Efficient Hydrogenation of Ketones
FULL PAPER
2.50–2.38 (m, 2H, PCH
7.82 Hz, 6H, PCH
(CH3)2), 1.40 (dd, 3J
6H, PCH
(CH3)2), 1.22 (dd, 3J(H,P)=15.9 Hz, 3J
PCH (H,H)=6.7 Hz, 6H, PCH-
(CH3)2), 0.95 (dd, 3J(H,P)=13.4 Hz, 3J
G
E
E
ACHTUGTNRNENUG(H,H)=6.8 Hz, 6H, PCHACHTUGNTREN(NUGN CH3)2); the two hydrogen atoms bound to the
G
G
E
metal center are not observable at room temperature; 1H NMR
N
G
E
(500 MHz, [D8]toluene, ꢀ608C): d=ꢀ6.43 (td, 2J
ACHTUNGTRENNUNG
G
E
G
(H,H)=13.7 Hz, 1H, Fe(CO)HH), ꢀ18.65 ppm (td, 2J
ACHTUNGTRENNUNG
2
A
E
(H,H)=13.7 Hz, 1H, Fe(CO)HH); 1H NMR (500 MHz, [D8]toluene,
ACHTUNGTRENNUNG
908C): d=ꢀ12.95 ppm (br, 2H, Fe(CO)HH); 31P{1H} NMR (162 MHz,
Fe-H); IR (thin film): n˜ =2318 (m, nBH), 2269 (m, nBH), 2028 (br, nBH),
1916 (s, nCO), 1052 cmꢀ1 (s, dBH3); ESI-MS (pos.): m/z (%): 424.13 (50)
[M+ꢀBH4]; elemental analysis calcd (%) for C20H40BFeNOP2: C 54.70,
H 9.18, N 3.19; found: C 54.27, H 9.14, N 3.26.
C6D6, 258C): d=116.86 ppm (s); 13C{1H} NMR (101 MHz, C6D6, 258C):
d= 223.0 (t, 2J(C,P)=14.9 Hz, Fe-CO), 162.6 (vt, 2J
ACTHNUGTRENNUGN ACHTUNGTRENNNUG
3
dine-C2,6), 131.3 (s, pyridine-C4), 117.7 (vt, J
42.5 (vt, 1J
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG[(iPr-PNP)FeHACHTUNGTRENNUNG(BH4)] (2): FeBr2 (21.6 mg, 0.10 mmol) and iPr-PNP
A
E
N
ACHTUNGTRENNUNG
(34.0 mg, 0.10 mmol) were dissolved in a mixture of MeCN (3 mL) and
EtOH (3 mL), to give a pale red-orange solution. After 30 min, NaBH4
(15.0 mg, 0.40 mmol) was added in one portion. Gas evolution took place
and the color of the solution turned immediately to deep red. After 2 h
of stirring at ambient temperature the solvent was removed in vacuo.
Pentane (10 mL) was added to the residue, the mixture was filtered and
the solvent of the resulting filtrate was removed in vacuo, to yield pure 2
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
CO)Br] (20.0 mg, 0.04 mmol) and TlPF6 (14.0 mg, 0.04 mmol) were sus-
pended in CD3OD (1 mL). A white precipitate of TlBr was formed im-
mediately. After 30 min the mixture was filtered through a syringe filter
to give an orange solution. The coordinated CD3OD is labile and maybe
removed from the iron center in vacuo or displaced by addition of other
donor ligands. In addition, complex 5-CD3OD slowly decomposes in alco-
holic solvents as described below. For this reason complex 5-CD3OD was
characterized in solution by multinuclear NMR spectroscopy. 1H NMR
1
as a dark red solid (34.3 mg, 83%). H NMR (400 MHz, C6D6, 258C): d=
3
3
6.41 (t, J
pyridine-H3,5), 4.95 (brd, 2H, FeH2BH2), 3.07–2.85 (m, 4H+2H,
CH2PiPr2 + PCH(CH3)2), 2.25–2.10 (m, 2H, PCH(CH3)2), 1.40–1.24 (m,
18H, PCH (H,H)=6.8 Hz, 6H,
(CH3)2), 1.09 (dd, 3J(H,P)=13.1 Hz, 3J
PCH (H,P)=56.3 Hz,
ACHTUNGTRENNUNG(H,H)=7.4 Hz, 1H, pyridine-H4), 6.18 (d, 2H, JACHTUTGNREN(NUGN H,H)=7.4 Hz,
A
ACHTUNGTRENNUNG
(500 MHz, CD3OD, 258C): d=7.77 (t, 3J
H4), 7.50 (d, 3J(H,H)=7.7 Hz, 2H, pyridine-H3,5), 3.82 (dvt, 2J
17.3 Hz, 2J(H,P)=5.0 Hz, 2H, CHHPiPr2), 3.71 (dvt, 2J
(H,H)=17.3 Hz,
2J
(H,P)=3.4 Hz, 2H, CHHPiPr2), 2.52–2.40 (m, 4H, PCH(CH3)2), 1.49
(dd, 3J(H,P)=14.1 Hz, 3J (CH3)2), 1.43 (dd, 3J-
(H,H)=7.2 Hz, 6H, PCH
(H,P)=13.4 Hz, 3J (CH3)2), 1.18 (dd, 3J
(H,H)=7.1 Hz, 6H, PCH (H,P)=
15.9 Hz, 3J (CH3)2), 0.88 (dd, 3J
(H,H)=7.0 Hz, 6H, PCH (H,P)=14.1 Hz,
3J
(H,H)=6.9 Hz, 6H, PCH (H,P)=54.2 Hz,
(CH3)2), ꢀ25.65 ppm (t, 2J
1H, Fe-H); 1H{31P} NMR (500 MHz, CD3OD, 258C): d=7.80 (t, 3J-
(H,H)=7.7 Hz, 2H, pyridine-H4), 7.53 (d, 3J
(H,H)=7.7 Hz, 2H, pyri-
(H,H)=7.7 Hz, 1H, pyridine-
(H,H)=
A
R
ACHTUNGTRENNUNG
(CH3)2), ꢀ9.63 (br, 1H, FeHHBH2), ꢀ18.18 (t, 2J
ACHTUNGTRENNUNG
N
ACHTUNGTRENNUNG
1H, Fe-H), ꢀ28.67 ppm (br, 1H, FeHHBH2); 31P{1H} NMR (162 MHz,
A
ACHTUNGTRENNUNG
C6D6, 258C): d=97.68 ppm (s); 13C{1H} NMR (101 MHz, C6D6, 258C)
A
ACHTUNGTRENNUNG
d=167.1 (t, 2J
(t, 3J
24.4 (t, 1J
(CH3)2), 19.3 (t, 2J
(s, PCH(CH3)2), 18.2 ppm (s, PCHACHTNUGTRENNUNG
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
A
E
N
ACHTUNGTRENNUNG
R
G
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
E
G
G
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
N
AHCTUNGTRENNUNG
nBHt), 2322 (s, nBHt), 1818 (br, nBHb), 1189 cmꢀ1 (s, dBH); ESI-MS (pos.): m/
A
ACHTUNGTRENNUNG
(%): 396.16 (100) [M+ꢀBH4]; elemental analysis calcd (%) for
2
2
z
dine-H3,5), 3.85 (d, J
17.6 Hz, 2H, CHHPiPr2), 2.54–2.42 (m, 4H, PCH
(H,H)=7.3 Hz, 6H, PCH (H,H)=7.1 Hz, 6H, PCH-
(CH3)2), 1.46 (d, 3J
(CH3)2), 1.20 (d, 3J (CH3)2), 0.91 (d, 3J
(H,H)=6.9 Hz, 6H, PCH (H,H)=
6.8 Hz, 6H, PCH
G
ACHTUNGTRENNUNG(H,H)=
C19H40BFeNP2: C 55.51, H 9.81, N 3.41; found: C 54.89, H 9.74, N 3.42.
