
slightly elongated W-O bond length. However, neither
the W-O nor W-P distances appear to be sensitive to
the nature of the phosphine ligand. Of most interest are
the structural parameters for the W-η6-arene interac-
tion. There are a large number of structurally charac-
terized tungsten compounds that contain an η6-arene
ligand. Ubiquitous examples are the [W(arene)2] and
[(arene)W(CO)3] 18-electron series. Analysis of typical
W-C(arene) distances for representative compounds of
this type show a narrow range of values: cf. 2.25(2)-
2.32(2) Å for [W(η6-C6H5Me)2],14 2.244(8)-2.28(1) Å for
[W(η6-C6F6)2],15 2.353(5)-2.375(5) Å for [(η6-C6H6)W-
(CO)3],16 and 2.32(2)-2.37(2) Å for [(η6-C6H3Me3)W-
(CO)3].17 The W-C(arene) distances for 4b-e (Table 1)
are more dissimilar. It can be seen that the W-C{ipso,
C(121)} carbon distance is short, ranging from 2.16(1)
W-O(2)
W-C(121)
W-C(122)
W-C(123)
W-C(124)
W-C(125)
W-C(126)
W-P(3)
C(121)-C(122) 1.440(6) 1.452(7)
C(122)-C(123) 1.396(6) 1.402(7)
C(123)-C(124) 1.439(7) 1.431(7)
C(124)-C(125) 1.424(7) 1.424(8)
C(125)-C(126) 1.417(6) 1.411(7)
C(126)-C(121) 1.439(6) 1.440(7)
P(3)-W-O(1)
P(3)-W-O(2)
O(1)-W-O(2)
W-O(1)-C(11) 118.4(2) 119.3(3)
W-O(2)-C(21) 130.2(3) 126.2(3)
78.58(8) 79.6(1)
82.99(9) 85.9(1)
116.3(1) 112.2(1)
82.0(1)
83.4(1)
114.1(2)
118.4(4)
133.9(4)
80.2(3)
85.6(3)
115.3(8)
119.5(8)
130.8(9)
to 2.189(5) Å for the series. This distance is very close
to that reported for discrete tungsten-aryl σ bonds: cf.
2.096(5)-2.199(5) Å in [W(O)(C6H2Me3-2,4,6)3(THF)],18
2.18(2) Å in [W(OC6H3Ph-C6H4)2(PMePh2)2],19 2.155(6)
Å in [Cp*W(O)(NC6H4Me-4)(C6H4Me-2)],20 2.203(6) Å in
[W(O)2(Ph)2(bipy)],21 2.14(3) and 2.10(3) Å in [W2(OPri)4-
(C6H4Me-4)2(HNMe2)],22 and 2.120(5) and 2.160(5) Å in
[Cp*W(NO)(C6H4Me-2)2].23 It can also be seen that the
W-C{para, C(124)} distance is also shorter, 2.18(1)-
2.228(5) Å, than the remaining W-C{ortho, C(122) and
C(126; meta, C(123) and C(125)} distances (Table 1).
This particular type of distortion of π-bound arene rings
has been observed in other early d-block metal sys-
tems.24 This is not to be confused with the situation
where arene rings interact through part or all of the
ring carbons with high-valent, electron-deficient d0-
metal centers.25,26 Instead, the more dramatic distortion
is sometimes observed when the arene is bound to a
(12) (a) Lockwood, M. A.; Fanwick, P. E.; Eisenstein, O.; Rothwell,
I. P. J . Am. Chem. Soc. 1996, 118, 2762. (b) Kerschner, J . L.; Rothwell,
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I. P. J . Am. Chem. Soc. 1994, 116, 5225.
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624, 887.
(19) Kerschner, J . L.; Rothwell, I. P.; Huffman, J . C.; Streib, W. E.
Organometallics 1988, 7, 1871.
(20) Legzdins, P.; Rettig, S. J .; Ross, K. J .; Veltheer, J . E. J . Am.
Chem. Soc. 1991, 113, 4361.
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(22) Chisholm, M. H.; Eichhorn, B. W.; Folting, K.; Huffman, J . C.;
Tatz, R. J . Organometallics 1986, 5, 1599.
(14) Prout, K.; Gourdon, A.; Couldwell, C.; Meunier, B.; Miao, F.
M.; Woolcock, J . Acta Crystallogr., Sect. B 1982, 38, 456.
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F. W. B. Organometallics 1995, 14, 5579.
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P. T. J . Am. Chem. Soc. 1988, 110, 4421. (b) Veige, A. S.; Kleckley, T.
S.; Chamberlin, R. M.; Neithamer, D. R.; Lee, C. E.; Wolczanski, P.
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332 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
highly reducing metal fragment.27-29 One thoroughly
studied system is the set of tantalum arene compounds
isolated by Wigley et al.30 These compounds are gener-
ated via the cyclotrimerization of alkynes at d2-Ta(III)
metal centers containing aryloxide ancillary ligation. A
theoretical analysis of the distortion has been carried
out, and a bonding description involving a tantalanor-
bornadiene resonance picture has been proposed.31 In
the case of compounds 4-6 the chelated arene is bound
to a formally d4-W(II) metal. It would appear that a
tungstanorbornadiene resonance picture is also valid
(Scheme 1) in which the arene ring is partially reduced
with incipient W-C(σ) bonds to the ipso and para
carbons. The shorter C(122)-C(123) and C(125)-C(126)
distances within the arene ring are consistent with this
picture. The distortion of the arene ring bound in 4b-e
and previously isolated 2,6-diphenylphenoxide ana-
logues is highlighted by the “radar” plots in Figure 2.
It can also be seen that there is an asymmetry involving
elongation of the ortho carbon located trans to the
F igu r e 2. “Radar” plot of the W-C(arene) distances in
compounds 4b -e, and [W(OC6H3Ph2-2,6)(OC6H3Ph-η6-
C6H5)(PMePh2)], and [W(OC6H3Ph2-2,6)(OC6H3Ph-η6-C6H5)-
(η1-dppm)] (solid lines). Also shown is the data for [(η6-
C6H6)W(CO)3] (dashed line). The arene coordination is
exaggerated by using a plot scale of 2.0-2.4 Å from the
metal center.
(25) (a) Thorn, M. G.; Etheridge, Z. C.; Fanwick, P. E.; Rothwell, I.
P. Organometallics 1998, 17, 3636. (b) Thorn, M. G.; Etheridge, Z. C.;
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Organometallics 1995, 14, 2456.
(26) The chelation of o-arylphenoxides to lanthanide metal centers
has been observed in the solid state; see: (a) Deacon, G. B.; Feng, T.;
Forsyth, C. M.; Gitlits, A.; Hockless, D. C. R.; Shen, O.; Skelton, B.
W.; White, A. H. J . Chem. Soc., Dalton Trans. 2000, 961 and references
therein. (b) Deacon, G. B.; Fanwick, P. E.; Gitlits, A.; Rothwell, I. P.;
Skelton, B. W.; White, A. H. Eur. J . Inorg. Chem. 2001, 16, 1505.
(27) (a) Hagadorn, J . R.; Arnold, J . Angew. Chem., Int. Ed. 1998,
37, 1729. (b) Cassani, M. C.; Duncalf, D. J .; Lappert, M. F. J . Am.
Chem. Soc. 1998, 120, 12958.
(28) (a) Thewalt, U.; Stollmaier, F. J . Organomet. Chem. 1982, 228,
149. (b) Stollmaier, F.; Thewalt, U. J . Organomet. Chem. 1981, 208,
327. (c) Solari, E.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J . Chem.
Soc., Chem. Commun. 1989, 1747. (d) Solari, E.; Floriani, C.; Schenk,
K.; Chiesi-Villa, A.; Rizzoli, C.; Rosi, M.; Sgamellotti, A. Inorg. Chem.
1994, 33, 2018. (e) Cotton, F. A.; Kibala, P. A.; Wojtczak, W. A. J . Am.
Chem. Soc. 1991, 113, 1462. (f) Troyanov, S. I.; Rybakov, V. B.
Metalloorg. Khim. 1992, 5, 1082. (g) Troyanov, S. I.; Meetsma, A.;
Teuben, J . H. Inorg. Chim. Acta 1998, 271, 180. (h) Ozerov, O. V.;
Patrick, B. O.; Ladipo, F. T. J . Am. Chem. Soc. 2000, 122, 6423. (i)
Kupfer, V.; Thewalt, U. Z. Anorg. Allg. Chem. 2001, 627, 1423. (j)
Gardner, T. G.; Girolami, G. S. Angew. Chem., Int. Ed. Engl. 1988,
27, 1693. (k) Troyanov, S. I.; Mach, K. J . Organomet. Chem. 1990, 389,
41. (l) Diamond, G. M.; Green, M. L. H.; Walker, N. W. J . Organomet.
Chem. 1991, 413, C1. (m) Solari, E.; Musso, F.; Ferguson, R.; Floriani,
C.; Chiesi-Villa, A.; Rizzoli, C. Angew. Chem., Int. Ed. Engl. 1995, 34,
1510. (n) Solari, E.; Musso, F.; Ferguson, R.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C. Angew. Chem., Int. Ed. Engl. 1995, 34, 1510. (o)
Troyanov, S.; Pisarevsky, A.; Struchkov, Yu. T. J . Organomet. Chem.
1995, 494, C4.
(29) (a) Stollmaier, F.; Thewalt, U. J . Organomet. Chem. 1981, 222,
227. (b) Thewalt, U.; Stollmaier, F. Angew. Chem., Int. Ed. Engl. 1982,
21, 133. (c) Kesanli, B.; Fettinger, J .; Eichhorn, B. Angew. Chem., Int.
