2
M. Aydemir et al. / Inorganica Chimica Acta 398 (2013) 1–10
(cod]BF4, 7, [Rh((Ph2P)2N-C6H4-4-CH(CH3)2)(cod)]BF4, 8, [Rh((Ph2P)2-
N-C6H4-2-CH(CH3)2)2]BF4, 9, and [Rh((Ph2P)2N-C6H4-4-CH (CH3)2)2]-
BF4, 10 complexes and their application in the transfer hydrogenation
of ketones.
rel. to TMS, J Hz, in CDCl3): 138.74 (C-2), 132.54 (d, 2J = 4.3 Hz, o-
carbons of phenyls), 131.65 (p-carbons of phenyls), 131.33 (d,
1J = 10.1 Hz, i-carbons of phenyls), 129.01 (d, 3J = 3.0 Hz, m-carbons
of phenyls), 128.33 (C-3), 127.56 (C-5), 126.77 (C-4), 47.08 (-CH2-),
assignment was based on the 1H–13C HETCOR and 1H–1H COSY
spectra; 31P NMR (d in ppm rel. to H3PO4, in CDCl3): 70.07 (d,
2. Experimental
JRhP = 120.83 Hz); IR, (KBr):
m = 1436 (P-Ph), 1098, 1058 (BF4), 996
(P–N–P), cmÀ1; Anal. Calc. [C58H50N2S2P4Rh]BF4 (1152.78 g/mol):
C, 60.43; H, 4.37; N, 2.43; S, 5.56. Found: C, 60.34; H, 4.32; N,
2.37; S, 5.51%.
2.1. Materials and methods
Unless otherwise stated, all reactions were carried out under an
atmosphere of argon using conventional Schlenk glass-ware, sol-
vents were dried using established procedures and distilled under
argon immediately prior to use. Analytical grade and deuterated
solvents were purchased from Merck. PPh2Cl, 2-isopropylaniline,
4-isopropylaniline, furfurylamine and thiophene-2-methylamine
are purchased from Fluka and were used as received. The starting
2.4.2. Synthesis of [Rh((Ph2P)2NCH2-C4H3O)2]BF4, 6
To a solution of [Rh(cod)2]BF4 (0.04 g, 0.107 mmol) in tetrahy-
drofuran,
a solution (thf, 30 mL) of [(Ph2P)2NCH2-C4H3O], 2
(0.10 g, 0.215 mmol) was added. The resulting reaction mixture
was allowed to proceed with stirring at room temperature for
0.5 h. After this time, the solution was filtered and the solvent
evaporated under vacuum, the solid residue thus obtained was
washed with diethyl ether (3 Â 10 mL) and then dried under vac-
uum. Following recrystalization from diethylether/CH2Cl2, a yellow
crystalline powder was obtained. Yield 112 mg, 93.1%, m.p. = 214–
217 °C. 1H NMR (d in ppm rel. to TMS, J Hz, in CDCl3): 7.53–7.47 (m,
16H, o-protons of phenyls), 7.28–7.24 (m, 24H, m- and p- protons
of phenyls), 6.77 (br, 2H, H-5), 5.15 (br, 2H, H-4), 5.47 (br, 2H, H-3),
3.89 (br, 4H, –CH2–); 13C NMR (d in ppm rel. to TMS, J Hz, in CDCl3):
152.00 (br, C-2), 142.04 (C-5), 133.45 (br, i-carbons of phenyls),
132.47 (br, o-carbons of phenyls), 131.51 (br, p-carbons of phen-
yls), 128.95 (br, m-carbons of phenyls), 110.56 (C-4), 109.81 (C-
3), 43.23 (-CH2-), assignment was based on the 1H–13C HETCOR,
DEPT and 1H–1H COSY spectra; 31P NMR (d in ppm rel. to H3PO4,
materials [Rh(l-Cl)(cod)]2 [40] and [Rh(cod)2]BF4, [41,42] were
prepared according to the literature procedures. The IR spectra
were recorded on a Mattson 1000 ATI UNICAM FT-IR spectrometer
as KBr pellets. 1H (400.1 MHz), 13C NMR (100.6 MHz) and 31P-{1H}
NMR spectra (162.0 MHz) were recorded on a Bruker Avance 400
spectrometer, with d referenced to external TMS and 85% H3PO4,
respectively. Elemental analysis was carried out on a Fisons EA
1108 CHNS-O instrument. Melting points were recorded by Gal-
lenkamp Model apparatus with open capillaries.
2.2. GC analyses
GC analyses were performed on a Shimadzu 2010 Plus Gas
Chromatograph equipped with capillary column (5% biphenyl,
95% dimethylsiloxane) (30 m  0.32 mm  0.25
lm). The GC
in CDCl3): 68.95 (d, JRhP = 119.88 Hz); IR, (KBr):
m = 1437 (P-Ph),
parameters for transfer hydrogenation of ketones were as follows;
initial temperature, 110 °C; initial time, 1 min; solvent delay,
4.48 min; temperature ramp 80 °C/min; final temperature,
200 °C; final time, 21.13 min; injector port temperature, 200 °C;
1093, 1062 (BF4), 927 (P–N–P) cmÀ1; Anal. Calc. [C58H50N2O2P4-
Rh]BF4 (1120.65 g/mol): C, 62.16; H, 4.50; N, 2.50. Found: C,
62.03; H, 4.41; N, 2.45%.
detector temperature, 200 °C, injection volume, 2.0 lL.
