Synthesis and reactivity of iridium complexes with pyridine and piperidine ligands: Models for hydrodenitrogenation

Article abstract of DOI:10.1039/b406949h

The complexes [Ir(H)₂(η¹-N-L) ₂(PPh₃)₂]PF₆, L = py (1), iQ (2) and pip (3) (py = pyridine, iQ = isoquinoline, pip = piperidine) have been synthesized in high yields by hydrogenation of [Ir(cod)(PPh₃) ₂]PF₆ in the presence of the appropriate nitrogen compound. When hydrogen is bubbled through 1,2-dichloroethane solutions of 1 or, two new species were formed in each case by C-Cl bond activation of the solvent, ηIr(H)₂Cl(η¹-N-L)(PPh₃) ₂ (L = py, 4; iQ, 5) and IrH(Cl)₂( ¹-N-L)(PPh₃)₂ (L = py, 6; iQ, 7). Reaction of 3 with py or iQ yielded complexes 1 and 2, respectively, while under a slow stream of carbon monoxide the complex [Ir(H)₂(η ¹-N-pip)(CO)(PPh₃)₂]PF₆ (8) was produced. Complex 3 also reacts with halide and 4-bromothiophenolate anions leading to the corresponding neutral species Ir(H)₂(X)(η ¹-N-pip)(PPh₃)₂, X = Cl (9), I (10) and 4-BrC₆H₄S (11), or with [MoS₄]^2- to yield the hetero-bimetallic complex [Ir(H)(PPh₃) ₂(μ-S)₂MoS₂]^- (13). All the new complexes were characterized by analytical and spectroscopic methods. The X-ray structures of 1, 2 and 8 consist of distorted octahedra with a mutually cis disposition of the two hydrides and mutually trans phosphines. Complexes 1, 2 and 3 and their derivatives are of interest as models for the chemisorption step in hydrodenitrogenation reactions on solid catalysts.

Full text of DOI:10.1039/b406949h

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F U L L P A P E R
Synthesis and reactivity of iridium complexes with pyridine and
piperidine ligands: models for hydrodenitrogenation†
Merlín Rosales,*a Teresa González,b Reinaldo Atenciob and Roberto A. Sánchez-Delgado*b
a
La Universidad del Zulia, Facultad Experimental de Ciencias, Departamento de Química,
Laboratorio de Química Inorgánica, Apdo. 526, Maracaibo, Venezuela.
E-mail: merlin2002@cantv.net
Instituto Venezolano de Investigaciones Científicas (IVIC), Chemistry Centre, Apartado. 21827,
b
Caracas 1020-A, Venezuela. E-mail: merlin2002@cantv.net
Received 10th May 2004, Accepted 6th July 2004
First published as an Advance Article on the web 24th August 2004
The complexes [Ir(H)2(1-N-L)2(PPh3)2]PF6, L = py (1), iQ (2) and pip (3) (py = pyridine, iQ = isoquinoline,
pip = piperidine) have been synthesized in high yields by hydrogenation of [Ir(cod)(PPh3)2]PF6 in the presence of the
appropriate nitrogen compound. When hydrogen is bubbled through 1,2-dichloroethane solutions of 1 or 2, two new
species were formed in each case by C–Cl bond activation of the solvent, Ir(H)2Cl(1-N-L)(PPh3)2 (L = py, 4; iQ, 5) and
IrH(Cl)2(1-N-L)(PPh3)2 (L = py, 6; iQ, 7). Reaction of 3 with py or iQ yielded complexes 1 and 2, respectively, while
under a slow stream of carbon monoxide the complex [Ir(H)2(1-N-pip)(CO)(PPh3)2]PF6 (8) was produced. Complex
3 also reacts with halide and 4-bromothiophenolate anions leading to the corresponding neutral species Ir(H)2(X)(1-
N-pip)(PPh3)2, X = Cl (9), I (10) and 4-BrC6H4S (11), or with [MoS4]2− to yield the hetero-bimetallic complex
[Ir(H)(PPh3)2(-S)2MoS2]− (13). All the new complexes were characterized by analytical and spectroscopic methods.