Ed. 2001, 40, 2300. (d) Tayebani, M.; Feghali, K.; Gambarotta, S.; Yap,
G. Organometallics 1998, 17, 4282. (e) Bandy, J . A.; Prout, K.; Cloke,
F. G. N.; de Lemos, H. C.; Wallis, J . M. J . Chem. Soc., Dalton Trans.
1988, 1475. (f) Goldberg, S. Z.; Spivack, B. D.; Stanley, G.; Eisenberg,
R.; Braitsch, D. M.; Miller, J . S.; Abkowitz, M. J . Am. Chem. Soc. 1977,
99, 110. (g) Green, M. L. H.; O’Hare, D.; Watkin, J . G. J . Chem. Soc.,
Chem. Commun. 1989, 698. (h) Calderazzo, F.; Pampaloni, G.; Rocchi,
L.; Strahle, J .; Wurst, K. J . Organomet. Chem. 1991, 413, 91.
(30) (a) Bruck, M. A.; Copenhaver, A. S.; Wigley, D. E. J . Am. Chem.
Soc. 1987, 109, 6525. (b) Arney, D. J .; Bruck, M. A.; Wigley, D. E.
Organometallics 1991, 10, 3947. (c) Smith, D. P.; Stickler, J . R.; Gray,
S. D.; Bruck, M. A.; Holmes, R. S.; Wigley, D. E. Organometallics 1992,
11, 1275. (d) Arney, D. J .; Wexler, P. A.; Wigley, D. E. Organometallics
1990, 9, 1282. (e) Arney, D. S. J .; Fox, P. A.; Bruck, M. A.; Wigley, D.
E. Organometallics 1997, 16, 3421.
terminal aryloxide oxygen atom (Figure 2). Strong
support for the tungstanorbornadiene resonance picture
comes from reactivity studies, where it has been shown
that ketones and aldehydes will insert directly into the
W-C(para) bond.12
Sp ectr oscop ic P r op er ties a n d Solu tion Dyn a m -
ics of W(II) Ar yloxid es. Solution studies of these
compounds are important, in that they indicate that
phosphine dissociation (in the absence of decrease in
π-arene interaction) provides the open coordination site
for substrate binding. For the compounds 4b-f contain-
ing a monodentate phosphine ligand, a sharp resonance
is observed in the 31P NMR spectrum with well-resolved
1
183W satellites. The value of the J (183W-31P) coupling
constant varies from 362 Hz for the PMePh2 compound
4f to 372 Hz for the PMe3 compound 4b. In the case of
the dppm derivatives 4a , 5a , and 6a , two doublets are
observed. The resonance in the δ 52-58 ppm region
1
exhibits 183W satellites, J (183W-31P) ) 342-358 Hz,
and can be assigned to the metal-bound phosphorus
atom. The second doublet at δ -24 to -25 ppm lies very
close to that of free dppm and can be assigned to the
uncoordinated, “dangling” phosphorus atom of the mono-
dentate dppm ligand.
1
At ambient temperatures the H NMR spectra of all
compounds show the expected phosphine ligand reso-
nances. In the case of compound 4e the W-PMe2Ph
methyl groups are diastereotopic and appear as two
distinct doublets, consistent with the geometry observed
in the solid state. A complex multiplet pattern in the
aromatic region is observed for all compounds due to
the majority of aryloxide protons and any phosphine
ligand phenyl ring protons. The π-bound arene ring
protons appear considerably upfield of the aromatic
region (Figure 3) as five distinct resonances. The lack
of a plane of symmetry through the three-legged piano-
stool geometry results in nonequivalent ortho and meta
(31) Wexler, P. A.; Wigley, D. E.; Koerner, J . B.; Albright, T. A.
Organometallics 1991, 10, 2319.

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 333
Ta ble 2. Mea su r ed Cou p lin g Con sta n ts for 4ba
proton shift (ppm) 3J (1H-1H)b 3J (1H-1H)c 3J (31P-1H)c
Hm′
Ho
Hm
Ho′
Hp
3.37
2.92
1.89
1.45
1.02
5.57
5.95
5.88
5.95
5.57
5.53
5.84
5.86
5.88
5.56
4.18
4.04
3.31
1.62
3.37
a
Errors in measured coupling constants on the Varian Unity
Inova 300 are (0.15 Hz. b Average measured coupling (in Hz) from
the 1H{31P} NMR experiment at -30 °C. c Average measured
coupling (in Hz) from the 1H NMR experiment at -30 °C using
weighing functions.
F igu r e 3. 1H NMR spectra (toluene-d8, -30 °C) of the η6-
C6H5 protons in [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)-
(PMe3)] (4b): (a) δ 1.0-3.5 ppm region, 31P decoupled; (b)
31P decoupled spectrum with use of weighing functions; (c)
31P coupled with solvent suppression and weighing func-
tions. The asterisk indicates protio impurities within the
solvent.
pairs of protons. The upfield shifting of these arene
protons is a consequence of the π-coordination to the
metal center. This upfield shifting is also enhanced by
the presence of the adjacent 2,3,5,6-tetraphenylphenox-
ide ligand. Previous work has demonstrated that the
ortho phenyl rings of such ligands cause a diamagnetic
shielding of the protons of adjacent ligands.8a
We have undertaken a number of NMR experiments
in order to gain as much information as possible about
the π-bound arene resonances of the PMe3 derivative
4b. The use of homodecoupling and 2D COSY experi-
ments has allowed the ortho, meta, and para protons
to be assigned. However, these experiments on their
own do not allow unequivocal assignment of the non-
equivalent pairs of ortho and meta protons on the ring:
i.e., which pair is on the side of the ring adjacent to the
terminal aryloxide and which pair is adjacent to the
1
F igu r e 4. High-temperature H NMR spectra (p-xylene-
d
10, δ 0.0-4.0 ppm) of the η6-C6H5 protons in [W(OC6HPh3-
η6-C6H5)(OC6HPh4-2,3,5,6)(PMe3)] (4b).
1
The temperature dependence of the H NMR spectra
is highly informative. As the temperature of a solution
of 4b in perdeutero-p-xylene is raised, the ortho and
meta proton resonances broaden. At 125 °C they have
collapsed completely into the baseline. Unfortunately,
high-temperature limiting spectra could not be obtained
due to thermal decomposition to a compound discussed
below. However, it can be seen (Figure 4) that although
exchange of pairs of ortho and meta protons is occurring
on the NMR time scale, the para proton resonance
remains sharp. We interpret the changes in the NMR
1
phosphine ligand. From the H{31P} NMR spectrum at
3
-30 °C (Figure 3) the J H-H coupling constants could
be derived by simulation of the observed spectrum.
Simulation of the 31P-coupled spectrum then allowed
3
measurement of the J P-H coupling constants. Finally,
low-temperature NOE difference experiments involving
irradiation of the PMe3 protons allowed the unequivocal
assignment of the five aromatic protons attached to the
η6-bound phenyl ring (Table 2).

334 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
Sch em e 2
spectrum as reflecting a fluxional process for the
molecule in which the sides of the bound arene ring are
becoming equivalent (Scheme 2). Furthermore, the
sharp resonance for the para proton implies that dis-
sociation of the bound arene ring does not take place.
If arene ring dissociation followed by rotation was the
mechanism of o,o′ and m,m′ exchange (intermediate [A]
in Scheme 2), then one would expect the bound arene
to exchange with the other ortho phenyl rings. It
therefore appears that exchange of the phosphine and
terminal aryloxide ligands is taking place. This could
occur via two distinct pathways. If one ignores oxygen-p
to metal-d π-bonding, then 4-6 are formally 16-electron
compounds. The previously isolated compounds [W(OC6-
HPh3-η6-C6H5)(X)(L)2] (X ) H, Cl; L ) tertiary phos-
phine) contain a hydrido or chloro ligand in place of an
aryloxide and form 18-electron bis(phosphine) adducts.32
It therefore is feasible that the exchange process occurs
through an associative pathway via the 18-electron
intermediate [B] in Scheme 2. This would require the
exchange to be catalyzed by trace amounts of free
phosphine in solution. However, we find that adding
excess PMe3 to solutions of 4b does not lead to an
increase in exchange of nonequivalent ortho and meta
protons; i.e., no increase in line broadening is observed
in the 1H NMR spectra. However, we do know that
exchange of free and coordinated phosphine can occur
rapidly. Hence, addition of PMe2Ph to a solution of 4b
rapidly sets up equilibrium between 4b/4e and PMe3/
PMe2Ph. Hence, we propose that the fluxional process
occurs via a dissociative exchange of phosphine ligand.
Furthermore, exchange of the nonequivalent ortho and
para protons is not inhibited by added phosphine,
indicating that the two-legged piano-stool intermediate
must contain a mirror plane ([C] in Scheme 2). A
preequilibrium step to generate a species of lower
(32) Kerschner, J . L.; Torres, E. M.; Fanwick, P. E.; Rothwell, I. P.;
Huffman, J . C. Organometallics 1989, 8, 1424.

Reduction of Double Bonds by W(II) Aryloxide Compounds
Sch em e 3
Organometallics, Vol. 23, No. 3, 2004 335
symmetry followed by an “inversion” process ([D, D′],
Scheme 2) would lead to inhibition by added phosphine.
