A new family of flexible scorpionate ligands based on 2-mercaptopyridine

Article abstract of DOI:10.1039/b905409j

A new family of flexible scorpionate ligands based on 2-mercaptopyridine is reported. The tris- and bis-substituted ligands, K[HB(mp)₃] (1) and Na[H₂B(mp)₂] (2) (mp = 2-mercaptopyridine) have been prepared and fully characterised. The structural characterisation of 1 reveals an unprecedented μ₃-κ³-SS′H- η¹η¹η²-κ²- S″C-η¹η¹-κ¹-S′- η¹ coordination mode. The coordination of both 1 and 2 to copper(i) complexes containing triphenylphosphine and tricyclohexylphosphine co-ligands is investigated suggesting κ³-SSS coordination modes for [Cu{HB(mp)₃}(PR₃)] {where R = Ph (3); R = Cy, (4)} and κ³-SSH coordination modes for [Cu{H₂B(mp) ₂}(PR₃)] {where R = Ph (5); R = Cy (6)} the latter confirmed by structural characterisation of 5. A structural comparison with the sulfur based scorpionates, HB(mt)₃ and H₂B(mt)₂ (mt = methyl-2-mercaptoimidazole) is made in terms of the degree of tautomerisation of the heterocyclic rings. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b905409j

View Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/dalton | Dalton Transactions
A new family of flexible scorpionate ligands based on 2-mercaptopyridine†
Gavin Dyson, Alex Hamilton, Byron Mitchell and Gareth R. Owen*‡
Received 17th March 2009, Accepted 6th May 2009
First published as an Advance Article on the web 11th June 2009
DOI: 10.1039/b905409j
A new family of flexible scorpionate ligands based on 2-mercaptopyridine is reported. The tris- and
bis-substituted ligands, K[HB(mp)3] (1) and Na[H2B(mp)2] (2) (mp = 2-mercaptopyridine) have been
prepared and fully characterised. The structural characterisation of 1 reveals an unprecedented
3
1
1
2
2
1
1
1
1
m3-k -SS¢H-h h h -k -S¢¢C-h h -k -S¢-h coordination mode. The coordination of both 1 and 2 to
copper(I) complexes containing triphenylphosphine and tricyclohexylphosphine co-ligands is
3
investigated suggesting k -SSS coordination modes for [Cu{HB(mp)3}(PR3)] {where R = Ph (3);
3
R = Cy, (4)} and k -SSH coordination modes for [Cu{H2B(mp)2}(PR3)] {where R = Ph (5); R = Cy
(6)} the latter confirmed by structural characterisation of 5. A structural comparison with the sulfur
based scorpionates, HB(mt)3 and H2B(mt)2 (mt = methyl-2-mercaptoimidazole) is made in terms of the
degree of tautomerisation of the heterocyclic rings.
formation of metal–borane (metallaboratrane) complexes8 giving
Introduction
rise to reactivity not observed in the analogous Tp compounds.9
The bis-substituted version of this ligand, Bm [dihydro-
bis(methylimidazolyl)borate], was later reported in 1997.10 Follow-
ing the publication of these flexible scorpionate ligands, there have
been a number of other bis-substituted11 and tris-substituted12
flexible scorpionates reported.
Ever since Trofimenko reported the first scorpionate ligand1 in
1966, Tp [hydrotris(pyrazolyl)borate] (Fig. 1), there has been great
interest in their chemistry and application.2–4 Since then, there has
been a vast array of derivative and further generation ligands.1c,1d,5
For a long time, scorpionate ligands were generally thought of
as inert spectator ligands that could easily be tuneable in terms
of their steric and electronic properties.6 Such ligands could be
used to alter the properties of the transition metal centre without
getting directly involved in its reactivity.
Our interests lie in the potential reversibility of hydride mi-
gration between transition metal and boron centres and the
application of this process to metal mediated transformations.
During the course of our investigations we isolated a compound
where a hydride was observed at an intermediate point between
the metal and boron centres (Fig. 2).13 Crossley and Hill have
also provided an example where the position of the hydride
(i.e. at either the boron or metal centre) could be controlled by
judicious choice of co-ligand.14 We have further exploited hydride
migration reactivity within the relatively unexplored ligand, Tai
[hydrotris(azaindoyl)borate] (Fig. 1), providing the first nitrogen
based metallaboratrane complexes.15 Additionally, we reported
a series of group nine transition metal complexes containing
Tai and highlighted their catalytic application in the transfer
hydrogenation of ketones.16
Fig. 1 Tp and the flexible scorpionates Tm, Bm and Tai.
This outlook changed following the introduction of a new more
flexible scorpionate ligand, Tm [hydrotris(methylimidazolyl)-
borate], which is based upon a N-methyl-2-mercaptoimidazol-1-yl
ring system (Fig. 1).7 This new generation ligand had two major
differences when compared to Trofimenko’s original scorpionates.
The Tm ligand was based on soft sulfur donor atoms and perhaps
more significantly, greater flexibility had been incorporated into
the ligand by addition of an extra atom between the boron and
the donor atom. The greater flexibility of this ligand structure
opened up the potential for activation at the boron bridgehead and
Fig. 2 Previously reported complex where the hydride is found at an
intermediate point between the ruthenium and boron centres.
The School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK
BS8 1TS. E-mail: gareth.owen@bristol.ac.uk; Fax: +44 (0)117 925 1295;
Tel: +44 (0)117 928 7652
† CCDC reference numbers 724276 and 724277. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/b905409j
‡ Royal Society Dorothy Hodgkin Research Fellow
It was of interest to us to provide other examples of flexible scor-
pionate ligands in order to further explore and exploit potential
B–H activation. We wondered what effect changing the heterocycle
would have on the electronic properties of the ligand. We aimed at
6120 | Dalton Trans., 2009, 6120–6126
This journal is
The Royal Society of Chemistry 2009
©

View Online
1
1
1
as a yellow powder and characterised by H, 13C{ H}, 11B{ H}
providing a more electron rich donor system and therefore targeted
scorpionate ligands containing 2-mercaptopyridine heterocycles.
