Dicarbonyl{[2-(diphenylphosphino)ethyl]cyclopentadienyl} group VI metal hydrides, halides, and anions: Precursors for olefin epoxidation catalysts

Article abstract of DOI:10.1021/om300057n

Oxidative decarbonylation of (η⁵-C₅R ₅)Mo(CO)₃X and isoelectronic four-legged piano-stool Mo(II) precursors to homogeneous olefin epoxidation catalysts has garnered significant attention as an alternative to organorhenium oxides RReO ₃. An emerging theme has been the introduction of donor-functionalized cyclopentadienyl ligands to tune catalyst performance. However, the utility of the [2-(diphenylphosphino)ethyl]cyclopentadienyl (Cp^PPh) ligand under oxidative decarbonylation conditions has not been explored. The application of Mo(VI) and W(VI) compounds containing mono- and bidentate phosphine oxide ligands as epoxidation catalysts suggests that screening MoX(CO)₂(η⁵:η¹-Cp ^PPh) as catalyst precursors is a worthy objective. To this end, HM(CO)₂(η⁵:η¹-Cp^PPh) (M = Cr (1), Mo (2), W (3)) were synthesized; the hydrides 1 and 3 are of interest, since 2 is an established precursor for ionic hydrogenation catalysts. Hydrogen-halogen exchange using 1-3 afforded MX(CO)₂(η ⁵:η¹-Cp^PPh) (M = Cr, X = I (4); M = Mo, X = Cl (5), Br (6), I (7); M = W, X = Br (8)), while deprotonation of 1-3 provided [K(18C6)][M(CO)₂(η⁵:η¹-Cp ^PPh)] (M = Cr (9), Mo (10), W (11)). Complexes 1 and 3-11 have been characterized in solution and by X-ray crystallography. Treatment of 5-7 with t-BuOOH resulted in active cyclooctene and 1-dodecene epoxidation catalysts, with conversion curves and activities similar to those afforded by MoCl(CO) ₃(η⁵-C₅R₅) and MoR(CO) ₃(η⁵-C₅R₅) precursors.

Full text of DOI:10.1021/om300057n

Article
pubs.acs.org/Organometallics
Dicarbonyl{[2-(diphenylphosphino)ethyl]cyclopentadienyl} Group VI
Metal Hydrides, Halides, and Anions: Precursors for Olefin
Epoxidation Catalysts
Paul J. Fischer,* Michelle C. Neary, Laura Avena, Kevin P. Sullivan, and Kent C. Hackbarth
Department of Chemistry, Macalester College, Saint Paul, Minnesota 55105-1899, United States
S
* Supporting Information
ABSTRACT: Oxidative decarbonylation of (η5-C5R5)Mo-
(CO)3X and isoelectronic four-legged piano-stool Mo(II)
precursors to homogeneous olefin epoxidation catalysts has
garnered significant attention as an alternative to organo-
rhenium oxides RReO3. An emerging theme has been the
introduction of donor-functionalized cyclopentadienyl ligands to tune catalyst performance. However, the utility of the [2-
(diphenylphosphino)ethyl]cyclopentadienyl (CpPPh) ligand under oxidative decarbonylation conditions has not been explored.
The application of Mo(VI) and W(VI) compounds containing mono- and bidentate phosphine oxide ligands as epoxidation
catalysts suggests that screening MoX(CO)2(η5:η1-CpPPh) as catalyst precursors is a worthy objective. To this end,
HM(CO)2(η5:η1-CpPPh) (M = Cr (1), Mo (2), W (3)) were synthesized; the hydrides 1 and 3 are of interest, since 2 is an
established precursor for ionic hydrogenation catalysts. Hydrogen−halogen exchange using 1−3 afforded MX(CO)2(η5:η1-
CpPPh) (M = Cr, X = I (4); M = Mo, X = Cl (5), Br (6), I (7); M = W, X = Br (8)), while deprotonation of 1−3 provided
[K(18C6)][M(CO)2(η5:η1-CpPPh)] (M = Cr (9), Mo (10), W (11)). Complexes 1 and 3−11 have been characterized in
solution and by X-ray crystallography. Treatment of 5−7 with t-BuOOH resulted in active cyclooctene and 1-dodecene
epoxidation catalysts, with conversion curves and activities similar to those afforded by MoCl(CO)3(η5-C5R5) and
MoR(CO)3(η5-C5R5) precursors.
An emerging theme has been introduction of donor-
functionalized cyclopentadienyl ligands to tune catalyst
performance (Figure 1).12 Molybdenum carbonyl complexes
INTRODUCTION
The application of cyclopentadienyl molybdenum(II) carbonyl
complexes as precursors to Mo(VI) oxidation catalysts has been
■
intensively investigated since 2003, when Kuhn and Romao
̈
̃
reported the facile preparation of (η5-C5R5)MoO2Cl for olefin
epoxidation by reaction of (η5-C5R5)Mo(CO)3Cl and t-
BuOOH (TBHP).1 While oxidative decarbonylation of (η5-
C5R5)Mo(CO)3X and isoelectronic four-legged piano-stool
Mo(II) precursors to homogeneous olefin epoxidation
catalysts2 has garnered significant attention as a less toxic and
more economical alternative to organorhenium oxides RReO3,3
this strategy has been extended to sulfoxidation,4 olefin cis-
dihydroxylation,5 amine oxidation,6 and alcohol oxidation.7
Olefin epoxidation with cyclopentadienyl molybdenum(II)
carbonyl precatalysts upon their grafting to molecular sieves
and zeolites,8 introduction into two-phase mixtures with ionic
liquids,9 immobilization in ß-cyclodextrins,10 and promotion by
microwave-assisted heating11 reflect the tolerance and robust-
ness of these systems.
Figure 1. Divalent molybdenum complexes with donor-functionalized
cyclopentadienyl ligands that are olefin epoxidation catalyst precursors.
