Metalloligands containing aminofulvene-aldiminate (AFA) ligands and their bimetallic complexes

Article abstract of DOI:10.1039/c2dt32804f

A simple and convenient route to η⁵-coordinated Ru and Rh aminofulvene-aldiminate (AFA) complexes is described. The metalloligands [Cp*Ru{η⁵-(Ph₂AFAH)}][BF₄] (3), [Cp*Ru{η⁵-(benzyl₂AFAH)}][OTf] (7), [Cp*Rh{η⁵-(Cy₂AFA)H}][BF₄] ₂ (8) and [Cp*Rh{η⁵-(Cy₂AFA)}] [BF₄] (9) have been synthesised and characterised. The basicity of 9 has been found to be significantly less than its neutral analogue and thus eliminates the need for a deprotonation step to ligate to a second metal in the κ²-N,N′-coordination mode. The reaction of 9 with a palladium precursor provides a mixed-metal complex [Cp*Rh(η ⁵/κ²-Cy₂AFA)PdCl₂][BF ₄] (12). Cyclic voltammetry studies of the Ph₂AFAH ligand shows an irreversible one electron oxidation peak at +1.0 V (vs. Fc/Fc ⁺). Complex 3 shows an irreversible oxidation at +1.5 V and a reduction peak at -1.0 V. The oxidation of 3 occurs on the AFA ligand backbone whereas the structurally analogous neutral 1,2-bis(imidoyl)pentamethyl- ruthenocene shows reversible oxidation at the Ru center.

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Metalloligands containing aminofulvene-aldiminate
(AFA) ligands and their bimetallic complexes†
Cite this: Dalton Trans., 2013, 42, 2879
Philip J. Bailey,* Mahmudur Rahman, Simon Parsons, Muhammad R. Azhar and
Fraser J. White
A simple and convenient route to η5-coordinated Ru and Rh aminofulvene-aldiminate (AFA) complexes is
described. The metalloligands [Cp*Ru{η5-(Ph2AFAH)}][BF4] (3), [Cp*Ru{η5-(benzyl2AFAH)}][OTf] (7),
[Cp*Rh{η5-(Cy2AFA)H}][BF4]2 (8) and [Cp*Rh{η5-(Cy2AFA)}][BF4] (9) have been synthesised and character-
ised. The basicity of 9 has been found to be significantly less than its neutral analogue and thus elimin-
ates the need for a deprotonation step to ligate to a second metal in the κ2-N,N’-coordination mode. The
reaction of 9 with a palladium precursor provides a mixed-metal complex [Cp*Rh(η5/κ2-Cy2AFA)PdCl2]-
[BF4] (12). Cyclic voltammetry studies of the Ph2AFAH ligand shows an irreversible one electron oxidation
peak at +1.0 V (vs. Fc/Fc+). Complex 3 shows an irreversible oxidation at +1.5 V and a reduction peak at
−1.0 V. The oxidation of 3 occurs on the AFA ligand backbone whereas the structurally analogous neutral
1,2-bis(imidoyl)pentamethyl-ruthenocene shows reversible oxidation at the Ru center.
Received 23rd November 2012,
Accepted 19th December 2012
DOI: 10.1039/c2dt32804f
www.rsc.org/dalton
We have previously reported the serendipitous synthesis of
Introduction
the η5-coordinated complex [Cp*Ru(η5-Ph2AFA)] (2) via ligand
The aminofulvene-aldiminate (AFA) ligand (1)1,2 is ambiden- transfer from the tetrahedral bis-ligand zinc complex [Zn(κ2-
tate in character, capable of coordinating in both η5- and κ2-N, Ph2AFA)2] on reaction with two equivalents of [Cp*Ru(MeCN)3]-
N′-coordination modes through the C5 cyclopentadienyl ring [BF4].3b Presumably, this complex is formed through a Zn/Ru
or the two N donor atoms respectively (Fig. 1).3 In recent years bimetallic or Ru/Zn/Ru trimetallic intermediate which sub-
much attention has been paid to this ligand system due to this sequently fragments with the release of 2. In the solid state 2
feature, and the possibility of introducing a range of nitrogen is air- and moisture-stable, but in solution it was observed to
substituents to tune the steric and/or electronic properties for be readily protonated at nitrogen by adventitious water
their possible application in catalysis. Johnson has developed forming [Cp*Ru(η5-Ph2AFAH)]+ (3).
a one-pot synthesis of AFA ligands and explored their Cu, Al
The 6-amino-2-imidoyl-pentafulvenes 4a and 4b (Scheme 1)
and Zn chemistry exploiting their κ2-N,N′-coordination are structural analogues of the fulvene aldimine [N,N]H
modes.2 Examples in which both types of coordination occur ligands (1). Bildstein and co-workers have developed a syn-
in the same complex, and in which the ligand therefore links thetic route to these molecules and also synthesised the corres-
two metal centres, are also known.3
ponding 1,2-bis(imidoyl)pentamethylruthenocenes (5a, 5b) by
treatment of the ligands with [Cp*Ru(CH3CN)3]PF6.4 Here we
report a more rational route to the synthesis of η5-coordinated
Ru and Rh–AFA complexes and a Rh–Pd bimetallic complex.
Fig. 1 Resonance forms of the aminofulvene-aldiminate (AFA) ligand (1) and
the numbering scheme used in discussion of NMR spectra.
School of Chemistry, University of Edinburgh, The King’s Buildings, West Mains
Road, Edinburgh, EH9 3JJ, UK. E-mail: Philip.Bailey@ed.ac.uk; Tel: +44 (0) 131 650
6448
†CCDC 911986–911989. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt32804f
Scheme 1 Synthesis of bis(imidoyl)(pentamethyl)ruthenocenes.
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The electrochemistry of the AFAH ligand and complex 3 is also
explored.
