Rhodium(I) - (N-heterocyclic carbene) - Diphosphine complexes

Article abstract of DOI:10.1139/V09-118

Reactions of [RhCl(COE)(IPr)]₂ (1) and [RhCl(COE)(IMes)] ₂ (2) (COE = cyclooctene; IPr = N,N'-bis(2,6-diisopropylphenyl) imidazolin-2-ylidene; IMes = N,N'-bis(2,4,6-trmiethylphenyl)miidazomi-2-ylidene) with the diphosphines Ph₂P(CH₂)_nPPh ₂ and 1,2-bis(diphenylphosphino)benzene (dppbz) give the N-heterocyclic carbene (NHC)-diphosphine-rhodium(I) complexes: RhCl(NHC)[Ph ₂P(CH₂)_nPPh₂] [NHC = IPr, n =1(3); NHC = IMes, n =1 (4); NHC = IPr, n = 2 (5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4(8)] and RhCl(NHC)(dppbz) [NHC = IPr (9); NHC = IMes (10)]. All the complexes are characterized by ¹H, ³¹P{¹H}, and ¹³C{¹H} NMR spectroscopy, elemental analysis, and mass spectrometry. Complexes 3, 7, and 9 are also characterized crystallographically. In benzene solution, the complexes decompose in the presence of O₂ with formation of the diphosphine dioxide, whereas reaction with CO leads to replacement of the NHC ligand to give known carbonyl-diphosphine complexes.

Full text of DOI:10.1139/V09-118

1
248
Rhodium(I) – (N-heterocyclic carbene) – diphosphine
complexes
Hongsui Sun, Xiao-Yan Yu, Paolo Marcazzan, Brian O. Patrick, and Brian R. James
Abstract: Reactions of [RhCl(COE)(IPr)]2 (1) and [RhCl(COE)(IMes)]2 (2) (COE = cyclooctene; IPr = N,N’-bis(2,6-
diisopropylphenyl)imidazolin-2-ylidene; IMes = N,N’-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) with the diphosphines
Ph2P(CH2)nPPh2 and 1,2-bis(diphenylphosphino)benzene (dppbz) give the N-heterocyclic carbene (NHC) – diphosphine –
rhodium(I) complexes: RhCl(NHC)[Ph2P(CH2)nPPh2] [NHC = IPr, n = 1 (3); NHC = IMes, n = 1 (4); NHC = IPr, n = 2
(
5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4 (8)] and RhCl(NHC)(dppbz) [NHC = IPr (9);
1
31
1
13
1
NHC = IMes (10)]. All the complexes are characterized by H, P{ H}, and C{ H} NMR spectroscopy, elemental analy-
sis, and mass spectrometry. Complexes 3, 7, and 9 are also characterized crystallographically. In benzene solution, the
complexes decompose in the presence of O2 with formation of the diphosphine dioxide, whereas reaction with CO leads to
replacement of the NHC ligand to give known carbonyl–diphosphine complexes.
Key words: rhodium, N-heterocyclic carbenes, bis(diphenylphosphino) ligands, crystallography.
R e´ sum e´ : Les r e´ actions du [RhCl(COE)(IPr)]2 (1) et du [RhCl(COE)(IMes)]2 (2) [COE = cyclooct e` ne; IPr = N,N’-bis(2,6-
diisopropylph e´ nyl)imidazoline-2-ylid e` ne; IMes = N,N’-bis(2,4,6-trim e´ thylph e´ nyl)imidazoline-2-ylid e` ne] avec les diphosphi-
nes Ph2P(CH2)nPPh2 et 1,2-bis(diph e´ nylphosphino)benz e` ne (dppbz) conduisent a` la formation de complexes carb e` ne N-h e´ -
t e´ rocyclique (NHC) – diphosphine – rhodium(I): RhCl(NHC)[Ph2P(CH2)nPPh2] [NHC = IPr, n = 1 (3); NHC = IMes, n = 1
(
[
4); NHC = IPr, n = 2 (5); NHC = IMes, n = 2 (6); NHC = IPr, n = 4 (7); NHC = IMes, n = 4 (8)] et RhCl(NHC)(dppbz)
NHC = IPr (9); NHC = IMes (10)]. Tous les complexes ont e´ t e´ caract e´ ris e´ s par des analyses e´ l e´ mentaires, par spectrosco-
1
31
1
13
1
pie RMN du H, du P{ H} et du C{ H} et par spectrom e´ trie de masse. Les complexes 3, 7 et 9 ont aussi e´ t e´ caract e´ ri-
s e´ s par diffraction des rayons X. En solution dans le benz e` ne, les complexes se d e´ composent en pr e´ sence de O2 avec
formation d’oxyde de diphosphine, alors qu’une r e´ action avec le CO conduit au remplacement du ligand NHC pour
conduire aux complexes carbonyl–diphosphines connus.
Mots-cl e´ s : rhodium, carb e` nes N-h e´ t e´ rocycliques, ligands bis(diph e´ nylphosphino), cristallographie.
