Synthesis and structural characterization of diorganotin(IV) complexes with a tridentate N‐heterocyclic podand ligand and investigation of their catalytic activity in Baeyer–Villiger oxidation of cyclic ketones to lactones

Applied Organometallic Chemistry, vol. 37

Abstract

Diorganotin(IV) complexes of composition [Me2SnL] (1), [n‐Bu2SnL] (2), and [Bz2SnL] (3) were synthesized by reacting the N2,N6‐di(pyridin‐2‐yl)pyridine‐2,6‐dicarboxamide pro‐ligand (H2L, where H2 denotes the two acidic protons) with Me2SnO, n‐Bu2SnO, and Bz2SnO, respectively, in refluxing toluene. The amide ligand leads to highly stable diorganotin(IV) complexes via the dianionic tridentate donor set (Npy, N−, N−) with pendent pyridine arms, and the coordination domain is completed by the respective two alkyl ligands. Solution‐state structures of the compounds 1–3 were studied by 1H, 13C, and 119Sn nuclear magnetic resonance (NMR) spectroscopy, revealing that the complexes adopt a five‐coordinate structure in non‐coordinating solvent. Additionally, homogenity and purity of the bulk materials of 1–3 were judged using the high‐resolution mass spectrometry in acetonitrile solution. The molecular and crystal structures of 1·0.5C6H6, 2, and 3 in the solid phase were established by single‐crystal X‐ray diffraction analysis. For all three compounds, the core defined by the rigid tridentate pyridine dicarboxamide ligand and the Sn‐coordinating C atoms adopts nearly C2v symmetry and thus matches none of the most popular geometries for five‐coordinated species, namely square‐pyramidal or trigonal‐bipyramidal coordination. Thermogravimetric analysis (TGA) was performed to probe the thermal stabilities of 1–3. The results serve as a basis for designing highly efficient diorganotin(IV) mimics for catalytic applications. Catalytic studies of ε‐caprolactone formation via Baeyer–Villiger oxidation of cyclohexanone with aqueous H2O2 were performed under microwave (MW) irradiation. The consequences of several reaction parameters like catalyst quantity, time, temperature, and solvent were studied.

Authors 9

1. Tushar S. Basu Baul corresponding

   North Eastern Hill University

   Affiliation as printed

   Centre for Advanced Studies in Chemistry North‐Eastern Hill University, NEHU Permanent Campus Shillong India

   Sophisticated Analytical Instrument Facility North‐Eastern Hill University, NEHU Permanent Campus Shillong India

   Centre for Advanced Studies in Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Shillong, India

   Sophisticated Analytical Instrument Facility, North-Eastern Hill University, NEHU Permanent Campus, Shillong, India

2. Avishek Khatiwara

   North Eastern Hill University

   Affiliation as printed

   Centre for Advanced Studies in Chemistry North‐Eastern Hill University, NEHU Permanent Campus Shillong India

   Centre for Advanced Studies in Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Shillong, India

3. Maheswara Rao Addepalli

   North Eastern Hill University · Jawaharlal Nehru Technological University-Gurajada, Vizianagaram

   Affiliation as printed

   Centre for Advanced Studies in Chemistry North‐Eastern Hill University, NEHU Permanent Campus Shillong India

   Department of Basic Sciences and Humanities and Social Sciences Jawaharlal Nehru Technological University‐Gurajada Vizianagaram India

   Centre for Advanced Studies in Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Shillong, India

   Department of Basic Sciences and Humanities and Social Sciences, Jawaharlal Nehru Technological University-Gurajada, Vizianagaram, India

4. Bietlaichhai Hlychho

   North Eastern Hill University

   Affiliation as printed

   Centre for Advanced Studies in Chemistry North‐Eastern Hill University, NEHU Permanent Campus Shillong India

   Centre for Advanced Studies in Chemistry, North-Eastern Hill University, NEHU Permanent Campus, Shillong, India

5. Andrew Duthie

   Deakin University

   Affiliation as printed

   School of Life & Environmental Science Deakin University Geelong Victoria Australia

   School of Life & Environmental Science, Deakin University, Geelong, Victoria, Australia

6. Hans Gildenast Aachen Institut für Anorganische Chemie

   RWTH Aachen University

   Affiliation as printed

   Institut für Anorganische Chemie RWTH Aachen University Aachen Germany

7. Ulli Englert Aachen Institut für Anorganische Chemie

   RWTH Aachen University

   Affiliation as printed

   Institut für Anorganische Chemie RWTH Aachen University Aachen Germany

8. Abdallah G. Mahmoud

   University of Lisbon · Instituto Superior Técnico · Centro de Química Estrutural · Helwan University

   Affiliation as printed

   Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal

   Department of Chemistry, Faculty of Science Helwan University Cairo Egypt

   Department of Chemistry, Faculty of Science, Helwan University, Cairo, Egypt

9. Maria Fátima C. Guedes da Silva corresponding

   University of Lisbon · Instituto Superior Técnico · Centro de Química Estrutural

   Affiliation as printed

   Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal

   Departamento de Engenharia Química, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal