Highly versatile heteroditopic ligand scaffolds for accommodating group 8, 9 & 11 heterobimetallic complexes

Article abstract of DOI:10.1039/c7dt02854g

Two highly versatile xanthene scaffolds containing pairs of heteroditopic ligands were found to be capable of accommodating a range of transition metal ions, including Au(i), Ir(i), Ir(iii), Rh(i), and Ru(ii) to generate an array of heterobimetallic complexes. The metal complexes were fully characterised and proved to be stable in the solid and solution state, with no observed metal-metal scrambling. Heterobimetallic complexes containing the Rh(i)/Ir(i) combinations were tested as catalysts for the two-step dihydroalkoxylation reaction of alkynediols and sequential hydroamination/hydrosilylation reaction of alkynamines.

Full text of DOI:10.1039/c7dt02854g

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ISSN 1477-9226
PAPER
Joseph T. Hupp, Omar K. Farha et al.
Efficient extraction of sulfate from water using
framework
a Zr-metal–organic
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Highly Versatile Heteroditopic Ligand Scaffolds for
Accommodating Group 8, 9 & 11 Heterobimetallic Complexes
Mark R. D. Gatus,ab Mohan Bhadbhadec and Barbara A. Messerleab*
Received 00th January 20xx,
Accepted 00th January 20xx
Two highly versatile xanthene scaffolds containing pairs of heteroditopic ligands were found to be capable of
accommodating a range of transition metal ions, including Au(I), Ir(I), Ir(III), Rh(I), and Ru(II) to generate an array of
heterobimetallic complexes. The metal complexes were fully characterised and proved to be stable in the solid and
solution state, with no observed metal-metal scrambling. Heterobimetallic complexes containing the Rh(I)/Ir(I)
combinations were tested as catalysts for the two-step dihydroalkoxylation reaction of alkynediols and sequential
hydroamination/hydrosilylation reaction of alkynamines.
DOI: 10.1039/x0xx00000x
www.rsc.org/
synergistic effects between the metal centres can occur during
catalytic reactions and enhance the efficiency of catalysis. One
of the most significant influences on these synergistic effects is
Introduction
Bimetallic complexes, particularly heterobimetallic
complexes are an increasingly important avenue of research
primarily due to their potential as highly effective and versatile
catalysts.1 Heterobimetallic complexes have been shown to
exhibit unique catalytic activity and selectivity towards organic
transformations which are often not achieved using
arranging the two metal centres in close proximity to one
another with restricted deviation from the short metal-metal
distance.6 Heterobimetallic complexes containing ligand
architectures with short metal-metal distances that have
structurally constrained ligating sites are finding applications in
many types of catalysed reactions.7 Peris, et al. has
demonstrated the versatility of heterobimetallic complexes at
promoting two-step catalysed reactions whereby the two
different metal sites work cooperatively,; this is particularly
promoted in two-step reactions with different mechanistic
steps.8
monometallic
or
homobimetallic
complexes.1c
Heterobimetallic complexes are used for many interesting
applications such as photo- and chemical switches for catalytic
applications,2 enhanced functional materials such as non-linear
optics,3 and for polymerisation catalysts.4 All of these
heterobimetallic complexes utilise a range of transition metals
and lanthanides allowing investigation of a range of metal-
metal combinations giving rise to unique cooperativity effects
enhancing catalysis reactions.5
One key consideration in the preparation of effective
heterobimetallic complexes is the degree of exchange
occurring between the pairs of metal ions in solution. To
ensure a well-defined system, minimising such intermetallic
exchange is preferable. We have shown previously that metal-
metal exchange in a heterobimetallic system can occur readily
even at room temperature for complexes containing the
bis(pyrazol-1-yl)methane ligand (bpm) (Figure 1).9 The metal-
metal exchange leads to a mixture of species in solution, thus
making it difficult to identify which catalyst species is the most
reactive.10 One approach to avoid metal-metal exchange is to
When describing homo- and heterobimetallic complexes
multiple definitions exist ranging from multinuclear clusters
and solids, enzymatic cofactors, to molecular wires. Of
particular interest are discrete heterobimetallic complexes
defined by organic ligands, which exist as two metal ion single
molecule systems. These systems are of interest due to the
possibility of fine-tuning the ligand architecture by variation of
the scaffold in which the coordinating ligands are tethered. A
well defined scaffold architecture may lead to a beneficial
spatial arrangement of the metal ions in such a way that
use
a heteroditopic scaffold (a scaffold containing two
different ligand moieties) that contains at least one ligand
Figure 1. Metal-metal exchange of a Rh(I)/Ir(I) heterobimetallic complex.
J. Name., 2013, 00, 1-3 | 1
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system capable of binding with sufficient strength to the (BPh4)–
Journal Name
(4) salt (Scheme 1). We were also interested in
chosen metal centre in order to prevent metal-metal exchange coordination chemistry of a bidentate carbene triazole (BzCAT)
occurring. Here we targeted strongly binding -donor NHC ligand donor due to the relative ease of synthesis, similar to
σ
5.
groups as a part of the ligand scaffold. With a heteroditopic This system gives access to other coordination environments
ligand scaffold in hand containing NHC donors, the different for transition metals as well as accommodating a charged Rh(I)
catalytic properties of two different metals can be taken centre as opposed to the neutral Rh(I) centre that is provided
advantage of with the intention that the single catalytic unit by the monodentate carbene ligand.13 We can also gauge
may result in pronounced synergistic properties giving rise to whether there is any change in reactivity of the complex by
far greater activity and selectivity compared to homobimetallic variation of the denticity of the ligand moiety that contains
complexes reported previously.9, 11
Herein, we report the synthesis of a series of new imidazole of
heterobimetallic complexes with different combinations of salt ( ), followed by a [2+3] azide-alkyne cycloaddition with
pairs of group 8 (Ru(II)), group 9 (Rh(I), Ir(I) and Ir(III)) and benzylazide, the proligand imidazolium-triazole bromide salt
group 11 (Au(I)) metals. The coordination chemistry of these ) we
) was formed.14 With the imidazolium-triazole salt (
metals was investigated using the previously reported carried out a salt metathesis reaction with BPh4, isolating the
heteroditopic ligand scaffold containing N-heterocyclic heteroditopic proligand ( ).
carbene ligand donor. Alkylation of the free N-position of
with propargylbromide gave the imidazolium
1
2
(
3
3
a
4
carbene and bis(pyrazole-1-yl)methane ligand.12 Additionally, a
new combination of heteroditopic ligands on a xanthene
scaffold (tXan) containing a bidentate N-heterocyclic carbene-
triazole donor and a bidentate bis(pyrazol1-yl)methane donor
were investigated. Rh(I)/Ir(I) heterobimetallic complexes were
tested as catalysts for the two-step dihydroalkoxylation
reaction and the sequential hydroamination-hydrosilylation
reaction.
Heterobimetalllic Complexes Containing a mixture of Rh(I)
and Ir(I) 11,12, and 14
Selective complexation of the heteroditopic ligands 4 and 5
to generate heterobimetallic combinations of Ir(I) and Rh(I)
proved to be fruitful. Three new heterobimetallic complexes
denoted
[(Rh(CO)2ClLNHC)/(Ir(CO)LBpm)tXan][BPh4]
(
11),
[(Ir(CO)2ClLNHC)/(Rh(CO)LBpm)tXan][BPh4]
[(Rh(CO)2ClLBnCAT)/(Rh(CO)LBpm)tXan][BPh4]
(
12),
14
and
(
)
was
successfully synthesised via a step-wise approach (Scheme 2).
