Weakly coordinating counter-ions for highly efficient catalysis of intramolecular hydroamination

Article abstract of DOI:10.1039/b814168a

A series of cationic rhodium(i) and iridium(i) complexes of the type [M(L^∩L)(C₂)]BAr^F₂₄ (where M = Rh or Ir, L^∩L = bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylphosphino)ethyl)-3,5- diphenylpyrazole (Ph₂PyP), C₂ = 1,5-cyclooctadiene (COD) or (CO)₂ and BAr^F₂₄ = tetrakis[3,5- bis(trifluoromethyl)phenyl]borate) were synthesised in good yields. The solid-state structure of a number of complexes, including [Ir(Ph ₂PyP)(COD)]BAr^F₂₄, [Ir(bpm)(COD)]BAr ^F₂₄ and [Ir(bim)(COD)]BAr^F₂₄ was determined using X-ray crystallography. The efficiency of the complexes as catalysts for the intramolecular hydroamination of 4-phenyl-3-butyn-1-amine, 4-pentyn-1-amine and 2-(2-phenylethynyl)aniline was established. The incorporation of the BAr^F₂₄^- counter-ion in the Rh(i) and Ir(i) complexes was found to significantly improve the catalytic activity of the complexes, compared to the analogous Rh(i) and Ir(i) complexes containing BPh₄^- as the counter-ion. Excellent conversions were achieved for the cyclisation of 2-(2-phenylethynyl)aniline to 2-phenylindole using [Rh(bpm)(CO)₂]BAr^F₂₄ as a catalyst. The use of a microwave reactor for enhancing the catalysed reactions was also investigated. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b814168a

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www.rsc.org/dalton | Dalton Transactions
Weakly coordinating counter-ions for highly efficient catalysis of
intramolecular hydroamination†
Serin L. Dabb,a Joanne H. H. Ho,a Richard Hodgson,a Barbara A. Messerle*a and Jo¨rg Waglerb,c
Received 14th August 2008, Accepted 19th September 2008
First published as an Advance Article on the web 18th November 2008
DOI: 10.1039/b814168a
A series of cationic rhodium(I) and iridium(I) complexes of the type [M(L«L)(C2)]BArF (where
24
M = Rh or Ir, L«L = bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim) or
1-(2-(diphenylphosphino)ethyl)-3,5-diphenylpyrazole (Ph2PyP), C2 = 1,5-cyclooctadiene (COD) or
(CO)2 and BArF24 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) were synthesised in good yields. The
solid-state structure of a number of complexes, including [Ir(Ph2PyP)(COD)]BArF
,
24
[Ir(bpm)(COD)]BArF and [Ir(bim)(COD)]BArF was determined using X-ray crystallography. The
24
24
efficiency of the complexes as catalysts for the intramolecular hydroamination of
4-phenyl-3-butyn-1-amine, 4-pentyn-1-amine and 2-(2-phenylethynyl)aniline was established. The
-
incorporation of the BArF counter-ion in the Rh(I) and Ir(I) complexes was found to significantly
24
improve the catalytic activity of the complexes, compared to the analogous Rh(I) and Ir(I) complexes
-
containing BPh4 as the counter-ion. Excellent conversions were achieved for the cyclisation of
2-(2-phenylethynyl)aniline to 2-phenylindole using [Rh(bpm)(CO)2]BArF as a catalyst. The use of a
24
microwave reactor for enhancing the catalysed reactions was also investigated.
In particular, Rh(I) and Ir(I) catalysts have been used to promote
Introduction
the formation of synthetically useful N-heterocycles via the
cyclisation of alkynylamines.17–23 The efficiency of the catalysis
was found to be significantly affected by substitution of the
alkyne moiety. Work within our research group has centered
on the intramolecular hydroamination of a range of different
alkynylamines, such as 4-pentyn-1-amine (1), which yields 2-
methyl-1-pyrroline (2), using rhodium(I) and iridium(I) catalysts
with the general formula [M(L«L)(C2)]BPh4 where L«L is a
bidentate N,N -, P, C -, C,C- or P, N -donor ligand (N«N,17,20,21,23
P«C,19 C«C22 or P«N18) and C2 is either two carbon monoxide
(CO) co-ligands or a chelating 1,5-cyclooctadiene (COD) ligand.
Of this group of complexes the most efficient catalysts for the
formation of 2 were found to be iridium(I) complexes containing
either a combination of P«N and COD ligands,18 or N«N and
CO ligands,17 with conversions of 98% in less than 1.5 hours at
60 ◦C. Catalysts containing a mixed P, N -donor ligand, such as 3b,
promoted turnover frequencies ranging from 1200 to 3100 h-1 for
the cyclisation of 1 to 2 (Fig. 1).18 These turnover frequencies are
among the highest of any rates reported to date for the catalysed
cyclisation of 1 by a late transition metal catalyst.9,13
Nitrogen containing heterocycles are sub-units in biologically
active compounds which are important in the pharmaceutical
and agrochemical industries. Their synthesis via convenient and
direct approaches is highly desirable. The hydroamination reac-
tion, which involves the direct addition of an N–H bond to a
carbon–carbon multiple bond, is an atom-efficient pathway for
the formation of N–C bonds.1,2 Although thermodynamically
favorable, the high activation barrier for the hydroamination
reaction under normal conditions means a catalyst is required
to make the reaction practical.1–3 Catalysed cyclisation of alkynyl-
and alkenylamines via intramolecular hydroamination has shown
great potential in the energy and atom efficient synthesis of
N-heterocycles.1,2 Catalytic systems employed for the intramolec-
ular hydroamination reaction include calcium,4 lanthanides,5,6
actinides7 and both early8 and late9–13 transition metals. Late tran-
sition metal complexes have an advantage over lanthanides and
early transition metal complexes due to their lower oxophilicity,
which means they are less sensitive to moisture and air and have a
greater functional group tolerance.
A number of rhodium and iridium complexes have been re-
ported to effectively catalyse intramolecular hydroamination.14–23
aSchool of Chemistry, The University of New South Wales, NSW 2052,
Australia. E-mail: b.messerle@unsw.edu.au; Fax: +61 2 9385 6141; Tel: +61
2 9385 4653
bResearch School of Chemistry, Australian National University, ACT 0200,
Australia
cInstitut fu¨r Anorganische Chemie, TU Bergakademie Freiberg, 09596,
Freiberg, Germany
Fig. 1 Intramolecular hydroamination with Rh(I) and Ir(I) catalysts.
† Electronic supplementary information (ESI) available: Further crystallo-
graphic information: ORTEP diagrams and crystallographic tables. CCDC
reference numbers 697500–697505. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b814168a
The nature of the counter-ion is known to strongly influence the
efficiency of ionic metal complexes as catalysts.24 Tetraphenylbo-
rate (BPh4 ) is larger and more weakly co-ordinating than other
-
634 | Dalton Trans., 2009, 634–642
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-
anions, such as PF6- and BF4 , and has been commonly utilised as
from [IrCl(COD)]2, respectively) when compared to the synthesis
directly from [IrCl(COD)]2 (66% and to 54%, respectively).
Rhodium(I) and iridium(I) complexes bearing two carbon
monoxide ligands and the N,N -donor ligands bpm and bim
were prepared via the addition of a solution containing both the
a counter-ion for charged metal catalysts as weak coordination is
highly desirable for catalytic systems.25 We have previously demon-
strated that Rh(I) complexes incorporating the BPh4 counter-
ion are more efficient catalysts for intramolecular hydroami-
nation than those incorporating PF6 or BF4 .21 The BArF
-
ligand and NaBArF to a solution containing either the metal
-
-
-
24
24
(tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) anion, and other
fluorinated analogues of BPh4 , have properties such as low
nucleophilicity, chemical inertness, high solubility and weak co-
ordinating strength,26 all of which can improve catalyst efficiency.
For example, studies of iridium phosphino–oxazole (P, N -donor
precursor [RhCl(CO)2]2, or the in situ generated metal complex
“[IrCl(CO)2]n” (prepared by stirring a solution of [IrCl(COE)2]2
(COE = cyclooctene) under an atmosphere of CO(g)) (Scheme 1).
-
The complexes [M(N«N)(CO)2]BArF (N«N = bpm, M = Ir
24
(8a), M = Rh (9a); or N«N = bim, M = Ir (10a), M =
ligands) complexes as enantioselective hydrogenation catalysts
Rh (11a)) were isolated as yellow crystalline solids in good
-
-
have shown that charged complexes with the BArF counter-
yields (62–76%). The BPh4 analogues of Ir complexes 8a and
24
-
ion (and other fluorinated analogues of BPh4 ) are more efficient
10a, [Ir(bpm)(CO)2]BPh4 (8b) and [Ir(bim)(CO)2]BPh4 (10b), have
previously been synthesised by the displacement of the COD
ligand of [Ir(N«N)(COD)]BPh4 (N«N = bpm or bim) with carbon
monoxide.21,32 Complex 8a was also synthesised from 4a via this
method with a lower yield than that obtained for the synthesis of
8a from [IrCl(COE)2]2 (Scheme 1).
-
-
-
catalysts than complexes containing the PF6 , BF4 and BPh4
anions.27–31 Complexes containing BArF as a counter-ion also
appear to be more moisture tolerant27–29 and, in general, exhibit a
longer lifetime and higher catalytic activity.30,31
-
24
Here we present the synthesis of a range of rhodium(I) and
-
iridium(I) complexes containing the BArF
counter-ion. The
24
activity of these complexes as catalysts for the intramolecular
hydroamination reaction was tested, and compared to the catalytic
-
activity of previously studied BPh4 analogues.
Results and discussion
Synthesis of metal complexes
Rhodium(I) and iridium(I) complexes bearing COD and
the bidentate ligands bis(pyrazol-1-yl)methane (bpm), bis(N-
methylimidazol-2-yl)methane (bim) or 1-(2-(diphenylpho-
sphino)ethyl)-3,5-diphenylpyrazole (Ph2PyP) were prepared using
Scheme 1
Single crystals of [Ir(Ph2PyP)(COD)]BArF (3a), [Ir(bpm)-
24
either [MCl(COD)]2 or [M(COD)2]BArF (M = Rh or Ir) as
(COD)]BArF
(4a), [Rh(bpm)(COD)]BArF
(5a), [Ir(bim)-
24
24
24
(COD)]BArF (6a), [Ir(bim)(CO)2]BArF (10a), and [Rh(bim)-
starting materials (Fig. 2). The addition of a solution of both
24
24
the bidentate ligand and NaBArF to a solution of the metal
(CO)2]BArF (11a) suitable for X-ray diffraction analysis were
24
24
precursor [MCl(COD)]2 (M = Rh or Ir) in tetrahydrofuran
obtained by the slow diffusion of n-hexane into a concentrated
solution of the respective complex in dichloromethane.† The
yielded [M(N«Y)(COD)]BArF (where N«Y = Ph2PyP, M =
24
Ir (3a); N«Y = bpm, M = Ir (4a), M = Rh (5a); or N«N =
bim, M = Ir (6a), M = Rh (7a)) as yellow or orange crystalline
solids in moderate to high yields (54–82%). Complexes 4a–7a
were also synthesised by stirring a tetrahydrofuran solution of
ORTEP diagrams of the cations of 3a, 4a and 6a are shown in
Fig. 3. The cations of the solid-state structures of the BArF
-
24
complexes 5a, 10a and 11a exhibit the same molecular shape
found previously for complexes which contain the identical
cations, [Rh(bpm)(COD)]ClO4,33 [Ir(bim)(CO)2]BPh4 (10b) and
the N,N -donor ligand and [M(COD)2]BArF (M = Rh or Ir) for
21
24
34
1 hour. The overall yields of the Ir complexes 4a and 6a were
[Rh(bim)(CO)2]BPh4 (11b), respectively.
somewhat improved using this second method (76% and 58%
The crystals of 4a and 6a consisted of two crystallographically
independent but almost identical sets of ions. Selected bond
lengths and bond angles for the solid-state structures of the cation
of 3a and one of the cations of each 4a and 6a are given in
Table 1. The Ir coordination spheres of 3a, 4a and 6a are essentially
square planar (regarding COD as a bidentate chelator). The six-
membered metallocycle of 3a, 4a and 6a, formed from the chelate
N,N -donor ligand or P, N -donor ligand, adopts a distorted boat
conformation in all three complexes. The Ir-N, Ir-P and Ir-C
bond lengths are comparable to those observed in the structures
of rhodium(I) and iridium(I) complexes containing bpm, bim or
phosphino-pyrazole ligands previously reported.18,21,22,32-37
The Ir–C bond lengths of the carbon atoms trans to P in
3a (see Fig. 3) are significantly longer than the Ir–C bond
˚
lengths of the carbon atoms trans to N (~2.23 A compared
Fig. 2 Synthesis of Ir(I) and Rh(I) complexes containing COD and the
bidentate ligands Ph2PyP, bpm and bim (3a–7a).
˚
to ~2.13 A, respectively) which can be explained by the high
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Table 1 Selected bond angles and bond lengths for the solid state structures of the cations of 3a, 4a and 6a
Bond Angles (◦)
3a
4a
6a
˚
Bond Lengths (A)
3a
4a
6a
Ir(1)–N(1)a
Ir(1)–N(4)b
Ir(1)–P(1)
Ir(1)–C(1)
Ir(1)–C(2)
Ir(1)–C(5)
Ir(1)–C(6)
C(1)–C(2)
C(5)–C(6)
2.1160(13)
—
2.083(3)
2.093(4)
—
2.117(4)
2.125(5)
2.118(4)
2.139(5)
1.394(8)
1.407(7)
2.087(4)
2.076(4)
—
2.123(5)
2.135(5)
2.141(5)
2.106(5)
1.412(7)
1.409(7)
P(1)–Ir(1)–N(1)
N(1)–Ir(1)–N(4)
N(1)a–Ir(1)–C(1)
N(1)a–Ir(1)–C(2)
P(1)–Ir(1)–C(5)
P(1)–Ir(1)–C(6)
N(4)b–Ir(1)–C(5)
N(4)b–Ir(1)–C(6)
C(1)–Ir(1)–C(6)
C(2)–Ir(1)–C(5)
86.72(4)
—
—
87.56(13)
90.19(17)
93.7(2)
—
87.28(16)
91.70(18)
97.6(2)
—
2.2886(4)
2.2241(16)
2.2364(15)
2.1291(15)
2.1449(16)
1.392(2)
1.414(2)
88.73(6)
96.58(5)
92.68(4)
95.31(4)
—
—
80.24(6)
80.72(6)
—
—
92.45(16)
92.85(15)
81.46(19)
81.9(2)
94.60(18)
89.01(18)
80.24(6)
80.9(2)
a N(1) = N(4) for 4a, b N(4) = N(1) for 4a.
