Elsevier

Inorganica Chimica Acta

Volume 462, 1 June 2017, Pages 209-214
Inorganica Chimica Acta

Research paper
Piperidin-1-ylamidomethyltellurium derivatives: Synthesis and solid state structures

https://doi.org/10.1016/j.ica.2017.03.032Get rights and content

Highlights

  • Te(0) and Te(II) insert readily into the C–Br bond of α-bromoacetylpiperidine.

  • Reduction of (C5H10NCOCH2)2TeBr2 affords a telluroether, but (C5H10NCOCH2)ArTeBr2 give Ar2Te2.

  • Piperidin-1-ylamidomethyl group acts as a small-bite (C, O) chelating ligand towards Te(IV).

  • Te involved associative forces are absent in the lattice of (C5H10NCOCH2)2TeX2 (X = Br, I).

Abstract

Oxidative insertion of low valent tellurium, Te(0) and Te(II), into the Csingle bondBr bond of α-bromoacetylpiperidine proceeds readily under mild conditions and provides a direct synthetic route to stable, crystalline piperidin-1-ylamidomethyltellurium(IV) dibromides, (C5H10NCOCH2)2TeBr2, 1b and (C5H10NCOCH2)ArTeBr2 (Ar = 2,4,6-Me3C6H2, 2b; 1-C10H7, 3b; 4-MeC6H4, 4b). While the bisulfite reduction of 1b affords a yellow coloured telluroether, (C5H10NCOCH2)2Te, 1 as an oil, that of the unsymmetrical diorganotellurium dibromides, (C5H10NCOCH2)ArTeBr2 leads to the isolation of the respective diarylditellurides, ArTeTeAr. The symmetrical telluroether, 1 adds dihalogens oxidatively to give piperidin-1-ylamidomethyltellurium(IV) dihalides, (C5H10NCOCH2)2TeX2 (X = Cl, 1a; Br, 1b and I, 1c;). All the new piperidin-1-ylamidomethyltellurium derivatives have been characterized by elemental and 1H, 13C, 125Te NMR spectral analyses. Single-crystal X-ray diffraction data for 1b and 1c indicated a butterfly molecular shape for the two halo analogues in which the six-member heterocyclic rings in the organic ligands retain the chair conformation of the independent piperidine molecule. The piperidin-1-yl appended organic ligand invariably results in the amido O atom being involved in an intramolecular Te O secondary bonding interaction and acts as a small-bite (C, O) chelating agent, at least in the solid state. Steric congestion around the six-coordinate Te(IV) atom and the partial positive charge on N owing to the resonating character of the Npartial double bond, top dashedCpartial double bond, top dashedO amido group prevents these atoms from participating in the intermolecular associative forces. Instead, the weak Csingle bondH⋯O and Csingle bondH⋯Br interactions take centre-stage in the solid state self-assembly.

Introduction

The O-hydro-C-alkyl/aryl addition of Grignard reagents or organolithiums to aldehydes or ketones is an established method to prepare alcohols. Such reagents are however inaccessible in cases where the organic halide possesses a functional group. It is therefore not surprising that the C-bonded acyl, alkoxycarbonyl and amido (N-bonded as well) functionalized organometallic derivatives are known to only a limited extent. In the Reformatsky reaction, the addition of α-haloesters or α-halo N,N-disubstituted amides to an aldehyde or a ketone in the presence of zinc metal is believed to involve an organozinc compound, O=C(Y)CH2ZnBr (similar to RMgX) as an intermediate, albeit the alternative O-bonded structure CH2=C(Y)OZnBr cannot be ruled out on the basis of the X-ray diffraction data for the solid intermediate isolated in the reaction between t-BuOCOCH2Br and Zn [1].

The carbonyl activation of Csp3–X bond to insert elemental Te has been studied and practiced in our laboratory to obtain functionalized diorganotellurium diiodies from the organic iodides, YCOCH2I (Y = R, RO, NH2) [2], [3], [4]. This strategy has been successfully applied for the direct synthesis of the corresponding dibromides from α-bromo acylmethanes [5], but α-bromo alkoxycarbonylmethanes failed to react with tellurium powder when heated together up to about 100 °C [4]. Recently, the oxidative addition of α-bromo acetamides derived mainly from acyclic amines to elemental tellurium has been reported [6]. The structural diversity and broad range of pharmacological properties of natural and synthetic piperidine derivatives in general and N-acylpiperidine in particular [7], [8] prompted us to prepare tellurated N-acyl piperidines by a simple method and study (i) their reactions with aldehydes and ketones (cf. Reformatsky reagents) and (ii) change in the conformation of the heterocyclic ring upon telluration.

Section snippets

General procedures

Preparative work was performed under dry nitrogen. All solvents were purified and dried before use. α-Bromacetylpiperidine was prepared by slight modification in the literature method [9]. Bis(1-naphthyl)ditelluride, dimesitylditelluride and ditolylditelluride were prepared by reported methods [10], [11], [12]. Melting points were recorded in capillary tubes and are uncorrected. Microanalyses were carried out using a Carlo Erba 1108 analyzer. NMR spectra were recorded in CDCl3 on Bruker DRX300 (

Synthesis and spectra

α-Bromoacetylpiperidine adds oxidatively to tellurium powder under mild conditions to afford bis{(piperidin-1-yl)amidomethyl}tellurium dibromide (1b) and to aryltellurium(II) bromides (prepared in situ from the stoichiometric amounts of Br2 and diarylditellurides, ArTeTeAr) to give alkylaryltellurium dibromides, (C5H10NCOCH2)ArTeBr2 (Ar = 2,4,6-Me3C6H2, Mes, 2b; 1-C10H7, Nap, 3b; 4-MeC6H4, Tol, 4b (Scheme 1). While partial biphasic reduction of 1b with Na2S2O5 yields the symmetrical telluroether,

Conclusions

The piperidin-1-yl appended amidomethyl bromide adds readily to the low valent tellurium species to provide single-step syntheses of dialkyl- and alkylaryltellurium dibromides (1b4b). The symmetrical telluroether, bis(piperidin-1-ylamidomethyl)telluride (1) is obtained by the reduction of the parent Te(IV) dibromide (1b) with aqueous sodium sulfite solution. However, the (piperidin-1-ylamidomethyl)aryltellurium bromides (2b4b) are unstable in solution towards symmetrization and afford Ar2TeX2

Acknowledgments

SM is thankful to the Department of Science and Technology, Government of India, New Delhi, India for financial assistance under Women Scientists Fellowship Scheme (SR/WOS-A/CS-55/2012). The authors are thankful to the Director, C.D.R.I., Lucknow for 1H NMR and C, H analyses, at the Sophisticated Analytical Instrument Facility (SAIF). The authors also wish to acknowledge the assistance of Dr. Matthias Zeller in the collection of diffraction data for compound 1c and NSF Grant CHE 0087210, Ohio

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