Results and discussion
The two heterobimetallic complexes 11 and 12 containing the
ligand scaffold
equivalent of the metal precursor [M(COD)(
Rh(I) or Ir(I) and COD = 1,5-cyclooctadiene) with the silver
carbene complex (Scheme 2a). These reactions yielded both
the monometallic Rh(I) and Ir(I) carbene complexes and as
bright yellow solids at yields of 92% and 75%, respectively. The
Rh(I) monometallic complex was further reacted with half a
molar equivalent of the metal precursor [Ir(COD)( -Cl)]2
yielding the heterobimetallic complex as a yellow solid at a
5
were synthesized by reacting half a molar
Preparation of Heteroditopic Ligands (3, 4 & 5)
ꢀ
-Cl)]2 (where M =
The preparation of the ligand scaffold (
containing the N-methylimidazolium and bpm moieties (
and the silver carbene complex of ) were carried out using
1), the proligand
5
),
6
5 (6
7
8
the method we reported previously as summarised in Schemes
1 and 2.12
7
Using scaffold
heteroditopic ligand pair containing a bidentate N-heterocyclic
carbene-triazole donor and bidentate bis(pyrazol-1-
) or tetraphenylborate
1 we were also able to synthesise a new
ꢀ
9
a
yield of 79%. The COD coligands of the resultant complex were
yl)methane donor either as a halide (
3
N
Br
N
Br
N
N
N
N
N
N
N
N
N
N
N
N
N
BnN3, NaAsc,
CuSO4
O
O
Br
2-PrOH/H2O (2:1), r.t 48 h
64 %
CH3CN, r.t, 48 h
82 %
3
2
N
N
N
N
N
CH2Cl2
99 %
Na[BPh4]
N
O
N
N
[BPh4]
I
N
N
N
N
N
N
N
N
N
N
N
N
N
1
O
O
CH3I
CH3CN, r.t, 16 h
93 %
5
4
Scheme 1. Synthesis of the two heteroditopic ligands 3/4 and 5 using the xanthene scaffold.
2 | J. Name., 2012, 00, 1-3
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Scheme 2. Synthesis of heteroditopic complexes a) 11 and 12, and b) 14.
then displaced with carbonyl ligands under an atmosphere of
carbon monoxide (CO), yielding the Rh(I)/Ir(I) heterobimetallic
carbonyl complex 11 as a pale yellow solid at a yield of 88 %.
The analogous Ir(I)/Rh(I) heterobimetallic complex was
Table 1. Carbonyl stretching frequencies of complexes 11, 12 and 14
using IR spectroscopy (25 °C)
υ
(CO) (cm-1) (DCM)
Complex
RhNHC IrNHC
Rhbpm
Irbpm
2091
2027
synthesised following the same procedure as that used for 11
,
2091
-
11
12
14
-
however, [Rh(COD)(ꢀ-Cl)]2 was used for the introduction of the
2011
second metal centre and the resultant heterobimetallic
Ir(I)/Rh(I) complex with a COD coligand 10 was carbonylated
without full characterisation of the intermediate (10) with the
COD coligand yielding the Ir(I)/Rh(I) carbonyl complex 12 as a
pale yellow solid, at an overall yield of 54%.
2072
1993
2103
2045
-
-
2088
-
2088
2024
-
2024
addition of half a molar equivalent of [Rh(COD)(
ꢀ
-Cl)]2 yielding
A different approach was required to coordinate Rh(I) to the monometallic complex 13 as a bright yellow solid at a yield
the imidazolium-triazole proligands and 4. Attempts at of 71 % (Scheme 2b). Introduction of the Ir(I) centre at the
introducing Rh(I) to the proligand containing the bromide bpm site and carbonylation of the resultant Rh(I)/Ir(I) complex
counterion by in situ Ag(I) transmetallation were with a COD coligand were carried out sequentially without
unsuccessful leading to a decomposition products. Instead, we isolation of the heterobimetallic Rh(I)/Ir(I) complex with a COD
were able to deprotonate the imidazolium proligand ( coligands in a similar approach to the method used for
containing the BPh4 counterion with sodium ethoxide (NaOEt) complex 12. The Rh(I)/Ir(I) complex 14 with CO coligands was
3
(3)
4
)
followed
by
isolated as a light orange solid at a yield of 51%.
Using 1H and 13C{1H} NMR, and IR spectroscopy it was
established that there was no exchange of the metal centres
between the two ligand binding sites in three heterobimetallic
complexes 11, 12, and 14. This was the expected outcome due
to the strongly binding nature of NHCs to transition metals. In
particular, in the 13C NMR spectra of the three complexes 11
12 and 14 combination of the two spectra of the
,
,
a
heterobimetallic complexes was not observed indicating that
there is no intermetallic exchange (Figure 2a, 2b and 2c).
Similarly, the 13C{1H} NMR spectra of the heterobimetallic
complexes 11 and 12 exhibited almost identical chemical shifts
for the 13C resonances due to the carbene and carbonyl
carbons to those of the equivalent carbon nuclei of the
homobimetallic Rh(I) and Ir(I) complexes for their respective
metal sites that we have previously reported.12 The metal-
carbonyl signals in the solution state FTIR spectra for the three
Figure 2. 13C{1H} NMR spectra of the carbonyl and carbene resonance regions for a)
complex 14, b) complex 11, and c) complex 12.
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Figure 3. ORTEP depictions of the solid state structures of a) the Rh(I)/Ir(I) heterobimetallic complex 9, and b) the Rh(I) monometallic complex 13 at 50 % probability for thermal
ellipsoids. Hydrogen atoms and BPh4 counterions were omitted for clarity.
complexes were also matched with the previously reported
monometallic Rh(I) and Ir(I) half unit analogues of the showed Rh(I) bound to the carbene and N1 of the triazole
heterobimetallic complexes with the exception of the Ir(I) NHC ligand. The rhodacycle existed in distorted boat
As expected the solid state structure of 13 (Figure 3b)
a
half unit as attempts to synthesise this complex have been conformation with the Rh(I) centre bound to the carbene-
unsuccessful thus far (Table 1).11b, 13b, 15
triazole and COD ligands in a distorted square planar geometry
(85.2(2) ). The metal to NHC-Rh(I) (C5-Rh) bond length was
2.049(4) Å which is similar in length to the NHC-Rh(I) bond
(2.035(4) Å) of complex . The bond length between the
triazole nitrogen ( 1) and Rh(I) centre was 2.078(4) Å, and is
Solid-state Structures of Rh(I)/Ir(I) Bimetallic Complex 9 and
the Rh(I) monometallic complex 13
Solid state structures were obtained using X-ray analysis of
°
9
both the Rh(I)/Ir(I) heterobimetallic complex
9 and the Rh(I)
N
monometallic complex 13. The crystals were grown by slow
diffusion of n-pentane into a saturated solution of the
complexes in dichloromethane (Figure 3).
comparable to other reported rhodium(I) complexes
containing the carbene-triazole ligand.13b
In complex
9 (Figure 3a), the rhodium(I) metal centre
Heterobimetalllic Complexes Containing a mixture of
Au(I), and Rh(I) 15 and 16
bound to the NHC ligand exhibited a square planar geometry
whilst the iridium(I) centre coordinated to the COD and bpm
ligands exhibited a distorted square planar geometry (N1-Ir-N2
bond angle of 88.0(1)°
) typical of other Ir(I)bpm complexes.9,
Due to the ability of NHCs to coordinate a vast array of
transition metals, the viability of the NHC or NHC-triazole
ligand for accommodating group 8 and group 11 metals or +III
15a
Additionally, the iridacycle displayed a distorted boat
conformation. The bond length between the carbene carbon
and the rhodium centre (C5-Rh) was 2.035(4) Å and was similar
to the C-Rh bond length of other Rh(I) carbene complexes
reported.16 The intermetallic distance between the two metal
centres (Ir···Rh) was 8.263(2) Å. The length between the two
metals centres in this complex is greater than the ideal 2-5 Å
required for cooperative effects to take place,1a however, this
is a precursor to the tetracarbonyl complex which would have
much less bulky coligands and is therefore not representative
of how the metals will orient themselves particularly during
catalysis when the temperature of the reaction is elevated.
group
9 metals was investigated. The potential for
coordinating a group 9 metal (+I) to the bpm ligand of the
resultant NHC complexes was also investiagted.
