Rotaxane synthesis exploiting the M(i)/M(III) redox couple

Article abstract of DOI:10.1039/c7dt02648j

In the context of advancing the use of metal-based building blocks for the construction of mechanically interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes (1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of robust and bulky complexes of rhodium(iii) and iridium(iii) through hydrogenation of readily accessible rhodium(i) and iridium(i) complexes [M(COD)(PPh₃)₂][BAr^F₄] (M = Rh, 2a; Ir, 2b) and reaction with a bipyridyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies examining the hydrogenation of 1p;:p;1 mixtures of 2 and bipy in CH₂Cl₂, which proceeds with disparate rates to afford [M(bipy)H₂(PPh₃)₂][BAr^F₄] (M = Rh, 4a[BAr^F₄], t = 18 h @ 50 °C; Ir, 4b[BAr^F₄], t < 5 min @ RT) in CH₂Cl₂ (1 atm H₂). These rates are reconciled by (a) the inherently slower reaction of 2a with H₂ compared to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh₃. On the basis of this information, operationally convenient and mild conditions (CH₂Cl₂, RT, 1 atm H₂, t ≤ 2 h) were developed for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form [Rh(PPh₃)₂]₂[BAr^F₄]₂ (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic characterisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.

Full text of DOI:10.1039/c7dt02648j

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Rotaxane synthesis exploiting the M(I)/M(III) redox
couple†
Cite this: DOI: 10.1039/c7dt02648j
Jack Emerson-King,
Adrian B. Chaplin
Richard C. Knighton, Matthew R. Gyton
and
*
In the context of advancing the use of metal-based building blocks for the construction of mechanically
interlocked molecules, we herein describe the preparation of late transition metal containing [2]rotaxanes
(1). Capture and subsequent retention of the interlocked assemblies are achieved by the formation of
robust and bulky complexes of rhodium(III) and iridium(III) through hydrogenation of readily accessible
rhodium(I) and iridium(I) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) and reaction with a bipyri-
dyl terminated [2]pseudorotaxane (3·db24c8). This work was underpinned by detailed mechanistic studies
examining the hydrogenation of 1 : 1 mixtures of 2 and bipy in CH2Cl2, which proceeds with disparate rates
to afford [M(bipy)H2(PPh3)2][BArF4] (M = Rh, 4a[BArF4], t = 18 h @ 50 °C; Ir, 4b[BArF4], t < 5 min @ RT) in
CH2Cl2 (1 atm H2). These rates are reconciled by (a) the inherently slower reaction of 2a with H2 compared
to that of the third row congener 2b, and (b) the competing and irreversible reaction of 2a with bipy, leading
to a very slow hydrogenation pathway, involving rate-limiting substitution of COD by PPh3. On the basis of
this information, operationally convenient and mild conditions (CH2Cl2, RT, 1 atm H2, t ≤ 2 h) were develo-
ped for the preparation of 1, involving in the case of rhodium-based 1a pre-hydrogenation of 2a to form
[Rh(PPh3)2]2[BArF4]2 (8) before reaction with 3·db24c8. In addition to comprehensive spectroscopic charac-
terisation of 1, the structure of iridium-based 1b was elucidated in the solid-state using X-ray diffraction.
Received 20th July 2017,
Accepted 15th August 2017
DOI: 10.1039/c7dt02648j
rsc.li/dalton
involves coordination of a bulky metal fragment to a donor
functionalised “axle” interpenetrated within a macrocycle, viz.
Introduction
Coordination chemistry is an increasingly prominent feature metal complex capping of a [2]pseudorotaxane (Scheme 1).1
of contemporary methods for preparing mechanically inter- Indeed, the successful application of such a synthesis was
locked molecules.1,2 In most cases metal ions are employed as demonstrated as early as 1981, with Ogino using cobalt(III)
well-defined templates, pre-organising the fusion of hetero- fragments to capture [2]rotaxanes comprised of a cyclodextrin
atom-based molecular building blocks, but thereafter jetti- macrocycle and diaminoalkane axle (A).4 With the notable
soned to confer an interwoven organic product. An alternative exception of Sauvage’s bis(terpyridine)-ruthenium(II) system B,5
but comparatively underdeveloped approach, resulting instead the overwhelming majority of subsequent [2]rotaxanes prepared
in retention of the metal complex within the final framework, through metal complex capping (e.g. C–E) have, however,
involves capture of the entangled topology itself through for- involved relatively weak dative bonding of mono-dentate pyridine
mation of a persistent metal–ligand bond. Such an approach donors.6
represents a potentially versatile means for preparing new and
Seeking to further develop synthetic methods involving
interesting metal-containing interlocked systems, as exempli- metal complex capping, we targeted the construction of
fied through the recent emergence of polyrotaxane metal– [2]rotaxanes though formation of robust complexes of chelat-
organic frameworks.3
ing ligands with bulky late transition metal fragments. To this
In the context of archetypical [2]rotaxane systems, a straight end, we herein report the preparation of 1 though installation
forward scheme employing metal-based building blocks of rhodium(III) and iridium(III) fragments {M(PPh3)2H2}+, gen-
erated in situ by hydrogenation of readily accessible rhodium(I)
and iridium(I) complexes [M(COD)(PPh3)2][BArF4] (M = Rh, 2a;
Ir, 2b; COD = 1,5-cyclooctadiene; ArF = 3,5-(CF3)2C6H3), upon
bipyridyl terminated [2]pseudorotaxane 3·db24c8 (Chart 1;
Department of Chemistry, University of Warwick, Gibbet Hill Road,
Coventry CV4 7AL, UK. E-mail: a.b.chaplin@warwick.ac.uk
†Electronic supplementary information (ESI) available: 1H, 13C{1H} and 31P{1H}
db24c8 = dibenzo-24-crown-8). Mechanistic and structural
NMR and ESI-MS spectra of new compounds and selected reactions.
aspects relevant to this process are first detailed using 2,2′-
CCDC 1563158–1563164. For ESI and crystallographic data in CIF or other elec-
bipyridine (bipy) as a model.
tronic format see DOI: 10.1039/c7dt02648j
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Scheme 1 Synthesis of [2]rotaxanes through capping methodology.
the presence of bipy to afford 4[BArF4], although curiously
the former required significantly more forcing conditions (t =
18 h @ 50 °C) than the latter (t < 5 min @ RT). In each case
the identity of the dihydride products was confirmed by iso-
lation on a preparative scale and full structural characteris-
ation. Spectroscopic data for 4[BArF4] are unsurprisingly in
close agreement with precedents bearing different counter
anions;10,11 useful markers include low frequency hydride
Chart 1 Components of target [2]rotaxanes 1.
1
signals at δ −15.66 (app. q, JRhH
≈
2JPH = 14 Hz; M =
2
Rh)/−19.48 (t, JPH = 16.6 Hz; M = Ir) and 31P resonances at δ
47.1 (d, 1JRhP = 115 Hz; M = Rh)/20.1 (M = Ir).
Results and discussion
Crystallographic data was also obtained in both cases for 4a
[BArF4] and 4b[BArF4]. For the iridium(III) complex two poly-
morphs were identified and studied, one of which features two
independent cations in the asymmetric unit (Z′ = 2). All
cations bear the expected pseudo-octahedral metal geometries
with trans-phosphine ligands (Fig. 1).12–14 Illustrating the
subtle effects of crystal packing, originating though variation
of the anion and in some cases presence of solvent molecules,
a wide range of geometries are observed for 4+ in the solid-
state: including both staggered and eclipsed conformations of
the phosphine substituents (cf. 4a[BArF4] vs. 4b[OTf]), and
alternative orientations of the phosphines about the metal–
phosphine vector (cf. 4a[BArF4] vs. 4b[BArF4] (Z′ = 1)).
The hydrogenation of [M(diene)(PPh3)2]+ (M = Rh, Ir) to afford
metal fragments of the type {M(PPh3)2H2}+ is well established and
evidenced through characterisation as adducts of solvent, e.g.