The geometry proposed for the intermediate is strikingly
similar to that found for the bis(aryloxide) [Ta(η6-C6-
A deep green C6D6 solution of 4b rapidly became
brown upon exposure to an atmosphere of O2 at ambient
temperatures. Analysis by 1H and 31P NMR showed
aromatic resonances for terminal aryloxide ligands and
a coordinated PMe3 ligand. Structural analysis of crys-
tals obtained from benzene/hexane confirms the formu-
lation as the W(VI) dioxo species 7 (Scheme 3) with a
pentagonal-bipyramidal geometry about tungsten. The
coordinated PMe3 ligand occupies an axial site, trans
to one of the aryloxo ligands (Figure 5, Table 3).
Reaction of 4b with the trans-diazines PhNdNPh,
TolNdNTol, and PhNdNTol (Tol ) 4-methylphenyl) led
to the corresponding bis(arylimido) derivatives 8-10
(Scheme 3). The reactions were noticeably slower than
the dioxygen reaction and were amenable to kinetic
studies (see below). Besides evidence for the coordinated
PMe3 ligand, the 1H NMR spectra of 8-10 showed
Et6)(OC6H3Pri -2,6)2] reported by Wigley,31 although the
2
tungsten compound has one extra electron. Although it
is unsatisfying that high-temperature limiting spectra
could not be obtained, the o,o′ and m,m′ exchange rate
can be estimated at the coalescence temperatures. For
the PMe3 derivative 4b this is estimated as 940 s-1 at
95 °C. The coalescence temperature for the PMe2Ph
derivative is slightly lower, yielding an exchange rate
of 1060 s-1 at 80 °C. This trend is consistent with a
phosphine dissociative exchange pathway.
Syn th esis a n d Solid -Sta te Str u ctu r e of Oxo a n d
Ar ylim id o P r od u cts. In this section we describe the
utility of 4b for the synthesis of corresponding oxo
and arylimido compounds. Preliminary studies on the
reaction of 4a with O2 and aryldiazines showed the
formation of the corresponding bis(oxo) and bis(imido)
derivatives.11a Spectroscopic data showed the lack of
coordination of the dppm ligand to the W(VI) products.
A crystal structure of the compound [W(OC6HPh4-
2,3,5,6)2(dNPh)2] showed a pseudo-tetrahedral W(VI)
metal center with terminal aryloxides and no coordi-
nated phosphine ligand. However, the dppm derivative
proved unsuitable for mechanistic/kinetic studies due
to a number of factors, including the low solubility of
both 4a and the free dppm produced during the reaction.
Furthermore, imido compounds produced via cleavage
of diazines were found to undergo ligand exchange
reactions.11a Related ligand exchange reactions have
been observed for tetrahedral molybdenum compounds
and studied in detail.33 These problems were resolved
by utilizing the more soluble PMe3 compound 4b, which
will react with dioxygen, aryldiazines, and nitrosoben-
zene to form a series of oxo and imido derivatives of
W(VI) that are five-coordinate, containing coordinated
PMe3, and do not undergo facile intermolecular scram-
bling of ligands (Scheme 3).
F igu r e 5. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
(O)2(PMe3)] (7).
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(O)2(OC6HP h 4-2,3,5,6)2(P Me3)] (7)
W-O(1)
W-O(2)
W-O(3)
1.943(3)
1.902(3)
1.710(3)
W-O(4)
W-P
1.709(4)
2.638(1)
O(2)-W-O(1)
O(3)-W-O(2)
O(4)-W-O(2)
O(3)-W-O(4)
87.5(1)
119.6(2)
128.1(2)
108.5(2)
O(1)-W-P
167.42(9)
87.12(13)
137.0(3)
176.6(3)
O(4)-W-P
W-O(1)-C(11)
W-O(2)-C(21)
(33) Blackmore, I. J .; Gibson, V. C.; Graham, A. J .; J olly, M.;
Marshall, E. L.; Ward, B. P. Dalton 2001, 3242.

336 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
F igu r e 7. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
(NPh)(O)(OPMe3)] (11).
Ta ble 5. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(O)(NP h )(OC6HP h 4-2,3,5,6)2(OP Me3)]
(11)
F igu r e 6. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
(NPh)(Ntol)(PMe3)] (10).
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(NP h )(Ntol)(OC6HP h 4-2,3,5,6)2(P Me3)]
(10)
W-O(1)
W-O(2)
W-O(3)
1.966(4)
1.973(4)
2.117(4)
W-O(4)
W-N(5)
1.694(4)
1.752(5)
W-N(1)
W-N(2)
W-O(3)
1.751(5)
1.774(5)
1.965(4)
W-O(4)
W-P
2.010(3)
2.538(1)
O(1)-W-O(2)
O(1)-W-O(3)
O(1)-W-O(4)
O(3)-W-O(2)
O(2)-W-O(4)
O(4)-W--(3)
139.9(2)
77.9(2)
109.1(2)
78.6(2)
106.0(2)
97.9(2)
O(1)-W-N(5)
O(4)-W-N(5)
O(2)-W-N(5)
O(3)-W-N(5)
W-O(1)-C(11)
W-O(2)-C(21)
94.4(2)
104.1(2)
95.4(2)
158.0(2)
124.6(4)
125.1(3)
N(1)-W-N(2)
N(1)-W-O(3)
N(2)-W-O(3)
N(2)-W-O(4)
109.4(2)
117.6(2)
129.2(2)
99.3(2)
N(1)-W-P
O(4)-W-P
W-O(3)-C(31)
W-O(4)-C(41)
84.5(2)
166.2 (1)
170.5(3)
134.0(3)
Unfortunately this intermediate could not be character-
ized fully, and it converted rapidly to 13 at higher
temperatures. The product diaza metallacyclic products
12-14 are spectroscopically similar to 8-10. Crystal-
lographic studies of 12-14 (Figures 8-10, Tables 6-8)
showed a tbp geometry in all cases similar to that found
in 10.34 In compound 13 the two benzene rings fused to
the diaza metallacycle are twisted with a torsion angle
of 33°. This generates a puckering of the seven-
membered ring. In contrast, the products of ring opening
of pyridazine, 12, and phthalazine, 14, have planar
seven-membered rings.
The structural parameters for the five-coordinate oxo
and imido compounds 7 and 10-14 are of considerable
interest. The W-OAr distances span the narrow range
of 1.902(3)-2.010(3) Å. This range is comparable to that
for other W(VI) aryloxides in the literature.1 There are
a large number of terminal oxo and imido derivatives
of W(VI) now known. However, analysis of the Cam-
bridge Structural Database shows that few five-coordi-
nate adducts of this type have been structurally char-
acterized, although there is a much larger set of such
molybdenum compounds. In the phosphine adducts 7
and 10 the OdWdO and NdWdN angles are 108 and
109°, respectively. This compares well with NdWdN
angles found in the related molecules [W(dNBut)2{OC-
(CF3)2 C(CF3)2O}(H2NBut)] (110°),35 [W{dNSi(But)3}2-
Cl2(py)] (111°),36 and [W(dNSiMe3)2Cl2(PMePh2)] (110°).37
distinctive aromatic resonances slightly upfield of the
aryloxide proton resonances. These can be assigned to
the aromatic protons of the arylimido groups, shifted
upfield by the diamagnetic anisotropy of the adjacent
2,3,5,6-tetraphenylphenoxide ligands. The 1H NMR
spectrum of 10 showed no evidence for the formation of
either 8 or 9 in the reaction mixture. The mixed-imido
species 10 was also crystallized and shown to contain a
structure similar to that of 7 with the phenyl- and
tolylimido ligands both equatorial (Figure 6, Table 4).
The reaction of 4b with nitrosobenzene was found to
generate a significantly different compound. In this case
the 31P NMR spectrum of the product showed a broad
resonance at δ +32.7 ppm, considerably downfield of the
region found for the PMe3 ligands in 7-10. This new
product 11 (Scheme 3) was structurally characterized
and shown to contain an OPMe3 ligand bound to
tungsten (Figure 7, Table 5). Analysis of the reaction
mixture showed proton resonances in the aromatic
region identical with those for an authentic sample of
oxazoline. In an independent NMR experiment it was
shown that nitrosobenzene reacts with PMe3 to produce
the phosphine oxide and oxazoline. The molecular
structure of 11 contains a geometry about tungsten best
described as square pyramidal. An oxo group occupies
the axial site, with the phosphine oxide adduct located
trans to a basal phenylimido ligand.
Compound 4b was also found to ring open the
substrates pyridazine, benzo[c]cinnoline, and phthala-
zine to form 12-14, respectively (Scheme 4). These
constrained cis-diazo substrates were found to react
significantly faster with 4b than the trans diazines used
in Scheme 3. However, evidence was obtained by 1H and
31P NMR for the formation of a deep blue-green inter-
mediate species which was stable for hours at -30 °C.
(34) A nine-membered ring containing a tungsten bis(imido) function
has been reported, [Cp*WCl(NC6H4-CH2CH2-C6H4N)]; see: Redshaw,
C.; Gibson, V. C.; Clegg, W.; Edwards, A. J .; Miles, B. J . Chem. Soc.,
Dalton Trans. 1997, 3343.
(35) Chan, D. M.-T.; Fultz, W. C.; Nugent, W. A.; Roe, D. C.; Tulip,
T. H. J . Am. Chem. Soc. 1985, 107, 251.
(36) Holmes, S. M.; Schafer, D. F., II; Wolczanski, P. T.; Lobkovsky,
E. B. J . Am. Chem. Soc. 2001, 123, 10571.
(37) Lichtenhan, J . D.; Critchlow, S. C.; Doherty, N. M. Inorg. Chem.
1990, 29, 439.

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 337
F igu r e 9. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
(NC12H8N)(PMe3)] (13).
