P. I. Volkers, T. B. Rauchfuss, S. R. Wilson
FULL PAPER
(dd, 2 H, SCHa), 1.85 [m, 3 H, SCHb and (SCH2)2CH], 1.11 (t, 3
H, NCH2CH3) ppm. IR (MeOH): νCO = 2076 (vs), 2037 (vs), 1997
(vs), 1660 [m, C(O)N], 1563 (w, C–N stretch coupled to N–H defor-
mation), 1310 (w, C–N) cm–1. FD-MS: m/z = 456.9 (100) [M+],
428.9 (23) [M+ – CO], 400.8 (80%, M+ – 2 CO).
Experimental Section
General: Nylon syringe filters (0.2 µm) were acquired from
Nalgene. (Benzotriazol-1-yloxy)tris(dimethylamino)phosphonium
hexafluorophosphate (BOP) was acquired from ChemImpex Intl.
All other chemicals were acquired from Aldrich and used without
further purification. Solvents were dried by distillation or were dis-
pensed through two 1-m columns of activated alumina. Solvents
were further purified by degassing with a nitrogen purge. Reactions
were performed under purified nitrogen using either standard
Schlenk techniques or a glove box.
Fe2[(SCH2)2CHCONHCH2CO2tBu](CO)6: [BOP]PF6 (123 mg,
0.279 mmol) was added to a solution of Fe2(aspH)(CO)6 (120 mg,
0.279 mmol) in CH2Cl2 (5 mL) followed by the addition of Gly–
OtBu·HCl (42 mg, 0.211 mmol). Addition of NEtiPr2 (110 µL,
0.63 mmol) and stirring for 2 h produced a clear, dark red solution.
A concentrated CH2Cl2 solution was chromatographed on silica
gel, eluting with MeOH/CH2Cl2 (5:95, v:v). Evaporation of solvent
from the first red-orange band yielded a red-orange solid. Single
crystals were grown by layering a CH2Cl2 solution of the com-
pound with hexane followed by cooling to –20 °C. Yield: 38 mg
(28%). C16H17Fe2NO9S2 (543.14): calcd. C 35.38, H 3.15, N 2.58;
Dihydroasparagusic Acid [3-Mercapto-2-(mercaptomethyl)propanoic
Acid]: The free ligand was prepared based on the method of Singh
and Whitesides.[4] After concentrating the EtOAc extract, the di-
thiol was extracted into hexane and subsequent slow evaporation
of solvent yielded white crystals in 54% yield based on 2-(bro-
momethyl)propenoic acid.
1
found C 35.31, H 3.18, N 2.89. H NMR (500 MHz, CDCl3): δ =
5.81 (t, 1 H, NH), 3.84 (d, 2 H, NCH2), 2.71 (dd, 2 H, SCHH),
1.91 (m, 3 H, SCHH and CHCO), 1.46 [s, 9 H, C(CH3)3] ppm. IR
(MeOH): νCO = 2075 (m), 2036 (vs), 1997 (s), 1748 [w, C(O)-
OCMe3], 1668 [w, NC(O), amide I]; 1558 (w, C–N and N–H, amide
II) cm–1. FD-MS: m/z = 542.9 [M+], 487 [M+ – 2 CO].
Fe2(aspH)(CO)6: NEtiPr2 (921 µL, 5.29 mmol) was added to a
THF solution (20 mL) of 3-mercapto-2-(mercaptomethyl)propa-
noic acid (805 mg, 5.29 mmol). An additional 45 mL of THF was
added followed by Fe3(CO)12 (2.421 g, 4.81 mmol). Gas evolution
commenced immediately, and the color of the solution changed
from green-black to yellow-red, concomitant with the formation of
a yellow precipitate. The mixture was refluxed for 2.25 h. The re-
sulting dark red solution was filtered in air through a pad of Celite;
removal of the solvent gave a red oil. The product was extracted
into MeOH, and this extract was filtered again through Celite and
concentrated in vacuo. The residue was taken up in 15 mL of
CH2Cl2, treated with trifluoroacetic acid (600 µL, 8.08 mmol), and
chromatographed on silica gel, eluting with MeCN/CH2Cl2 (1:7,
v:v). The second red band was collected and concentrated in vacuo
Ni(aspH)(dppe): NaOMe (2 equiv.) in MeOH (40 mL) was added to
a mixture of NiCl2(dppe) (835 mg, 1.58 mmol) and aspH3 (240 mg,
1.58 mmol) in MeOH (40 mL). The immediately resulting dark red
solution yielded a bright orange precipitate after 1 h. After 4 h,
volatiles were removed in vacuo. The residue was washed with
3ϫ5 mL of MeOH to remove [Ni2(µ,µЈ-aspH)(dppe)2]2+ and other
impurities, leaving a bright orange powder. Yield: 577 mg (60%).
Single crystals were grown by layering a CH2Cl2 solution of the
compound with Et2O. C30H30NiO2P2S2 (607.34): calcd. C 59.33, H
4.98; found C 59.06, H 4.93. 1H NMR (500 MHz, CDCl3): δ =
10.30 (br. s, 1 H, COOH), 7.83–7.79 and 7.55–7.46 (m, 20 H,
PC6H5), 3.10 [quint, 1 H, (SCH2)2CH], 2.79–2.64 (m, 4 H, SCH2),
2.18 (d, 4 H, PCH2) ppm. 31P NMR (202 MHz, CDCl3): δ = 57.92
(s). FD-MS: m/z = 606.1 [M+ – H], 398 [dppe].
to give
a red crystalline product. Yield: 888 mg (43%).
