Low-valent tungsten aryloxide compounds with pyridine ancillary ligation: Intramolecular reduction of heterocyclic and aromatic rings including formation of an η5-cyclohexadienyl group

Article abstract of DOI:10.1021/om030054s

The sodium amalgam reduction (2 Na per W) of hydrocarbon solutions of [W(OC₆HPh₄-2,3,5,6)₂Cl₄] in the presence of pyridine or 4-tert-butylpyridine leads to the W(IV) compounds [W(OC₆HPh₄-2,3,5,6)₂Cl₂ (py)₂] (1) and [W(OC₆HPh₄2,3,5,6)₂Cl₂(4-tert-butylp yridine)₂] (2) in good yields. The ambient-temperature ¹H NMR spectra of both 1 and 2 were found to be sharp and to exhibit extensive contact shifts due to the paramagnetic tungsten center. The addition of 2,2′-bipyridine to an emerald green solution of [W(OC₆HPh₃-η⁶-C₆H₅)(O C₆HPh₄-2,3,5,6)(PEt₃)] produced [W(OC₆HPh₄-2,3,5,6)₂(bipy)₂] (3), containing two bipy rings and two terminal aryloxide ligands coordinated mutually cis. The W-N(bipy) distances of 2.092(2), 2.093(2), 2.096(2), and 2.115(2) A in 3 are among the shortest so far reported for bipy ligands bound to either molybdenum or tungsten. The solid state and solution data for 3 indicate that reduction of both bipy ligands has occurred, but whether this involves four-electron reduction to yield d⁰-W(VI) is unclear. The addition of 4-tert-butylpyridine to [W(OC₆HPh₃-η⁶-C₆H₅)(O C₆HPh₄-2,3,5,6)(PEt₃)] was found (¹H NMR) to lead only to partial substitution of the phosphine ligand to produce [W(OC₆HPh₃-η⁶-C₆H₅)(O C₆HPh₄-2,3,5,6)(py-Bu^t-4)] (4). The sodium amalgam reduction (4 Na per W) of hydrocarbon solutions of [W(OC₆HPh₄-2,3,5,6)₂Cl₄] in the presence of 4-tert-butylpyridine produced a mixture found to contain the expected compound 4 along with a new salt compound, [W(OC₆HPh₃-η⁵-C₆H₆) (OC₆HPh₃-η¹-C₆H₄) (OC₆HPh₄-2,3,5,6)][Cl] (5), containing a total of three aryloxides in 5 is terminally bound, the obtained containing a 1:1 ratio of 4/5. One of the aryloxides in 5 is terminally bound, the second is cyclometalated, while the third chelates to the metal center via an η⁵-interaction with an ortho-cyclohexadienyl ring. The formal oxidation state of the metal center in 5 is (VI), and the unit cell contains one chloride ion to balance the positive charge on the tungsten. In compound 5 the hydride ligand formed via the cyclometalation has been transferred to the ortho-position of a phenyl ring. The structural parameters for the π-bound rings in 4 and 5 and their relevance to catalytic arene hydrogenation are discussed.

Full text of DOI:10.1021/om030054s

Organometallics 2003, 22, 2259-2266
2259
Low -Va len t Tu n gsten Ar yloxid e Com p ou n d s w ith
P yr id in e An cilla r y Liga tion : In tr a m olecu la r Red u ction
of Heter ocyclic a n d Ar om a tic Rin gs In clu d in g F or m a tion
of a n η5-Cycloh exa d ien yl Gr ou p
Margaret R. Lentz, Phillip E. Fanwick, and Ian P. Rothwell*
Department of Chemistry, Purdue University, 560 Oval Drive,
West Lafayette, Indiana 47907-2038
Received J anuary 22, 2003
The sodium amalgam reduction (2 Na per W) of hydrocarbon solutions of [W(OC6HPh4-
2,3,5,6)2Cl4] in the presence of pyridine or 4-tert-butylpyridine leads to the W(IV) compounds
[W(OC6HPh4-2,3,5,6)2Cl2(py)2] (1) and [W(OC6HPh4-2,3,5,6)2Cl2(4-tert-butylpyridine)2] (2) in
1
good yields. The ambient-temperature H NMR spectra of both 1 and 2 were found to be
sharp and to exhibit extensive contact shifts due to the paramagnetic tungsten center. The
addition of 2,2′-bipyridine to an emerald green solution of [W(OC6HPh3-η6-C6H5)(OC6HPh4-
2,3,5,6)(PEt3)] produced [W(OC6HPh4-2,3,5,6)2(bipy)2] (3), containing two bipy rings and two
terminal aryloxide ligands coordinated mutually cis. The W-N(bipy) distances of 2.092(2),
2.093(2), 2.096(2), and 2.115(2) Å in 3 are among the shortest so far reported for bipy ligands
bound to either molybdenum or tungsten. The solid state and solution data for 3 indicate
that reduction of both bipy ligands has occurred, but whether this involves four-electron
reduction to yield d0-W(VI) is unclear. The addition of 4-tert-butylpyridine to [W(OC6HPh3-
η6-C6H5)(OC6HPh4-2,3,5,6)(PEt3)] was found (1H NMR) to lead only to partial substitution
of the phosphine ligand to produce [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(py-But-4)] (4).
The sodium amalgam reduction (4 Na per W) of hydrocarbon solutions of [W(OC6HPh4-
2,3,5,6)2Cl4] in the presence of 4-tert-butylpyridine produced a mixture found to contain the
expected compound 4 along with a new salt compound, [W(OC6HPh3-η5-C6H6)(OC6HPh3-η1-
C6H4)(OC6HPh4-2,3,5,6)][Cl] (5), containing a total of three aryloxide ligands. Crystals were
obtained containing a 1:1 ratio of 4/5. One of the aryloxides in 5 is terminally bound, the
second is cyclometalated, while the third chelates to the metal center via an η5-interaction
with an ortho-cyclohexadienyl ring. The formal oxidation state of the metal center in 5 is
(VI), and the unit cell contains one chloride ion to balance the positive charge on the tungsten.