[
Traduit par la R e´ daction]
Introduction
A just-published special issue of European Journal of
nated NHC ligands with or without ancillary phosphine
ligands. We have shown that RhCl(NHC)(P–N) and cis-
RhCl(NHC)(PPh ) complexes oxidatively add O to gener-
3
2
2
Inorganic Chemistry demonstrates the growing interest in
transition-metal N-heterocyclic carbene (NHC) complexes.1
ate ‘‘standard’’ six-coordinate Rh(III)–peroxide species
see Scheme 1), where P–N = P,N-chelated o-(diphenyl-
(
Seven of the papers in the issue are concerned with Rh–
NHC chemistry, including one from our group, which de-
scribes reactions of [RhCl(COE)(NHC)] complexes with H2
5
phosphino)-N,N-dimethylaniline and NHC = IPr or IMes;
in an as yet unpublished work, our X-ray data for a five-
2
coordinate RhCl(IPr) (O ) are also consistent with a perox-
and with CO, where COE is cyclooctene and NHC is either
N,N’-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene (IPr) or
N,N’-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (IMes).2
More generally, studies on Rh–NHC systems often pertain
to comparisons with the chemistry and catalytic activity of
Rh – tertiary phosphine systems, i.e., with replacement of PR3
ligand(s) by NHC ligand(s) or use of mixed NHC – tertiary
phosphine species.2–5 Of prime interest to our group is the
2
2
6
ide. However, recent communications by Crudden and co-
workers3 report that RhCl(NHC) (O ) (NHC = IPr or
,4a
2
2
IMes) and RhCl(IMes)(PPh )(O ) are best described as
3
2
being Rh(I) singlet oxygen species. In efforts to understand
the nature of this important discrepancy, we decided to
synthesize Rh(I)–diphosphine–NHC complexes in the hope
that their reactivity toward O2 might prove helpful — a
hope that was not fulfilled!
interaction of O with Rh(I) complexes containing coordi-
2
Received 5 May 2009. Accepted 7 July 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 21 August 2009.
This tardy article is dedicated to Professor R.J. Puddephatt on the occasion of his 66th birthday (should have been submitted last year
for his 65th!), and in recognition of his contributions to the development of Canadian organometallic chemistry. This article is a belated
contribution to a Special Issue dedicated to Professor R.J. Puddephatt (Canadian Journal of Chemistry, January 2009).
1
H. Sun, X.-Y. Yu, P. Marcazzan, B.O. Patrick, and B.R. James. Department of Chemistry, The University of British Columbia,
Vancouver, BC V6T 1Z1, Canada.
1Corresponding author (e-mail: brj@chem.ubc.ca).
Can. J. Chem. 87: 1248–1254 (2009)
doi:10.1139/V09-118
Published by NRC Research Press

Sun et al.
1249
(
(
(
s, 2H, m-IMes), 6.95–7.09 (m, 12H, o-Ph (4H) + m-Ph
Experimental section
4H) + p-Ph (4H)?), 7.43–7.49 (m, 4H, m-Ph), 7.80–7.87
General procedures
13
m, 4H, o-Ph). C{H} NMR d: 19.45 (Me), 21.02 (Me),
All manipulations were performed under an atmosphere of
dry Ar using standard Schlenk techniques or in a glove box.
Solvents (Fisher Scientific) were dried using standard proce-
dures and, before use, were purged with a stream of Ar.
C D (Cambridge Isotope Laboratory) was distilled from Na
21.61 (Me), 51.11 (dd, JCP = 18, JCP = 23, PCH P), 122.93
(NCH), 122.97 (NCH), 128.99, 129.40, 130.31, 131.70,
131.92, 133.84 (d, JCP = 20, C P), 133.96 (d, J = 16,
C P), 135.35, 136.69, 136.98, 137.79, 138.07, 138.33,
138.54, 193.15 (ddd, J
Rh–C). P{H} NMR: AB portion of the P , P , Rh
(ABX) spin system simulated by the parameters dA = –
33.57, dB = –19.93, JAB = 107.0, JAX = 102.0, J
179.0 (see text). MS (EI) (m/z): 826 [M] , 790 [M –
HCl] , 303 [IMes – 1] . Anal. calcd. for C H N ClP Rh:
2
Ph
CP
Ph
6
6
CPA
= 10, JCPB = 47, JCRh = 129,
31
and stored under Ar. The diphosphines were used as received
from Strem Chemicals. Complexes [RhCl(COE)(IPr)] (1)
A B
2
and [RhCl(COE)(IMes)] (2) were prepared by our literature
=
BX
2
5
+
procedure. NMR spectra were recorded in C D at room
6
6
+
+
temperature (~20 8C) either on a Bruker AV 400 or AV 300
spectrometer, data being reported in ppm relative to TMS
46 46 2 2
C 66.81, H 5.61, N 3.39; found: C 66.8, H 5.6, N 3.3.
1
with the solvent signals as internal references ( H, d 7.16;
1
3
C, d 128.38); 31P{H} NMR shifts are relative to external
RhCl(IPr)(Ph PCH CH PPh ) (5)
2
2
2
2
8
5% H PO . J values are given in Hz (s = singlet, d =
3 4
Complex 5 was prepared using 50.0 mg (0.04 mmol) of 1,
doublet, t = triplet, spt = septet, m = multiplet, br = broad,
3
6
1.0 mg (0.08 mmol) of dppe, and 10 mL C H . Yield:
6
6
ps = pseudo); assignments were sometimes aided by the use
1
6 mg (91%). H NMR d: 0.40 (d, 6H, J = 6.8, Me), 0.90
1
3
1
1
13
1
of C{ H}-APT and H– C{ H}–HSQC experiments. Mass
spectra were obtained on a Kratos MS-50 spectrometer oper-
ating in the EI mode or on a Bruker Biflex IV spectrometer
operating with a MALDI ion source. Elemental analyses
were done on a Carlo Erba EA 1108 elemental analyzer.
(
(
d, 6H, J = 6.8, Me), 1.11 (d, 6H, J = 6.8, Me), 1.42–1.64
m, 4H, CH -dppe), 1.68 (d, 6H, J = 6.8, Me), 3.38 (m, 2H,
2
CHMe ), 3.81 (m, 2H, CHMe ), 6.81 (s, 2H, NCH), 6.87 (d,
2
2
2
H, J = 7.4, m-IPr), 6.93 (t, 4H, J = 7.0, m-Ph), 7.02 (t, 2H,
J = 7.0, p-Ph), 7.07–7.14 (m, 6H, o-Ph (4H) + p-Ph (2H)?),
.26 (t, 2H, J = 7.7, p-IPr), 7.35 (d, 2H, J = 7.6, m-IPr), 7.45
(t, 4H, J = 8.5, m-Ph), 7.73–7.78 (m, 4H, o-Ph).