[M(PPh3)2H2(OCMe2)2]+ and [Ir(PPh3)2H2(ClCH2CH2Cl)]+,7,8 or the
counter anion, e.g. [Ir(PPh3)2H2(1-closo-CB11H6X6)] (X = Cl, I).9
Acetone adducts in particular are well-defined M(III) synthons
and have enabled isolation of [M(bipy)H2(PPh3)2]+ (M =
Rh, 4a+; Ir, 4b+) through subsequent reaction with bipy in
acetone solution.10 In the context of our envisioned synthesis
of 1, where robust retention of 3·db24c8 in solution is critical,
we sought instead to adapt a procedure reported by Crabtree
for the preparation of 4b+ by hydrogenation of a mixture of
[Ir(COD)(PPh3)2]+ and bipy in dichloromethane solution (for a
range of anions).11 As such we first studied hydrogenation
reactions (1 atm) of 1 : 1 mixtures of 2 (20 mM) and bipy in
CD2Cl2, using NMR spectroscopy, to gauge the viability of this
procedure for enacting metal complex capping of 3·db24c8
(Scheme 2 and vide infra). Satisfyingly both the rhodium(I) and
iridium(I) complexes were hydrogenated quantitatively in
Despite both resulting in formation of the desired products,
the disparate rates prompted us to interrogate the mechanism
of 2 + bipy hydrogenation in dichloromethane. To this end the
kinetics of reactions of 2 (20 mM) with bipy and H2 (1 atm)
1
were examined individually in CD2Cl2 at RT using H and 31P
NMR spectroscopy (Scheme 3). Presumably driven by the
chelate effect, reaction between 2 and bipy resulted in irrevers-
ible formation of five coordinate [M(bipy)(COD)(PPh3)][BArF
]
4
(M = Rh, 5a; Ir, 5b) alongside concomitant liberation of PPh3,
although under vastly different kinetic regimes (t1/2 = 1.3 h, 2a;
34 h, 2b). Moreover dynamic exchange between bound/free
phosphine is observed on the NMR timescale in the rhodium
system, leading to a single broad 31P signal at δ 10.6 (fwhm =
55 Hz) at 298 K that decoalesced into two sharp resonances at
1
δ 33.3 (d, JRhP = 129 Hz) and −8.3 in a 1 : 1 ratio on cooling to
200 K. Equivalent reaction mixtures are obtained from reac-
Scheme 2 Preparation of 4[BArF4].
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Fig. 1 Solid-state structures of 4+. Left: Selected independent cation from the X-ray structure of 4b[BArF4] (Z’ = 2) with thermal ellipsoids drawn at
the 50% probability level; non-hydridic hydrogen atoms omitted for clarity. Right: Conformations of 4+ viewed along the P–M–P vector, with phos-
phine ligands differentially coloured to aid comparison. a This work, polymorph with Z’ = 2; b this work, polymorph with Z’ = 1; c this work; d ref. 12;
e ref. 13; f ref. 14. Selected bond lengths (Å) and angles (°): 4a[BArF4], Rh1–P31, 2.3119(6); Rh1–N2, 2.154(2); P31–Rh1–P31*, 174.05(4); *1 − x, +y, 1 − z; 4b
[BArF4] (Z’ = 2), Ir1–P31, 2.2924(8); Ir1–P51, 2.3009(7); Ir1–N2, 2.118(2); Ir1–N13, 2.151(2); P31–Ir1–P51, 166.53(3); Ir11–P131, 2.3048(7); Ir11–P151,
2.3035(7); Ir11–N102, 2.115(2); Ir11–N113, 2.145(2); P131–Ir11–P151, 166.40(3); 4b[BArF4] (Z’ = 1), Ir1–P31, 2.3000(8); Ir1–P51, 2.2945(8); Ir1–N2, 2.138(2);
Ir1–N13, 2.128(3); P31–Ir1–P51, 164.08(3).
−
Scheme 3 Hydrogenation of 2 in the presence of bipy. Conditions: 20 mM, CD2Cl2, RT and 1 atm H2 (where relevant). Counter anion = [BArF
]
4
throughout. COE = cyclooctene.
tions between [M(bipy)(COD)][BArF4] (M = Rh, 6a; Ir, 6b) and (COA).16 Complex 8 was subsequently isolated on a preparative
two equivalents of PPh3 in CD2Cl2, but on a much faster scale and reacted with bipy (under an argon atmosphere) to
timescale (t < 5 min). Indeed, 5 were subsequently isolated from afford 7 (t < 5 min).15 Placing isolated 7 under hydrogen
reactions between 6 and one equivalent of PPh3 for independent (1 atm) thereafter quantitatively produced 4a[BArF4] (t <
structural verification in solution and the solid-state (see 5 min).15 Reaction of 2b with hydrogen rapidly (t < 5 min) gave
Experimental section, Fig. 2 and CIF). While no further reac- rise to a mixture of Ir(III) complexes of the formulation
tion of 5b with PPh3 was observed in solution, COD is slowly [Ir(PPh3)2H2L2][BArF4] (9; L = H2, CD2Cl2), with concomitant
and reversibly displaced from the lighter congener by PPh3 generation of COA, which then afforded 4b[BArF4] quantitat-
resulting in equilibrium formation of [Rh(bipy)(PPh3)2][BArF ] ively upon addition of bipy under hydrogen (t < 5 min).8,17
4
7 (t1/2 = 107 h; K = 2.4) at RT.15
Together these mechanistic experiments allow the disparate
Hydrogenation of 2a in CD2Cl2 proceeded at a moderate rates of 2 + bipy hydrogenation in dichloromethane to be
rate (t1/2 = 0.8 h) to produce Rh(I) dimer [Rh(PPh3)2]2[BArF ] (8) reconciled by (a) the inherently slower reaction of 2a with H2
4 2
as the exclusive organometallic product alongside cyclooctane compared to that of third row congener 2b,18 and (b) compet-
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began with preparation of amine 10, which was readily
obtained following a straightforward four step synthesis start-
ing from previously reported 5-chloromethylbipyridine
(Scheme 4; 66% yield over 4 steps).21 Subsequent protonation
and halide exchange, using citric acid and Na[BArF4] under
biphasic conditions (CH2Cl2/H2O), enabled isolation of the
corresponding ammonium derivative 3 in high yield (84%).
Under our chosen conditions, employing anhydrous dichloro-
methane and strategic incorporation of the weakly coordinat-
ing [BArF − counter anion,22 analysis by 1H NMR spectroscopy
]
4
indicated [2]pseudorotaxane 3·db24c8 was assembled rapidly
(t < 5 min) and quantitatively on dissolution of a 1 : 1 mixture
of 3 and db24c8 in CD2Cl2 at RT. Distinctive features in the
1H NMR spectrum associated with the formation of 3·db24c8
include methylene resonances at δ 4.82 (bipyCH
2̲ ) and 4.71
(ArCH2) coupled to a partially obscured ammonium resonance
̲
at δ 7.70, and significantly perturbed db24c8 resonances (see
ESI† for stack plots). Additional experiments involving vari-
ation of the components (2 : 1, 1 : 2) confirmed that the system
is under slow exchange on the NMR timescale (500 MHz,
298 K) consistent with robust retention of 3·db24c8 in
solution.
Fig. 2 Solid-state structure of 5b. Thermal ellipsoids drawn at the 50%
probability level; anion and hydrogen atoms omitted for clarity. Selected
bond lengths (Å) and angles (°): 5a, Rh1–P31, 2.3306(7); Rh1–N2,
2.262(2); Rh1–N13, 2.161(2); Rh1–Cnt(C14,C15), 1.996(3); Rh1–Cnt(C18,
C19), 2.072(3); P31–Rh1–C18, 179.36(9); 5b, Ir1–P31, 2.3426(6); Ir1–N2,
2.213(2); Ir1–N13, 2.121(2); Ir1–Cnt(C14,C15), 2.013(2); Ir1–Cnt(C18,C19),
2.017(2); P31–Ir1–C18, 171.56(8).
Guided by the aforementioned mechanistic studies,
rhodium-based 1a was prepared in high isolated yield (75%)
by reaction between 3·db24c8 and 8, individually prepared
in situ from 3 + db24c8 and 2a + H2 respectively, under hydro-
gen (1 atm) in dichloromethane at RT (t = 2 h). A more opera-
tionally straightforward procedure was possible for iridium-
based 1b, involving addition of 2b to a solution 3·db24c8 and
subsequently placing the reaction mixture under H2 (1 atm,
t = 1 h), enabling isolation of the analytically pure product
in high yield (78%). Employing this hydrogenation procedure,
but heating at elevated temperature (50 °C, t = 27 h; cf.
Scheme 2), with 2a and 3·db24c8 did result in the formation
of 1a, but as the major component of an intractable
mixture (ca. 60%). Such an observation is not unexpected
given the greater complexity associated with the hydrogenation
of 2a + bipy.
ing and irreversible reaction of 2a with bipy, leading to a very
slow hydrogenation pathway, involving rate-limiting substi-
tution of COD by PPh3. Consistent with these proposals inter-
mediate presence of 5a is observed in situ during the
formation of 4a[BArF4] from hydrogenation of 2a + bipy in
dichloromethane at 50 °C (Schemes 2 and 3). Under these con-
ditions a (COA + COE) : COD ratio of 42 : 58 was established at
reaction completion by GC analysis,19,20 broadly in line with
the relative rates of reaction of 2a with H2 (t1/2 = 0.8 h) and
bipy (t1/2 = 1.3 h) determined in dichloromethane at RT.
In contrast, no COD was detected by GC analysis on
hydrogenation of 2b
+ bipy in dichloromethane at RT
(Schemes 2 and 3).
Moving on from the mechanistic studies associated with
metal complex capping reaction, the construction of 1 itself
The capture of 1 was conviently established by ESI-MS, with
strong [M]2+ signals observed at 732.7929 (1a, calcd 732.7937)
and 777.8218 (1b, calcd 777.8228) m/z with the expected half
Scheme 4 Synthesis of [2]rotaxanes 1. Reagents and conditions: i. Potassium phthalimide, DMF (40 °C); ii. hydrazine monohydrate, EtOH (reflux);
iii. 3,5-di-tert-butylbenzaldehyde, 3 Å molecular sieves, MeOH (RT); iv. Na[BH4] (0 °C to reflux); v. Na[BArF4], citric acid monohyrate, CH2Cl2/H2O (RT).
