Inorganic Chemistry
Article
iPr Cbz
iPr
II
iPr
II
such example to be fully characterized. As X-ray structure
analysis left some ambiguity in distinguishing between the
(
PNP)CoH (3 -Co H). A solution of 2 -Co Cl (16 mg, 316
mmol, 1.0 equiv) in toluene (5 mL) was treated with a 1 M solution
of NaHBEt (316 μL, 316 mmol, 1.0 equiv) in toluene. The resulting
mixture was stirred for 2 h and filtrated using a syringe filter, and the
solvent was removed. After washing the residue with n-pentane (0.5
mL), the product was obtained as an orange solid (100 mg, 167 μmol,
3%). μeff = 2.36 μ . H NMR (600.13 MHz, C D , 295 K): δ [ppm]
48.7 (s, 4H, CH /CH(CH ) ), 37.1 (s, 4H, CH /CH(CH ) ), 26.2
(s, 2H, HCarb), 7.6 (bs, 12H, PCH(CH ) ), 2.4 (s, 18H,C(CH ) ), 0.1
II
I
observed Co −H and Co complexes, which result from halide
3
for hydride exchange, we have utilized DFT-assisted evaluation
iPr
of paramagnetic NMR spectra to establish the existence of 3 -
II
tBu
I
Co H and 4 -Co unambiguously. Apart from the expected
1
5
=
B
6
6
t
tBu
I
one-electron reactivity with BuCl and PhSSPh, 4 -Co also
2 3 2 2 3 2
reacted with dihydrogen under oxidative addition to its metal
3 2 3 3
tBu
III
13
center to form the dihydride complex 6 -Co (H) . The
(s, 2H, HCarb), −8.2 (bs, 12H, PCH(CH )). C NMR (150.90 MHz,
2
3
cleavage of H in the process was demonstrated in the rapid
C
(
8
6
D
6
, 295 K): δ [ppm] = 196.2 (s, CCarb‑4), 175.3 (s, CCarb‑6), 115.3
2
s, CCarb‑2), 88.2 (d, J = 130.9 Hz, CCarb‑3/5), 84.7 (s, CH(CH ) ),
3.0 (s, CH(CH ) ), 53.0 (d, J = 156.5 Hz, CCarb‑3/5), 50.8 (q, J =
exchange between the isotopomers H /HD/D upon exposure
3 2
2
2
to a mixture of H and D . Whereas the cobalt(III) dihydrido
3 2
2
2
tBu
III
124.8, 124.1 Hz, C(CH ) ), 15.3 (s, C(CH ) ), −30.4 (s, CH-
3
3
3 3
complex 6 -Co (H) showed little reactivity in the hydro-
2
−1
iPr
II
(CH
3
)
2
), −98.0 (s, CCarb‑1), −298.4 (s, CH
). IR: νCoH (KBr), cm
2
genation of alkenes, the cobalt(II) monohydride 3 -Co H
was found to readily catalyze the hydrogenation of
monosubstituted alkenes.
1
820. Anal. Calcd for C H CoNP : C, 68.21; H, 9.26; N, 2.34.
3
4
55
2
Found: C, 68.29; H, 9.16; N, 2.19.
tBu Cbz
PNP)CoCl (2 -Co Cl). A solution of tBu(cbzPNP)H (1tBu
1.0 g, 1.68 mol, 1.0 equiv) in toluene (5 mL) was treated with a
solution of LiHMDS (295 mg, 1.76 mmol, 1.05 equiv) in toluene (2
mL) and stirred for 15 min. Subsequently, solid [CoCl (thf)1.1] (185
tBu
II
(
)
(
EXPERIMENTAL SECTION
Computational Methods. All calculations were carried out using
■
2
3
3
density functional theory (DFT) employing the Gaussian 09
mg, 1.76 mmol, 1.05 equiv) was added in portions. After 4 h, the
reaction mixture was filtrated over Celite;, the solvent was removed
under vacuum, and the residue was washed with n-pentane to yield a
17a,34
package. As previously established,
the spin densities for the
NMR shift determinations were calculated with the B3LYP
3
5a,b
functional.
In the optimization and frequency calculation, the
crystalline, purple product (1.05 g, 1.52 mmol, 91%). μeff = 4.25 μ .
B
29
1
atoms C, H, N, and P were represented with the 6-311G(d,p) basis
set and Co, with the def2-tzvp basis set.