In compound 5 the hydride ligand formed via the cyclometalation has been transferred to
the ortho-position of a phenyl ring. The structural parameters for the π-bound rings in 4
and 5 and their relevance to catalytic arene hydrogenation are discussed.
In tr od u ction
phine, the deep-green compound [W(OC6H3Ph-η6-
C6H5)(OC6H3Ph2-2,6)(L)] (II) can be isolated and shown
to thermally convert to the cyclometalated species III
and H2.4
The chemistry of tungsten aryloxides continues to be
an area of intense research interest.1 Aryloxide ligands
are an important component of many tungsten meta-
thesis catalysts.2 Also there has been an awareness that
the combination of π-donating aryloxide ligands with
lower valent, mononuclear tungsten metal centers can
lead to interesting structures and reactivity. Previous
studies by our group 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 (via the intermediacy of I
and II) to the bis-cyclometalated compounds [W(OC6H3-
Ph-η1-C6H4)2(L)2] (III).3 With choice of a suitable phos-
* Corresponding author. E-mail: rothwell@purdue.edu.
(1) Bradley, D. C.; Mehrota, R. C.; Rothwell, I. P.; Singh, A. Alkoxo
and Aryloxo Derivatives of Metals; Academic Press: San Deigo, 2001.
(2) (a) Schrock, R. R. Polyhedron 1995, 14, 3209. (b) Lefebvre, F.;
Leconte, M.; Pagano, S.; Mutch, A.; Basset, J . M. Polyhedron 1995,
14, 3209.
In contrast, reduction of the compounds [W(OC6HPh2-
2,6-R2-3,5)2Cl4] (containing metalation-resistant aryl-
oxides; R ) Ph, Me, But) in the presence of a variety of
10.1021/om030054s CCC: $25.00 © 2003 American Chemical Society
Publication on Web 05/01/2003

2260 Organometallics, Vol. 22, No. 11, 2003
Lentz et al.
Sch em e 1
phosphine ligands generates the W(II) species of type
II [W(OC6HR2Ph-η6-C6H4)(OC6HPh2-2,6-R2-3,5)(L)] in
moderate yield.5 Solutions of these deep-green com-
pounds in C6D6 are unchanged (NMR) after being
heated at 100 °C for hours. These compounds prove to
be valuable substrates for the four-electron reduction
of a variety of small molecules.6
Ta ble 1. Tem p er a tu r e Dep en d en ce of th e 1H NMR
Ch em ica l Sh ifts of th e 4-ter t-Bu tylp yr id in e Sign a ls
in [W(OC6HP h 4-2,3,5,6)2Cl2(p y-Bu t-4)2]
temp (°C)
δ ortho-H (ppm)
δ meta-H (ppm)
δ But (ppm)
95
85
75
65
55
45
35
25
15
5
-30.99
-31.52
-32.04
-32.62
-33.18
-33.75
-34.32
-34.92
-35.50
-36.06
-36.63
-37.21
14.85
14.75
14.64
14.51
14.39
14.26
14.11
13.96
13.80
13.63
13.45
13.27
0.58
0.52
0.45
0.38
0.31
0.24
0.16
0.09
0.01
The majority of these studies have focused on the use
of tertiary phosphine ligands as the ancillary Lewis base
used to stabilize mononuclear, electron-deficient tung-
sten aryloxides. In one case it was shown that pyridine
and bipyridine adducts of the bis-cyclometalated com-
pounds III exhibited extremely interesting temperature-
dependent NMR spectra, from which the singlet-triplet
energy gap of these d2-metal compounds were exquis-
itely sensitive to the π-acidity of the coordinated N-
heterocycle ring.7 Previous work has also shown that
the adducts of formally titanium(II) with ligands of this
type have interesting electronic and structural proper-
ties.8 In this context we report here on an investigation
of the effects of pyridine and bipyridine ligands on the
reduction chemistry of the W(VI) aryloxide [W(OC6-
HPh4-2,3,5,6)2Cl4]. Besides generating some new ad-
ducts with interesting electronic properties, an aryloxide
compound was fortuitously isolated that contains an η5-
cyclohexadienyl ring bound to tungsten. This compound
is highly significant to the mechanism of arene hydro-
genation, which can be catalyzed by related aryloxide
compounds.9
-0.08
-0.16
-0.25
-5
-15
reduction (2 Na per W) of hydrocarbon solutions of
[W(OC6HPh4-2,3,5,6)2Cl4] in the presence of pyridine or
4-tert-butylpyridine leads to the W(IV) compounds 1 and
2 in good yields (Scheme 1). Both [W(OC6HPh4-2,3,5,6)2-
Cl2(py)2] (1) and [W(OC6HPh4-2,3,5,6)2Cl2(4-tert-butyl-
pyridine)2] (2) were found to be highly insoluble in
straight chain hydrocarbon solvents and somewhat
soluble in aromatic hydrocarbons. Compounds 1 and 2
can be purified easily using hot toluene, yielding the
pure product as small red needles. Both 1H NMR and
elemental analysis agree with the assigned formulation.
The assignment of an all-trans geometry is based upon
previously isolated phosphine complexes.10 Also the
direct d1-group 5 analogues [M(OC6H3Pri -2,6)2Cl2(py)2]
2
(M ) Nb, Ta) have been reported and fully characterized
Resu lts a n d Discu ssion
(crystallographic inversion center).11
1
The ambient-temperature H NMR spectra of both 1
Syn t h esis a n d Sp ect r oscop ic P r op er t ies of
and 2 were found to be sharp and to exhibit extensive
contact shifts due to the paramagnetic tungsten center.