Similar to the methyl-2-mercaptoimidazol-1-yl and 7-azaindolyl
ligand “arms” within Tm and Tai, respectively, the 2-mercapto-
pyridine unit can undergo tautomerisation between pyridine-2-
thionate and 2-thiopyridone forms (Fig. 3). It has been shown that
although the thione–thiolate tautomeric equilibrium generally
favours the thione form, there is a strong dependence on its
environment with only a small difference in the energy between
the two tautomeric forms.17
NMR, IR spectroscopies and ESI- mass spectrometry. The H
1
NMR spectrum was particularly broad, however it revealed four
signals between 7.83 and 6.46 ppm each integrating to three
protons corresponding to the ring protons. A very broad signal
centred at 4.83 ppm which integrated to one proton was assigned as
the B–H proton. This assignment was further confirmed following
a boron decoupled proton NMR experiment where a sharp singlet
signal was observed in place of the broad signal. The 13C{ H}
1
NMR spectrum of 1 also gave broad signals, nevertheless it showed
five signals in the low field region of the spectrum. The chemical
=
shift corresponding to the C S group was found at 182.5 ppm.
It has previously been shown that 13C NMR spectroscopy can
provide a means of estimating the equilibrium composition of the
two tautomeric forms and the observed chemical shift is indicative
of a high degree of the thiopyridone tautomeric form as expected.18
The formation of 1 was further confirmed by an X-ray single
crystal diffraction study. Crystals suitable for X-ray diffraction
were grown when diethyl ether was allowed to diffuse into a
saturated tetrahydrofuran solution of 1. ORTEP representations
of 1 are presented in Fig. 5 and 6. Selected bond distances and
angles, and crystallographic parameters are given in Tables 1 and
2 respectively.†
Fig. 3 Tautomerisation between pyridine-2-thionate and 2-thiopyridone
forms.
It was envisaged that the aromaticity of the thiolate tautomer
might provide greater electron density upon the sulfur atoms thus
furnishing more electron rich ligands (Fig. 4). Herein, we wish to
report the synthesis and characterisation of this new family of flex-
ible scorpionate ligands together with a preliminary investigation
of their coordination chemistry to a series of copper(I) complexes.
Fig. 4 Tautomerisation of tris-substituted ligand resulting in a greater
negative charge at sulfur.
Results and discussion
Synthesis and characterisation of ligands
Fig. 5 Structure of K[Tmp] (1). Hydrogen atoms (except for H1) have
been omitted for clarity (thermal ellipsoids drawn at the 50% level).
The syntheses of our target ligands were performed by similar
methods to those used for other scorpionate ligands.7,11,12 The tris-
substituted ligand potassium hydrotris(2-thiopyridone)borate,
K[HB(mp)3] (mp = 2-mercaptopyridine), K[Tmp] (1) was readily
prepared by heating a xylene suspension of KBH4 in the presence
of an excess of 2-mercaptopyridine (4 equivalents) at 170 ◦C under
a nitrogen atmosphere (Scheme 1). The extent of the reaction could
be followed by taking aliquots from the reaction mixture and
The X-ray solution of 1 revealed an extended structure involving
3
1
1
2
2
1
1
1
1
an unprecedented m3-k -SS¢H-h h h -k -S¢¢C-h h -k -S¢-h coor-
dination mode of the ligand to the potassium centres. Two sulfur
atoms (S,S¢) and the B–H functionality coordinate and interact
with one of the potassium atoms. The ligand bridges to further
potassium atoms in two different ways. Firstly, one of the indicated
sulfur groups (S¢) bridges to a second potassium centre. Secondly,
a third sulfur donor (S¢¢) coordinates to a third potassium. The
latter potassium interacts with a carbon in the 5-position of the
mercaptopyridine ring which is bridging the two former potassium
centres. Each potassium atom is coordinated to three sulfur atoms,
a B–H group, a carbon atom of a mercaptopyridine ring and one
molecule of tetrahydrofuran.19 The structure also reveals that the
thione tautomeric form predominates for the thiopyridyl units
(Table 1).
1
recording their 11B{ H} NMR spectra (in DMSO-d6). A single
broad peak at 4.4 ppm (h.h.w. = 560 Hz) was observed after a
period of ca. 48 h. The solid product (1) was obtained in high yield
Scheme 1 Synthesis of 1.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6120–6126 | 6121
©

View Online
◦
˚
The preparation of the bis-substituted ligand sodium
dihydrobis(2-thiopyridone)borate, Na[H2B(mp)2] (mp = 2-merca-
ptopyridine), Na[Bmp] (2) required some optimisation. It
was found that the best conditions for the preparation of
this ligand involved heating NaBH4 and two equivalents of
2-mercaptopyridine in a 3 : 1 mixture of toluene and tetrahydro-
furan at 80 ◦C for 12 h (Scheme 2). The sodium borohydride
salt gave much better selectivity for the desired product over the
corresponding potassium salt in this case. The product was isolated
in good yield, as a pale yellow solid by filtration of the reaction
mixture and washing the solid with a further quantity of toluene.
The bis-substituted ligand was also characterised by NMR, IR
spectroscopy and mass spectrometry.
Table 1 Selected bond distances (A) and angles ( ) for 1
S(1)–K(1)
S(2)–K(1)
S(3)–K(1)
H(1)–K(1)
H(1)–B(1)
C(1)–S(1)
C(5)–S(2)
C(10)–S(3)
N(1)–B(1)
N(2)–B(1)
N(3)–B(1)
K(1)–C(8)
N(2)–B(1)–N(1)
N(1)–B(1)–N(3)
N(3)–B(1)–N(2)
C(10)–S(3)–K(1)
C(1)–S(1)–K(1)
C(5)–S(2)–K(1)
K(1)–H(1)–B(1)
3.294(5)
3.271(5)
3.216(5)
2.748(18)
1.051(18)
1.703(15)
1.705(14)
1.695(16)
1.573(18)
1.567(19)
1.579(19)
3.312(16)
109.55(10)
110.14(11)
108.76(11)
96.00(5)
162.17(5)
121.59(5)
149.64(12)
Table 2 Crystallographic data and parameters for 1 and 5
Scheme 2 Synthesis of 2.