Initially, a Au(I) carbene complex was synthesised via
the transmetallation of the Ag(I) complex
6 with AuCl(SMe2)
from which we obtained a solid state structure of the Au(I)
complex 17 (Scheme 3b) containing a terminally bound
chloride attached to the Au(I) (vide infra). Repeated attempts
to synthesise pure complex 17 was unsuccessful, with the
unreacted silver complex (
17, so we chose instead to deprotonate the imidazolium ring
of the proligand with potassium carbonate followed by
6) difficult to separate from complex
5
The xanthene scaffold is planar with a torsion angle of 4.37(9)°,
addition of AuCl(SMe2) yielding the Au(I) iodide complex 15
(Scheme 2a) as a white solid at a yield of 92%. Rh(I) was then
coordinated to the bpm ligand by reacting 15 with half a molar
with the two metal centres pointing away from one another
on opposite sides of the xanthene scaffold leading to a greater
metal-metal distance, this may have an affect on the catalytic
activity of the complex.
equivalent of [Rh(COD)(ꢀ-Cl)]2, resulting In complex 16 as a
pale yellow solid (81% isolated yield).
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Scheme 3. Synthesis of a) Au(I)/Rh(I) heterobimetallic complex 16, b) Au(I) monometallic complex 17 and the Ir(III)/Rh(I) heterobimetallic complex 19, and c) Ru(II)/Ir(I)
heterobimetallic complex 21.
Variable temperature (VT) NMR experiments revealed that coordination of Au(I) in a linear fashion to the NHC ligand (C1-
the complex (16) was stable up to 60
further or prolonged heating of the mixture resulted in slow centre. The bond lengths between the carbene carbon and
decomposition of the complex. However, the 1H NMR chloride were 1.999(6) and 2.286(2)
respectively which is
°C at which point any Au-Cl, 177.6(2)°) with a terminal chloride bound to the Au(I)
°
spectrum was not sufficiently resolved to be able to similar to other Au(I) carbene complexes reported in the
characterise due to conformational exchange of the ligand literature.17 As was observed for the other two structures
moieties or dissociation of the Cl- coligand. The 1H NMR shown in Figure 3 (
9
and 13), the planarity of the xanthene
spectrum resolved sufficiently at 100 °C where two scaffold of 17 is still intact deviating by only 9.7(1)
conformations of the complex in solution were observed The solid state structure of the heterobimetallic Au(I)/Rh(I)
°
.
existing in a ratio of 1:1, albeit we could not fully characterise complex 16 shows successful coordination of the two metal
the complex before decomposition (see SI for stacked VT 1H centres to the desired ligands. The Rh(I) centre exhibited a
NMR spectra of complex 16).
Unsuccessful attempts were also made to stabilise complex to only one of the pyrazole nitrogen’s (N1) while retaining the
16 by carrying out salt metathesis reactions with OTf, BArF
chloride coligand. The geometry of the Au(I) coordinated to
(tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) and BF4 salts the carbene ligand was linear (C1-Au-I, 178.0(2) ) analogous to
distorted square planar geometry and was found to be bound
4
°
for both complex 15 and 16. As we could not confirm the bulk the Au(I) monometallic complex 17. In this particular case the
sample of complex 16 was completely pure we did not attempt two metal centres of 16 sit on the same face of the xanthene
any catalytic reactions with this complex.
scaffold with an intermetallic distance (Au···Rh) of 5.6865(7) Å.
Solid-State Structures of the Au(I)Cl Monometallic
Complex 17 and the Au(I)/Rh(I) Bimetallic Complex 16
As expected, the solid state structure of the Au(I)
monometallic complex 17 demonstrated successful
Heterobimetalllic Complexes Containing a mixture of
Ru(II), Ir(III), Rh(I) and Ir(I) 18-21
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Figure 4. ORTEP depictions of the solid state structures for a) the Au(I)Cl monometallic complex 17, and b) the Au(I)I/Rh(I) bimetallic complex 16 at 50 % probability for thermal
ellipsoids. Hydrogen atoms were omitted for clarity.
Ir(III) was our next candidate for complexation with the phenyl and triazole rings, and the CH2 group between the
NHC of proligand
5, this was achieved by transmetallation with triazole and NHC rings. Additionally, the carbon resonance of
producing the Ir(III) monometallic the NHC ring bound to Ru(II) centre in the 13C NMR spectra
the Ag(I) complex
6,
1
complex 18 as an orange solid at a yield of 77%. The H NMR appeared at 174.4 ppm (CD2Cl2). We then proceeded to add
spectrum of the complex at room temperature did not provide Ir(I) to the bpm ligand of complex 20 using half of a molar
any structural information, as all proton resonances were equivalent of [Ir(COD)(
extremely broad. We were able to resolve the broad proton Na[BPh4] yielding the heterobimetallic Ru(II)/Ir(I) complex (21
resonances of 18 by variable temperature experiments and as an orange solid at a yield of 78%. Similar to complex 18, the
found that the complex existed as two conformers at 40 C in a methine proton resonance belonging to the bpm ligand of 20
ꢀ-Cl)]2 and one molar equivalent of
)
°
ratio of 2:1. The 1H-1H NOESY spectrum exhibited exchange shifted downfield significantly from 7.7 ppm to 9.0 ppm for 21
correlations between the two different conformers indicating indicative of coordination of Ir(I) to the bpm in addition to the
that there are indeed two conformations of the complex splitting of the COD alkene and alkane proton resonances.
exchanging on the NMR timescale. Complexation of the free
bpm ligand of 18 with a half molar equivalent of [Rh(COD)(
ꢀ
Cl)]2 and one molar equivalent of Na[BPh4] resulted in the
-
Catalysis
We have recently reported the catalysed two-step
isolation of the desired Ir(III)/Rh(I) complex 19 as an orange dihydroalkoxylation of alkynediols 2-(5-hydroxypent-1-
solid at a yield of 49 %. The complex 19 was fully characterised ynyl)benzyl alcohol (25a, Figure 6) and 2-(4-hydroxybut-1-
by 1H, 13C NMR spectroscopy, mass spectrometry and ynyl)benzyl alcohol
(
26a
elemental analysis. The 1H NMR spectrum revealed the hydroamination/hydrosilylation reactions of 4-pentynamine
presence of only one conformation of the complex at room 27a, Figure 8) and 5-phenyl-4-pentynamine (28a, Figure 9)
temperature. We determined that the Rh(I) centre was using Rh(I) and Ir(I) homobimetallic complexes of the proligand
successfully bound to the bpm ligand because of the large scaffold 5 12
Considering the capability of both Rh(I) and Ir(I)
downfield shift of the resonance due to the bpm methine complexes to catalyse these reactions we were interested in
proton from 7.8 ppm for the Ir(III) monometallic complex 18 to testing the Rh(I) and Ir(I) heterobimetallic complexes 11 12
, Figure 7), and the two-step
(
.
,
,
9.0 ppm for the Ir(III)/Rh(I) bimetallic complex 19, in addition and 14 as catalysts to establish their efficiency and determine
to the change in positions of the proton resonances due to the if they led to an enhancement of activity relative to those of
COD alkene and alkane protons of the complexes 18 and 19
.
the monometallic and homobimetallic complexes 22, 23 and
Finally, we were also able to successfully synthesise the 24 (Figure 5). Note, for all catalysis reactions two molar
heterobimetallic Ru(II)/Ir(I) complex (21). Firstly, an in situ equivalents of Na[BArF ] relative to catalyst were added to the
4
complexation of Ag(I) to the bidentate NHC-triazole proligand mixture (except complexes 14 and 24 which only required one
3, followed by transmetallation with half a molar equivalent of molar equivalent). Complexes 22 and 23 did not require
[Ru(η6 C6H6)Cl2]2 and Na[BPh4] resulted in the isolation of the addition of Na[BArF ] as they already contain the BArF
-
4
4
monometallic Ru(II) complex (20) as a yellow solid at a yield of counterion. It has been shown that the presence of a suitable
75%. The 1H NMR spectrum confirmed coordination of the counterion has a marked effect on the catalytic activity of Rh(I)
Ru(II) centre to the NHC-triazole ligand with the appearance of and Ir(I) NHC complexes containing a halide (salt metathesis
two pairs of proton resonances attributed to the reaction).11b, 12
diastereotopic protons of the CH2 group situated between the
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ratio is similar to other catalysts our group has tested for the
dihydroalkoxylation reaction of 25a except for our most recent
report where we have reversed the regioselectivity producing
more of the spiroketal 25c using the Ir(I) homobimetallic
[BArF
]
4
N
CO
Rh
OC CO
M
CO
N
N
N
N
N
I
complex of the proligand (5
).12 Difficulties in the synthesis and
isolation of the Ir(I) NHC analogue of 24 hindered our efforts in
a complete comparison of all bimetallic half units in this study
for all catalysed reactions and therefore the discussion of the
comparative catalysis results only contains the three bimetallic
22: M = Rh(I)
23: M = Ir(I)
24
Figure 5. Monometallic Rh(I) and Ir(I) half units 22, 23 and 24.
