A surprisingly stable 1-(chlorosilyl)-2-phosphaethenyllithium compound, RCl2SiC(Li)=PMes

Article abstract of DOI:10.1002/ejic.200400595

RCl₂Si-C(Li)=PMes* (1) (R = 9-methylfluoren-9-yl, Mes* = 2,4,6-tri-tert-butylphenyl), considered as a key intermediate in the synthesis of the heteroallene RClSi=C=PMes*, was obtained from RCl₂Si-C(Cl)=PMes* by lithium/chlorine exchange with nBuLi and evidence for its identity was obtained by hydrolysis. Remarkably, however, it failed to undergo a lithium salt elimination to form the corresponding chlorophosphasilaallene, RClSi=C=PMes*, even under prolonged heating in toluene, As shown by theoretical studies (RHF/ 3-21G* and RHF/6-31G* //RHF/3-21G* level), interactions between the lithium ion and the π-systems of the substituents at the phosphorus and silicon atoms could partly account for this stability. The lithium compound 1 reacts with methanol or chlorotrimethylsilane leading to new silylphosphaalkenes. The reaction of the lithium derivative 1 with benzaldehyde gave a four-membered heterocycle with an exocyclic P=C bond which virtually corresponds to the product of a [2+2] cycloaddition between the Si=C and C=O double bonds. Wiley-VCH Verlag GmbH & Co. KGaA, Germany, 2005.