Dinuclear Iron-Imide Cluster Core [Fe2(µ-NR)2]2+
p-TolNH2 (107 mg, 1.0 mmol) was added via syringe. The solution,
which developed a brown color within 2 min, was allowed to stir
for 12 h, after which time a significant quantity of purplish-black
precipitate was evident. The slurry was filtered, and the collected
material was washed with THF until the rinses were nearly colorless
(∼5 mL). The solid (260 mg) was recrystallized from 20 mL of
MeCN at -30 °C to afford microcystalline product, which was
isolated by filtration and washed with MeCN (1 mL) and Et2O (1
mL). Yield: 115 mg (32%). Anal. Calcd for C30H54Cl4Fe2N4: C,
49.75; H, 7.52; N, 7.74. Found: C, 49.58; H, 7.56; N, 7.50.
(n-Bu4N)2[Fe2(µ-NMes)2Cl4] ([n-Bu4N]23c). A mixture of 1 (968
mg, 2.0 mmol) and (n-Bu4N)Cl (282 mg, 2.0 mmol) in MeCN (30
mL) was stirred for 3 h to produce an orange-red solution. Neat
MesNH2 (0.282 mL, 2.0 mmol) was added via syringe, resulting
in a slow solution color change, first to light brown, then to dark
green, over the course of several hours. The solution was stirred
for 24 h, then treated with Et2O (15 mL), and cooled to -30 °C to
give large, dark green crystals, which were isolated by filtration,
rinsed with Et2O (3 × 2 mL), and dried in vacuo for 2 h (588 mg).
Concentration of the filtrate to ∼10 mL, addition of Et2O (5 mL),
and cooling to -30 °C produced a second crop of crystalline product
(160 mg). Total yield: 748 mg (74%). Anal. Calcd for C50H94Cl4-
Fe2N4: C, 59.77; H, 9.43; N, 5.58. Found: C, 59.78; H, 10.08; N,
5.44.
reduction (to 2 mL) and further diffusion of Et2O at -30 °C for 5
d (33 mg). Total yield: 107 mg (81%). Anal. Calcd for C24H58-
Cl4Fe2N4: C, 43.90; H, 8.91; N, 8.54. Found: C, 43.95; H, 8.86;
N, 8.45.
Fe2(µ-NtBu)2Cl2(NH2 Bu)2 (9). A dark red solution of 1 (1.937
t
g, 4.0 mmol) in THF (30 mL) was treated with neat tBuNH2 (1.68
mL, 16 mmol), which deepened the solution color to red-brown
within minutes. The reaction was stirred for 9 h, evaporated in
vacuo, and washed with n-pentane (40 mL) to afford a rust-colored
solid. This material was dissolved in THF (30 mL), charged with
n-pentane (15 mL), concentrated, and held at -30 °C for 2 d to
yield microcrystalline 9, which was isolated by filtration and dried
in vacuo (218 mg). A second crop of 9 was obtained by volume
reduction of the filtrate to incipient crystallization, cooling to -30
°C, and diffusion of pentane (294 mg). Total yield: 512 mg (54%).
Anal. Calcd for C16H40Cl2Fe2N4: C, 40.79; H, 8.56; N, 11.89.
Found: C, 41.00; H, 8.08; N, 11.51.
Fe2(µ-NtBu)2Cl2(DMAP)2 (10). A solution of 4-dimethylami-
nopyridine (DMAP, 0.049 g, 0.40 mmol) in THF (2 mL) was added
to a solution of 9 (0.094 g, 0.20 mmol) in THF (10 mL), and the
resulting solution was stirred for 24 h. The orange-black solution
was filtered to isolate crude 10, dried in vacuo to ensure complete
removal of THF solvent, then washed with n-pentane (20 mL), and
dried again. Diffraction-quality crystals of 10‚2PhMe were grown
by storage of a concentrated toluene solution of this solid at -30
°C; as discussed in the main text, efforts to obtain analytically pure
10 in bulk were unsuccessful.
Fe4(µ3-NtBu)4Cl4 (6). To a stirred, dark red solution of 1 (1.937
t
g, 4.0 mmol) in THF (25 mL) was added neat BuNH2 (0.42 mL,
4.0 mmol) via gastight syringe. Within 15 min, the solution color
began to change to dark brown. The reaction was allowed to stir at
room temperature for 6 h, then filtered, evaporated to a dark brown
glass (∼6 h in vacuo), and extracted with 40 mL of n-pentane (in
portions; to minimize the dissolution of contaminating species, the
extraction was not exhaustive, and the final pentane wash was still
dark in color). The dark brown filtrate was evaporated to dryness
(∼130 mg), redissolved in benzene (10 mL), filtered, and concen-
trated to ∼4 mL. Evaporative diffusion with HMDS at room
temperature for 2 d afforded crystals of 6, which were isolated,
rinsed with cold HMDS (1 mL), and dried under nitrogen flow for
20 min. Yield: 78 mg (12%). Compound identity was established
by 1H NMR and crystallographic analysis.2 Anal. Calcd for C16H36-
Cl4Fe4N4: C, 29.58; H, 5.58; N, 8.62. Found: C, 29.90; H, 5.82;
N, 8.29. LDI-MS: 649.1 (Theory: 649.7).
