Stoichiometric synthesis reaction patterns

Among more recent innovations, the alkylative metallacyclobutane and metallacyclobutene synthesis, involving central carbon addition and addition/elimination reactivity patterns, holds considerable promise for near-term synthetic developments (Section 2.12.12). This is equally true in both the nucleophilic and free radical versions of this process, for both catalytic and stoichiometric transformations and multistep reaction cascades. 

The synthesis of multimetallic transition metal complexes where the metals are held at specific distances from each other is an important objective because of their potential role in multimetal-centered catalysis in both biological and industrial reactions (1). Moreover, such systems, through cooperative electronic and/or steric effects between metal centers, might give rise to distinct reactivity patterns for both their stoichiometric and catalytic reactions, which are not available to their monometallic analogues (2). Of the ligands that are able to maintain the metal centers in close proximity, the pyrazolate ion (pz ) appears to be a particularly suitable candidate. Pyrazoles (Hpz ) are weak bases (3, 4) and behave as 2-monohapto ligands. 

---