With (η5-C5R5)Mo(CO)3R and (η5-C5R5)Mo(CO)3X, re-
tention of ancillary R/X and cyclopentadienyl to afford unique
catalysts with (η5-C5R5)MoO2 fragments upon oxidative
decarbonylation is well established; different tricarbonyl
precursor ancillary ligands significantly impact catalyst perform-
ance.1,2 Ligands that render the Mo(II) center less electron rich
are advantageous; decreasing Cp donor ability generally
increases catalyst activity, as demonstrated by the exceptionally
high olefin epoxidation activity of (η5-(C5(CH2Ph)5)MoO2Cl.1
with functionalized η5-cyclopentadienyl ligands and stereogenic
centers located in the tethered side chain are precursors for
asymmetric olefin epoxidation catalysts,13 and related Mo
Received: January 24, 2012
Published: March 15, 2012
© 2012 American Chemical Society
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complexes with cycloalkyl moieties as pendant units display a
high selectivity in the epoxidation of cis- and trans-stilbene.14
Molybdenum(II) complexes containing cyclopentadienyl func-
tionalized N-heterocyclic carbenes15 and Cp ligands bearing a
chiral oxazoline pendant group16 exhibit catalytic olefin
epoxidation activity with enhanced stability under oxidative
conditions, permitting longer reaction times. The utility of the
[2-(diphenylphosphino)ethyl]cyclopentadienyl (CpPPh) ligand
under oxidative decarbonylation conditions has not been
explored, undoubtedly due to the expectation of phosphine
oxide pendant group formation. However, the application of
Mo(VI) and W(VI) compounds containing mono- and
bidentate phosphine oxide ligands as epoxidation catalysts
with TBHP and H2O2 as oxidants suggests that screening
MoX(CO)2(η5:η1-CpPPh) as catalyst precursors is a worthy
objective.17
Scheme 1
Hydrogen−halogen exchange using HM(CO)2(η5:η1-CpPPh
)
(M = Cr (1), Mo (2), W (3)) was hypothesized as a
convenient route to MX(CO)2(η5:η1-CpPPh). Bullock reported
2, HMo(CO)2(η5:η1-C5H4(CH2)2PR′2) (R′ = Cy, Bu), and
t
HW(CO)2(η5:η1-C5H4(CH2)2PtBu2) as precursors for solvent-
free ketone ionic hydrogenation catalysts.18 While 2 was fully
characterized in solution and the solid state, pure 3 could not
be isolated, due to the high kinetic stability of the HW-
(CO)3(η5-CpPPh) intermediate.18a
As part of our ongoing exploration of CpPPh group VI metal
carbonyl complexes,19 we have fully characterized hydrides 1
and 3 and have explored the reactivity of 1−3 toward
hydrogen−halogen exchange and deprotonation. The resulting
metal halides MX(CO)2(η5:η1-CpPPh) (M = Cr, X = I (4); M =
Mo, X = Cl (5), Br (6), I (7); M = W, X = Br (8) and
[K(18C6)][M(CO)2((η5:η1-CpPPh)] (M = Cr (9), Mo (10), W
(11)),20 salts of the hydride conjugate bases, have been
characterized in solution and by X-ray crystallography. The
utility of 5−7 as catalyst precursors for cyclooctene and 1-
dodecene epoxidation with TBHP as an oxidant was
investigated for comparison to the MoCl(CO)3(η5-Cp)
benchmark.
(1, δ −5.66 (2JPH = 66), 13, δ −5.56 (2JPH = 80) are very
similar. Isoelectronic HW(CO)3(PPh3)(η5-Cp) (14)24 and 3
exhibit nearly indistinguishable IR ν(CO) spectra (3, 1936,
1
1856 cm−1; 14, 1944, 1865 cm−1) and broad H NMR W−H
singlets at ambient temperature (3, δ −6.80; 14, δ −6.97).
These data confirm weaker donation of PPh3 and pendant 2-
(diphenylphosphino)ethyl tethered ligand, respectively, relative
to that in HW(CO)2(η5:η1-C5H4(CH2)2PtBu2) (IR ν(CO),
1917, 1836 cm−1; 1H NMR, W−H δ −7.29 (d, 2JPH = 27.1)).18a
Broad resonances in the 1H and 31P NMR spectra of 3 (e.g., 31
P
NMR δ 40.8 (s, w1/2 = 38 Hz)) are reminiscent of those
exhibited by 1424 and 2,18a indicative of cis−trans isomerization
in solution. Isomerization between the cis and trans isomers of
HMo(CO)2(PR3)(η5-Cp) has long been known25 and was
recently examined in the related HMo(CO)2(η5:η1-
RESULTS AND DISCUSSION
■
Synthesis and Characterization. Moderately air-sensitive,
pale yellow (1) and colorless (3) microcrystalline hydrides
were synthesized (Scheme 1) via a modification of the
18a
t
C5H4(CH2)2PR2) (R = Ph (2), Cy, Bu).
Deprotonation of 1−3 with KH, followed by complexation
with 18C6, afforded salts 9−11 as analytically pure bright
yellow to orange microcrystals in 50−80% yields (Scheme 1).
The zerovalent chromium anion of 9 is related to [Cr-
(CO)2(PR3)(η5-Cp)]− (R = Ph, Et, OCH3); the PEt3
dicarbonyl anion is sufficiently electron rich to engage unique
charge transfer with bis(triphenylphosphine)iminium
(PPN+).26 The IR ν(CO) spectra of 9 and [Et4N][Cr-
(CO)2(PPh3)(η5-Cp)] (15) in THF (1, 1785, 1700 cm−1;
15, 1780, 1704 cm−1) are unsurprisingly very similar. Charge
transfer between the cation and anion in 15 was deemed
essentially absent in THF. The nearly identical IR ν(CO)
spectra of 9 in both THF and Nujol (1781, 1698 cm−1) suggest
the extent of interaction between [K(18C6)]+ and [Cr-
(CO)2(η5:η1-CpPPh)]− is not significantly different in these
procedure reported for 2.18a Reactions of NaCpPPh and
21
M(CO)3(RCN)3 provided Na[M(CO)3(η5-CpPPh)] on the
basis of IR spectroscopy.19b Addition of acetic acid resulted
in formation of HM(CO)3(η5-CpPPh); the chromium hydride
converted to dicarbonyl 1 within 1 h at ambient temperature.
The kinetic stability of intermediate HW(CO)3(η5-CpPPh
)
(12)18a toward CO dissociation and intramolecular pendant
phosphine coordination was surmounted by an extended
toluene reflux of mixtures of 3 and 12. Pure 3 was ultimately
separated from residual 12 by fractional crystallization.
Decomposition of 12 and 3 under reflux is likely responsible
for the reduced isolated yield of analytically pure 3 (36%)
relative to 1 (70%).22
Hydrides of general formula HCr(CO)2(PR3)(η5-Cp) have
been of interest as trapping products of 17-electron Cr-
(CO)2(PR3)(η5-Cp),23 but solution NMR and IR spectroscopic
data have only been reported for HCr(CO)2(PPh3)(η5-Cp)
and HCr(CO)2(PPh2(C6H11))(η5-Cp) (13).23b,e The IR
ν(CO) spectral data of 1 and 13 in toluene (1, 1930, 1857
cm−1; 13, 1925, 1858 cm−1) and their 1H NMR Cr−H doublets
media. The anions of 10 and 11 are isoelectronic with
27a
[Mo(CO)2(PPh3)(η5-Cp)]−
and [M(CO)2(P(OMe)3)(η5-
Cp)]− (M = Mo, W).27b These readily accessible yet highly
nucleophilic species continue to find application. It was recently
reported that N−O ligand bond cleavage occurs, resulting in
CO2 release, when [M(CO)2L(η5-Cp)]− (M = Mo, W; L =
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PPh3, P(OMe)3) react with [M′(CO)2(NO)(η5-Cp′)]BF4 (M′
= Mn, Re) to give the heterobimetallic derivatives [MM′(η5-
Cp)(η5-Cp′)(μ-N)(CO)3L] with linearly bridging nitride
ligands.28 The anions of 10 and 11 are worthy alternatives
for these studies, due to their slightly more electron rich metal
centers, coupled with the kinetic stability for phosphine binding
leveraged by η5:η1-CpPPh ligand chelation. The 13CO NMR
resonances for 9−11 ((C4D8O) 9, δ 252; 10, δ 242; 11, δ 232)
are 5−6 ppm downfield from those of [K(18C6)][M(CO)3(η5-
CpPPh)] (M = Cr (16), Mo (17), W (18))19b with unbound
tethered phosphines ((CD3CN) 16, δ 247; 17, δ 237; 18, δ
227). The substitution of a carbonyl ligand in 16−18 by the
phosphine of the CpPPh ligand has a rather modest effect on the
chemical shift of the 13CO NMR resonances.