7
RhCl(IPr)(Ph PCH PPh ) (3)
2
2
2
1
3
63.8 mg (0.05 mmol) of 1 and 38.5 mg (0.10 mmol) of
C{H} NMR d: 22.90, 24.34, 27.04, 27.17, 28.90, 29.71,
32.84 (d, JCP = 25, CH ), 33.17 (d, J = 23, CH ), 123.90,
dppm were dissolved in C H (6 mL). The resulting yellow
6
6
2
CP
2
solution became orange on being stirred at room temperature
for 5 h and was then concentrated to ~2 mL; hexane
124.86, 124.94, 127.83, 127.92, 127.98, 128.93, 129.16,
129.75, 133.64 (d, JCP = 12, C P), 135.16 (d, J = 12,
Ph
CP
(
~2 mL) was then added to precipitate the product, which
C P), 136.20, 136.60, 137.94, 138.25, 144.91, 149.61,
Ph
1
31
was filtered off and dried in vacuo. Yield: 85 mg (93%). H
NMR d: 0.53 (6H, d, J = 6.7, Me), 1.00 (6H, d, J = 6.7,
Me), 1.16 (6H, d, J = 6.7, Me), 1.89 (d, 6H, J = 6.7, Me),
196.72 (dd, J ~ 48, JCRh = 121). P{H} NMR d: 62.10
CP
2
1
2
1
(dd, J = 38, J
MS (EI) (m/z): 924 [M] , 536 [M – IPr] , 387 [IPr – 1] .
= 123), 65.84 ( J = 38, J
= 208).
PP
RhP
PP
RhP
+
+
+
3
2
.35 (br t, 2H, JHPA = 9.0, JHPB = 8.7, PCH P), 3.62 (spt,
Anal. calcd. for C H N ClP Rh: C 68.81, H 6.54, N 3.03;
found: C 68.5, H 6.4, N 3.0.
2
53 60
2
2
H, J = 6.7, CHMe ), 3.74 (spt, 2H, J = 6.7, CHMe ), 6.79
2
2
(
s, 2H, NCH), 6.88 (ps t, 6H, m-Ph (4H) + m-IPr (2H)?),
.96–6.99 (m, 8H, o-Ph (4H) + p-Ph (4H)?), 7.23 (t, 2H,
6
RhCl(IMes)(Ph PCH CH PPh ) (6)
Complex 6 was prepared using 75.0 mg (0.07 mmol) of 2,
2
2
2
2
3
JHH = 7.6, p-IPr), 7.30–7.37 (ps t, 6H, m-Ph (4H) + m-IPr
1
3
(
2H)?), 7.88–7.95 (m, 4H, o-Ph). C{H} NMR d: 22.87,
4.36, 26.87, 27.03, 29.09, 29.69, 48.29 (dd, JCP = 19,
JCP = 30, PCH P), 123.78, 124.52, 124.91, 128.05, 128.21,
54.0 mg (0.14 mmol) of dppe, and 10 mL C H . Yield:
6
6
1
2
98 mg (86%). H NMR d: 1.23–1.24 (m, 4H, CH -dppe),
2
2
1.61 (s, 6H, o-Me), 2.23 (s, 6H, o-Me), 2.79 (s, 6H, p-Me),
6.23 (s, 2H, NCH), 6.60 (s, 2H, m-IMes), 6.85 (s, 2H, m-
IMes), 6.97–7.11 and 7.04–7.08 (m, 12H, o-Ph (4H) + m-
Ph(4H) + p-Ph (4H)?), 7.51 (t, 4H, J = 8, m-Ph), 7.80 (m,
1
1
1
28.31, 128.88, 129.48, 129.77, 133.01 (d, JCP = 22, C P),
Ph
33.96 (d, JCP = 12, C P), 136.35, 136.65, 136.73, 137.02,
Ph
38.13, 144.89, 149.16, 195.45 (ddd, J
= 10, JCPB = 48,
CPA
3
1
13
JCRh = 128, Rh–C). P{H} NMR: AB portion of the PA,
4H, o-Ph). C{H} NMR d: 19.72 (Me), 21.56 (Me), 21.59
PB, Rh (ABX) spin system simulated by the parameters:
d = –35.68, d = –20.92, J = 101.0, J = 104.0, JBX
(Me), 32.05 (d, JCP = 25, CH ), 32.40 (d, J = 25, CH2),
2
CP
=
123.16 (NCH), 127.77, 127.86, 127.93, 128.87, 128.93,
129.01, 129.14, 130.39, 134.52 (d, JCP = 11, C P), 135.04
A
B
AB
AX
+
+
1
78.0 (see text). MS (EI) (m/z): 910 [M] , 387 [IPr – 1] .
Ph
Anal calcd. for C H N ClP Rh: C 68.55, H 6.42, N 3.08;
(d, JCP = 10, C P), 135.58, 137.57, 138.49, 138.53, 139.04,
52
58
2
2
Ph
found: C 68.8, H 6.4, N 2.9. X-ray quality crystals of 3 con-
taining 0.5 mol C H solvate were grown by layering a C H
solution of the compound with hexane.
139.36. AB portion of the P , P , Rh (ABX) spin system
A
B
6
6
6
6
simulated by the parameters dA = –64.26, dB = –64.96,
JAB = 36.6, J = 125.7, JBX = 205.7 (see text). MS (EI)
AX
+
+
+
(
m/z): 840 [M] , 804 [M – HCl] , 536 [M – IMes] , 303
[IMes – 1] . Anal. calcd. for C H N ClP Rh: C 67.13,
+
RhCl(IMes)(Ph PCH PPh ) (4)
2
2
2
47 48 2 2
The synthetic procedure for complexes 4–10 follows that
given for 3; here, 55.0 mg (0.05 mmol) of 2, 38.6 mg
H 5.76, N 3.33; found: C 67.0, H 5.8, N 3.23.