Complex
1
5
Chemical formula
Formula weight
Crystal system
Space group
C19H21BKN3OS3
453.48
Triclinic
¯
P1
7.5891(3)
10.2493(4)
14.4333(6)
96.181(2)
94.557(2)
105.418(2)
2
1069.11(7)
173
1.409
0.557
33 398
6548
1.143
0.0289
0.0338
0.1057
C28H25BCuN2PS2
558.94
Monoclinic
P21/c
14.8949(7)
8.9263(4)
19.1954(8)
90
92.750(2)
90
4
2549.2(2)
173
1.456
1.104
75 804
7807
1.067
0.0590
0.0295
0.0821
Synthesis and characterisation of copper complexes
The coordination chemistry of Tp, Tm and their derivatives has
been extensively investigated using a wide range of transition
metal centres. In particular, the coordination to copper has been
reportedina number of examples.1,20,21 The coordination chemistry
of ligands 1 and 2 with copper was investigated.
The complexes [({HB(mp)3})Cu(PR3)] {where R = Ph (3); R =
Cy (4)} and [({H2B(mp)2})Cu(PR3)] {where R = Ph3 (5); R =
Cy3 (6)} were readily prepared by the addition of one equivalent
of either K[Tmp] or Na[Bmp] to methanol solutions containing
CuCl and the corresponding phosphine ligand (Scheme 3). One
equivalent of the phosphine was added to furnish complexes
3–6. The same products were also obtained in the presence of
two equivalents of phosphine. Yellow solids precipitated from
the reaction mixtures within a few minutes. The products were
isolated in high yields and fully characterised by NMR and IR
spectroscopy, mass spectrometry and elemental analysis.
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
Z
V
T/K
Dc/Mg m-3
m/mm-1
No. of data collected
No. of unique data
Goodness of fit on F2
Rint
Final R(|F|) for Fo > 2s(Fo)
Final R(F2) for all data
Fig. 6 ORTEP representation of the extended solid state structure of 1.
One molecule of tetrahydrofuran is coordinated to each potassium atom.
Hydrogen atoms (except for H1) have been omitted for clarity. (Colours
representing atoms are: yellow: sulfur; blue: carbon; brown: boron; pink:
nitrogen; white: hydrogen).
Scheme 3 Synthesis of copper complexes 3–6.
1
The 31P{ H} NMR spectra of 3 and 5 revealed broad signals
at -2.4 ppm (h.h.w. = 85 Hz) and 1.7 ppm (h.h.w. = 265 Hz)
6122 | Dalton Trans., 2009, 6120–6126
This journal is
The Royal Society of Chemistry 2009
©

View Online
1
11
respectively. In contrast, the 31P{ H} NMR spectra of the tricy-
4.12 ppm and 3.99 ppm respectively in the 1H{ B} NMR spectra
(in CDCl3). The equivalence of the BH2 protons in the NMR
spectrum, suggest no significant interaction of the B–H group with
the metal centre in solution. The 1H NMR data therefore suggests
clohexylphosphine complexes 4 and 6 revealed relatively sharp
signals at 17.4 ppm and 19.0 ppm. This is consistent with a more
labile coordination of the aryl phosphine relative to the alkyl
phosphine ligands. Similar observations have been recorded in
other examples.20,21
2
the formation of [Cu{k -SS-H2B(mp)2}(PR3)] [R = Ph (5); Cy (6)]
in solution. The IR spectra, on the other hand, showed two bands
at 2425 cm-1 and 2374 cm-1 (solid state) and 2417 and 2393 cm-1
(dichloromethane solution) for 5 and 6 respectively, for the
The 11B{ H} NMR spectra of complexes 3 and 4 revealed single
1
broad peaks at -0.1 ppm (h.h.w. = 412 Hz) and -0.5 ppm (h.h.w. =
331 Hz), respectively [upfield from the free ligand (1), 4.4 ppm
3
B–H stretching frequencies suggesting k -SSH coordination both
(h.h.w. = 560 Hz)]. The H and 13C{ H} NMR data for both 3
in solution and solid state. The presence of a BH–Cu interaction
was confirmed by a X-ray diffraction study on 5 (Fig. 8). Single
crystals were obtained by layering a tetrahydrofuran solution
containing the complex with hexane.
1
1
3
and 4 suggested the formation of [Cu{k -SSS-HB(mp)3}(PPh3)]
3
and [Cu{k -SSS-HB(mp)3}(PCy3)] since signals corresponding
to only one chemical environment for the thiopyridone units
were observed in both cases. A variable temperature investigation
was carried out on complex 4 in CD2Cl2. At -90 ◦C, the
signals corresponding to the ring protons became broad. At this
temperature however, the spectrum still indicated one chemical
environment for these protons. It was not possible to locate the BH
resonance for complex 3, however, the corresponding signal for 4
was located as a singlet at 5.86 ppm in a 1H{ B} NMR experiment
11
(in CDCl3). The downfield shift of this signal in comparison to
the free ligand [d (DMSO) 4.83 ppm] suggested no significant
interaction of the BH group with the metal centre in solution.
Infrared spectroscopy gave no evidence of a BH–Cu interaction
in the solid state for complex 3. The spectrum showed a band
at 2458 cm-1 characteristic of a non-coordinated B–H stretching
frequency, while no B–H band was observed in the case of complex
4. All of the spectroscopic data is therefore consistent with a
3
k -SSS coordination mode of Tmp in complexes 3 and 4.
