Substituted m-terphenyl ligands in main group and transition metal chemistry

m-Terphenyls are bowl-shaped molecules that have been shown to be effective ligands for main group and transition metal complexes with unusual coordination environments. Many m-terphenyl complexes are formed via direct element-carbon bonds, but the chemistry of substituted m-terphenyls, in which the primary interaction is through a functional group, is relatively unexplored. The introduction of functional groups allows for more varied coordination modes, and therefore, more varied structures. To explore this chemistry, a series of 13 m-terphenyl molecules in which the aryl group was either phenyl or 2,4,6-trimethylphenyl were prepared and substituted in the m-terphenyl pocket with oxygen containing donors including carboxylic and boronic acids, aldehydes, Schiff bases, amides, and alcohols. A survey of their coordination chemistry was performed, and, in most cases, the new molecules were characterized by standard spectroscopic methods, and when possible, single crystal X-ray diffraction. The protonolysis reactions of the carboxylic acid, Schiff base and alcohol ligands with main group elements [AlMe3, Sn[N(SiMe3)2]2, Ge[N(SiMe3)2]2, and Si(NMe2)4] and transition metals [Ti(NMe2)4 and ZnEt2] produced nearly 20 new complexes. Particularly notable results of this study include an aluminium Schiff base complex TPIP•AlMe2•AlMe3 [TPIP = N-(2',4',6'-triphenylbenzylidene)2-iminophenol] that acts as an initiator in the ring-opening polymerization of epsilon-caprolactone, and the first structurally characterized mixed aryloxy/amido germanium (II) complex [(Mes2C6H3O)Ge(N{SiMe3}2)]. Most exciting is the serendipitous discovery of a Sn2N2 analogue of 1,3-cyclobutadienide, namely [(Mes2C6H3CO2)Sn(mu-NSiMe3)]2, produced by the oxidation of [(Me3Si)2NSn(mu-O2CC6H3Mes2)]2 with AgOCN. The chemistry of m-terphenyls was also extended beyond discrete molecular complexes with the synthesis of two bifunctional ligands 2,6-diphenylterephthalic acid and 4-mercaptomethyl-2,6-diphenylbenzoic acid. The latter was used in a collaborative project to form a low-surface density self-assembled monolayer on gold that adsorbed adenine, a model compound for biological macromolecules. The former was used to prepare six 1-D metal-organic chains and 2-D networks from nitrate salts of zinc, copper, cobalt and silver.