An η1-Aldehyde Complex and the Role of Hydrogen Bonding in Its Conversion to an η1-Imine Complex

Article abstract of DOI:10.1021/ic9508076

2-Pyridinecarboxaldehyde displaces Me₂CO from [IrH₂(Me₂CO)₂(PPh₃) ₂]⁺ to give a chelating N,O-bound product containing an η¹-O-bound aldehyde group. This is converted to the η¹-N-bound imine complex with a variety of substituted amines. When the amine contains a suitably positioned -OH group, intramolecular O-H?H-Ir dihydrogen bonds are detected in the products. This hydrogen bonding influences the relative rates of product formation from 2- and 4-aminophenol (rate ratio 6:1), where only the 2-isomer is capable of forming an intramolecular H-bond.

Full text of DOI:10.1021/ic9508076

Inorg. Chem. 1996, 35, 3007-3011
3007
An η1-Aldehyde Complex and the Role of Hydrogen Bonding in Its Conversion to an
η1-Imine Complex
Wenbin Yao and Robert H. Crabtree*
Yale Chemistry Laboratory, 225 Prospect Street, New Haven, Connecticut 06520-8107
ReceiVed June 28, 1995X
2-Pyridinecarboxaldehyde displaces Me2CO from [IrH2(Me2CO)2(PPh3)2]+ to give a chelating N,O-bound product
containing an η1-O-bound aldehyde group. This is converted to the η1-N-bound imine complex with a variety of
substituted amines. When the amine contains a suitably positioned -OH group, intramolecular O-H‚‚‚H-Ir
dihydrogen bonds are detected in the products. This hydrogen bonding influences the relative rates of product
formation from 2- and 4-aminophenol (rate ratio 6:1), where only the 2-isomer is capable of forming an
intramolecular H-bond.
Introduction
A new type of hydrogen bond involving an H‚‚‚H interaction
has been observed for a number of complexes containing the
M-H‚‚‚H-X group (M ) transition metal; X ) O or N).1,2
An intermolecular case has been verified by neutron diffrac-
tion: [ReH5(PPh3)3(indole)].1e The M-H‚‚‚H-X H-bond
energy, typically 4-6 kcal‚mol-1,1 should be sufficient to have
significant effects on equilibrium constants if an H-bond is
present in one isomer but not the other. There could also be a
strong effect on rate constants if an H-bond is present in only
one of two related transition states. In trying to develop this
aspect of the chemistry, we have looked at the imination of a
coordinated aldehyde and find a small effect of H-bonding on
the product distribution. We have also observed examples of
η1-aldehyde and η1-imine complexes and an unexpected long-
range coupling between the aldehyde proton and one of the
metal hydride protons.
(1)
NMR spectra, aldehyde carbons in η1-bound complexes typically
exhibit coordination shifts of <20-30 ppm from their unco-
ordinated values, while the η2-bound complexes exhibit upfield
shifts of ∼50 ppm and more.
Our complex 3 shows νCdO at 1616 cm-1, versus the
uncoordinated ligand νCdO at 1734 cm-1 (∆ν(CO) ) 118 cm-1).
The 13C NMR for 3, which can be completely assigned by the
DEPT technique, shows a carbonyl chemical shift of 201.1 ppm,
versus 193.5 ppm for the uncoordinated ligand (∆δ ) +7.6
ppm). Both IR and 13C NMR data are therefore consistent with
the presence of an η1-aldehyde. This is unsurprising because
the closely related complex 1 is known (X-ray structure) to have
η1-ketone binding and the chelation implicit in 3 only permits
η1-aldehyde binding.
Results and Discussion
[IrH2(Me2CO)2(PPh3)2]BF4 (1)3 reacts at room temperature
with 2-pyridinecarboxaldehyde (2) to give the fully characterized
orange microcrystalline derivative (3) in 95% yield (eq 1).
Assigning the Aldehyde-Binding Mode. A variety of
complexes containing coordinated aldehyde or ketone ligands
have been reported. Both σ (η1) and π (η2) binding modes have
been reported in the literature,4 and the mode of binding can
be assessed by IR and NMR.5 In IR spectra, coordination shifts
∆ν(CO) for η1-aldehydes are in the range 50-100 cm-1, while
∆ν(CO) values for η2-aldehydes are 500-750 cm-1. In 13C
Long-Range Coupling. A surprise in the 1H NMR spectrum
of 3 is the presence of an unusual long-range coupling between
Ha and Hc. In order to clearly assign the peaks due to the non-
phosphine ligands, we studied the H NMR of the PPh3-d15
substituted complex, 3-d30. Hb is assigned as trans to N rather
1
than O because of the chemical shift; in this Ir(III) system, the
(4) (a) Bullock, R. M.; Rappoli, B. J.; Samsel, E. G.; Rheingold, A. L. J.
Chem. Soc., Chem. Commun. 1989, 261. (b) Shambayati, S.; Crowe,
W. E.; Schreiber, S. L. Angew. Chem., Int. Ed. Engl. 1990, 29, 256.
(c) Huang, Y.; Gladysz, J. A. J. Chem. Educ. 1988, 65, 298. (d)
Bullock, R. M.; Ricci, J. S.; Szalda, D. J. J. Am. Chem. Soc. 1989,
111, 2741. (e) Mendez, N. Q.; Arif, A. M.; Gladysz, J. A. Angew.