At 25 °C the aryloxide protons are unusually spread
apart but still remain close to the aromatic region, with
the exception of the singlet from the phenoxy proton,
which is located at δ 5.00 and 4.93 ppm for 1 and 2,
respectively. The protons that exhibited the most con-
tact shift were those of the pyridine rings. In both
compounds the ortho-protons were found to resonate at
very high field, δ -26.14 and -34.92 ppm for 1 and 2,
respectively. The para-protons of the pyridine ring in 1
are also upfield shifted to δ -23.71. In contrast the
meta-protons appear downfield at δ 12.15 and 13.96
ppm for 1 and 2, respectively. The CMe3 protons in 2
[W(OAr )2Cl2(p y)2] Com p ou n d s. The sodium amalgam
(3) (a) Kerschner, J . L.; Torres, E.; Fanwick, P. E.; Rothwell, I. P.;
Huffman, J . C. Organometallics 1989, 8, 1424. (b) Kerschner, J . L.;
Rothwell, I. P.; Huffman, J . C.; Streib, W. E. Organometallics 1988, 7,
1871. (c) Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. Organome-
tallics 1989, 8, 1431.
(4) (a) Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem.
Soc. 1987, 109, 5840. (b) Kriley, C. E.; Kerschner, J . L.; Fanwick, P.
E.; Rothwell, I. P. Organometallics 1993, 12, 2051. (c) Kerschner, J .
L.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc. 1988, 110, 8235.
(5) Lentz, M. R.; Vilardo, J . S.; Lockwood, M. A.; Fanwick, P. E.;
Rothwell, I. P. J . Am. Chem. Soc., submitted for publication.
(6) (a) Lockwood, M. A.; Fanwick, P. E.; Eisenstein, O.; Rothwell, I.
P. J . Am. Chem. Soc. 1996, 118, 2762. (b) Maseras, F.; Lockwood, M.
A.; Eisenstein, O.; Rothwell, I. P. J . Am. Chem. Soc. 1998, 120, 6598.
(c) Lockwood, M. A.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc.,
Chem. Commun. 1996, 2013. (d) Lockwood, M. A.; Fanwick, P. E.;
Rothwell, I. P. Organometallics 1997, 16, 3574. (e) Lentz, M. R.;
Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Chem. Commun. 2002,
2482.
(7) Kriley, C. E.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc.
1994, 116, 5225.
(8) (a) Durfee, L. D.; Fanwick, P. E.; Rothwell, I. P.; Folting, K.;
Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 4720. (b) Durfee, L. D.;
Hill, J . E.; Kerschner, J . L.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chem.
1989, 28, 3095.
(9) Rothwell, I. P. J . Chem. Soc., Chem. Commun. (Feature Article)
1997, 1331.
(10) For related W(II) aryloxides/alkoxides see: (a) Atagi, L. M.;
Mayer, J . M. Angew. Chem., Int. Ed. Engl. 1993, 32, 439. (b) Rothfuss,
H.; Huffman, J . C.; Caulton, K. G. Inorg. Chem. 1994, 33, 187.
(11) Schweiger, S. W.; Freeman, E. S.; Clark, J . R.; Potyen, M. C.;
Fanwick, P. E.; Rothwell, I. P. Inorg. Chim. Acta 2000, 307, 63.

Low-Valent Tungsten Aryloxide Compounds
Organometallics, Vol. 22, No. 11, 2003 2261
Sch em e 2
appear as a sharp singlet at δ 0.09 ppm, upfield of the
normal diamagnetic position for these protons.
which generate the hyperfine shifts and Curie temper-
ature dependence. Other d2 octahedral systems that
exhibit this type of behavior, such as [WCl4(PR3)2], can
be found in the literature.13
The variation of these shifts around the pyridine ring
is indicative of considerable spin density from the metal
being transferred through the aromatic ring of the
pyridine by a hyperconjugative mechanism.12 The tem-
Syn th esis, Str u ctu r e, a n d Sp ectr oscop ic P r op -
er ties of [W(OAr )2(bip y)2]. The compounds [W(OC6-
HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(L)] (L ) tertiary phos-
phines) have been shown to react with aromatic diazines
to cleave the NdN bond and yield novel seven-mem-
bered diaza-metallacycles.6e The addition of 2,2′-bipy-
ridine to an emerald green solution of the PEt3 adduct
was found to produce a deep-purple solution after a few
minutes. The solution was layered with pentanes to
induce crystal formation of the product 3 (Scheme 2).
Compound 3 was found to be diamagnetic and soluble
in both straight chain and aromatic hydrocarbon solu-
tions. The material was analyzed by 1-D and 2-D NMR
techniques, elemental analysis, and X-ray diffraction,
and all results corresponded to the structure of [W(OC6-
HPh4-2,3,5,6)2(bipy)2] containing two bipy rings and two
terminal aryloxide ligands coordinated mutually cis.
1
perature dependence of the H NMR spectrum of 2 in
d8-toluene was measured. In Table 1 are collected the
variation of the chemical shifts of the tert-butylpyridine
ligand as a function of temperature. This behavior is
dramatically different from that observed for the bis-
cyclometalated compounds of type III [W(OC6H3Ph-η1-
C6H4)2(L)2] (L ) pyridines or bipyridines), where chemi-
cal shifts approached their diamagnetic positions as the
temperature was lowered.7 This was interpreted in
terms of a ground state diamagnetic singlet state for
the d2-tungsten metal center with a thermally populated
triplet state. The ground state electronic structure has
also been shown to be very sensitive to the nature of
the aryloxide in [W(OAr)2Cl2(PR3)2] species.10 It appears
that compounds 1 and 2 contain triplet ground states,
(12) (a) Drago, R. S. Physical Methods in Chemistry; Saunders Co.:
Philadelphia, 1977. (b) Holm, R. H.; Hawkins, C. T. In NMR of
Paramagnetic Molecules; La Mar, G. N., Horrocks, W. D., Holm, R.
H., Eds.; Academic Press: New York, 1973.
(13) (a) Shaw, B. D.; Moss, J . R. J . Chem. Soc. A 1970, 595. (b)
Butcher, A. V.; Chatt, J .; Leigh, G. J .; Richards, P. L. J . Chem. Soc.,
Dalton Trans. 1972, 1064.

