Journal of the American Chemical Society
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−0.95 (m, Fe-CH2, isomer B + C), 0.55−1.60 (m, Fe-P(CH3)3 + Fe-
P(CH3)2 + CH(CH3)(CH3)′, isomers A, B, and C), 2.43 (sept,
benzene-d6, 298 K): δ = 1.05 (br d, J(H,H) = 6.2 Hz, 12 H, 2 ×
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CH(CH3)2), 1.44 (br d, J(H,H) = 5.4 Hz, 12 H, 2 × CH(CH3)2),
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3J(H,H) = 6.8 Hz, CHA(CH3)(CH3)), 2.64 (sept, J(H,H) = 7.4 Hz,
3.41 (br m, 4 H, 4 × CH(CH3)2), 4.43 (br s, 2 H, 1 × NCH2N), 6.19
(br s, 4 H, 2 × CHACHB), 6.90−7.40 (solvent signal + m, 6 H, Ar-
H). 31P{1H} NMR (81.01 MHz, benzene-d6, 298K): silent.
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CHB(CH3)(CH3)), 2.79 (ps sept, J(H,H) = 6.5 Hz, CHC+D(CH3)-
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(CH3)), 3.05 (ps sept, J(H,H) = 6.7 Hz, CHE+F(CH3)(CH3)), 3.38
[Fe{(DippC:)2CH2}(η6-C7H8)] (3). A Schlenk tube was charged with 1
(0.141 g, 0.237 mmol) and an excess of KC8 (0.081 g, 0.60 mmol). A
1:1 (by volume) THF/toluene solution was added with rapid stirring
at room temperature to the solid mixture via cannula. The initial
reaction appears as a beige suspension. The reaction was stirred at
room temperature overnight during which the reaction appearance
changed to a dark-brown solution. All volatiles were removed under
reduced pressure, and the resulting brown residue extracted with
hexane (60 mL). The brown filtrate was concentrated to 1 mL and
allowed cooled to −30 °C overnight to complete crystallization. The
mother liquor was subsequently decanted, and the remaining brown
solid dried in vacuo at room temperature for 0.5 h affording a brown
solid as product. Yield: 0.089 g (0.144 mmol, 61%). (The reaction can
be scaled up, where we found that concentration of the reaction
mixture to ∼5 mL, followed by adding hexane, and then extraction,
followed by workup provided the best yields. In this way the resulting
dark-brown filtrate was pumped down affording an oily brown residue.
Two freeze−pump−thaw cycles and scratching this residue into a
powder was subsequent followed by resolvation of the solid and
“stripping” in Et2O, with drying in vacuo for 0.5 h which affords 3·
OEt2 as product). Crystals suitable for single crystal X-ray diffraction
analysis were grown from a concentrated Et2O solution at −30 °C. 1H
NMR (400.13 MHz, cyclohexane-d12, 298 K): δ = 1.80 (br d, 3J(H,H)
= 14.4 Hz, 24 H, 4 × CH(CH3)2), 2.74 (br s, Δν1/2 = 21.0 Hz, 3 H, 1
× CH3, η6-toluene), 3.48 (br s, Δν1/2 = 26.2 Hz, 2 H, Ar-H, η6-
toluene), 3.68 (br s, Δν1/2 = 71.8 Hz, 4 H, 4 × CH(CH3)2), 4.33 (br s,
Δν1/2 = 25.1 Hz, 2 H, Ar-H, η6-toluene), 5.15 (br s, Δν1/2 = 44.1 Hz, 2
H, 1 × NCH2N), 5.30 (br s, Δν1/2 = 32.4 Hz, 1 H, Ar-H, η6-toluene),
(ps sept, 3J(H,H) = 7.1 Hz, CHG+H+I+J(CH3)(CH3)), 3.58 (sept,
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3J(H,H) = 7.5 Hz, CHK(CH3)(CH3)), 4.00 (sept, J(H,H) = 7.1 Hz,
CHL(CH3)(CH3)), 4.39−5.28 (m, NCH2N, isomers A + B + C),
6.16−6.64 (m, CHCH, isomers A + B + C), 6.94 − 7.70 (m, ArH,
isomers A + B + C). 1H NMR (400.13 MHz, benzene-d6, 298 K): δ =
