Di-tert-butyl thiopyridazine boratrane complexes of Co, Ni and Cu

Article abstract of DOI:10.1016/j.poly.2016.10.021

The thiopyridazine based scorpionate ligand sodium tris(3,5-di-tert-butyl-6-thioxopyridazin-1(6H)-yl)hydroborate (NaTn^tBu,tBu) with two tert-butyl substituents in ortho- and para-position of the thio group was synthesized and fully characterized. Corresponding metallaboratrane complexes [M{B(Pn^tBu,tBu)₃}Cl] (M = Co, Ni, Cu) as well as [M{B(Pn^Me,tBu)₃}Cl] (M = Co, Ni) were prepared in good yields. All complexes were characterized by spectroscopic means as well as by single crystal X-ray diffraction studies exhibiting short metal boron bonds (between 2.0186(17) ? and 2.069(3) ?) compared to previously reported boratranes. The two tert-butyl groups attached to the heterocycle significantly increases the solubility of NaTn^tBu,tBuand the derived metal complexes in apolar solvents compared to the system bearing the smaller substituents. The higher steric demand of the tert-butyl versus methyl group enhances the distortion from trigonal bipyramidal towards square pyramidal which effects the electronic situation within the complexes evidenced by the elongated metal chlorine bond trans to boron.

Full text of DOI:10.1016/j.poly.2016.10.021

Accepted Manuscript
Di-tert-butyl thiopyridazine boratrane complexes of Co, Ni and Cu
Stefan Holler, Michael Tüchler, Anna M. Knaus, Ferdinand Belaj, Nadia C.
Mösch-Zanetti
PII:
S0277-5387(16)30518-6
DOI:
http://dx.doi.org/10.1016/j.poly.2016.10.021
POLY 12274
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
6 July 2016
12 October 2016
14 October 2016
Please cite this article as: S. Holler, M. Tüchler, A.M. Knaus, F. Belaj, N.C. Mösch-Zanetti, Di-tert-butyl
thiopyridazine boratrane complexes of Co, Ni and Cu, Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.
2
016.10.021
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Di-tert-butyl thiopyridazine boratrane complexes of Co, Ni and Cu.
a
Stefan Holler, Michael Tüchler, Anna M. Knaus, Ferdinand Belaj, Nadia C. Mösch-Zanetti
a
a
a
*a
a
Institute of Chemistry, University of Graz, Schubertstrasse 1, 8010 Graz, Austria
*
Corresponding author. Tel.: +43 (0)316 380 - 5286; fax: +43 (0)316 380 - 9835;
E-mail address: nadia.moesch@uni-graz.at
1

Abstract
The thiopyridazine based scorpionate ligand sodium tris(3,5-di-tert-butyl-6-thioxopyridazin-
tBu,tBu
1
(6H)-yl)hydroborate (NaTn
) with two tert-butyl substituents in ortho- and para-position of
the thio group was synthesized and fully characterized. Corresponding metallaboratrane
tBu,tBu
Me,tBu
complexes [M{B(Pn
)
3
}Cl] (M = Co, Ni, Cu) as well as [M{B(Pn
3
) }Cl] (M = Co, Ni)
were prepared in good yields. All complexes were characterized by spectroscopic means as well
as by single crystal X-ray diffraction studies exhibiting short metal boron bonds (between
2
.0186(17) Å and 2.069(3) Å) compared to previously reported boratranes. The two tert-butyl
tBu,tBu
groups attached to the heterocycle significantly increases the solubility of NaTn
and the
derived metal complexes in apolar solvents compared to the system bearing the smaller
substituents. The higher steric demand of the tert-butyl group vs. methyl enhances the distortion
from trigonal bipyramidal towards square pyramidal which effects the electronic situation within
the complexes evidenced by the elongated metal chlorine bond trans to boron.
Keywords: Thiopyridazine, boratrane, cobalt, nickel, copper.
2

1
. Introduction
Ligands featuring Lewis basic as well as Lewis acidic moieties (ambiphilic ligands) have
1
received considerable attention in coordination chemistry in recent years. Due to their
simultaneous electron donating and electron withdrawing properties they can form interesting
new complexes. In 1999 Hill and coworkers introduced a new ambiphilic ligand class which
2
creates cage-like complexes called boratranes exhibiting a direct metal-boron σ bond. Beside
3
their Lewis acidic boron moiety the ligands exhibit three donor sites, which allow fine tuning of
their electronic as well as steric influence on the metal. Since the discovery of boratranes several
different systems regarding donor atoms (N, P and S) and backbones (5 and 6 membered carbo-
4
–11
and heterocycles) were developed
and used in catalytic applications as well as stoichiometric
reactions. For example, first row transition metal triphosphine-borane complexes were found to
1
2–17
be capable of fixation of dinitrogen and conversion to ammonia.
Also B-M bond cleavage
reactions, redox reactions and substitution reactions at the metal center have been described in
18–22
literature.
Among the different boratrane systems triphosphine-borane and tris(methimazolyl)borate
complexes were investigated most intensively. This is due to easy substitution chemistry within
2
3
the ligand systems allowing fine-tuning of electronic and steric properties. In other boratranes,
substitution chemistry at the ligand is limited hampering their use in coordination chemistry.
In 2011 our group developed the thiopyridazine (Pn) based borate ligand Na[HB(Pn)
which shows high selectivity for the formation of boratranes of the type [M{B(Pn)
3
] (NaTn)
3
}X] with
9
,24
cobalt, nickel and copper.
In contrast, the mixed borate ligand with methimazole and
2
5,26
thiopyridazine heterocycles does not form boratrane complexes.
3

Me,tBu
Recently, we reported the methyl substituted variant of the Tn ligand (KTn
) which showed
tBu 22
improved solubility in a limited number of organic solvents compared to NaTn . However, in
solvents such as tetrahydrofuran or toluene, majorly used in coordination chemistry, the solubility
was still found unsatisfactory for subsequent reactivity. Thus, there is a need for pyridazine
molecules with larger substituents which increase both the solubility as well as the steric demand,
both beneficial for the development of novel coordination chemistry of these unusual ligands.
tBu,tBu
Here, we present the synthesis of a new thiopyridazine based borate ligand (NaTn
)
substituted by two tert-butyl groups in 4- and 6-position (ortho and para to sulfur) of the
heterocycle. Its reactivity towards cobalt, nickel and copper halogenides was explored where we
found exclusive formation of boratrane complexes. For comparative reasons, related cobalt and
Me,tBu 22
nickel boratrane complexes were also prepared with the previously reported KTn
.
2
. Results and discussion
2
.1 Synthesis and characterization of the ligand
tBu,tBu
The ligand sodium tris(3,5-di-tert-butyl-6-thioxopyridazin-1(6H)-yl)hydroborate (NaTn
was prepared via a 5-step synthetic sequence in approx. 54 % overall yield as shown in Scheme
. Addition of tBuMgCl to commercially available diethyl oxalate at -78°C led selectively to the
)
1
2
7
tert-butyl α-oxo ester. Lithium enolate mediated crossed aldol reaction of pinacolone and the α-
oxo ester at -78°C occurred smoothly forming the α-hydroxy-γ-keto ester with two tert-butyl
substituents. After cyclization with hydrazine and subsequent water elimination, the desired
substituted pyridazine was obtained in a one pot procedure. Notably, the last two mentioned steps
occurred with high selectivity, thus the crude material could be used without further purification.
4

