Exploring the potential role of heavy pnictogen elements in ligand design for new metal-ligand cooperative chemistry

Abstract

The field of metal-ligand cooperativity (MLC) has expanded into a new area of inorganic and organometallic catalysis. Most often MLC is associated with ligand-based proton or electron transfer, with limited instances involving other functional group transfer. Additionally, the majority of the cooperative partners with transition metals are light, main group elements such as carbon or nitrogen. A newly developing area of MLC now involves the use of heavier main group elements such as silicon or phosphorus. The heavier main group elements tend to offer advantages over lighter elements in the form of hypervalency and access to a range of stable redox states. This review covers the use of heavy pnictogen elements such as phosphorus, arsenic, antimony, and bismuth as cooperative partners in MLC. Examples of true MLC with phosphorus are considered along with possible future directions. In the case of arsenic through bismuth, examples are provided to support the premise that these elements may also be suitable as cooperative ligand species in catalysis. Properties such as pnictogen coordination environment, viable redox pairs, and ambiphilicity are discussed.