Synthesis and structural characterisation of the phenyl/scorpionate hybrid ligand [Ph(pz)BC5H10]-

Article abstract of DOI:10.1016/j.ica.2009.02.002

The new phenyl/scorpionate hybrid ligand [Ph(pz)BC₅H₁₀]^- has been synthesised and structurally characterised as K⁺ and Tl⁺ salt. The ligand is specifically designed to create half-sandwich complexes i

Full text of DOI:10.1016/j.ica.2009.02.002

Inorganica Chimica Acta 362 (2009) 4372–4376
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and structural characterisation of the phenyl/scorpionate hybrid
ligand [Ph(pz)BC5H10]ꢀ
*
Kerstin Kunz, Florian Blasberg, Michael Bolte, Hans-Wolfram Lerner, Matthias Wagner
Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, D-60438 Frankfurt (Main), Germany
a r t i c l e i n f o
a b s t r a c t
ꢀ
Article history:
The new phenyl/scorpionate hybrid ligand [Ph(pz)BC5H10
] has been synthesised and structurally char-
acterised as K+ and Tl+ salt. The ligand is specifically designed to create half-sandwich complexes in which
the metal ion is chelated by the p-electron system of the phenyl ring and by the electron lone pair of the
Received 28 November 2008
Accepted 2 February 2009
Available online 12 February 2009
pyrazolyl nitrogen atom. This structural motif is established both by K[Ph(pz)BC5H10
] and by
Tl[Ph(pz)BC5H10].
Dedicated to the memory of Swiatoslaw
Trofimenko, the pioneer of scorpionate
chemistry.
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Boron
Ligand design
N-ligands
Arene ligands
1. Introduction
able derivative can easily be selected for the rational de novo
design of efficient catalysts. In another context we have already
investigated the two ligand series R3P/[R2(BH3)P]ꢀ/[R3Si]ꢀ and
R3PE/[R2(BH3)PE]ꢀ/[R3SiE]ꢀ (E = O, S, Se, Te) with the aim to evalu-
ate the impact of subtle differences in the charge distribution of
these isoelectronic species on their coordination behaviour [9–
Since the pioneering work of Ewen, Brintzinger, Kaminsky et al.
on the stereoselective polymerisation of
metallocene catalysts [1,2], there is an increasing interest in the
development of novel custom-tailored ansa-complexes. Nowadays,
these compounds are still used mainly for catalytic purposes [3],
but have also found medical applications [4,5].
a-olefins with ansa-
12]. We are now extending our research to the p-donor-containing
ansa-ligands [Ph-BR2pz]ꢀ and [Cp-CR2pz]ꢀ. The rationale behind
the design of these molecules is the following: (i) A cyclopentadi-
enyl and a phenyl ring are both potential six-electron donors but
differ in their charge state. (ii) By the same token, poly(pyrazol-
1-yl)borates (‘‘scorpionates” [13,14]) are the negatively charged
analogues of poly(pyrazol-1-yl)methanes [15]. Thus, similar to
the examples mentioned above, the linked systems [Ph-BR2pz]ꢀ
and [Cp-CR2pz]ꢀ are ideally suited to study the effect of slight
alterations in the electronic structure of otherwise closely related
ligands on their binding properties.
Initially, the term ‘‘ansa-complex” was coined for metallocenes
containing an interannular bridge between both cyclopentadienyl
rings (g5 5-coordination mode) [6]. Later on, this definition was
:g
expanded to include compounds in which a
linked to any one of the other ligands on the same metal centre
(in many cases this results in an g5 1-coordination mode). The
function of the bridging handle is to restrict the free rotation of
the -bonded ligand and/or to reduce the angle between the cen-
troid of the -system, the metal ion, and the second donor group
p-bonded moiety is
:g
p
p
to a value smaller than in comparable unbridged molecules (‘‘con-
strained geometry complexes”) [7,8].