(
7
0.10 mmol) of dppm, and C H (5 mL) were used. Yield:
4 mg (89%). H NMR d: 1.73 (s, 6H, o-Me), 2.22 (s, 6H,
RhCl(IPr)[Ph2P(CH2)4PPh2] (7)
6
6
1
Complex 7 was prepared by using 63.8 mg (0.05 mmol)
of 1, 42.7 mg (0.10 mmol) of dppb, and 10 mL C H . Yield:
o-Me), 2.77 (s, 6H, p-Me), 3.40 (br t, 2H, JHPA = 9.1, JHPB
=
6
6
1
8
.8, PCH P), 6.25 (s, 2H, NCH), 6.60 (s, 2H, m-IMes), 6.88
76 mg (80%). H NMR d: 0.59 (br s, 6H, Me), 1.05 (m,
2
Published by NRC Research Press

1
250
Can. J. Chem. Vol. 87, 2009
2H, Me), 1.29 (br s, 6H, Me), 1.72 (br s, 4H, CH ), 1.85
6H, o-Me), 2.16 (s, 6H, o-Me), 2.74 (s, 6H, p-Me), 6.21 (s,
2H, NCH), 6.53 (s, 2H, m-IMes), 6.66–6.71 (m, 2H, o-
C H ), 6.74 (s, 2H, m-IMes), 6.95–7.04 (m, 12H, o-Ph
2
2
2
6
4
C{H} NMR d: 21.86 (Me), 23.89 (CH ), 23.97, 25.14,
(4H) + m-Ph (4H) + p-Ph (4H)), 7.25 (ps t, 2H, m-C H ),
2
6 4
2
5.58 (d, JCP = 20, PCH ), 27.34 (Me), 29.64 (Me), 29.73
7.67 (t, 4H, J = 8.6, m-Ph), 7.79 (m, 4H, o-Ph).
C{H} NMR d: 18.58, 20.79, 122.48, 127.09, 127.18,
2
13
(Me), 30.24 (CH ), 36.17 (d, J = 25, PCH ), 123.61,
2
CP
2
1
1
J
24.05, 125.20, 127.15 (d, JCP = 9, C P), 128.30, 128.69,
127.25, 127.34, 127.81, 127.96, 128.16, 128.37, 128.88 (d,
Ph
28.93, 129.03, 129.61, 131.42, 131.51, 131.58, 133.36 (d,
JCP = 3, C P?), 129.21 (d, J = 4, C P?), 129.65, 130.57,
Ph
CP
Ph
3
1
= 11, C P), 145.10, 150.55. P{H} NMR d: 13.85
130.70, 131.68, 131.83, 133.99, 134.11, 134.22, 134.32,
134.68, 136.38, 136.80, 137.53, 137.64, 138.02, 138.36,
CP
Ph
2J = 48, J
1
= 114), 48.94 (dd, J = 48, J
2
1
= 208).
(
PP
RhP
PP
RhP
+
31
MS (MALDI) (m/z): 952 [M] . Anal. calcd. for
192.32 (dd, JCP ~ 9, JCRh = 118, Rh–C). P{H} NMR: AB
C H ClN P Rh: C 69.30, H 6.77, N 2.94; found: C 69.5,
H 6.7, N 3.1. X-ray quality crystals of 7 were grown by
layering a C H solution of the compound with hexane.
portion of the P , P , Rh (ABX) spin system simulated by
5
5
64
2
2
A
B
the parameters dA = –66.77, dB = –67.33, JAB = 39.60,
JAX = 206.8, JBX = 125.6 (see text). MS (EI) (m/z): 888
6
6
+
+
[
M] , 303 [IMes – 1] . Anal. calcd. for C H ClN P Rh:
51 48 2 2
RhCl(IMes)[Ph P(CH ) PPh ] (8)
C 68.90, H 5.45, N 3.15; found: C 69.0, H 5.3, N 3.3.
2
2 4
2
The yellow complex 8 was obtained using 75.0 mg
(
1
(
(
(
(
0.07 mmol) of 2, 58.0 mg (0.14 mmol) of dppb, and
X-ray crystallographic analysis of complexes 3, 7, and 9
Measurements were made at 173.0(1) K on a Bruker X8
1
0 mL of benzene. Yield: 91 mg (77%). H NMR d: 1.91
s, 6H, o-Me), 2.09 (m, 4H, CH ), 2.26 (s, 6H, o-Me), 2.46
APEX diffractometer with graphite-monochromated Mo-Ka
2
br s, 4H, CH ), 2.83 (s, 6H, p-Me), 6.29 (s, 2H, NCH), 6.75
radiation (0.71 069 A˚ ). Data were collected and integrated
2
s, 2H, m-IMes), 6.90–7.11 (m, 14H, o-Ph (4H) + m-Ph
4H) + p-Ph (4H) + m-IMes (2H)?), 7.32 (t, 4H, J = 8, m-
7
using the Bruker SAINT software package and were cor-
rected for absorption effects using the multi-scan SADABS
1
3
Ph), 7.62 (m, 4H, o-Ph). C{H} NMR d: 19.90 (Me), 21.89
8
9
technique. All structures were solved by direct methods,
(
3
Me), 22.48 (Me) 24.08 (CH ), 32.74 (d, J = 18, P–CH ),
2
2
and refinements were performed using the SHELXTL pro-
2.99 (CH ), 122.03, 122.05, 123.11, 126.84 (d, J = 10,
10
2
CP
gram. All non-hydrogen atoms were refined anisotropically
C P), 127.64, 127.82, 129.13, 129.54 (d, J = 8, C P),
Ph
CP
Ph
and all H atoms were included in calculated positions but
not refined.
