Instability of square planar N3-ligand iridium(I) ethene complexes

Article abstract of DOI:10.1021/om050594k

New, five-coordinate, iridium(I) bis-ethene complexes [fac-(bpa-R)Ir ^I(ethene)₂]⁺ (1⁺: R = H, 2 ⁺: R = Me, 3⁺: R = Bz; bpa-H = N,N-di(2-pyridylmethyl) amine, bpa-Me = N-methyl-N,N-di(2-pyridylmethyl)amine, bpa-Bz = N-benzyl-N,N-di(2-pyridylmethyl)amine) were prepared. In contrast to their previously reported rhodium analogues, these iridium species do not readily lose one of their two ethene fragments to form square planar mono-ethene complexes [mer-(bpa-R)Ir^I(ethene)]⁺. Heating complex 1⁺ results in N-H activation at the bpa-H ligand and formation of the dinuclear iridium(III) species [{(mer-μ₂-bpa^#)Ir ^III(ethyl)-(MeCN)}₂]²⁺ (4²⁺) with bridging amides (bpa^# = bpa-H deprotonated at NH_amine). Heating bpa-Bz complex 3⁺ results in aromatic C-H activation of the ligand benzyl group to form dinuclear iridium(III) species [{(bpa-Bz ^#)Ir^III(μ2-H)}₂]²⁺ (5 ²⁺) with unsupported hydride bridges (bpa-Bz^# = bpa-Bz cyclometalated at the benzylic C2-position). The dimeric structure of 5 ²⁺ easily breaks up in MeCN, giving the mononuclear species [(bpa-Bz^#)Ir^III(H)(MeCN)]⁺ (6⁺). Complex 5²⁺ is also light-sensitive: glass-filtered daylight converts it to a geometrical isomer, 7²⁺, in which the cyclometalated benzyl functionality of one of the two ligands has switched its position with a pyridyl donor.

Full text of DOI:10.1021/om050594k

5964
Organometallics 2005, 24, 5964-5972
Instability of Square Planar N3-Ligand Iridium(I) Ethene
Complexes
Simone Thewissen, Maike D. M. Reijnders, Jan M. M. Smits, and Bas de Bruin*
Department of Molecular Materials, Institute for Molecules and Materials, University of
Nijmegen, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands
Received July 14, 2005
New, five-coordinate, iridium(I) bis-ethene complexes [fac-(bpa-R)IrI(ethene)2]+ (1+: R )
H, 2+: R ) Me, 3+: R ) Bz; bpa-H ) N,N-di(2-pyridylmethyl)amine, bpa-Me ) N-methyl-
N,N-di(2-pyridylmethyl)amine, bpa-Bz ) N-benzyl-N,N-di(2-pyridylmethyl)amine) were
prepared. In contrast to their previously reported rhodium analogues, these iridium species
do not readily lose one of their two ethene fragments to form square planar mono-ethene
complexes [mer-(bpa-R)IrI(ethene)]+. Heating complex 1+ results in N-H activation at the
bpa-H ligand and formation of the dinuclear iridium(III) species [{(mer-µ2-bpa#)IrIII(ethyl)-
(MeCN)}2]2+ (42+) with bridging amides (bpa# ) bpa-H deprotonated at NHamine). Heating
bpa-Bz complex 3+ results in aromatic C-H activation of the ligand benzyl group to form
dinuclear iridium(III) species [{(bpa-Bz#)IrIII(µ2-H)}2]2+ (52+) with unsupported hydride bridges
(bpa-Bz# ) bpa-Bz cyclometalated at the benzylic C2-position). The dimeric structure of 52+
easily breaks up in MeCN, giving the mononuclear species [(bpa-Bz#)IrIII(H)(MeCN)]+ (6+).
Complex 52+ is also light-sensitive: glass-filtered daylight converts it to a geometrical isomer,
72+, in which the cyclometalated benzyl functionality of one of the two ligands has switched
its position with a pyridyl donor.
Introduction
RhI and IrI d8 transition metals commonly adopt a
16 VE (valence electron) four-coordinate square planar
coordination geometry.1 However, 18 VE five-coordinate
square pyramidal or trigonal bipyramidal geometries
are also relatively abundant. Observation of five-
coordinate species in solution is usually associated with
chelating olefins, chelating donor ligands, and/or donor
ligands that do not allow formation of a square planar
geometry because of geometrical constraints. The strictly
facially coordinating tri-aza-cyclononanes,2-7 tri-thia-
cyclononanes,8-10 and tris-pyrazolylmethanes and tris-
pyrazolylborates11-18 are examples of such ligands
* To whom correspondence should be addressed. Fax: +31 24 355
34 50. E-mail: B.deBruin@science.ru.nl.
Figure 1. Rigid podal ligands and the flexible coordination
(1) Housecroft, C. E.; Sharpe, A. G. Inorganic Chemistry, second
edition; Pearson Education Limited: Edinburgh, 2005.
(2) de Bruin, B.; Brands, J. A.; Donners, J. J. J. M.; Donners, M. P.
J.; de Gelder, R.; Smits, J. M. M.; Gal, A. W.; Spek, A. L. Chem.-Eur.
J. 1999, 5 (10), 2921-2936.
modes of bpa-R ligands.
“forcing” five-coordinate geometries. The bpa-R ligands
used in this paper (R ) H, Me, Bz; see Figure 1) are
more flexible. Like tris-pyrazolylborates, they can adopt
both κ2 and κ3 coordination modes, but unlike trispyra-
zolylborates they can coordinate in both facial and
meridional κ3 modes.
(3) Baker, M. V.; Brown, D. H.; Skelton, B. W.; White, A. H. J. Chem.
Soc., Dalton Trans. 2002, 2595.
(4) Baker, M. V.; Brown, D. H.; Skelton, B. W.; White, A. H. J. Chem.
Soc., Dalton Trans. 2000, 4607.
(5) Flood, T. C.; Iimura, M.; Perotti, J. M.; Rheingold, A. L.;
Concolino, T. E. Chem. Commun. 2000, 1681.
(6) de Bruin, B.; Donners, J. J. J. M.; de Gelder, R.; Smits, J. M.
M.; Gal, A. W. Eur. J. Inorg. Chem. 1998, 401.
(7) Gott, A. L.; McGowan, P. C.; Temple, C. N. Dalton Trans. 2004,
1841, and references therein.
(14) Oldham, W. J., Jr.; Heinekey, D. M. Organometallics 1997, 16,
467.
(15) Esteruelas, M. A.; Oro, L. A.; Apreda, M. C.; Foces-Foces, C.;
Cano, F. H.; Claramunt, R. M.; Lopez, C.; Elguero, J.; Begtrup, M. J.
Organomet. Chem. 1988, 344, 93.
(16) Boutry, O.; Gutie´rrez, E.; Monge, A.; Nicaso, M. C.; Pe´rez, P.
J.; Carmona, E. J. Am. Chem. Soc. 1992, 114, 7288.
(17) Ciriano, M. A.; Ferna´ndez, M. J.; Modegro, J.; Rodr´ıguez, M.
J.; Oro, L. A. J. Organomet. Chem. 1993, 443, 249.
(18) Nicasio, M. C.; Paneque, M.; Pe´rez, P. J.; Pizzano, A.; Poveda,
M. L.; Rey, L.; Sirol, S.; Taboada, S.; Trujillo, M.; Monge, A.; Ruiz, C.;
Carmona, E. Inorg. Chem. 2000, 39, 180, and references therein.
(8) Blake, A. J.; Halcrow, M. A.; Schroder, M. Chem. Commun. 1991,
253.
(9) Blake, A. J.; Gould, R. O.; Halcrow, M. A.; Schroder, M. J. Chem.
Soc., Dalton Trans. 1994, 2197.
(10) Blake, A. J.; Halcrow, M. A.; Schroder, M. J. Chem. Soc., Dalton
Trans. 1994, 1631, and references therein.
(11) Trofimenko, S. Chem. Rev. 1993, 93, 943-980.
(12) Kitajima, N.; Tolman, W. B. Prog. Inorg. Chem. 1995, 43, 419.
(13) Albinati, A.; Bovens, M.; Ru¨egger, H.; Venanzi, L. M. Inorg.
Chem. 1997, 36, 5991.
10.1021/om050594k CCC: $30.25 © 2005 American Chemical Society
Publication on Web 10/25/2005

N3-Ligand Iridium(I) Ethene Complexes
Organometallics, Vol. 24, No. 24, 2005 5965
Scheme 1. Radical Type Behavior of IrII(olefin)
Species
Figure 2. Synthesis of [(κ3-bpa-R)IrI(C2H4)2]+ (R ) H, Me,
We previously described the coordination modes of
bpa-R ligands to [RhI(cod)]+, [IrI(cod)]+ (cod ) Z,Z-1,5-
cyclooctadiene), and [RhI(ethene)]+ fragments. Reaction
of bpa-R ligands with [{(µ2-Cl)MI(cod)}2] resulted in
formation of five-coordinate species [(bpa-R)MI(cod)]+,
in which the bpa-R ligand adopts a κ3-fac bpa-R coor-
dination mode.2,19,20 Reaction of bpa-R ligands with
[{(µ2-Cl)RhI(ethene)2}2]+ however resulted in loss of
ethene and formation of square planar [(bpa-R)RhI-
(ethene)]+ complexes in which the bpa-R ligand coordi-
nates in a κ3-mer mode (see Figure 1).21 Such [(bpa-
R)MI(ethene)]+ species are potential catalysts for olefin
oxygenation,21 which explains our interest in the iridium
analogues.
We were further inspired to prepare these species by
our recent investigations concerning the unusual radical
type behavior of organometallic iridium(II)-olefin spe-
cies.22 An intriguing aspect of this chemistry concerns
our recent discovery that the unpaired spin-density is
not located solely on the metal. Upon solvent coordina-
tion, a large amount of the spin-density is transferred
from the metal to the “redox noninnocent” olefinic
substrate (Scheme 1).22c,d This allows direct radical
reactions at the olefin.
Bz).
to an AB pattern. The two ethene molecules are in-
equivalent, and each reveals two triplet-like signals in
1H NMR, indicating that the ethene fragments do not
rotate rapidly on the NMR time-scale. For each complex,
one of these ethene fragments reveals intense NOE
contacts with the amine-R group in the 1H-NOESY
1
spectra. This ethene fragment gives rise to broader H
NMR signals, which indicates that this fragment is
somewhat more fluxional and perhaps less strongly
coordinated to the iridium center than the other ethene
fragment.
The other NOE contacts in the 1H-NOESY spectrum
are indicative of a mer coordination mode of the bpa-R
ligands. The methylene Heq signal reveals NOE contacts
with both Py-H3 and the broadened signal of the ethene
fragment close to the R group of the bpa-R ligand. The
methylene Hax signal reveals NOE contacts with an-
other ethene fragment (the one revealing sharp 1H NMR
signals). The Py-H6 signal reveals NOE contacts with
both ethene fragments. From these observations we
propose the trigonal-bipyramidal coordination geom-
etries shown in Figure 2. The trigonal plane is formed
by the two ethene molecules and the amine-N donor.
The axial positions are taken by the pyridyl donors. This
structure is similar to that observed for the analogous
complexes [(κ3-mer-tpa)IrI(ethene)2]+ and [(iPr-pybox)-
IrI(ethene)2]+,24,25 but differs from the sterically more
hindered Me2-bpa-Me and Me3-tpa complexes [(κ3-fac-
The significance of these new insights needs to be
further established, and therefore we took an interest
in square planar [(bpa-R)IrI(ethene)]+ precursors to
prepare unsaturated analogues. In attempts to prepare
these species, we discovered that the square planar
[(bpa-R)MI(ethene)]+ coordination geometry is not stable
for iridium. Access to these species is prevented by the
reactions described in this paper.
Me2-bpa-Me)Ir(ethene)2]+
and
[(κ3-fac-Me3-tpa)-
Ir(ethene)2]+, in which the ligands adopt a facial coor-
dination mode.26
Results and Discussion
All three iridium(I) bis-ethene complexes are quite
stable in solution at rt under an inert atmosphere.
Bubbling nitrogen through a solution for about 30 min
does not result in ethene dissociation. Upon heating a
solution of the bpa-Me complex 2+, no reaction was
observed at all. This bis-ethene complex is apparently
very stable. Heating the bpa-H and bpa-Bz complexes
1+ and 3+ also does not result in formation of the
expected square planar [(bpa-R)IrI(C2H4)]+ (R ) H, Bz)
complexes. Instead these species escape via the follow-
up reactions described below.
Reaction of the bpa-R ligands (R ) H, Me, Bz) with
in situ-generated [(C2H4)4IrI(Cl)]23 in MeOH results in
formation of the cationic bis-ethene complexes [(bpa-
H)IrI(C2H4)2]+ (1+), [(bpa-Me)IrI(C2H4)2]+ (2+), and [(bpa-
Bz)IrI(C2H4)2]+ (3+). See Figure 2.
1H NMR data of 1+, 2+, and 3+ reveal two equivalent
N-CH2-Py groups. As expected, the diastereotopic N-CH2-
Py methylene protons (Hax, Heq, see Figure 2) give rise
(19) de Bruin, B.; Budzelaar, P. H. M.; Gal, A. W. Angew. Chem.,
Int. Ed. 2004, 43 (32), 4142-4157.
Reactivity of bpa-H Iridium(I) Bis-ethene upon
Heating: N-H Activation. Heating a solution of
bpa-H iridium(I) bis-ethene complex 1+ in CD3CN to
about 70 °C for 2 h results in formation of the dinuclear
iridium(III) ethyl complex 42+ (see Figure 3). The same
reaction at room temperature requires about 20 days.
(20) de Bruin, B.; Boerakker, M. J.; Donners, J. J. J. M.; Christiaans,
B. E. C.; Schlebos, P. P. J.; de Gelder, R.; Smits, J. M. M.; Spek, A. L.;
Gal, A. W. Angew. Chem., Int. Ed. 1997, 36 (19), 2064-2067.
(21) de Bruin, B.; Verhagen, J. A. W.; Schouten, C. H. J.; Gal, A.
W.; Feichtinger, D.; Plattner, D. A. Chem.-Eur. J. 2001, 7 (2), 416-
422.
(22) (a) de Bruin, B.; Peters, T. P. J.; Thewissen, S.; Blok, A. N. J.;
Wilting, J. B. M.; de Gelder, R.; Smits, J. M. M.; Gal, A. W. Angew.
Chem., Int. Ed. 2002, 41 (12), 2135-2138. (b) de Bruin, B.; Thewissen,
S.; Yuen, T.-W.; Peters, T. P. J.; Smits, J. M. M.; Gal, A. W.
Organometallics 2002, 21, 4312-4314. (c) Hetterscheid, D. G. H.;
Kaiser, J.; Reijerse, E.; Peters, T. P. J.; Thewissen, S.; Blok, A. N. J.;
Smits, J. M. M.; de Gelder, R.; de Bruin, B. J. Am. Chem. Soc. 2005,
127, 1895-1905. (d) Hetterscheid, D. G. H.; Bens, M.; de Bruin, B.
Dalton Trans. 2005, 979-984.
1
According to H NMR, no byproducts are formed.
(24) Krom, M.; Peters, T. P. J.; Coumans, R. G. E.; Sciarone, T. J.
J.; Hoogboom, J.; ter Beek, S. I.; Schlebos, P. P. J.; Smits, J. M. M.; de
Gelder, R.; Gal, A. W. Eur. J. Inorg. Chem. 2003, 6, 1072-1087.
(25) D´ıez, J.; Gamasa, M. P.; Gimeno, J.; Paredes, P. Organometal-
lics 2005, 24, 1799.
(26) de Bruin, B.; Peters, T. P. J.; Wilting, J. B. M.; Thewissen, S.;
Smits, J. M. M.; Gal, A. W. Eur. J. Inorg. Chem. 2002, 10, 2671-2680.
(23) Onderlinden, A. L.; van der Ent, A. Inorg. Chim. Acta 1972, 6,
420-426.

5966 Organometallics, Vol. 24, No. 24, 2005
Thewissen et al.
Figure 3. Formation of 42+ from 1+.
Figure 5. X-ray structure of 42+
.
acidic, and it thus seems also unlikely that breaking of
this weak N-H bond would be rate determining.
Considering the fact that we never observed a mono-
ethene intermediate, rate-limiting ethene dissociation
from 1+ provides a plausible explanation for the ob-
served first-order kinetics.
Figure 4. Plot of ln([1+]t/[1+]0) vs time in the conversion
of 1+ to 42+ showing first-order kinetics in 1+.