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integer spacing. The structures of 1 were additionally fully cor- Fourier difference map, and the presence of two strong hydro-
roborated in solution using by a combination of 1H, 13C and gen bonds between the ammonium cation and ether linkages
31P NMR spectroscopy. With the exception of the expected loss of db24c8 (N15–O71, 3.057(3); N15–O77, 3.030(3) Å).
of symmetry, the metrics associated with the metal fragment
are directly comparable to those of the model systems 4[BArF4].
For instance the hydride resonances of 1a/1b are observed at
Summary and perspectives
δ −15.50 and −15.85 (cf. −15.66)/−19.30 and −19.64 (cf. −19.48)
with associated 2JHH (11.8/7.4 Hz) coupling, while the 31P reso-
We have presented a new reaction manifold for preparing
[2]rotaxanes (1) using coordination chemistry. Our scheme
involves topology capture through construction of bulky and
robust rhodium(III) and iridium(III) complex stoppering groups
from a bipyridyl terminated [2]pseudorotaxane (3·db24c8) and
nances of 1a/1b are observed at δ 46.2 (1JRhP = 115 Hz; cf.
1
47.1, JRhP = 115 Hz)/19.8 (cf. 20.1). Likewise the spectroscopic
indicators associated with interpenetration of the ammonium
axle within db24c8 in 1 are very similar to those seen in the
[2]pseudorotaxane 3·db24c8: for example, the methylene 1H
synthetically
convenient
metal
precursors
[M(COD)
(PPh3)2][BArF4] (M = Rh, 2a; Ir, 2b) in CH2Cl2 under hydrogen
(1 atm). Guided by detailed mechanistic studies, examining
the hydrogenation of 1 : 1 mixtures of 2 and bipy, operationally
convenient and mild conditions were developed for both
metal-based systems. In the case of rhodium-based 1a, pre-
resonances bipyCH̲2 (1a, 4.31; 1b, 4.30; cf. 4.82) and ArCH2 (1a,
4.68; 1b, 4.69; cf. 4.71). Gratifyingly, we were also been able to
grow single crystals of 1b and elucidate its solid-state structure
using X-ray diffraction. [2]Rotaxane 1b crystallises from di-
ˉ
chloromethane/hexane in the triclinic space group P1 with one
hydrogenation of 2a to form [Rh(PPh3)2]2[BArF
] (8, t = 4 h,
4 2
full molecule in the asymmetric unit (Fig. 3). The iridium centre
adopts the expected distorted octahedral geometry, with com-
parable metrics to those of 4b[BArF4] and analogues thereof
bearing different counter anions (Fig. 1).12,13 Notably there is
no meaningful steric buttressing apparent from close proxi-
mity of the interlocked db24c8 to the metal fragment
(Ir1⋯N15, 6.540(2) Å), evident for example by the similarity of
P31–Ir1–P51 bond angles in 1a (165.76(3)°) to those observed
in 4b[BArF4] (166.53(3)°, 166.40(3)°, 164.08(3)°). Other salient
features include the location of the hydride ligands off the
RT, 1 atm H2) before reaction with 3·db24c8 (t = 2 h, RT, 1 atm
H2) is necessary to avoid an exceptionally slow hydrogenation
pathway involving substitution of COD by PPh3. The chemistry
associated with the iridium(I)/iridium(III) redox couple is much
more attractive; in comparison to 2a the iridium precursor 2b
shows sluggish reaction with bipy at RT (t1/2 = 34 h), whilst
introduction of hydrogenation results in rapid and quantitative
stoppering of 3·db24c8 (t < 1 h). Together this work showcases
a facile route to the construction of new metal-containing
Fig. 3 Solid-state structure of 1b. Thermal ellipsoids drawn at the 50% probability level; anions, most hydrogen atoms, and minor disordered com-
ponents omitted for clarity. Selected bond lengths (Å) and angles (°): Ir1–P31, 2.3103(5); Ir1–P51, 2.2950(5); Ir1–N2, 2.151(2); Ir1–N13, 2.137(2);
Ir1⋯N15, 6.540(2); N15–O71, 3.057(3); N15–O77, 3.030(3); P31–Ir1–P51, 165.76(2).
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interlocked molecules via formation of robust metal–ligand 4.28–4.36 (m, 2H, bipyCH2
̲
), 4.05–4.12 (m, 4H, OCH2),
bonds. In addition to synthetic ease, the installation of {M 3.94–4.02 (m, 4H, OCH2), 3.52–3.63 (m, 8H, OCH2), 3.33–3.47
t
(PPh3)2H2}+ metal fragments in entangled architectures (m, 8H, OCH2), 1.17 (s, 18H, Bu), −15.50 (app. p, J = 14 (1JRhH
2
proffers a number of advantages, including (a) useful spectro- = 15.2, JHH = 11.8), 1H, RhH), −15.85 (app. p, J = 14 (1JRhH
=
2
scopic handles (distinctive low frequently hydride and 31P 15.6, JHH = 11.8), 1H, RhH). 13C{1H} NMR (126 MHz, CD2Cl2):
1
signals); (b) large steric profile (trans-phosphine ligands); (c) δ 162.4 (q, JBC = 50, ArF), 155.2 (s, bipy), 154.2 (s, bipy), 153.7
the presence of heavy transition metals amenable for routine (s, bipy), 153.3 (s, bipy), 152.8 (s, C6H3), 147.8 (s, C6H4), 138.2
analysis by X-ray diffraction (e.g. Fig. 3); and perhaps more (s, bipy), 136.3 (s, bipy), 135.4 (s, ArF), 133.6 (app. t, JPC = 6,
importantly, (d) the possibly to exploit interesting reactivity Ph), 132.5 (app. t, JPC = 24, Ph), 131.1 (s, Ph), 131.0 (s, bipy),
and spectroscopic properties of the metal fragment. We are 130.2 (s, C6H3), 129.4 (qq, 2JCF = 32, 2JCB = 3, ArF), 129.2 (app. t,
particularly interested in exploring the latter as part of our on- JPC = 5, Ph), 127.1 (s, bipy), 125.4 (s, C6H3), 125.2 (q, 1JFC = 272,
going research in this area.
ArF), 124.8 (s, C6H3), 123.21 (s, bipy), 123.16 (s, C6H4), 122.7 (s,
3
bipy), 118.1 (sept., JFC = 4, ArF), 113.8 (s, C6H4), 71.1 (s,
OCH2), 70.7 (s, OCH2), 68.8 (s, OCH2), 55.1 (s, ArC̲H2), 49.3 (s,
t
t
bipyC̲
H2), 35.3 (s, Bu), 31.6 (s, Bu). 31P{1H} NMR (202 MHz,
Experimental
General methods
CD2Cl2): δ 46.2 (d, 1JRhP = 115). HR ESI-MS (positive ion, 4 kV):
732.7929 [M]2+ (calcd 732.7937) m/z. Anal. calcd for
150H122B2F48P2Rh (3193.04 g mol−1): C, 56.42; H, 3.85; N,
Manipulations were performed under an argon atmosphere
using Schlenk and glove box techniques unless otherwise
stated. Glassware was oven dried at 150 °C overnight and
flame-dried under vacuum prior to use. Molecular sieves (3 Å)
were activated by heating at 300 °C in vacuo overnight.
Anhydrous solvents (Et2O, CH2Cl2, CHCl3, pentane, hexane,
THF and toluene) were purchased from Acros Organics or
Sigma-Aldrich and stored over molecular sieves (3 Å). CD2Cl2
C
1.32. Found: C, 56.50; H, 4.02; N, 1.34.
Attempted preparation of 1a by hydrogenation of 2a +
3·db24c8
To a solution of 3 (20.2 mg, 16.1 µmol) and db24c8 (7.2 mg,
16.1 µmol) in CH2Cl2 (0.8 mL) was added 2a (25.7 mg,
16.1 µmol). The resulting solution was freeze–pump–thaw
degassed, placed under dihydrogen (1 atm), and stirred at
50 °C for 27 h. Volatiles were removed in vacuo and the solid
redissolved in CH2Cl2 (ca. 2 mL) and layered with hexane
(ca. 15 mL) to afford the crude product as a dark yellow gum,
which was isolated through decantation of the supernatant
and dried in vacuo. Analysis by 1H NMR spectroscopy in
CD2Cl2 indicated a mixture of products with the major con-
stituent being 1a in ca. 60% purity.
was dried over molecular sieves (3 Å) and stored under argon.
5-Chloromethylbipyridine,21 Na[BArF
]
and [M(COD)2Cl]2
23
4
(M = Rh, Ir)24 were synthesised using established procedures.
All other reagents are commercial products and were used as
received. NMR spectra were recorded on Bruker spectrometers
at 298 K unless otherwise stated. Chemical shirts are quoted
in ppm and coupling constants in Hz. ESI-MS were recorded
on Bruker Maxis Plus (HR) or Agilent 6130B single Quad (LR)
instruments. Gas chromatography analyses were performed on
an Agilent 7820A GC system fitted with a 7693A auto-injector.