1
1
1
2
33.44, 134.39, 134.65, 134.92, 135.43, 135.68, 137.38,
3
1
37.41, 138.20, 138.60, 138.90, 144.34. P{H} NMR d:
2
1
2
1
2.38 (dd, J = 48, J
= 118), 54.04 ( J = 48, J
=
Crystal data for 3
PP
RhP
PP
RhP
+
07). MS (MALDI) (m/z): 868 [M] . Anal. calcd. for
C H N ClP RhÁ0.5C H , fw = 949.31, orange tablet,
52
58
2
2
6
6
C H ClN P Rh: C 67.70, H 6.04, N 3.23; found: C 67.9,
4
9
52
2
2
size 0.15 mm  0.20 mm  0.50 mm, monoclinic, space
H 6.0, N 3.3.
˚ ˚
group P 2 /n (No. 14), a = 11.0616(2) A, b = 21.9905(4) A,
1
˚
˚ 3
c = 20.1095(4) A, b = 90.774(1)8, V = 4891.2(2) A , Z = 4,
RhCl(IPr)(Ph PC H PPh ) (9)
–3
–1
2
6
4
2
Dcalcd = 1.291 g cm , m = 0.507 mm . F(000) = 1988.00,
The orange complex 9 was obtained using 55.0 mg
0.04 mmol) of 1 and 44.0 mg (0.10 mmol) of dppbz in
62 508 total reflections (11 674 independent of symmetry,
8726 for I > 2s(I)), 558 variables, residuals (refined on F ,
all data): R1 = 0.038, wR2 = 0.088.
2
(
5
mL of C H . Crystalline material contained 0.5 mol sol-
6
6
vate C H . Yield: 82 mg, 96%. Dried material was of the
6
6
1
formulation C H ClN P Rh. H NMR d: 0.70 (d, 6H, J =
Crystal data for 7
57
60
2 2
6
.7, Me), 0.90 (d, 6H, J = 6.7, Me), 1.10 (d, 6H, J = 6.7,
C H N ClP Rh, fw
=
952.33, orange plate, size
55
64
2
2
Me), 1.65 (d, 6H, J = 6.5, Me), 3.37 (m, 2H, CHMe ), 3.91
0.20 mm  0.25 mm  0.50 mm, monoclinic, space group
2
˚ ˚
P 2 /n (No. 14), a = 11.1595(6) A, b = 20.971(1) A, c =
1
(m, 2H, CHMe ), 6.72 (br s, 2H, NCH), 6.80–6.82 (m, 4H,
2
˚
˚ 3
20.938(1) A, b = 95.693(2)8, V = 4875.8(5) A , Z = 4,
m-Ph), 6.89–6.95 (br t, 6H, J ~ 6.5), 7.09–7.15 (m, 8H),
–3
–1
7
.25 (d, 2H, J = 7.6), 7.43 (ps t, 6H), 7.81 (m, 4H).
C{H} NMR d: 22.73, 24.27, 26.99, 27.14, 29.21, 29.62,
23.63, 124.99, 127.87, 127.97, 128.32, 128.51, 128.69,
Dcalcd = 1.299 g cm , m = 0.509 mm . F(000) = 2000.00,
1
3
69 860 total reflections (11 679 independent of symmetry,
9737 for I > 2s(I)), 558 variables; residuals (refined on F ,
all data): R1 = 0.037, wR2 = 0.067.
2
1
1
1
28.92, 129.10, 129.81, 133.10, 133.22, 135.13 (d, JCP
=
1, CC H P?), 137.10 (d, J = 45, C P?), 138.55, 139.57
6
4
CP
Ph
(
1
(
d, JCP = 36, C P?), 144.47, 149.05, 194.96 (ddd, J
=
Crystal data for 9
Ph
CPA
3
1
1, JCP = 48, J
= 122, Rh–C). P{H} NMR d: 65.96
C H N ClP RhÁ0.5C H , fw = 1011.32, orange plate,
B
CRh
57 60
2
2
6
6
2
1
2
1
dd, J = 39, J
= 205), 71.36 ( J = 39, J = 124).
size 0.04 mm  0.15 mm  0.25 mm, triclinic, space group
PP
RhP
PP
RhP
+
+
˚ ˚
MS (EI) (m/z): 972 [M] , 387 [IPr – 1] . Anal. calcd:
C 70.35, H 6.22, N 2.88; found: C 70.6, H 6.3, N 2.7. The
layering method given for complex 3 yielded X-ray quality
crystals of 9 again containing 0.5 mol C H solvate.
P-1 (No. 2), a = 12.6856(8) A, b = 17.438(1) A, c =
24.693(2) A˚ , a = 80.911(3)8, b = 81.812(2)8, g =
86.156(3)8, V = 5333.1(6) A˚ , Z = 4, D
3
–3
= 1.256 g cm ,
calcd
–1
6
6
m = 0.476 cm . F(000) = 2116.00, 69 026 total reflections
18 891 independent of symmetry, 14 480 for I > 2s(I)),
(
2
RhCl(IMes)(Ph PC H PPh ) (10)
1200 variables, residuals (refined on F , all data): R1 =
0.061, wR2 = 0.103. The material crystallized with two mol-
ecules of the Rh-complex, one C H molecule and one addi-
2
6
4
2
The orange complex 10 was obtained using 55.0 mg
(
5
0.05 mmol) of 2 and 44.0 mg (0.10 mmol) of dppbz in
6
6
1
mL of C H . Yield: 71 mg (80%). H NMR d: 1.62 (s,
tional solvent molecule, in the asymmetric unit; the solvent
6
6
Published by NRC Research Press

Sun et al.
