Abstract The compounds H 2 Si [P (SiMe 3) 2] 2 and [H 2 SiP (SiMe 3) 2] 2 were prepared and characterized by 29 Si NMR, 31 P NMR, IR and Raman spectroscopy. After thermolysis of these compounds no cyclic silylphosphanes could be detected in the reaction mixture, although this did contain P (SiMe 3) 3.