Rhodium(III) peroxo complexes containing carbene and phosphine ligands

Article abstract of DOI:10.1021/om060576i

The Rh(I) carbene precursors [RhCl(COE)(NHC)]₂, where the N-heterocyclic carbene is 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes), were used to synthesize the RhCl(NHC)(P-N) co

Full text of DOI:10.1021/om060576i

4870
Organometallics 2006, 25, 4870-4877
Rhodium(III) Peroxo Complexes Containing Carbene and Phosphine
Ligands
Xiao-Yan Yu, Brian O. Patrick, and Brian R. James*
Department of Chemistry, The UniVersity of British Columbia, 2036 Main Mall, VancouVer, British
Columbia, Canada V6T 1Z1
ReceiVed June 29, 2006
The Rh(I) carbene precursors [RhCl(COE)(NHC)]2, where the N-heterocyclic carbene is 1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes),
were used to synthesize the RhCl(NHC)(P-N) complexes 4 (NHC ) IPr) and 5 (NHC ) IMes), where
P-N is P,N-chelated o-(diphenylphosphino)-N,N-dimethylaniline, and the corresponding cis-RhCl(NHC)-
(PPh3)2 complexes 6 and 7. The synthesis of 4 surprisingly requires the reaction to be carried out under
a hydrogen atmosphere and occurs via the intermediate dihydride RhCl(H)2(IPr)(P-N) (3). Complexes
4-7 in benzene readily undergo irreversible oxidative addition of O2 to form the corresponding Rh(III)
peroxide complexes 9-12. For comparative purposes, RhCl(PPh3)(P-N) (8) was synthesized from RhCl-
(PPh3)3, and this also added O2 to form a peroxo complex (13). All of the complexes were generally
1
characterized by elemental analysis and H, 31P{1H}, and 13C{1H} NMR and IR spectroscopies and, in
the cases of 9, 10, and 13, by X-ray crystallography.
[RhCl(COE)(NHC)]2 are of a known type,7 although neither
the IPr nor the IMes derivative has been previously reported.
For purposes of comparison in reactivity between species
containing either a PPh3 or an NHC ligand, RhCl(PPh3)(P-N)
was also synthesized and its reactivity toward O2 investigated.
During a presentation of the studies described in this paper
at the 89th Canadian Chemistry Conference,8 we learned of the
synthesis and characterization of peroxo complexes of the type
RhCl(O2)(NHC)2, and some preliminary data on their potential
for catalytic aerobic oxidation of alcohols,9 but we are unaware
of the details of this work.
Introduction
Although transition-metal peroxo complexes containing ancil-
lary tertiary phosphine ligands are well-known,1 there have been
few reports on peroxo complexes with N-heterocyclic carbene
ligands (NHCs): two palladium(II) species2 and one cobalt-
(III) complex3 have been crystallographically characterized,
while a nickel peroxo species has been postulated in an allylic
oxidation effected at a Ni-NHC center.4 An iridium peroxide,
IrCl(O2)(NHC)2, has been reported in the Supporting Informa-
tion of a recent paper, but only elemental analysis supports the
peroxide formulation.5 We now report syntheses of the Rh(I)
carbene complexes RhCl(NHC)(P-N) and the known6 cis-RhCl-
(NHC)(PPh3)2 from the [RhCl(COE)(NHC)]2 precursors and
their reactions with O2 to give, respectively, the Rh(III) η2-
peroxo species RhCl(O2)(NHC)(P-N) and RhCl(O2)(NHC)-
(PPh3)2, where NHC is IPr (1,3-bis(2,6-diisopropylphenyl)-
imidazol-2-ylidene)orIMes(1,3-bis(2,4,6-trimethylphenyl)imidazol-
2-ylidene), and P-N is P,N-chelated o-(diphenylphosphino)-N,N-
dimethylaniline. The required cyclooctene precursor complexes
Results and Discussion
[RhCl(COE)(NHC)]2 Complexes 1 (NHC ) IPr) and 2
(NHC ) IMes). The yellow complex [RhCl(COE)(IPr)]2 (1)
was prepared by stirring [RhCl(COE)2]2 with 2 equiv of IPr in
THF, hexane, or benzene for 4 h under Ar at room temperature
(Scheme 1); the resulting yellow solution was concentrated, and
when necessary, hexane was added to precipitate 1, which was
isolated and dried in vacuo. The use of excess IPr does not
lead to a bis(carbene) complex, in contrast to the reaction using
IMes, which in THF generates Rh(H)Cl(IMes′)(IMes) (2a),
where IMes′ is the cyclometalated carbene formed from a methyl
group via intramolecular C-H activation.10 The difference is
presumably caused by the more bulky IPr (vs IMes),11 which
hinders replacement of the cyclooctene ligand of 1.
* To whom correspondence should be addressed. Tel.: +1 (604) 822-
6645. Fax: +1 (604) 822-2847. E-mail: brj@chem.ubc.ca.
(1) (a) Bakac, A. AdV. Inorg. Chem. 2004, 55, 1. (b) Barton, D. H. R.;
Martell, A. E.; Sawyer, D. T. ActiVation of Dioxygen in Homogeneous
Catalytic Oxidations; Plenum Press: New York, 1993. (c) Sheldon, R. A.;
Kochi, J. K. Metal-Catalyzed Oxidations of Organic Compounds; Academic
Press: New York, 1981.
(2) (a) Yamashita, M.; Goto, K.; Kawashima, T. J. Am. Chem. Soc. 2005,
127, 7294. (b) Konnick, M. M.; Guzei, I. A.; Stahl, S. S. J. Am. Chem.
Soc. 2004, 126, 10212.
(3) Hu, X.; Castro-Rodriguez, I.; Meyer, K. J. Am. Chem. Soc. 2004,
126, 13464.
(4) Dible, B. R.; Sigman, M. S. J. Am. Chem. Soc. 2003, 125, 872.
(5) Deboef, B.; Pastine, S. J.; Sames, D. J. Am. Chem. Soc. 2004, 126,
6556.
(6) (a) Allen, D. P.; Crudden, C. M.; Calhoun, L. A.; Wang, R.; Decken,
A. J. Organomet. Chem. 2005, 690, 5736. (b) Grasa, G. A.; Moore, Z.;
Martin, K. L.; Stevens, E. D.; Nolan, S. P.; Paquet, V.; Lebel, H. J.
Organomet. Chem. 2002, 658, 126. (c) Chen, A. C.; Ren, L.; Decken, A.;
Crudden, C. M. Organometallics 2000, 19, 3459.
(7) (a) Scott, N. M.; Dorta, R.; Stevens, E. D.; Correa, A.; Cavallo, L.;
Nolan, S. P. J. Am. Chem. Soc. 2005, 127, 3516. (b) Dorta, R.; Stevens, E.
D.; Nolan, S. P. J. Am. Chem. Soc. 2004, 126, 5054.
(8) James, B. R.; Yu, X.-Y.; Patrick, B. O. Proceedings of the 89th
Canadian Chemistry Conference; Halifax, Nova Scotia, May 2006; Abstract
1038.
(9) Praetorius, J. M.; Allen, D. P.; Crudden, C. M. Proceedings of the
89th Canadian Chemistry Conference; Halifax, Nova Scotia, May 2006;
Abstract 1450.
(10) Huang, J.; Stevens, E. D.; Nolan, S. P. Organometallics 2000, 19,
1194.
(11) Huang, J.; Nolan, S. P. J. Am. Chem. Soc. 1999, 121, 9889.