Oxygen sulphur exchange was achieved via reaction with Lawesson’s reagent to obtain the
tBu,tBu
desired 4,6-di-tert-butylpyridazine-3(2H)-thione (HPn
) in a multiple gram scale. In analogy
tBu
Me,tBu 9,22
to KTn and KTn
hydroborate ligand NaTn
KBH instead of NaBH
,
reaction with NaBH
4
in toluene at 111°C yields the sodium salt of the
tBu,tBu
. Attempts to synthesize the potassium salt of the ligand using
4
4
led to unsatisfactory conversion of the thiopyridazine.
tBu
As previously observed for NaTn , the di-tert-butyl substituted ligand shows analogous photo-
2
8
tBu,tBu
reactivity. Thus, a DMSO-d
6
solution of NaTn
was exposed to day-light for one day and a
1
tBu,tBu
H NMR spectrum was recorded which revealed complete depletion of NaTn
and the
tBu,tBu
tBu,tBu
formation of HPn
together with the reduced heterocycle HPnH
2
which is hydrogenated
tBu,tBu
in C4 and C5 position. However, NaTn
can be stored under exclusion of day-light and
moisture as a solid as well as in solution without any sign of decomposition. Simple precautions
wrapping all glassware with aluminum foil) ensure clean reactivity and were applied for further
reactions.
(
5

tBu,tBu
Scheme 1. Preparation of NaTn
9
: a) (i) tBuMgCl, THF, tol, -78°C (ii) HCl, -78°C to rt,
Cl, -78°C to rt, 94
O, ethylene glycole, 110°C, 3 d 73 %; d) Lawesson’s reagent, xyl, 139°C, 18 h, 98
], tol, 111°C, 4 d, 84 % (approx. 83 % purity).
6 %; b) (i) LDA, THF, -78 °C, pinacolone; 45 min (ii) L2, - 78 °C (iii) NH
4
%
; c) N
2
H
4
·H
2
%
; e) Na[BH
4
The material obtained after the reaction with NaBH contained next to the product significant
4
tBu,tBu
1
13
tBu,tBu
tBu,tBu
amounts of HPn
as evidenced by H and C NMR spectroscopy (NaTn
/HPn
=
1
8
6/14). A new broad signal in the H NMR spectrum at 6.36 ppm for the B-H atom corroborates
-1
the formation of the ligand. The characteristic IR absorption for the B-H stretch at 2419 cm in
the IR spectrum also indicates the formation of the product salt.
Various methods including sublimation, flash column chromatography and recrystallization did
not allow purification. Also the attempt using excess borohydride did not lead to pure ligand.
Hence, the yellow powder obtained after the reaction and removal of the solvent was used as
tBu,tBu
such, with residual HPn
and possible boron species not detected by NMR spectroscopy
2
9
remaining in the material. However, these impurities could be removed in the subsequent
complex syntheses as described below.
6

As desired the introduction of the second tert-butyl group significantly increased its solubility
tBu
Me,tBu
compared to KTn and KTn
. Whereas the latter were only soluble in polar organic solvents
tBu,tBu
such as acetone, methanol and methylene chloride, NaTn
is additionally soluble in
9
,22
tBu,tBu
hydrocarbons like benzene or pentane, and thus to similar solubility properties to HTn
.
2
.2 Synthesis of the complexes
tBu,tBu
Me,tBu 22
Both ligands, NaTn
and previously described KTn
, were reacted with metal(II)-halide
precursors of cobalt, nickel and copper in CH
2
Cl
2
. We found excess of metal precursor to lead to
tBu,tBu
higher yields. Possibly this ensured full conversion and consumed residual HPn
forming
unknown species which were removed by the workup procedure. In analogy to previously
Me,tBu
22
tBu,tBu
reported [Cu{B(Pn
)
3
}Cl] (3b) the desired boratrane complexes [M{B(Pn
3
) }Cl]
Me,tBu
(
M = Co (1a), Ni (2a), Cu (3a)) and [M{B(Pn
3
) }Cl] (M = Co (1b), Ni (2b)) could be
isolated in good yields as shown in Scheme 2.
The metal center is thereby formally reduced by one electron presumably under oxidation of the
hydride at boron to molecular hydrogen, indicated by the observed gas evolution. In contrast to
the ligand precursor, the reduced M(I) complexes were found to be photo-stable. Hence, work-up
was performed without additional precautions and under ambient atmosphere. After filtration of
unreacted metal chloride and the formed sodium chloride the crude complexes were purified via
recrystallization or flash column chromatography using silica gel and an ethyl acetate/
cyclohexane mixture, depending on the stability of the complex.
While the Ni and Cu complexes are stable enough to store them for indefinite time in solution
and to purify them on silica gel, the electron deficient Co complexes show decomposition to yet
7

unidentified products after prolonged storage in solution. Therefore, we were not able to purify
tBu,tBu
[
Co{B(Pn
3
) }Cl] without decomposition via silica gel chromatography and recrystallized it
instead. Nevertheless complexes with all three metals are stable enough to oxygen and moisture
to handle at ambient atmosphere indicating a strong M-B bond.
Scheme 2. Synthesis of metallaboratranes 1a, 2a, 3a, 1b and 2b.
Me,tBu
22
The solubility of the new complexes together with [Cu{B(Pn
) }Cl] (3b) in various
3
solvents was investigated. Thus, 1 mL of the respective solvent was added to approx. 5 mg of
each compound and the mixtures were placed into an ultrasonic bath for 2 min. All compounds
were classified according to three solubility criteria: (a) completely dissolved (++), (b) colored
solution but remaining insoluble precipitate (+), and (c) completely insoluble (-). These data are
tBu,tBu
summarized in Table 1. Pn
based boratrane complexes show increased solubility in
chlorinated solvents as well as in THF. In more polar solvents like ethanol and acetonitrile cobalt
complexes 1a and 1b seem to be better soluble than their nickel and copper counterparts, whereas
3
a is totally insoluble in these solvents. Unfortunately, introduction of the second tert-butyl
substituent did not lead to solubility in non-polar solvents like toluene or pentane. Nevertheless
the observed solubility in THF enhances the applicability of Pn based boratrane complexes in
coordination chemistry.
Table 1. Solubilities of complexes 1-3 in selected solvents.
1
a
2a
+
3a
-
1b
++
2b
+
3b
+
EtOH
++
8