2262 Organometallics, Vol. 22, No. 11, 2003
Lentz et al.
denum or tungsten. In [Mo(OPri)2(bipy)2] the Mo-N
distances are 2.108(2), 2.123(2), 2.115(2), and 2.126(2)
Å, while those for the titanium compound are in the
2.1-2.2 Å range. The only comparable W-N(bipy)
distances are found in [WCl2(PMe3)2(bipy)], 2.085(6) and
2.071(7) Å,16 and [WBr2(py-Me-4)2(bipy)], 2.081(6) and
2.079(6) Å.17
These short W-N distances raise the question as to
the formal oxidation state of tungsten in 3. Reduction
of each bipy ring by two electrons would lead to a W(VI)
metal center bound to two diamido ligands (Scheme 2).
A comparison of the interatomic distances within the
bipryridine ligands of 3 is inconclusive (Scheme 2).
However, possible support for this resonance picture
comes from the 1H NMR spectrum of diamagnetic 3. The
aromatic signals for the tetraphenylphenoxide ligands
appear in the “normal” aromatic region. There are eight
distinct proton resonances for the bipy ligands in 3,
1
which can be assigned using a H COSY spectrum. Five
of these bipy ligand signals are shifted upfield, appear-
ing at δ 4.65-5.07 ppm (4 triplets and 1 doublet). This
is the region normally occupied by olefinic protons. A
caveat to the argument of olefinic protons, however, is
the fact that 2,3,5,6-tetraphenylphenoxide ligands are
well known to cause upfield shifting of adjacent ligand
protons due to the diamagnetic shielding caused by the
ortho-phenyl rings. Hence the data for 3 indicate that
reduction of bipy ligands has occurred, but whether this
involves four-electron reduction to yield d0-W(VI) is
unclear.
Isola t ion a n d St r u ct u r a l Ch a r a ct er iza t ion of
[W(OC6H P h 3-η6-C6H 5)(OC6H P h 4-2,3,5,6)(p y-Bu t -
4)] (4) an d [W(OC6HP h 3-η5-C6H6)(OC6HP h 3-η1-C6H4)-
(OC6HP h 4-2,3,5,6)][Cl] (5). Although bipy was found
to react with [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)-
(PEt3)], leading to displacement of the π-arene, addition
of 4-tert-butylpyridine was found (1H NMR) to lead only
to partial substitution of the phosphine ligand. Hence
[W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(py-But-4)] (4)
was observed in solution only as a component of an
equilibrium mixture. In an attempt to generate this
compound directly, the sodium amalgam reduction (4
Na per W) of hydrocarbon solutions of [W(OC6HPh4-
2,3,5,6)2Cl4] in the presence of 4-tert-butylpyridine was
attempted. This reaction led to a very dark reaction
mixture from which red crystals of 2 could be isolated
from toluene/pentane mixtures. In one experiment
further treatment of the supernatant led to the isolation
of a few deep-green crystals, one of which was subjected
to X-ray diffraction analysis (Figures 2 and 3, Tables 3
and 4). These crystals were found to contain the
expected compound 4 along with a new salt compound
5 (Scheme 3).
F igu r e 1. Molecular structure of [W(OC6HPh4-2,3,5,6)2-
(bipy)2], 3. The phenyl rings attached to the aryloxide
nucleus have been removed for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(OC6HP h 4-2,3,5,6)2(bip y)2] 3
W-O(3)
1.999(2)
2.092(2)
2.096(2)
1.366(4)
1.381(4)
1.374(3)
1.374(3)
1.412(4)
W-O(4)
2.005(2)
2.093(2)
2.115(2)
1.383(3)
1.383(3)
1.380(3)
1.380(3)
1.409(4)
W-N(11)
W-N(12)
W-N(21)
W-N(22)
N(11)-C(11)
N(12)-C(1A)
N(21)-C(21)
N(22)-C(2A)
C(15)-C(16)
N(11)-C(15)
N(12)-C(16)
N(21)-C(25)
N(22)-C(26)
C(25)-C(26)
O(3)-W-O(4)
110.24(7)
73.45(8)
169.30(8)
127.7(2)
119.2(2)
118.7(2)
N(11)-W-N(12)
N(11)-W-N(21)
W-O(3)-C(31)
W-N(11)-C(15)
W-N(21)-C(25)
74.00(9)
79.57(8)
134.2(2)
119.2(2)
120.1(2)
N(21)-W-N(22)
N(12)-W-N(22)
W-O(4)-C(41)
W-N(12)-C(16)
W-N(22)-C(26)
The monomeric complex crystallized with a molecule
of benzene per unit cell (Figure 1, Table 2). The
structural parameters are worthy of some discussion.
There have been a number of alkoxides and aryloxides
of general formula [M(OAr)2(bipy)2] that have been
structurally characterized. All of the compounds contain
a cis-arrangement of aryloxide or alkoxide ligands. In
compound 3 the O-W-O angle is 110°, whereas this
parameter is smaller at 105° in [Mo(OPri)2(bipy)2],14 94°
in [Ti(OC6H3Pri -2,6)2(bipy)2],8 and 101° and 102° in the
2
d10-[M(OC6H4Cl-2-NO2-4)2(bipy)2] (M ) Zn, Cd).15 Of
particular interest are the coordination parameters for
the bipy ligands in 3. It is well known that bipyridine
ligands can undergo reduction when coordinated to
electron-rich, reducing metal centers. The electron
density located on the bipy rings typically leads to a
shortening of the M-N bond length below values typical
for dative interactions. In the case of 3 the W-N bond
lengths are all very short. Their values of 2.092(2),
2.093(2), 2.096(2), and 2.115(2) Å are among the shortest
so far reported for bipy ligands bound to either molyb-
Compound 5 can be seen to contain a total of three
aryloxide ligands. One of them is terminally bound, the
second is cyclometalated, while the third chelates to the
metal center via an η5-interaction with an ortho-
cyclohexadienyl ring. The formal oxidation state of the
metal center in 5 is (VI), and the unit cell contains one
chloride ion to balance the positive charge on the
tungsten. The origin of 5 is uncertain. However, one
(14) Chisholm, M. H.; Huffman, J . C.; Rothwell, I. P.; Bradley, P.