10.1021/om060576i CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/16/2006

Rhodium(III) Peroxo Complexes
Organometallics, Vol. 25, No. 20, 2006 4871
Scheme 2. Formation of 3, 4, 5, 9, and 10
Scheme 1. Formation of Complexes 1 and 2
[RhCl(COE)2]2 +
hexane, THF, or benzene
[RhCl(COE)(IPr)]
2IPr
8
2
1
[RhCl(COE)2]2 +
hexane
2IMes
[RhCl(COE)(IMes)]
2IMes
8
8
2
benzene
2
2Rh(H)Cl(IMes′)(IMes)
2a
On investigating the reaction of [RhCl(COE)2]2 with IMes
in hexane, even in the presence of 4 equiv of the carbene, we
isolated the yellow species [RhCl(COE)(IMes)]2 (2), which was
stable in hexane. However, reaction of 2 with 2 equiv of IMes
in benzene/C6D6 or THF generates 2a over several hours, as
monitored by 1H NMR; the methyl δ 2.31 singlet of 2 is replaced
by a singlet at δ 1.70 for the metalated CH2, and a broad, high-
field hydride resonance is found at δ -27.3. Clearly 2 is the
precursor to 2a. Similar solvent-dependent reactivity has been
found by Nolan’s group in reactions of [RhCl(COE)2]2 with
ItBu (1,3-bis(tert-butyl)imidazol-2-ylidene) and was attributed
to differences in solvent polarities and solubilities of the carbene
complexes.7
bond.12 Because of the decomposition of 3 to 4, satisfactory
13C{1H} NMR spectra for this species could not be obtained.
After a further 6 h of reaction, 3 had been quantitatively
converted to 4, which does not react with H2 to regenerate 3.
Complex 4 is isolated as a yellow powder in 89% yield; 3 has
not been isolated pure, but IR data of the 3/4 mixture reveal
νRhH at 2111 cm-1. The JRhP value of 114 Hz for 3 indicates
that the P atom is trans to the carbene and cis to the Cl, while
the JRhP value of 225 Hz for 4 supports a geometry with the P
atom cis to carbene and trans to Cl.6 Of note, the two hydrides
in 3 are equivalent and thus mutually trans, although a
cis-dihydrido species formed via oxidative addition of H2 is a
likely, but not essential,13 precursor to 3. The principle of
microscopic reversibility implies that reductive elimination of
H2 from a trans-dihydride is not impossible. Trans hydrido
ligands are unusual but are not unknown for octahedral
dihydrido complexes of platinum metals, including Rh.14,15
Complex 4 was characterized by elemental analysis, mass
Complexes 1 and 2 in benzene are O2-sensitive and decom-
pose to give free COE and possibly paramagnetic Rh(II) carbene
1
species, as judged by the loss of all of the carbene ligand H
NMR signals. However, in the presence of added phosphines
or the P-N ligand, oxidation products of the type RhCl(O2)-
(NHC)L2 may be synthesized, where L2 ) P-N, (PPh3)2 (see
below).
Reactions of [RhCl(COE)(NHC)]2 with P-N and with
PPh3. The synthesis of RhCl(IPr)(P-N), the precursor for the
peroxide, is unusual in that there is no direct reaction between
complex 1 and 2 equiv of the P-N ligand in benzene under Ar,
but surprisingly, under 1 atm of H2, formation of RhCl(IPr)-
(P-N) (4) does occur over a few hours via the intermediate
dihydride species Rh(H)2Cl(IPr)(P-N) (3) (Scheme 2). This two-
step synthesis of 4, unlike the direct synthesis under Ar of the
IMes analogue 5 from 2 (see Scheme 2 and below), requires
removal of the COE by hydrogenation; the synthetic process
for 4 was readily monitored in C6D6 by in situ 1H and 31P{1H}
NMR spectroscopy. During the first 1 h, the 1H NMR spectrum
shows a singlet at δ 1.50 for the cyclooctane CH2 protons and
a doublet of doublets for two equivalent hydrides of 3 at δ
-20.99 (JRhH ) 29, JPH ) 18 Hz); the 31P{1H} NMR spectrum
displays two doublets at δ 39.2 (JRhP ) 114 Hz) and 44.5 (JRhP
) 225 Hz), attributed to species 3 and 4, respectively (free P-N
has a singlet 31P{1H} resonance at δ -11.2). A yellow mixture
of 3 and 4 could be isolated after 30 min, and after this was
redissolved in C6D6 in the absence of H2, the ratio of 4 to 3
gradually increased and the signal for dissolved H2 then became
evident at δ 4.50. NMR resonances for 3 were assigned from
the mixed sample of 3 and 4, on the basis of the NMR data of
isolated pure 4. Other 1H signals for 3 were a singlet at δ 6.69
for NCH, a septet at δ 3.32 for the equivalent methines of the
IPr ligand, a singlet at δ 2.28 for the methyl protons of the P-N
ligand, and two doublets for the methyl groups of the IPr ligand
at δ 1.45 and 1.12, implying free rotation around the Rh-C
1
spectra, and H and 13C{1H} NMR spectroscopies, as well as
1
by the 31P{1H} data given above. The H spectrum shows a
singlet at δ 6.77 for NCH, two septets at δ 4.20 and 3.53 for
the IPr methine protons, a singlet at δ 3.12 for the equivalent
methyl protons of the P-N ligand, and four sets of doublets for
inequivalent IPr methyl groups, now indicating restricted rotation
around the Rh-C bond or less likely the Nimid-Carene bond.12
The 13C{1H} NMR signal for the carbene carbon appears as a
doublet of doublets centered at δ 186.8 (JRhC ) 57, JPC ) 15
Hz), 34 ppm upfield from the corresponding resonance for free
IPr, but not beyond the range for other Rh(I) carbene com-
plexes.16
The mechanistic details of the fascinating 1 f 3 f 4
conversions remain to be elucidated; they are clearly governed
by the steric bulk of IPr (vs that of IMes), because the
corresponding RhCl(IMes)(P-N) complex (5) is prepared via a
more conventional route, not involving H2 (Scheme 2).
(13) Pearson, R. G. Theor. Chim. Acta 1970, 16, 107.
(14) (a) Chatwin, S. L.; Davidson, M. G.; Doherty, C.; Donald, S. M.;
Jazzar, R. F. R.; Macgregor, S. A.; McIntyre, G. J.; Mahon, M. F.;
Whittlesey, M. K. Organometallics 2006, 25, 99. (b) Rybtchinski, B.; Ben-
David, Y.; Milstein, D. Organometallics 1997, 16, 3786. (c) Paonessa, R.
S.; Trogler, W. C. J. Am. Chem. Soc. 1982, 104, 1138.
(15) (a) Ingleson, M. J.; Mahon, M. F.; Raithby, P. R.; Weller, A. S. J.
Am. Chem. Soc. 2004, 126, 4784. (b) Westcott, S. A.; Marder, T. B.; Baker,
R. T.; Harlow, R. L.; Calabrese, J. C.; Lam, K. C.; Lin, Z. Polyhedron
2004, 23, 2665.
(12) (a) Park, K. H.; Kim, S. Y.; Son, S. U.; Chung, Y. K. Eur. J. Org.
Chem. 2003, 4341. (b) Herrmann, W. A.; Koecher, C.; Goossen, L. K.;
Artus, G. R. J. Chem. Eur. J. 1996, 2, 1627. (c) Herrmann, W. A.; Elison,
M.; Fischer, J.; Koecher, C. Chem. Eur. J. 1996, 2, 772.
(16) (a) Yu, X.-Y.; Patrick, B. O.; James, B. R. Organometallics 2006,
25, 2359. (b) Bazinet, P.; Yap, G. P. A.; Richeson, D. S. J. Am. Chem.
Soc. 2003, 125, 13314. (c) Danopoulos, A. A.; Winston, S.; Hursthouse,
M. B. Dalton Trans. 2002, 3090.

4872 Organometallics, Vol. 25, No. 20, 2006
Yu et al.
Scheme 3. Formation of 6, 7, 11, and 12
Scheme 4. Formation of 8 and 13
data for 7 have not been given previously, although such data
were later reported for some related cis-RhCl(IMes)(PAr3)2
complexes, and these similarly show a ddd pattern for the
carbene C resonance.6a The new synthetic method described here
for 6 and 7 provides a convenient, obvious route into rhodium-
(I) mono(carbene) complexes containing other tertiary phosphine
ligands.