Hydrides 1−3 react with haloforms, resulting in divalent
group VI metal halides 4−8 (Scheme 1) in 50−75% yields.
Immediately upon CHX3 addition, solutions contain kinetic
mixtures of cis and trans isomers on the basis of IR
spectroscopy.29 These metal dicarbonyl halides react slowly
with haloforms, or presumed methylene halide products, to
afford uncharacterized species; prompt workup is necessary to
obtain pure 4−8. Isomerization leading to enrichment in the
trans isomers occurs during the workup. The consistently
obtained ratios of trans to cis isomers in analytically pure
isolated samples on the basis of 31P NMR spectroscopy range
from 74:26 (4), to 80:20 (5), 93:7 (6), 94:6 (8), and 100:0 (7,
cis undetectable). Thermodynamic and kinetic investigations of
these isomerizations have not been carried out to date. Four-
legged piano-stool complexes 4−8 are analogous to classical
MX(CO)2(PPh3)(η5-Cp);30 the latter parent Cp complex with
X = Br has been utilized recently as a precursor to
cyclopentadienyl molybdenum(II) N-heterocyclic carbene
complexes.15
Figure 2. Molecular structure of 1 (50% thermal ellipsoids). Selected
bond lengths (Å) and angles (deg): Cr−C(1) = 1.8241(16), Cr−C(2)
= 1.8202(16), Cr−P = 2.3072(4), Cr−H = 1.52(2), Cr−C(3) =
2.2248(15), Cr−C(4) = 2.2180(15), Cr−C(5) = 2.1775(15), Cr−
C(6) = 2.1715(16), Cr−C(7) = 2.2029(15), Cr−C(dienyl) (av) =
2.20(2), C(1)−O(1) = 1.1627(19), C(2)−O(2) = 1.1689(19); C(1)−
Cr−C(2) = 102.04(7), C(2)−Cr−P = 90.87(5), C(1)−Cr−P =
84.70(5), P−Cr−H = 134.8(9), C(1)−Cr−H = 67.6(9), C(2)−Cr−H
= 62.9(9), Cr−P−C(9) = 104.25(5).
Structural Characterization. Hydride 1 (Figure 2) joins
1323c as the only structurally characterized HCr(CO)2(PR3)-
(η5-Cp) complexes. Although the hydride position could not be
determined in 13, its position was inferred as cis relative to the
phosphine on the basis of a large P−Cr−C(O) angle (106.2(2)
°). The hydride ligand of 1 was located trans to the pendant
phosphine, with large P−Cr−H (134.8(9)°) and C(1)−Cr−
C(2) (102.04(7)°) angles supportive of this isomer. The
apparent Cr−H distance (1.52(2) Å) in 1 is significantly longer
than that recently determined for HCr(CO)3(η5-Cp) (1.30(6)
Å) but very similar to the DFT calculated distance in
HCr(CO)3(η5-Cp) (1.58 Å).31 This DFT study suggested
that in X-ray crystallography a Cr−H distance between 1.45
and 1.50 Å is reasonable for this class of complexes.31 Tungsten
hydride 3 (Figure 3) is isostructural with Mo−H 2, with the
hydride trans to the phosphine. The W−H distances in 3
(1.65(3) Å), 2 (1.680(23) Å),18a and HW(CO)3(η5-Cp)
(1.61(8) Å)31 are statistically indistinguishable and longer
than the apparent W−H distance in cis-WH(CO)2(PMe3)(η5-
Cp) (1.30(8) Å).32 The DFT calculated W−H distance in
HW(CO)3(η5-Cp) is 1.72 Å, and W−H distances are typically
underestimated by X-ray crystallography.31
Figure 3. Molecular structure of 3 (50% thermal ellipsoids). Selected
bond lengths (Å) and angles (deg): W−C(1) = 1.961(3), W−C(2) =
1.954(3), W−P = 2.4309(6), W−H = 1.65(3), W−C(3) = 2.360(2),
W−C(4) = 2.374(2), W−C(5) = 2.318(2), W−C(6) = 2.305(2), W−
C(7) = 2.342(2), W−C(dienyl) (av) = 2.34(3), C(1)−O(1) =
1.160(3), C(2)−O(2) = 1.166(3); C(1)−W−C(2) = 99.47(10),
C(2)−W−P = 89.35(7), C(1)−W−P = 83.32(7), P−W−H =
138.2(12), C(1)−W−H = 69.8(12), C(2)−W−H = 65.3(12), W−
P−C(9) = 103.36(8).
Salts 9−11, containing three-legged piano stool anions, were
characterized by X-ray crystallography. The molecular structure
of 10 is shown in Figure 4; those of 9 and 11 are given in the
Supporting Information. Caulton’s [Cat][Cr(CO)2(PEt3)(η5-
Cp)] (Cat = Et4N, PPN) and Bullock’s [C5H9N2][W-
(CO)2(PMe3)(η5-Cp)] are the only previous structurally
characterized salts containing an anion of general formula
[M(CO)2(PR3)(η5-Cp)]−.26 In both triethylphosphine-substi-
tuted chromium salts, no structural perturbations due to
cation/anion interactions were observed in the solid state,
despite ion pairing in THF solutions of [PPN][Cr-
(CO)2(PEt3)(η5-Cp)] resulting in charge transfer from the
anion to the cation.26a While solvent molecules do not occupy
the axial positions of [K(18C6)]+ in the related 9, and the
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Figure 4. Molecular structure of 10 (50% thermal ellipsoids). Selected bond lengths (Å) and angles (deg): Mo−C(1) = 1.928(2), Mo−C(2) =
1.916(2), Mo−P = 2.3566(5), C(1)−O(1) = 1.191(2), C(2)−O(2) = 1.182(2), Mo−C(3) = 2.3504(18), Mo−C(4) = 2.3735(19), Mo−C(5) =
2.3534(18), Mo−C(6) = 2.3458(19), Mo−C(7) = 2.3595(19), Mo−C(dienyl) (av) 2.36(1), K−Mo = 3.7562(5); C(1)−Mo−C(2) = 89.52(8), P−
Mo−C(1) = 95.58(5), P−Mo−C(2) = 90.96(6), Mo−P−C(9) = 103.59(6).
potassium ion is directed toward the Cr center (K−Cr =
3.7128(9) Å), the C(1)−Cr−C(2) angle in 9 (90.26(7)°), one
that might be expected to widen due to approach of the cation,
is very similar to that in [Et4N][Cr(CO)2(PEt3)(η5-Cp)]
(90.00(13)°). No perturbation of the anion of 9 due to its
electrostatic interaction with [K(18C6)]+ is detectable. Neither
is distortion of the three-legged piano-stool geometries evident
in the more electron-rich and isostructural anions of 10 and 11,
which feature slightly longer K−M separations (10, 3.7562(5)
Å; 11, 3.7611(10) Å) and unremarkable C(1)−M−C(2) angles
(10, 89.52(8)°; 11, 89.98(16)°) despite the cation approach.