Chem., Int. Ed. Engl. 1990, 29, 1473. (f) Klein, D. P.; Dalton, D. M.;
Mendez, N. Q.; Arif, A. M.; Gladysz, J. A. J. Organomet. Chem. 1991,
412, C7. (g) Saura-Llamas, I.; Dalton, D. M.; Arif, A. M.; Gladysz,
J. A. Organometallics 1992, 11, 683. (h) Dalton, D. M.; Fernandez,
J. M.; Emerson, K.; Larsen, R. D.; Arif, A. M.; Gladysz, J. A. J. Am.
Chem. Soc. 1990, 112, 9198. (i) Agbossou, F.; Ramsden, J. A.; Huang,
Y.; Arif, A. M.; Gladysz, J. A. Organometallics 1992, 11, 693. (j)
Faller, J. W.; Ma, Y. J. Am. Chem. Soc. 1991, 113, 1579.
(5) (a) Garner, C. M.; Mendez, N. Q.; Kowalczyk, J. J.; Fernandez, J.
M.; Emerson, K.; Larsen, R. D.; Gladysz, J. A. J. Am. Chem. Soc.
1990, 112, 5146. (b) Faller, J. W.; Ma, Y.; Smart, C. J.; DiVerdi, M.
J. J. Organomet. Chem. 1991, 420, 237. (c) Brown, J. M.; Chaloner,
P. A. J. Chem. Soc., Perkin Trans. 1982, 2, 711. (d) Courtot, P.;
Pichon, R.; Salaun, J. Y. J. Organomet. Chem. 1985, 286, C17. (e)
Auffret, J.; Courtot, P.; Pichon, R.; Salaun, J. Y. J. Chem. Soc., Dalton
Trans. 1987, 1687.
X Abstract published in AdVance ACS Abstracts, April 1, 1996.
(1) (a) Lee, J. C., Jr.; Rheingold, A. L.; Muller, B.; Pregosin, P. S.;
Crabtree, R. H. J. Chem. Soc., Chem. Commun. 1994, 1021. (b) Lee,
J. C., Jr.; Peris, E.; Rheingold, A. L.; Crabtree, R. H. J. Am. Chem.
Soc. 1994, 116, 11014. (c) Peris, E.; Lee, J. C., Jr.; Crabtree, R. H. J.
Chem. Soc., Chem. Commun. 1994, 2573. (d) Peris, E.; Lee, J. C., Jr.;
Rambo, J. R.; Eisenstein, O.; Crabtree, R. H. J. Am. Chem. Soc. 1995,
117, 3485. (e) Wessel, J.; Lee J. C., Jr.; Peris, E.; Yap, G. P. A.;
Fortin, J. B.; Ricci, J. S.; Sini, G.; Albinati, A.; Koetzle, T. F.;
Eisenstein, O.; Rheingold, A. L.; Crabtree, R. H. Angew. Chem., Int.
Ed. Engl. 1995, 34, 2507. (f) Patel, B. P.; Yao, W.; Yap, G. P. A.;
Rheingold, A. L.; Crabtree, R. H. J. Chem. Soc., Chem. Commun.,
submitted.
(2) (a) Park, S.; Ramachandran, R.; Lough, A. J.; Morris, R. H. J. Chem.
Soc., Chem. Commun. 1994, 2201. (b) Lough, A. J.; Park, S.;
Ramachandran, R.; Morris, R. H. J. Am. Chem. Soc. 1994, 116, 8356.
(3) Crabtree, R. H.; Demou, P. C.; Eden, D.; Mihelcic, J. M.; Parnell, C.;
Quirk, J. M.; Morris, G. E. J. Am. Chem. Soc. 1982, 104, 6994.
S0020-1669(95)00807-X CCC: $12.00 © 1996 American Chemical Society

3008 Inorganic Chemistry, Vol. 35, No. 10, 1996
Yao and Crabtree
hydride resonance positions are known3 to depend on the nature
of the trans ligand, and Hb at -18.93 ppm is in the typical range
for H trans to pyridine nitrogen (-15 to -20 ppm), while Ha
at -27.60 ppm is in the typical range for H trans to oxygen
(-25 to -30 ppm). Hc resonates at 9.78 ppm as a single broad
peak with w1/2 ) 7.5 Hz, while Ha resonates at -27.60 ppm as
a doublet of doublets of triplets. Decoupling experiments
revealed the presence of a 2.5 Hz coupling between Ha and Hc:
when the peak due to Hc was irradiated, the doublet of doublets
of triplets due to Ha collapsed to a doublet of triplets. To our
knowledge, this type of four-bond coupling has not previously
been observed.
Reactions of 3 with Amines. In the hope of synthesizing a
series of examples of hydrogen-bonded species, we synthesized
a variety of substituted imine complexes. For example, complex
3 rapidly reacts with ethanolamine to give the η1-NdCH- Schiff
base complex 4 (eq 2).
to νO-H; in CH2Cl2, the H-bonded and non-H-bonded forms
coexist, as shown by the presence of bands at 3379 and 3600
cm-1, respectively. The ∆νO-H of 221 cm-1 corresponds to
an H-bond strength of about 4.5 kcal‚mol-1. However, the
H‚‚‚H coupling constant was too small to be observed by NMR.