The purpose of this paper is to report on the phenyl/mono(pyr-
azol-1-yl)borate hybrid ligand [2]ꢀ und to describe its K+ and Tl+
complexes K[2] and Tl[2] (Scheme 1).
A wealth of information has been gathered on numerous ligand
classes that are able to create ansa-complexes. These ligands must
be thoroughly compared in order to establish their relationship to
one another. The goal is to create versatile toolboxes of donor envi-
ronments with smoothly varying properties, so that the most suit-
2. Results and discussion
Transition metal complexes bearing an ansa-[Cp-BMe2pz]2ꢀ li-
gand are already known in the literature and have been shown to
possess a largely unstrained molecular framework [16,17]. We
therefore directed our initial synthesis efforts to the corresponding
* Corresponding author. Fax: +49 69 798 29260.
E-mail address: Matthias.Wagner@chemie.uni-frankfurt.de (M. Wagner).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.02.002

K. Kunz et al. / Inorganica Chimica Acta 362 (2009) 4372–4376
4373
Table 1
K
Selected crystallographic data for (K[2])2 and Tl[2].
+ Kpz
(i)
B
B
N
Compound
(K[2])2
Tl[2]
Formula
C28H36B2K2N4
528.43
colourless, block
173(2)
C14H18BN2Tl
429.48
colourless, block
173(2)
Formula weight
Colour, shape
T (K)
1
N
Radiation
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Mo K
a
, 0.71073 Å
Mo Ka, 0.71073 Å
monoclinic
P21/c
K[2]
triclinic
ꢀ
P1
+ TlNO3 (ii)
9.8824(9)
11.5100(10)
13.0560(12)
79.856(7)
77.938(7)
79.111(7)
1411.6(2)
2
8.8624(5)
10.0019(8)
16.0146(9)
90
104.154(4)
90
1376.45(16)
4
2.073
Tl[2]
Scheme 1. Synthesis of K[2] and Tl[2]. (i) toluene, r.t., 2 d. (ii) H2O/THF, r.t., 15 min.
a
(°)
b (°)
c
(°)
V (Å3)
phenyl/mono(pyrazol-1-yl)borate hybrid ligand [Ph-BMe2pz]ꢀ
bearing two methyl groups at the boron atom. However, the
preparation of the required starting material PhBMe2 turned out
to be a challenge, as has already been noted by Nöth et al., who ob-
tained mixtures of BMe3, PhBMe2, Ph2BMe, and Ph3B when they
tried to replace the two chloro substituents of PhBCl2 by methyl
groups using SnMe4 [18]. In our hands, the reactions between
PhBBr2 and MeMgCl in toluene/THF, PhB(OMe)2 or PhB(O2C6H4)
and (AlMe3)2 in hexane/heptane, as well as BrBMe2 and PhLi in tol-
uene/n-Bu2O gave equally poor results. In view of this background,
we decided to switch from PhBMe2 to Ph-BC5H10 [19,20] (1; Scheme
1), because a boracyclohexane fragment is less likely to take part in
substituent scrambling than a BMe2 moiety. The cations K+ and Tl+
were chosen as counterions, because potassium and thallium salts
of poly(pyrazol-1-yl)borates are valuable reagents for further syn-
theses of transition metal scorpionate complexes.
Z
Dcalcd. (g cmꢀ3
F(000)
)
1.243
560
0.359
808
11.717
l
(mmꢀ1
)
Crystal size (mm3)
0.19 ꢁ 0.16 ꢁ 0.15 0.18 ꢁ 0.12 ꢁ 0.10
No. of reflections collected
No. of independent reflections [R(int)
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
15456
18358
]
5266 (0.0541)
5266/0/325
1.034
0.0499, 0.1231
0.0703, 0.1317
0.796, ꢀ0.307
2581 (0.0877)
2581/0/164
1.115
0.0314, 0.0757
0.0346, 0.0773
1.557, ꢀ1.933
R1, wR2 (I > 2
R1, wR2 (all data)
Largest difference peak and hole (e Åꢀ3
r
(I))
)
molecules, (K[2])A2 and (K[2])2B, in the asymmetric unit. Single crys-
tals of Tl[2] were also grown from toluene. Crystal data and structure
refinement details of (K[2])2 and Tl[2] are compiled in Table 1.