3
The coordination mode k -NNN is observed in all structurally
characterised mono-phosphine copper complexes containing ei-
3
Fig. 8 Molecular structure of [Cu{k -SSH-H2B(mp)2}(PPh3)] (5). Hy-
ther Tp or its derivatives.20 This is with the exception of one
drogen atoms {except for H(100) and H(101)} have been omitted for clarity
2
example, where a coordination mode k -NN was observed,20g
(thermal ellipsoids drawn at the 50% level).
resulting from the use of particularly large sterically hindered
ligands. The sulfur based scorpionates, on the other hand, are
more flexible than the pyrazole based ligands, the former ligands
forming eight-membered rings upon coordination (Fig. 7). The
B–H–metal interaction therefore has a particular stabilising effect
in the flexible scorpionates since it leads to the formation of two
six-membered rings rather than one eight-membered ring.16 As a
3
The molecular structure of 5 confirmed a k -SSH coordina-
tion mode for Bmp. Selected bond distances and angles and
crystallographic parameters are highlighted in Tables 2 and 3.†
The geometry at the metal centre is somewhat distorted between
tetrahedral and trigonal pyramidal. The sum of the angles defining
the trigonal plane, involving the atoms copper, two sulfur atoms
and phosphine, is 350.4◦. The angles S(1)–Cu–H(101), S2–Cu–
H(101) and P–Cu–H(101) are 88.8(5)◦, 92.7(5)◦ and 117.8(5)◦
3
3
result of this, both k -SSS and k -SSH coordination modes are
commonly observed within complexes containing the Tm ligand.1,5
◦
˚
Table 3 Selected bond distances (A) and angles ( ) for 5
P(1)–Cu(1)
Cu(2)–S(2)
2.216(3)
2.248(4)
Cu(1)–S(1)
C(1)–S(1)
C(6)–S(2)
B(1)–N(1)
2.255(4)
1.707(14)
1.708(14)
1.592(2)
B(1)–N(2)
1.583(18)
1.832(17)
1.150(17)
1.090(18)
111.88(15)
124.56(14)
133.02(13)
113.98(18)
109.08(10)
109.83(5)
106.49(5)
Cu(1)–H(101)
B(1)–H(101)
B(1)–H(100)
S(1)–Cu(1)–P(1)
S(2)–Cu(1)–P(1)
Cu(1)–H(101)–B(1)
S(1)–Cu(1)–S(2)
N(1)–B(1)–N(2)
C(6)–S(2)–Cu(1)
C(1)–S(1)–Cu(1)
Fig. 7 Comparison of chelation sizes for the pyrazole and 2-mercaptopy-
ridine based scorpionates.
1
The 11B{ H} NMR spectra of complexes 5 and 6 revealed single
broad (albeit sharper than in the cases of 3 and 4) peaks at 0.7 ppm
(h.h.w. = 265 Hz) and -0.7 ppm (h.h.w. = 248 Hz), respectively
[upfield from the free ligand (2), -3.7 ppm (h.h.w. = 211 Hz)]. The
BH2 resonances for complexes 5 and 6 were located as singlets at
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6120–6126 | 6123
©

View Online
respectively. The BH–Cu, B–H and Cu–B distances are
were purchased from Aldrich, Alfa Aesar or Acros and used
as received. Solvents were dried on a Grubbs column system
˚
˚
˚
1.832(17) A, 1.150(17)
A
and 2.748
closely related complex
A which are close
˚
to the analogues values for
a
and stored in Young’s Ampoules over 4 A molecular sieves.
[Cu{k -SSH-Ph(H)B(mtPh)2}PPh3] (where mtPh
=
phenyl-2-
1H, H{ B}, 13C{ H}, 11B{ H} and 31P{ H} NMR spectra were
acquired on a Jeol ECP 300 MHz, Jeol Lambda 300 MHz,
Varian 400 MHz or Varian 500 MHz Spectrometer. Spectra were
obtained at ambient temperature and referenced to the residual
3
1
11
1
1
1
mercaptoimidazole) (7).21b
Of particular interest to us were the copper–sulfur and boron–
nitrogen bond distances within complex 5 in order to determine
the extent of tautomerisation of the mercaptopyridine units. To
date there are no reported examples of bis-substituted ligands
of the type [H2BR2]- (where R π H) and so it is not possible
to make a direct comparison. Nevertheless the aforementioned
complex 7 is similar enough to make some comparison. In complex
protio-solvent (1H NMR), the solvent signal (13C{ H} NMR)
1
or referenced internally to BF3.OEt2 (11B{ H} NMR) or H3PO4
1
(31P{ H} NMR). ESI Mass Spectra were recorded on a Bru¨ker
1
Daltonics Apex IV instrument. Elemental analyses were recorded
at the micro-analytical laboratory of the School of Chemistry at
the University of Bristol.
˚
˚
˚
7, the copper–sulfur distances are 2.2892(8) A and 2.3210(8) A
while in complex 5 the corresponding distances are 2.248(4) A
and 2.255(4) A. The boron–nitrogen distances in complex 7 are
1.567(4) A and 1.564(4) A and in the case of 5 the boron–
˚
˚
˚
Potassium hydrotris(2-thiopyridone)borate, K[Tmp] (1)
˚
˚
nitrogen distances are 1.583(18) A and 1.592(2) A. The copper–
sulfur distances are shorter and boron–nitrogen distances longer in
complex 5. Furthermore, the boron–nitrogen distances are larger
than those found for all other structurally characterised transition
metal complexes containing either the HB(mtR)3 or H2B(mtR)2
motifs.22 The longer boron–nitrogen and shorter copper–sulfur
distances indicate that, although the thiopyridone tautomer is
still predominant, a higher degree of the thiolate tautomer occurs
within the resulting complexes compared to the analogous Tm and
Bm complexes. This suggests a small but increased localisation of
the negative charge at the metal centre with Tmp and Bmp as
compared to the other sulfur based scorpionate ligands.