The steric impact of the coordinated phosphine in 9−11 is
mostly manifested by expansion of the P−M−C(1) angle (9,
97.09(5)°; 10, 95.58(5)°; 11, 95.79(11)°). These angles are
roughly 10° larger than the average O(C)−M−C(O) angles
that define the three-legged piano-stool geometries of [K-
(18C6)][M(CO)3(η5-CpPPh)] (16, 87(1)°; 17, 85.0(6)°; 18,
85.5(5)°).19b The P−W−C(O) angles in 11 (91.17(12),
95.79(11)°; the O(C)−W−C(O) angle is 89.98(16)°) are
also substantially larger relative to the corresponding angles in
[C5H9N2][W(CO)2(PMe3)(η5-Cp)] (86.68(10), 86.45(8)°;
the (O)C−W−C(O) angle is 90.32(12)°). This is interesting
since the W−P distances in 11 (2.3539(10) Å) and
[C5H9N2][W(CO)2(PMe3)(η5-Cp)] (2.3646(10) Å) are nearly
identical.26b On the basis of these structural parameters, the
impact of trimethylphosphine is less relative to the tethered
diphenylphosphinoethyl ligand in this system. It is noteworthy
that the average Cr−C(O), C−O, and Cr−C(dienyl) distances
in 9 (1.793(7), 1.187(4), 2.20(1) Å), as well as the average W−
C(O), C−O, and W−C(dienyl) lengths in 11 (1.921(8),
1.191(5), 2.35(1) Å), are statistically indistinguishable from the
corresponding averages in 16 (1.80(1), 1.179(4), 2.23(2) Å)
and 18 (1.913(6), 1.198(6), 2.38(3) Å), respectively. The
different donor/acceptor ability of the pendant phosphine
relative CO does not significantly impact these structural
parameters.
The four-legged piano-stool structures of metal halides 4−8
were determined by X-ray crystallography and are displayed in
Figure 5 (5) and the Supporting Information (4, 6−8). In each
case, crystals of trans isomers (the more prevalent isomer in
isolated bulk samples on the basis of NMR spectroscopy) were
selected for analysis, but visual differences among crystals of 4−
8, respectively, could not be perceived. Few chromium iodides
of general formula CrI(CO)3−x(PR3)x(η5-Cp) (x = 0, 1) have
been structurally characterized, with [CrI(CO)3(η5-
C5H4(CH2)2NMe3]I33 (19) and 4 the only examples. The
Cr−I and average Cr−(dienyl) distances in 4 (2.8094(4),
2.21(2) Å) and 19 (2.7817(8), 2.19(3) Å) are nearly identical.
Substitution of a more bulky pendant phosphine for CO trans
to the iodide ligand modestly impacts angles between the trans
ligands of the CrI(CO)2(PR3) fragment; these angles in 4
(C(1)−Cr−C(2), 106.69(10)°; P−Cr−I, 140.34(2)°) are
roughly 10° more acute and obtuse, respectively, than the
related angles in 19 (116.5(2)°, 131.71(17)°). Complexes 5−8
join MoX(CO)2(PPh3)(η5-Cp) (X = Br,34a I34b), MoI-
(CO)2(PnBu3)(η5-Cp),34c MoI(CO)2(PEt2Ph)(η5-Cp),34d and
WCl(CO)2(PH(tBu)2)(η5-Cp)34e as structurally characterized
M′X(CO)2(PR3)(η5-Cp) (M′ = Mo, W) complexes. The
geometric parameters that define the unremarkable four-legged
piano-stool structures of 5−8, except for the increasing M−X
lengths with greater halide radius (5, 2.5338(6) Å; 6, 2.6647(4)
Å; 7, 2.8619(6) Å; 8, 2.6654(10) Å), are nearly indistinguish-
able.
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No appreciable oxidation products other than cyclooctene
oxide (e.g., diols or other byproducts) were observed by GC/
MS during these reactions. With 5−7, essentially quantitative
conversion to cyclooctene oxide occurred within 24 h, with
catalytic epoxidation activity still evident at this point upon
injection of additional cyclooctene. After 5 h of reaction time
(Figure 6), conversions to cyclooctene oxide did not vary
dramatically with precatalyst (5, 86(2)%; 6, 82(4)%; 7,
75(2)%). However, initial catalyst TOF (measured at 2 min
into each catalytic run for comparison to TOF values measured
by Kuhn and Romao1) afforded by oxidation of 5 (1400 h−1)
̈
̃
was significantly higher than those of 6 (370 h−1) and 7 (230
h−1). The highly electronegative chloride ligand renders its
catalyst most active toward cyclooctene, as expected. It is
noteworthy that precatalyst 5, despite the coordinated
phosphine, affords a catalyst with a TOF very similar to that
produced by MoCl(CO)3(η5-Cp) (20); an initial TOF of 1300
h−1 was determined for the latter via the same precatalyst to
cyclooctene to TBHP ratio (0.01:1:2 (1 mol % catalyst
loading)) at 55 °C in CHCl3.1 However, the catalyst afforded
by oxidative decarbonylation of 20 effected 100% conversion of
cyclooctene to cyclooctene oxide after 4 h under the same
conditions. The reduced activities of the catalysts afforded by
5−7 relative to that from 20 may be due to the reduced
solubilities of the former catalysts in CHCl3. While 20 gives a
yellow-orange solution in CHCl3 upon oxidative decarbon-
ylation,1 5−7 afford white suspensions. The unactivated alkene
1-dodecene was much less reactive than cyclooctene toward the
catalysts generated by 5−7, with relatively low conversions to
1,2-epoxydodecane after 24 h (5, 38(4)%; 6, 33(2)%; 7,
19(3)%). No diols or other byproducts were detected by GC/
MS during these catalyst trials, run under the same conditions
as those described for cyclooctene epoxidation. It is noteworthy
that this conversion from catalyst precursor 5 is higher than
that reported for 20 and 1-octene under the same conditions
(<20% conversion to 1,2-epoxyoctane after 24 h).