Catalysed Dihydroalkoxylation Reactions of Alkynediols
half units 22, 23 and 24 (Figure 5). However, we did test a
25a and 26a
We initially tested the heterobimetallic complexes 11
combination of complexes 23 (0.5 mol%) and 24 (0.5 mol%) in
the one-pot for the catalysed dihydroalkoxylation reaction of
25a. The reaction progressed to completion extremely slowly
taking up to 2.3 h (TOF = 43 h-1).
,
12
and 14 as catalysts for the dihydroalkoxylation reactions of 25a
and 26a. The heterobimetallic Rh(I)NHC/Ir(I)bpm complex 11
was somewhat more efficient at catalysing the
dihydroalkoxylation reaction of 25a (22 min >95 % conv., TOF =
Similar reactivity trends were observed for the
dihydroalkoxylation of 26a when using the heterobimetallic
1014 h-1) than the heterobimetallic complexes 12
, 14 and the
complexes 11, 14 and monometallic complex 23 (Figure 7)
monometallic complex 23 completing the reaction in 43, 29
and 46 mins respectively with TOFs of 622 h-1, 778 h-1 and 374
h-1 respectively (Figure 6). The monometallic Rh(I) bpm
catalysing the reaction in 20, 18 and 19 mins respectively with
TOFs of 1380 h-1, 1552 h-1 and 535 h-1 respectively. However, in
this case the heterobimetallic complex containing the Ir(I)NHC
complex (12) was slightly less reactive, completing the reaction
in 38 mins with a TOF of 485 h-1. For this particular reaction
the two heterobimetallic complexes containing Rh(I) at the
NHC/NHC-triazole ligand (11 and 14) which outperformed the
heterobimetallic complex containing an Ir(I)NHC (12) formed
the tetracyclic dimer side-product (26c) at yields of 10% and
19% respectively (Figure 7). In contrast the heterobimetallic
complex containing the Ir(I) NHC (12) only formed the desired
spiroketal 26b. This was also observed for the previously
reported Ir(I) homobimetallic complex containing the
complex 22
,
was the most active catalyst for
dihydroalkoxylation reactions for both 25a (Figure 6) and 26a
(Figure 7). The monometallic Rh(I) NHC complex 24 was the
least efficient complex tested of all the mono- and bimetallic
complexes tested, being so unreactive for catalysing the
dihydroalkoxylation reaction of 25a and 26a that it had only
promoted a conversion of <10% of either 25a or 26a to their
products by 30 mins, while all other complexes had catalysed
the reaction to completion within this time frame.
We did not observe any selectivity towards either of the
two spiroketal products 25b or 25c when testing the three
proligand
reaction.12
5, which was also very slow at catalysing the
heterobimetallic complexes 11
produced similar ratios of 2:1 of the two products 25b
(Figure 6) during the dihydroalkoxylation of 25a. This product
,
12 and 14, each reaction
:
25c
The reactivity of the heterobimetallic complexes 11, 12 and
Figure 6. Reaction profiles for the catalysed dihydroalkoxylation reactions of 25a using Figure 7. Reaction profiles for the catalysed dihydroalkoxylation reactions of 26a
bimetallic complexes 11, 12 and 14 and monometallic complexes 22-24 and. Note: 1 using bimetallic complexes 11, 12 and 14 and monometallic complexes 22-24. Note:
mol% of Na[BArF4] was added to the reaction mixtures when bimetallic complexes 11 1 mol% of Na[BArF4] was added to the reaction mixtures when bimetallic complexes
and 12 and 24 were used and 0.5 mol% of Na[BArF4] was added to the reaction
11 and 12 were used and 0.5 mol% of Na[BArF4] was added to the reaction mixture
mixture when the bimetallic complex 14 was used.
when the bimetallic complex 14 was used.
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14 for the catalysed dihydroalkoxylation reactions of the NHC ligand and Rh(I) at the bpm ligand (12) which
alkynediols 25a and 26a was comparable to that of the promoted the reaction to completion in 35 minutes (Table 2).
monometallic Rh(I) bpm half unit (22). However, as a result of The complexes 11 and 14 were less effective as catalysts than
the lower catalyst loading of the bimetallic complexes we were the monometallic Ir(I) bpm complex (23) which was capable of
able to achieve higher turn over frequencies of the substrate. catalysing the reaction within 2.4 minutes. Interestingly, when
Additionally, when a combination of complexes 23 and 24 was a combination of 23 (1 mol%) and 24 (1 mol%) in the one-pot
used to catalyse the reaction of 26a the reaction plateaued at was used for the hydroamination reaction of 27a, the reaction
91 % conversion after 2.2 h (TOF = 77 h-1). So, in the case of took almost the same amount of time to complete as 11 (0.29
the two monometallic half units 23 and 24 mixed into the h vs. 0.24 h respectively).
same reaction vessel, there is clearly some poisoning of the
reaction occurring.
The hydroamination reaction of 5-phenyl-4-pentyn-1-
amine (28a) was much slower in the presence of all bimetallic
Clearly the results from the catalysed dihydroalkoxylation complexes than that of 4-pentyn-1-amine (27a) (Figure 8). The
reactions of 25a and 26a demonstrate that incorporation of an relative reaction rates promoted by the complexes were
extremely inefficient catalyst (24) into a bimetallic system slightly different for this substrate with the two
containing this half unit with another more reactive catalyst heterobimetallic complexes catalysing the reaction the fastest
(
22 or 23) on the xanthene scaffold does not impact the
(11; 1.9 h, and 12; 2.6 h), compared to the monometallic
catalytic activity of the bimetallic system containing the Rh(I) complexes (23; 3.6 h, 22; 4.9 h, and 24; 5.0 h) (Table 2). The
NHC half unit (11).
combination of 23 and 24 in this particular reaction was much
more efficient than the heterobimetallic complex 11 at
Sequential Hydroamination/Hydrosilylation Reactions of catalysing the reaction of 28a completing the reaction in half
alkyneamines 27a and 28a catalyzed by 11, 12, 14, 22-24.
The heterobimetallic complexes 11 12 14
monometallic complexes 22
the time (1.04 h vs. 1.88 h respectively).
,
,
,
and
There was a clear differentiation of the reaction rates of
-
24 were used to promote the the two substrates tested. One obvious trend observed on
sequential two-step hydroamination/hydrosilylation reactions catalysing the reaction of both substrates 27a and 28a was
of 4-pentyn-1-amine (Figure 8, 27a) and 5-phenyl-4-pentyn-1- that any complexes containing at least one Ir(I) centre always
amine (Figure 9, 28a).
outperformed the Rh(I) counterparts for the hydroamination
The heterobimetallic complexes containing Rh(I) at the reactions. This was also demonstrated by our group previously
NHC or triazole-NHC ligand and Ir(I) at the bpm ligand (11 and with an Ir(I) homobimetallic complex contained on the
14 respectively) displayed similar catalytic activity towards the heteroditopic ligand scaffold outperforming the analogous
hydroamination reaction of 4-pentyn-1-amine
promoting complete conversion within 15 minutes in each monometallic Ir(I)bpm complex
case (Figure 8). With both complexes being more active hydroamination of 5-phenyl-4-pentyn-1-amine (28a) (Figure 9)
(
27a), Rh(I)
homobimetallic
complex.12
Interestingly
the
(
23) catalysed the
catalysts than the heterobimetallic complex containing Ir(I) at at
a
much slower rate than was observed for the
2.0 mol% 22, 23 or 24
2.0 mol% 22, 23 or 24
or
or
NH2
2 equiv. Ph2SiH2
1.0 mol% 11 or 12
2 equiv. Ph2SiH2
1.0 mol% 11, 12 or 14
NH2
N
N
N
Toluene-d8, 100 oC
Toluene-d8, 100 oC
N
Ph2HSi
Toluene-d8, 100 oC
Toluene-d8, 100 o
C
27a
28a
27b
27c
SiHPh2
28b
28c
100 %
100 %
Ph2SiH2
addition
Ph2SiH2
addition
* =
* =
100 %
*
*
100 %
0 %
0 %
*
*
*
*
*
*
*
*
*
11
Rh/Ir
11
Rh/Ir
12
Ir/Rh
12
Ir/Rh
14
RhbzCat
R2hb2pm
22
RhBpmBPh4
Irbpm
23
23
IrBpmBPH4
Rh monocarbene
24
24
RhNHC
0 %
0 %
0
1
2
3
4
5
6
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Time (h)
Time (h)
Figure 8. Reaction profiles for the catalysed hydroamination/hydrosilylation
reactions of 27a using bimetallic complexes 11, 12 and 14 and monometallic
complexes 22-24. Note: 2 mol% of Na[BArF4] was added to the reaction mixtures
when bimetallic complexes 11, 12 and 24 were used and 1.0 mol% of NaBArF4 was
added when 14 was used.
