Transition metal complexes with sterically demanding ligands, 3. Synthetic access to square-planar terdentate pyridine-diimine rhodium(I) and iridium(I) methyl complexes: Successful detour via reactive triflate and methoxide complexes

Article abstract of DOI:10.1021/om010185y

The synthesis of novel square-planar, terdentate, aryl-substituted pyridine-diimine Rh(I) and Ir(I) chloro complexes from the free ligands and the bis(μ-chloro) ethylene-bridged dimers [(C₂H₄)RhIrCl]₂ is reported. Since at

Full text of DOI:10.1021/om010185y

Organometallics 2001, 20, 4345-4359
4345
Tr a n sition Meta l Com p lexes w ith Ster ica lly Dem a n d in g
Liga n d s, 3.1 Syn th etic Access to Squ a r e-P la n a r
Ter d en ta te P yr id in e-Diim in e Rh od iu m (I) a n d Ir id iu m (I)
Meth yl Com p lexes: Su ccessfu l Detou r via Rea ctive
Tr ifla te a n d Meth oxid e Com p lexes
Stefan Nu¨ckel and Peter Burger*
Anorganisch-chemisches Institut der Universita¨t Zu¨rich, Winterthurerstrasse 190,
CH-8057 Zu¨rich, Switzerland
Received March 8, 2001
The synthesis of novel square-planar, terdentate, aryl-substituted pyridine-diimine Rh(I)
and Ir(I) chloro complexes from the free ligands and the bis(µ-chloro) ethylene-bridged dimers
[(C2H4)RhIrCl]2 is reported. Since attempts to achieve direct conversion to the corresponding
hydride and methyl complexes through metathesis of the chloro ligand in these compounds
were unsuccessful, synthetic access to more reactive methoxy- and triflate-substituted
starting materials was developed. The methoxy and triflate complexes could be successfully
converted to the Rh(I) η2-BH4 and Rh,Ir(I) methyl complexes. The structure and bonding
and thermodynamics of the methoxy and η2-BH4 species were analyzed by DFT methods.
X-ray crystal structures of selected Rh,Ir(I,III) representatives are reported.
In tr od u ction
used with great success in the synthesis and catalysis
of transition-metal complexes.11-23 The groups of Vrieze
and van Leeuwen have reported, for instance, on the
reversible coordination of O2 to sq-pl pyridine-diimine
Rh(I) chloro complexes to give the corresponding peroxo
Rh(III) compounds.19 In context with our longstanding
interest in aerobic oxidation catalysis,24 this prompted
us to investigate the corresponding novel Rh(I) and Ir(I)
alkyl and hydride complexes, for which no synthesis had
been published previously. Herein, we describe the
synthetic detour we had to follow to achieve this goal
and report on the sq-pl pyridine-diimine Rh(I) triflate
and Rh(I),Ir(I) methoxide starting materials, which were
developed in the course of these investigations.
Square-planar (sq-pl) Rh(I) complexes play an impor-
tant role as precursors and intermediates in hydrogena-
tion, hydrosilylation, and hydroformylation catalysis
and the Monsanto acetic acid process.2 While the
chemistry of these compounds is in principle well
explored, there is still room for surprises. In particular,
Milstein’s group reported recently on exciting intramo-
lecular Rh-mediated C-C and C-O cleavage reactions.3-8
In their studies, terdentate cyclometalated bis-phos-
phine donors (P,C,P) were applied. Similar reactivity
patterns were observed for the related 1,3-(dimethyl-
amino)phenyl N,C,N pincer ligands (1,3-(NMe2)2-C6H3),
which were introduced and used with success by van
Koten et al.9,10 Recently, we reported on our unsuccess-
ful attempts to achieve metal complexation of a related
1,3-diimine-phenyl “ligand” (N,C,N), which we at-
tributed to a potentially difficult C-H activation step.1
We have therefore switched to the corresponding pyri-
dine-diimine (N,N,N) ligand system, which has been
(11) Alyea, E. C.; Merrel, P. H. Inorg. Met.-Org. Chem. 1974, 4, 535.
(12) Bruin, B.; Bill, E.; Bothe, E.; Weyhermu¨ller, T.; Wieghardt, K.
Inorg. Chem. 2000, 39, 2936.
(13) Bianchini, C.; Lee, H. M. Organometallics 2000, 19, 1833.
(14) Britovsek, G. J . P.; Gibson, V. C.; Kimberley, B. S.; Maddox, P.
J .; McTavish, S. J .; Solan, G. A.; White, A. J . P.; Williams, D. J . Chem.
Commun. 1998, 849.
(15) Britovsek, G. J . P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.;
Maddox, P. J .; Mastroianni, S.; McTavish, S. J .; Redshaw, C.; Solan,
G. A.; Stro¨mberg, S.; White, A. J . P.; Williams, D. J . J . Am. Chem.
Soc. 1999, 121, 8728.
(16) Dias, E. L.; Brookhart, M.; White, P. S. Organometallics 2000,
19, 4995.
(17) Cetinkaya, B.; Cetinkaya, E.; Brookhart, M.; White, P. S. J .
Mol. Catal., A 1999, 142, 101.
(18) Haarman, H. F.; Ernsting, A. L.; Kranenburg, M.; Kooijman,
H.; Veldman, N.; Spek, A. L.; Elsevier, C. J .; van Leeuwen, P. W. N.
M.; Vrieze, K. Organometallics 1997, 16, 887.
(19) Haarman, H. F.; Bregman, F. R.; van Leeuwen, P. W. N. M.;
Vrieze, K. Organometallics 1997, 16, 979.
(1) Nu¨ckel, S.; Burger, P. Organometallics 2000, 19, 3305.
(2) Cornils, B., Herrmann, W. A., Eds. Applied Homgeneous Cataly-
sis with Organometallic Compounds; Wiley-VCH: Weinheim, Ger-
many, 2000.
(3) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Gozin, M.;
Milstein, D. J . Am. Chem. Soc. 1998, 120, 13415.
(4) van der Boom, M. E.; Liou, S.-Y.; Ben-David, Y.; Vigalok, A.;
Milstein, D. Angew. Chem., Int. Ed. 1997, 36, 625.
(5) Sundermann, A.; Uzan, O.; Milstein, D.; Martin, J . M. L. J . Am.
Chem. Soc. 2000, 122, 7095.
(6) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature 1993,
364, 699.
(7) Gandelman, M.; Vigalok, A.; Konstantinovski, L.; Milstein, D.
J . Am. Chem. Soc. 2000, 122, 9848.
(8) Blum, O.; Milstein, D. J . Am. Chem. Soc. 1995, 117, 4582.
(9) Rietveld, M. H. P.; Grove, D. M.; van Koten, G. New J . Chem.
1997, 21, 751.
(20) Haarman, H. F.; Kaagman, J .-W.; Smeets, W. J . J .; Spek, A.
L.; Vrieze, K. Inorg. Chim. Acta 1998, 270, 34.
(21) Kooijman, H.; Kaagman, J . W.; Mach, K.; Spek, A. L.; Schreurs,
A. M. M.; Haarman, H. F.; Vrieze, K.; Elsevier, C. J . Acta Crystallogr.,
Sect. C 1999, C55, 1052.
(22) Small, B. L.; Brookhart, M.; Bennett, A. M. A. J . Am. Chem.
Soc. 1998, 120, 4049.
(10) Albrecht, M.; Gossagem, R. A.; Spek, A. L.; van Koten, G. J .
Am. Chem. Soc. 1999, 121, 11898.
(23) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(24) Cremer, C.; J acobsen, H.; Burger, P. Chimia 1997, 51, 650.
10.1021/om010185y CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/11/2001

4346 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
Sch em e 1
Sch em e 2
Resu lts a n d Discu ssion
Liga n d s. The class of pyridine-diimine ligands used
herein was introduced by Aleya et al.11 and its chemistry
more recently extended by several groups.12-23 Due to
solubility restrictions, dichloromethane solvent is most
commonly used in these systems. This is of particular
interest, since Vrieze et al. showed that, in addition to
more common electrophiles, oxidative addition of dichlo-
romethane also proceeds rather easily in sq-pl rho-
dium(I) systems bearing this ligand system to give
chloromethyl Rh(III) (Rh-CH2Cl) complexes.18,20 To
avoid this solvent, a modified version of the ligand
system was sought to increase the solubility in less
polar/reactive solvents: e.g., benzene. Therefore, we
introduced a tert-butyl group into the peripheral 4-posi-
tion of the pyridine ring through radical nucleophilic
substitution in 2,6-diacetylpyridine with t-Bu• radicals
using Minisci conditions (Scheme 1).25 From this reac-
tion the novel pyridine derivative 1 could be isolated in
82% yield (Scheme 1). Further conversion of 1 to the
novel pyridine-diimine ligands 2 and 3 was achieved
from 1 and 2,6-dimethylaniline and 4-tert-butylaniline,
respectively, using standard conditions as described in
the literature for the unsubstituted pyridine derivatives
(Scheme 1).11,15,19,22
Com p lexes. Initially, the rhodium(I) and iridium(I)
chloro complexes 4-9 were sought as starting materials
for the synthesis of their corresponding Rh,Ir(I) alkyl
and hydride compounds. In analogy to the syntheses by
Vrieze et al.,18 complexes 4-6 were obtained according
to Scheme 2 from the bis(µ-chloro) dimer [Rh(C2H4)2-
Cl]2, in excellent yields. It should be noted that the
synthesis of complex 5 was independently reported by
Brookhart et al.,16 while we were in the last stage of
composing our paper.
complex 6 significantly increases its solubility in sol-
vents of low polarity so that benzene or toluene can be
used for further transformations.
Following a synthetic procedure by Crabtree et al. for
Ir compounds,26 we obtained the analogous novel Ir
complexes 7-9 from the reaction of the free ligands and
[(C2H4)2IrCl]2 (Scheme 2). Although 7-9 can also be
obtained from [(C2H4)2IrCl]2 prepared in situ (from
ethylene and [(cyclooctene)2IrCl]2), compounds 7-9 are
prepared preferably from the isolated Ir starting mate-
rial (cf. the Experimental Section).
The Rh and Ir chloro complexes 4-9 were obtained
in moderate to excellent yields as dark green (Rh) or
brown (Ir) analytically pure compounds. The structural
assignment was initially based on 1H and 13C NMR
spectroscopic data, which provided support for a square-
planar C2v-symmetrical ligand environment. This was
unambiguously confirmed by an X-ray crystal structure
analysis of the rhodium compound 4, presented in
Figure 1. Details of the data collection are compiled in
Table 1.
The square-planar coordination mode in complex 4
was clearly evidenced through the sum of angles of
360.0° around the Rh center. The Rh-Cl unit (Rh1-
Cl1 ) 2.3250(6) Å) leaves a small coordination gap for
the aryl substituents of the imine moieties and thus
apparently enforces a torsional angle (averaged) of 79.7°
between these groups.
In analogy to the aforementioned results by Vrieze
et al.,19 both the Rh and Ir compounds react quickly and
quantitatively with O2 to give the corresponding per-
oxide adducts. Details of the chemistry of the Rh(III)
Complexes 4 and 5 are sparingly soluble in aromatic
solvents and diethyl ether and dissolve well in THF and
dichloromethane. As anticipated, the incorporation of
the tert-butyl substituent into the pyridine ring of
(25) Fontana, F.; Minisci, F.; Barbosa, M. C. N.; Vismara, E.
Tetrahedron 1990, 46, 2525.
