Synthesis of Organosilicon Macrocycles. Palladium-Catalyzed Ring-Enlargement Oligomerization of Cyclic Disilanes via Si−Si σ-Bond Metathesis

Abstract

Bis(tert-alkyl isocyanide)palladium(0) complexes catalyzed a ring-enlargement oligomerization of 1,1,2,2-tetramethyl-1,2-disilacyclopentane through Si−Si σ-bond metathesis to give cyclic oligomers up to the 40-membered octamer. The cyclic structure of the tetramer was established by the single-crystal X-ray diffraction method, which showed that the four Si−Si bonds of the tetramer were in a close to parallel arrangement. Reactivities of the dimer, trimer, and tetramer in the presence of bis(tert-butyl isocyanide)palladium(0) revealed that the present Si−Si σ-bond metathesis proceeded reversibly, in which the −Me2Si(CH2)3SiMe2− unit of the disilacyclopentane was successively inserted into the Si−Si bond of the oligomer to give higher oligomers. The intermediary 6-membered bis(organosilyl)bis(tert-alkyl isocyanide)palladium complex, which arose from oxidative addition of the disilacyclopentane onto bis(tert-alkyl isocyanide)palladium(0), was isolated and characterized by the single-crystal X-ray method. The insertion of the −Me2Si(CH2)3SiMe2− unit also occurred with linear disilanes and digermane to give linear oligomers. The cyclic trimer and tetramer reacted with 2,6-diisopropylphenyl isocyanide in the presence of Pd(OAc)2 to afford an 18-membered-ring triimine and 24-membered-ring tetraimine, respectively, in which the isocyanides were inserted into all the Si−Si linkages. Oxidation of the cyclic oligomers with trimethylamine oxide gave the corresponding cyclic oligo(disiloxane) species in quantitative yields. Unexpected polymerization of the disilacyclopentane occurred in the presence of the (η5-cyclopentadienyl)(η3-allyl)palladium(II) catalyst to give poly(Me2Si(CH2)3SiMe2) compounds with high molecular weights.

Activation of silicon–silicon σ bonds by transition-metal complexes: synthesis and catalysis of new organosilyl transition-metal complexes

“…1). 21 It should be noted that addition of phosphine ligands to a solution of 3 induced reductive elimination of the Si᎐Si bond to give 2, suggesting that tert-alkyl…”

“…In fact, a stoichiometric reaction of 2 with Pd II Cp(CH 2 CH᎐ ᎐ CH 2 ) gave the ring-opened product 30, which could be formed through initial oxidative addition of the Si᎐Si bond onto palladium() (giving 31) followed by a stepwise reductive elimination of the Si-allyl and Si᎐Cp bonds probably via the cyclopentadienyl(organosilyl)palladium complex 32 [equation (17)]. 21 Similar treatment of the spirocyclic trisilane 10 with Pd II Cp(CH 2 CH᎐ ᎐ CH 2 ), however, afforded a novel Pd IV complex 33 having three silyl groups and an η 5 -Cp or η 5 -Cp* group at the palladium center [equation (18)]. 23 A single-crystal X-ray analysis of the corresponding Cp* derivative 33b revealed a tetrahedral structure, in which the average bonding distance between palladium and silicon is identical with those for the bis-and tetrakis-(organosilyl)palladium complexes so far characterized (Fig.…”

Mechanistic Study on the Platinum-Catalyzed Reaction between Disilacyclobutene and Acetylene

“…21,22 Bis-silylation of unsaturated hydrocarbons catalyzed by group 10 metals is a useful method for synthesizing organosilicon compounds, in which two Si-C bonds are created in a single chemical process. Although several elementary processes of bis-silylation have been investigated experimentally [23][24][25][26][27][28][29][30][31][32][33][34] and theoretically, [35][36][37][38][39] the mechanism of the metal-catalyzed reaction has not yet been fully understood. According to Nagai and coworkers, 24 the bis-silylation of acetylene proceeds in the sequence of the elementary processes shown in Scheme 3.…”

Supramolecular approach for synthesis and functionalization of cyclic macromolecules

“…Transition metal catalyzed insertion reaction of 3-membered sulfide into a cyclic dithioester has also been used to prepare cyclic polymers [23]. A cyclic dithiane has been reported to give a cyclic polymer through bulk polymerization [24], while a cyclic disilane gave cyclic oligomers by transition metal catalyzed silicon-silicon bond metathesis [25]. In general, however, applicable monomers for these methods are limited.…”