Michael Ferguson

PhD Student

Michael

DBB.XX.XXX
+44 (0) 28 9097 XXXX
mferguson19@qub.ac.uk

PhD Project:


Understanding mechanochemical reactions through experimental and modelling approaches.


Supervisors

Stuart James (School of Chemistry and Chemical Engineering) Jorge Kohanoff

Interests

    Most Recent Publication

    One-pot two-step mechanochemical synthesis: ligand and complex preparation without isolating intermediates. , Green Chemistry, 2014, 16, pp. 1374
    doi: 10.1039/c3gc42141d Abstract
    Although the use of ball milling to induce reactions between solids (mechanochemical synthesis) can provide lower-waste routes to chemical products by avoiding solvent during the reaction, there are further potential advantages in using one-pot multistep syntheses to avoid the use of bulk solvents for the purification of intermediates. We report here two-step syntheses involving formation of salen-type ligands from diamines and hydroxyaldehydes followed directly by reactions with metal salts to provide the corresponding metal complexes. Five salen-type ligands 2,2’-[1,2-ethanediylbis[(E)-nitrilomethylidyne]]bis-phenol,‘salenH2’,1; 2,2’-[(±)-1,2-cyclohexanediylbis-[(E)-nitrilomethylidyne]]bis-phenol,2 ;2,2’-[1,2-phenylene-bis(nitrilomethylidyne)]-bis-phenol, ‘salphenH2’ 3; 2-[[(2-aminophenyl)imino]methyl]-phenol, 4; 2,2’-[(±)-1,2-cyclohexanediylbis[(E)-nitrilomethylidyne]]-bis[4,6-bis(1,1-dimethylethyl)]-phenol, ‘Jacobsen ligand’,5) were found to form readily in a shaker-type ball mill at 0.5 to 3 g scale from their corresponding diamine and aldehyde precursors. Although in some cases both starting materials were liquids, ball milling was still necessary to drive those reactions to completion because precipitation of the product and or intermediates rapidly gave in thick pastes which could not be stirred conventionally. The only ligand which required the addition of solvent was the Jacobsen ligand 5 which required 1.75 mol equivalents of methanol to go to completion. Ligands 1–5 were thus obtained directly in 30–60 minutes in their hydrated forms, due to the presence of water by-product, as free-flowing yellow powders which could be dried by heating to give analytically pure products. The one-armed salphen ligand 4 could also be obtained selectively by changing the reaction stoichiometry to 1 : 1. SalenH2 1 was explored for the one-pot two-step synthesis of metal complexes. In particular, after in situ formation of the ligand by ball milling, metal salts (ZnO, Ni(OAc)2·4H2O or Cu(OAc)2·H2O) were added directly to the jar and milling continued for a further 30 minutes. Small amounts of methanol (0.4–1.1 mol equivalents) were needed for these reactions to run to completion. The corresponding metal complexes [M(salen)] (M = Zn,6; Ni,7;or Cu,8) were thus obtained quantitatively after 30 minutes in hydrated form, and could be heated briefly to give analytically pure dehydrated products. The all-at-once ‘tandem’ synthesis of [Zn(salen)] 6 was also explored by milling ZnO, ethylene diamine and salicylaldehyde together in the appropriate mole ratio for 60 minutes. This approach also gave the target complex selectively with no solvent needing to be added. Overall, these syntheses were found to be highly efficient in terms of time and the in avoidance of bulk solvent both during the reaction and for the isolation of intermediates. The work demonstrates the applicability of mechanochemical synthesis to one-pot multi-step strategies.

    All of Michael's publications


    Figure 1: An example of a solvent free chemical reaction induced by the mechanical agitation of two solids via vibrational ball milling.

    A mechanochemical reaction can be defined as any reaction that is induced by the direction absorption of mechanical energy. Historically these reactions would be performed using a pestle and mortar, it is now more common to use high energy ball mills to induce chemical reactivity. Over the past three decades research in the field has grown and there are now a wide range of reactions that can be performed in the solid state without the requirement of bulk solvents. However the mechanisms by which the reactions occur is poorly understood. Therefore in this project, using both classical and quantum techniques, we hope to gain some insight into solid state chemical reactivity between molecular crystals.