AHCTUNGTRENNUNG
T
E
ACHTUNGTRENNUNG
trans-[(iPr-PNP)Fe(H)2(CO)] (4a) and cis-[(iPr-PNP)Fe(H)2(CO)] (4b):
[(iPr-PNP)FeH(CO)ACHTUNGTRENNUNG(BH4)] (1) (16.0 mg, 0.036 mmol) was dissolved in
R
A
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
C6D6 or [D8]toluene (0.5 mL) and PhNH2 (3.4 mg, 0.036 mmol) was
added. The reaction mixture was allowed to stand at ambient tempera-
ture for 5 d, during which the color of the solution became reddish-
brown. The solution contained a mixture of two complexes in approxi-
mately 1:1 ratio, which were identified as trans-[(iPr-PNP)Fe(H)2(CO)]
(4a) and cis-[(iPr-PNP)Fe(H)2(CO)] (4b). Both complexes are difficult
to manipulate and undergo decomposition in vacuo. All attempts to pre-
cipitate or crystallize either complex from the reaction mixture were to
no avail owing to their intrinsic solubility in common organic solvents.
For this reason both complexes were characterized in solution by multi-
(162 MHz, CD3OD, 258C): d=88.13 (s, P-Fe-P), ꢀ141.44 ppm (sept, 1J-
AHCTUNGTRENNUNG
(P,F)=707.7 Hz, PF6); ESI-MS (pos., CH3OH): m/z (%): 456.08 (5) [M+
], 452.15 (100) [{(iPr-PNP)FeH(CO)2}+, decomp prod.], 378.15 (25) [{iPr-
PNP+K}+, decomp prod.], 362.18 (30) [{iPr-PNP+Na}+, decomp prod.];
ESI-MS (neg., CH3OH): m/z (%): 144.84 (100) [PF6ꢀ].
A
N
U
(5-CD3CD2OD):
[(iPr-
PNP)Fe(H)(CO)Br] (20.0 mg, 0.04 mmol) and TlPF6 (14.0 mg,
0.04 mmol) were suspended in [D6]ethanol (1 mL). A white precipitate of
TlBr was formed immediately. After 30 min the mixture was filtered
1
nuclear NMR spectroscopy and assignments are based on H,31P-HMQC,
through
CD3CD2OD is less stable than 5-CD3OD and decomposes much faster.
1H NMR (500 MHz, [D6]ethanol, 258C): d=7.77 (d, 3J
(H,H)=7.1 Hz,
2H, pyridine-H4), 7.54 (d, 3J
(H,H)=7.1 Hz, 2H, pyridine-H3,5), 3.88 (d,
2J(H,H)=15. 4 Hz, 2H, CHHPiPr2), 3.72 (d, 2J
(H,H)=15.4 Hz, 2H,
CHHPiPr2), 2.56–2.40 (m, 4H, PCH (H,P)=
(CH3)2), 1.57 (dd, 3J
13.6 Hz,=7.0 Hz, 6H, PCH
(CH3)2), 1.44 (dd, 3J(H,P)=12.1 Hz, 3J-
(H,H)=6.6 Hz, 6H, PCH (H,H)=7.1 Hz, 6H,
(CH3)2), 1.19 (dd,=15.6, 3J
PCH (H,H)=8.4 Hz, 6H, PCH-
(CH3)2), 0.88 (dd, 3J(H,P)=16.0 Hz, 3J
(CH3)2), ꢀ25.59 ppm (t, 2J(H,P)=54.4 Hz, 1H, Fe-H); 31P{1H} NMR
(162 MHz, [D6]ethanol, 258C): d=85.88 (s, P-Fe-P), ꢀ141.31 ppm (sept,
a syringe filter to give an orange solution. Complex 5-
1H-COSY, 1H,13C-HSQC and 1H,13C-HMBC NMR. The IR spectrum of
the mixture measured as a thin film exhibits only one band for the CO
vibration. IR (thin film): n˜ =1870 cmꢀ1 (CO).
