C-O bond homolysis in a tungsten alkoxide: The mechanism of alcohol deoxygenation by WCl2(PMe3)4 and WH2Cl2(PMe3)4

Article abstract of DOI:10.1021/ja970929s

Reactions of alcohols with WCl₂(PMe₃)₄ (1) or WH₂Cl₂(PMe₃)₄ (2) yield W(O)Cl₂(PMe₃)₃ (3), PMe₃, and hydrocarbons. Cyclopropanemethanol is deoxygenated to give 1-butene and a trace of trans-2-butene as the organic products; benzyl alcohol yields toluene and bibenzyl. These products indicate the intermediacy of organic radicals. Benzyl radicals in the reaction of 1 with PhCH₂OH can be trapped by added 2 or by 9,10-dihydroanthracene (DHA), leading to increased yields of toluene vs bibenzyl. With WD₂Cl₂(PMe₃)₄ (2-d₂) or DHA-d₁₂, PhCH₂D is formed. The reaction of methanol with 1 proceeds similarly in the presence of DHA, forming 3 and methane. Kinetic studies on the reaction of 1 with benzyl alcohol indicate that the reaction proceeds via alkoxide intermediates. A mechanism involving homolysis of the C-O bond in an alkoxide intermediate is suggested by these results. The thermodynamics of this unusual transformation are discussed.

Full text of DOI:10.1021/ja970929s

J. Am. Chem. Soc. 1997, 119, 8485-8491
8485
C-O Bond Homolysis in a Tungsten Alkoxide: The
Mechanism of Alcohol Deoxygenation by WCl2(PMe3)4 and
WH2Cl2(PMe3)4
Thomas J. Crevier1 and James M. Mayer*
Contribution from the Department of Chemistry, Box 351700, UniVersity of Washington,
Seattle, Washington 98195-1700
ReceiVed March 24, 1997X
Abstract: Reactions of alcohols with WCl2(PMe3)4 (1) or WH2Cl2(PMe3)4 (2) yield W(O)Cl2(PMe3)3 (3), PMe3,
and hydrocarbons. Cyclopropanemethanol is deoxygenated to give 1-butene and a trace of trans-2-butene as the
organic products; benzyl alcohol yields toluene and bibenzyl. These products indicate the intermediacy of organic
radicals. Benzyl radicals in the reaction of 1 with PhCH2OH can be trapped by added 2 or by 9,10-dihydroanthracene
(DHA), leading to increased yields of toluene vs bibenzyl. With WD2Cl2(PMe3)4 (2-d2) or DHA-d12, PhCH2D is
formed. The reaction of methanol with 1 proceeds similarly in the presence of DHA, forming 3 and methane.
Kinetic studies on the reaction of 1 with benzyl alcohol indicate that the reaction proceeds via alkoxide intermediates.
A mechanism involving homolysis of the C-O bond in an alkoxide intermediate is suggested by these results. The
thermodynamics of this unusual transformation are discussed.
Introduction
mediate which eliminates an alkyl radical to form a tungsten-
oxo species. This conclusion is opposite to that in our
preliminary report,6 in which we overlooked the evidence for
radical intermediates. The C-O bond homolysis is surprising
given the stability of most metal alkoxide complexes10 and the
strength of this bond in alcohols, 81 kcal/mol in benzyl alcohol
and 94 kcal/mol in methanol.11 To our knowledge, there are
only two other well-characterized examples of C-O bond
homolysis in alkoxide complexes: thermolysis of homoleptic
titanium(IV) alkoxides at 550-700 °C gives titanium oxides
by a number of pathways including homolysis3a and a molyb-
denum/titanium µ-nitrido tert-butoxide has recently been re-
ported to lose tBu• under mild conditions.12 Homolytic cleavage
of C-O bonds is a likely mechanism in other systems, such as
in the titanium-mediated reductive coupling of alcohols to
hydrocarbons which proceeds through LnTi-OR intermediates.13
The microscopic reverse, trapping of an alkyl or aryl radical
by a metal-oxo complex to form an alkoxide, is a common
mechanism of C-O bond formation. For instance, permanga-
nate traps alkyl radicals at near the diffusion limit,14 and the
cytochrome P-450 rebound mechanism is a closely related
process.15 The ability of the tungsten alkoxide to homolyze its
The activation of C-O bonds by transition metal complexes
has received increasing attention in recent years due to the
importance of such steps in catalytic and stoichiometric
transformations.2 Cleavage of C-O bonds is important in the
conversion of alkoxide precursors to metal oxide ceramics.3
Additionally, C-O bond cleavage reactions may provide insight
into the reverse reaction, C-O bond formation, which is of
importance in hydrocarbon oxidation. The tungsten complexes
WCl2L4 (L ) PMe3 (1), PMePh2 (4)) activate C-O bonds in a
wide variety of organic substrates, including ketones, epoxides,
isocyanates, sulfoxides, CO2, and alcohols.4 WCl2L4 complexes
are unusual in their ability to deoxygenate non-allylic alcohols
(eq 1), as first reported by Wilkinson5 and subsequently explored
in our labs.4,6,7
The deoxygenation of alcohols is a more complicated process
than the oxygen atom transfer pathway often utilized by 1 and
related reductants.4b,8,9 The mechanistic data reported here
indicate that reaction 1 occurs via a tungsten alkoxide inter-
t
(8) W2(OCH2 Bu)6(py)2 deoxygenates alcohols by a nonradical process:
Yang, Y.; Chisholm, M. H. Polyhedron 1992, 11, 2813-2815.
(9) Holm, R. H. Chem. ReV. 1987, 87, 1401-1449. (b) Holm, R. H.;
Donahue, J. P. Polyhedron 1993, 12, 571-589.
X Abstract published in AdVance ACS Abstracts, August 15, 1997.
(1) University of Washington Saeggebarth Fellow, 1993-1994; Univer-
sity of Washington David M. Ritter Fellow, 1995-1996.
(2) Yamamoto, A. AdV. Organomet. Chem. 1992, 34, 111-147.
(3) (a) Nandi, M.; Rhubright, D.; Sen, A. Inorg. Chem. 1990, 29, 3066-
3068. (b) Baxter, D. V.; Chisholm, M. H.; DiStasi, V. F.; Haubrich, S. T.
Chem. Mater. 1995, 7, 84-92.
