Syntheses of Allyl- and 3-Silylpropyl-substituted Salen-like Tetradentate Ligands via Hypercoordinate Silicon Complexes

Abstract

The reaction of allylchlorosilanes (AllSiCl3, AllSiPhCl2) with the tetradentate salen-like ligand 1, o-HO-p-MeO-C6H3-C(Ph)=N-(CH2)2-N=C(Ph)-C6H3-p-OMe-o-OH, yields pentacoordinate silicon complexes of an allyl-substituted ligand system (o-O-p-MeO-C6H3-C(Ph)=N-(CH2)2- N-C(Ph,All)-C6H3-p-OMe-o-O)SiR (2a: R = Ph, 3: R = Cl). The allyl shift step involved in the formation of 2a and 3 probably occurs via an intermediate hexacoordinate silicon complex. This reaction is diastereoselective. The missing diastereomer of 2 (2b) was prepared using an alternative synthesis route, which starts from the trimethylsilyl derivative of ligand 1 o-Me3SiO-p-MeO-C6H3-C(Ph)=N- (CH2)2-N=C(Ph)-C6H3-p-OMe-o-OSiMe3. The diastereomers of 2 obtained from modified reaction pathways give rise to suggestions about the mechanism of formation of these complexes. Further functionalization of the allyl-substituted ligand system of 3 was carried out by hydrosilylation with HSiCl3 to yield complex 4 (o-O-p-MeO-C6H3-C(Ph)=N-(CH2)2-N-C(Ph)[(CH2)3-SiCl3]- C6H3-p-OMe-o-O)SiCl.

Photo‐Driven Si‐C Bond Cleavage in Hexacoordinate Silicon Complexes

“…As soon as Si−X bonds other than Si-Halide are getting activated by Sihypercoordination, the groups X may exhibit reactivities of camouflaged nucleophiles, i.e., group X may attack electrophilic centres in the ligand backbone such as carbonyl and imine carbon atoms. Such reactivity was shown for hexacoordinate silacyclobutanes [4], allylsilanes [5], disilanes [6], cyanosilanes [7] and H-silanes [8]. Even an unexpected alkyl group shift towards an imine ligand was reported recently [9].…”

Hexacoordinate Silicon Compounds with a Dianionic Tetradentate (N,N′,N′,N)-Chelating Ligand

“…Whereas SiCl 4 , PhSiCl 3 , and Ph 2 SiCl 2 were commercially available, (Anis) 2 SiCl 2 and (4-Me 2 N-C 6 H 4 )PhSiCl 2 were prepared from SiCl 4 and PhSiCl 3 , respectively, and suitable Grignard reagents (see Experimental Section). [7][8][9][10][11]18,19,[73][74][75][76][77] chelators, we have now explored silicon coordination chemistry with a dianionic tetradentate (N,N′,N′,N) chelator. Thus far, macrocyclic π-conjugated (porphyrine-and phthalocyanine-type) ligands [78][79][80][81] have been explored in silicon coordination chemistry (e.g., D [81]), and our study aims at building a bridge between these cyclic (N, …”

“…Whereas the former preferentially bind to Si atoms that carry strongly electron withdrawing groups (e.g., formation of pyridine adducts of halosilanes, Scheme 1, A, [1][2][3]), the latter offer greater opportunities of creating five-and six-coordinate silicon compounds even in case of the absence of halides from the silicon coordination sphere (e.g., pentacoordinate silicon with SiC 5 coordination sphere, B [4][5][6]; and hexacoordinate silicon with a tetradentate chelator and two Si-CH 3 groups, C [7]). For various reasons, such as activation of Si-X bonds by silicon hypercoordination [8][9][10][11][12][13][14][15][16], exploring special electronic/optical properties arising from the higher coordination number of silicon in combination with selected ligands [17][18][19][20] or the aim of creating and exploring hitherto unusual Si coordination compounds, e.g., with transition metals [21][22][23][24][25][26][27][28][29] or very soft Lewis bases in their ligand sphere [30][31][32][33][34][35][36][37][38], silicon coordination chemistry continues to be an attractive research field, reflected by frequently published research articles [39][40]…”

Silicon(IV) Chelates of an (ONN')-Tridentate Pyrrole-2-Carbaldimine Ligand: Syntheses, Structures and UV/Vis Properties

“…Silicon compounds with a silicon coordination number of five or six [1,2] are of interest for their enhanced reactivity [3] and electronic properties [4]. Of the many ligands that are explored for their coordination behavior to silicon, our focus is on the tridentate ONNchelators and in particular on the doubly deprotonated 2-(N-2-hydroxyphenyl)pyrrolcarbaldimine (LH 2 ) [5].…”

“…Of the many ligands that are explored for their coordination behavior to silicon, our focus is on the tridentate ONNchelators and in particular on the doubly deprotonated 2-(N-2-hydroxyphenyl)pyrrolcarbaldimine (LH 2 ) [5]. This tridentate chelator can in principle occupy different coordination sites of the trigonal-bipyramidal silicon coordination sphere, as shown for the neutral compounds LSi(CH 2 ) 3 and LSiPhMe (Scheme 1) [5d]. Relatively little is known about the coordinative abilities of the L 2− ligand [8], except in transition metal complexes of copper, nickel, rhodium, iridium and rhenium [6], some of which have found use as catalysts in the polymerization of ethylene and α-olefins [7].…”