Bi- and tri-metallic Rh and Ir complexes containing click derived bis- and tris-(pyrazolyl-1,2,3-triazolyl) N-N′ donor ligands and their application as catalysts for the dihydroalkoxylation of alkynes

Article abstract of DOI:10.1039/c3dt53295j

A series of bi-topic and tri-topic pyrazolyl-1,2,3-triazolyl donor ligands (1a-d; 1a-c = 1,X-bis((4-((1H-pyrazol-1-yl)methyl)-1H-1,2,3-triazol-1-yl)methyl) benzene (X = 2, 3 and 4; o-C₆H₄(PyT)₂, m-C ₆H₄

Full text of DOI:10.1039/c3dt53295j

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Bi- and tri-metallic Rh and Ir complexes
containing click derived bis- and tris-
(pyrazolyl-1,2,3-triazolyl) N–N’ donor ligands
and their application as catalysts for the
dihydroalkoxylation of alkynes†
Cite this: Dalton Trans., 2014, 43,
7540
Khuong Q. Vuong,a,b Chin M. Wong,a Mohan Bhadbhadea,c and
Barbara A. Messerle*a
A series of bi-topic and tri-topic pyrazolyl-1,2,3-triazolyl donor ligands (1a–d; 1a–c = 1,X-bis((4-((1H-
pyrazol-1-yl)methyl)-1H-1,2,3-triazol-1-yl)methyl)benzene (X = 2, 3 and 4; o-C6H4(PyT)2, m-C6H4(PyT)2
and p-C6H4(PyT)2) and 1d = 1,3,5-tris((4-((1H-pyrazol-1-yl)methyl)-1H-1,2,3-triazol-1-yl)methyl)benzene,
1,3,5-C6H3(PyT)3) were conveniently synthesised in ‘one pot’ reactions using the Cu(I) catalysed ‘click’
reaction. Rh(I), Ir(I), Rh(III) and Ir(III) complexes with ligands 1a–d of the general formulae C6H6−n[(PyT)M-
(CO)2]n[BArF4]n (M = Rh, Ir; n = 2, 3; 2a–d; 3a–d) and C6H6−n[(PyT)MCp*Cl]n[BAr4F]n (M = Rh, Ir; n = 2, 3;
4a–d; 5a–d) were synthesised and fully characterised. In solution each of the bi- or tri-metallic com-
plexes 4a–d and 5a–d exists as a mixture of two (4a–c, 5a–c) or three (4d and 5d) diastereomers due to
the presence of a chiral centre at each metal centre in these complexes. The solid state structures of
complexes 2b–c and 4a were determined by single crystal X-ray crystallography and showed that each
bidentate arm of these multitopic ligands coordinates to the Rh or Ir centre in a bidentate fashion via the
pyrazolyl-N2 and 1,2,3-triazolyl N3’ donors. The intermetallic distances in these solid state structures vary
from 8.66 Å to 15.17 Å. These complexes were assessed as catalysts for the dihydroalkoxylation of alkynes
using the cyclisation of 2-(5-hydroxypent-1-ynyl)benzyl alcohol, S, to a mixture of two spiroketals,
2,3,4,5-tetrahydro-spirol[furan-2,3’-isochroman], P1, and 3’,4’,5’,6’-tetrahydro-spiro[isobenzofuran-
1(3H),2’(2H)pyran], P2, as the model reaction. The Rh(I) complexes (2a–d), with the highest TOF of
2052 h−1 for complex 2d, were the most active catalysts when compared with the other complexes under
investigation here. The Ir(I) complexes (3a–d) were moderately active as catalysts for the same transform-
ation. No significant enhancement in catalytic reactivity was observed with the Rh(I) series bi- and tri-
metallic complexes (2a–d) when compared with their monometallic analogues. The bi- and trimetallic
Ir(I) complexes (3a–d) were much more efficient as catalysts for this transformation than their mono-
metallic analogues, suggesting some intermetallic cooperativity. Rh(III), 4a–d, and Ir(III), 5a–d, complexes
were not active as catalysts for this transformation.
Received 22nd November 2013,
Accepted 5th March 2014
DOI: 10.1039/c3dt53295j
www.rsc.org/dalton
aSchool of Chemistry, The University of New South Wales, Kensington, NSW 2052,
Australia
Introduction
bInstitute of Chemical and Engineering Sciences, 1 Pesek Road, Jurong Island,
Singapore 627833. E-mail: b.messerle@unsw.edu.au; Fax: +61-2-93856141;
Tel: +61-2-93854653
The Cu(I) catalysed Huisgen cycloaddition reaction (CuAAC) or
‘click’ reaction between an alkyne and an azide is a highly ver-
satile reaction.1,2 The reaction is a convenient and expedient
way to increase the complexity of organic compounds. The
cX-ray Diffraction Laboratory, Mark Wainwright Analytical Centre, The University of
New South Wales, Kensington, NSW 2052, Australia
†Electronic supplementary information (ESI) available: Synthetic procedures product of the reaction, 1,4-disubstituted 1,2,3-triazole, has
and characterisation data for compounds 1b–d; 2b–d; 3b–d; 4b–d and 5b–d;
been widely used as a linker for biological applications and in
Table S1 provides the νCO and 13C δ of complexes 2a–d and 3a–d; Table S2: the
the modification of surfaces and nanoparticles.2 More recently,
ratios of different stereoisomers of complexes 4a–d; 5a–d. Experimental for X-ray
1,2,3-triazole has also been shown to be a highly versatile sp2
crystallography and crystal data for compounds 1b–c, 2b–c, 4a, 6 and 7 are also
N donor ligand. The 1,2,3-triazolyl moiety has two potential
N-donors N2 and N3, of which the N3 donor is the more
included here. CCDC 966297–966300, 966302, 966304–966305. For ESI and crys-
tallographic data in CIF or other electronic format see DOI: 10.1039/c3dt53295j
7540 | Dalton Trans., 2014, 43, 7540–7553
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common donor and appears to have higher electron donating activity of the corresponding monometallic complex.28,29,33,34
ability than the N2 donor on binding to transition metals.3–5 In this paper, we have used the CuAAC reaction to conveniently
Using ‘click’ chemistry a variety of bi- and tridentate triazolyl synthesise a series of bi- and tri-topic bidentate pyrazolyl-tri-
containing donor ligands and their metal complexes have azolyl donor ligands in ‘one pot’. Rh(I), Ir(I), Rh(III) and Ir(III)
been prepared.3,4 These ‘click’ derived ligands include bi-tri- bi- and trimetallic complexes with these multi-topic ligands
azolyl,6 triazolyl-pyridine,7,8 triazolyl-pyrazolyl,9,10 triazolyl- (Fig. 1) were synthesised, characterised and assessed as cata-
NHC,11 and triazolyl-phosphine12 donors. Metal complexes lysts for the tandem dihydroalkoxylation of alkynes using 2-(5-
containing these ligands have been shown to be active as cata- hydroxypent-1-ynyl)benzyl alcohol (S) as the substrate.
lysts for a number of reactions including ethylene oligomerisa-
tion,7 allylic alkylation,12a,b hydrogenation of alkenes12b and
hydroamination.9,10
Results and discussion
In recent years, there has been a significant increase in the
Synthesis of ligands
number of reports on bimetallic and trimetallic complexes in
Bi- and tri-topic bidentate pyrazolyl-1,2,3-triazolyl donor
ligands were synthesised using the Cu(I) catalysed alkyne–
azide cycloaddition reaction between bis and tris(azidomethyl)-
benzene and two or three molar equivalents of 1-propargyl-
pyrazole to afford the desired multi-topic ligands 1a–d in good
yields (57–88%). The bis and tris(azidomethyl)benzene inter-
mediates were generated in situ by the reaction between
sodium azide and commercially available bis and tris(bromo-
methyl)benzene in dimethylsulfoxide.1,2 The isolation of these
bis and tris(azidomethyl)benzene intermediates was not per-
formed due to the potential danger in handling neat samples
of polyazido organic compounds. The Cu catalyst was removed
from the reaction mixture by multiple washings with saturated
aqueous Na2EDTA (disodium ethylenediaminetetraacetic acid)
until the filtrate turned colourless (Scheme 1).
which the metal centres are tethered together on a bridging
ligand scaffold.13–20 A number of these homo multi-metallic
complexes have been demonstrated to be highly efficient as
catalysts for a variety of chemical reactions including hydro-
formylation,14 olefin polymerization,13 hydroamination18 and
Suzuki–Miyaura coupling.17h,18 Significant enhancement in
catalytic reactivity and selectivity achieved by the multimetallic
catalysts in comparison with their monometallic analogues
has been observed and this enhancement has been attributed
to cooperative interactions between proximate metal centres in
the multi-metallic complexes.15,18,19,21 On the other hand,
there have also been cases where the use of multi-metallic
complexes did not lead to any enhancement in catalytic reac-
tivity in comparison with their monometallic counterparts.