Figure 5. Molecular structure of 5 (50% thermal ellipsoids). Selected
bond lengths (Å) and angles (deg): Mo−C(1) = 2.000(2), Mo−C(2)
= 1.992(2), Mo−P = 2.4695(6), Mo−Cl = 2.5338(6), Mo−C(3) =
2.349(2), Mo−C(4) = 2.370(2), Mo−C(5) = 2.329(2), Mo−C(6) =
2.317(2), Mo−C(7) = 2.347(2), Mo−C(dienyl) (av) = 2.34(2),
C(1)−O(1) = 1.129(3), C(2)−O(2) = 1.138(2); C(1)−Mo−C(2) =
103.53(8), C(2)−Mo−P = 80.87(6), C(1)−Mo−P = 80.95(6), P−
Mo−Cl = 145.625(19), C(1)−Mo−Cl = 78.23(6), C(2)−Mo−Cl =
77.83(6), Mo−P−C(9) = 105.77(7).
Olefin Epoxidation Catalysis. Complexes 5−7 were
examined as precatalysts for the epoxidation of cyclooctene
and 1-dodecene with tert-butyl hydroperoxide (TBHP) by
employing the in situ catalyst generation protocol pioneered by
Kuhn and Romao1 to examine the impact of the pendant
̈
̃
phosphine and halide variation on catalytic activities. Standard
conditions (CHCl3, 55 °C, precatalyst:alkene substrate:TBHP
= 0.01:1:2 (1 mol % catalyst loading), alkene concentration
0.84 M) were employed to permit direct comparison to related
four-legged piano-stool molybdenum(II) precatalysts. Control
experiments showed that no significant amount of epoxide
formed in the absence of precatalyst. Treatment of 5−7 with
TBHP resulted in active cyclooctene epoxidation catalysts, with
conversion curves (Figure 6) similar to those afforded by
MoCl(CO)3(η5-C5R5) and MoR(CO)3(η5-C5R5) precursors.1,2
Attempts to isolate these presumed MoXO2(η5-Cp) catalysts
via oxidative decarbonylation of 5−7 were unsuccessful due to
their apparent temperature instability as solids. However,
conversion of precatalysts 5−7, respectively, to catalysts was
examined by 31P NMR spectroscopy in CDCl3. In each case,
the 31P resonances due to the cis and trans isomers of 5− 7
disappeared upon addition of TBHP with the appearance of a
single resonance (5, δ 36.28; 6, δ 36.18; 7, δ 35.03) indicative
of phosphine oxide (e.g., δ (Ph3PO) (CDCl3) 29.0). These data
suggest the olefin epoxidation catalysts afforded by oxidative
decarbonylation of 5−7 are MO2X(η5-C5H4(CH2)2P(O)Ph2)
with dangling phosphine oxide pendant groups. There is no
spectroscopic evidence for a phosphine oxide to metal
interaction that could modulate catalyst activity. While these
complexes are clearly viable olefin epoxidation catalysts, the
lack of apparent advantages leveraged by a pendant phosphine
oxide outweighs the disadvantages of 5−7 phosphine ligand
oxidation consuming additional TBHP and the reduced catalyst
solubility relative to MoO2Cl(η5-Cp) likely produced by this
pendant group. The development of CpPPh metal complexes as
catalysts for organic transformations continues in this research
group.
Figure 6. Time-dependent conversion of cyclooctene (0.84 M) to
cyclooctene oxide using 5−7 as catalyst precursors at 55 °C in CHCl3
((5−7):cyclooctene:TBHP = 0.01:1:2 (1 mol % catalyst loading)).
EXPERIMENTAL SECTION
■
Similar procedures were conducted to synthesize 1 and 3, 4−8, and
9−11, respectively. Representative procedures for 1, 5, and 9 are
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Organometallics
Article
provided below. General procedures and complete experimental
details are given in the Supporting Information.
4.28. Mp: 150−153 °C dec. IR: in CHCl3, ν(CO) 1987 (m), 1902 (s)
cm−1; in benzene, ν(CO) 1982 (m), 1901 (s) cm−1; in Nujol, ν(CO)
1971 (s), 1949 (m, sh), 1886 (s) cm−1. NMR spectroscopy indicated a
80:20 trans:cis mixture. Data for trans-5 are as follows. 1H NMR
(C4D8O, 400 MHz): δ 7.68−7.63 (m, 4H, ortho, Ph), 7.51−7.48 (m,
6H, meta/para, Ph), 5.88 (m, 2H, Cp), 5.29 (app. t, 2H, J = 2.4, Cp),
HCr(CO)2(η5:η1-CpPPh) (1). THF (50 mL) was added to Cr-
(CO)3(CH3CN)3 (0.690 g, 2.66 mmol) and NaCpPPh (0.800 g, 2.66
mmol); the yellow solution was refluxed for 1.5 h. Addition of a 10%
v/v glacial acetic acid/THF solution (1.61 mL, containing 0.168 g,
2.80 mmol of HC2H3O2) resulted in a viscous solution, which was
stirred for 1 h until all Na[Cr(CO)3(η5-CpPPh)] was consumed and 1
was the only carbonyl complex in solution. The solvent was removed
in vacuo, and toluene (50 mL) was added to extract the hydride. The
bright yellow solution was filtered through Celite. The filtrate was
concentrated in vacuo until ∼10 mL remained; the filtrate was cooled
to −40 °C. Addition of pentane (25 mL, −30 °C) resulted in the
precipitation of a yellow solid that was isolated by filtration at −30 °C,
washed with pentane (−35 °C, 3 × 15 mL), and dried in vacuo.
Recrystallization from toluene/pentane (−20 °C) provided yellow, air-
sensitive microcrystals (0.725 g, 70%). Anal. Calcd for C21H19O2CrP:
C, 65.29; H, 4.96. Found: C, 65.16; H, 5.33. Mp: 136−137 °C dec. IR:
in THF, ν(CO) 1928 (s), 1855 (m) cm−1; in toluene, ν(CO) 1930
(s), 1857 (m) cm−1; in Nujol, ν(CO) 1945 (s), 1938 (s, sh), 1854 (s,
sh), 1836 (s), 1780 (m) cm−1. 1H NMR (C4D8O, 400 MHz): δ 7.60−
7.55 (m, 4H, ortho, Ph), 7.39−7.31 (m, 6H, meta/para, Ph), 4.81 (app
3
2
2.85 (dt, 2H, JPH = 9.2, JHH = 6.9, CH2CH2P), 2.17 (dt, 2H, JPH
=
27.8, JHH = 7.0, CH2CH2P) 13C{1H} NMR (C4D8O, 101 MHz): δ
2
2
233.1 (d, JPC = 22.1, CO), 135.2 (d, JPC = 44.8, ipso, Ph), 132.1 (d,
2JPC = 9.9, ortho, Ph), 130.3 (d, JPC = 2.3, para, Ph), 128.5 (d, JPC
10.0, meta, Ph), 114.9 (d, JPC = 5.5, quat, Cp), 97.8 (s, Cp), 91.5 (s,
Cp), 44.5 (d, JPC = 28.8, CH2CH2P), 21.1 (d, JPC = 6.9, CH2CH2P).
