X.-Y. Yu, H. Sun, B. O. Patrick, B. R. James
FULL PAPER
1
H 6.7, N 6.1. IR: ν = 2103 cm–1. H NMR (C D ): δ = 6.75 (s, 4
˜
Cl(NHC)]2, NHC = IPr (3) and IMes (4), the bis-carbene
dihydride Rh(H)2Cl(IPr)2 (5), which was characterized crys-
tallographically, and the known IMes analogue 5Ј. The
mixed dihydride, Rh(H)2Cl(IPr)(IMes) was also charac-
terized in situ. Complex 5 undergoes reversible exchange
with D2 to form the dideuteride. Complexes 5 and 5Ј are
not effective precursors for catalytic hydrogenation of cyclo-
octene and 1-octene. Reactions of CO with the [RhCl-
(COE)(NHC)]2 or [Rh(H)2Cl(NHC)]2 complexes yield the
dicarbonyl compounds RhCl(CO)2(NHC), while the mono-
carbonyl complex RhCl(CO)(IPr)2 is prepared by reaction
of CO with the dihydride 5. The νCO data for these RhI
complexes support the premise that PPh3 is a better π-ac-
ceptor than the NHC ligands.
6
6
H, m-ArH), 6.11 (s, 2 H, NCH), 2.18 (s, 6 H, p-CH3), 2.13 (s, 12
H, o-CH3), –21.61 (br. s, 2 H, Rh-H) ppm. 13C{1H} NMR (C6D6):
δ = 138.3 (s, NC), 137.7 (s, p-ArC), 136.6 (s, o-ArC), 129.5 (s, m-
ArCH), 121.9 (s, NCH), 21.8 (s, CH3), 19.3 (s, CH3) ppm.
Synthesis of Rh(H)2Cl(IPr)2 (5): A yellow suspension of 1 (64 mg,
0.050 mmol) and IPr (39 mg, 0.100 mmol) in hexane (10 mL) was
purged with H2, with stirring for 2 h at room temperature. The
clear yellow solution was then concentrated to one third of the
volume; cooling the solution at 0 °C afforded a light yellow crystal-
line solid that was collected and dried in vacuo. Yield 81 mg (88%).
C54H74ClN4Rh (916.46): calcd. C 70.71, H 8.14, N 6.11; found C
1
70.6, H 8.3, N 6.2. IR: ν = 2125 cm–1. H NMR (C D ): δ = 7.26
˜
6
6
(t, J = 7 Hz, 4 H, p-ArH), 7.05 (d, J = 7 Hz, 8 H, m-ArH), 6.44 (s,
4 H, NCH), 3.04 [sept, J = 7 Hz, 8 H, CH(CH3)2], 1.10 [d, J =
6 Hz, 24 H, CH(CH3)2], 1.00 [d, J = 6 Hz, 24 H, CH(CH3)2], –22.90
(d, J = 33 Hz, 2 H, Rh-H) ppm. 13C{1H} NMR (C6D6): δ = 194.5
(d, JRh-C = 36 Hz, NCN), 146.8 (s, NC), 138.2 (s, iPr-C), 129.6 (s,
p-CH), 124.4 (s, m-CH), 123.9 (s, NCH), 28.9 [s, CH(CH3)2], 26.3
(s, CH3), 23.8 (s, CH3) ppm.
Experimental Section
General: All manipulations were performed under Ar, using stan-
dard Schlenk or glove-box techniques. Reagent grade solvents
(Fisher Scientific) were dried using standard procedures, and prior
to use were purged with a stream of Ar. Deuterated solvents (Cam-
bridge Isotope Laboratories) were similarly dried, and then distilled
under N2 prior to use. Common chemicals were obtained from
Fisher Scientific, and were used as received. The [RhCl(COE)-
(NHC)]2 complexes 1 and 2 (NHC = IPr, IMes, respectively),[15]
and RhCl(PPh3)3,[37] were synthesized according to the reported
procedures.
Synthesis of Rh(H)2Cl(IPr)(IMes) (5a): A yellow suspension of 1
(64 mg, 0.050 mmol) and IMes (30 mg, 0.100 mmol) in hexane
(10 mL) was purged with H2, with stirring for 6 h at room tempera-
ture. The yellow suspension was then filtered through Celite and
the solid obtained was washed with hexane (5 mL) followed by cold
Et2O (3 mL). The hexane filtrate was vacuumed to dryness to give
5 in ca. 25% yield, and the collected yellow solid was the known
Rh(H)2Cl(IMes)2 (5Ј).[18] The cold ether filtrate was vacuumed to
dryness to give a light yellow mixture of 5a and 5Ј. Yield of mix-
ture: 81 mg (25%). Data for 5a: IR: ν = 2094 cm–1. 1H NMR
˜
NMR spectra were recorded at room temperature (ca. 20 °C) with
Bruker AV 300 (300.0 MHz for H and 75.0 MHz for 13C{1H}) or
1
(C6D6): δ = 7.27 (t, J = 7 Hz, 2 H, p-ArH-IPr), 7.06 (d, J = 7 Hz,
4 H, m-ArH-IPr), 6.62 (s, 4 H, m-ArH-IMes), 6.54 (s, 2 H, NCH-
IPr), 6.08 (s, 2 H, NCH-IMes), 3.04 [sept, J = 7 Hz, 4 H, CH-
(CH3)2], 2.29 (s, 6 H, p-CH3), 2.11 (s, 12 H, o-CH3), 1.28 [d, J =
7 Hz, 12 H, CH(CH3)2], 1.05 [d, J = 7 Hz, 12 H, CH(CH3)2], –23.21
(d, J = 36 Hz, 2 H, Rh-H) ppm.