Examples of these ‘unsuccessful’ enhancement attempts
include bimetallic Hoveyda–Grubbs metathesis catalysts
reported by Barbasiewicz et al.20 and bimetallic lanthanide
1
The H NMR spectra of each of the bi and tri-topic biden-
tate pyrazolyl–triazolyl donor ligands 1a–1d contain only one
set of resonances due to protons on the pyrazolyl and 1,2,3-
triazolyl rings as each of the bidentate donors are equivalent
to each other due to the symmetry of these ligands. X-ray
quality crystals of m-C6H4(PyT)2 (1b) and p-C6H4(PyT)2 (1c)
were obtained by re-crystallisation of each of the compounds
from hot methanol and the ORTEP diagrams of three dimen-
sional structures determined in the solid state using X-ray
crystallography are presented in Fig. 2. Crystal data are given
in the ESI (ESI, Table S3†).
hydroamination catalysts reported by the Marks’ group.16
A
full understanding of the cooperative effect remains illusive
but factors such as the intermetallic distance, the rigid three
dimensional geometry of the scaffold as well as the integrity of
the multi-metallic structure during the catalytic cycle are all
thought to play important roles.15,18,19,21 In addition to homo
multi-metallic complexes, a number of hetero-bimetallic com-
plexes which could promote two mechanistically distinct reac-
tions in tandem have been reported in the literature.22
The catalysed tandem dihydroalkoxylation of alkyne diols is
an efficient, atom economical method for the synthesis of O,O-
acetals including O,O-spiroketals which are an important class
Synthesis of metal complexes
Rh(I) and Ir(I) complexes. Cationic bi- and trimetallic Rh(I)
of biologically active compounds.23,24 A number of metal com- complexes C6H6−n[(PyT)Rh(CO)2]n[BAr4F]n (2a–d; Scheme 2(a))
plexes with a variety of metal centres are efficient catalysts for were synthesised by the reaction of the appropriate ligands
the dihydroalkoxylation reaction including complexes of with 0.5 × n molar equivalents of the Rh precursor [Rh(Cl)-
Pd(II),25 Pt(II),26 Rh(I),27–29 Ir(I),28,29 Ir(III),30 Hg(II)31 and Au(I) (CO)2]2 (n is the number of PyT motifs on the ligands 1a–d,
and Au(III).24,32
n = 2 or 3) in dichloromethane followed by a counteranion
We have recently shown that Rh(I) and Ir(I) complexes con- exchange using NaBArF4. The products were collected as very
taining bidentate pyrazolyl–triazolyl donor ligands are effective pale yellow (2c) or yellow solids (2a, 2b and 2d) in very good to
catalysts for the intramolecular hydroamination of alkynes and excellent yields (79–92%).
alkenes,9 and Ir(III) complexes with these ligands are active
The analogous cationic Ir(I) complexes, 3a–d, were prepared
catalysts for tandem C–N/C–C bond formation in the synthesis in a similar fashion (Scheme 2(b)) using the [IrCl(COD)]2
of tricyclic indoles.10 We have also shown that bimetallic Rh(I) (COD = 1,5-cyclooctadiene) precursor in place of [RhCl(CO)2]2.
and Ir(I) complexes containing bis(pyrazolyl) bidentate donor The iridium 1,5-cyclooctadiene intermediates were not isolated
ligands lead to remarkable enhancements in catalytic activity and the COD co-ligand was displaced with carbon monoxide to
for the dihydroalkoxylation of alkyne reactions relative to the form the Ir dicarbonyl complexes C6H6−n[(PyT)Ir(CO)2]n[BArF4]n
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Fig. 1 Bi- and tri-topic bidentate pyrazolyl-1,2,3-triazolyl donor ligands and their rhodium and iridium complexes.
Scheme 1 Synthesis of bi- and tri-topic pyrazole-1,2,3-triazole donor ligands.
(3a–d). The desired products 3a–d were collected as orange
solids in very good yields (75–91%). All of these complexes
(Rh(I), 2a–d and Ir(I), 3a–d) are air stable in the solid state and
in solution.
Complexes 2a–d and 3a–d were fully characterised by NMR
spectroscopy, mass spectrometry, infrared spectroscopy and
1
elemental analyses. In each of the H and 13C NMR spectra of
each of these complexes, only one set of resonances due to the
protons of the metal complexes was observed, as would be
expected from the symmetry of these bi- and trimetallic com-
plexes. The IR spectra (in dichloromethane solution) of these
complexes contain two strong ν(CO) bands of similar intensity,
as is to be expected in the case of dicarbonyl complexes where
two CO substituents are coordinated in a cis manner (Table S1,
ESI†). No notable difference in the ν(CO) values was observed
Fig. 2 ORTEP diagrams of the solid state structures of m-C6H4(PyT)2
(1b) and p-C6H4(PyT)2 (1c) at 40% thermal ellipsoid for the non-hydro-
gen atoms.
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Scheme 2 Synthesis of Rh(I), Ir(I), Rh(III) and Ir(III) complexes.
in each of the Rh (2a–d) and Ir (3a–d) series of complexes and plexes. The observation of two and three separate sets of reso-
also when compared with the values for the corresponding nances where there are two and three metal complexes bound
monometallic complexes9 suggesting that there is little inter- to the scaffold respectively is due to the formation of diastereo-
action between the pairs of metal centres in these bi- and tri- mers where there are two or three chiral centres in the bi-
metallic complexes. In the same way, the chemical shift (δ) metallic and trimetallic complexes. In order to confirm that
values of the 13CO resonances in each of the Rh and Ir series the presence of multiple sets of NMR resonances is due to the
of the complexes 2a–d and 3a–d (in the same solvents) are very presence of groups of diastereomers and not due to the pres-
similar.
ence of different steric conformers, 1H NMR spectra of a
Rh(III) and Ir(III) complexes. Cationic Rh(III) and Ir(III) com- sample of m-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4c) in CDCl2CDCl2
plexes C6H6−n[(PyT)M(Cp*)Cl]n[BArF4]n (M = Rh, 4a–d and M = were acquired over a range of temperatures (235 K to 355 K) in
Ir, 5a–d, Scheme 2(c)) were synthesised by the reaction of the 10° intervals. No significant change either in the ratios of the
bi- or tri-topic ligand (1a–d) with the metal precursor intensities or the chemical shifts of the two sets of resonances
[MCp*Cl2]2 (M = Rh or Ir) in dichloromethane, followed by a attributed to the two metal complex substituents was observed
counteranion exchange with NaBArF4. The desired metal com- over this temperature range, confirming that the presence of
plexes 4a–d and 5a–d were collected as air stable orange (Rh) different sets of resonances arises from the chirality of the
or yellow (Ir) solids in good to excellent yields (73–95%). These individual metal complex substituents.
complexes were also found to be stable in solution (dichloro-
The ratios of the diastereoisomers in these complexes (as
methane or acetone). All of the complexes 4a–d and 5a–d were determined by integration of the 1H NMR spectra at room
fully characterised by NMR spectroscopy, mass spectrometry temperature) are summarised in Table S2 (ESI†). In the case of
and elemental analysis.
the bimetallic complexes, four diastereomers are expected; two
The chemical shifts of the H and 13C resonances of com- of which are pairs of enantiomers which will pairwise give rise
plexes C6H6−n[M(PyT)(Cp*)Cl]n[BArF4]n (M = Rh, 4a–d or Ir, to identical chemical shifts in the NMR spectra. A close to
5a–d) are similar to those reported for the analogous mono- 1.0 : 1.0 ratio of the two pairs of diastereomers formed was
metallic complexes [M(PyT)(Cp*)Cl][BArF4] (M = Rh or Ir).10 observed for all of the bimetallic complexes containing two
However, due to the fact that each of the metal centres in com- chiral centres; however, an exact 1.0 : 1.0 ratio was only
plexes 4a–d and 5a–d is chiral, two (4a–c and 5a–c) and three observed for the pair of diastereomers formed for p-C6H4[(PyT)-
1
(4d and 5d) sets of resonances were observed for the H and MCp*Cl]2[BArF4]2 (M = Rh, 4c and M = Ir, 5c) where the two
1
13C resonances of the cationic fragment in each of the com- metal centres are the furthest apart. In the case of the trimeric
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Fig. 3 Section of the 1H–1H NOESY spectrum of o-C6H4[(PyT)Rh(Cp*)Cl]2[BAr4F]2 (4a) in (a) acetone-d6 showing the exchange cross-peaks (in red
squares) between resonances due to protons of two magnetically different diastereomers (I1 and I2) and (b) in dcm-d2 not showing any exchange
cross-peaks.
complexes, 8 diastereomers could form; however, by symmetry diastereomeric ratios was observed upon prolonged storage
only three different sets of NMR resonances would be expected in solution at room temperature, specifically for samples
in an ideal ratio of 1 : 2 : 1. The observed ratios of formation of of o-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4a) in dcm-d2 and in
the groups of diastereomers of the trimeric complexes by NMR acetone-d6.
were all close to 1.0 : 2.0 : 1.0, as expected by symmetry. The
Two possible mechanisms for the epimerization process at
fact that the relative amount of diastereomers formed varies the metal centres are proposed (Fig. 4(a) and (b)). In the first
from the expected 1 : 1 (for dimeric complexes) and 1 : 2 : 1 (for case (Fig. 4(a)), the epimerization involves intermolecular
trimeric complexes) suggests that upon coordination of a halogen exchange, with initial de-coordination of the Cl−
MCp*Cl motif to a set of pyrazolyl–triazolyl donors, the newly donor from the metal centre to form a 16e− [(PyT)MCp*]2+
formed intermediate complex may have a diastereo-selective intermediate which could be either planar or pyramidal. The
‘directing effect’ on the coordination of the next metal precur- re-coordination of the Cl− to the opposite side of the complex
sor fragment to the remaining ‘vacant’ ligand donor site(s). if the [(PyT)MCp*]2+ intermediate is planar, or after inversion
This stereo-directing effect could be attributed to the steric if the intermediate is pyramidal, leads to the epimerization of
interactions between the newly formed complex and the the metal centre. In the second case (Fig. 4(b)) the de-coordi-
approaching Cp*M fragment, both of which have the bulky nation-rotation followed by re-coordination of one arm of the
Cp* moiety. However, the variation from the expected ratio
could also be due to the epimerization of the chiral metal
centres leading to equilibrium between diastereomers particu-
larly in coordinating solvents (see below).
1
The H–1H NOESY spectra of complexes 4a–d and 5a–d in
acetone-d6 contain exchange cross-peaks between resonances
due to protons of magnetically different diastereomers (Fig. 3).
Analogous exchange cross-peaks were not observed in the
1H–1H NOESY spectra of similar complexes when the spectra
were acquired in dichloromethane-d2. The 1H–1H NOESY
spectra of the o-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4a) were
acquired in both acetone-d6 and dcm-d2. Exchange cross-peaks
were observed only when the spectrum was acquired in
acetone-d6. This observation indicates that the chiral metal
centres in these complexes epimerize constantly in coordinat-
ing solvents such as acetone-d6. However, the diastereomers
are in dynamic equilibrium with each other and no change in
Fig. 4 Proposed epimerization processes at the chiral metal centres of
4a–d and 5a–d (Cp* is considered as a single donor).
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PyT donor ligand is invoked. In each case, the vacant coordi-
nation site which appears during the de-coordination of either
the Cl− or one arm of the N–N donor is likely to be stabilised
by a coordinating solvent such as acetone-d6. The Cl− exchange
mechanism (Fig. 4(a)) has been proposed by Carmona and
Davies in their studies of similar Cp*M (M = Rh, Ir) com-
plexes.35,36 We have previously observed the high lability of
N–N donor ligands such as bis(pyrazolyl)methane in rhodium
and iridium complexes which supports the second case
(Fig. 4(b)).37 In the absence of further studies each of the pro-
posed mechanism is equally valid.
Single crystal solid state structures. X-ray quality crystals of
complexes m-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2b), p-C6H4[(PyT)Rh-
(CO)2]2[BArF4]2 (2c) and o-C6H4[(PyT)RhCp*Cl]2[BAr4F]2 (4a) were
obtained by layering a concentrated dichloromethane solution
with n-pentane. The ORTEP depictions of the solid state struc-
tures of the cationic fragments of 2b and 2c, and 4a are shown
in Fig. 5 and 6 respectively. Table 1 gives the selected bond
lengths, bond angles and metal–metal distances of the solid
state structures of complexes 2b, 2c and 4a. The crystallo-
graphic data for these structures obtained by single crystal
X-ray analysis are provided in the ESI (Table S4†). During
various attempts to obtain X-ray quality crystals of complexes
1,3,5-C6H3[(PyT)RhCp*Cl]3[BArF4]3 (4d) and m-C6H4[(PyT)-
IrCp*Cl]2[BArF4]2 (5b) from pure samples of 4d and 5b, we
obtained some additional yellow–orange plates and yellow
cubic crystals respectively which were found to have the bi-
metallic bridged structure [Cp*M(μ-Cl)3MCp*][BArF4] with M =
Rh (6) or Ir (7) respectively. The ORTEP depictions of the solid
Fig. 6 ORTEP depiction of the cationic fragment of the single crystal
X-ray structure of o-C6H4[(PyT)RhCp*Cl]2[BArF4]2 (4a) at 40% thermal
ellipsoid for the non-hydrogen atoms.
Table 1 Selected bond lengths (Å), bond angles (°) and intermetallic
distances (Å)a of the inner coordination spheres of m-C6H4[(PyT)Rh-
(CO)2]2[BAr4F]2 (2b), p-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2c) and o-C6H4[(PyT)-
Rh(Cp*)Cl]2[BArF4]2 (4a)
Complex
2b
2c
4a
Bond lengths (Å)
M–N(Pz)
M–N(Tz)
2.075(3)
2.072(4)
1.856(4)
1.869(6)
—
2.078(3)
2.065(3)
1.868(4)
1.869(4)
—
2.109(4)
2.097(3)
—
—
2.409(1)
1.770
M–CO (trans to Pz)
M–CO (trans to Tz)
M–Cl
M–C*b
—
—
Bond angles (°)
N(Pz)–M–N(Tz)
N(Tz)–M–CO (trans to Pz)
CO (trans to Pz)–M–CO (trans to Tz) 89.0(2)
CO (trans to Tz)–M–N(Pz)
N(Tz)–M–Cl
Cl–M–N(Pz)
87.4(1)
90.2(2)
84.9(1)
94.6(1)
88.5(2)
92.0(1)
—
84.7(1)
—
—
—
88.9(1)
86.2(1)
93.6(2)
—
—
—
M–M distance (Å)
M–M
13.275(1) 15.171(4) 8.6641(6)
a Standard deviations in the least significant figures are given in
parentheses. b C* is the centroid of the Cp* ring.
state structures and crystal data for complexes 6 and 7 are
given in Fig. S1 and Table S3 (ESI†). The pathways leading to
the formation of 6 and 7 are not clear.