=
4
3
3
2
31P{1H} NMR (C4D8O, 162 MHz): δ 73.6 (s, PPh2).
MoBr(CO)2(η5:η1-CpPPh) (6). Yield: 68%. Anal. Calcd for
C21H18O2BrMoP: C, 49.54; H, 3.56. Found: C, 49.77; H, 3.86. Mp:
193−194 °C dec. IR: in THF, ν(CO) 1977 (m), 1897 (s) cm−1; in
Nujol, ν(CO) 1984 (m), 1976 (m), 1953 (w), 1887 (vs), 1862 (s, sh)
cm−1. NMR spectroscopy indicated a 93:7 trans:cis mixture. Data for
trans-6 are as follows. 1H NMR (C4D8O, 400 MHz): δ 7.65−7.59 (m,
4H, ortho, Ph), 7.48−7.45 (m, 6H, meta/para, Ph), 5.79 (m, 2H, Cp),
3
5.30 (app t, 2H, J = 2.4, Cp), 2.88 (dt, 2H, JPH = 9.2, JHH = 6.8,
CH2CH2P), 2.13 (dt, 2H, 2JPH = 28.0, JHH = 7.0, CH2CH2P). 13C{1H}
NMR (C4D8O, 101 MHz): δ 232.2 (d, 2JPC = 22.5, CO), 136.0 (d, 2JPC
= 45.2, ipso, Ph), 133.3 (d, 2JPC = 9.7, ortho, Ph), 131.4 (d, 4JPC = 2.5,
t, 2H, J = 2.0, Cp), 4.60 (app t, 2H, J = 2.0, Cp), 3.16 (dt, 2H, 3JPH
=
2
8.8, JHH = 7.2, CH2CH2P), 2.24 (dt, 2H, JPH = 23.6, JHH = 7.2,
CH2CH2P), −5.66 (d, 1H, 2JPH = 65.6, CrH). 13C{1H} NMR (C4D8O,
3
3
para, Ph), 129.5 (d, JPC = 10.0, meta, Ph), 117.3 (d, JPC = 5.9, quat,
Cp), 97.2 (s, Cp), 92.3 (s, Cp), 46.3 (d, JPC = 29.3, CH2CH2P), 21.9
(d, 2JPC = 6.4, CH2CH2P). 31P{1H} NMR (C4D8O, 162 MHz): δ 72.0
(s, PPh2).
2
101 MHz): δ 244.6 (d, JPC = 24.1, CO), 139.8 (d, JPC = 19.1, ipso,
2
4
Ph), 132.7 (d, JPC = 9.7, ortho, Ph), 130.8 (d. JPC = 1.8, para, Ph),
129.0 (d, 3JPC = 9.5, meta, Ph), 120.6 (d, 3JPC = 3.6, quat, Cp), 86.0 (s,
Cp), 82.0 (s, Cp), 49.3 (d, JPC = 27.9, CH2CH2P), 22.2 (d, 2JPC = 7.7,
CH2CH2P). 31P{1H} NMR (C4D8O, 162 MHz): δ 94.6 (s, w1/2 = 8
Hz, PPh2). While satisfactory elemental analyses were obtained for
solvent-free 1, NMR spectra of recrystallized 1 consistently indicated
trace toluene even after extended drying (4 h) in vacuo.
MoI(CO)2(η5:η1-CpPPh) (7). Yield: 74%. Anal. Calcd for
C21H18O2IMoP: C, 45.37; H, 3.26. Found: C, 45.47; H, 3.59. Mp:
203−205 °C dec. IR: in benzene, ν(CO) 1969 (m), 1894 (s) cm−1; in
THF, ν(CO) 1968 (m), 1893 (s) cm−1; in Nujol, ν(CO) 2036 (w),
2018 (w), 1961 (m, sh), 1952 (M), 1873 (s) cm−1. NMR spectroscopy
indicated only the trans isomer. 1H NMR (C4D8O, 400 MHz): δ
7.68−7.62 (m, 4H, ortho, Ph), 7.50−7.48 (m, 6H, meta/para, Ph),
5.70 (app. t, 2H, J = 2.2, Cp), 5.42 (app t, 2H, J = 2.4, Cp), 3.02 (dt,
HW(CO)2(η5:η1-CpPPh) (3). Yield: 36%. Anal. Calcd for
C21H19O2PW: C, 48.67; H, 3.70. Found: C, 48.72; H, 4.16. Mp:
189−190 °C dec. IR: in toluene, ν(CO) 1936 (m), 1859 (s) cm−1; in
Nujol, ν(CO) 1922 (s), 1840 (s) cm−1. 1H NMR (C4D8O, 400 MHz):
δ 7.59−7.53 (m, 4H, ortho, Ph), 7.42−7.34 (m, 6H, meta/para, Ph),
5.42 (s, br, 2H, Cp), 5.07 (s, br, 2H, Cp), 3.15 (s, br, 2H, CH2CH2P),
2H, 3JPH = 9.2, JHH = 6.8, CH2CH2P), 2.19 (dt, 2H, 2JPH = 28.1, JHH
=
7.0, CH2CH2P). 13C{1H} NMR (C4D8O, 101 MHz): δ 232.2 (d, 2JPC
2
2
= 22.5, CO), 136.0 (d, JPC = 45.2, ipso, Ph), 133.3 (d, JPC = 9.7,
ortho, Ph), 131.4 (d, 4JPC = 2.5, para, Ph), 129.5 (d, 3JPC = 10.0, meta,
Ph), 117.3 (d, 3JPC = 5.9, quat, Cp), 97.2 (s, Cp), 92.3 (s, Cp), 46.3 (d,
JPC = 29.3, CH2CH2P), 21.9 (d, 2JPC = 6.4, CH2CH2P). 31P{1H} NMR
(C4D8O, 162 MHz): δ 70.3 (s, PPh2).
2
2.35 (dt, 2H, JPH = 26.8, JHH = 7.0, CH2CH2P), −6.80 (s, br, 1H,
WH). 13C{1H} NMR (C4D8O, 101 MHz): δ 219.5 (s, br, CO), 135.8
2
4
(m, ipso, Ph), 132.2 (d, JPC = 10.6, ortho, Ph), 129.6 (d. JPC = 1.8,
para, Ph), 128.0 (d, 3JPC = 10.0, meta, Ph), 121.8 (s, br, quat, Cp), 86.3
(s, br, Cp), 77.3 (s, br, Cp), 47.6 (s, br, CH2CH2P), 21.7 (d, 2JPC = 6.3,
WBr(CO)2(η5:η1-CpPPh) (8). Yield: 52%. Anal. Calcd for
C21H18O2BrPW: C, 42.24; H, 3.04. Found: C, 42.15; H, 3.35. Mp:
199−201 °C dec. IR: in benzene, ν(CO) 1969 (m), 1885 (s) cm−1; in
Nujol, ν(CO) 1973 (m), 1966 (m), 1944 (w), 1896 (m, sh), 1871
(vs), 1846 (s, sh) cm−1. NMR spectroscopy indicated a 94:6 trans:cis
mixture. Data for trans-8 are as follows. 1H NMR (C4D8O, 400 MHz):
CH2CH2P). 31P{1H} NMR (C4D8O, 162 MHz): δ 40.8 (s, br, w1/2
=
38 Hz (183W−31P satellites: 41.7 (s, br), 39.9 (s, br), JWP = 292),
PPh2).