CH
CH
3
CN
Cl
++
++
++
+
-
-
+
-
+
++
+
-
-
-
+
+
+
-
-
-
-
2
2
++
++
+
-
-
++
++
+
-
-
+
+
-
-
-
CHCl
THF
Et
Toluene
3
2
O
5
mg in 1 mL solvent: ++ completely dissolved, + suspension with colored solution, – totally insoluble.
2
2
.3 Characterization of the complexes
.3.1 NMR spectroscopy
1
13
The H and C NMR spectra of the copper compounds 3a and 3b show one set of sharp
resonances for the thiopyridazines, which are shifted compared to the respective Pn ligands.
Thus, the three heterocycles exhibit identical chemical environments pointing to symmetric
1
species in solution. Furthermore, the disappearance of the B-H resonances in the H NMR and IR
spectra indicate the successful formation of the desired boratrane complexes. NMR spectra of the
cobalt and nickel complexes 1a,b and 2a,b show broad resonances over a wide range of chemical
shifts consistent with the expected paramagnetism of these compounds. Integration of all signals
1
nicely fits to the expected proton count. Signals for H NMR shifts of complexes 1-3 are given in
Table 2.
1
Table 2. H NMR shifts in ppm of complexes 1-3 (1a-3a in CDCl
3
and 1b-3b in CD
2
Cl ).
2
3b22
1
a
2a
16.48
3a
7.25
1b
13.62
2b
15.45
Ar-H
14.40
7.29
9

tBu/Me
tBu
2.35
1.60
2.79
1.72
1.52
1.04
7.70
2.18
3.48
2.92
2.45
1.10
2
.3.2 Magnetic measurements
The number of unpaired electrons (u.e.) of the paramagnetic complexes 1a, 2a, 1b and 2b was
3
0
determined by the Evans method. The determined values (1a, 2.18 u.e.; 2a, 1.23 u.e.; 1b 1.98
u.e. and 2b, 1.12 u.e.) support the spin states for cobalt being S = 1 and for nickel S = ½
6
7
consistent with trigonal bipyramidal Co(III) d and Ni(III) d centers, respectively. Similarly,
Me,tBu
calculations of the recently reported copper complex [Cu{B(Pn
)
3
}Cl] (3b) provided evidence
8
10
22
for a Cu(III) d low spin center rather than a Cu(I) d configuration. The configuration is
attributed to the strong electron withdrawing power of the Z-type ligand and the resulting
distortion of the bonding σ orbital towards the boron atom. In analogy, the nickel compound with
7
one unpaired electron may be considered exhibiting a trigonal bipyramidal Ni(III) d low spin
9
center. However, a Ni(I) d center would also reveal one unpaired electron. The difficulty in
7
,31
assigning oxidation states in boratrane complexes was previously discussed.
2
.3.3 Molecular structures
10

Molecular views of all described complexes are shown in Figures 1-3, selected bond lengths and
angles are given in Table 3 and crystallographic data is provided in Table 4.
As common features, all here described boratrane complexes exhibit a distorted trigonal
bipyramidal environment with B-M-Cl angles of 176.56(8)° - 177.94(7)° and B-M-S angles of
7
9.54(8)° - 85.93(5)°. The metal boron distances of 2.0186(17) Å - 2.069(3) Å are short
indicating strong σ-bonding from the metal center to the Lewis acidic Z-type boron moiety. Due
to steric reasons, the thiopyridazine heterocycles are aligned around the metal center in a
paddlewheel like twisted fashion with S–M–B–N torsion angles between 20.49(10)° and
3
8.65(16)°. Detailed comparison of the structures is discussed below.
tBu,tBu
Me,tBu
Figure 1. Molecular view of [Co{B(Pn
)
3
}Cl] (1a, left) and [Co{B(Pn
3
) }Cl] (1b, right).
Hydrogen atoms and solvent molecules have been omitted for clarity.
11

tBu,tBu
Me,tBu
Figure 2. Molecular view of [Ni{B(Pn
)
3
}Cl] (2a, left) and [Ni{B(Pn
)
3
}Cl] (2b, right).
Hydrogen atoms and solvent molecules have been omitted for clarity.
tBu,tBu
Me,tBu
22
Figure 3. Molecular view of [Cu{B(Pn
)
3
}Cl] (3a) and [Cu{B(Pn
)
3
}Cl] (3b, right).
Hydrogen atoms and solvent molecules have been omitted for clarity.
12

Table 3. Selected bond lengths (Å) and angles (°) of complexes 1a, 2a, 3a, 1b, 2b and 3b.
3b 22
1
a
2a
3a
1b
2b
M-B
M-Cl
M-S
2.050(3)
2.2939(9)
2.2644(8)
2.0186(17) 2.069(3)
2.064(2)
2.2782(7)
2.2782(7)
2.2282(7)
2.2912(6)
1.546(3)
1.552(3)
1.553(3)
2.027(3)
2.3193(7)
2.2489(8)
2.2582(8)
2.2688(7)
1.542(4)
1.545(4)
1.550(3)
2.065(2)
2.2871(6)
2.2815(6)
2.3205(6)
2.3169(6)
1.531(3)
1.533(3)
1.542(3)
109.99(17)
111.20(17)
109.52(17)
2.3123(6)
2.2422(5)
2.2389(5)
2.2220(5)
1.555(2)
1.564(2)
1.563(2)
2.3055(8)
2.2888(8)
2.3253(8)
2.2804(8)
1.511(4)
1.531(4)
1.545(3)
2
2
.2568(8)
.2625(8)
B-N
1.554(4)
1
.566(4)
1
.562(4)
N-B-N
N-B-M
B-M-S
B-M-Cl
109.0(2)
110.47(12) 109.1(2)
108.76(12) 111.3(2)
107.90(12) 110.65(18) 107.94(18) 108.3(2)
108.42(19) 111.0(2)
109.26(19) 109.5(2)
1
1
09.2(2)
06.7(2)
111.63(19) 109.13(10) 108.20(14) 110.14(15) 109.39(17) 109.30(14)
1
09.99(18) 110.45(10) 108.51(18) 110.20(15) 109.97(17) 108.33(14)
1
10.22(15) 110.11(10) 109.05(18) 110.81(15) 108.69(18) 108.44(14)
81.10(9)
85.93(5)
82.87(5)
82.38(5)
177.21(5)
81.97(8)
79.54(8)
80.41(8)
178.39(8)
80.81(8)
81.46(8)
80.11(7)
176.56(8)
82.44(9)
84.80(9)
82.37(9)
177.07(9)
80.94(7)
80.32(7)
81.60(7)
177.94(7)
8
8
1.46(9)
0.87(9)
177.47(9)
Table 4. Crystallographic data and structure refinement.
1
a
2a
3a
CHCl
Triclinic
P -1
1b
2b
CHCl
Monoclinic
P 2 /c
Crystallized from
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
CH
Triclinic
P -1
2
Cl
2
/hept CHCl
3
/pent
Monoclinic
C 2/c
3
CH
Monoclinic
P 2 /c
2
Cl
2
/hept
3
1
1
14.068(3)
18.065(4)
22.249(5)
90.398(2)
103.968(2) 128.819(4)
110.204(3) 90
28.272(4)
18.391(3)
21.215(3)
90
17.242(4)
18.221(4)
18.555(4)
76.758(3)
76.100(3)
76.624(3)
9.7441(4)
20.8928(8)
18.4021(7)
90
99.5934(16)
90
9.7632(3)
23.0798(7)
18.2794(5)
90
98.0849(14)
90
Data/parameters
Final R1 [I>2σ(I)] 0.0517
18031 / 914 10362 / 472
21248 / 915 7227 / 405
7993 / 461
0.0386
0.0343
0.0513
0.0360
CCDC number
1
491096
1491097
1491098
1491099
1491100
Comparison of boron metal bond lengths in our complexes to those in metallaboratranes
described in literature reveals the thiopyridazine based systems exhibiting the shortest Z-type
tBu,tBu
Me,tBu
bonds. Thus, the Co-B distances in [Co{B(Pn
)
3
}Cl] (1a) and [Co{B(Pn
3
) }Cl] (1b) are
13