F igu r e 8. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
{NCHCHCHCHN}(PMe3)] (12).
Ta ble 7. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(OC6HP h 4-2,3,5,6)2(NC12H8N)(P Me3)] (13)
Ta ble 6. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for
[W(OC6HP h 4-2,3,5,6)2{NCHCHCHCHN}(P Me3)] (12)
W-N(1)
W-N(2)
W-O(3)
W-O(4)
W-P(5)
1.753(4)
1.751(4)
1.991(3)
1.987(3)
2.566(1)
N(1)-C(11)
N(2)-C(21)
C(11)-C(12)
C(12)-C(22)
C(21)-C(22)
1.393(6)
1.390(6)
1.426(7)
1.496(7)
1.426(6)
molecule 1
molecule 2
W(1)-N(11)
1.740(7) W(2)-N(21)
1.783(7)
1.701(7)
1.965(5)
1.969(6)
2.558(2)
1.37(1)
1.34(2)
1.38(1)
1.46(1)
1.39(2)
O(3)-W-O(4)
N(1)-W-N(2)
N(1)-W-O(3)
N(1)-W-O(4)
N(2)-W-O(3)
N(2)-W-O(4)
N(1)-W-P(5)
85.8(1)
N(2)-W-P(5)
P(5)-W-O(3)
P(5)-W-O(4)
W-O(3)-C(31)
W-O(4)-C(41)
W-N(1)-C(11)
W-N(2)-C(21)
84.6(1)
162.52(9)
76.71(9)
144.6(3)
166.4(3)
143.8(3)
143.0(3)
W(1)-N(16)
W(1)-O(11)
W(1)-O(12)
W(1)-P(1)
1.744(7) W(2)-N(26)
1.961(6) W(2)-O(21)
1.970(6) W(2)-O(22)
2.580(2) W(2)-P(2)
97.9(2)
103.7(1)
134.5(2)
105.2(1)
122.8(2)
88.9(1)
N(11)-C(12)
N(16)-C(15)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
1.39(1)
1.42(1)
1.38(1)
1.43(1)
1.34(1)
N(21)-C(22)
N(26)-C(25)
C(22)-C(23)
C(23)-C(24)
C(24)-C(25)
C(13)-C(12)-C(22)-C(23)a
-31.2(6)
a
Torsion angle.
O(11)-W(1)-O(12) 88.8(2)
O(21)-W(2)-O(22) 86.6(2)
N(11)-W(1)-N(16) 101.0(4) N(21)-W(2)-N(26) 103.6(4)
N(11)-W(1)-O(11) 102.3(3) N(21)-W(2)-O(21) 101.0(3)
N(11)-W(1)-O(12) 127.0(3) N(21)-W(2)-O(22) 135.7(3)
N(16)-W(1)-O(11) 104.3(3) N(26)-W(2)-O(21) 103.1(3)
N(16)-W(1)-O(12) 126.5(3) N(26)-W(2)-O(22) 117.2(3)
N(11)-W(1)-P(1)
N(16)-W(1)-P(1)
P(1)-W(1)-O(11)
P(1)-W(1)-O(12)
84.9(2)
83.5(2)
N(21)-W(2)-P(2)
N(26)-W(2)-P(2)
86.8(2)
86.5(2)
165.7(2)
79.5(2)
168.0(2) P(2)-W(2)-O(21)
79.2(2)
P(2)-W(2)-O(22)
W(1)-O(11)-C(111) 140.5(5) W(2)-O(21)-C(211) 135.1(5)
W(1)-O(12)-C(161) 162.4(5) W(2)-O(22)-C(261) 159.9(5)
W(1)-N(11)-C(12) 143.0(7) W(2)-N(21)-C(22) 144.2(7)
W(1)-N(16)-C(15) 141.2(7) W(2)-N(26)-C(25) 135.4(8)
N(11)-C(12)-C(13) 122.5(10) N(21)-C(22)-C(23) 121.2(10)
C(12)-C(13)-C(14) 135.1(11) C(22)-C(23)-C(24) 133.5(10)
C(13)-C(14)-C(15) 131.7(11) C(23)-C(24)-C(25) 129.0(11)
N(16)-C(15)-C(14) 125.4(10) N(26)-C(25)-C(24) 132.5(13)
F igu r e 10. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
{NCH(C6H4)CHN}(PMe3)] (14).
These all contain the oxo or imido groups equatorial in
a tbp structure. A slightly smaller angle of 104° is found
for square-pyramidal 11. The WdO and WdN distances
within 7, 10, and 11 appear to be in the range reported
for other W(VI) derivatives of these ligands. The struc-
tural parameters for the three diazametallacyclic com-
pounds 12-14 are highlighted in Scheme 5. The pres-
ence of the seven-membered ring constrains the NdWd
N angles to slightly smaller values of 101, 98, and 99°,
respectively, compared to the terminal bis(imido) species
10. There are two possible resonance forms which can
be drawn for 12-14 (Scheme 5). In form A there is a
d0-W(VI) metal center with a 2,7-diazatungstahepta-
1,3,5,7-tetraene ring and two tungsten-imido bonds. In
contrast, form B has a formally d2-W(IV) metal center
with a 2,7-diazatungstahepta-2,4,6-triene ring. The
structural parameters for 12 and 13 (Scheme 5) are
consistent with the bis(imido) form. There is a definite
lengthening of the W-N distances in 14, with distances
around the ring showing a perturbation toward reso-
nance form B. The W-N distances are not, however,
as long as those found for single bonds such as in known
[W-NdC]-containing structures. For example, the W-N
distances of 1.791(3) and 1.797(3) Å in 14 are shorter
than those in [CpMo(CO)2(NdCBut )] (1.892 Å)38 and
2
[(tpb)W(CO)(η2-PhCCMe)(NdCMePh)] (1.898 Å),39 which
contain single M-NdC bonds.

338 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
Sch em e 4
Ta ble 8. Selected Bon d Dista n ces (Å) a n d
An gles (d eg) for
Sch em e 5
[W(OC6HP h 4-2,3,5,6)2{NCH(C6H4)CHN}(P Me3)] (14)
W-N(1)
1.797(3)
1.791(3)
1.982(2)
1.959(2)
2.565(1)
1.326(5)
1.335(4)
C(2)-C(3)
C(3)-C(4)
C(3)-C(8)
C(4)-C(5)
C(5)-C(6)
C(6)-C(7)
C(7)-C(8)
C(8)-C(9)
1.417(5)
1.434(5)
1.456(5)
1.363(6)
1.400(6)
1.347(6)
1.449(5)
1.411(5)
W-N(10)
W-O(1)
W-O(2)
W-P(3)
N(1)-C(2)
N(10)-C(9)
O(2)-W-O(1)
N(1)-W-N(10)
N(1)-W-O(2)
N(10)-W-O(1)
N(1)-W-O(1)
N(10)-W-O(2)
N(10)-W-P(3)
N(1)-W-P(3)
P(3)-W-O(1)
91.3(1)
98.7(1)
135.0(1)
107.0(1)
95.1(1)
121.8(1)
83.6(9)
86.34(9)
168.90(7)
P(3)-W-O(2)
80.07(8)
143.0(2)
162.0(2)
142.9(2)
141.4(3)
128.6(3)
128.8(3)
130.1(3)
129.3(3)
W-O(1)-C(11)
W-O(2)-C(21)
W-N(1)-C(2)
W-N(10)-C(9)
N(1)-C(2)-C(3)
C(2)-C(3)-C(8)
C(3)-C(8)-C(9)
C(8)-C(9)-N(10)
Kin etic a n d Mech a n istic Stu d ies. The reactions
of 4b with the various substrates represents the overall
four-electron reduction of OdO, NdN, and NdO bonds
by the d4-W(II) metal center. A reaction of this type
could be imagined to take place via numerous possible
pathways. A theoretical analysis of the reaction of the
model compound [(η6-C6H6)W(OH)2(PH3)] with cis-HNd
NH shows there to be no electronic barriers to the
reaction occurring in a purely intramolecular fashion
at one metal center.11 There is precedence for the single-
site cleavage of diazo substrates into bis(imido) products
in the work of Burns et al.40 There is strong precedence
for the cleavage of azobenzene by d2-metal fragments
to occur via bimolecular intermediates.41-43 Further-
more, the fundamentally important activation and
cleavage of dioxygen typically occurs at more than one
metal center.44 Analysis of the product stoichiometry
implies that the reactions involving 4b are occurring
at a single metal center. A number of earlier studies
(41) (a) Cotton, F. A.; Duraj, S. A.; Roth, W. J . J . Am. Chem. Soc.
1984, 106, 4749. (b) Hill, J . E.; Profilet, R. D.; Fanwick, P. E.; Rothwell,
I. P. Angew. Chem., Int. Ed. Engl. 1990, 29, 664. (c) Hill, J . E.; Fanwick,
P. E.; Rothwell, I. P. Inorg. Chem. 1991, 30, 1143. (d) Durfee, L. D.;
Hill, J . E.; Fanwick, P. E.; Rothwell, I. P. Organometallics 1990, 9,
75. (e) Zambrano, C. H.; Fanwick, P. E.; Rothwell, I. P. Organometallics
1994, 13, 1174.
(38) Shearer, H. M. M.; Sowerby, J . D. J . Chem. Soc., Dalton Trans.
1973, 2629.
(39) Francisco, L. W.; White, P. S.; Templeton, J . L. Organometallics
1996, 15, 5127.
(40) (a) Peters, R. G.; Warner, B. P.; Burns, C. J . J . Am. Chem. Soc.