In the solid state, the pyrazolyl–triazolyl bidentate donor
coordinates to the metal centre via the pyrazolyl-N2 and tri-
azolyl-N3′ atoms to form 6-membered metallocycles which
adopt distorted boat conformations (Fig. 5, 6). The cationic
Rh(I) (2b and 2c) complexes adopt the expected square
planar coordination around the metal centre. The coordi-
nation around the Rh(III) centre in complex 4a has a piano
stool geometry as is normally observed for complexes of this
nature. The N–M–N bite-angles in these complexes range from
84.1° to 87.4° which are similar to those observed in analogous
monometallic Rh/Ir complexes previously reported by us9,10
and literature values for Rh/Ir complexes with N–N donor
Fig. 5 ORTEP depictions of the cationic fragments of the single crystal
X-ray structures of m-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2b) and p-C6H4[(PyT)-
Rh(CO)2]2[BArF4]2 (2c) at 40% thermal ellipsoid for the non-hydrogen
atoms.
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ligands.38 The M–N (M = Rh, Ir) bond lengths in complexes 3′,4′,5′,6′-tetrahydro-spiro[isobenzofuran-1(3H),2′(2H)pyran].
2b–c and 4a did not show any significant variation from other During the course of the catalysed reaction, a portion of the P2
M–N bond lengths reported in the literature.9,10,38 In the solid formed isomerised to P1 so that the molar ratio of P1 : P2
state structure of o-C6H4[(PyT)RhCp*Cl]2 (4a) the absolute increased as the reaction progressed, and after complete con-
stereochemistry at the metal centres is (R,R). The stereo- version of S the isomerisation continued until equilibrium
chemistry observed here is of course not a reflection of the between P1 and P2 was reached (Table 2).
stereochemistry of the bulk solid as only a single crystal was
selected from each of the complexes for X-ray diffraction ligands [Rh(PyT)(CO)2][BArF4], C6H6−n[Rh(PyT)(CO)2]n[BAr4F]n
analysis. (n = 2 or 3; 2a–d) were the most active amongst all the com-
Table 2 shows that Rh(I) complexes with dicarbonyl co-
The X-ray structure of 4a (Fig. 6) shows a folded structure plexes assessed here for the dihydroalkoxylation of S to a
where the two metal centres are quite close to each other mixture of P1 and P2 (entries 1–5) with a TOF (calculated at
(8.66 Å). One factor which could contribute to this observed the point of 50% conversion of the substrate) of 2052 h−1
folding is the interaction between the Rh–Cl⋯H (triazole) recorded for the trimetallic complex 2d. The monometallic
atoms in the structure of 4a (Rh2, Cl1B and H5A′ atoms, Rh– complex [Rh(PyT)(CO)2][BArF] (Table 1, TOF = 770 h−1) is
Cl⋯H distance = 2.750(1) Å and Rh–Cl–H angle = 102.93(4)°). slightly less reactive than the similar complex with the bis-
This interaction in 4a can be classified as hydrogen bonding (1-pyrazolyl)methane donor, bpm, [Rh(bpm)(CO)2][BArF4] (TOF
according to the requirements that (i) the H–Cl distance is less of 961 h−1).28a The bi- and tri-nuclear Rh(I) complexes C6H6
than the sum of van der Waals radii for neutral H and Cl −n[Rh(PyT)(CO)2]n[BArF4]n (n = 2 or 3; 2a–d) did not show any
atoms (2.95 Å) and that (ii) the M–Cl⋯H angle is in between significant cooperativity between metal centres during cata-
90 and 130°.39 However it is well accepted that solid state lysis, with small cooperativity indices between −0.3 and 0.4
structures can arise from a large number of intra and inter- (calculated using literature methods).28b,40
molecular forces. A thorough analysis of these forces is clearly
beyond the scope of this paper.
The Ir(I) dicarbonyl complexes [Ir(PyT)(CO)2][BArF4], C6H6−n
-
[Ir(PyT)(CO)2]n[BArF4]n (n = 2 or 3; 3a–d), were found to be less
active catalysts for the cyclisation of S to P1 and P2 (Table 2,
entries 6–10) than their Rh analogues, [Rh(PyT)(CO)2][BArF4]
and 2a–d (entries 1–5). The TOF values obtained when using
these complexes as catalysts varied significantly, from 38 to
489 h−1. The TOF value determined for the monometallic
complex [Ir(PyT)(CO)2][BArF4] is significantly lower than that of
the analogous Ir(I) complex containing the bis(1-pyrazolyl)-
methane (bpm) donor [Ir(bpm)(CO)2][BArF4] (TOF = 374 h−1).28a
In contrast to the catalytic reactivities observed in the Rh
Catalysis: catalysed dihydroalkoxylation of alkynes
A selection of the homo-, bi- and trimetallic Rh or Ir complexes
2–5 were assessed as catalysts for the dihydroalkoxylation of
alkynes using 2-(5-hydroxypent-1-ynyl)benzyl alcohol (S) as the
substrate (Table 2). As has previously been reported with this
reaction, when catalysed by Rh(I) and Ir(I) complexes,27–29,34
a
mixture of two spiroketal products P1 and P2 was formed with
P1 = 2,3,4,5-tetrahydro-spirol[furan-2,3′-isochroman] and P2 =
Table 2 Catalysed cyclisation of (5-hydroxypent-1-ynyl)benzyl alcohol (S) with mono-, bi- and trimetallic Rh and Ir complexesa
Entry
Catalyst
TOFb (P1 : P2 ratio at 50% conv.)
Final conversion, % (h, P1 : P2)
Coop. index
1
2
3
4
5
6
7
8
[Rh(PyT)(CO)2][BArF4]
770 (2.0 : 1.0)
1534 (2.0 : 1.0)
1736 (1.9 : 1.0)
1840 (1.6 : 1.0)
2052 (1.7 : 1.0)
38 (1.5 : 1.0)
489 (1.1 : 1.0)
284 (1.1 : 1.0)
299 (1.0 : 1.5)
422 (1.0 : 1.2)
3
≥98 (0.53, 2.7 : 1.0)
≥98 (0.67, 2.1 : 1.0)
≥98 (0.72, 2.2 : 1.0)
≥98 (0.20, 2.2 : 1.0)
≥98 (0.50, 2.0 : 1.0)
97 (8.4, 2.2 : 1.0)
98 (1.5, 3.4 : 1.0)
97c (2.7, 1.3 : 1.0)
≥98 (≤4.5, 1.3 : 1.0)
100 (≤19.5, 1.8 : 1.0)
51 (17, 25 : 1.0)
—
o-C6H4[Rh(PyT)(CO)2]2[BArF4]2 (2a)
m-C6H4[Rh(PyT)(CO)2]2[BArF4]2 (2b)
p-C6H4[Rh(PyT)(CO)2]2[BArF4]2 (2c)
1,3,5-C6H3[Rh(PyT)(CO)2]3[BArF4]3 (2d)
[Ir(PyT)(CO)2][BArF4]
0.0
0.3
0.4
−0.3
—
10.8
5.5
5.9
8.1
—
o-C6H4[Ir(PyT)(CO)2]2[BArF4]2 (3a)
m-C6H4[Ir(PyT)(CO)2]2[BArF4]2 (3b)
p-C6H4[Ir(PyT)(CO)2]2[BArF4]2 (3c)
1,3,5-C6H3[Ir(PyT)(CO)2]3[BArF4]3 (3d)
[Rh(PyT)(Cp*)Cl][BArF4]
9
10
11
12
13
14
m-C6H4[Rh(PyT)(Cp*)Cl]2[BArF4]2 (4b)
[Ir(PyT)(Cp*)Cl][BArF4]
n/a
n/a
n/a
34 (16.5, 24 : 1.0)
2 (20, 16.0 : 1.0)
22 (16, 9.0 : 1.0)
n/a
n/a
n/a
m-C6H4[Ir(PyT)(Cp*)Cl]2[BArF4]2 (5b)
a Catalysed reactions were conducted in a Young’s NMR tube with 0.6 mL of C2D2Cl4 and [S] = 0.30 0.01 M. b TOF (h−1) = (moles of products/
moles of catalyst)/time (h) at the point of 50% conversion of the substrate to products P1 and P2. c 100% conversion reached at ≤7.0 h (P1 : P2 =
3.0 : 1.0).