1251
resembled hexane, but could not be modeled satisfactorily
and was thus removed from the model, with the SQUEEZE
program11 used to correct data for any residual electron den-
sity found in the space formerly occupied by the solvent.
Scheme 2. Synthesis of complexes and their numbering.
Scheme 1. Reactions of O2 with some Rh – N-heterocyclic carbene
(
NHC) – phosphine complexes.
Fig. 1. The experimental (upper) and simulated (lower)
31
1
P{ H} NMR spectra of RhCl(IPr)(dppm) (3). dPA = –35.68,
dPB = –20.92, JAB = 101.0 Hz, JRhPA = 104.0 Hz, JRhPB = 178.0 Hz.
Reactivity of the complexes
The complexes (~0.05 mmol) were dissolved in C D6
1 mL), and a sample (~0.7 mL) of the solution was placed
6
(
in a J-Young NMR tube and subjected to an atmosphere of
3
1
1
O , CO, or H at room temperature; P{ H} NMR spectral
2
2
changes were then monitored.
Results and discussion
Synthesis and spectroscopic characterization of
complexes
The diphosphines Ph P(CH ) PPh (n = 1, dppm; n =2,
2
2 n
2
dppe; n = 4, dppb) and 1,2-bis(diphenylphosphino)benzene
dppbz) react at room temperature with [RhCl(COE)(NHC)]2
(
The two singlets seen for the m-protons of the IMes ligand
similarly imply inequivalence of these protons within one
ring; the same description has been noted for the analogous
complexes in benzene to give yellow RhCl(NHC)(P–P)
species in 77%–96% isolated yields (NHC = IPr or IMes, and
P–P is the chelating diphosphine). All eight complexes (3–10)
have been synthesized (see Scheme 2) and well characterized
4j
cis-RhCl(IMes)(PPh ) complex. Where possible, we have
3
2
assigned the m- and p-protons of the IPr ligand, the m-protons
of the IMes ligand, and the phenyl protons of the PPh2
groups, based on (i) expected splitting patterns (e.g., the
m-H of IPr and of IMes are doublets and singlets, respec-
1
31
1
13
1
by elemental analysis, H, P{ H}, and C{ H} NMR spec-
troscopy, mass spectrometry and, for 3, 7, and 9, by X-ray
crystallography.
The solution NMR data for the complexes are generally
straightforward, and most of the shifts are readily assigned
based on previously reported data, for example, for cis-
RhCl(NHC)(PPh ) and RhCl(NHC)(P–N) species (see
2
,5,14
tively, and the p-H of IPr is a triplet),
(ii) data for free
15
16
IPr and IMes, , and (iii) data for the free diphosphines.
The more tentative assignments of these aromatic protons
are indicated by a query (?) in the Experimental section.
3
2
5
1
Scheme 1). All the complexes show a H singlet for NCH
The CH protons of the carbon backbone of the diphos-
2
between d 6.79–6.89 and 6.21–6.29 for the IPr- and IMes-
H
phine ligand in 5–8 appear as a multiplet or broad singlets.
Those of dppm in 3 and 4 are seen as a broadened triplet,
which is in fact a set of overlapping doublets that result
from two equivalent protons coupling to the two inequiva-
lent P atoms; the 31P-decoupled spectra showed a slightly
broadened singlet.
containing species, respectively. The IPr species 3, 5, and 9
show four sets of doublets for inequivalent IPr–Me groups,
with coupling of ~6.7 Hz to a IPr–methine proton; the dou-
blets indicate restricted rotation about the Rh–C bond or,
1
2
less likely, the Nimid–Carene bond. Complex 7 shows broad
signals for these methyls, presumably because of the relative
greater flexibility of the dppb chelate ring, which might al-
The 31P{ H} NMR spectra reveal the expected inequiva-
1
1
3
lent P atoms. For 5 and 7–9, first-order spectra show dou-
low for more rotational motion. The Me signals are some-
times shifted downfield (e.g., to d 1.89 for 3), which could
blets of doublets with JPP values of 48–38 Hz and JRhP
values of 123–114 and 208–205 Hz (for the P atom cis and
d,4e,5
H
result from a deshielding effect from a phenyl ring of the di-
phosphine (see the following section for the structure of 3).
The IPr–methine protons appear as two septets (for 3), two
multiplets (for 5), or one broad singlet (for 7). For each of
the IMes species 4, 6, 8, and 10, the Me protons are seen as
trans to Cl, respectively4
). For the other complexes, the
spectra are more complex ABX systems but are readily si-
mulated. Figure 1 shows the data for 3 and those of 4 (the
other dppm derivative) are very similar: the JPP values are
now ~100 Hz, with JRhP values of ~100 and 180 Hz, respec-
tively, for the P atoms cis and trans to Cl. The ABX spectra
of 6 (Fig. 2) and 10 are similar to each other, with JPP and
three singlets at d ~2.8, ~2.2, and between 1.9 and 1.6, im-
H
plying that the two o-Me groups on one aromatic ring are
inequivalent, consistent again with some restricted rotation.
Published by NRC Research Press

1
252
Can. J. Chem. Vol. 87, 2009
Fig. 2. The experimental (upper) and simulated (lower)
Fig. 3. ORTEP diagram of RhCl(IPr)(dppm) (3) with 50% prob-
ability thermal ellipsoids; H atoms are omitted for clarity. Selected
bond lengths ( A˚ ) and angles (8): Rh1—C1, 2.067(2); Rh1—Cl1,
3
1
1
P{ H} NMR spectra of RhCl(IMes)(dppe) (6) dP = –64.26,
A
dPB = –64.96, JAB = 36.6 Hz, JRhPA = 125.7 Hz, JRhPB = 205.7 Hz.