Bruker AV 400 (400.0 MHz for 1H, 61 MHz for 2D, and 100.6 MHz
for 13C{1H}) spectrometers. Shifts are reported relative to external
TMS; a residual protonated species in C6D6 (δ = 7.15 ppm) was
used as the internal reference for 1H data, with J values given in
Hz (s = singlet, d = doublet, t = triplet, sept = septet, br. = broad).
IR spectra (KBr) were recorded with ATI Mattson Genesis or
Bomem–Michelson MB-100 FT-IR spectrometers. Elemental
analyses were performed by Mr. M. Lakha of this department on
a Carlo Erba EA 1108 analyzer. GC analyses for product yields of
the catalytic hydrogenations were performed on a Hewlett–Packard
HP 5890, equipped with an FID and an HP-17 capillary column
(with pre-column).
Synthesis of RhCl(CO)2(IPr) (6): A yellow suspension of 1 (64 mg,
0.050 mmol) in hexane (5 mL) was purged with CO, with stirring
for 1 h at room temperature, and then the mixture was concentrated
to half the volume. The precipitated white solid was collected and
dried in vacuo. Yield 56 mg (96%). C29H36ClN2O2Rh (582.15):
calcd. C 59.78, H 6.23, N 4.81; found C 60.1, H 6.4, N 4.6. IR: ν
˜
= 2073, 1990 cm–1. H NMR (C6D6): δ = 7.20 (t, J = 7 Hz, 2 H,
1
p-ArH), 7.15 (d, J = 7 Hz, 4 H, m-ArH), 6.63 (s, 2 H, NCH), 3.14
[sept, J = 7 Hz, 4 H, CH(CH3)2], 1.72 (d, J = 7 Hz, 12 H, CH3),
0.96 (d, J = 7 Hz, 12 H, CH3) ppm. 13C{1H} NMR (C6D6): δ =
186.0 (d, JRh-C = 54 Hz, CO ?), 184.2 (d, JRh-C = 72 Hz, CO), 182.1
(d, JRh-C = 45 Hz, NCN ?), 146.7 (s, NC), 135.9 (s, iPr-C), 131.1
(s, p-CH), 125.3 (s, m-CH), 124.7 (s, NCH), 29.5 [s, CH(CH3)2],
26.9 (s, CH3), 23.4 (s, CH3) ppm.
Synthesis of [Rh(H)2Cl(IPr)]2 (3): A yellow suspension of 1 (64 mg,
0.050 mmol) in hexane (5 mL) was purged with H2, with stirring
for 2 h at room temperature, and then the mixture reduced to half
the volume under vacuum. The resulting yellowish suspension was
refrigerated and then, while cold, filtered through Celite. The col-
lected solid was dried in vacuo at room temperature. Yield 41 mg
(74%). C54H76Cl2N4Rh2·0.5C8H16 (1112.42): calcd. C 62.57, H
1
7.60, N 5.03; found C 62.4, H 7.6, N 4.8. IR: ν = 2124 cm–1. H
˜
Synthesis of RhCl(CO)2(IMes) (7): This complex was prepared in
a manner analogous to that described for 6 but using 2 as precursor
(58 mg, 0.050 mmol). Yield 49 mg (98%). C23H24ClN2O2Rh
NMR (C6D6): δ = 7.23 (t, J = 7 Hz, 2 H, p-ArH), 7.07 (d, J =
6 Hz, 4 H, m-ArH), 6.43 (s, 2 H, NCH), 2.92 [sept, J = 7 Hz, 4 H,
CH(CH3)2], 1.34 [d, J = 5 Hz, 12 H, CH(CH3)2], 1.02 [d, J = 5 Hz,
12 H, CH(CH3)2], –22.78 (d, J = 27 Hz, 2 H, Rh-H) ppm. 13C{1H}
NMR (C6D6): δ = 182.7 (d, JRh-C = 58 Hz, NCN), 147.8 (s, NC),
137.5 (s, iPr-C), 131.2 (s, p-CH), 126.6 (s, m-CH), 124.4 (s, NCH),
33.1 [s, CH(CH3)2], 27.0 (s, CH3), 24.4 (s, CH3) ppm.
(498.06): calcd. C 55.42, H 4.86, N 5.62; found C 55.3, H 5.0, N
1
5.7. IR: ν = 2070, 1990 cm–1. H NMR (C D ): δ = 6.76 (s, 4 H,
˜
6
6
ArH), 6.13 (s, 2 H, NCH), 2.25 (s, 12 H, o-CH3), 2.05 (s, 6 H, p-
CH3) ppm. 13C{1H} NMR (C6D6): δ = 186.0 (d, JRh-C = 54 Hz,
CO), 179.2 (d, JRh-C = 45 Hz, NCN), 139.8 (s, NC), 136.1 (s, p-
ArC), 135.9 (s, o-ArC), 129.4 (s, m-CH), 123.7 (s, NCH), 23.4 (s,
p-CH3), 19.0 (s, o-CH3) ppm.
[Rh(H)2Cl(IMes)]2 (4): This complex was prepared in a manner
analogous to that described for 3, but using 2 as the precursor
(58 mg, 0.050 mmol). Yield 36 mg (76%). C42H52Cl2N4Rh2·
0.5C8H16 (944.23): calcd. C 58.46, H 6.40, N 5.93; found C 58.5,
Synthesis of RhCl(CO)(IPr)2 (8): This complex was prepared in a
manner analogous to that described for 6 but using 5 as precursor
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Eur. J. Inorg. Chem. 2009, 1752–1758