H NMR (600.13 MHz, C
CH ), 63.9 (s, 2H, HCarb), 24.4−17.4 (bs, 18H, PC(CH
2H, HCarb), 5.1 (s, 18H, C(CH ) ), 3.4 (bs, 18H, PC(CH ) ).
6
D
6
, 295 K): δ [ppm] = 138.1 (s, 4H,
30
)
3 3
), 16.8 (s,
2
1
3
The determination of a viable functional was conducted in two
C
3
3
3 3
separate steps. Initially, complex 4tBu-Co was computed with three
I
NMR (150.90 MHz, C D , 295 K): δ [ppm] = 797.6 (s), 526.6 (s),
6
6
3
5a,b
36
different well established functionals, B3LYP,
PBE0, and
464.8 (s), 411.7 (s), 349.0 (s), 285.9 (s), 195.4 (s), 119.5 (q, J =
124.5 Hz), −3.2 (d, J = 137.0 Hz), −56.2 (s), −64.3 (d, J = 140.5
Hz), −75.6 (s).
28
29
M06L as well as two basis sets for nonmetal atoms (6-311G(d,p)
and def2svp ). Subsequently, the obtained bond lengths of the donor
atoms to the metal center were compared with those of the obtained
molecular structure of 4 -Co (cf. Table S1). Additionally, the first
three intermediates of the HD exchange mechanism, 4 -Co ,
37
tBu Cbz
tBu
I
tBu
II
(
PNP)Co (4 -Co ). A solution of 2 -Co Cl (600 mg, 871
tBu
I
μmol, 1.0 equiv) in THF (10 mL) was cooled to −40 °C and slowly
added to a stirring mixture of Na/Hg (24 mg, 958 μmol, 1.1 equiv. Na
in 2.5 g of Hg). The mixture was allowed to warm to room
temperature and stirred overnight. After the organic phase was
extracted, the solvent was removed under vacuum. The residue was
absorbed with n-pentane and filtrated over Celite. After the solvent
was removed, the product was obtained as a green solid (495 mg, 757
μmol, 87%). μeff = 3.13 μ . H NMR (600.13 MHz, C D , 295 K): δ
[ppm] = 29.0 (s, 2H, HCarb), 17.3 (s, 4H, CH ), 13.0 (s, 2H, HCarb),
11.0 (s, 36H, PC(CH ) ), 1.9 (s, 18H, C(CH ) ). C NMR (150.90
MHz, C D , 295 K): δ [ppm] = 536.9 (s, PC(CH ) ), 487.0 (s,
6 6 3 3
tBu
I
tBu III
6
- (H) , and A-1, were computed, and the energies compared
28
(
cf. Figure S2). It turned out that the M06L functional in
29 30
combination with the 6-311G(d,p) and def2-tzvp (Co) basis sets
best represented the properties determined experimentally. Therefore,
this functional and these basis sets were utilized in geometry
optimizations for the HD exchange reaction sequence. Frequency
calculations were carried out with def2-tzvp for all atoms. The solvent
1
B
6
6
2
1
3
(
benzene) influence was considered by an additional SCRF
3 3 3 3
38
30
calculation within the PCM model, employing the def2-tzvp
basis set for all atoms. Energies are reported as Gibbs free energies,
including the gas-phase Gibbs contributions at 298 K and 8 atm.
CCarb‑2), 263.5 (s, PC(CH ) ), 224.0 (s, CCarb‑4), 200.3 (s, CCarb‑6),
3 3
69.8 (d, CCarb‑3), 58.6 (q, C(CH ) ), 54.4−53.7 (m, CCarb‑5, CCarb‑1),
3
3
−
1
−1
Vibrational modes below −100 cm were replaced by 100 cm as
4.8 (s, C(CH ) ), −521.9 (s, CH ). Anal. Calcd for C H CoNP : C,
3
3
2
38 62
2
39
40
suggested by Cramer and co-workers using the GoodVibes
69.81; H, 9.56; N, 2.14. Found: C, 69.53; H, 9.38; N, 2.22.
tBu Cbz
tBu
III
program developed by Funes-Ardoiz and Paton. All DFT-optimized
structures are provided in a separate XYZ file, and a detailed
(
PNP)Co(H) (6 -Co (H) ). In a high-pressure NMR tube, a
2
2
tBu
I
solution of 4 -Co (20 mg, 31 μmol) in benzene-d was exposed to a
6
dihydrogen atmosphere (8 bar) resulting in an instant color
conversion from a green to a dark green/brown solution and an
iPr Cbz
iPr
II
equilibrium of dihydride complex 6 -Co (H) to reagent 4 -CoI
tBu
III
tBu
Synthetic Procedures.