Figure 9. Reaction profiles for the catalysed hydroamination/hydrosilylation
reactions of 28a using bimetallic complexes 11 and 12 and monometallic complexes
22-24. Note: 2 mol% of Na[BArF4] was added to the reaction mixtures when
bimetallic complexes 11, 12 and 24 were used.
8 | J. Name., 2012, 00, 1-3
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ARTICLE
Table 2 Comparison of Rh(I)/Ir(I) heterobimetallic complexes with Rh(I) and Ir(I) monometallic complexes for the two-step hydroamination/hydrosilylation
reactions of 27a and 28a.
Hydroamination step
Entry Cat.
Hydrosilylation stepe
Substrate
Time/h (% conv.) TOF/he
Time/min (% conv.)
TOF/hf
1a
OC CO
Ir
27a
28a
0.24 (>95)
1.88 (>95)
2378
265
3.6 (>98)
2.4 (>98)
1287
2380
[BPh4
]
2a
N
OC
Rh
N
N
N
N
OC
N
Cl
11
O
3a
4a
OC CO
Rh
27a
28a
0.78 (>95)
2.6 (>95)
1845
418
1.2 (>98)
<1.0 (>98)
3805
>11531
[BPh4
]
N
OC
Ir
N
N
N
N
OC
N
Cl
12
O
5b
6b
4
4
27a
28a
0.4 (>95)
4.9 (>95)
1726
53
6.0 (>98)
18.0 (>98)
459
199
[BArF
]
OC CO
Rh
N
N
N
N
22
7b
8b
27a
28a
0.04 (>95)
3.6 (>95)
3983
62
1.0 (>98)
1.6 (>98)
>1365
>1694
[BArF
]
OC CO
Ir
N
N
N
N
23
9c
27a
28a
0.6 (>95)
5.0 (>95)
436
140
3.6 (>98)
13.2 (>98)
365
212
N
OC
Rh
10c
OC
N
Cl
24
11d
12d
27a
28a
0.29 (>95)
1.04(>95)
1814
156
9 (>98)
1.5 (>98)
407
1804
aConditions – 1.0 mol % cat., 2 mol % Na[BArF4], 2x10-4 mol substrate, Toluene-d8, 100 °C; bConditions – 2.0 mol % cat., 2x10-4 mol substrate, Toluene-d8, 100 °C;
cConditions – 2.0 mol % cat., 2.0 mol % Na[BArF4], 2x10-4 mol substrate, Toluene-d8, 100 °C; dConditions – 1.0 mol % of each cat., 1 mol % Na[BArF4], 2x10-4 mol
f
substrate, Toluene-d8, 100 °C; e4x10-4 mol of Ph2SiH2 was added to the mixture; TOFs (Turn Over Frequency) were calculated at the point of 50% conversion of
substrate to product(s).
hydroamination of 4-pentyn-1-amine (27a) (Figure 8).
The complexes (both bi- and monometallic) that
The hydrosilylation reactions of the cyclic imines formed on contain an Ir(I) metal centre were significantly better catalysts
hydroamination of 27a and 28a respectively, 2- for the hydrosilylation reactions of 27b and 28b than the
methylpyrroline (Figure 8, 27b) and 2-benzylpyrroline (Figure monometallic Rh(I) complexes, as had been observed for the
9, 28b), were carried out using Ph2SiH2 as the silane source.
hydroamination reaction of 27a and 28a. This trend was
The heterobimetallic complex 12 and the monometallic Ir(I) also observed for catalytic activity of the Ir(I) homobimetallic
complex 23 were extremely efficient catalysts for the reported previously which also significantly outperformed the
hydrosilylation of 2-methylpyrroline (27b), completing the Rh(I) homobimetallic complex for both the hydroamination
reaction within 1.2 minutes (Figure 8). The two and hydrosilylation reactions of 27a and 28a 12
heterobimetallic complexes containing Rh(I) at the NHC or There are some clear trends in the relative activities of
triazoleNHC ligand 11 and 12, and the monometallic Rh(I) the heterobimetallic complexes 11 12 and 14 as catalysts for
.
,
complex 24 also promoted the reaction of 27b extremely the sequential two-step hydroamination-hydrosilylation
rapidly, with the three complexes completing the reaction reactions of 27a and 28a. The heterobimetallic complexes that
within 3.6 minutes with TOFs of 1287 h-1, 1279 h-1, and 365 h-1 contain a Rh(I) NHC or Rh(I) triazole-NHC with an Ir(I) bpm
respectively. The monometallic Rh(I) bpm complex
promoted the completion of the reaction within 6 minutes dihydroalkoxylation reactions of 25a and 26a compared to
with a TOF of 459 h-1.
complex 12 which contained Ir(I) at the NHC site and Rh(I) at
(
22)
ligand (11 and 14) were more efficient at catalysing the
Similar trends in the relative reaction rates of the the bpm site. This is in contrast to what has been observed
complexes were observed for the hydrosilylation of 2- previously for bis(pyrazolyl)methane containing homoditopic
benzylpyrroline (28b) (Figure 9), with the heterobimetallic homobimetallic Rh(I) and Ir(I) complexes where the Rh(I)
complex 12 promoting completion of the reaction in less than bimetallic was far superior at catalysing the reaction compared
1 minute and the monometallic Ir(I)bpm complex 23 in 1.6 to the Ir(I) bimetallic.11a
minutes with TOFs of >11531 h-1 and >1694 h-1 respectively
In this work the bimetallic complexes containing a Rh(I)
(Table 2, entires 4 and 8). The reaction containing the NHC half unit (which is a poor catalyst when used as the
heterobimetallic complex 11 took a slightly longer time (2.4 monometallic analogue) and an Ir(I) bpm half unit (which is
mins) to complete (Table 2, entry 2), while the monometallic less reactive as the monometallic analogue compared to the
complexes (Rh(I)NHC (24) and Rh(I)bpm (22)) were again Rh(I) derivative) for the catalysed reactions undertaken in this
relatively sluggish taking more than 13 min. to complete the study appear to work synergistically and there is some change
reaction (Table 2, entries 6 and 10).
in the roles the individual metal centres play when part of this
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bimetallic unit. In this study the heterobimetallic complexes 11 enhancement for the hydrosilylation reactions. As the
and 14, which contain the Rh(I) NHC or triazole-NHC, and Ir(I) hydrosilylation reaction has a different mechanistic pathway
bpm perform more efficiently than complex 12 which contains compared to the alkyne activated dihydroalkoxylation and
the Ir(I) NHC and Rh(I) bpm for the hydroamination reaction. hydroamination reactions, any observed cooperativity is
This reactivity is reflective of that of the analogous clearly dependent on a specific step within the reaction
monometallic half units, with the monometallic Ir(I) bpm mechanism.