The X-ray structures of 1, 2 and 8 consist of distorted octahedra with a mutually cis disposition of the two hydrides and
mutually trans phosphines. Complexes 1, 2 and 3 and their derivatives are of interest as models for the chemisorption step
in hydrodenitrogenation reactions on solid catalysts.
Introduction
Results and discussion
The interaction of pyridine and piperidine with transition metal
centres is of interest as model chemistry for the industrially impor-
tant hydrodenitrogenation (HDN) reaction, the catalytic removal
of organic nitrogen from petroleum and coal derived liquids. This
process is essential to reduce NOx emissions produced upon burning
of fuels, and also to avoid deactivation or poisoning of e.g. hydro-
treating or hydrocracking catalysts by nitrogen compounds. HDN
is generally carried out over sulfided CoMo/Al2O3, NiMo/Al2O3
or NiW/Al2O3 catalysts under rather severe hydrogenation condi-
tions (350–500 °C and 1500–3000 psi H2), ultimately removing the
organic nitrogen as NH3.1 Kinetic, mechanistic and thermodynamic
studies have established that hydrogenation of the N-containing
aromatic ring occurs prior to C–N bond cleavage; for instance, in
the HDN of pyridine (py), reduction to piperidine (pip) takes place
first, followed by hydrogenolysis of the C–N bonds to produce n-
pentylamine and finally pentane + NH3.2
Homogeneous modelling of heterogeneous catalytic reactions by
use of well-defined metal complexes can help in the understanding
of specific elementary steps of the reaction mechanisms. This has
been extensively used in hydrodesulfurisation (HDS)3 but HDN
model studies using coordination or organometallic complexes are
scarce.3–5 Modelling work has primarily focused on the coordina-
tion of N-heterocycles on mononuclear metal centres, on the homo-
geneous catalytic hydrogenation of N-aromatic compounds and on
C–N bond activation.5–8 As part of the organometallic modelling
of the chemisorption and subsequent steps involved in HDN, it is
important to study the coordination and reactivity of pyridines and
of their hydrogenated derivatives with metal centres. In this paper,
we report the synthesis and reactivity of stable 1-N-bonded com-
plexes of the type [Ir(H)2(1-N-L)2(PPh3)2]PF6, L = py (1), iQ (2),
and pip (3); the X-ray structures of complexes 1, 2 and of a carbonyl
derivative of 3 are also described. Although the coordination chem-
istry of pyridines is rather extensive, stable metal complexes of
piperidine are scarce.
Syntheses of [Ir(H)2(1-N-L)2(PPh3)2]PF6 complexes
The complex [Ir(cod)(PPh3)2]PF6 reacts readily with hydro-
gen in the presence of N-aromatic compounds such as pyri-
dine and isoquinoline to form the corresponding derivatives
[Ir(H)2(1-N-L)2(PPh3)2]PF6 (L = py (1) and iQ (2)) in good yields
(eqn. (1), L = py (1), iQ (2)). Complex 1 has been previously men-
tioned briefly by Moore et al. when studying solvent exchange reac-
tions of complexes of the type [Ir(H)2(solvent)2(PPh3)2]+ with py.9
[Ir(cod)(PPh3)2]PF6 + 6H2 + 2L →
[Ir(H)2(1-N-L)2(PPh3)2]PF6 + C8H16 (1)
In the case of piperidine, this method led to the analogous
complex [Ir(H)2(1-N-pip)2(PPh3)2]PF6 (3) but usually mixed
with a number of other species. A better synthetic route for
compound 3 is the addition of an excess of pip to a thf solution
of [Ir(H)2(thf)2(PPh3)2]PF6 (eqn. (2)), previously generated by
hydrogenation of [Ir(cod)(PPh3)2]PF6 in thf.10 For quinoline (Q),
any one of the two methods produced the corresponding complex
[Ir(H)2(1N–Q)2(PPh3)2]PF6 in a pure form.
