TETRARYLMETHANE ANALOGS IN GROUP-14 .2. PH4-NSI-PARA-TOLN AND PH4-NSN-PARA-TOLN (N=0 TO 4) - INFLUENCE OF PARA-TOLYL SUBSTITUENTS ON STRUCTURE AND NMR CHEMICAL-SHIFTS

The title compounds have been synthesized by Li and Grignard reactions. The crystal structure of Ph3Si-p-Tol has been determined. The substitution of only one phenyl by one p-tolyl group causes only a slight deviation from the ideal S4 symmetry of Ph4Si. Gradual replacement of phenyl by p-tolyl groups leads to increasing low field shifts for all C-13(ipso) atoms. The substitution of the first phenyl group by p-tolyl in Ph4Si and Ph4Sn results in a high field shift both for delta(Si-29) (- 0.3 ppm) and for delta(Sn-119) (-1 ppm). Further replacement shows nearly linear dependencies (DELTAdelta(Si-29)= -0.1 ppm, DELTAdelta(Sn-119)= +1.5 ppm per p-tolyl group).