Pyridine-2-thiolate bridged tin-palladium complexes with Sn(PdN 2Cl2), Sn(PdN2S2), Sn(PdN 2C2) and Sn(Pd2N4) skeletons

Article abstract of DOI:10.1039/c3cc47912a

Reactions of tin(IV) complexes of the type Sn(PyS)₂X₂ (X = Cl, PyS, Ph; PyS = pyridine-2-thiolate) with Pd(PPh₃) ₄ provide easy access to novel heterometallic complexes with Pd-Sn bonds. Electronic characteristi

Full text of DOI:10.1039/c3cc47912a

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Pyridine-2-thiolate bridged tin–palladium
complexes with Sn(PdN2Cl2), Sn(PdN2S2),
Sn(PdN2C2) and Sn(Pd2N4) skeletons†‡
Cite this: Chem. Commun., 2014,
50, 5382
Received 16th October 2013,
Accepted 2nd December 2013
Erik Wachtler,a Robert Gericke,a Lyuben Zhechkov,b Thomas Heine,b
¨
Thorsten Langer,c Birgit Gerke,c Rainer Pottgenc and Jorg Wagler*a
¨
¨
DOI: 10.1039/c3cc47912a
www.rsc.org/chemcomm
Reactions of tin(IV) complexes of the type Sn(PyS)2X2 (X = Cl, PyS,
Ph; PyS = pyridine-2-thiolate) with Pd(PPh3)4 provide easy access
to novel heterometallic complexes with Pd–Sn bonds. Electronic
characteristics of this connection were analysed by X-ray crystallography,
119Sn Mossbauer spectroscopy and quantum chemical analyses.
¨
The chemistry of heterodinuclear complexes with the TM-E
bonding situation (TM = transition metal, E = main group metal
or metalloid) is currently being explored across the periodic table,
and a great variety of novel complexes with transition metal
s-donors in the coordination sphere of a main group metal
(or metalloid) have been reported in the past few years. The
well-explored group of metallaboratranes (i.e., compounds
featuring TM-B bonds)1 has been joined by complexes with
TM-E (E = Be,2 Al,3 Ga,4 In,5 Si,6 Sn,7 Sb,8 Bi,9 Te10) bonds, just to
name a selection. Recently, we have shown that even in complexes
with a formal TM’E bonding situation (e.g., in a stannylene
complex, Sn acts as a lone pair s-donor), significant contributions
Scheme 1
Our further investigations addressed the elucidation of the
of the reverse bonding mode TM-E (upon formal change of the currently ‘‘pure formalism’’ with respect to usability of this general
oxidation numbers of metal and metalloid elements) may add to principle in synthetic approaches and with regard to the influence
the bonding situation (Scheme 1, I).11 The same findings have of the further metalloid coordination sphere on the directionality of
been reported by Jambor et al. (for compound II).12
the formally dative bonding mode, i.e., on the TM’E vs. TM-E
competition. The (N,S)-bidentate pyridine-2-thiolato ligand (PyS),
which is a constituent of compound II (and related to the
methimazolyl ligand in compound I), was a helpful tool for
our study, as the desired precursor compounds III–VI (Scheme 1)
were already known from the literature,13 and the mesomerism
of this anion serves the purpose of our investigation.
Whereas compound I was prepared in a one-pot synthesis
from tin(II) and palladium(II) precursors,11 we now aim at
synthesis using a combination of different starting materials
a
¨
Institut fur Anorganische Chemie, TU Bergakademie Freiberg, D-09596 Freiberg,
Germany. E-mail: joerg.wagler@chemie.tu-freiberg.de; Fax: +49 3731 39 4058
b School of Engineering and Science, Theoretical Physics – Theoretical Materials
Science, Jacobs University Bremen gGmbH, D-28759 Bremen, Germany
c
¨
¨
¨
Institut fur Anorganische und Analytische Chemie, Universitat Munster,
¨
Corrensstrasse 30, D-48149 Munster, Germany
† This article is part of the ChemComm ‘Emerging Investigators 2014’ themed
issue.
