Synthetic, Spectroscopic, Structural and Computational Studies of Enyl and Ynyl Carbon-Rich Complexes

Abstract

This thesis describes the synthesis and analysis of organometallic complexes that feature either enyl or ynyl linkages. Chapter 1 introduces a general overview of electron transfer, classification of mixed-valence complexes and the modelling of mixed-valence complexes using density functional theory.

The synthesis of a range of trans-RuCl(C≡CC6H4R)(dppe)2 complexes, in which R is either an electron donor (Me, OMe, C5H11) or acceptor (NO2, CO2Me), from the five-coordinate complex [RuCl(dppe)2]OTf is described. This synthetic route represents an alternative to the long-standing methods based on cis-RuCl2(dppe)2. Improved synthetic routes to both [RuCl(dppe)2]OTf and cis-RuCl2(dppe)2 are also given. These compounds were fully characterised spectroscopically and the molecular structures of [RuCl(dppe)2]OTf, trans-RuCl(C≡CC6H4OMe)(dppe)2, trans-RuCl(C≡CC6H4Me)(dppe)2, and trans-RuCl(C≡CC6H4CO2Me)(dppe)2 determined and analysed. The structures conform with literature precedence.

The synthesis of ruthenium complexes based on RuCl(dppe)2 and Ru(dppe)Cp* units, featuring 1,3-diethynylbenzene bridging ligands has been achieved. The electronic structures of 1,3-c2C6H4, 1,3-2C6H4 and 1,3-2-5-(HC≡C)C6H3 have been investigated using a combination of UV-vis-NIR and IR spectroscopies and computational studies. In contrast to the case of closely related iron compounds, for the ruthenium complexes 1,3-2C6H4, 1,3-2C6H4 and 1,3-2-5-(HC≡C)C6H3 the bridging aryl moiety is heavily involved in the oxidation process, and consequently descriptions of the electronic structures and electronic transitions in terms of the language developed for mixed-valence systems with clearly identifiable metal oxidation states are not appropriate. The description of the low-energy absorption bands from the mixed-valence complexes are therefore better described as charge transfer transitions rather than IVCT transitions.

A range of mono vinyl Ru(CH=CHC6H4R-4)(CO)(PPh3)Tp complexes have been obtained from the reaction of RuHCl(CO)(PPh3)3 with para- substituted ethynylphenylenes, and KTp. (R = NO2, CO2Me, CN, Me and OMe). These complexes have been fully characterised spectroscopically, with molecular structures for Ru(CH=CHC6H4NO2-4)(CO)(PPh3)Tp, Ru(CH=CHC6H4CN-4)(CO)(PPh3)Tp, Ru(CH=CHC6H4CH3)(CO)(PPh3)Tp and Ru(CH=CHC6H4OMe-4)(CO)(PPh3)Tp being determined and analysed. The electronic structures of these mono vinyl complexes have been also investigated using a combination of UV-vis-NIR and IR spectroscopies and computational studies, revealing the redox activity of the styrene-derived ligand. Hydroruthenation of 1,3-, 1,4- diethynylbenzene and 1,3,5-triethynylbenzene affords the di- and trimetalled vinyl complexes, which have been characterised spectroscopically. The bridging ligand is shown to be redox non-innocent.

A simple protocol that allows the preparation of either “symmetric” A3 or “asymmetric” AB2 triethynyl methanol derivatives through the reaction of acetylide anions with chloroethylformate, has been explored. This synthetic protocol is not only high yielding, but avoids the harsh conditions used in literature methods. The molecular structures of Me3SiC≡C(COH)(C6H4I)2 and HC≡C(COH)(C6H4I)2 have been determined and analysed, with the packing motifs in the solid state arising from halogen interactions identified. The use of these ligands as branched core ligands has also been investigated, and whilst difficulties have been encountered synthetic work to resolve these has been initiated.

A selection of pro-ligands and both mono- and tris-metallated ligand complexes based on a triarylamine core have been prepared. The electronic and structural nature of Me3SiC≡C(C6H4)NTol2, Fe(C≡C(C6H4)NTol2)(dppe)Cp and [3(μ-(C≡CC6H4)3N)] have been investigated using a combination of UV-vis-NIR and IR spectroscopies and computational studies indicating electronic interactions between the remote metal centres in the case of [3(μ-(C≡CC6H4)3N)]n+ (n = 1, 2). The molecular structures of Me3SiC≡C(C6H4)NTol2, HC≡C(C6H4)NTol2, Ru(C≡C(C6H4)NTol2)(dppe)Cp* and Fe(C≡C(C6H4)NTol2)(dppe)Cp have been determined and analysed.