Results and discussion
We have now found that [Cp*Ru(Ph2AFAH)][BF4] (3) may be
synthesised via a more rational route through the direct reac-
tion of the Ph2AFAH ligand with [Cp*Ru(CH3CN)3][BF4]5,6 in
CH2Cl2 at room temperature (Scheme 2). The 1H NMR spec-
trum of 3 in CDCl3 shows low frequency coordination shifts of
the C5-ring protons (H3/H5 and H4, see Fig. 1 for numbering
scheme) of the AFA ligand due to its η5-coordination to Ru.
The N–H signal and that for H1/H7 are shifted to slightly
higher frequency (δ 16.51 and 8.93 respectively) compared to
the Ph2AFAH ligand (δ 15.59 and 8.29 respectively). The H1/H7
protons appear as a doublet due to coupling to the N–H
proton. The mass spectrum (EI) of 3 shows the molecular ion
peak at m/z 509 consistent with the expected formulation. The
η5- rather than κ2-coordination of the Cp*Ru+ fragment to the
C5-ring of the AFA is consistent with its known affinity for
π-aromatic ligands.5
Fig. 2 Thermal ellipsoid drawing of [Cp*Ru(Ph2AFA)H][BF4] (3) (50% ellip-
−
soids). Hydrogen atoms, BF4 and minor disorder components have been
removed for clarity. Selected bond-lengths (Å) and angles (°) are provided in
Table 1.
The X-ray crystal structure of 3 (Fig. 2) confirms η5-coordi-
nation of the Cp*Ru+ fragment to the AFA ligand. The struc-
ture shows that the AFA ligand has lost its planarity on
coordination to Ru. The maximum deviation of non-Ph atoms
from the C5 plane is 0.354 Å (N15A) which is similar to its
previously characterised deprotonated analogue [Cp*Ru-
(Ph2AFA)].3b One of the two imine C–N arms is tilted out of the
ligand C5 mean plane and moved towards the Ru centre, and
as a result the distance between Ru and the two imine carbon
atoms [C(14A) and C(8A)] differ substantially (2.960 and
3.234 Å respectively). The N–H hydrogen atom has been placed
geometrically and it is evident that there is a strong N–H–N
intramolecular hydrogen bond to the second nitrogen. The
donor (N15A)–acceptor (N7A) distance is 2.69 Å which com-
pares with the value of 2.79 Å in the free ligand Ph2AFH.1d The
C–C bond lengths in the C5 ring are intermediate between
typical single and double bond lengths. One of the imine C–N
bonds is shorter [C(8A)–N(7A) 1.276(8) Å] than the other
[(C(14A)–N(15A) 1.297(8) Å] consistent with the placement of
the hydrogen atom on N15A. The distances between Ru and
the C5-ring carbon atoms are in the range of 2.159 to 2.222 Å.
The methyl groups in the Cp* appear large due to atomistic
modelling of free rotation of this ligand which forms a con-
tinuous band of electron density.
In a similar manner, the reaction of (Benzyl)2AFAH (6) with
[Cp*Ru(CH3CN)3][OTf] in acetonitrile at room temperature
gives the metalloligand [Cp*Ru{η5-(benzyl)2AFAH}][OTf] (7)
(Scheme 3). The 1H NMR study of 7 shows similar coordi-
nation shifts for the ligand protons as seen in 3.
The X-ray crystal structure of 7 (Fig. 3) shows that the
Cp*Ru+ fragment coordinates to the benzyl AFA ligand (6) via
the expected η5-coordination mode, the structure being very
similar to that of 3.
In order to reduce the steric interaction between the two
benzyl groups, one of them is tilted towards, and the other
away from, the Ru centre. Thus the distance between Ru and
one of the benzyl carbon atoms C(12A) is shorter (5.153 Å)
than the other C(72A) (5.362 Å).
The dicationic Rh(III) analogue of 3 and 7, [Cp*Rh{η5-
(Cy2AFA)H}][BF4]2 (8), containing the cyclohexyl substituted
AFA ligand, may also be synthesised by reaction of [Cp*Rh-
(CH3CN)3][BF4]2 with Cy2AFAH in CH2Cl2 (Scheme 4). This
complex is stable to air and moisture and is highly soluble in
CH2Cl2 and acetonitrile, but insoluble in hexane and
chloroform.
The 1H NMR spectrum of 8 indicates that the Cp*Rh2+
moiety has coordinated to the C5-ring of the Cy2AFAH ligand
in the η5-coordination mode. On the basis of the spectra for
the Ru complexes it was expected that coordination of
Cp*Rh2+ to the C5-ring would shift the H4 protons to lower
frequency, however they are instead shifted to 6.15 ppm (cf. δ
6.12 ppm in the free ligand). The N–H peak and H1/H7 of 8
are shifted to higher frequency (δ 16.80 and 8.55) compared to
Cy2AFAH (δ 13.66 and 7.91 respectively). The H1/H7 protons
appear as a doublet due to coupling with the N–H proton.
Coupling of 103Rh with the C5-ring protons (H3/H5) provides a
doublet of doublets and H4 appears as a doublet of triplets
(J = 2.65, 1.0 Hz) due to coupling with Rh and its neighbouring
Scheme 2 Synthesis of [Cp*Ru(Ph2AFA)H][BF4] (3).