(26) Tanke, R. S.; Crabtree, R. H. Inorg. Chem. 1989, 28, 3444.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4347
Ta ble 1. Cr ysta l a n d Da ta Collection P a r a m eter s for Com p ou n d s 4, 11, 13, 18, 19, a n d 21
4‚THF
11‚2CH2Cl2
13‚2CH2Cl2
18
19
21‚(toluene)
formula
C
29H30ClN3ORh C33H42Cl5F3-
N3O3RhS
C30H34Cl4F6-
N3O6RhS2
955.4
orange rect
parallelepiped
C29H32F6N3-
O6RhS2
799.6
orange rect
parallelepiped
C25H31BN3Rh
C33H38N3OIr
fw
habitus
574.9
green cube
897.9
487.3
green rect
parallelepiped
684.9
green
brown rect
parallelepiped
0.2 × 0.2 × 0.3
monoclinic
P21/n (No. 14)
16.173(1)
11.947(1)
21.088(1)
109.81(1)
3833.5(4)
4
cryst size (mm)
cryst syst
space group
a (Å)
b (Å)
c (Å)
0.2 × 0.2 × 0.2
monoclinic
P21/n (No. 14)
9.778(1)
10.731(1)
26.763(2)
95.71(1)
0.1 × 0.15 × 0.25 0.2 × 0.2 × 0.3
0.15 × 0.40 × 0.50 0.1 × 0.2 × 0.25
monoclinic
P21/c (No. 14)
21.188(2)
8.592(1)
21.242(2)
91.21(1)
3865.9(7)
4
monoclinic
P21/n (No. 14)
12.789(1)
17.025(1)
15.886(1)
110.91(3)
3231.1(4)
4
orthorhombic
P212121 (No. 19)
12.897(1)
orthorhombic
Pbca (No. 61)
7.891(1)
21.861(2)
34.144(2)
12.919(1)
14.349(1)
â (deg)
V (Å3)
2794.2(4)
4
2390.8(3)
4
1.35
5890.2(8)
8
1.545
Z
calcd density (g/cm3) 1.37
1.56
1.64
1.64
temp (K)
183
183
183
183
123
183
λ(Mo KR) (Å)
0.710 73
image plate
4-48
0.710 73
image plate
4-48
0.710 73
image plate
4-48
0.710 73
image plate
4-52
0.710 73
image plate
5-53
0.710 73
image plate
4-45
scan type
2θ range (deg)
no. of rflns measd:
total, unique
no. of params
R1(F2 > 2σ(F2))
wR2(F2 > 2σ(F2))
GOF, S
17 922, 4204
12 914, 5815
24 059, 5604
24 576, 6168
15 427, 4584
14 823, 3625
322
452
516
431
293
351
0.0313
0.085
0.0233
0.0640
1.023
0.0573
0.1577
1.003
0.0441
0.1295
1.005
0.0190
0.0387
1.004
0.0210
0.0425
1.025
1.004
residual electron
0.54, -0.45
0.85, -1.29
0.52, -0.59
0.34, -0.38
0.43, -0.30
1.059, -0.659
density (e/Å3)
4 and 7 with hydride transfer reagents, e.g. LiAlH4,
NaBH4, and Red-Al, were also unsuccessful, a better
leaving group, e.g. a triflate ligand (OTf), was sought
to facilitate the substitution at the metal center. There-
fore, metathesis of the chloride groups in compounds 4
and 5 with 1 equiv of AgOTf was attempted. However,
this was thwarted by the fact that a competing reaction
leading to the corresponding oxidized Rh,Ir(III) com-
plexes and elemental silver occurred. This could be
F igu r e 1. Ortep plot of the rhodium chloro complex 4
shown at the 50% probability level. A molecule of cocrys-
tallized THF has been omitted for clarity. Selected bond
distances (Å) and angles (deg): Rh1-Cl1 ) 2.3250(6),
Rh1-N1 ) 1.8899(19), Rh1-N2 ) 2.0348(17), Rh1-N3 )
2.0286(18); Cl1-Rh1-N1 ) 178.98(5), Cl1-Rh1-N2 )
101.66(5); Cl1-Rh1-N3 ) 99.83(6), N1-Rh1-N2 )
79.25(7), N1-Rh1-N3 ) 79.25(8), N2-Rh1-N3 ) 158.46(8).
1
confirmed by comparison of the H NMR spectrum of
the Rh(III) tris(triflate) product obtained from the
reaction of 4 with 3 equiv of AgOTf in dimethoxyethane.
Alternative routes to the triflate-substituted starting
materials such as the conversion of the chloro complexes
with (trimethylsilyl)triflate (Me3SiOTf) and trifluo-
romethanesulfonic acid (HOTf) were therefore at-
tempted. However, rather expectedly (cf. below), these
reactions led to the corresponding Rh,Ir(III) oxidative
addition products. In the reaction of the chloro com-
plexes 4 and 7 with HOTf, for instance, we obtained in
excellent yields the pseudo-octahedral hydrido chloro
triflate Rh,Ir(III) complexes 10 and 12 with the chloro
ligand in the equatorial plane and the hydride and OTf
ligands in the (trans) axial positions (Scheme 3).27 An
alternative access to the Rh,Ir(I) alkyl complexes was
therefore sought by reduction of the corresponding
Rh(III),Ir(III) alkyl compounds. Since Vrieze et al. had
previously shown that oxidative addition of dichlo-
romethane and benzyl chloride to diimine-pyridine
Rh(I) metal centers is facile,18 we anticipated a similar
reactivity of compounds 4-9 toward methyl triflate,
MeOTf. Indeed, the desired bis(triflate) Rh,Ir(III) meth-
yl complexes 13-15 were obtained in excellent yields
from the reaction of Rh,Ir(I) compounds with excess
(5-6 equiv) MeOTf (Scheme 3).28
and Ir(III) peroxide complexes and the X-ray crystal
structures of 8 and its peroxide adduct will be published
in a separate communication in due course.
In a next step, we intended to convert complexes 4
and 7 to the corresponding methyl compounds. However,
even using a wide variety of alkylating reagents, such
as MeMgCl, AlMe3, SnMe4, LiMe, n-Bu2Mg, and Li2-
CuMe2, either just unreacted starting material was
recovered (AlMe3, SnMe4) or complicated, intractable
1
mixtures of products were obtained. Since the H NMR
spectra of the major component in these mixtures
evidenced a symmetry lower than C2v, this provided
some evidence that nucleophilic attack (deprotonation)
occurred also at the ketimine group, which therefore
interfered with chloride substitution at the metal center.
This was further substantiated through the following
experiment: when complex 4 was stirred with NaOMe
in methanol-d4, in addition to metathesis of the chloride
ligand with the methoxide group (vide infra), complete
H/D exchange in the imine methyl groups to give
-C(CD3)dN(aryl) was observed.
(27) The structural assignment is based on an X-ray crystal
structure of compound 10. Crystal data: orthorhombic crystal system,
space group P212121 (No. 19), a ) 12.997(1) Å, b ) 14.833(2) Å,
19.596(1) Å. Nu¨ckel, S.; Burger, P. Unpublished results.
Since attempts to obtain Rh,Ir(I) hydride complexes
from the reaction of the corresponding chloro complexes

4348 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
Sch em e 3
It is noteworthy that the corresponding chloro triflate
complexes were obtained when these reactions were
carried out with the stoichiometric amount of MeOTf.
For both the rhodium chloro triflate compound 11 and
the rhodium bis(triflate) complex 13, we performed
X-ray crystal structure analyses (Figures 2 and 3). The
details of the data collection and refinement are tabu-
lated in Table 1.
) 1.3 S cm-2 mol-1; 5 × 10-6 M, ΛM ) 20 S cm-2 mol-1).
Finally, the 19F NMR spectrum of 13 in CD2Cl2, which
displays resonances for two inequivalent OTf groups
with a 1:1 integration ratio at δ -81.6 and -80.76 ppm,
respectively, is also noteworthy.
The electronic properties of the metal methyl unit in
complexes 11 and 13-15 deserve a special mention.
From the fact that the rhodium- and iridium(III) methyl
compounds are recovered quantitatively when reacted
with even a large excess of HOTf, it can be readily seen
that the metal-attached methyl groups display a low
nucleophilicity. This is also emphasized by the fact that
the methyl chloro compound 11 can be converted to the
bis(triflate) complex 14 by reaction with excess (3 equiv)
HOTf. This is in contrast with the chemistry of the
The geometric parameters around the Rh center in
the X-ray crystal structures of complexes 11 and 13 are
quite similar and clearly evidence the anticipated
pseudo-octahedral ligand environment. The trans posi-
tion of the methyl and triflate groups in the chloro
triflate compound 11 is consistent with the generally
accepted mechanism29 for the reaction of sq-pl d8 transi-
tion-metal complexes with polar electrophiles; i.e., nu-
cleophilic attack of the metal center at the electrophile
is followed by recombination of the cationic metal
complex and the triflate anion. It deserves special
mention that the methyl group in the pseudo-octahedral
complexes exhibits a pronounced trans influence, which
is best seen by comparison of the Rh-O distances of
2.093(3) Å (Rh1-O1) for the equatorial (cis) and 2.305(4)
Å for the axial (trans) triflate groups (Rh1-O4) in 13.
On the basis of a comparison with distances observed
in the X-ray crystal structures of related Rh(III) and
Ir(III) triflate complexes,24,30-35 covalent bonding of the
equatorial triflate ligand is deemed, while the bond to
the axial OTf group is suggested to have a pronounced
ionic character. This is supported by the IR spectrum
of 13 in CD2Cl2, which displays two bands at 1328 and
1293 cm-1 in the expected range for covalent and ionic
triflate groups.36,37 Furthermore, we have carried out
molar conductivity measurements in CH2Cl2. Although
the latter study clearly showed that the OTf ligand in
complex 13 is not fully dissociated in this solvent, i.e.,
not a 1:1 electrolyte, concentration-dependent measure-
ments in the range of 10-3 to 5 × 10-6 M provided clear
evidence for a weakly dissociated ionophore (10-3 M, ΛM
33
related Cp*Ir(PMe3)Me2 and CnRhMe3 (Cn ) tri-
methylazacyclonane)38 complexes, which undergo fast
reactions with 1 or 2 equiv of HOTf to give the
corresponding mono- and bis(triflate) complexes. There-
fore, we wish to attribute an electrophilic character to
the methyl group in these rhodium(III) compounds, i.e.,
[Rh]-Meδ+, which would parallel the findings of Bercaw
et al. in related aquo chloro d6-Pt(IV) alkyl complexes.39
In a next step, we attempted to prepare the desired
Rh(I),Ir(I) methyl compounds by reduction of the Rh(III)
and Ir(III) complexes 13 and 15 with either (Me2N)2Cd
C(NMe2)2 or cobaltocene (Cp2Co) in dimethoxyethane
(dme). However, rather than the expected sq-pl d8-
configured methyl compounds, in a very clean reaction
we obtained the corresponding Rh(I) and Ir(I) triflate
complexes and ethane (Scheme 4). The formation of the
rhodium triflate complex 16 was unambiguously estab-
lished by comparison with the spectroscopic data of the
independently prepared compound (see below), while the
exclusive formation of ethane was confirmed by 1H NMR
spectroscopy and GC/MS spectrometry. Although the
desired Ir,Rh(I) methyl complexes could thus not be
obtained by reduction, the observed C-C coupling
process has prompted us to investigate this reaction in
more detail. As will be detailed in a separate publication
in due course, the proposed mechanism involves reduc-
tive elimination of ethane from a dimethyl mono(triflate)
(28) After this part of this study, a closely related complex was very
recently reported by Brookhart et al. in ref 16.
(29) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry, 2nd
ed.; University Science Books: Mill Valley, CA, 1987.
(30) Woerpel, K. A.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115,
7888.
(31) Schnabel, R. C.; Roddick, D. M. Organometallics 1996, 15, 3550.
(32) J ime´nez, M. V.; Sola, E.; Mart´ınez, A. P.; Lahoz, F. J .; Oro, L.
A. Organometallics 1999, 18, 1125.
(33) Burger, P.; Bergman, R. G. J . Am. Chem. Soc. 1993, 115, 10462.
(34) Bosch, M.; Laubender, M.; Weberndorfer, B.; Werner, H. Chem.
Eur. J . 1999, 5, 2203.
-
intermediate, i.e., (N3)RhMe2+OTf (not shown; N3 )
terdentate N,N,N ligand), which is formed from 13 and
the initially formed corresponding Rh(I) methyl com-
pound 22. The proposed mechanism is supported by the
reaction of the Rh(I) methyl compound 22 with the
methyl bis(triflate) complex 13, which leads to the Rh(I)
(35) Bleeke, J . R.; Behm, R. J . Am. Chem. Soc. 1997, 119, 8503.
(36) Lawrance, G. A. Chem. Rev. 1986, 86, 17.
(37) Stang, P. J .; Huang, Y.-H.; Arif, A. M. Organometallics 1992,
11, 231.
(38) Wang, L.; Flood, T. C. J . Am. Chem. Soc. 1992, 114, 3169-
3179.
(39) Luinstra, G. A.; Labinger, J . A.; Bercaw, J . E. J . Am. Chem.
Soc. 1993, 115, 3004.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4349
Sch em e 4
F igu r e 2. Ortep plot of the Rh(III) methyl chloro triflate
complex 11 shown at the 50% probability level. Two
molecules of cocrystallized dichloromethane have been
omitted for clarity. Selected bond distances (Å) and angles
(deg): Rh1-Cl1 ) 2.3532(16), Rh1-N1 ) 1.916(5), Rh1-
N2 ) 2.073(5), Rh1-N3 ) 2.075(5), Rh1-O3 ) 2.388(4),
Rh1-C30 ) 2.029(6); Cl1-Rh1-N1 ) 176.25(14); Cl1-
Rh1-N2 ) 100.50(14); Cl1-Rh1-N3 ) 101.15(14), Cl1-
Rh1-O3 ) 95.09(12), Cl1-Rh1-C30 ) 88.0(2), N1-Rh1-
N2 ) 79.32(19), N1-Rh1-N3 ) 79.18(19), N1-Rh1-O3
) 81.17(18), N1-Rh1-C30 ) 95.7(2), N2-Rh1-N3 )
158.30(19), N2-Rh1-O3 ) 89.83(17), N2-Rh1-O3 )
89.6(2), N3-Rh1-O3 ) 89.74(17), N3-Rh1-C30 ) 89.6(2),
O3-Rh1-N3 ) 176.9(2).
triflate starting material [Rh(C2H4)2(THF)nOTf], in
analogy to a route described by Taube et al. for the
synthesis of a related rhodium complex with a P,N,P
pincer ligand (Scheme 5).40 Complex 17 was obtained
according to Scheme 5 in excellent yield as an analyti-
cally pure, microcrystalline green compound. The NMR
spectroscopic data and the limited results of a strongly
disordered X-ray crystal structure of 17 clearly evi-
denced a square-planar ligand environment with an
ionic, noncoordinated triflate group. Although a com-
parison of the 1H NMR and the 13C NMR chemical shifts
(1H NMR, 3.39 ppm; 13C NMR, 78.7 ppm) of the C2H4
ligand with the chemical shifts of free ethylene sug-
gested sizable back-donation to the coordinated ethyl-
ene, this was questioned by the essentially unchanged
1J C-H(C2H4) coupling constant of 158 Hz in 17. There-
fore, it was sought that ethylene could be thermally
deliberated from the ethylene complex. In a nearly
quantitative reaction, this could be indeed be achieved
upon heating 17 to 100 °C in dimethoxyethane (dme)
using a dynamic vacuum for several days (Scheme 5).