‡ Electronic supplementary information (ESI) available: Detailed syntheses and char-
119
¨
acterisation (NMR and Sn Mossbauer spectroscopy, CHNS microanalyses), tables with different ligand combinations and with palladium and tin
with parameters of data collection and structure refinement of the crystal structures
in different oxidation states (Scheme 2). Thus, routes A, C and
D start from tin(II) precursors and may involve a formal tin(III)
intermediate (the stannyl complex 2 in route D). The utilisation
of tin(IV) precursors opens further access routes (B) to such
reported in this paper and CIF. CCDC 963362 ([Pd(PyS)2(PPh3)2]), 963363 (1, modifica-
tion 1), 963364 (1, modification 2), 963365 (1Á(CHCl3)2), 963366 (2Á(CHCl3)2), 963367
(3Á(THF)), 963368 (4), 963369 (5Á(THF)2) and details of quantum chemical analyses. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c3cc47912a
complexes. We must stress that this is particularly important
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Scheme 2
for metalloid compounds which appear to be less stable in the case
of lower oxidation numbers of the metalloid (e.g., significantly
lower stability of SnPh2 relative to SnCl2).
All four routes shown in Scheme 2 proved to be suitable to
access compound 1, however routes A, B and C produced
similar yields (>70%), whereas route D proved to be less efficient
(see ESI‡). (Note: the intermediate and starting materials 2 and
[Pd(PyS)2(PPh3)2],14 respectively, the crystal structures of which have
not been reported so far, were characterized by X-ray crystallo-
graphy, see ESI.‡) Thus, route B was chosen to access related
compounds 3, 4 and 5 through suitable tin(IV) starting materials
(Scheme 3). As shown by X-ray crystallography (Fig. 1), compounds
1, 3 and 4 exhibit similar molecular architectures, i.e., distorted
trigonal-bipyramidal coordination of tin with two axial Sn–N bonds
as a fundamental motif, t15 = 0.66, 0.57 and 0.75, respectively. (Three
different crystal structures of 1, i.e., two solvent free modifications
and a chloroform solvate, were determined, see ESI.‡ In the discus-
sion we refer to the solvent free modification which was obtained
along the synthesis.) Noteworthily, the monodentate (PyS) ligands in
3 are S-bound to tin, while their N atoms (N3 and N4) cap two of the
equatorial edges with SnÁÁÁN separations of 2.95 and 3.03 Å,
respectively, thus making the Sn atom [5+2]-coordinate in a rather
pseudo-pentagonal-bipyramidal fashion. As a result, the sharp
S3–Sn1–S4 angle arises (85.98(7)1), whereas the related Cl–Sn–Cl
(in 1) and C–Sn–C (in 4) angles are 104.48(2)1 and 107.71(7)1,
respectively. The Sn–Pd bonds slightly increase from 1 via 3 to 4
Fig. 1 Molecular structures of 1, 3 and 4 in the crystal structures of 1,
3ÁTHF and 4. Selected atoms are labelled, displacement ellipsoids show
50% probability, H atoms are omitted for clarity and PPh3 groups are
simplified as a stick model.
(2.5052(2), 2.5328(2) and 2.5370(2) Å, respectively), and the Sn–N
bonds (2.287(2), 2.292(2) (1); 2.335(2), 2.386(2) (3); 2.347(2), 2.387(2) Å
(4)) exhibit the same trend and reflect response to the lowering
of the Lewis acidity of the tin atom upon substitution of Cl for (PyS)
for Ph. Similar behaviour (i.e., elongation of axial Sn–Cl bonds
upon substitution of Sn bound equatorial Cl atoms for Ph groups)
has been observed with pentacoordinate stannates [SnCl5]À and
[SnCl3Ph2]À.16 Except for the Sn–Pd bonds, the Pd coordination
spheres do not exhibit any noteworthy response to the different Sn
coordination spheres, i.e., the Pd–S bonds range from 2.297 to
2.312 Å, and the Pd–P bond lengths (2.3751(4), 2.3531(5) and
2.3786(5) Å in 1, 3 and 4, respectively) do not exhibit systematic
changes with respect to the features observed in the Sn coordi-
nation spheres.
In general, the Pd atoms are housed in nearly square-planar
coordination spheres. Despite the seemingly low influence of
the Sn coordination sphere on Pd, the electronic situation
along the Sn–Pd–P axis still varies significantly, as reflected
2
by the different J(119Sn,31P) couplings in solution (4311, 4598
and 2677 Hz for 1, 3 and 4, respectively). Further differences
were revealed by Natural Bonding Orbital (NBO) analyses.