We thus propose that formation of 42+ involves
dissociation of one of the ethene fragments to give a
reactive four-coordinate iridium(I) complex. The subse-
quent (inter- or intramolecular) N-H activation of the
bpa-H ligand seems to be relatively fast. Since the
NHamine fragment of 1+ is rather acidic, the ethyl
formation might well involve protonation of (solvated)
IrI(ethene) species by NHamine, either directly at ethene
or via an IrIII-hydride species, to form an IrIII(ethyl)
fragment.27
Crystals suitable for X-ray diffraction were obtained
by vapor diffusion of diethyl ether into a solution of
4(PF6)2 in acetonitrile. The X-ray structure of 42+ is
shown in Figure 5. Selected bond lengths and angles
are given in Table 1. Unfortunately, during the X-ray
measurement the crystals decomposed due to evaporat-
ing solvent molecules from the lattice, which degraded
the quality of the measurements.
Complex 42+ proves to be air stable in solution. This
complex must have formed from 1+ by deprotonation of
the amine-nitrogen of the bpa-H ligand (to give bpa#),
allowing formation of a bridging amide functionality.
When the reaction is carried out in CH3CN, solvent
1
coordination is clearly recognized by a H NMR signal
at 2.70 ppm. Upon dissolving the CH3CN-coordinated
complex in CD3CN, no exchange between coordinated
CH3CN and the solvent takes place, indicating a very
strong bond between the iridium(III) center and the
nitrile.
1H-NOE contacts are characteristic of a dinuclear
complex with a mer-coordination mode of the deproto-
nated bpa-ligand with the ethyl group at a position cis
to the two pyridyl donors and the Namide. Furthermore,
strong NOE contacts between one of the N-CH2-Py
methylene protons and two of the pyridine protons (Py-
H3 and -H6) are observed, which confirm the dinuclear
nature of the complex.
The dinuclear iridium complex 42+ has an inversion
center and a slightly distorted octahedral geometry
around each metal center with the N3 ligand still
coordinated in a meridional fashion. The MeCN ligands
are coordinated in the plane of the mer-bpa# ligand, cis
to the pyridyl donors. The ethyl group occupies an axial
position, cis to the pyridyl and MeCN donors. The end-
of-chain carbon of the ethyl group (atom C4) is disor-
dered. The pyridine rings are positioned in such a way
that π-stacking between the two N3 ligands is optimal,
which could be one of the driving forces for the reaction.
Reactivity of bpa-Bz Iridium(I) Bis-ethene upon
Heating: C-H Activation. Heating a saturated solu-
tion of [(bpa-Bz)IrI(ethene)2]+ complex 3+ in acetone for
24 h at 50 °C results in precipitation of pure complex
When the reaction is carried out in pure CD3CN, 42+
is obtained without incorporation of any deuterium
atoms at the ethyl moiety. In contrast, H/D exchange
at the NHamine position of 1+ occurs almost instanta-
neously in a mixture of CD3CN and CD3OD, yielding
1+-D (containing the ligand bpa-D). Heating a sample
of thus obtained 1+-D in CD3CN leads to formation of
4
2+-D2, containing two monodeuterated ethyl fragments
1
-CH2CH2D, as indicated by H NMR. Therefore, the
proton used to convert the olefin into an ethyl group
must stem from the NHamine fragment.
The rate of formation of complex 42+ from 1+ at 40
°C was followed by 1H NMR (Figure 4). Plots of ln([1+]t/
[1+]0) vs time result in straight lines, characteristic of
first-order kinetics in 1+. The kinetic data are clearly
inconsistent with second-order kinetics associated with
rate-determining intermolecular N-H activation or
bridge formation steps. Considering the above-described
rapid H/D exchange, the NHamine fragment (which
strongly resembles an ammonium ion) must be rather
(27) For similar protonation reactions see: (a) de Bruin, B.; Boer-
akker, M. J.; Verhagen, J. A. W.; de Gelder, R.; Smits, J. M. M.; Gal,
A. W. Chem. Eur. J. 2000, 6 (2), 298-312. (b) Brookhart, M.; Lincoln,
D. M.; Bennet, M. A.; Pelling, S. J. Am. Chem. Soc. 1990, 112, 2691.
(b) O¨ hrstro¨m, L.; Stro¨mberg, S.; Glaser, J.; Zetterberg, K. J. Orga-
nomet. Chem. 1998, 558, 123. (c) Ciriano, M. A.; Ferna´ndez, M. J.;
Modegro, J.; Rodr´ıguez, M. J.; Oro, L. A. J. Organomet. Chem. 1993,
443, 249, and references therein.

N3-Ligand Iridium(I) Ethene Complexes
Organometallics, Vol. 24, No. 24, 2005 5967
Table 1. Selected Bond Lengths and Angles of 42+
bond length (Å)
angle (deg)
angle (deg)
Ir1-N1
Ir1-N2
Ir1-N3
Ir1-N4
Ir1-C3
Ir1-N3′
Ir-Ir1
2.034(8)
2.011(8)
2.036(7)
2.014(8)
2.113(10)
2.266(8)
3.305(6)
N1-Ir1-N2
N1-Ir1-N3
N1-Ir1-N4
N2-Ir1-N3
N2-Ir1-N4
N1-Ir1-C3
N2-Ir1-C3
N3-Ir1-C3
163.7(3)
83.4(3)
98.7(3)
83.8(3)
95.2(3)
85.8(4)
85.6(4)
96.2(4)
N4-Ir1-C3
90.8(4)
94.5(3)
93.2(3)
79.7(3)
175.9(3)
100.3(3)
-8.40
N3′-Ir1-N1
N3′-Ir1-N2
N3′-Ir1-N3
N3′-Ir1-C3
Ir1-N3-Ir1′
torsion: N1-Ir1-Ir1′-N2′
Table 2. Selected Bond Lengths and Angles of 52+
bond length (Å)
angle (deg)
Ir1-Ir1′
Ir1-N1
Ir1-N2
Ir1-N4
Ir1-C37
2.6877(6)
2.043(6)
2.036(6)
2.070(6)
2.005(7)
N1-Ir1-C37
87.3(2)
86.1(2)
81.1(2)
81.8(2)
162.4(2)
16.23
N2-Ir1-C37
N4-Ir1-N1
N4-Ir1-N2
Figure 8. Dinuclear iridium complexes with bridging
hydrogen atoms by Fujita et al.
N1-Ir1-N2
torsion: N1-Ir1-Ir1′-N2′
can display such NOE contacts only if two N3 ligands
are in close proximity to one another (Figures 6 and 7).
The cyclometalation causes an upfield shift of more than
0.7 ppm in the 1H NMR for most of the aromatic benzyl
signals of 52+ as compared to 3+. The two pyridine rings
and the N-CH2-Py methylene groups show up as equiva-
52+ as a yellow solid. Complex 52+ is a dinuclear
iridium(III) species with a cyclometalated benzyl-amine
fragment and bridging hydrides (see Figure 6).
The equivalent bridging hydrides of 52+ give rise to a
sharp 1H NMR signal at δ ) -14.73 ppm in acetone-d6.
A clear indication of the dinuclear nature of the complex
is obtained from NOESY experiments. NOE contacts are
observed between the Py-H6 and both the Py-H3 and
one of the N-CH2-Py methylene protons. A Py-H6 proton
1
lent functionalities in the H NMR.
Crystals of 5(PF6)2, suitable for X-ray diffraction, were
obtained from an acetone solution of 3(PF6), from which
5(PF6)2 slowly precipitated as a crystalline material over
the course of three weeks at room temperature. The
X-ray structure of 52+ is shown in Figure 7. Selected
bond lengths and angles are given in Table 2.
In the crystal structure, dinuclear Ir complex 52+ is
located at an inversion center, with an Ir-Ir distance
of 2.6877(6) Å. We were not able to locate the bridging
hydrogen atoms in 52+ with X-ray diffraction.
Short Ir-Ir contacts bridged solely by hydrides are
uncommon, but some examples of (poly)hydride-bridged
iridium complexes are known.28-32 Hydrogen-bridged
dinuclear iridium(III) complexes containing additional
diphosphine bridges were reported by Fujita et al.33-35
For these complexes (Figure 8) the bridging hydrogen
atoms are observed at δ ) -17.82 ppm in acetone-d6.
Addition of acetylene to this dinuclear iridium hydride
complex gives a µ-vinyl complex, [(Cp*Ir)2(µ-dmpm)-
(µ2,η1,η2-CHdCH2)(µ-H)]2+, via addition of one of the
iridium hydrides to the carbon-carbon triple bond. In
this complex the bridging hydride is found at δ ) -20.36
ppm (in acetone-d6). When tert-butylisocyanide is added,
one of the iridium-hydride bonds is broken and the
isocyanide coordinates to one of the iridium centers. The
chemical shift of the bridging hydride in this case is
Figure 6. Proposed pathway for the formation of 52+ from
3+.
(28) Taw, F. L.; Mellows, H.; White, P. S.; Hollander, F. J.; Bergman,
R. G.; Brookhart, M.; Heinekey, D. M. J. Am. Chem. Soc. 2002, 124
(18), 5100-5108.
(29) Chen, M. J.; Nunez, L.; Rathke, J. W.; Rogers, R. D. Organo-
metallics 1996, 15 (9), 2338-2344.
(30) Schnabel, R. C.; Carroll, P. S.; Roddick, D. M. Organometallics
1996, 15 (2), 655-662.
(31) Heinekey, D. M.; Fine, D. A.; Harper, T. G. P.; Michel, S. T.
Can. J. Chem.-Rev. Can. Chim. 1995, 73 (7), 1116-1125.
(32) Robertson, G. B.; Tucker, P. A. Austr. J. Chem. 1984, 37 (2),
257-263.
(33) Fujita, K.; Hamada, T.; Yamaguchi, R. J. Chem. Soc., Dalton
Trans. 2000, 12, 1931-1936.
(34) Fujita, K.; Nakaguma, H.; Hamada, T.; Yamaguchi, R. J. Am.
Chem. Soc. 2003, 125 (41), 12368-12369.
(35) Fujita, K.; Nakaguma, H.; Hanasaka, F.; Yamaguchi, R. Or-
ganometallics 2002, 21 (18), 3749-3757.
Figure 7. X-ray structure of 52+ (bridging hydrides were
not located).

5968 Organometallics, Vol. 24, No. 24, 2005
Thewissen et al.
Figure 9. C-H activation of a pyridyl donor in a Me3-tpa
iridium(I) ethene complex.
-24.00 ppm and that of the terminal hydride is -15.51
ppm (in CD2Cl2).
Figure 10. Reaction of 52+ in acetonitrile.
From the above data it is clear that heating complex
3+ leads to cyclometalation of the bpa-Bz benzyl func-
tionality. The poor solubility of the product 52+, and its
immediate precipitation upon formation, severely ham-
pers any kinetic measurements for this reaction. There-
fore we can only speculate about the mechanism of this
reaction. As in the formation of 42+, we propose that,
prior to cyclometalation, dissociation of one of the ethene
fragments occurs to give a reactive four-coordinate
iridium(I) complex. Apparently iridium activates the
aromatic C-H bond at the 2-position of the phenyl ring
to yield a hydride species. Two of such resulting iridium-
(III) hydride species apparently dimerize to form the
observed hydride-bridged species 52+. The ethene frag-
ments as present in 3+ have dissociated from the metal
along this process (Figure 6).
We previously reported a similar aromatic C-H
activation of a pyridyl donor for the Me3-tpa iridium(I)
ethene complex.26 But in this case the ethene fragment
remains coordinated to the metal center in acetone and
no bridging hydride species are formed (Figure 9).
For [(Me3-tpa)IrI(ethene)]+ we proposed that pyridyl
dissociation generates a monovacant trigonal-bipyra-
midal ethene complex.26 The distortion from the ideal
square planar geometry was thought to be the reason
for the observed oxidative addition of the C-H bond at
the 3-position of the pyridine ring. However, for bpa-R
iridium(I) mono-ethene complexes square planar geom-
etries would be expected on the basis of analogy with
the corresponding rhodium complexes.22 Also work by
Goldberg36-38 shows that for platinum systems a three-
coordinate 14 VE metal complex is needed for oxidative
addition. To what extent this is applicable to our iridium
species is not clear, but at least it shows that the
mechanism of aromatic C-H activation in 3+ can be
quite complicated.
Figure 11. Proposed structure of 72+
.
formation is perhaps most adequately described to be
solely the result of two 3c-2e bonds, leaving each iridium
center with an unsaturated formal 16 VE count (Figure
10). This is in better agreement with the observed
reactivity of 52+ toward coordinating solvents.
Hydride-bridged dinuclear complex 52+ is stable in the
weakly coordinating solvent acetone (in the dark), but
in the coordinating solvent acetonitrile it easily converts
to the acetonitrile-coordinated mononuclear iridium(III)
hydride species, [(bpa-Bz#)IrIII(H)(CD3CN)]+ (6+, Figure
10). Upon dissolving 52+ in CD3CN, the 1H signal of the
original dinuclear complex (δ ) -14.73 ppm in acetone-
d6, δ ) -15.12 in CD3CN) disappears very rapidly,
whereas a new hydride signal comes up at δ ) -18.30
ppm. Within 25 min 87% of dinuclear complex 52+ is
converted to the mononuclear complex 6+. The reaction
1
goes to completion within an hour. On the basis of H
NMR we conclude that this yields 95% of complex 6+
and 5% of an unknown species with a hydride signal at
-18.82. This could be an isomer of 6+, having the
hydride trans to the metal-carbon bond. ESI+-MS
measurements confirm the composition of 6+ as [(bpa-
Bz#)IrIII(H)(MeCN)]+. Complex 6+ is stable at room
temperature in CD3CN in the presence of air.
Irrespective of the exact mechanism, these square
planar iridium(I) mono-ethene complexes appear to be
more reactive than their rhodium analogues, so that
Although 52+ is stable in acetone in the dark, it proves
to be very light sensitive. As soon as an acetone solution
of the complex is exposed to glass-filtered daylight, it
immediately starts to convert to complex 72+. Complete
conversion of symmetrical complex 52+ to asymmetrical
complex 72+ requires only a few hours. On the basis of
1H-COSY, 1H-NOESY, and ESI+-MS we propose 72+ to
be the asymmetrical, dinuclear hydride-bridged species
depicted in Figure 11.
1
they tend to “escape” via oxidative reactions. With H
NMR, we never observed these four-coordinate N3-
ligand iridium(I) ethene species (not from 3+, nor from
1+ or 2+).
To obtain a formal saturated 18 VE counting, complex
5
2+ should be drawn with two metal-metal bonds (see
Figure 6). However, these “bonds” are not likely to have
any physical or chemical meaning, and the bridge
Formation of 72+ stops when a solution of 52+ is no
longer exposed to daylight. Upon prolonged exposure of
an acetone solution of 72+ to daylight, no further
rearrangements take place: the other benzyl ring
remains to be coordinated in a position trans to one of
the hydrides.
(36) Crumpton-Bregel, D. M.; Goldberg, K. I. J. Am. Chem. Soc.
2003, 125 (31), 9442-9456.
(37) Fekl, U.; Goldberg, K. I. Homogeneous hydrocarbon C-H bond
activation and functionalization with platinum; Advances in Inorganic
Chemistry: Including Bioinorganic Studies, Volume 54; Academic
Press Inc.: San Diego, 2003.
We propose that one of the Ir-H bonds breaks upon
irradiation (most probably the one with the aromatic
(38) Jensen, M. P.; Wick, D. D.; Reinartz, S.; White, P. S.; Templeton,
J. L.; Goldberg, K. I. J. Am. Chem. Soc. 2003, 125 (28), 8614-8624.

N3-Ligand Iridium(I) Ethene Complexes
Organometallics, Vol. 24, No. 24, 2005 5969
Table 3. T1 of the Hydride Signals of the bpa-Bz#
Iridium(III) Hydride Complexes
compound
δ (ppm)
T1 (ms)
δ (ppm)
T1 (ms)
5
6
7
7
2+ (acetone-d6)
+ (CD3CN)
-14.7
-18.3
-14.9
-15.0
650
2300
725
2+ (acetone-d6)
2+ (CD3CN)
-23.89
-24.0
725
700
700
Figure 12. Assignment of NMR signals in [(bpa-R)IrI-
carbon trans coordinated, which is the weakest Ir-H
bond due to the strong trans-effect of a metal-carbon
fragment). Hereafter the dinuclear complex rearranges
to the more stable complex 72+, in which only one of
the bridging hydrides is located trans to a metal-carbon
(ethene)2]+ complexes.
coordinate bis-ethene species [(bpa-R)IrI(ethene)2]+. Re-
markably, these do not easily lose one of their ethene
fragments. Thermal activation leads to ethene dissocia-
tion, but this does not lead to formation of square planar
[(bpa-R)IrI(ethene)]+ analogues of the rhodium species.