Further NMR Studies of 5. To obtain further information
about the hydrogen bond found in complex 5, the T1(min),
measured for the hydrides at 300 MHz, was found at -40 °C
(CD2Cl2). The Ha and Hb hydrides had T1(min) values of 200
and 167 ms, respectively, implying an excess relaxation rate of
1.0 s-1 for the H-bonded hydride, Hb. Applying the standard
equation7 allows this excess relaxation to be interpreted in terms
of an Hb‚‚‚H(O) distance of 2.4 Å. This is a longer distance
than the 1.7-1.8 Å range found for the strong X-H‚‚‚H-M
hydrogen bonds (X ) O, N) previously studied;1,2 this lengthen-
ing is in line with the weak bonding found for 5 by IR
spectroscopy. Milstein et al. found the same long H‚‚‚H
distance of 2.4 Å for a weak O-H‚‚‚H-Ir interaction in cis-
[IrH(OH)(PMe3)4][PF6] by neutron diffraction, however.8
This study also allows us to assign the peak at -19.81 ppm
(ddt) to Ha. This in turn shows that it is the hydride trans to
the imine N which shows long-range coupling to Hc. Addition
of D2O to the sample causes no significant change in the hydride
region of the NMR spectrum of 5, unlike the cases having strong
hydrogen bonding.1,2 There is therefore no significant exchange
between the OH and IrH sites.
(2)
Synthesis of 6. In order to compare with 5, we looked at
the reaction of complex 3 with 4-aminophenol (eq 4), which
Spectroscopy of 4. Complex 4 has been characterized by
IR, 1H NMR, 31P NMR, and elemental analysis. In particular,
the imine proton is observed at 8.78 ppm as a broad singlet
peak (w1/2 ) 5.6 Hz) and shows a similar long-range 1.2 Hz
1
coupling with one of the hydrides in the H NMR.
H-Bonding in 4. A weak Ir-H‚‚‚H-O interaction is present
in complex 4, because the IR spectrum (thin film) shows νO-H
at 3540 cm-1; in CH2Cl2, the hydrogen-bonded and non-
hydrogen-bonded forms coexist, as shown by the presence of
bands at 3541 and 3601 cm-1, respectively. The ∆νO-H of 60
cm-1 corresponds to an H-bond strength of about 2.4 kcal‚mol-1,
according to the Iogansen equation for the enthalpy of hydrogen-
bonding (∆Η ) -1.28(∆ν)1/2).6
(4)
gave complex 6, fully characterized by analytical and spectral
data. The solution IR (in CH2Cl2) shows only free νO-H at 3601
cm-1, very close to free νO-H at 3600 cm-1 for complex 5,
indicating the very similar electronic effects of 2-amino and
4-amino groups.
Other Derivatives. In an attempt to obtain a more flexible
system, we looked at the reaction of complex 3 with 2-ami-
nobenzyl alcohol, but no reaction took place.
Synthesis of 5. In the hope of moving to a more acidic OH
and therefore a stronger hydrogen-bonding interaction, we
looked at the reaction of complex 3 with 2-aminophenol (eq
1
3), which gave complex 5, characterized by IR, H NMR, 31P
NMR, and elemental analysis.
With 2,6-pyridinedicarboxaldehyde (7), 1 reacts at room
temperature to give the orange microcrystalline species 8 in 81%
yield (eq 5), in which only one of the two carbonyl groups are
(3)
Spectroscopy of 5. The 1H NMR spectrum in CD2Cl2
solution shows that the imine proton Hc is observed at 8.83
ppm as a broad singlet peak (w1/2 ) 5.0 Hz) and also shows a
similar long-range 1.7 Hz coupling with one of the hydrides,
Ha, which resonates as a doublet of doublets of triplets (ddt).
Hydrogen Bonding in 5. The hydrogen bonding is some-
what stronger in this case. The IR spectrum of 5 in a thin film
or as a KBr pellet shows a broad peak around 3384 cm-1 due
(5)
coordinated, as expected by analogy with 3. The IR spectrum
of 8 shows a strong peak at 1708 cm-1 due to the uncoordinated
(7) (a) Hamilton, D. G.; Crabtree, R. H. J. Am. Chem. Soc. 1988, 110,
4126. (b) Luo, X. L.; Crabtree, R. H. Inorg. Chem. 1990, 29, 2788.
(c) Desrosiers, P. J.; Cai, L.; Lin, Z.; Richards, R.; Halpern, J. J. Am.
Chem. Soc. 1991, 113, 4173.
(8) (a) Milstein, D.; Calabrese, C.; Williams, I. D. J. Am. Chem. Soc.
1986, 108, 6387. (b) Stevens, R. C.; Bau, R.; Milstein, D.; Blum, O.;
Koetzle, T. F. J. Chem. Soc., Dalton Trans. 1990, 1429.
(6) (a) Iogansen, A. V.; Kurkchi, G. A.; Furman, V. M.; Glazunov, V.
P.; Odinokov, S. E. Zh. Prikl. Spektrosk. 1980, 33, 460. (b) Kazarian,
S. G.; Hamley, P. A.; Poliakoff, M. J. Am. Chem. Soc. 1993, 115,
9069.

An η1-Aldehyde Complex
Inorganic Chemistry, Vol. 35, No. 10, 1996 3009
carbonyl and a weak peak at 1620 cm-1 due to the coordinated
1
carbonyl. The H NMR spectrum shows a broad peak at 9.88
ppm (w1/2 ) 2.2 Hz) due to the uncoordinated aldehyde
hydrogen and a broader peak at 10.11 ppm (w1/2 ) 4.2 Hz) due
to the coordinated aldehyde hydrogen. Decoupling experiments
confirmed the presence of a 2.4 Hz long-range coupling between
the coordinated aldehyde hydrogen and the hydride at -26.25
ppm, which allowed the coordinated and free aldehyde signals
to be assigned.