Fe2(µ-NtBu)2Cl2(PEt3)2 (11). To an orange-black solution of 9
(190 mg, 0.40 mmol) in MeCN (8 mL) was added PEt3 (0.472
mL, 3.2 mmol), causing an immediate color change to reddish-
purple. The solution was stored at -30 °C for 3 d and then filtered
to isolate crystalline 11 as very long black needles. Yield: 170 mg
(76%). Anal. Calcd for C20H48Cl2Fe2N2P2: C, 42.81; H, 8.62; N,
4.99. Found: C, 42.47; H, 8.32; N, 5.05.
t
Fe2(µ-NPh)2Cl2(NH2 Bu)2 (12). Neat PhNH2 (0.182 mL, 2.0
mmol) was added to a solution of 9 (0.471 g, 1.0 mmol) in THF
(10 mL), instantly changing the solution color to brown-purple.
The solution was stirred for 4 h and then concentrated in vacuo to
∼6 mL. n-Pentane was diffused into the solution at -30 °C over
several days to yield a purple microcrystalline product, which was
collected by filtration, washed with n-pentane (3 × 2 mL), and
dried in vacuo for 4 h (300 mg). A second crop (47 mg) was
obtained by concentrating the filtrate to ∼3 mL and diffusing
n-pentane into this solution at -30 °C. Total yield: 347 mg (68%).
Anal. Calcd for C20H32Cl2Fe2N4: C, 47.00; H, 6.31; N, 10.96.
Found: C, 47.18; H, 6.03; N, 10.89.
GC Analysis of Benzylamine Protolysis. A solution of 1 (10
mg, 0.018 mmol) in MeCN (1 mL) was reacted with PhCH2NH2
(1.9 µL, 0.018 mmol) under pure N2 atmosphere. After 20 h, the
black-brown solution was opened to air and treated with 6 M HCl
(∼2-3 mL) to liberate iron-bound nitrogen ligands. The acidified
solution was stirred for 1 h and then extracted with CH2Cl2 (3 ×
1 mL). The organic fraction was dried over anhydrous Na2SO4 and
then analyzed by GC (vide infra) to reveal benzaldehyde (16% yield
based on PhCH2NH2) as the principal product. A further partition
with CH2Cl2 (2 mL) showed no remaining products extractable from
the acidic phase. The aqueous fraction was then cooled in an ice
bath, treated with Na2EDTA‚2H2O (50 mg),22 made basic to litmus
with 20% NaOH, stirred vigorously for 2 h at room temperature,
and extracted with CH2Cl2 (3 × 1 mL). The organic fraction was
dried over anhydrous Na2SO4 and then analyzed by GC (vide infra)
to reveal PhCH2NH2 (18% recovery) as the predominant extracted
component.
[Fe3(µ-Cl)4(DME)5][Fe4(µ3-NtBu)4Cl4]2 ([Fe3(µ-Cl)4(DME)5]-
[7]2). To a stirred, dark red solution of 1 (1.937 g, 4.0 mmol) in
THF (25 mL) was added a solution of tBuNH2 (0.293 g, 4.0 mmol)
in THF (5 mL), followed by an additional 20 mL of THF. The
dark red solution was heated to 80 °C for 12 h, then allowed to
cool to room temperature, filtered, and evaporated to dryness in
vacuo. The residue was rinsed with n-pentane until the washings
were clear, and the resulting gray-black solid was dried under
nitrogen flow for 20 min. This solid contained monoanionic cluster
1
7 as the only significant Fe-NR product by H NMR assay.14
Although we were unable to obtain analytically pure 7 from this
system, storage of a concentrated DME solution of this material at
-30 °C provided single crystals of [Fe3(µ-Cl)4(DME)5][7]2‚DME
for diffraction analysis.13
(Et4N)2[Fe2(µ-NtBu)2Cl4] ([Et4N]28). A solution of (Et4N)Cl (66
mg, 0.4 mmol) in MeCN (4 mL) was added to a stirred, dark
orange-black solution of 9 (94 mg, 0.2 mmol) in MeCN (10 mL).
After 2 h, the color had changed to a deeper brown. The solution
was evaporated to dryness in vacuo (3 h), and the residue was
dissolved in a minimal amount of MeCN (4 mL). Diffusion of Et2O
into this solution at -30 °C for 5 d gave microcrystalline [Et4N]8
(74 mg). A second crop of crystals was obtained by volume
Inorganic Chemistry, Vol. 46, No. 4, 2007 1079