Instead, upon heating bpa-H complex 1+, the presumed
four-coordinate intermediate escapes via N-H activa-
tion at the NHamine fragment of the bpa-H ligand, to
form dinuclear species 42+ with bridging amides. Upon
heating bpa-Bz complex 3+, the presumed four-coordi-
nate intermediate escapes via an aromatic C-H activa-
tion process of the aromatic benzyl fragment of the bpa-
Bz ligand to form dinuclear species 52+ with bridging
hydrides. Upon heating bpa-Me complex 2+, no reaction
was observed at all, illustrating the unusually large
affinity of these complexes for both coordinated ethene
fragments.
1
fragment. The H NMR signal at δ ) -14.90 probably
corresponds to the hydride with the carbon trans (only
a shift of 0.2 ppm to higher field as compared to 52+).
The hydride located trans to the Namine and NPy donors
then appears at a chemical shift of -23.92 ppm in the
1H NMR spectrum. Since the latter hydride is no longer
coordinated in a position trans to a carbon donor, this
hydride bridge will be much stronger, thus making the
dinuclear complex more stable. From ESI+-MS mea-
surements it can indeed be concluded that upon spray-
ing acetone solutions of the dicationic dinuclear com-
plexes, fragmentation to monocationic mononuclear
complexes is much easier for 52+ than for 72+
.
Another indication that the bridge in 72+ is stronger
compared to 52+ comes from the fact that addition of
CD3CN does not result in formation of an isomer of 6+.
The dinuclear complex 72+ remains intact even in pure
CD3CN solutions, as confirmed by NMR and ESI+-MS
measurements.
Experimental Section
General Methods. All procedures were performed under
a nitrogen atmosphere using standard Schlenck techniques,
unless indicated otherwise. Solvents (p.a.) were deoxygenated
by bubbling through a stream of nitrogen or by the freeze-
pump-thaw method. The temperature indication rt corre-
sponds to ca. 20 °C.
The proton spin-lattice relaxation times (T1) were
measured for 52+ (acetone-d6), 6+ (CD3CN), and 72+
(both in acetone-d6 and in CD3CN). The results are
shown in Table 3. From such relaxation times informa-
tion about the coordination mode of the hydrides can
be deduced.39
NMR experiments were carried out on a Bruker DPX200
(200 and 50 MHz for 1H and 13C, respectively), a Bruker AC300
Since these relaxation times are mainly determined
by H-H spin-spin relaxation processes, the large
differences in T1 between mononuclear complex 6+ and
the dinuclear complexes 52+ and 72+ are expected. For
the dinuclear complexes, the H-H distance will domi-
nate T1. Apparently there is no large change on going
from 52+ to 72+, supporting our assumption that both
these complexes contain two bridging hydrides.
The hypothesis that 72+ might also be a complex with
one bridging and one terminal hydride can be ruled
out: in such a complex the H-H distance should have
changed considerably, which should have had its impact
on T1. The fact that the T1 values of 72+ in acetone-d6
and in CD3CN are similar is a further indication that
the bridging structure of 72+ remains intact even in
coordinating solvents such as MeCN.
1
(300 and 75 MHz for H and 13C, respectively), and a Varian
Inova 400 (400 and 100 MHz for 1H and 13C, respectively).
Solvent shift references for 1H NMR are as follows: CD2Cl2 δ
(1H) ) 5.31 ppm, CD3CN δ (1H) ) 1.94 ppm, methanol-d4
δ
(1H) ) 3.35 ppm, and acetone-d6 δ (1H) ) 2.05 ppm. Solvent
shift references for 13C NMR are as follows: CD3CN δ (13C) )
1.24 (and 118.25), CD2Cl2 δ (13C) ) 54.20, methanol-d4 δ (13C)
) 49.3 ppm, and acetone-d6 δ (13C) ) 29.83 ppm (and 206.18
ppm). Abbreviations used: s ) singlet, d ) doublet, dd )
double doublet, ddd ) double doublet of doublets, t ) triplet,
dt ) double triplet, q ) quartet, qq ) quartet of quartets, m
) multiplet, dm ) double multiplet, br ) broad.
Spin-lattice relaxation times (T1) were measured at 298 K
and at 500 MHz.
Since the κ3-bpa-R iridium(I) bis-ethene complexes have two
chemically different ethene molecules (one above the trigonal
plane having NOE contacts with the amine-R group (C2H4, A),
the other below this plane (C2H4, B)), the NMR signals
belonging to the different olefins and the diastereotopic
methylene protons of the N-CH2-Py groups are assigned as
shown in Figure 12.
Elemental analyses (C, H, N) were carried out on a Carlo
Erba NCSO analyzer.
Mass spectra (ESI- or FAB-MS) were recorded on a Finnigan
MAT 900S (Radboud University Nijmegen) or a Finnigan TSQ
700 (ETH-Zurich). All spectra were obtained in the positive
ion mode. Daughter ion spectra were measured on the TSQ
700 and TSQ 7000 using argon as a collision gas.
Conclusions
If we compare the N3-ligand complexes [(bpa-R)RhI]+
and [(bpa-R)IrI]+ (R ) H, Me, Bz) in complexation with
ethene we see some remarkable differences. Whereas
the Rh complexes readily form stable four-coordinate
square planar mono-ethene [(bpa-R)RhI(ethene)]+ spe-
cies,21 the corresponding Ir complexes form stable five-
(39) Bakhmutov, V. I.; Vorontsov, E. V.; Nikonov, G. I.; Lemenovskii,
D. A. Inorg. Chem. 1998, 37 (2), 279-282.

5970 Organometallics, Vol. 24, No. 24, 2005
Table 4. Crystallographic Data for 4(PF6)2 and 5(PF6)2
Thewissen et al.
4(PF6)2
5(PF6)2‚4(CH3)2CO
empirical formula
cryst size [mm]
cryst color
fw
C
32H40F12Ir2N8P2
C25H30F6Ir1N3O2P1
0.62 × 0.50 × 0.39
light yellow-green
1211.06
0.70 × 0.70 × 0.22
transparent brown-red
741.69
T [K]
150(2)
208(2)
cryst syst
space group
a [Å]
tetragonal
I41/acd
21.8924(7)
21.8924(7)
32.8309(8)
90
monoclinic
P21/c
12.0391(14)
15.756(2)
14.3507(18)
90
94.045(11)
90
2715.3(6)
1.814
4
b [Å]
c [Å]
R [deg]
â [deg]
90
90
γ [deg]
V [Å3]
15735.1(8)
2.045
16
F
calcd. [gcm-3
]
Z
diffractometer (scan)
Nonius KappaCCD
area detector φ and ω scan
Mo KR (graphite mon.)
0.71073
Nonius KappaCCD
area detector φ and ω scan
Mo KR (graphite mon.)
0.71073
radiation
wavelength [Å]
F(000)
9280
1452
θ range [deg]
index ranges
1.81 to 25.12
-25 e h e 22
-26 e k e 26
-38 e l e 39
12 483
3.13 to 25.00
-14 e h e 14
-18 e k e 18
-17 e l e 17
31 699
no. of measd reflns
no. of unique reflns
no. of obsd reflns [Io > 2σ(Io)]
no. of refined params
goodness-of-fit on F2
R [Io > 2σ(Io)]
2952
4656
2406
3811
259
384
1.029
1.110
0.0436
0.0381
wR2 [all data]
0.1142
0.1285
F
fin(max./min.) [e Å-3
]
2.222/-1.219
1.969/-2.221
Bpa-Me,21 bpa-Bz,2 and [{(coe)2Ir(µ-Cl)}2]40 were prepared
according to literature procedures. All other chemicals are
commercially available and were used without further puri-
fication, unless stated otherwise.
X-ray Diffraction. A Nonius KappaCCD with area detec-
tor, æ and ω scans, was used, applying graphite-monochro-
matized Mo KR radiation. The structures were solved by the
program system DIRDIF41 using the program PATTY42 to
locate the heavy atoms. The structure was refined with
standard methods (refinement against F2 of reflections with
Io > 2σ(Io) using SHELXL9743). Selected bond lengths and
angles are summarized in Tables 1 and 2. Drawings were
generated with the program PLATON.44 Other relevant crystal
data are summarized in Table 4.
The compound crystallizes in the rather highly symmetrical
space group I41/acd. The dinuclear iridium complex forms a
dimer around an inversion center. The end-of-chain carbon
atom C4 is disordered and has been split up over two separate
positions. However, it proved to be impossible to refine these
two positions anisotropically. The hydrogen atoms calculated
on C4A, C4B, and C3 should be considered unreliable.