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
NMR data for trans-[(iPr-PNP)Fe(H)2(CO)] (4a): 1H NMR (400 MHz,
A
ACHTUNGTRENNUNG
ACTHNUTRGNEUNG
C6D6, 258C): d=6.58 (t, 3J(H,H)=7.5 Hz, 1H, pyridine-H4), 6.33 (d, 3J-
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(H,H)=7.5 Hz, 2H, pyridine-H3,5), 2.95 (br s, 4H, CH2PiPr2), 2.17–2.04
3
3
A
R
ACHTUNGTRENNUNG
(m, 4H, PCH
PCH
(CH3)2), 1.11 (dd, 3J
(CH3)2), ꢀ7.27 ppm (t, 2J
(162 MHz, C6D6, 258C): d=120.06 ppm (s); selectively decoupled 31P{1H}
NMR (162 MHz, C6D6, 258C): d=120.07 ppm (t, 2J
(P,H)=36.2 Hz);
13C{1H} NMR (101 MHz, C6D6, 258C): d=225.9 (t, 2J
(C,P)=27.0 Hz, Fe-
CO); 163.6 (vt, 2J
(C,P)=6.2 Hz, pyridine-C2,6), 132.0 (s, pyridine-C4),
117.9 (vt, 3J(C,P)=4.8 Hz, pyridine-C3,5), 39.2 (vt, 1J
(C,P)=7.1 Hz,
CH2PiPr2), 26.6 (vt, 1J
(C,P)=10.9 Hz, PCH(CH3)2), 19.2 (s, PCH(CH3)2),
18.2 ppm (s, PCH(CH3)2).
NMR data for cis-[(iPr-PNP)Fe(H)2(CO)] (4b): 1H NMR (400 MHz,
C6D6, 258C): d=6.64 (t, 3J(H,H)=7.5 Hz, 1H, pyridine-H4), 6.42 (d, 3J-
(H,H)=7.5 Hz, 2H, pyridine-H3,5), 3.06–2.87 (superimposed, 4H,
CH2PiPr2), 2.31–2.16 (m, 2H, PCH(CH3)2), 1.99–1.85 (m, 2H, PCH-
(CH3)2), 1.32 (dd, 3J(H,P)=14.1 Hz, 3J
(H,H)=7.1 Hz, 6H, PCH(CH3)2),
(CH3)2), 0.96 ppm (dd, 3J(H,P)=13.6 Hz, 3J-
U
N
ACHTUNGTREN(NUGN H,H)=7.0 Hz, 12H,
A
R
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
1J
ACHTNUGTRNE(UGN P,F)=709.2 Hz, PF6); ESI-MS (pos., CH3CH2OH): m/z (%): 470.10
AHCTUNGTRENNUNG
(30) [M+], 452.15 (80) [{(iPr-PNP)FeH(CO)2}+, decomp prod.], 378.15
(100) [{iPr-PNP+K}+, decomp prod.]; ESI-MS (neg., CH3CH2OH):
144.84 (100) [PF6ꢀ].
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
When the above reaction was performed in EtOH, followed by evapora-
tion of the solvent, an orange brown solid was obtained, which was in-
soluble in non-polar organic solvents, but formed a yellow solution in
acetone. The 1H NMR showed a slightly shifted hydride signal at d=
ꢀ22.98 ppm together with the byproducts, which were also observed in
alcoholic solvents (see below). It is likely that the coordinated EtOH is
replaced by acetone under these conditions. Although free ethanol could
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
E
N
ACHTUNGTRENNUNG
1
1.29–1.18 (m, 12H, PCH
N
U
not be detected by H NMR spectroscopy, it is likely that it was removed
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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