Cage Silaphosphanes with a P→Si Dative Bond

Abstract

The design of the cage silaphosphanes XSi(−L−)3P (X = Me (a), F (b); L = YCH2Z (4−19), YC6H4 (20−23), C6H4Z (24−27), C10H6 (28), YCH2CH2Z (29-37), YC6H4Z (38−46); Y, Z = O, NH, CH2, S) has been carried out by MP2 and B3LYP methods using 6-31G(d) and 6-311+G(d) basis sets. These species can exist in two forms, namely, with the phosphorus lone electron pair (LEP) directed inside the cage (endo), enabling P→Si coordination, or outside the cage (exo), excluding it. The relative stabilities of the two isomers depend on the properties of the Si and P bridgehead atom surroundings as well as on the size and nature of the side chains (L). Among the 50 studied cage species XSi(−L−)3P possessing the bridgehead Si and P atoms in the 1- and 5-positions, only 3 structures (L = SC6H4 (23a,b), C10H6 (28b)) exist exclusively in the endo form with the pentacoordinate silicon atom. On going from the systems XSi(−L−)3P with the 1,5-bridgehead Si and P atoms to the similar 1,6-bridgehead systems, the number of stable endo iso...