Pushing the Frontiers of Hard and Soft Scorpionate Chemistry

Article abstract of DOI:10.1021/ic035167i

The preparation and structure of the first scorpionate complex of a group 16 element, [Te(κ²-Tm^Me)₂], is reported. It displays square planar geometry at the Te atom and two distinct ligand conformations. In addition, the first pyrazolylborate complex of a group 15 element, [Bi(Tp)₂(pzH)Cl], has been synthesized and characterized.

Full text of DOI:10.1021/ic035167i

Inorg. Chem. 2004, 43, 394−395
Pushing the Frontiers of Hard and Soft Scorpionate Chemistry
Christopher A. Dodds, Alan R. Kennedy, John Reglinski,* and Mark D. Spicer*
Department of Pure & Applied Chemistry, UniVersity of Strathclyde, Glasgow, G1 1XL U.K.
Received October 8, 2003
The preparation and structure of the first scorpionate complex of
a group 16 element, [Te(κ2-TmMe)2], is reported. It displays square
planar geometry at the Te atom and two distinct ligand conforma-
tions. In addition, the first pyrazolylborate complex of a group 15
element, [Bi(Tp)2(pzH)Cl], has been synthesized and characterized.
Since its introduction into the chemical catalog in 1966,
the hydrotris(pyrazolyl)-borate anion (Tp) has been used ex-
tensively in coordination chemistry.1 Thus far, it has been
observed to form complexes with most metals in the periodic
table. However, the limit of its capacity to complex to ele-
ments would seem to have been reached at tin2 in the fifth
period and lead3 in the sixth period. Attempts to form new
combinations with the elements beyond group 14 have appar-
ently been abandoned in the belief that no stable species
could be obtained. Our recent studies on soft analogues of Tp,
in particular the hydrotris(methimazolyl)borate anion (TmMe),
have allowed us and other workers to investigate the scor-
pionate complexes of groups 13,4 14,5c-e and 15.5a,e Two
structural motifs5a are observed which parallel those observed
for the bismuth complexes with CpR ligands,6 while a bent
metallocene halide, [(CpR)2BiCl] (Figure 1), is also formed.
In the lower main group, the cationic sandwich complexes
of TmMe, [E(κ3-TmMe)2]n+, would seem to be the dominant
Figure 1. Structural motifs reported for Tp, Cp, and Tm bismuth
complexes.5a,e,6 Cp shares two motifs with Tm; no Tp complexes exist.
motif, recurring with tin(IV)7 and arsenic(III)7 and in
bismuth(III) complexes5e of other related soft scorpionates
(eq 1). In view of these observations, two questions enticed
us. First, given the formation of both Cp and TmMe
complexes of bismuth, could Tp complexes also be formed?
Second, could the chemistry of Tm be further extended to
group 16? We answer both questions in the affirmative, and
in so doing, a number of intriguing aspects of the chemistry
of these ligands have become apparent.
EXn + MTmMe [excess] f [E(TmMe)2](n-2)+ + 2MX (1)
* To whom correspondence should be addressed. E-mail: j.reglinski@
strath.ac.uk (J.R.); m.d.spicer@strath.ac.uk (M.D.S.). Phone: +44-141-548-
2349 (J.R.); +44-141-548-2800 (M.D.S.). Fax:+44-141-552-0876.
(1) (a) Trofimenko, S. J. Am. Chem. Soc. 1966, 88, 1842. (b) Trofimenko,
S. In Scorpionates: The Coordination Chemistry of Polypyrazolylbo-
rate Ligands; Imperial College Press: London, 1999.
n ) 3: E ) As3+, Bi3+, “Tl3+” post oxidation of Tl+
n ) 4: E ) Sn4+; M ) Na, Tl
(2) (a) Cowley, A. H.; Geerts, R. L.; Nunn, C. M.; Carrano, C. J. J.
Organomet. Chem. 1988, 341, C27. (b) Reger, D. L.; Ding, Y.
Polyhedron 1994, 13, 869.
