Cage Silaphosphanes with a P→Si Dative Bond

• Published in: Organometallics 2009-09, Vol.28 (18), p.5305-5315
• Main Authors: Sidorkin, Valery F, Doronina, Evgeniya P
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om900250f

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 isomers increases to 16. Remarkable among the latter is the molecule FSi(NHC6H4NH)3P (42b), with a record short P→Si dative bond of covalent character, as follows from the AIM and ELF analyses. The configuration of the bonds around the SiV atom in 42b corresponds to practically an ideal trigonal bipyramid (ηe = 100%).