Synthesis, structures and reactivities of novel silatranes

Abstract

Silatranes, 5-aza-2,8,9-trioxal-1-silabicyclo[3.3.3]-undecanes, which feature a hypervalent silicon atom with a transannular bonding interaction between the silicon and the bridgehead nitrogen atom, are cyclic organosilicone ethers of tris(2-oxyalkyl) amines and their derivatives, and constitute the unique and well studied class of pentacoordinated silicon derivatives. The properties of silatranes such as the chemical reactivities, the strength of the transannular $N \to {Si}$ bonding, and the range of biological activities, are largely affected by the nature of 1-substituents. As part of our synthetic efforts in diversifying 1-substituent X of silatranes, tris(nitrilo-2,2``,2"-triethoxysiloxyethyl)amine $(1:N\{CH_2CH_2OSi\; (OCH_2CH_2)_3N\}_3)$ has been employed to derive $1-HOSi(OCH_2CH_2)_3N$, 1-hydroxysilatrane (2), a useful synthon for the preparation of novel silatranyloxides. The elimination reactions of 2 with main group element halides in THF in the presence of $NEt_3$ afford a new class of silatranyloxides of main group elements such as $Ph_3MOSi(OCH_2CH_2)_3N\; (M = Si, 3; Ge, 4),\; Ph_2CIMOSi(OCH_2CH_2)_3N\; (M = Si, Sn),\; Ph_2Si\{OCH_2CH_2)_3N\}_2$ (5), $Si\{OSi(OCH_2CH_2)_3N\}_4$, and $Ph2PSi(OCH_2CH_2)_3N$ (6). It is interesting to note that the compounds 4 and 5 adopt bent $Si-O-M(M = Ge, Si)$ angle while the compound 3 contains a linear $Si-O-Si$ geometry. The compound 6, a new type of phosphine, reacts with elemental sulfur and CuCl to yield a thiophosphinite containing a silatranyl group with a relatively strong transannular $N \to {Si}$ bonding and a dinuclear complex with the planar $Cu_2Cl_2$ rhomb, respectively. The reaction of 1 with lanthanide metal (III) chlorides afforded $[Ln(2-\kappa^6O,\kappa{N})(CF_3SO_3-\kappa{O})_2](CF_3SO_3)$ (Ln=La, Nd (7), Sm, Gd, Er and Yb). Single crystal X-ray diffraction study of 7 shows that neodymium in 7 adopts the coordination number of 9 with the coordination sphere of distorted capped square antipr...