Complex 5 is synthesized in high yield as a yellow powder
by direct reaction of 2 with 2 equiv of P-N ligand under Ar,
the reaction generating cyclooctene (detected by 1H NMR
spectroscopy) rather than the cyclooctane generated during
formation of 4. The geometry of 5 corresponds to that of 4 (with
the phosphine cis to carbene and trans to Cl), as judged by the
1
31P{1H} NMR doublet at δ 48.1 with JRhP ) 230 Hz. The H
Reaction of RhCl(PPh3)3 with P-N. For the purpose of
comparing properties of the RhCl(NHC)(P-N) complexes 4 and
5 with those of a corresponding complex containing a PPh3
ligand instead of a carbene ligand, RhCl(PPh3)(P-N) (8) was
synthesized. The exchange reaction of RhCl(PPh3)3 with 1 equiv
of P-N in toluene generates this species, which is readily isolated
by precipitation with hexane (Scheme 4). The yellow complex
is soluble in benzene, CH2Cl2, and THF, and the 31P{1H} NMR
spectrum in C6D6 shows two doublets of doublets at δ 57.6
(JRhP ) 197, JPP ) 45 Hz), likely due to the P-N ligand, and at
δ 52.4 (dd, JRhP ) 175, JPP ) 45 Hz), likely due to the PPh3
ligand (on the basis of 31P{1H} data for complexes 4-7), the P
atoms being mutually cis as judged by the JRhP values;17 an in
situ spectrum during the synthesis of 8 shows generation of the
PPh3 singlet at δ -4.0 and disappearance of the P-N singlet at
spectrum shows singlets at δ 6.20 (for NCH), δ 3.07 (for the
P-N methyl protons), δ 3.01 (for the p-methyl protons of IMes),
and δ 2.13 and 1.57 (for inequivalent o-methyl protons of IMes,
presumably again because of restricted rotation around the
Rh-C bond). The 13C{1H} doublet of doublets for the carbene
carbon is seen at δ 183.9 (JRhC ) 54, JPC ) 17 Hz). If the
synthesis of 5 is carried out under H2, no intermediate hydride
is seen, although cyclooctane is now observed. It seems that
the bulkier IPr hinders direct replacement of coordinated COE
by the P-N ligand, while IMes does not. The dramatically
different steric effects of IMes and IPr were noted also in the
reactivities of 1 or 2 in benzene with further NHC ligand. Worth
noting is that the known monomeric RhCl(COD)(NHC)
complexes16a do not react with the P-N ligand at room
temperature even under an atmosphere of H2.
1
δ -11.2. The H spectrum shows a singlet at δ 3.38 for the
P-N methyl protons. The geometry of 8 has the Cl trans to the
P atom of the P-N ligand and the PPh3 trans to the N atom, and
is analogous to that of 4 and 5 with the NHC replaced by PPh3.
Reactions of O2 with RhCl(NHC)(P-N) (NHC ) IPr (4),
IMes (5)), RhCl(NHC)(PPh3)2 (NHC ) IPr (6), IMes (7)),
and RhCl(PPh3)(P-N) (8). Exposure of a toluene solution of 4
or 5 at room temperature to 1 atm of O2 results in rapid and
complete conversion to the peroxo complexes RhCl(O2)(NHC)-
(P-N), where NHC ) IPr (9), IMes (10) (Scheme 2). Brown
crystals of 9 and orange crystals of 10 suitable for X-ray analysis
were grown by addition of hexane to benzene solutions of the
Reactions of the rhodium precursor 1 or 2 with 4 equiv of
PPh3 under Ar at room temperature rapidly generate the readily
isolated, yellow cis-RhCl(NHC)(PPh3)2 complexes 6 (NHC )
IPr) and 7 (NHC ) IMes) (Scheme 3). The 31P{1H} NMR data
for 6 and 7 show two doublets of doublets for the inequivalent
phosphines. The 13C{1H} signal of the carbene carbon of 6 is
a doublet of doublets of doublets at δ 187.2 because of coupling
to the Rh and the two inequivalent P atoms; a similar signal is
seen for 7. Complex 7 has been prepared previously by reacting
1
RhCl(PPh3)3 with IMes,6 and our H and 31P{1H} NMR data
(measured in CDCl3) agree with reported values;6c the 13C{1H}
Table 1. Crystallographic Data for the Complexes RhCl(O2)(IPr)(P-N) (9), RhCl(O2)(IMes)(P-N) (10), and
RhCl(O2)(PPh3)(P-N) (13)
9
10
13
formula
fw
C47H56N3O2PRhCl‚C6H14
950.45
C41H44N3O2PRhCl
780.12
C38H35NO2P2RhCl‚C6H6
816.08
cryst color, habit
cryst size (mm)
crystal system
space group
a (Å)
brown, needle
0.40 × 0.15 × 0.10
monoclinic
P21/n (No. 14)
14.684(2)
16.898(2)
19.798(2)
90.927(8)
4912(1)
orange, prism
0.20 × 0.15 × 0.05
monoclinic
P21/c (No. 14)
12.0059(4)
31.748(1)
10.2883(4)
108.068(2)
3728.1(2)
4
orange, needle
0.30 × 0.10 × 0.07
orthorhombic
P212121 (No. 19)
10.7428(8)
12.605(1)
28.474(2)
90
3855.8(6)
4
0.633
17 126
6501
b (Å)
c (Å)
â (deg)
V (Å3)
Z
4
µ (mm-1
)
0.477
52 494
9721
0.057
0.612
29 996
6514
0.043
total no. of rflns
no. of unique rflns
Rint
0.056
no. of variables
R1 (I > 2σ(I), all data)
wR2 (all data)
GOF (all data)
555
450
463
0.091
0.043
0.066
0.061a
0.072b
0.100c
0.82
1.05
0.98
a w ) 1/[σ2(Fo ) + (0.0152P)2], where P ) (Fo + 2Fc )/3 in all cases. b w ) 1/[σ2(Fo ) + (0.0334P)2 + (0.9607P)]. c w ) 1/[σ2(Fo ) + (0.0476P)2].
2
2
2
2
2

Rhodium(III) Peroxo Complexes
Organometallics, Vol. 25, No. 20, 2006 4873
Table 2. Selected Bond Distances (Å) and Angles (deg) for
RhCl(O2)(IPr)(P-N) (9) with Estimated Standard Deviations
in Parentheses
Rh(1)-C(1)
Rh(1)-O(1)
Rh(1)-O(2)
Rh(1)-N(3)
2.029(3)
Rh(1)-P(1)
2.2681(9)
2.4192(8)
1.450(3)
2.0476(19) Rh(1)-Cl(1)
1.9625(18) O(1)-O(2)
2.221(2)
O(2)-Rh(1)-O(1)
42.32(7)
N(3)-Rh(1)-Cl(1)
85.55(6)
O(1)-Rh(1)-Cl(1) 117.73(6)
C(1)-Rh(1)-N(3) 169.14(10)
N(3)-Rh(1)-P(1)
O(2)-Rh(1)-Cl(1) 159.62(6)
C(1)-Rh(1)-Cl(1) 98.38(8)
83.78(6)
Rh(1)-O(2)-O(1)
Rh(1)-O(1)-O(2)
71.98(11)
65.70 (10)
Table 3. Selected Bond Distances (Å) and Angles (deg) for
RhCl(O2)(IMes)(P-N) (10) with Estimated Standard
Deviations in Parentheses
Rh(1)-C(1)
Rh(1)-O(1)
Rh(1)-O(2)
Rh(1)-N(3)
2.038(2)
Rh(1)-P(1)
2.2901(7)
2.4339(6)
1.450(2)
1.9710(16) Rh(1)-Cl(1)
2.0645(17) O(1)-O(2)
2.235(2)
O(2)-Rh(1)-O(1)
42.03(7)
N(3)-Rh(1)-Cl(1)
84.53(5)
O(1)-Rh(1)-Cl(1) 159.97(6)
C(1)-Rh(1)-N(3) 171.52(8)
Figure 2. ORTEP diagram of RhCl(O2)(IMes)(P-N) (10) with 50%
probability thermal ellipsoids.
