Carbocations unsaturated silanes

Because it is similar to RjSi as an electron-donating group, the CpMo(CO)2 fragment is cap le of stabilizing a P-carbocation center. By analogy with the allyl compounds of silane, borane, and tin, CpMo(CO)2(Tl -cyclohexadienyl) and its 6-substituted derivatives 106 a-c undergo BFj-promoted electrophilic addition to aldehydes and a,P-unsaturated enones by generating cyclohexadiene cationic precipitates 107, as shown in Scheme 22. 

---