Metal—ligand bonds complex hydrides

The reactions of tin hydrides with metal-metal bonded clusters has proven to be a successful route to a range of metal-tin bonded complexes. Products usually result in the cleavage of the M—M bond however, under special conditions, for example with bridging ligands, the bond can remain intact and result in either bridging or terminal tin groups, as shown for some ruthenium and osmium clusters (equations 102 and 103). 

These are in principle reversible, hut because the position of equilibrium obeys the overall thermodynamics, in practice the reactions often tend to go in the oxidative or reduchve direchon only, depending on the case. Which is seen depends on the relative stabilities of the oxidahon states or, more quanhtahvely, on the A-B versus M-A and M-B bond strengths. Alkyl hydride complexes commonly eliminate alkane, but only rarely do alkanes oxidahvely add to a metal. Third row elements, which tend to have stronger metal-ligand bonds tend to give oxidahve addihon more easily. Occasionally, an equilibrium is established in which both the forward and back reachons are observed. It is typical for the two hydrogens to end up cis to one another in the product in Eq. 2.10 [6]. 

Ketenes can react in several ways with organometaUic compounds and complexes. They can add as ligands to coordinated metals forming stable ketene, ketenyl, and ketenyfldene complexes. Ketenes can be inserted into metal—hydride, metal—alkyl, metal—OR, and metal—NR2 bonds, react with metal—oxide complexes, and with coordinated Hgands. This chemistry has been reviewed (9,51). 

In the presence of H2, perhydrocarbyl surface complexes loose their ligands through the hydrogenolysis of their metal carbon bonds to generate putative hydride complexes, which further react with the neighbouring surface ligands, the adjacent siloxane bridges (Eqs. 8-9) [46,47]. 

Not included in the present review is the fascinating new chemistry which results from reaction between diazo compounds and low-valent transition-metal complexes bearing easily displaceable two-electron ligands as well as with metal-metal multiple bonds and metal hydrides whereby a variety of novel organometallic molecules could be obtained. This field has been covered, in accord with its rapid development, by successive reviews of Hermann 19 22) and Atbini23). 

---