Microanalyses were performed at the London Metropolitan
University by Mr Stephen Boyer.
Preparation of 1b
To a solution of 3 (40.0 mg, 32.0 µmol) and db24c8 (14.4 mg,
32.1 µmol) in CH2Cl2 (1.8 mL) was added 2b (54.1 mg,
32.0 µmol). The resulting solution was freeze–pump–thaw
degassed and placed under dihydrogen (1 atm), and stirred at
Preparation of 1a
A solution of 2a (50.8 mg, 32.0 µmol) in CH2Cl2 (0.9 mL) was RT for 1 h. Volatiles were removed in vacuo and the solid redis-
freeze–pump–thaw degassed and placed under dihydrogen solved in Et2O (ca. 2 mL) and layered with hexane (ca. 15 mL).
(1 atm). After stirring at RT for 4 h, the resulting deep red solu- Storage at ambient temperature overnight afforded a yellow oil,
tion was added under dihydrogen to a solution of 3 (40.0 mg, which was isolated through decantation of the supernatant
32.0 µmol) and db24c8 (14.4 mg, 32.1 µmol) in CH2Cl2 and dried in vacuo overnight to afford the product as a bright
(0.9 mL). The solution was stirred at RT for 2 h and then yellow foam. Yield = 82.2 mg (78%).
added to pentane (ca. 30 mL) under hydrogen with stirring,
1H NMR (500 MHz, CD2Cl2): δ 8.26 (s, 1H, bipy), 8.16 (d,
3
whereupon an orange-red gum precipitated. The supernatant 3JHH = 5.4, 1H, bipy), 7.82 (d, JHH = 9.7, 1H, bipy), 7.71–7.75
was decanted away and the product dried in vacuo for 5 min to (m, 16H, ArF), 7.67 (vbr, fwhm = 43 Hz, 2H, NH2
̲ ), 7.54–7.59
afford the product as a dark-yellow foam. Yield = 76.7 mg (obscured, 1H, bipy), 7.55 (br, 8H, ArF), 7.51 (d, JHH = 8.6, 1H,
3
3
(75%).
bipy), 7.47 (d, JHH = 8.2, 1H, bipy), 7.45 (s, 1H, C3H3),
1H NMR (500 MHz, CD2Cl2): δ 8.17 (s, 1H, bipy), 7.98 (d, 7.22–7.31 (m, 18H, Ph), 7.13–7.22 (m, 14H, C6H3 + Ph),
3JHH = 5.0, 1H, bipy), 7.80 (d, JHH = 9.0, 1H, bipy), 7.71–7.76 6.86–6.97 (m, 8H, C6H4), 6.81–6.86 (m, 1H, bipy), 4.66–4.73 (m,
3
(m, 16H, ArF), 7.67 (vbr, fwhm = 26 Hz, 2H, NH2
̲
), 7.50–7.61 2H, ArCH
2̲ ), 4.26–4.34 (m, 2H, bipyCH̲2), 4.05–4.14 (m, 4H,
(obscured, 3H, bipy), 7.55 (br, 8H, ArF), 7.45 (br, 1H, C6H3), OCH2), 3.95–4.04 (m, 4H, OCH2), 3.52–3.64 (m, 8H, OCH2),
t
2
7.23–7.32 (m, 18H, Ph), 7.14–7.22 (m, 14H, C6H3 + Ph), 3.35–3.46 (m, 8H, OCH2), 1.17 (s, 18H, Bu), −19.30 (td, JPH
=
2
2
2
6.84–6.96 (m, 9H, bipy + C6H4), 4.65–4.72 (m, 2H, ArCH2
̲
), 16.9, JHH = 7.4, 1H, IrH), −19.64 (td, JPH = 16.1, JHH = 7.4,
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1
1H, IrH). 13C{1H} NMR (126 MHz, CD2Cl2): δ 162.3 (q, JBC
=
The hydrogenation of 2a + bipy was monitored in situ by
50, ArF), 156.9 (s, bipy), 155.3 (s, bipy), 154.9 (s, bipy), 154.8 (s, 1H and 31P NMR spectroscopy at 50 °C. After 1 h, 2a was con-
bipy), 152.7 (s, C6H3), 147.8 (s, C6H4), 137.6 (s, bipy), 135.5 (s, sumed with concomitant formation of 4a[BArF4] (ca. 58% [Rh])
bipy), 135.4 (s, ArF), 133.5 (app. t, JPC = 6, Ph), 131.9 (s, bipy), and 5a (ca. 42% [Rh]). Complete conversion to 4a[BArF4] was
131.8 (t, 1JPC = 27, Ph), 131.1 (s, Ph), 130.1 (s, C6H3), 129.4 (qq, observed after 18 h. Analysis by GC gave a hydrocarbon distri-
2
2JCF = 32, JCB = 3, ArF), 129.1 (app. t, JPC = 5, Ph), 127.9 (s, bution of: COA (6%), COE (36%), COD (58%).
bipy), 125.4 (s, C6H3), 125.2 (q, 1JFC = 272, ArF), 124.9 (s, C6H3),
Immediate analysis of the hydrogenation of 2b + bipy at RT
1
123.7 (s, bipy), 123.20 (s, bipy), 123.17 (s, C6H4), 118.0 (sept., (<5 min) by H and 31P NMR spectroscopy indicated quantitat-
3JFC = 4, ArF), 113.8 (s, C6H4), 71.0 (s, OCH2), 70.7 (s, OCH2), ive conversion to 4b[BArF4]. Analysis by GC gave a hydrocarbon
t
68.7 (s, OCH2), 55.1 (s, ArC
̲
̲
31.5 (s, Bu). 31P{1H} NMR (202 MHz, CD2Cl2): δ 19.8 (vbr,
Reaction between 2 and bipy. A solution of 2 (10 μmol) and
t
fwhm = 43 Hz). HR ESI-MS (positive ion, 4 kV): 777.8218 [M]2+ bipy (1.6 mg, 10 μmol) in CD2Cl2 (0.5 mL) was prepared in
(calcd 777.8228), 1554.6401 [M − H]+ (calcd 1554.6384) m/z. J. Young’s NMR tube and then left to stand in a water bath at
Anal. calcd for C150H122B2F48P2Ir (3285.14 g mol−1): C, 54.89; 25 °C. The ensuing reaction was monitored periodically in situ
H, 3.75; N, 1.28. Found: C, 54.83; H, 3.74; N, 1.31.
by 1H and 31P NMR spectroscopy.
Reaction between 2a and bipy resulted in formation of 5a
(t1/2 = 1.3 h) and subsequently slow equilibrium formation of 7,
Preparation of 2
General procedure. A suspension of [M(COD)Cl]2 (M = Rh, Ir; alongside liberation of COD. Modelling the kinetics of the
25.0 μmol), PPh3 (26.2 mg, 100 μmol) and Na[BArF ] (44.3 mg, approach to equilibrium over 8 days,26 enabled determination of
4
50.0 μmol) in CH2Cl2 (5 ml) was stirred overnight at RT. Hexane the equilibrium constant (K = 2.4) and rate of forward reaction
(1 mL) was added and the solution filtered and layered with (t1/2 = 107 h).
excess hexane (45 mL) to afford the products on diffusion.
Reaction between 2b and bipy resulted in the slow and
quantitative formation of 5b (t1/2 = 34 h). No subsequent reac-
tion was observed.
2a
Yield = 69.9 mg (87%, orange solid).
Hydrogenation of 2. A solution of 2 (10 μmol) in CD2Cl2
1H NMR (500 MHz, CD2Cl2): δ 7.70–7.75 (m, 8H, ArF), 7.56 (0.5 mL) was prepared in J. Young’s NMR tube and freeze–
3
(br, 4H, ArF), 7.42 (t, JHH = 7.4, 6H, Ph), 7.35–7.40 (m, 12H, pump–thaw degassed three times and placed under dihydro-
3
Ph), 7.27 (t, JHH = 7.2, 12H, Ph), 4.55 (br, 4H, CHvCH), gen (1 atm) at RT. The ensuing reaction was monitored
2.54–2.42 (m, 4H, CH2), 2.28–2.20 (m, 4H, CH2). 13C{1H} NMR periodically in situ by 1H and 31P NMR spectroscopy.
1
(126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 135.4 (s, ArF),
The smooth conversion of 2a to 8 was observed over 4 h
134.5 (app. t, JPC = 6, Ph), 131.7 (s, Ph), 130.5–131.3 (m, Ph), with a t1/2 = 0.8 h, alongside concomitant generation of COA.
129.4 (qq, JCF = 32, JCB = 3, ArF), 129.2 (app. t, JPC = 5, Ph), No COE or COD was evident by 1H NMR spectroscopy.
