Inorganic Chemistry
Article
(THF-d8): log D/m2 s−1 = −9.0. DOSY (C6D6): log D/m2 s−1 = −9.2.
UV/vis [THF; λmax, nm (ε, M−1 cm−1)]: 322 (42780), 447 (6245).
CV (THF): Ep = −1.78 V (qrev; oxidative follow-up wave at Ep =
−1.37 V).
(d, 3JHH = 8.6 Hz, 2H, H3,5), 6.84 (s, 1H, H9), 4.30 (pseudo sept, 3JHH
3
= 7.2 Hz, 1H, H14), 3.03 (pseudo sept, JHH = 6.6 Hz, 1H, H16), 1.43
(s, 9H, H13), 1.28 (d, 3JHH = 7.2 Hz, 3H, H15′), 1.22 (d, 3JHH = 6.6 Hz,
3
3
3H, H17), 1.07 (d, JHH = 6.6 Hz, 3H, H17′), 0.99 (d, JHH = 7.2 Hz,
3H, H15). 13C{1H} NMR (THF-d8): δ 163.6 (s, C11), 157.2 (s, C7),
149.1 (s, C4), 148.8 (s, C1), 138.6 (s, C8), 137.6 (s, C10), 126.5 (s,
C3,5), 123.6 (s, C2,6), 122.7 (s, C9), 35.2 (s, C12), 31.9 (s, C13), 30.7 (s,
C14), 26.5 (s, C16), 25.2 (s, C17′), 24.9 (s, C17), 22.7 (s, C15), 21.8 (s,
C15′). 15N{1H} NMR (THF-d8): δ 211.6 (s, Ni), 211.4 (s, Np). DOSY
(THF-d8): log D/m2 s−1 = −9.1. DOSY (C6D6): log D/m2 s−1 = −9.2.
UV/vis [THF; λmax, nm (ε, M−1 cm−1)]: 308 (28240), 450 (22720).
One-Electron Reduction of iPr21. To decamethylcobaltocene
CoCp*2 (2.2 mg, 6.7 × 10−3 mmol) suspended in CH2Cl2 (0.5 mL)
was added iPr21 (5 mg, 6.7 × 10−3 mmol) dissolved in CH2Cl2 (1 mL).
The solution was stirred for 5 h at room temperature and turned
orange. After removal of the solvent under reduced pressure, an orange
powder was obtained. Elem anal. Calcd for C62H90CoMoN4O2
(1078.30). ESI+-MS: m/z 329.1 (100%; [CoCp*2]+). IR (CsI): ν
̃
1
Final major product in solution, slow species. H NMR (C6D6): δ
2962 (m, CH), 1618 (m), 1587 (s), 1482 (m, Cp*), 1265 (m), 1167
(m), 1103 (m, Cp*), 1050 (m, Cp*), 1024 (m, Cp*), 874 (m, MoO),
801 (m, MoO) cm−1. EPR (298 K, CH2Cl2): g = 1.9439, A(95/97Mo) =
40 × 10−4 cm−1 (44 G). EPR (77 K, CH2Cl2): g1,2,3 = 1.9664, 1.9450,
1.9248. UV/vis [CH2Cl2; λmax, nm (ε, M−1 cm−1)]: 296 (47855), 344
(32810), 429 (6640).
7.32 (d, 3JHH = 8.4 Hz, 2H, H3b,5b), 6.95 (d, 3JHH = 8.4 Hz, 2H, H3a,5a),
6.95 (s, 1H, H7b), 6.90 (s, 1H, H7a), 6.77 (s, 1H, H9b), 6.53 (s, 1H
3
3
H9a), 6.25 (d, JHH = 8.3 Hz, 2H, H2b,6b), 6.18 (d, JHH = 8.4 Hz, 2H,
H
2a,6a), 5.09 (pseudo sept, 3JHH = 7.2 Hz, 1H, H14b), 3.45 (pseudo sept,
3JHH = 6.6 Hz, 1H, H16b), 3.10 (pseudo sept, 3JHH = 6.6 Hz, 1H, H16a),
Synthesis of iPr22. The dioxido complex iPr21 (50 mg, 0.069
mmol) was dissolved in THF (3 mL), and trimethylphosphane (1 M
in THF, 1.02 mL, 1.02 mmol) was added. After stirring for 3 days at
room temperature, volatiles were removed under reduced pressure to
give a yellow-green powder. Attempts to completely remove
phosphane oxide by recrystallization from petroleum ether, THF, or
toluene failed (ca. 0.16 equiv by 1H NMR). Yield: 40 mg (0.047 mmol,
68% calculated including 0.16 equiv of OPPh3). Elem anal. Calcd for
C45H67N4MoOP (806.97). FD-MS: m/z 806.5 (16%; [M]+). IR (CsI):
2.33 (pseudo sept, JHH = 7.2 Hz, 1H, H14a), 1.85 (d, JHH = 7.0 Hz,
3
3
3H, H15b), 1.71 (d, 3JHH = 7.0 Hz, 3H, H15b′), 1.43 (d, 3JHH = 7.1 Hz,
3H, H15a), 1.42 (d, JHH = 7.0 Hz, 3H, H17b), 1.42 (d, JHH = 7.0 Hz,