Selective Reaction of 8 with Amines. Addition of 1 equiv
of ethanolamine to complex 8 results in complete reaction only
with the coordinated carbonyl group, leading to the formation
of complex 9. Addition of another equivalent of ethanolamine
results in reaction with the uncoordinated carbonyl group and
the formation of complex 10 (eq 6). This clearly shows that
Figure 1. Experimental and simulated concentrations of 3, 5, and 6
versus time: 9, experimental [3]; 2, experimental [5]; b, experimental
[6]; 0, simulated [3]; 4, simulated [5]; O, simulated [6].
(6)
coordination of the carbonyl group to the metal enhances its
reactivity with amine. Indeed, the second step takes several
hours and is obviously much slower than the first step, which
takes place on mixing.
(7)
(rate ) k[amine][complex]) was assumed and the rate constants
were varied until agreement with experiment was achieved. The
values k5/k6 ) 6.0 ((0.2) and k6 ) 0.0014 ((0.0002) M-1 s-1
gave the best fit with the observations (Figure 1). No other
assumption fitted the data so well.
Complexes 9 and 10 have been characterized by IR, 1H NMR,
31P NMR, and elemental analyses. The hydrogen bonds in these
complexes are weak like that found in complex 4. The ∆νO-H
of ∼70 cm-1 corresponds to an H-bond strength of about 2.5
kcal/mol in complex 9 and 10.
Since the ratio of rate constants for the formation of 5 and 6
is 6.0, we can deduce the difference in free energy of activation
∆∆Gq is 1.1 kcal‚mol-1. The H-bond strength we found in 5
(4.5 kcal‚mol-1) is much larger than this value, and the
difference, 3.4 kcal‚mol-1, presumably results from an unfavor-
able chelate ring conformation being required for efficient
H-bonding in the transition state for the reaction of eq 7 in the
case of 5.
Kinetic Study of the Reaction of 3 with Amines. The Ir-
H‚‚‚H-O interaction in complex 5 suggested that the product
ratios might be affected if one product could form such a
hydrogen bond and the other could not. So that the electronic
effects would be comparable (although the pKa’s have not been
measured), we chose to study a competition between 4-ami-
nophenol and 2-aminophenol. Since 2-aminophenol has larger
steric hindrance than 4-aminophenol, any increase in reactivity
could be ascribed to intramolecular H-bond formation, possible
only for the 2-isomer.
Conclusion
We have synthesized and clearly characterized an η1-
coordinated aldehyde complex, 3, which shows an unusual long-
range coupling and reacts with amine to give η1 Schiff-base
complexes.
Complex 3 reacts with 2-aminophenol to give complex 5,
which possesses an Ir-H‚‚‚H-O interaction. Reaction of
complex 3 with 2-aminophenol and 4-aminophenol gave a
mixture that favored the complex containing the intramolecular
H-bond.
The limited solubility of the aminophenols in common
solvents such as methylene chloride prevents us from using
pseudo-first-order conditions. Instead, an equimolar mixture
of 2-aminophenol, 4-aminophenol, and complex 3 was placed
in 1 mL of CD2Cl2 in a 5 mm NMR tube, at room temperature
1
(298 K), and monitored by H NMR spectroscopy for 5 h (eq
1
7). The H NMR spectrum showed that both 5 and 6 were
formed to give a final ratio of 4.2:1. Free 2-aminophenol did
not react with the 4-aminophenol complex, 6, so we conclude
that the observed product ratio reflects the kinetic and not
thermodynamic product ratio.
Experimental Section
We simulated the kinetic processes using the program shown
in the Supporting Information, in which a second-order reaction
General Procedures and Materials. All experiments were per-
formed under a dry nitrogen atmosphere using standard Schlenk

3010 Inorganic Chemistry, Vol. 35, No. 10, 1996
Yao and Crabtree
techniques. Solvents were dried by standard procedures. Ligands, such
as PPh3-d15, 2-pyridinecarboxaldehyde, ethanolamine, 2-aminophenol,
4-aminophenol, 2,6-pyridinedicarboxaldehyde, 2-aminobenzyl alcohol
(Aldrich), were used as received. [IrH2(acetone)2(PPh3)2][BF4] was
obtained according to the literature methods.3 [IrH2(acetone)2(PPh3-
d15)2][BF4] was obtained by a similar method, using the PPh3-d15 ligand
instead of the regular PPh3.
1H, 13C, and 31P NMR measurements were recorded on a GE Omega-
300 or QE 300-plus spectrometer; chemical shifts were measured
relative to residual solvent (1H, 13C NMR) or to external 85% H3PO4
(31P NMR). IR spectra were recorded on a MIDAC M1200 FT-IR
spectrometer. Elemental microanalyses were carried out by Atlantic
Microlabs. Melting points were not determined because the complexes
decomposed.
at room temperature under N2 atmosphere for 36 h, during which time
the color changed from orange to brown. The solution was filtered
through Celite, the volume of the filtrate was concentrated under
reduced pressure to ca. 3 mL, and addition of Et2O (5 mL) caused the
precipitation of a mustard yellow solid, which was collected by
filtration, washed with hexanes, and dried in Vacuo. Yield: 72 mg
(0.07 mmol, 64%). Recrystallization from CH2Cl2/Et2O afforded a
yellow orange product. Anal. Calcd for C48H42BF4IrN2OP2‚0.2CH2-
Cl2: C, 56.71; H, 4.19; N, 2.74. Found: C, 56.62; H, 4.30; N, 2.72.