The key structural parameters of the borate anions in (K[2])2A
and (K[2])B2 are rather similar, however, subtle but noteworthy dif-
ferences are observed regarding the coordination of the K+ ion to
the anionic moiety.
2.1. Synthesis, NMR spectroscopic and mass spectrometric
characterisation
The potassium salt K[2] was synthesised in good yields from 1
and 1 equiv. of Kpz in toluene (Scheme 1). Transmetallation to
the thallium complex Tl[2] was achieved by treatment of K[2] with
1 equiv. of TlNO3 in a mixture of carefully degassed H2O and THF
(Scheme 1).
Each ligand molecule in (K[2])A2 and (K[2])2B chelates a K+ ion by
the phenyl ring and the pyrazolyl group and thus adopts an ansa-
mode (the molecular structure of (K[2])A2 is shown in Fig. 1).
K+-phenyl coordination occurs via the
p-electron system of the
Both compounds were characterised by 11B, 1H and 13C NMR
spectroscopy in d8-THF solutions. The 11B NMR spectra of K[2]
and Tl[2] are characterised by signals at ꢀ4.4 ppm and ꢀ4.0 ppm,
respectively, thereby testifying to the presence of four-coordinate
boron nuclei [21]. The 1H NMR spectrum of K[2] reveals three mul-
tiplets for the phenyl protons (d(1H) = 6.82, 6.96, 7.06). Resonances
at 5.99 ppm (pzH-4), 7.24 ppm and 7.66 ppm (pzH-3,5), each inte-
grating to 1H, can be assigned to the protons of the pyrazolyl
group. The borinane ring gives rise to two multiplets at
d(1H) = 0.65–0.85 and 1.29–1.60. A similar picture is shown by
the 1H NMR spectrum of Tl[2]. The 13C NMR spectra of K[2] and
Tl[2] do not show any peculiarities and therefore do not merit fur-
ther discussion.
The ESI mass spectrum of K[2] in THF shows three peaks at
m/z = 225, 331 and 489 (negative measurement mode). While the
first peak is clearly due to the free ligand [2]ꢀ, the peak at m/
z = 489 can be assigned to a potassium ion wrapped by two ligand
molecules. These findings indicate that monomers K[2] coexist
with dimeric aggregates (K[2])2 in THF solution. The peak at m/
z = 331, which fits to ions of the composition [K[2]+pz]ꢀ, gives
interesting insight into the reactivity of our scorpionate ligand, be-
cause it points towards a rather weak B–N adduct bond.
organic moiety. In (K[2])A2, the K+ ions are displaced from positions
above the centroids (COG(Ph)) of the phenyl rings (K(1)–
COG(Ph) = 3.281 Å) towards the ipso-carbon atoms. As a conse-
quence, the corresponding K(1)–C distances are spread over the wide
range from 3.096(3) Å to 3.995(4) Å; the shortest contact, K(1)–
C(21) = 3.096(3) Å, is equal to the sum of the ionic radius of K+ and
the half-thickness of benzene (3.03 Å [22]). Contrary to (K[2])A2, the
K+ ions in (K[2])B2 adopt an
g
6-coordination mode (K–COG(Ph) =
3.010 Å) as evidenced by the narrow spread of K–C distances
(3.253(3)–3.399(3) Å).