7546 | Dalton Trans., 2014, 43, 7540–7553
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series of complexes (Table 2, entries 1–5), significant enhance- co-operativity between metal centres was seen for the bi- and
ment in reactivity was observed for the bi- and trimetallic trimetallic Rh(I) complexes with pyrazolyl–triazolyl N,N′-donor
complexes 3a–d, when compared with their monometallic ligands (PyT) under investigation here (2a–d, Table 2). Simi-
analogues. The cooperativity indexes were calculated to be larly, whereas the analogous Ir(I) complexes based on the bis-
greater than 5, with an index as high as 10.8 observed for the (1-pyrazolyl)methane donor ligands were less effective catalysts
ortho-bimetallic Ir complex 3a, possibly due to the closer for the dihydroalkoxylation reaction under consideration here
arrangement of the two Ir centres in this complex when com- than their Rh(I) counterparts, with TOF ranging from 374 h−1
pared with complexes 3b–d. The fact that the Ir series of com- to 2468,28b the Ir complexes with bis(1-pyrazolyl)methane
plexes shows enhancement of catalytic activity when multi- donor ligands28b were again much more efficient than the ana-
metallic complexes are used whereas the Rh series does not logous Ir(I) catalysts (3a–c) presented here. The intermetallic
show this enhancement is surprising, and will be a part of our cooperativity observed previously for the Ir(I) complexes with
ongoing computational and mechanistic investigations into bis(1-pyrazolyl)methane donor ligands was much lower than
understanding the intermetallic cooperativity for dihydro- those observed here for the complexes with the PyT ligands.
alkoxylation.
These differences between the complexes containing the PyT
Table 3 lists the efficiencies of some of the most effective dinitrogen donor ligands and the bis(1-pyrazolyl)methane
catalysts reported to date for the dihydroalkoxylation reaction donor ligands can be largely attributed to the difference in the
of 2-(5-hydroxypent-1-ynyl)benzyl alcohol (S) as the model sub- nature of the ligand donors, where the PyT ligand system con-
strate. Monobimetallic Rh(I) dicarbonyl complexes with bis(1- tains a triazolyl N-donor in place of one of the pyrazolyl
pyrazolyl)methane donor ligands28b,29 (8–10) have TOFs for the N-donors. The triazolyl-N′3 donor is a somewhat stronger
reaction that are between 2–5 fold greater than those found donor than the pyrazolyl-N donor and this is likely to be the
here for the analogous Rh bimetallic complexes containing the cause for the decrease in catalytic reactivity of the complexes
pyrazolyl-triazolyl N,N′-donor ligands (2a–d) under similar con- containing the pyrazolyl–triazolyl donor ligand, PyT, when
ditions. Additionally, significant intermetallic co-operativities compared with analogous complexes containing bis(1-pyrazo-
were observed for complexes 8–10, with calculated cooperativity lyl)methane ligands.9 A similar effect has been previously
indexes of between 2.8 and 7.9 and, in contrast, no significant observed by us in the case of catalyzed dihydroalkoxylation
Table 3 Comparison of the efficiency of some representative metal complexes in the catalysed dihydroalkoxylation of alkynediol S to form a
mixture of spiroketal products P1 and P2
Complexes
ta (h)
TOFb (h−1
)
Coop. indexc
Reference
[Rh(bpm)(CO)2][BArF4]
[Rh2(CO)4(Lm)][BArF4]2 (8)
[Rh2(CO)4(LAnt)][BArF4]2 (9)
[Rh2(CO)4(LDib)][BArF4]2 (10)
Ir(III) hydride (11)
0.22
0.06
0.08
0.99
5.0d
72e
961
—
28b
28b
28b
29
30a
32a
5988
9522
4597
—
4.2
7.9
2.8
—
Au–carbene (12)
440 000f
—
a Time at >98% total conversion, reactions in C2D2Cl4 at 100 °C. b TOF = (moles of products/moles of catalyst)/time (h) at 50% conversion.
c Calculated using literature methods.28b,40 d Reaction at 60 °C in CDCl3, 85% isolated yield. e 33% conversion at 72 h. f Calculated over the
reaction time of 72 hours, in CD2Cl2 at 40 °C.
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reactions using Rh(I) and Ir(I) complexes with bis(1-methylimid- nances of different diastereomers in 1H–1H NOESY in acetone-
azol-2-yl)methane (bim) and bis(1-pyrazolyl)methane (bpm) d6. The epimerization process observed here could have signifi-
donor ligands as catalysts, where the metal complexes with the cant implications when using chiral Cp*Rh/Cp*Ir complexes
more strongly donating bim donor ligands were not as in asymmetric catalysis. The single crystal X-ray structures of
effective as catalysts as the metal complexes with bpm donor complexes 2b–c and 4a show that each of the bidentate
ligands.28a
ligands coordinates to the metal centre to form a distorted
The Ir(III) hydride complex (11) by Crabtree et al. was also boat conformation. The intermetallic distances in these struc-
reported to be an efficient catalyst for the dihydroalkoxylation tures vary from 8.66 Å to 15.17 Å.
of S; however, as the reaction was performed under somewhat
On testing all of the complexes synthesized here as catalysts
different conditions, a direct comparison is difficult. Clearly, for the dihydroalkoxylation of the alkyne diol 2-(5-hydroxy-
as can be seen in Table 3, the Au(I)–carbene complex (12) pent-1-ynyl)benzyl alcohol (S), the Rh(I) dicarbonyl complexes
reported by Hashmi and co-workers,32a in the presence of 2a–d were the most active catalysts, with a TOF of 2052 h−1
AgSbF6 to remove the chloride donor, is by far the most active observed on using the trimetallic complex 2d. In comparison
complex reported for this transformation with the TOF of with some of the most active catalysts that our group and
greater than 400 000 h−1, using an extremely low catalyst others have developed for the dihydroalkoxylation reaction of
loading of only 0.000001 mol% for each of the Au–carbene alkynes, the catalysts based on pyrazolyl–triazolyl N–N′ donor
complex (10) and the silver salt AgSbF6.
ligands have a lower activity for this transformation, and
The Rh(III) and Ir(III) complexes [Rh(PyT)(Cp*)Cl][BArF4], display different trends in terms of intermetallic cooperativity.
m-C6H4[Rh(PyT)(Cp*)Cl]2[BArF4]2 (4b), [Ir(PyT)(Cp*)Cl][BArF4] The activity trend of the complexes with PyT ligands for the
and m-C6H4[Ir(PyT)(Cp*)Cl]2[BArF4]2 (5b) were not active as cata- cyclisation of S can be grouped as Rh(I) > Ir(I) ≫ Rh(III) > Ir(III).
lysts for this transformation (Table 2, entries 11–14) and com- The Ir(I) complexes are moderately active whereas the Rh(III)
plete conversion of the alkyne diols S was not achieved in and Ir(III) complexes are ineffective catalysts for promoting the
these reactions. The Rh(III) complexes were more reactive than dihydroalkoxylation reaction under investigation here. Signifi-
analogous Ir(III) complexes assessed here (Table 2, entries cant enhancement in activity was observed on using the multi-
11–14). In the cyclisation of 2-(5-hydroxypent-1-ynyl)benzyl metallic Ir complexes 3a–d as catalysts relative to that of the
alcohol (S) using Rh(III) and Ir(III) complexes here, P1 was monometallic complex for the same reaction, leading to high
formed almost exclusively (with P1 : P2 ratios of up to 25 : 1). levels of intermetallic cooperativity. In contrast, no significant
Recently, Fensterbank and co-workers reported that the Ir intermetallic cooperativity in catalyst activity for the
dimer [Cp*IrCl2]2 is highly effective for the cycloisomerisation dihydroalkoxylation reaction was observed on using the Rh
of homopropargylic diols to O,O-acetals at room tempera- multimetallic complexes 2a–d when compared with their
ture.30b This implies that the N–N′ donor ligands used in this monometallic counterparts.
work might have a detrimental effect on the catalytic reactivity
of the Cp*IrCl fragment for this cyclisation reaction. The
decrease in reactivity could be due to the fact that the N–N′
donor ligands can compete with the substrate for coordination
sites on the metal centre in these Cp*Ir complexes.