IR (film) in cm-1: 3375 (br, O-H), 2178 (br, Ir-H), 1588 (w, CdN).
IR (KBr) in cm-1: 3376 (br, O-H), 2184 (br, Ir-H), 1587 (w, CdN).
IR (CH2Cl2) in cm-1: 3600 (s, O-H), 3379 (br, O-H), 2186 (br, Ir-
H), 1575 (w, CdN). 1H NMR (CD2Cl2, 298 K): δ 8.83 (s, br, w1/2
5.0 Hz, 1H, -HCdN-), 7.0-7.9 (m, 34H, PPh3, C5H4N), 6.95 (d, 1H,
)
3JHH ) 8.0 Hz, aromatic hydrogen ortho to -OH), 6.73 (d, 1H, 3JHH
)
Dihydrido(η2-2-pyridinecarboxaldehyde-N,O-)bis(triphenylphos-
phine)iridium(III) Tetrafluoroborate (3). A suspension of [IrH2-
(acetone)2(PPh3)2][BF4] (310 mg, 0.34 mmol) in benzene (15 mL) was
treated with 2-pyridinecarboxaldehyde (73 µL, 0.77 mmol) at room
temperature. The off-white suspension immediately turned to an orange
suspension, and the mixture was stirred under N2 atmosphere for 2 h.
The resulting orange precipitate was collected by filtration, washed
with hexanes (15 mL), and dried in Vacuo. Yield: 292 mg (0.32 mmol,
95%). Recrystallization from CH2Cl2/hexane afforded brilliant orange
prisms. Anal. Calcd for C42H37BF4IrNOP2: C, 55.27; H, 4.09; N, 1.53.
Found: C, 55.11; H, 4.10; N, 1.46. IR (film) in cm-1: 2250, 2166
(br, Ir-H), 1616 (s, CdO). 1H NMR (CD2Cl2, 298 K): δ 9.78 (s, br,
w1/2 ) 7.5 Hz, 1H, HC(O)-), 5.3-7.9 (m, 34H, PPh3, C5H4N), -18.93
(dt, 1H, 2JHP ) 15.6 Hz, 2JHH ) 9.0 Hz, Ir-H), -27.60 (ddt, 1H, 2JHP
5.9 Hz, aromatic hydrogen ortho to -NdCH-), 6.69 (s, 1H, HO-), 6.65
3
(t, 1H, JHH ) 6.2 Hz, aromatic hydrogen para to -NdCH-), 6.51 (t,
3JHH ) 7.7 Hz, aromatic hydrogen para to -OH), -19.20 (dt, 1H, 2JHP
2
2
) 16.1 Hz, JHH ) 7.3 Hz, Ir-H), -19.81 (ddt, 1H, JHP ) 6.8 Hz,
2JHH ) 7.3 Hz, JHH ) 1.7 Hz Ir-H). 31P{partially H decoupled}
NMR (CD2Cl2, 298 K): δ 19.9 (t, JPH ) 12.9 Hz).
4
1
2
5-d30. In a 5 mm NMR tube, a solution of 3-d30 (12 mg, 0.013
mmol) in CD2Cl2 was treated with 2-aminophenol (1 mg, 0.009 mmol),
1
and the solution was monitored by H NMR spectroscopy. After 2
1
days, the H NMR showed the absence of 3-d30 and the presence of
4
5-d30. 1H NMR (CD2Cl2, 298 K): δ 8.64 (d, JHH ) 2.0 Hz, 1H,
-HCdN-), 7.90 (d, 1H, 3JHH ) 5.1 Hz, aromatic hydrogen ortho to N),
3
7.68 (t, 1H, JHH ) 7.2 Hz, aromatic hydrogen para to -C(N)H), 7.57
(d, 1H, 3JHH ) 8.0 Hz, aromatic hydrogen ortho to -CH)N-), 7.06 (dt,
2
4
1
) 15.6 Hz, JHH ) 9.0 Hz, JHH ) 2.5 Hz, Ir-H). 31P{partially H
decoupled} NMR (CD2Cl2, 298 K): δ 23.2 (t, 2JPH ) 13.6 Hz). 13C{H}
NMR (CD2Cl2, 298 K): δ 201.1 (s, -C(O)H), 154.4 (s, C5H4N), 151.6
(s, C5H4N), 137.9 (s, C5H4N), 133.8 (virtual t, JCP ) 6.3 Hz, PPh3),
133.4 (s, C5H4N), 132.2 (s, C5H4N), 131.8 (virtual t, JCP ) 27.5 Hz,
PPh3), 131.0 (s, PPh3), 128.9 (virtual t, JCP ) 5.0 Hz, PPh3).
