Methanide shift

It must be noted that the saturated ring system, the 1 -chloro-A -phosphirane was synthesized [84] a cyclic phospheniiun cation was postulated which is stable towards ring opening [85]. A corresponding cation could not be isolated, due to a methanid shift from a trimethylsilyl substituent. 

Gas chromatography-mass spectrometry analysis of the dimer and trimer fractions of the polymerisation products of propene and but-l-ene also suggested intramolecular hydride and methanide shifts as the source of the isomers formed. A mechanistic scheme for the oligomerisation of propene has been proposed, Reaction sequence (2.4) [31]. In most of the studies described above, the products have been analysed after hydrogenation. However, a study analysed the Cy product of a propene/but-l-ene copolymerisation before hydrogenation and confirmed the role of hydride and methanide shifts in determining the structures of the products [32],... 

The reaction, known as the pinacol rearrangement, involves a 1,2-methanide shift to the positive center produced from the loss of the protonated —OH group. 

Cavell also reported alkyl derivatives. Tetrabenzyl zirconium was found to react separately with one molar equivalent of two parent methanes to afford complexes 135 and 136 in excellent yields.66 The 13C NMR chemical shifts of the methandiide centres in 135 (Ad = adamantyl) and 136 of 82.8 and 84.4 ppm are clearly different from the dichloride congeners and reflect the substitution of the chlorides by alkyls. The corresponding hafnium dialkyl 137 was also prepared from 133 and neopentyl lithium and the methanide resonance for this complex appeared at 71.6 ppm in its 13C NMR spectrum.63 Noteably, these alkyls displayed far greater stability than their homoleptic tetraalkyl cousins. 

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