(4) (a) Hall, K. A.; Mayer, J. M. J. Am. Chem. Soc. 1992, 114, 10402-
10411. (b) Mayer, J. M. AdV. Trans. Met. Coord. Chem. 1996, 1, 105-
157.
(10) (a) Chisholm, M. H.; Rothwell, I. P. In ComprehensiVe Coordination
Chemistry; Wilkinson, G., Ed.; Pergamon: New York, 1987; Vol. 2, pp
335-365. (b) Mayer, J. M. Polyhedron 1995, 14, 3273-3292.
(11) Bond strengths calculated from gas phase heats of formation, for
•
instance D(PhCH2-OH) ) -∆Hf°(PhCH2OH) + ∆Hf°(PhCH2 ) + ∆Hf°-
(OH•). Data from: (a) Berkowitz, J.; Ellison, G. B.; Gutman, D. J. Phys.
Chem. 1994, 98, 2744-65 and references therein. (b) Thermodynamic
Tables: Hydrocarbons and Thermodynamic Tables: Non-Hydrocarbons;
Thermodynamic Research Center, Texas A&M University, College Station,
Texas. (c) Bordwell, F. G.; Liu, W.-Z. J. Am. Chem. Soc. 1996, 118, 10819-
10823.
(5) Chiu, K. W.; Lyons, D.; Wilkinson, G.; Thorton-Pett, M.; Hursthouse,
M. B. Polyhedron 1983, 2, 803-810.
(12) Peters, J. C.; Johnson, A. R.; Odom, A. L.; Wanandi, P. W.; Davis,
W. M.; Cummins, C. C. J. Am. Chem. Soc. 1996, 118, 10175-10188.
(13) van Tamelen, E. E.; Schwartz, M. A. J. Am. Chem. Soc. 1965, 87,
3277-3278.
(6) Jang, S.; Atagi, L. M.; Mayer, J. M. J. Am. Chem. Soc. 1990, 112,
6413-6414.
(7) For L ) PMePh2, the bisalkoxide complex, W(OR)2Cl2(PMePh2)2,
is also formed.
(14) Steenken, S.; Neta, P. J. Am. Chem. Soc. 1982, 104, 1244-1248.
S0002-7863(97)00929-3 CCC: $14.00 © 1997 American Chemical Society

8486 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
CreVier and Mayer
1
C-O bond can be understood through a thermodynamic analysis
of the homolysis step, on the basis of bond strengths in the
reactants and products.
W(O)Cl2(PMe3)3 and H2, as identified by H NMR (eq 4).
Results
Reaction of WCl2(PMe3)4 (1) with Alcohols. WCl2(PMe3)4
reacts with 2 equiv of cyclopropanemethanol in benzene at 80
°C over 20 h to give a mixture of W(O)Cl2(PMe3)3 (3), PMe3,
1-butene, and a trace amount of trans-2-butene (eq 2). The
Significant amounts of 2 are produced during the reaction and
are only slowly consumed. Also seen as the reaction progresses
is a small amount of W2(µ-O)(µ-Cl)(PMe3)5Cl3, known to form
slowly under these conditions from 1 and 3.17 This reaction is
not very clean, as several small, unidentified peaks appear in
1
the H NMR over the course of the reaction. However, there
is no evidence under these conditions for the methoxide
intermediate reported by Wilkinson.5 Following the reaction
of excess CD3OD with 1 by 2H NMR shows only the
disappearance of the starting material; there is no observable
product containing the methyl group.
The methyl product is seen as methane when the reaction of
WCl2(PMe3)4 and 7 equiv of methanol is run in the presence of
10 equiv of 9,10-dihydroanthracene (DHA). The reaction also
produces W(O)Cl2(PMe3)3, PMe3, and H2, just as in the absence
of DHA. The methane was identified by comparison of its 1H
NMR with that of an authentic sample and by gas phase IR
analysis. Methane (0.2 equiv) is observed in solution by NMR
but this is a minimum yield as some is present in the gas phase.
No reaction is observed between DHA and 1 or 2 over days at
80 °C in benzene solution in the absence of alcohol. These
data are consistent with DHA acting as a trap for methyl
radicals.18
butenes were identified by GC and 1H NMR and compared with
authentic samples. No methyl cyclopropane was detectable by
these techniques. A small amount of WH2Cl2(PMe3)4 (2)16 is
formed but it is consumed by the end of the reaction.
Benzene solutions of 1 react with excess benzyl alcohol at
80 °C over 40 h to give 3, toluene, bibenzyl, PMe3, and
dihydrogen (eq 3). Again 2 is produced and consumed by the
end of the reaction. The reaction is quite clean, with >97%
The addition of 6 equiv of DHA to the reaction of 1 plus 7
equiv of benzyl alcohol (benzene, 80 °C, 2 days) produces
predominantly toluene with only a trace of bibenzyl, in addition
to 3 and PMe3. This contrasts with the 0.8:1 ratio observed in
the absence of DHA. Increasing the amount of DHA from 6
to 10 equiv results in no bibenzyl being observed by 1H NMR.
A similar reaction in the presence of 10 equiv of perdeutero-
9,10-dihydroanthracene (DHA-d12) produces 3, PMe3, trace
mass balance observed when the reaction is carried out in a
sealed NMR tube and referenced to Me4Si. The final molar
ratio of toluene to bibenzyl is 0.8:1 when a 2.0 × 10-2
M
1
bibenzyl, and both PhCH3 and PhCH2D (∼1:2 by H NMR).
solution of 1 is reacted with 6 equiv of PhCH2OH. The addition
of 20 equiv of PMe3 stops reaction 3, with no appreciable change
observed by NMR after 1 week at 80 °C. When PhCH2OD is
the substrate, the reaction is slower. Both PhCH2D and PhCH3
are produced, in a roughly 3:1 ratio (1H NMR) which remains
roughly constant throughout the reaction. No deuterium
incorporation into the bibenzyl is observed by 2H NMR. WD2-
Cl2(PMe3)4 (2-d2) is observed as an intermediate, while WH2-
These data again suggest that DHA is a radical trap, in this
case for benzyl radicals. Complex 2 is not observed in reactions
containing DHA (1H NMR), and surprisingly, no anthracene is
visible by 1H NMR or by GC. When PhCH2OD is used,
deuterium incorporation into the 9,10 positions of DHA is seen
2
by H NMR.
