Medium-Nuclearity Mixed-Metal Cluster Chemistry

Abstract

The thesis is comprised of nine scientific articles and is preceded by an overview that contextualises all of publications.

Mixed-metal clusters of group 6 and 9 have been of longstanding interest. The polar metal-metal bonds in these clusters exhibit great potential for substrate activation, and the widely disparate metals could increase cluster reactivity. Our previous studies of group 6 and 9 mixed-metal clusters have been mainly concentrated on low-nuclearity tetranuclear molybdenum/tungsten-iridium clusters, including the study of their structure, fluxionality, reactivity, electrochemistry, spectroelectrochemistry and optical properties. The thesis project herein mainly focuses on the synthesis of medium-nuclearity clusters of group 6 and 9.

The first part of this body of work is concerned with the synthesis of medium-nuclearity molybdenum/tungsten-iridium clusters. Publication 1 details the synthesis of pentanuclear clusters by core expansion of tetranuclear molybdenum/tungsten-iridium clusters with capping reagents tetramethylcyclopentadienyl iridium dicarbonyl and pentamethylcyclopentadienyl iridium dicarbonyl. Publication 2 describes phosphine, isocyanide, and alkyne reactivity at several pentanuclear molybdenum/tungsten-iridium clusters that are reported in Publication 1.Three structurally characterized medium-nuclearity molybdenum-iridium clusters are presented in Publication 3.

The second part of the thesis includes the synthesis of medium-nuclearity molybdenum/tungsten-rhodium-iridium clusters by core expansion reactions of tetranuclear molybdenum/tungsten-iridium clusters with capping reagents tetramethylcyclopentadienyl rhodium dicarbonyl and pentamethylcyclopentadienyl rhodium dicarbonyl. Publication 4 delineates a dynamic permutational isomerism in a pentanuclear ditungsten-rhodium-diiridium closo-cluster, together with the proposed mechanism and studies of the chemical and physical properties of the permutational isomers. Publications 5 and 6 detail the syntheses of penta- and hexa-nuclear molybdenum/tungsten-rhodium-iridium clusters by core expansion of tetranuclear molybdenum/tungsten-iridium clusters with the rhodium capping reagents, and phosphine and alkyne chemistry of the pentanuclear clusters. Publication 7 demonstrates the synthesis and structural studies of a hexanuclear trimolybdenum-triiridium cluster and a heptanuclear trimolybdenum-rhodium-triiridium cluster.

In addition, Publication 8 describes alkyne chemistry at a phosphine-substituted cluster and explores the impact of phosphine ligation to dimolybdenum-diiridium on optical limiting properties. Finally, Publication 9 reports a four-valence-electron-deficient butterfly tetrairidium cluster and a heptairidium cluster, together with theoretical studies of the tetrairidium cluster.