The space group has a multiplicity of the general position
of 32, and thus the cell unit contains 16 molecules (Z ) 16),
C32H40N8Ir2‚2(PF6). The P atoms of the PF6 moieties occupy
three special positions, and especially the PF6 moieties around
P2 and P3 are highly disordered and should be considered very
unreliable. Lowering the symmetry did not solve any of the
problems described here. On the contrary, various atoms got
unacceptable thermal displacement parameters (nonpositive
definite) or could not be located at all in the Fourier map.
Geometrical calculations with PLATON43 revealed neither
unusual geometric features nor unusual short intermolecular
contacts. The calculations revealed no higher symmetry and
no (further) solvent accessible areas.
[{(bpa-Bz#)IrIII(H)}2](PF6)2, 5(PF6)2. Crystals suitable for
X-ray diffraction of this same compound were obtained when
an acetone solution of 3+ was allowed to stand at rt for three
weeks. A single crystal was mounted in air on a glass fiber.
Intensity data were collected at 208 K. Unit cell dimensions
were determined from the angular setting of 31 699 reflections.
All non-hydrogen atoms were refined with anisotropic tem-
perature factors. The hydrogen atoms were placed at calcu-
lated positions and refined isotropically in riding mode. The
structure consists of the Ir complex dimerized via an inversion
center, two acetone moieties, and a rather disordered PF6
moiety. The Ir-Ir distance is 2.6877(6) Å. Geometrical calcula-
tions with PLATON43 revealed neither unusual geometric
features nor unusual short intermolecular contacts. The
calculations revealed no higher symmetry and no (further)
solvent accessible areas.
[{(mer-µ2-bpa#)IrIII(C2H5)(CH3CN)}2](PF6)2, 4(PF6)2. Crys-
tals suitable for an X-ray structure determination were
obtained from vapor diffusion of diethyl ether into an aceto-
nitrile solution at rt. A single crystal was mounted in air on a
glass fiber. Intensity data were collected at 150 K. Unit cell
dimensions were determined from the angular setting of
12 483 reflections. All non-hydrogen atoms were refined with
anisotropic temperature factors, except C4A and C4B. The
hydrogen atoms were placed at calculated positions and refined
isotropically in riding mode.
(40) Herde, J. L.; Lambert, J. C.; Senoff, C. V. Inorg. Synth. 1974,
15, 18-20.
(41) Beurskens, P. T.; Beurskens, G.; Bosman, W. P.; de Gelder, R.;
Garc´ıa-Granda, S.; Gould, R. O.; Israe¨l, R.; Smits, J. M. M. DIRDIF-
96. A computer program system for crystal structure determination by
Patterson methods and direct methods applied to difference structure
factors; Laboratory of Crystallography, Department of Inorganic
Chemistry, University of Nijmegen: The Netherlands, 1996.
(42) Beurskens, P. T.; Beurskens, G.; Strumpel, M.; Nordman, C.
E. Patterson and Pattersons, Glusker, J. P., Patterson, B. K., Rossi,
M., Vol. Eds.; Clarendon Press: Oxford, 1987; p 356.
(43) Sheldrick, G. M. SHELXL-97. Program for the refinement of
crystal structures; University of Go¨ttingen: Germany, 1997.
(44) Spek, A. L. PLATON-93. Program for display and analysis of
crystal and molecular structures; University of Utrecht: The Nether-
lands, 2003.

N3-Ligand Iridium(I) Ethene Complexes
Organometallics, Vol. 24, No. 24, 2005 5971
Synthesis. [(K3-bpa)IrI(C2H4)2]PF6, 1(PF6). [Ir(coe)2(µ-
Cl)]2 (155 mg, 0.17 mmol) was dissolved in 5 mL of methanol,
and ethene was bubbled through the solution at room tem-
perature until a clear solution was obtained. Under ethene
atmosphere a solution of 120 mg (0.60 mmol, about 1.7 equiv)
of bpa-H in 1,5 mL of methanol was added, and the mixture
was stirred for a few minutes while bubbling through ethene.
Subsequently 100.0 mg (0.54 mmol) of KPF6 was added and
the solution was stirred for 45 min under an ethene atmo-
sphere. The solution was cooled to -78 °C to allow precipita-
tion of 1(PF6). The thus obtained yellow-green solid was
collected by filtration, washed three times with ice-cold
methanol under a nitrogen atmosphere, and dried under
vacuum. Yield: 115 mg (0.20 mmol, 61%). This complex was
also synthesized using 70 mg (0.43 mmol) of NH4PF6 instead
of KPF6.
was collected by filtration, washed three times with ice-cold
methanol under a nitrogen atmosphere, and dried under
vacuum. Yield: 123.7 mg (0.18 mmol, 54%).
1H NMR (400.15 MHz, CD2Cl2, T ) 298 K): δ (ppm) 7.85
(t, 2H, J(H,H) ) 7.77 Hz, Py-H4), 7.70 (d, 2H, J(H,H) ) 5.57
Hz, Py-H6), 7.58 (m, 3H, Ph-H3, Ph-H4 and Ph-H5), 7.50 (d,
2H, J(H,H) ) 7.92 Hz, Py-H3), 7.24 (m, 4H, Py-H5, Ph-H2 and
Ph-H6), 5.39 (s, 4H, free C2H4), 5.10 (d[AB], 2H, J(H,H) )
15.53 Hz, Py-CHAH-N), 4.64 (d[AB], 2H, J(H,H) ) 15.68 Hz,
Py-CHHB-N), 4.36 (s, 2H, N-CH2-Ph), 3.44 (t, 2H, J(H,H) )
10.11 Hz, C2H4A), 3.27 (t, 2H, J(H,H) ) 9.67 Hz, C2H4B), 2.03
(t, 2H, J(H,H) ) 9.67 Hz, C2H4B), 1.94 (t, 2H, J(H,H) ) 9.89
Hz, C2H4A). 13C{1H} NMR (50.03 MHz, CD3CN, T ) 298 K): δ
(ppm) 165.62 (s, 2C, Py-C2), 150.65 (s, 2C, Py-C6), 138.97 (s,
2C, Py-C4), 133.32 (s, 2C, Ph-C2, Ph-C6), 132.25 (s, 1C, Ph-
C1), 130.04 (d, 3C, Ph-C3, Ph-C4, Ph-C5), 126.82 (s, 2C, Py-
C5), 125.04 (s, 2C, Py-C3), 64.92 (s, 1C, Ph-CH2-N), 64.47 (s,
2C, Py-CH2-N), 35.00 (s, 2C, C2H4A), 30.60 (s, 2C, C2H4B). ESI+-
MS: m/z 538 3+, 510 {3-C2H4}+, 482 {3-2‚C2H4}+. Anal.
Calcd for C23H27N3IrPF6: C 40.47, H 3.99, N 6.16. Found: C
40.53, H 4.03, N 6.05.
1H NMR (400.15 MHz, CD3CN, T ) 298 K): δ (ppm) 7.73
(dt, 2H, J(H,H)triplet ) 7.82 Hz and J(H,H)doublet ) 1.71 Hz, Py-
H4), 7.63 (d, 2H, J(H,H) ) 5.62 Hz, Py-H6), 7.31 (d, 2H, J(H,H)
) 7.82 Hz, Py-H3), 7.38 (s, 1H, N-H), 7.11 (t, 2H, J(H,H) )
6.72 Hz, Py-H5), 4.99 (dd[AB], 2H, J(H,H) ) 15.76 Hz and
J(H,H) ) 5.50 Hz, Py-CHAH-N), 4.65 (dd[AB], 2H, J(H,H) )
16.13 Hz and J(H,H) ) 10.26, Py-CHHB-N), 3.02 (t, 2H, J(H,H)
) 10.14 Hz, C2H4A), 2.89 (t, 2H, J(H,H) ) 9.53 Hz, C2H4B),
1.77 (t, 2H, J(H,H) ) 9.53 Hz, C2H4B and C2H4A). 13C{1H} NMR
(50.03 MHz, CD3CN, T ) 298 K): δ (ppm) 167.54 (s, 2C, Py-
C2), 150.58 (s, 2C, Py-C6), 138.53 (s, 2C, Py-C4), 126.29 (s,
2C, Py-C3), 123.08 (s, 2C, Py-C5), 60.97 (s, 2C, Py-CH2-N),
36.64 (s, 2C, C2H4), 31.01 (s, 1C, C2H4A), 25.61 (s, 1C, C2H4B).
ESI+-MS: m/z 448 1+, 420 {1-C2H4}+, 392 {1-2*C2H4}+. Anal.