N(3)-Rh(1)-P(1)
O(2)-Rh(1)-Cl(1) 118.28(6)
C(1)-Rh(1)-Cl(1) 94.39(7)
80.35(5)
Rh(1)-O(2)-O(1)
Rh(1)-O(1)-O(2)
65.53(9)
72.44(10)
of 9 and 10, respectively, are twisted significantly with respect
to the central imidazole ring, for example, in 9 by an average
of 85.95°, but this is not unusual.16a The Rh-C bond lengths
of 2.029 and 2.038 Å are close to those reported for other Rh
carbene complexes (whether they are formally Rh(I) or Rh-
(III)),6,7,16 and the O-O bond length of 1.450(3) Å is typical
for coordinated peroxide.1,18,19 The peroxide IR band for 9 and
10 is seen in the expected region1,18,19 at 871 and 870 cm-1
,
respectively, and positive ion ESI-MS analyses in MeOH show
a major m/z peak corresponding to [M + H]+.
The solid-state structures of 9 and 10 are maintained in
solution, as evidenced by NMR data in C6D6, which for 9 show
a
31P{1H} doublet at δ 35.3 (JRhP ) 149 Hz) and a 13C{1H}
doublet of doublets at δ 159.9 (JRhC ) 51, JPC ) 9 Hz) shifted
some 25 ppm upfield from that of the precursor 4. Similar data
are seen for 10: δP 34.7 (JRhP ) 149 Hz) and δC 159.4 (JRhC
)
50, JPC ) 9 Hz). The 1H NMR spectrum of 9 shows inequivalent
Me groups for the P-N ligand (singlets at δ 3.37 and 2.11),
while broad signals at δ 4.44 and 2.76 are due to the IPr methine
protons, and four broad peaks in the δ 1.87-0.88 region result
from the inequivalent IPr methyl protons. For 10, the 1H NMR
spectrum similarly shows two singlets for the P-N methyls and
IMes-methyl signals at δ 2.26 and 2.14 for the p- and o-methyl
groups, respectively.
Like the RhCl(NHC)(P-N) species, the RhCl(NHC)(PPh3)2
complexes 6 (NHC ) IPr) and 7 (NHC ) IMes) also readily
undergo oxidative addition of O2 to generate the corresponding
orange Rh(III) peroxo complexes RhCl(O2)(NHC)(PPh3)2 (11
and 12). We were unable to grow crystals suitable for X-ray
analysis, but a simple doublet in the 31P{1H} spectrum at δ 18.4
for 11 and at δ 16.9 for 12 reveals equivalent P atoms that are
almost certainly trans, as judged by the JRhP values of 105 and
104 Hz, respectively;6,17 the peroxide oxygens are then trans to
the Cl and carbene C atoms (Scheme 3), as opposed to being
trans to the Cl and P atoms in 9 and 10 (Scheme 2). The trans
phosphines, in comparison with the P atom (of P-N) trans to
Figure 1. ORTEP diagram of RhCl(O2)(IPr)(P-N) (9) with 50%
probability thermal ellipsoids.
complexes. Some crystal data are given in Table 1, and selected
bond lengths and angles are given in Tables 2 and 3. Complex
9 crystallizes with one disordered hexane molecule in the
asymmetric unit, which was modeled in two orientations. The
structures (Figures 1 and 2) show distorted-octahedral geometry
at the Rh, with the carbene carbon and the N-donor atom being
mutually trans (C-Rh-N ) 169-172°) and the side-on η2-
peroxide and the Cl and P atoms constituting a highly distorted
square-planar arrangement; within each structure, the Rh-O
bond lengths differ by 0.08-0.09 Å, while the O-Rh-O angle
is about 42°. The diisopropylphenyl and mesityl substituents
(18) Haarman, H. F.; Bregman, F. R.; van Leeuwen, P. W. N. M.; Vrieze,
K. Organometallics 1997, 16, 979.
(19) (a) Cˆırcu, V.; Fernandes, M. A.; Carlton, L. Polyhedron 2002, 21,
1775. (b) Nicasio, M. C.; Paneque, M.; Pe´rez, P. J.; Pizzano, A.; Poveda,
M. L.; Rey, L.; Sirol, S.; Taboada, S.; Trujillo, M.; Monge, A.; Ruiz, C.;
Carmona, E. Inorg. Chem. 2000, 39, 180. (c) Vigalok, A.; Shimon, L. J.
W.; Milstein, D. J. Chem. Soc., Chem. Commun. 1996, 1673.
(17) (a) Marcazzan, P.; Patrick, B. O.; James, B. R. Inorg. Chem. 2004,
43, 6838. (b) Marcazzan, P.; Abu-Gnim, C.; Sereviratne, K. N.; James, B.
R. Inorg. Chem. 2004, 43, 4820.

4874 Organometallics, Vol. 25, No. 20, 2006
Yu et al.
Figure 3. ORTEP diagram of RhCl(O2)(PPh3)(P-N) (13) with 50% probability thermal ellipsoids.
an O atom in 9 and 10, give rise to higher field 31P signals and
that are “stable towards air and moisture”.20 Clearly, our work
shows that such statements cannot be taken literally in a general
sense, because solutions of [RhCl(COE)(NHC)]2, RhCl(NHC)-
(P-N), and RhCl(NHC)(PPh3)2 species are all reactive toward
oxygen. Indeed, our interest and that of others9 are in the use
of such Rh complexes for catalytic oxidations; whether Rh-
NHC catalysts can lead to O atom transfer oxidations more
selective than the more common free-radical processes initiated
by NHC-free Rh(III) peroxo complexes21 remains to be inves-
tigated.
1
lower JRhP values by ∼45 Hz. The H NMR spectrum of 11
reveals two sets of equivalent IPr methyl protons (doublets at
δ 1.43 and 1.09) and that for 12 shows singlets at δ 2.33 and
2.14 for the o- and p-methyl substituents, respectively. The
carbene 13C resonances could not be delineated, presumably
because they are shifted into the phenyl C atom region of the
spectrum. The IR peroxide band is seen at 852 and 851 cm-1
for 11 and 12, respectively.
The O2 is strongly bonded in all of the above four NHC
phosphine complexes 9-12 and, for example, is not removed
from the complexes under vacuum at room temperature or by
introduction of 1 atm of N2 (or H2) to benzene solutions of the
complexes. Such irreversible O2 binding within Rh complexes
is relatively rare.18 Further, solutions of complexes 9-12 are
completely stable when stored for 1 day under an atmosphere
of air or oxygen. Our paper, together with the recent conference
abstracts,8,9 report the first examples of Rh peroxo complexes
bearing ancillary NHC ligands. These complexes are of
significance in that there is a report noting that cis-RhCl(IMes)-
(PPh3)2, which was being used as a catalyst in hydroformylation
of styrene,6c decomposes in solution under O2 to generate a
green solution containing uncomplexed PPh3 and triphenylphos-
phine oxide.6c Presumably, any such dissociation involves the
peroxo product that we report on here. There is a growing
amount of literature reporting on the replacement in Rh
complexes of phosphines by NHC ligands in attempts to devise
more effective catalysts, particularly within hydrogenation and
hydroformylation systems,6,20 and the replacement of phosphine
ligands by NHC ligands has been noted to generate complexes
Of note, reaction of O2 with the NHC-free complex RhCl-
(PPh3)(P-N) (8) in toluene (Scheme 4) follows that with the
RhCl(NHC)(P-N) complexes 4 and 5 (Scheme 2), again rapidly
giving RhCl(O2)(PPh3)(P-N) (13) quantitatively and irreversibly
in solution in high isolated yield. Although 13 was isolated and
was characterized as a toluene solvate by spectroscopy and
elemental analysis, an orange crystal suitable for X-ray analysis
was obtained by recrystallization of the complex from benzene;
the structure is shown in Figure 3, with selected bond distances
and angles listed in Table 4. The complex crystallizes with one
molecule of benzene in the asymmetric unit. The structure
corresponds to that of 9 and 10, but with the PPh3 in place of
the NHC: the distorted-octahedral geometry now has the PPh3
and the N-donor atom essentially trans (P-Rh-N ) 174.18°),
with the η2-peroxide, the Cl atom, and the P atom of the P-N
ligand again forming a quite distorted square-planar arrange-
ment. The structure is remarkably analogous to those of 9 and
10 (Tables 2-4). The Rh peroxo moieties have very similar
(21) (a) James, B. R.; Ezhova, M. B. Educ. Chem. 2002, 8, 93. (b) Aresta,
M.; Tommasi, I.; Quaranta, E.; Fragale, C.; Mascetti, J.; Tranquille, M.;
Galan, F.; Fouassier, M. Inorg. Chem. 1996, 35, 4254. (c) James, B. R.
