A Transient V(III) Neopentylidene Complex
Organometallics, Vol. 28, No. 3, 2009 851
stripped of volatiles in vacuo. Complex 4 was extracted from the
crude mixture using hexamethyldisiloxane (TMS2O), and the extract
was filtered and dried under vacuum. The identity of the yellow
and stored at -36 °C. Storage overnight allows for isolation of
crude brown powders of 7 in ∼27% yield (85 mg, 0.126 mmol).
1H NMR (25 °C, 400.1 MHz, C6D6): δ 7.24 (m, 1H, Ar H),
7.07 (m, 1H, Ar H), 6.90 (m, 2H, Ar H), 6.80 (s, 1H, CHtBu), 6.79
(m, 1H, Ar H), 6.72 (m, 1H, Ar H), 2.35 (overlapped septets, 2H,
CH(CH3)2), 2.25 (m (obscured by Ar CH3 resonance), 2H,
CH(CH3)2), 2.17 (s, 3H, Ar CH3), 2.05 (s, 3H, Ar CH3), 1.65 (s,
9H, CHtBu), 1.62 (m, 3H, CH(CH3)2), 1.35 (doublet of doublets,
6H, CH(CH3)2), 1.25 (doublet of doublets, 3H, CH(CH3)2), 1.17
(doublet of doublets, 3H, CH(CH3)2), 1.10 (doublet of doublets,
3H, CH(CH3)2), 0.98 (m, 6H, CH(CH3)2). 13C{1H} NMR (25.0 °C,
125.7 MHz, C6D6): 332.3 (VdCHtBu), 160.4 (Ar), 160.2 (Ar),
132.7 (Ar), 132.3 (Ar), 132.2 (Ar), 127.0 (Ar), 125.5 (Ar), 120.9
(Ar), 119.4 (Ar), 117.9 (Ar), 116.6 (Ar), 116.0 (Ar), 45.3 (CtBu),
36.2 (CtBu), 28.1 (CMe2), 26.6 (CMe2), 21.8 (CMe2), 21.1 (ArMe),
20.9 (ArMe), 19.8 (CMe2), 19.2 (CMe2), 18.7 (CMe2), 18.2 (CMe2),
17.6 (CMe2), 17.4 (CMe2), 17.2 (CMe2), 16.6 (CMe2), 16.3 (CMe2);
one aryl resonance not located, likely obscured by solvent peak.
31P NMR (25 °C, 121.5 MHz, C6D6): δ 95 (doublet, broad). 51V
NMR (25 °C, 131.5 MHz, C6D6): δ 1249 ppm (ν1/2 ) 864 Hz).
gHMQC (-13 °C, C7H8): a strong correlation between peaks at
332 ppm (13C dimension) and 6.68 ppm (1H dimension) is observed.
MS-CI: theoretical [M]+, m/z 679.1915; found [M]+, m/z 679.1901.
Synthesis of (PNP)VdN(SiMe3)(CHtBu) (8). To a stirred -76
°C hexane solution of 2 (100 mg, 0.161 mmol) was slowly added
a -76 °C hexane solution of trimethylsilyl azide (19 mg, 0.16
mmol). The mixture was slowly warmed to room temperature and
stirred overnight, followed by removal of the volatiles in vacuo.
The red residue was taken up into hexane (∼5 mL) and filtered.
From the filtrate, yellow powder was obtained by concentration
and storage of this solution (∼1 mL). X-ray-quality crystals suitable
for diffraction studies can be manually separated from the powder.
The yellow powder and crystals are collected in approximately 24%
yield (25 mg, 0.039 mmol) as crude material.
1
product was confirmed by comparing the H NMR and 31P NMR
spectra and MS-CI spectrum with those of an authentic sample of
4. The yield was 49.0% based on 2 (66.7 mg, 0.118 mmol).
Synthesis of 4 via Treatment of 2 with Pyridine N-Oxide. To
a room-temperature C6D6 solution of 2 (28 mg, 0.045 mmol) in an
NMR tube with a J. Young screw top was added 1 equiv of pyridine
N-oxide (4.6 mg, 0.048 mmol). This mixture was then heated to
50 °C for 8 h, over which time the color of the solution became
significantly lighter. The identity of the product was confirmed to
1
be 4 by comparison of the H NMR and 31P NMR spectra and
MS-CI spectrum with those of an authentic sample.26 The yield of
4 as determined by use of a 5 µL 1,4-dioxane NMR internal
integration standard was 43%.
Synthesis of 4 via Treatment of 2 with Trimethylamine
N-Oxide. To a room-temperature C6D6 solution of 2 (29 mg, 0.047
mmol) NMR tube with a J. Young screw top was added 1 equiv of
trimethylamine N-oxide (3.6 mg, 0.048 mmol). This mixture was
then heated to 50 °C for 8 h. This was accompanied by a change
in color to yellow. The identity of the product was confirmed by
comparing the 1H NMR and 31P NMR spectra and MS-CI spectrum
with those of an authentic sample of (PNP)VdCHtBu(dO).26 The
yield of 4 as determined by use of a 5 µL 1,4-dioxane NMR internal
integration standard was 20%.
Synthesis of (PNP)VdCHtBu(Se) (6). To a room-temperature
C6D6 solution of 2 (75 mg, 0.12 mmol) in a NMR tube with a J.
Young screw top was added 2 equiv of Se (19 mg, 0.24 mmol).
The tube was sealed, and this mixture was then heated to 60 °C
for 5 h. The yield of 6 was 45%, as determined by as an internal
NMR integration standard (1,4-dioxane, 5 µL). The NMR solution
was then dried, extracted with pentane, filtered through Celite, and
concentrated in vacuo. Storage of this solution at -36 °C allowed
for isolation of green microcrystalline clumps, which were dried
and collected in 69% yield (52.2 mg, 0.083 mmol).
1H NMR (25 °C, 400.1 MHz, C6D6): δ 9.24 (s, 1H, dCHtBu),
7.20 (d of d, 1H, Ar H), 7.10 (d of d, 1H, Ar H), 6.91 (d, 1H, Ar
H), 6.83 (d, 2H, Ar H), 6.74 (d, 1H, Ar H), 2.37 (overlapped septets,
2H, CH(CH3)2), 2.24 (m (obscured), 1H, CH(CH3)2), 2.17 (m
(obscured), 1H, CH(CH3)2), 2.16 (s, 3H, Ar CH3), 2.09 (s, 3H, Ar
CH3), 1.58 (s, 9H, CHtBu), 1.55 (doublet of doublets, 3H,
CH(CH3)2), 1.40 (doublet of doublets, 3H, CH(CH3)2),; 1.34
(doublet of doublets, 3H, CH(CH3)2), 1.28 (doublet of doublets,
3H, CH(CH3)2), 1.13 (doublet of doublets, 3H, CH(CH3)2), 1.07
(doublet of doublets, 3H, CH(CH3)2), 0.99 (m, 6H, CH(CH3)2).
13C{1H} NMR (6.0 °C, 125.7 MHz, C6D6): δ 328.4 (VdCHtBu),
161.3 (Ar), 160.9 (Ar), 132.7 (Ar), 132.4 (Ar), 131.9 (Ar), 127.3
(Ar), 125.3 (Ar), 120.4 (Ar), 119.8 (Ar), 118.5 (Ar), 115.6 (Ar),
48.5 (CtBu), 35.2 (CtBu), 29.8 (CMe2), 26.4 (CMe2), 20.8 (Ar Me),
20.7 (Ar Me), 20.4 (CMe2), 19.5 (CMe2), 19.3 (CMe2), 18.8 (CMe2),
18.4 (CMe2), 18.0 (CMe2), 17.7 (CMe2), 17.6 (CMe2), 17.1 (CMe2),
16.1 (CMe2); one aryl resonance not located, likely obscured by
solvent resonances. 31P NMR (25 °C, 121.5 MHz, C6D6): δ 73.0
(broad). 51V NMR (25 °C, 131.5 MHz, C6D6): δ 809 (∆ν1/2 ) 993
Hz). MS-CI: theoretical [M]+, m/z 629.2018; found [M]+, m/z
629.2007.
1H NMR (25 °C, 400.1 MHz, C6D6): δ 12.51 (s, 1H, VdCHtBu),
7.26 (m, 2H, Ar H), 6.84 (m, 2H, Ar H), 6.78 (m, 2H, Ar H), 2.30
(overlapped septets, 2H, CH(CH3)2), 2.22 (septet, 1H, CH(CH3)2),
2.18 (s, 3H, Ar CH3), 2.13(s, 3H, Ar CH3), 2.08 (septet, 1H,
CH(CH3)2), 1.41 (doublet of doublets, 3H, CH(CH3)2), 1.27 (m,
12 H, CH(CH3)2), 1.05 (m, 6H, CH(CH3)2), 0.88 (m, 3H,
CH(CH3)2), 0.32 (s, 9H, SiMe3). 13C{1H} NMR (25 °C, 125.7 MHz,
C6D6): δ 322.5 (VdCHtBu), 162.1 (Ar), 161.5 (Ar), 132.4 (Ar),
132.1 (Ar), 131.7 (Ar), 125.5 (Ar), 124.6 (Ar), 120.4 (Ar), 118.1
(Ar), 117.7 (Ar), 117.5 (Ar), 116.4 (Ar), 45.7 (CtBu), 34.4 (CtBu),
26.6 (CMe2), 26.5 (CMe2), 20.8 (Ar Me), 20.7 (Ar Me), 20.3
(CMe2), 19.5 (CMe2), 19.4 (CMe2), 19.1 (CMe2), 18.9 (CMe2), 18.7
(CMe2), 18.6 (CMe2), 18.1 (CMe2), 16.3 (CMe2), 16.1 (CMe2), 4.3
(SiMe3). 31P NMR (25 °C, 121.5 MHz, C6D6): δ 52.4. 51V NMR
(25 °C, 131.5 MHz, C6D6): δ -123 (∆ν1/2 ) 1014 Hz). MS-CI:
theoretical [M]+, m/z 636.3357; found [M]+, m/z 636.3340.
Synthesis of [(PNP)VdNC(tBu))CHtBu]2(µ2,η1:η1-N2) (9). To
a stirred hexane solution of 2 (123 mg, 0.198 mmol) was added
NtCtBu at room temperature. The solution was stirred for 24 h,
and the volatiles were removed in vacuo. The red residue was taken
up into diethyl ether (∼5 mL) and the solution then filtered. X-ray-
diffraction-quality crystals were grown by concentration and storage
of a diethyl ether solution at room temperature. Storage of a
concentrated hexane solution at -36 °C allowed for isolation of
the complex as brown-red crystals in 30.7% yield (39.3 mg, 0.030
mmol). The crystalline material appeared to consist of only one
isomer. Over time in solution, complex 9 decomposed into an as
yet unidentified species.
Synthesis of (PNP)VdCHtBu(Te) (7). In a glovebox, to a room-
temperature THF solution of 2 (285 mg, 0.458 mmol) in a side-
arm reaction tube was added 7 equiv of Te powder (409 mg 3.21
mmol). The reaction tube was sealed, placed under vacuum, and
then removed from the glovebox. This mixture was heated to 50
°C with stirring in an oil bath for 2 days. The reaction mixture was
then dried in vacuo and then reintroduced into the glovebox under
vacuum. To the residue was added n-hexanes. The resulting brown
solution was filtered through a pad of Celite, concentrated in vacuo,
1H NMR (25 °C, 400.1 MHz, C6D6): δ 7.23 (m, 1H, Ar H),
7.19 (m, 1H, Ar H), 7.03 (m, 2H, Ar H), 6.83 (m, 2H, Ar H), 4.37
(s, 1H, N(tBu)CdCH(tBu)), 2.71 (septet, 1H, CH(CH3)2), 2.61
(septet, 2H, CH(CH3)2), 2.33 (septet, 2H, CH(CH3)2), 2.24 (s, 3H,
Ar CH3), 2.23 (s, 3H, Ar CH3), 1.54 (m, 3H, CH(CH3)2), 1.50 (s,