C10H6Fe2O8S2 (429.98): calcd. C 27.93, H 1.41; found C 27.79, H
1
1.13. H NMR (500 MHz, CD3OD): δ = 2.92 (dd, 2 H, SCHH),
2.16 (br., 1 H, CHCOO), 1.81 (dd, 2 H, SCHH) ppm. The solid
product decomposed at 118 °C. IR (MeOH): νCO = 2076 (vs), 2037
(vs), 1997 (vs), 1730 (m, monomer), 1710 (m, dimer) cm–1. FD-
MS: m/z = 429.8 [M+], 373.8 [M+ – 2 CO].
[Ni2(aspH)(dppe)2](X)2 (X = Cl–, BPh4 ): NaOMe (2 equiv.) in
–
MeOH (5 mL) was added to a mixture of NiCl2(dppe) (200 mg,
0.379 mmol) and aspH3 (58 mg, 0.379 mmol) in MeOH (5 mL).
The solvent was removed in vacuo from the resulting clear, dark
red solution after 5.5 h. 31P NMR (202 MHz, CD3CN): δ = 59.889
[s, 1 P, NiCl2(dppe)], 57.738 [s, 1 P, Ni(aspH)(dppe)], 53.149 and
53.028 (d, 9 P, [Ni2(aspH)(dppe)2]2+), 50.470 and 50.349 (d, 9 P,
[Ni2(aspH)(dppe)2]2+) ppm. ESI-MS: m/z (%) = 1099.4 (100)
[{[Ni2(aspH)(dppe)2]Cl}+], 1063.1 (2) [Ni2(asp)(dppe)2]+, 532.3 (12)
[Ni2(aspH)(dppe)2]2+. The product was extracted into 5 mL of
MeOH, filtered through a pad of Celite, and treated with a solution
of NaBPh4 (140 mg, 0.40791 mmol) in MeOH (3 mL). The re-
sulting yellow-orange precipitate was washed with 15 mL MeOH
and dried in vacuo. Yield: 173 mg (27%). Single crystals were
grown from an acetone solution layered with methanol. 31P NMR
(202 MHz, CD3CN): δ = 57.46 (br. s) ppm. ESI-MS: m/z (%) =
Alternative Synthesis of Fe2(aspH)(CO)6: A mixture of Fe3(CO)12
(5.00 g, 9.92 mmol) and 3-mercapto-2-(mercaptomethyl)propanoic
acid (1.51 g, 9.92 mmol) in toluene (100 mL) was heated at 80 °C
for 30 min, resulting in a red solution and a fine orange precipitate.
The cooled reaction mixture was filtered through a pad of Celite,
and the filtrate was concentrated to dryness. The product was ex-
tracted with MeCN and was filtered through a nylon membrane
(0.2 µm). The solvent was removed to afford a red powder. Single
crystals were grown by cooling a concentrated CH2Cl2 solution to
–20 °C. Yield: 1.55 g (36%).
Fe2[(SCH2)2CHC(O)NHEt](CO)6: (Benzotriazol-1-yloxy)tris(di-
methylamino)phosphonium hexafluorophosphate (103 mg,
0.233 mmol) was added to a solution of Fe2(aspH)(CO)6 (100 mg,
0.233 mmol) in CHCl3 (5 mL) followed by H2Net (17 µL,
0.2114 mmol). After stirring for 2 min, the coupling reaction was
initiated upon addition of NEtiPr2 (55 µL, 0.317 mmol). The reac-
tion was monitored by TLC. After 21 h, the reaction solution was
concentrated in vacuo before being chromatographed on silica gel,
eluting with MeOH/CH2Cl2 (5:95, v:v). The first red band was
collected, and solvent removal by rotary evaporation yielded an
orange powder. Single crystals were grown from a MeOH solution
1063.3 (10) [Ni2(asp)(dppe)2]+, 532.0 (100) [Ni2(aspH)(dppe)2]2+
.
Ni3(asp)2(dppe)2: mixture of NiCl2(dppe) (100 mg,
A
0.18939 mmol) and aspH3 (28.8 mg, 0.18939 mmol) in MeCN
(15 mL) in air was treated with NEt3 (79.2 µL, 0.56817 mmol).
Upon standing for 3 h, a crystalline black precipitate began form-
ing. After 1 d, the supernatant was decanted. The extremely dark
that was cooled to –20 °C. Yield: 30 mg (31%). C12H11Fe2NO7S2 maroon crystalline solid was collected and dried in air. Yield: 59 mg
(457.05): calcd. C 31.54, H 2.43, N 3.06; found C 32.76, H 2.51, N
(74%). C60H58Ni3P4O4S4 (1271.35): calcd. C 56.68, H 4.60; found
C 56.41, H 4.48.
3.37. 1H NMR (400 MHz, CDCl3): δ = 3.21 (dq, 2 H, NCH2), 2.66
4798
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Eur. J. Inorg. Chem. 2006, 4793–4799