1999, 121, 5585. (b) Warner, B. P.; Scott, B. L.; Burns, C. J . Angew.
Chem., Int. Ed. 1998, 37, 959. (c) Arney, D. S. J .; Burns, C. J . J . Am.
Chem. Soc. 1995, 117, 9448.
(42) (a) Walsh, P. J .; Hollander, F. J .; Bergman, R. G. J . Am. Chem.
Soc. 1990, 112, 894. (b) Walsh, P. J .; Hollander, F. J .; Bergman, R. G.
J . Organomet. Chem. 1992, 428, 13. (c) Aubart, M. A.; Bergman, R. G.
Organometallics 1999, 18, 811.

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 339
Sch em e 6
F igu r e 11. Plots of [4b] vs time for various initial
concentrations of 4b, [W]0 and Tol-NdN-Tol, [A]0 as
1
monitored by H NMR in C6D6 at 28.0(5) °C. The data is
fit to the kinetic model in Scheme 6 (solid curves) yielding
the rate constants shown.
proton signals for 4b as a function of time while varying
the concentration of both 4b and trans-4,4′-dimethyl-
azobenzene. The resulting curves were successfully fit
to a kinetic model using a simulation program.47 The
model used is shown in Scheme 6. We propose an initial
fast preequilibrium involving exchange of coordinated
PMe3 for the diazine. This equilibrium lies to the left
and accounts for the inhibition by added phosphine.
Whether this ligand exchange occurs via an associative
or a dissociative pathway is unknown. However, we do
know that phosphine exchange as monitored by the
fluxionality of 4b is dissociative. The diazine intermedi-
ate then undergoes a relatively slow conversion to the
bis(imido) complex. To fit the kinetic data accurately,
it was found necessary to include the final equilibrium
between the bis(imido) complex and PMe3 to form 9. We
know that this last step is fast compared to the overall
rate of the reaction. The 1H NMR spectrum of the
product 9 shows a single broad resonance for the PMe3
group at ambient temperatures. When the temperature
is lowered, the resonance shifts further upfield and
sharpens. The broadening and downfield shift upon
raising the temperature is due to the fast (on the NMR
time scale) exchange of free and coordinated PMe3 as
well as a shift in the equilibrium toward free PMe3
(which resonates downfield of the coordinated ligand).
If the model is correct, then fitting of individual kinetic
runs should yield a consistent set of values for the terms
{k2k1/k-1} and the final equilibrium constant {k3/k-3}.
The results (Figure 11) for data obtained at 28.0(5) °C
support the kinetic model. An independent estimate of
{k3/k-3} was obtained using the PMe3 chemical shift
observed in the 1H NMR spectrum of 9 at 28 °C and
indicated a significant barrier to the conversion of d2-
peroxo species into the corresponding d0-bis(oxo) com-
pound. In one case it was found that the symmetry of
the system precluded the flow of the two metal-based
electrons into the O-O σ* orbital.45 Another significant
discovery by Maatta and Wentworth was the complete
lack of thermal or photochemical interconversion of the
η2-nitrosobenzene complex [Mo(ONPh)(S2CNEt2)2] and
the oxo imido valence isomer [Mo(O)(NPh)(S2CNEt2)2].46
To gain even more insight into this reactivity, we have
carried out a kinetic study of the reaction of 4b with
trans-4,4′-dimethylazobenzene. The reaction was moni-
tored via 1H NMR spectroscopy. During the course of
the reaction, only the reagents and product were
observed. No intermediate species were detectable by
NMR. The reaction was also strongly inhibited by the
addition of free PMe3. A series of kinetic runs were
carried out by monitoring the disappearance of the
(43) For the coordination of simple diazine, HNdNH, see: (a)
Albertin, G.; Antoniutti, S.; Bacchi, A.; Boato, M.; Pelizzi, G. J . Chem.
Soc., Dalton Trans. 2002, 3313. (b) Smith, M. R.; Cheng, T.-Y.;
Hillhouse, G. L. J . Am. Chem. Soc. 1993, 115, 8638. (c) Cheng, T.-Y.;
Peters, J . C.; Hillhouse, G. L. J . Am. Chem. Soc. 1994, 116, 204.
(44) Que, L., J r. J . Chem. Soc., Dalton Trans. 1997, 3933.
(45) Brown, S. N.; Mayer, J . M. Inorg. Chem. 1992, 31, 4091.
(46) Maatta, E. A.; Wentworth, R. A. Inorg. Chem. 1980, 19, 2597.
(47) KINETIC version 1.04; ARSoftware, 1994.

340 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
F igu r e 12. Energy level diagram for cis-/ trans-azobenzene.
Sch em e 7
comparing it to the low-temperature limiting spectrum
of 9 and the chemical shift of free PMe3. This calculation
yielded a value of 9900 M-1 L. This is slightly higher
than that obtained from the kinetic data, but a signifi-
cant error will be involved in assuming that the chemi-
cal shift of the fully formed complex 9 is invariant with
temperature.
The kinetic data, combined with the observed reaction
products, clearly show these reactions to occur at a
single metal center. However, they do not give us any
direct insight into the intimate mechanism of the
reaction. Of particular significance is the fact that the
kinetic and synthetic studies were carried out using
trans-azobenzenes. Thermodynamic data show that
trans-azobenzene is ∼10.8 kcal mol-1 more stable than
the cis isomer.48 Furthermore, there is a sizable barrier
to interconversion (Figure 12). The trans form is ideally
suited for the bimolecular activation of the NdN bond
via σ-coordination to two different metal centers. How-
ever, activation by one metal center eventually requires
η2-coordination (diazametallacyclopropane intermedi-
ate). There are many examples in the literature of the
formation of η2-azobenzene complexes directly from
trans-azobenzene.41 Recent studies by Bergman et al.42
show that the reaction of trans-azobenzene with the d2
reagent [Cp2TaMe] can lead either to terminal imido
complexes via cleavage or to the η2-azobenzene complex.
This latter species does not contain the electrons needed
to cleave the NdN bond. Hence, it is certain that η2
coordination can result via reaction with the trans
isomer. How this takes place is unknown. It is possible
that the barrier to isomerization of σ-bound trans-
azobenzene is lower than for the free ligand. Alterna-
tively, it is possible that coordination to the π-bond
(pseudo-olefin) could lead directly to the η2-azobenzene
intermediate. The cis isomer of azobenzene can be
generated photochemically by irradiation of solutions
of the trans isomer. Furthermore, it has a lifetime of
hours at ambient temperatures. When a photogenerated
mixture of cis-/trans-azobenzene was treated with 4b,
the ratio of cis/trans isomers rapidly dropped with the
formation of 8. This result implies that the cis isomer
reacts considerably faster than the trans form. This was
confirmed by studying the reactivity of bis(2,4,6-tri-
methylphenyl)diazine, MesNdNMes (NMes ) NC6H3-
Me3-2,4,6).49 Reaction between trans-MesNdNMes and
4b in C6D6 solution does not occur over days at room
temperature, as monitored by 1H NMR. Even at 100 °C
reaction is slow, needing days to generate a product
whose spectroscopic properties are consistent with the
formulation [W(OC6HPh4-2,3,5,6)2(NMes)2] (15) (Scheme
7). Uncoordinated PMe3 was also observed. When trans-
MesNdNMes is photolyzed in C6D6, the formation of the
cis isomer is observed by NMR. Addition of 4b to this
1
mixture was found to lead to 15 (verified by H NMR)
at ambient temperatures within 30 min (Scheme 7).
Hence, this is conclusive proof of the much faster
reactivity of cis-diazines over trans-diazines with the
W(II) aryloxides 4. Taken together, the evidence makes
a compelling argument that these cleavage reactions
(four-electron reductions) are taking place at a single
metal center.50
Exp er im en ta l Section
All operations were carried out either under a dry nitrogen
atmosphere in a Vacuum Atmospheres Dri-Lab or by standard
(48) (a) Forber, C. L.; Kelusky, E. C.; Bunce, N. J .; Zerner, M. C. J .
Am. Chem. Soc. 1985, 107, 5884. (b) Dias, A. R.; Minas Da Piedade,
M. E.; Martinho Simo˜es, J . A.; Simoni, J . A.; Teixeira, C.; Diogo, H. P.
J . Chem. Thermodyn. 1992, 24, 439. (c) Brown, E. V.; Granneman, G.
R. J . Am. Chem. Soc. 1975, 97, 621.
(49) Gabe, E. J .; Wang, Y.; Barclay, L. R. C.; Dust, J . M. Acta
Crystallogr., Sect. B: Struct. Crystallogr., Cryst. Chem. 1981, 37, 978.