G.; Kress, N.; Woodruff, W. H. J . Am. Chem. Soc. 1981, 103, 4945.
(15) (a) Evans, C. C.; Masse, R.; Nicoud, J .-F.; Bagieu-Beucher M.
J . Mater. Chem. 2000, 10, 1419. (b) Evans, C. C.; Le Fur, Y.; Masse,
R. Z. Kristallogr.-New Cryst. Struct. 2001, 216, 61.
(16) Barrera, J .; Sabat, M.; Harman W. D. Organometallics 1993,
12, 4381.
(17) Leban, I.; Brencic, J . V.; Ceh B. Acta Crystallogr. Sect. C: Cryst.
Struct. Commun. 1995, 51, 817.

Low-Valent Tungsten Aryloxide Compounds
Organometallics, Vol. 22, No. 11, 2003 2263
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [W(OC6HP h 3-η5-C6H6)(OC6HP h 3-
η1-C6H4)(OC6HP h 4-2,3,5,6)][Cl], 5
W(1)-O(1)
2.144(3)
1.951(4)
2.253(5)
2.331(5)
2.221(5)
W(1)-O(2)
2.029(3)
2.202(5)
2.407(6)
2.231(6)
W(1)-O(3)
W(1)-C(121)
W(1)-C(123)
W(1)-C(125)
W(1)-C(122)
W(1)-C(124)
W(1)-C(222)
O(1)-W(1)-O(2)
O(1)-W(1)-O(3)
W(1)-O(2)-C(21)
O(2)-W(1)-C(222)
79.4(1) O(2)-W(1)-O(3)
78.6(1) W(1)-O(1)-C(11)
124.3(3) W(1)-O(3)-C(31)
112.9(2)
115.6(3)
145.8(3)
81.7(2) C(121)-C(122)-C(123) 118.9(5)
C(122)-C(123)-C(124) 117.9(5) C(123)-C(124)-C(125) 118.1(5)
C(124)-C(125)-C(126) 117.3(5) C(125)-C(126)-C(121)
C(126)-C(121)-C(122) 115.9(5)
97.7(4)
ylphenoxide by Mo(IV) has precedence in previous
work.18,19 Although metalation-resistant due to the
buttressing effect of the meta-phenyl rings, the tet-
raphenylphenoxide ligand is not immune to this type
of reaction.20 The intramolecular hydrogenation of ortho-
phenyl rings also has precedence (see final discussion
section).
The structural parameters for the π-bound rings in 4
and 5 are of interest. The η6-interaction in the pyridine
adduct 4 is very similar to that observed in related
phosphine adducts. There is a shortening of the W-C-
(ipso) and W-C(para) distances, with an elongation of
the W-C(ortho) trans to the terminal aryloxide in the
three-legged piano stool geometry. This has been as-
cribed to a tungsta-norbornadiene resonance contribu-
tion. A comparison of the W-C distances for 4 and the
PMe3 analogue is shown in Figure 4. There is a slight
shortening of the W-arene distances overall on replacing
the phosphine by pyridine. Also shown in Figure 4 are
the W-C distances to the η5-cyclohexadienyl ring in 5.
The W-CH2 distance is 2.861 Å. Three of the remaining
W-C distances are close to those found in 4, while two
of them are slightly longer. The overall geometry for 5
is best described as a four-legged piano stool with the
W-C σ-bond trans to the oxygen of the aryloxide
containing the η5-cyclohexadienyl ring. The W-C(phen-
yl) bond distance of 2.202(5) Å demonstrates how short
the W-C π-interactions are in both 4 and 5.
The demonstrated ability of early transition metal
hydrido aryloxides to carry out the catalytic hydrogena-
tion of arene rings has raised many mechanistic ques-
tions. We have focused particular attention on the
identification and study of potential intermediates
within the catalytic cycle. Especially important are the
structures and reactivity of compounds containing
partially hydrogenated arene rings. The literature
contains examples for all ηn-fragments, n ) 5,21,22 4,23
3, 24 2,25 1,26 bound to group 4-6 metals. Previous work
by our group has allowed the isolation of η4-cyclohexa-
F igu r e 2. Molecular structure of [W(OC6HPh3-η6-C6H5)-
(OC6HPh4-2,3,5,6)(py-But-4)], 4, in crystals of 4/5.
F igu r e 3. Molecular structure of [W(OC6HPh3-η5-C6H6)-
(OC6HPh3-η1-C6H4)(OC6HPh4-2,3,5,6)][Cl], 5, in crystals of
4/5.
Ta ble 3. 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)(p y-Bu t-4)], 4
W(2)-O(4)
2.010(4)
2.199(5)
2.320(6)
2.202(6)
2.239(6)
W(2)-O(5)
1.987(4)
2.161(6)
2.252(6)
2.248(6)
W(2)-N(61)
W(2)-C(422)
W(2)-C(424)
W(2)-C(426)
W(2)-C(421)
W(2)-C(423)
W(2)-C(425)
O(4)-W(2)-O(5)
O(5)-W(2)-N(61)
W(2)-O(5)-C(51)
114.5(2) O(4)-W(2)-N(61)
80.3(2) W(2)-O(4)-C(41)
81.3(2)
119.3(3)
(18) Kerschner, J . L.; Yu, J .; Fanwick. P. E.; Rothwell, I. P.;
Huffman, J . C. Organometallics 1989, 8, 1414.
135.6(3) C(421)-C(422)-C(423) 120.5(6)
(19) 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. J . Chem Soc., 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.
(20) Vilardo, J . S.; Lockwood, M. A.; Hanson, L. G.; Clark, J . R.;
Parkin, B. C.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton
Trans. 1997, 3353.
(21) Fryzuk, M. D.; Kozak, C. M.; Bowridge, M. R.; Patrick, B. O.
Organometallics 2002, 21, 5047.
