PHOSPHONIUM YLIDES WITH FUNCTIONALIZED SI LYL SUBSTITUENTS

Two series of aminophosphonium ylides with reactive alkoxychlorosilyl substituents (R(2)N)(3)P=CHSi(OR')(2)Cl (1-8, R = Me, Et/R' = Me, Et, iPr, tBu) have been prepared by reaction of the aminophosphonium ylide s (R(2)N)(3)P=CH2 with the corresponding dialkoxydichlorosilanes Cl2Si (OR')(2). Substituent effects have been investigated by heteronuclear solution NMR studies of the nuclei H-1, C-13, N-15, O-17, Si-29, and P -31. These studies show an alternating shielding effect along the C-O- Si-C backbone. Further reactions of the chlorosilylated ylides with th e aminomethylenephosphorane (Me(2)N)(3)P=CH2 lead to the formation of the bis-ylidic compounds [(Me(2)N)(3)P=CH]Si-2(OR')(2) (9, 10), which are also available in one-pot syntheses. The molecular structure of [( Me(2)N)(3)P=CH]Si-2(OiPr)(2) (9) has been confirmed by single-crystal X-ray diffraction. In the crystal the molecules have two ylidic carbon centers with planar configuration, which are bridged by a nearly tetr ahedral silicon atom. Short P-C- and Si-C distances indicate a stabili zing effect of the carbanionic centers.