Fig. 3 ORTEP depictions and atom numbering schemes of the cations of 3a, 4a and 6a with thermal ellipsoids at the 50% probability level. Hydrogen
atoms are omitted for clarity.
trans-influence of phosphorus compared to that of nitrogen.
The N–Ir–P bond angle of 3a followed the trend previously
observed for P«N ligand bite angles of complexes with the general
formula [Ir(R2PyP)(COD)]BPh4, where R = H (PyP = 1-(2-
(diphenylphosphino)ethyl)pyrazole)36 or Me (Me2PyP = 1-(2-
(diphenylphosphino)ethyl)-3,5-dimethylpyrazole).18 The R2PyP
ligand bite angle of the complexes decreases with increasing steric
bulk of the R substituents, H < Ph < Me, (89.47,36 86.72(4) and
84.31(5) ◦,18 respectively), which is most likely due to interaction
of the substituents at the 3 position of the pyrazole group with the
COD ligand.
amine (12) and 2-(2-phenylethynyl)aniline (13) (Tables 2–4) to
yield the synthetically useful N-heterocycles 2-methyl-1-pyrroline
(2), 2-phenyl-1-pyrroline (14) and 2-phenylindole (15), respec-
tively, was tested. All the reactions were carried out at 60 ◦C with
a catalyst loading of 2.1–2.3 mol%. The effect of solvent on the
efficiency of the complexes as catalysts was also investigated. The
use of NaBArF as a catalyst was tested as a control experiment
24
and it did not promote any conversion of 1 to 2 (Table 2).
Cyclisation of 4-pentyn-1-amine (1). To allow direct com-
-
parison of the activity of the BArF
complexes as cat-
24
The coordination spheres of the COD complexes 4a and 6a
are almost identical, with similar Ir–N and Ir–C bond lengths,
and similar bond angles about the metal centre. The Ir–C bond
lengths of the COD ligands are longer than those of the carbon
monoxide ligands in complexes [Ir(bpm)(CO)2]BPh4 (8b)32 and
[Ir(bim)(CO)2]BPh4 (10b),21 which is expected as carbon monoxide
is a more strongly binding ligand than 1,5-cyclooctadiene. The
bond lengths and angles of the structure of Ir complex 4a are
almost identical to those of Rh analogue 5a (see Table 1).
alysts with two of the most catalytically active analogous
-
17
BPh4 complexes reported previously, [Ir(bpm)(CO)2]BPh4
18
(8b) and [Ir(Ph2PyP)(COD)]BPh4 (3b), the catalysed cycli-
sation of 1 was tested using [Ir(bpm)(CO)2]BArF (8a) and
24
[Ir(Ph2PyP)(COD)]BArF (3a) (Table 2). When the catalysis was
24
performed in benzene the catalytic efficiency of 8a was very high,
reaching 97% conversion after only 0.7 hours with a turnover
frequency (TOF) of 387 h-1. Complex 8a, however, showed similar
-
catalytic activity to the BPh4 analogue 8b, in tetrahydrofuran-
d8, with 97% conversion in 1.12 hours and a turnover frequency
of 86 h-1, in comparison to 8b (1.5 mol%) which promoted a
conversion of 100% of 1 after 1.5 hours, TOF = 89 h-1.17 Complex
3a promoted 97% conversion of 1 to 2 in 2.87 hours (TOF =
Catalysis
The efficiency of Rh(I) and Ir(I) complexes containing the BArF
counter-ion as catalysts for the intramolecular hydroamination
-
24
384 h-1) which is less efficient than the BPh4 analogue 3b, which
-
of the alkynylamines 4-pentyn-1-amine (1), 4-phenyl-3-butyn-1-
reached 97% conversion after only 0.2 hours, with a TOF of
636 | Dalton Trans., 2009, 634–642
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1800 h-1.18 The BArF - complexes 3a and 8a exhibited similar TOF
for the hydroamination reaction; however a significant reduction in
Table 2 Catalysed hydroamination of 4-pentyn-1-amine (1) to produce
2-methyl-1-pyrroline (2)
24
activity was observed towards the end of the reaction using 3a. The
catalytic activity of rhodium(I) complex [Rh(bpm)(CO)2]BArF
24
(9a) was also tested, but showed lower catalytic efficiency than the
iridium(I) analogue 8a.
Catalyst
Solvent t [h]a
C6D6 0.70
TOF [h-1]b
-
The catalytic efficiency of 8a, containing the BArF anion, is
24
-
[Ir(bpm)(CO)2]BArF (8a)
387
86
89
384
44
1800
34
much improved over that of the BPh4 analogue 8b, where both
24
THF-d8 1.12
catalysts contain a N,N -donor ligand and carbonyl co-ligands. In
[Ir(bpm)(CO)2]BPh4 (8b)17,c
THF-d8 1.50 (100%)
contrast, the catalytic efficiency of 3a (with the BArF anion)
-
24
[Ir(Ph2PyP)(COD)]BArF (3a)
CDCl3
2.87
24
-
is much less than that of 3b (with the BPh4 anion), where
both catalysts contain a P, N -donor ligand and a COD coligand.
This suggests that the mechanism of catalysed intramolecular
hydroamination varies for the two different catalyst systems, and
that the effect of the weakly coordinating counter-ion BArF is
not necessarily beneficial for all catalytic systems.
THF-d8 9.55 (96%)
CDCl3 0.20
THF-d8 5.27 (88%)
C6D6
[Ir(Ph2PyP)(COD)]BPh4 (3b)18,c
[Rh(bpm)(CO)2BArF (9a)
24
NaBArF
—
—
24
-
a Time to > 97% conversion, unless otherwise stated, b Turnover fre-
quency = moles of product per moles of catalyst used per hour; calculated
at time of 50% conversion, c 1.5 mol%.
24
Table 3 Catalysed hydroamination of 4-phenyl-3-butyn-1-amine (12) to
produce 2-phenyl-1-pyrroline (14)
Cyclisation of 4-phenyl-3-butyn-1-amine (12). The rate of cy-
clisation of alkynylamines is affected by the terminal substituents
on the alkyne, with a decrease in substrate reactivity in the order
H > Me > Ph observed previously for 5-substituted 4-pentynyl-
1-amines,5,9,17,23 and Ph > n-alkyl > H for 4-substituted 3-butynyl-
1-amines.11,17 The efficiency of all the complexes containing
-
BArF (3a–11a) as catalysts for the intramolecular hydroam-
t [h]a
TOF [h-1]b
24
Catalyst
Solvent
ination of 4-phenyl-3-butyn-1-amine (12) to yield 2-phenyl-1-
pyrroline (14) was tested (Table 3). The most effective cata-
[Rh(bpm)(CO)2]BArF (9a)
C6D6
C6D6
THF-d8
C6D6
0.40
1.73
2.00
3.67
9.15
9.15
12.0 (71%)
12.0 (39%)
12.0 (13%)
0.45
201
119
108
22
30
29
3
—
—
50
188
15
12
1
24
[Ir(bpm)(COD)]BArF (4a)
24
lysts for the hydroamination of 12 were [Rh(bpm)(CO)2]BArF
[Rh(bim)(CO)2]BArF (11a)
24
24
(9a), [Ir(bpm)(COD)]BArF24 (4a) and [Rh(bim)(CO)2]BArF24 (11a)
which reached 97% conversion after 0.40, 1.73 and 2.00 hours,
respectively (TOF = 201, 119 and 108 h-1, respectively). The
catalytic efficiency of the Rh(I) complexes is significantly improved
[Ir(bpm)(CO)2]BArF (8a)
24
[Rh(bpm)(COD)]BArF (5a)
CDCl3
24
[Ir(Ph2PyP)(COD)]BArF (3a) C6D6
24
[Ir(bim)(CO)2]BArF (10a)
CDCl3
C6D6
CDCl3
THF-d8
Toluene-d8
CD3CN
CDCl3
24
[Ir(bim)(COD)]BArF (6a)
24
-
[Rh(bim)(COD)]BArF (7a)
over the efficiency of the BPh4 analogues [Rh(bpm)(CO)2]BPh4
24
[Rh(bpm)(CO)2]BArF (9a)
24
(9b) and [Rh(bim)(CO)2]BPh4 (11b), which led to 100% conversion
of 12 after 2.5 and 6 hours (in tetrahydrofuran-d8), respectively.17
The turnover frequencies reported here are the highest of any rates
reported to date for the catalysed cyclisation of 12.11,17 The largest
increase in catalytic efficiency of the BArF24- complexes compared
0.50
2.77 (95%)
17.3
CD3OD
41.5
a Where catalysis was tested in more than one solvent, only the best result
is presented here (except for 9a), b Time to > 97% conversion, unless
otherwise stated, c Turnover frequency = moles of product per moles of
catalyst used per hour; calculated at time of 50% conversion.