Stud. Surf. Sci. Catal. 1991, 66, 195. (d) James, B. R. AdV. Chem. Ser.
1980, No. 191, 253 and references therein.
(20) Bortenschlager, M.; Schu¨tz, J.; von Preysing, D.; Nuyken, O.;
Herrmann, W. A.; Weberskirch, R. J. Organomet. Chem. 2005, 690, 6233.

Rhodium(III) Peroxo Complexes
Organometallics, Vol. 25, No. 20, 2006 4875
Table 4. Selected Bond Distances (Å) and Angles (deg) for
RhCl(O2)(PPh3)(P-N) (13) with Estimated Standard
Deviations in Parentheses
that NHC ligands behave much like PPh3, at least qualitatiVely,
in oxygenation reactivity of the Rh(I) complexes RhCl(L)(P-
N), where L ) IPr, IMes, PPh3 and L is trans to the N-donor
atom; the π-acceptor PPh3 might have been expected to decrease
the propensity for oxidative addition,23 and more quantitative
kinetic data may still reveal this.
Rh(1)-N(1)
Rh(1)-O(1)
Rh(1)-O(2)
Rh(1)-P(2)
2.213(5)
1.998(4)
2.054(3)
2.2725(14)
Rh(1)-P(1)
Rh(1)-Cl(1)
O(1)-O(2)
2.2747(15)
2.3931(14)
1.445(5)
O(2)-Rh(1)-O(1)
N(1)-Rh(1)-P(2)
N(1)-Rh(1)-P(1)
O(2)-Rh(1)-Cl(1)
N(1)-Rh(1)-Cl(1)
41.76(15)
82.72(12)
174.18(13)
111.17(12)
88.59(13)
P(2)-Rh(1)-P(1)
O(1)-Rh(1)-Cl(1)
Rh(1)-O(2)-O(1)
Rh(1)-O(1)-O(2)
101.42(6)
152.81(12)
67.0(2)
Experimental Section
All manipulations were performed under Ar unless stated
otherwise, using standard Schlenk techniques. Reagent grade
solvents (Fisher Scientific) were dried using standard procedures
and prior to use were purged with a stream of Ar. Deuterated
solvents (Cambridge Isotope Laboratories) were similarly dried and
then distilled under N2 prior to use. Common chemicals were
obtained from Fisher Scientific; these and 1,3-bis(2,4,6-trimeth-
ylphenyl)imidazolium chloride (IMes‚HCl; Strem) were used as
received. IPr,24 IMes,25 the P-N ligand,26 RhCl(PPh3)3,27 and [RhCl-
(COE)2]228 were synthesized according to the reported procedures.
NMR spectra were recorded at room temperature (∼20 °C) on
71.2(2)
geometries, and even the Rh-N bond lengths (trans to carbene
or PPh3) are within 0.01-0.02 Å of each other, the shortest
one being in 13, which contains the trans π-acceptor PPh3. The
Rh-P bond lengths of about 2.27 Å lie between those of 9 and
10 and are not exceptional.
The solution 31P{1H} NMR spectrum of 13 is consistent with
the solid-state structure and shows two doublets of doublets at
1
Bruker AV 300 (300.0 MHz for H, 121.4 MHz for 31P{1H}, and
δ 45.2 (JRhP ) 148, JPP ) 27 Hz) and 38.9 (JRhP ) 130, JPP
)
75.0 MHz for 13C{1H} NMR) and Bruker AV 400 (400.0 MHz for
1H, 162.0 MHz for 31P{1H}, and 100.6 MHz for 13C{1H} NMR)
spectrometers. Residual protonated species in the deuterated solvents
27 Hz), tentatively assigned (by comparison with data for 9
and 10) to the P-N and PPh3 ligands, respectively, the JRhP values
being consistent with the two P atoms being mutually cis.6,17
The 1H spectrum shows singlets at δ 3.69 and 2.31 for
inequivalent methyl protons of the P-N ligand. The peroxide
1
were used as internal references (δ 7.15 for C6D6); all H shifts
are reported in ppm (s ) singlet, d ) doublet, m ) multiplet, spt
) septet, and br ) broad), relative to external TMS, with J values
in Hz. 31P{1H} NMR shifts are reported relative to external 85%
aqueous H3PO4. Mass spectral data (reported as m/z values) were
acquired on a Bruker Esquire ES spectrometer in this department
(Dr. Y. Ling). IR spectra (KBr) were recorded on ATI Mattson
Genesis and Bomem-Michelson MB-100 FT-IR spectrometers; the
peroxide bands in the 850-875 cm-1 range were readily identified
by comparing the IR spectra of the peroxide complexes with those
of their precursor complexes. Elemental analyses were performed
by Mr. M. Lakha of this department on a Carlo Erba EA 1108
analyzer.
Crystal Structure Determinations. Measurements were per-
formed at 173 ( 0.1 K on a Rigaku/ADSC CCD area detector with
graphite-monochromated Mo KR radiation (0.710 69 Å). Some
crystallographic data and selected bond lengths and angles for
complexes 9, 10, and 13 are shown in Tables 1-4. All the structures
were solved using direct methods29 and expanded using Fourier
techniques.30 For 9, carbons in a disordered solvate hexane molecule
were refined isotropically; all other non-hydrogen atoms were
refined anisotropically. Complex 13 crystallizes as a racemic twin
with a molecule of benzene in the asymmetric unit; final refinements
were carried out using the TWIN/BASF functions of SHELXL,
with a final value indicating a roughly 2:1 ratio of the two
enantiomers. All refinements were performed using the SHELXTL
program.31 All hydrogen atoms were included in calculated positions
but were not refined.
stretch in the IR is seen at 873 cm-1
.
Of note, the clean oxygenation chemistry of complexes 4-8
contrasts markedly with the complicated O2 oxidation of RhCl-
(PPh3)3 and [RhCl(PPh3)2]2 complexes, where formation of
OPPh3 and a bridging oxo species is seen, depending on
conditions.22 However, this reactivity results, at least in the case
of RhCl(PPh3)3, from dissociation of a phosphine ligand. The
clean formation of a peroxo species via oxidative addition clearly
does not result simply from the presence of a less oxidizable
NHC ligand, since the RhCl(PPh3)(P-N) complex shows the
same oxygenation chemistry as the RhCl(NHC)(P-N) analogues.
The more complex reactivity possibly results from the presence
of trans PPh3 ligands that promotes dissociation a PPh3 ligand;
none of the complexes 4-8 contains trans phosphine moieties,
although the peroxides 11 and 12 have trans phosphines. The
established mechanism for formation of phosphine oxides from
phosphine complexes of low-valent platinum metals involves
the presence of some free phosphine, which initially acts as a
nucelophile that replaces the coordinated peroxide; the subse-
quently generated H2O2 and the oxidized metal turn out to be
the actual oxidizing agents of the phosphine.21d In line with this
mechanism, preliminary tests suggest that the peroxides 9-13
do catalyze the O2 oxidation of phosphines, but we do not intend
to pursue this mundane catalysis.
(23) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; Chapter 5.