[Ir(H)2(thf)2(PPh3)2]PF6 + 2pip →
[Ir(H)2(1-N-pip)2(PPh3)2]PF6 + 2thf (2)
Complexes 1–3 are rather air stable materials in the solid state.
They are soluble in dichloromethane and chloroform, sparingly
soluble in benzene, toluene and alcohols and insoluble in diethyl
ether and n-pentane. Their 1H NMR spectra display high field trip-
lets at −21.6 ppm, JHP 17.5 Hz for 1; −21.4 ppm, JHP 17.6 Hz for 2;
and −23.35 ppm, JHP 18.9 Hz for 3. The corresponding 31P{1H} spec-
tra consist of singlets at 22.8 ppm for 1 and 2, and 21.5 for 3, which
are split into triplets upon selective coupling with the two hydride
ligands. The 1H NMR signals of the piperidine ligands of complex
3 could all be assigned by 2D COSY/HETCORR and NOEDIFF
NMR experiments (see ESI†). These results are consistent with the
presence of two equivalent hydrides coupled with two equivalent
PPh3 ligands in a stereochemistry involving mutually trans phos-
phines and mutually cis pairs of hydrides and N-donor ligands:
† Electronic supplementary information (ESI) available: Preparation of
complexes. See http://www.rsc.org/suppdata/dt/b4/b406949h/
2 9 5 2
D a l t o n T r a n s . , 2 0 0 4 , 2 9 5 2 – 2 9 5 6
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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At room temperature Py or iQ immediately displace pip from
3 to generate 1 and 2, respectively. On the other hand, under a
slow stream of carbon monoxide at room temperature, only one
piperidine ligand of 3 is displaced by CO to produce a stable mono-
piperidine derivative [Ir(H)2(1N-pip)(CO)(PPh3)2]PF6 (8). The 1H
NMR spectrum displays two distinct high-field signals at −8.0 ppm,
(triplet of doublets, JHP = 17.2 Hz, JHH = 4.8 Hz) and −18.8 ppm,
(triplet of doublets, broadened possibly by the N quadrupolar effect
or by interaction with the proton on NH) while the 31P NMR spec-
trum consists of a singlet at 15.1 ppm. In the IR spectrum, two Ir–H
and a C–O stretching vibrations are observed at 2205m, 2155m
and 2040vs cm−1. The solution structure thus corresponds to an
octahedral arrangement with mutually cis hydrides, cis CO and pip
ligands, and trans phosphines, and this structure is maintained in the
solid state as confirmed by an X-ray diffraction study (vide infra).
Reactions of 3 with anionic ligands X− generate the corresponding
neutral complexes Ir(H)2(X)(1-N-pip)(PPh3)2 (X = Cl, 9; I, 10;
4-BrC6H4S, 11) by substitution of one piperidine ligand; the
analytical and spectroscopic data (see ESI†) are in agreement with
the proposed formulation and with the stereochemistry depicted
in Scheme 1 for these compounds. Complex 11 slowly loses the
remaining pip ligand and the hydrides at room temperature (or very
rapidly at 60 °C) to generate a compound whose 31P NMR spectrum
displays only one singlet at −2.1 ppm, and only peaks attributable
The solution spectroscopic data are in accord with the solid-
state structures determined by X-ray diffraction (vide infra). It is
interesting to note that all the complexes prefer to adopt the more
crowded stereochemistry containing the two nitrogen ligands in
mutually cis positions rather than an all trans disposition of the
three pairs of ligands, most likely as a result of the strong trans
effect of the hydrides. The Ir–H stretching gives rise to bands of
medium intensity in the region from 2212 to 2150 cm−1.
