Sequential, kinetically controlled synthesis of multicomponent stereoisomeric assemblies.

Graphical abstract: Abstract The vast difference in labilities of cis -exchangeable platinum coordination sites has been exploited to selectively synthesise multicomponent stereoisomeric assemblies using a template-free, sequential, kinetically controlled approach. The reversibility of non-covalent and metal ligand interactions has widely been exploited to synthesise a plethora of supramolecular and coordination based assemblies under thermodynamic control. [1] Occasionally, entrapment in local energy minima leads to the formation of metastable products, which are often converted into lower energy products upon prolonged reaction times. [2] In contrast, self-assembled products in Nature almost always arise according to the most expedient reaction pathway, rather kinetically selected. [3] Here we demonstrate a kinetically-controlled approach to self-assembly in which the sequence of addition [4] of molecular tectons leads to the stereoselective formation of metallosupramolecular isomers. The use of platinum(II) (and other 3 rd row TMs) is particularly well suited to a kinetic approach to self-assembly, not just because Pt ligand bonds can be kinetically inert, but also because the metal ion can be conveniently tuned to produce a vast range of different ligand exchange labilities. For instance, assemblies which utilise bis -phosphine ligands as corner protecting groups often readily assemble at room temperature, [5] while those which exploit neutral N -donor bidentate ligands, such as ethylene diamine, typically require several hours at elevated temperature to reach equilibrium. [6] Furthermore, the mechanism of labilisation, i.e. the trans effect, is such that it is possible for a single metal centre to possess cis exchangeable sites with dramatically different kinetic properties. We have recently prepared a metallosupramolecular trigonal prism that possesses an unsymmetrical cyclometallated CˆN corner protecting group, which was assembled in two steps by treating [ L 1 Pt(DMSO)] (where H 2 L 1 = 2,6-diphenylpyridine) sequentially with 4,4′-bipy and tpt.3CSA (where tpt = tris(4-pyridyl)triazine and CSA = camphorsulfonic stereoisomeric assemblies using a template-free, sequential, kinetically controlled approach. We anticipate that this approach to non-covalent, and in particular coordination driven self-assembly will facilitate the generation of multicomponet, ultimately functional systems.