with 2.050(3) and 2.064(2) Å, respectively, similar to our previously reported boratrane
tBu
9
[
Co{B(Pn )
3
}Cl] (2.068(3) Å) but significantly shorter than in the rare other cobalt boratranes.
In the single example with the tris(methimazolyl)borane ligand the Co-B distances was reported
3
2
to be 2.131 Å and in the six examples with the triphosphine-borane ligand they are in the range
1
6,33
tBu,tBu
Me,tBu
of 2.256-2.463 Å.
Also in the [Ni{B(Pn
)
3
}Cl] (2a) and [Ni{B(Pn
3
) }Cl] (2b) with
bond lengths of 2.0186(17) and 2.027(3) Å, respectively, the Ni-B bond lengths are much shorter
1
9,34
than in methimazolyl based systems (2.08-2.11 Å)
and the only known triphosphine-borane
3
5
boratrane (2.168 Å). In copper chemistry no tris(methimazolyl)borate derived boratrane
complex is known so far and triphosphine-borane boratranes have again significantly longer
3
5,36
tBu,tBu
metal-boron distances (2.198-2.495 Å)
than in complexes [Cu{B(Pn
3
) }Cl] (3a) and
Me,tBu
22
[
Cu{B(Pn
3
) }Cl] (3b) (2.069(3) and 2.065(2) Å).
The M-B bond lengths within our series follow the order Cu > Co > Ni pointing to a strong Ni-B
bond. Consequently, the M-Cl bond is longer in the Ni compound than in the Co and Cu
analogues in accordance with a trans influence induced by the strong Ni-B interaction.
Furthermore, the geometry of the nickel compound is significantly more distorted from a trigonal
bipyramid towards a square pyramid (τ
5
= 0.71 2a, Table 5) compared to the Co and Cu complex
(
τ
5
= 0.95 1a and 0.88 3a), which was previously reasoned to enhance labilization of the bond
37
tBu,tBu
Me,tBu
trans to boron. Generally, comparison of the bond lengths in the Pn
vs. the Pn
system
reveals little differences pointing to a small electronic influence. In contrast, the steric influence
of the tert-butyl group is significant in the nickel and copper complexes as evidenced by the τ
5
values (Table 5).
14

Table 5. τ values for complexes 1-3.
5
tBu,tBu
Me,tBu
B(Pn
)
3
B(Pn
)
3
Co, 1a
177.47
120.53
Ni, 2a
177.21
134.86
0.71
Cu, 3a
178.39
125.55
0.88
Co, 1b
176.56
119.52
0.95
Ni, 2b
177.07
129.48
0.79
Cu, 3b
177.94
119.79
0.97
α
β
0
.95
τ
5
3
8
τ
5
= (β – α) / 60° where β > α are the two largest valence angles of the coordination center.
3
. Conclusion
In the present work, the synthesis and characterization of a thiopyridazine based scorpionate
ligand featuring two tert-butyl substituents is reported. This substitution pattern leads to
significantly increased solubility in moderately polar and nonpolar organic solvents. This is
important because it will allow for more diverse future chemical applications of the ligand. The
tBu,tBu
corresponding cobalt, nickel and copper boratrane complexes [M{B(Pn
3
) }Cl] (M = Co 1a,
Me,tBu
Ni 2a, Cu 3a) and the Me, tert-butyl substituted complexes [M{B(Pn
)
3
}Cl] (M = Co 1b, Ni
2
2
2
b, Cu 3b ) were prepared in good yields. The unusual electronic situation created by the Z-type
ligand system is discussed in spectroscopic, magnetic and structural terms. Single crystal X-ray
diffraction analysis revealed short metal boron distances (between 2.0186(17) Å and 2.069(3) Å)
in all presented complexes indicating strong bonding interactions. Furthermore, we could
demonstrate that substitution in the pyridazine backbone does not only influence the steric
properties of the complexes, but the induced change in geometry also leads to different metal
boron and metal chloride bond lengths.
15

4
. Material and methods
4
.1 General Information.
If not otherwise noted, reactions were carried out under N
technique and work-up was done under ambient atmosphere. Diisopropylamine was dried via
refluxing over CaH and distillation. Xylene was distilled and stored over 4 Å molecular sieves.
2
atmosphere, using standard Schlenk-
2
Tetrahydrofuran, methylenechloride and toluene were purified via a Pure-Solv MD-4-EN solvent
purification system from Innovative Technology, Inc. Ethylene glycol, hydrazine hydrate,
pinacolone, nBuLi (2.5M in hexanes), NaBH
CoCl
was prepared in THF from tBuCl with elemental magnesium. KTn
4
, anhydrous NiCl
2
, anhydrous CuCl
2
and anhydrous
2
were purchased from commercial sources and used without further purification. tBuMgCl
Me,tBu
, and Lawesson’s reagent
3
9,22
were prepared according to literature procedures.
Synthesis of complexes was done under
exclusion of light. Therefore glassware was wrapped into aluminum foil. NMR spectra were
measured on a Bruker Avance III 300 MHz spectrometer at 25 °C. Chemical shifts are given in
ppm and are referenced to residual protons in the solvent. GC-MS analyses were performed with
an Agilent 7890A GC system with an Agilent 19091J-433 column coupled to a 5975C inert XL
EI/CI mass selective detector (MSD). Helium was used as the mobile phase. Electrospray mass
spectra were recorded using a Thermo Scientific Q-Exactive mass spectrometer. Spectra were
obtained using flow injection of approximately 1 µM solutions of compounds in
acetonitrile/acetone mixtures. Both, positive and negative modes were employed. Infrared spectra
were recorded on a Bruker Alpha Platinum ATR spectrometer and only strong and medium bands
are listed. The number of unpaired electrons for paramagnetic complexes was determined via the
3
0
Evans method and is provided without solvent or diamagnetic correction. Therefore a solution
of tert-butanol in CD Cl was used as internal reference. Additional measurements of magnetic
susceptibilities (χ) were performed on a Johnson Matthey Magnetic Susceptibility Balance Auto
2
2
16