3H, H17b′), 1.40 (s, 9H, H13b), 1.29 (d, 3JHH = 7.0 Hz, 3H, H17a), 1.26
(d, 3JHH = 6.8 Hz, 3H, H15a′), 1.20 (d, 3JHH = 6.8 Hz, 3H, H17a′), 0.99
(s, 9H, H13a); the resonances of coordinated PPh3/OPPh3 are
indistinguishable from those of free PPh3/OPPh3. 13C NMR
(C6D6): δ 163.5 (s, C11a), 155.50 (s, C11b), 151.9 (s, C1a), 149.1 (s,
C1b), 147.8 (s, C4b), 146.6 (s, C4a), 136.9 (s, C10b), 136.9 (s, C8a),
135.8 (s, C8b), 138.3 (s, C10a), 159.1 (s, C7a), 156.8 (s, C7b), 125.9 (s,
3
3
̃
ν 2963 (s, CH), 1608 (m), 1580 (s), 1514 (m), 1163 (m), 1101 (m),
1
946 (m, MoO), 800 (br) cm−1. H NMR (THF-d8): δ 7.93 (s, 1H,
C
3a,5a) 124.9 (s, C3b,5b), 124.0 (s, C2b,6b), 124.1 (s, C2a,6a), 122.0 (s,
4
3
H7a), 7.73 (d, JPH = 0.96 Hz, 1H, H7b), 7.62 (d, JHH = 8.6 Hz, 2H,
H
H
C9a), 119.6 (s, C9b), 34.3 (s, C12b), 34.2 (s, C12a), 30.4 (s, C14b), 31.5
(s, C13b), 31.2 (s, C13a), 29.2 (s, C14a), 26.24 (s, C16a), 26.1 (s, C16b),
25.8 (s, C17b,17b′), 25.8 (s, C17a), 24.8 (s, C17a′), 23.8 (s C15b′), 23.5 (s,
C15a′), 23.4 (s, C15a), 23.3 (s C15b); the resonances of coordinated
PPh3/OPPh3 are indistinguisable from those of free PPh3/OPPh3.
DOSY (C6D6): log D/m2 s−1 = −9.3. UV/vis (petroleum ether 40−60
°C; λmax, nm): 329, 456.
2b,6b), 7.45 (d, 3JHH = 8.6 Hz, 2H, H3a,5a), 7.38 (d, 3JHH = 8.6 Hz, 2H,
3b,5b), 7.28 (d, 3JHH = 8.6 Hz, 2H, H2a,6a), 6.91 (s, 1H, H9a), 6.30 (br
s, 5JPH < 1 Hz, 1H, H9b), 3.30 (pseudo sept, 3JHH = 7.2 Hz, 1H, H14a),
3.00 (pseudo sept, 3JHH = 6.8 Hz, 1H, H16a), 2.81 (pseudo sept, 3JHH
=
6.8 Hz, 1H, H16b), 2.60 (pseudo sept, JHH = 7.2 Hz, 1H, H14b), 1.35
(s, 18H, H13a,13b), 1.19 (d, 3JHH = 7.1 Hz, 3H, H17a), 1.16 (d, 3JHH = 7.7
3
Hz, 3H, H15a), 1.14 (d, JHH = 7.7 Hz, 1H, H15b), 1.12 (d, JHH = 7.1
Hz, 3H, H17a′), 1.04 (d, 3JHH = 6.7 Hz, 1H, H17b), 1.01 (d, 3JHH = 6.8
Hz, 1H, H17b′), 0.83 (d, 3JHH = 7.1 Hz, 1H, H15b′), 0.73 (d, 3JHH = 7.1
Hz, 1H, H15a′), 0.71 (d, 2JPH = 8.4 Hz, 9H, PMe3). 1H NMR (residual
3
3
One-Electron Oxidation of iPr22. To iPr22 (2.5 mg, 0.003 mmol)
dissolved in THF (1 mL) was added AgSbF6 (1.1 mg, 0.003 mmol) in
THF (0.5 mL). The solution was filtered into an EPR tube. EPR (295
K, THF): g = 1.9667, A(95/97Mo) = 31 × 10−4 cm−1 (33.5 G), A(31P)
= 16.5 × 10−4 cm−1 (18.0 G) [70%]; g = 1.9455, A(95/97Mo) = 42.5 ×
10−4 cm−1 (47.0 G) [30%]. ESI+-MS: m/z 824.5 (58%; [iPr22 + O]+),
OPMe3): δ 1.34 (d, JHH = 13.0 Hz, OPMe3). 13C{1H} NMR (THF-
3
d8): δ 164.6 (s, C11a), 157.8 (s, C11b), 157.6 (s, C7a), 156.2 (s, C1a),
153.0 (s, C1b), 149.2 (s, C7b), 148.0 (s, C4b), 149.3 (s, C4a), 140.8 (s,
C8a), 138.6 (s, C8b), 136.9 (s, C10a), 134.1 (s, C10b), 126.5 (s, C3a,5a),
126.0 (s, C3b,5b), 123.6 (s, C2a,6a/2b,6b), 120.5 (s, C9a), 115.4 (s, C9b),
35.2 (s, C12a,12b), 31.9 (s, C13a,13b), 31.2 (s, C14b), 30.8 (s, C14a), 26.7 (s,
808.5 (74%; [iPr22]+), 732.4 (100%; [iPr22 − PMe3]+). IR (CsI): ν
̃
2963 (s, CH), 1660 (m), 1586 (s), 1511 (m), 1162 (m), 1102 (m),
1017 (s), 960 (m, MoO), 800 (br), 555 (s) cm−1. UV/vis (THF; λmax
nm (ε, M−1 cm−1)]: 328 (11325), 387 (9545), 468 (3510).