In (K[2])A2, the torsion angle B(1)–N(11)–N(12)–K(1) possesses a
value of 41.3(3)° which indicates that the pyrazolyl donor binds to
the metal centre partly via the electron lone pair and partly via
the p-orbital of N(12); the corresponding K(1)–N(12) bond length
amounts to 2.857(2) Å. K(1) is not only attached to N(12), but also
to N(12B), thereby creating a dimeric structure containing a central
K2N2 four-membered ring (K(1)–N(12B) = 2.909(2) Å; B(1B)–
N(11B)–N(12B)–K(1) = ꢀ70.2(2)°). The general structural motif of
K+-pyrazolyl binding is the same in (K[2])2A and (K[2])B2. However,
in the latter dimer, the pyrazolyl bridge is less symmetrically coordi-
nating, because it acts as true
r
-donor towards one potassium ion
-donor to-
(B–N–N–K = ꢀ2.3(3)°; K–N = 2.751(2) Å) and as true
p
wards the other (B–N–N–K = 97.9(2)°; K–N = 3.118(2) Å). For more
information on the structural diversity of related potassium (pyra-
zol-1-yl)borates, the reader is referred to Refs. [16,22–24].
2.2. X-ray crystal structure determination
The potassium salt K[2] crystallises from toluene as centrosym-
metric dimer (K[2])2 with two crystallographically independent
In Tl[2], the phenyl(pyrazol-1-yl)borate again acts as ansa-li-
gand towards the metal centre (Fig. 2). We observe Tl(1)–C bond

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K. Kunz et al. / Inorganica Chimica Acta 362 (2009) 4372–4376
lengths in the interval from Tl(1)–C(21) = 3.160(5) Å to Tl(1)–
C(24) = 3.381(5) Å and a distance Tl(1)–COG(Ph) of 2.959 Å. The
Tl(1)–N(12) bond length of 2.579(5) Å and a torsion angle B(1)–
N(11)–N(12)–Tl(1) of only 18.8(6)° are in accord with a
r-coordi-
nation mode of the pyrazolyl tether. In the crystal lattice, the indi-
vidual molecules of Tl[2] are packed in a way that each Tl+ ion is
closely approached by the phenyl ring of a neighbouring complex
(Tl(1)–COG(Ph#) = 3.588 Å). In turn, this means that ‘‘inverse sand-
wich” complexes of the form Tl+ꢂ ꢂ ꢂ(C6H5R)ꢂ ꢂ ꢂTl+ are present in the
solid state. These are reminiscent of the solid state structure of the
ditopic thallium scorpionate Tl2[1,3-C6H4(tBuBpz2)2], which shows
antifacial binding of the two Tl+ ions to the bridging phenylene ring
[25].
3. Conclusion
ꢀ
The new phenyl/scorpionate hybrid ligand [Ph(pz)BC5H10
]
([2]ꢀ) has been designed with the aim to create half-sandwich
complexes in which the metal ion is chelated by the -electron
p
system of the phenyl ring and by the electron lone pair of the pyr-
azolyl nitrogen atom. We have shown that the aimed-for structural
motif is indeed established in the compounds K[Ph(pz)BC5H10] and
Tl[Ph(pz)BC5H10].
Fig. 1. Molecular structure and numbering scheme of compound (K[2])A2; displace-
ment ellipsoids are drawn at the 50% probability level; hydrogen atoms are omitted
for clarity. Selected bond lengths (Å), atomꢂ ꢂ ꢂatom distances (Å), bond angles (°),
torsion angles (°), and dihedral angles (°): B(1)–N(11) = 1.613(4), B(1)–C(2) = 1.654(4),
B(1)–C(6) = 1.633(4), B(1)–C(21) = 1.623(4), K(1)–N(12) = 2.857(2), K(1)–N(12B) =
2.909(2), K(1)–C(21) = 3.096(3), K(1)–C(22) = 3.293(3), K(1)–C(26) = 3.364(3), K(1)–
COG(Ph) = 3.281, K(1)ꢂ ꢂ ꢂK(1B) = 4.334(1); N(12)–K(1)–N(12B) = 82.6(1), K(1)–N(12)–
K(1B) = 97.5(1), B(1)–C(21)–K(1) = 99.3(2); C(2)–B(1)–C(21)–C(22) = 82.5(3), B(1)–
N(11)–N(12)–K(1) = 41.3(3), B(1B)–N(11B)–N(12B)–K(1) = ꢀ70.2(2); Ph//pz = 89.1.