1
. The values χm for the solid samples were measured under ambient conditions and the number
4
0
of unpaired electrons calculated by the spin-only formula.
4
.2 X-ray Structure Determination.
X-ray data collection was performed with a Bruker AXS SMART APEX 2 CCD diffractometer
by using graphite-monochromated Mo-Kα radiation (0.71073 Å) from a Incoatec microfocus
41
sealed tube at 100(2) K. SHELXS-97 was used as the structure solution and structure
2
refinement program SHELXL-2014/6. Full-matrix least-squares cycles on F were employed as
the refinement method.
Further details on the solution of the structures can be found in the supporting information.
4
.3 Synthesis of ethyl 3,3-dimethyl-2-oxobutanoate (L1).
2
7
L1 was synthesized similar to a modified literature procedure. A solution of diethyl oxalate
(
(
81 mL, 599 mmol) in toluene (300 mL) was cooled to -78°C and freshly prepared tBuMgCl
500 mL, 1.32 mol/L in THF, 660 mmol) was added over a period of 2 h at -78°C. After 14 h,
2
H O (100 mL) and HCl (5 M, 100 mL) were added at -78°C and the reaction mixture was
allowed to warm to room temperature. Ethyl acetate (200 mL) was added, the layers were
separated and the aqueous layer was extracted with ethyl acetate (2 x 100 mL). The combined
organic layers were washed with brine (50 mL), dried over MgSO and concentrated in vacuo to
4
obtain 121.1 g of crude L1. The product was purified via vacuum distillation (35 mbar, 80°C) to
1
obtain pure L1 as a colorless liquid (90.7 g, 96 %). H NMR (300 MHz, CDCl
3
) δ 4.29 (q,
J = 7.1 Hz, 2H, ethyl-CH
2
), 1.33 (t, J = 7.1 Hz, 2H, ethyl-CH
3
), 1.23 (s, 9H, tBu);
-1
IR (ATR, cm ): 2974, 1736 (C=O), 1051, 728.
17

4
.4 Synthesis of ethyl-2-(tert-butyl)-2-hydroxy-5,5-dimethyl-4-oxohexanoate (L2).
To a stirred solution of diisopropylamine (53 mL, 378 mmol) in THF (500 mL) at -78°C n-BuLi
150 mL, 2.5 M in hexanes, 375 mmol) was added over a period of 1 h. The resulting colorless
solution was allowed to warm to -50°C and cooled again to -78°C before pinacolone (46 mL,
(
3
4
67 mmol) was added over a period of 10 min. The resulting suspension was stirred at -78°C for
5 min before ethyl 3,3-dimethyl-2-oxobutanoate (L1, 60 g, 378 mmoL) was added over a period
of 10 min. The reaction mixture was stored over the weekend at -78°C before it was quenched
with saturated NH Cl (80 mL) and allowed to reach room temperature. After the addition of H
100 mL) and Et O (100 mL) the layers were separated. The aqueous layer was extracted with
Et O (2 x 100 mL), dried over MgSO and concentrated to dryness to obtain L2 as a colorless
liquid (89.5 g, 94 %). H NMR (300 MHz, CDCl ) δ 4.22 (dq, J = 7.2 Hz, 2.1 Hz, 2H,
4
2
O
(
2
2
4
1
3
diastereotopic ethyl-methylene Hs), 3.74 (s, 1H, O-H), 3.14 (d, J = 17.3 Hz, 1H, diasterotopic
methylene C-H), 2.90 (d, J = 17.3 Hz, 1H, diasterotopic methylene C-H), 1.24 (t, J = 7.2 Hz, 3H,
1
3
ethyl-CH
ketone C=O), 175.0 (ester C=O), 79.3 (C-OH), 61.2 (ethyl-CH
tBu), 37.2 (α-CH ), 26.2 (tBu-CH ), 25.4 (tBu-CH ), 14.1 (ethyl-CH
OH), 2963, 2875, 1722 (C=O), 1466, 1264, 1190; EI-MS (70 eV) m/z (%): 202 (18) [MH -tBu],
3
group), 1.12 (s, 9H, tBu), 0.98 (s, 9H, tBu); C NMR (75 MHz, CDCl
3
) δ 215.4
(
2
), 44.3 (quart. tBu), 40.5 (quart.
-1
2
3
3
3
); IR (ATR, cm ): 3527
+
(
+
+
1
85 (25) [M -COOEt], 173 (14) [M -COtBu], 155 (17), 117 (35), 85 (41), [tBuCO], 57 (100)
+
[
tBu ].
18

4
.5 Synthesis of 4,6-di-tert-butylpyridazin-3(2H)-one (L3).
This reaction was performed under ambient atmosphere. To a stirred solution of ethyl 2-(tert-
butyl)-2-hydroxy-5,5-dimethyl-4-oxohexanoate (L2, 65.0 g, 252 mmol) in ethylene
glycol (195 mL) hydrazine hydrate (18.9 g, 64% in H O, 377 mmol) was added. The resulting
2
solution was heated to 110°C and the reaction progress was monitored via GC-MS analysis.
Additional hydrazine (18.9 g and 9.45g) was added twice after 23h and after four days. After
6
days and full conversion the reaction mixture was cooled to -25°C whereupon a white solid
precipitated. The product was filtered and washed with small amounts of cold ethylene glycol and
water. After drying in vacuo L3 was obtained as a white crystalline solid (38.3 g, 73 %) and used
1
for the next step without further purification. H NMR (300 MHz, CDCl
3
) δ 11.36 (bs, 1H, N-H),
) δ 161.0
C=O), 155.4 (arom. C-tBu), 150.3 (C=N), 125.1 (arom. C-H), 36.2 (quart. tBu), 35.4 (quart.
1
3
7
.21 (s, 1H, Ar-H), 1.38 (s, 9H, tBu), 1.27 (s, 9H, tBu) ppm; C NMR (75 MHz, CDCl
3
(
-1
tBu), 29.3 (tBu-CH
3
) 28.0 (tBu-CH ) ppm; IR (ATR, cm ): 2954, 2866, 1644 (C=O), 1586, 913,
3
+
+
+
6
66; EI-MS (70 eV) m/z (%): 208 (21) [M ], 193 (51) [M -Me], 166 (100), 151 (31) [M -tBu].
tBu,tBu
4
.6 Synthesis of 4,6-di-tert-butylpyridazine-3(2H)-thione (HPn
).
4
7
,6-di-tert-butylpyridazin-3(2H)-one (L3, 27.0 g, 129.6 mmol) and Lawessons’s reagent (31.5 g,
7.9 mmol) were suspended in 80 mL xylene and heated to reflux whereupon the solids got
dissolved. The reaction progress was monitored via GC-MS and TLC analysis. After 18 h and
full conversion, the reaction mixture was allowed to cool to room temperature and concentrated
in vacuo. The resulting orange solid was purified via flash column chromatography (silica gel,
tBu,tBu
1
cyclohexane/ethyl acetate) to obtain HPn
as a yellow solid (28.5 g, 98 %). H NMR (300
19

