Synthesis of (tBu3SiNH)2ClWtWCl(NHSitBu3)2
J. Am. Chem. Soc., Vol. 123, No. 43, 2001 10581
4. (tBu3SiN)2(tBu3SiO)WH (3). To a glass bomb reactor containing
NaW2Cl7(THF)5 (308 mg, 0.308 mmol) and tBu3SiNHLi (280 mg, 1.26
mmol) was transferred 10 mL of benzene. The vessel warmed to 23
°C and was stirred for 45 min, as above. After removal of all volatiles,
TlOSitBu3 (330 mg, 0.308 mmol) was loaded into the reaction vessel
followed by 20 mL of THF. The reaction was stirred for 5 h at 0 °C
and 8 h at 60 °C. After removal of all volatiles and filtration in hexane,
the solution volume was reduced to 3 mL and cooled to -78 °C,
precipitating a light yellow powder that was collected by filtration to
yield 135 mg (tBu3SiN)2(tBu3SiO)WH (53%). Anal. Calcd for C36H82N2-
OSi3W: C, 52.27; H, 9.99; N, 3.39. Found: C, 51.92; H, 9.77; N,
3.72.
5. (tBu3SiN)2WHCl(py) (4-py). To a flask containing 1 (375 mg,
289 mmol) and 3 mL of pyridine was added 40 mL of benzene. The
mixture was stirred for 16 h at 60 °C. The dark purple solution was
evacuated to dryness, and the residue was triturated three times with
pentane (5 mL). The purple residue was washed with pentane and
filtered. The filtrate volume was reduced to 2 mL and deposited 4-py
as white crystals (118 mg, 28%). Anal. Calcd for C30H60N3Si2ClW:
C, 47.91; H, 8.34; N, 5.78. Found: C, 47.44; H, 8.07; N, 5.58.
6. (tBu3SiN)2HW(µ-Cl)(µ-H)2W(NSitBu3)py2 (5-py2). To a flask
containing 1 (375 mg, 0.289 mmol) and 3 mL of pyridine was added
40 mL of benzene. The mixture was stirred for 16 h at 60 °C. The
dark purple solution was evacuated to dryness, and the residue was
triturated three times with pentane (5 mL). The purple residue was
washed with pentane and filtered. The filtrate volume was reduced to
2 mL and deposited 4-py as white crystals. After three crystallizations,
5-py2 was obtained as dark purple crystals (25 mg).
the direct reaction of transient “(tBu3SiN)2WHCl” (4). It is also
noteworthy that no (tBu3SiN)2(tBu3SiNH)WX derivatives,11
which are extremely thermally and kinetically stable, were
identified in any degradations.
Summary. The bulk of the primary amide, tBu3SiNH, hinders
NH activation paths that eventually decompose (tBu3SiNH)2Cl-
WtWCl(NHSitBu3)2 (1). Related dinuclear species that feature
secondary amide ligands have substantially greater thermal
stability, while smaller primary amide-containing metal-metal
triply bonded species do not exist. Through mass balance and
the isolation and identification of primary and “scavenged”
degradation products, the decomposition of 1 is most simply
considered as a series of NH activations by the WtW unit to
afford the penultimate intermediate, “(tBu3SiN)2WHCl” (4).
Experimental Section
General Considerations. All manipulations were performed using
glovebox or high vacuum techniques. Hydrocarbon and ethereal solvents
were dried over and vacuum transferred from purple sodium benzo-
phenone ketyl (with 3-4 mL tetraglyme/L added to hydrocarbons).
Benzene-d6 was sequentially dried over sodium and 4 Å molecular
sieves and then stored over and vacuum transferred from sodium
benzophenone ketyl. All glassware was base-washed and oven-dried.
NMR tubes for sealed tube experiments were flame-dried under
dynamic vacuum prior to use. Organic reagents and solutions of lithium
7
alkyls were obtained from Aldrich Chemical. NaW2Cl7(THF)5 and
tBu3SiNHLi10 were prepared according to literature procedures.
1H, 13C{1H}, and 2H{1H] NMR spectra were obtained using Varian
XL-200, XL-400, and Unity-500 spectrometers. Infrared spectra were
recorded on a Nicolet Impact 410 spectrophotometer interfaced to a
Gateway PC. Combustion analyses were performed by Oneida Research
Services, Whitesboro, NY, or Robertson Microlit Laboratories, Madison,
NJ.
7. (tBu3SiN)2WCl2 (6). A flask containing 1 (386 mg, 0.298 mmol)
and SnCl4(THF)2 (120 mg, 0.297 mmol) in 20 mL of benzene was
stirred for 16 h at 60 °C. The yellow-green mixture was evacuated to
dryness, and the residue was triturated three times with pentane (5 mL).
The yellow-green residue was washed with pentane and filtered through
Celite until a colorless filtrate was obtained. The filtrate was dried under
vacuum, yielding yellow microcrystals of 6 (205 mg, 50%). In a separate
experiment attached to a Toepler pump, 0.95 equiv H2 (vs 1) was
released. Anal. Calcd for C24H54N2Si2Cl2W: C, 42.25; H, 8.00; N, 4.11.
Found: C, 41.55; H, 7.86; N, 3.84.
8. (tBu3SiN)2WCl2(py) (6-py). When 6 was recrystallized from
pyridine, 6-py was generated. Anal. Calcd for C29H59N3Si2Cl2W: C,
45.75; H, 7.83; N, 5.52. Found: C, 44.63; H, 7.73; N, 5.17.
9. (tBu3SiN)2WCl(OMe) (7). A flask containing 1 (430 mg, 0.332
mmol) and 10 mL of DME was magnetically stirred for 16 h at 55 °C.
The orange-brown solution was concentrated to 4 mL and filtered. The
volatiles were removed, and the solid was triturated three times with
pentane (5 mL) and dried under vacuum at 23 °C for 6 h. The solid
was dissolved in Et2O, filtered, and concentrated to 2 mL. Upon cooling
to -20 °C, pale yellow crystals of 7 were isolated (76 mg, 17%). Anal.
Calcd for C25H57N2Si2ClOW: C, 44.70; H, 8.58; N, 4.17. Found: C,
42.97; H, 8.24; N, 4.13.
10. (tBu3SiN)2(tBu3SiNH)WOnBu (8). A glass reaction vessel was
charged with 1-H (501 mg, 6.06 × 10-4 mol) followed by 30 mL of
THF, and the solution was stirred at 145 °C for 25 h followed by
removal of all volatiles. The residue was taken up in hexanes and
transferred into a frit assembly for workup. Four milliliters of
bistrimethylsilyl ether was vacuum transferred onto the remaining
material, and this suspension was heated to 70 °C for 1 h, over which
time all material dissolved. The solution was allowed to slowly cool
to 23 °C, and after 30 min, yellow crystals had formed. The flask was
cooled to 0 °C for an additional 30 min, and the crystals were collected
by filtration, yielding 280 mg 1-OnBu (51%).
Procedures. 1. [(tBu3SiNH)2WCl]2 (1). To a glass bomb reactor
t
containing NaW2Cl7(THF)5 (400 mg, 0.400 mmol) and Bu3SiNHLi
(400 mg, 1.81 mmol, 4.5 equiv) was transferred 10 mL of benzene via
vacuum transfer. The vessel warmed to room temperature and was
stirred at 23 °C until the green color had faded (∼55 min) and the
solution became brown. After removal of all volatiles, the remaining
solids were triturated with hexanes two times and filtered to remove
salt byproduct. The solution volume was reduced to 4 mL and cooled
to -78 °C, producing 250 mg orange-brown 1 (48%) which was
collected by filtration. Elemental analysis was not attempted, because
some solid-state decomposition (23 °C) was noted after a few days.
2. (tBu3SiN)2(tBu3SiNH)WH (2). To a glass bomb reactor containing
t
NaW2Cl7(THF)5 (6.01 g, 6.01 mmol) and Bu3SiNHLi (8.46 g, 38.2
mmol) was transferred 100 mL of benzene. The vessel warmed to 23
°C and was stirred at room temperature until the green color had faded
(∼45 min) and the solution became brown. All volatiles were removed
in vacuo, and fresh benzene (200 mL) was distilled into the reaction
mixture. The bomb was immersed in a 100 °C bath for 6 h, and the
volatiles were removed. The reaction mixture was taken up in hexane
and filtered and the white residue slurried in 30 mL THF at -78 °C
and filtered to separate 1-H (5.42 g) from the brown solution in 55%
isolated yield. In a separate experiment, all volatiles removed from the
reaction vessel were passed through three LN2 traps, and 0.78 equiv of
H2 (1H NMR: δ 4.46 ppm) per equiv of NaW2Cl7(THF)5 was collected
by Toepler pump. Anal. Calcd for C36H83N3Si3W: C, 52.34; H, 10.13;
N, 5.09. Found: C, 51.71; H, 10.53; N, 5.01.
3. (tBu3SiO)Tl. To a flask containing TlOEt (5.1 g, 22.6 mmol) and
tBu3SiOH (4.94 g, 22.7 mmol) was added 40 mL of THF via vacuum
transfer. The mixture was allowed to warm to 23 °C and stirred for an
additional 30 min. The mixture was evacuated to dryness, yielding an
opaque, gelatinous mass. The residue was triturated three times with
hexanes (30 mL) and dissolved in 40 mL of hexanes. The mixture was
filtered and the filtrate concentrated to 15 mL and cooled to -78 °C.
The white solid obtained upon cold filtration was dried under vacuum
11. (tBu3SiN)2W(neoHex)Cl (10). To a flask containing 1 (367 mg,
0.283 mmol) and 30 mL of benzene was added an excess of
3,3′-dimethyl-1-butene (2 mL, 16 mmol). The mixture was stirred for
16 h at 60 °C. The yellow-brown solution was evacuated to dryness,
and the residue was triturated three times with pentane (5 mL). The
residue was washed with pentane and filtered through Celite until a
colorless filtrate was obtained. The filtrate was evacuated to dryness
and afforded 10 as a viscous yellow-brown oil (393 mg, 95%). Waxy
crystals were obtained by dissolving the brown oil in a minimum of
1:5 Et2O/TMS2O at 23 °C. Decanting the mother liquor and drying the
1
at 23 °C to afford 7.43 g (78%) of (tBu3SiO)Tl. H NMR (C6D6): δ
1.21 (s); 13C{1H} NMR: δ 24.01 (CMe3), 31.45 (CH3).
Holmes