Reactivity of complexes 1 and 2 with H2
When hydrogen was bubbled through a 1,2-dichloroethane
solution of complexes 1 or 2 at 80 °C, the appearance of two new
singlets in the 31P{1H} NMR spectrum was observed in each case,
corresponding to the formation of two new species in equilibrium
with each starting complex (integral ratios: 1:5:2 and 1:2:3 after
24 h, where the value of 1 is assigned to the relative integral of
1 or 2, respectively). When such mixtures were precipitated as
solids and subsequently re-dissolved in 1,2-dichloroethane, the
31P NMR features remained essentially unaltered, except for the
fact that the signal corresponding to PF6− in those cases integrated
approximately 1:1 with respect to the signals of complexes 1 or
2, indicating that the new complexes formed are neutral. They
1
to phenyl protons in the H NMR spectrum. A possible structure
that would be in agreement with these data is the dimer [Ir2(-
SC6H4Br)2(PPh3)4] (12), analogous to the known [Ir2(-SR)2(CO)4]
derivatives.11 Finally complex 3 reacts with the tetrathiomolybdate
anion [MoS4]2− to produce NH4[Ir(H)(PPh3)2(-S)2MoS2] (13).
Solid-state structures of [Ir(H)2(1-N-L)2(PPh3)2]PF6, L = py
(1), iQ (2), and [Ir(H)2(1N-pip)(CO)(PPh3)2]PF6 (8)
1
display characteristic H NMR spectra (see ESI†) that allowed
their identification as Ir(H)2Cl(1-N-L)(PPh3)2 (L = py, 4; iQ, 5)
(two distinct Ir–H signals as high-field doublets of triplets arising
from the coupling to two equivalent phosphine ligands and to the
other hydride) and IrH(Cl)2(1-N-L)(PPh3)2 (L = py, 6; iQ, 7) (a
single Ir–H triplet signal). The number of hydrides in each case
was also determined by selective coupling in the 31P NMR spectra.
These chlorinated complexes are presumably formed by activation
of the C–Cl bonds of the 1,2-dichloroethane solvent, since there is
no other source of Cl in the reaction medium, but no attempt was
made to study the mechanism of these reactions. A fourth species
was detected in some cases in small proportions in the region of
56 to 50 ppm of the 31P{1H} spectrum, which corresponds to the
square planar Ir(I) complexes [Ir(1-N-L)2(PPh3)2]PF6, formed
through reductive elimination of hydrogen from the corresponding
dihydride 1 or 2. The analogous reactions of complex 3 with
hydrogen at room temperature or at 60 °C in the absence or in
the presence of excess free piperidine led to intractable complex
mixtures. No transformations of the N-donor ligands themselves
were observed for any of the three new complexes.
The molecular structures of the complexes 1 and 2 are shown in
Figs. 1 and 2, and selected bond distances and angles are listed in
Tables 1 and 2, respectively.
Reactivity of complex 3
The piperidine ligands in 3 are more labile than py or iQ in 1 or 2,
and consequently they are readily substituted by different ligands at
room temperature, as summarized in Scheme 1.
Fig. 1 ORTEP drawing of [Ir(H)2(1-N-C5H5N)2(PPh3)2]+.
The coordination geometry around iridium consists in each case
of a distorted octahedron with presumed mutually cis-hydrides, cis
N-ligands (py or iQ) and trans-phosphines. The two phosphines
are bent [P–Ir–P = 164.49(7)° for 1 and 161.79(8)° for 2] toward
the smaller hydride ligands in order to minimize steric repulsions.
The Ir–N distances in 1 and 2 [2.212(6) and 2.193(7) Å for 1 and
2.199(7) and 2.185 Å for 2] are slightly longer than those found
in the closely related bipyridyl complex [Ir(H)2(bipy)(PPh3)2]PF6
[average 2.150(5) Å],12 as well as in [AuIr(H)2(bipy)(PPh3)3](BF4)2
[2.102(8) Å]13 and [Ir(bipy)3]+ [average 2.04(1) Å].14 The mean
planes of the six-membered pyridine rings adopt different mutual
orientations, allowing dihedral angles between them of 71.1 and
57.3° for 1 and 2, respectively. All other structural parameters
concerning the coordinated py and iQ compare well with those
found in other complexes containing these ligands. The Ir–P
Scheme 1 Piperidine displacement reactions from complex 3.
