title: Titanium, zinc and alkaline-earth metal complexes supported by bulky O,N,N,O-multidentate ligands: syntheses, characterisation and activity in cyclic ester polymerisation.
abstract: The reactions of the bulky amino-bis(phenol) ligand Me(2)NCH(2)CH(2)N[CH(2)-3,5-Bu(t)(2)-C(6)H(2)OH-2](2)(1-H(2)) with Zn[N(SiMe(3))(2)](2)(4), [Mg[N(SiMe(3))(2)](2)](2)(5) and Ca[N(SiMe(3))(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 N(2)O(3) donor set, while the sixth is taken up by an intramolecular close contact to an o-Bu(t) substituent, a rare case of a Ca...H-C agostic interaction (Ca...H distances of 2.37 and 2.41 Angstroms). Another sterically hindered calcium complex, Ca[2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)O](2)(THF)(2).(C(7)H(8))(2/3)(7), was prepared by reaction of 6 with the iminophenol 2-Bu(t)-6-(C(6)F(5)N=CH)C(6)H(3)OH (3-H). According to the crystal structure 7 is monomeric and octahedral, with trans THF ligands. The complex Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(2)(2-Ti) was prepared by treatment of Ti(OPr(i)(4)) with the new amino-bis(phenol) Me(2)NCH(2)CH(2)N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)OH-2](2)(2-H(2)). The reduction of 2-Ti with sodium amalgam gave the titanium(III) salt Ti[N[CH(2)-3-Bu(t)-5-Me-C(6)H(2)O-2](2)[CH(2)CH(2)NMe(2)]](OPr(i))(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 pi-bonding from the oxygen atoms of the isopropoxide groups to titanium. 1-Ca and 8 were active initiators for the ring-opening polymerisation of epsilon-caprolactone (up to 97% conversion of 200 equivalents in 2 hours) and yielded polymers with narrow molecular weight distributions.
authors.affiliation: Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich, UK.
authors.forename: Yann
authors.initials: Y
authors.lastname: Sarazin
authors.forename: Ruth H
authors.initials: RH
authors.lastname: Howard
authors.forename: David L
authors.initials: DL
authors.lastname: Hughes
authors.forename: Simon M
authors.initials: SM
authors.lastname: Humphrey
authors.forename: Manfred
authors.initials: M
authors.lastname: Bochmann
mesh_terms: D001672:Biocompatible Materials / Q000138:chemical synthesis*; D018360:Crystallography, X-Ray; D003500:Cyclization; D004952:Esters / Q000737:chemistry*; D008024:Ligands; D008673:Metals, Alkaline Earth / Q000737:chemistry*; D008970:Molecular Weight; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010100:Oxygen / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D013237:Stereoisomerism; D014025:Titanium / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D001672:Biocompatible Materials; D004952:Esters; D008024:Ligands; D008673:Metals, Alkaline Earth; D009942:Organometallic Compounds; D011108:Polymers; C102815:titanium isopropoxide; D014025:Titanium; D015032:Zinc; D010100:Oxygen