(
PNP)CoCl (2 -Co Cl). A solution of
2
iPr( PNP)H (1 ) (1.0 g, 1.85 mmol, 1.0 equiv) in toluene (10 mL)
was treated with a solution of LiHMDS (341 mg, 2.04 μmol, 1.1
equiv) in toluene (5 mL) and stirred for 15 min. Subsequently, solid
cbz
Pr
III
with a ratio of 4:1 at 295 K. Complex Co (H) is only stable under
2
1
hydrogen pressure. H NMR (600.13 MHz, C
D
, 295 K): δ [ppm] =
), 1.59 (s,
), −37.0 (t, 2H, JHP
). C NMR (150.90 MHz, C6D6, 295 K): δ [ppm]
6
6
8.31 (s, 2H, HCarb‑3), 7.43 (s, 2H, HCarb‑5), 3.43 (s, 4H, CH
18H, C(CH ), 1.13−1.11 (m, 36H, PC(CH
61.1 Hz, Co(H)
2
[
CoCl (thf) ] (412 mg, 2.04 μmol, 1.1 equiv) was added in portions.
3
)
3
3
)
3
=
2
1.1
1
3
After 4 h, the reaction mixture was filtrated over Celite; the solvent
was removed under vacuum, and the residue was washed with n-
2
= 147.5 (s, CCarb‑1), 138.3 (s, CCarb‑4), 125.9 (s, CCarb‑2), 122.7 (s,
CCarb‑5), 120.9 (s, CCarb‑6), 113.8 (s, CCarb‑3), 33.8 (t, J = 9.7 Hz,
PC(CH ) ), 33.5 (s, C(CH ) ), 31.3 (s, C(CH ) ), 28.3 (s,
pentane to yield a crystalline, purple product (1.03 g, 1.63 mmol,
1
8
8%). μeff = 4.50 μ . H NMR (600.13 MHz, toluene-d , 293 K): δ
B
8
3
3
3
3
3 3
[
ppm] = 333.4 (s, 4H, CH ), 197.1 (s, 2H, CH(CH ) ), 170.0 (s, 2H,
PC(CH ) ), 22.1 (s, CH ).
2
3
2
3 3 2
tBu Cbz
tBu
I
CH(CH ) ), 61.1 (s, 2H, HCarb), 18.1 (s, 2H, HCarb), 9.8 (s, 12H,
CH(CH ) ), 5.0 (s, 18H, C(CH ) ), −4.6 (s, 12H, CH(CH ) ).
NMR (150.90 MHz, toluene-d , 355 K): δ [ppm] = 842.8 (s, CH ),
(
PNP)CoCO (5 -Co CO). In a high-pressure NMR tube, a
3
2
1
3
tBu
I
C
solution of 4 -Co (31 mg, 47 μmol) in benzene-d was exposed to a
3
2
3
3
3
2
6
carbon monoxide atmosphere (5 bar). After removal of the solvent,
8
2
4
25.7 (s, CCarb), 401.1 (s, CCarb), 153.1 (s, CH(CH ) ), 116.5 (q, J =
the residue was washed with n-pentane. The product was obtained as
a light purple solid (23 mg, 34 μmol, 71%). H NMR (600.13 MHz,
3
2
1
1
C
23.0 Hz, C(CH ) ), 25.1 (s, CH(CH ) ), −12.5 (d, J = 136.5 Hz,
3
3
3 2
), −53.3 (s, C(CH ) ), −52.3 (d, J = 140.0 Hz, C
).
Carb‑3/5
C D , 295 K): δ [ppm] = 8.28 (d, J = 1.9 Hz, 2H, HCarb‑3), 7.31 (d, J
Carb‑3/5
3
3
6
6
Anal. Calcd for C H CoNP Cl: C, 64.50; H, 8.60; N, 2.21. Found:
C, 64.71; H, 8.10; N, 2.22.
= 1.9 Hz, 2H, HCarb‑5), 3.22−3.17 (m, 4H, CH ), 1.58 (s, 18H,
34
54
2
2
13
C(CH ) ) 1.39−1.32 (m, 36H, PC(CH ) ). C NMR (150.90 MHz,
3
3
,
3 3
H
Inorg. Chem. XXXX, XXX, XXX−XXX