D a l t o n T r a n s . , 2 0 0 4 , 2 9 5 2 – 2 9 5 6
2 9 5 3

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Table 1 Selected bond distances (Å) and angles (°) for [Ir(H)2(1-N-
C5H5N)2(PPh3)2]PF6 (1)
Table 3 Selected bond distances (Å) and angles (°) for [Ir(H)2(CO)(1-N-
C5H11N)(PPh3)2]PF6 (8)
Ir(1)–P(1)
Ir(1)–P(2)
Ir(1)–N(1)
Ir(1)–N(2)
N(1)–C(5)
N(1)–C(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
P(1)–C(11)
C(11)–C(12)
2.304(2)
2.316(2)
2.212(6)
2.193(7)
1.331(11)
1.334(10)
1.394(12)
1.378(14)
1.365(15)
1.406(13)
1.841(8)
1.387(12)
N(1)–Ir(1)–N(2)
P(2)–Ir(1)–N(2)
P(2)–Ir(1)–N(1)
P(1)–Ir(1)–N(2)
P(1)–Ir(1)–N(1)
P(1)–Ir(1)–P(2)
Ir(1)–N(1)–C(5)
Ir(1)–N(1)–C(1)
C(1)–N(1)–C(5)
N(1)–C(1)–C(2)
C(1)–C(2)–C(3)
C(2)–C(3)–C(4)
C(3)–C(4)–C(5)
C(4)–C(5)–N(1)
96.3(3)
90.42(17)
98.12(18)
97.61(18)
94.18(17)
164.49(7)
122.4(6)
119.6(5)
117.5(7)
124.1(9)
117.1(10)
120.3(9)
118.5(10)
122.5(9)
Ir(1)–P(1)
Ir(1)–P(2)
Ir(1)–N(1)
2.337(8)
2.346(9)
1.98(3)
2.01(3)
1.57(3)
1.37(5)
1.52(6)
1.43(7)
1.49(9)
1.54(8)
1.06(4)
C(37)–N(1)–Ir(1)
P(2)–Ir(1)–C(42)
P(2)–Ir(1)–N(1)
P(1)–Ir(1)–C(42)
P(1)–Ir(1)–N(1)
120(3)
97.4(10)
91.4(6)
89.7(10)
99.5(7)
165.70(18)
120(3)
101.3(11)
113(3)
116(4)
Ir(1)–C(42)
N(1)–C(41)
N(1)–C(37)
C(37)–C(38)
C(38)–C(39)
C(39)–C(40)
C(40)–C(41)
C(42)–O(42)
P(1)–Ir(1)–P(2)
Ir(1)–N(1)–C(41)
C(42)–Ir(1)–N(1)
C(37)–N(1)–C(41)
N(1)–C(37)–C(38)
C(37)–C(38)–C(39)
C(38)–C(39)–C(40)
C(39)–C(40)–C(41)
C(40)–C(41)–N(1)
Ir(1)–C(42)–O(42)
112(5)
109(4)
117(4)
107(2)
172(3)
Table 2 Selected bond distances (Å) and angles (°) for [Ir(H)2(1-N-
C9H7N)2(PPh3)2]PF6 (2)
Ir(1)–P(1)
Ir(1)–P(2)
Ir(1)–N(1)
Ir(1)–N(2)
2.314(2)
2.306(2)
2.199(7)
2.185(7)
N(1)–Ir(1)–N(2)
P(2)–Ir(1)–N(2)
P(2)–Ir(1)–N(1)
P(1)–Ir(1)–N(1)
P(1)–Ir(1)–N(2)
95.3(3)
90.02(19)
100.02(19)
91.94(19)
100.56(19)
161.79(8)
121.7(6)
121.0(6)
115.6(7)
125.2(8)
122.7(9)
120.1(10)
115.6(8)
123.5(9)
N(1)–C(37)
N(1)–C(45)
C(45)–C(44)
C(44)–C(43)
C(43)C(38)
C(43)–C(42)
C(42)–C(41)
C(41)–C(40)
C(40)–C(39)
C(39)–C(38)
C(38)–C(37)
1.332(10)
1.374(10)
1.320(12)
1.416(13)
1.410(10)
1.414(13)
1.384(15)
1.385(15)
1.350(14)
1.418(13)
1.385(12)
P(1)–Ir(1)–P(2)
Ir(1)–N(1)–C(37)
Ir(1)–N(1)–C(45)
C(37)–N(1)–C(45)
N(1)–C(37)–C(38)
C(37)–C(38)–C(39)
C(38)–C(39)–C(40)
C(38)–C(43)–C(44)
C(44)–C(45)–N(1)
Fig. 3 ORTEP drawing of [Ir(H)2(CO)(1-N-C5H11N)(PPh3)2]+.
distance in 8 [1.98(3) Å], which might suggest that the piperidine is
more loosely bound to rhodium in that compound than to iridium in
complex 8. The bond distances and angles in the piperidine ring are
