Chemistry Without Borders Between Main Group and Transition Elements: Metal-Containing Cyclic Phosphazenes and Siloxanes

The syntheses and reactivities of six- and eight-membered metallacyclophosphazenes are described. The properties of soluble metal nitrides of titanium and tantalum are reported and eight-membered titanium containing siloxanes have been synthesized. A concept which has aided the synthesis of the target molecules is that phosphazene and siloxane groups are isoelectronic. Some of the compounds in this article might function as precursors for generating new materials. A majority of the molecules has been characterized by single crystal X-ray diffraction. 1. Introduction 2. Synthesis of Metallacyclophosphazenes 2.1. Six-membered Metallacyclophosphazenes 2.2. Reactions of Metallacyclophosphazenes 2.3. Six-membered Carbon-Containing Metallacyclophosphazenes 2.4. Six-membered Triazatritantalines 2.5. Metallatriazaphosphorines 3. Eight-membered Dimetallacyclophosphazenes 3.1. Synthesis of Dimetallacyclophosphazenes 4. A Nine-membered Heterocycle Containing Oxidic and Nitridic Structural Elements 5. "Inverse Cryptands" 6. Polymers and Molecular Precursors for Polymeric Materials 7. Cyclic Heterosiloxanes 7.1. Metallacyclosiloxanes with Elements of Group 4 8. Conclusion