Calcd for C16H21N3IrPF6: C 32.43, H 3.57, N 7.09. Found: C
32.25, H 3.55, N 6.99.
[{(mer-µ2-bpa#)IrIII(C2H5)(CH3CN)}2](PF6)2, 4(PF6)2. (bpa#
) N,N-di(2-pyridylmethyl)amine ()bpa) with the amine-
nitrogen deprotonated.) 1(PF6) (115 mg, 0.19 mmol) was
dissolved in acetonitrile and heated to approximately 70 °C
under stirring for 2 h. The solvent was removed, and the
product was analyzed. In another experiment 1(PF6) was
dissolved in acetonitrile-d3 and left standing at room temper-
ature for 2 weeks. Here also product 4(PF6)2 was formed.
Crystals, suitable for X-ray diffraction, were obtained by vapor
diffusion of diethyl ether into a solution of 4(PF6)2 in acetoni-
trile. Yield: 73.5 mg (81.5%).
[(K3-bpa-Me)IrI(C2H4)2]PF6, 2(PF6). [Ir(coe)2(µ-Cl)]2 (150
mg, 0.17 mmol) was dissolved in 5 mL of methanol, and ethene
was bubbled through the solution at room temperature until
a clear solution was obtained. Under ethene atmosphere a
solution of 71 mg (0.33 mmol) of bpa-Me in 1.5 mL of methanol
was added, and the mixture was stirred for a few minutes
while bubbling through ethene. Subsequently 80.0 mg (0.43
mmol) of KPF6 was added, and the solution was stirred for 45
min under an ethene atmosphere. The solution was cooled to
-78 °C to allow precipitation of 2(PF6). The thus obtained light
green solid was collected by filtration, washed three times with
ice-cold methanol under a nitrogen atmosphere, and dried
under vacuum. Yield: 66.8 mg (0.11 mmol, 33%).
1H NMR (400.15 MHz, CD3CN, T ) 298 K): δ (ppm) 8.49
(d, 4H, J(H,H) ) 5.08 Hz, Py-H6), 7.50 (dt, 4H, J(H,H)triplet
)
7.80 Hz, J(H,H)doublet ) 1.49 Hz, Py-H4), 7.08 (t, 4H, J(H,H) )
6.54 Hz, Py-H5), 6.84 (d, 4H, J(H,H) ) 7.84 Hz, Py-H3), 4.75
(d[AB], 4H, J(H,H) ) 17.57 Hz, Py-CHHB-N), 4.62 (d[AB], 4H,
J(H,H) ) 17.57, Py-CHAH-N), 2.70 (s, 6H, coordinated CH3-
CN), 1.06 (q, 4H, J(H,H) ) 7.63 Hz, -CH2CH3), 0.01 (t, 6H,
J(H,H) ) 7.62 Hz, -CH2CH3). 13C{1H} NMR (50.03 MHz, CD3-
CN, T ) 298 K): δ (ppm) 172.39 (s, 4C, Py-C2), 150.39 (s, 4C,
Py-C6), 137.66 (s, 4C, Py-C4), 124.96 (s, 4C, Py-C5), 122.73
(s, 4C, Py-C3), 119.02 (s, 2C, coordinated CH3CN), 69.36 (s,
4C, Py-CH2-N), 15.10 (s, 2C, -CH2CH3), 4.78 (s, 2C, coordi-
nated CH3CN), -10.29 (s, 2C, -CH2CH3). ESI+-MS: m/z 463.5
[4]2+. Anal. Calcd for C33H43N9Ir2P2F12 ([4](PF6)2‚CH3CN): C,
32.61; H, 3.46; N, 10.07. Found: C, 32.62; H, 3.31; N, 9.87.
1H NMR (400.15 MHz, CD3CN, T ) 298 K): δ (ppm) 7.79
(dt, 2H, J(H,H)triplet ) 7.68 Hz and J(H,H)doublet ) 1.63 Hz, Py-
H4), 7.70 (d, 2H, J(H,H) ) 5.62 Hz, Py-H6), 7.40 (d, 2H, J(H,H)
) 8.30 Hz, Py-H3), 7.19 (t, 2H, J(H,H) ) 6.72 Hz, Py-H5), 4.98
(d[AB], 2H, J(H,H) ) 15.15 Hz, Py-CHHB-N), 4.78 (d[AB], 2H,
J(H,H) ) 15.39 Hz, Py-CHAH-N), 3.32 (t, 2H, J(H,H) ) 10.14
Hz, C2H4A), 3.18 (s, 3H, N-CH3), 3.03 (t, 2H, J(H,H) ) 9.65
Hz, C2H4B), 1.87 (t, 2H, J(H,H) ) 9.65 Hz, C2H4B), 1.76 (t, 2H,
J(H,H) ) 9.77 Hz, C2H4A). 13C{1H} NMR (50.03 MHz, CD3CN,
T ) 298 K): δ (ppm) 166.07 (s, 2C, Py-C2), 150.40 (s, 2C, Py-
C6), 138.67 (s, 2C, Py-C4), 126.62 (s, 2C, Py-C5), 124.61 (s,
2C, Py-C3), 71.05 (s, 2C, Py-CH2-N), 53.81 (s, 1C, N-CH3),
39.67 (s, 1C, C2H4A), 36.38 (s, 1C, C2H4A), 33.97 (s, 1C, C2H4B),
28.53 (s, 1C, C2H4B). ESI+-MS: m/z 462 2+, 434 {2-C2H4}+,
406 {2-2*C2H4}+. Anal. Calcd for C17H23N3IrPF6: C 33.66, H
3.82, N 6.93. Found: C 33.72, H 3.86, N 7.07.
[{(K4-C,N,N′-bpa-Bz)IrIII(µ2-H)}2]PF6 (or [{(bpa-Bz#)IrIII
-
(µ2-H)}2]PF6, 5(PF6)2). (bpa-Bz# ) N-benzyl-N,N-di(2-pyridyl-
methyl)amine ()bpa-Bz) with the benzyl ring deprotonated at
C2.) A saturated solution of 100 mg (0.15 mmol) of 3+ in 15
mL of acetone was heated to 50 °C for about 3 days, leading
to precipitation of 5(PF6)2 as a fine, light yellow powder. The
powder was separated from the solution and subsequently
washed twice with acetone at -30 °C. Yield: 33.6 mg (0.027
mmol, 18%). The phenyl group is cyclometalated at C2.
1H NMR (400.14 MHz, acetone-d6, 298 K): δ (ppm) 7.94 (td,
4H, J(H,H)doublet ) 5.68 Hz, J(H,H)triplet ) 1.16 Hz, Py-H6), 7.8-
7.7 (m, 8H, Py-H3 and -H4), 7.55 (dd, 2H, J(H,H) ) 7.42 Hz,
J(H,H) ) 0.96 Hz, Ph-H3), 6.65 (dt, 2H, J(H,H)triplet ) 9.56
Hz, J(H,H)doublet ) 1.56 Hz, Ph-H4), 6.62 (m, 4H, Py-H5), 6.58
(dt, 2H, J(H,H)triplet ) 7.40 Hz, J(H,H)doublet ) 1.36 Hz, Ph-
H5), 6.45 (dd, 2H, J(H,H) ) 7.14 Hz, J(H,H) ) 1.00 Hz, Ph-
H6), 6.15 (d[AB], 4H, J(H,H) ) 14.85 Hz, N-CH2-Py), 5.64
(d[AB], 4H, J(H,H) ) 15.05 Hz, N-CH2-Py), 4.67 (s, 4H, N-CH2-
Ph), -14.73 (s, 2H, Ir-H-Ir). Due to the extremely low solubility
in acetone-d6, it was not possible to measure a 13C NMR
spectrum. However, it was possible to measure gHSQC and
gHMBC (C-H correlation spectra), from which some of the
13C chemical shifts could be deduced. 13C{1H} NMR (50.03
MHz, acetone-d6, 298 K): δ (ppm) 166.1 (Py-C2), 155.8 (Py-
[(K3-bpa-Bz)IrI(C2H4)2]PF6, 3(PF6). [Ir(coe)2(µ-Cl)]2 (150
mg, 0.17mmol) was dissolved in 5 mL of methanol, and ethene
was bubbled through the solution at room temperature until
a clear solution was obtained. Under ethene atmosphere a
solution of 97 mg (0.34 mmol) of bpa-Bz in 1.5 mL of methanol
was added and stirred for a few minutes while bubbling
through ethene. Subsequently 80.0 mg (0.43 mmol) of KPF6
was added, and the solution was stirred for 45 min under an
ethene atmosphere. The solution was cooled to -78 °C to allow
precipitation of 3(PF6). The thus obtained light yellow solid

5972 Organometallics, Vol. 24, No. 24, 2005
Thewissen et al.