2
2
125.2 (q, 1JFC = 272, ArF), 118.1 (sept., 3JFC = 4, ArF), 99.6 (app. dt,
Hydrogenation of 2b resulted in the immediate colour
J = 8, J = 5, CHvCH), 31.2 (s, CH2). 31P{1H} NMR (162 MHz, change from red to colourless within 5 min. Analysis by
CD2Cl2): δ 26.5 (d, 1JRhP = 145). HR ESI-MS (positive ion, 4 kV): 1H and 31P NMR spectroscopy indicated the formation of a
735.1812 [M]+ (calcd 735.1811) m/z. Anal. calcd for mixture of hydride species 9, alongside concomitant gene-
C78H54BF24P2Rh (1589.89 g mol−1): C, 57.09; H, 3.40; N, 0.00. ration of COA. No COE or COD was evident by 1H NMR
Found: C, 57.18; H, 3.56; N, 0.00.
spectroscopy. Subsequent transfer of this solution into a
J. Young’s NMR tube charged with bipy (1.6 mg, 10.0 μmol)
resulted in the quantitative formation of 4b[BArF4] within
2b
Yield = 49.0 mg (58%, red solid). Spectroscopic data are in 5 min as gauged by 1H and 31P NMR spectroscopy.
agreement with the literature values.25
1H NMR (400 MHz, CD2Cl2): δ 7.70–7.76 (m, 8H, ArF), 7.56 (s, Selected data for 9.
4H, ArF), 7.42 (t, 3JHH = 7.4, 6H, Ph), 7.35–7.40 (m, 12H, Ph), 7.27
1H NMR (500 MHz, CD2Cl2): δ 7.71–7.76 (m, 8H, ArF), 7.56
(t, 3JHH = 7.2, 12H, Ph), 4.20 (br, 4H, CHvCH), 2.40–2.20 (m, 4H, (s, 4H, ArF), 7.47–7.58 (m, 30H, Ph), −26.24 (vbr, fwhm =
CH2), 2.06–1.85 (m, 4H, CH2). 31P{1H} NMR (162 MHz, CD2Cl2): 190 Hz). 31P{1H} NMR (202 MHz, CD2Cl2): δ 23.4 (vbr, fwhm =
δ 17.6 (s). LR ESI-MS (positive ion): 825.2 [M]+ (calcd 825.2) m/z.
130 Hz). 1H NMR (500 MHz, CD2Cl2, 185 K): δ 7.70–7.76 (m,
8H, ArF), 7.52 (br, 4H, ArF), 7.34–7.53 (m, 30H, Ph), −1.75 (br,
NMR scale reactions of 2
T1 = 54 ms, IrH2(H2 2
̲
) ), −12.43 (br, T1 = 51 ms, IrH2(H2
(H2)2),* −25.11 (t, 2JPH
into a J. Young’s NMR tube containing 2 (10 μmol) and bipy 14.6, T1 = 401 ms, IrH2(CD2Cl2)2), −26.72 (br, T1 = 361 ms,
(1.6 mg, 10 μmol) cooled in a Dewar of liquid nitrogen, then IrH2(H2)(CD2Cl2)2), −28.13 (br, T1 = 358 ms, IrH2(H2)(CD2Cl2)2).
̲ )
=
Hydrogenation of 2 + bipy. CD2Cl2 (0.5 mL) was condensed (CD2Cl2)2), −23.59 (br, T1 = 49 ms, IrH2
̲
̲
̲
thawed to RT under dihydrogen (1 atm). The NMR tube was * This resonance is assigned to a hydride despite the short T1
sealed, inverted several times, and then left at the desired reaction value, which we attribute to chemical exchange on the NMR
temperature. At the conclusion of the reaction the solution was timescale. 31P{1H} NMR (202 MHz, CD2Cl2, 185 K): δ 27.0 (s,
passed through a short plug of SiO2 (CH2Cl2) and analysed by GC.
IrH2(H2)(CD2Cl2)2), 23.2 (s, IrH2(H2)2), 15.7 (s, IrH2(CD2Cl2)2).
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Preparation of 3
pump–thaw degassed three times then placed under dihydro-
gen (1 atm). The solution was agitated (M = Rh, 18 h at 50 °C;
M = Ir; 10 min at RT), then layered with hexane (20 mL) to
afford the products as crystalline solids on diffusion.
A suspension of 10 (100 mg, 258 μmol), Na[BArF4] (229 mg,
258 μmol) and citric acid monohydrate (54.2 mg, 258 μmol) in
CH2Cl2/H2O 1 : 1 (6 mL) was stirred vigorously at RT for 10 min
(air). The organic phase was separated, washed with H2O (5 ×
5 mL) and dried over MgSO4. The solvent was removed
in vacuo to give the product as an off-white solid. Yield =
270 mg (84%).
4a[BArF
]
4
Yield = 17.6 mg (53%, off white solid).
1H NMR (500 MHz, CD2Cl2): δ 8.06 (d, 3JHH = 5.2, 2H, bipy),
7.71–7.75 (m, 8H, ArF), 7.71 (obscured, 2H, bipy), 7.64 (t,
3JHH = 7.5, 2H, bipy), 7.56 (br, 4H, ArF), 7.30–7.38 (m, 18H, Ph),
1H NMR (500 MHz, CD2Cl2): δ 8.64 (s, 1H, bipy), 8.57 (d,
3JHH = 5.0, 1H, bipy), 8.08 (app. t, JHH = 8, 1H, bipy), 7.97 (d,
3
3
3
4
3JHH = 7.6, 1H, bipy), 7.93 (d, JHH = 7.9, 1H, bipy), 7.81 (d,
3
7.23 (t, JHH = 7.4, 12H, Ph), 6.82 (ddd, JHH = 7.6, 5.5, JHH
=
1.0, 2H, bipy), −15.66 (app. q, J = 14 (1JRhH = 15.5), 2H, RhH).
3JHH = 7.6, 1H, bipy), 7.69–7.75 (m, 8H, ArF), 7.62 (dd, JHH
=
3
13C{1H} NMR (126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF),
1
7.6, 5.1, 1H, bipy), 7.54 (br, 4H, ArF), 7.43 (t, JHH = 1.8, 1H,
4
154.5 (s, bipy), 154.3 (s, bipy), 137.8 (s, bipy), 135.4 (s, ArF),
4
C6H3), 7.22 (d, JHH = 1.8, 2H, C6H3), 4.26 (br, 2H, CH2), 4.24
t
133.7 (app. t, JPC = 7, Ph), 132.5 (app. t, JPC = 24, Ph), 130.8 (s,
(br, 2H, CH2), 1.24 (s, 18H, Bu). The NH2 resonance was not
2
3
Ph), 129.4 (qq, JFC = 32, JCB = 3, ArF), 129.0 (app. t, JPC = 5,
unambiguously located. 13C{1H} NMR (126 MHz, CD2Cl2):
Ph), 126.4 (s, bipy), 125.2 (q, JFC = 272, ArF), 122.6 (s, bipy),
3
1
δ 162.3 (q, JCB = 50, ArF), 152.8 (s, C6H3), 148.4 (s, bipy), 142.9
118.0 (sept., JFC = 4, CH, ArF). 31P{1H} NMR (162 MHz,
3
(s, bipy), 141.8 (s, bipy), 135.4 (s, ArF), 129.4 (qq, 2JFC = 32, 3JBC
=
CD2Cl2): δ 47.1 (d, 1JRhP = 115). HR ESI-MS (positive ion, 4 kV):
785.1723 [M]+ (calcd 785.1716) m/z. Anal. calcd for
C78H52BF24N2P2Rh (1648.91 g mol−1): C, 56.82; H, 3.18; N,
1.70. Found: C, 57.04; H, 2.91; N, 1.80.
3, ArF), 127.5 (s, bipy), 125.1 (q, JFC = 272, ArF), 124.0 (s, bipy),
1
123.7 (s, C6H3), 123.5 (s, bipy), 123.1 (s, C6H3), 118.0 (sept.,
3JFC = 4, ArF), 54.9 (s, CH2), 50.2 (s, CH2), 35.3 (s, Bu), 31.6 (s,
t
tBu). Not all resonances unambiguously located. HR ESI-MS
(positive ion, 4 kV): 1252.3484 [M + H]+ (calcd 1252.3484) m/z.
4b[BArF
]
4
Reaction of 3 with db24c8: preparation of 3·db24c8
Yield = 11.2 mg (34%, yellow solid).
1H NMR (500 MHz, CD2Cl2): δ 8.16 (d, 3JHH = 5.3, 2H, bipy),
7.71–7.56 (m, 8H, ArF), 7.71 (obscured, 2H, bipy), 7.64 (t,
3JHH = 7.8, 2H, bipy), 7.56 (br, 4H, ArF), 7.28–7.36 (m, 18H, Ph),
A solution of 3 (6.3 mg, 5.0 μmol) and db24c8 (2.3 mg,
5.1 μmol) in CD2Cl2 (0.5 mL) was prepared within a J. Young’s
NMR tube. Analysis in situ by NMR spectroscopy indicated the
quantitative formation of 3·db24c8 (slow exchange at 500 MHz).
Repeating the reaction using 0.5 and 2 equiv. db24c8
resulted in the formation of a 1 : 1 mixture of 3 and 3·db24c8,
and 1 : 1 mixture of 3·db24c8 and db24c8, respectively (both
slow exchange at 500 MHz).
3
3
4
7.22 (t, JHH = 7.4, 12H, Ph), 6.75 (ddd, JHH = 7.5, 5.5, JHH
=
2
1.0, 2H, bipy), −19.48 (t, JPH = 16.6, 2H, IrH). 13C{1H} NMR
1
(126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 156.0 (s, bipy),
155.8 (s, bipy), 137.2 (s, bipy), 135.4 (s, ArF), 133.6 (app. t, JPC = 6,
Ph), 131.8 (app. t, JPC = 27, Ph), 130.9 (s, Ph), 129.4 (qq,
2JFC = 31, 3JCB = 3, ArF), 128.9 (app. t, JPC = 5, Ph), 127.3 (s, CH,
1H NMR (500 MHz, CD2Cl2): δ 8.60 (d, 3JHH = 4.6, 1H, bipy),
1
bipy), 125.2 (q, JFC = 272, ArF), 123.2 (s, bipy), 118.0 (sept.,
4
3
8.48 (d, JHH = 1.6, 1H, bipy), 8.18 (d, JHH = 7.9, 1H), 8.04 (d,
3JFC = 4, ArF). 31P{1H} NMR (162 MHz, CD2Cl2): δ 20.1 (s).
HR ESI-MS (positive ion, 4 kV): 875.2286 [M]+ (calcd 875.2293)
m/z. Anal. calcd for C78H52BF24IrN2P2 (1738.22 g mol−1): C,
53.90; H, 3.02; N, 1.61. Found: C, 54.03; H, 2.85; N, 1.69.
3JHH = 8.2, 1H, bipy), 7.79 (app. td, JHH = 8, JHH = 1.8, 1H,
3
4
bipy), 7.70–7.76 (m, 8H, ArF), 7.70 (obscured, 2H, NH2), 7.63
(dd, JHH = 8.2, JHH = 2.0, 1H, bipy), 7.56 (br, 4H, ArF), 7.47 (t,
3
4
4JHH = 1.8, 1H, C6H3), 7.30–7.34 (m, 3H, C6H3 + bipy),
6.69–6.79 (m, 8H, C6H4), 4.79–4.85 (m, 4H, bipyCH2
̲ ),
Attempted hydrogenation of COD mediated by 4a[BArF
]
4
4.67–4.74 (m, 4H, ArCH2), 4.01–4.19 (m, 8H, OCH2), 3.71–3.87
̲
A solution of 4a[BArF4] (16.5 mg, 10.0 µmol) in CD2Cl2
(0.5 mL) was freeze–pump–thaw degassed, placed under di-
hydrogen (1 atm), COD (1.2 µL, 10 µmol) added under a hydro-
gen atmosphere, and finally heated at 50 °C for 18 h. The solu-
tion was passed through a short plug of SiO2 (CH2Cl2).
Analysis by GC gave a hydrocarbon distribution of: COA (0%),
COE (1%), COD (99%).
(m, 8H, OCH2), 3.58–3.68 (m, 4H, OCH2), 3.45–3.56 (m, 4H,
t
OCH2), 1.23 (s, 18H, Bu).13C{1H} NMR (126 MHz, CD2Cl2):
1
δ 162.3 (q, JBC = 50, ArF), 157.2 (s, bipy), 155.5 (s, bipy), 152.5
(s, C6H3), 150.4 (s, bipy), 149.6 (s, bipy), 147.6 (s, C6H4), 138.0
(s, bipy), 137.3 (s, bipy), 135.4 (s, ArF), 131.4 (s, C6H3), 129.4 (qq,
2
1
2JCF = 32, JCB = 3, ArF), 127.8 (s, bipy), 125.2 (q, JFC = 272, ArF),
124.6 (s, bipy), 124.4 (s, C6H3), 124.0 (s, C6H3), 122.3 (s, C6H4),
3
121.6 (s, bipy), 120.5 (s, bipy), 118.0 (sept. JFC = 4, ArF),
113.0 (s, C6H4), 71.2 (s, OCH2), 70.9 (s, OCH2), 68.4 (s, OCH2), Preparation of 5a
54.0 (s, ArC
̲H2), 50.6 (s, bipyC̲
H2), 35.4 (s, tBu), 31.6 (s, tBu).
A solution of 6a (24.6 mg, 20.0 μmol) and PPh3 (5.2 mg,
20 μmol) in CH2Cl2 (5 mL) was stirred for 30 min at RT. The
solvent was removed in vacuo to give an orange solid, which
Preparation of 4[BArF
]
4
General procedure. A solution of [M(COD)Cl]2 (20.0 μmol) was washed with hexane (10 mL). Yield = 12.0 mg (40%,
and bipy (3.1 mg, 20 μmol) in CH2Cl2 (1 mL) was freeze– orange powder).
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1H NMR (500 MHz, CD2Cl2): δ 9.00 (d, 3JHH = 5.1, 2H, bipy), 32, 3JCB = 3, ArF), 128.1 (s, bipy), 125.2 (q, 1JFC = 272, ArF), 123.4
3
3
3
1
7.90 (t, JHH = 7.4, 2H, bipy), 7.77 (d, JHH = 8.1, 2H, bipy), (s, bipy), 118.0 (sept., JFC = 4, ArF), 86.5 (d, JRhC = 12,
7.70–7.75 (m, 8H, ArF), 7.56 (br, 4H, ArF), 7.55 (obscured, 2H, CHvCH), 30.7 (s, CH2). HR ESI-MS (positive ion, 4 kV):
bipy), 7.38 (t, 3JHH = 7.3, 3H, Ph), 7.26 (br app. t, J = 8, 6H, Ph), 367.0677 [M]+ (calcd 367.0676) m/z. Anal. calcd for
3
7.21 (t, JHH = 8.4, 6H, Ph), 3.80 (s, 4H, CHvCH), 2.55–2.67 C50H32BF24N2Rh (1230.50 g mol−1): C, 48.81; H, 2.62; N, 2.28.
(m, 4H, CH2), 2.03–2.15 (m, 4H, CH2). 13C{1H} NMR (126 MHz, Found: C, 48.89; H, 2.52; N, 2.46.
CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 154.5 (s, bipy), 151.7 (s,
1
2
6b
bipy), 139.6 (s, bipy), 135.4 (s, ArF), 133.9 (d, JPC = 12, Ph),
131.3 (d, 1JPC = 28, Ph), 130.8 (s, Ph), 129.5 (qq, 3JFC = 32, 3JCB = 3, Yield = 91.5 mg (67%, dark green solid).
ArF), 129.1 (d, JPC = 9, Ph), 127.1 (s, bipy), 125.2 (q, JFC = 272,
1H NMR (500 MHz, CD2Cl2): δ 8.20 (app. td, 3JHH = 8, 4JHH
=
3
1
ArF), 123.4 (s, bipy), 118.0 (sept., 3JFC = 4, ArF), 82.8 (d, 1JRhC = 11, 1.2, 2H, bipy), 8.14 (d, 3JHH = 8.1, 2H, bipy), 8.11 (d, 3JHH = 5.6,
CHvCH), 31.8 (s, CH2). 31P{1H} NMR (162 MHz, CD2Cl2): δ 22.31 2H, bipy), 7.71–7.75 (m, 8H, ArF), 7.69 (ddd, JHH = 7.8, 5.6,
3
(vbr, fwhm = 45 Hz). HR ESI-MS (positive ion, 4 kV): 367.0679 4JHH = 1.0, 2H, bipy), 7.56 (s, 4H, ArF), 4.40 (br, 4H, CHvCH),
[M
−
PPh3]+ (calcd 367.0676) m/z. Anal. calcd for 2.36–2.48 (m, 4H, CH2), 2.00–2.12 (m, 4H, CH2). 13C{1H} NMR
C68H47BF24N2PRh·CH2Cl2 (1577.72 g mol−1): C, 52.53; H, 3.13; N, (126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 158.4 (s, bipy),
1.78. Found: C, 52.91; H, 3.17; N, 2.15.
1
149.6 (s, bipy), 142.6 (s, bipy), 135.4 (s, ArF), 129.4 (qq, JFC
=
2
32, 3JCB = 3, ArF), 128.9 (s, bipy), 125.2 (q, 1JFC = 272, ArF), 123.7
5b
3
(s, bipy), 118.0 (sept., JFC = 4, ArF), 72.2 (s, CHvCH), 31.5 (s,
A solution of 6b (10.0 mg, 7.58 μmol) and PPh3 (2.2 mg, CH2). HR ESI-MS (positive ion, 4 kV): 457.1250 [M]+ (calcd
8.4 μmol) in CH2Cl2 (1 mL) was agitated for 10 min at RT then 457.1251) m/z. Anal. calcd for C50H32BF24IrN2 (1319.81
layered with excess hexane (ca. 20 mL) to afford the product as g mol−1): C, 45.50; H, 2.44; N, 2.12. Found: C, 45.83; H, 2.56;
red crystals on diffusion. Yield = 6.7 mg (56%).