Experimental
General consideration
All manipulations of metal complexes and air sensitive
reagents were performed using either standard Schlenk tech-
niques or a nitrogen or argon filled Braun glove-box. Reagents
Conclusions
were purchased from Aldrich Chemical Company Inc. or Alfa
A series of bi- and tri-topic bidentate pyrazolyl–triazolyl donor Aesar Inc. and were used without further purification unless
ligands were conveniently prepared in a one-pot approach otherwise stated. Iridium(III) chloride hydrate and rhodium(III)
using the Cu(I) catalysed alkyne–azide ‘click’ reaction. Homo-, chloride hydrate were obtained from Precious Metals Online,
bi- and trimetallic Rh and Ir complexes of these multi-topic PMO P/L. [RhCl(CO)2]2,41 [IrCl2Cp*]2,42 [RhCl2Cp*]2,42
ligands of the general formulae C6H6−n[(PyT)M(CO)2]n[BArF4]n NaBArF4,43 and 1-propargylpyrazole44 were prepared using lit-
(M = Rh/Ir and n = 2, 3) and C6H6−n[(PyT)MCp*Cl]n[BArF4]n (M = erature methods.
Rh/Ir and n = 2, 3) were also successfully prepared and fully
For the purposes of air sensitive manipulations and in the
characterised. Each of the complexes C6H6−n[(PyT)MCp*Cl]n- preparation of air sensitive complexes, n-pentane and dichloro-
[BArF4]n (M = Rh/Ir and n = 2, 3) exists as a mixture of two (n = methane were dispensed from a PuraSolv solvent purification
2) and three (n = 3) diastereomers and it appears that the rela- system. The bulk compressed gases argon (>99.999%) and
tive position of each bidentate donor arm of the ligands on the carbon monoxide (>99.5%) were obtained from Air Liquide
phenylene scaffold has some influence on the diastereomeric and used as received. Nitrogen gas for Schlenk line operation
ratio. In a coordinating solvent (acetone), the diastereomers comes from in house liquid nitrogen boil-off. Dimethylsulf-
are in exchange equilibrium with each other due to the solvent oxide was dried and stored over activated 4 Å molecular sieves.
assisted epimerization of the chiral metal centre. This was con-
firmed by the observation of exchange peaks between reso- DPX300, DMX400, DMX500 and DMX600 spectrometers oper-
1H and 13C{1H} NMR spectra were recorded on Bruker
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ating at 300, 400, 500 and 600 MHz (1H) respectively and 75,
Elemental analysis, Found: C, 59.63; H, 5.14 and N, 34.81;
100, 125 and 150 MHz (13C) respectively. Unless otherwise Calculated for C20H20N10: C, 59.99; H, 5.03 and N, 34.98%.
stated, spectra were recorded at 25 °C and chemical shifts (δ)
HR-MS (ESI+, MeOH): m/z (%): 423.3333 (100%, [M + Na]+)
are quoted in ppm. Coupling constants (J) are quoted in Hz amu.
1
3
and have uncertainties of 0.05 Hz for H and 0.5 Hz for 13C.
1H NMR (600 MHz, CDCl3): δ 7.51 (d, J = 2.0 Hz, 2H, Pz-
1H and 13C NMR chemical shifts were referenced internally to H5), 7.50 (d, J = 2.0 Hz, 2H, Pz-H3), 7.39 (s, 2H, Tz-H5′), 7.36
residual solvent resonances. Deuterated solvents were pur- (m, 2H, Ar-H3 and H6), 7.20 (m, 2H Ar-H4 and H5), 6.25
chased from Cambridge Stable Isotopes and used as received. (apparent t, 2H, Pz-H4), 5.56 (s, 4H, Pz-NCH2), 5.40 (s, 4H, Pz-
Air sensitive NMR samples were prepared in an inert gas glove- NCH2) ppm.
3
box or by vacuum transfer of deuterated solvents into NMR
13C{1H} NMR (150 MHz, CDCl3): δ 144.21 (Tz-C4′), 139.96
tubes fitted with a Young’s Teflon valve. For air sensitive NMR (Pz-C3), 133.13 (ipso-C of C6H4), 130.56 (C4 and C5 of C6H4),
samples CD2Cl2 and CDCl3 were distilled over calcium 130.05 (C3 and C6 C6H4), 129.64 (Pz-C5), 106.25 (C4), 51.40
hydride. Acetone-d6 was distilled from calcium sulfate.
(Tz-NCH2), 47.41 (Pz-NCH2) ppm.
Infrared spectra were measured using a Nicolet 380 Avatar
FTIR spectrometer of solutions in dichloromethane. Melting
points were measured using Stanford Research Systems Opti-
Synthesis of Rh(CO)2 complexes
melt melting point apparatus in glass capillaries and are un- The synthesis of o-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2a) is presented
corrected. Microanalyses were carried out at the Campbell here. The syntheses of m-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2b),
Micro-analytical Laboratory, University of Otago, New Zealand p-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2c) and 1,3,5-C6H3[(PyT)Rh-
or at The Research School of Chemistry, Australian National (CO)2]3[BArF4]3 (2d) were conducted in an analogous fashion
University, Canberra, Australia. Mass spectra were acquired and are provided in the ESI.†
using a Thermo LTQ Orbitrap XL located in the Bioanalytical
Synthesis of o-C6H4[(PyT)Rh(CO)2]2[BArF4]2 (2a). Dichloro-
Mass Spectrometry Facility (BMSF). M is defined as the mole- methane (25 mL) was added to a mixture of [Rh(Cl)(CO)2]2
cular weight of the neutral compound of interest or cationic (0.039 g, 0.10 mmol) and o-C6H4(PyT)2 (1a) (0.040 g,
fragment for cationic metal complexes.
0.10 mmol) in a Schlenk flask under an atmosphere of argon.
The yellow solution obtained was stirred at room temperature
for 30 minutes. NaBArF4 (0.177 g, 0.20 mmol) was added and
Synthesis of ligands
The syntheses of o-C6H4(PyT)2 (1a) is presented here. The the colour of the reaction solution changed to orange with
syntheses of m-C6H4(PyT)2 (1b), p-C6H4(PyT)2 (1c) and 1,3,5- some cloudy white solid. The reaction mixture was filtered
C6H3(PyT)3 (1d) were conducted in a similar fashion and are through
a pad of Celite and the orange–yellow filtrate
described in the ESI†. was reduced until about 2–3 mL of solution was left. Pentane
Synthesis of o-C6H4(PyT)2 (1a). Dimethylsulfoxide (20 mL) (ca. 40 mL) was added to the filtrate with vigorous stirring and
was added to a Schlenk flask containing sodium azide the thick oil-solid was collected by filtration and washed with
(0.715 g, 11.0 mmol) under an atmosphere of nitrogen. The pentane (3 × 5 mL) and dried in vacuo to afford a yellow solid.
reaction mixture was stirred at room temperature for one hour. Yield: 0.209 g, 86%; m.p. 67–79 °C (melted and then
1,2-Bis(bromomethyl)benzene (1.32 g, 5.00 mmol) was added decomposed).
to the reaction mixture and the slightly yellow reaction mixture
was stirred at room temperature for three days.