1H, 3JHH ) 8.0 Hz, 4JHH ) 1.4 Hz, aromatic hydrogen para to N), 6.73
3
4
(s, 1H, -OH), 6.72 (dt, 1H, JHH ) 8.0 Hz, JHH ) 2.2 Hz, aromatic
3
4
hydrogen para to -NdCH-), 6.68 (dd, 1H, JHH ) 7.3 Hz, JHH ) 1.5
3
Hz, aromatic hydrogen ortho to -OH), 6.62 (dd, 1H, JHH ) 8.0 Hz,
4JHH ) 1.4 Hz, aromatic hydrogen ortho to -NdCH-), 6.56 (dt, 3JHH
)
4
7.2 Hz, JHH ) 1.4 Hz, aromatic hydrogen para to -OH), -19.13 (dt,
3-d30. A suspension of [IrH2(acetone)2(PPh3)2][BF4] (30 mg, 0.027
mmol) in benzene (2 mL) was treated with 2-pyridinecarboxaldehyde
(6 µL, 0.063 mmol) at room temperature. The off-white suspension
immediately turned to an orange suspension, which was stirred under
N2 atmosphere for 2 h. The resulting orange precipitate was collected
by filtration, washed with hexanes (5 mL), and dried in Vacuo. Yield:
28 mg (0.025 mmol, 93%). 1H NMR (CD2Cl2, 298 K): δ 9.66 (s, br,
2
2
2
1H, JHP ) 15.9 Hz, JHH ) 7.2 Hz, Ir-H), -19.67 (ddt, 1H, JHP
)
2
4
16.6 Hz, JHH ) 7.2 Hz, JHH ) 2.2 Hz, Ir-H).
Dihydrido(η2-2-pyridinecarboxaldehyde 4-hydroxybenzylimine-
N,N′)bis(triphenylphosphine)iridium(III) Tetrafluoroborate (6). A
solution of 3 (100 mg, 0.11 mmol) in CH2Cl2 (20 mL) was treated
with 4-aminophenol (12 mg, 0.11 mmol), and the solution was stirred
at room temperature under N2 atmosphere for 60 h, during which time
the color changed from orange to yellow-orange. The solution was
filtered through Celite, the volume of filtrate was concentrated under
reduced pressure to ca. 3 mL, and addition of Et2O (5 mL) caused the
precipitation of a yellow orange solid, which was collected by filtration,
washed with hexanes, and dried in Vacuo. Yield: 82 mg (0.08 mmol,
73%). Recrystallization from CH2Cl2/Et2O afforded a yellow-orange
product. Anal. Calcd for C48H42BF4IrN2OP2‚0.2CH2Cl2: C, 56.71;
H, 4.19; N, 2.74. Found: C, 56.64; H, 4.30; N, 2.72. IR (CH2Cl2) in
cm-1: 3601 (s, O-H), 2185 (br, Ir-H), 1576 (w, CdN). 1H NMR
(CD2Cl2, 298 K): δ 8.40 (s, br, w1/2 ) 4.8 Hz, 1H, -HCdN-), 7.99 (d,
3
w1/2 ) 5.3 Hz, 1H, HC(O)-), 7.94 (d, 1H, JHH ) 4.3 Hz, aromatic
3
hydrogen ortho to N), 7.83 (t, 1H, JHH ) 7.4 Hz, aromatic hydrogen
para to -C(O)H), 7.74 (d, 1H, 3JHH ) 7.8 Hz, aromatic hydrogen ortho
3
4
to -C(O)H), 6.96 (dt, 1H, JHH ) 7.8 Hz, JHH ) 1.7 Hz aromatic
hydrogen para to N), -18.93 (dt, 1H, 2JHP ) 15.6 Hz, 2JHH ) 8.7 Hz,
Ir-H), -27.61 (ddt, 1H, JHP ) 15.6 Hz, JHH ) 8.7 Hz, JHH ) 2.6
Hz, Ir-H).
2
2
4
Dihydrido(η2-2-pyridinecarboxaldehyde 2-hydroxyethylimine-
N,N′)bis(triphenylphosphine)iridium(III) Tetrafluoroborate (4). A
suspension of 3 (51 mg, 0.056 mmol) in benzene (5 mL) was treated
with ethanolamine (5 µL, 0.083 mmol) at room temperature. The
orange suspension turned immediately to a clear yellow solution and
after 20 min to a yellow suspension, which was stirred under N2
atmosphere for 3 h. The resulting yellow precipitate was collected by
filtration, washed with hexanes (10 mL), and dried in Vacuo. Yield:
41 mg (0.043 mmol, 77%). Recrystallization from CH2Cl2/hexane
afforded a bright yellow product. Anal. Calcd for C44H42BF4IrN2-
OP2: C, 55.29; H, 4.43; N, 2.93. Found: C, 55.04; H, 4.50; N, 2.91.
IR (film) in cm-1: 3540 (br, O-H), 2223, 2144 (br, Ir-H), 1586 (w,
CdN). IR (CH2Cl2) in cm-1: 3601 (s, O-H), 3541 (br, O-H), 2185
(br, Ir-H), 1574 (w, CdN). 1H NMR (CD2Cl2, 298 K): δ 8.78 (s, br,
w1/2 ) 5.6 Hz, 1H, -HCdN-), 6.7-8.0 (m, 34H, PPh3, C5H4N), 3.35
1H, 3JHH ) 5.4 Hz, aromatic hydrogen ortho to N), 7.67 (t, 1H, 3JHH
)
3
7.7 Hz, aromatic hydrogen para to -C(N)H), 7.57 (d, 1H, JHH ) 7.7
Hz, aromatic hydrogen ortho to -C(N)H), 7.2-7.5 (m, 30H, PPh3), 6.89
(s, 1H, -OH), 6.87 (d, 2H, 3JHH ) 8.5 Hz, aromatic hydrogen ortho to
-OH), 6.73 (t, 1H, 3JHH ) 6.3 Hz, aromatic hydrogen para to N), 6.55
3
(d, 2H, JHH ) 8.5 Hz, aromatic hydrogen meta to -OH), -19.28 (dt,
2
2
2
1H, JHP ) 16.1 Hz, JHH ) 6.9 Hz, Ir-H), -19.49 (ddt, 1H, JHP
)
16.9 Hz, JHH ) 6.9 Hz, JHH ) 2.3 Hz, Ir-H). 31P{partially 1H
decoupled} NMR (CD2Cl2, 298 K): δ 19.7 (t, JPH ) 11.7 Hz).
