NOVEL 2,4-DISILATHIETANE RING SYSTEM FROM CYCLOADDITION OF 1,1-DIMETHYL-1-SILAETHYLENE, Me2Si=CH2, TO DIMETHYLSILANTHIONE, Me2Si=S. PERTURBATION MOLECULAR ORBITAL (PMO) STUDY ON REACTIVITY OF INTERMEDIATES WITH A DOUBLE-BONDED SILICON ATOM

Article abstract of DOI:10.1016/0022-328X(84)85175-X

Copyrolysis of 1,1-dimethyl-1-silacyclobutane (I) with both hexamethylcyclotrisilthiane (II) and tetramethylcyclodisilthiane (III) at 500 deg C involves 1,1-dimethyl-1-silaethylene, Me2Si=CH2 (IV), and dimethylsilanthione, Me2Si=S (V), intermediates and yields the following cycloaddition products: the new 2,2,4,4-tetramethyl-2,4-disilathietane (VI), 1,1,3,3-tetramethyl-1,3-disilacyclobutane (VII), and III.Six-membered cyclocarbosilthianes, 1,1,3,3,5,5-hexamethyl-2-thia-1,3,5-trisilacyclohexane (VIII) and 1,1,3,3,5,5-hexamethyl-2,4-dithia-1,3,5-trisilacyclohexane (IX) have also been derived by inserting IV and V into the Si-S bond of VI.Copyrolysis of I with thiethane (X) also results in four- and six-membered cyclocarbosilthianes, the major product being VI.This is discussed in terms of dimethylsilanthione formation via <2 + 2>cycloaddition of IV to thioformaldehyde (XI) followed by <4 <*> 2 + 2>cyclodecomposition of the 2-silathiethane intermediate.A perturbation molecular orbital study of <2 + 2>cycloaddition involving intermediates IV, V, and XI has shown that IV reacts more readily with V and XI than it cyclodimerizes.Dimerization of V is the most prominent reaction.