N, 2.19.
1H NMR (500 MHz, CD2Cl2): δ 9.13 (br, 2H, bipy), 7.89 (t,
3
NMR scale reactions of 6
3JHH = 7.6, 2H, bipy), 7.81 (d, JHH = 7.9, 2H, bipy), 7.70–7.76
3
(s, 8H, ArF), 7.56 (br, 4H, ArF), 7.50 (t, JHH = 6.4, 2H, bipy),
Reaction between 6a and PPh3. In a J. Young’s NMR tube, 6a
7.38 (t, 3JHH = 7.3, 3H, Ph), 7.25 (br app t, J = 8, 6H, Ph), 7.13 (t, (12.3 mg, 10.0 μmol) and PPh3 (5.2 mg, 10 μmol) was dissolved
3JHH = 8.9, 6H, Ph), 3.23 (br, 4H, CHvCH), 2.37–2.51 (m, 4H, in CD2Cl2 (0.5 mL) resulting in the immediate formation of
CH2), 1.81–1.94 (m, 4H, CH2). 13C{1H} NMR (126 MHz, fast exchanging mixture of 5a and free PPh3, which was ana-
CD2Cl2): δ 162.3 (q, 1JCB = 50, ArF), 155.6 (HMBC, bipy)152.5 (s, lysed by VT-NMR spectroscopy.
bipy), 138.9 (s, bipy), 135.4 (s, ArF), 133.6 (d, JPC = 10, Ph),
31P{1H} NMR (202 MHz, CD2Cl2): δ 10.6 (vbr, fwhm =
2
2
3
131.1 (s, Ph), 130.8 (HMBC, Ph), 129.4 (qq, JFC = 32, JCB = 3, 55 Hz).31P{1H} NMR (202 MHz, CD2Cl2, 200 K): δ 33.3 (d,
3
1
ArF), 129.1 (d, JPC = 9, Ph), 127.7 (s, bipy), 125.2 (q, JFC = 272, 1JRhP = 129, 5a), −8.3 (s, PPh3).
3
ArF), 123.9 (s, bipy), 118.0 (sept., JFC = 5, ArF), 65.2 (br,
Reactions between 6 and H2. A solution of 6 (10.0 μmol) in
CHvCH), 33.0 (s, CH2). 31P{1H} NMR (162 MHz, CD2Cl2): CD2Cl2 (0.5 mL) within a J. Young’s NMR tube was freeze–
δ 10.1 (s). HR ESI-MS (positive ion, 4 kV): 719.2168 [M]+ (calcd pump–thaw degassed three times then placed under dihydro-
719.2163) m/z. Anal. calcd for C68H47BF24N2PIr (1582.10 gen (1 atm). The tube was sealed, inverted several times then
g mol−1): C, 51.62; H, 2.99; N, 1.77. Found: C, 51.43; H, 2.87; left to stand at ambient temperature for 24 h. No significant
1
N, 1.84.
reaction was observed by H NMR spectroscopy for 6a. In the
case of 6b, the presence of small amount of a dihydride
complex can be detected initially (<15%), however, this species
Preparation of 6
General procedure.
A
suspension of [M(COD)Cl]2 does not grow in further over 48 h (or even extended heating at
(50.0 μmol), bipy (15.6 mg, 100 μmol) and Na[BArF4] (88.6 mg, 50 °C). Consistent with an unfavourable equilibrium reaction
1
100 μmol) in CH2Cl2 (5 mL) was stirred overnight at RT. with dihydrogen, the only species observed by H NMR spec-
Hexane (1 mL) was added, the solution filtered and then troscopy after freeze–pump–thaw degassing the solution is 6b.
layered with excess hexane (ca. 45 mL) to afford the products
on diffusion.
Preparation of 7
A solution of 8 (14.9 mg, 5.00 μmol) and bipy (1.6 mg,
10 μmol) in CH2Cl2 (1 mL) was agitated for 10 min at RT.
6a
Yield = 91.9 mg (75%, red solid).
Addition of excess hexane (ca. 20 mL) afforded the product as
an orange-red oil that solidified on extended drying in vacuo.
1H NMR (500 MHz, CD2Cl2): δ 8.11 (app. td, 3JHH = 8, 4JHH
=
1.5, 2H, bipy), 8.07 (d, 3JHH = 8.2, 2H, bipy), 7.79 (d, 3JHH = 5.5, Yield = 2.4 mg (15%).
2H, bipy), 7.70–7.75 (m, 8H, ArF), 7.59 (ddd, JHH = 7.2, 5.5,
1H NMR (500 MHz, CD2Cl2): δ 7.97 (d, 3JHH = 8.1, 2H, bipy),
3
4JHH = 1.5, 2H, bipy), 7.55 (br, 4H, ArF), 4.57 (br, 4H, CHvCH), 7.89 (br d, JHH = 5, 2H, bipy), 7.82 (app. t, JHH = 8, 2H, bipy),
3
3
2.54–2.65 (m, 4H, CH2), 2.14–2.23 (m, 4H, CH2). 13C{1H} NMR 7.71–7.75 (m, 8H, ArF), 7.62–7.68 (m, 12H, Ph), 7.56 (br, 4H,
1
3
3
(126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 156.8 (s, bipy), ArF), 7.30 (t, JHH = 7.4, 6H, Ph), 7.15 (t, JHH = 7.5, 12H, Ph),
149.1 (s, bipy), 141.7 (s, bipy), 135.4 (s, ArF), 129.4 (qq, JFC
=
6.82 (dd, JHH = 7.5, 5.8, 2H, bipy). 13C{1H} NMR (126 MHz,
2
3
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1
CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 156.5 (s, bipy), 153.8 (s, 5JHH = 0.8, 1H, bipy), 7.88 (dd, 3JHH = 8.2, 4JHH = 2.3, 1H, bipy),
bipy), 138.6 (s, bipy), 135.4 (s, ArF), 135.2 (app. t, JPC = 6, Ph), 7.83–7.88 (m, 2H, Phth), 7.79 (app. td, 3JHH = 8, 4JHH = 1.8, 1H,
3
4
133.0–134.1 (m, Ph), 130.8 (s, Ph), 129.4 (qq, 2JFC = 32, 3JCB = 3, bipy), 7.69–7.74 (m, 2H, Phth), 7.28 (ddd, JHH = 7.6, 4.8, JHH
1
ArF), 128.6 (app. t, JPC = 5, Ph), 126.3 (s, bipy), 125.2 (q, JCF
=
= 1.2, 1H, bipy), 4.91 (s, 2H, CH2). 13C{1H} NMR (101 MHz,
272, ArF), 122.5 (s, bipy), 118.0 (sept., JFC = 4, ArF). 31P{1H} CDCl3): δ 168.0, 155.9, 155.9, 149.6, 149.3, 137.5, 137.0, 134.3,
3
1
NMR (162 MHz, CD2Cl2): δ 46.6 (d, JRhP = 182). HR ESI-MS 132.1, 132.1, 123.9, 123.6, 121.3, 121.1, 39.1. HR ESI-MS (posi-
(positive ion, 4 kV): 815.1458 [M + MeOH]+ (calcd 815.1458) m/z.
tive ion, 4 kV): 338.0903 [M + Na]+ (calcd 338.0900) m/z.
Hydrogenation of 7
Preparation of 5-aminomethylbipyridine
A solution of 7 (16.5 mg, 10.0 μmol) in CD2Cl2 (0.5 mL) within
A
solution of 5-phthalimidomethylbipyridine (1.50 g,
a J. Young’s NMR tube was freeze–pump–thaw degassed three 4.76 mmol) and hydrazine monohydrate (2.31 mL, 47.6 mmol)
times and placed under dihydrogen (1 atm) resulting in quan- in EtOH (100 mL) under N2 was heated at reflux for 18 h. An
titative formation of 4a[BArF4] within 5 min as gauged by 1H aqueous solution of NaOH (2 M, 50 mL) was added and the
and 31P NMR spectroscopy.
mixture extracted with CH2Cl2 (3 × 100 mL). The organic phase
was dried over MgSO4 and the solvent removed in vacuo to give
the compound as a waxy off-white solid. Yield = 0.794 g (90%).
Preparation of 8
3
4
A solution of 2a (64.0 mg, 40.0 μmol) in CH2Cl2 (5 mL) was
freeze–pump–thaw degassed three times and placed under = 1.9, JHH = 0.9, 1H, bipy), 8.63 (d, JHH = 2.3, 1H, bipy), 8.37
dihydrogen (1 atm). After stirring for 5 h the solution was (app. dt, JHH = 8.0, J = 1, 1H, bipy), 8.33 (d, JHH = 8.1, 1H,
freeze–pump–thaw degassed three times and placed under bipy), 7.92 (app. td, JHH = 8, JHH = 1.9, 1H, bipy), 7.90 (dd,
argon. The solution was layered with excess hexane (ca. 45 mL) 3JHH = 8.1, 4JHH = 2.3, 1H, bipy), 7.42 (ddd, 3JHH = 7.5, 4.8, 4JHH
to afford the product as a dark orange crystalline solid on = 1.2, 1H, bipy), 3.82 (s, 2H, CH2). 13C{1H} NMR (101 MHz,
1H NMR (400 MHz, (CD3)2SO): δ 8.67 (ddd, JHH = 4.8, JHH
5
4
3
3
3
4
diffusion. Yield = 33.7 mg (57%).
