Neopentane synthesis

The tris-neopentyl Mo(VI) nitride, Mo(-CH2- Bu)3(=N) [134], reacts with surface silanols of silica to yield the tris-neopentyl derivative intermediate [(=SiO)Mo (-CH2- Bu)3(=NH)] followed by reductive elimination of neopentane, as indicated by labeling studies from labeled starting organometallic complex, to yield the final imido neopentylideneneopentyl monosiloxy complex [(=SiO)Mo(=CH- Bu)(-CH2 - Bu)(=NH)] [135]. The surface-bound neopentylidene Mo(VI) complex is an active olefin metathesis catalyst [135]. Improved synthesis of the same surface complex with higher catalytic activity by benzene impregnation rather than dichlorometh-ane on silica dehydroxylated at 700 °C has been reported [136],... 

Indeed, the reaction was first observed in the synthesis of the hydrides. As mentioned above, when 5 is heated under dry hydrogen to 150 °C for three hours, (=SiO)3ZrH (14) is formed together with nine equivalents of methane and three equivalents of ethane. The formation of methane and ethane rather than neopentane was clear evidence of hydrogenolysis under the synthesis conditions [5, 15, 16]. It was observed that the reaction of neopentane occurred by stepwise formation of firstly isobutane and methane, then conversion of the former to a second equivalent of methane and propane which is further converted to ethane and a third equivalent of methane. The C-C bond of ethane cannot be cleaved by P-methyl elimination because a surface metal-ethyl fragment has no methyl group in the S-position. 

The synthesis of 79, 80 and related spiranes has been of interest because of their potential conversion to centrohexacyclic derivatives bearing three additional bridges across the neopentane carbon atoms C-9, C-10 and C-l l,in analogy to some unusual non-benzoannelated analogues such as the Simmons-Paquette molecule [37,81,82]. In fact, triptindanetrione 72 has been used in several cases to construct three additional five-membered rings (Schemes 15 and 56). A surprisingly efficient three-fold bridging with aliphatic diatomic units has been achieved by treatment of 72 with an excess of lithium acetylides. In this way, centrohexacyclic triptindanes 81-83 and related compounds have become accessible, as shown in Scheme 15 [83]. 

A general mediod for the synthesis of aryloxy(chloro)neopentylidene-tungsten complexes involves the reaction of WCl4(OAr)2 (OAr = 2,6-disubstituted phenoxide) [20] with 1 equiv or 1.5 equiv of MgNp2(dioxane) (Np=CH2C(CH3)3) [11, 21] (Scheme 1). The reaction proceeds via a double (or triple) kylation of tungsten followed by an a-H abstraction and elimination of neopentane [22]. In the particular case of the 2,6-diphenyl-phenoxide complexes, the activation of m ortho C-H bond in one of the phenyl substituents of the aryloxide ligands leads to the elimination of HCl with the formation of a cyclometalated compound (Scheme 2) [23, 24]. 

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