(50) Theoretical studies indicate that the final cleavage of the N-N
bond in the diazine complex [(HO)2W(HNNH)] occurs during
a
structural change from pseudo square planar to pseudo tetrahedral.11

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 341
Schlenk techniques. The hydrocarbon solvents were distilled
from sodium benzophenone and stored over sodium ribbon
under nitrogen until use. The syntheses of 2,3,5,6-tetraphen-
ylphenol, 2,6-diphenyl-3,5-dimethylphenol, and 2,6-diphenyl-
3,5-di-tert-butylphenol were previously reported. All phos-
phines were purchased from Strem Chemical Co. and stored
over 4 Å molecular sieves (liquids) or dried under vacuum
(solids) for 24 h prior to use. The 1H and 13C NMR spectra
(where solubility allowed) were recorded on Varian Associates
Gemini-200 and Inova-300 spectrometers and referenced to
protio impurities of commercial benzene-d6. 31P NMR spectra
were recorded on a Varian Associates Inova-300 spectrometer
and referenced to external 85% H3PO4. Elemental analyses
and crystallographic studies were obtained in house at Purdue
University.
lized in a minimum amount of benzene layered with hexane,
giving 4a (1.5 g, 40%) as crystals suitable for an X-ray
diffraction study. Anal. Calcd for C63H52PO2W: C, 71.66; H,
4.96; P, 2.93. Found: C, 71.83; H, 5.02; P, 2.83. For 1H NMR
1
data at -30 °C in toluene-d8 see Table 2. H NMR (C6D6, 30
°C): δ 7.00-8.00, 3.45, 2.94, 1.94, 1.52, 1.19 (m, η6-C6H5), 0.96
(d, PMe3). 13C NMR (C6D6, 30 °C): δ 169.7, 165.9, 143.1, 141.4,
141.3, 140.2, 139.4, 138.4, 137.2, 132.9, 132.3, 130.5, 130.2,
129.9, 129.3, 129.0, 128.5, 128.1, 127.8, 127.0, 126.3, 125.7,
124.6, 120.0 (aromatic C), 100.6, 96.2, 94.0, 92.0 (br, η6-C6H5),
16.0 (d, PMe3). 31P NMR (C6D6, 30 °C): δ 31.6 (1J (183W-31P)
) 372 Hz).
[W(OC6H P h 3-η6-C6H 5)(OC6H P h 4-2,3,5,6)(P E t3)] (4c). A
solution of 1 (4.06 g, 3.63 mmol) and PEt3 (1.33 mL, 9.0 mmol)
in toluene (100 mL) was stirred over a sodium amalgam (0.40
g of Na, 17.4 mmol) for 24 h at room temperature. The olive
green solution was decanted off the mercury pool, filtered
through Celite, and evaporated in vacuo to yield a dark green
solid. The crude solid was recrystallized in a minimal amount
of toluene layered with pentanes, giving 4c (1.82 g, 45.8%) as
emerald green crystals suitable for an X-ray diffraction study.
Anal. Calcd for C66H57O2PW: C, 72.26; H, 5.24; P, 2.82.
Found: C, 72.55; H, 5.42; P, 2.65. 1H NMR (d6-benzene, 25
°C): δ 7.72 (d, 2H, aromatic), 7.72-6.88 (m, aromatics), 3.65
(broad m, 1H, m-η6-arene), 2.99 (broad m, 1H, o-η6-arene), 1.83
(broad m, 1H, m-η6-arene), 1.57 (broad m, 1H, o-η6-arene), 1.28
(m, 7H, p-η6-arene and P-CH2CH3), 0.57 (m, 9H, P-CH2CH3).
13C NMR (C6D6, 20° C): δ 142.7, 141.3, 141.2, 138.5, 132.3,
130.3, 129.9, 129.7, 129.0, 128.7, 128.4, 128.3, 126.8, 126.3,
126.0, 125.6, 125.5, 125.4, 124.3, 119.8 (aromatic C), 16.3 (d,
P-CH2-), 7.4 (-CH3). 31P NMR (C6D6, 20° C): δ 59.0 (1J (183W-
31P) ) 363 Hz).
[W(OC6HP h 4-2,3,5,6)2Cl4] (1). A 1 L round-bottom flask
was charged with [WCl6] (26.7 g, 0.067 mol) under a nitrogen
flush, and 400 mL of toluene was added. With stirring, 2,3,5,6-
tetraphenylphenol (53.4 g, 0.14 mol) was added over a 20 min
period using a solid addition funnel. Part of the solvent, as
well as the HCl gas that was generated, was removed in vacuo
and the purple solution refluxed for the next 6 h. The
remaining solvent was removed in vacuo to leave the crude
product. The purple solid was washed with a small amount of
pentane and dried in vacuo to give 1 (75 g, 88%). Anal. Calcd
for C60H42Cl4O2W: C, 64.31; H, 3.78; Cl, 12.65. Found: C,
1
64.48; H, 3.42; Cl, 12.39. H NMR (C6D6, 30 °C): δ 7.00-8.00
(m, 42 H, aromatics).
[W(OC6HP h 2-2,6-Me2-3,5)2Cl4] (2). To a solution contain-
ing [WCl6] (14.1 g, 0.035 mol) in toluene (200 mL) was added
2,6-diphenyl-3,5-dimethylphenol (20.0 g, 0.073 mol) in portions
over a 30 min period. Upon complete addition the dark purple
mixture was heated to reflux and vented occasionally to
remove HCl from the reaction. The reaction mixture was
refluxed for several hours and cooled and the solvent removed
in vacuo. The purple solid was washed with a small portion of
pentane and dried to give 2 (26.8 g, 89%). Anal. Calcd for
[W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(P Bu n 3)] (4d ). A
solution of 1 (2.00 g, 1.8 mmol) and PBun (0.40 g, 1.8 mmol)
3
in toluene (25 mL) was stirred over a sodium amalgam (0.20
g of Na, 8.70 mmol) for 24 h at room temperature. The olive
green solution was decanted off the mercury pool, filtered
through a pad of Celite, and evaporated in vacuo to yield a
green solid. The crude solid was recrystallized in a minimum
amount of benzene layered with hexane, giving 4e (0.55 g,
25%) as a green powder. Anal. Calcd for C72H69O2PW: C, 73.22;
C
40H34O2Cl4W: C, 56.88; H, 4.14; Cl, 15.47. Found: C, 56.93;
1
H, 4.14; Cl, 15.56. H NMR (C6D6, 30 °C): δ 7.0-7.4 (m, 20H,
aromatics), 6.34 (s, para H), 1.83 (s, CH3). 13C NMR (C6D6, 30
°C): δ 127-140 (aromatics), 20.8 (CH3).
1
[W(OC6HP h 2-2,6-Bu t2-3,5)2Cl4] (3). To a suspension of
[WCl6] (0.54 g, 1.4 mmol) in toluene (100 mL) was added 2
equiv of 3,5-di-tert-butyl-2,6-diphenylphenoxide (1.0 g, 2.9
mmol). The solution was stirred for 24 h and filtered, and the
solvent was removed under vacuum. The remaining purple
powder was recrystallized from toluene layered with hexane
as a deep purple powder, giving 3 (0.81 g, 56%). Anal. Calcd
for C52H58Cl4O2W: Cl, 13.63. Found: Cl, 13.24. 1H NMR (C6D6,
30 °C): 7.52-7.00 (m, aromatics); 1.12 (s, C(CH3)3).
H, 5.89; P, 2.62. Found: C, 73.46; H, 6.22; P, 2.31. H NMR
(C6D6, 30 °C): δ 6.8-7.7 (m, 37 H, aromatic protons), 3.76 (q,
1 H), 3.03 (t, 1 H), 1.86 (q, 1 H), 1.71 (d, 1 H, η6-C6H5), 1.5 (m),
1.2 (m), 0.9 (m, PBu3). 13C NMR (C6D6, 30 °C): δ 179.2 (d),
165.2 (d), 143.4, 143.0, 142.2, 141.5, 139.8, 139.6, 139.2, 138.5,
137.4, 132.6, 131.0, 130.6, 129.5, 129.2, 129.0, 127.0, 126.8,
126.2, 125.6, 120.2 (aromatic C), 99.4, 98.7, 98.4, 97.0, 96.8,
93.2 (η6-C6H5), 25.8, 24.7, 24.6 (d), 14.2 (PBu3). 31P NMR (C6D6,
30 °C): δ 52.9 (1J (183W-31P) ) 364 Hz).
[W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(P Me2P h )] (4e).
A solution of 1 (2.00 g, 1.8 mmol) and PMe2Ph (0.25 g, 1.8
mmol) in toluene (25 mL) was stirred over a sodium amalgam
(0.20 g of Na, 8.70 mmol) for 48 h at room temperature. The
olive green solution was decanted off the mercury pool, filtered
through a pad of Celite, and evaporated in vacuo to yield a
green solid. The crude solid was recrystallized in a minimum
amount of benzene layered with hexane, giving 4b (0.75 g,
40%) as emerald green crystals suitable for an X-ray diffraction
study. Anal. Calcd for C68H53O2PW: C, 73.10; H, 4.83; P, 2.83.
Found: C, 72.78; H, 4.92; P, 2.49. 1H NMR (C6D6, 30 °C): δ
6.8-7.8 (m, 37 H, aromatic protons), 3.50, 3.04, 2.02, 1.70, 1.38
(m, η6-C6H5), 1.22 (d, PMe2Ph); 1.13 (d, PMe2Ph). 13C NMR
(C6D6, 30 °C): δ 177.5 (d), 165.5 (d), 142.9, 142.3, 141.6, 141.4,
141.2, 140.6, 140.1, 139.6, 139.2, 138.7, 137.0, 132.7, 132.3,
131.4, 131.2, 130.5, 130.1 129.3, 129.0, 128.3, 127.7, 126.9,
126.6, 126.3, 125.9, 124.5, 119.9 (aromatic C); 100.2, 97.6, 95.5,
92.2 (br, η6-C6H5), 15.5 (d, PMe2Ph), 14.4 (d, PMe2Ph). 31P NMR
(C6D6, 30 °C): δ 38.1 (1J (183W-31P) ) 367 Hz).
[W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(η1-d p p m )] (4a ).
