Regioselectivity of the addition of O2 on SPS-based rhodium(i) and iridium(i) complexes

Article abstract of DOI:10.1021/om049198c

The addition of O₂ on SPS-type pincer-based Rh(i) and Ir(i) complexes was studied by means of DFT calculations. The regioselectivity and the influence of the nature of the metal center on the reaction thermicity were related through a thermodyn

Full text of DOI:10.1021/om049198c

1608
Organometallics 2005, 24, 1608-1613
Regioselectivity of the Addition of O2 on SPS-Based
Rhodium(I) and Iridium(I) Complexes
Marjolaine Doux, Louis Ricard, Pascal Le Floch,* and Yves Jean*
Laboratoire “He´te´roe´le´ments et Coordination” UMR CNRS 7653, Ecole Polytechnique,
91128 Palaiseau Cedex, France
Received October 15, 2004
The addition of O2 on SPS-type pincer-based Rh(I) and Ir(I) complexes was studied by
means of DFT calculations. The regioselectivity and the influence of the nature of the metal
center on the reaction thermicity were related through a thermodynamic cycle to the
electronic properties of the metal complex and to the energetics of the M-O bonds. The
synthesis and the X-ray crystal structure analysis of the Ir(I) complex are also presented.
Introduction
reported on the synthesis,5 the coordination chemistry,6
and the use in catalysis7 of a new type of SPS pincer
ligand featuring two PdS groups as ancillary ligands
and a central phosphorus atom as binding site. The
anionic tridentate ligands, which are easily assembled
from the corresponding phosphinines through a nucleo-
philic attack on phosphorus, were found to strongly
activate 16e Rh(I) centers. Thus, a neutral Rh(I) com-
plex, [Rh(SPS)(PPh3)] (4), reacted with O2 and CS2 to
yield the corresponding pseudo-octahedral η2-Rh(III)
complexes 5, which are depicted in Scheme 1.8 Surpris-
ingly, all these reactions proceeded with complete
regioselectivity, the attack taking place on the syn face
(to the substituent at phosphorus) of the square-planar
complex. This unusual facial discrimination had not
been rationalized before, and in this paper we present
the results of a DFT study that shed some light on this
surprising reactivity. Additional experiments and cal-
culations regarding the reactivity of the Ir complexes
6-9 are also reported.
Polydentate ligands featuring different heteroatoms
as binding sites are currently attracting great attention
both in coordination chemistry and in catalysis.1 Indeed,
it is now well recognized that the combination of very
different electronic and steric effects can lead to subtle
changes in the coordinating behavior of ligands as well
as the reactivity of their respective complexes. Modula-
tion of these electronic effects were found to play an
important role in many catalytic processes.2 Among
different possible combinations only little attention has
been paid to mixed P-S ligands, probably because of
the reputation of sulfur to act as a poison for catalysis.3
However, some P-S-based catalytic systems, even
operating at high temperature with low-valent metals,
already proved to be efficient catalysts.4 Recently, we
* To whom correspondence should be addressed. Tel:
+33.1.69.33.45.70. Fax:
+33.1.69.33.39.90. E-mail:
lefloch@
poly.polytechnique.fr, yves.jean@polytechnique.fr.
(1) (a) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27. (b)
Hovestad, N. J.; Eggeling, E. B.; Heidbu¨chel, H. J.; Jastrzebski, J. T.
B. H.; Kragl, U.; Keim, W.; Vogt, D.; van Koten, G. Angew. Chem.,
Int. Ed. 1999, 38, 1655. (c) Weber, R.; Englert, U.; Ganter, B.; Keim,
W.; Mo¨thrath, M. Chem. Commun. 2000, 1419. (d) Braunstein, P.;
Naud, F.; Rettig, S. New J. Chem. 2001, 25. (e) Albrecht, M.; Van
Koten, G. Angew. Chem. 2001, 113, 3866. (f) Dai, W.-M.; Yeung, K. K.
Y.; Liu, J.-T.; Zhang, Y.; Williams, I. D. Org. Lett. 2002, 4, 1615. (g)
Andrieu, J.; Richard, P.; Camus, J.-M.; Poli, P. Inorg. Chem. 2002, 41,
3876. (h) Thoumazet, C.; Melaimi, M.; Ricard, L.; Mathey, F.; Le Floch,
P. Organometallics 2003, 22, 1580. (i) Agbossou-Niedercorn, F.; Suisse,
I. Coord. Chem. Rev. 2003, 242, 145. (j) van der Boom, M. E.; Milstein,
D. Chem. Rev. 2003, 103, 1759. (k) Barloy, L.; Malaise´, G.; Ramdeehul,
S.; Newton, C.; Osborn, J. A.; N., K. Inorg. Chem. 2003, 42. (l)
Bunlaksananusorn, T.; Polborn, K.; Knochel, P. Angew. Chem., Int.
Ed. 2003, 42. (m) Franco, D.; Go´mez, M.; Jime´nez, F.; Muller, G.;
Rocamora, M.; Maestro, M. A.; Mah´ıa, J. Organometallics 2004, 23,
3177. (n) Maire, P.; Deblon, S.; Breher, F.; Geier, G.; Bo¨hler, C.;
Ru¨egger, H.; Scho¨nberg, H.; Gru¨tzmacher, H. Chem. Eur. J. 2004, 10,
4198.