This reaction led to a green-brownish product, which
was analyzed correctly as 16‚dme. At present, we do not
have X-ray diffraction data for 16‚dme, so that the
structural assignment is based mostly on the IR and
NMR spectroscopic data. The IR spectrum of 16 displays
a band at 1317 cm-1, which is in the typical range of a
covalent triflate group.37 However, since the correspond-
ing chloro complex 4 displays a band at the same
position, the latter cannot be unambiguously assigned
to a vibration of the triflate ligand. The 1H NMR
chemical shifts of a dme sample and the dme protons
in 16‚dme display identical chemical shifts in CD2Cl2,
with no detectable homonuclear NOEs between the
protons of 16 and those of dme. These data thus provide
evidence for a covalently bound triflate group in 16. This
was also supported through concentration-dependent
molar conductivity measurements in CH2Cl2. Neverthe-
less, the latter evidenced substantial ionization of the
triflate ligand through molar conductivities of ΛM ) 12
S cm-2 mol-1 and ΛM ) 50 S cm-2 mol-1 at 10-3 and
10-5 M, respectively. Support for the ionization of the
triflate ligand in 16 was provided also by the X-ray
crystal structure of 16‚THF, which was obtained in the
course of the study of the C-C coupling process shown
in Scheme 4. The molecular structure of the latter
complex clearly evidenced an ionic triflate ligand with
F igu r e 3. Ortep plot (50% probability level) of the Rh(III)
methyl bis(triflate) complex 13. Two molecules of cocrys-
tallized dichloromethane have been omitted for clarity.
Selected bond distances (Å) and angles (deg): Rh1-N1 )
1.917(4), Rh1-N2 ) 2.073(4), Rh1-N3 ) 2.085(4), Rh1-
O1 ) 2.093(3), Rh1-O4 ) 2.305(4), Rh1-C26 ) 2.015(5);
N1-Rh1-N2 ) 79.32(16), N1-Rh1-N3 ) 80.16(16), N2-
Rh1-N3 ) 158.84(16), N1-Rh1-O1 ) 172.20(16), N1-
Rh1-O4 ) 86.85(15), N1-Rh1-C26 ) 95.3(2), N2-Rh1-
O1 ) 97.87(15), N2-Rh1-O4 ) 93.80(15), N2-Rh1-C26
) 87.24(19), N3-Rh1-O1 ) 103.14(14), N3-Rh1-O4 )
90.18(14), N3-Rh1-C26 ) 89.58(19), O1-Rh1-O4 )
86.07(14), O1-Rh1-C26 ) 91.76(18), O4-Rh1-C26 )
177.71(17).
triflate complex 16 and ethane within a few seconds at
room temperature.
Although the yields of the triflate complex 16 obtained
by reduction of 13 were quite reasonable, we attempted
to find a more convenient approach to prepare this
starting material. In a first step, we synthesized the
novel ethylene complex 17, from the bis(ethylene) Rh(I)
(40) Hahn, C.; Sieler, J .; Taube, R. Chem. Ber./ Recl. 1997, 130, 939.

4350 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
Sch em e 5
the THF ligand coordinated to the Rh center to give a
sq-pl cationic Rh(I) fragment.41 Finally, it is noteworthy
that a related cationic tricoordinate Rh complex was
reported by Brookhart et al. while this paper was under
for migratory insertion into M-Me compared to a M-H
bond have been previously established.43 Considering
the low nucleophilicty of the Rh-Me methyl moiety in
the methyl bis(triflate) complex 13 (vide supra), we
anticipate that this contributes additionally to the
higher barrier for the methyl migratory process.
42
review.
The reaction of the ethylene complex 17 with HOTf
is particularly noteworthy and leads to the olefin
insertion product, i.e., the ethyl bis(triflate) complex 18
(Scheme 5). The latter compound was isolated as an
analytically pure compound in quantitative yield and
has been fully characterized by 1H and 13C NMR
spectroscopy and additionally by X-ray crystallography
(Figure 4). The details of data collection and refinement
are tabulated in Table 1.
This is in contrast with the reaction of the olefin
complex 17 with MeOTf, which leads in excellent yields
to the Rh(III) oxidative addition product 13 and free
ethylene (Scheme 5). It deserves a special mention that
we could not detect the resonances of an intermediate,
e.g. the Rh(III) ethylene methyl triflate complex, while
monitoring the reaction by 1H NMR spectroscopy. It
should be noted, however, that a closely related rhodium
ethylene methyl complex was obtained by a different
route in the aforementioned very recent publication of
Brookhart et al.16
Furthermore, direct conversion of the Rh(I) triflate
complex 16 to the corresponding methyl complex 22
with methylating reagents such as ZnMe2, SnMe4 (no
reaction), and AlMe3 was attempted. While the 1H NMR
spectrum of the dark green crude reaction mixture
obtained from 16 and AlMe3 looked quite promising, we
had problems in isolating the pure methyl complex 22,
which we attributed to coordination of the aluminum
species formed in this reaction to 22. Some support for
-
this view was provided through the BH4 adduct 19,
which was obtained from the reaction of 16 with NaBH4
(Scheme 6). This reaction led in good yield to the η2-
coordinated BH4 adduct 19. It deserves special mention
that 19 is not available from the chloro complex 4, which
emphasizes the importance of a good leaving group in
1
the Rh(I) starting material. The H NMR resonances of
the BH4 unit are rather broad and could only be located
at -100 °C as a broad pseudo-doublet. The IR bands
originating from the BH4 group are located at ν(10BH4/
11BH4) 2405/2363 and 1914/1901 cm-1, with the assign-
ment being confirmed by the IR spectrum of the BD4
isotopomer (see the Experimental Section). Prior to the
X-ray crystal structure analysis of 19, the IR bands thus
provided support for an η2-coordination of the BH4 group
by comparison with the IR data of previously character-
In comparison with the reaction of the ethylene
complex 17 with HOTf, this implies a higher barrier for
the insertion of the olefin into the rhodium-methyl
bond to give the corresponding propyl triflate complex.
It should be noticed that larger activation enthalpies
(41) Nu¨ckel, S.; Burger, P. Manuscript in preparation.
(42) Dias, E. L.; Brookhart, M.; White, P. S. Chem. Commun. 2001,
423.
(43) Tempel, D. J .; J ohnson, L. K.; Huff, R. L.; White, P. S.;
Brookhart, M. J . Am. Chem. Soc. 2000, 122, 6686.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4351
F igu r e 5. Ortep plot of the Rh(I) BH4 complex 19 shown
at the 50% probability level. The hydrogen atoms of the
BH4 unit have been located in the difference Fourier map
and were refined isotropically. Selected bond distances (Å)
and angles (deg): Rh1-N1 ) 1.8939(17), Rh1-N2 )
2.0267(16), Rh1-N3 ) 2.0332(16), Rh1‚‚‚B1 ) 2.271(3),
Rh1-B1 ) 2.271(3), Rh1-H50 ) 1.77(2), Rh1-H51 )
1.75(3), B1-H50 ) 1.26(3), B1-H51 ) 1.21(3), B1-H52
) 1.15(2), B1-H53 ) 1.14(2); N1-Rh1-N2 ) 79.05(7),
N1-Rh1-N3 ) 78.72(7), N2-Rh1-N3 ) 157.70(7), N1-
Rh1-B1 ) 178.77(9), N2-Rh1-B1 ) 100.11(8), N3-Rh1-
B1 ) 102.15(8), N1-Rh1-H50 ) 147.2(8), N1-Rh1-H51
) 147.3(9), N2-Rh1-H50 ) 96.8(7), N2-Rh1-H51 )
98.1(8), N3-Rh1-H50 ) 100.9(7), N3-Rh1-H51 ) 101.5(8),
B1-Rh1-H50 ) 33.7(8), B1-Rh1-H51 ) 31.8(9), H50-
Rh1-H51 ) 65.4(12), H50-B1-H52 ) 103.9(15), H50-
B1-H53 ) 113.0(16), H51-B1-H52 ) 114.4(17), H51-
B1-H53 ) 110.0(16), H52-B1-H53 ) 114.2(17).
F igu r e 4. Ortep plot (50% probability level) of complex
18. Selected bond distances (Å) and angles (deg): Rh1-
N1 ) 1.9117(14), Rh1-N2 ) 2.0912(14), Rh1-N3 )
2.0731(14), Rh1-O1 ) 2.1008(13), Rh1-O4 ) 2.3489(13),
Rh1-C26 ) 2.0559(17); N1-Rh1-N2 ) 79.92(6), N1-
Rh1-N3 ) 79.84(6), N1-Rh1-O1 ) 172.26(5), N1-Rh1-
O4 ) 84.42(6), N1-Rh1-C26 ) 95.72(7), N2-Rh1-N3 )
159.64(6), N2-Rh1-O1 ) 98.26(5), N2-Rh1-O4 ) 89.04(5),
N2-Rh1-C26 ) 90.86(7), N3-Rh1-O1 ) 102.10(5), N3-
Rh1-O4 ) 91.22(5), N3-Rh1-C26 ) 88.93(7), O1-Rh1-
O4 ) 88.04(5), O1-Rh1-C26 ) 91.82(6), O4-Rh1-C26 )
179.81(6).
Sch em e 7
Sch em e 6
aged Rh1-Hb distance of 1.76(3) Å, B1-Hb ) 1.24(3) Å
and B1-Ht ) 1.15(2) Å were derived.
To address (a) the binding mode of the BH4- unit and
(b) the thermodynamics for coordination of BH3 to the
Rh-H moiety, we performed DFT calculations on the
unsubstituted model complexes I and II (BP-86 func-
tional; for details see the Experimental Section).
This revealed that extrusion of BH3 from the rhodium
model complex I is an extraordinarily endothermic
process and is uphill by 51 kcal mol-1 (Scheme 7). This
readily explains why attempts to obtain the correspond-
ing Rh hydride complex from 19 by removal of BH3 as
the quinuclidine‚BH3 adduct, for which we calculate a
bond energy of 39 kcal mol-1, were unsuccessful. In
addition, we carried out a Mulliken overlap population
analysis for the η2-BH4 model complex I. This evidenced
a direct bonding interaction between the Rh and boron
centers (0.21 e), while values of 0.31 and 0.44 e were
derived for the interaction of the bridging hydrides and
the Rh and B centers, respectively. As expected, a larger
overlap population of 0.81 e was determined for the
terminal B-H bonds.
ized transition-metal BH4 adducts.44 This was unam-
biguously confirmed by X-ray crystallography (Figure
5). Data collection parameters of complex 19 are col-
lected in Table 1.
It deserves special mention that the BH4 adduct 19
is a rare case of a crystallographically characterized
monomeric square-planar complex with a BH4- moiety.
One of the few known compounds is the closely related
terpyridine η2-BH4 Co(I) complex, which displays a
Co-B distance of 2.162 Å.45 Considering the larger
covalent radius of rhodium, this compares well with the
observed Rh1-B1 distance of 2.271(3) Å in 19. The
positions of the bridging and terminal hydrides Hb and
Ht of the BH4- ligand could be located in the difference
Fourier map and refined isotropically. From this aver-
The RhBH4 unit proved to be quite robust toward
methanol and trifluoroacetic acid and gave unreacted
19, while addition of HOTf led to decomposition. There-
fore, we attempted to prepare the desired corresponding
hydride complex from reaction of the triflate complex
16 with hydride transfer reagents, e.g. LiBEt3H and
Red-Al. However, since in all cases complicated mix-
(44) Marks, T. J .; Kolb, J . R. Chem. Rev. 1977, 77, 263.
(45) Corey, E. J .; Cooper, N. J .; Canning, W. M.; Lipscomb, W. N.;
Koetzle, T. F. Inorg. Chem. 1982, 21, 192.

4352 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
Sch em e 8
F igu r e 6. Ortep plot of the iridium methoxide complex
21 (50% probability level). A molecule of cocrystallized
toluene has been omitted for clarity.