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Table 1 Selected bond distances (Å) and angles (°) for compounds 3, 7, 8 and 11
3
7
8
11
C(9A)–C(13A)
C(9A)–C(10A)
1.443(9)
1.450(8)
1.400(10)
1.401(9)
1.439(9)
1.441(9)
1.424(8)
1.276(8)
1.297(8)
2.222(6)
2.189(6)
2.194(6)
2.170(6)
2.159(6)
122.7(6)
124.9(6)
129.6(6)
130.6(6)
106.0(6)
109.2(6)
Ru1–C(2A)
Ru1–C(3A)
Ru1–C(4A)
Ru1–C(5A)
Ru1–C(6A)
C(1A)–N(11A)
C(7A)–N(71A)
N(11A)–C(12A)
N(71A)–C(72A)
C(2A)–C(1A)–N(11A)
C(6A)–C(7A)–N(71A)
C(1A)–N(11A)–C(12A)
C(7A)–N(71A)–C(72A)
N(11A)–C(12A)–C(13A)
N(71A)–C(72A)–C(73A)
2.177(4)
2.181(5)
2.209(5)
2.201(5)
2.183(4)
1.284(6)
1.272(6)
1.474(6)
1.481(6)
124.4(5)
124.6(4)
122.4(4)
118.3(4)
112.5(4)
111.0(4)
C(9A)–C(13A)
1.450(3)
1.432(3)
1.410(4)
1.419(3)
1.430(3)
1.454(3)
1.453(3)
1.272(3)
1.268(3)
2.210(2)
2.205(2)
2.209(2)
2.197(2)
2.199(2)
124.8(2)
123.1(2)
107.84(19)
106.3(2)
130.6(2)
131.10(19)
C(7)–N(2)
C(1)–N(1)
C(6)–C(7)
C(2)–C(1)
C(2)–C(6)
C(6)–C(5)
C(5)–C(4)
C(4)–C(3)
C(3)–C(2)
C(6)–C(7)–N(2)
C(2)–C(1)–N(1)
C(7)–C(6)–C(2)
C(1)–C(2)–C(6)
C(2)–C(6)–C(5)
C(6)–C(2)–C(3)
C(2)–C(3)–C(4)
C(6)–C(5)–C(4)
C(3)–C(4)–C(5)
1.324(3)
1.324(3)
1.388(4)
1.393(4)
1.469(3)
1.412(4)
1.389(4)
1.396(4)
1.408(4)
124.8(3)
124.0(3)
125.1(2)
125.1(3)
106.0(2)
107.1(2),
108.4(3)
109.1(2)
109.4(3)
C(13A)–C(12A)
C(12A)–C(11A)
C(11A)–C(10A)
C(10A)–C(9A)
C(9A)–C(8A)
C(13A)–C(14A)
C(8A)–N(7A)
C(14A)–N(15A)
Rh1–C(11A)
Rh1–C(12A)
Rh1–C(13A)
Rh1–C(10A)
C(10A)–C(11A)
C(11A)–C(12A)
C(12A)–C(13A)
C(9A)–C(8A)
C(13A)–C(14A)
C(8A)–N(7A)
C(14A)–N(15A)
Ru1–C(11A)
Ru1–C(12A)
Ru1–C(10A)
Ru1–C(9A)
Ru1–C(13A)
C(9A)–C(8A)–N(7A)
C(13A)–C(14A)–N(15A)
C(14A)–C(13A)–C(9A)
C(13A)–C(9A)–C(8A)
C(13A)–C(9A)–C(10A)
C(9A)–C(10A)–C(11A)
Rh1–C(9A)
C(9A)–C(8A)–N(7A)
C(13A)–C(14A)–N(15A)
C(13A)–C(9A)–C(10A)
C(9A)–C(13A)–C(12A)
C(8A)–C(9A)–C(13A)
C(9A)–C(13A)–C(14A)
Scheme 4 Synthesis of [Cp*Rh(Cy2AFA)H][BF4]2.
Scheme 3 Synthesis of [Cp*Ru{(benzyl)2AFA}H][OTf] (7).
Fig. 4 Thermal ellipsoid drawing of [Cp*Rh(Cy2AFA)H][BF4]2 (8) (50% ellip-
Fig. 3 Thermal ellipsoid drawing of [Cp*Ru{(benzyl)2AFA}H][OTf] (7) (50%
ellipsoids). Hydrogen atoms and OTf have been removed for clarity. Selected
bond-lengths (Å) and angles (°) are provided in Table 1.
−
soids). Hydrogen atoms and BF4 have been removed for clarity. Selected bond-
lengths (Å) and angles (°) are provided in Table 1.
deviations of the imine nitrogen atoms (N7A and N15A) from
protons. In a similar manner, 103Rh couples with the AFA C5- the C5 plane are only 0.127 and 0.059 Å respectively. In con-
trast to 3, the two imine C–N arms are not tilted towards the
ring carbon atoms and provides four distinct doublets.
The X-ray crystal structure of 8 (Fig. 4) shows that Cp*Rh2+ metal centre; the distance between the Rh center and the two
coordinates to AFA ligand via the expected η5-coordination imine carbon atoms C14A and C8A are thus very similar (3.257
and 3.251 Å). As in 3 and 7, an N–H–N intramolecular
mode. The C5-ring of the AFA moiety is planar and the
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Scheme 5 Synthesis of [Cp*Rh(Cy2AFA)][BF4] (9).
hydrogen bond exists, and in 8 the donor (N7A)–acceptor
(N15A) distance is 2.687 Å. The N–H hydrogen atom was found
in a difference Fourier map and its position allowed to refine.
Although a large difference was observed between the imine
C–N bond lengths in 3, this feature is not evident in 8; the
imine C–N bond lengths are not crystallographically dis-
tinguishable [C(8A)–N(7A) and C(14A)–N(15A) are 1.272(3) and
1.268(3) respectively]. The C–C bond lengths in the C5 ring are
intermediate between typical single and double bond lengths.
Formation of K[Cy2AFA], by deprotonation of Cy2AFAH with
KH in THF, and its reaction with [Cp*Rh(CH3CN)3][BF4]2 in
THF affords [Cp*Rh(Cy2AFA)][BF4] (9) as an air- and moisture-
stable product (Scheme 5).
The basicity of the metalloligand 9 is significantly less than
that of its Ru analog [Cp*Ru(η5-Ph2AFA)] (2) and 1,2-bis-
(imidoyl)pentamethylruthenocenes (5a, 5b), as would be
anticipated for a cationic species. The nitrogen atoms of 9 are
not protonated even in wet solvents. This is significant as syn-
thesis of bimetallic complexes employing [Cp*Rh(η5-Cy2AFA)]
[BF4] (9) would not require any additional deprotonation step
to ligate to the second metal.
Fig. 5 Thermal ellipsoid drawing of [Ph2AFAH2][OTf] (11) (50% ellipsoids).
