Group 1 and group 2 metal complexes supported by a bidentate bulky iminopyrrolyl ligand: synthesis, structural diversity, and ε-caprolactone polymerization study.
We report here a series of alkali and alkaline earth metal complexes, each with a bulky iminopyrrolyl ligand [2-(Ph3CN=CH)C4H3NH] (1-H) moiety in their coordination sphere, synthesized using either alkane elimination or silylamine elimination methods or the salt metathesis route. The lithium salt of molecular composition [Li(2-(Ph3CN=CH)C4H3N)(THF)2] (2) was prepared using the alkane elimination method, and the silylamine elimination method was used to synthesize the dimeric sodium and tetra-nuclear potassium salts of composition [(2-(Ph3CN=CH)C4H3N)Na(THF)]2 (3) and [(2-(Ph3CN=CH)C4H3N)K(THF)0.5]4 (4) respectively. The magnesium complex of composition [(THF)2Mg(CH2Ph){2-(Ph3CN=CH)C4H3N}] (5) was synthesized through the alkane elimination method, in which [Mg(CH2Ph)2(OEt2)2] was treated with the bulky iminopyrrole ligand 1-H in 1 : 1 molar ratio, whereas the bis(iminopyrrolyl)magnesium complex [(THF)2Mg{2-(Ph3CN=CH)C4H3N}2] (6) was isolated using the salt metathesis route. The heavier alkaline earth metal complexes of the general formula {(THF)nM(2-(Ph3CN=CH)C4H3N)2} [M = Ca (7), Sr (8), and n = 2; M = Ba (9), n = 3] were prepared in pure form using two synthetic methods: in the first method, the bulky iminopyrrole ligand 1-H was directly treated with the alkaline earth metal precursor [M{N(SiMe3)2}2(THF)n] (where M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent at ambient temperature. The complexes 7-9 were also obtained using the salt metathesis reaction, which involves the treatment of the potassium salt (4) with the corresponding metal diiodides MI2 (M = Ca, Sr and Ba) in 2 : 1 molar ratio in THF solvent. The molecular structures of all the metal complexes (1-H, 2-9) in the solid state were established through single-crystal X-ray diffraction analysis. The complexes 5-9 were tested as catalysts for the ring-opening polymerization of ε-caprolactone. High activity was observed in the heavier alkaline earth metal complexes 7-9, with a very narrow polydispersity index in comparison to that of magnesium complexes 5 and 6.
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi - 502 285, Sangareddy, Telangana, India. tpanda@iith.ac.in.
Ravi K
RK
Kottalanka
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi - 502 285, Sangareddy, Telangana, India. tpanda@iith.ac.in.
A
A
Harinath
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi - 502 285, Sangareddy, Telangana, India. tpanda@iith.ac.in.
Supriya
S
Rej
Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi - 502 285, Sangareddy, Telangana, India. tpanda@iith.ac.in.
Tarun K
TK
Panda
D002208:Caproates / Q000138:chemical synthesis / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D007097:Imines / Q000138:chemical synthesis / Q000737:chemistry; D007783:Lactones / Q000138:chemical synthesis / Q000737:chemistry*; D008024:Ligands; D008673:Metals, Alkaline Earth / Q000138:chemical synthesis / Q000737:chemistry*; D008958:Models, Molecular; D058105:Polymerization; D011758:Pyrroles / Q000138:chemical synthesis / Q000737:chemistry*
D002208:Caproates; D056831:Coordination Complexes; D007097:Imines; D007783:Lactones; D008024:Ligands; D008673:Metals, Alkaline Earth; D011758:Pyrroles; C121056:caprolactone