Elemental Analysis, Found: C, 43.32; H, 1.88 and N, 5.76.
Calculated for C88H44B2F48N10O4Rh2: C, 43.23; H, 1.81; N,
1-Propargylpyrazole (1.06 g, 10.0 mmol) was added to the 5.73%.
reaction mixture. The reaction mixture was deoxygenated by
HR-MS (ESI, MeOH): m/z (%, assignment): 1581.0396 (10,
placing the flask under vacuum (house vacuum ca. 20 mmHg) [M + BArF4]+), 531.0852 (100, [Ligand + RhCO]+) amu.
and back-filling with nitrogen (×3). Sodium L-ascorbate
(0.400 g, 2.00 mmol) and CuSO4·5H2O (0.125 g, 0.50 mmol,
FT-IR (dcm): ν 2109 (s, ν CO), 2051 (s, ν CO) cm−1
.
1H NMR (600 MHz, acetone-d6): δ 8.62 (s, 2H, Tz-H5′), 8.28
10 mol%) were added and the yellowish brown reaction (s, 2H, Pz-H5), 8.27 (s, 2H, Pz-H3), 7.79 (br m, 16H, ortho-CH
mixture was stirred for two days at room temperature.
of BArF4), 7.67 (br s, 8H, para-CH of BArF4), 7.60 (m, 2H, C6H4-
3
The reaction mixture was poured into a conical flask con- H3 & H6), 7.56 (m, 2H, C6H4-H4 & H5), 6.71 (apparent t, J =
taining aqueous Na2EDTA (0.025 M, 200 mL) and was stirred 2.5 Hz, 2H, Pz-H4), 6.24 (s, 4H, Tz-NCH2), 5.90 (s, 4H,
rigorously for 2 hours. The aqueous solution was extracted Pz-NCH2) ppm.
with dichloromethane (3 × 80 mL). The combined organic
13C{1H} NMR (150 MHz, acetone-d6): δ 183.76 (br d,
layer was washed with saturated aqueous Na2EDTA solution 1JRh−C ∼ 71 Hz, Rh-CO), 162.60 (q, JB–C = 49.4 Hz, ipso-C-B of
(3 × 20 mL), water (2 × 20 mL) and dried over anhydrous BArF4), 147.88 (Pz-C3), 141.96 (Tz-C4′), 136.95 (Pz-C5), 135.55
sodium sulfate, filtered and the solvent was removed in vacuo (ortho-C of BArF4), 133.49 (C6H4 C1 & C2), 132.11 (C6H4 C3 &
to yield a thick oil which solidified upon standing. The crude C6), 131.44 (C6H4 C4 & C5), 130.02 (q, 2JF–C = 30.0 Hz, ipso-C of
product was recrystallised from ethanol–water to afford a very CCF3), 126.50 (Tz-C4′), 125.39 (q, 1J = 272.1, CF3), 118.45 (para-
1
pale cream solid. Yield: 1.41 g, 71%.
C of BArF4), 108.93 (Pz-C4), 53.74 (Tz-NCH2), 46.16 (Pz-NCH2)
m.p. 139–142 °C.
ppm.
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Synthesis of Ir(CO)2 complexes
night. The reaction mixture was filtered through a pad of
Celite, rinsed with dichloromethane (2 × 15 mL) and the fil-
The synthesis of o-C6H4[(PyT)Ir(CO)2]2[BArF4]2 (3a) is presented trate was reduced until approximately
2 mL of solvent
here. The syntheses of m-C6H4[(PyT)Ir(CO)2]2[BArF4]2 (3b), remained. Pentane (25 mL) was added to the reaction mixture
p-C6H4[(PyT)Ir(CO)2]2[BArF4]2 (3c) and 1,3,5-C6H3[(PyT)Ir- and the orange precipitate formed was collected by filtration
(CO)2]3[BArF4]3 (3d) were conducted in an analogous fashion and washed with pentane (2 × 5 mL). Yield: 0.124 g, 93%; m.
and are described in the ESI.†
Synthesis of o-C6H4[(PyT)Ir(CO)2]2[BArF4]2 (3a). Dichloro- mixture of two diastereoisomers, I1 and I2 (I1 : I2 = 1.16 : 1.00).
methane (20 mL) was added to a mixture of o-C6H4(PyT)2 (1a) Elemental Analysis: Found, C, 45.88; H 2.71 and N, 5.10.
p. 98–103 °C (melted and turned red). The product is a
(0.020 g, 0.050 mmol) and [Ir(Cl)(COD)]2 (0.034 g, 0.050 mmol) Calculated for: C104H74B2Cl2F48N10Rh2·CH2Cl2: C, 45.71, H,
in a flask under an atmosphere of argon. The bright yellow 2.78 and N, 5.08%.
solution obtained was stirred at RT for 30 minutes and NaBAr4F
HR-MS (MeOH): m/z (%, assignment): 1809.2349 (100,
(0.090 g, 0.10 mmol) was added. The slightly cloudy yellow [M + BArF4]+), 473.0861 (12, [M]2+) amu.
solution was stirred at RT for 1 hour, filtered through a pad of
1H NMR (acetone-d6, 600 MHz): δ 8.60 (I1, s, 2H, Tz-H5′),
Celite and rinsed with dichloromethane (2 × 15 mL). The com- 8.45 (I2, s, 2H, Tz-H5′), 8.12 (I1, d, 3J = 2.4 Hz, 2H, Pz-H5), 8.04
3
3
bined organic layer was deoxygenated via freeze–pump–thaw (I2, d, J = 2.4 Hz, 2H, Pz-H5), 7.95 (I1, d, J = 2.4 Hz, 2H, Pz-
(×2) and was placed under an atmosphere of carbon monoxide H3), 7.94 (I2, d, 3J = 2.4 Hz, 2H, Pz-H3), 7.79 (I1 + I2, br m,
and stirred overnight. The solvent was reduced to approxi- 16H + 16H, o-CH of BArF4), 7.67 (I1 + I2, br, 8H + 8H, p-CH of
mately 3 mL and pentane (25 mL) was added to the reaction BArF4), 7.46–7.38 (I1 + I2, m, 4H + 4H, C6H4-H), 6.60 (I1, appar-
mixture with vigorous stirring. The yellow solid and thick oil ent t, J = 2.4 Hz, Pz-H4), 6.58 (I2, apparent t, J = 2.4 Hz, Pz-
residue obtained was collected by filtration, washed with H4), 6.27 (I1, d, J = 15.7 Hz, 1H, Tz-NCHH), 6.19 (I2, d, J =
pentane (3 × 5 mL) and dried in vacuo to afford 3a as an 15.5 Hz, 1H, NCHH), 6.14–6.11 (I1 + I2, m, 3H, Tz-NCHH and
3
3
2
2
2
2
orange solid. Yield: 0.098 g, 75%.
m.p. 73–76 °C.
NCHH), 6.04 (I1, d, J = 16.3 Hz, 1H, NCHH), 5.43 (I1, d, J =
16.3 Hz, 1H, Pz-NCHH), 5.40 (I2, d, 2J = 16.2 Hz, 1H, Pz-
NCHH), 1.77 (I2, 15H, CCH3), 1.74 (I1, 15H, CCH3) ppm.
13C{1H} NMR (acetone-d6, 150 MHz): δ 162.60 (I1 + I2, q,
1JB–C = 49.50 Hz, ipso-CB of BArF4), 146.03 (I1, Pz-C3), 145.95
FT-IR (dcm): ν 2099 (s, νCO), 2034 (s, νCO) cm−1
.
