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

Abstract

Abstract. The syntheses of lithium and alkaline earth metal complexes with the bis(borane-diphenylphosphanyl)amido ligand (1-H) of molecular formulas [{κ 2 -N(PPh 2 (BH 3 )) 2 }Li(THF) 2 ] (2) and (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

Small Chains of Main Group Elements by BH3 Adduct Formation of tBu2E‐N(H)‐EtBu2 (E = P, As)

“…In comparison to these examples, the binding motif in 4a is rather unusual. Moreover, the corresponding lithium complex of the phenyl‐substituted bis ‐borane adduct [Ph 2 P(BH 3 )‐N‐P(BH 3 )Ph 2 ] – exhibits a central lithium atom in a distorted tetrahedral coordination environment by two THF‐ligands and the κ 2 ‐coordinated bis ‐borane . In this compound, the Li–N distances are longer (2.08 Å) than in 4a and the phosphine‐borane group binds in a η 1 ‐fashion.…”

“…Moreover, the corresponding lithium complex of the phenyl-substituted bis-borane adduct [Ph 2 P(BH 3 )-N-P(BH 3 )Ph 2 ]exhibits a central lithium atom in a distorted tetrahedral coordination environment by two THF-ligands and the κ 2 -coordinated bis-borane. [46] In this compound, the Li-N distances are longer (2.08 Å) than in 4a and the phosphineborane group binds in a η 1 -fashion. However, the observed bond lengths in 4a are very similar to related tert-butyl-substituted chain compound tBu 2 P(BH 3 )-NH-BH-NH-P(BH 3 )tBu 2 , which was selectively obtained by the reaction of tBu 2 P-NH 2 with BH 3 •SMe 2 .…”

Alkali and Alkaline Earth Metal Complexes as Versatile Catalysts for Ring‐Opening Polymerization of Cyclic Esters

“…Further, our group introduced a series of monomeric lithium complexes ( 40 – 41, 48 ), dimeric sodium complexes ( 42 – 44 ), and potassium ( 45 – 47 ) complexes bearing 2‐picolylaminod iphenylphosphane chalcogenide 1,2‐phenylene (bis‐diphenyl‐phosphino‐thioic/selenoic amines) and bis(diphenylphosphino‐borane)amido ligands [57–59] . Even the Ae metal complexes with these ligands have proved as superior iso‐selective catalysts in rac ‐LA and lactone chemistry, the corresponding alkali metal complexes are not competent catalysts for the ROP of rac ‐LA (Scheme 3).…”

“…Further, our group has reported the syntheses of alkaline earth metal complexes of bis(diphenylphosphino‐borane)amido ligand with molecular formulas [{κ 3 ‐N(PPh 2 (BH 3 )) 2 } 2 M(THF) 2 ] [(M=Ca ( 93 ), Sr ( 94 ), Ba ( 95 )] (Scheme 11). [59] The molecular structure of the barium complex ( 95 ) was established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of complex 95 , κ 3 coordination mode from the ligand was observed and the barium ion adopted a distorted octahedral geometry.…”

Lithium Quinolyl‐Amidinates Efficiently Promoting Ring‐Opening Polymerization of ε‐Caprolactone: Synthesis and 7Li NMR Spectroscopic Studies

“…Concern over petrochemical resources has been driving research attention toward the synthesis of polymeric materials from renewable resources The ring‐opening polymerization (ROP) of cyclic esters promoted by metal catalysts is the most promising method of preparing biomedical polyesters, because the catalysts use nontoxic metals, such as alkali and alkaline‐earth metals, and Al, Mg, and Zn complexes, of which lithium compounds have become interesting, due to their advantage of being efficient, cheap, nontoxic, and having high activity, as well as various types of coordination sites . Initially, simple lithium compounds, such as lithium tert ‐butoxide, butyllithium, and lithium chloride, were used as catalysts in ring‐opening polymerization of cyclic esters .…”