Results and Discussion
The ability of the SPS-type pincer-based Rh(I) and
Ir(1) complexes to activate the O2 molecule was studied
by means of DFT calculations, using model complexes
(noted as [M(SPS)(PH3)] with M ) Rh, Ir) in which the
phenyl groups were replaced by H atoms. Four modes
of attack were considered (syn-SS, anti-SS, syn-PP, and
anti-PP) depending whether the incoming O2 molecule
is located (i) syn or anti to the P-Me bond and (ii)
coplanar to the M-S bonds (SS) or to the M-P bonds
(PP) (Scheme 2). The regioselectivity of the addition
reaction as well as the influence of the nature of the
metal center on its thermicity were related through a
thermodynamic cycle to the electronic properties of the
metal complex and to the energetics of the M-O
bonding.
(2) See for example: Braunstein, P.; Naud, F. Angew. Chem., Int.
Ed. 2001, 40, 680.
(3) (a) Bayo´n, J. C.; Claver, C.; Masdeu-Bulto´, A. M. Coord. Chem.
Rev. 1999, 193-195, 73. (b) Mizuta, T.; Imamura, Y.; Miyoshi, K. J.
Am. Chem. Soc. 2003, 125, 2068. (c) Kostas, I. D.; Steele, B. R.;
Andreadaki, F. J.; Potapov, V. A. Inorg. Chim. Acta 2004, 357, 2850.
(4) (a) Baker, M. J.; Giles, M. F.; Orpen, A. G.; Taylor, M. J.; Watt,
R. J. Chem. Commun. 1995, 197. (b) Suranna, G. P.; Mastrorilli, P.;
Nobile, C. F.; Keim, W. Inorg. Chim. Acta 2000, 305, 151. (c) Gonsalvi,
L.; Adams, H.; Sunley, G. J.; Ditzel, E.; Haynes, A. J. Am. Chem. Soc.
2002, 124, 13597. (d) Liang, H.; K., N.; Ito, S.; Yoshifuji, M. Tetrahedron
Lett. 2003, 44, 8297. (e) Ito, S.; Liang, H.; Yoshifuji, M. Chem. Commun.
2003, 398.
(5) Doux, M.; Bouet, C.; Me´zailles, N.; Ricard, L.; Le Floch, P.
Organometallics 2002, 21, 2785.
(6) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P. Eur. J. Inorg.
Chem. 2003, 3878.
(7) Doux, M.; Me´zailles, N.; Melaimi, M.; Ricard, L.; Le Floch, P.
Chem. Commun. 2002, 1566.
(8) Doux, M.; Me´zailles, N.; Ricard, L.; Le Floch, P. Organometallics
2003, 22, 4624.
10.1021/om049198c CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/19/2005

Regioselectivity of the Addition of O2
Organometallics, Vol. 24, No. 7, 2005 1609
Scheme 1
Scheme 2
Table 1. Main Geometical Parameters Optimized
for the [M(SPS)(PH3)] Complex for M ) Rh, Ir (see
Figure 1 for the atom numbering)a
around the Rh center with P1-Rh-P4 and S1-Rh-S2
angles of 174.3° and 173.9°, respectively (exptl 174.7°
and 172.5°, respectively). There is an excellent agree-
ment between the experimental and theoretical bond
lengths (deviations smaller than 0.020 Å) with the
exception of the Rh-S distance, which is overestimated
by 0.080 Å (Figure 1).9
[M(SPS)PH3]
M ) Rh
M ) Ir
M-P1
2.259 (2.243)
2.303 (2.303)
2.401 (2.320)
2.401 (2.321)
1.839 (1.820)
1.799 (1.794)
1.799 (1.805)
1.762 (1.763)
1.762 (1.769)
2.030 (2.024)
2.030 (2.022)
99.8 (101.4)
311.0 (311.2)
173.9 (172.5)
174.3 (174.7)
111.9 (113.6)
111.9 (111.1)
111.9 (109.8)
111.9 (109.6)
99.4 (107.7)
99.4 (101.3)
2.274
2.272
2.380
2.380
1.837
1.797
1.797
1.763
1.763
2.041
2.041
100.1
312.6
172.7
171.4
111.7
111.6
111.4
111.4
97.9
M-P4
M-S1
M-S2
The geometry of the addition complex [(Rh(SPS)(PH3)-
(O2)] was studied for the syn-SS, syn-PP, anti-PP, and
anti-SS attacks of O2 (Scheme 2). Four different isomers
(Ia-IVa) were actually optimized and further charac-
terized as minima on the potential energy surface. Their
structures are depicted in Figure 2 together with
selected geometrical parameters (see also the Support-
ing Information). A pseudo-octahedral complex featur-
ing an η2 coordination of O2 was found for three first
approaches (Ia-IIIa). On the other hand, the anti-SS
attack led to the breaking of a metal-sulfur bond and
the formation of a complex with a distorted trigonal
bipyramid geometry (IVa), the oxygen atoms of the η2-
O2 molecule occupying two equatorial sites.10 In agree-
ment with the experimental data, the syn-SS isomer was
found to be the most stable isomer, the energy ordering
being (in kcal mol-1) syn-SS (Ia) (0) < anti-PP (IIa)
(+7.1) < anti-SS (IVa) (+11.7) < syn-PP (IIIa) (+13.7).
The energy differences are large enough to understand
why only the syn-SS isomer (Ia) has been observed
experimentally. Furthermore, it is the only isomer that
was found to be more stable than the isolated reactants
(∆ER ) -5.1 kcal mol-1). The O-O distance, elongated
from 1.208 Å in free O2 to 1.386 Å (exptl 1.431(2) Å),
and the Rh-O distances of 2.021 and 2.023 Å (exptl
(2.027(2))av Å) are consistent with a RhIII peroxo struc-
P1-Me
P1-C2
P1-C6
P2-C2
P3-C6
P2-S1
P3-S2
C2-P1-C6
∑ (C-P1-C)
S1-M-S2
P1-M-P4
P1-C2-P2
P1-C6-P3
C2-P2-S1
C6-P3-S2
M-S1-P2
M-S2-P3
97.9
a Bond lengths are in Å and angles in deg. Experimental values
are given in parenthesis for the Rh complex.8
Figure 1. Optimized geometry of 1[Rh(SPS)(PH3)]. Hy-
(9) The discrepancy between the experimental and theoretical
structure was slightly reduced when the phenyl substituents on the
phosphorus centers and as well as on the phosphinine ring were taken
into account by means of QM/MM calculation (see computational
details and Supporting Information). The optimized Rh-S distance
(2.388 Å) is 0.067 Å longer than the experimental value.
(10) A pseudo-octahedral structure associated with the anti-SS
attack on the Rh complex was also characterized as a minimum on
the potential energy surface. However its energy is located 9.7 kcal
mol-1 above that of IVa. The same holds for the anti-SS attack on the
Ir complex, the energy of the pseudo-octahedral structure being found
to be 17.7 kcal mol-1 above that of IVb.
drogen atoms are omitted for clarity.
In a first set of calculations, the geometry of the
complex [Rh(SPS)(PH3)] was optimized in its lowest
singlet state without any symmetry constraint. The
main theoretical parameters are reported in the first
column of Table 1 together with the experimental
values. A nearly square-planar arrangement was found

1610 Organometallics, Vol. 24, No. 7, 2005
Doux et al.
Figure 2. Optimized geometries of rhodium complexes Ia-IVa. Hydrogen atoms are omitted for clarity. E: relative energy
in kcal mol-1. Selected geometrical parameters (in Å and deg). Ia: O1-O2 1.386, Rh-O1 2.021, Rh-O2 2.023, Rh-S1
2.494, Rh-S2 2.500, Rh-P1 2.297, Rh-P4 2.358, S1-Rh-S2 93.2, P1-Rh-P4 173.4. IIa: O1-O2 1.384, Rh-O1 1.989,
Rh-O2 2.062, Rh-S1 2.420, Rh-S2 2.4420, Rh-P1 2.307, Rh-P4 2.321, S1-Rh-S2 177.7, P1-Rh-P4 104.6. IIIa: O1-
O2 1.380, Rh-O1 2.005, Rh-O2 2.061, Rh-S1 2.425, Rh-S2 2.426, Rh-P1 2.265, Rh-P4 2.345, S1-Rh-S2 171.5, P1-
Rh-P4 101.5. IVa: O1-O2 1.359, Rh-O1 2.003, Rh-O2 1.999, Rh-S1 5.601, Rh-S2 2.328, Rh-P1 2.327, Rh-P4 2.400,
S2-Rh-O1 161.3, S2-Rh-O2 158.2, P1-Rh-P4 175.1.
Table 2. Energy Decomposition (kcal mol-1) for
the Formation of I-IV Isomers by the Addition of
O2 on the [M(SPS)(PH3)] Complex: (a) M ) Rh; (b)
M ) Ir
Scheme 3
(a)
syn-SS
(Ia)
anti-PP
(IIa)
syn-PP
(IIIa)
anti-SS
(IVa)
M ) Rh
∆Edist(ML4)
∆ES/T
+27.1
-1.4
+25.7
+20.6
-51.4
-5.1
+31.2
-0.8
+30.4
+20.2
-48.6
+2.0
+35.3
-1.9
+33.4
+19.4
-44.2
+8.6
+31.9
+4.9
+36.8
+15.6
-45.8
+6.6
a
∑ ) ∆ET dist
∆Estrech3(O2)
2∆Ebond(M-O)
b
∆ER
ture (Figure 2, Ia). The bond angles in the plane defined
by the two sulfur ligands and the oxygen molecule are
satisfactorily reproduced: S1-Rh-S2 ) 93.2° (exptl
98.7°) and O1-Rh-O2 ) 40.1° (exptl 41.3°).
(b)
syn-SS
(Ib)
anti-PP
(IIb)
syn-PP
(IIIb)
anti-SS
(IVb)
M ) Ir
The electronic factors responsible for the regioselec-
tivity of this oxidative addition reaction can be analyzed
by means of a thermodynamic cycle which connects the
separate reactants (1[Rh(SPS)(PH3)] + 3O2) to the peroxo
complex (Ia-IVa) (Scheme 3). The reaction is decom-
posed into the following steps: (i) distortion of the
1[Rh(SPS)(PH3)] complex from its equilibrium geometry
to its geometry in the product (∆Edist(ML4)); (ii) forma-
tion of the triplet state (∆ES/T); the distorted metal
fragment with two unpaired electrons is now in the
optimal situation to form two new bonds; (iii) stretching
∆Edist(ML4)
∆ES/T
+36.9
-6.3
+30.6
+26.8
-73.4
-16.0
+39.1
-2.3
+36.8
+27.4
-77.7
-13.5
+48.1
-5.7
+42.4
+27.3
-74.2
-4.5
+41.2
-0.6
+40.6
+20.4
-63.7
-2.7
a
∑ ) ∆ET dist
∆Estrech3(O2)
2∆E bond(M-O)
b
∆ER
a ∑ ) ∆ET
)∆Edist(ML4) + ∆ES/T.
b ∆ER ) ∆Edist(ML4) +
dist
∆ES/T + ∆Estrech3(O2) + 2∆Ebond(M-O).
Similar calculations were performed on the Ir ana-
logue. The syn-SS isomer (Ib) was still found to be the
most stable isomer, the energy ordering being (in kcal
mol-1) syn-SS (Ib) (0) < anti-PP (IIb) (+2.5) < syn-PP
(IIIb) (+11.5) < anti-SS (IVb) (+13.3). The energy
decomposition shows that this result can be mainly
traced to triplet state energy of the distorted metal
fragment (∆ET dist, Table 2b). As a matter of fact, this
term parallels the relative energies of the three most
stable isomers, whereas the Ir-O bonding energy favors
an addition trans to the Ir-P bonds (anti-PP and syn-
PP isomers). As it has been shown previously,11 the ∆ET
dist term comes out to be an important factor to predict
the outcome of an oxidative addition reaction. The
energy difference between the two most stable isomers
of O2 to its actual bond distance in the product (∆Estretch
-
(O2)); (iv) formation of the M-O bonds (2∆Ebond(M-O)).
The energy change associated with the addition reaction
(∆ER) can thus be expressed as ∆ER ) ∆Edist(ML4) +
∆ES/T + ∆Estretch(O2) + 2∆E bond(M-O). In the following
discussion, the two first terms will be most often
considered together since their sum (quoted as ∑ ) ∆ET
dist) represents the energy required to “prepare” the
metal fragment for the oxidative addition reaction.
Results of this energy decomposition are given in
Table 2a. Both the triplet state energy of the distorted
metal fragment and the energies of the bonds under
formation come out to be important factors to rationalize
the selectivity observed experimentally. It is noteworthy
that the syn-SS isomer (Ia) is favored with respect to
the other isomers by the smallest triplet metal fragment
energy (∆ET dist) and by the strongest Rh-O bonding
energy. For instance, if one compares the two most
stable isomers, syn-SS (Ia) and anti-PP (IIa), both ∆ET
dist(Rh-O) (by 4.7 kcal mol-1) and 2∆E bond(Rh-O) (by
2.8 kcal mol-1) terms work in favor of the experimen-
tally observed syn-SS isomer.
(syn-SS and the anti-PP) is rather small (2.5 kcal mol-1
)
since the Ir-O bonding energy and the ∆ET dist terms
work in opposite directions. From a structural point of
view, the O-O and Ir-O distances optimized in the syn-
SS isomer (Ib) were found to be equal to 1.418 Å and
2.025 Å, respectively, a result consistent with an IrIII
(11) (a) Su, M.-D.; Chu, S.-Y. J. Am. Chem. Soc. 1997, 119, 5373.
(b) Tomas, J.; Lledos, A.; Jean, Y. Organometallics 1998, 17, 4932. (c)
Lesnard, H.; Demachy, I.; Jean, Y.; Lledos, A. Chem. Commun. 2003,
850.

Regioselectivity of the Addition of O2
Organometallics, Vol. 24, No. 7, 2005 1611
bipyramid (Scheme 4). In 6, the 31P NMR signals of the
SPS moiety appear as expected sets of a triplet and
doublet at 7.9 ppm (P-Me) and 47.8 ppm (PPh2S),
respectively, with a 2J(P-P) coupling constant of 112.4
Hz. Compared to its rhodium analogue, in 6 the chemi-
cal shift of the P-Me moiety is shifted toward high field
(∆δ ) -25.2 ppm). The other important difference issues
from the spin system pattern of the vinylic CH (COD)
in the 13C NMR spectrum. Indeed, in 6, these signals
appear as a doublet at 62.0 ppm (2J(C-P) ) 6.3 Hz),
whereas, in 3, they appear as a broad singlet at 78.6
ppm. This could be explained by a better back-bonding
of the metal into the alkene bond in the case of the
iridium complex 6. Apart from these data, these iridium
and rhodium complexes did not differ to a great extent.
Figure 3. ORTEP view of complex 9. Phenyl groups have
been omitted for clarity. Ellipsoids are scaled to enclose
50% of the electron density. The numbering is arbitrary
and different from that used in the assignment of NMR
spectra. Relevant distances (Å) and bond angles (deg): O1-
Ir 2.01(1), O2-Ir 2.03(1), P1-Ir 2.263(4), P4-Ir 2.337(4),
S1-Ir 2.405(5), S2-Ir 2.397(4), O1-O2 1.46(2), P1-C1
1.78(2), C1-C2 1.43(2), C2-C3 1.40(2), C3-C4 1.41(3),
C4-C5 1.39(2), C5-P1 1.79(2), C1-P2 1.74(2), C5- P3
1.75(2), P2-S1 2.030(6), P3-S2 2.033(6), P1-Ir-P4 172.4-
(2), S1-Ir-O1 113.3(4), O1-Ir-O2 42.5(5), O2-Ir-S2
118.7(4), C1-P1-C5 100.8(7).
The displacement of the COD ligand in 6 by triph-
enylphosphine was attempted. Unfortunately, despite
many efforts (temperature up to 80 °C, presence of H2
up to 20 atm, reaction carried out in THF and in MeOH,
use of PMe3), no reaction occurred. Therefore, we turned
our attention to the [Ir(COE)2Cl]2 precursor (COE )
cyclooctene) in which the COE ligand was supposed to
be more labile than the COD ligand. Following the same
procedure, the iridium(I) complex 8 was readily syn-
thesized from the reaction of anion 2 with half an
equivalent of the [Ir(COE)2Cl]2 precursor (Scheme 5).
Unfortunately, complex 8 was found to be not stable
enough to be isolated and decomposed within 30 min
in solution. Complex 8 was only characterized on the
basis of its 31P NMR spectrum, in which the signals of
the SPS moiety appeared as sets of a triplet and doublet
at 13.9 ppm (P-Me) and 33.6 ppm (PPh2S), respectively,
with a 2J(P-P) coupling constant of 114.2 Hz. Note that
7 can also be synthesized from the reaction of half an
equivalent of [Ir(COE)2Cl]2 with a solution of anion 2
followed by reaction with triphenylphosphine. The solu-
tion immediately turned from red (anion 2) to dark
brown. After 1 h, the formation of complex 7 was
completed. However, complex 7 proved to be highly
reactive (vide supra). Any attempts of purification
(drying or precipitation) caused the decomposition of the
product. Therefore, complex 7 was stored in a THF
solution in the glovebox without any possible purifica-
tion. Like 8, complex 7 was characterized only by 31P
NMR spectroscopy, which revealed that the PPh2S
groups are magnetically equivalent and that therefore
the structure is symmetrical. This spectrum exhibits an
AB2C spin system pattern. As expected, the 31P NMR
signals of the SPS moiety appear as sets of a doublet of
triplets and doublet of doublets at 19.8 ppm (PA-Me) and
37.7 ppm (Ph2PBdS), respectively, and the triphenylphos-
phine (PCPh3) ligands appear as a doublet of triplets at
peroxo structure (see also Supporting Information and
experimental X-ray structure given in Figure 3).
The larger exothermicity of the addition reaction
(-16.0 instead of -5.1 kcal mol-1, Table 2) as well as
the increase of the O-O distance in the most stable syn-
SS isomer (from 1.386 in Ia to 1.418 Å in Ib) suggest
that the activation of O2 increases on going from Rh to
Ir. The use of the thermodynamic cycle described in
Scheme 3 offers a clear rationalization of this result.
Comparison of the energy decomposition for the Rh (Ia)
and Ir (Ib) syn-SS isomers (Table 2) shows that the
evolution of the ∆ET dist term is opposite that of ∆ER, so
that, taken alone, it would favor the reaction of the Rh
complex. The only factor that makes the reaction with
the Ir complex more exothermic is the M-O bonding
energy, which is found to be much larger for M ) Ir
(-73.4 kcal mol-1) than for M ) Rh (-51.4 kcal mol-1).
This result examplifies the second important factor to
rationalize the behavior of a complex in an oxidative
addition reaction, i.e., the strength of the metal-ligand
bonds under formation.
With these results at hand, we were stimulated to
synthesize the iridium analogue of the rhodium complex
4 and to test its reactivity toward oxygen. A synthetic
procedure analogous to the one used for the synthesis
of 4 was followed (Scheme 1).
Complex 6 was easily prepared from the reaction of
anion 2 with half an equivalent of the [Ir(COD)Cl]2
precursor (Scheme 4). Complex 6, which was isolated
as a very stable orange solid, was fully characterized
by NMR techniques and elemental analyses. Unfortu-
nately, despite many attempts, 6 could not be crystal-
lized and information about the spatial arrangement of
the SPS ligand could not be obtained. Although 31P
NMR spectroscopy revealed that the PPh2S groups are
magnetically equivalent, two geometries can be pro-
posed for 6: one in which the ligand is located in the
plane and a second in which it caps one face of the
2
2
30.9 ppm with J(PA-PB) ) 128.1, J(PA-PC) ) 370.2,
3
and J(PB-PC) ) 37.9 Hz.
Finally, reaction with O2 was attempted. Coordination
readily occurred in THF by bubbling O2 (1 atm) into a
solution of 7 at -78 °C to form complex 9 (Scheme 5).
The solution became orange and a precipitate formed
within 2 h. The geometry of 9 could not be unambigu-
ously established on the sole basis of NMR data.