Reaction of [Te(tu)4Cl2] (tu ) thiourea)8 with excess
NaTm results in the formation of a stable yellow complex,
[Te(κ2-TmMe)2], the X-ray crystal structure of which indicates
that the central tellurium atom lies in a distorted square planar
environment (Figure 2) with the TmMe ligands coordinated
in the κ2-mode. Square planar geometry has been previously
observed for tellurium(II) monodentate thione adducts (e.g.,
(3) (a) Reger, D. L.; Huff, M. F.; Rheingold, A. L.; Haggerty, B. S. J.
Am. Chem. Soc. 1992, 114, 579. (b) Reger, D. L. Synlett 1992, 469.
(4) (a) Slavin, P. A.; Reglinski, J.; Spicer, M. D.; Kennedy, A. R. J. Chem.
Soc., Dalton Trans. 2000, 239. (b) Ojo, J. F.; Slavin, P. A.; Reglinski,
J.; Garner, M.; Spicer, M. D.; Kennedy, A. R.; Teat, S. J. Inorg. Chim.
Acta 2001, 313, 15. (c) Kimblin, C.; Bridgewater, B. M.; Hascall, T.;
Parkin, G. J. Chem. Soc., Dalton Trans. 2000, 891. (d) Kimblin, C.;
Bridgewater, B. M.; Hascall, T.; Parkin, G. J. Chem. Soc., Dalton
Trans. 2000, 1267.
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Chem. Soc. 1999, 121, 2317. (b) Bridgewater, B. M.; Parkin, G. J.
Am. Chem. Soc. 2000, 122, 7140. (c) Bridgewater, B. M.; Parkin, G.
Inorg. Chem. Commun. 2000, 3, 534. (d) Santini, C.; Pellei, M.;
Lobbia, G. G.; Pettinari, C.; Drozdov, A.; Troyanov, S. Inorg. Chim.
Acta 2001, 325, 20. (e) Bailey, P. J.; Lanfranchi, M.; Marchio, L.;
Parsons, S. Inorg. Chem. 2001, 40, 5030.
(6) (a) Sitzmann, H.; Wolmershauser, G.; Boese, R.; Blaser, D. Z. Anorg.
Allg. Chem. 1999, 625, 2103. (b) Sitzmann, H.; Wolmershauser, G.
Chem. Ber. 1994, 127, 1335. (c) Sitzmann, H.; Wolmershauser, G. Z.
Naturforsch., B: Chem. Sci. 1997, 52, 398.
(7) Dodds, C. A.; Jagoda, M.; Reglinski, J.; Spicer, M. D. Polyhedron, in
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(8) Foss, O.; Hauge, S. Acta Chem. Scand. 1961, 15, 1616.
394 Inorganic Chemistry, Vol. 43, No. 2, 2004
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Figure 2. X-ray structure of [Te(κ2-TmMe)2]. Selected distances (Å) and
angles (deg): Te(1)-S(1), 2.5837(9); Te(1)-S(2), 2.7083(10); Te(1)-S(4),
2.8617(10); Te(1)-S(5), 2.6805(10); S(1)-Te(1)-S(2), 86.51(3); S(4)-
Te(1)-S(5), 97.79(3); S(1)-Te(1)-S(5), 88.44(3); S(2)-Te(1)-S(4),
87.43(3).
Figure 3. X-ray crystal structure of [Bi(κ3-Tp)2(pzH)Cl] (pzH ) pyrazole).
Selected bond distances (Å) and angles (deg): Bi(1)-Cl(1), 2.837(4); Bi-
(1)-NTp, 2.54 (av); Bi(1)-N(13), 2.80(1); N-Bi(1)-N bite angles in the
range 68.7-77.6°.
[Te(L)4]2+; L ) thiourea9 S-Te-S; 90.6°, 89.3°, 180°;
Te-S, 2.686 Å, 2.690 Å; L ) ethylenethiourea10 90.2°,
89.3°, 172.1°; Te-S 2.702 Å, 2.654 Å) which are unre-
strained by a bridgehead atom.
progression. In view of the structural motifs observed for
bismuth TmMe and Cp complexes (Figure 1) and the recently
reported bismuth phthalocyanine structures,13 we reasoned
that a Tp complex of bismuth should also be attainable.
Treating BiCl3 with a sufficient amount of NaTp in cold
(0 °C) acetone leads to the copious formation of elemental
bismuth. However, filtration and reduction of the solution
volume at low temperature led to the formation of a small
number of white crystals and a white powder. X-ray
diffraction reveals an eight coordinate geometry for the
elusive [Bi(Tp)2(pzH)Cl]. The Tp ligands lie at an angle of
∼46° to one another exposing sites to which the halide and
pyrazole coordinate. The free pyrazole is undoubtedly formed
as a byproduct of the reduction of BiIII to metallic Bi by the
Tp ligand. The various donors are arranged around the central
atom at angles which generate minimal distortion consistent
with a stereochemically inactive lone pair3 and indicative of
predominantly electrostatic bonding. This contrasts with the
six coordinate thiazolylborato complexes of bismuth5a,e which
display greater covalent character. The species reported here
is structurally most similar to the Cp homologue6b and,
strikingly, the trivalent yttrium complex of Reger et al.14
Thus, it is instructive that this bismuth-Tp complex adopts
the one motif that is absent from soft Tm chemistry (Figure
1) elegantly demonstrating that the combination of metal and
ligand character controls the structural outcome.
The most striking structural feature of the complex is the
asymmetric disposition of the ligand about the tellurium
center. Unusually in TmR chemistry two different ligand
conformations are observed in the same compound. In one
ligand the sulfur atoms adopt a syn, syn, syn conformation
with respect to the boron hydride, reminiscent of the
arrangement in the uncomplexed TmMe anion,11 while in the
other ligand they adopt a syn, syn, anti arrangement. Both
ligands are coordinated in a bidentate (κ2) fashion, which is
known for TmR where R is a bulky group,12 but this is the
first observation of this arrangement for the parent TmMe. It
is also notable that when such bidentate coordination occurs,
there is usually a short M‚‚‚H-B contact, generally described
as an agostic interaction,5c but in this case no such interaction
occurs. The lack of ligand coordination in the axial sites is
clearly a result of significant lone pair electron density on
tellurium, which serves to repel the electron rich thione
sulfurs and the hydridic hydrogens. The ligand conformation
also has a marked influence on the tellurium coordination
sphere. The all syn arrangement of the ligand appears to be
far more sterically strained as evidenced by a bite angle of
97.79° and one average (2.68 Å) and one very long (2.86
Å) Te-S distance. The “twisted” ligand conformation on
the other hand has a small bite angle (86.51°) and one short
(2.58 Å) and one average (2.60 Å) Te-S distance, suggesting
a much more energetically favored conformation. It is unclear
why both conformations are observed in the solid state, since
in the solution NMR spectrum of this compound single,
broad resonances due to the ring protons are observed,
suggesting significant fluxionality.
Acknowledgment. We thank the EPSRC for financial
support.
Supporting Information Available: Text giving experimental
details. Crystallographic data in CIF format. This material is
available free of charge via the Internet at http://pubs.acs.org. Details
of the X-ray crystal structure determinations (226549 and 226550)
may be obtained from the Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, U.K. (Fax: +44-1223-336033. E-mail:
deposit@ccdc.cam.ac.uk. Web: http://ccdc.cam.ac.uk.)
In our analysis of the comparative chemistry of TmR, Tp,
and Cp,11 we find both a structural homology and structural
(9) Fosheim, K.; Foss, O.; Scheie, A.; Solheimsnes, S. Acta Chem. Scand.
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IC035167I
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Chem ReV. 1994, 94, 301.
(11) Reglinski, J.; Garner, M.; Cassidy, I.; Slavin, P. A.; Spicer, M. D.;
Armstrong, D. R. J. Chem. Soc., Dalton Trans. 1999, 2119.
(12) Tesmer, M.; Shu, M.; Vahrenkamp, H. Inorg. Chem. 2001, 40, 4022.
(13) (a) Ostendorp, G.; Homborg, H. Z. Anorg. Allg. Chem. 1996, 622,
873. (b) Janczak, J.; Kubiak, R.; Hahn, F. Inorg. Chim. Acta 1998,
281, 195. (c) Kubiak, R.; Ejsmont, K. Pol. J. Chem. 1999, 73, 1771.
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