(24) Jarapour, L.; Stevens, E. D.; Nolan, S. P. J. Organomet. Chem. 2000,
606, 49.
(25) Arduengo, A. J., III; Dias, H. V. R.; Harlow, R. L.; Kline, M. J.
Am. Chem. Soc. 1992, 114, 5530.
(26) Fritz, H. P.; Gordan, I. R.; Schwarzhans, K. E.; Venanzi, L. M. J.
Chem. Soc. 1965, 5210.
(27) Osborn, J. A.; Wilkinson, G. Inorg. Synth. 1967, 10, 67.
(28) van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1973, 14, 92.
(29) SIR97: Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.
L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(30) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF-94 Program System;
Technical Report of the Crystallography Laboratory; University of Nijmegen,
Nijmegen, The Netherlands, 1994.
Conclusions
The complexes RhCl(NHC)(P-N) and cis-RhCl(NHC)(PPh3)2,
where NHC ) IPr, IMes and P-N ) P,N-chelated o-(diphen-
ylphosphino)-N,N-dimethylaniline, were synthesized from [RhCl-
(COE)(NHC)]2 precursors; production of RhCl(IPr)(P-N) re-
quires use of a hydrogen atmosphere and the intermediate
formation of the dihydrido intermediate RhCl(H)2(IPr)(P-N). The
RhCl(PPh3)(P-N) complex was also made. All five of the Rh-
(I) complexes undergo rapid, irreversible oxidative addition of
O2 under ambient conditions to generate the corresponding stable
Rh(III) peroxo complexes, three of which have been character-
ized crystallographically. The studies show, perhaps surprisingly,
(22) Geoffroy, G. L.; Keeney, M. E. Inorg. Chem. 1977, 16, 205.
(31) SHELXTL Version 5.1; Bruker AXS Inc., Madison, WI, 1997.

4876 Organometallics, Vol. 25, No. 20, 2006
Yu et al.
[RhCl(COE)(IPr)]2 (1). A suspension of [RhCl(COE)2]2 (0.036
g, 0.050 mmol) and IPr (0.039 g, 0.100 mmol) in hexane (10 mL)
was stirred for 4 h at room temperature. Initial dissolution after a
few minutes was followed by precipitation. The resulting suspension
was concentrated to half its original volume, and the yellow solid
was collected and dried in vacuo. Yield: 0.050 g (79%). 1H NMR
(C6D6): δ 7.32 (br, 2H, Ar p-H), 7.26 (br, 4H, Ar m-H), 6.37 (s,
2H, NCH), 3.29 (br, 4H, CHMe2), 2.71 (br, 2H, CHdCH olefin),
1.82 (br, 4H, CH2), 1.62 (br, 12H, CH(CH3)2), 1.42 (br, 4H, CH2),
1.18 (m, 4H, CH2), 1.00 (br, 12H, CH(CH3)2). 13C{1H} NMR
(C6D6): δ 181.7 (d, JRhC ) 64, NCN), 146.8 (s, NC), 138.2 (s,
iPr-C), 128.7 (s, p-CH), 124.9 (s, m-CH), 124.4 (s, NCH), 59.6 (d,
JRhC ) 17, dCH olefin), 30.8 (s, CH2), 30.6 (s, CH2), 29.3 (s,
CHMe2), 27.6 (s, CH2), 26.8 (s, CH3), 24.3 (s, CH3). Anal. Calcd
for C70H100N4Cl2Rh2: C, 65.98; H, 7.91; N, 4.40. Found: C, 65.82;
H, 8.00; N, 4.45.
(10 mL) precipitated a yellow powder that was collected and dried
in vacuo. Yield: 0.069 g (92%). H NMR (C6D6): δ 7.84-7.78
1
(m, 2H, Ar H), 7.04-6.49 (m, 18H, Ar H), 6.20 (s, 2H, NCH),
3.07 (s, 6H, N(CH3)2), 3.01 (s, 6H, p-CH3), 2.13 (s, 6H, o-CH3),
1.57 (s, 6H, o-CH3). 31P{1H} NMR (C6D6): δ 48.1 (d, JRhP ) 230).
13C{1H} NMR (C6D6): δ 183.9 (dd, JRhC ) 54, JPC ) 17, NCN),
161.0 (s, NC), 160.7 (s, NC), 142.4 (s, Ar C), 141.9 (s, Ar C),
138.8 (s, Ar C), 138.5 (s, Ar C), 138.3 (s, Ar C), 135.5(s, Ar C),
134.6 (s, Ar C), 134.4 (s, Ar C), 133.6 (s, Ar C), 132.3 (s, Ar C),
132.1 (s, Ar C), 130.2 (s, Ar C), 129.1 (s, Ar C), 128.6 (s, Ar C),
128.1 (s, Ar C), 127.3 (s, Ar C), 127.2 (s, Ar C), 123.3 (s, Ar C),
121.7 (s, NCH), 121.6 (s, NCH), 52.2 (s, N(CH3)2), 21.9 (s, p-CH3),
21.5 (s, o-CH3), 19.5 (s, o-CH3). ESI-MS (MeOH): m/z 710, [M
- Cl]+ (100%); 305, [IMes + H]+ (22%). Anal. Calcd for
C41H44N3PClRh (M ) 748.1): C, 65.82; H, 5.93; N, 5.62. Found:
C, 65.74; H, 6.19; N, 5.62.
[RhCl(COE)(IMes)]2 (2). This yellow complex was prepared
in a manner analogous to that described for 1, but using IMes (0.030
g, 0.100 mmol). Yield: 0.047 g (85%). H NMR (C6D6): δ 6.90
(s, 4H, Ar m-H), 6.01 (s, 2H, NCH), 2.76 (br, 2H, CHdCH olefin),
2.31 (s, 18H, CH3), 1.93 (br, 4H, CH2), 1.68 (br, 4H, CH2), 1.45
(br, 4H, CH2). 13C{1H} NMR (C6D6): δ 150.9 (s, NC), 138.3 (s,
Ar p-C), 137.8 (s, Ar o-C), 129.7 (s, Ar m-CH), 123.5 (s, NCH),
59.6 (d, JRhC ) 17, dCH olefin), 31.2 (s, CH2), 30.3 (s, CH2),
27.8 (s, CH2), 23.4 (s, CH3). Anal. Calcd for C58H76N4Cl2Rh2: C,
62.99; H, 6.93; N, 5.07. Found: C, 63.30; H, 7.20; N, 5.00.
RhCl(IPr)(PPh3)2 (6). A solution of 1 (0.064 g, 0.050 mmol)
and PPh3 (0.052 g, 0.200 mmol) in benzene (5 mL) was stirred for
4 h at room temperature; subsequent workup, as described for
complex 5, gave the yellow complex 6. Yield: 0.097 g (92%). 1H
NMR (C6D6): δ 7.80-6.59 (m, 38H, Ar H), 3.76 (spt, 2H, J ) 7,
CH(CH3)2), 3.36 (spt, 2H, J ) 7, CH(CH3)2), 1.49 (d, 6H, J ) 7,
CH(CH3)2), 1.08 (d, 6H, J ) 7, CH(CH3)2), 0.88 (d, 6H, J ) 7,
CH(CH3)2), 0.56 (d, 6H, J ) 7, CH(CH3)2). 31P{1H} NMR
(C6D6): 47.3 (dd, JRhP ) 210, JPP ) 40, P trans to Cl), 36.4 (dd,
JRhP ) 120, JP-P ) 40, P cis to Cl). 13C{1H} NMR (C6D6): δ 187.2
(ddd, JRhC ) 114, JPC ) 52, JPC ) 15, NCN), 146.8 (s, NC), 145.2
(s, NC), 136.4 (s, Ar C), 134.9(s, Ar C), 134.8 (s, Ar C), 132.3 (s,
Ar C), 132.2 (s, Ar C), 132.1 (s, Ar C), 132.0 (s, Ar C), 128.7 (s,
Ar C), 128.6 (s, Ar C), 127.7 (s, Ar C), 127.6 (s, Ar C), 124.8 (br,
NCH), 123.9 (br, NCH), 29.2 (s, CH(CH3)2), 28.9 (s, CH(CH3)2),
26.5 (s, CH3), 25.0 (s, CH3), 23.9 (s, CH3), 22.8 (s, CH3). Anal.