However, it is clear that the structure of 9 remains
symmetrical and 31P NMR signals of the PPh2 and PPh3
moieties are highly shifted from ∆δ ) +12.5 ppm and
-26.0 ppm, respectively. As expected, all signals appear

1612 Organometallics, Vol. 24, No. 7, 2005
Doux et al.
Scheme 4
Scheme 5
Table 3. Crystal Data and Structural Refinement
Details for 9
2.025, 2.302, 2.335 Å vs 1.78(2), 1.74(2), 2.030(6), 1.46-
(2), 2.01(1), 2.263(4), 2.337(4) Å in 5a. Moreover no
discrepancies arise from the Ir-S distances: 2.468 in
Ib vs 2.405(5) and 2.397(4) Å in 9.
formula
Mr
cryst syst
space group
a [Å]
b [Å]
c [Å]
C60H49IrO2P4S2,C4H8O
1254.30
monoclinic
P21/n
In conclusion, the regioselectivity of the addition of
O2 to the [Rh(SPS)(PH3)] complex is well reproduced by
DFT calculations. The syn-SS isomer is found to be
favored by a factor related to a metal fragment property,
i.e., the energy required to form the distorted complex
in its lowest triplet state, and by the energetics of the
Rh-O bonds under formation. Synthesis of the iridium
analogue was also achieved and a syn-SS geometry is
proposed on the basis of DFT calculations and confirmed
by X-ray data. Finally, the increase of the exothermicity
of the addition reaction on going from Rh to Ir is found
to reflect the increase of the M-O bonding energy (Ir
> Rh).
16.891(2)
13.1160(10)
28.127(3)
106.870(10)
5963.2(11)
4
â [deg]
V [Å3]
Z
F [g cm-3
]
1.397
2.460
µ [cm-1
]
cryst size [mm]
F(000)
0.14 × 0.10 × 0.03
2536
index ranges
2θmax [deg]/criterion
-19 19; -14 13; -31 31
23.82/I > 2σI
no. of params refined; data/param 669; 11
no. of reflns collected
no. of independ reflns
no. of reflns used
wR2
16 433
9044
7935
Experimental Section
0.2296
R1
0.0767
General Considerations. All reactions were routinely
performed under an inert atmosphere of argon or nitrogen by
using Schlenk and glovebox techniques and dry deoxygenated
solvents. Dry THF and hexanes were obtained by distillation
from Na/benzophenone dry ether from CaCl2 and then NaH
and dry CH2Cl2 from P2O5. CDCl3 was dried from P2O5 and
stored on 4 Å Linde molecular sieves. CD2Cl2 was stored on 4
Å Linde molecular sieves in the glovebox. [Ir(COD)Cl]2 was
purchased from Strem chemicals and stored under nitrogen.
Nuclear magnetic resonance spectra were recorded on a
Bruker Advance 300 spectrometer operating at 300.0 MHz for
1H, 75.5 MHz for 13C, and 121.5 MHz for 31P. Solvent peaks
are used as internal reference relative to Me4Si for 1H and
13C chemical shifts (ppm); 31P chemical shifts are relative to a
85% H3PO4 external reference. Coupling constants are given
in hertz. The following abbreviations are used: s, singlet; d,
doublet; t, triplet; q, quadruplet; p, pentuplet; m, multiplet; v,
virtual. Elemental analyses were performed by the “Service
d’analyse du CNRS”, at Gif sur Yvette, France. Phosphinine
goodness of fit
1.027
largest diff peak/hole [e Å-3
]
1.812(0.191)/-3.036(0.191)
as sets of doublets of triplets and doublets of doublets
at 17.7 ppm (PA-Me) and 50.2 ppm (PBPh2S), respec-
tively, and the triphenylphosphine (PCPh3) as a doublet
2
2
of triplets at 4.9 ppm with J(PA-PB) ) 100.1, J(PA-
3
PC) ) 428.5, and J(PB-PC) ) 24.2.9 Hz. Apart from
this, the spectra of 9 do not deserve further comment.
Fortunately, small, twined crystals of complex 9 could
be grown and analyzed by X-ray structure analysis. An
ORTEP view of one molecule of 9 is presented in Figure
3 with the most significant metric parameters. Crystal
data and structure refinement details are presented in
Table 3. As predicted by DFT calculations, the overall
geometry of complex 9 results from the syn-SS attack
of O2: the SPS ligand caps one face of the trigonal
bipyramid. Examination of the O-O distance (1.46(2)
Å) reveals that 9 is a IrIII peroxo complex.12 As can be
seen by examining these data, there is an excellent fit
between theoretical and experimental parameters. In
Ib the SPS ligand, O-O, Ir-O, and Ir-P bond distances
are very close to those of the X-ray structure of 9: for
instance, in Ib the P1-C1, C1-P2, P2-S1, O1-O2, Ir-
O1, Ir-P1, and Ir-P4 are 1.793, 1.756, 2.032, 1.418,
1,5 anion 2,6 and [Ir(COE)2Cl]2 were prepared according to
13
reported procedures.
Synthesis of Complex 6. A solution of MeLi in Et2O (95
µL, C ) 1.6 M, 0.15 mmol) was syringed into a solution of 1
(100 mg, 0.15 mmol) in THF (5 mL) at -78 °C. The solution
was warmed to room temperature and stirred for 20 min.
