Palladium complexes containing novel cyclic selenium imides

Article abstract of DOI:10.1039/b910049k

The first metal complexes of cyclic selenium(II) imide ligands, [PdCl ₂{Se,Se′-Se₄(N^tBu)₃}] and [PdCl₂{Se,Se′-Se₄(N^tBu)₄}], which are obtained from the reaction of Se(

Full text of DOI:10.1039/b910049k

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Palladium complexes containing novel cyclic selenium imides†
Maarit Risto,a Aino Eironen,a Elisa Ma¨nnisto¨,a Raija Oilunkaniemi,a Risto S. Laitinen*a and
Tristram Chivers*b
Received 21st May 2009, Accepted 11th August 2009
First published as an Advance Article on the web 25th August 2009
DOI: 10.1039/b910049k
The first metal complexes of cyclic selenium(II) imide ligands,
produces dinuclear complexes [M2{m-N,N¢-Se(NR)2}2](CF3SO3)2
(M = Ag, Cu) in which selenium diimide acts as a bridging ligand.8
We report here the formation and X-ray structures of the
selenium(IV) diimide adduct [PdCl2{N,N¢-Se(NtBu)2}] (1) and
the complexes [PdCl2{Se,Se¢-Se4(NtBu)n}] (2, n = 3; 3, n = 4),
which are the first examples of metal complexes containing cyclic
selenium imides. The ligands Se4(NtBu)3 and Se4(NtBu)4 in 2 and
3, respectively, are new members of the family of cyclic selenium
imides.
[PdCl2{Se,Se¢-Se4(NtBu)3}] and [PdCl2{Se,Se¢-Se4(NtBu)4}],
which are obtained from the reaction of Se(NtBu)2
with [PdCl2(NCPh)2], contain the novel Se–N heterocycles
Se4(NtBu)3 and Se4(NtBu)4.
Selenium diimides have been known as in situ reagents for
more than 30 years.1 Multinuclear NMR studies of Se(NtBu)2,
a yellow oil, indicated a Z,E configuration2 and this structural
arrangement was subsequently confirmed in the solid state for
the crystalline derivative Se(NAd)2 (Ad = 1-adamantyl) by X-ray
crystallography.3 Thermal decomposition of selenium diimides
at room temperature for several days leads to the formation of
cyclic selenium imides.4,5 The major products are five-, six-, eight-
The reaction of Se(NtBu)2 with [PdCl2(NCPh)2] in a 1:1 molar
ratio in tetrahydrofuran at room temperature for 2.5 h produces
a wine-red powder with an elemental (C, H, N) composition
consistent with that expected for the 1:1 adduct [PdCl2{N,N¢-
Se(NtBu)2}] (1).‡ The 77Se NMR spectrum of 1 in MeCN at
room temperature exhibits a singlet at 1717 ppm. The resonance
falls within the range of 1700–1800 ppm typical for selenium(IV)
diimides coordinated to a transition metal.8 An X-ray structure§
of 1 (Fig. 1) revealed that the acyclic selenium(IV) diimide is
N,N¢-chelated to the palladium centre with Se–N bond lengths of
t
and fifteen-membered rings, Se3(NR)2, Se3(NR)3 (R = Bu, Ad),
Se6(NtBu)2 and Se9(NtBu)6, respectively (Scheme 1).
˚
1.731(4)–1.736(4) A. Upon complexation, the diimide expectedly
assumes the E,E-configuration, even though it is energetically less
favoured.9
Fig. 1 The molecular structure of [PdCl2{N,N¢-Se(NtBu)2}] (1) indicat-
ing the numbering of the atoms. Thermal ellipsoids are drawn at 50%
probability level. Hydrogen atoms have been omitted for clarity. Selected
◦
˚
bond lengths (A) and angles ( ): Pd1–N1 2.053(4), Pd1–N2 2.047(4),
Pd1–Cl1 2.2912(13), Pd1–Cl2 2.2767(13), Se1–N1 1.731(4), Se1–N2
1.736(4), N1–Pd1–N2 73.18(16), N1–Pd1–Cl1 100.23(11), N1–Pd1–Cl2
171.01(11), Cl1–Pd1–Cl2 88.60(5), Cl1–Pd1–N2 173.38(12), Cl2–Pd1–N2
98.01(12), N1–Se1–N2 89.64(18).