The kinetics of the reaction of 1 with benzyl alcohol at 70.0
1
1
Cl2(PMe3)4 and WHDCl2(PMe3)4 are not detected by H{31P}
°C in sealed NMR tubes were monitored by H NMR using
Me4Si as an internal standard. The 1H NMR spectrum of
paramagnetic 1 is a broad singlet, the chemical shift of which
is quite temperature dependent. To obtain base line resolution
from the PhCH2OH resonance (δ 4.25 in C6D6), we acquired
spectra at 55 °C, when the peak due to 1 is shifted to 3.3 ppm
(from δ 4.1 at ambient temperatures). As noted above, this
reaction is inhibited by added PMe3 which is a product of the
reaction. To achieve pseudo-first-order conditions of phosphine
initially and yet still have the reaction proceed at a reasonable
rate, we added roughly 1 equiv of PMe3. Plots of ln[1] vs time
were reasonably linear for approximately half of a half-life, after
NMR at any point during the reaction. Thus, the hydride ligands
in 2 derive from the hydroxyl proton of the benzyl alcohol.
The formation of both PhCH2D and PhCH3 from PhCH2OD
indicates that the hydroxyl is not the sole source of the hydrogen
added to the benzyl group. Reaction of WCl2[P(CD3)3]4 (1-
d36) with PhCH2OD gives PhCH2D and PhCH3 in the same ratio
as observed from protio-1 plus PhCH2OD, indicating that the
phosphine ligands are not involved. When a mixture of 1 and
2-d2 is reacted with PhCH2OH, PhCH2D is the major initial
product; protiotoluene and bibenzyl are produced as the reaction
proceeds. Thus, the PhCH2D can come from the hydride ligands
in 2.
(17) Hall, K. A.; Mayer, J. M. Inorg. Chem. 1994, 33, 3289-3298.
•
WCl2(PMe3)4 reacts with several equivalents of methanol in
benzene solution over a period of 2 weeks at 80 °C to produce
(18) We have not found a rate constant for CH3 + DHA, but DHA
should react faster than Ph3CH (which has a weaker C-H bond). The rate
constant for CH3• + Ph3CH can be estimated as 104 M-1 s-1 based on data
in: (a) Asmus, K.-D.; Bonifacˇic´, M. Carbon-Centered Radicals II. In Radical
Reaction Rates in Liquids; Landolt-Bo¨rnstein New Series; Fischer, H., Ed.;
Springer-Verlag: Berlin, 1984; Vol. 13. b.
(15) Watanabe, Y.; Groves, J. T. In The Enzymes, 3rd ed.; Academic
Press: New York, 1992; Vol. XX, pp 405-452.
(16) Sharp, P. R.; Frank, K. G. Inorg. Chem. 1985, 24, 1808-1813.

C-O Bond Homolysis in a Tungsten Alkoxide
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8487
which point the plots became concave upward (as expected from
to give a bis-p-cresolate complex and H2 (eq 7). Again, reaction
with 2 gives the same product as found for 1,20 though slower.
the buildup of PMe3). Pseudo-first-order rate constants, kobsd
,
were obtained from the slopes of the first-order plots over the
first half of a half-life. At the same PMe3 concentration, kobsd
is independent of the initial tungsten concentration (for [1]i )
17.7 and 35.4 mM, kobsd ) 1.5((0.2) × 10-5 and 1.2((0.2)×
10-5 s-1 at 70.0 °C) and is directly related to the benzyl alcohol
concentration (for [PhCH2OH] ) 0.62 and 1.24 M, kobsd ) 1.5
× 10-5 and 2.7 × 10-5 s-1). These data and the inhibition by
phosphine are consistent with the rate law of eq 5. The reaction
of PhCH2OD under the same conditions shows an isotope effect
kROH/kROD ) 3.3 ( 0.5.
d[WCl2(PMe3)4]
[WCl2(PMe3)4][PhCH2OH]
[PMe3]
) -k1
(5)
dt
Reaction of WH2Cl2(PMe3)4 (2) with Alcohols. A benzene
solution of 2 and benzyl alcohol converts over 60 h at 80 °C to
W(O)Cl2(PMe3)3 (3), PMe3, toluene, bibenzyl, and H2ssimilar
to the reaction of 1 except slower. In the initial stages, toluene
is the sole product, but toward the end of the reaction both
toluene and bibenzyl are being formed. The final ratio of
toluene to bibenzyl is 1:1 when a 1.8 × 10-2 M solution of
WH2Cl2(PMe3)4 is reacted with 6 equiv of PhCH2OH. The
addition of 20 equiv of PMe3 to the reaction results in only
minor quantities of the products being observable after 1 week
of heating at 80 °C. Running the reaction under 0.60 atm of
H2 has no observable effect on the rate of the reaction.
Qualitatively, the reaction proceeds faster at higher initial alcohol
concentrations.
Reactions of WCl2(PMePh2)4 (4) with Alcohols. As previ-
ously reported,6 reactions of 4 with alcohols ROH give a mixture
of RH + W(O)Cl2(PMePh2)3 and H2 + bis-alkoxides W(OR)2-
Cl2(PMePh2)2. More careful examination of the reaction with
benzyl alcohol at room temperature for 15 h reveals bibenzyl
in addition to the above products (eq 8). No dihydride products
Reaction of 2 with PhCH2OD gives both PhCH3 and PhCH2D.
Early in the reaction, the toluene produced is primarily protio,
with toluene-d1 becoming a more significant product as the
reaction nears completion. 1H{31P} NMR shows the formation
of WHDCl2(PMe3)4 (2-d2) as the reaction proceeds. Species
2-d1 exhibits an intrinsic upfield isotopic shift of 42 ppb in the
hydride resonance vs 2, higher than the 20 ppb shift reported
for WH2Cl2(PMe2Ph)4.19 No deuterium incorporation into the
bibenzyl is observed.
are observed; WH2Cl2(PMePh2)4 is not known and does not
appear to be a stable compound.21 When the reaction is run in
the presence of 10 equiv of DHA, toluene is the only detectable
organic product.
Reactions with Thiols. Benzene solutions of 1 react with
excess benzyl thiol in 3 h at 80 °C to form W2(µ-S)(µ-
Cl)(PMe3)5Cl3, PMe3, toluene, bibenzyl, and H2 (eq 9). The
The reaction of WD2Cl2(PMe3)4 (2-d2) with PhCH2OH
behaves identically to the reaction of protio-2 with benzyl
alcohol, except that both PhCH3 and PhCH2D are produced.