Elemental Analysis, Found: C, 40.21; H, 1.76; N, 5.41. Calcu-
lated for C88H44B2F48Ir2N10O4: C, 40.29; H, 1.69; N, 5.34%.
HR-MS (ESI, MeOH): m/z (%, assignment): 1759.1572 (100, (I2, Pz-C3), 141.80 (I1, Pz-C4′), 141.71 (I2, Pz-C4′), 135.91 (I1 +
[M + BArF4]+), 649.1388 (65, [M − Ir(CO)2]+), 448.0471 (28, [M]2+) I2, Pz-C5), 135.55 (br s, o-CH of BArF4), 134.30, 134.05 (I1 + I2,
amu.
ipso-C of C6H4 (last two resonances), 131.53, 130.89, 130.76
2
1H NMR (600 MHz, acetone-d6): δ 8.74 (s, 2H, Tz-H5′), 8.46 (last three resonances, CH of o-C6H4), 130.02 (q, JF–C = 31.8
(d, 3J = 2.3 Hz, 2H, Pz-H3), 8.39 (d, 3J = 2.5 Hz, 2H, Pz-H5), 7.79 Hz, CCF3), 126.59 (I1, Tz-C5′), 126.37 (I2, Tz-C5′), 125.41 (I1 +
(br m, 16H, ortho-CH of BArF4), 7.70 (m, 2H, C6H4-H3 & H6), I2, q, JF–C = 271.5 Hz, CF3), 118.46 (I1 + I2, p-CH of BAr4F),
1
7.67 (br s, 8H, para-CH of BArF4), 7.60 (m, 2H, C6H4-H4 & H5), 108.87 (I1, Pz-C4), 108.80 (I2, Pz-C4′), 98.06 (I1, CCH3 (Cp*)),
6.82 (apparent t, 3J = 2.5 Hz, 2H, Pz-H4), 6.29 (s, 4H, Tz-NCH2), 98.00 (I2, CCH3 (Cp*)), 53.24 (I1 + I2, Tz-NCH2), 45.82 (I1, Pz-
6.00 (s, 4H, Pz-NCH2) ppm.
NCH2), 45.72 (I2, PzNCH2), 9.36 (I1 + I2, CH3) ppm.
13C{1H} NMR (150 MHz, acetone-d6): δ 171.88 (CO), 171.20
1
Synthesis of Ir(Cp*) complexes
(CO), 162.62 (q, JB–C = 49.8 Hz, ipso-C-B of BArF4), 149.08 (Pz-
C3), 141.69 (Tz-C4′), 137.74 (Pz-C5), 135.56 (ortho-C of BArF4), The synthesis of o-C6H4[(PyT)Ir(Cp*)Cl]2[BAr4F]2 (5a) is pre-
133.31 (C6H4 C1 & C2), 132.64 (C6H4 C3 & C6), 131.66 (C6H4 C4 sented here. The syntheses of m-C6H4[(PyT)Ir(Cp*)Cl]2[BArF4]2
2
& C5), 130.04 (q, JF–C = 31.0 Hz, ipso-C of CCF3), 126.88 (Tz- (5b), p-C6H4[(PyT)Ir(Cp*)Cl]2[BArF4]2 (5c) and 1,3,5-C6H3[(PyT)-
1
C4′), 125.38 (q, JF–C = 270.3, CF3), 118.47 (para-C of BArF4), Rh(Cp*)Cl]3[BAr4F]3 (5d) were conducted in an analogous
108.93 (Pz-C4), 54.13 (Tz-NCH2), 46.52 (Pz-NCH2) ppm.
Synthesis of Rh(Cp*) complexes. The synthesis of
fashion and are described in the ESI.†
Synthesis of o-C6H4[(PyT)Ir(Cp*)Cl]2[BArF4]2 (5a). Dichloro-
o-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4a) is presented here. The methane (15 mL) was added to a mixture of o-C6H4(PyT)2 (1a,
syntheses of m-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4b), p-C6H4- 0.020 g, 0.050 mmol) and [IrCp*Cl2]2 (0.040 g, 0.050 mmol) in
[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4c) and 1,3,5-C6H3[(PyT)Rh(Cp*)- a flask and the yellow reaction mixture was stirred for
Cl]3[BArF4]3 (4d) were conducted in an analogous fashion and 30 minutes at RT. NaBArF4 (0.090 g, 0.10 mmol) was added and
are described in the ESI.†
the cloudy yellow solution was stirred for 1 hour at RT. The
Synthesis of o-C6H4[(PyT)Rh(Cp*)Cl]2[BArF4]2 (4a). Dichloro- reaction mixture was filtered through a pad of Celite and
methane (20 mL) was added to a mixture of [Rh(Cp*)Cl2]2 rinsed with dichloromethane (2 × 15 mL). The combined
(0.031 g, 0.05 mmol) and o-C6H4(PyT)2 (1a, 0.020 g, organic layer was reduced to approximately 2 mL and pentane
0.05 mmol) in a flask under argon. The orange solution (20 mL) was added with rigorous stirring. The yellow thick oil
obtained was stirred for 30 minutes and NaBArF4 (0.090 g, and solid formed were collected by filtration, washed with
0.10 mmol) was added to the reaction mixture. The slightly pentane (2 × 5 mL) and dried in vacuo. o-C6H4[(PyT)Ir(Cp*)-
orange reaction mixture was stirred under argon at RT over- Cl]2[BArF4]2 (5a) was collected as a light yellow solid. Yield:
7550 | Dalton Trans., 2014, 43, 7540–7553
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0.103 g, 73%; m.p. 102–106 °C. The product is a mixture of 5.19 (doublet or broad) for P2) relative to the substrate reso-
1
two diastereoisomers I1 and I2, I1 : I2 = 1.10 : 1.00.
nance (singlet at 4.84 ppm) in the H NMR spectra. The turn-
Elemental analysis; found: C, 43.72; H, 2.69 and N, 5.11; over frequency (TOF) was calculated as the number of moles of
calculated for C104H74B2Cl2F48Ir2N10: C, 43.79; H, 2.61 and N, product/moles of catalyst h−1 and was calculated at the point
4.91%.
of 50% conversion of the substrate.
HR-MS (MeOH): m/z (%, assignment): 1989.3486 (47, [M +
BArF4]+), 563.1397 (100, [M]2+) amu.
1H NMR (acetone-d6, 600 MHz): δ 8.63 (I1, s, 2H, Tz-H5′),
8.55 (I2, s, 2H, Tz-H5′), 8.14 (I1, d, 3J = 2.4 Hz, 2H, Pz-H5), 8.09
Acknowledgements
We would like to acknowledge financial support from the Aus-
tralian Research Council and The University of New South
Wales, Australia. We thank Drs Gavin Edwards and Jason
Harper for the discussion on stereochemistry. The use of
beamline time at the Australian Synchrotron is also gratefully
acknowledged.
3
3
(I2, d, J = 2.4 Hz, 2H, Pz-H5), 7.90 (I1, d, J = 2.3 Hz, 2H, Pz-
H3), 7.89 (I2, d, 3J = 2.3 Hz, 2H, Pz-H3), 7.79 (I1 + I2, br m,
16H + 16H, o-CH of BArF4), 7.67 (I1 + I2, br s, 8H + 8H, p-CH of
BArF4), 7.48–7.37 (I1 + I2, m, 4H + 4H, CH of C6H4), 6.65 (I1,
apparent t, 3J = 2.4 Hz, 2H, Pz-H4), 6.63 (I2, apparent t, 3J = 2.4
Hz, 2H, Pz-H4), 6.28–6.11 (I1 + I2, m, 6H + 6H, CH2 (AB
systems)), 5.29 (I1, d, 2J = 15.8 Hz, 2H, Pz-NCH), 5.28 (I2, d,
2J = 16.1 Hz, 2H, Pz-NCH), 1.73 (I1, s, 15H, CH3), 1.70 (I2, s,
15H, CH3) ppm.
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