C6), 148.8 (Ph-C2), 138.64 (Ph-C3), 138.52 (Py-C3 or -C4),
134.9 (Ph-C1), 126.73 (Py-C5), 126.40 (Ph-C4), 124.69 (Py-C3
or -C4), 124.40 (Ph-C5), 119.87 (Ph-C6), 73.45 (N-CH2-Py),
68.52 (N-CH2-Ph). ESI+-MS (acetone-d6 solution diluted with
acetone): m/z 481 52+ (dicationic dinuclear complex), 482 [(bpa-
Bz#)Ir(H)]+ (monocationic, monomeric complex), 540 [(bpa-Bz#)-
Ir(H)(acetone)]+. Anal. Calcd for C38H38N6Ir2P2F12: C, 36.42;
H, 3.06; N, 6.71. Found: C, 36.25; H, 3.12; N, 6.81.
Hz, J(H,H)triplet ) 1.20 Hz, Py-H6), 7.95 (m, 1H, Py′-H6), 7.88-
7.85 (m, 2H, Py-H3 and -H4), 7.81-7.78 (m, 2H, Py′-H3 and
-H4), 7.72-7.66 (m, 3H, Py′′′-H3 and H4, Py′′-H4), 7.38 (td,
1H, J(H,H)doublet ) 5.64 Hz, J(H,H)triplet ) 0.96 Hz, Py′′-H6),
7.23 (dd, J(H,H) ) 7.68 Hz, J(H,H) ) 1.20 Hz, Ph-H3), 7.21-
7.15 (m, 2H, Py′′-H3, Py′′′-H5), 7.08 (d, 1H, J(H,H) ) 7.32 Hz,
Ph′-H6), 6.9 (m, 1H, Py-H5), 6.69 (m, 1H, Py′-H5), 6.66 (m,
1H, Ph-H4), 6.65-6.55 (m, 3H, Py′′-H5, Ph-H5, Ph′-H5), 6.52
[(K4-C,N,N′-bpa-Bz)IrIII(H)(CD3CN)]PF6 (or [(bpa-Bz#)-
IrIII(H)(CD3CN)]PF6, 6(PF6)). Upon dissolving 3+ in CD3CN,
conversion to 6+ takes place very rapidly. After 25 min only
13% of the original dinuclear complex is left. Within a few
hours, full conversion to 6+ takes place. The phenyl group is
cyclometalated at C2.
1
(dd, H, J(H,H) ) 7.58 Hz, J(H,H) ) 1.00 Hz, Ph′-H3), 6.39
(dd, 1H, J(H,H) ) 7.32 Hz, J(H,H) ) 1.24 Hz, Ph-H6), 6.2-6.1
(m, 2H, N-CH2-Py′ and Ph′-H4, 6.01 (d[AB]Py and Py′′′, 1H,
J(H,H) ) 16.61 Hz, N-CH2-Py and -Py′′′), 5.67 (d[AB]Ph′, 1H,
J(H,H) ) 12.68 Hz, N-CH2-Ph′), 5.61 (d[AB]Py, 1H, J(H,H) )
14.93 Hz, N-CH2-Py), 5.36 (d[AB]Py′, 1H, J(H,H) ) 14.89 Hz,
N-CH2-Py′), 5.30 (d[AB]Py′′′, 1H, J(H,H) ) 14.65 Hz, N-CH2-
Py′′′), 5.20 (d[AB]Ph′, 1H, J(H,H) ) 12.96 Hz, N-CH2-Ph′), 4.95
1H NMR (400.14 MHz, CD3CN, 298 K): δ (ppm) 8.66 (dd,
2H, J(H,H) ) 5.60 Hz, J(H,H) ) 0.48 Hz, Py-H6), 7.74 (dt,
2H, J(H,H)triplet ) 7.82 Hz, J(H,H)doublet ) 1.68 Hz, Py-H4), 7.65
(d, 1H, J(H,H) ) 7.58 Hz, Ph-H3), 7.40 (dd, 2H, J(H,H) ) 7.84
Hz, J(H,H) ) 0.48 Hz, Py-H3), 7.08 (mt, 2H, J(H,H) ) 8.56
(d[AB]Py′′, 1H, J(H,H) ) 19.29 Hz, N-CH2-Py′′), 4.88 (d[AB]Py′′
,
1H, J(H,H) ) 19.05 Hz, N-CH2-Py′′), 4.63 (s, 2H, N-CH2-Ph),
-14.90 (s, 1H, Ir-H-Ir), -23.92 (s, 1H, Ir-H′-Ir). Due to the
extremely low solubility in acetone-d6, it was not possible to
measure a 13C NMR spectrum. ESI+-MS (actone-d6 solution
diluted with acetone): m/z 481 72+ (dicationic dinuclear
complex), 482 [(bpa-Bz#)Ir(H)]+ (monocationic, monomeric
complex), 540 [(bpa-Bz#)Ir(H)(acetone)]+. In contrast with 5+
much less [(bpa-Bz#)Ir(H)]+ is present in the mass spectrum,
indicating a much more strongly bound dinuclear complex.
ESI+-MS (acetone-d6/CD3CN solution diluted with CH3CN):
m/z 481 72+, 503 {7(CD3CN)}2+, 523 [(bpa-Bz#)Ir(H)(CH3CN)]+,
526 [(bpa-Bz#)Ir(H)(CD3CN)]+. In contrast with previous ESI+-
MS measurements of 5+ and 7+ in acetone, no [(bpa-Bz#)Ir-
(H)(solvent)]+ and hardly any [(bpa-Bz#)Ir(H)]+ is present in
the spectrum.
Hz, Py-H5), 6.68-6.63 (m, 1H, Ph-H4), 6.60 (dt, J(H,H)triplet
)
7.56 Hz, J(H,H)doublet ) 1.48 Hz, Ph-H5), 6.58 (m, 1H, Ph-H6),
5.09 (d[AB], 2H, J(H,H) ) 15.41 Hz, N-CH2-Py), 5.02 (d[AB],
2H, J(H,H) ) 15.41 Hz, N-CH2-Py), 4.47 (s, 2H, N-CH2-Ph),
-18.30 (s, 1H, Ir-H). 13C{1H} NMR (50.03 MHz, CD3CN, 298
K): δ (ppm) 166.89 (s, Py-C2), 158.23 (s, Py-C6), 149.85 (s,
Ph-C2), 139.56 (s, Ph-C1), 142.17 (s, Ph-C3), 138.04 (s, Py-
C4), 126.64 (s, Ph-C4), 126.46 (s, Py-C5),124.08 (s, Py-C3),
123.02 (s, Ph-C5), 120.14 (s, Ph-C6), 69.92 (s, N-CH2-Py), 69.75
(s, N-CH2, Ph). ESI+-MS (CD3CN solution diluted with CH3-
CN) [(bpa-Bz#)IrIII(H)(CH3CN)]+: m/z 523 6+, 482 {6-CH3-
CN}+. Anal. Calcd for C21H22IrN4: 523.14745. Found: 523.14433
(∆ ) -5.8 ppm). [(bpa-Bz#)IrIII(H)(CH3CN)]+: m/z 526 6+, 482
{6-CD3CN}+. Anal. Calcd for C21H19IrN4D3: 526.16626.
Found: 526.16337 (∆ ) -5.3 ppm).
[(bpa-Bz#)IrIII(µ2-H)Ir(H)(bpa-Bz#)](PF6)2, 7(PF6)2. Com-
plex 72+ was obtained as the only product by exposing an
acetone-d6 solution of 5+ for about 5 h to glass-filtered light.
The phenyl group is cyclometalated at C2. Py, Py′′, and Ph′
belong to the asymmetrically coordinated N3 ligand and Py′,
Py′′′, and Ph belong to the symmetrically coordinated N3
ligand.
Acknowledgment. This work was supported by the
Dutch National Science Foundation (NWO). We thank
Dr. Peter H. M. Budzelaar for helpful discussions.
Supporting Information Available: Crystallographic
data in CIF format. This material is available free of charge
via the Internet at http://pubs.acs.org.
1H NMR (400.14 MHz, acetone-d6, 298 K): δ (ppm) 9.22 (d,
1
1H, J(H,H) ) Hz, Py′′′-H6), 8.11 (td, H, J(H,H)doublet ) 5.36
OM050594K