-
to that of the BPh4 complexes was observed for the Ir complex,
[Ir(bpm)(CO)2]BArF (8a), which promoted 97% conversion of
24
12 after 3.67 hours whereas [Ir(bpm)(CO)2]BPh4 (8b) promoted
the conversion of 12 to only 30% after 20 hours. Complex 4a,
with a COD co-ligand, promoted a 97% conversion of 12 in
1.73 hours, whereas the dicarbonyl analogue 8a took 3.67 hours,
with a TOF of 119 and 22 h-1, respectively. The other complexes
incorporating a N,N -donor ligand and COD, 5a–7a, were less
efficient catalysts than the analogous dicarbonyl complexes, 9a–
Table 4 Catalysed hydroamination of 2-(2-phenylethynyl)aniline (13) to
produce 2-phenylindole (15)
11a, for the cyclisation of 12.
-
Overall the rhodium(I) complexes containing BArF
were
24
more efficient catalysts for the intramolecular hydroamination
of 12 than the Ir(I) complexes with BArF -, which is consistent
24
Catalyst
Solvent
t [h]a
TOF [h-1]b
with the trend previously observed for the reactivity of analo-
[Rh(bpm)(CO)2]BArF (9a)
C6D6
CDCl3
C6D6
C6D6
0.67
1.97
10.70
27.52
87
50
6
-
24
gous complexes containing BPh4 towards substrates containing
internal versus terminal alkyne substituents.17 Kinetic studies
are currently underway to determine the mechanism of the
catalysed hydroamination reaction, and the possible reasons for
differences in substrate preference of the Rh(I) and Ir(I) catalysts.
Complexes containing the bispyrazolyl N,N -donor ligand bpm
showed much greater catalytic efficiency than those incorporating
[Ir(bpm)(CO)2]BArF (4a)
24
[Rh(bim)(CO)2]BArF (11a)
2
24
a Time to > 97% conversion, unless otherwise stated, b Turnover fre-
quency = moles of product per mole of catalyst used per hour; calculated
at time of 50% conversion.
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 634–642 | 637
©

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the bisimidazolyl N,N -donor ligand bim or the P, N -donor ligand
Ph2PyP, which are both more strongly binding ligands.
The intramolecular hydroamination of 13 to yield 15 was
investigated using [Rh(bpm)(CO)2]BArF (9a) as a catalyst in a
24
Of the solvents tested for the cyclisation of 12 using Rh complex
9a benzene-d6, toluene-d8 and tetrahydrofuran-d8 allowed the
highest rate of conversion, with 97% conversion of 12 in under
0.5 hours in each case (Table 3). The catalytic efficiency of 9a was
significantly lower in methanol-d4 than in any other solvent tested,
with 97% conversion of 12 to 14 taking over 40 hours.
microwave reactor at 60 and 100 ◦C. The rate of conversion of 13
to 15 was only slightly improved when the reaction was performed
at 60 ◦C by employing microwave irradiation as the heating
source. Conversion of 13 to 15 reached 99% after 0.5 hours using
microwave irradiation compared to conventional heating when a
conversion of 97% took 0.67 hours. Increasing the temperature
of the catalytic reaction to 100 ◦C in the microwave reactor
significantly improved the rate of conversion, with 99% conversion
of 13 to 15 occurring in only 0.08 hours.
Cyclisation of 2-(2-phenylethynyl)aniline (13). The catalysed
intramolecular hydroamination of 2-(2-phenylethynyl)aniline (13)
to yield 2-phenylindole (15) has previously been shown to be
less facile than the catalysed cyclisation of 1 or 12,12,15,16,23,38 with
the catalysed hydroamination of 13 using [Rh(bim)(CO)2]BPh4
(11b) (1 mol%, acetone-d6, 55 ◦C) reaching 50% conversion
after 3 hours, and not reaching 100% conversion until 40 hours
Conclusions
A method was developed for the synthesis of a series of
cationic rhodium(I) and iridium(I) complexes of the type
(TOF = 17 h-1).23 The iridium BPh4 complexes 8b and 10b
[M(L«L)(C2)]BArF where M = Rh or Ir, L«L = bis(pyrazol-
-
24
both failed to catalyse the cyclisation of 13.38 Here the use of
[Rh(bpm)(CO)2]BArF24 (9a) as the catalyst improved the hydroam-
1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim)
or1-(2-(diphenylphosphino)ethyl)-3,5-diphenylpyrazole(Ph2PyP)
ination reaction dramatically compared to the BPh4 complexes
and C2 = cyclooctadiene (COD) or (CO)2 and BArF
=
-
24
previously tested,23,38 with 97% conversion reached in 0.67 hours.
These results are comparable to the best previously reported
catalyst for the cyclisation of 13, which is an iridium(III) complex
tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) 4a–11a. The solid-
state structures of the complexes containing a COD ligand,
[Ir(Ph2PyP)(COD)]BArF (3a), [Ir(bpm)(COD)]BArF (4a) and
24
24
◦
which achieved 93% conversion after 1 hour (35 C, 1 mol%).15
[Ir(bim)(COD)]BArF (6a), were determined using X-ray diffrac-
24
The rhodium and iridium complexes containing BArF -, 4a and
tion analysis.
24
11a, also successfully catalysed the hydroamination of 13 with
97% conversion reached in under 30 hours for both complexes
(Table 4).
The highest rate of conversion for the cyclisation of the
alkynylamine 4-pentyn-1-amine (1) was achieved using the iridium
catalyst [Ir(bpm)(CO)2]BArF (8a), whereas the alkynylamines
24
Weakly coordinating anions, such as BArF -, allow greater
4-phenyl-3-butyn-1-amine (12) and 2-(2-phenylethynyl)aniline
(13) were most efficiently cyclised using the rhodium catalyst
[Rh(bpm)(CO)2]BArF24 (9a), confirming that the Rh(I) complexes
are more reactive toward internal alkynes than the iridium
24
separation of the ions of the catalyst, which in turn allows greater
availability of the metal centre to bind to the substrate. This
effect is significant when comparing the improvement of catalytic
efficiency of complexes containing the BArF - counter-ion, to the
complexes. The use of Rh(I) and Ir(I) complexes which incorporate
24
analogous complexes containing BPh4 , with different substrates.
the BArF counter-ion exhibited a marked improvement in rates
-
-
24
-
Improvements in catalytic activity of the BArF complexes were
of conversion for the intramolecular hydroamination reaction,
compared to analogous metal complexes which contained the
24
most significant with the much bulkier substrate 13 compared
to those observed for the smaller aliphatic substrate 1. These
results indicate that binding of bulkier substrates to the metal
centre of the catalyst is more hampered by the close proximity
-
BPh4 counter-ion. The most significant improvement in the
rate of the catalysed intramolecular hydroamination reaction
was for the alkynylamine 2-(2-phenylethynyl)aniline (13), which
reached a conversion of 97% conversion after 0.67 hours.