Addition of a second equivalent of [Pd(PPh3)4] to 3 furnishes
5 with a change from the Sn–S to Sn–N coordination mode of
the dangling (PyS) ligands of 3 and insertion of PdPPh3 into the
S2-clamp. As shown by crystallography (Fig. 2), the tin coordi-
nation sphere in 5 is distorted octahedral with trans Pd–Sn
bonds. The four Sn–N bonds exhibit slightly different lengths,
i.e., short and long Sn–N bonds oppose each other, and the
average Sn–N bond length exceeds those observed in com-
pounds 1, 3 and 4. With respect to the again nearly square-
planar Pd coordination spheres, the Pd–S bonds are similar to
those of compounds 1, 3 and 4, but the Pd–Sn bonds are
significantly longer (by up to 0.09 Å) as well as the Pd–P bonds
Scheme 3
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compounds is intermediate between tin(II) and tin(IV), but
closer to tin(IV) (isomer shifts of III, IV and V are 3.17(1)/
3.15(1), 0.7913c and 0.8213c mm sÀ1, respectively). In the context
of the transition metal rich coordination sphere, even the isomer
shift of 5 (2.05(1) mm sÀ1) is still characteristic of tin(IV), because
compounds Sn[Fe(CO)2C5H5]4 and PhSn[Fe(CO)2C5H5]3, which
are considered tin(IV) compounds, exhibit similar isomer shifts
(of 2.14 and 2.00 mm sÀ1, respectively).19
In conclusion, we have shown that the TM-E coordination
mode is relevant in a great variety of ‘‘stannylene’’ complexes
and that these compounds can be easily accessed from tin(IV)
precursors by coordination of a palladium(0) complex moiety.
In this course, compound 5 revealed a novel coordination
Fig. 2 Molecular structure of 5 in the crystal structure of 5Á(THF)2.
Selected atoms are labelled, displacement ellipsoids show 50% probability, pattern, i.e., with two trans-disposed TM donor moieties in
H atoms are omitted for clarity and PPh3 groups are simplified as a stick
the octahedral tin coordination sphere.
model. Selected bond lengths [Å]: Pd1ÀP1 2.4139(5), Pd2ÀP2 2.4033(5),
Pd1ÀS1 2.3085(5), Pd1ÀS2 2.2969(6), Pd2ÀS3 2.2989(5), Pd2ÀS4 2.3017(6),
Pd1ÀSn1 2.5946(2), Pd2ÀSn1 2.5945(2), Sn1ÀN1 2.464(2), Sn1ÀN2 2.361(2),
Notes and references
Sn1ÀN3 2.397(2), Sn1ÀN4 2.457(2).
1 H. Braunschweig and R. D. Dewhurst, Dalton Trans., 2011, 549.
2 H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem., Int. Ed.,
2009, 48, 4239.
(by up to 0.06 Å). We attribute this bond lengthening along the
P–Pd–Sn axis to the now trans-disposed Pd–Sn bonds. In contrast to
other tin compounds with more than one transition metal in the
Sn coordination sphere, which could be interpreted as bridging
stannylene or stannide complexes,17 the tin atom in 5 cannot exhibit
directional s-lone-pair donation due to the opposing Pd–Sn bonds.
Currently, 5 reveals the widest TM–Sn–TM angle observed in such
heterometallic complexes (175.15(1)1), which is much larger than
the related angle observed in compound VII18 (151.71).
3 H. Braunschweig, K. Gruss and K. Radacki, Angew. Chem., Int. Ed.,
2007, 46, 7782.
4 H. Braunschweig, K. Gruss and K. Radacki, Inorg. Chem., 2008,
47, 8595.
5 E. J. Derrah, M. Sircoglou, M. Mercy, S. Ladeira, G. Bouhadir,
K. Miqueu, L. Maron and D. Bourissou, Organometallics, 2011,
30, 657.
6 J. Wagler and E. Brendler, Angew. Chem., Int. Ed., 2010, 49, 624.
7 J. Wagler, A. F. Hill and T. Heine, Eur. J. Inorg. Chem., 2008, 4225.
´
¨
8 T.-P. Lin, C. R. Wade, L. M. Perez and F. P. Gabbaı, Angew. Chem.,
Int. Ed., 2010, 49, 6357.
¨
9 T.-P. Lin, I.-S. Ke and F. P. Gabbaı, Angew. Chem., Int. Ed., 2012,
To elucidate differences in the Pd–Sn bonding situations of
1, 3, 4 and 5, NBO analyses were performed (see ESI‡). The
electronic populations of the Pd–Sn NBOs are similar (1.79,
1.71, 1.69 and 1.67 electrons for 1, 3, 4 and 5, respectively). The
tin contributions to these NBOs are 57, 54, 52 and 48% in the
same order, reflecting a decrease of s-donor action of tin
(transition towards a s-lone-pair acceptor) along this series.
The natural charges of Pd (ca. À0.6 in 1, 3 and 4; À0.7 in 5)
underline the pronounced role of Pd as the lone pair donor in 5
(i.e., pronounced Pd0-SnIV’Pd0 characteristics). The hybrid
orbital contribution of Pd to the Pd–Sn NBO is always close to
sp2d. In sharp contrast, the Sn hybrid orbital contribution to
the same NBO lacks significant d character and it strongly depends
on the Sn coordination sphere (%s, %p = 73, 27; 51, 49; 40, 60 and
50, 50 for 1, 3, 4 and 5, respectively). Whereas the sp hybrid
contribution of tin within the linear Pd–Sn–Pd coordination in 5
appears plausible, the striking shift from predominant s to p
orbital contributions along the series 1, 3, 4 signals a decrease in
stannylene character in the same direction.
51, 4985; C. Tschersich, C. Limberg, S. Roggan, C. Herwig,
N. Ernsting, S. Kovalenko and S. Mebs, Angew. Chem., Int. Ed.,
2012, 51, 4989.
¨
10 T.-P. Lin and F. P. Gabbaı, Angew. Chem., Int. Ed., 2013, 52, 3864.
11 E. Brendler, E. Wachtler, T. Heine, L. Zhechkov, T. Langer,
¨
¨
R. Pottgen, A. F. Hill and J. Wagler, Angew. Chem., Int. Ed., 2011,
50, 4696.
´
´
ˇ
12 J. Martincova, L. Dostal, S. Herres-Pawlis, A. Ru˚ˇzicka and R. Jambor,
Chem.–Eur. J., 2011, 17, 7423.
13 (a) J. Ichikawa and T. Mukaiyama, Chem. Lett., 1985, 1009;
(b) M. Masaki and S. Matsunami, Bull. Chem. Soc. Jpn., 1976,
49, 3274; (c) F. Huber, R. Schmiedgen, M. Schu¨rmann, R. Barbieri,
G. Ruisi and A. Silvestri, Appl. Organomet. Chem., 1997, 11, 869;
ˆ
(d) M. Boualam, J. Meunier-Piret, M. Biesemans, R. Willem and
M. Gielen, Inorg. Chim. Acta, 1992, 198–200, 249; (e) E. Wachtler,
R. Gericke, S. Kutter, E. Brendler and J. Wagler, Main Group Met.
Chem., 2013, 36, 181.
¨
14 Y. Nakatsu, Y. Nakamura, K. Matsumoto and S. Ooi, Inorg. Chim.
Acta, 1992, 196, 81.
15 A. W. Addison, T. N. Rao, J. Reedijk, J. van Rijn and G. C. Verschoor,
J. Chem. Soc., Dalton Trans., 1984, 1349.
16 (a) U. Mu¨ller, J. Siekmann and G. Frenzen, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1996, 52, 330; (b) D. Weber, S. H. Hausner,
¨
A. Eisengraber-Pabst, S. Yun, J. A. Krause-Bauer and H. Zimmer,
119
À1
Inorg. Chim. Acta, 2004, 357, 125.
¨
Sn Mossbauer data (isomer shifts in mm s for 1, 3, 4
17 (a) R. D. Ball and D. Hall, J. Organomet. Chem., 1973, 56, 209;
(b) E. Simon-Manso and C. P. Kubiak, Angew. Chem., Int. Ed.,
2005, 44, 1125.
18 A. Balch, H. Hope and F. E. Wood, J. Am. Chem. Soc., 1985, 107, 6936.
19 V. I. Gol’danskii, B. V. Borshagovskii, E. F. Makarov, R. A. Stukan,
K. N. Anisimov, N. E. Kolobova and V. V. Skripkin, Teor. Eksp. Khim.,
1967, 3, 478.
and 5 are 1.63(1), 1.81(1), 1.54(1) and 2.05(1), respectively)
indicate varying 5s level populations in the tin atoms of these
compounds, which are in good agreement with the calculated
5s populations (1.05, 1.11, 0.94 and 1.09 electrons in the same
order). Thus, the electronic population of the Sn atom in these
5384 | Chem. Commun., 2014, 50, 5382--5384
This journal is ©The Royal Society of Chemistry 2014