A solution of 1 (2.00 g, 1.8 mmol) and dppm (0.69 g, 1.8 mmol)
in toluene (25 mL) was stirred over a sodium amalgam (0.20
g of Na, 8.70 mmol) for 48 h at room temperature. The olive
green solution was decanted off the mercury pool, filtered
through a pad of Celite, and evaporated in vacuo to yield a
green solid. The crude solid was recrystallized in a minimum
amount of benzene layered with hexane, giving 4d (1.8 g, 25%)
as green crystals. Anal. Calcd for C85H64O2PW: C, 74.90; H,
4.72; P, 4.51. Found: C, 74.56; H, 4.73; P, 4.18. 1H NMR (C6D6,
30 °C): δ 6.8-7.7 (m, 37 H, aromatic protons), 4.44, 3.16, 2.07,
1.82, 1.79 (m, η6-C6H5), 3.19, 2.55 (multiplet, diastereotopic
methylene protons of dppm). 31P NMR (C6D6, 30 °C): δ 52.9
(d, J (31P-31P) ) 45.3 Hz, J (183W-31P) ) 358 Hz), -24.9 (d).
[W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(P Me3)] (4b). A
solution of 1 (4.00 g, 3.6 mmol) and an excess (2.2-2.5 equiv
per W) of PMe3 in toluene (50 mL) was stirred over a sodium
amalgam (0.40 g of Na, 17.4 mmol) for 24 h at room temper-
ature. The resulting olive green solution was decanted off the
mercury pool, filtered through a pad of Celite, and evaporated
in vacuo to yield a green solid. The crude solid was recrystal-
2
1
[W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)(P MeP h 2)] (4f).
A solution of 1 (2.00 g, 1.8 mmol) and PMePh2 (0.40 g, 1.8

342 Organometallics, Vol. 23, No. 3, 2004
Lentz et al.
mmol) in toluene (25 mL) was stirred over a sodium amalgam
(0.20 g of Na, 8.70 mmol) for 24 h at room temperature. The
olive green solution was decanted off the mercury pool, filtered
through a pad of Celite, and evaporated in vacuo to yield a
green solid. The crude solid was recrystallized in a minimum
amount of benzene layered with hexane, giving 4c (0.55 g,
the emerald green solution quickly turned orange-brown; after
several hours the product was analyzed using NMR spectros-
1
copy. H NMR (C6D6, 30 °C): δ 6.9-7.5 (aromatics), 6.82 (d,
8.30 Hz, m-H), 6.51 (d, 8.05 Hz, o-H), 2.12 (s, p-Me), 0.10 (br,
PMe3). 31P NMR (C6D6, 30 °C): δ 4.1 ppm (br, PMe3).
P r epar ation of [W(OC6HP h 4-2,3,5,6)2(NP h )(NTol)(P Me3)]
(10). A saturated C6D6 solution of [W(OC6HPh3-η6-C6H5)(OC6-
HPh4-2,3,5,6)(PMe3)] was treated with an excess of TolNdNPh,
and the emerald green solution quickly turned orange-brown.
Layering the solution with hexanes induced the formation of
1
25%) as green crystals. H NMR (C6D6, 30 °C): δ 6.8-7.7 (m,
37 H, aromatic protons), 3.66, 3.12, 2.04, 1.48 (m, η6-C6H5),
1.26 (d, P-Me). 13C NMR (C6D6, 30 °C): δ 178.4 (d), 165.7 (d),
143.0, 141.6, 141.4, 140.2, 139.7, 139.3, 138.0, 137.2, 133.7,
132.8, 130.5, 130.0, 129.6, 129.3, 127.0, 126.7, 126.3, 126.2,
125.5, 124.7, 120.3 (aromatic C), 99.9, 99.8, 99.1, 98.2, 93.3,
93.0 (η6-C6H5), 15.8 (d, PMePh2). 31P NMR (C6D6, 30 °C): δ
49.1 (1J (183W-31P) ) 362 Hz).
1
crystals that were suitable for an X-ray diffraction study. H
NMR (C6D6, 30 °C): δ 6.94-8.03 (aromatics), 6.80 (d, 8.06 Hz,
m-H of NTol), 6.66 (t, 7.45 Hz, p-H of NPh), 6.59 (d, 8.01 Hz,
o-H of NPh), 6.67 (d, 8.06 Hz, o-H of NTol), 2.11 (s, 3H, p-Me),
0.26 (br, PMe3). 31P NMR (C6D6, 30 °C): δ 3.0 ppm (br, PMe3).
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(NP h )(O)(OP Me3)]
(11). A saturated C6D6 solution of [W(OC6HPh3-η6-C6H5)(OC6-
HPh4-2,3,5,6)(PMe3)] was treated with an excess of nitrosoben-
zene, and the emerald green solution quickly turned brown.
Layering the solution with hexanes induced the formation of
[W(OC6HP h -η6-C6H5-Me2-3,5)(OC6HP h 2-2,6-Me2-3,5)(η1-
d p p m )] (5a ). A solution of 2 (1.30 g, 1.5 mmol) and dppm (0.65
g, 1.65 mmol) in toluene (25 mL) was stirred over a sodium
amalgam (0.16 g of Na, 6.7 mmol) for 3 h at room temperature.
The solution was decanted off the mercury pool, filtered
through a Celite pad, and evaporated in vacuo to yield 5 as a
deep green solid. Anal. Calcd for C65H56O2P2W: C, 71.90; H,
5.16. Found: C, 71.80; H, 5.32. 1H NMR (C6D6, 30 °C): δ 6.6-
7.6 (m, aromatic H), 6.57 (s, p-H), 6.46 (s, p-H), 4.34, 3.36, 3.07,
2.47, 1.73 (m, η6-C6H5), 2.72 (m, dppm). 13C NMR (C6D6, 30
°C): δ 177.6 (d, W-O-C, 3J (31P-13C) ) 10.1 Hz), 164.9 (d,
W-O-C, 3J (31P-13C) ) 5.6 Hz), 139.0, 135.3, 134.8, 133.9,
133.7, 133.6, 133.5, 133.3 133.2, 133.0, 132.9, 132.7, 132.6,
132.5, 131.8, 129.2, 127.8, 127.3, 126.5, 125.6, 124.1 (d, 1J (31P-
13C) ) 5.5 Hz), 99.1, 98.9, 98.8, 98.6, 92.6, 92.4 (η6-C6H5), 26.6
(m, dppm), 24.6, 20.6, 19.2 (m-Me). 31P NMR (C6D6, 30 °C): δ
57.0 (d, 2J (31P-31P) ) 56.3 Hz, 1J (183W-31P) ) 357 Hz), -24.73
1
crystals that were suitable for an X-ray diffraction study. H
NMR (C6D6, 30 °C): δ 6.5-7.9 (aromatics), 6.74 (t, p-H of NPh),
6.19 (d, o-H of NPh), 0.58 (br, OPMe3). 31P NMR (C6D6, 30
°C): δ 32.7 ppm (br, OPMe3).
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(NC4H4N)(P Me3)]
(12). A sample of 4b (97.4 mg, mmol) was dissolved in 1 mL
of d6-benzene, and to this solution was added 1 equiv of
pyridazine (6.7 µL, mmol). Upon addition the solution went
from emerald green to red. The sample was analyzed by NMR
spectroscopy. 12 was recrystallized in hot benzene, and red
crystals suitable for an X-ray diffraction study formed. Anal.
Calcd for C67H55N2O2W: C, 70.90; H, 4.88; N, 2.47; P, 2.73.
2
(d, J (31P-31P) ) 56.3 Hz).
P r epa r a tion of [W(OC6HP h -η6-C6H5-Bu t2-3,5)(OC6HP h 2-
2,6-Bu t2-3,5)(η1-d p p m )] (6a ). A solution of 3 (0.30 g, 0.3
mmol) and dppm (0.20 g, 0.5 mmol) in 15 mL of toluene was
stirred over a sodium amalgam (0.03 g of Na, 1.3 mmol) for 3
h at room temperature. The solution was decanted off the
mercury pool, filtered through a Celite pad, and evaporated
in vacuo to yield 6a (0.31 g, 80%) as a deep green solid. 1H
NMR (C6D6, 30 °C): δ 6.5-7.8 (m, aromatics), 3.93, 2.75, 2.5,
2.35 (m, protons of the η6-C6H5 group and methylene protons
from dppm), 1.31 (s, C(CH3)3), 1.12, 1.25 (s, inequivalent
C(CH3)3 from η6-bound aryloxide). 13C NMR (C6D6, 30 °C): δ
180.2 (W-O-C from η6-bound aryloxide), 167.5 (W-O-C),
147.3, 147.1, 140.8, 139.6, 137.7, 133.2, 131.9, 129.5, 129.3,
127.9, 127.5, 127.0, 126.4, 126.0, 125.8, 125.6, 125.5 (aromat-
ics), 101.8, 99.9, 98.0, 91.7 (η6-C6H5), 37.4, 37.3, 36.6 (C(CH3)3),
33.8, 33.7, 33.1 (C(CH3)3). 31P NMR (C6D6, 30 °C): δ 58.3
1
Found: C, 69.89; H, 4.91; N, 2.12; P, 2.38. H NMR (C6D6, 25
°C): δ 7.6 (dd, HC-N), 7.3-6.9 (m, aromatics), 5.8 (dd, 2H,
HCdCH), -0.24 (d, PMe3). 31P NMR (C6D6, 25 °C): δ -11 (br,
PMe3).