rather similar in both structures within experimental errors. Since
the Rh derivative is a neutral square-planar compound, comparisons
with our cationic octahedral structure must be taken with caution.
Final remarks in relation to HDN
Adsorption of pyridines to the active sites of heterogeneous
catalysts, followed by hydrogenation to the corresponding
saturated cyclic amines constitute the initial steps of the commonly
accepted mechanism of HDN. The N-bonded complexes 1 and 2
herein reported can be considered as molecular analogues of the
chemisorbed N-heteroaromatics. It is interesting to note that in
these complexes two hydrides coexist with two N-heteroaromatic
ligands in a cis disposition, which can be considered as a model
of the simultaneous adsorption of an organo-nitrogen compound
and activation of dihydrogen on a single metal site. This should
be favourable for a subsequent attack of the hydride to the
heterocyclic ring, but no such reactivity was observed for these
very stable complexes. Although the py ligand of complex 1 could
not to be directly hydrogenated to piperidine, the corresponding
bis(piperidine) analogue 3 could be obtained by an alternative
route, thus completing the model for the adsorption of piperidine
to a catalytic site. Several reports of pyridine, quinoline and indole
metal-complexes are available, but analogues containing their
hydrogenated derivatives, e.g. tetrahydroquinoline and indoline
are less common;19 and are particularly scarce in the case of
piperidine.20 Unfortunately, it was not possible to activate the C–H
or C–N bonds of the nitrogen ligands in complexes 1–3, due to the
stability of the complexes 1 and 2 and the lability of the piperidine
ligands in 3 and related complexes.
Fig. 2 ORTEP drawing of [Ir(H)2(1-N-C9H7N)2(PPh3)2]+.
distances in complexes 1 [2.304(2) and 2.316(2) Å] and 2 [2.314(2)
and 2.306(2) Å] are rather similar to those found in related com-
plexes [Ir(H)2(S)2(PPh3)2]+, S = acetone [average 2.32(2) Å],15
(THF)(H2O) [2.300(3) and 2.297(3) Å],10 thiophene [2.325(2) Å],
tetrahydrothiophene [2.309(3) and 2.303(3) Å],16 and 2,3-dihydro-
benzothiophene [2.319(2) Å].17
Fig. 3 shows an ORTEP view of the complex cation of 8.
Selected bond distances and angles are collected in Table 3. The
geometry around the iridium atom consists of a distorted octahedron
as in complexes 1 and 2, with presumed mutually cis hydrides (not
depicted), mutually trans phosphines, which bend toward the small
hydrides, and the piperidine and carbonyl ligands in cis positions
with respect to each other.
