O'HARE GROUP

Permethylindenyl

A series of group 3, 4 and 13 permethylindenyl chrloride, aryloxide, and borohydride complexes have been synthesised and fully characterised. Their activities for the ring-opening polymerisation (ROP) of L-, D-, meso- and rac-lactide have been tested. The ROP of L- and rac-lactide produced isotactic polylactide (PLA) and moderately heterotactic PLA (Pr = 0.68–0.72), respectively. Good agreement between experimental and theoretical molecular weights of PLA (Mn) and relatively narrow dispersities were obtained. 

Few initiators displayed second order dependence on monomer concentration and produced isotactic and heterotactic (Pr = 0.81) polylactides for the polymerisation of L-, D- and rac-lactide respectively. The effects of temperature, catalyst concentration, co-initiator concentration, solvent and scale were studied. 

 

Graphical abstract: Constrained geometry scandium permethylindenyl complexes for the ring-opening polymerisation of l- and rac-lactideGraphical abstract: Group 4 permethylindenyl complexes for the polymerisation of l-, d- and rac-lactide monomers

 

“Constrained geometry scandium permethylindenyl complexes for the ring-opening polymerisation of L- and rac-lactide”. N. Diteepeng, J.-C. Buffet, Z. R. Turner and D. O’Hare, Dalton Trans., 201948, 16099.

“Group 4 permethylindenyl complexes for the polymerisation of L-, D- and rac-lactide monomers”. J. V. Lamb, J.-C. Buffet, J. E. Matley, C. M. R. Wright, Z. R. Turner and D. O’Hare, Dalton Trans., 201948, 2510.

 

Permethylpentalene

A family of group 4 alkoxide and aryloxide complexes of a chiral cyclopentadienyl-derived (hydro)permethylpentalenyl ligand (C8Me6H; Pn*(H)) have been prepared and fully characterised. Both racemic and enantiopure complexes of all group 4 congeners were prepared with a wide variety of alkoxide and aryloxide ligands. The complexes were investigated as initiators for the ring-opening polymerization of L- and rac-lactide in order to ascertain if these mixtures of diastereomers could exert any stereocontrol on the resulting polymerization. Kinetic studies were completed to explore the effects of the metal cation, chiral (hydro)permethylpentalenyl ligand, ancillary ligands, initiator concentration and temperature. Both Pn*(H)Zr(S–OCH{CH3}C6H5)3 and Pn*(H)Zr(rac-OCH{CH3}C6H5)3 demonstrated very high rates of propagation for l- and rac-lactide (1.885 < kobs < 3.442 h–1) at 100 °C. 

https://pubs.acs.org/na101/home/literatum/publisher/achs/journals/content/orgnd7/2014/orgnd7.2014.33.issue-14/om500634a/production/images/medium/om-2014-00634a_0022.gif

“Chiral group 4 cyclopentadienyl complexes and their use in polymerization of lactide monomers”. Z. R. Turner, J.-C. Buffet and D. O’Hare, Organometallics201433, 3891.

 

Metallocenes

A family of well-defined cyclopentadienyl and indenyl group 4 complexes has been prepared. The complexes were investigated as catalysts for the polymerization of L- and rac-lactide. (Ind)2ZrMe(OtBu) was shown to be the fastest catalyst. At 100 °C, the rates of polymerization (kobs) for L- and rac-lactide were very similar (0.317 and 0.293 h−1 respectively). However, at 80 °C it was found that polymerization of L-LA (kobs = 0.217 h−1) was twice as fast as rac-LA (kobs = 0.120 h−1).

https://ars.els-cdn.com/content/image/1-s2.0-S0022328X15301959-fx1.jpg

“Zirconocene alkoxides and aryloxides for the polymerization of L- and rac-lactide”. J.-C. Buffet, G. R. Harris, J. J. Coward, T. A. Q. Arnold, Z. R. Turner and D. O’Hare, J. Organomet. Chem.2016801, 87.