Scheme 1
Unlike monomeric sulfur diimides and dimeric tellurium di-
imides, which are thermally stable and have proven to be versatile
precursors for the preparation of metal complexes,6 the ligand
chemistry of selenium(IV) diimides is very limited and metal com-
plexes of cyclic selenium imides are unknown. Tert-butyl selenium
diimide forms an N,N¢-chelated adduct with SnCl4 7 and the reac-
When Se(NtBu)2 was treated with [PdCl2(NCPh)2] in a molar
ratio of 2:1 in tetrahydrofuran for 16 h at room temperature,
1 was not observed, and a mixture containing small amounts
of two palladium complexes [PdCl2{Se,Se¢-Se4(NtBu)3}] (2)
and [PdCl2{Se,Se¢-Se4(NtBu)4}] (3) together with seleninylamine
t
tion of Se(NR)2 (R = Bu, Ad) with Ag(CF3SO3) or Cu(CF3SO3)
t
OSe(m-NtBu)SeO4 and [PdCl2(NH2 Bu)2]10 were isolated from the
aDepartment of Chemistry, University of Oulu, P.O. Box 3000, FI-90014,
Finland
reaction solution.‡ The identities of 2 and 3 were established
by X-ray crystallography.§ The isolation of OSe(m-NtBu)SeO
bDepartment of Chemistry, University of Calgary, 2500 University Drive
NW, Calgary, Alberta T2N 1N4, Canada
t
and [PdCl2(NH2 Bu)2] from the reaction solution suggests the
partial hydrolysis of the moisture-sensitive Se(NtBu)2 under these
conditions, as previously observed.4
† CCDC reference numbers 733388–733390. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b910049k
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The molecular structure of 2·C6H5CN consists of a puckered
seven-membered SeSeNSeNSeN ring which is chelated to PdCl2
via the two selenium atoms that have two nitrogen neighbours
˚
(Fig. 2). The Pd–Se bond lengths are 2.3439(8) and 2.3830(10) A.
The metal centre Pd1 shows a slightly distorted square-planar
coordination [R < Pd1 = 359.9◦]. The Se–Se bond distance
˚
of 2.3307(11) A is comparable to the single bond lengths of
t
11
˚
˚
2.331(1) A and 2.331(3)–2.345(3) A observed for Se6(N Bu)2
and Se9(NtBu)6,11 respectively, but shorter than the value of
˚
2.404(1) A found in the five-membered ring Se3(NAd)2 in which
ring strain contributes to the bond elongation.5 As expected,
˚
the Se–N bond lengths of 1.825(5)–1.902(6) A are longer than
those of the selenium(IV) diimide ligand in 1, but comparable
to the values reported for the cyclic selenium imides Se3(NtBu)3
Fig. 3 The molecular structure of [PdCl2{Se,Se¢-Se4(NtBu)4}] (3). The
thermal ellipsoids have been drawn at 50% probability level. Hy-
drogen atoms have be◦en omitted for clarity. Selected bond distances
4
t
11
[1.825(4)–1.842(4) A], Se6(N Bu)2 [1.830(4) A], and Se9(NtBu)2
˚
11
˚
˚
[1.80(2)–1.90(1) A]. The benzonitrile molecule interacts with a
˚
˚
(A) and bond angles ( ): Pd(1)–Se(1) 2.3923(8), Pd(1)–Se(3) 2.3887(8),
chlorine atom of 2 via a weak Cl ◊ ◊ ◊ H hydrogen bond (2.7 A)
Pd(1)–Cl(1) 2.3446(14), Pd(1)–Cl(2) 2.3502(14), Se(1)–N(1) 1.842(5),
Se(2)–N(1) 1.876(4), Se(2)–N(2) 1.849(4), Se(3)–N(2) 1.844(4), Se(3)–N(3)
1.873(4), Se(4)–N(3) 1.853(4), Se(4)–N(4) 1.845(5), Se(1)–N(4) 1.886(4);
Cl(1)–Pd(1)–Cl(2) 95.14(5), Se(1)–Pd(1)–Cl(1) 81.93(4), Se(1)–Pd(1)–Se(3)
100.28(2), Se(3)–Pd(1)–Cl(2) 82.51(4).
(Fig. 2).
In this context we carried out the complexation reaction with
[PdCl2(NCPh)2] by using a THF solution of Se(NtBu)2 that had
been allowed to decompose for a prolonged period of time.13
The 77Se NMR spectrum of the resulting solution indicated the
presence of ca. 60 mol% of Se3(NtBu)3, 20 mol% of Se3(NtBu)2,
and 20 mol% of Se9(NtBu)6. Upon treatment of this solution with
[PdCl2(NCPh)2], the 77Se resonance of Se3(NtBu)3 disappeared
with the emergence of the resonance at 1487 ppm that is tentatively
assigned to cyclic tetramer Se4(NtBu)4 (vide supra), while the
resonances for [Se3(NtBu)2]n (n = 1, 3) are relatively unaffected.
A small amount of complex 2 was isolated from the solution and
identified by X-ray crystallography. Thus, the palladium centre
may engender an expansion of the six-membered selenium imide
ring to the seven- and eight-membered rings observed in 2 and 3.
Metal-mediated expansions of saturated inorganic ring systems14
have been reported for Si–O,15 As–O,16 and As–S17 heterocycles,
as well as a silicon-containing selenetane.18
In summary, the heterocycles Se4(NtBu)3 and Se4(NtBu)4 are
new members of the family of cyclic selenium imides and the
palladium complexes 2 and 3 described herein represent the first
metal complexes of this unexplored class of ligands. The formation
of the seven-membered ring Se4(NtBu)3 in reactions of either
Se(NtBu)2 or in situ-generated Se3(NtBu)3 with [PdCl2(NCPh)2]
is an incentive for further studies of the templating effect of
metal centres in reactions of selenium imides. Such studies are
in progress.
Fig. 2 The molecular structure of [PdCl2{Se,Se¢-Se4(NtBu)3}]·C6H5CN
(2·C6H5CN). The thermal ellipsoids have been drawn at 50% probability
level. Hydrogen atoms of the tert-butyl groups have been omitted for clar-
◦
˚
ity. Selected bond distances (A) and bond angles ( ): Pd(1)–Se(1) 2.3439(8),
Pd(1)–Se(2) 2.3830(10), Pd(1)–Cl(1) 2.3471(17), Pd(1)–Cl(2) 2.3417(16),
Se(1)–N(1) 1.879(5), Se(2)–N(1) 1.825(5), Se(2)–N(2) 1.902(6), Se(3)–N(2)
1.853(6), Se(4)–N(3) 1.863(5), Se(1)–N(3) 1.833(5), Se(3)–Se(4) 2.3307(11);
Cl(1)–Pd(1)–Cl(2) 94.06(6), Se(1)–Pd(1)–Cl(1) 90.10(5), Se(1)–Pd(1)–Se(2)
77.85(4), Se(2)–Pd(1)–Cl(2) 97.91(5).
The X-ray structural determination of 3 revealed an eight-
membered Se4(NtBu)4 ring linked to the PdCl2 unit via two Pd–Se
˚
bonds of 2.3887(8) and 2.3923(8) A, and a weak intramolecular
˚
Pd–Se contact of 3.1475(11) A (Fig. 3); the palladium atom is
in a distorted square-planar coordination geometry [R < Pd1 =
◦
˚
359.9 ]. The Se–N bond distances range from 1.842(5)–1.886(4) A
and correspond to the typical single bond length.12
The cyclic ligands Se4(NtBu)3 and Se4(NtBu)4 have not pre-
viously been identified among the mixture of cyclic selenium
imides formed by decomposition of Se(NtBu)2.4 However, the 77Se
NMR spectrum of the products formed by the cyclocondensation
Acknowledgements
Financial support from the Academy of Finland, Finnish Cultural
Foundation, and NSERC (Canada) is gratefully acknowledged.
t
of BuNH2 and SeCl2 shows a strong resonance at 1487 ppm,4
that may be due to the eight-membered ring Se4(NtBu)4. Since
no palladium complexes of the known cyclic selenium imides
(see Scheme 1) were formed in the reaction of Se(NtBu)2 with
[PdCl2(NCPh)2], we were interested in investigating further the
role of the palladium reagent in the formation of the new cyclic
selenium imides.
Notes and references
‡ All manipulations were carried out under dry argon. The reagents
Se(NtBu)2 and [PdCl2(NCPh)2]19 were prepared by the procedures de-
2
scribed earlier. Tetrahydrofuran and n-hexane were dried by distillation
over Na/benzophenone.
8474 | Dalton Trans., 2009, 8473–8475
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A solution of Se(NtBu)2 (0.210 g, 0.949 mmol) in THF (10 mL) was added
to a slurry of [PdCl2(NCPh)2] (0.364 g, 0.949 mmol) in THF (25 mL) at
-78 ◦C. The reaction mixture was stirred for 15 min at -78 ◦C and for a
further 2.5 h at room temperature. A wine-red precipitate of 1 was filtered
off, washed with n-hexane and dried in vacuo. Yield 0.206 g (0.517 mmol,
55%). Anal. Calcd. for C8H18Cl2N2PdSe (1): C, 24.11; H, 4.55; N, 7.03%.
Found: C, 24.48; H, 4.53, N, 6.81%. 77Se NMR (MeCN): d 1717 ppm
(referenced externally to a saturated aqueous solution of SeO2 and the
chemical shifts are reported relative to neat Me2Se [d(Me2Se) = d(SeO2) +
1302.6]). X-ray quality crystals were obtained from the MeCN solution
after 24 h at -20 ◦C.
3
-3
˚
V = 5106.4(18) A , Z = 8, Dc = 2.023 g cm , F(000) = 3008, m (Mo-Ka) =
6.649 mm-1, crystal dimensions 0.12 ¥ 0.10 ¥ 0.08 mm. Reflections (14480
total, 4892 unique, q range 2.93–25.99◦, Rint = 0.0699), the final R1
=
0.0412 and wR2 = 0.0998 [4186 reflections with Fo > 4s(Fo)] (R1 = 0.0523
and wR2 = 0.1111 all data).
1 K. B. Sharpless, T. Hori, L. K. Truesdale and C. O. Dietrich, J. Am.
Chem. Soc., 1976, 98, 269.
2 M. Herberhold and W. Jellen, Z. Naturforsch., B, 1986, 41b, 144.
3 T. Maaninen, R. Laitinen and T. Chivers, Chem. Commun., 2002, 1812.
4 T. Maaninen, T. Chivers, R. Laitinen, G. Schatte and M. Nissinen,
Inorg. Chem., 2000, 39, 5341.
5 T. Maaninen, H. M. Tuononen, G. Schatte, R. Suontamo, J. Valkonen,
R. Laitinen and T. Chivers, Inorg. Chem., 2004, 43, 2097.
6 (a) T. Chivers, A Guide to Chalcogen-Nitrogen Chemistry, World
Scientific Publishing Co. Pte. Ltd., Singapore, 2005; (b) T. Chivers, and
R. S. Laitinen, in: F. A. Devillanova, (Ed.), Handbook of Chalcogen
Chemistry, New Perspectives in Sulfur, Selenium and Tellurium, RSC
Press, Cambridge, 2007, pp. 223–285.
7 J. Gindl, M. Bjo¨rgvinsson, H. W. Roesky, C. Freire-Erdbru¨gger and
G. M. Sheldrick, J. Chem. Soc., Dalton Trans., 1993, 811.
8 M. Risto, T. T. Takaluoma, T. Bajorek, R. Oilunkaniemi, R. S. Laitinen
and T. Chivers, Inorg. Chem., 2009, 48, 6271.
A solution of Se(NtBu)2 (0.427 g, 1.930 mmol) in THF (10 mL) was
added to a solution of [PdCl2(NCPh)2] (0.370 g, 1.032 mmol) in THF
(15 mL) at -78 ◦C. The reaction mixture was stirred overnight and allowed
to warm slowly to room temperature to give a red solution. After the
reduction of the solution volume to ca. 7 mL in vacuo, the solution was
cooled to -22 ◦C to give X-ray quality red crystals of 2·C6H5CN, brown
t
crystals of 3, and crystals of OSe(m-NtBu)SeO and [PdCl2(NH2 Bu)2]. The
crystals were separated manually. The seleninylamine OSe(m-NtBu)SeO3
and [PdCl2(NH2 Bu)2]10 were identifed by comparison of the unit cell
t
parameters with the lit. values. Anal Calcd. for C19H32Cl2N4PdSe4
(2·C6H5CN): C, 28.19; H, 3.98; N, 6.92%. Found: C, 29.49; H, 3.47; N,
7.63%. Anal. Calcd. for C16H36Cl2N4PdSe4 (3): C, 24.71; H, 4.67; N, 7.21%.
Found: C, 25.81; H, 4.77; N, 7.44%. Attempts to observe the 77Se NMR
resonances for 2 and 3 were unsuccessful.
9 H. Tuononen, R. J. Suontamo, J. U. Valkonen, R. S. Laitinen and T.
Chivers, Inorg. Chem., 2003, 42, 2447.
10 N. M. Boag and S. Clapham, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2005, 61, m2172.
§ The diffraction data for 1, 2·C6H5CN and 3 were collected on a Nonius
Kappa CCD diffractometer at 100(2) K using Mo-Ka radiation (l =
˚
11 H. W. Roesky, K.-L. Weber and J. W. Bats, Chem. Ber., 1984, 117, 2686.
0.71073 A). The structures were solved by direct methods and refined on
F2.20 The calculated hydrogen atoms were included in the final refinement
˚
12 The sum of the covalent radii of selenium and nitrogen is 1.87 A; J.
˚
Emsley, The Elements, 3rd ed., Clarendon Press, Oxford, 1998.
13 It has previously been demonstrated that, after two weeks, such
a solution contains a mixture containing mainly the six-membered
ring Se3(NtBu)3 together with smaller amounts of the cyclic
oligomers[Se3(NtBu)2]n (n = 1, 3)4.
(methyl groups: C–H = 0.98 A; phenyl rings: C–H = 0.95
˚
A). Crystal data for 1: C8H18Cl2N2PdSe, M = 398.50, orthorhombic,
˚
space group Pbca, a = 13.399(3), b = 11.096(2), c = 18.280(4) A, V =
3
-3
˚
2717.8(10) A , Z = 8, Dc = 1.948 g cm , F(000) = 1552, m(Mo-Ka) =
4.406 mm-1, crystal dimensions 0.30 ¥ 0.10 ¥ 0.03 mm. Reflections (15052
total, 2660 unique, q range 3.04–25.99◦, Rint = 0.0892), the final R1
=
14 For a brief review, see J. S. Ritch and T. Chivers, Angew. Chem., Int.
Ed., 2007, 46, 4610.
0.0403 and wR2 = 0.0691 [2150 reflections with Fo > 4s(Fo)] (R1 = 0.0608
and wR2 = 0.0740 all data).
15 A. Decken, F. A. LeBlanc, J. Passmore and X. Wang, Eur. J. Inorg.
Chem., 2006, 4033.
16 M. Heller, O. Teichert and W. S. Sheldrick, Z. Anorg. Allg. Chem., 2005,
631, 709.
17 O. M. Kekia and A. L. Rheingold, Organometallics, 1998, 17, 726.
18 E. Block, E. V. Dikarev, R. S. Glass, J. Jin, B. Li, X. Li and S.-Z. Zhang,
J. Am. Chem. Soc., 2006, 128, 14949.
19 M. S. Kharasch, R. C. Seyler and F. R. Mayo, J. Am. Chem. Soc., 1938,
60, 882.
20 G. M. Sheldrick, Acta Crystallogr., Sect. A, 2008, 64, 112.
Crystal data for 2·C6H5CN: C19H32Cl2N4PdSe4, M = 809.63, triclinic,
˚
space group P-1, a = 10.174(2), b = 11.088(2), c = 12.827(3) A, a =
◦
3
˚
71.65(3), b = 86.40(3), g = 75.21(3) , V = 1327.7(6) A , Z = 2, Dc =
2.025 g cm-3, F(000) = 780, m (Mo-Ka) = 6.398 mm-1, crystal dimensions
0.20 ¥ 0.20 ¥ 0.10 mm. Reflections (19036 total, 5100 unique, q range
2.98–26.00◦, Rint = 0.0663), the final R1 = 0.0446 and wR2 = 0.0990 [4127
reflections with Fo > 4s(Fo)] (R1 = 0.0611 and wR2 = 0.1076 all data).
Crystal data for 3: C16H36Cl2N4PdSe4, M = 777.63, monoclinic, space
◦
˚
group C2/c, a = 26.816(5), b = 9.7383(19), c = 20.082(4) A, b = 103.16(3) ,
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8473–8475 | 8475
©