Extremely large one-bond 31p13C and two-bond 31P18O isotope shifts in [(HsOzCH]3Si0C===P, a new representative of landa(3)-phosphaalkynes, and isotope shifts of several derivatives and some landa(3)-phosphaalkenes

The structure of the heteroatom-substituted landa(3)-phosphaalkyne [(H3C)2CH]3Si- 0- C= = =P (1) was derived from the 31P, 13C, 29Si and 170 NMR spectra. The phosphorus atom of the non-isotope-enriched compound exhibits an extremely negative 31P13C one-bond and 31P18O two-bond isotope shift of -0.209 and -0.094ppm, respectively. The 31P{ʹH} NMR spectrum shows all carbon, silicon and oxygen satellite signals of the (mono-13C]-, [mono-29Si]- and [mono-18O]- as well as the [bis-13C, 29Si]- and [bis-13C, 13C]isotopomers; even over five bonds a 13P13C isotope effect can also be observed. Additivity of the corresponding isotope effects has been confirmed. The coupling constant (1)J(31P,13C) is unexpectedly large, 91.9 Hz. 31P13C one-bond isotope shifts of other landa(3)-phosphaalkynes and landa(3) -phosphaalkenes are presented and discussed. Copyright © 1999 John Wiley & Sons, Ltd.