complex 23 catalysing the reaction more effectively than the
There are a few possible reasons why we did not observe
monometallic Rh(I) bpm complex 22. Similarly, any complex any positive enhancement for the dihydroalkoxylation and
containing an Ir(I) centre, whether it be at the NHC or the bpm hydroamination reactions: 1) The two metal centres were
site was much more efficient at catalysing the hydrosilylation competing with one another for one substrate molecule, or 2)
reaction than the two monometallic Rh(I) complexes 22 and metal-metal stabilization of a reactive intermediate that would
24. Again, this reactivity was similar to what was observed for be otherwise inaccessible by a monometallic complex was not
the heteroditopic homobimetallic complexes reported occurring.
previously with the heteroditopic homobimetallic Ir(I) complex
While the Rh(I)/Ir(I) heterobimetallic complexes 11, 12, and
outperforming by far the analogous heteroditopic Rh(I) 14 did not yield more reactive catalysts than the previously
homobimetallic complex.12 It is possible that there is some reported Rh(I) and Ir(I) homobimetallic catalysts, for the
decomposition of the Rh(I) NHC complex during the catalysed dihydroalkoxylation and hydroamination reactions, they may
hydrosilylation reaction as this was observed previously when however, provide enhancements for promoting reactions of
using 24 for the hydrosilylation of diphenylacetylene, hence, more challenging substrates.11a, 11d Further investigation of the
the lower catalytic activity displayed by the heterobimetallic heterobimetallic complexes containing a mix of group 9 metals
complexes containing Rh(I)NHC complex (11 and 14).11b
with group 8 and 11 metals, as well as adding additional
transition metals to the current complexes we have
synthesised is currently underway.
Conclusions
The utilisation of the heteroditopic ligands
4 and 5 which
Experimental
contain a xanthene scaffold have proven to be effective for
accommodating a range of heterobimetallic systems of Rh(I),
All manipulations of metal complexes and air sensitive
Ir(I), Ir(III), Au(I) and Ru(II), with the potential to add a greater reagents were carried out using standard Schlenk or vacuum
list of metals and oxidation states to this repertoire. Through techniques,18 or in a nitrogen-filled or argon-filled M-Braun
careful ligand design we have restricted the ability of the glove box. Reagents were purchased from Aldrich Chemical Co.
metals of the heterobimetallic systems to undergo Inc. or Alfa Aesar Inc. and were used as received. The metal
intermetallic exchange. Characterisation data (NMR halide salts RhCl3.xH2O and IrCl3.xH2O, RuCl3.xH2O were
spectroscopy, X-ray crystallography, elemental analysis and purchased from Precious Metals Online PMO P/L and were
mass spectrometry) confirmed the structure of these used without further purification. The metal precursors,
complexes.
The heterobimetallic complexes 11
[Pd(PPh3)4],19 [Rh(COD)(
ꢀ
-Cl)]2,20 [Rh(CO)2(ꢀ−Cl)]2,21 [Ir(COD)(
ꢀ-
,
12 and 14 catalysed Cl)]2,22 [Ir(Cp*)Cl2]2,23 [Ru(η6
-
C6H6)Cl2]2,24 Na[BArF ] 25 and
4 ,
the dihydroalkoxylation reactions of 25a and 26a more [AuCl(SMe2)]26 were synthesised according to literature
efficiently than the Rh(I) and Ir(I) homobimetallic complexes methods.
Complexes
[Rh(CO)2bpm][BArF ]
(
22),15a
4
previously reported, albeit they were still less reactive than the [Ir(CO)2bpm][BArF ] (23
)
and [Rh(CO)2IPhNHC] (24
)
were
15a
11b
4
monometallic Ir(I)bpm complex 23 12
complexes 11 14 had similar catalytic activity to that of the
.
The heterobimetallic synthesised according to literature methods. The synthesis of
, the pro-ligand and silver complex were reported in
,
1
5
6
Ir(I) homobimetallic complex for the hydroamination reaction previously.12 For the purposes of air sensitive manipulations
of 27a presented previously, while 12 was slightly less and in the preparation of metal complexes, solvents were
reactive.12 The relative catalytic activity of the dried and distilled under an atmosphere of nitrogen or argon
heterobimetallics was flipped when carrying out the using standard procedures27 and stored under nitrogen or
hydrosilylation of 2-methylpyrroline (27b) with complex 12 argon in glass ampoules, each fitted with a Youngs Teflon valve
catalysing the reaction more efficiently than 11 or 14. In prior to use. Tetrahydrofuran (THF), diethyl ether, n-hexane, n-
comparison to the monometallic complexes 22-24, the pentane, and toluene were distilled from sodium-
heterobimetallic complexes 11 and 14 exhibited cooperative benzophenone ketyl. DCM and acetonitrile were distilled from
enhancement towards the hydrosilylation reactions of 27b and calcium hydride. Methanol (MeOH) and ethanol (EtOH) were
28b
hydroamination/hydrosilylation of 5-phenyl-4-pentyn-1-amine respectively. The bulk compressed gases argon (>99.999%) and
28a carbon monoxide (>99.5%) were obtained from Air Liquide and
While we do not observe positive enhancement for the used as received. Nitrogen gas for Schlenk line operation came
dihydroalkoxylation and hydroamination reactions when using from in-house liquid nitrogen boil-off. 1H and 13C{1H} NMR
the heterobimetallic complexes 11 12, and 14 relative to the spectra were recorded on Bruker Avance III 300, 400, 500, and
monometallic complexes 22 and 23
. A similar trend was observed for the sequential distilled from dimethoxymagnesium and diethoxymagnesium
.
,
,
we do observe 600 spectrometers operating at 300, 400, 500, and 600 MHz
10 | J. Name., 2012, 00, 1-3
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(1H), respectively, and 75, 100, 125, and 150 MHz (13C), equivalents of diphenylsilane (Ph2SiH2) relative to substrate
respectively. Unless otherwise stated, spectra were recorded were added to the mixture and the reaction was again heated
at 25 °C and chemical shifts (δ) are quoted in ppm. Coupling to 100 °C in the NMR instrument. The reactions were
constants (J) are quoted in Hz and have uncertainties of ±0.05 monitored by 1H NMR spectroscopy and the conversion (%)
1
1
Hz for H and ±0.5 Hz for 13C. H and 13C NMR chemical shifts was determined by the relative integral ratios of selected 1H
were referenced internally to residual solvent resonances. resonances of the substrate and product(s). Turn over
Deuterated solvents were purchased from Cambridge Stable frequencies (TOF) were calculated at the point of 50%
Isotopes and used as received. Air-sensitive NMR samples conversion of the substrate to product(s).
were prepared in an inert-gas glovebox or by vacuum transfer
of deuterated solvents into NMR tubes fitted with a Young
[2,7-Ditertbutyl-4-N-propargylimidazolium-5-bpm-9,9-
Teflon valve. For air-sensitive NMR samples CD2Cl2 and CDCl3 dimethyl-xanthene][Br] (2)
were distilled over calcium hydride. Acetone-d6 was distilled
Compound
1 (1.10 g, 2.05 mmol) and propargyl bromide
from calcium sulfate.
(976 mg, 8.20 mmol) were added to CH3CN (20 mL) and the
Infrared spectra were measured using a Nicolet 380 Avatar mixture was stirred for 48 h at r.t. The solvent was removed in
FTIR spectrometer as solutions in dichloromethane. vacuo and the solid was recrystallised by dissolving in the
Microanalyses were carried out at the Campbell minimum amount of DCM and adding excess n-hexane until
Microanalytical Laboratory, University of Otago, Otago, New precipitation occurred yielding a white solid. Yield: 1.10 g (1.67
Zealand, or the Microanalytical Unit, Research School of mmol), 82 %. ESI-MS (MeOH), m/z (%): 573.62 (100) [M - Br]+
Chemistry, Australian National University, Canberra, Australia. amu. Anal. Found: C, 64.69; H, 6.21; N, 12.60. Calcd. for
Mass spectra were acquired using a Thermo LTQ Orbitrap XL C36H41BrN6O + H2O : C, 64.37; H, 6.45; N, 12.51%.
