Theoretical and experimental investigation of the basicity of phosphino(silyl)carbenes.

{Protonation of phosphino(trimethylsilyl)carbenes by weak C-H-acids gave the corresponding ylides and olefination products; the pKa values of the conjugate acids were estd. Reaction of the phosphinosilyl carbene (iPr2N)2PCSiMe3 (1b) with PhC≡CH gave the addn. product, (iPr2N)2P(C≡CPh):CHSiMe3 (4), whereas reaction of cyclohexyl analog (1c) with acetonitrile gave (Cy2N)2P(:CHCN)CH2SiMe3 (6). Reaction of 1b with MeCOSiMe3 is accompanied by rapid intramol. olefination of the addn. product (iPr2N)2P[OC(SiMe3):CH2]:CHSiMe3 (9), finally affording (iPr2N)2PO[CH(SiMe3)C(:CH2)SiMe3] (10). Carbenes 1 react efficiently with C-org. acids, which have pKa values in DMSO in the range 18-31. However, the irreversible reaction of the conjugate acids 1H+ with the anion precludes the detn. of the thermodn. basicity of 1. Theor. calcns. were performed in order to evaluate the basicity of phosphino(trimethylsilyl)carbenes R12PCSiR23 (1a

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Soumis le 21 janvier 2019