Complete formation of 2 is checked by 31P NMR (THF): δ 44.83
(d, 2J(P-P) ) 156.7, PPh2), -66.52 (t, 2J(P-P) ) 156.7, PMe).
In the glovebox, [Ir(COD)Cl]2 (49.3 mg, 0.07 mmol) was added
(12) See for example: (a) Ho, D. G.; Ismail, R.; Franco, N.; Gao, R.;
Leverich, E. P.; Tsyba, I.; Ho, N. N.; Baub, R.; Selke, M. Chem.
Commun. 2002, 570. (b) Teixidor, F.; Ayllon, J. A.; Vinas, C.; Sillanpaa,
R.; Kivekas, R.; Casabo, J. Inorg. Chem. 1994, 33, 4815.
(13) Herde, J. L.; Lambert, J. C.; Senoff, C. V.; Cushing, M. A. In
Inorganic Syntheses; Parshall, G. W., Ed.; R. E. Krieger Publishing
Company: Malabar, FL, 1982; Vol. 15, p 19.

Regioselectivity of the Addition of O2
Organometallics, Vol. 24, No. 7, 2005 1613
and the solution was stirred for 30 min. After removing the
solvent, the solid was washed first with hexanes (3 × 2 mL)
then with ether (3 × 2 mL). The resulting solid was dissolved
in CH2Cl2 and filtrated through Celite. After drying, 5 was
recovered as an orange solid. Yield: 126 mg (86%). Anal. (%)
calcd for C50H46IrP3S2: C 60.28, H 4.65. Found: C 59.92, H
also optimized at the ONIOM(B3PW91/UFF) level,20 where the
QM part was treated within the framework of density func-
tional theory at the B3PW91 and the UFF force field21 was
used for the molecular mechanics calculations (phenyl groups).
In this QM/MM calculation, the basis set for the QM part is
the same as that described above.
X-ray Crystallographic Study. A crystal of compound 10
suitable for X-ray diffraction deposited from a THF solution.
Data were collected at 150.0(1) K on a Nonius Kappa CCD
diffractometer using a Mo KR (λ ) 0.71070 Å) X-ray source
and a graphite monochromator. All data were measured using
phi and omega scans. Experimental details are described in
Table 3. The crystal structures were solved using SIR 9722 and
SHELXL-97.23 ORTEP drawings were made using ORTEP III
for Windows.24 CCDC-262573 contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac.uk/conts/retriev-
ing.html [or from the Cambridge Crystallographic Data Cen-
tre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)
+44-1223/336-033; e-mail: deposit@ccdc.cam.ac.uk].
2
4.17. 31P (CDCl3): δ 7.86 (t, J(PA-PB) ) 112.4, PAMe), 47.84
2
1
2
(d, J(PA-PB) ) 112.4, PBPh2). H (CDCl3): δ 1.29 (d, J(H-
PA) ) 8.4, 3H, CH3), 1.51 (s, 8H, CH2 of COD), 3.32 (s, 4H, CH
of COD), 5.53 (t, 4J(H-PB) ) 4.2, 1H, H4), 6.67-8.05 (m, 30H,
CH of Ph). 13C (CDCl3): δ 5.7 (s, J(C-PA) ) 40.2, CH3), 32.9
1
(s, CH2), 62.0 (d, 2J(C-PA) ) 6.3, CH of COD), 72.3 (dd, 1J(C-
P) ) 95.9, 1J(C-P) ) 39.3, C2,6), 117.1 (v q, 4J(C-PA) ) 4J(C-
PB) ) 10.7, C4H), 127.4-133.1 (m, CH of Ph), 134.4 (s, C of
Ph), 135.7 (s, C of Ph), 143.3 (br s, C3,5), 153.5 (br s, C of Ph).
Synthesis of Complex 7. A solution of MeLi in Et2O (95
µL, C ) 1.6 M, 0.15 mmol) was syringed into a solution of 1
(100 mg, 0.15 mmol) in THF (5 mL) at -78 °C. The solution
was warmed to room temperature and stirred for 20 min.
Complete formation of 2 is checked by 31P NMR (THF): δ 44.83
(d, 2J(P-P) ) 156.7, PPh2), -66.52 (t, 2J(P-P) ) 156.7, PMe).
In the glovebox, [Ir(COE)2Cl]2 (63 mg, 0.8 mmol) and PPh3 (40
mg, 15 mmol) were added, and the solution was stirred for 2
h. 7 was too sensitive to be dried or give satisfactory elemental
data. Yield: 100%. 31P (THF-d8): δ 19.8 (td, 2J(PC-PA) ) 370.2,
2J(PB-PA) ) 128.1, PAMe), 30.9 (td, 2J(PA-PC) ) 370.2, 3J(PB-
PC) ) 37.9, PCPh3), 37.7 (dd, 2J(PB-PA) ) 128.1, 3J(PB-PC) )
37.9, PBPh2).
Acknowledgment. The authors thank the CNRS,
the DGA, and the Ecole Polytechnique for supporting
this work and IDRIS (Orsay, Paris XI) for the allowance
of computer time.
Supporting Information Available: Optimized geometry
of [M(SPS)(PH3)] (M ) Rh, Ir) and I-IV(a,b). This material
is available free of charge via the Internet at http://pubs.acs.org.