COG(Ph): centroid of the phenyl ring. Symmetry transformations used to generate
equivalent atoms: ꢀx + 1, ꢀy + 1, ꢀz + 1 (B).
A systematic study on the coordination behaviour of [2]ꢀ to-
wards selected transition metal ions (especially RuII) is currently
conducted in our laboratories. However, a problem with [2]ꢀ arises
from the fact that its B–N bond is easily cleaved in the presence of
strong Lewis acids. It is known that bis(pyrazol-1-yl)borates tend
to be less stable than corresponding tris(pyrazol-1-yl)borate li-
gands [26,27], and this trend appears to continue if we proceed
from bis- to mono(pyrazol-1-yl)borates. We have already shown
that exchange of alkyl substituents R in bis(pyrazol-1-yl)borates
[R(R0)Bpz2]ꢀ for phenyl or pentafluorophenyl groups leads to a dra-
matic increase in ligand stability [28,29]. Replacement of the Ph-
BC5H10 moiety by Ph-B(C6F5)2 may therefore help to remediate
the problem of ligand degradation.
4. Experimental
4.1. General remarks
All reactions were carried out under a nitrogen atmosphere
using Schlenk tube techniques. Solvents were freshly distilled un-
der argon from Na/Pb alloy (pentane) and Na/benzophenone (tolu-
ene, THF, d8-THF) prior to use. NMR: Bruker Avance 300 and
Avance 400. Chemical shifts are referenced to residual solvent sig-
nals (1H, 13C{1H}) or external BF3ꢂEt2O (11B{1H}); all NMR spectra
were run at 300 K. Abbreviations: d = doublet, vtr = virtual triplet,
mult = multiplet, n.r. = multiplet expected in the 1H NMR spectrum
but not resolved, n.o. = signal not observed. The compound
PhBC5H10 (1) is known in the literature [19,20]. However, since
no detailed synthesis protocol has been published we are describ-
ing our optimised procedure below.
4.2. Synthesis of 1
Few drops of neat Br-(CH2)5-Br were added at r.t. to a stirring
mixture of Mg turnings (1.75 g, 71.99 mmol) in Et2O (100 mL)
whereupon the solvent started refluxing. A solution of Br-(CH2)5-
Br (4.86 mL, 8.27 g, 35.96 mmol) in Et2O (15 mL) was then added
dropwise. After the addition was complete, the mixture was first
heated to reflux for 2 h and then cooled to 0 °C. Neat PhBCl2
(3.93 mL, 4.75 g, 29.92 mmol) was added dropwise and stirring
was continued for 1 h at r.t. The liquid phase was transferred into
another flask via cannula and the solid residue extracted with Et2O
Fig. 2. Molecular structure and numbering scheme of compound Tl[2]; displace-
ment ellipsoids are drawn at the 50% probability level; hydrogen atoms are omitted
for clarity. Selected bond lengths (Å), bond angles (°), torsion angles (°), and
dihedral angles (°): B(1)–N(11) = 1.614(7), B(1)–C(2) = 1.629(7), B(1)–C(6) =
1.644(6), B(1)–C(21) = 1.645(6), Tl(1)–N(12) = 2.579(5), Tl(1)–COG(Ph) = 2.959,
Tl(1)–COG(Ph#) = 3.588; B(1)–C(21)–Tl(1) = 110.1(3); C(2)–B(1)–C(21)–C(22) =
55.8(6), B(1)–N(11)–N(12)–Tl(1) = 18.8(6); Ph//pz = 75.8. COG: centroid of the
respective phenyl ring. Symmetry transformations used to generate equivalent
atoms: ꢀx + 1, ꢀy + 1, ꢀz (#).