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(NC12H8N)(P Me3)]
(13). A sample of 4b (100 mg, 0.095 mmol) was dissolved in 4
mL of benzene, and to this solution was added an excess of
benzo[c]cinnoline (35 mg, 0.20 mmol). The solution was stirred
for 2 h at room temperature. Afterward, the solution was
layered with hexanes and the yellow precipitate was dried in
vacuo (65 mg, 55.6%). The product was analyzed by NMR
spectroscopy. Yellow-green X-ray-quality crystals were ob-
tained by dissolving the crude product in a minimum amount
of benzene and layering the solution with hexane. Anal. Calcd
for C75H59N2O2PW: C, 72.93; H, 4.82; N, 2.27. Found: C, 73.11;
H, 5.02; N, 2.38. 1H NMR (C6D6, 25 °C): δ 6.94-7.5 (m,
aromatics), 7.6 (d, o-H), 6.8 (t, p-H), 6.6 (d, m-H), -0.09 (d,
PMe3). 31P NMR (C6D6, -50 °C): δ -0.477 (1J (183W-31P) ) 338
Hz).
P r epar ation of [W(OC6HP h 4-2,3,5,6)2{NCH(C6H4)CHN}-
(P Me3)] (14). A sample of 4b (150 mg, 0.142 mmol) was
dissolved in 4 mL of benzene, and to this solution was added
phthalazine (19 mg, 0.146 mmol). The solution was stirred for
20 min at room temperature and then layered with hexanes,
giving dark green crystals of 14 (85.7 mg, 50.9%) suitable for
X-ray diffraction study (0.0857 g, 50.9%). Anal. Calcd for
1
(unresolved doublet with 183W satellites, J (183W-31P) ) 342
2
Hz), -24.1 (d, J (31P-31P) ) 32.2 Hz).
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(O)2(P Me3)] (7). A
saturated C6D6 solution of [W(OC6HPh3-η6-C6H5)(OC6HPh4-
2,3,5,6)(η1-PMe3)] in a 5 mm J . Young NMR tube was degassed
and placed under an atmosphere of pure oxygen. The emerald
green solution faded to yellow brown within minutes. Layering
the solution with hexane induced the formation of yellow
crystals that were suitable for an X-ray diffraction study. Anal.
Calcd for C63H51PO2W‚C6H6: C, 71.14; H, 4.93. Found: C,
1
71.52; H, 4.79. H NMR (30 °C, C6D6): δ 6.8-7.5 (aromatics),
C
71H57N2O2PW: C, 71.96; H, 4.85; N, 2.36; P, 2.61. Found: C,
0.18 (d, PMe3). 31P NMR (30 °C, C6D6): δ -2.5 (br, PMe3).
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(NP h )2(P Me3)] (8).
A saturated C6D6 solution of [W(OC6HPh3-η6-C6H5)(OC6HPh4-
2,3,5,6)(PMe3)] was treated with an excess of azobenzene, and
the emerald green solution quickly turned orange-brown. After
several hours the product was analyzed using NMR spectros-
copy. 1H NMR (C6D6, 30 °C): δ 6.8-7.5 (aromatics), 6.63 (t,
p-H of NPh); 6.59 (d, o-H of NPh). 31P NMR (C6D6, 30 °C): δ
0.30 ppm (br, PMe3).
1
72.41; H, 5.07; N, 2.38; P, 2.50. H NMR (C6D6, 25 °C): δ 8.5
(s, o-H to N), 7.0-7.4 (m, aromatics), 7.2 (dd, aromatics), -0.5
(d, PMe3). 31P NMR (toluene-d8, -30 °C): δ -17.58 (1J (183W-
31P) ) 296 Hz).
P r ep a r a t ion of [W(OC6HP h 4-2,3,5,6)2(NMes)2] (15). A
sample of 4b (81.6 mg, 0.077 mmol) was placed in a J . Young
valve solvent seal NMR tube along with d6-benzene (1 mL).
To this solution was added an excess of trans-azomesitylene
(25.8 mg, 0.097 mmol). The solution was photolyzed for
20 min using a mercury-tungsten lamp and then heated for
5 min at 100 °C. Yield: 0.0752 g (78%). Anal. Calcd for
P r ep a r a tion of [W(OC6HP h 4-2,3,5,6)2(NTol)2(P Me3)] (9).
A saturated C6D6 solution of [W(OC6HPh3-η6-C6H5)(OC6HPh4-
2,3,5,6)(PMe3)] was treated with an excess of TolNdNTol, and
C
78H64N2O2W: C, 75.23; H, 5.18; N, 2.26. Found: C, 74.85; H,

Reduction of Double Bonds by W(II) Aryloxide Compounds
Organometallics, Vol. 23, No. 3, 2004 343
Ta ble 9. Cr ysta l Da ta a n d Da ta Collection P a r a m eter s
4b
4c
4d
7
10
11
12
13
14
formula
fw
WPO2C63
H56
1059.97
-
WPO2C66
H57‚C6H6
1175.13
-
WPO2C72
H69
1181.18
-
WPO4C63
-
WPO2N2-
WPO4NC69
H56‚C6H6
1256.16
-
WPO2N2C67
H55‚2C6H6
1291.25
-
WPO2N2C75
H59‚2C6H6
1391.37
-
WPO2N2-
H51‚C6H6
1165.05
P21/n (No. 14) P21/n (No. 14) P21/n (No. 14) P21/c (No. 14) P21/c (No. 14) P1h (No. 2)
C
76H63
C
71H57
1251.19
1185.08
space group P1h (No. 2)
P21/c (No. 14) P1h (No. 2)
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å
Z
11.5631(3) 10.7808(2)
12.3496(2) 23.9094(9)
18.2185(4) 22.8885(8)
82.6659(16) 90
72.7035(11) 90.541(2)
86.8764(16) 90
2463.25(13) 5899.5(5)
11.620(3)
14.612(3)
18.953(2)
102.809(12) 90
91.441(15) 98.1813(8)
109.153(17) 90
2947
2
1.331
296.
12.4708(2)
14.9833(2)
30.1291(5)
11.4420(3)
27.6755(7)
19.8378(4)
90
104.9040(13) 97.4297(17)
90
6070.6(5)
4
1.369
203.
14.5298(4)
17.7437(5)
23.2712(6)
90
24.8331(5)
11.5704(3)
44.5364(12)
90
101.3130(8)
90
12548.0(10)
8
1.367
12.2150(2)
32.4594(5)
17.0957(2)
90
93.0186(9)
90
6768.9(3)
4
1.365
11.3255(1)
16.3547(3)
18.3239(3)
70.6136(7)
73.1055(6)
71.103(1)
2964.6(1)
2
90
5572.4(3)
4
1.389
203.
5997.7(5)
4
1.391
203.
2
4
F
calcd, g cm-3 1.429
1.323
150.
1.327
150.
temp, K
203.
150.
150.
radiation (λ)
R
Rw
Mo KR (0.710 73 Å)
0.042
0.111
0.050
0.115
0.040
0.042
0.051
0.106
0.044
0.098
0.048
0.092
0.051
0.084
0.042
0.089
0.038
0.085
2
2
2
5.33; N, 2.12. 1H NMR (C6D6, 25 °C): δ 6.8-7.3 (m, aromatics)
6.69 (s, m-H on NMes), 2.15 (s, o-Me on mesitylene), 1.86 (s,
p-Me on mesitylene).
∑w(|Fo| - |Fc| )2 and the weight w is defined as w ) 1/[σ2(Fo
)
+ (0.0585P)2 + 1.4064P], where P ) (Fo + 2Fc2)/3. Scattering
2
factors were taken from ref 54. Refinement was performed on
X-r a y Da ta Collection a n d Red u ction . Crystal data and
data collection parameters are contained in Table 9. A suitable
crystal was mounted on a glass fiber in a random orientation
under a cold stream of dry nitrogen. Preliminary examination
and final data collection were performed with Mo KR radiation
(λ ) 0.710 73 Å) on a Nonius Kappa CCD diffractometer.
Lorentz and polarization corrections were applied to the data.51
An empirical absorption correction using SCALEPACK was
applied.52 Intensities of equivalent reflections were averaged.
The structure was solved using the structure solution program
PATTY in DIRDIF92.53 The remaining atoms were located in
succeeding difference Fourier syntheses. Hydrogen atoms were
included in the refinement but restrained to ride on the atom
to which they are bonded. The structure was refined in full-
matrix least squares, where the function minimized was
a
AlphaServer 2100 using SHELX-97.55 Crystallographic
drawings were done using the ORTEP program.56
Ack n ow led gm en t. We thank the National Science
Foundation (Grant No. CHE-0078405) for financial
support of this research. We thank Prof. Greg Hillhouse
for a generous sample of trans-azomesitylene. We thank
Drs. Klaas Halenga and Edwin Rivera for all their
helpful NMR advice and instruction.
Su p p or tin g In for m a tion Ava ila ble: Tables giving X-ray
crystallographic data for 4b-d , 7, and 10-14. This material
is available free of charge via the Internet at http://pubs.acs.org.
OM030604M
(51) McArdle, P. C. J . Appl. Crystallogr. 1996, 239, 306.
(54) International Tables for Crystallography; Kluwer Academic:
Dordrecht, The Netherlands, 1992; Vol. C, Tables 4.2.6.8 and 6.1.1.4.
(55) Sheldrick, G. M. SHELXS97, A Program for Crystal Structure
Refinement; University of Gottingen, Gottingen, Germany, 1997.
(56) J ohnson, C. K. ORTEPII; Report ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.
(52) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276.
(53) Beurskens, P. T.; Admirall, G.; Beurskens, G.; Bosman, W. P.;
Garcia-Granda, R. S.; Gould, O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF92 Program System; Technical Report; Crystallography Labo-
ratory, University of Nijmegen, Nijmegen, The Netherlands, 1992.