CrI(CO)2(η5:η1-CpPPh) (4). Yield: 61%. Anal. Calcd for
C21H18O2CrIP: C, 49.24; H, 3.54. Found: C, 49.12; H, 3.81. Mp:
133−134 °C dec. IR: in benzene, ν(CO) 1961 (s), 1893 (m) cm−1; in
Nujol, ν(CO) 1955 (m, sh), 1947 (m), 1873 (s) cm−1. NMR
spectroscopy indicated a 74:26 trans:cis mixture. Data for trans-4 are as
δ 7.60−7.56 (m, 4H, ortho, Ph), 7.48−7.42 (m, 6H, meta/para, Ph),
3
5.99 (m, 2H, Cp), 5.28 (app t, 2H, J = 2.3, Cp), 2.99 (dt, 2H, JPH
=
2
9.2, JHH = 6.8, CH2CH2P), 2.24 (dt, 2H, JPH = 26.4, JHH = 7.0,
1
2
CH2CH2P) 13C{1H} NMR (C4D8O, 101 MHz): δ 224.5 (d, JPC
=
follows. H NMR (C4D8O, 400 MHz): δ 7.66−7.59 (m, 4H, ortho,
15.2, CO), 136.0 (d, 2JPC = 50.5, ipso, Ph), 133.4 (d, 2JPC = 10.0, ortho,
Ph), 7.44−7.42 (m, 6H, meta/para, Ph), 5.21 (app. t, 2H, J = 2.2, Cp),
5.06 (app. quartet, 2H, J = 1.4, Cp), 3.17 (dt, 2H, 3JPH = 9.6, JHH = 7.2,
CH2CH2P), 2.20 (dt, 2H, 2JPH = 21.5, JHH = 7.2, CH2CH2P). 13C{1H}
NMR (C4D8O, 101 MHz): δ 250.1 (d, 2JPC = 44.2, CO), 137.1 (d, 2JPC
= 41.3, ipso, Ph), 133.2 (s, br, ortho, Ph), 131.3 (s, br, para, Ph), 129.5
(s, br, meta, Ph), 118.0 (d, 3JPC = 6.3, quat, Cp), 94.4 (s, Cp), 89.9 (s,
br, Cp), 47.8 (m, CH2CH2P), 21.4 (m, CH2CH2P). 31P{1H} NMR
(C4D8O, 162 MHz): δ 95.0 (s, PPh2).
4
3
Ph), 131.4 (d, JPC = 2.0, para, Ph), 129.4 (d, JPC = 11.1, meta, Ph),
114.2 (d, 3JPC = 6.2, quat, Cp), 94.6 (s, Cp), 91.1 (s, Cp), 47.1 (d, JPC
= 32.3, CH2CH2P), 22.0 (d, JPC = 6.0, CH2CH2P). 31P{1H} NMR
2
(C4D8O, 162 MHz): δ 37.7 (s, (183W−31P satellites: 38.5 (m), 36.9
(m), JWP = 260), PPh2).
[K(18C6)][Cr(CO)2(η5:η1-CpPPh)] (9). THF (20 mL) was added to
1 (0.519 g, 1.34 mmol) and KH (0.065 g, 1.61 mmol). The yellow
solution was stirred for 1 h until it turned red-orange. The reaction was
complete on the basis of IR spectroscopy (ν(CO) 1764 (s), 1685 (s)
cm−1). The solution was filtered through Celite into 18-crown-6
(0.426 g, 1.61 mmol) and stirred 2 h before filtration at −10 °C. The
filtrate was concentrated in vacuo to ∼3 mL. Addition of Et2O (50
mL) resulted in the precipitation of an orange solid that was isolated
by filtration, washed with Et2O (4 × 10 mL), and dried in vacuo.
Recrystallization from THF/Et2O provided red-orange, air-sensitive
microcrystals (0.716 g, 77%). Anal. Calcd for C33H42O8CrKP: C,
MoCl(CO)2(η5:η1-CpPPh) (5). Chloroform (35 mL) was added to 2
(0.400 g, 0.930 mmol), affording a deep red solution. The reaction was
complete within 10 min on the basis of IR spectroscopy. The solvent
was immediately removed in vacuo; the residue was dissolved in
benzene (50 mL). The solution was filtered through Celite and
concentrated to ∼2 mL in vacuo. The addition of Et2O (50 mL)
afforded a microcrystalline red solid. Recrystallization from benzene/
Et2O (0 °C) afforded deep red microcrystals (0.233 g, 54%). Anal.
Calcd for C21H18O2ClMoP: C, 54.27; H, 3.90. Found: C, 54.37; H,
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Organometallics
Article
57.55; H, 6.15. Found: C, 57.73; H, 6.53. Mp: 198−200 °C dec. IR: in
THF, ν(CO) 1785 (s), 1700 (m) cm−1; in Nujol, ν(CO) 1781 (s),
3−11, epoxidation catalysis procedures, standard curves,
epoxide conversion graphs, and GC/MS data. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
1698 (s) cm−1. H NMR (C4D8O, 300 MHz): δ 7.79 (app t, 4H, J =
7.5, ortho, Ph), 7.17 (app t, 4H, J = 7.2, meta, Ph), 7.06 (app t, 2H, J =
7.2, para, Ph), 4.11 (s, 2H, Cp), 3.97 (s, 2H, Cp), 3.58 (s, 24H, 18C6),
2.80 (s, br, 2H, CH2CH2P), 1.86 (dt, 2JPH = 21.9 Hz, JHH = 6.0 Hz, 2H,
CH2CH2P). 13C{1H} NMR (C4D8O, 101 MHz): δ 252 (s, br, CO),
AUTHOR INFORMATION
Corresponding Author
*E-mail: fischer@macalester.edu.
■
2
145.8 (s, br, ipso, Ph), 133.5 (d, JPC = 11.0 Hz, ortho, Ph), 127.5 (d,
3JPC = 8.0 Hz, meta, Ph), 127.2 (s, para, Ph), 77.8 (s, Cp), 77.6 (s, Cp),
Notes
2
71.1 (s, 18C6), 48.3 (d, JPC = 15.3, CH2CH2P), 23.8 (d, JPC = 14.6,
The authors declare no competing financial interest.
CH2CH2P). 31P{1H} NMR (C4D8O, 162 MHz): δ 107.4 (s, br, PPh2).