−15.26 (dd, 2J(H,Pa) = 69.6 Hz, 2J(H,Pb) = 81.2 Hz, 1 × Fe-H, isomer
C, 32% abundance), −13.95 (dd, 2J(H,Pa) = 57.7 Hz, 2J(H,Pb) = 68.2
Hz, 1 × Fe-H, isomer B, 28% abundance), −11.33 (dd, 2J(H,Pa) = 34.7
Hz, 2J(H,Pb) = 71.9 Hz, 1 × Fe-H, isomer A, 40% abundance), −1.97
− −1.17 (m, Fe-CH2, isomer A), −1.47 − −0.99 (m, Fe−CH2, isomer
B + C), 0.57 − 1.56 (m, Fe-P(CH3)3 + Fe-P(CH3)2 + CH(CH3)-
(CH3)′, isomers A, B, and C), 2.33−2.50 (overlapping septs,
CHA+B(CH3)(CH3)), 2.65 (sept, 3J(H,H) = 6.9 Hz, CHC(CH3)-
(CH3)), 2.80 (sept, 3J(H,H) = 6.7 Hz, CHD(CH3)(CH3)), 2.99 (sept,
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3J(H,H) = 6.7 Hz, CHE(CH3)(CH3)), 3.07 (sept, J(H,H) = 6.7 Hz,
CHF(CH3)(CH3)), 3.31−3.45 (overlapping septs,, CHG+H+I+J(CH3)-
(CH3)), 3.58 (sept, 3J(H,H) = 6.8 Hz, CHK(CH3)(CH3)), 4.02 (sept,
3J(H,H) = 7.1 Hz, CHL(CH3)(CH3)), 4.40−5.26 (m, NCH2N,
isomers A + B + C), 6.16 − 6.64 (m, CHCH, isomers A + B + C),
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6.94−7.70 (m, ArH, isomers A + B + C). H{31P} NMR (200.13
MHz, benzene-d6, 298K): δ = −15.26 (s, 1 × Fe-H, isomer C) −13.95
(s, 1 × Fe-H, isomer B), −11.33 (s, 1 × Fe-H, isomer A) (all other
resonance signals omitted). 31P{1H} NMR (81.01 MHz, benzene-d6,
298K): δ = −48.2 (d, 2J(Pa,Pb) = 46.3 Hz, Fe-CH2PMe2, isomer B), δ
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= −42.1 (ps d, J(Pa,Pb) = 56.1 Hz, Fe-CH2PMe2, isomer C), δ =
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−36.7 (d, J(Pa,Pb) = 27.5 Hz, Fe-CH2PMe2, isomer A), δ = 12.5 (d,
2J(Pa,Pb) = 27.5 Hz, Fe-PMe3, isomer A), δ = 23.0 (d, 2J(Pa,Pb) = 46.3
Hz, Fe-PMe3, isomer B), δ = 28.5 (ps d, 2J(Pa,Pb) = 56.1 Hz, Fe-PMe3,
isomer C). Recording a 13C{1H} NMR spectrum of 2 with an
acquisition time of ∼6 h shows only 4-d6. DEPT 135 13C{1H} (100.61
MHz, benzene-d6, 298 K, short acquisition time) shows a very complex
pattern (see Supporting Information), consistent with several
coexisting stereoisomers. ESI-MS (THF), m/z: calcd for
[C37H58N4P2Fe]•+: 676.3481. Found: 676.3508.
6.61 (br s, Δν1/2 = 22.3 Hz, 2 H, 2 × CHACHB), 6.96 (br s, Δν1/2
=
26.2 Hz, 2 H, 2 × CHACHB), 7.40−7.80 (br m, 6 H, Ar-H, Dipp).
Spectra of 3 exhibit sharper signals in benzene-d6, (400.13 MHz,
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benzene-d6, 298 K): δ = 1.06 (d, J(H,H) = 6.30 Hz, 12 H, 2 ×
CH(CH3)2), 1.48 (d, 3J(H,H) = 6.30 Hz, 12 H, 2 × CH(CH3)2), 2.68
(s, 3 H, 1 × CH3, η6-toluene), 3.44 (br m, 4 H, 4 × CH(CH3)2), 3.60
(br, 2 H, Ar-H, η6-toluene), 4.37 (s, 4 H, 1 × NCH2N + 2 × Ar-H, η6-
toluene), 5.55 (s, 1 H, Ar-H, η6-toluene), 6.19 (s, 4 H, 2 × CHA
CHB), 7.40 − 7.80 (br m, 6 H, Ar-H, Dipp).13C{1H} NMR (100.61
MHz, cyclohexane-d12, 298 K): δ = 23.5 (s, 4 × CH(CH3)2), 25.0 (s, 1
× CH3, η6-toluene), 29.0 (s, 4 × CH(CH3)2), 60.3 (s, 1 × NCH2N),
74.2 (s, Ar-C, η6-toluene), 77.4 (s, C4, η6-toluene), 77.7 (s, Ar-C, η6-
toluene), 77.9 (s, C1, η6-toluene), 115.7 (s, 2 × CHACHB), 123.4 (s,
2 × CHACHB), 124.2 (s, 2 × C3,5-H, Dipp), 129.1 (s, 2 × C4-H,
Dipp), 140.9 (s, 2 × C1, Dipp), 148.2 (s, 2 × C2,6, Dipp), 198.4 (s, 2 ×
NC:N). ESI-MS (THF), m/z: calcd for [C38H48FeN4]•+: 616.3223.
