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


Soumis le 21 janvier 2019