2.3. General procedure for the transfer hydrogenation of ketones
2.4.3. Synthesis of [Rh((Ph2P)2N-C6H4-2-CH(CH3)2)(cod)]BF4, 7
To a solution of [Rh(cod)2]BF4 (0.08 g, 0.199 mmol) in 10 mL thf,
a solution (thf, 15 mL) of [(Ph2P)2N-C6H4-2-CH(CH3)2], 3 (0.10 g,
0.199 mmol) was added. The resulting reaction mixture was al-
lowed to proceed under stirring at room temperature for 15 min.
After this time, the solution was filtered off and the solvent evap-
orated under vacuum, the solid residue thus obtained was washed
with diethyl ether (3 Â 15 mL) and then dried under vacuum
(Scheme 2). Following recrystalization from diethylether/CH2Cl2,
a yellow crystalline powder was obtained (yield 142 mg, 89.2%),
m.p. = 178–182 °C. 1H NMR (d in ppm rel. to TMS, J Hz, in CDCl3):
7.75 (dd, 8H, 2J = 4.8 Hz and 2J = 6.2, o-protons of phenyls), 7.29–
7.69 (m, 12H, m- and p-protons of phenyls), 7.12 (d, 1H,
J = 7.8 Hz, H-3), 7.07 (dd, 1H, J = 7.2 and 7.8 Hz, H-4), 6.39 (dd,
1H, J = 6.8 and 8.40 Hz, H-5), 5.14 (d, 1H, J = 8.0 Hz, H-6), 5.32 (br,
4H, CH of cod), 3.27 (m, 1H, –CH(CH3)2– of aniline), 2.50 (br, 4H,
CH2 of cod), 1.60 (br, 4H, CH2 of cod), 0.56 (d, 6H, J = 5.1 Hz, –
CH(CH3)2– of aniline) ppm; 13C NMR (d in ppm rel. to TMS, J Hz,
in CDCl3): 146.77 (C-1), 136.95 (C-2), 134.00 (i-carbons of phenyls),
133.83 (o-carbons of phenyls), 132.85 (s, p-carbons of phenyls),
132.13 (C-6), 129.43 (m-carbons of phenyls), 128.65 (C-4), 127.38
(C-3), 125.21 (C-5), 103.25 (–CH– of cod), 29.75 (–CH2– of cod),
28.67 (–CH(CH3)2– of aniline), 23.60 (–CH(CH3)2– of aniline),
assignment was based on the 1H–13C HETCOR and 1H–1H COSY
spectra; 31P NMR (d in ppm rel. to H3PO4, in CDCl3): 60.85 (d,
Typical procedure for the catalytic hydrogen transfer reaction: a
solution of ruthenium complexes the [Rh((Ph2P)2NCH2-C4H3S)2]-
BF4, 5, [Rh((Ph2P)2NCH2-C4H3O)2]BF4, 6, Rh((Ph2P)2N-C6H4-2-
CH(CH3)2)(cod)]BF4, 7, [Rh((Ph2P)2N-C6H4-4-CH(CH3)2)(cod)]BF4,
8, [Rh((Ph2P)2N-C6H4-2-CH(CH3)2)2]BF4, 9 or [Rh((Ph2P)2N-C6H4-
4-CH(CH3)2)2]BF4, 10, NaOH (0.025 mmol) and the corresponding
ketone (0.5 mmol) in degassed iso-PrOH (5 mL) were refluxed until
the reactions were completed. After this period a sample of the
reaction mixture was taken off, diluted with acetone and analyzed
immediately by GC. Conversions obtained are related to the resid-
ual unreacted ketone.
2.4. Synthesis of rhodium complexes
2.4.1. Synthesis of [Rh((Ph2P)2NCH2-C4H3S)2]BF4, 5
A mixture of [Rh(cod)2]BF4 (0.04 g, 0.104 mmol) and [(Ph2P)2-
NCH2-C4H3S], 1 (0.10 g, 0.208 mmol) in 20 mL of thf was stirred
at room temperature for 0.5 h. The volume of the solvent was then
reduced to 0.5 mL before addition of diethyl ether (10 mL). The
precipitated product was filtered off and dried in vacuo yielding
5 as a yellow microcrystalline powder (Scheme 1). Yield 111 mg,
92.7%, m.p. 187 °C (dec.). 1H NMR (d in ppm rel. to TMS, J Hz, in
CDCl3): 7.53–7.51 (m, 16H, o-protons of phenyls), 7.27–7.22 (m,
24H, m- and p-protons of phenyls), 7.09 (d, 2H, 3J = 4.6 Hz, H-5),
6.50 (dd, 2H, 3J = 3.6 and 4.8 Hz, H-4), 6.32 (d, 2H, 3J = 2.8 Hz, H-
3), 4.15 (dd, 4H, 3J = 5.2 and 5.4 Hz, –CH2–); 13C NMR (d in ppm
JRhP = 140.94 Hz); IR, (KBr):
m = 1436 (P-Ph), 1095, 1053 (BF4), 852
(P–N–P) cmÀ1; Anal. Calc. [C41H43NP2Rh]BF4 (801.45 g/mol): C,
61.45; H, 5.41; N, 1.75. Found: C, 61.35; H, 5.36; N, 1.71%.