(HR-ESI-MS, high-resolution electrospray ionization mass
spectrometry), located in the Bioanalytical Mass Spectrometry
Facility (BMSF) at the University of New South Wales, or using
[(LBnCAT)/(LBpm)tXan][Br] (3)
Benzyl azide (222 mg, 1.67 mmol) and 2 (1.10, 1.67 mmol)
a Micromass ZQ massspectrometer (ESI-MS). M is defined as were added to a solution of 2-propanol/H2O (2:1, 10 mL)
the molecular weight of the compound of interest or cationic followed by the addition of sodium ascorbate (66.0 mg, 334
fragment for cationic metal complexes.
µmol) and CuSO4 (586 mg, 3.67 mmol). The mixture was
All NMR data established for new compounds are stirred for 48 h followed by the removal of 2-propanol in
presented in the Supporting Information.
vacuo. The crude product was extracted from the water with
EtOAc (3 x 25 mL). The organic layer was stirred in a sat.
General Procedure for the dihydroalkoxylation reactions solution of Na2[EDTA] (30 mL) for 30 min, the orgainc layer
of 25a and 26a
The general
extracted and then stirred in a second fresh solution of
procedure
for
the
catalysed Na2EDTA (30 mL) for 30 min. The organic layer was extracted,
dihydroalkoxylation reactions of 25a and 26a were undertaken dried over MgSO4, filtered and the solvent removed in vacuo.
by dissolving the substrate, catalyst (0.5 mol% for bimetallic The crude product was dissolved in the minimum amount of
complexes 11, 12 and 14 and 1.0 mol% for 22, 23 and 24) and DCM and the mixture was added dropwise to a vigorously
Na[BArF ] (1.0 mol% for 11 and 12, 0.5 mol% for 14 and 24) in stirring flask of cooled n-pentane (100 mL). The white
4
1,1,2,2-tetrachloroethane-d2 in an NMR tube fitted with a precipitate was collected yielding
Teflon (Youngs) value under an inert atmosphere. The NMR mg (1.07 mmol), 64%. ESI-MS (MeOH), m/z (%): 706.70 (100)
tube was injected in the NMR spectrometer at 100
C and the [M – Br]+ amu.
3 as a white solid. Yield: 846
°
reactions were monitored by 1H NMR spectroscopy. The
conversion (%) was determined by the relative integral ratios
of selected 1H resonances of the substrate and product(s).
[(LBnCAT)/(LBpm)tXan][BPh4] (4)
Compound (831 mg, 1.18 mmol) was dissolved in DCM
3
Turn over frequencies (TOF) were calculated at the point of (50 mL), Na[BPh4] (361 mg, 1.06 mmol) was added and the
50% conversion of substrate to product(s).
mixture was stirred for 2 hours and then filtered through
celite. The solvent was removed in vacuo and the crude
the product was recrystallised from the minimum amount of DCM
followed by slow addition of hexane until precipitation
General
hydroamination/hydrosilylation reactions of 27a and 28a
The general procedure for the
Procedure
for
catalysed occurred. The product (4) was collected as a white solid. Yield:
hydroamination/hydrosilylation reactions of 27a and 28a were 1.21 g (1.18 mmol), > 99%. ESI-MS (MeOH), m/z (%): 706.69
undertaken by dissolving the substrate, catalyst (1 mol% for (100), [M – BPh4]+ amu.
bimetallic complexes 11, 12 and 14 and 2 mol% for 22, 23 and
24) and Na[BArF ] (2.0 mol% for 11 and 12, 1.0 mol% for 14
[Rh(COD)Cl(LNHC)/(LBpm)tXan] (7)
Complex (149 mg, 190 µmol) was dissolved in DCM (20
Cl)]2 (47.0 mg, 95.0
4
and 24) in toluene-d8 in an NMR tube fitted with a Teflon
6
(Youngs) value under an inert atmosphere. The NMR tube was mL) followed by addition of [Rh(COD)(
ꢀ
injected in the NMR spectrometer at 100 °C and the reactions µmol), the mixture turned brown and was stirred for 1.5 h. The
were monitored by 1H NMR spectroscopy. Upon completion of mixture was then filtered through celite, the celite washed
the hydroamination step (>95% conversion), two molar with DCM (30 mL). The solvent was removed in vacuo from the
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filtrate yielding a yellow oil. The oil was dissolved in the added and the mixture stirred for an additional 1 hour. The
minimum amount of DCM and excess n-hexane was added (30 mixture was filtered into another flask and the filtrate was
mL), the mixture was then reduced to ca. 5 mL resulting in a degassed via three freeze, pump, thaw cycles. An atmosphere
precipitation of a bright yellow which was collected by of CO(g) was introduced into the flask and the mixture was
filtration to yield the product (7). Yield: 162 mg (176 µmol), stirred for 1 h with the solution turning a pale yellow colour.
92%. ESI-MS (MeOH), m/z (%): 759.58 (100) [M – Cl]+ amu. The mixture was then cooled to 0 °C and excess n-pentane was
Anal. Found: C, 62.86; H, 6.75; N, 10.40. Calcd for: added to the flask with vigorous stirring until a pale yellow
C42H52ClN6ORh + 0.5 H2O ; C, 62.72; H, 6.64; N, 10.45%.
solid precipitated. The precipitate was collected by filtration
and washed with additional n-pentane (20 mL). The solid was
dried in vacuo to yield the complex (12). Yield: 144 mg (110
[Ir(COD)Cl(LNHC)/(LBpm)tXan] (8)
Following the same procedure that was used to synthesise µmol), 54%. IR (DCM) vCO = 2103, 2072, 2045, 1993 (s) cm-1. IR
7, the following reagents and amounts were used:
6
(441 mg, (solid) vCO = 2103, 2062, 2046, 1972 (s) cm-1.
563 µmol), [Ir(COD)(ꢀ Cl)]2 (189 mg, 281 µmol), DCM (20 mL).
After filtration of the product through celite, n-hexane (50 mL)
[Rh(COD)(LBzCAT)/(LBpm)tXan][BPh4] (13)
Pro-ligand (300 mg, 292 µmol) was dissolved in THF (50
was added and the solvent removed in vacuo to yield the
4
complex 8 as a bright yellow solid. Yield: 373 mg (422 µmol), mL) and added dropwise to a stirring mixture of NaOEt (50 mg,
75%. Anal. Found: C, 57.67; H, 6.29; N, 9.12. Calcd for: 731 µmol), [Rh(COD)(ꢀ−Cl)]2 (72.0 mg, 146 µmol) in EtOH (15
C42H52ClIrN6O: C, 57.03; H, 5.93; N, 9.50%.
mL) and the mixture was stirred for 1 h. The solvent was
removed in vacuo and the crude product dissolved in DCM (20
mL) and filtered through celite. The solvent was reduced to
[Rh(COD)Cl(LNHC)/Ir(COD)(LBpm)tXan][BPh4] (9)
Complex
mL) followed by the addition of [Ir(COD)(
µmol) and the mixture was stirred for 30 min. The colour of formed and was collected by filtration to yield complex 13
7
(358 mg, 484 µmol) was dissolved in DCM (30 approximately 10 mL and excess n-hexane was added to the
ꢀ
Cl)]2 (162 mg, 242 mixture while stirring vigorously, a bright yellow precipitate
.
the mixture turned green, Na[BPh4] (166 mg, 484 µmol) was Yield: 258 mg (208 µmol), 71%. ESI-MS (MeOH), m/z (%):
added and the mixture was stirred for an additional 30 min 916.77 (100), [M – BPh4]+ amu. Anal. Found: C, 72.55; H, 6.64;
upon which the colour of the mixture had turned orange. The N, 10.23. Calcd. for: C75H79BN9ORh : C, 72.87; H, 6.44; N,
mixture was filtered through celite and the celite washed with 10.20%.