Ta ble 2. Selected Dista n ces (Å) a n d An gles (d eg)
of Com p ou n d 21
Ir1-O1
Ir1-N2
O1-C26
1.949(4)
2.019(5)
1.392(8)
Ir1-N1
Ir1-N3
1.891(5)
2.012(5)
O1-Ir1-N1
O1-Ir1N3
N1-Ir1-N3
Ir1-O1-C26
172.63(19)
108.00(19)
79.0(2)
O1-Ir1-N2
N1-Ir1-N2
N2-Ir1-N3
93.29(18)
79.7(2)
158.7(2)
127.7(4)
tures of products were obtained, a different starting
material was sought for the syntheses of alkyl and
hydride complexes. In particular, we intended to intro-
duce a leaving group/ligand in the starting material,
which (a) might provide a better driving force for ligand
substitution and (b) would also help to reduce the Lewis
acidity of the converted hydride/methyl transfer reagent
after metathesis through π-donation, e.g. H2BOMe.
Alkoxide complexes were thus sought as ideal starting
materials. In this regard, it deserves special mention
that although there are various sq-pl d8-configured
complexes bearing O-R ligands, where R ) alkyl, aryl,
the absolute number is still rather small.20,21,46-55 The
related aryloxide Rh complexes bearing alkyl (t-Bu and
i-Pr)-substituted diimine-pyridine ligands, which have
been very recently prepared by Vrieze et al. from the
corresponding chloro compounds and sodium aryloxide,
were therefore of particular interest.20,21 However, since
we also intended to use â-hydride elimination from the
metal alkoxides as a potential route to metal hydride
complexes, the methoxide-substituted compounds 20
and 21 were chosen as target molecules. The latter
complexes are readily available from either the chloro
and triflate complexes 4, 7, and 16 (Scheme 8). As has
been briefly mentioned above, in addition to substitution
of the chloro ligand, reaction of the rhodium and iridium
chloro complexes 4 and 7 with NaOMe in deuterated
methanol-d4 led to complete H/D exchange of the
N1-Ir1-O1-C26
-153.5(13)
N3-Ir1-O1-C26
9.2(6)
Sch em e 9
ketimine methyl groups, which was clearly evidenced
through the absence of these resonances in the 1H NMR
spectrum and the observation of singlets at δ 1.00 and
0.42 ppm in the deuterium NMR spectrum of complexes
20-d 6 and 21-d 6 in benzene-H6. For the Ir complex 21
we performed an X-ray crystal structure analysis, which
led to the molecular structure presented in Figure 6.
The data collection parameters are collected in Table 1
and selected bond distances and angles in Table 2; the
structural parameters of 21 will be discussed in detail
in a later section.
Complexes 20 and 21 are thermally robust, which was
noticed in the attempted synthesis of the corresponding
rhodium and iridium hydride complexes through â-hy-
drogen elimination. Upon heating complexes 20 and 21
in C6D6 for several days, essentially just unreacted
starting material along with some minute decomposition
product was observed. This is in contrast with the rather
facile â-hydrogen elimination process observed by At-
wood et al. and others49-51 in sq-pl rhodium and iridium
complexes in the presence of phosphine donors. Support
that the reaction leading to formaldehyde and the
corresponding hydride complex is thermodynamically
unfavorable was provided by DFT calculations. In the
latter, we also included the â-hydrogen elimination
process from the rhodium ethyl model complex III (X
) CH2) presented in Scheme 9. A similar energetically
unfavorable situation toward â-H elimination to give
acetone and the [Rh]-H complex was estimated for the
corresponding 2-propanolate model complex [Rh]-iOPr,
(46) Bergman, R. G. Polyhedron 1995, 14, 3227.
(47) Bryndza, H. E.; Tam, W. Chem. Rev. 1988, 88, 1163.
(48) Mehrotra, R. C.; Singh, A. Prog. Inorg. Chem. 1997, 46, 239.
(49) Thompson, J . S.; Bernard, K. A.; Rappoli, B. J .; Atwood, J . D.
Organometallics 1990, 9, 2727.
(50) Bernard, K. A.; Rees, W. M.; Atwood, J . D. Organometallics
1986, 5, 390.
(51) Fernandez, M. J .; Esteruelas, M. A.; Covarrubias, M.; Oro, L.
A. J . Organomet. Chem. 1986, 316, 343.
(52) Miller, C. A.; J anik, T. S.; Lake, C. H.; Toomey, L. M.; Churchill,
M. R.; Atwood, J . D. Organometallics 1994, 13, 5080.
(53) Kapteijn, G. M.; Dervisi, A.; Grove, D. M.; Kooijman, H.; Lakin,
M. T.; Spek, A. L.; van Koten, G. J . Am. Chem. Soc. 1995, 117, 10939.
(54) Kegley, S. E.; Schaverien, C. J .; Freudenberger, J . H.; Bergman,
R. G.; Nolan, S. P.; Hoff, C. D. J . Am. Chem. Soc. 1987, 109, 6563.
(55) Kuznetsov, V. F.; Yap, G. P. A.; Bensimon, C.; Alper, H. Inorg.
Chim. Acta 1998, 280, 172.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4353
F igu r e 7. Selected bonding parameters of the DFT-
optimized (BP-86 functional) model complex III, with the
data observed for the X-ray crystal structure of 21 given
in parentheses.
F igu r e 8. Fragment molecular orbital analysis (DFT,
BP86) of the HOMO in the iridium methoxide model
complex III.
configured sq-pl ML3X complex (X
)
π-donor
for which an endothermicity of +24 kcal mol-1 was
derived. Even though steric congestion in the 2,6-
dimethylphenyl-substituted complexes 20 and 21 might
favor the â-hydrogen elimination products compared to
the unsubstituted model complexes, it was anticipated
that the thermodynamic situation is essentially un-
changed. In an exemplary fashion this was confirmed
through the results of the DFT calculations on the
geometrically optimized methoxide complex 20 and its
hydride congener, for which an energy difference of 33
kcal mol-1 in favor of 20 was derived.
The reluctance of the methoxide complexes 20 and 21
to undergo â-H elimination and, in particular, the
calculated strong endothermicity for the elimination of
formaldehyde prompted us to study the electronic
structure of the methoxide starting material in more
detail. This was further stimulated by the excellent
agreement of the bonding parameters of the DFT-
optimized geometry of the model compound III (X ) O,
M ) Ir) with the X-ray crystal structure of the Ir
methoxide complex 21 (Figure 7).
The observed Ir1-O1 bond distance of 1.949(4) Å in
21 is particularly noteworthy, since to the best of our
knowledge it is the shortest Ir-O bond distance ob-
served so far for a square-planar d8-configured Rh or
Ir(I) complex bearing a monodentate alkyl- or aryloxide
ligand. A comparison of the M-O distance with previ-
ously characterized compounds has to be considered
with care, however, since most of the latter incorporate
ligands trans to the alkoxide group, which have a
significantly stronger trans influence than the pyridine
group in 21: i.e., a CO ligand or phosphine donors.
Nevertheless, a particular structural feature caught our
attention. This is the observed Ir-O-C bond angle of
127.7(4)° and the arrangement of the methoxide group
within the plane of the Ir center and the terdentate
ligand, which inferred sp2 hybridization of the oxygen
atom and, in addition, suggested π-interaction of the Ir
center and the OMe group.
ligand).46,47,56 While this type of π-interaction has also
been put forward by Caulton et al.,57,58 this was recently
questioned by Atwood et al. through a combined X-ray
crystallographic and IR study for a series of square-
planar Ir alkoxide complexes.52 Considering these con-
troversal results, we were interested to see whether we
could establish a stabilizing interaction leading to a
preference for the observed in-plane orientation of the
methoxide ligand in complex 21. This was indeed
provided by the inspection of the HOMO in the model
complex III (X ) O, M ) Ir), which is presented
schematically in Figure 8.
The HOMO clearly displays the previously suggested
π-antibonding interaction between the metal-based dxz
and the oxygen pz orbital (notation for D4h symmetry).
This interaction, however, is strongly stabilized by in-
phase mixing of a ligand (pyridine)-based π* acceptor
orbital. To quantify this interaction, we studied the total
energy dependence on the Nimine-Ir-O-C torsion angle
in the methoxide model compound III, with the remain-
ing geometrical parameters being fully optimized by
DFT methods (BP86 functional, linear transit, Figure
9).
This evidenced a significant 11 kcal mol-1 preference
for the in-plane coordination of the methoxide group,
with the out-of-plane coordination (R ) 90°) identified
as a transition state (see the Experimental Section).
Since a slight preference for the out-of-plane orientation
of the methoxide group is deemed sterically favorable,
this emphasizes the importance of the aforementioned
π-back-donation to the ligand-based π* orbital, which
stabilizes the otherwise four-electron-two-orbital de-
stabilizing interaction.
Syn th eses of th e Rh (I) a n d Ir (I) Meth yl Com -
p lexes 22 a n d 23. As anticipated, the Rh and Ir
methoxy complexes 20 and 21 could be converted in
excellent yields to the corresponding methyl complexes
22 and 23 through reaction with AlMe3 and, for the
rhodium complex 22, also with MeMgCl (Scheme 8).
As has been previously discussed by Mayer et al. and
others, this is in principle a four-electron-two-orbital
destabilizing interaction considering the absence of an
unoccupied metal-based dπ-acceptor orbital in a d8-
(56) Mayer, J . M. Comments Inorg. Chem. 1988, 8, 125.
(57) Lunder, D. M.; Lobkovsky, E. B.; Streib, W. E.; Caulton, K. G.
J . Am. Chem. Soc. 1991, 113, 1837.
(58) Caulton, K. G. New J . Chem. 1994, 18, 25.

4354 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
Ch a r t 1
Con clu sion
We have reported the syntheses of novel, reactive
Rh(I) and Ir(I) triflate and methoxide complexes, which
are excellent starting materials for the synthesis of Rh(I)
BH4 and Rh,Ir(I) methyl compounds. The Rh,Ir(I,III)
methyl complexes described herein display very inter-
esting reactivity patterns: i.e., C-C coupling under
reactive conditions in the tervalent d6-configured com-
plexes and facile thermal intermolecular C-H activation
in benzene in the Ir(I) methyl system. In due course,
we will report further details of these transformations
and will also elaborate on the reactions of the novel
Rh(I),Ir(I) methyl complexes with H2. In particular, we
will describe the extraordinarily facile Si-H and C-H
bond activation in silanes, arenes, and alkanes observed
for a related diimine-pyridine Ir system.
F igu r e 9. Walsh diagram (linear transit, DFT, BP86
functional) for the rotation about the Ir-O bond in the
iridium methoxide model complex III.
The rhodium and iridium methyl complexes 22 and
23 were obtained as green air-sensitive analytically pure
complexes, which dissolve well in aromatic solvents, e.g.
benzene (for the reaction of 23 with C6D6 see below).
The 1H and 13C NMR data allowed us to assign C2v-
symmetrical square-planar structures to 22 and 23. The
1H NMR chemical shifts of the Rh- and Ir-bound methyl
groups deserve special comment. While the resonance
of the Rh-Me group was in the expected range at δ 2.21
ppm, in the analogous Ir complex 23 this resonance was
detected surprisingly downfield as a singlet at δ 6.91
ppm. Support for the assignment of the methyl reso-
nance in 23 was provided by a cross-peak between this
unique singlet and the 13C NMR methyl resonance
located at δ 2.7 ppm (assignment based on DEPT-90/
135 13C NMR) in the 13C-1H-HSQC NMR spectrum.
This assignment was unambiguously confirmed by the
15N-1H correlated spectrum, which displayed two cross-
peaks between the Ir-Me protons and the 15N reso-
nances of the diimine and pyridine groups.
Exp er im en ta l Section
Reactions were carried out under a dinitrogen atmosphere
with thoroughly dried and N2-saturated solvents using glove-
box and Schlenk techniques. 2,6-Diacetylpyridine, 2,6-di-
methylaniline, 4-tert-butylaniline, pivalic acid, HOTf, MeOTf,
NaBH4, NaOMe, and AlMe3 were purchased from Fluka and
Aldrich and used as received. The starting materials, [Rh-
(C2H4)2Cl]2,59 [Rh(THF)x(C2H4)2OTf],40 [Ir(C2H4)2Cl]260 and the
2,6-dimethyl-substituted (ligand A, N-(2,6-dimethylphenyl)-
N-((1E)-1-{6-[(1E)-N-(2,6-dimethylphenyl)ethanimidoyl]pyridin-
2-yl}ethylidene)amine) and 2,6-diisopropyl-substituted ligands
(ligand B, N-(2,6-diisopropylphenyl)-N-((1E)-1-{6-[(1E)-N-(2,6-
diisopropylphenyl)ethanimidoyl]pyridin-2-yl}ethylidene)-
amine)15,22 were prepared as described in the literature. 1H,
13C, and 19F NMR spectra were recorded on Varian Mercury
200 and Gemini 300 and Bruker Avance-500 spectrometers
at 298 K unless otherwise specified. Chemical shifts are given
The downfield shift of the methyl resonance in 23 is
likely due to the position of the methyl protons in the
(downfield) anisotropic environment generated by the
aryl substituents of the imine groups. This is supported
by the X-ray crystal structure of the iridium complex
23, which displays a perfect sq-pl coordination mode of
the Ir center.41 Considering that complexes of Rh and
Ir are in general isostructural and display essentially
identical bond angles and distances, we find the differ-
ences of the 1H NMR chemical shifts of the metal-
bonded methyl protons in 22 and 23 quite unusual and
beyond the expected contribution of the metal center to
the chemical shift. At present, we can therefore not offer
an explanation for this observation; we anticipate,
however, that an X-ray crystal structure of the analo-
gous Rh complex might elucidate further details. Fi-
nally, it should be noted that we observed facile thermal
intermolecular C-H activation of benzene in 23 to give
the corresponding Ir(I) phenyl complex and methane
within a few hours at room temperature. Details of this
transformation, including mechanistic and theoretical
studies, will be reported in due course in a separate
publication.41
1
in ppm and referenced to the residual H or 13C NMR solvent
shifts and for the 19F NMR resonances against trifluorotoluene.