-
of the BPh4 anion than binding of smaller substrates to the
metal centre. Intermolecular proton–proton cross-peaks due to
Rh(bpm)(CO)2]BArF (9a) promoted comparable, if not higher,
24
-
through-space interactions between the BPh4 counter-ion and
rates of cyclisation of 12 and 13 to the most efficient late transition
the ligands have been previously observed in the 1H–1H NOESY
spectra of [Rh(bpm)(CO)2]BPh4 (9b), [Ir(bpm)(CO)2]BPh4 (4b)
and [Rh(bim)(CO)2]BPh4 (11b), indicating there is a long-lived
metal catalysts reported previously.11,15,17
The substrate dependence of the improvement of catalytic effi-
ciency of complexes containing the BArF - counter-ion, compared
24
-
-
association between the cations and BPh4 anion in the reaction
to that of the analogous complexes containing BPh4 , indicates
mixture.21
that the ability of bulkier substrates to bind to the metal centre
is more dependent on the coordinating ability of the anion than
that of smaller substrates. As a result the catalysts containing the
Catalysis undertaken with microwave heating. Microwave heat-
ing, as against conventional thermal heating, can dramatically
improve the efficiency of both standard synthetic, as well as
catalysed, reactions.39,40 Microwave irradiation provides a much
more energy efficient heating technique due to its ability to
directly heat the reaction mixture. The level of power input,
and therefore degree of heating, can also be better controlled.39,40
Recent investigations into the microwave-assisted hydroamination
of alkynes have shown there is a marked improvement in reaction
times of the microwave assisted reactions, when compared to those
undertaken using conventional heating methods.41
weakly coordinating BArF - counter-ion have a broader substrate
24
-
scope than those containing the BPh4 counter-ion.
In most cases the solvent leading to best conversions for
the intramolecular hydroamination reactions was benzene. The
use of microwave irradiation as a heating source compared to
conventional thermal heating only slightly increased the rate of
conversion of 13 at 60 ◦C. The increase in rate of cyclisation of 13
when microwave irradiation was employed at 100 ◦C is more likely
◦
due to the increase in temperature (from 60 C) than the use of
microwave heating over thermal heating.
638 | Dalton Trans., 2009, 634–642
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©

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istry, University of Sydney. Microanalyses were carried out at
the Campbell Analytical Laboratory, University of Otago, New
Zealand. Single Crystal X-ray analysis was performed by Dr Jo¨rg
Wagler at the Research School of Chemistry, Australian National
University, Canberra. X-ray diffraction data was collected in phi
and omega scans on a Nonius KappaCCD diffractometer using
Mo–Ka radiation. The structures were solved with direct methods
(SHELXS97) and refined by full-matrix least-squares refinement
of F2 using SHELXL97.49 Crystals of 3a–6a, 10a and 11a suitable
for X-ray crystallography were grown from layering hexane over
a concentrated CH2Cl2 solution of the respective compound.
Crystallographic data for 3a–6a, 10a and 11a is given in Table 5.
Experimental
All manipulations of metal complexes and air sensitive reagents
were performed using Schlenk techniques under a dinitrogen
atmosphere or in a dinitrogen filled dry box. All solvents were
distilled under argon from a drying agent prior to use: sodium
benzophenone ketyl (benzene, diethyl ether, tetrahydrofuran,
hexane and pentane), calcium hydride (dichloromethane), or mag-
nesium turnings (methanol). Deuterated solvents for NMR were
distilled under vacuum from a drying agent prior to use: sodium
benzophenone ketyl (benzene-d6, THF-d8 and toluene-d8) or
calcium hydride (methanol-d4, acetonitrile-d3, dichloromethane-
d2 and chloroform-d3).
4-Pentyn-1-amine,42 4-phenyl-3-butyn-1-amine,11 2-(2-phenyl-
ethynyl)aniline,43 bis(1-pyrazolyl)methane (bpm),44 bis(N-methyl-
imidazolyl)methane (bim),23 Ph2PyP,18 [Ir(COE)2Cl]2,45 [Rh-
(COD)Cl]2,45 [Rh(CO)2Cl]2,46 [Ir(COD)Cl]2,45 [Rh(COD)2]-
[Ir(Ph2PyP)(COD)]BArF (3a)
24
To a solution of [Ir(COD)Cl]2 (100 mg, 0.14 mmol) in MeOH
(10 mL) was added dropwise a solution of Ph2PyP (130 mg,
47
47
48
BArF
,
[Ir(COD)2]BArF
and NaBArF
were prepared
0.30 mmol) and NaBArF (284 mg, 0.32 mmol) in THF (5 mL).
24
24
24
24
according to literature procedures.
The orange solution was stirred at room temperature for 2 hours,
during which time it became cloudy. The suspension was filtered,
the filtrate reduced to approximately 1 mL and hexane (10 mL)
added. Collection of the subsequent precipitate by filtration
followed by recrystallisation from diethyl ether and hexane
gave 3a as an orange solid (278 mg. 62%). Mp 144–147 ◦C
(from CH2Cl2/n-hexane). Anal. found: C, 51.94; H, 3.00; N,
1.57%. C69H49BF24IrN2P requires C, 51.92; H, 3.09, N, 1.76%.
1
1
1H, 13C{ H}, 31P{ H} NMR spectra were recorded on Bruker
DPX300, DMX500 or DPX600 spectrometers. All spectra were
recorded at 298 K, unless otherwise stated. H and 13C NMR
1
chemical shifts are referenced to internal solvent shifts. 31P NMR
chemical shifts were referenced externally to phosphoric acid
(85%) in D2O at 0.0 ppm. J values are given in Hz.