K. Kunz et al. / Inorganica Chimica Acta 362 (2009) 4372–4376
4375
(3 ꢁ 10 mL). The Et2O was distilled off from the combined liquids
at atmospheric pressure and the crude product was purified by
fractional distillation in vacuo. Yield: 2.20 g (47%).
funding. F.B. is grateful to the ‘‘Dr. Albert Hloch-Stiftung” for finan-
cial support.
1H NMR (300 MHz, C6D6): d 1.52–1.60, 1.64–1.74 (2 ꢁ mult,
10H, CH2), 7.22–7.33, 7.77–7.80 (2 ꢁ mult, 5H, PhH). 11B{1H} and
13C{1H} NMR shift values of 1 have already been published else-
where [20].
Appendix A. Supplementary material
CCDC 710879 and 710880 contain the supplementary crystallo-
graphic data for (K[2])2 and Tl[2]. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.02.002.
4.3. Synthesis of K[2]
A suspension of Kpz (1.48 g, 13.92 mmol) in toluene (50 mL)
was added dropwise at r.t. to a stirred solution of 1 (2.20 g,
13.92 mmol) in toluene (50 mL). The reaction mixture was stirred
for 2 d, all volatiles were evaporated in vacuo, pentane (25 mL)
was added to the colourless residue and the resulting suspension
was stirred for 30 min. The supernatant was discarded, the solid
material was washed again with pentane (3 ꢁ 10 mL) and subse-
quently dried in vacuo. Single crystals of the dimer (K[2])2 were
obtained upon recrystallisation of the crude product from hot tol-
uene. Yield: 2.71 g (74%).
References
[1] J.A. Ewen, J. Am. Chem. Soc. 106 (1984) 6355.
[2] W. Kaminsky, K. Külper, H.H. Brintzinger, F.R.W.P. Wild, Angew. Chem., Int. Ed.
Engl. 24 (1985) 507.
[3] P.W.N.M.v. Leeuwen, Homogeneous Catalysis. Understanding the Art, Kluwer
Academic Publishers, Dordrecht, Boston, London, 2004.
[4] Z. Guo, P.J. Sadler, Angew. Chem., Int. Ed. 38 (1999) 1512.
[5] M. Melchart, A. Habtemariam, O. Novakova, S.A. Moggach, F.P.A. Fabbiani, S.
Parsons, V. Brabec, P.J. Sadler, Inorg. Chem. 46 (2007) 8950.
[6] J.A. Smith, J.v. Seyerl, G. Huttner, H.H. Brintzinger, J. Organomet. Chem. 173
(1979) 175.
11B{1H} NMR (96.3 MHz, d8-THF): d ꢀ4.4 (h1/2 = 90 Hz). 1H NMR
(300 MHz, d8-THF): d 0.65–0.85, 1.29–1.60 (2 ꢁ mult, 10H, CH2),
3
5.99 (vtr, 1H, JHH = 1.8 Hz, pzH-4), 6.82 (mult, 1H, PhH-p), 6.96
[7] G.J.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem., Int. Ed. 38 (1999) 428.
[8] H. Braunschweig, F.M. Breitling, Coord. Chem. Rev. 250 (2006) 2691.
[9] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, Eur. J. Inorg. Chem. (2006)
1777.
[10] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, Eur. J. Inorg. Chem. (2006)
5138.
[11] T.I. Kückmann, F. Dornhaus, M. Bolte, H.-W. Lerner, M.C. Holthausen, M.
Wagner, Eur. J. Inorg. Chem. (2007) 1989.
[12] F. Dornhaus, M. Bolte, H.-W. Lerner, M. Wagner, J. Organomet. Chem. 692
(2007) 2949.