,
C
16a,16b), 26.1 (s, C17b′), 25.5 (s, C17a), 25.5 (s, C17b), 25.4 (s, C17a′),
24.3 (s, C15b), 23.0 (s, C15b′), 22.6 (s, C15a), 22.5 (s, C15a′), 18.3 (d,
3JHH = 69.0 Hz, PMe3). 15N{1H} NMR (THF-d8): δ 226.9 (s, Npb),
225.1 (s, Nib), 223.9 (s, Npa), 208.4 (s, Nia). 31P{1H} NMR: δ −1.70.
DOSY (THF-d8): log D/m2 s−1 = −9.1. DOSY (C6D6): log D/m2 s−1
= −9.1. UV/vis [THF; λmax, nm (ε, M−1 cm−1)]: 345 (28450), 425
(16250), 505 (sh, 2120), 685 (230). CV (THF): E1/2 = −0.40 V.
OAT with PPh3. The dioxido complex iPr21 (5.86 mg, 0.0078
mmol) was dissolved in C6D6 (0.6 mL), and triphenylphosphane (3.85
mg, 0.015 mmol, 1.92 equiv) was added. In other NMR experiments 5
RESULTS AND DISCUSSION
■
Ligand Synthesis. Initial attempts to prepare the
monosubstituted 1H-pyrrole-5-isopropyl-2-carbaldehyde via an
in situ Vilsmeier formylation of pyrrole followed by Friedel−
Crafts alkylation23,24 yielded a mixture of the 4- and 4,5-
substituted products. Hence, the synthesis of 1H-pyrrole-4,5-
diisopropyl-2-carbaldehyde was pursued, and optimized con-
ditions for its synthesis were developed. Subsequent Schiff base
condensation with 4-tert-butylaniline yielded ligand iPr2HL
(Scheme 1).
equiv of PPh3 was used. H and 31P NMR spectra were recorded
1
during the following days. At the final stage of the reaction, 2D NMR
1
1
1
spectra (1H1H COSY, H1H NOESY, H13C HSQC, H13C HMBC,
1H31P HMBC, DOSY) of the reaction mixture were acquired. For UV/
vis experiments, the dioxido complex iPr21 dissolved in petroleum
ether 40−60 °C (5.4 × 10−5 M, 3 mL) and triphenylphosphane
dissolved in petroleum ether 40−60 °C (1.9 × 10−4 M, 1.7 mL) were
combined (1:2 equiv). UV/vis spectra were recorded during the
following 35 h. In one experiment conducted in THF, a few crystals of
the decomposed complex iPr24·THF separated from the solution upon
standing for several weeks. iPr24. FD-MS: m/z 875.2 (100%; [M]+). IR
The 2,4,5-substitution pattern of 1H-pyrrole-4,5-diisopropyl-
2-carbaldehyde is proven by NMR spectroscopy as well as by
single-crystal XRD (Figure 1). The substituted pyrrole-2-
carbaldehyde forms centrosymmetric dimers with NH···O
hydrogen bonds in the solid state [N···O distance 2.862(2)
Å] similar to the imine chelate ligand H2HL.12 The bulky
chelate ligand iPr2HL is readily available from 1H-pyrrole-4,5-
diisopropyl-2-carbaldehyde and 4-tert-butylaniline using molec-
ular sieves. In addition to the increased steric bulk, the pyrrole
in iPr2HL is much more electron-rich than that in H2HL, which
is also reflected in the bathochromic shift of the pyrrole(π) →
̃
(CsI): ν 2966 (m, CH), 1585 (m), 1261 (s), 1099 (s, residual PO),
1020 (s, residual OPPh3), 970 (m, MoO), 953 (sh, MoO), 800 (br),
1
743 (m), 698 (m, MoO2Mo), 692 (sh, MoO2Mo) cm−1. H NMR
(THF-d8): δ 8.23 (s, 1H, H7), 7.58 (d, 3JHH = 8.5 Hz, 2H, H2,6), 7.52
12419
dx.doi.org/10.1021/ic501751p | Inorg. Chem. 2014, 53, 12416−12427