Octahedral coordination compounds of the Ni, Pd, Pt triad

Article abstract of DOI:10.1002/anie.200704814

(Figure Presented) Aiming high: The coordination of the tin ligand stanna-closo-dodecaborate at Ni, Pd, and Pt results in the formation of compounds with high negative charges. These complexes contain metal centers with high coordination numbers and in high formal oxidation states. In the case of the platinum derivative, a far upfield chemical shift in the ¹⁹⁵Pt NMR spectrum (δ = -7724 ppm) was observed.

Full text of DOI:10.1002/anie.200704814

Angewandte
Chemie
DOI: 10.1002/anie.200704814
Tin Coordination
Octahedral Coordination Compounds of the Ni, Pd, Pt Triad**
Marius Kirchmann, Klaus Eichele, Falko M. Schappacher, Rainer Pöttgen, and Lars Wesemann*
Coordination compounds of the nickel triad with tin are well-
established, and in the case of the ligands [SnCl3]À, [SnPh3]À,
Sn(NtBu)2SiMe2, Sn{N(SiMe3)2}2, Sn{CH(SiMe3)2}2, and
[SnB11H11]2À, a variety of complexes has been characterized,
predominantly with the transition metal in the formal
oxidation state II.[1,2] We present herein a homoleptic series
of octahedrally tin-coordinated complexes [M(SnB11H11)6]8À
(M = Ni, Pd, Pt)with the metal in the formal oxidation state
IV. Our investigations of the coordination chemistry of
stanna-closo-dodecaborate have revealed that this borate
serves as a versatile ligand in coordination chemistry.[2] In its
reaction with platinum electrophiles, we found complexes
which are active catalysts in hydroformylation reactions; with
the coinage metals, cluster formation is the dominant
Figure 1. Molecular structure of the anion of [Bu3NH]8[Ni(SnB11H11)6]
(1); H atoms and cations have been omitted for clarity; ellipsoids are
reaction; and with ruthenium complex fragments, ambident
coordination modes together with dynamic behavior of the
heteroborate were characterized.[3–10]
set at 30% probability. Selected bond lengths [Š] and angles [8]: Ni–
Sn1 2.5475(4), Ni–Sn2 2.5343(4), Ni–Sn3 2.5274(4); Sn1-Ni-Sn2
90.12(1), Sn1-Ni-Sn3 90.96(1), Sn2-Ni-Sn3 89.14(1).
To synthesize a diazabutadiene nickel complex with
stanna-closo-dodecaborate as ligand, we treated the nickel
halide [Ni(dpp-bian)Br2] with three equivalents [SnB11H11]2À
(Scheme 1).[11] The octahedral nickel complex 1 was isolated
NMR spectroscopy (Figures 3 and 4)and 119Sn Mössbauer
spectroscopy (Figure 6).
The octaanionic complex [Ni(SnB11H11)6]8À with nickel in
the formal oxidation state IV is the product of an oxidation
reaction, raising the question of the corresponding reduction
product. It has been reported that [Ni(dab)Br2] (dab = 1,4-
diaza-1,3-butadiene or a-diimine)can readily be reduced in
the presence of additional dab, resulting in the formation of
[Ni(dab)2][12–14] with nickel in its common oxidation state II
and anionic radical dab ligands.[15–18] To our knowledge, the
reduction product [Ni(dpp-bian)2] has not been reported to
date, and we were not able to identify the dark violet
compound in the remaining reaction mixture (Scheme 1). To
investigate whether a reduction of [Ni(dab)Br2] is possible
with our stannaborate [SnB11H11]2À, we carried out the
reaction of [Ni(4-MePh-dab)Br2] (4-MePh-dab = 1,4-bis(4-
methylphenyl)-1,4-diaza-1,3-butadiene) with [Bu3NH]2-
[SnB11H11]. Although the yield of 1 was strongly reduced to
about 5%, [Ni(4-MePh-dab)2] could be isolated and identi-
fied by 1H and 13C NMR spectroscopy.[12] This result, as well as
the reaction stoichiometry of 1:3, supports the suggested
oxidation of the nickel(II)starting material to nickel(IV)
coupled with a reduction of [Ni(dpp-bian)Br2] (Scheme 1).[19]
Hence, the yield of 1 can be corrected to 64% with respect to
the nickel(II)starting material. At the end of the workup
procedure of 1, dark red crystals of [Bu3NH]6[Ni(SnB11H11)4]
(2)were isolated and, owing to the small amount, only
characterized by single crystal structure analysis. This com-
plex completes the series of the square-planar hexaanions
[M(SnB11H11)4]6À (M = Pd, Pt), and the square-planar coor-
dination mode of 2 is further convincing evidence for the
substantial ligand strength of the tin ligand stanna-closo-
dodecaborate.[3]
Scheme 1. Synthesis of [Bu3NH]8[Ni(SnB11H11)6] (1).