(mult, 2H, PhH-m), 7.06 (mult, 2H, PhH-o), 7.24, 7.66 (2 ꢁ dd,
3
4
2 ꢁ 1H, JHH = 1.8 Hz, JHH = 0.6 Hz, pzH-3,5). 13C{1H} NMR
(100.6 MHz, d8-THF): d 25.9, 27.8, 32.5 (CH2), 101.9 (pzC-4),
123.7 (PhC-p), 127.4 (PhC-m), 133.0 (PhC-o), 133.1, 137.5
(pzC-3,5), n.o. (PhC-i). Anal. Calc. for C14H18BKN2 (264.21): C,
63.64; H, 6.87; N, 10.60. Found: C, 63.32; H, 6.87; N, 10.29%.
MS(ESIꢀ) m/z (%): 224.8 (100) [2]ꢀ, 331.2 (39) [K[2]+pz]ꢀ, 489.4
(76) [K[2]2]ꢀ.
[13] S. Trofimenko, Scorpionates
–
The Coordination Chemistry of
Polypyrazolylborate Ligands, Imperial College Press, London, 1999.
[14] C. Pettinari, Scorpionates II: Chelating Borate Ligands, Imperial College Press,
London, 2008.
4.4. Synthesis of Tl[2]
[15] H.R. Bigmore, S.C. Lawrence, P. Mountford, C.S. Tredget, Dalton Trans. (2005)
635.
[16] K. Kunz, H. Vitze, M. Bolte, H.-W. Lerner, M. Wagner, Organometallics 26
(2007) 4663.
[17] For important examples of boron-bridged ansa-complexes see: (a) R. Littger, N.
Metzler, H. Nöth, M. Wagner, Chem. Ber. 127 (1994) 1901;
(b) H. Braunschweig, R. Dirk, M. Müller, P. Nguyen, R. Resendes, D.P. Gates, I.
Manners, Angew. Chem., Int. Ed. Engl. 36 (1997) 2338;
(c) P.J. Shapiro, Eur. J. Inorg. Chem. (2001) 321;
A solution of TlNO3 (0.128 g, 0.481 mmol) in degassed H2O
(10 mL) was added dropwise at r.t. to a stirring solution of K[2]
(0.127 g, 0.481 mmol) in THF (20 mL). The reaction mixture was
stirred for 15 min and extracted with Et2O (2 ꢁ 25 mL). The
combined extracts were evaporated in vacuo, and the remaining
colourless solid recrystallised from hot toluene. Yield: 0.158 g
(77%).
(d) H. Braunschweig, F.M. Breitling, E. Gullo, M. Kraft, J. Organomet. Chem. 680
(2003) 31;
(e) H. Braunschweig, F.M. Breitling, C.v. Koblinski, A.J.P. White, D.J. Williams,
Dalton Trans. (2004) 938;
(f) H. Braunschweig, M. Homberger, C. Hu, X. Zheng, E. Gullo, G. Clentsmith, M.
Lutz, Organometallics 23 (2004) 1968;
(g) H. Braunschweig, M. Gross, M. Kraft, M.O. Kristen, D. Leusser, J. Am. Chem.
Soc. 127 (2005) 3282;
(h) H. Braunschweig, M. Lutz, K. Radacki, A. Schaumlöffel, F. Seeler, C.
Unkelbach, Organometallics 25 (2006) 4433;
(i) H. Braunschweig, T. Kupfer, K. Radacki, Angew. Chem., Int. Ed. 46 (2007)
1630;
11B{1H} NMR (96.3 MHz, d8-THF): d ꢀ4.0 (h1/2 = 90 Hz). 1H NMR
(300 MHz, d8-THF):
6.15 (vtr, 1H, JHH = 2.0 Hz, pzH-4), 7.01 (mult, 1H, PhH-p), 7.15–
d
0.81, 1.34–1.56 (2 ꢁ mult, 10H, CH2),
3
3
7.24 (mult, 4H, PhH-o,m), 7.28, 7.85 (1 ꢁ n.r., 1 ꢁ d, 2 ꢁ 1H, JHH
=
1.5 Hz, pzH-3,5). 13C{1H} NMR (100.6 MHz, d8-THF): d 26.9, 27.7,
32.3 (CH2), 102.7 (pzC-4), 125.8 (PhC-p), 129.2, 134.9 (PhC-o,m),
135.6, 137.3 (pzC-3,5), n.o. (PhC-i). Anal. Calc. for C14H18BN2Tl
(429.48): C, 39.15; H, 4.22; N, 6.52. Found: C, 39.06; H, 4.23; N,
6.33%.
