Proton tolyl group

We referred earlier to the significance of reactions at the alkylidyne carbon atoms of the dimetal species. Our studies in this area are in a preliminary stage, but Schemes 1 and 2 summarise some chemistry at the bridged carbon centres for the compounds (1 ) and (3,)(12). It will be noted that protonation of the neutral bridged al ylidyne compounds yields cationic alkylidene species in which one C—C bond of the tolyl group is n2 co-ordinated to tungsten, a feature revealed by both n.m.r. and X-ray diffraction studies. 

Small Vhc couplings (less than 2.3 Hz) between the iV-methyl protons and the quaternary carbons of the tolyl group have been reported by Tokunaga et for several triarylstibanes bearing an amino side chain. No clear relationship between these couplings and the steric parameters has been observed. 

In 1969, Elschenbroich and Cais reported the ESR spectra of several ferrocenyl anion radicals, including benzoyl, p-tolyl, p-carbomethoxy-benzoyl, p-nitrophenyl, p-cyanophenyl, and nitroferrocene, prepared by electrolytic reduction in either acetonitrile or DMF (5S). In general, the ferrocenyl group destabilizes the anion radicals compared to a phenyl substituent. When both groups are present, delocalization of the unpaired electron into the phenyl substituent is more extensive, and the ESR spectra resemble, for the most part, anion radicals of substituted aromatics. There is small spin density in the ferrocenyl moiety, which appears as small hyperfine couplings for the cyclopentadienyl protons ortho to the point of substitution (38). 

Styrenes with less bulky alkyl groups at silicon, such as 1-phenyl-2-trimethylsilylethene 335, l-p-tolyl-2-trimethylsilylethene 337 and even the relatively more bulky substituted l-p-tolyl-2-dimethylisopropylsilyl ethene 338, on protonation using either FSC>3H/SbF5 or FSO3H, do not lead to solutions of persistent /i-trimethylsilyl-substituted carbocations such as 336 from 335 but undergo fast /i-silyl fragmentation to silyl-free cations such as 78 (equation 51). 

The Cjg—Si bond fragmentation in cation 401 occurs already at temperatures where the corresponding 1-mesityl-, l-(p-tolyl)- and 1 -phenylvinyl-/l-(tri isopropyl Jsi lyl-substi tutcd vinyl cations 375, 389a and 393 are stable. The facile formation of the 1 (p-anisyl)vinyl cation 403 can be ascribed to a second protonation of 401 at the oxygen of the anisyl group. 

Protonation with HCIO4 of 2-(/ -tolyl)-2,3-didehydrosparteine 76 resulted in the formation of an immonium bond gave 77 which, upon reaction with cyanide ion, led to the introduction of the cyano group in position 2 of the sparteine system affording 78 (Scheme 12) <2004JST(688)111>. 

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