Synthesis and reactivity of complexes containing a group 13-group 11 bond
Keywords: small molecule activation
aluminium
Main group
group 13
bimetallic

This thesis describes the synthesis of heterobimetallic complexes which contain an unsupported bond between a group 13 and a group 11 metal (Cu, Ag, Au). While the primary focus is on bonds to aluminium, which are lesser known, the analogous gallium-coinage metal compounds are also investigated as a point of comparison. The methodology used in this work makes use of the first of a new class of nucleophilic aluminium ‘aluminyl’ anions, K2[(NON)Al]2 (NON = 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene), which is reacted with group 11 electrophiles of the form R3PMI (R = Ph, tBu, Cy) in a salt metathesis reaction. This approach gives access to rich structural variety, producing bimetallic complexes of the form (NON)AlMPtBu3, a 2:1 di(aluminyl)cuprate system, K[Cu{Al(NON)}2], and trimetallic iodide bridged complexes, (NON)Al(MPPh3)2I. These compounds are characterised by X-ray crystallography and multinuclear NMR, with spectroscopic comparisons to the heavier congeners (prepared using the gallyl reagent K2[(NON)Ga]2 giving insight into the properties of the aluminyl fragment as a metalloligand. The reactivity of the linear (NON)AlMPtBu3 series towards small molecules is then explored. The compounds in this bimetallic series readily insert carbon based electrophiles (CO2, carbodiimides) into the Al–M bond to give a complexes containing an M(CE2)Al bridging unit (E = O, NR), with an unusual μ-κ1(C):κ2(E,E′) binding mode. While the carbodiimide insertion products are stable to further reaction, it is observed that the CO2 bridged species have the potential to react onwards, and that this ability depends on the identity of the group 11 metal. (NON)Al(O2C)AuPtBu3 is inert to further reaction, while (NON)Al(O2C)AgPtBu3 reacts slowly with a second equivalent of CO2 to give a bridging carbonate complex and CO. Copper compound (NON)AlCuPtBu3 reacts rapidly even at very low temperatures, proceeding straight to the carbonate complex. The mechanism of this CO2 to CO transformation can be investigated and is found to be consistent with rate determining extrusion of CO to form a bridging Al–O–M oxide, followed by uptake of a second molecule of CO2. The behaviour of the Al–M bond towards alkynes is then investigated. Internal alkynes insert into the Al–Cu bond of (NON)AlCuPtBu3, giving (aluminylalkenyl)copper compounds with M–C bonds of differing natures. The insertion gives access to both syn and anti dimetallated alkenes, depending on the reaction conditions. It is also regioselective, producing only one regioisomer when unsymmetrically substituted alkynes are used. The mechanism of the insertion, and a subsequent isomerisation step, are investigated through kinetics studies. The differential reactivity of the (aluminylalkenyl)copper compounds is exploited by selective functionalisation with CO, which inserts only into the Cu–C bond. This results in formation of the first structurally characterised example of a copper acyl complex, a feat made possible by cooperative action of copper and the proximal aluminium centre. In all, this thesis aims to demonstrate the utility of the potassium aluminyl reagent K2[(NON)Al]2 as a means to forming direct Al–M bonds, and investigate the reactivity of such heterobimetallic compounds towards challenging small molecules.