The assignment of 1H NMR and 13C NMR resonances is based
1
on DEPT and two-dimensional H-1H COSY, 13C-1H HSQC,
and 13C-1H, 15N-1H HMBC experiments. The applied NMR
numbering scheme shown in Chart 1 was used. IR spectra
were measured on a Biorad FTS-45 Fourier IR spectrometer.
X-ray crystal structure analyses were performed on a Stoe
IPDS image plate system with a graphite-monochromated Mo
KR (0.707 13 Å) beam. CHN analyses were carried out with a
LECO CHNS-932 elemental analyzer at our institute. GC/MS
analyses were performed with a Varian Saturn 2000 GC/MS
(ion trap) spectrometer with the reaction solution containing
the ethane gas previously transferred/collected by standard
high-vacuum manometry. Conductivity measurements were
performed with an Amel-160 conductometer using glass cells
with Pt electrodes (K ) 0.94 and 0.11).
Syn th esis of 4-ter t-Bu tyl-2,6-d ia cetylp yr id in e (1). A
mixture of 6.0 g (37 mmol) of 2,6-diacetylpyridine, 18.8 g (184
mmol) of pivalic acid, 1.0 g (5.9 mmol) of silver nitrate, 31.0 g
(59) Cramer, R.; McCleverty, J . A.; Bray, J . Inorg. Synth. 1990, 28,
86.
(60) Arthurs, M. A.; Bickerton, J .; Stobart, S. R.; Wang, J . Organo-
metallics 1998, 17, 2743.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4355
(129 mmol) of sodium peroxodisulfate (Na2S2O8), and 5.4 g (55
mmol) of concentrated sulfuric acid was dissolved in a mixture
of 350 mL of water and 60 mL of chlorobenzene and refluxed
for 8 h. After the mixture was cooled to room temperature,
NaOH was added until pH 9 was reached, which was followed
by filtration through a sintered-glass frit. The filtrate (two-
phase system) was extracted with four 10 mL portions of CH2-
Cl2. The combined organic phases were dried over Na2SO4, and
finally the solvent was evaporated in vacuo. The oily crude
product was purified by Kugelrohr distillation at 10-2 mbar
130.3 (Carom,ipsoCH3); 149.0 (Carom,ipsoN); 156.6 (C(1,5)); 168.2
(CdN). MS: 507 (M+, 10%); 471 (M+ - Cl, 100%); 324 (ligand,
95%). Anal. Calcd for C29H35ClN3RhO: C, 60.06; H, 6.08; N,
7.25. Found: C, 60.31; H, 6.15; N, 7.45. The crystalline
material contains one molecule THF per complex 4, which was
1
confirmed by H NMR integration.
Syn th esis of th e Rh od iu m (I) Ch lor o Com p lex 5. To a
suspension of 329 mg (683 µmol) of ligand B (see text above)
in 6 mL of THF was added dropwise a solution of 133 mg (341
µmol) of [Rh(C2H4)2Cl]2 in 5 mL of THF. After 5 min the slurry
turned dark green. The mixture was stirred for 18 h, and then
the solvents were removed under high vacuum. The resulting
dark green solid is pure enough for most synthetic purposes;
recrystallization from THF/pentane (1/1 v/v) at -35 °C yields
5 as an analytically pure solid. Yield: 416 mg (672 µmol), 98%.
1H NMR (CD2Cl2): δ 1.03 (d, 3J ) 7 Hz, 12 H, CH(CH3)2); 1.13
1
(175 °C). Yield: colorless oil, 6.6 g (30 mmol), 82%. H NMR
(CDCl3): δ 1.37 (s, 9 H, tBu); 2.79 (s, 6 H, -C(O)CH3); 8.23 (s,
2 H, CH(2,4)). 13C{1H} NMR (CDCl3): δ 25.7 (-C(O)CH3); 30.4
(C(CH3)3); 35.4 (C(CH3)3); 121.7 (CH (2,4)); 152.8 (C (1,5)); 162.6
(C(3)); 200.0 (-C(O)CH3). Anal. Calcd for C13H17NO2: C, 71.21;
H, 7.81; N, 6.39. Found: C, 70.95; H, 7.56; N, 6.39.
3
(d, J ) 7 Hz, 12 H, CH(CH3)2); 1.64 (s, 6 H, CN-CH3); 3.03
Syn th esis of Liga n d 2. To a suspension of 2.01 g (9.2
mmol) of 4-tert-butyl-2,6-diacetylpyridine (1) and 4.44 g (36.7
mmol) of 2,6-dimethylaniline were added 6 g of molecular
sieves (4 Å) in 5 mL of toluene and 5 drops of formic acid, and
the mixture was stirred for 35 days. The molecular sieve was
filtered off and washed with five 10 mL portions of toluene.
The organic phase was concentrated under vacuum, methanol
was added until a yellow precipitate was obtained, and then
this mixture was placed in a refrigerator at 10 °C overnight
to complete crystallization. The product was collected by
filtration, washed with cold methanol, and dried in vacuo. A
second crop could be obtained from the filtrate as described
above. Yield: yellow crystals, 771 mg (1.73 mmol), 19%
3
(sept, J ) 7 Hz, 4 H, CH(CH3)2); 7.30 (m, 6 H, CHarom); 7.70
3
3
(d, J ) 8 Hz, 2 H, CH(2,4)); 8.51 (t, J ) 8 Hz, 1 H, CH(3)).
13C{1H} NMR (CD2Cl2): δ 17.8 (CN-CH3); 23.58 (CH(CH3)2);
23.64 (CH(CH3)2); 28.5 (CH(CH3)2); 123.5 (CaromH); 124.0
(CH(3)); 125.3 (CH(2,4); 126.7 (CaromH); 140.8 (Carom,ipsoiPr);
146.1 (Carom,ipsoN); 156.5 (C(1,5)); 168.0 (CdN). MS: 619 (M+,
100%); 583 (M+ - Cl, 100%); 568 (M+ - Cl - CH3, 100%), 540
(M+ - Cl - iPr, 44%). Anal. Calcd for C33H43N3ClRh: C, 63.92;
H, 6.99; N, 6.78. Found: C, 64.04; H, 6.74; N, 6.71.
Syn th esis of th e Rh od iu m (I) Ch lor o Com p lex 6. A
solution of 9 mg (23 µmol) of [Rh(C2H4)2Cl]2 and 20 mg (46
µmol) of 2 in 5 mL of THF was stirred for 1.5 h at room
temperature, giving a dark green solution. The solvent was
removed in vacuo to yield a dark green solid. Recrystallization
from THF/diethyl ether at -35 °C yields 27 mg (44 µmol, 98%)
1
t
(unoptimized). H NMR (CDCl3): δ 1.16 (s, 9 H, Bu); 2.07 (s,
12 H, CH3); 2.25 (s, 6 H, CN-CH3); 6.96-7.08 (m, 6 H, CHarom);
8.85 (s, 2 H, CH(2,4)). 13C{1H} NMR (CDCl3): δ 16.6 (CN-
CH3); 18.1 (CH3); 30.5 (C(CH3)3); 35.1 (C(CH3)3); 119.6 (CH-
(2,4)); 123.4 (CaromH); 125.5 (Carom,ipsoCH3); 128.4 (CaromH); 149.5
(Carom,ipsoN); 155.8 (C(1,5)); 161.4 (C(3)); 167.3 (CdN). IR (imine
range, toluene): 1644 (s, CdN), 1649 (s, CdN) cm-1. Anal.
Calcd for C29H35N3: C, 81.83; H, 8.29; N, 9.88. Found: C, 81.76;
H, 7.97; N, 9.93.
1
of 6. H NMR (C6D6): δ 1.11 (s, 6 H, CN-CH3); 1.25 (s, 9 H,
1
1
tBu); 1.51 (m, /2 THF); 2.33 (s, 12 H, CH3); 3.68 (m, /2 THF);
7.26 (s, 6 H, CHarom); 7.42 (s, 2 H, CH(2,4)). 13C{1H} NMR
(C6D6): δ 16.1 (CN-CH3); 18.9 (CH3); 25.5 (THF); 29.1
(C(CH3)3); 36.5 (C(CH3)3); 67.5 (THF); 120.8 (CH(2,4)); 125.8
(CaromH); 128.2 (CaromH); 129.9 (Carom,ipsoCH3); 146.2 (C(3));
149.1 (Carom,ipsoN); 156.3 (C(1,5)); 166.1 (CdN). Anal. Calcd for
Syn th esis of Liga n d 3. A solution of 1.0 g (4.6 mmol) 4-tert-
butyl-2,6-diacetylpyridine (1) and 1.7 g (11.4 mmol) 4-tert-
butylaniline in 15 mL MeOH was treated with five drops of
formic acid (98%) and stirred for 36 h at 50 °C. After 1 h the
formation of a yellow solid precipitate was observed. The
mixture was cooled to room temperature and the yellow solid
was collected by filtration and washed with cold methanol.
Recrystallization from hexane yields bright yellow crystals,
which are also suitable for X-ray crystal diffraction. Yield: 407
mg (0.85 mmol) 18% (unoptimized). 1H NMR (C6D6): δ 1.12
1
C
31H39ClN3O1/2Rh (contains
/
molecule THF per molecule,
2
confirmed by 1H NMR integration): C, 62.05; H, 6.55; N, 7.00.
Found: C, 62.28; H, 6.55; N, 6.78.
Syn th esis of th e Ir id iu m (I) Ch lor o Com p lex 7. To a
solution of 516 mg (0.91 mmol) [Ir(C2H4)2Cl]2 in 8 mL of toluene
was added slowly a solution of 672 mg (1.82 mmol) of ligand
A dissolved in 20 mL of toluene. First a color change to dark
green was noticed, and then a brown solid precipitated. After
the mixture was stirred for 30 min, the solvent was removed
in vacuo. The brown solid was washed twice with 5 mL of
pentane and then dried in vacuo. Unreacted free ligand was
removed by washing the solid with ether (2 × 10 mL). After
drying in vacuo, a brown solid is obtained; analytically pure
brown (sometimes green) material is obtained by recrystalli-
zation from THF/pentane at -35 °C. Yield: 842 mg (1.41
mmol), 78%. 1H NMR (CD2Cl2): δ 1.05 (s, 6 H, CN-CH3); 2.04
t
(s, 6 H, CN-CH3); 1.25 (s, 18 H, Bu); 2.50 (s, 9H, C(3)-tBu);
6.93 (m, 4 H, CHarom); 8.82 (s, 2 H, CH(2,4)). 13C{1H} NMR
(C6D6): δ 16.4 (C(3)-C(CH3)3); 30.4 (CN-CH3); 31.6 (C(CH3)3);
34.3 (C(CH3)3); 35.3 (C(3)-C(CH3)3); 119.5 (CaromH); 119.8
(CH(2,4)); 126.2 (CaromH); 146.3, 149.6, 156.1, 161.1 (C(3),
C
arom,ipsotBu, C(1,5), Carom,ipsoN); 167.3 (CdN). IR (imine range,
toluene): 1639 (s, CdN) cm-1. Anal. Calcd for C33H43N3: C,
82.28; H, 9.00; N, 8.72. Found: C, 82.34; H, 9.12; N, 8.73.
Syn th esis of th e Rh od iu m (I) Ch lor o Com p lex 4. To a
solution of 460 mg (1.18 mmol) of [Rh(C2H4)2Cl]2 in 20 mL of
THF was slowly added 874 mg (2.37 mmol) of ligand A (see
text above) as a solid. The resulting dark green solution was
stirred for 30 min. The solvent was removed in vacuo, and the
dark green solid was washed with pentane (2 × 10 mL). After
drying under vacuum, the product was obtained in 99% yield
(1.36 g, 2.34 mmol) as an analytically pure compound. Crystals
suitable for X-ray diffraction were obtained by diffusion of
pentane into a solution of 4 in THF. 1H NMR (CD2Cl2): δ 1.61
(s, 6 H, CN-CH3); 1.82 (m, 4 H, THF); 2.11 (s, 12 H, CH3);
3
(s, 12 H, CH3); 7.19 (m, 6 H, CHarom); 7.85 (d, J ) 8 Hz, 2 H,
3
CH(2,4)); 8.74 (t, J ) 8 Hz, 1 H, CH(3)). 13C{1H} NMR (CD2-
Cl2): δ 18.7 (CH3); 18.9 (CN-CH3); 123.2 (CH(2,4)); 123.5
(CH(3)); 126.5, 128.1 (CaromH); 130.8 (Carom,ipsoCH3); 152.6
(Carom,ipsoN); 163.9 (C(1,5)); 173.4 (CdN). Anal. Calcd for C25H27
-
ClIrN3: C, 50.28; H, 4.56; N, 7.04. Found: C, 50.57; H, 4.63;
N, 7.01.