DCM (30mL). The mixture was reduced to ca. 10 mL and excess
n-pentane was added to the filtrate with vigorous stirring until
a yellow solid precipitated. The precipitate was collected by
[Rh(CO)2(LBzCAT)/Ir(CO)2(LBpm)tXan]2[BPh4] (14)
Complex 13 (156 mg, 126 µmol) and [Ir(COD)(ꢀ−Cl)]2 (42.3
filtration and washed with n-pentane (20 mL) to yield the mg, 63.0 µmol) were dissolved in DCM (20 mL) and the mixture
complex ( ) as a yellow solid. Yield: 578 mg (384 µmol), 79%. was stirred for 1 hour. Na[BPh4] (43.1 mg, 126 µmol) was
9
ESI-MS (MeOH), m/z (%): 1095.38 (48) [M – BPh4]+, 759.54 added to the mixture stirred for 1 hour. The mixture was
(100) [M – Ir(COD) – Cl]+ amu. Anal. Found: C, 59.95; H, 5.76; filtered into another flask and the filtrate was degassed via
N, 5.95. Calcd for: C74H84BClIrN6ORh + CH2Cl2 : C, 60.06; H, three freeze, pump, thaw cycles. An atmosphere of CO(g) was
5.78; N, 5.60%.
introduced into the flask and the mixture was stirred for 1 h.
Excess n-pentane was then added to the flask with vigorous
stirring until an organe solid precipitated which was collected
[Rh(CO)2Cl(LNHC)/Ir(CO)2(LBpm)tXan][BPh4] (11)
Complex
9 (207 mg, 137 µmol) was dissolved in DCM (20 by filtration and dried in vacuo yielding complex 14 as an
mL) and the mixture was degassed via three freeze, vac, thaw orange powder. Yield: 73.1 mg (41.9 µmol), 51%. ESI-MS
cycles. An atmosphere of CO(g) was introduced into the flask (MeOH), m/z (%): 836.93 (100) [M – Ir(CO)2 – 2BPh4 – CO]+
and the mixture was stirred for 1 h with the solution turning a amu. Anal. Found: C, 63.38; H, 5.16; N, 7.29. Calcd. for:
pale yellow colour. The mixture was then cooled to 0 °C and C95H91B2IrN9O5Rh + 0.75 CH2Cl2: C, 63.35; H, 4.91; N, 6.94%. IR
excess n-pentane was added to the flask with vigorous stirring (DCM) vCO = 2097, 2032 (br, s) cm-1. IR (solid) vCO = 2088, 2024
until a pale yellow solid precipitated. The precipitate was (br, s) cm-1.
collected by filtration and washed with additional n-pentane
(20 mL). The solid was dried in vacuo to yield the complex (11).
Yield: 168 mg (120 µmol), 88%. ESI-MS (MeOH), m/z (%):
[AuI(LNHC)/(LBpm)tXan] (15)
Compound (700 mg, 1.03 mmol), ground K2CO3 (569 mg,
5
707.25 (100), [M – Ir(CO)2 – Cl – BPh4]+ amu. Anal. Found: C, 4.12 mmol) and AuCl(SMe2) (303 mg, 1.03 mmol) were added
54.05; H, 4.50; N, 6.37. Calcd for: C62H60BClIrN6O5Rh + CH2Cl2 : to acetone (40 mL) and the mixture was refluxed for 4 h. The
C, 54.22; H, 4.48; N, 6.02%.IR (DCM) vCO = 2091, 2027 (s), 2011 mixture was filtered through celite and the solvent was
(br shoulder) cm-1. IR (solid) vCO = 2080, 2017, 2002 (s) cm-1.
removed from the filtrate leaving a clear oil. The oil was
redissolved in the DCM (10 mL) and n-hexane was added (30
mL), the solvent was removed in vacuo yield the product 15 as
[Ir(CO)2Cl(LNHC)/Rh(CO)2(LBpm)tXan][BPh4] (12)
Complex
8
(181 mg, 205
) and [Rh(COD)(ꢀ Cl)]2 (50.5 an off-white solid. Yield: 826 mg (946 µmol), 92%. ESI-MS
mg, 102
ꢀ
mol) were dissolved in DCM (20mL). The mixture (MeOH), m/z (%): 895.23 (100) [M + Na]+, 745.49 (5) [M – I]+
was stirred for 30 min and Na[BPh4] (70.1 mg, 205 ꢀmol) was
12 | J. Name., 2012, 00, 1-3
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ARTICLE
amu. Anal. Found: C, 48.87; H, 5.24; N, 8.75. Calcd. for: additional 2.5 hours. The mixture was filtered through celite
C34H40AuIN6O + 0.6 C6H14: C, 48.86; H, 5.28; N, 9.09%.
and the solvent removed in vacuo. The crude material was
dissolved in the minimum amount of DCM and added
dropwise to a vigorously stirring solution of n-pentane. An off
[AuI(LNHC)/Rh(COD)Cl(LBpm)tXan] (16)
Complex 15 (301 mg, 385
mg, 193
ꢀmol) and [Rh(COD)(ꢀ−Cl)]2 (94 yellow precipitate formed and was collected by filtration to
mol) were added to THF (20 mL) and the mixture yield the product 20. Yield: 115 mg (86.6 µmol), 75%. ESI-MS
ꢀ
was stirred for 1 hour. The volume was reduced by half and (MeOH), m/z (%): 920.42 (100) [M – BPh4]+ amu.
with vigourous stirring excess n-pentane was added until a
yellow solid precipitated. The complex (16) was collected by
filtration. Yield: 239 mg (233 mol), 61%.
[Ru(C6H6)Cl(LBzCAT)/Ir(COD)(LBpm)tXan][BPh4] (21)
ꢀ
Complex 20 (66.1 mg, 49.8 µmol) and [Ir(COD)(ꢀ−Cl)]2
Note: Confirmation of complexation was confirmed by X- (16.7 mg, 24.9 µmol) were dissolved in DCM (15 mL) and the
ray crystallography. For 1H NMR spectrum (VT experiments) mixture was stirred for 30 min, the mixture turned a green-
see supporting information.
orange colour and Na[BPh4] (17 mg, 49.8 µmol) was added and
the mixture was stirred for an additional 1 hour. The mixture
was filtered and excess through celite followed by addition of
[AuCl(LNHC)/(LBpm)tXan] (17)
o
Complex
149
6
(111mg, 142
ꢀ
mol) were dissolved in acetone (20 mL) and the mixture occurred. Orange solid was filtered and dried in vacuo to yield
mol) and [AuCl(SMe2)] (44.0 mg, excess n-pentane at 0 C until precipitation of an orange solid
ꢀ
was stirred for 3 hours. The mixture was filtered through celite the complex 21. Yield: 75.6 mg (38.8 µmol), 78%. ESI-MS
and the celite was with acetone (20 mL). The solvent was (MeOH), m/z (%): 610.98 (100) [M- 2 x BPh4]2+, 920.54 (85) [M
removed in vacuo to yield the complex 17 as a white solid. – Ir(COD) – 2 x BPh4]+, 1540.33 (25) [M- BPh4]+ amu. Anal.
Yield: 110 mg (141 ꢀmol), 99%. ESI-MS (MeOH), m/z (%): Found: C, 63.20; H, 5.52; N, 6.29. Calcd. for:
745.45 (14) [M – Cl]+, 803.27 (5) [M + Na]+ amu.
C105H105B2ClIrN9ORu + 2 CH2Cl2: C, 63.33; H, 5.41; N, 6.21%.
[Ir(Cp*)Cl2(LNHC)/(LBpm)tXan] (18)
Acknowledgements
Complex 3.18 (197 mg, 251 µmol) and [IrCp*Cl2]2 (100 mg,
126 µmol) were dissolved in acetone (20 mL). The brown
mixture was stirred for three hours, with the mixture turning a
greyish yellow. The mixture was filtered through celite and the
solvent was removed in vacuo. The crude product was
redissolved in the minimum amount of DCM and was added
The research was supported under the Australian Research
Council’s Discovery Projects funding scheme (project number
DP110101611). We gratefully acknowledge the University of
New South Wales (UNSW) for financial support and
acknowledge and the Australian Government for the Ph.D.
stipend (M.G). Additionally we thank the Mark Wainwright
Analytical Centre (UNSW) and Macquarie University.
dropwise to vigorously stirring pentane at 0 °C. The complex
18 precipitated and was collected by filtration as a light peach
coloured solid. Yield: 184 mg (194 µmol), 77%. ESI-MS (MeOH),
m/z (%): 877.50 (100) [M – 2Cl + H-]+ amu. Anal. Found: C,
53.01; H, 5.68; N, 8.53. Calcd. for C44H55Cl2IrN6O + 0.75 CH2Cl2:
C, 53.18; H, 5.63; N, 8.31%.
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