MHz, CDCl
3
) δ 12.67 (bs, 1H, N-H), 7.24 (s, 1H, Ar-H), 1.57 (s, 9H, tBu), 1.30 (s, 9H, tBu)
ppm; C NMR (75 MHz, CDCl ) δ 178.7 (C=S), 161.3 (C=N), 158.9 (arom. C-tBu), 122.2
arom. C-H), 37.4 (quart. tBu), 36.4 (quart. tBu), 29.2 (tBu-CH ) 27.9 (tBu-CH ) ppm; IR (ATR,
cm ): 3133, 3056, 2960, 1581, 1363, 1260, 1158 (C=S); Rf=0.51 (5:1 cyclohexane/ethyl
1
3
3
(
3
3
-1
+
+
+
acetate); EI-MS (70 eV) m/z (%): 224 (100) [M ], 209 (88) [M -Me], 192 (32%) [M -S], 182
+
+
(
60), 167 (59) [M -tBu], 140 (97), 57 (24) [tBu ].
4
.7 Synthesis of Sodium tris(3,5-di-tert-butyl-6-thioxopyridazin-1(6H)-yl)hydroborate
tBu,tBu
(
NaTn
).
tBu,tBu
In a Schlenk type flask, 4,6-di-tert-butylpyridazine-3(2H)-thione (HTn
6.36 mmol) and sodium borohydride (0.206 g, 5.44 mmol) were suspended in toluene (10 mL).
The reaction mixture was protected from day-light via covering the flask with aluminum foil and
heated to reflux where H evolution was observed. After 4 days the reaction was allowed to cool
to room temperature and all volatiles were removed in vacuo to obtain 3.89 g of a yellow solid
, 3.67 g,
1
2
tBu,tBu
tBu,tBu
1
containing NaTn
, HPn
and toluene in the ratio 83/14/3 (according to H NMR
spectroscopy). Possible boron contaminants due to unreacted NaBH
4
were not observed. This
tBu,tBu
1
corresponds to approx. 3.23 g, (4.58 mmol) of NaTn
(84%). H NMR (300 MHz, DMSO-
1
d
6
) δ 6.96 (s, 3H, Ar-H), 5.99 (bs, 1H, BH), 1.54 (s, 9H, tBu), 0.90 (s, 27H, tBu) ppm; H NMR
(
300 MHz, CDCl
3
) δ 7.16 (s, 3H, Ar-H), 6.36 (br s, 1H, BH), 1.56 (s, 9H, tBu), 0.96 (s, 27H, tBu)
ppm; C NMR (75 MHz, CDCl ) δ 179.2 (C=S), 158.2 (C=N), 157.4 (arom. C-tBu), 119.4
arom. C-H), 37.6 (t quart. tBu), 36.0 (quart. tBu), 29.3 (tBu-CH ), 28.9 (tBu-CH ).; IR (ATR,
1
3
3
(
3
3
-1
cm ): 2957, 2419 (B-H), 1477, 1395, 1170 (C=S), 1021, 916, 812, 727, 627, 541; HRMS-
tBu,tBu -
ESI (m/z): [Tn
] calcd for C36
H58BN
6
S : 681.3979, found: 681.3969.
3
20

tBu,tBu
4
.8 Synthesis of [Co{B(Pn
3
) }Cl] (1a).
tBu,tBu
A Schlenk type flask was charged with CoCl
2
(10 mg, 0.08 mmol) and Na[HB(Pn
3
) ]
tBu,tBu
(
80 mg, approx. 83% NaTn
, 0.09 mmol). CH Cl (6 mL) was added to the reactants
2
2
whereupon a color change to dark green occurred. After 15 min the reaction mixture was filtered
and the solvent was removed in vacuo. The obtained green powder was purified via
1
recrystallization from chloroform /cyclohexane to obtain green crystals of 1a (32 mg, 54 %). H
NMR (300 MHz, CDCl
3
): 14.40 (bs, 3H, Ar-H), 2.35 (bs, 27H, tBu), 1.60 (bs, 27H, tBu); IR
-1
(
ATR, cm ): 2964, 1728, 1596, 1575, 1397, 1379, 1169 (C=S), 1046, 905, 818, 731, 680, 627,
-1
-1
5
39; UV-vis (CH
2
Cl , nm{M cm }): 668{250}, 727{160}; unpaired e¯ (Evans method): 2.18;
2
tBu,tBu
+
HRMS-ESI (m/z): [Co{B(Pn
)
3
}] calcd for C36
H
57BCoN
6
S
3
: 739.3229, found: 739.3223.
tBu,tBu
4
.9 Synthesis of [Ni{B(Pn
3
) }Cl] (2a).
tBu,tBu
A Schlenk type flask was charged with NiCl
2
(368 mg, 2.84 mmol) and NaTn
(1.00 g,
tBu,tBu
approx. 83% NaTn
, 1.18 mmol). CH
2
Cl (20 mL) was added to the reactants whereupon a
2
color change to dark brown occurred. After 2 h the reaction mixture was filtered and all volatiles
were removed in vacuo. The obtained brown powder was purified via flash column
chromatography (silica gel, cyclohexane/ethyl acetate) to obtain 2a as an air and moisture stable
brown solid (850 mg, 93 %). Single crystals suitable for X-ray diffraction analysis were obtained
1
by slow evaporation of a CHCl
3
/pentane solution. H NMR (300 MHz, CDCl
3
) δ 16.48 (s, 3H,
-1
Ar-H), 2.79 (s, 27H, tBu), 1.72 (s, 27H, tBu) ppm; IR (ATR, cm ): 2963, 1732, 1576, 1476,
1
398, 1380, 1290, 1239, 1202, 1171 (C=S), 1045, 910, 818, 670, 609, 553; UV-vis (CH Cl
2
2
,
21