Alter n a tive Syn th esis of th e Ir id iu m (I) Ch lor o Com -
p lex 7. A slow flow of ethylene was bubbled through a
suspension of 408 mg (455 µmol) of [Ir(COE)2Cl]2 in 12 mL of
hexane at 0 °C. After a color change from dark red to light
red was noticeable, indicating the formation of [Ir(C2H4)4Cl],
a solution of 336 mg (909 µmol) of ligand A in 5 mL of THF
was added slowly via a drain tube, yielding a dark green
(sometimes also dark brown) mixture, which was stirred for a
further 10 min at 0-5 °C. After this time, the reaction mixture
3
3.68 (m, 4 H, THF); 7.14 (s, 6 H, CHarom); 7.67 (d, J ) 8 Hz,
2 H, CH(2,4)); 8.47 (t, J ) 8 Hz, 1 H, CH(3)). 13C{1H} NMR
3
(CD2Cl2): δ 16.8 (CN-CH3); 18.7 (CH3); 25.9 (THF); 68.1
(THF); 124.3 (CH(3)); 125.2 (CH(2,4)); 125.9, 127.8 (CaromH);

4356 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
was evaporated to dryness in vacuo. Recrystallization from
THF/pentane at -35 °C yielded dark green crystals: 265 mg
(444 µmol), 49%.
crystals, which were separated by centrifugation, washed with
a small amount of diethyl ether, and finally dried under high
1
vacuum. Yield: 25 mg (33.5 µmol), 71%. H NMR (CD2Cl2): δ
t
1.53 (s, 3 H, Rh-CH3); 1.54 (s, 9 H, Bu); 2.10 (s, 6 H, CN-
Syn th esis of th e Ir id iu m (I) Ch lor o Com p lex 8. A
solution of ligand B (141 mg, 292 µmol) dissolved in 20 mL of
THF was added slowly to a solution of 83 mg (146 µmol) of
[Ir(C2H4)2Cl]2 in 5 mL of Et2O, and the resulting brown mixture
was stirred for 3 h at room temperature. The solvents were
removed under vacuum, and the remaining brown solid was
washed with pentane (2 × 5 mL) and dried in vacuo. After
this solid was dissolved in methanol and the solution was
filtered via cannula, the green solution was evaporated to
dryness in vacuo and the brown solid residue recrystallized
from a mixture of THF/Et2O, yielding 60 mg (85 µmol, 29%)
of brown crystals, which dissolve in dichloromethane, toluene,
or THF as a green solution. Single crystals suitable for X-ray
diffraction can be obtained by the same method. 1H NMR
CH3); 2.42 (s, 12 H, CH3); 7.12-7.20 (m, 6 H, CHarom); 8.02 (s,
2 H, CH(2,4)). 13C{1H} NMR (CD2Cl2): δ 1.3 (d, 1J (Rh,C) ) 25
Hz, Rh-CH3); 18.9 (CH3); 19.0 (CN-CH3); 20.6 (CH3); 30.5
(C(CH3)3); 36.8 (C(CH3)3); 125.6 (CH(2,4)); 127.9, 128.6, 128.8
(CaromH); 129.5, 133.9 (Carom,ipsoCH3); 144.1 (Carom,ipsoN); 158.0
(C(1,5)); 165.3 (C(3)); 180.1 (CdN). 19F NMR (CD2Cl2):
δ
-80.72 (s, OTf). Anal. Calcd for C31H35N3ClF3O3RhS: C, 51.35;
H, 4.87; N, 5.80. Found: C, 50.99; H, 5.21; N, 5.61.
Syn th esis of Ir (III) Ch lor o Hyd r id e Tr ifla te Com p lex
12. A 10 µL (115 µmol) portion of HOTf was added to a solution
of 46 mg (77 µmol) of complex 7 in 5 mL of CH2Cl2 and the
dark green mixture stirred for 45 min. The volume was
reduced to half in vacuo and then layered with pentane.
Crystallization at -35 °C yielded 12 as dark green crystals:
53 mg (71 µmol), 92%. 1H NMR (CD2Cl2): δ -36.27 (s, 1 H,
Ir-H); 1.97 (s, 6 H, CH3); 2.30 (s, 6 H, CH3); 2.68 (s, 6 H, CN-
CH3); 7.10-7.19 (m, 6 H, CHarom); 7.91 (s, 3 H, CH(2,4) and
CH(3)). 13C NMR (CD2Cl2): δ 17.1 (CN-CH3); 17.4 (CH3); 18.7
(CH3); 126.4 (CH(2,4) or CH(3)); 127.8, 128.7, 128.8, 129.0
(CaromH); 132.0 (Carom,ipsoCH3); 137.7 (CH(2,4) or CH(3)); 145.2
(Carom,ipsoN); 162.6 (C(1,5)); 183.4 (CdN). 19F NMR (CD2Cl2):
δ -80.71 (s, OTf). Anal. Calcd for C26H28ClF3IrN3O3S: C, 41.79;
H, 3.78; N, 5.62. Found: C, 41.79; H, 3.78; N, 5.45.
3
(toluene-d8): δ 0.55 (s, 6 H, CN-CH3); 1.02 (d, J ) 7 Hz, 12
H, CH(CH3)2); 1.04 (d, 3J ) 7 Hz, 12 H, CH(CH3)2); 2.97 (sept,
3J ) 7 Hz, 4 H, CH(CH3)2); 6.91-7.05 (m, 6 H, CHarom); 7.16
3
3
(d, J ) 8 Hz, 2 H, CH(2,4)); 8.12 (t, J ) 8 Hz, 1 H, CH(3)).
13C{1H} NMR (toluene-d8): δ 19.6 (CN-CH3); 23.9 (CH(CH3)2);
24.2 (CH(CH3)2); 28.2 (CH(CH3)2); 121.6 (CH(3)); 122.3 (CH(2,4));
123.5, 127.5 (CaromH); 140.8 (Carom,ipsoiPr); 149.8 (Carom,ipsoN);
164.0 (C(1,5)); 171.8 (CdN). Anal. Calcd for C33H43N3ClIr: C,
55.87; H, 6.11; N, 5.92. Found: C, 55.60; H, 6.20; N, 5.93.
Syn th esis of th e Ir id iu m (I) Ch lor o Com p lex 9. A
solution of 27 mg (56 µmol) of ligand 3 in 3 mL of toluene was
added slowly (3 min) to a solution of 16 mg (28 µmol) of [Ir-
(C2H4)2Cl]2 in 4 mL of toluene, upon which the color changed
to brown. The solvent was evaporated to dryness in vacuo, the
residue redissolved in toluene, and this solution once more
evaporated to dryness. The remaining dark green solid was
washed twice with pentane (5 mL each) and dried in vacuo.
The solid was further washed with pentane until the washing
solutions were nearly colorless, yielding a bright green solid,
which was dried in vacuo. Yield: 31 mg (44 µmol), 79%. 1H
NMR (C6D6): δ 0.57 (s, 6 H, CN-CH3); 1.21 (s, 18 H, C(CH3)3);
1.23 (s, 9 H, C3-C(CH3)3); 7.36 (“d”, J ) 9 Hz, 4 H, CHarom);
7.57 (“d”, J ) 9 Hz, 4 H, CHarom); 7.60 (s, 2 H, CH(2,4)). 13C-
{1H} NMR (C6D6): δ 20.6 (CN-CH3); 29.2 (C(3)-C(CH3)3); 31.8
(C(CH3)3); 34.9 (C(CH3)3); 37.9 (C(3)-C(CH3)3); 119.0 (CH(2,4));
124.6, 125.7 (CaromH); 146.1 (C(3)); 149.6 (Carom,ipsotBu); 152.5
(Carom,ipsoN); 164.9 (C(1,5)); 171.1 (CdN). Anal. Calcd for
Syn th esis of th e Rh od iu m (III) Meth yl Bis(tr ifla te)
Com p lex 13. A 0.36 mL (3.28 mmol) portion of methyl triflate
was added to a vigorously stirred solution of 380 mg (656 µmol)
of complex 4 in 30 mL of CH2Cl2, yielding an orange solution.
From time to time MeCl was removed by applying a weak
vacuum. After 4 h, the volume of the solvent was reduced
under vacuum to ca. 5 mL, upon which the product precipi-
tated as a microcrystalline orange solid. The solvent was
decanted off, and the solid was washed with three 5 mL
portions of ether and then dried under high vacuum. Analyti-
cally pure complex 13 was obtained by recrystallization from
a mixture of dichloromethane and pentane at -35 °C. Yield:
yellow solid, 433 mg (551 µmol), 84%. Single crystals suitable
for X-ray diffraction were obtained upon cooling a pentane-
layered dichloromethane solution to -35 °C. 1H NMR (CD2-
2
Cl2): δ 1.91 (d, J (Rh,H) ) 2 Hz, 3 H, Rh-CH3); 2.13 (s, 6 H,
CH3); 2.44 (s, 6 H, CH3); 2.47 (s, 6 H, CN-CH3); 7.12-7.21
C
33H43N3ClIr: C, 55.87; H, 6.11; N, 5.92. Found: C, 56.24; H,
3
3
(m, 6 H, CHarom); 8.07 (d, J ) 8 Hz, 2 H, CH(2,4)); 8.37 (t, J
) 8 Hz, 1 H, CH(3)). 13C{1H} NMR (CD2Cl2): δ 4.7 (d, 1J (Rh,C)
) 24.5 Hz, Rh-CH3); 19.0 (CN-CH3), 19.1 (CH3), 20.0 (CH3),
128.4 (CH(2,4)); 128.5, 128.9, 129.0, 130.5 (CaromH); 133.8
(Carom,ipsoCH3); 140.4 (CH(3)); 143.4 (Carom,ipsoN); 159.7 (C(1,5));
179.5 (CdN). 19F NMR (CD2Cl2): δ -81.60 (s, 3 F, OTf); -80.76
(s, 3 F, OTf). Anal. Calcd for C28H30F6N3O6RhS2: C, 42.81; H,
3.85; N, 5.35. Found: C, 42.86; H, 3.94; N, 4.95. IR (CD2Cl2,
triflate range): 1328 (OTf, covalent); 1293 (OTf, ionic); 1211
cm-1 (s, OTf, covalent).
6.45; N, 5.59.
Syn th esis of Rh (III) Ch lor o Hyd r id e Tr ifla te Com p lex
10. A solution of 97 mg (167 µmol) of 4 in 5 mL of CH2Cl2 was
reacted with 15 µL (167 µmol) of HOTf, which led to an
immediate color change from dark green to bright orange.
After the mixture was stirred for 30 min, the volume of the
solvent was reduced to half in vacuo and then layered with
pentane. Recrystallization at -35 °C yielded 104 mg (158 µmol,
95%) of orange crystals, which were also suitable for X-ray
1
1
diffraction. H NMR (CD2Cl2): δ -23.8 (d, J (Rh,H) ) 24 Hz,
1 H, Rh-H); 2.10 (s, 6 H, CH3); 2.32 (s, 6 H, CH3); 2.36 (s, 6
Syn th esis of th e Rh od iu m (III) Meth yl Bis(tr ifla te)
Com p lex 14. To a solution of 37 mg (60 µmol) of 11 in 2 mL
of C2H4Cl2 was added 39.6 µL (360 µmol) of MeOTf, yielding
an orange solution, which was stirred for 36 h at room
temperature. The reaction was evaporated to dryness under
vacuum, and the solid remainder was washed with pentane
(2 × 5 mL) to remove traces of excess MeOTf. Recrystallization
from dichloromethane/pentane at -35 °C yielded 36 mg (42.8
3
H, CN-CH3); 7.08-7.18 (m, 6 H, CHarom); 8.04 (d, J ) 8 Hz,
2 H, CH(2,4)); 8.29 (t, J ) 8 Hz, 1 H, CH(3)). 13C NMR (CD2-
3
3
Cl2): δ 17.9 (d, J (Rh,C) ) 1 Hz, CN-CH3); 18.4 (CH3); 18.9
(CH3); 127.5 (CH(2,4)); 127.8, 128.61, 128.63, 129.1 (CaromH);
131.6 (Carom,ipsoCH3); 139.5 (CH(3)); 144.4 (Carom,ipsoN); 158.8
(C(1,5)); 180.0 (CdN). 19F NMR (CD2Cl2): δ -80.76 (s, OTf).
15N NMR (CD2Cl2): δ -323.8 (pyridine); -324.5 (CdN). Anal.
Calcd for C26H28ClF3N3O3RhS: C, 47.46; H, 4.29; N, 6.39.
Found: C, 47.37; H, 4.45, N, 6.41.