2
1
9
.3793(6); Rh1—P1, 2.2005(6); Rh1—P2, 2.2516(6); P1—C28,
.854(2); P2—C28, 1.845(2); C1–Rh1–Cl1, 90.30(6); Cl1–Rh1–P2,
3.94(2); P2–Rh1–P1, 72.81(2); P1–Rh1–C1, 103.07(6); C1–Rh1–
P2, 175.28(6); Cl1–Rh1–P1, 166.32(2).
JRhP values close to those seen in the first-order spectra of 5
and 7–9. Spectra akin to those of Fig. 2 have been noted
previously for analogous cis-RhCl(IMes)[P(OPh) ] spe-
3
2
cies.4
e
The expected ddd pattern (coupling to Rh and inequiva-
1
3
1
lent P atoms) in the C{ H} spectra for the Rh–C signals is
seen at d ~195 for 3, 4, and 9, with JRhC being ~125 Hz and
the JPC values being ~10 and ~50 Hz. For 5 and 10, only
somewhat broader dd patterns are seen, whereas for 6–8
these signals are not seen and are presumably broadened
into the baseline by some exchange processes, reflecting a
relatively labile Rh–carbene bond (see the last section on
the reactivity toward CO); the flexibility of the dppb ring
might account in part for the lack of the Rh–C signal in 7
and 8. The non-appearance of carbene-carbon resonances in
Fig. 4. ORTEP diagram of RhCl(IPr)(dppb) (7) with 50% probabil-
ity thermal ellipsoids; H atoms are omitted for clarity. Selected
˚
bond lengths (A) and angles (8): Rh1—C1, 2.0484(15); Rh1—Cl1,
2
1
.3846(4); Rh1—P1, 2.2888(4); Rh1—P2, 2.2043(4); P1—C28,
.8427(18); P2—C31, 1.8681(16); C1–Rh1–Cl1, 86.01(4); Cl1–
Rh1–P1, 82.569(15); P1–Rh1–P2, 91.046(15); P2–Rh1–C1,
00.39(4); C1–Rh1–P1, 168.34(4); Cl1–Rh1–P2, 173.587(15).
1
2
,4e,5
Rh–NHC species is not unusual.
There is no question
about the identity of the complexes, which are all essentially
square-planar Rh(I) species, with some distortion induced by
the chelating phosphines, as seen particularly in the structure
of 3, the dppm derivative (see the following section). For 3
and 4, the 13C{ H} signal for the PCH P carbon is seen as a
1
2
doublet of doublets at d ~50 with JCP values for the inequi-
valent P atoms in the 18–30 Hz range. For complexes 5–10,
1
3
1
C{ H} signals for the C atoms attached to P atoms are
seen as doublets in the expected regions d 25–36 and 125–
C
1
39, respectively, for alkyl and aryl carbons; uncertain as-
signments are again indicated by ?.
Mass spectral data reveal the parent peak for all the com-
plexes using either the EI mode (for 3–6, 9, and 10) or the
MALDI-TOF ion source (for 7 and 8).
Cl1–Rh1–P2 and P1–Rh1–C1 bond angles are 93.94 and
03.07(6)8, respectively. In 7, the more flexible dppb allows
for a P1–Rh–P2 bond angle of 91.058. Steric interactions be-
1
Structural characterization of 3, 7, and 9
The crystal structures of 3, 7, and 9 (all containing IPr)
were established by X-ray analysis; the molecular structures
and selected bond lengths and angles are shown in Figs. 3,
tween the IPr and a PPh –phenyl ring are evident in all three
2
structures, this accounting for cis C–Rh–P angles of ~1008.
The Rh–C and Rh–Cl bond lengths are in the established
range for such chloro(carbene)–Rh(I or III) complex-
4
, and 5, respectively. Complex 3 crystallized with one-half
of a benzene molecule, whereas 9 crystallized as two inde-
pendent molecules with one benzene molecule and one addi-
tional solvent molecule (likely hexane) in the asymmetric
unit; 7 was nonsolvated. The essentially square-planar struc-
tures show some distortion, particularly in the dppm of 3
where the P1–Rh–P2 bond angle is 72.818 and the adjacent
2
,5,4d,17–21
es.
In all three complexes, the Rh–P bond trans to
˚
the carbene is 0.04–0.08 A longer than the one cis to the
carbene, a finding compatible with data for cis-RhCl(I-
˚
4d
Mes)(PPh3)2, where the difference is about 0.09 A. Our
data also agree with a finding from Crudden’s group that
Published by NRC Research Press

Sun et al.
1253
Fig. 5. ORTEP diagram of RhCl(IPr)(dppbz) (9) with 50% prob-
ability thermal ellipsoids; the other independent molecule in the
asymmetric unit, and H atoms, are omitted for clarity. Selected
strated previously,22 although the chelating diphosphine li-
gands are retained when Rh(dppm)2+ and Rh(dppe)2+ react
in solution with O at ambient conditions to form the respec-
2
˚
+
bond lengths (A) and angles (8): Rh1—C1, 2.101(3); Rh1—Cl1,
tive cis-Rh(P–P) (O ) peroxide species, where (P–P) is the
chelating diphosphine.
2
2
2
1
8
.3929(8); Rh1—P2, 2.2239(8); Rh1—P1, 2.1796(9); P1—C28,
.852(3); P2—C33, 1.832(3); C1–Rh1–Cl1, 91.58(8); Cl1–Rh1–P2,
3.92(3); P2–Rh1–P1, 85.30(3); P1–Rh1–C1, 99.66(8); C1–Rh1–
13b
Our findings at this stage on the
reactivity of O toward the RhCl(NHC)(P–P) complexes un-
2
fortunately cannot contribute to the question of the nature of
P2, 173.14(9); Cl1–Rh1–P1, 173.73(3).
the coordinated O in Rh–NHC complexes with and without
2
an ancillary phosphine ligand, in which singlet oxygen has
been suggested (see Introduction).3 Studies on such sys-
tems are ongoing.