A round bottomed flask was charged with KBH4 (0.10 g,
1.85 mmol), 2-mercaptoypyridine (0.82 g, 7.38 mmol) and de-
gassed xylene (50 mL). The mixture was gradually heated to
180 ◦C over a period of 1 h under a nitrogen atmosphere. H2
gas was observed during the course of the reaction. The reaction
mixture was kept at 170 ◦C for 48 h. The mixture was then allowed
to cool and the resulting solid was isolated by filtration, washed
further with two portions of cold tetrahydrofuran (2 ¥ 10 mL)
and dried under vacuum to give 1 as a yellow powder. Yield =
0.52 g, 74%. Crystals suitable for a X-ray diffraction study were
grown by vapour diffusion of diethyl ether into a tetrahydrofuran
solution of the compound. IR (cm-1, powder film), 2468 w (B–H),
1613 s, 1527 s; in THF (cm-1) 2455 (B–H), 1618 s, 1527 s. 1H NMR
(DMSO-d6, 300 MHz) d 4.83 (1H, br, BH), 6.46 (3H, br, mpCH),
7.17 (3H, br, mpCH), 7.27 (3H, br, mpCH), 7.83 (3H, br, mpCH).
Attempted synthesis of other copper complexes
It was of interest to probe the electronic nature of the new ligands 1
and 2, so we therefore attempted to prepare complexes containing
carbonyl and isocyanide ligands in place of the phosphine groups.
The resulting complexes would provide useful information about
the electronic nature of the metal centre.23 Despite a range of
examples being reported with the pyrazole based ligands,23,24 we
were unsuccessful in synthesising the analogous complexes. A
similar observation was recorded by Reglinski et al. in an attempt
to prepare the complex [Cu(CO)(Tm)].7
1
13C{ H} NMR (DMSO-d6, 101 MHz) d 110.1 (br, mpCH), 132.5
mp
(br, mpCH), 135.0 (br, mpCH), 146.9 (br, CH), 182.5 (br, C S).
=
11B{ H} NMR (DMSO-d6, 96.2 MHz) 4.4 (s, br, h.h.w. = 560 Hz).
1
MS (ESI), m/z = 342 [M - K]-, 100%. HRMS (ESI) [calc. (found)]
for C13H13BN3S3 = 342.0365 (342.0375).
Sodium dihydrobis(2-thiopyridone)borate, Na[Bmp] (2)
A 200 mL Schlenk flask was charged with NaBH4 (224 mg,
5.94 mmol) and mercaptopyridine (1.13 g, 12.0 mmol). A degassed
75 : 25 toluene : tetrahydrofuran mixture (50 mL) was added, and
heated to reflux with stirring overnight. The resulting mixture
was filtered, the solid was washed with toluene (3 ¥ 20 mL) and
dried under vacuum to give 2 as a yellow powder. Yield = 0.88 g,
85%. IR (cm-1, powder film), 2438 w, 2370 w (B–H), 1603 s,
Conclusions
By comparing the structural properties of complex 5 to previously
reported compounds, it has been found that the boron–nitrogen
bond distances are longer in our system, while the corresponding
copper–sulfur distances are shorter. This is consistent with a
more electron rich ligand as compared to other sulfur based
scorpionates. This can be ascribed to the greater negative charge
of the sulfur atoms via tautomerisation of the mercaptopyridine
arms as indicated in Fig. 4. Further investigations are currently
being carried out in order to explore the effect on tautomerisation
on the electronic environment of both the boron and transition
metal centres.
1
1534 s; in THF (cm-1) 2412, 2354 w (B–H), 1612 s, 1531 s. H
NMR (DMSO-d6, 400 MHz) d 6.45 [2H, td, J = 6.5 Hz, 4JHH
1.5 Hz, mpCH-(5)], 7.04 [2H, ddd, 3JHH = 8.5 and 6.5 Hz, 4JHH
=
=
1.5 Hz, mpCH-(4)], 7.29 [2H, dd, 3JHH = 8.5 Hz, 4JHH = unresolved,
3
4
mpCH-(3)], 8.44 (2H, dd, JHH = 6.5, JHH = 1.5 Hz, mpCH-(6)].
1H{ B} NMR (DMSO-d6, 400 MHz) d 3.64 (2H, s, BH2). 13C{ H}
11
1
NMR (CD3CN, 101 MHz) d 109.8 [mpCH-(5)], 133.1 [mpCH-(4)],
133.9 [mpCH-(3)], 150.6 [mpCH-(6)], 182.6 (C S). 11B{ H} NMR
1
=
Experimental
(DMSO-d6, 96.2 MHz) d -3.7 (h.h.w. = 211 Hz). 11B (CD3CN,
General remarks
1
96.2 MHz) d -0.92 (t, JBH = 10.1 Hz). MS (ESI), m/z = 233
All manipulations were carried out using standard Schlenk
techniques or with the use of a M Braun glove box. All reagents
[M - Na]- 100%. HRMS (ESI) [calc. (found)] for C10H10BN2S2 =
233.0378 (233.0382).
6124 | Dalton Trans., 2009, 6120–6126
This journal is
The Royal Society of Chemistry 2009
©

View Online
Cu(Tmp)(PPh3) (3)
[d, JC–P = 15 Hz, P(C6H5)3], 135.0 (s br, mpCH), 145.7 (s br, mpCH),
1
PCipso and C S signals not observed. 11B{ H} d 0.71 (h.h.w. =
=
To a methanol (10 mL) suspension of CuCl (22 mg, 2.21 ¥ 10-4 mol)
and PPh3 (116 mg, 2.21 ¥ 10-4 mol) was added K[Tmp] (70 mg,
2.21 ¥ 10-4 mol), a precipitate immediately formed and the mixture
was stirred for 2 h. This was filtered and the solid washed with
methanol (1 ¥ 5 mL), diethyl ether (2 ¥ 5 mL) and extracted into
DCM to give 3 as a bright yellow solid. Yield = 118 mg, 80%. IR
(cm-1, powder film) 2458 w (B–H), 1611 s, 1531 s; in THF (cm-1)
1614 s, 1535 s, B–H not observed. 1H NMR (CDCl3, 300 MHz) d
6.66 (3H, t, J = 6.0 Hz, mpCH), 7.19–7.43 [21H, m, P(C6H5)3 + 2 ¥
1
265 Hz). 31P { H} (CDCl3, 122 MHz) d 1.71 (s, br, h.h.w. = 265 Hz).
Anal. [Found (calc.)] for C28H25N2BCuPS2: C 60.33 (60.12), H 4.71
(4.51), N 4.92 (5.01).