1
µmol, 71%) of 14. H NMR (CD2Cl2): δ 1.53 (s, 9 H, C(CH3)3);
1.89 (d, 2J (Rh,H) ) 2 Hz, 3 H, Rh-CH3); 2.13 (s, 6 H, CN-
CH3); 2.43 (s, 6 H, CH3); 2.46 (s, 6 H, CH3); 7.11-7.21 (m, 6
H, CHarom); 7.98 (s, 2 H, CH(2,4)). 13C{1H} NMR (CD2Cl2): δ
4.5 (Rh-CH3); 19.0 (CH3); 19.1 (CN-CH3); 19.9 (CH3); 30.5
(C(CH3)3); 36.9 (C(CH3)3); 125.8 (CH(2,4)); 128.4, 129.0, 130.4
(CaromH); 133.7 (Carom,ipsoCH3); 143.5 (Carom,ipsoN); 159.0 (C(1,5);
166.8 (C(3)); 179.8 (CdN). 19F NMR (CD2Cl2): δ -80.71 (s, 3
Syn th esis of th e Rh od iu m (III) Meth yl Ch lor o Tr ifla te
Com p lex 11. To a solution of 6 (28 mg, 47 µmol) in 5 mL of
CH2Cl2 was added 5 µL (47 µmol) of MeOTf, leading to a color
change from green to brown. The solution was stirred for 1 h;
the solvent was then reduced to half by evaporation in vacuo.
Recrystallization from CH2Cl2/pentane yielded 11 as orange

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4357
F, OTf); -81.60 (s, 3 F, OTf). Anal. Calcd for C32H38N3F6O6-
RhS2: C, 45.60; H, 4.55; N, 4.99. Found: C, 45.65; H, 4.73; N,
5.14.
NMR: Rh(C2H4) resonance, δ 78.7 (dt, 1J (C,H) ) 158 Hz,
1J (Rh,C) ) 11 Hz). 19F NMR (THF-d8): δ -80.87 (s, OTf). IR
(imine range, CH2Cl2): 1593 (m, CdN) cm-1. Anal. Calcd for
C
29H33N3F3O3.25RhS (17‚0.25 THF): C, 52.18; H, 4.98; N, 6.29.
Syn th esis of th e Ir id iu m (III) Meth yl Bis(tr ifla te) Com -
p lex 15. To a solution of 124 mg (207 µmol) of complex 7 in 8
mL of C2H2Cl4 was added 114 µL (1.03 mmol) of MeOTf. The
mixture was stirred for 2 h; during this time MeCl formed in
the reaction was removed by applying a weak vacuum three
times. The solvent was then removed in vacuo and the solid
recrystallized from a mixture of CH2Cl2 and pentane at -35
°C. This yielded 111 mg (127 µmol) (61%) of 15 as dark green,
Found: C, 52.41; H, 5.02; N, 5.96. The presence of 1/4 molecule
of THF per molecule of 17 in the crystalline material was
confirmed by H NMR integration of several batches.
1
Syn th esis of th e Rh (III) Eth yl Bis(tr ifla te) Com p lex
18. To 35 mg (48 µmol) of 17 dissolved in 5 mL of dichlo-
romethane was added 4.7 µL (53 µmol) of HOTf, upon which
a color change from dark brown to orange was noticed. After
the solution was stirred for 1.5 h, the solvent was reduced to
half in vacuo and layered with pentane. Crystallization of this
mixture at -35 °C yielded 16 mg (19 µmol, 40%) of 18 as red
crystals. Crystals suitable for X-ray diffraction were also
1
almost black crystals. H NMR (CD2Cl2): δ 1.13 (s, 3 H, Ir-
CH3); 2.17 (s, 6 H, CH3); 2.44 (s, 6 H, CH3), 2.85 (s, 6 H, CN-
CH3); 7.18-7.27 (m, 6 H, CHarom); 7.99 (s, 3 H, CH(2,3,4)).
13C{1H} NMR (CD2Cl2): δ 14.2 (Ir-CH3); 18.4 (CN-CH3); 19.6
(broad, CH3); 127.4 (CH(2,4) or CH(3)); 128.5, 129.2, 130.4
(CaromH); 133.6 (Carom,ipsoCH3); 138.7 (CH(2,4) or CH(3)); 144.4
(Carom,ipsoN); 162.8 (C(1,5)); 183.5 (CdN). 19F NMR (CD2Cl2):
δ -80.6 (s, 3 F, OTf); -81.3 (s, 3 F, OTf). Anal. Calcd for
1
3
obtained in this way. H NMR (CD2Cl2): δ 0.29 (t, J ) 8 Hz,
3 H, Rh-CH2-CH3); 2.19 (s, 6 H, CH3); 2.44 (s, 6 H, CH3);
2
3
2.48 (s, 6 H, CN-CH3); 3.30 (dq, J (Rh,H) ) 3 Hz, J ) 8 Hz,
2 H, Rh-CH2-CH3); 7.13-7.22 (m, 6 H, CHarom); 8.05 (d, 3J )
3
C
28H30F6IrN3O6S2: C, 38.44; H, 3.46; N, 4.80. Found: C, 38.06;
8 Hz, 2 H, CH(2,4)); 8.36 (t, J ) 8 Hz, 1 H, CH(3)). 13C{1H}
H, 3.42; N, 4.73.
NMR (CD2Cl2): δ 18.1 (Rh-CH2-CH3); 18.7 (CH3); 18.8 (CN-
CH3); 20.2 (CH3); 21.4 (d, 1J (Rh,C) ) 24 Hz, Rh-CH2CH3);
128.4 (Carom H), 128.7 (CH(2,4)); 129.0, 130.6 (CaromH); 133.8
(Carom,ipsoCH3); 140.1 (CH(3)); 143.4 (Carom,ipsoN); 159.4 (C(1,5));
179.7 (CdN). 19F NMR (CD2Cl2): δ -80.6 (s, 3 F, OTf); -81.6
(s, 3 F, OTf). Anal. Calcd for C29H32N3F6O6RhS2: C, 43.56; H,
4.03; N, 5.26. Found: C, 43.71; H, 4.09; N, 5.27.
Syn th esis of th e Rh od iu m (I) BH 4 Com p lex 19. A
mixture of 118 mg (165 µmol) of 16‚dme and 6.5 mg (172 µmol)
of NaBH4 was suspended in 10 mL of THF, which was stirred
for 10 min, upon which a color change from brown to green-
blue was observed. The solvent was removed in vacuo, leaving
a solid remainder, which was washed with 10 mL of pentane
and then dried under high vacuum. The product was extracted
into diethyl ether, filtered, and evacuated to dryness. It was
dissolved in a small amount of THF and recrystallized from a
solvent mixture of diethyl ether and pentane at -35 °C,
yielding 19 as dark green, analytically pure crystals. Yield:
Syn th esis of th e Rh od iu m Com p lex 16‚d m e. A solution
of 961 mg (1.44 mmol) of 17 in 10 mL of dme was degassed in
a high-vacuum Teflon tap (Young) sealed Schlenk tube by a
freeze-pump-thaw (fpt) cycle and then heated under vacuum
to 100 °C. After 1 day the solvent was evaporated under high
vacuum, the solid residue was redissolved in dme, and the
solution was degassed (fpt cycle) and heated again to 100 °C.
This procedure was repeated three times; the total duration
was 5 days. After removal of the solvent under high vacuum,
the residual brown microcrystalline powder was washed with
pentane (2 × 5 mL) and finally dried in vacuo, yielding 995
mg (1.4 mmol), 97%, of the analytically pure product 16‚dme.
1H NMR (THF-d8): δ 2.01 (s, 6 H, CN-CH3); 2.32 (s, 12 H,
CH3); 3.29 (s, dme); 3.49 (s, dme); 7.16 (s, 6 H, CHarom); 8.12
3
3
(d, J ) 8 Hz, 2 H, CH(2,4)); 8.45 (t, J ) 8 Hz, 1 H, CH(3)).
13C{1H} NMR (THF-d8): δ 16.7 (CN-CH3); 18.4 (CH3); 59.1,
72.9 (dme); 127.5 (CH(2,4) and CaromH); 129.6 (Carom H); 131.1
(CH(3)); 132.8 (Carom,ipsoCH3); 148.2 (Carom,ipsoN); 158.8 (C(1,5));
172.7 (CdN). 19F NMR (THF-d8): δ -80.9 (s, OTf). IR (OTf
range, CD2Cl2): 1317 (s), 1211 (s) cm-1 (covalent OTf, tenta-
tive, see text). Anal. Calcd for C30H37N3F3O5RhS: C, 50.64; H,
5.24; N, 5.90. Found: C, 50.90; H, 5.58; N 5.82.
1
41 mg (84 µmol), 51%. H NMR (C6D6, 298 K): δ 1.25 (s, 6 H,
CN-CH3); 2.06 (s, 12 H, CH3); 7.02-7.07 (m, 6 H, CHarom);
7.12 (d, 3J ) 8 Hz, 2 H, CH(2,4)); 7.40 (t, 3J ) 8 Hz, 1 H,
CH(3)). The signals of the BH4 group could not be detected at
this temperature. In the 1H NMR spectrum at -100 °C in
THF-d8 a broad pseudo-doublet at -5.82 ppm (1J (B,H) ) 40
Hz) was observed for the BH4 group. 13C{1H} NMR (C6D6): δ
15.9 (CN-CH3), 18.8 (CH3); 116.2 (CH(3)); 124.7 (CH(2,4));
Syn th esis of th e Rh (I) Eth ylen e Com p lex 17. To a
solution of 646 mg (1.66 mmol) of [Rh(C2H4)2Cl]2 in 20 mL of
THF and 5 mL of diethyl ether was added slowly a solution of
853 mg (3.32 mmol) of AgOTf in 15 mL of THF with vigorous
stirring. The yellow suspension was stirred for 5 min and
stored at -35 °C for 20 min. The precipitated AgCl was
removed by centrifugation; the supernatant yellow solution
was filtered and then reduced in vacuo to 20 mL. The
concentrated dark orange solution was filtered again to remove
further traces of AgCl. To this filtrate was added slowly a
solution of 1.228 g (3.32 mmol) of ligand A in a mixture of 10
mL diethyl ether and 5 mL of THF, yielding a dark brown
solution which was stirred for 1 h, upon which the formation
of a dark green (sometimes brown) microcrystalline precipitate
was observed. The solvent was reduced to 20 mL in vacuo,
and then 10 mL diethyl ether was added to complete precipita-
tion of the product. The supernatant solvent was decanted off,
and the solid was dried under high vacuum, washed with
pentane (2 × 10 mL), and finally dried under high vacuum.
This yielded 2.26 g (3.13 mmol, 94%) of 17 as an analytically
pure green microcrystalline solid. 1H NMR (CD2Cl2): δ 1.81
126.1, 129.9 (CaromH); 148.5, 148.6, 149.3 (Carom,ipsoN, Carom,ipso
-
CH3, C(1,5)); 163.8 (CdN). Anal. Calcd for C25H31N3BRh: C,
61.63; H, 6.41; N, 8.62. Found: C, 61.30; H, 6.33; N, 8.44. IR
(KBr, B-H range): 2405 (s), 2363 (s) (B-H terminal); 1914
(w), 1901 (vw) (B-H bridging) cm-1. IR (BD4 isotopomer): 1828
(w), 1811 (s) (B-D terminal); 1740 (vs) (B-D bridging) cm-1
.
Single crystals suitable for X-ray diffraction were obtained by
slow diffusion of pentane into a solution of 19 in diethyl ether
at room temperature.
Syn th esis of th e Rh (I) Meth oxid e Com p lex 20. A
solution of 42 mg (72 µmol) of the rhodium chloro complex 4
in 5 mL of MeOH and 5 mg (87 µmol) of NaOMe was stirred
for 30 min. The reaction mixture was evaporated to dryness,
the remaining green solid washed with pentane (2 × 5 mL),
and the product finally extracted into toluene. The toluene
fraction was filtered, the solvent was removed under high
vacuum, and the obtained dark green solid was washed with
pentane (2 × 5 mL) and then dried under high vacuum,
yielding 35 mg (70 µmol, 96%) of 20 as a dark green analyti-
cally pure compound. 1H NMR (C6D6): δ 1.00 (s, 6 H, CN-
CH3); 2.14 (s, 12 H, CH3); 4.47 (s, 3 H, OCH3); 6.98-7.06 (m,
1
(m, /4 THF); 1.95 (s, 6 H, CN-CH3); 2.18 (s, 12 H, CH3); 3.39
3
1
(d, J (Rh,H) ) 2 Hz, 4 H, C2H4); 3.68 (m, /4 THF); 7.12 (s, 6
3
3
H, CHarom); 8.04 (d, J ) 8 Hz, 2 H, CH(2,4)); 8.32 (t, J ) 8
Hz, 1 H, CH(3)). 13C{1H} NMR (CD2Cl2): δ 17.3 (CN-CH3);
17.9 (CH3); 25.9 (THF); 68.1 (THF); 78.7 (d, 1J (Rh,C) ) 11 Hz,
C2H4); 126.2 (CH(2,4)); 127.5, 128.3, 129.1 (CaromH); 142.0
(CH(3)); 143.6 (Carom,ipsoN); 156.2 (C(1,5)); 175.5 (CdN). 13C
3
3
6 H, CHarom); 7.12 (d, J ) 8 Hz, 2 H, CH(2,4)); 7.80 (t, J ) 8
Hz, 1 H, CH(3)). 13C{1H} NMR (C6D6): δ 17.1 (CN-CH3); 19.2
(CH3); 61.2 (OCH3); 116.4 (CH(3)); 124.9 (CH(2,4)), 126.0, 128.9
(CaromH); 131.0 (Carom,ipsoCH3), 150.5 (Carom,ipsoN); 155.2 (d,

4358 Organometallics, Vol. 20, No. 21, 2001
Nu¨ckel and Burger
2J (Rh,C) ) 2.6 Hz, C(1,5)); 163.4 (CdN). Anal. Calcd for
Ch a r t 2
C
26H30N3ORh: C, 62.03; H, 6.01; N, 8.35. Found: C, 62.32; H,
6.34; N, 8.45.