2
4
2
6-d30. In a 5 mm NMR tube, a solution of 3-d30 (12 mg, 0.013
mmol) in CD2Cl2 was treated with 4-aminophenol (1 mg, 0.009 mmol),
3
3
1
(t, 2H, JHH ) 4.5 Hz, -CH2CH2OH), 3.13 (q, 2H, JHH ) 4.9 Hz,
-CH2CH2OH), 1.95 (t, 1H, 3JHH ) 5.2 Hz, -CH2CH2OH), -19.04 (ddt,
1H, 2JHP ) 17.0 Hz, 2JHH ) 6.9 Hz, 4JHH ) 1.2 Hz, Ir-H), -19.62 (dt,
1H, 2JHP ) 16.4 Hz, 2JHH ) 6.9 Hz, Ir-H). 31P{partially 1H decoupled}
and the solution was monitored by H NMR spectroscopy. After 1
1
week, the H NMR showed the absence of 3-d30 and the presence of
6-d30. 1H NMR (CD2Cl2, 298 K): δ 8.36 (s, br, w1/2 ) 6.4 Hz, 1H,
-HCdN-), 7.95 (d, 1H, 3JHH ) 5.1 Hz, aromatic hydrogen ortho to N),
2
3
NMR (CD2Cl2, 298 K): δ 19.4 (t, JPH ) 15.0 Hz).
7.67 (t, 1H, JHH ) 8.1 Hz, aromatic hydrogen para to -C(N)H), 7.54
Dihydrido(η2-2-pyridinecarboxaldehyde 2-hydroxybenzylimine-
N,N′)bis(triphenylphosphine)iridium(III) Tetrafluoroborate (5). A
solution of 3 (100 mg, 0.11 mmol) in CH2Cl2 (20 mL) was treated
with 2-aminophenol (12 mg, 0.11 mmol), and the solution was stirred
(d, 1H, 3JHH ) 7.2 Hz, aromatic hydrogen ortho to -CH)N-), 6.92 (s,
3
1H, -OH), 6.84 (d, 2H, JHH ) 8.4 Hz, aromatic hydrogen ortho to
-OH), 6.73 (t, 1H, 3JHH ) 6.0 Hz, aromatic hydrogen para to N), 6.49
3
(d, 2H, JHH ) 8.4 Hz, aromatic hydrogen meta to -OH), -19.26 (dt,

An η1-Aldehyde Complex
Inorganic Chemistry, Vol. 35, No. 10, 1996 3011
2
2
2
1H, JHP ) 16.4 Hz, JHH ) 7.2 Hz, Ir-H), -19.46 (ddt, 1H, JHP
)
by filtration, washed with hexanes, and dried in Vacuo. Yield: 42 mg
(0.042 mmol, 68%). Anal. Calcd for C47H47BF4IrN3O2P2‚0.7CH2Cl2:
C, 52.74; H, 4.43; N, 3.87. Found: C, 52.63; H, 4.66; N, 3.87. IR
(CH2Cl2) in cm-1: 3601 (s, free O-H), 3531 (br, O-H), 2188 (br,
Ir-H), 1643 (s, uncoordinated CdN), 1574 (w, coordinated CdN).
1H NMR (CD2Cl2, 298 K): δ 8.77 (s, br, w1/2 ) 2.3 Hz, 1H,
uncoordinated HC(N)-), 8.56 (s, br, w1/2 ) 5.1 Hz, 1H, coordinated
HC(N)-), 7.2-7.8 (m, 33H, PPh3, C5H3N), 3.59 (q, 2H, -CH2CH2OH),
2
4
16.4 Hz, JHH ) 7.2 Hz, JHH ) 2.1 Hz Ir-H).
Dihydrido(η2-2,6-pyridinedicarboxaldehyde)bis(triphen-
ylphosphine)iridium(III) Tetrafluoroborate (8). A suspension of
[IrH2(acetone)2(PPh3)2][BF4] (115 mg, 0.12 mmol) in benzene (5 mL)
was treated with 2,6-pyridinedicarboxaldehyde (37 mg, 0.27 mmol) at
room temperature. The off-white suspension immediately turned to
an orange suspension, which was stirred under N2 atmosphere for 2 h.
The resulting orange precipitate was collected by filtration, washed
with pentane (15 mL), and dried in Vacuo. Yield: 95 mg (0.10 mmol,
81%). Recrystallization from CH2Cl2/pentane afforded a pure orange
product. Anal. Calcd for C43H37BF4IrNO2P2: C, 54.90; H, 3.96; N,
1.49. Found: C, 54.63; H, 4.21; N, 1.34. IR (film) in cm-1: 2263,
2185 (br, Ir-H), 1708 (s, uncoordinated CdO), 1620 (w, coordinated
CdO). 1H NMR (CD2Cl2, 298 K): δ 10.11 (s, br, w1/2 ) 4.2 Hz, 1H,
coordinated HC(O)-), 9.88 (s, br, w1/2 ) 2.2 Hz, 1H, uncoordinated
HC(O)-), 7.2-8.5 (m, 33H, PPh3, C5H3N), -19.04 (dt, 1H, 2JHP ) 15.4
3
3.48 (br, 2H, -CH2CH2OH), 3.40 (q, 2H, JHH ) 5.7 Hz, -CH2CH2-
3
OH), 3.12 (t, 2H, JHH ) 5.7 Hz, -CH2CH2OH), 2.57 (br, 1H, -CH2-
3
CH2OH), 1.68 (t, 1H, JHH ) 5.7 Hz, -CH2CH2OH), -18.82 (dt, br,
2
2
2
1H, JHP ) 16.9 Hz, JHH ) 7.2 Hz, Ir-H), -19.92 (dt, 1H, JHP
)
15.3 Hz, JHH ) 7.2 Hz, Ir-H). 31P{partially H decoupled} NMR
(CD2Cl2, 298 K): δ 19.4 (t, JPH ) 13.0 Hz).