,4a
Reaction of a benzene solution of RhCl(NHC)(dppe)
[
NHC = IPr (5), IMes (6)] with CO at ambient conditions
rapidly precipitated a yellow solid, which was recrystallized
by layering of a CH Cl solution of the compound with hex-
2
2
ane. The material, however, was shown by elemental analy-
sis and 31P{ H} NMR and IR spectroscopies to be the
1
known compound RhCl(CO)(dppe).2
4,25
Reactions of CO
with the dppm and dppb analogues (complexes 3, 4, 7, and
) also resulted in displacement of the NHC ligand by CO
8
1
as shown by in situ H NMR, when resonances of the free
carbenes were generated.26
Rh–P bonds in cis-RhCl(NHC)(PPh ) complexes are mar-
The Rh products were not investigated, but are pre-
sumed to be the well-known dimeric, bridged-diphosphine
complexes trans-[RhCl(CO)]2(m-P–P)2 that are formed
3
2
˚
ginally shorter (by up to 0.03 A) than corresponding bonds
4
d
in RhCl(PPh ) and trans-RhCl(CO)(PPh ) ; in the case of
3
3
3 2
˚
25
RhCl(IPr)(dppbz) (9), the difference is up to 0.08 A. Data
with dppm and dppb. The substitution of an NHC ligand
from Herrmann’s group on other chloro(carbene)phosphine–
by CO, to the best of our knowledge, has not been re-
ported, and implies a relatively labile NHC ligand; in-
1
8
phosphite–Rh(I) complexes
also support this finding,
which is likely general within analogous Rh–carbene and
Rh–phosphine species.
deed, substitution of IMes by PPh has been reported (see
3
the following).3,4f Within Rh–NHC–carbonyl systems,
RhCl(CO)(NHC)22
,14,27
and RhCl(CO) (NHC)
2,19,28
com-
2
Reactivity of the complexes
plexes have been synthesized by reacting CO with Rh–
Complexes 3–10 are all highly soluble in benzene, tol-
uene, CH Cl , CHCl , and polar aprotic solvents, but are in-
NHC precursors, whereas RhCl(CO)(PPh )(NHC) has
3
3
,4d,4f,4j
2
2
3
been made from RhCl(PPh ) (NHC) and CO.
3 2
soluble in solvents such as hexane. In the solid state, these
complexes are air-stable, but in solution (e.g., in C H /
The RhCl(NHC)(P–P) complexes in benzene solution do
6
6
not react with H at ambient conditions. Known hydrido com-
2
C D ), they are sensitive to air or oxygen and rapidly de-
6
6
plexes of the type Rh(H) Cl(NHC) and [Rh(H) Cl(NHC)]
2
2
2
2
compose at room temperature with formation of free diphos-
have been made by reaction of H with Rh(I)–NHC precur-
2
3
1
1
phine dioxide, as demonstrated by in situ P{ H} NMR
sors,2
,3,14,27
whereas Rh–hydrido–NHC species have also
data; singlets were seen at d = 24.4, 12.2, 31.7, and 32.0,
P
been generated via intramolecular C–H activation of the
respectively, for the dioxides of dppm, dppe, dppb, and
Me group of IMes.1
4,29
Hydrido derivatives of Rh–NHC–
22,23
dppbz, in agreement with literature data,
and were iden-
phosphine species have not yet been reported.
tical to values measured by in situ oxidation of the free di-
phosphine in C D with H O . The reactivity toward O of
6
6
2
2
2
these diphosphine complexes is markedly different to that
of the analogous cis-RhCl(NHC)(PPh3)2 complex, which
under the same conditions undergoes irreversible oxidative
addition to form a Rh(III)–peroxide that contains, however,
Supplementary data
Supplementary data for this article are available on the
journal Web site (http://canjchem.nrc.ca) or may be pur-
chased from the Depository of Unpublished Data, Document
Delivery, CISTI, National Research Council Canada, Build-
ing M-55, 1200 Montreal Road, Ottawa, ON K1A 0R6,
Canada. DUD 3999. For more information on obtaining
material refer to http://cisti-icist.nrc-cnrc.gc.ca/eng/ibp/cisti/
collection/unpublished-data.html. CCDC numbers 739246–
739248 contain the crystallographic data for complexes 3,
7, and 9, respectively. These data can be obtained, free of
charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or
deposit@ccdc.cam.ac/uk).
5
trans-PPh ligands (see Scheme 1) ; this peroxide is stable
3
in both the solid state, and even in solution shows no sign
5
of decomposition to OPPh over 24 h in air. The necessa-
3
rily cis-chelating diphosphines clearly do not allow for for-
mation at ambient conditions of a stable peroxide, although
the chelated P–N ligand mentioned in the Introduction
5
(
Scheme 1) does so. Whether oxidation of the diphosphines
occurs via an intermediate with coordinated O requires de-
2
tailed low-temperature studies. Loss of a chelating diphos-
phine as the dioxide during oxygenation of a Rh(I)–
tris(pyrazolyl)borate–dppe complex in solution in attempts
to study formation of peroxide species has been demon-
Published by NRC Research Press

1
254
Can. J. Chem. Vol. 87, 2009
Acknowledgment
(13) (a) Zhou, Z.; Facey, G.; James, B. R.; Alper, H. Organome-
tallics 1996, 15 (10), 2496–2503. doi:10.1021/om960112s.;
We thank the Natural Sciences and Engineering Research
Council of Canada (NSERC) for financial support.
(
b) James, B. R.; Mahajan, D. Can. J. Chem. 1980, 58 (10),
96–1004. doi:10.1139/v80-157.
14) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics
000, 19, (6), 1194–1197. doi:10.1021/om990922e.
9
(
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