from this reaction mixture as purple crystals and was
characterized by elemental analysis, mass spectrometry,
X-ray crystal structure analysis (Figure 1), heteronuclear
[*] M. Kirchmann, Dr. K. Eichele, Prof. Dr. L. Wesemann
Institut für Anorganische Chemie
Universität Tübingen
Auf der Morgenstelle 18, 72076 Tübingen (Germany)
E-mail: lars.wesemann@uni-tuebingen.de
F. M. Schappacher, Prof. Dr. R. Pöttgen
Institut für Anorganische und Analytische Chemie
Universität Münster
Corrensstrasse 30, 48149 Münster (Germany)
[**] This work was supported by the Deutsche Forschungsgemeinschaft.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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The homologous complexes of 1 with hexacoordinate
palladium and platinum [M(SnB11H11)6]8À (M = Pd (3) , Pt (4))
were synthesized by substitution reactions starting with the
respective hexachloride complexes and the sodium salt
Na2[SnB11H11] in a mixture of water and THF (Scheme 2).
Figure 2. Molecular structure of the anion of [Bu3NH]6[Ni(SnB11H11)4]
(2); H atoms and cations have been omitted for clarity; ellipsoids are
set at 30% probability. Selected bond lengths [Š] and angles [8]: Ni–
Sn1 2.4761(4), Ni–Sn2 2.4706(5); Sn1-Ni-Sn2 89.81(2).
Scheme 2. Synthesis of [Bu3NH]2K2Na4[M(SnB11H11)6]; M=Pd (3) , Pt
(4).
(2.6162(5)–2.6186(5) Š) fall within the range of known
palladium–tin and platinum–tin distances.[1,3,4] In addition,
the cationic part of both compounds consists of four cations
([Bu3NH], K, 2Na)per asymmetric unit. The Pd–Sn and Pt–
Sn distances observed in the two coordination compounds are
considerably shorter than those observed in intermetallic
stannides, for example, 2.78–2.84 Š in PdSn2, PdSn3, and
PdSn4,[25] 2.77–2.80 Š in CaPdSn2,[26] 2.64–2.92 Š in
Ca2Pt3Sn5,[26] and 2.64–2.85 Š in Yb2Pt3Sn5.[27]
To examine the composition of 1, 3, and 4 in solution, the
respective salts were dissolved in dichloromethane or THF,
and 11B, 119Sn, and 195Pt NMR spectroscopy experiments were
carried out (Table 1, Figures 3–5). The signal around d =
The unusual combination of cations was found accidentally to
give large crystals of 3 and 4 when diethyl ether was slowly
diffused into a THF solution. The complexes 3 and 4 were
characterized by elemental analyses, X-ray crystal structure
analyses, and heteronuclear NMR spectroscopy.[20] It is note-
worthy that the octahedral complexes 1, 3, and 4 all show
remarkable stability towards moisture and air.
The structure refinement for 1 in space group P21/c
reveals that the nickel center is almost ideally octahedrally
coordinated by six stannaborate ligands, whereby the nickel
atom lies on a center of symmetry. In addition, there are four
[Bu3NH]+ counterions and three partially disordered toluene
molecules included in the asymmetric unit, which confirms
the eight-fold negative charge of the anion. The structure of
Table 1: 11B{1H}, 119Sn{1H}, and 195Pt NMR spectroscopic data for 1, 3,
and 4.