Hydrogen atoms have been removed for clarity. Selected bond-lengths (Å) and
angles (°) are provided in Table 1.
compared to the free Ph2AFAH (N–H, 15.59 ppm). Upon proto-
nation all other AFA protons are also shifted. For example, H1/
H7, H3/H5 and H4 protons shifted from 8.29, 7.05 and
6.47 ppm in Ph2AFAH to 8.68, 7.80 and 6.93 ppm in 11. The
formation of the protonated ligand 11 in this reaction was con-
firmed by comparison with an authentic sample prepared by
treatment of Ph2AFAH with triflic acid (TfOH) in toluene.
The X-ray crystal structure of 11 (Fig. 5) shows that indeed
one of the imine nitrogen atoms has been protonated and
intermolecular hydrogen bonding is present with the triflate
counter ion. Donor–acceptor distances of 2.914(3) Å (N1–O3A)
and 2.875(3) Å (N2–O1) are observed. The AFA moiety is quite
planar; the maximum deviations of non-Ph atoms from the C5-
plane are only 0.136 (N1) and 0.190 Å (N2). The carbon–carbon
and carbon–nitrogen distances are intermediate between
typical single and double bonds. The C2–C1–N1 and C6–C7–
N2 angles are 124.0(3)° and 124.8(3)° respectively, consistent
with sp2 hybridization at the imine carbon atoms. The most
significant feature of 11 is that the imines have a different con-
formation in comparison to the neutral Ph2AFAH ligand since
there is no internal N–H–N hydrogen bond. The rotation of the
C1–C2 and C7–C6 bonds directs the N–H protons outwards
whereas in the neutral ligand an inward rotation of C–C bonds
occurs for the N–H to form a hydrogen bond with the imine
nitrogen.
The 1H NMR spectrum of 9 shows no signal due to N–H,
and consistent with its absence, the H1/H7 protons appear as
a sharp singlet. Coordination shifts for the H1/H7 and H3/H5
protons similar to those found in 3 and 7 are observed on the
coordination of the [Cp*Rh]2+ fragment to the Cy2AFAH
ligand. The 103Rh couples with the C5-ring protons and thus
the H3/H5 protons appear as a doublet of doublets, and the
H4 proton appears as a doublet of triplets due to coupling
with Rh and its neighbouring protons. As in 8, the 103Rh
couples with the C5-ring carbon atoms and provides four dis-
tinct doublets in the 13C NMR spectrum.
In an attempt to synthesise the cobalt(III) complex [CpCo-
(η5-Cy2AFA)][OTf] (10), Ph2AFAH was reacted with [CpCo-
(CH3CN)3][OTf]2 in acetonitrile. Unfortunately the reaction
provided only the protonated ligand [Ph2AFAH2]+ (11)
In order to assess the ability of the cationic species [Cp*Rh-
(Cy2AFA)][BF4] (9) to behave as a metalloligand through κ2-
N,N′-coordination to a second metal it was treated with
[(PhCN)2PdCl2] in acetonitrile which provided the mixed-metal
complex [Cp*Rh(η5/κ2-Cy2AFA)PdCl2][BF4] (12) (Scheme 7).
This monocationic complex is soluble in acetonitrile and
CH2Cl2, but insoluble in ether and hexane. Unfortunately all
attempts at obtaining crystals suitable for X-ray crystallography
were unsuccessful. However, spectroscopic data clearly support
1
(Scheme 6). The H NMR spectrum of 11 shows a broad N–H
signal for two protons at 10.52 ppm, shifted substantially
1
its formulation as 12. The H NMR spectrum shows that upon
coordination of palladium to 9, the H1/H7 protons are shifted
from 8.43 to 7.82 ppm, H3/H5 from 5.93 to 6.31 ppm and H4
from 5.68 to 6.18 ppm. The H1/H7 protons appear as a sharp
singlet. As in 9 coupling of 103Rh to the C5-ring, H3/H5 and H4
protons is observed. In the 13C spectrum of 12 the four carbon
Scheme 6 Formation of the protonated ligand (11) during the attempted syn-
thesis of [CpCo(Ph2AFA)][OTf] (10).
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Scheme 7 Synthesis of Rh/Pd bimetallic complex, [Cp*Rh(η5/κ2-Cy2AFA)PdCl2]-
[BF4] (12).
doublets for the AFA C5-ring are shifted significantly from
those for the staring metalloligand 9. The Cp* methyl groups
appear as singlets in both the 1H and 13C NMR spectra, and
are again shifted from their values in
coordination.
9 on the Pd
Fig. 7 Cyclic voltammetry of [Cp*Ru(Ph2AFA)H][BF4] (3). Conditions: 3 mmol of
[Cp*Ru(Ph2AFA)H][BF4] in DCM, 0.1 M nBu4NPF6 electrolyte, Internal standard
Several attempts at the synthesis of a similar Ru–Pd bime-
tallic complex, [Cp*Ru(η5/κ2-Cy2AFA)PdCl2] (13) were unsuc-
ferrocene (Fc/Fc+ 0.49 V), scan rate 300 mV s−1
.
cessful. The reaction of the potassium salt of
3 with
[(PhCN)2PdCl2] in THF resulted in products which proved
difficult to characterise. The complex 13 could be a mimic of
Brookhart’s palladium α-diimine pre-catalysts,7 while 12, with
its cationic metalloligand, is an unusual example of a species
which may provide a dicationic methyl species on activation
with MAO and would thus be anticipated to display interesting
alkene polymerisation properties. Such chemistry is the
subject of ongoing studies.
Electrochemistry
Scheme 8 Oxidation of 3 and generation of hydrogen.
Cyclic voltammetry studies were carried out on the Ph2AFAH
ligand (Fig. 6) and complex 3 (Fig. 7). The CV response of
Ph2AFAH shows an irreversible one electron oxidation peak at
+1.0 V (vs. Fc/Fc+), at a scan-rate of 100 mV s−1. The low temp-
erature (−40 °C) experiment also confirms this feature.
The complex 3 shows an irreversible oxidation at +1.5 V.
The acidity of the N–H proton in the resulting dication (14)
results in a reduction peak at −1.0 V due to reduction of the
H+ liberated (Scheme 8).
structurally analogous neutral 1,2-bis(imidoyl)pentamethyl-
ruthenocene4 complexes show reversible oxidation features in
their cyclic voltammograms attributed to Ru centered
oxidation.