Synthesis of Complex 8. A solution of MeLi in Et2O (95
µL, C ) 1.6 M, 0.15 mmol) was syringed into a solution of 1
(100 mg, 0.15 mmol) in THF (5 mL) at -78 °C. The solution
was warmed to room temperature and stirred for 20 min.
Complete formation of 2 is checked by 31P NMR. In the
glovebox, [Ir(COE)2Cl]2 (63 mg, 0.8 mmol) was added and the
solution was stirred for 5 min. 8 decomposed within 30 min
in THF; no NMR signal is then observed. 31P (THF): δ 13.9
(t, 2J(PA-PB) ) 114.2, PAMe), 33.6 (d, 2J(PB-PA) ) 114.2,
PBPh2).
OM049198C
(14) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; J. A. Montgomery, J.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa,
J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene,
M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A.
J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma,
K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;
Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui,
Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.;
Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challa-
combe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.;
Gonzalez, C.; Pople, J. A. GAUSSIAN 03, Revision B.04; Gaussian,
Inc.: Pittsburgh, PA, 2003.
Synthesis of Complex 9. A solution of 5 (0.15 mmol) in
THF (5 mL) was stirred under an O2 atmosphere (1 atm) for
2 h, and an orange solid precipitated. The solid was filtered
off and washed with THF (5 mL) and hexane (5 mL). 9 was
recovered as an orange solid. Crystals of compound 9 suitable
for X-ray diffraction deposited from a THF solution. Yield: 145
mg (82%). Anal. (%) Calcd for C60H49IrO2P4S2: C 60.95, H 4.18.
2
Found: C 60.53, H 3.91. 31P (CD2Cl2): δ 4.9 (td, J(PC-PA) )
428.5, 3J(PC-PB) ) 24.2, PCPh3), 17.7 (td, 2J(PA-PC) ) 428.5,
2J(PA-PB) ) 100.1, PAMe), 50.2 (dd, 2J(PB-PA) ) 100.1, 3J(PB-
(15) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, U.K., 1989. Ziegler, T.
Chem. Rev. 1991, 91, 651.
1
2
PC) ) 24.2, PBPh2). H (CD2Cl2): δ 1.32 (dd, J(H-P) ) 11.3,
4J(H-P) ) 1.9, 3H, CH3), 5.77 (t, 4J(H-PB) ) 4.4, 1H, H4),
6.87-8.07 (m, 45H, H of Ph). 13C (CD2Cl2): δ 1.0 (m, CH3),
69.5 (m, C2,6), 116.2 (t, 3J(C-PB) ) 11.8, C4), 126.4-133.8 (m,
CH and C of Ph), 141.7 (∑ J ) 10.6, C3,5), 153.5 (bs, C of Ph).
Computational Details. Calculations were performed with
the GAUSSIAN 03 series of programs14 on the model systems
[M(SPS)(PH3)] and [M(SPS)(PH3)(O2)] (M ) Rh, Ir) with the
phenyl groups replaced by H atoms. Density functional theory
(DFT)15 was applied with the B3PW91 functional.16 A qua-
sirelativistic effective core potential operator was used to
represent the 28 innermost electrons of the rhodium atom and
the 60 innermost electrons of the iridium atom.17 The basis
set for the metal was that associated with the pseudopoten-
tial,17 with a standard double-ú LANL2DZ contraction17 com-
pleted by a set of f-polarization functions.18 The 6-31+G* basis
set was used for O, P, and S atoms, 6-31G* for C atoms, and
6-31G for H atoms.19 The minimum energy structures were
characterized by full vibration frequencies calculations. The
fully substituted square-planar complex [Rh(SPS)(PPh3)] was
(16) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(17) Hay, P. J.; Wadt, W. R. J. Chem. Phys. 1985, 82, 299.
(18) Ehlers, A.; Bohme, M.; Dapprich, S.; Gobbi, A.; Hollwarth, A.;
Jonas, V.; Kohler, K.; Stegmenn, R.; Veldkamp, A.; Frenking, G. Chem.
Phys. Lett. 1993, 208, 111.
(19) (a) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972,
56, 2257. (b) Hariharan, P. C.; Pople, J. A. Theor. Chim. Acta 1973,
28, 213. (c) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.;
Gordon, M. S.; DeFrees, D. J.; Pople, J. A. J. Chem. Phys. 1982, 77,
3654. (d) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P.
v. R. J. Comput. Chem. 1983, 4, 294.
(20) Svensson, M.; Humbel, S.; Froese, R. D. J.; Matsubara, T.;
Sieber, S.; Morokuma, K. J. J. Phys. Chem. 1996, 100, 19357.
(21) Rappe´, A. K.; Casewitt, C. J.; Colwell, K. S.; Goddard, W. A.;
Skiff, W. M. J. Am. Chem. Soc. 1992, 114, 10024.
(22) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R.
SIR97, an integrated package of computer programs for the solution
and refinement of crystal structures using single-crystal data; Institute
of Crystallography, Bari, Italy, 1988.
(23) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Go¨ttin-
gen, Germany, 1997.
(24) Farrugia, L. J. ORTEP-3; Department of Chemistry, University
of Glasgow, Glasgow, Scotland, 2003.