Infra-red spectra were obtained using an Avatar 370 FT-IR
(Thermo Nicolet) spectrometer. ESI-MS and MALDI-MS were
carried out by the Biological Mass Spectrometry Facility (BMSF),
University of NSW, the Mass Spectrometry Unit, UNSW School
of Chemistry and the Mass Spectrometry Unit, School of Chem-
d
H (500 MHz; CD2Cl2; 200 K) 7.88–7.77 (4H, m, CH of Ph), 7.74
(8H, br s, o-CH of BArF24), 7.60–7.50 (8H, m, CH of Ph), 7.53
(4H, br s, p-CH of BArF24), 7.46–7.36 (6H, m, CH of Ph), 7.10 (2H,
m, CH of Ph), 6.63 (1H, s, H4), 5.23–5.01 (2H, m, NCH2), 4.87
Table 5 Summary of crystallographic data for 3a, 4a, 6a, 5a, 10a and 11a
3a
4a
6a
5a
10a
11a
C43H24BF24N4O2Rh.0.5
C47H32BF24N4Rh C43H24BF24IrN4O2 (CH2Cl2)
Empirical formula
C69H49BF24IrN2P
C47H32BF24IrN4
C49H36BF24IrN4
M (g mol-1)
Crystal system
Space group
1596.10
Monoclinic
P21/n
12.5044(3)
35.3357(9)
14.8836(4)
1311.78
Triclinic
P1
1339.85
Triclinic
P1
1222.49
Triclinic
P1
1287.67
Monoclinic
P21/n
12.40560(10)
24.5181(3)
16.1804(2)
1240.84
Monoclinic
P21/n
13.1291(3)
25.6224(6)
15.3207(4)
¯
¯
¯
˚
a (A)
14.9389(3)
15.8085(2)
20.8606(4)
107.512(1)
92.128(1)
91.166(1)
4692.34(14)
1.843
17.0661(2)
18.5517(2)
19.3024(2)
65.834(1)
64.306(1)
75.404(1
5003.69(10)
1.779
13.0057(2)
13.6112(2)
15.8258(3)
68.912(1)
69.271(1)
68.368(1)
2349.38(7)
1.728
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
100.956(1)
111.584(1)
113.072(1)
3
˚
V (A )
6456.5(3)
1.642
4
4576.36(9)
1.869
4
4741.6(2)
1.738
4
Dc (g.cm-3)
Z
4
4
2
T (K)
100(2)
100(2)
100(2)
100(2)
100(2)
100(2)
Crystal size (mm)
q range (◦)
Completeness (%)
Index ranges
0.31 ¥ 0.29 ¥ 0.25 0.45 ¥ 0.42 ¥ 0.28 0.30 ¥ 0.27 ¥ 0.21 0.49 ¥ 0.44 ¥ 0.18 0.39 ¥ 0.24 ¥ 0.15
0.39 ¥ 0.32 ¥ 0.24
2.73–30.00
99.6
-18 ≥ h ≥ 18
-33 ≥ k ≥ 36
-21 ≥ l ≥ 21
75612
2.61–33.00
99.7
2.59–30.00
99.7
2.57–30.00
99.9
2.73–30.00
99.7
2.71–30.00
99.9
-19 ≥ h ≥ 18
-54 ≥ k ≥ 54
-22 ≥ l ≥ 20
130673
-21 ≥ h ≥ 21
-22 ≥ k ≥ 21
-29 ≥ l ≥ 29
90419
-24 ≥ h ≥ 24
-26 ≥ k ≥ 26
-27 ≥ l ≥ 27
135754
-18 ≥ h ≥ 18
-19 ≥ k ≥ 19
-22 ≥ l ≥ 22
55288
-17 ≥ h ≥ 17
-34 ≥ k ≥ 34
-22 ≥ l ≥ 22
74647
Reflns measured
Unique reflns
Rint
24270
27296
29145
13658
13330
13785
0.0649
0.0393
0.0619
0.0445
0.0383
0.0664
GoF(all)
1.046
0.0254
0.0552
0.0346
1.105
0.0491
0.1305
0.0718
1.251
0.0516
0.1192
0.0624
1.068
0.0478
0.1267
0.0589
1.055
0.0470
0.1225
0.0650
1.052
0.0424
0.1030
0.0608
R1 (I > 2s(I))
wR2 (I > 2s(I))
R1 (all data)
wR2 (all data)
0.0574
0.1399
0.1218
0.1323
0.1306
0.1102
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Dalton Trans., 2009, 634–642 | 639
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(1H, br s, CH of COD), 4.10 (1H, br s, CH of COD), 3.32 (1H,
m, CH of COD), 3.15 (1H, m, CH of COD), 2.50 (4H, m, CH2 of
COD), 2.36 (m, 1H, PCH2), 2.26 (m, 1H, PCH2), 1.74 (m, 1H, CH2
of COD), 1.42–1.18 (3H, m, CH2 of COD) ppm. dP{H} (121 MHz;
CD2Cl2) 14.8 (s) ppm. dC (75 MHz; CD2Cl2; 218 K) 163.0 (q, 1JB-C
49.8, ipso-C to B), 153.8 (PhCN), 149.2 (PhCN), 135.9 (s, o-CH
to B), 134.0 (d, 2JP-C 10.9, o-C to P), 132.4 (s, ipso-C of Ph), 132.0
(s, ipso-C of Ph), 131.5 (d, 1JP-C 52.4, ipso-C to P), 130.8 (d, 2JP-C
10.3, o-C to P), 130.4 (s, C of Ph), 130.2 (qq, 2JF-C 31.5, 3JB-C 2.9,
CCF3), 130.1 (s, C of Ph), 129.8 (s, C of Ph), 129.4 (s, C of Ph),
129.1 (s, C of Ph), 128.9 (s, C of Ph), 128.8 (s, C of Ph), 128.6 (d,
1JP-C 50.2, ipso-C to P), 128.5 (s, C of Ph), 128.3 (s, C of Ph), 128.0
(s, C of Ph), 125.7 (q, 1JF-C 272.3, CF3), 118.5 (sept, 3JF-C 4.0, p-CH
to B), 107.8 (s, C4), 98.8 (d, 2JP-C 8.4, CH of COD), 91.0 (d, 2JP-C
13.9, CH of COD), 66.7 (s, CH of COD), 62.9 (s, CH of COD),
47.9 (s, NCH2), 37.1 (s, CH2 of COD), 32.0 (s, CH2 of COD), 27.8
(2H, d, 3J 2.7, CH), 7.82 (8H, br s, o-CH of BArF24), 7.76 (2H, d,
3J 2.3, CH), 7.60 (4H, br s, p-CH of BArF24), 6.81 (2H, s, CH2),
6.49 (2H, apparent t, J 2.5, CH), 4.57 (4H, br s, CH of COD),
2.56 (4H, m, CH2 of COD), 2.08 (4H, m, CH2 of COD) ppm. dC
(75 MHz; THF-d8) 163.0 (q, 1JB-C 49.8, ipso-C to B), 143.8 (s, CH),
135.8 (s, o-CH to B), 134.8 (s, CH), 130.3 (qq, 2JF-C 31.5, 3JB-C 2.9,
CCF3), 125.7 (q, 1JF-C 272.3, CF3), 118.4 (sept, 3JF-C 4.0, p-CH to
B), 108.9 (s, CH), 85.5 (d, 1JRh-C 12.5, CH of COD), 64.6 (s, CH2),
31.4 (s, CH2 of COD) ppm. MALDI-MS m/z 359 ([M]+, 100%).
3
[Ir(bim)(COD)]BArF (6a)
24
Obtained as an orange solid. Yield: 54% (Method (a)), 74%
(Method (b)). Mp: 124–128 ◦C (from CH2Cl2/n-hexane). Anal.
found: C, 43.92; H, 3.08; N, 4.12%. C49H36BF24IrN4 requires C,
43.93; H, 2.71; N, 4.18%. dH (300 MHz; THF-d8) 7.79 (8H, br s,
o-CH of BArF24), 7.57 (4H, br s, p-CH of BArF24), 7.35 (2H, d, 3J
2
(d, JP-C 36.4, CH of COD), 27.1 (s, CH2 of COD), 26.1 (s, CH2
3
1.8, CH), 7.11 (2H, d, J 1.8, CH), 4.48 (2H, s, CH2), 4.10 (4H,
of COD). MALDI-MS m/z 733 ([M]+, 100%).