Experimental
The oxidation of complex 3 occurs on the AFA ligand, but
subsequent loss of the NH proton results in formation of the
anionic AFA ligand and formal oxidation to Ru(III). The
All reactions and manipulations of moisture- and air-sensitive
compounds were carried out in an atmosphere of dry nitrogen
using Schlenk techniques or in a conventional nitrogen-filled
glovebox (Saffron Scientific), fitted with oxygen and water
scavenging columns. Toluene, THF, diethyl ether, CH2Cl2, and
acetonitrile solvents were dried and purified by passage
through activated alumina columns using a solvent purifi-
cation system from Glass Contour. Hexane was distilled from
Na/benzophenone under a nitrogen atmosphere. NMR solvents
were degassed using freeze–thaw cycles and stored over 4 Å
molecular sieves. All solvents and reagents were purchased
from Sigma-Aldrich, Fischer or Acros and used as received
unless otherwise stated. NMR spectra were recorded on Bruker
AC 250, 360 and 500 MHz spectrometers operating at room
1
temperature. H and 13C chemical shifts are reported in ppm
relative to SiMe4 (δ = 0) and were referenced internally with
respect to the protio solvent impurity and the 13C resonances
respectively. Multiplicities and peak types are abbreviated:
Fig. 6 Cyclic voltammetry of Ph2AFAH. Conditions: 1 mmol of Ph2AFAH in
CH2Cl2, 0.1
0.49 V), scan rate 100 mV s−1
M =
nBu4NPF6 electrolyte. Internal standard ferrocene (Fc/Fc+
.
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singlet, s; doublet, d; triplet, t; multiplet, m; broad, br; aro- at −20 °C afforded 3.0 g (42%) of the desired product. 1H NMR
matic, ar. Mass spectra were recorded on a Kratos MS50TC (CDCl3, 360 MHz, 25 °C): δ 14.12 (br, 1H, NH), 7.87 (s-broad,
spectrometer (FAB-MS). Elemental analyses were performed 2H, H1/H7), 7.36–7.02 (m, 10H, C6H5), 6.75 (d, 2H, H3/H5,
using
a
Perkin Elmer 2400 CHN Elemental Analyser. J = 3.67 Hz), 6.24 (t, H4, J = 3.67 Hz), 4.48 (s, 4H, CH2); 13C{1H}
[Cp*RuIIICl2]2,8,9 [Cp*RuII(μ3-Cl)]4,5 [Cp*RuII(CH3CN)3][BF4],5,6 NMR (CDCl3, 90.6 MHz, 25 °C): δ 157.08 (C1/C7), 138.95 (ipso-
[Cp*RuII(CH3CN)3][OTf],5 [RhIII(η5-C5Me5)Cl2]2,10,11 [Cp*RhIII- C, Ar), 131.09 (C3/C5), 128.88 (C, Ar), 127.77 (C, Ar), 127.49 (C,
(CH3CN)3][BF4]2,10,12
[CpCoI(CO)2],13,14
[CpCo(CO)I2],15 Ar), 120.37 (C2/C6), 118.41 (C4), 58.42 (CH2); MS (+FAB, m/z):
[CpCoIII(CH3CN)3][OTf]2,16 and [(PhCN)2PdCl2]17 were syn- 301.7 (M+). Anal. Calcd for C21H20N2: C, 83.96; H, 6.71; N, 9.33.
thesised according to literature procedures. Electrochemical Found: C, 82.98; H, 6.50; N, 9.37.
studies were carried out using a DELL GX110 PC with General
Purpose Electrochemical System (GPES), version 4.8 software
connected to an autolab system containing a PGSTAT 20 poten-
tiostat. The techniques used a three-electrode configuration,
with a 0.5 mm diameter Pt disk working electrode, a Pt rod
counter electrode, and an Ag/AgCl (saturated KCl) reference
electrode against which the Fc/Fc+ couple was measured to be
E1/2 = +0.49 V. The supporting electrolyte was 0.1 M tetrabutyl-
ammonium hexafluorophosphate (TBAPF6) in CH2Cl2.
Synthesis of [Cp*Ru{(benzyl)2AFA}H][OTf] (7)
mixture of N,N′-bis(benzyl)-6-aminofulvene-2-aldimine
A
(0.5 g, 1.66 mmol) and [Cp*Ru(CH3CN)3][SO3CF3] (0.85 g,
1.66 mmol) was dissolved in 40 cm3 dry acetonitrile. The resul-
tant solution was stirred for 3 hours. Dry diethyl ether (20 cm3)
was added dropwise to the reaction mixture and the product
slowly crystallised. The solid product was then filtered and
washed with diethyl ether (3 × 20 cm3) and dried. Crystals suit-
able for X-ray analysis were obtained by slow diffusion of
diethyl ether into a solution of the complex in acetonitrile.
Yield: 0.45 g (39.8%). 1H NMR (CDCl3, 360 MHz, 25 °C): δ
15.17 (br, 1H, NH), 8.64 (s-broad, 2H, H1/H7), 7.39–7.29 and
7.19–7.10 (m, 10H, C6H5), 5.24 (d, 2H, H3/H5, J = 2.70 Hz),
4.88 (t, 1H, H4, J = 2.70 Hz), 4.66 (q, 4H, CH2), 1.70 (s, 15H,
Cp-CH3); 13C{1H} NMR (CDCl3, 90.6 MHz, 25 °C): δ 166.82
(C1/C7), 136.09 (C, Ar), 129.45 (C, Ar), 128.78 (C, Ar), 122.43
(ipso-C, Ar), 91.04 (C2/C6), 84.09 (C3/C5), 82.30 (C4), 78.58
(C5Me5), 59.54 (CH2), 11.66 (C5Me5); MS (+FAB, m/z): 536.8
(M+). Anal. Calcd for C31H35N2RuCF3SO3: C, 56.05; H, 5.14; N,
4.09. Found: C, 55.99; H, 4.26; N, 3.98.
Synthesis of [Cp*RuII(Ph2AFA)H][BF4] (3)
An orange-yellow solution of Ph2AFAH (0.37 g, 1.37 mmol) in
25 cm3 CH2Cl2 was added via cannula to a yellow solution of
[Cp*Ru(CH3CN)3][BF4] (0.61 g, 1.37 mmol) in 30 cm3 CH2Cl2.
