Syntheses, reactivities and catalytic applications of low-valent compounds with p-block elements

Abstract

The chemistry of heavier group 14 elements in their low oxidation state has gained much attention over the last decades. The higher congeners of group 14 known as tetrylenes are very much known for their amphiphilic nature which is mainly due to the presence of both vacant p-orbital as well as lone pair of electrons. The compounds featuring group 14 elements along with sulfur and selenium are well known for their chemical and physical properties. In the first chapter, we have worked on synthesizing tin chalcogenide complexes. Since 2-aminopyridine ligands offer a wide range of substitution patterns due to the presence of both anionic amide and neutral pyridine, we have employed aminopyridinate ligands to synthesize two types of stannylenes. Subsequently, we performed their reactivity with elemental sulfur and selenium, which afforded a four-membered cyclic Sn2E2 (E= S, Se) moiety. Initially according to the “double bond rule”, the heavy homologues of carbon are not able to form stable multiple bonds. This rule got invalid with the first isolation of disilene by West and coworkers in 1981. In the second part of our work, we have studied the reactivity pattern of a previously reported disilene [(TMS)2N(η1-Me5C5)Si=Si(η1-Me5C5)-N(TMS)2] with the halides of group 13-15 elements which resulted in the formation of Si-E bonds (E = B, Al, Ge and P). The treatment of the disilene with BCl3 resulted in the formation of cationic boron species [Cp*BSi(Cl)2N(TMS)2)][BCl3SiCl3], on the other hand with BCy2Cl it afforded oxidative addition product [(TMS)2N(η1 - Me5C5)Si(BCy2)(Cl)] via the insertion of Si center into B-Cl bond. While with AlCl3/AlBr3 simple Lewis acid-base adduct formation is observed. But in the case of GeCl2, a totally different pattern of reactivity was obtained resulting in a hybrid dendrimeric compound [HGe(Si(Cl)2N(TMS)2)3]. Lastly, the reaction with PPh2Cl also proceeded in a similar pattern to that of BCy2Cl leading to the formation of the oxidative addition product [(TMS)2N(η1-Me5C5)Si(PPh2)(Cl). The burgeoning chemistry of cations of group 15 elements in the field of catalysis is mainly considered due to their enhanced electrophilic nature which makes them more Lewis acidic. Owing to the presence of a lone pair of electrons and vacant p-orbital stibenium and bismuthenium cations are considered to be amphoteric in nature. It has been established that group 15 cationic species are strong π acceptors and weak σ donors. The last part of our work mainly focuses on the synthesis of stibenium and bismuthenium ions as well as the study of their efficiency in the field of homogeneous catalysis. Although Sb(V) is well known as Lewis acid catalysts but Sb(III) cation remains unexplored in this area. So, we have reported a novel donor-free stibenium as well as a bismuthenium cation and subsequently utilized them as an efficient catalyst for the cyanosilylation of carbonyls.