Complexes 4a–7a were synthesised by two different methods,
(a) and (b):
br s, CH of COD), 3.81 (6H, s, CH3), 2.28 (4H, m, CH2 of COD),
1.80 (4H, m, CH2 of COD) ppm. dC (75 MHz; THF-d8) 163.0 (q,
1JB-C 49.9, ipso-C to B), 142.4 (s, NC(CH2-)N), 135.8 (s, o-CH to
Method (a): To a solution of [M(COD)Cl]2 (M = Rh or Ir)
2
3
1
B), 130.2 (qq, JF-C 31.65, JB-C 2.9, CCF3), 125.7 (q, JF-C 272.2,
CF3), 125.4 (s, CH), 124.2 (s, CH), 118.4 (sept, 3JF-C 4.0, p-CH to
B), 66.7 (s, CH of COD), 34.3 (s, NCH3), 32.0 (s, CH2 of COD),
24.5 (s, CH2) ppm. MALDI-MS m/z 477 ([M]+, 100%).
(0.14 mmol) in THF (10 mL) was added dropwise a solution of
either bim or bpm (0.30 mmol) and NaBArF (0.32 mmol) in
24
THF (5 mL). The solution was stirred at room temperature for
2 hours, resulting in a yellow, cloudy suspension. The suspension
was filtered, the filtrate reduced to approximately 1 mL and
hexane (10 mL) added. Collection of the subsequent precipitate
by filtration followed by washing with hexane (3 ¥ 10 mL) or
recrystallization from diethyl ether and hexane gave the product
as a yellow or orange solid.
[Rh(bim)(COD)]BArF (7a)
24
Obtained as a yellow crystalline solid. Yield: 80% (Method
(a)), 79% (Method (b)). Mp: 146–148 ◦C (from CH2Cl2/n-
hexane). Anal. found: C, 47.15
; H, 3.16; N, 4.49%.
Method (b): A solution of bpm or bim (0.16 mmol) and
C49H36BF24RhN4requires C, 47.06; H, 2.90; N, 4.48%. dH
[M(COD)2]BArF (M = Rh or Ir) (~0.17 mmol) in THF (5 mL)
(300 MHz; THF-d8) 7.83 (8H, br s, o-CH of BArF24), 7.61 (4H,
4
were stirred for 1 hour. The solution was reduced to 2 mL and
hexane added slowly. Collection of the resulting solid by filtration
followed by washing with hexane (3 ¥ 10 mL) gave the product as
a yellow or orange solid.
3
3
br s, p-CH of BArF24), 7.20 (2H, d, J 1.6, CH), 6.82 (2H, d, J
1.6, CH), 4.39 (2H, s, CH2), 4.35 (4H, br s, CH of COD), 3.77
(6H, s, CH3), 2.47 (4H, m, CH2 of COD), 2.01 (4H, m, CH2 of
COD) ppm. dC (75 MHz; THF-d8) 163.0 (q, 1JB-C 49.9, ipso-C to
2
B), 142.6 (s, NC(CH2-)N), 135.8 (s, o-CH to B), 130.3 (qq, JF-C
3
31.6, JB-C 2.9, CCF3), 125.7 (q, 1JF-C 272.3, CF3), 125.7 (s, CH),
[Ir(bpm)(COD)]BArF (4a)
24
3
1
123.7 (s, CH), 118.4 (sept, JF-C 4.0, p-CH to B), 82.9 (d, JRh-C
12.6, CH of COD), 34.0 (s, NCH3), 31.4 (s, CH2 of COD), 24.4 (s,
CH2) ppm. MALDI-MS m/z 387 ([M]+, 100%).
Obtained as a yellow crystalline solid. Yield: 66% (Method (a)),
97% (Method (b)). Mp: 162–165 ◦C (from CH2Cl2/n-hexane).
Anal. found: C, 43.32; H, 2.76; N, 4.49%. C47H32BF24IrN4 requires
C, 43.03; H, 2.46; N, 4.27%. dH (300 MHz; THF-d8) 8.08 (2H, d, 3J
2.6, CH), 7.98 (2H, br s, CH), 7.83 (8H, br s, o-CH of BArF24), 7.61
(4H, br s, p-CH of BArF24), 6.74 (2H, s, CH2), 6.60 (2H, apparent
t, 3J 2.4, CH), 4.33 (4H, br s, CH of COD), 2.37 (4H, m, CH2 of
COD), 1.90 (4H, m, CH2 of COD) ppm. dC (75 MHz, THF-d8)
[Ir(bpm)(CO)2]BArF (8a)
24
Method (a): A solution of [Ir(COE)2Cl]2 (134 mg, 0.15 mmol)
in THF (20 mL) was degassed via 3 cycles of freeze–vac–thaw
and stirred under an atmosphere of CO(g) for 5 minutes. To
the resulting blue–black suspension was added a solution of
1
163.0 (q, JB-C 49.9, ipso-C to B), 144.0 (s, CH), 135.8 (s, o-CH
2
3
to B), 135.4 (br s, CH), 130.2 (qq, JF-C 31.6, JB-C 2.9, ipso-C to
bpm (46 mg, 0.30 mmol) and NaBArF (284 mg, 0.32 mmol)
24
1
3
CF3), 125.7 (q, JF-C 272.2, CF3), 118.4 (sept, JF-C 4.0, p-CH to
B), 109.1 (s, CH), 70.1 (s, CH of COD), 64.5 (s, CH2), 32.0 (s, CH2
of COD) ppm. MALDI-MS m/z 449 ([M]+, 100%).
in THF (5 mL). Within 1 hour formation of a yellow solution
containing a small quantity of colourless solid was observed. This
suspension was stirred for a further hour at room temperature
and filtered. The filtrate was reduced to approximately 1 mL and
hexane (10 mL) added. Collection of the subsequent precipitate
by filtration followed by washing with hexane (3 ¥ 10 mL) and
recrystallization from diethyl ether and hexane gave 8a as a yellow
solid (269 mg, 71%).
[Rh(bpm)(COD)]BArF (5a)
24
Obtained as a bright yellow crystalline solid. Yield: 82% (Method
(a)), 72% (Method (b)). Mp: 158–160 ◦C (from CH2Cl2/n-hexane).
Anal. found: C, 46.17; H, 2.95; N, 4.49%. C47H32BF24RhN4
requires C, 46.18; H, 2.64; N, 4.58%. dH (300 MHz; THF-d8) 7.99
Method (b): A solution of 4a (150 mg) in CH2Cl2 (5 mL) was
stirred under an atmosphere of CO(g) at room temperature for
640 | Dalton Trans., 2009, 634–642
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30 min. After completion of the reaction, the solution was reduced
to 1 mL and hexane was added slowly. Collection of the resulting
solid by filtration followed by washing with hexane (3 ¥ 10 mL)
gave 8a as a pale yellow crystalline solid (105 mg, 66%).
135.9 (s, o-CH to B), 131.8 (s, CH), 130.3 (qq, 2JF-C 31.5, 3JB-C 2.9,
CCF3), 125.8 (q, 1JF-C 272.4, CF3), 124.8 (s, CH), 118.5 (sept, 3JF-C
3.9, p-CH to B), 34.5 (s, NCH3), 24.3 (s, CH2) ppm. MALDI-MS
m/z 425 ([M]+, 100%).
Mp 113–116 ◦C (from CH2Cl2/n-hexane). Anal. found: C,
39.42; H, 1.88; N, 4.46%. C41H20BF24IrN4O requires C, 39.09;
H, 1.60; N, 4.45%. umax/cm-1 2100 m (CO), 2035 m (CO). dH
(300 MHz; THF-d8) 8.23 (2H, br s, CH), 8.18 (2H, d, J 2.7, CH),
7.83 (8H, br s, o-CH of BArF24), 7.60 (4H, br s, p-CH of BArF24),
[Rh(bim)(CO)2]BArF (11a)
24
To a solution of [Rh(CO)2Cl]2 (54.4 mg, 0.14 mmol) in diethyl ether
(5 mL) was added dropwise a solution of bim (54 mg, 0.30 mmol)
and NaBArF (284 mg, 0.32 mmol) in diethyl ether (10 mL). The
3
24
6.78 (2H, s, CH2), 6.64 (2H, apparent t, J = 2.6, CH) ppm. dC
solution was stirred at room temperature for 2 hours, resulting
in a yellow, cloudy suspension. The suspension was filtered, the
filtrate reduced to approximately 1 mL and hexane (10 mL) added.