C(422)-C(423)-C(424) 118.6(6) C(423)-C(424)-C(425) 119.1(6)
C(424)-C(425)-C(426) 123.1(6) C(425)-C(426)-C(421) 117.0(6)
C(426)-C(421)-C(422) 119.1(5)
scenario involves the presence of the tris(aryloxide)
[W(OAr)3Cl3] in the initial starting material. Reduction
to the W(IV) intermediate is followed by cyclometalation
of one of the aryloxide ligands and then transfer of the
generated hydride ligand to one of the ortho-phenyl
rings (Scheme 3). The cyclometalation of 2,6-diphen-

2264 Organometallics, Vol. 22, No. 11, 2003
Lentz et al.
Sch em e 3
diene,27 η2-cyclohexene,28 and η1-cyclohexyl,29 examples
supported by aryloxide ligation, formed either via in-
tramolecular hydrogenation of phenyl rings or by other
routes. The first key intermediate proposed in the
mechanistic pathway (Scheme 4) is an η5-cyclohexa-
dienyl formed by initial attack of a metal-hydride on
an arene ring.21 This has previously been missing in
aryloxide chemistry. Recently Fryzuk et al. have re-
ported cyclohexadienyl complexes of niobium amido-
phosphine ligands.21 Tilley and Gavenonis have also
demonstrated the formation of an η5-cyclohexadienyl
ring by hydride transfer from tantalum to an ortho-aryl
ring in an amido ligand. In this case reversible transfer
to the meta-position of a [Ta-NHAr*] ring (Ar* ) 2,6-
dimesitylphenyl) takes place.30 In compound 5 the
hydride ligand formed via the cyclometalation has been
transferred to the ortho-position of a phenyl ring. The
intramolecular hydrogenation of ortho-phenylphenoxide
rings to chelated cyclohexadiene, cyclohexene, and non-
bound cyclohexyl groups has been observed. The site of
(22) (a) DiMauro, P. T.; Wolczanski, P. T. Organometallics 1987, 6,
1947. (b) Stepnicka, P.; Cisarova, I.; Horacek, M.; Mach, K. Acta
Crystallogr., Sect. C: Cryst. Struct. Commun. 2000, 56, 1204. (c) Feng,
S.; Klosin, J .; Kruper, W. J .; McAdon, M. H.; Neithamer, D. R.; Nickias,
P. N.; Patton, J . T.; Wilson, D. R.; Abboud, K. A.; Stern, C. L.
Organometallics 1999, 18, 1159. (d) DiMauro, P. T.; Wolczanski, P.
T.; Parkanyi, L.; Petach H. H. Organometallics 1990, 9, 1097. (e)
Fretzen, A.; Ripa, A.; Liu, R.; Bernardinelli, G.; Kundig, E. P.Chem.-
Eur. J ., 1998, 4, 251. (f) Wilson, A. M.; West, F. G.; Rheingold, A. L.;
Ernst, R. D. Inorg. Chim. Acta 2000, 300, 65. (g) Wilke, G.; Benn, H.;
Goddard, R.; Kruger, C.; Pfeil, B. Inorg. Chim. Acta 1992, 198, 741.
(h) Heppert, J . A.; Aube, J .; Thomas-Miller, M. E.; Milligan, M. L.;
Takusagawa, F. Organometallics 1990, 9, 727. (i) Kundig, E. P.;
Cunningham J unior, A. F.; Paglia, P.; Simmons, G. Bernardinelli Helv.
Chim. Acta 1990, 73, 386. (j) Semmelhack, M. F.; Hall J unior, H. T.;
Farina, R.; Yoshifuji, M.; Clark, G.; Bargar, T.; Hirotsu, K.; Clardy J .
J . Am. Chem. Soc. 1979, 101, 3535. (k) Varga, V.; Polasek, M.; Hiller,
J .; Thewalt, U.; Sedmera, P.; Mach K. Organometallics 1996, 15, 1268.
(23) Prout, K.; Daran J .-C. Acta Crystallogr., Sect. B: Struct.
Crystallogr. Cryst. Chem. 1977, 33, 2303.
(24) (a) Faller, J . W.; Murray, H. H.; White, D. L.; Chao, K.-H.
Organometallics 1983, 2, 400. (b) Pearson, A. J .; Khan, M. N. I.; Clardy,
J . C.; Cun-heng, He J . Am. Chem. Soc. 1985, 107, 2748. (c) Kralik, M.
S.; Hutchinson, J . P.; Ernst, R. D. J . Am. Chem. Soc. 1985, 107, 8296.
(d) Kralik, M. S.; Rheingold, A. L.; Hutchinson, J . P.; Freeman, J . W.;
Ernst, R. D. Organometallics 1996, 15, 551. (e) de Azevedo, C. G.;
Calhorda, M. J .; de C. T. Carrondo, M. A. A. F.; Dias, A. R.; Duarte,
M. T.; Galvao, A. M.; Gamelas, C. A.; Goncalves, I. S.; da Piedade, F.
M.; Romao, C. C. J . Organomet. Chem. 1997, 544, 257. (f) Pearson, A.
J .; Blystone, H S.; Nar, L.; Pinkerton, A. A.; Roden, B. A.; Yoon, J . J .
Am. Chem. Soc. 1989, 111, 134. (g) Carfagna, C.; Green, M.; Mahon,
M. F.; McInnes, J . M.; Rumble, S. J .; Woolhouse, C. M. J . Chem. Soc.,
Dalton Trans. 1996, 3379. (h) Ward, Y. D.; Villanueva, L. A.; Allred,
G. D.; Liebeskind, L. S. Organometallics 1996, 15, 4201. (i) Chou, S.
P.; Sheng, H.-T Organometallics 1996, 15, 4113. (j) Wang, S.-H.; Cheng,
Y.-C.; Lee, G.-H.; Peng, S.-M.; Liu, R.-S. Organometallics 1993, 12,
3282.
(25) (a) Buchwald, S. L.; Lum, R. T.; Dewan, J . C. J . Am. Chem.
Soc. 1986, 108, 7441. (b) Tran, E.; Legzdins, P. J . Am. Chem. Soc. 1997,
119, 5071. (c) Adams, C. S.; Legzdins, P.; Tran, E. J . Am. Chem. Soc.
2001, 123, 612.
(26) (a) Stavropoulos, P.; Savage, P. D.; Tooze, R. P.; Wilkinson, G.;
Hussain, B.; Motevalli, M.; Hursthouse, M. B. J . Chem. Soc., Dalton
Trans. 1987, 557. (b) Schrock, R. R.; Seidel, S. W.; Mosch-Zanetti, N.
C.; Shih, K.-Y.; O’Donoghue, M. B.; Davis, W. M.; Reiff, W. M. J . Am.
Chem. Soc. 1997, 119, 11876.
F igu r e 4. “Radar” plot of the W-C(arene) distances in
compound [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(PMe3)]
and [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(py-But-4)], 4,
and the W-C(cyclohexadienyl) distances in [W(OC6HPh3-
η5-C6H6)(OC6HPh3-η1-C6H4)(OC6HPh4-2,3,5,6)][Cl], 5. The
coordination is exaggerated by using a plot scale of 2.0-
2.4 Å from the metal center.

Low-Valent Tungsten Aryloxide Compounds
Organometallics, Vol. 22, No. 11, 2003 2265
Sch em e 4
P r ep a r a tion of a ll-tr a n s-[W(OC6HP h 4-2,3,5,6)2Cl2(p y-
Bu t-4)2] (2). A purple suspension of [W(OC6HPh4-2,3,5,6)2Cl4]
(2.00 g, 1.78 mmol) in benzene (75 mL) was added to a Na/Hg
alloy (0.09 g, 3.91 mmol). To the suspension was added 2.2
equiv of 4-tert-butylpyridine (0.58 mL, 3.93 mmol). The reac-
tion was allowed to stir for 20 h, after which the solution
appeared red. The solution was filtered and dried in vacuo,
affording a red solid. The crude material was recrystallized
from hot toluene, yielding the pure product as small red
needles (1.40 g, 59.4%). Anal. Calc for C78H68Cl2N2O2W: C,
70.97; H, 5.19; Cl, 5.37; N, 2.12. Found: C, 70.99; H, 5.14; Cl,
initial attack has been discussed in terms of the ster-
eochemical outcome,27 particularly as it relates to
deuterium incorporation.
Exp er im en ta l Section
All operations were carried out under
a dry nitrogen
atmosphere in a Vacuum Atmospheres Dri-Lab or by standard
Schlenk techniques. The hydrocarbon solvents were distilled
from sodium benzophenone and stored under nitrogen until
use. All organic reagents were bought from Aldrich Chemical
Co., Milwaukee, WI, and used as received. The compounds
[W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(PMe3)], W(OC6HPh3-
η6-C6H5)(OC6HPh4-2,3,5,6)(PEt3)], and [W(OC6HPh4-2,3,5,6)2-
1
5.49; N, 2.03. H NMR ( 300 MHz, d8-toluene, 25 °C): δ 13.96
(d, 4H, meta-H on 4-tert-butylpyridine), 9.26 (d, 8H, aromatics),
8.07 (d, 8H, aromatics), 7.24 (t, 8H, aromatics), 6.38 (t, 8H,
aromatics), 5.75 (t, 8H, aromatics), 4.93 (s, 2H, aromatics), 0.09
(s, 18H, -CH3 of 4-tert-butylpyridine), -34.92 (d, 4H, ortho-H
on 4-tert-butylpyridine).
1
Cl4] were obtained by previously reported procedures.5 All H
NMR and DQF-COSY spectra were recorded on either a
Varian Inova 300 or Varian Unity 600 spectrometer and
referenced to protio impurities of commercial d6-benzene or
d8-toluene. Dynamic NMR experiments were all preformed on
a Varian Unity Inova 300 using a 5 mm, 4 nucleus probe. X-ray
diffraction studies were preformed in-house at Purdue Uni-
versity.
P r ep a r a t ion of [W(OC6H P h 4-2,3,5,6)2(b ip y)2] (3). A
sample of [W(OC6HPh3-η6-C6H5)(OC6HPh4-2,3,5,6)(PEt3)] (80
mg, 0.073 mmol) was dissolved in 5 mL of benzene, and to
this solution was added 2 equiv of 2,2′-bipyridine (25 mg, 0.160
mmol). After a few minutes of stirring, the solution went from
emerald green to dark purple. The solution was layered with
pentanes to induce crystal formation. The sample was analyzed
by NMR spectrometry and X-ray diffraction study. Anal. Calc
P r ep a r a tion of a ll-tr a n s-[W(OC6HP h 4-2,3,5,6)2Cl2(p y)2]
(1). A purple suspension of [W(OC6HPh4-2,3,5,6)2Cl4] (2.00 g,
1.78 mmol) in benzene (75 mL) was added to a Na/Hg alloy
(0.09 g, 3.91 mmol). To the suspension was added 2.2 equiv of
pyridine (0.32 mL, 3.93 mmol). The reaction was allowed to
stir for 14 h, after which the solution appeared red. The
solution was filtered and dried in vacuo, affording a red solid.
The crude material was recrystallized in hot toluene, yielding
the pure product as small red needles (1.53 g, 71.6%). Anal.
Calc for C70H52Cl2N2O2W: C, 69.60; H, 4.34; Cl, 5.87; N, 2.32.
Found: C, 69.69; H, 4.47; Cl, 5.48; N, 2.19. 1H NMR (300 MHz,
d8-toluene, 25 °C): δ 12.15 (t, 4H, meta-H on pyridine), 8.67
(d, 8H, aromatics), 7.92 (d, 8H, aromatics), 6.92 (m, 12H,
aromatics), 6.41 (t, 8H, aromatics), 5.86 (t, 4H, aromatics), 5.00
(s, 2H, aromatics), -23.71 (t, 2H, para-H on pyridine), -26.14
(d, 4H, ortho-H on pyridine).
for
C80H58N4O2W: C, 74.42; H, 4.53; N, 4.34. Calc for
C
86H64N4O2W (benzene solvate): C, 75.43; H, 4.71; N, 4.09.
