Abstract
The addition reaction of 1,1-bis(diphenylphosphino)methane (dppm) and haloalkanes R-X yields the corresponding phosphonium salts (Ph2PCH2PPh2R)X (1a: R = Me, X = I; 1b: R = Et, X = Br; 1c: R = iPr, X = I; 1d: R = CH2Mes, X = Br; 1e: R = tBu, X = Br). In case of the synthesis of 1e, (Ph2MePH)Br (3) was identified as a by-product. Deprotonation of 1 by KOtBu offers access to the corresponding phosphonium ylides (Ph2PCHPPh2R) (2a: R = Me; 2b: R = Et; 2c: R = iPr; 2d: R = CH2Mes) in good yields. Further deprotonation of 2a using n-butyllithium allows the isolation of the lithium complex (Li(Ph2PCHPPh2CH2))n (4) and its monomeric tmeda adduct ((tmeda)Li(Ph2PCHPPh2CH2)) (4a). All compounds were characterized by NMR measurements and, except of 4, by X-ray diffraction experiments.
Highlights
Phosphonium ylides gained tremendous importance in organic chemistry, since Wittig and coworkers developed their alkene synthesis in the early 50’s.1 Nowadays, the Wittig reaction is text book chemistry[2] and numerous applications and variations of this reaction are known.[3]
The Wittig reaction is text book chemistry[2] and numerous applications and variations of this reaction are known.[3]. Beside their impact on synthetic organic chemistry, the bonding situation of phosphonium ylides is a subject of considerable interest; for instance the d-orbital participation and hypervalence have been studied intensively.[4]
The stepwise deprotonation of phosphonium salts obtained from dppm and simple alkyl halides have been previously used by e.g. the groups of Issleib[9] and Schmidbaur.[10]
Summary
Phosphonium ylides gained tremendous importance in organic chemistry, since Wittig and coworkers developed their alkene synthesis in the early 50’s.1 Nowadays, the Wittig reaction is text book chemistry[2] and numerous applications and variations of this reaction are known.[3]. The corresponding chloride derivative gives the same yield under identical reaction conditions.10a Tables 2 and 3 summarize selected NMR data and structural parameters of the isolated compounds 1a-e. The deprotonation of [Ph2PCHPPh2CH3] (2a) at the CH3 group by methyllithium or n-butyllithum has been reported earlier 10b,14 and the resulting solutions have been used to transfer the anionic ligand to e.g. yttrium or nickel complexes,[14,15] but little is known about the intermediately formed lithium compound itself.
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