The reaction mixture immediately turned to red. After stirring
overnight at room temperature, the solvent was removed
in vacuo. To remove unreacted ligand, the reaction mixture was
dissolved in 20 cm3 acetonitrile and hexane (20 cm3) was
added and was vigorously shaken. The unreacted ligand dis-
solved in the hexane. The top layer (hexane containing free
ligand) was decanted and the bottom layer of acetonitrile solu-
tion was collected. Acetonitrile was removed in vacuo and the
product was washed with hexane (3 × 10 cm3). Crystals suitable
for X-ray analysis were obtained by layering hexane on a
CH2Cl2 solution of the complex. Yield: 0.70 g (86.4%). The
complex is stable to air and moisture and highly soluble in
Synthesis of [Cp*Rh(Cy2AFA)H][BF4]2 (8)
CH2Cl2 and acetonitrile but insoluble in hexane. 1H NMR An orange-yellow solution of Cy2AFAH (0.10 g, 0.351 mmol) in
(CDCl3, 400 MHz, 25 °C): δ 16.51 (t, 1H, N–H), 8.93 (d, 2H, 10 cm3 CH2Cl2 was added via cannula to a yellow solution of
H1/H7, J = 7.57 Hz), 7.51–7.35 (m, 10H, C6H5), 5.66 (d, 2H, [Cp*Rh(CH3CN)3][BF4]2 (0.187 g, 0.351 mmol). The reaction
H3/H5, J = 2.65 Hz), 5.17 (t, 1H, H4, J = 2.77 Hz), 1.83 (s, 15H, mixture immediately turned to red. After stirring overnight at
CpCH3); 13C{1H} NMR (CDCl3, 100 MHz, 25 °C): δ 161.73 room temperature, the solvent was removed in vacuo and pure
(C1/C7), 142.53 (ipso-C, Ar), 130.53 (C, Ar), 128.27 (C, Ar), product was obtained. Yield: 0.20 g (81.7%). Orange block crys-
119.78 (C, Ar), 92.30 (C2/C6), 85.73 (C3/C5), 84.70 (C4), 79.37 tals suitable for X-ray analysis were obtained by layering ether
(C5Me5), 11.58 (C5Me5); MS (EI, m/z): 509.1 (M+). Anal. Calcd on top of an acetonitrile solution of the complex. The complex
for C29H31BF4N2Ru: C, 58.50; H, 5.25; N, 4.70. Found: C, 58.53; is stable in air and moisture and highly soluble in CH2Cl2 and
1
H, 5.27; N, 4.74.
acetonitrile but insoluble in hexane and chloroform. H NMR
(acetonitrile-d3, 500 MHz, 25 °C): δ 16.80 (t, 1H, NH), 8.55 (d,
2H, H1/H7, J = 7.25 Hz), 6.43 (dd, 2H, H3/H5, J = 2.64 Hz, J =
Synthesis of N,N′-bis(benzyl)-6-aminofulvene-2-aldimine (6)
A solution of 6-dimethylaminofulvene-2-N,N′-dimethylaldim- 0.73 Hz), 6.15 (dt, 1H, H4, J = 2.65 Hz, J = 1.0 Hz), 3.80 (m, 2H,
monium chloride (5.0 g, 23.50 mmol) in 50 cm3 of dry ethanol ipso-CyH), 2.04 (s, 15H, Cp*), 1.96–1.27 (m, 20H, CyH); 13C{1H}
was heated to reflux with benzyl amine (5.13 cm3, 47.0 mmol) NMR (acetonitrile-d3, 125 MHz, 25 °C): δ 161.27 (s, C1/C7),
overnight. The solvent and volatiles were removed in vacuo, 106.44 (d, quaternary-C of Cp*, J = 7.72 Hz), 99.06 (d, C3/C5,
activated charcoal was added and the residue heated to reflux J = 5.90 Hz), 96.08 (d, C4, J = 5.45 Hz), 94.95 (d, C2/C6, J =
in 150 cm3 of hexane overnight. The mixture was filtered while 6.36 Hz), 67.27 (s, ipso-C, Cy), 26.0 (C, Cy), 25.82 (C, Cy), 25.70
still hot and 2 portions of hot hexane (50 cm3) were used to (C, Cy), 11.11 (s, Cp*); MS (EI, m/z): 520.2 (M+ − 2H). Anal.
extract more products from the solid residue. The solutions Calcd for C29H43N2RhB2F8: C, 50.03; H, 6.23; N, 4.02. Found:
were combined and the volume reduced to about 25%. Storage C, 50.25; H, 6.38; N, 4.05.
2884 | Dalton Trans., 2013, 42, 2879–2886
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Synthesis of [Cp*Rh(Cy2AFA)][BF4] (9)
was filtered and the solvent was removed in vacuo. Crystals
suitable for X-ray analysis were obtained by diffusion of chloro-
form into acetonitrile solution of the product. Yield: 0.06 g
(85%). The obtained protonated ligand is insoluble in hexane,
chloroform, toluene, diethylether, CH2Cl2 but soluble in aceto-
To a solution of Cy2AFAH (0.30 g, 1.05 mmol) in THF (15 cm3)
at −70 °C, KH (0.04 g, 1.05 mmol) in 15 cm3 THF was added
dropwise via cannula. The mixture was stirred for 1 h at room
temperature. [Cp*Rh(CH3CN)3][BF4]2 (0.56 g, 1.05 mmol) was
added as the solid to the deprotonated ligand. The reaction
mixture was heated at 70 °C for 2 h and then stirred at room
temperature overnight. Some yellow-brown precipitate was
formed. The reaction mixture was filtered and the yellow-
brown precipitate was dried in vacuo to provide pure product.