(CD3)2SO): δ 155.3, 153.6, 149.2, 148.4, 139.3, 137.2, 136.0,
1H NMR (500 MHz, CD2Cl2): δ 7.72–7.77 (m, 16H, ArF), 7.56 123.9, 120.2, 119.9, 42.8. HR ESI-MS (positive ion, 4 kV):
(s, 8H, ArF), 7.43–7.50 (m, 4H, Ph), 7.32–7.40 (m, 6H, Ph), 208.0846 [M + Na]+ (calcd 208.0845) m/z.
3
7.15–7.26 (m, 40H, Ph), 6.87 (t, JHH = 6.9, 4H, η-Ph), 6.37 (t,
3
Preparation of 10
3JHH = 6.4, 4H, η-Ph), 5.51 (t, JHH = 6.5, 2H, η-Ph). 13C{1H}
NMR (126 MHz, CD2Cl2): δ 162.3 (q, JCB = 50, ArF), 135.4 (s, A solution of 5-aminomethylbipyridine (730 mg, 3.94 mmol)
1
2
2
ArF), 135.1 (d, JPC = 12, Ph), 134.1 (d, JPC = 11, Ph), 132.9 (s, and 3,5-di-tert-butylbenzaldehyde (860 mg, 3.94 mmol) in
4
3
Ph), 132.1 (d, JPC = 3, Ph), 129.5 (d, JPC = 8, C, Ph), 129.4 (qq, MeOH (30 mL) was stirred at RT for 18 h over 3 Å molecular
3
3
2JFC = 32, JCB = 3, ArF), 129.2 (d, JPC = 11, Ph), 129 (obscured, sieves under N2. The resulting mixture was cooled to 0 °C and
1
1
2
Ph), 125.2 (q, JCF = 272, ArF), 123.1 (dd, JPC = 33, JRhC = 7, NaBH4 (298 mg, 7.88 mmol) added in portions. The mixture
3
2
η-Ph), 118.0 (sept., JFC = 4, ArF), 106.5 (br d, JPC = 10, η-Ph), was warmed to ambient temperature and stirred for 30 min,
105.4 (br, η-Ph), 102.4–102.6 (m, η-Ph). 31P{1H} NMR and then heated at reflux for 2 h. The solvent was removed
1
2
(162 MHz, CD2Cl2): δ 45.9 (ddd, JRhP = 217, JPP = 38, in vacuo and the crude extracted with CH2Cl2 (30 mL). The
1
2
2JRhP = 5), 43.2 (dd, JRhP = 198, JPP = 38). HR ESI-MS organic phase was washed with H2O (3 × 30 mL) and dried
(positive ion, 4 kV): 627.0869 [12M]+ (calcd 627.0872) m/z.
over MgSO4. The solvent was removed in vacuo and the product
purified by column chromatography (SiO2, CH2Cl2/MeOH
95 : 5) to give a colourless oil. The product was freeze-dried
Reaction of 8 with bipy
In a J. Young’s NMR tube, 8 (14.9 mg, 5.0 μmol) and bipy in vacuo to give an off-white solid. Yield = 1.185 g (78%).
(1.6 mg, 10.0 μmol) was dissolved in CD2Cl2 (0.5 mL) resulting
1H NMR (500 MHz, CD2Cl2): δ 8.63–8.67 (obscured, 1H,
3
in quantitative formation of 7 within 5 minutes as gauged by bipy), 8.65 (br, 1H, bipy), 8.44 (d, JHH = 8.0, 1H, bipy), 8.41 (d,
1H and 31P NMR spectroscopy.
3JHH = 8.2, 1H, bipy), 7.85 (dd, 3JHH = 8.2, 4JHH = 2.2, 1H, bipy),
3
4
4
7.82 (app. td, JHH = 8, JHH = 1.8, 1H, bipy), 7.35 (t, JHH = 1.9,
Preparation of 5-phthalimidomethylbipyridine
1H, C6H3), 7.31 (ddd, 3JHH = 7.5, 4.8, 4JHH = 1.2, 1H, bipy), 7.22
4
A
stirred solution of 5-chloromethylbipyridine (3.00 g, (d, JHH = 1.9, 2H, C6H3), 3.90 (s, 2H, CH2), 3.82 (s, 2H, CH2),
t
14.7 mmol) and potassium phthalimide (4.07 g, 21.9 mmol) in 1.35 (s, 18H, Bu). The NH resonance was not unambiguously
DMF (70 mL) under N2 was heated at 40 °C for 18 h. The located. 13C{1H} NMR (126 MHz, CD2Cl2): δ 156.7, 155.4,
solvent was removed in vacuo and the mixture dissolved in 151.4, 149.7, 149.7, 140.0, 137.3, 137.2, 136.9, 124.1, 122.9,
CH2Cl2 (100 mL) and washed with H2O (2 × 100 mL), brine 121.5, 121.2, 121.0, 54.4, 51.0, 35.3, 31.8. HR ESI-MS (positive
(100 mL), and then dried over MgSO4. The solvent was ion, 4 kV): 388.2747 [M + H]+ (calcd 388.2747) m/z.
removed in vacuo and the product recrystallised from hot EtOH
Crystallography
(ca. 450 mL). Yield = 4.19 g (94%, white crystals).
4
5
1H NMR (400 MHz, CDCl3): δ 8.76 (dd, JHH = 2.3, JHH
=
Full details about the collection, solution and refinement are
0.8, 1H, bipy), 8.65 (ddd, JHH = 4.8, JHH = 1.8, JHH = 0.9, 1H, documented in the CIF, which have been deposited with the
bipy), 8.36 (app. dt, 3JHH = 7.9, J = 1, bipy), 8.35 (dd, 3JHH = 8.2, Cambridge Crystallographic Data Centre under CCDC 1563158
3
3
5
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(1b), 1563159 (4a[BArF4]), 1563160 (4b[BArF4]; Z′ = 1), 1563161
T. Maeda, H. Miyake and H. Tsukube, Supramol. Chem.,
2011, 23, 244–248.
(4b[BArF ]; Z′ = 2), 1563162 (5a), 1563163 (5b) and 1563164 (8).†
4
7 J. A. Osborn and R. R. Schrock, J. Am. Chem. Soc., 1971, 93,
2397–2407; J. R. Shapley, R. R. Schrock and J. A. Osborn,
J. Am. Chem. Soc., 1969, 91, 2816–2817.
8 G. L. Moxham, S. K. Brayshaw and A. S. Weller, Dalton
Trans., 2007, 1759–1761.
Conflicts of interest
There are no conflicts to declare.
9 G. L. Moxham, T. M. Douglas, S. K. Brayshaw, G. Kociok-
Köhn, J. P. Lowe and A. S. Weller, Dalton Trans., 2006, 88,
5492–5505.
Acknowledgements
10 B. D. Alexander, B. J. Johnson, S. M. Johnson,
A. L. Casalnuovo and L. H. Pignolet, J. Am. Chem. Soc.,
1986, 108, 4409–4417; R. R. Schrock and J. A. Osborn,
J. Am. Chem. Soc., 1976, 98, 2134–2143.
We gratefully acknowledge the EPSRC (J. E.-K.), Leverhulme
Trust (RPG-2012-718, R. C. K), ERC (M. R. G., grant agreement
637313), and Royal Society (A. B. C.) for financial support.
Crystallographic data for 4a[BArF4] and high-resolution mass- 11 A. Macchioni, C. Zuccaccia, E. Clot, K. Gruet and
spectrometry data were collected using instruments purchased
R. H. Crabtree, Organometallics, 2001, 20, 2367–2373.
through support from Advantage West Midlands and the 12 P. Alam, C. U. Climent, G. Kaur, D. Casanova, A. Roy
European Regional Development Fund. Crystallographic data
Choudhury, A. Gupta, P. Alemany and I. R. Laskar, Cryst.
Growth Des., 2016, 16, 5738–5752.
for 1b, 4b[BArF4], 5, and 8 were collected using an instrument
that received funding from the ERC under the European 13 I. A. Guzei, A. L. Rheingold, D. H. Lee and R. H. Crabtree,
Union’s Horizon 2020 research and innovation programme
(grant agreement no. 637313).
Z. Kristallogr. – New Cryst. Struct., 1998, 213, 585–587.
14 Á. Álvarez, R. Macías, M. J. Fabra, M. L. Martín, F. J. Lahoz
and L. A. Oro, Inorg. Chem., 2007, 46, 6811–6826.
15 C. Cocevar, G. Mestroni and A. Camus, J. Organomet.
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16 A. Rifat, N. J. Patmore, M. F. Mahon and A. S. Weller,
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M. B. Ezhova, B. O. Patrick and B. R. James, C. R. Chim.,
2002, 5, 373–378. See CIF for solid-state structure.
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