1
Found: C, 74.88; H, 4.87; N, 4.08. H NMR (600 MHz, C6D6,
25 °C): δ 8.70 (d, aromatics), 8.49 (d, aromatics), 7.37 (d,
aromatics of bpy), 7.28 (s, aromatics), 7.19 (t, aromatics + bpy
aromatics), 6.96 (m, aromatics), 6.89 (m, aromatics + bpy
aromatic), 6.68 (s, aromatics), 6.64 (dd, aromatics), 5.08 (d,
aromatics of bpy), 4.96 (t, aromatics of bpy), 4.93 (t, aromatics
of bpy), 4.88 (t, aromatics of bpy), 4.65 (t, aromatics of bpy).
P r epa r a tion of [W(OC6HP h 3-η6-C6H5)(OC6HP h 4-2,3,5,6)-
(p y-Bu t-4)] (4) a n d [W(OC6HP h 3-η5-C6H6)(OC6HP h 3-η1-
C6H4)(OC6HP h 4-2,3,5,6)][Cl] (5). A purple suspension of
[W(OC6HPh4-2,3,5,6)2Cl4] (2.00 g, 1.78 mmol) in benzene (75
mL) was added to a Na/Hg alloy (0.20 g, 8.0 mmol). To the
suspension was added 2.2 equiv of 4-tert-butylpyridine (0.58
mL, 3.93 mmol). The reaction was allowed to stir for 24 h, after
which the solution appeared almost black. The solution was
filtered, evaporated to dryness, and taken up in toluene.
Addition of a small amount of pentane intially yielded red
crystals of 2. Further addition of pentane gave a few dark
green crystals identified as containing a mixture of 4 and 5 in
a 1:1 ratio.
(27) (a) Steffey, B. D.; Chesnut, R. W.; Kerschner, J . L.; Pellechia,
P.; Fanwick, P. E.; Rothwell, I. P. J . Am. Chem. Soc. 1989, 111, 378.
(b) Steffey, B. D.; Rothwell, I. P. J . Chem Soc., Chem. Commun. 1990,
213. (c) Lockwood, M. A.; Potyen, M. C.; Steffey, B. D.; Fanwick, P. E.;
Rothwell, I. P. Polyhedron 1995, 14, 3293. (d) Visciglio, V. M.; Clark,
J . R.; Nguyen, M. T.; Mulford, D. R.; Fanwick, P. E.; Rothwell, I. P. J .
Am. Chem. Soc. 1997, 119, 3490.
(28) Lockwood, M. A.; Fanwick, P. E.; Rothwell, I. P. Polyhedron
1995, 14, 3363.
(29) Schweiger, S. W.; Salberg, M. M.; Pulvirenti, A. L.; Freeman,
E. E.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc., Dalton Trans. 2001,
2020.
X-r a y Da ta Collection a n d Red u ction . Crystal data and
data collection parameters are contained in Table 5. A suitable
crystal was mounted on a glass fiber in a random orientation
(30) Gavenonis, J .; Tilley, T. D. J . Am. Chem. Soc. 2002, 124, 8536.

2266 Organometallics, Vol. 22, No. 11, 2003
Lentz et al.
in DIRDIF92.33 The remaining atoms were located in succeed-
ing difference Fourier syntheses. Hydrogen atoms were in-
cluded 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
Ta ble 5. Cr ysta l Da ta a n d Da ta Collection
P a r a m eter s
3‚C6H6
4/5
formula
fw
space group
a, Å
C
86H64N4O2W
C159H118ClNO5W2
2525.87
1369.34
P (No. 2)
12.9675(2)
14.2048(2)
18.0995(3)
76.783(1)
82.922(1)
86.671(1)
3219.4(1)
2
2
2
2
∑w(|Fo| - |Fc| )2 and the weight w is defined as w ) 1/[σ2(Fo
)
P (No. 2)
11.7261(1)
19.1182(2)
29.6646(3)
87.8455(5)
79.6683(5)
72.8854(5)
6251.9(2)
2
+ (0.0585P)2 + 1.4064P] where P ) (Fo + 2Fc2)/3. Scattering
factors were taken from the International Tables for Crystal-
lography.34 Refinement was performed on a AlphaServer 2100
using SHELX-97.35 Crystallographic drawings were done using
the programs ORTEP.36
2
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE-0078405) for financial support
of this research.
Z
F
calc, g cm-3
1.413
1. 342
temperature, K
150
150
radiation (wavelength) Mo KR (0.71073 Å) Mo KR (0.71073 Å)
Su p p or tin g In for m a tion Ava ila ble: This material is
available free of charge via the Internet at http://pubs.acs.org.
R
0.032
0.077
0.052
0.138
Rw
OM030054S
under a cold stream of dry nitrogen. Preliminary examination
and final data collection were performed with Mo KR radiation
(λ ) 0.71073 Å) on a Nonius Kappa CCD. Lorentz and
polarization corrections were applied to the data.31 An empiri-
cal absorption correction using SCALEPACK was applied.32
Intensities of equivalent reflections were averaged. The struc-
ture was solved using the structure solution program PATTY
(33) 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: The Netherlands, 1992.
(34) International Tables for Crystallography, Kluwer Academic
Publishers: Dordrecht, The Netherlands, 1992; Vol. C, Tables 4.2.6.8
and 6.1.1.4.
(35) Sheldrick, G. M. SHELXS97. A Program for Crystal Structure
Refinement; University of Gottingen: Germany, 1997.
(36) J ohnson, C. K. ORTEPII, Report ORNL-5138; Oak Ridge
National Laboratory: Oakridge, TN, 1976.
(31) McArdle, P. C. J . Appl. Crystallogr. 1996, 239, 306.
(32) Otwinowski, Z.; Minor, W. Methods Enzymol. 1996, 276.