1
nitrile and acetone. H NMR (acetonitrile-d3, 500 MHz, 25 °C):
δ 10.52 (br, 2H, NH), 8.68 (d, 2H, H1/H7, J = 15.09 Hz), 7.80 (d,
2H, H3/H5, J = 3.84 Hz), 7.65–7.55 (m, 8H, Ph), 7.44–7.40 (m,
2H, Ph), 6.93 (t, 1H, H4, J = 3.84 Hz); 13C{1H} NMR (aceto-
nitrile-d3, 125 MHz, 25 °C): δ 148.32 (C1/C7), 138.34 (C2/C6),
131.74 (C3/C5), 128.80 (C4), 124.60 (ipso-C, Ar), 127.65 (C, Ar),
129.93 (C, Ar), 119.06 (C, Ar); MS (+ve FAB, m/z): 273.3. Anal.
Calcd for C20H17N2F3SO3: C, 56.87; H, 4.06; N, 6.63. Found: C,
56.93; H, 4.10; N, 6.69.
1
Yield: 0.19 g (29%). H NMR (acetonitrile-d3, 500 MHz, 25 °C):
δ 8.43 (s, 2H, H1/H7), 5.93 (dd, 2H, H3/H5, J = 2.68 Hz, J = 0.79
Hz), 5.68 (dt, 1H, H4, J = 2.68 Hz, J = 1.1 Hz), 3.30 (m, 2H, ipso-
CyH), 1.98 (s, 15H, Cp*), 1.8–1.3 (m, 20H, CyH); 13C{1H} NMR
(acetonitrile-d3, 125 MHz, 25 °C): δ 152.34 (s, C1/C7), 103.46
(d, quaternary-C of Cp*, J = 8.17 Hz), 99.24 (d, C2/C6, J = 6.36
Hz), 90.98 (d, C4, J = 6.81 Hz), 90.29 (d, C3/C5, J = 6.36 Hz),
71.13 (s, ipso-C, Cy), 35.91 (C, Cy), 35.77 (C, Cy), 25.64 (C, Cy),
10.85 (s, Cp*); MS (EI, m/z): 521.2 (M+). Anal. Calcd for
C29H42RhN2BF4: C, 57.25; H, 6.96; N, 4.60. Found: C, 57.36; H,
7.0; N, 4.53.
Synthesis of [Cp*Rh(η5/κ2-Cy2AFA)PdCl2][BF4] (12)
A solution of [(PhCN)2PdCl2] (0.03 g, 0.08 mmol) in acetonitrile
(15 cm3) was transferred via cannula to a solution of [Cp*Rh-
(Cy2AFA)][BF4] (0.05 g, 0.08 mmol) in acetonitrile (15 cm3). The
reaction mixture was heated at 70 °C for 2 h and then stirred
over night at room temperature. The solvent was removed
in vacuo and the residue was washed with ether to remove
remaining benzonitrile. Hexane was layered on top of a CH2Cl2
Synthesis of [Ph2AFAH2][OTf] (11)
An orange solution of Ph2AFAH (0.045 g, 0.165 mmol) in solution of the complex but no suitable crystals were formed
10 cm3 acetonitrile was added via cannula to a light blue solu- for X-ray analysis. Yield: 0.03 g (38%). 1H NMR (acetonitrile-d3,
tion of [CpCo(CH3CN)3][OTf]2 (0.089 g, 0.165 mmol) in 20 cm3 500 MHz, 25 °C): δ 7.82 (s, 2H, H1/H7), 6.31 (dd, 2H, H3/H5,
acetonitrile. The reaction mixture immediately turned to red. J = 2.14 Hz, J = 0.92 Hz), 6.18 (dt, 1H, H4, J = 2.70 Hz, J =
After stirring 1 h at room temperature, the reaction mixture 0.92 Hz), 4.26 (m, 2H, ipso-CyH), 2.08 (s, 15H, Cp*), 1.78–1.20
Table 2 Crystal data for compounds 3, 7, 8 and 11
3
7
8
11
Chemical formula
Mr
Crystal system, space
C29H31N2Ru·BF4
595.44
Monoclinic, P21/c
C31H35N2Ru·CF3O3S
685.75
Orthorhombic, Pbca
C29H43N2Rh·2(BF4)
696.18
Monoclinic, P21/n
C20H17F3N2O3S
422.43
Monoclinic, P21/n
group
a, b, c (Å)
8.4632 (2), 22.8818 (6),
13.7328 (4)
90, 91.7806 (13), 90
2658.12 (12)
4
14.3116 (10), 19.3121 (14),
22.0786 (16)
90, 90, 90
6102.2 (8)
8
15.1769 (10), 13.6304 (9),
15.9647 (11)
90, 109.470 (1), 90
3113.7 (4)
4
0.62
10.6175 (5), 16.2766 (9),
11.6321 (6)
90, 109.216 (3), 90
1898.22 (17)
4
0.22
α, β, γ (°)
V (Å3)
Z
μ (mm−1
)
0.64
0.64
Crystal size (mm)
Absorption correction
0.36 × 0.18 × 0.13
Multi-scan
SADABS 2007/2
0.806, 0.924
21 093, 5447, 4742
[I > 2σ(I)]
0.55 × 0.23 × 0.13
Multi-scan
SADABS
0.781, 0.924
55 411, 5199, 4705
[I > 2σ(I)]
0.43 × 0.38 × 0.23
Multi-scan
SADABS 2007/2
0.747, 0.865
18 536, 6361, 5679
[I > 2σ(I)]
55.00 × 0.37 × 0.25
Multi-scan
SADABS (Siemens, 1996)
0.71, 0.95
16 727, 4982, 2842
[I > 2.0σ(I)]
Tmin, Tmax
No. of measured,
independent and
observed reflections
Rint
0.039
0.043
0.058, 0.138, 1.22
5199
0.032
0.032, 0.081, 1.04
6361
424
0.070
0.060, 0.179, 0.74
4982
262
R[F2 > 2σ(F2)], wR(F2), S 0.082, 0.180, 1.17
No. of reflections
No. of parameters
H-atom treatment
5447
325
387
H-atom parameters
constrained
H atoms treated by a mixture of
independent and constrained
refinement
H atoms treated by a mixture H-atom parameters not
of independent and
constrained refinement
w = 1/[σ2(Fo2) + (0.0401P)2 +
1.2941P]
refined
w = 1/[σ2(Fo2) +
w = 1/[σ2(Fo2) + (0.0503P)2 +
15.2474P]
Method = modified
Sheldrick w = 1/[σ2(F2) +
(0.1P)2 + 4.26P],
where P = (max(Fo2,0) +
2Fc2)/3