[K(18C6)][Mo(CO)2(η5:η1-CpPPh)] (10). Yield: 71%. Anal. Calcd for
C33H42O8KMoP: C, 54.10; H, 5.78. Found: C, 53.89; H, 6.09. Mp:
199−200 °C dec. IR: in THF, ν(CO) 1788 (s), 1702 (s) cm−1; in
Nujol, ν(CO) 1787 (s), 1701 (s) cm−1. 1H NMR (C4D8O, 300 MHz):
δ 7.85−7.78 (m, 4H, ortho, Ph), 7.22−7.17 (m, 4H, meta, Ph), 7.12−
7.07 (m, 2H, para, Ph), 4.82 (app t, 2H, J = 2.1, Cp), 4.50 (app t, 2H, J
= 2.1, Cp), 3.58 (s, 24H, 18C6), 3.58 (app quartet, 2H, J = 6.6,
CH2CH2P), 1.97 (dt, 2H, 2JPH = 24.9, JHH = 7.2, CH2CH2P). 13C{1H}
ACKNOWLEDGMENTS
■
The National Science Foundation supported this research
under grants CHE-1011800 and DBI-1039655. The donors of
the Petroleum Research Fund, administered by the American
Chemical Society (ACS-PRF 46626-B), also supported this
work. P.J.F. thanks Victor G. Young, Jr. (University of
Minnesota X-ray Crystallographic Laboratory), Rebecca C.
Hoye, and Robert C. Rossi (Macalester College) for helpful
discussions and R. Morris Bullock (Pacific Northwest National
Laboratory) for additional details regarding 2.
NMR (C4D8O, 75 MHz): δ 241.7 (d, 2JPC = 9.7, CO), 145.2 (d, JPC
=
2
25.4, ipso, Ph), 133.6 (d, JPC = 12.8, ortho, Ph), 129.1 (s, para, Ph),
127.6 (d. 3JPC = 8.8, meta, Ph), 120.8 (d, 3JPC = 4.9, quat, Cp), 80.3 (s,
Cp), 80.1 (s, Cp), 71.2 (s, 18C6), 49.2 (d, JPC = 19.6, CH2CH2P), 24.3
(d, 2JPC = 9.7, CH2CH2P). 31P{1H} NMR (C4D8O, 121 MHz): δ 91.0
(s, PPh2).
REFERENCES
[K(18C6)][W(CO)2(η5:η1-CpPPh)] (11). Yield: 53%. Anal. Calcd for
C33H42O8KPW: C, 48.30; H, 5.16. Found: C, 48.58; H, 5.45. Mp:
199−201 °C dec. IR: in THF, ν(CO) 1781 (s), 1698 (s) cm−1; in
Nujol, ν(CO) 1783 (s), 1698 (s) cm−1. 1H NMR (C4D8O, 400 MHz):
δ 7.88−7.83 (m, 4H, ortho, Ph), 7.25−7.21 (m, 4H, meta, Ph), 7.14−
7.10 (m, 2H, para, Ph), 4.85 (app t, 2H, J = 1.9, Cp), 4.55 (app. t, 2H,
J = 2.0, Cp), 3.62 (s, 24H, 18C6), 3.03 (app quartet, 2H, J = 6.9,
CH2CH2P), 2.00 (dt, 2H, 2JPH = 24.0, JHH = 7.0, CH2CH2P). 13C{1H}
■
(1) Abrantes, M.; Santos, A. M.; Mink, J.; Kuhn, F. E.; Romao, C. C.
̈
̃
Organometallics 2003, 22, 2112. It is remarkable that (η5-
(C5(CH2Ph)5)MoO2Cl exhibits even higher olefin epoxidation activity
than MeReO3, a common benchmark for these studies.
(2) (a) Zhao, J.; Santos, A. M.; Herdtweck, E.; Kuhn, F. E. J. Mol.
̈
Catal. A: Chem. 2004, 222, 265. (b) Valente, A. A.; Seixas, J. D.;
Gonca
̧
lves, I. S.; Abrantes, M.; Pillinger, M.; Romao, C. C. Catal. Lett.
̃
NMR (C4D8O, 101 MHz): δ 232.0 (d, 2JPC = 3.1, CO), 143.8 (d, JPC
=
2005, 101, 127. (c) Martins, A. M.; Romao, C. C.; Abrantes, M.;
Azevedo, M. C; Cui, J.; Dias, A. R.; Duarte, M. T.; Lemos, M. A.;
̃
2
4
32.9, ipso, Ph), 132.6 (d, JPC = 12.0, ortho, Ph), 126.5 (d, JPC = 1.5,
3
3
Lourenco
̧ , T.; Poli, R. Organometallics 2005, 24, 2582. (d) Kuhn, F. E.;
̈
para, Ph), 126.5 (d. JPC = 9.0, meta, Ph), 117.9 (d, JPC = 5.1, quat,
Cp), 77.5 (s, Cp), 75.6 (app. d, J = 2.3, Cp), 70.1 (s, 18C6), 50.8 (d,
JPC = 25.5, CH2CH2P), 22.9 (d, 2JPC = 9.6, CH2CH2P). 31P{1H} NMR
(C4D8O, 162 MHz): δ 57.8 (m, (183W−31P satellites: 59.3 (m, br),
56.2 (m, br), JWP = 502), PPh2).
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Recrystallization for X-ray Analysis. X-ray-quality crystals were
obtained by diffusion of pentane into nearly saturated toluene
solutions (1, 3), of Et2O into nearly saturated THF solutions (6−
11), and of Et2O into nearly saturated benzene solutions (4, 5).
Crystals were selected from the mother liquor in a N2-filled glovebag.
Catalytic Reactions. Cyclooctene (0.397 g, 3.6 mmol),
tetradecane (0.143 g, 0.72 mmol, internal standard), and catalyst
precursors 5−7 (1 mol %, 0.036 mmol), respectively, were dissolved in
CHCl3 (3 mL) in air at 55 °C. The reaction was started by the
addition of TBHP (5.0−6.0 M in n-decane; 7.2 mmol, 1.31 mL),
resulting in an initial cyclooctene concentration of 0.84 M. The clear
red solutions immediately turned milky white, with the exception of
solutions of 7, which took 90 min to change from milky pink to white.
Reactions were monitored by quantitative GC/MS analysis. Aliquots
of 250 μL were removed every 30 min for 5 h, diluted with CH2Cl2,
and treated with a catalytic amount of MnO2 to destroy excess
peroxide and MgSO4 and remove water. The resulting mixtures were
filtered and run on the GC/MS column. The conversion of
cyclooctene and the formation of cyclooctene oxide were calculated
from prior standard curves (r2 = 0.995). The procedure for catalytic 1-
dodecene epoxidation is nearly identical and is described in the
Supporting Information.
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ASSOCIATED CONTENT
■
Chem. 2004, 4194. (c) Sakthivel, A.; Zhao, J.; Kuhn, F. E. Catal. Lett.
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S
* Supporting Information
Text, figures, tables, and CIF files giving general procedures,
syntheses, and characterization details for 1 and 3−11,
molecular structure drawings, crystallographic data including
data collection, solution, and refinement information for 1 and
̈
̈
̈
2443
dx.doi.org/10.1021/om300057n | Organometallics 2012, 31, 2437−2444

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