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Dalton Trans., 2006, 340 - 350, DOI: 10.1039/b511851d
Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation
Yann Sarazin, Ruth H. Howard, David L. Hughes, Simon M. Humphrey and Manfred Bochmann
The reactions of the bulky amino-bis(phenol) ligand Me2NCH2CH2N{CH2-3,5-But2-C6H2OH-2}2( 1- H2) with Zn[N(SiMe3)2]2( 4), [Mg{N(SiMe3)2}2]2( 5) and Ca[N(SiMe3)2]2(THF)2( 6) yield the complexes 1- Zn, 1- Mg and 1- Ca in good yields. The X-ray structure of 1- Ca showed the complex to be dimeric, with calcium in a distorted octahedral coordination geometry. Five of the positions are occupied by an N2O3 donor set, while the sixth is taken up by an intramolecular close contact to an o-But substituent, a rare case of a Ca
H–C agostic interaction (CaH distances of 2.37 and 2.41 Å). Another sterically hindered calcium complex, Ca{2-But-6-(C6F5N
CH)C6H3O}2(THF)2·(C7H8)2/3( 7), was prepared by reaction of 6 with the iminophenol 2-But-6-(C6F5NCH)C6H3OH ( 3- H). According to the crystal structure, 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N{CH2-3-But-5-Me-C6H2O-2}2{CH2CH2NMe2}](OPri)2( 2- Ti) was prepared by treatment of Ti(OPri4) with the new amino-bis(phenol) Me2NCH2CH2N{CH2-3-But-5-Me-C6H2OH-2}2( 2- H2). The reduction of 2- Ti with sodium amalgam gave the titanium(III) salt Ti[N{CH2-3-But-5-Me-C6H2O-2}2{CH2CH2NMe2}](OPri)2·Na(THF)2( 8). A comparison of the X-ray structures of 2- Ti and 8 showed that the additional electron in 8 significantly reduced the intensity of the 
-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1- Ca and 8 were active initiators for the ring-opening polymerisation of 
-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.
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