The final molar ratio of toluene to bibenzyl is 1.2:1 when a
3.0 × 10-2 M solution of WD2Cl2(PMe3)4 is reacted with
6 equiv of PhCH2OH at 80 °C. The toluene produced early
in the reaction is primarily PhCH2D, with protiotoluene be-
coming a more significant product toward the end of the
reaction. Deuterium incorporation into the OH group of the
benzyl alcohol is seen over the course of the reaction by
2H NMR, indicating exchange of hydride and hydroxide
protons.
(9)
tungsten µ-sulfido dimer has been previously reported as the
product of conproportionation of 1 and W(S)Cl2(PMe3)3.17 This
reaction is not as clean as the reactions with alcohols, as yields
of dimer are 80-90% and many small peaks are observed in
The reaction of cyclopropanemethanol with 2 is very similar
to its reaction with 1, forming 1-butene and a trace amount of
trans-2-butene as the only observed organic products. The
reaction with 2 is slower, taking 2 days at 80 °C for completion
vs 20 h for 1. H2 is also observed as a product of the reaction.
The reaction of 2 with methanol in benzene solution is again
about a factor of 2 slower than that of 1, requiring 3-4 weeks
of heating at 80 °C to go to completion (eq 6). In addition to
3, PMe3, and H2, a small amount of methane is observed by 1H
NMR. p-Cresol reacts with 2 over a period of weeks at 80 °C
1
the H NMR. In the presence of 10 equiv of DHA, toluene is
the only identifiable organic product and W2(µ-S)(µ-Cl)(PMe3)5-
Cl3 is still the observed tungsten product. Excess methane thiol
reacts with 1 in C6D6 over 5 h at 80 °C to form W(S)Cl2(PMe3)3,
methane, and PMe3 (eq 10). The methane is clearly observed
(20) Atagi, L. M.; Mayer, J. M. Angew. Chem., Int. Ed. Eng. 1993, 32,
439-441.
(21) WH2Cl2(PMe3)4 (2) and WH2Cl2(PMePh2)4 are formed by H2
oxidative addition,16,19 but 4 + H2 does not give WH2Cl2(PMePh2)4.
(19) Rothfuss, H.; Huffman, J.; Caulton, K. Inorg. Chem. 1994, 33,
2946-2953.

8488 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
CreVier and Mayer
in the 1H NMR, and added DHA does not have a sizable effect
on the methane yield.
dihydrogen oxidative addition has been proposed by Caulton
and co-workers to explain isotopic exchange between D2 and
the closely related WH2Cl2(PMe2Ph)4.19 Nine-coordinate hy-
dride complexes of the form WH6(PR3)3 are known25 but the
chloride derivatives are unstable to reductive elimination.
Therefore, it is likely that W(OR)H3Cl2(PMe3)3 reductively
eliminates H2 to give the tungsten(IV) complex W(OR)HCl2-
(PMe3)3 (as in eq 11). The pathways for deoxygenation of
alcohols by 1 and 2 therefore appear to converge, not by initial
conversion of 2 to 1 but by H2 loss after oxidative addition of
ROH (Scheme 1). We cannot, however, rule out that H2 loss
occurs even later in the pathway from 2, perhaps after C-O
cleavage (Scheme 1).
C-O Bond Homolysis and Radical Trapping. The cleav-
age of C-O bonds in alcohols and alkoxides is unusual because
of the strength of these bonds: D(PhCH2-OH) ) 81 kcal/mol
and D(CH3-OH) ) 94 kcal/mol.11 These values are pertinent
because all of the data point toward a homolytic cleavage of
the C-O bond (eq 13). C-O bond cleavage likely occurs in
an alkoxide complex, from the kinetic evidence above and the
thermodynamic arguments below.
Discussion
Formation of an Alkoxide Intermediate. The rate of
deoxygenation of benzyl alcohol by WCl2(PMe3)4 (1) is first
order in both 1 and alcohol and inhibited by added PMe3 (eq
5). This implies pre-equilibrium loss of a phosphine ligand, as
is typical of the reactions of WX2P4 compounds.4,22 The kOH
OD isotope effect of 3.3 shows that PhCH2O-H bond cleavage
/
k
occurs in the rate-limiting step. Pre-equilibrium oxidative
addition of the O-H bond is calculated to have an isotope effect
of only 2.4, on the basis of stretching frequencies νOH ) 3600
cm-1 and νWH ) 2000 cm-1. These data indicate a pathway
of oxidative addition of the O-H bond to an unsaturated
tungsten species (eq 11). The O-H oxidative addition to
tungsten(II) also occurs in the formation of WH3(OR)(PMe3)4
from WH2(PMe3)5 and MeOH or PhCH2OH23,24 and likely
occurs in the reaction of 1 with phenols to form W(OAr)2Cl2-
(PMe3)2 and H2.20
LnW-O-R f LnWtO + R•
(13)
Both 1 and 2 react with cyclopropanemethanol to give
primarily 1-butene, indicative of an intermediate cyclopropyl-
carbinyl radical. This ring opens (k ) 6 × 108 s-1 at 75 °C26)
to the 3-butenyl radical which is then trapped by addition of a
hydrogen atom. The products are not consistent with the
formation of cyclopropylcarbinyl cation, since no cyclobutane
derivatives are seen.27 The formation of bibenzyl from benzyl
alcohol and either 1 or 2 indicates the presence of free benzyl
radicals. The effects of added 9,10-dihydroanthracene (DHA)
also imply radical intermediates, as DHA readily traps radicals
by hydrogen atom transfer.28 DHA increases toluene yields over
bibenzyl and converts methyl radicals to methane. With
perdeutero-DHA (DHA-d12), the major products are PhCH2D
and CH3D. Larger amounts of bibenzyl are observed when the
DHA is deuterated, indicating a significant primary kinetic
WCl2(PMe3)4 a PMe3 + [WCl2(PMe3)3] ROH8
[W(OR)HCl2(PMe3)3] ff (11)
WH2Cl2(PMe3)4 (2) is observed to grow in and then be
consumed in all of the reactions of 1 with alcohols. It is likely
formed by ligand redistribution reactions of intermediate
tungsten hydride complexes. It is also likely that 2 forms by
the known addition of H2 to 1,16 as H2 is an observed product.
Oxidative addition of H2 to the iodide derivative WI2(PMe3)4
has been shown to occur by initial phosphine loss analogous to
eq 11.22
•
isotope on hydrogen atom transfer from DHA to PhCH2 . The
presence of DHA in the reaction does not have a noticeable
effect on the overall rate of alcohol deoxygenation, indicating
that it becomes involved after the rate-limiting step. In sum,
the deoxygenation reaction can generate not only stabilized
Complex 2 also deoxygenates benzyl alcohol, as shown by
independent reactions. These do not proceed by initial formation
of 1, since 2 is thermally stable to reductive elimination of H2.16
In addition, pre-equilibrium loss of H2 is ruled out by the lack
of inhibition of alcohol deoxygenation by 0.6 atm of H2. These
data and the inhibition by added PMe3 indicate that 2 reacts by
pre-equilibrium loss of phosphine followed by reaction with
PhCH2OH, presumably to form a nine-coordinate, 18-electron
tungsten(VI) alkoxy-hydride species, WH3Cl2(OR)(PMe3)3 (eq
12). The PhCH2OH oxidative addition appears to be reversible
•
radicals such as PhCH2 but also the highly reactive primary
•
•
radicals CH3 and c-C3H5CH2 .
ROH compounds are deoxygenated to RH even in the absence
of DHA, indicating that these reactions contain other radical
traps that can reduce R• to RH. Radical trapping is relatively
slow in this system, as no methylcyclopropane is formed and
the benzyl radical concentration is high enough to observe
bibenzyl. The reaction of 1 with PhCH2OD results in a 3:1
ratio of PhCH2D to PhCH3, indicating that the major source of
the hydrogen atoms is the hydroxyl proton. Since hydroxyl
groups do not trap alkyl radicals, this trapping is done by species
derived from ROH, apparently tungsten hydride species formed
by RO-H oxidative addition (see above). WH2Cl2L4 (2) is
observed during the reaction and clearly functions as a hydrogen
atom donor. For instance, at early times the reaction of 2 plus
WH2Cl2(PMe3)4 a PMe3 + [WH2Cl2(PMe3)3] {ROH
}
[W(OR)H3Cl2(PMe3)3] f H2 + [W(OR)HCl2(PMe3)3] ff
(12)
1
2
as H/D exchange is observed by H and H NMR in reactions
of WD2Cl2(PMe3)4 + PhCH2OH and WH2Cl2(PMe3)4 + PhCH2-
OD. A similar mechanism of reversible phosphine loss and
(25) Lyons, D.; Wilkinson, G. J. Chem. Soc., Dalton Trans 1985, 587-
590.
(22) Rabinovich, D.; Parkin, G. J. Am. Chem. Soc. 1993, 115, 353-
354.
(26) Beckwith, A. L. J.; Bowry, V. W. J. Am. Chem. Soc. 1994, 116,
2710-2716.
(27) Lowry, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry; Harper & Row: New York, 1987; pp 454-463.
(28) Vetter, W. M.; Sen, A. Organometallics 1991, 10, 244-250.
(23) Chiu, K. W.; Jones, R. A.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B.; Abdul Malik, K. M. J. Chem. Soc., Dalton Trans. 1981,
1204-1211.
(24) Crevier, T. J.; Mayer, J. M. Inorg. Chim. Acta In press.

C-O Bond Homolysis in a Tungsten Alkoxide
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8489
Scheme 1
benzyl alcohol produces toluene with just a trace of bibenzyl
but as the reaction proceeds and the concentration of 2 drops,
bibenzyl becomes an increasingly significant product. In the
reaction of 2-d2 with PhCH2OH, the initial product is PhCH2D
but as hydroxyl protons are incorporated into 2 by the reversible
addition of the alcohol, PhCH3 is produced in increasing
amounts. The ability of 2 to donate a hydrogen atom to an
alkyl radical has ample precedent in metal hydride chemistry.29
In the reaction of 1 with methanol and without DHA, the fate
of the methyl fragment is unknown; presumably, the reactive
methyl radical shows little selectivity and forms a variety of
products.
The formation of PhCH3 as well as PhCH2D from PhCH2-
OD shows that the hydroxyl proton is not the only hydrogen
atom source. Too much PhCH3 is formed to be the result of
the protic impurity in the PhCH2OD (<1%), and the PhCH2D/
PhCH3 ratio does not change over the course of the reaction as
would be expected for consumption of a small impurity. The
reaction of WCl2[P(CD3)3]4 (1-d36) with PhCH2OD gives the
same PhCH2D/PhCH3 ratio as the reaction of protio-1, ruling
out the PMe3 ligands as the secondary hydrogen atom donor
for benzyl radicals. The source of the hydrogen atoms is likely
the methylene protons of the benzyl alcohol, although this has
not been demonstrated.30
When dihydroanthracene (DHA) is used as the radical trap,
no anthracene is produced. Deuterium exchange with the 9,10
positions is however observed in the reaction of 1 + PhCH2-
OD + DHA. Reactions that contain DHA also do not show
formation of 2, though 2 is visible in all other reactions of 1 +
ROH. In an independent control experiment, no hydrogenation
of anthracene by 2 is observed even after reaction for several
days at 77 °C. These initially puzzling results indicate that DHA
acts as a hydrogen transfer catalyst: alkyl radicals are trapped
by DHA to give RH and the relatively stable monohydroan-
thracenyl radical, which is then reduced by trace amounts of 2
or other tungsten hydrides present in the solution (eq 14). The
The methyldiphenylphosphine complex WCl2(PMePh2)4 (4)
appears to deoxygenate alcohols by a similar mechanism, as
bibenzyl is formed from benzyl alcohol. This product was
overlooked in our earlier report,6 leading to the erroneous
conclusion that radicals were not involved. This report, which
dealt only with PMePh2 compounds, also mentioned the absence
of characteristic radical products: no ethane was formed from
MeOH, no butane or ethylene was formed from EtOH, and no
CH3D was formed from MeOH in toluene-d8 solvent. The lack
of radical coupling products is understandable because the
various radical traps in this system keep the radical concentra-
tions lowsand MeOH and EtOH react very slowly with 4. Little
CH3D is formed because CH3• + toluene-d8 is a slow reaction31
and proceeds in part by methyl addition rather than by D-atom
transfer.32 The desulfurization of thiols by 1 and 44,6 is also
likely to involve alkyl radicals. Thus, benzyl thiol reacts with
1 to give toluene and bibenzyl and added DHA leads to the
production of only toluene. Methanethiol is desulfurized to
methane by 14 and EtSH plus 4 gives ethane.6 Presumably the
sulfhydryl proton acts as the trap for Me• and Et•.33 Homolytic
cleavage of C-S bonds has been demonstrated in other systems,
such as hydrodesulfurization (HDS) model systems, and there
is recent evidence in a catalytic HDS process.34 Additionally,
C-S bonds appear to be cleaved homolytically in some
enzymatic reactions.35
Our attempts to synthesize isolable alkoxides that would
undergo C-O homolysis when thermolyzed are reported
elsewhere.24 WH3(OCH2Ph)(PMe3)4, synthesized by the addi-
tion of benzyl alcohol to WH2(PMe3)5, does not undergo C-O
bond homolysis on heating. Rather, it undergoes C-H bond
activation, eventually leading to WH2(CO)(PMe3)4 and benzene.