11B{1H}
[ppm]
119Sn{1H}
[ppm]
2J(119Sn-117Sn)
cis [Hz]
2J(119Sn-117Sn)
trans [Hz]
À
the octaanion of 1 is depicted in Figure 1. The Ni Sn bond
lengths are between 2.5211(6)and 2.5403(7)Š, which is in
1[a]
3[b]
4[c]
À15.9
À15.2
À15.6
À319
À284
À470
1931
1135
1050
13489
19700
15287
À
good agreement with the Ni Sn separation in the five-
coordinate nickel–tin complex [Ni(np3)(SnPh3)][BPh4] (np3 =
tris(2-(diphenylphosphino)ethyl)amine)[1,21] and somewhat
[a] In CD2Cl2. [b] In [D8]THF. [c] In [D8]THF at 58C; 195Pt NMR: d=À7724
À
longer than the Ni Sn bonds of the compounds [Ni(Sn-
(1J(195Pt-119Sn)=7900 Hz, 1J(195Pt-117Sn)=7550 Hz).
(NtBu)2SiMe2)4Br2] (2.459(4)–2.460(4) Š)[1] and [Bu4N][Ni-
(PPh3)Cp(SnB11H11)] (2.412(1) Š; Cp = cyclopentadienyl).[22]
À
The Ni Sn distances are comparable with those in the
intermetallic stannides Ni3Sn4 (2.54–2.77 Š)and AuNiSn
À15 ppm in the 11B NMR spectrum, as well as the resonances
in the 119Sn NMR spectra of 1, 3, and 4, are an unambiguous
indicator for coordination of the tin ligand (for comparison,
signals of the uncoordinated cluster: 11B NMR: d = À6, À11,
À12 ppm; 119Sn NMR: d = À550 ppm).[2] The 119Sn NMR
resonances exhibit 117Sn satellites corresponding to small cis
coupling constants (1931, 1135, 1050 Hz)and large trans
coupling constants (13489, 19700, 15287 Hz; Figure 3). The
119Sn NMR spectrum of [Ni(SnB11H11)6]8À in solution is in
good accordance with the solid-state 119Sn VACP/MAS NMR
spectrum showing a signal at À329 ppm (Figure 4).
2
(2.64 Š).[23,24] Compound 2 crystallizes in space group P1.
¯
The molecular structure of the anion is shown in Figure 2 and
reveals an almost ideal square-planar coordination. As in
compound 1, the nickel atom lies on a center of symmetry.
Furthermore, besides the three partly disordered [Bu3NH]+
counterions, one spatially disordered benzene molecule is
included in the asymmetric unit. In contrast to compound 1,
À
the Ni Sn bonds (2.4761(4)and 2.4706(5)Š)are shorter but
À
are also in good accordance with known Ni Sn distan-
ces.[1,21,22]
Examination of the crystal structure solutions of 3 and 4
revealed that both compounds crystallize in the same space
group P21/n with almost identical unit cell constants and
angles. The metals display nearly ideal octahedral coordina-
tion by six tin ligands and lie on a center of symmetry. The
metal–tin separations of 3 (2.6122(5)–2.6144(5) Š) and 4
Furthermore, the presence of platinum in compound 4
gives rise to 195Pt satellites with 1J(195Pt-119Sn) = 7900 Hz in the
119Sn{1H} NMR spectrum of 4. Since no resonances of
uncoordinated stannaborate are visible in the 11B and 119Sn
spectra of 1, 3, and 4, all six ligands remain mainly
coordinated in solution. The examination of the 195Pt spec-
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by 117Sn and 119Sn satellites with 1J(195Pt-119Sn) = 7900 Hz and
1J(195Pt-117Sn) = 7550 Hz (Figure 5). With the 195Pt resonance
at d = À7724 ppm, we have found the first example of a
coordination compound exhibiting a 195Pt NMR signal in such
an upfield chemical shift area. Thus, the stannaborate
[SnB11H11]2À is a very strong shielding ligand.
The 119Sn Mössbauer spectrum of compound 1 recorded at
77 K is presented in Figure 6 together with a transmission
integral fit. The spectrum was reproduced well with a single
Figure 3. 119Sn{1H} NMR spectra of 1, 3, and 4.