(0.0457P)2 + 18.4846P]
where P = (Fo2 + 2Fc2)/3
2.37, −1.00
where P = (Fo2 + 2Fc2)/3
0.96, −0.75
where P = (Fo2 + 2Fc2)/3
0.57, −0.36
Δ〉max, Δ〉min (e Å−3
)
0.77, −0.88
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Dalton Transactions
(m, 20H, CyH); 13C{1H} NMR (acetonitrile-d3, 125 MHz, 25 °C):
δ 161.76 (s, C1/C7), 105.87 (d, quaternary-C of Cp*, J = 7.72
Hz), 95.13 (d, C3/C5, J = 5.90 Hz), 95.01 (d, C4, J = 5.90 Hz),
94.69 (d, C2/C6, J = 6.36 Hz), 72.19 (s, ipso-C, Cy), 38.10 (C, Cy),
34.43 (C, Cy), 27.17 (C, Cy), 11.42 (s, Cp*); MS (EI, m/z): 521.1
(M+ − PdCl2). Anal. Calcd for C29H42RhN2PdCl2BF4: C, 44.33;
H, 5.39; N, 3.57. Found: C, 44.13; H, 5.05; N, 3.77.
3 (a) P. J. Bailey, A. Collins, P. Haack, S. Parsons, M. Rahman,
D. Smith and F. J. White, Dalton Trans., 2010, 39, 1591;
(b) P. J. Bailey, M. Melchionna and S. Parsons, Organometal-
lics, 2007, 26, 128; (c) P. J. Bailey, D. Lorono-Gonzalez and
S. Parsons, Chem. Commun., 2003, 1426.
4 B. Enk, D. Eisenstecken, H. Kopacka, K. Wurst, T. Muller,
F. Pevny, R. F. Winter and B. Bildstein, Organometallics,
2010, 29, 3169.
X-ray crystallography
5 P. J. Fagan, M. D. Ward and J. C. Calabrese, J. Am. Chem.
Soc., 1989, 111, 1698.
6 J. L. Schrenk, A. M. McNair, F. B. McCormick and
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Data were collected with Mo-Kα radiation at 150 K on a Bruker
Smart APEX diffractometer equipped with an Oxford Cryosys-
tems low-temperature device. Multi-scan absorption correc-
tions were applied using the programs SADABS18 or
TWINABS.18 The structures were solved with direct (SIR92)19 or
Patterson methods (DIRDIF)20 and refined using SHELXL or
Crystals.21,22 Crystal data for 3, 7, 8 and 11 are provided in
Table 2. CCDC 911986–911989 contain the supplementary
crystallographic data for this paper.†
11 J. W. Kang, K. Moseley and P. M. Maitlis, J. Am. Chem. Soc.,
1969, 91, 5970.
Conclusions
12 C. White, S. J. Thompson and P. M. Maitlis, J. Chem. Soc.,
Dalton Trans., 1977, 1654.
13 M. D. Rausch and R. A. Genetti, J. Org. Chem., 1970, 35, 3888.
14 R. B. King and M. B. Bisnette, J. Organomet. Chem., 1967, 8,
287.
Metalloligands 3, 7 and 8 and the Rh–Pd bimetallic complex
12 containing AFA ligands have been synthesised and charac-
terised. The basicity of the cationic metalloligand 9 containing
Rh(III) is significantly less than that of its neutral ruthenium
analog [Cp*Ru(η5-Ph2AFA)] and the 1,2-bis(imidoyl)penta-
methyl-ruthenocenes, and does not undergo protonation in
solution. Thus it opens a potentially easy synthetic route to
bimetallic complexes which eliminates the need for a deproto-
nation step.
15 R. B. King, Inorg. Chem., 1966, 5, 82.
16 U. Koelle, J. Organomet. Chem., 1980, 184, 379.
17 G. K. Anderson and M. Lin, Inorg. Synth., 1990, 28, 60.
18 G. M. Sheldrick, SADABS and TWINABS, University of
Göttingen, Germany, 2005.
19 A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi,
M. C. Burla, G. Polidori and M. Camalli, J. Appl. Crystal-
logr., 1994, 27, 435.
Notes and references
1 (a) K. Hafner, K. H. Vopel, G. Ploss and C. Konig, Justus 20 P. T. Beurskens, G. Beurskens, W. P. Bosman, R. de Gelder,
Liebigs Ann. Chem., 1963, 661, 52; (b) K. Hafner,
K. H. Vopel, G. Ploss and C. Konig, Org. Synth., 1967, 47,
52; (c) U. Muller-Westerhoff, J. Am. Chem. Soc., 1970, 92,
4849; (d) H. L. Ammon and U. Mueller-Westerhoff, Tetra-
hedron, 1974, 30, 1437.
S. Garcia-Granda, R. O. Gould, R. Israel and J. M. M. Smits,
The DIRDIF96 Program System, Technical Report of the Crys-
tallography Laboratory, University of Nijmegen, The Nether-
lands, 1996.
21 G. M. Sheldrick, Acta Crystallogr., Sect. A: Fundam. Crystal-
logr., 2008, 64, 112.
2 A. M. Willcocks, A. Gilbank, S. P. Richards, S. K. Brayshaw,
A. J. Kingsley, R. Odedra and A. L. Johnson, Inorg. Chem., 22 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout
2011, 50, 937.
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2886 | Dalton Trans., 2013, 42, 2879–2886
This journal is © The Royal Society of Chemistry 2013