Syn th esis of th e Ir (I) Meth oxid e Com p lex 21. To a
vigorously stirred solution of 105 mg (176 µmol) of 7 in 20 mL
of MeOH was added slowly a solution of 15 mg (278 µmol) of
NaOMe in 8 mL of MeOH, and the mixture was allowed to
react for 30 min. The solvent was removed in vacuo, washed
with pentane (3 × 5 mL), and dried again under high vacuum.
The crude reaction product was extracted into toluene, the
extract was centrifuged and filtered, the filtrate was evapo-
rated to dryness in vacuo, and the brown solid residue was
washed with pentane (2 × 5 mL). Drying under high vacuum
yielded 92 mg (155 µmol, 88%) of complex 21 as an analytically
C26H30N3Ir: C, 54.14; H, 5.24; N, 7.29. Found: C, 54.61; H,
5.21; N, 6.86.
DF T Ca lcu la tion s. The DFT calculations were performed
with the Turbomole program suite61 and using the BP-86
functional62,63 in its RI-DFT implementation64 for the geometry
optimizations and the calculation of the second derivatives.
As tested for a few cases, essentially identical energy differ-
ences were obtained with the BP-86 functional using the pure
DFT BP86 implementation rather than the RI-DFT method.
The parallel version of the Turbomole program package was
used on our 22 CPU Linux cluster in all cases. Initially, the
geometries were optimized using a TZVP basis65 with scalar-
relativistic Stuttgart-Dresden ECPs66 applied for the rhodium
and iridium centers and SVP basis sets67 for the residual
atoms. After convergence (gradients <10-3 hartree/bohr), a
TZVP basis was applied for all atoms and the geometry
optimization continued. Usually, this took just a few cycles to
converge. Second derivatives were calculated by finite differ-
ences and were used to identify the optimized geometries as
stationary points through the absence of imaginary frequen-
cies. The Rh and Ir model fragment, [Rh,Ir], used in the
calculation of the complexes is shown in Chart 2.
Final total energies Etot,SCF in hartrees with unscaled zero
point energies (ZPEs) in parentheses for the optimized geom-
etries using a Becke-Perdew (BP86) functional (RI-DFT
method), TZVP basis sets for all atoms, and scalar-relativistic
Stuttgart-Dresden pseudopotentials (ECP-28-mwb and ECP-
60-mwb) for the Rh and Ir centers are as follows: CH2O,
-114.554 57 (67.5);C2H4,-78.616 79 (0.049 83);BH3,-26.606 77
(0.025 73); quinuclidine, -329.425 69 (0.189 29); BH3‚qui-
nuclidine, -356.095 24 (0.222 61); acetone, -193.234 89
(0.081 66) ; [Rh](κ2-BH4), I, -573.362 632 (0.170 08); [Rh]-H,
II, -546.674 99 (0.138 28); [Rh]-OMe, III, -661.286 30
(0.171 79); [Rh]-OiPr, -739.949 20 (0.226 62); [Rh]-Et, III,
-625.331 22 (0.193 22); [Ir]-H, II, -540.513 29 (0.138 55);
[Ir]-OMe, III, -655.122 53 (0.171 91); [Ir]-OMe#, III# (TS in
Figure 9), 655.105 28 (0.170 95), +11 kcal mol-1 (one imagi-
nary frequency, νimag ) -300 cm-1). For the Rh methoxy and
hydride compounds, we have also performed geometry opti-
mizations using the B3LYP hybrid functional,68 which led to
the following total energies (ZPEs in parentheses) for the
optimized geometries and essentially identical reaction ener-
gies: [Rh]-H, II, -546.207 44 (0.140 95), [Rh]-OMe, III,
-660.750 65 (0.176 71) [hartrees]. The reaction energies ∆E
presented in Schemes 7 and 9 were calculated using the total
energies Etot given above corrected by their zero-point energies
1
pure brown solid. H NMR (C6D6): δ 0.42 (s, 6 H, CN-CH3);
2.06 (s, 12 H, CH3); 5.45 (s, 3 H, OCH3); 7.01-7.07 (m, 6 H,
3
3
CHarom); 7.73 (d, J ) 8 Hz, 2 H, CH(2,4)); 7.92 (t, J ) 8 Hz,
1 H, CH(3)). 13C{1H} NMR (C6D6): δ 18.6 (CH3); 19.1 (CN-
CH3); 67.6 (OCH3); 115.1 (CH(3)); 122.1 (CH(2,4)); 126.2, 128.5
(CaromH); 130.9 (Carom,ipsoCH3); 154.1 (Carom,ipsoN); 160.1 (C(1,5)),
165.0 (CdN). Anal. Calcd for C26H30N3OIr: C, 52.68; H, 5.10;
N, 7.09. Found: C, 52.82; H, 5.41; N, 6.90. Crystals suitable
for X-ray diffraction were obtained from a solution of 21 in
toluene layered with pentane at -35 °C.
Syn th esis of th e Rh (I) Meth yl Com p lex 22. A 57 µL
portion of MeMgCl (3 M in THF) was added to a solution of
86 mg (171 µmol) of 20 in 10 mL of toluene, and the mixture
was stirred for 20 min. The solvent was removed in vacuo and
the solid residue washed with pentane (2 × 5 mL) and then
dried again under high vacuum. The dark green solid was
extracted into diethyl ether, the extract was filtered through
a glass frit, and the solvent was evaporated to dryness under
high vacuum, yielding 58 mg (119 µmol, 70%) of 22 as an
analytically pure, green compound. 1H NMR (C6D6): δ 0.70
2
(s, 6 H, CN-CH3); 2.09 (s, 12 H, CH3); 2.21 (d, J (Rh,H) ) 1
3
Hz, 3 H, Rh-CH3); 7.04-7.10 (m, 6 H, CHarom); 7.31 (d, J )
3
8 Hz, 2 H, CH(2,4)); 8.16 (t, J ) 8 Hz, 1 H, CH(3)). 13C{1H}
NMR (C6D6): δ 0.2 (d, 1J (Rh,C) ) 33 Hz, Rh-CH3); 18.0 (CN-
CH3); 19.3 (CH3); 121.7 (CH(3)); 123.4 (CH(2,4)); 125.5 (CaromH);
130.2 (Carom,ipsoCH3); 151.4 (Carom,ipsoN); 155.2 (C(1,5)); 165.5
(CdN). One of the aromatic C-H resonances of the 2,6-
dimethyl-substituted phenyl ring could not be detected; pre-
sumably it is obscured by the resonance of the C6D6 solvent.
Anal. Calcd for C26H30N3Rh: C, 64.07; H, 6.20; N, 8.62.
Found: C, 64.26; H, 6.09; N, 8.47.
Syn th esis of th e Ir (I) Meth yl Com p lex 23. To a solution
of 182 mg (307 µmol) of 21 in 6 mL of THF was added 10 µL
(102 µmol) of neat AlMe3. The solvent was removed in vacuo,
the remaining solid was extracted into diethyl ether, and
finally the solvent was evaporated to dryness, leaving a green
solid material. Although the yield of the reaction appears to
be essentially quantitative (on the basis of the 1H NMR
spectrum of the crude reaction mixture), the isolation of pure
23 is somewhat cumbersome. This is due to the sensitivity of
the product, which restricts the purification process solely to
recrystallization (decomposition was observed in chromatog-
raphy attempts on alumina and silica support). Unfortunately,
in large-scale reactions, we have not found sufficiently good
conditions to remove residual small traces of aluminum-
containing species. An analytically pure sample (smaller
amount) was obtained by crystallization of a large reaction
scale batch. The 1H NMR spectrum of this sample proved to
be identical with that for 23 observed in the crude mixture.
Crystals suitable for X-ray diffraction were obtained from a
saturated solution of 23 in pentane at -35 °C. 1H NMR (THF-
d8): δ 0.21 (s, 6 H, CN-CH3); 1.96 (s, 12 H, CH3); 6.91 (s, 3 H,
(Etot ) Etot,SCF + ZPE) and using ∆E ) ∑∆Etot,products
-
∑∆Etot,starting material. In addition, the geometries of the methoxide
complex 20 and its corresponding hydride compound were
optimized using the BP86 functional (RI-DFT implementa-
tion), with TZVP basis sets for all atoms and a Stuttgart-
Dresden ECP for the rhodium center. Because of the size of
these systems, second derivatives were not calculated. Final
(61) Ahlrichs, R.; Ba¨r, M.; Ha¨ser, M.; Horn, H.; Ko¨lmel, C. Chem.
Phys. Lett. 1989, 162, 165.
(62) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(63) Perdew, J . P. Phys. Rev. B 1986, 33, 8822.
(64) Eichkorn, K.; Treutler, O.; Oehm, H.; Ha¨ser, M.; Ahlrichs, R.
Chem. Phys. Lett. 1995, 242, 652.
(65) Scha¨fer, A.; Huber, C.; Ahlrichs, R. J . Chem. Phys. 1994, 100,
5829.
(66) Andrae, D.; Ha¨ubermann, U.; Dolg, M.; Stoll, H.; Preub, H.
Theor. Chim. Acta 1990, 77, 123.
3
Ir-CH3); 7.02-7.18 (m, 6 H, CHarom); 8.40 (d, J ) 8 Hz, 2 H,
CH(2,4)); 8.91 (t, 3J ) 8 Hz, 1 H, CH(3)). 13C{1H} NMR (THF-
d8): δ 2.7 (Ir-CH3); 18.5 (CH3), 20.9 (CN-CH3), 120.7 (CH-
(2,4)); 123.5 (CH(3)); 126.0, 128.2 (CaromH), 130.8 (Carom,ipsoCH3),
156.1 (Carom,ipsoN); 163.7 (C(1,5)); 170.2 (CdN). Anal. Calcd for
(67) Scha¨fer, H.; Horn, H.; Ahlrichs, R. J . Chem. Phys. 1992, 97,
1992.
(68) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.

Complexes with Sterically Demanding Ligands
Organometallics, Vol. 20, No. 21, 2001 4359
total energies in hartrees (Cartesian gradients <5 × 10-4
hartree/bohr) are as follows: [Rh]-H -1 244.910 573; [Rh]-
OMe, 20, -1 359.518 54.
refined as a riding model. For complex 19, the hydrogen atoms
of the Rh-BH4 moiety were located in the difference Fourier
map and were refined isotropically. The absolute configuration
of 19 was confirmed by a Flack x parameter of -0.043(0.019)
and 1.03(0.02) for the inverted structure. The details of the
data collection and refinement, including R values, are sum-
marized in Table 1.
X-r a y Cr ysta l Str u ctu r e An a lyses. Suitable single crys-
tals were mounted on glass fibers in polyisobutylene oil and
transferred on the goniometer head to the diffractometer and
the crystal cooled to -90 °C under a N2 cryostream. The data
sets were collected with graphite-monochromated Mo KR
radiation (0.707 173 Å) on a Stoe IPDS image plate diffrac-
tometer. Intensities were corrected for Lorentz and polariza-
tion effects and absorption corrections performed numerically
with the faces and corresponding crystal dimensions deter-
mined using the STOE Faceit-Video CCD camera microscope
system. The structures were solved using direct methods with
the SHELX-97 program package.69 The refinements were
carried out with SHELXL-97 using all unique Fo2 values.69 All
non-hydrogen atoms were refined anisotropically. Except for
complex 19 the positions of the hydrogen atoms were calcu-
lated in idealized positions (C-H bonds fixed at 0.96 Å) and
Ack n ow led gm en t. We are indebted to Prof. Heinz
Berke for his generous support. We thank Dr. Thomas
Fox for recording the 15N-1H NMR HMBC spectrum.
Support of this work by the Swiss National Science
Foundation is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: 2-D 15H-1H HMBC
spectrum of the Ir methyl complex 23 and tables and figures
giving X-ray crystallographic data for 4, 11, 13, 18, 19, and
21. This material is available free of charge via the Internet
at http://pubs.acs.org.
(69) Sheldrick, G. M. SHELXL 97; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1997.
OM010185Y