Calcd for C63H66N2P2ClRh (M ) 1051.5): C, 71.96; H, 6.33; N,
2.66. Found: C, 72.06; H, 6.41; N, 2.67.
1
RhCl(H)2(IPr)(P-N) (3) and RhCl(IPr)(P-N) (4). A solution
of [RhCl(COE)(IPr)]2 (1; 0.064 g, 0.050 mmol) and P-N (0.031 g,
0.100 mmol) in toluene (5 mL) was stirred for 30 min at room
temperature under 1 atm of H2. The resulting yellowish solution
was then concentrated, when addition of hexane (10 mL) precipi-
tated a mixture of 3 and 4 as a yellow powder that was collected
and dried under vacuum. In toluene solution, complex 3 decom-
posed to 4 over several hours, and pure 3 could not be isolated or
its 13C{1H} NMR spectrum measured. 1H NMR and 31P{1H} NMR
spectra of 3 were obtained from the in situ reaction and from a
solution of the 3/4 mixture, since pure 4 could be isolated (see
below). IR (KBr): 2111 cm-1. 1H NMR (C6D6): δ 7.78-7.72 (m,
2H, Ar H), 7.42-6.81 (m, 18H, Ar H), 6.69 (s, 2H, NCH), 3.32
(spt, 4H, J ) 7, CH(CH3)2), 2.28 (s, 6H, N(CH3)2), 1.45 (d, 12H,
J ) 7, CH(CH3)2), 1.12 (d, 12H, J ) 7, CH(CH3)2), -20.99 (dd,
2H, JPH ) 18, JRhH ) 29, RhH). 31P{1H} NMR (C6D6): 39.2 (d,
JRhP ) 114).
RhCl(IMes)(PPh3)2 (7). This yellow complex was prepared in
a manner analogous to that described for 6, but using 0.055 g (0.050
mmol) of 2 and 0.052 g (0.200 mmol) of PPh3. Yield: 0.091 g
(94%). 1H NMR (CDCl3): 7.35-6.85 (m, 36H, Ar H), 3.01 (s, 6H,
p-CH3), 2.13 (s, 6H, o-CH3), 1.57 (s, 6H, o-CH3). 31P{1H} NMR
(CDCl3): 50.3 (dd, JRhP ) 210, JPP ) 40, P trans to Cl), 37.0 (dd,
JRhP ) 119, JPP ) 40, P cis to Cl). 13C{1H} NMR (CDCl3): δ
189.4 (ddd, JRhC ) 115, JPC ) 49, JPC ) 17, NCN), 138.8 (s, NC),
138.0 (s, NC), 137.7 (s, Ar C), 137.4 (s, Ar C), 137.1 (s, Ar C),
135.8(s, Ar C), 135.6 (s, Ar C), 134.9 (s, Ar C), 134.8 (s, Ar C),
129.7 (s, Ar C), 128.6 (s, Ar C), 128.2 (s, Ar C), 127.6 (s, Ar C),
126.8 (d, JP-C ) 9, NCH), 126.5 (d, JP-C ) 9, NCH), 22.0 (s,
p-CH3), 21.5 (s, o-CH3), 19.9 (s, o-CH3). Anal. Calcd for
C57H54P2N2ClRh (M ) 967.4): C, 70.77; H, 5.63; N, 2.90. Found:
C, 71.13; H, 5.76; N, 2.76.
When the reactant mixture of 1 and P-N was stirred under 1
atm of H2 for 6 h, pure 4 was isolated as a yellow powder, by
1
following the above procedure. Yield: 0.074 g (89%). H NMR
(C6D6): δ 7.78-7.72 (m, 2H, Ar H), 7.41-6.80 (m, 18H, Ar H),
6.77 (s, 2H, NCH), 4.20 (spt, 2H, J ) 7, CH(CH3)2), 3.53 (spt,
2H, J ) 7, CH(CH3)2), 3.12 (s, 6H, N(CH3)2), 1.98 (d, 6H, J ) 7,
CH(CH3)2), 1.21 (d, 6H, J ) 7, CH(CH3)2), 0.86 (d, 6H, J ) 7,
CH(CH3)2), 0.84 (d, 6H, J ) 7, CH(CH3)2). 31P{1H} NMR
(C6D6): 44.5 (d, JRhP ) 225). 13C{1H} NMR (C6D6): δ 186.8 (dd,
JRhC ) 57, JPC ) 15, NCN), 161.9 (s, NC), 161.7 (s, NC), 149.4
(s, Ar C), 144.6 (s, Ar C), 139.1 (s, Ar C), 138.6 (s, Ar C), 137.6
(s, Ar C), 137.1(s, Ar C), 134.1 (s, Ar C), 132.6 (s, Ar C), 132.3
(s, Ar C), 132.2 (s, Ar C), 131.1 (s, Ar C), 130.5 (s, Ar C), 128.7
(s, Ar C), 128.2 (s, Ar C), 128.1 (s, Ar C), 128.0 (s, Ar C), 126.8
(s, Ar C), 126.7 (s, Ar C), 122.4 (s, NCH), 122.2 (s, NCH), 52.6
(s, N(CH3)2), 29.9 (s, CH(CH3)2), 29.2 (s, CH(CH3)2), 27.1 (s, CH-
(CH3)2), 27.0 (s, CH(CH3)2), 24.7 (s, CH3), 23.2 (s, CH3). ESI-MS
(MeOH): m/z 794, [M - Cl]+ (100%); 389, [IPr + H]+ (27%).
Anal. Calcd for C47H56N3PClRh (M ) 832.3): C, 67.82; H, 6.78;
N, 5.05. Found: C, 67.42; H, 7.10; N, 5.13.
RhCl(PPh3)(P-N) (8). This yellow complex was prepared in a
manner analogous to that described for 5 but using 0.093 g (0.100
mmol) of RhCl(PPh3)3 as the Rh precursor. Yield: 0.057 g (81%).
1H NMR (C6D6): δ 7.78-6.12 (m, 29H, Ar H), 3.38 (s, 6H,
N(CH3)2). 31P{1H} NMR (C6D6): 57.6 (dd, JRhP ) 197, JPP ) 45),
52.4 (dd, JRhP ) 175, JPP ) 45). 13C{1H} NMR (C6D6): δ 161.0-
122.9 (Ar C), 52.8 (s, N(CH3)2). Anal. Calcd for C38H35P2NClRh
(M ) 706.0): C, 64.65; H, 5.00; N, 1.98. Found: C, 64.33; H,
5.08; N, 1.70.
