Electron mismatch-selective

Z-selectivity of the product through equilibration of the isomers that would be facile if Mo-methylidene is allowed to accumulate. The more stable alkoxy-substituted alkylidene does not undergo homocoupling due to an electronic mismatch, but can efficiently undergo productive cross metathesis with terminal alkenes in this way, a selective cross metathesis can be achieved. 

In contrast, in most ion-selective membranes the charge conduction is done by ions. Thus, a mismatch between the charge-transfer carriers can exist at the noble metal/membrane interface. This is particularly true for polymer-based membranes, which are invariably ionic conductors. On the other hand, solid-state membranes that exhibit mixed ionic and electronic conductivity such as chalcogenide glasses, perovskites, and silver halides and conducting polymers (Lewenstam and Hulanicky, 1990) form good contact with noble metals. 

---