Curiously, when thermolysis is conducted in the presence of
free benzyl alcohol, the reaction is almost an order of magnitude
faster and toluene and bibenzyl are formed in excellent yield.
The reason for this change in mechanism to C-O bond
homolysis is not understood. Free benzyl alcohol does not seem
to be requisite for C-O bond homolysis, as treatment of
WH3(OCH2Ph)(PMe3)4 with CDCl3 results in the rapid forma-
tion of toluene, bibenzyl, and W(O)Cl2(PMe3)3 (3). Presumably,
(30) No benzyl-R-d1 alcohol was observed by 2D NMR or GC-MS in
reactions of PhCH2OD. A reviewer suggested that this might be formed as
a minor product from trapping of PhC4 HOH radicals (although conversion
to PhCHO and other products seems equally likely).
(14)
(31) The rate constant for CH3 abstraction from toluene-h8 is 102-103
•
times smaller than that for abstraction from DHA, and reaction with toluene-
d8 is slower still due to the primary isotope effect.18a
(32) Reference 18a. Leffler, J. E. An Introduction to Free Radicals;
Wiley: New York, 1993; p 163.
monohydroanthracenyl radicals are trapped back to DHA by
tungsten hydride species faster than they undergo dispropor-
tionation or react with 1 or a second benzyl radical.
(33) k(CH3 + MeSH f CH4 + MeS•) ) 7 × 107 M-1 s-1 in H2O at
•
293 K.18a
(34) Dungey, K. E.; Curtis, M. D. J. Am. Chem. Soc. 1997, 119, 842-
843 and references therein.
(29) Bullock, R. M. In Transition Metal Hydrides; VCH: New York,
1992; pp 263-304.
(35) The Bioinorganic Chemistry of Nickel; Lancaster, J. R., Jr., Ed.;
VCH: New York, 1988; Chapters 11 and 12.

8490 J. Am. Chem. Soc., Vol. 119, No. 36, 1997
CreVier and Mayer
Scheme 2. Estimation of the LnWO-R Bond Dissociation
Energy
values are used, eq 16 gives an estimate of <33 ( 10 kcal/mol
for D(WO-R). This is an exceptionally low bond strength for
a C-O bond. This calculation thus provides a rationale for
how a C-O bond could cleave under such mild conditions.37
As suggested elsewhere,10b alkoxide ligands should be consid-
ered to have activated C-O bonds in systems that make strong
metal-oxo bonds.
The C-O bond homolysis also occurs in the reactions of 1
with methanol and cyclopropanemethanol. For R ) methyl,
D(R-O•) is 90 kcal/mol,11 so the estimated D(WO-R) is 12
kcal/mol higher than for benzyl alcohol. In reactions of aryl
alcohols, the C-O bond is not cleaved, consistent with a
calculated D(WO-Ph) on the order of 80 kcal/mol [D(Ph-O•)
) 125 kcal/mol11], more than 40 kcal/mol stronger than WO-
CH2Ph.
The thermodynamic analysis also provides a rationale for the
very rapid trapping of alkyl radicals by oxidizing metal-oxo
compounds, the reverse of eq 13. Permanganate, dichromate,
and CrO2Cl2 have all been shown to trap radicals at close to
the diffusion limit.38 In the tungsten case, which is the least
favorable situation because the metal-oxo complex is a reducing
agent, addition of R• to MdO is significantly downhill. For
an oxidizing metal center such as MnVII, CrVI, or FeIV, this
reaction should be even more favorable.
this involves a chlorobenzyloxide complex related to those
discussed here (Scheme 1).
Thermodynamics of C-O Bond Homolysis. To our
knowledge, the only other well-defined example of alkoxide
C-O bond homolysis under mild conditions is the loss of tBu•
from a molybdenum/titanium complex reported by Cummins
et al. while this report was in preparation.12 The key parameter
in any homolysis reaction is the strength of the bond being
broken, in this case LnWO-R. This is quite different than the
alcohol C-O bond strength, because while C-O cleavage in
an alcohol generates a hydroxyl radical, homolysis in an
alkoxide compound gives a metal-oxo complex (eq 13 above).
To show that this reaction is reasonable, we estimate this bond
strength using the thermochemical cycle in Scheme 2. The
mechanistic data do not uniquely define which tungsten alkoxide
is undergoing homolysis; we assume that homolysis occurs in
W(OR)Cl2(PMe3)3 in order to use data obtained in other studies.
This could be formed from WH(OR)Cl2(PMe3)3, generated as
in Scheme 1, by hydride redistribution or reductive elimination
(see above). Alternatively, the reactive alkoxide could be a
hydrido-alkoxide WHn(OR)Cl2(PMe3)m, as long as it has
valence electron count of 15 or fewer.
Conclusions
WCl2(PMe3)4 (1) and WH2Cl2(PMe3)4 (2) react with alcohols
to give W(O)Cl2(PMe3)3 (3), PMe3, hydrocarbons, and H2. A
mechanism involving alkyl radicals is indicated by the products,
butenes from cyclopropanemethanol and bibenzyl from benzyl
alcohol, and by trapping of radicals by 9,10-dihydroanthracene
(DHA) and DHA-d12. Methyl radicals are formed from
methanol. Kinetic studies suggest that the reactions proceed
through intermediate tungsten alkoxide species. The alkyl
radicals are formed by homolysis of the C-O bond in an
alkoxide complex, with formation of a stable tungsten-oxo
compound. A simple thermochemical analysis indicates that
the homolysis step is made more facile by the strength of the
tungsten-oxo triple bond, especially by the large difference
between W-O and WtO bonds. Deoxygenation of alcohols
by WCl2(PMePh2)4 (4) and desulfurization of thiols by 1 and 4
appear to proceed by similar mechanisms.