Found: 616.3240.
Thermal transformation of [FeH{(DippC:)2CH2}(PMe3)(η2-
PMe2CH2)] (2) to [Fe{(DippC:)2CH2}(η6-C6D6)] (4-d6). A concentrated
sample of isolated 2·hexane was dissolved in C6D6 in a sealed NMR
tube. A room temperature NMR spectrum revealed a spectrum
consistent with 2 and small amounts of free PMe3. The sample was
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slowly heated in the spectrometer and H and 31P{1H} NMR spectra
recorded at T = 310, 320, and 330 K, respectively. Progressive
liberation of PMe3, concomitant collapse of the hydride signals of 2 at
∼ −11 to −15 ppm into the baseline, and selective formation of 4-d6 is
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observed in the H NMR spectrum. Similarly, in the 31P{1H} NMR
[Fe{(DippC:)2CH2}(η6-C6H6)] (4). A Schlenk tube was charged with 1
(0.300 g, 0.504 mmol) and an excess of KC8 (0.272 g, 2.015 mmol). A
1:1 (by volume) THF/benzene solution was added under rapid
stirring to this solid mixture by cannula transfer at room temperature.
After stirring at 6.5 h a dark-brown solution is noticed. The solvent
was removed under reduced pressure and the remaining dark-brown
residue extracted with hexane (50 mL). The color of the filtrate was
light orange, and upon removal of solvent resulted in a mass of 15 mg
(brown solid, product). The remaining reaction residue was then
extracted with benzene (70 mL), and the dark-brown filtrate
concentrated to dryness, revealing a dark-brown solid as product.
Combined yield: 0.227 g (0.377 mmol, 75%). Crystals suitable for X-
ray diffraction analysis were grown from a 1:6 (benzene: Et2O)
solution at 5 °C. 1H NMR (200.13 MHz, benzene-d6, 298 K): δ = 1.05
(br d, 3J(H,H) = 6.8 Hz, 12 H, 2 × CH(CH3)2), 1.44 (br d, 3J(H,H) =
6.7 Hz, 12 H, 2 × CH(CH3)2), 3.43 (br m, Δν1/2 = 21.3 Hz, 4 H, 4 ×
CH(CH3)2), 4.43 (br s, Δν1/2 = 3.8 Hz, 2 H, 1 × NCH2N), 4.65 (br s,
Δν1/2 = 3.24 Hz, 6 H, η6-benzene), 6.19 (br s, Δν1/2 = 3.2 Hz, 4 H, 2
× CHCHB), 7.15 (solvent signal + br s, 6 H, Ar-H, Dipp − cross
peaks in 2D HMQC). 13C{1H} NMR (50 MHz, benzene-d6, 298 K): δ
spectrum, the three sets of doublet signals corresponding to the
isomeric mixture of 2 collapse progressively into the baseline, with
concomitant increase in the signal at δ = −63.3 ppm, corresponding to
free PMe3. (The spectra of 4-d6 are virtually identical to 4 (vide infra)
except for the signals corresponding to the deuterated arene ring, see
Supporting Information.) 1H NMR (400.13 MHz, benzene-d6, 298 K):
δ = 0.79 (br s, 18 H, 2 × PMe3 (free)), 1.05 (br d, 3J(H,H) = 6.2 Hz,
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12 H, 2 × CH(CH3)2), 1.44 (br d, J(H,H) = 5.4 Hz, 12 H, 2 ×
CH(CH3)2), 3.41 (br m, 4 H, 4 × CH(CH3)2), 4.43 (br s, 2 H, 1 ×
NCH2N), 6.19 (br s, 4 H, 2 × CHACHB), 6.90−7.40 (solvent signal
+ m, 6 H, Ar-H).
13C{1H} NMR (101 MHz, benzene-d6, 298 K): δ = 16.4 (m, free
PMe3), 23.1 (s, 2 × CH(CH3)2), 25.8 (s, 2 × CH(CH3)2), 28.6 (s, 4 ×
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CH(CH3)2), 59.7 (s, 1 × NCH2N), 75.5 (t, J(C,D) = 24.9 Hz, 6 ×
CD, η6-C6D6), 116.3 (s, 2 × CHACHB), 123.0 (s, 2 × CHACHB),
124.1 (s, 2 × C3,5-H, Dipp), 129.1 (s, 2 × C4-H, Dipp), 140.3 (s, 2 ×
C1, Dipp), 147.7 (s, C2,6, Dipp), 197.8 (s, 2 × NC:N). 31P{1H} NMR
(81.01 MHz, benzene-d6, 298 K): δ = −63.3 (free PMe3).
Removal of all volatiles from the NMR tube, followed by resolvation
in C6D6 affords 4-d6 (without PMe3). 1H NMR (400.13 MHz,
J
dx.doi.org/10.1021/ja410234x | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX