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Monomeric Ti(IV) homopiperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide.

Hancock SL, Mahon MF, Jones MD - Chem Cent J (2013)

Bottom Line: Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation.However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution.This shows the potential applicability of Ti(IV) to initiate the polymerisations.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. mj205@bath.ac.uk.

ABSTRACT

Background: The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics. Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation. Thus, in this paper we report the synthesis and characterisation of a series of monometallic homopiperazine Ti(IV) complexes where we have systematically varied the sterics of the phenol moieties.

Results: When the ortho substituent of the ligand is either a Me, tBu or amyl then the β-cis isomer is isolated exclusively in the solid-state. Nevertheless, in solution multiple isomers are clearly observed from analysis of the NMR spectra. However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution. The complexes have been screened for the polymerisation of rac-lactide in solution and under the industrially preferred melt conditions. Narrow molecular weight material (PDI 1.07 - 1.23) is formed under melt conditions with controlled molecular weights.

Conclusions: Six new Ti(IV) complexes are presented which are highly active for the polymerisation. In all cases atactic polymer is prepared with predictable molecular weight control. This shows the potential applicability of Ti(IV) to initiate the polymerisations.

No MeSH data available.


Related in: MedlinePlus

Solid-state structure for Ti(6)(OiPr)2 in the trans-configuration. Ellipsoids are shown at the 30% probability level, hydrogen atoms have been removed for clarity.
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Figure 3: Solid-state structure for Ti(6)(OiPr)2 in the trans-configuration. Ellipsoids are shown at the 30% probability level, hydrogen atoms have been removed for clarity.

Mentions: The solid-state structures Ti(2,4-6)(OiPr)2 have been determined by single crystal X-ray diffraction, and have yielded monometallic complexes with the titanium metal centres adopting a pseudo octahedral configuration. The structure obtained for Ti(2)(OiPr)2 is given as a representative example (Figure 2). Ti(2,4,5)(OiPr)2 adopt a β-cis configuration in the solid-state, this is in contrast to the Zr(IV)/Hf(IV) analogues which formed trans complexes. However, with less steric bulk in the ortho-phenol position a pseudo trans-octahedral titanium complex supported by a homopiperazine salan ligand, Ti(6)(OiPr)2 (Figure 3), was isolated.


Monomeric Ti(IV) homopiperazine complexes and their exploitation for the ring opening polymerisation of rac-lactide.

Hancock SL, Mahon MF, Jones MD - Chem Cent J (2013)

Solid-state structure for Ti(6)(OiPr)2 in the trans-configuration. Ellipsoids are shown at the 30% probability level, hydrogen atoms have been removed for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750606&req=5

Figure 3: Solid-state structure for Ti(6)(OiPr)2 in the trans-configuration. Ellipsoids are shown at the 30% probability level, hydrogen atoms have been removed for clarity.
Mentions: The solid-state structures Ti(2,4-6)(OiPr)2 have been determined by single crystal X-ray diffraction, and have yielded monometallic complexes with the titanium metal centres adopting a pseudo octahedral configuration. The structure obtained for Ti(2)(OiPr)2 is given as a representative example (Figure 2). Ti(2,4,5)(OiPr)2 adopt a β-cis configuration in the solid-state, this is in contrast to the Zr(IV)/Hf(IV) analogues which formed trans complexes. However, with less steric bulk in the ortho-phenol position a pseudo trans-octahedral titanium complex supported by a homopiperazine salan ligand, Ti(6)(OiPr)2 (Figure 3), was isolated.

Bottom Line: Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation.However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution.This shows the potential applicability of Ti(IV) to initiate the polymerisations.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. mj205@bath.ac.uk.

ABSTRACT

Background: The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics. Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation. Thus, in this paper we report the synthesis and characterisation of a series of monometallic homopiperazine Ti(IV) complexes where we have systematically varied the sterics of the phenol moieties.

Results: When the ortho substituent of the ligand is either a Me, tBu or amyl then the β-cis isomer is isolated exclusively in the solid-state. Nevertheless, in solution multiple isomers are clearly observed from analysis of the NMR spectra. However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution. The complexes have been screened for the polymerisation of rac-lactide in solution and under the industrially preferred melt conditions. Narrow molecular weight material (PDI 1.07 - 1.23) is formed under melt conditions with controlled molecular weights.

Conclusions: Six new Ti(IV) complexes are presented which are highly active for the polymerisation. In all cases atactic polymer is prepared with predictable molecular weight control. This shows the potential applicability of Ti(IV) to initiate the polymerisations.

No MeSH data available.


Related in: MedlinePlus