Across the top of Scheme 2 is the W-OR bond dissociation
energy, the quantity of interest. Going around the upper cycle
counterclockwise involves (i) removing the alkoxide ligand from
the metal, (ii) homolyzing the C-O bond, and (iii) reattaching
the oxygen to the metal. The values for step ii, D(R-O•), are
calculated from the lower cycle, given in algebraic form in eq
15. D(R-OH) values are determined from heats of formation
Experimental Section
General Considerations. All experiments were performed under
a nitrogen atmosphere or in Vacuo employing high vacuum line and
standard glovebox techniques. Solvents were dried according to
standard procedures.39 Gases were used directly from the cylinder
without further purification. All other reagents were degassed on the
vacuum line, checked for purity by NMR, and, if necessary, dried by
standard means. Deuterated solvents were purchased from Cambridge
Isotope Laboratories. Anthracene-d10 (Cambridge Isotope) was used
without further purification. 9,10-Dihydroanthracene (Aldrich) was
recrystallized two times from ethanol prior to use. WCl2(PMe3)4 (1),40
WH2Cl2(PMe3)4 (2),16 and WCl2(PMePh2)4 (4)40 were prepared follow-
ing published procedures. PMe3-d9 was prepared by Keith Hall from
D(R-O•) ) -D(RO-H) + D(R-OH) + D(•O-H) (15)
D(WO-R) ) D(R-O•) + D(W-OR) - D(WtO) ) 81 +
(90 ( 10) - (>138) kcal/mol (16)
of ROH, R•, and OH•.11 For R ) benzyl, the value for
D(PhCH2-O•) is 81 kcal/mol. The upper cycle yields eq 16
for D(W-OR). The tungsten-oxygen triple bond strength has
been estimated as at least 138 kcal/mol in W(O)Cl2(PMe3)3, on
the basis of the ability of 1 to deoxygenate CO2.4 The bond
strength of the tungsten oxygen single bond is crudely estimated
to be 90 ( 10 kcal/mol on the basis of data for W(OMe)6 and
a series of homoleptic tantalum alkoxides,36 although this could
vary significantly depending on the exact complex. When these
(37) Except in unusual circumstances, ∆Hq g ∆H°. Most homolysis
reactions have ∆Hq = ∆H° because the reverse reaction (recombination)
has at most a small barrier. Barriers for R• + LnMdO f LnMOR are not
known but such reactions can be very rapid.38
(38) (a) Reference 14. (b) Al-Sheikhly, M.; McLaughlin, W. L. Radiat.
Phys. Chem. 1991, 38, 203-211. (c) Cook, G. K.; Mayer, J. M. J. Am.
Chem. Soc. 1994, 116, 1855-1868.
(39) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd Ed.; Pergamon: New York, 1989.
(36) The mean W-O bond dissociation enthalpy for W(OMe)6 is 86
kcal/mol. Bond dissociation enthalpies for homoleptic tantalum alkoxides
lie between 86 and 100 kcal/mol. Connor, J. A. Topics Curr. Chem. 1977,
71, 71-110.
(40) Atagi, L. M.; Mayer, J. M. Polyhedron 1995, 14, 113-125 (as
adapted from Sharp, P. R. Organometallics 1984, 8, 1217-1223 and Sharp,
P. R.; Bryan, J. C.; Mayer, J. M. Inorg. Synth. 1990, 28, 326-332).

C-O Bond Homolysis in a Tungsten Alkoxide
J. Am. Chem. Soc., Vol. 119, No. 36, 1997 8491
CD3I following the published procedure.41 PhCH2OD was prepared
by exchange of PhCH2OH (15 mL) with 3 × 35 mL of D2O and dried
in Vacuo; 1H NMR of the sample in C6D6 showed no residual alcohol
protons, consistent with >98% deuterium incorporation.
Reaction of 1 with Benzyl Alcohol and DHA. By the above
procedure, 8.8 mg of 1 (16 µmol), 10 µL of PhCH2OH (96 µmol),
26.1 mg of DHA (145 µmol), and 0.5 mL of C6D6 were reacted in a
sealed NMR tube for 2 days at 80 °C. Upon completion of the reaction,
tube was broken open in the glove box, the contents were transferred
to a small round bottom flask, and the volatiles were removed on the
vacuum line. The residual solids were dissolved, in the air, in a 5%
ethyl acetate/hexane solution and chromatographed on a small silica
column, and analysis of the resulting fractions by GC revealed only
bibenzyl and DHA. A trace amount of anthracene was also visible in
the GC analysis, but the amount was consistent with the residual
anthracene seen in analysis of the initial reaction mixture (ca. 0.1%
anthracene remains in DHA samples even after multiple recrystalliza-
tions).
NMR spectra were acquired using Bruker WM-500, AM-499, AF-
300, or AC-200 at ambient temperatures (24 ( 2° C), except where
noted. 1H NMR spectra were referenced relative to TMS or the residual
protons in the solvent. 31P{1H} NMR spectra were recorded at 202.5
or 81.0 MHz and were referenced to external 85% H3PO4. 1H{31P}
2
NMR spectra and H spectra were recorded at 500.0 and 30.7 MHz,
1
2
respectively, and referenced to H or H in the solvent. IR spectra
were recorded on a Perkin-Elmer 1604 FTIR. GC analyses were
performed on HP 5790 or 5890 instruments equipped with an FID
detector. GC-MS were performed on a Kratos EI mass spectrometer
equipped with an HP 5890 instrument.
Reaction of 1 with Methanol and DHA. A 20 mL thick-walled,
sealable reaction vessel was charged with 73.3 mg (0.13 mmol) of 1,
134 mg (0.74 mmol) of DHA, and 1.5 mL of benzene in the drybox.
The vessel was degassed on a vacuum line, and ∼1.5 mmol of methanol
was vacuum transferred into the vessel. The vessel was sealed and
heated to 77 °C for 12 days, which resulted in a darkening of the
solution from bright yellow to a brownish/purple. The vessel was
hooked to a gas phase infrared cell via a short-path vacuum transfer
apparatus. The apparatus and cell were degassed, and the vessel was
immersed in 77 K bath and then opened to the cell. An infrared
spectrum of the collected gases revealed bands at 3016 and 1305 cm-1
with resolved rotational bands, in agreement with the spectrum of
methane.43
WCl2(P(CD3)3)4 (1-d36). A solution of 1 (10.3 mg, 19 µmol) in 0.5
mL of C6D6 was placed in a sealable NMR tube, degassed, and 300
µmol of P(CD3)3 was vacuum transferred into the tube. This solution
was heated at 80 °C for 48 h. The tube was then cooled to 0 °C, and
the volatiles were removed by vacuum. The tube was immersed in a
77 K bath, and 0.5 mL of benzene and 0.30 mmol of P(CD3)3 were
vacuum transferred into the tube, and the solution was heated to 80 °C
for 2 days. This was repeated three times. The NMR tube was then
sealed under vacuum with a torch, and the sample was determined to
1
be >95% deuterated by H NMR.