RhCl(O2)(IPr)(P-N) (9). A yellow solution of 4 (0.042 g, 0.050
mmol) in toluene (5 mL) was stirred under 1 atm of O2 for 10 min
at room temperature. The resulting brown solution was concentrated
to ∼2 mL, when hexane (10 mL) was added to precipitate the
product that was collected and dried in vacuo. Yield: 0.041 g
(95%). IR (KBr): 871 cm-1. 1H NMR (C6D6): δ 8.15 (m, 2H, Ar
H), 7.30-6.66 (m, 18H, Ar H), 6.47 (s, 2H, NCH), 4.44 (br, 2H,
CH(CH3)2), 3.37 (s, 3H, N(CH3)), 2.76 (br, 2H, CH(CH3)2), 2.11
(s, 3H, N(CH3)), 1.87 (br, 6H, CH(CH3)2), 1.23 (br, 6H, CH(CH3)2),
RhCl(IMes)(P-N) (5). A solution of [RhCl(COE)(IMes)]2 (2;
0.055 g, 0.050 mmol) and P-N (0.031 g, 0.100 mmol) in toluene
(5 mL) was stirred for 4 h at room temperature, and the resulting
yellowish solution was concentrated to ∼2 mL. Addition of hexane

Rhodium(III) Peroxo Complexes
Organometallics, Vol. 25, No. 20, 2006 4877
1.09 (br, 6H, CH(CH3)2), 0.88 (br, 6H, CH(CH3)2). 31P{1H} NMR
(C6D6): 35.3 (d, JRhP ) 149). 13C{1H} NMR (C6D6): δ 160.1 (s,
NC), 159.9 (dd, JRhC ) 51, JPC ) 9, NCN), 159.8(s, NC), 139.9 (s,
Ar C), 139.3 (s, Ar C), 136.4 (s, Ar C), 136.2 (s, Ar C), 136.2 (s,
Ar C), 134.6 (s, Ar C), 134.1 (s, Ar C), 133.8 (s, Ar C), 133.3 (s,
Ar C), 132.7 (s, Ar C), 131.1 (s, Ar C), 130.5 (s, Ar C), 130.2 (s,
Ar C), 129.7 (s, Ar C), 129.1 (s, Ar C), 129.0 (s, Ar C), 127.0 (s,
Ar C), 126.4 (s, Ar C), 126.0 (s, Ar C), 121.7 (s, NCH), 121.5 (s,
NCH), 52.7 (s, N(CH3)2), 50.2 (s, N(CH3)2), 29.7 (s, CH(CH3)2),
24.4 (s, CH3), 23.4 (s, CH3). ESI-MS (MeOH): m/z 864, [M +
H]+ (100%); 847, [M - O]+ (18%); 322, [(OP-N) + H]+ (37%).
Anal. Calcd for C47H56N3PClO2Rh (M ) 864.3): C, 65.31; H, 6.53;
N, 4.86. Found: C, 65.35; H, 6.66; N, 5.12.
31P{1H} NMR (C6D6): 18.4 (d, JRhP ) 105). 13C{1H} NMR
(C6D6): δ 147.6 (s, NC), 146.6 (s, Ar C), 145.6 (s, Ar C), 133.0
(s, Ar C), 132.5 (s, Ar C), 131.6 (s, Ar C), 130.3 (s, Ar C), 130.0
(s, Ar C), 128.9 (s, Ar C), 128.8 (s, Ar C), 127.4 (s, Ar C), 127.3
(s, Ar C), 124.0 (br, NCH), 29.1 (s, CH(CH3)2), 25.1 (s, CH3), 23.9
(s, CH3). Anal. Calcd for C63H66P2N2ClO2Rh (M ) 1083.5): C,
69.84; H, 6.14; N, 2.59. Found: C, 70.20; H, 6.42; N, 2.61.
RhCl(O2)(IMes)(PPh3)2 (12). This orange complex was prepared
in a manner analogous to that described for 11 but using 0.048 g
(0.050 mmol) of 7. Yield: 0.047 g (84%). IR (KBr): 851 cm-1
.
1H NMR (C6D6): δ 7.80-6.80 (m, 34H, Ar H), 6.27 (s, 2H, NCH),
2.33 (s, 12H, o-CH3), 2.14 (s, 6H, p-CH3). 31P{1H} NMR (C6D6):
16.9 (d, JRhP ) 104). 13C{1H} NMR (C6D6): δ 138.7 (s, NC), 135.8
(s, Ar C), 135.6 (s, Ar C), 132.9 (s, Ar C), 132.8 (s, Ar C), 132.7
(s, Ar C), 131.9 (s, Ar C), 129.7 (s, Ar C), 129.5 (s, Ar C), 129.1
(s, Ar C), 128.9 (s, Ar C), 128.6 (s, Ar C), 123.6 (br, NCH), 21.6
(s, p-CH3), 19.0 (s, o-CH3). Anal. Calcd for C57H54P2N2ClO2Rh‚
1.5C6H6 (M ) 1116.4): C, 71.00; H, 5.69; N, 2.51. Found: C,
71.01; H, 5.88; N, 2.91.
RhCl(O2)(IMes)(P-N) (10). This orange complex was prepared
in a manner analogous to that described for 9 but using 0.037 g
(0.050 mmol) of 5. Yield: 0.037 g (95%). IR (KBr): 870 cm-1
.
1H NMR (C6D6): δ 8.20 (m, 2H, Ar H), 7.88-6.60 (m, 18H, Ar
H), 6.05 (s, 2H, NCH), 3.39 (s, 3H, N(CH3)), 2.26 (s, 6H, CH3),
2.14 (s, 12H, CH3), 1.97 (s, 3H, N(CH3)). 31P{1H} NMR (C6D6):
34.7 (d, JRhP ) 149). 13C{1H} NMR (C6D6): δ 160.2 (s, NC), 159.8-
(s, NC), 159.4 (dd, JRhC ) 50, JPC ) 9, NCN), 141.0 (s, Ar C),
140.5 (s, Ar C), 139.6 (s, Ar C), 138.6 (s, Ar C), 138.1 (s, Ar C),
136.7 (s, Ar C), 136.5 (s, Ar C), 136.4 (s, Ar C), 136.3 (s, Ar C),
136.2 (s, Ar C), 135.6 (s, Ar C), 135.4 (s, Ar C), 135.0 (s, Ar C),
132.3 (s, Ar C), 132.2 (s, Ar C), 129.2 (s, Ar C), 126.3 (s, Ar C),
126.2 (s, Ar C), 125.0 (s, Ar C), 121.6 (s, NCH), 121.5 (s, NCH),
52.8 (s, N(CH3)2), 50.1 (s, N(CH3)2), 21.5 (s, CH3), 19.4 (s, CH3),
19.2 (s, CH3). ESI-MS (MeOH): m/z 780, [M + H]+ (82%); 763,
[M - O]+ (100%); 322, [(OP-N) + H]+ (17%). Anal. Calcd for
C41H44N3PClO2Rh (M ) 780.1): C, 63.12; H, 5.68; N, 5.39.
Found: C, 63.27; H, 5.50; N, 5.29.
RhCl(O2)(PPh3)(P-N) (13). This complex was prepared in a
manner analogous to that described for 9 but using 0.035 g (0.050
mmol) of 8. Yield: 0.037 g (89%). IR (KBr): 873 cm-1. 1H NMR
(CDCl3): δ 7.73-7.00 (m, 29H, Ar H), 3.62 (br, 3H, N(CH3)2),
2.36 (br, 3H, N(CH3)2). 31P{1H} NMR (CDCl3): 45.6 (dd, JRhP
)
149, JPP ) 26), 37.7 (dd, JRhP ) 127, JPP ) 26). 13C{1H} NMR
(CDCl3): δ 136.1-127.2 (Ar C), 54.5 (s, N(CH3)2). 50.4 (s,
N(CH3)2). Anal. Calcd for C38H35P2NClO2Rh‚C7H8 (M ) 830.0):
C, 65.06; H, 5.18; N, 1.69. Found: C, 65.29; H, 5.08; N, 1.78. An
orange crystal suitable for X-ray analysis was grown by recrystal-
lization of the solid from benzene.
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada for financial support.
RhCl(O2)(IPr)(PPh3)2 (11). A yellow solution of 6 (0.053 g,
0.050 mmol) in benzene (5 mL) was stirred under 1 atm of O2 for
2 h at room temperature. The resulting suspension was concentrated
to ∼2 mL; addition of hexane (10 mL) precipitated further orange
product that was collected and dried in vacuo. Yield: 0.051 g
Supporting Information Available: Crystallographic data for
RhCl(O2)(IPr)(P-N) (9), RhCl(O2)(IMes)(P-N) (10), and RhCl(O2)-
(PPh3)(P-N) (13) as CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.
1
(94%). IR (KBr): 852 cm-1. H NMR (C6D6): δ 7.80-6.99 (m,
36H, Ar H), 6.73 (s, 2H, NCH), 3.26 (spt, 4H, J ) 7, CH(CH3)2),
1.43 (d, 12H, J ) 7, CH(CH3)2), 1.09 (d, 12H, J ) 7, CH(CH3)2).
OM060576I