Tothebestofourknowledge, thisisthefirststructurallycharacter-
ized iridium complex containing the piperidine ligand and therefore
we cannot offer comparisons with other closely related structures.
In the somewhat related Rh–pip complex, RhCl(C2H4)(pip)2, the
Rh–N distance Rh–N [2.114(2) Å]18 in slightly longer than the Ir–N
2 9 5 4
D a l t o n T r a n s . , 2 0 0 4 , 2 9 5 2 – 2 9 5 6

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Table
4
Summary of crystal data for [Ir(H)2(1-N-C5H5N)2(PPh3)2]PF6 (1), [Ir(H)2(1-N-C9H7N)2(PPh3)2]PF6 (2) and [Ir(H)2(CO)(1-N-
C5H11N)(PPh3)2]PF6 (8)
1
2·EtOH
8
Empirical formula
M
Crystal system
Space group
C46H42F6IrN2P3
1021.93
Monoclinic
P21/n
C56H52F6IrN2OP3
1178.19
Triclinic
P1
C42H43F6IrNOP3
976.88
Triclinic
P1
a/Å
b/Å
c/Å
/°
15.043(3)
16.905(3)
17.553(4)
90.00
107.55(3)
90.00
4255.7(15)
4
3.312
12.141(2)
14.480(3)
15.414(3)
107.92(3)
99.80(3)
92.72(3)
2526.2(9)
2
9.440(2)
10.724(2)
11.638(2)
64.92(3)
74.76(3)
83.89(3)
1029.6(4)
1
/°
/°
V/Å3
Z
/mm−1
2.802
1.549
3.419
1.576
Dc/g cm−3
1.595
F(000)
2032
1192
486
Reflections collected
Independent reflections
GOF
7772
7455
1.007
9295
8909
1.012
3837
3837
1.156
max/min/e Å−3
R1, wR2 [I > 2(I)]
R1, wR2 (all data)
1.64a/−1.17
0.0481, 0.1096
0.0785, 0.1243
2.61a/−1.16
0.0562, 0.1108
0.0935, 0.1263
5.89b/−5.33
0.0880, 0.2321
0.0902, 0.2382
a Close to the Ir atom. b The first ten peaks (0.9–6 e Å−3) are very close (<1.12 Å) to the Ir and P atoms.
Experimental
Acknowledgements
General
Financial support from FONACIT (Project LAB-9700082), and
Universidad del Zulia for a fellowship to M. R. are gratefully
acknowledged.
All the reactions were carried out under argon using standard
Schlenk techniques. Solvents were distilled from appropriate drying
agents immediately prior to use. [Ir(cod)(PPh3)2]PF6 was prepared
by the method described in the literature.21 Pyridine, piperidine and
isoquinoline were purified by distillation under reduced pressure.
IrCl3·nH2O and all other chemicals were of commercial sources and
References
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were used without further purification. H and 31P NMR spectra
1
were obtained by use of a BrukerAM 300 instrument (300.234 MHz
for 1H and 121.496 MHz for 31P). Detailed experimental procedures
for the synthesis and reactivity studies described above, together
with complete microanalytical and spectroscopic data for all the
new compounds can be found as ESI.†
Single-crystal structure determinations for 1, 2 and 8
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Crystalsofcomplexes1,2and8wereobtainedbyslowconcentration
of a solution of each complex in a dichloromethane–ethanol mixture
at room temperature. The crystal structures of the three compounds
were determined using a Rigaku AFC7S diffractometer provided
with a graphite monochromated Mo-K radiation ( = 0.71073 Å)
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those corresponding to the disordered solvent in structure 2. All
these hydrogen atoms were refined riding on C or N atoms with
a common thermal parameter. The hydrides could not be observed
in any residual electron density map. For the crystal structure of 2
an ethanol molecule was found strongly disordered. Two different
orientation with a refined occupancy factor of 70:30% were
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