Cu(Bmp)(PCy3) (6)
To a methanol (10 mL) suspension of CuCl (56.8 mg, 5.74 ¥
10-4 mol) and PCy3 (161 mg, 5.74 ¥ 10-4) was added Na[Bmp]
(152 mg, 3.99 ¥ 10-4 mol). The solution turned yellow and was
stirred for 2 h during which time a yellow/orange precipitate
formed. This was filtered and washed with methanol (5 mL) and
hexane (2 ¥ 5 mL) to give 6 as a dark yellow solid. Yield = 278 mg,
84%. IR (powder film, cm-1) 2374 w (B–H), 1611 s, 1533 s; in DCM
(cm-1) 2393 w (B–H), 1611 s, 1536 s. 1H NMR (CDCl3, 300 MHz)
d 1.15–1.42 (15H, m, PCy3), 1.63–1.87 (18H, m, PCy3), 6.69 [2H,
mpCH], 7.72 (3H, d, 3JHH = 9.0 Hz, mpCH). 13C{ H} NMR (CDCl3,
1
101 MHz) d 115.6 (mpCH), 128.6 [d, JCP = 9.2 Hz, P(C6H5)3], 129.5
[s, P(C6H5)3], 134.0 [d, JCP = 16.1 Hz, P(C6H5)3], 134.4 (mpCH),
146.6 (mpCH), 149.1 (mpCH), 178.3 (C S). 11B{ H} NMR (CDCl3,
1
=
96.4 MHz) d -0.12 (h.h.w. = 413 Hz). 31P{ H} NMR (CDCl3,
1
122 MHz) d -2.4 (s, br, h.h.w. = 85 Hz). Anal. [Found (calc.)] for
C33H28N3BCuPS3.0.2 DCM: C 58.33 (58.20), H 4.18 (4.28), N 6.13
(5.85).
td, J = 6.5 Hz, 4JHH = 1.5 Hz, mpCH-(5)], 7.19 [2H, ddd, 3JHH
=
4
3
8.5 and 6.5 Hz, JHH = 1.5 Hz, mpCH-(4)], 7.70 [2H, d, JHH
=
11
8.5 Hz, mpCH-(3)], 7.99 [2H, d, 3JHH = 6.5 Hz, mpCH-(6)]. 1H{ B}
1
(CDCl3, 300 MHz) d 3.99 (2H, s br, BH2). 13C{ H} NMR (CDCl3,
Cu(Tmp)(PCy3) (4)
101 MHz) d 26.3 (PCy3), 27.5 (d, JCP = 10.9 Hz, PCy3), 30.3 (d,
JCP = 4.7 Hz, PCy3), 32.0 (d, 1JCP = 14.8 Hz, PCy3), 114.7 [mpCH-
(5)], 133.9 [mpCH-(3)], 134.5 [mpCH-(4)], 145.6 [mpCH-(6)], 178.2
To a methanol (10 mL) solution of CuCl (39.5 mg, 3.99 ¥ 10-4 mol)
and PCy3 (112 mg, 3.99 ¥ 10-4) was added K[Tmp] (152 mg, 3.99 ¥
10-4 mol). The solution turned yellow and was stirred for 2 h during
which time a yellow/orange precipitate formed. This was filtered
and the solid washed with methanol (1 ¥ 5 mL), hexane (2 ¥ 5 mL)
and dried under vacuum to give 4 as a dark yellow solid. Yield =
87%, 238 mg. IR (cm-1, powder film) 1611 s, 1524 s; in DCM (cm-1)
1615 s, 1534 s. B–H not observed in either solution or solid spectra.
1H NMR (CDCl3, 300 MHz) d 1.19–1.87 [33H, m, P(C6H11)3],
6.64 [3H, td, J = 8.5 Hz, 4JHH = 1.5 Hz, mpCH-(5)], 7.13 [3H, d,
3JHH = 6.5 Hz, mpCH-(6)], 7.21 [3H, ddd, 3JHH = 8.5 and 7.0 Hz,
4JHH = 1.5 Hz, mpCH-(4)], 7.73 [3H, d, 3JHH = 8.5 Hz, mpCH-(3)].
(C S). 11B (CDCl3, 96.4 MHz) d -0.7 (s, br, h.h.w. = 248 Hz).
=
1
31P{ H} (CDCl3, 122 MHz) d 19.0 (s, br, h.h.w = 67 Hz). MS (ESI),
m/z = 583.22 ([M + Li]+) 100%, 599.20 ([M + Na]+) 10%. Anal.
[Found (calc.)] for C28H43N2BCuPS2.0.4MeOH: C 57.53 (57.82),
H 7.43 (7.62), N 4.98 (4.76).
Crystallography†
The data for 1 and 5 were collected on a Bruker Kappa Apex
II CCD detector diffractometer with a fine-focus sealed tube Mo
Ka radiation source and a Cryostream Oxford Cryosystems low
temperature device, operating in w scanning mode with y and
w scans to fill the Ewald sphere. The program used for control
and integration were APEX II, SAINT v. 7.34A and XPREP
v2005/4.25 The crystal was mounted on a glass fibre with silicon
grease from paraffin oil.
All solutions and refinements were performed using the Bruker
SHELTXTL software and all software packages within.26 All
non-hydrogen atoms were refined using anisotropic thermal
parameters, and hydrogen atoms, with the exception of H(100)
and H(101), in 5 (which were refined using isotropic thermal
parameters), were added using a riding model.