WD2Cl2(PMe3)4 (2-d2). Following the procedure for 2,16 a thick-
walled glass vessel containing 102 mg of 1, 1 mL of toluene, and 250
Torr of D2 gas was heated at 80 °C for 22 h with stirring. Pentane (1
mL) was added, causing the formation of a fluffy bright yellow
precipitate. After 3 h of cooling to -78 °C, filtration in Vacuo yielded
44.5 mg of an air-sensitive yellow solid. 1H NMR: δ 1.38 (quartet
caused by overlapping virtual triplets, 36 H, JHP ) 4 Hz).
Reaction of WH2Cl2(PMe3)4 (2) with Methanol. A sealable NMR
tube was charged with 7.8 mg of 2 (14 µmol) and 0.5 mL of C6D6.
Methanol (140 µmol) was transferred into the tube by charging an
addition bulb of known size with a known pressure of methanol. The
tube was degassed and sealed in Vacuo with a torch. The tube was
heated in an 80 °C oil bath for 2 weeks, during which time the solution
turned from yellow to brownish/purple. The same procedure was used
for the reaction of 1 (16 µmol) with CH3SH (120 µmol) which turned
from yellow to brownish/purple over 3 h at 80 °C. CH4 was identified
in both reactions as a singlet at 0.14 ppm. A similar color change was
observed in the reaction of 1 (7.7 mg, 13 µmol) with PhCH2SH (9.0
µL, 76 µmol) over 5 h at 80 °C.
9,10-Dihydroanthracene-d12 (DHA-d12) was synthesized from an-
thracene-d10 by modification of a previously reported procedure for
protio-DHA.42 A 100 mL three-necked round bottom flask was charged
with 2.505 g (13.3 mmol) of anthracene-d10 and 42 mL of ethanol-d1.
The resulting solution was stirred and heated to 50 °C for 5 min, and
then small chunks of sodium metal (total of 3.91 g, 170 mmol) were
added over a 5 min period against a counterflow of nitrogen. The
resulting slurry was allowed to cool to room temperature. D2O (50
mL) was added to the reaction mixture. After 10 min of stirring, the
solution was filtered and the filtrate was washed with 20 mL of D2O.
This process was repeated three times to remove residual anthracene
(detected by GC analysis), yielding 2.24 g (11.7 mmol, 87%) of white
powder which was >98% 9,10-dihydroanthracene as analyzed by GC.
The product was analyzed by GC-MS and determined to be 96 ( 2%
deuterated in the 9,10 positions (assuming the other positions remain
99% enriched).
Reaction of WCl2(PMePh2)4 (4) with Benzyl Alcohol. A sealed
NMR tube containing 8.7 mg of 4 (8 µmol), 8.0 µL of PhCH2OH (77
1
µmol), and 0.5 mL of C6D6 was monitored by H NMR at ambient
temperatures for 24 h, during which time the solution turned from
yellow to purple.
Kinetics of the Reaction of 1 with Benzyl Alcohol. In the drybox,
a 5.00 mL stock solution of 49.8 mg of 1 (89 µmol) in C6D6 was
prepared. Aliquots of this solution (0.50 mL) were transferred into
four sealable NMR tubes. To the first was added 25 equiv of PhCH2-
OH (32.0 µL, 222 µmol); two times as much PhCH2OH was added to
the second tube. The third was charged with 25 equiv of PhCH2OD.
To the fourth were added 5.0 mg of 1 (8.9 µmol) and 25 equiv of
PhCH2OH. The tubes were each capped with a needle valve. Into
each tube was condensed 8.9 µmol of PMe3 (1 equiv) and 2.0 µmol of
Me4Si using a gas addition bulb of known volume. The tubes were
then flame sealed in Vacuo. The tubes were heated by complete
immersion in a regulated temperature bath at 70.0 °C, and the progress
Reactions were typically run in NMR tubes sealed with a torch. A
general procedure follows. Reaction of WCl2(PMe3)4 (1) plus Benzyl
Alcohol. A sealable NMR tube attached to a ground glass joint was
charged with 8.9 mg of 1 (16 µmol), 10.0 µL of PhCH2OH (96 µmol),
and 0.5 mL of C6D6. The tube was attached to a needle valve, placed
on the vacuum line, cooled to 77 K, evacuated, and sealed with a torch.
The tube was allowed to warm to ambient temperature and then
immersed in an 80 °C oil bath for 24 h. The progress of the reaction
was monitored by 1H and 31P NMR. Using 500 MHz 1H NMR
instruments, PhCH3 and PhCH2D were base line resolved. Reactions
with deuterated reagents (PhCH2OD, DHA-d12, etc.) were run in C6H6
1
of the reaction was monitored by H NMR measured at 55 °C.
2
and observed by H and 31P NMR.
Acknowledgment. We are grateful to the National Science
Foundation and the donors of the Petroleum Research Fund,
administered by the American Chemical Society, for financial
support. We thank Ms. Soonhee Jang, Dr. Lauren Atagi, Dr.
Keith Hall, and Dr. David Thorsell for their advice and previous
work in this system.
Reaction of 1 with Cyclopropanemethanol. Following the above
procedure, 8.8 mg of 1 (16 µmol), 10 µL of c-C3H5CH2OH (123 µmol),
and 0.5 mL of C6D6 were reacted in a sealed NMR tube at 80 °C for
48 h. When the reaction was completed, the tube was opened in the
glovebox and emptied into a 10 mL round bottom flask. The volatiles
were then vacuum transferred and analyzed by GC.
JA970929S
(41) Leutkens, M. L., Jr.; Elcesser, W. L.; Huffman, J. C.; Sattelberger,
A. P. Inorg. Chem. 1984, 23, 1718-1726.
(42) Bass, K. C. Org. Synth. 1958, 42, 48-49.
(43) Gray, D. L.; Robiette, A. G. Mol. Phys. 1979, 37, 1901.