2
1
2
T1 Study. Determination of T1(min) was performed on 5 using a
conventional inversion-recovery pulse sequence (CD2Cl2,193-293 K,
300 MHz).7
2
2
2
Hz, JHH ) 8.1 Hz, Ir-H), -26.25 (ddt, 1H, JHP ) 15.4 Hz, JHH
)
Kinetic Study of Complex 3 with 2-Aminophenol and 4-Ami-
nophenol. A 12 mg sample of 2-aminophenol and 12 mg of
4-aminophenol were dissolved in 5 mL of CH2Cl2 in a 5 mL volumetric
flask. A 1 mL portion of the solution was removed to a vial, and the
solvent was removed by a N2 stream. After this, 2.4 mg (2.2 × 10-2
mmol) of 2-aminophenol and 2.4 mg (2.2 × 10-2 mmol) of 4-ami-
nophenol were obtained. Then 20 mg (2.2 × 10-2 mmol) of 3 was
placed in a 5 mm NMR tube with 2.4 mg of 2-aminophenol and 2.4
8.1 Hz, 4JHH ) 2.4 Hz, Ir-H). 31P{partially 1H decoupled} NMR (CD2-
2
Cl2, 298 K): δ 22.7 (t, JPH ) 13.4 Hz).
Dihydrido(η2-2,6-pyridinedicarboxaldehyde 2-hydroxyethylimine-
N,N′)bis(triphenylphosphine)iridium(III) Tetrafluoroborate (9). A
suspension of 8 (29 mg, 0.031 mmol) in benzene (5 mL) was treated
with ethanolamine (1.8 µL, 0.030 mmol) at room temperature. The
orange suspension turned immediately to a clear yellow solution and
after 20 min to a yellow suspension, which was stirred under N2
atmosphere for 3 h. The resulting yellow precipitate was collected by
filtration, washed with pentane (5 mL), and dried in Vacuo. Yield: 28
mg (0.029 mmol, 93%). Anal. Calcd for C45H42BF4IrN2 O2P2‚0.5CH2-
Cl2: C, 53.25; H, 4.22; N, 2.73. Found: C, 52.99; H, 4.26; N, 3.00.
1
mg of 4-aminophenol. By monitoring of the solution by H NMR
spectroscopy for a 5-h period, the concentrations of complex 3 and
two competing products, 5 and 6, were determined from the integration
of the peaks due to -OdCH- and -NdCH-.
Simulation of the Kinetics. The kinetic processes were simulated
using the program shown in the Supporting Information, in which a
second-order reaction (rate ) k[amine][complex]) was assumed and
the rate constants were varied until agreement with experiment was
achieved. The values k5/k6 ) 6.0 ((0.2) and k6 ) 0.0014 ((0.0002)
M-1 s-1 gave the best fit with the observations (Figure 1). No other
assumption fitted the data so well.
IR (film) in cm-1
: 3533 (br, O-H), 2177 (br, Ir-H), 1707 (s,
uncoordinated CdO), 1592 (w, coordinated CdN). 1H NMR (CD2-
Cl2, 298 K): δ 9.98 (s, br, w1/2 ) 2.4 Hz, 1H, uncoordinated HC(O)-),
9.08 (s, br, w1/2 ) 4.9 Hz, 1H, coordinated HC(N)-), 7.3-8.0 (m, 33H,
PPh3, C5H3N), 3.52 (m, 2H, -CH2CH2OH), 3.11 (t, 2H, 3JHH ) 4.3 Hz,
-CH2CH2OH), 2.52 (br, 1H, -CH2CH2OH), -18.84 (dt, br, 1H, 2JHP
)
16.4 Hz, 2JHH ) 7.1 Hz, Ir-H), -19.68 (dt, 1H, 2JHP ) 15.7 Hz, 2JHH
) 7.1 Hz, Ir-H). 31P{partially H decoupled} NMR (CD2Cl2, 298
1
Acknowledgment. We thank the NSF for support of this
work.
2
K): δ 18.5 (t, JPH ) 14.7 Hz).
Dihydrido(η2-2,6-pyridinedicarboxaldehyde 2-hydroxyethylimine-
N,N′)bis(triphenylphosphine)iridium(III) Tetrafluoroborate (10). A
solution of 9 (60 mg, 0.062 mmol) in CH2Cl2 (10 mL) was treated
with ethanolamine (10 µL, 0.166 mmol), and the solution was stirred
at room temperature under N2 atmosphere for 36 h. The solution was
concentrated under reduced pressure to ca. 3 mL, and addition of Et2O
(10 mL) caused the precipitation of a yellow solid, which was collected
Supporting Information Available: The program used to simulate
the kinetic process and listings of experimental and simulated kinetic
data for 3-6 (2 pages). Ordering information is given on any current
masthead page.
IC9508076