11
1
1H{ B} (CDCl3, 300 MHz) d 5.86 (1 H, s br, BH). 13C{ H} NMR
(CDCl3, 101 MHz) d 26.3 (PCy3), 27.5 (d, JCP = 10.7 Hz, PCy3),
1
30.3 (d, JCP = 3.8 Hz, PCy3), 31.9 (d, JCP = 13.1 Hz, PCy3),
114.4 [mpCH-(5)] 134.1 [mpCH-(4)], 135.7 [mpCH-(3)], 142.0 [mpCH-
(6)], 181.0 (C=S). 11B{ H} NMR (CDCl3, 96.4 MHz) d -0.50
1
(h.h.w. = 331 Hz). 31P{ H} NMR d 17.4 (s, br, h.h.w. = 40 Hz).
1
MS (ESI), m/z = 684.2 ([M - H]+) 50%. Anal. [Found (calc.)]
for C33H46N3BCuPS3.0.2MeOH: C 57.30 (57.57), H 6.66 (6.81), N
6.03 (6.07).
Cu(Bmp)(PPh3) (5)
To a methanol (10 mL) solution of CuCl (49 mg, 4.92 ¥ 10-4 mol)
and PPh3 (258 mg, 4.92 ¥ 10-4 mol) was added Na[Bmp] (126 mg,
4.92 ¥ 10-4 mol). The solution turned yellow with a precipitate
forming, this was stirred for 2 h. This was filtered and the solid
washed with methanol (1 ¥ 5 mL), diethyl ether (2 ¥ 5 mL) and
dried under vacuum to give 5 as a yellow solid. Yield = 228 mg,
83%. Crystals suitable for X-ray diffraction were grown from a
tetrahydrofuran solution layered with hexane. IR (cm-1, powder
film), 2425 w (B–H), 1609 s, 1538 s; in DCM (cm-1) 2417 w (B–H),
1610 s, 1538 s. 1H NMR (CDCl3, 300 MHz) d 6.75 (2H, m, mpCH),
7.28–7.44 [17H, m, P(C6H5)3 + mpCH], 7.74 (2H, m, mpCH), 8.01
The data collection parameters and refinement information are
presented in Table 3. Anisotropic parameters, bond distances and
(torsion) angles for 1 and 5 are available from the cif files in the
ESI.†
Acknowledgements
The authors would like to thank the Royal Society (G. R. O.),
Leverhulme Trust (G. D.) and EPSRC (A. H.) for funding.
References
11
(2H, m, mpCH). 1H{ B} (CDCl3, 300 MHz) d 4.12 (2H, s br, BH2).
1 (a) S. Trofimenko, Scorpionates: The Coordination of Poly(pyrazolyl)-
borate Ligands, Imperial College Press, London, 1999; (b) S.
Trofimenko, Chem. Rev., 1993, 93, 943; (c) S. Trofimenko, Polyhedron,
1
13C{ H} (CDCl3, 126 MHz) d 115.4 (s br, mpCH), 128.6 [d, JC–P
=
8.3 Hz, P(C6H5)3], 129.8 [s, P(C6H5)3], 132.7 (s br, mpCH), 133.9
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 6120–6126 | 6125
©

View Online
2004, 23, 197; (d) C. Pettinari, Scorpionates II: Chelating Borate
Ligands, Imperial College Press, London, 2008.
1984, 37, 2391; (d) V. Martinez-Merino and M. J. Gil, J. Chem. Soc.,
Perkin Trans. 2, 1999, 33.
19 A similar structure has been reported for K[Tm]: L. F. Soares, R. M.
Silva, A. C. Doriguetto, J. Ellena, Y. P. Mascarenhas and E. E.
Castellano, J. Braz. Chem. Soc., 2004, 15, 695.
2 H. Vahrenkamp, Acc. Chem. Res., 1999, 32, 589.
3 C. Slugovc, I. Padilla-Martınez, S. Sirol and E. Carmona, Coord. Chem.
Rev., 2001, 213, 129.
4 C. Slugovc, R. Schmid and K. Kirchner, Coord. Chem. Rev., 1999,
185–186, 109.
5 (a) J. M. Smith, Comments Inorg. Chem., 2008, 29, 189; (b) M. D. Spicer
and J. Reglinski, Eur. J. Chem., 2009, 1553.
6 H. V. R. Dias and T. K. H. H. Goh, Polyhedron, 2004, 23, 273.
7 M. Garner, J. Reglinski, I. Cassidy, M. D. Spicer and A. R. Kennedy,
Chem. Commun., 1996, 1975.
8 A. F. Hill, G. R. Owen, A. J. P. White and D. J. Williams, Angew. Chem.,
Int. Ed., 1999, 38, 2759.
9 (a) I. Kuzu, I. Krummenacher, F. Armbruster and F. Breher, Dalton
Trans., 2008, 5836; (b) F.-G. Fontaine, J. Boudreau and M.-H. Thibault,
Eur. J. Inorg. Chem., 2008, 35, 5439; (c) H. Braunschweig, C. Kollann
and D. Rais, Angew. Chem., Int. Ed., 2006, 45, 5254.
10 (a) C. Kimblin, T. Hascall and G. Parkin, Inorg. Chem., 1997, 36, 5680;
(b) H. M. Alvarez, T. B. Tran, M. A. Richter, D. M. Alyounes and D.
Rabinovich, Inorg. Chem., 2003, 42, 2149; (c) M. R. St, J. Foreman, A. F.
Hill, N. Tshabang, A. J. P. White and D. J. Williams, Organometallics,
2003, 22, 5593.
20 (a) Copper complexes involving Tp: S. Kealey, N. J. Long, P. W.
Miller, A. J. P. White and A. D. Gee, Dalton Trans., 2008, 2677;
(b) G. G. Lobbia, C. Pettinari, C. Santini, M. Colapietro and P. Cecchi,
Polyhedron, 1997, 16, 207; (c) H. V. R. Dias, S. A. Richey, H. V. K.