(j) H. Braunschweig, M. Gross, K. Hammond, M. Friedrich, M. Kraft, A.
Oechsner, K. Radacki, S. Stellwag, Chem. Eur. J. 14 (2008) 8972.
[18] H. Nöth, B. Wrackmeyer, Chem. Ber. 107 (1974) 3089.
[19] B. Wrackmeyer, H. Nöth, Chem. Ber. 109 (1976) 1075.
[20] J.D. Odom, T.F. Moore, R. Goetze, H. Nöth, B. Wrackmeyer, J. Organomet. Chem.
173 (1979) 15.
4.5. X-ray crystal structure analysis of (K[2])2 and Tl[2]
Both single crystals were analysed with a STOE IPDS II two-cir-
cle diffractometer with graphite-monochromated Mo Ka radiation.
[21] H. Nöth, B. Wrackmeyer, in: P. Diehl, E. Fluck, R. Kosfeld (Eds.), NMR Basic
Principles and Progress, Springer, Berlin, 1978.
[22] A. Haghiri Ilkhechi, J.M. Mercero, I. Silanes, M. Bolte, M. Scheibitz, H.-W. Lerner,
J.M. Ugalde, M. Wagner, J. Am. Chem. Soc. 127 (2005) 10656.
[23] A. Haghiri Ilkhechi, M. Bolte, H.-W. Lerner, M. Wagner, J. Organomet. Chem.
690 (2005) 1971.
Empirical absorption corrections were performed using the MUL-
ABS [30] option in PLATON [31]. The structure was solved by direct
methods using the program SHELXS [32] and refined against F2 with
full-matrix least-squares techniques using the program SHELXL-97
[33].
[24] S. Bieller, M. Bolte, H.-W. Lerner, M. Wagner, Z. Anorg. Allg. Chem. 632 (2006)
319.
[25] F. Zhang, M. Bolte, H.-W. Lerner, M. Wagner, Organometallics 23 (2004) 5075.
[26] S. Bieller, F. Zhang, M. Bolte, J.W. Bats, H.-W. Lerner, M. Wagner,
Organometallics 23 (2004) 2107.
[27] F. Zhang, T. Morawitz, S. Bieller, M. Bolte, H.-W. Lerner, M. Wagner, Dalton
Trans. (2007) 4594.
Acknowledgments
M.W. is grateful to the ‘‘Deutsche Forschungsgemeinschaft”
(DFG) and the ‘‘Fonds der Chemischen Industrie” (FCI) for financial
[28] T. Morawitz, M. Bolte, H.-W. Lerner, M. Wagner, Z. Anorg. Allg. Chem. 634
(2008) 1409.

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K. Kunz et al. / Inorganica Chimica Acta 362 (2009) 4372–4376
[29] T. Morawitz, F. Zhang, M. Bolte, J.W. Bats, H.-W. Lerner, M. Wagner,
Organometallics 27 (2008) 5067.
[30] R.H. Blessing, Acta Crystallogr. A 51 (1995) 33.
[31] A.L. Spek, J. Appl. Crystallogr. 36 (2003) 7.
[32] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467.
[33] G.M. Sheldrick, SHELXL-97. A Program for the Refinement of Crystal Structures,
Universität Göttingen, 1997.