Figure 6. Experimental (dots)and simulated 119Sn Mössbauer spec-
trum (line)of 1, recorded at 77 K.[20]
tin signal at an isomer shift of d = 1.60(1)mms À1 and an
experimental line width of G = 0.88(1)mms À1 subjected to
quadrupole splitting of DEQ = 0.89(1)mms À1. The isomer
shift lies between the tin(II)specific isomer shift of
[SnB11H11]2À (d = 2.46 mmsÀ1)and the isomer shift of the
tin(IV)compound [MeSnB 11H11]À (d = 1.18 mmsÀ1)and is
therefore a good indicator for the strong electron-donating
effect of [SnB11H11]2À in 1.[7,34,35] Good agreement could be
found with [Pt(SnB11H11)4]6À (d = 1.66 mmsÀ1).[3]
Figure 4. a)Experimental [20] and b)simulated VACP-MAS 119Sn NMR
spectrum of 1 (VACP/MAS=variable amplitude cross polarization
magic angle spinning). The isotropic chemical shift diso is marked by
an asterisk. The chemical shift anisotropy has been determined by an
analysis of the spinning sideband intensities.[31,32] The value of the
span W (612 ppm)as well as the positive sign of the skew k (0.98)are
in good agreement with the reported results for h1(Sn)coordinated
stanna-closo-dodecaborate.[33]
The metal–tin stretching vibrations of 1, 3, and 4 could be
found at 224, 194, and 168 cmÀ1, respectively, which is in
À
À
analogy with the reported Pd Sn and Pt Sn stretching
vibrations.[3] Elemental analyses of 3 and 4 have been carried
out for the tributylmethylammonium salts.
To conclude, the first homoleptic series of octahedrally
coordinated tin complexes of Ni, Pd, and Pt in the formal
oxidation state IV was presented. Furthermore, the tetra-
coordinated nickel derivative completes the series of square-
planar complexes and is another example for the outstanding
ligand strength of stanna-closo-dodecaborate.
Experimental Section
All manipulations were carried out under argon atmosphere in
Schlenk glassware.
1: A solution of [Ni(dpp-bian)Br2] (120 mg, 0.16 mmol)was
added to a solution of [Bu3NH]2[SnB11H11] (311 mg, 0.5 mmol)in
dichloromethane (20 mL). The color of the solution changed from
brown to dark green to dark violet. The solvent was evaporated in
vacuum and the residue was extracted with toluene (100 mL). After
slow diffusion of hexane into the toluene solution, large dark crystals
could be isolated (155 mg, 64% yield). Elemental analysis (%) calcd
for C96H290B66N8NiSn6 (3041.89 gmolÀ1): C 37.91, H 9.61, N 3.68;
found: C 37.95, H 9.16, N 3.78. FIR (ATR): n˜ = 224 cmÀ1, nNi-Sn. ESI-
MS (negative ion mode): m/z = 2855.6 [Bu3NH]7[Ni(SnB11H11)6]À.
Figure 5. 195Pt NMR spectrum of 4.
trum of 4 met with difficulties, owing to the fact that the
reported platinum(IV)chemical shift window is very large ( d
ꢀ 15 000 ppm), and the resonance for 4 could not be found
within this range.[28–30] Extending the window towards lower
frequencies, however, reveals a signal at À7724 ppm flanked
Angew. Chem. Int. Ed. 2008, 47, 963 –966
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11B{1H} NMR (80.25 MHz, CD2Cl2): d = À15.9 ppm (11B, B2–B12).
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[8] T. Gädt, B. Grau, K. Eichele, I. Pantenburg, L. Wesemann,
Chem. Eur. J. 2006, 12, 1036 – 1045.
119Sn{1H} NMR (93.25 MHz, CD2Cl2): d = À319 ppm, cis 2J(119Sn-
117Sn) = 1931 Hz, trans 2J(119Sn-117Sn) = 13489 Hz.
2: The residue of 1 was further extracted with benzene (50 mL),
resulting in a dark red solution. Slow diffusion of hexane into this
solution yielded dark red crystals of 2 (5 mg, 1% yield).
3: A solution of [Na]2[SnB11H11] (176 mg, 0.6 mmol)in THF
(5 mL)was added to a solution of K 2PdCl6 (40 mg, 0.1 mmol)in H 2O
(2 mL), resulting in a dark red solution. The solvents were evaporated
in vacuum, and the red solid was redissolved in THF. After the
addition of [Bu3NH]Cl (44 mg, 0.2 mmol), slow diffusion of Et2O into
the red solution resulted in the formation of 3 as dark red crystals
(133 mg, 63% yield). Elemental analysis (%) for [Bu3NMe]6[Pd-
(SnB11H11)6], calcd for C104H306B66N8PdSn6 (3201.83 gmolÀ1): C 39.01,
H 9.63, N 3.50; found: C 39.75, H 9.20, N 2.94. FIR (ATR): n˜ =
[9] T. Gädt, L. Wesemann, Dalton Trans. 2006, 328 – 329.