Diyabalange and J. Thankamani, J. Organomet. Chem., 2005, 690, 1913;
(d) N. Kitajima, T. Koda, S. Hashimoto, T. Kitagawa and Y. Morooka,
J. Am. Chem. Soc., 1991, 113, 5664; (e) G. G. Lobbia, J. V. Hanna, M.
Pellei, C. Pettinari, C. Santini, B. W. Skelton and A. H. White, Dalton
Trans., 2004, 951; (f) M. Pellei, G. G. Lobbia, C. Santini, R. Spagna, M.
Camalli, D. Fedeli and G. Falcioni, Dalton Trans., 2004, 2822; (g) M.
Pellei, C. Pettinari, C. Santini, B. W. Skelton, N. Somers and A. H.
White, J. Chem. Soc., Dalton Trans., 2000, 3416; (h) R. R. Conry, G.
Ji and A. A. Tipton, Inorg. Chem., 1999, 38, 906; (i) H. V. R. Dias, W.
Jin, H.-J. Kim and H.-L. Lu, Inorg. Chem., 1996, 35, 2317; (j) G. G.
Lobbia, C. Pettinari, F. Marchetti, B. Bovio and P. Cecchi, Polyhedron,
1996, 15, 881.
21 (a) Copper complexes involving Tm: D. V. Patel, D. J. Mihalcik, K. A.
Kreisel, G. P. A. Yap, L. N. Zakharov, W. S. Kassel, A. L. Rheingold
and D. Rabinovich, Dalton Trans., 2005, 2410; (b) C. A. Dodds, M.
Garner, J. Reglinski and M. D. Spicer, Inorg. Chem., 2006, 45, 2733;
(c) M. Careri, L. Elviri, M. Lanfranchi, L. Marchio`, C. Mora and
M. A. Pellinghelli, Inorg. Chem., 2003, 42, 2109; (d) G. G. Lobbia, C.
Pettinari, C. Santini, N. Somers, B. W. Skelton and A. H. White, Inorg.
Chim. Acta, 2001, 319, 15.
11 (a) For example: V. K. Landry, D. Buccella, K. Pang and G. Parkin,
Dalton Trans., 2007, 866; (b) J. Wagler and A. F. Hill, Organometallics,
2008, 27, 2350.
12 (a) For example: C. Kimblin, B. M. Bridgewater, D. G. Churchill and
G. Parkin, Chem. Commun., 1999, 2301; (b) J. L. White, J. M. Tanski
and D. Rabinovich, J. Chem. Soc., Dalton Trans., 2002, 2987; (c) P. J.
Bailey, M. Lanfranchi, L. Marchi and S. Parsons, Inorg. Chem., 2001,
40, 5030; (d) J. F. Ojo, P. A. Slavin, J. Reglinski, M. Garner, M. D.
Spicer, A. R. Kennedy and S. J. Teat, Inorg. Chim. Acta, 2001, 313, 15;
(e) R. M. Silva, C. Gwengo, S. V. Lindeman, M. D. Smith and J. R.
Gardinier, Inorg. Chem., 2006, 45, 10998.
13 G. C. Rudolf, A. Hamilton, A. G. Orpen and G. R. Owen, Chem.
Commun., 2009, 553.
14 I. R. Crossley and A. F. Hill, Dalton Trans., 2008, 201.
15 N. Tsoureas, M. F. Haddow, A. Hamilton and G. R. Owen, Chem.
Commun., 2009, 2538.
22 (a) Cambridge Structural Database, March 2009. Out of 136 struc-
turally characterised examples there are four exceptions where one of
˚
the B–N bond distances is greater than 1.583 A and two which are
˚
greater than 1.592 A. The indicated examples however appear to be
well outside the typical range found in all of the other complexes. See
ref. 10b and: R. Garcia, A. Domingos, A. Paulo, I. Santos and R.
Alberta, Inorg. Chem., 2002, 41, 2422; (b) B. L. Tran and C. J. Carrano,
Inorg. Chem., 2007, 46, 5429; (c) A. Schneider and H. Vahrenkamp,
Z. Anorg. Allg. Chem., 2004, 630, 1059; (d) M. M. Ibrahim, Inorg.
Chim. Acta, 2006, 359, 4235.
16 N. Tsoureas, G. R. Owen, A. Hamilton and A. G. Orpen, Dalton Trans.,
2008, 6039.
17 (a) M. J. Nowak, L. Lapinski, H. Rostkowska, A. Les and L.
Adamowicz, J. Phys. Chem., 1990, 94, 7406; (b) D. Moran, K.
Sukcharoenphon, R. Puchta, H. F. Schaefer III, P. v. R. Schleyer and
C. D. Hoff, J. Org. Chem., 2002, 67, 9061.
18 (a) I. W. J. Still, N. Plavac, D. M. McKinnon and M. S. Chauhan,
Can. J. Chem., 1976, 54, 280; (b) L. Steaniak, Org. Magn. Reson., 1979,
12, 379; (c) G. B. Barlin, D. J. Brown and M. D. Fenn, Aust. J. Chem.,
23 (a) M. R. Churchill, B. G. DeBoer, F. J. Rotella, O. M. Abu Salah and
M. I. Bruce, Inorg. Chem., 1975, 14, 2051; (b) K. Fujisawa, T. Ono, Y.
Ishikawa, N. Amir, Y. Miyashita, K. Okamoto and N. Lehnert, Inorg.
Chem., 2006, 45, 1698; (c) E. T. Papish, T. M. Donahue, K. R. Wells
and G. P. A. Yap, Dalton Trans., 2008, 2923.
24 H. V. R. Dias and C. J. Lovely, Chem. Rev., 2008, 108, 3223.
25 Bruker-AXS, 2007; Bruker-AXS, 2005.
26 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008,
64, 112.
6126 | Dalton Trans., 2009, 6120–6126
This journal is
The Royal Society of Chemistry 2009
©