Iron(II) β-ketiminate complexes as mediators of controlled radical polymerisation

A series of tridentate, ONO- and ONN-chelating β-ketiminate ligands were synthesised via condensation reactions, and complexed with iron(ii) using [Fe(N(SiMe3)2)2THF]. The complexation reactions proceeded in high yields to generate novel, monomeric, tetracoordinate iron(ii) complexes, each bearing a bis(trimethylsilyl)amide ligand, as confirmed by X-ray crystallography. These complexes were amenable to further reaction (protonolysis) with alcohols and phenols, generating alkoxide/phenolate-containing complexes that were dimeric in the solid state. All complexes synthesised were screened as potential mediators of the controlled radical polymerisation (CRP) of styrene and methyl methacrylate under both atom transfer radical polymerisation (ATRP) and organometallic mediated radical polymerisation (OMRP) conditions. Whilst all of the complexes were relatively poor ATRP mediators under the conditions used here, regardless of monomer choice, dispersities (Đ) as low as 1.58 for styrene and 1.23 for methyl methacylate polymerisation under OMRP conditions could be achieved. The better performance in methacrylate polymerisation suggests the formation of a stronger metal-carbon bond in these systems. In particular, the use of a β-ketiminate ligand functionalised with an N,N-dimethylethylene pendant arm and a 2,6-diphenylphenolate ligand affords a potential Fe-based mediator of methyl methacrylate OMRP.


Iron(II) β-ketiminate complexes as mediators of controlled radical polymerisation
Benjamin R. M. Lake a and Michael.P. Shaver* a a EaStCHEM School of Chemistry, University of Edinburgh, Edinburgh, EH9 EJJ, UK.

CONTENT GPC DATA
Table S1 ATRP of styrene

Table S2
ATRP of MMA

Table S3
OMRP of styrene

Table S4
OMRP of MMA

Figure S1
First-order kinetic plot for the OMRP of MMA mediated by complex 1a

Figure S14 Complex 3b
Note.Crystals of complex 3b were generally observed to be of very poor quality.However, a suitable single crystal was eventually found and a data set obtained.The asymmetric unit of complex 3b was found to contain two crystallographically-distinct [Fe(L)OBn] units, with each representing half of a (µ 2 -OBn)2 bridged dimer.The two halves of each dimer are crystallographically related through inversion.After some preliminary structural refinement, a very large residual electron density peak was observed in the vicinity of Fe2, along with further, more diffuse electron density.Therefore, the [Fe(L)OBn] unit initially containing Fe2 was modelled as being split over two positions with SOFs of 0.75 for the major component (containing Fe2A) and 0.25 for the minor component (containing Fe2B).One of the β-ketiminate methyl groups (C23) was best modelled as being common to both disorder components.Unfortunately, the OBn group of the minor disorder component appeared disordered further, and could not be satisfactorily refined without the use of EADP constraints.Therefore, this group was refined isotropically.The disordered nature of this structure accounts for the large number of checkCIF alerts.

Figure S16 Complex 3c
Note.Regions of diffuse, poorly resolved electron density were observed in the crystalline lattice, but could not be modelled satisfactorily as solvent (toluene or hexane).This residual electron density was removed using the SQUEEZE routine in PLATON.In all, electron density (125 electrons) pertaining to 2.5 molecules of toluene (or hexane) per unit cell was removed.This is included in the chemical formula and as a result produces many errors in checkCIF which should be ignored.
Figure S1First-order kinetic plot for the OMRP of MMA mediated by complex 1a a

FinalFigure S15 Final
Figure S15 Complex 1cNote.The asymmetric unit of complex 1c was found to consist of two structurally analogous dimers (only one shown below), and two regions of co-crystallised solvent.One region could be easily modelled as a molecule of toluene with an SOF of 1.The contents of the additional solvent region were a little less clear, though could be modelled as containing either one molecule of toluene (SOF = 0.66) or one molecule of hexane (SOF = 0.33) (this explains the non-integer value in the chemical formula shown below).A number of geometric and ADP constraints/restraints were required to generate chemically sensible structures of the disordered solvent.

Table S1
ATRP of styrene a a Conditions:

Table S2
ATRP of MMA a

Table S3
OMRP of styrene a a Conditions: