Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone
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| Authors: | Jayeeta Bhattacharjee Suman Das T. Dhileep N. Reddy Hari Pada Nayek Bhabani S. Mallik Tarun K. Panda |
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| Affiliation: | 1. Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi – 502 285, Sangareddy, Telangana, India;2. Department of Applied Chemistry, Indian School of Mines, Dhanbad, 826004, Jharkhand, India |
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| Abstract: | The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ2‐N(PPh2(BH3))2}Li(THF)2] ( 2 ) and [{κ3‐N(PPh2(BH3))2}2M(THF)2] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH3 group in κ2‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ3‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described. |
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| Keywords: | Lithium Calcium Barium Boranes Metallacycles Chelating ligands |
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