Collection of the subsequent precipitate by filtration followed by
washing with hexane (3 ¥ 10 mL) gave 11a as a yellow crystalline
solid (256 mg, 76%). Mp 116–118 ◦C (from CH2Cl2/n-hexane).
Anal. found: C, 42.97; H, 2.33; N, 4.63%. C43H24BF24RhN4O2
requires C, 43.10; H, 2.02; N, 4.68%. umax/cm-1 2097 m (CO), 2030
m (CO). dH (300 MHz; THF-d8) 7.79 (8H, br s, o-CH of BArF24),
7.58 (4H, br s, p-CH of BArF24), 7.36 (2H, dAB, 3J 1.6, CH), 7.29
(2H, dAB, 3J 1.6, CH), 4.43 (2H, s, CH2), 3.83 (6H, s, CH3) ppm. dC
(75 MHz; THF-d8) 185.3 (d, 1JRh-C 67.6, CO), 163.0 (q, 1JB-C 49.8,
ipso-C to B), 143.8 (s, NC(CH2-)N), 135.8 (s, o-CH to B), 131.6
(d, 2JRh-C 1.2, CH), 130.2 (qq, 2JF-C 31.5, 3JB-C 2.9, CCF3), 125.7 (q,
(75 MHz; THF-d8) 171.2 (s, CO), 163.1 (q, 1JB-C 50.0, ipso-C to B),
148.5 (s, CH), 136.5 (s, CH), 135.9 (s, o-CH to B), 130.3 (qq, 2JF-C
31.9, 3JB-C 2.9, CCF3), 125.8 (q, 1JF-C 272.4, CF3), 118.5 (sept, 3JF-C
3.9, p-CH to B), 109.9 (s, CH), 64.4 (s, CH2) ppm. MALDI-MS
m/z (%): 397 ([M]+, 100). MALDI-MS m/z 397 ([M]+, 100%).
[Rh(bpm)(CO)2]BArF (9a)
24
Method (a): To a solution of [Rh(CO)2Cl]2 (54.4 mg, 0.14 mmol) in
diethyl ether (5 mL) was added dropwise a solution of bpm (46 mg,
0.30 mmol) and NaBArF (284 mg, 0.32 mmol) in diethyl ether
24
(10 mL). The solution was stirred at room temperature for 2 hours,
resulting in a pale yellow, cloudy suspension. The suspension
was filtered, the filtrate reduced to approximately 1 mL and
hexane (10 mL) added. Collection of the subsequent precipitate
by filtration followed by washing with hexane (3 ¥ 10 mL) and
recrystallisation from diethyl ether and hexane gave 9a as a pale
yellow solid (216 mg, 62%).
3
3
1JF-C 272.3 Hz, CF3), 124.3 (d, JRh-C 0.8, CH), 118.4 (sept, JF-C
4.0, p-CH to B), 34.4 (s, NCH3), 24.3 (s, CH2) ppm. MALDI-MS
m/z 335 ([M]+, 100%).
Mp 124–127 ◦C (from CH2Cl2/n-hexane). umax/cm-1 2110 m
(CO), 2052 m (CO). dH (300 MHz; THF-d8) 8.12 (4H, m, CH),
7.82 (8H, br s, o-CH of BArF24), 7.61 (4H, br s, p-CH of BArF24),
General procedure for catalysis
Thermal catalysed hydroamination reactions were conducted in
NMR tubes fitted with a concentric Teflon valve. The catalyst
complex (4.8 mmol, 2.30 mol%) was dissolved in dry, degassed
deuterated solvent (0.6 mL) in the NMR tube, and the substrate
(0.21 mmol) added by injection. All catalytic reactions were
conducted under a nitrogen atmosphere at 60 ◦C in the NMR
spectrometer. The temperature in the NMR magnet was calibrated
using neat ethylene glycol. Characterisation of products was
confirmed by comparison to literature data or an authentic sample,
only one product was formed in each reaction.11,17
3
6.71 (2H, s, CH2), 6.62 (2H, apparent t, J 2.5, CH) ppm. dC
(75 MHz; THF-d8) 183.4 (d, 1JRh-C 69.5, CO), 163.0 (q, 1JB-C 49.8,
ipso-C to B), 147.6 (s, CH), 135.8 (s, o-CH to B), 135.7 (s, CH),
130.3 (qq, 2JF-C 31.6, 3JB-C 2.9, CCF3), 125.7 (q, 1JF-C 272.5, CF3),
118.4 (sept, 3JF-C = 4.0, p-CH to B), 109.4 (s, CH), 64.4 (s, CH2)
ppm. MALDI-MS m/z 307 ([M]+, 82%).
[Ir(bim)(CO)2]BArF (10a)
24
Conversion rates and yields were determined by integration of
the product resonances relative to the substrate resonances in the
1H NMR spectra acquired at given time intervals. All yields refer
to the NMR yield. The turnover frequency (TOF) was calculated
as the number of moles of product/moles catalyst/hour and was
calculated at the point of 50% conversion of substrate.
A solution of [Ir(COE)2Cl]2 (134 mg, 0.15 mmol) in THF (20 mL)
was degassed via 3 cycles of freeze-vac-thaw and stirred under an
atmosphere of CO(g) for 5 minutes. To the resulting blue–black
suspension was added a solution of bim (54 mg, 0.30 mmol) and
NaBArF (284 mg, 0.32 mmol) in THF (5 mL). Within 1 hour
24
formation of a yellow suspension containing a small quantity
of colourless solid was observed. This suspension was stirred
for a further hour at room temperature and filtered. The filtrate
was reduced to approximately 1 mL and hexane (10 mL) added.
Collection of the subsequent precipitate by filtration followed by
washing with hexane (3 ¥ 10 mL) and recrystallisation from diethyl
ether and hexane gave 10a as a red crystalline solid (290 mg, 75%).
Mp 144–147 ◦C (from CH2Cl2/n-hexane). Anal. found: C, 40.49;
H, 2.22; N 4.39%. C43H24BF24IrN4O2 requires C, 40.11; H, 1.88;
N, 4.35%. umax/cm-1 2067 m (CO), 2005 m (CO). dH (300 MHz;
THF-d8) 7.90 (8H, br s, o-CH of BArF24), 7.67 (4H, br s, p-CH of
BArF24), 7.43 (2H, dAB, 3J 1.8, CH), 7.40 (2H, dAB, 3J 1.8, CH), 4.57
(2H, s, CH2), 3.88 (6H, s, CH3) ppm. dC (75 MHz; THF-d8) 173.8
(s, CO), 162.6 (q, 1JB-C 49.9, ipso-C to B), 144.0 (s, NC(CH2-)N),
Acknowledgements
Financial support from the Australian Research Council and the
University of New South Wales is gratefully acknowledged. J. W.
acknowledges his post-doctoral scholarship by the German Aca-
demic Exchange Services (DAAD). J. H. H. H. acknowledges the
University of New South Wales for her University International
Postgraduate Award (UIPA).
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642 | Dalton Trans., 2009, 634–642
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