-1
-1
nm{M cm }): 476{4240}, 405{11000}; unpaired e¯ (Evans method): 1.23; HRMS-ESI (m/z):
tBu,tBu
+
[
Ni{B(Pn
)
3
}] calcd for C36
H
57BNiN
6
3
S : 738.3250, found: 738.3242.
tBu,tBu
4
.10 Synthesis of [Cu{B(Pn
3
) }Cl] (3a).
tBu,tBu
A Schlenk type flask was charged with CuCl
2
(229 mg, 1.70 mmol) and NaTn
(1.00 g,
tBu,tBu
approx. 83% NaTn
, 1.18 mmol). CH
2
Cl
2
(20 mL) was added to the reactants whereupon a
color change to intense red occurred. After 2 h the reaction mixture was filtered using a filter-
cannula and all volatiles were removed in vacuo. The obtained orange powder (1.24 g) was
purified via flash column chromatography (silica gel, cyclohexane/ethyl acetate) to obtain 3a as
an air and moisture stable orange solid (910 mg, 99 %). Single crystals suitable for X-ray
1
diffraction analysis were obtained by slow evaporation of a CHCl
CDCl
CD Cl
CDCl ) δ 177.0 (C=S), 162.1 (C=N), 156.9 (arom. C-tBu), 122.2 (arom. C-H), 36.9 (quart. tBu),
3
solution. H NMR (300 MHz,
1
3
) δ 7.25 (s, 3H, Ar-H), 1.52 (s, 27H, tBu), 1.04 (s, 27H, tBu) ppm; H NMR (300 MHz,
1
3
2
2
) δ 7.33 (s, 3H, Ar-H), 1.54 (s, 27H, tBu), 1.04 (s, 27H, tBu) ppm; C NMR (75 MHz,
3
-
1
3
1
4
7
6.3 (quart. tBu), 29.2 (tBu-CH
3
) 28.4 (tBu-CH ) ppm; IR (ATR, cm ): 2964, 1732, 1577, 1476,
3
-1
-1
398, 1381, 1204, 1171 (C=S), 931, 819, 680, 633, 536; UV-vis (CH
2
Cl
2
, nm{M cm }):
tBu,tBu
+
48{1670}, 417{1920}; HRMS-ESI (m/z): [Cu{B(Pn
)
3
}] calcd for C36
H
57BCuN
6
3
S :
43.3194, found: 743.3188.
Me,tBu
4
.11 Synthesis of [Co{B(Pn
3
) }Cl] (1b)
Me,tBu
A Schlenk type flask was charged with CoCl
.504 mmol). CH Cl (10 mL) was added to the reactants whereupon a color change to dark green
occurred. After 48 h the reaction mixture was filtered, washed with CH Cl and the filtrate was
2
(65.5 mg, 0.504 mmol) and KTn
(300 mg,
0
2
2
2
2
22

concentrated in vacuo. The obtained green powder was purified via flash column chromatography
silica gel, CH Cl /MeOH) to obtain 1b as an air and moisture stable green solid (278 mg, 85 %).
(
2
2
Single crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a
1
CH
2
Cl
2
/heptane solution. H NMR (300 MHz, CD
2
Cl ) δ 13.62 (s, 3H, Ar-H), 7.70 (s, 9H, Me),
2
-
1
2
7
.18 (s, 27H, tBu) ppm; IR (ATR, cm ): 2963, 1594, 1524, 1478, 1378, 1199, 1168 (C=S), 926,
-
1
-1
32, 696, 629, 465; UV-vis (CH
2
Cl , nm{M cm }): 712{460}, 658{500}; unpaired e¯ (Gouy
2
Me,tBu
+
balance) : 1.93; unpaired e¯ (Evans method): 1.98; HRMS-ESI (m/z): [Co{B(Pn
) }] calcd
3
for C27
H
39BCoN
6
S
3
: 613.1819, found: 613.1815.
Me,tBu
4
.12 Synthesis of [Ni{B(Pn
)
3
}Cl] (2b).
Me,tBu
In a Schlenk type flask KTn
addition of NiCl
0 h, the reaction mixture was filtered using a filter-cannula and all volatiles were removed in
(200 mg, 0.336 mmol) was dissolved in CH
2
Cl
2
(20 mL). After
2
(65.4 mg, 0.504 mmol) the reaction mixture turned brown immediately. After
2
vacuo to obtain 2b as an air and moisture stable brown solid (180 mg, 83 %). Single crystals
1
suitable for X-ray diffraction analysis were obtained by slow evaporation of a CHCl
NMR (300 MHz, CD Cl
ATR, cm ): 2965, 1595, 1479, 1447, 1379, 1318, 1201, 1177 (C=S), 1012, 929, 814, 756, 695,
3
solution. H
2
2
) δ 15.45 (s, 3H, Ar-H), 3.48 (s, 9H, Me), 2.92 (s, 27H, tBu) ppm; IR
-1
(
-
1
-1
6
1
6
29, 465; UV-vis (CH
2
Cl , nm{M cm }): 488{1360}, 405{3870}; unpaired e¯ (Evans method):
2
Me,tBu
+
.12; HRMS-ESI (m/z): [Co{B(Pn
)
3
}] calcd for C27
H
39BNiN
6
3
S : 612.1844, found:
12.1839.
23

Appendix A. Supplementary data
CCDC reference numbers 1491096-1491101 contain the supplementary crystallographic data for
this
paper.
These
data
can
be
obtained
free
of
charge
via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgments
Support from NAWI Graz is gratefully acknowledged.
24