[10] T. Gädt, K. Eichele, L. Wesemann, Dalton Trans. 2006, 2706 –
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194 cmÀ1, nPd-Sn
.
11B{1H} NMR (80.25 MHz, [D8]THF): d = À15.2
(11B, B2–B12). 119Sn{1H} NMR (93.25 MHz, [D8]THF): d =
À284 ppm, cis 2J(119Sn-117Sn) = 1135 Hz, trans 2J(119Sn-117Sn) =
19700 Hz.
4: A solution of Na2[SnB11H11] (176 mg, 0.6 mmol)in THF (5 mL)
was added to a solution of K2PtCl6 (49 mg, 0.1 mmol)in H 2O (2 mL),
resulting in an orange solution. The solvents were evaporated in
vacuum, and the orange solid was redissolved in THF. After the
addition of [Bu3NH]Cl (44 mg, 0.2 mmol), slow diffusion of Et2O into
the orange solution resulted in the formation of 4 as orange crystals
(140 mg, 65% yield). Elemental analysis (%) for [Bu3NMe]6[Pt-
(SnB11H11)6], calcd for C104H306B66N8PtSn6 (3290.49 gmolÀ1): C 37.96,
H 9.37, N 3.41; found: C 38.22, H 8.66, N 2.93. FIR (ATR): n˜ =
[16] K. Chlopek, E. Bothe, F. Neese, T. Weyhermüller, K. Wieghardt,
Inorg. Chem. 2006, 45, 6298 – 6307.
[17] M. M. Khusniyarov, K. Harms, O. Burghaus, J. Sundermeyer,
Eur. J. Inorg. Chem. 2006, 2985 – 2996.
[18] N. Muresan, K. Chlopek, T. Weyhermüller, F. Nesse, K.
Wieghardt, Inorg. Chem. 2007, 46, 5327 – 5337.
[19] An interpretation of the XANES spectrum was difficult owing to
the observed pre-edge feature in the Ni K-edge XANES
spectrum of 1 (recorded by S. Anantharaman, H. Bertagnolli)
and the lack of a comparable reference compound.
[20] See the supporting informations for details on the experimental
section, X-Ray crystal structure analyses of 1–4, the Mössbauer
spectroscopy, and the 119Sn CP/MAS NMR spectrum of 1.
[21] S. Midollini, A. Orlandini, L. Sacconi, J. Organomet. Chem.
1978, 162, 109 – 120.
168 cmÀ1
,
nPt-Sn
.
11B{1H} NMR (80.25 MHz, [D8]THF): d =
À15.6 ppm (11B, B2–B12). 119Sn{1H} NMR (93.25 MHz, [D8]THF):
d = À470 ppm, 1J(195Pt-119Sn) = 7900 Hz, cis 2J(119Sn-117Sn) = 1050 Hz,
trans 2J(119Sn-117Sn) = 15278 Hz. 195Pt NMR (106.68 MHz, [D8]THF,
58C): d = À7724 ppm 1J(195Pt-119Sn) = 7900 Hz, 1J(195Pt-117Sn) =
7550 Hz.
[22] L. Wesemann, T. Marx, U. Englert, M. Ruck, Eur. J. Inorg.
Chem. 1999, 1563 – 1566.
Received: October 17, 2007
[23] W. Jeitschko, B. Jaberg, Acta Crystallogr. Sect. B 1982, 38, 598 –
600.
Published online: December 20, 2007
[24] S. Lange, T. Nilges, R.-D. Hoffmann, R. Pöttgen, Z. Anorg. Allg.
Chem. 2006, 632, 1163 – 1166.
[25] J. Nylꢀn, F. J. Garcꢁa, B. D. Mosel, R. Pöttgen, U. Häussermann,
Solid State Sci. 2004, 6, 147 – 155.
[26] R.-D. Hoffmann, D. Kußmann, U. Ch. Rodewald, R. Pöttgen, C.
Rosenhahn, B. D. Mosel, Z. Naturforsch. B 1999, 54, 709 – 717.
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mann, B. D. Mosel, C. Rosenhahn, Z. Kristallogr. 1999, 214, 143 –
150.
Keywords: coordination chemistry · NMR spectroscopy ·
structure elucidation · tin · X-ray diffraction
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