References
(
(
(
(
(
1) Bouhadir, G.; Bourissou, D. Chem. Soc. Rev. 2016, 45, 1065–1079.
2) Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J. Angew. Chem. Int. Ed. 1999, 38, 2759–2761.
3) Parkin, G. Organometallics 2006, 25, 4744–4747.
4) Pang, K.; Quan, S. M.; Parkin, G. Chem. Commun. 2006, 5015–5017.
5) Bontemps, S.; Gornitzka, H.; Bouhadir, G.; Miqueu, K.; Bourissou, D. Angew. Chem. Int. Ed. 2006, 45,
1
611–1614.
6) Blagg, R. J.; Charmant, J. P. H.; Connelly, N. G.; Haddow, M. F.; Orpen, A. G. Chem. Commun. 2006,
350–2352.
7) Landry, V. K.; Melnick, J. G.; Buccella, D.; Pang, K.; Ulichny, J. C.; Parkin, G. Inorg. Chem. 2006, 45,
588–2597.
8) Bontemps, S.; Bouhadir, G.; Gu, W.; Mercy, M.; Chen, C.-H.; Foxman, B. M.; Maron, L.; Ozerov, O. V.;
Bourissou, D. Angew. Chem. Int. Ed. 2008, 47, 1481–1484.
9) Nuss, G.; Saischek, G.; Harum, B. N.; Volpe, M.; Gatterer, K.; Belaj, F.; Mösch-Zanetti, N. C. Inorg.
Chem. 2011, 50, 1991–2001.
(
2
(
2
(
(
(
(
10) Tsoureas, N.; Haddow, M. F.; Hamilton, A.; Owen, G. R. Chem. Commun. 2009, 2538–2540.
11) Dyson, G.; Zech, A.; Rawe, B. W.; Haddow, M. F.; Hamilton, A.; Owen, G. R. Organometallics 2011,
30, 5844–5850.
(
(
(
(
(
12) Moret, M.-E.; Peters, J. C. J. Am. Chem. Soc. 2011, 133, 18118–18121.
13) Anderson, J. S.; Rittle, J.; Peters, J. C. Nature 2013, 501, 84–87.
14) Harman, W. H.; Lin, T.-P.; Peters, J. C. Angew. Chem. Int. Ed. 2014, 53, 1081–1086.
15) Creutz, S. E.; Peters, J. C. J. Am. Chem. Soc. 2015, 137, 7310–7313.
16) Del Castillo, T. J.; Thompson, N. B.; Suess, D. L. M.; Ung, G.; Peters, J. C. Inorg. Chem. 2015, 54,
9256–9262.
(
(
(
(
(
(
17) Del Castillo, T. J.; Thompson, N. B.; Peters, J. C. J. Am. Chem. Soc. 2016, 138, 5341–5350.
18) Figueroa, J. S.; Melnick, J. G.; Parkin, G. Inorg. Chem. 2006, 45, 7056–7058.
19) Pang, K.; Tanski, J. M.; Parkin, G. Chem. Commun. 2008, 1008–1010.
20) Crossley, I.; Hill, A.; Willis, A. Organometallics 2006, 25, 289–299.
21) Crossley, I.; Hill, A.; Willis, A. Organometallics 2008, 27, 312–315.
22) Holler, S.; Tüchler, M.; Belaj, F.; Veiros, L. F.; Kirchner, K.; Mösch-Zanetti, N. C. Inorg. Chem. 2016,
5
5, 4980–4991.
23) Steel, G.; Rajasekharan-Nair, R.; Stepek, I. A.; Kennedy, A. R.; Reglinski, J.; Spicer, M. D. Eur. J. Inorg.
Chem. 2016, 2409–2412.
24) Nuss, G.; Saischek, G.; Harum, B. N.; Volpe, M.; Belaj, F.; Mösch-Zanetti, N. C. Inorg. Chem. 2011, 50,
2632–12640.
25) Nuss, G.; Ozwirk, A.; Harum, B. N.; Saischek, G.; Belaj, F.; Mösch-Zanetti, N. C. Eur. J. Inorg. Chem.
012, 4701–4707.
26) Tüchler, M.; Holler, S.; Rendl, S.; Stock, N.; Belaj, F.; Mösch-Zanetti, N. C. Eur. J. Inorg. Chem. 2016,
609–2614.
(
(
1
(
2
(
2
25

(
27) Nelson, T. D.; LeBlond, C. R.; Frantz, D. E.; Matty, L.; Mitten, J. V.; Weaver, D. G.; Moore, J. C.; Kim, J.
M.; Boyd, R.; Kim, P.-Y.; Gbewonyo, K.; Brower, M.; Sturr, M.; McLaughlin, K.; McMasters, D. R.; Kress, M.
H.; McNamara, J. M.; Dolling, U. H. J. Org. Chem. 2004, 69, 3620–3627.
(
28) Tüchler, M.; Belaj, F.; Raber, G.; Neshchadin, D.; Mösch-Zanetti, N. C. Inorg. Chem. 2015, 54, 8168–
170.
29) Due to incomplete conversion boron contaminants not detectable by NMR spectroscopy must still
8
(
be in the obtained material. In absence of analytical data for the identity of the contaminants we assume
it to be a borate species and therefore to account for less than 2 % of the total mass.
(
(
(
30) Evans, D. F. J. Chem. Soc. 1959, 2003.
31) Spicer, M. D.; Reglinski, J. Eur. J. Inorg. Chem. 2009, 2009, 1553–1574.
32) Mihalcik, D. J.; White, J. L.; Tanski, J. M.; Zakharov, L. N.; Yap, G. P. A.; Incarvito, C. D.; Rheingold, A.
L.; Rabinovich, D. Dalton Trans. 2004, 1626–1634.
(
(
33) Suess, D. L. M.; Tsay, C.; Peters, J. C. J. Am. Chem. Soc. 2012, 134, 14158–14164.
34) Senda, S.; Ohki, Y.; Hirayama, T.; Toda, D.; Chen, J.-L.; Matsumoto, T.; Kawaguchi, H.; Tatsumi, K.
Inorg. Chem. 2006, 45, 9914–9925.
35) Sircoglou, M.; Bontemps, S.; Bouhadir, G.; Saffon, N.; Miqueu, K.; Gu, W.; Mercy, M.; Chen, C.-H.;
Foxman, B. M.; Maron, L.; Ozerov, O. V.; Bourissou, D. J. Am. Chem. Soc. 2008, 130, 16729–16738.
(
(
(
(
36) Moret, M.-E.; Zhang, L.; Peters, J. C. J. Am. Chem. Soc. 2013, 135, 3792–3795.
37) Owen, G. R. Transit. Metal Chem. 2010, 35, 221–228.
38) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984,
1349–1356.
(
(
39) Thomsen, I.; Clausen, K.; Scheibye, S.; Lawesson, S.-O. Org. Synth. 1984, 62, 158.
40) Buysser, K. de; Herman, G. G.; Bruneel, E.; Hoste, S.; van Driessche, I. Chem. Phys. 2005, 315, 286–
292.
(
41) Sheldrick, G. M. Acta Cryst. 2008, A64, 112–122.
26

The thiopyridazine based scorpionate ligand sodium tris(3,5-di-tert-butyl-6-thioxopyridazin-
tBu,tBu
1
(6H)-yl)hydroborate (NaTn
) with two tert-butyl substituents in ortho- and para-position of
the thio group was synthesized and fully characterized. Corresponding metallaboratrane
tBu,tBu
Me,tBu
complexes [M{B(Pn
)
3
}Cl] (M = Co, Ni, Cu) as well as [M{B(Pn
3
) }Cl] (M = Co, Ni)
were prepared in good yields. All complexes were characterized by spectroscopic means as well
as by single crystal X-ray diffraction studies exhibiting short metal boron bonds (between
2
.0186(17) Å and 2.069(3) Å) compared to previously reported boratranes. The two tert-butyl
tBu,tBu
groups attached to the heterocycle significantly increases the solubility of NaTn
and the
derived metal complexes in apolar solvents compared to the system bearing the smaller
substituents. The higher steric demand of the tert-butyl group vs. methyl enhances the distortion
from trigonal bipyramidal towards square pyramidal which effects the electronic situation within
the complexes evidenced by the elongated metal chlorine bond trans to boron.
27