Divalent silanes

The bi- and tridentate phosphines dppp (l,3-bis(diphenylphosphino)propane) and dppep (bis (2-diphenylphosphinoethyl)phenylphosphine) have been complexed with Co and their divalent four- and five-coordinated thiophenolate complexes Co(dppp)(SPh)2 and Co(dppep)(SPh)2 have been isolated and structurally characterized.379 Somewhat related to dppp is the bidentate silane Ph2PCH2SiMe2CH2PPh2, which forms high-spin, pseudo-tetrahedral dihalocobalt(II) complexes.380... 

Some years ago we were successful in our attempts to synthesize a Jt-complex with divalent silicon as the central atom. Starting from dihalogeno(pentamethylcyclopentadienyl)silanes, we have been able to prepare decamethylsilicocene (1) by reductive elimination processes [1]. Characteristic data concerning the synthesis, structure, and bonding of 1 have been published elsewhere together with preliminary results concerning the chemistry of this compound [2]. Here we describe some further progress in this field. 

Another hindered silane, di-t-butyldichlorodisilane, gives high yields of the reactive divalent species, di-t -butylsilylene, which was characterized by its insertion reactions into Si-H bonds(35) ... 

A third photochemical access to silylenes, beside the isomerization of silenes and the photolysis of tri- or cyclopolysilanes, is the irradiation of geminal diazidosilanes, which under nitrogen loss often gives the corresponding divalent silicon species. However, silan-imines are frequent by-products164 or in some cases even the only products (Section IV). 

This article starts with a discussion of the parent hydrides, MH (M = C, Si, and Ge, n = 2-4), highlighting the major differences between the methane series and the silane and germane series. Some attention is paid to substituent effects on bond energies and geometries, and we introduce the important notion of the divalent state stabilization energy (DSSE). After laying this foundation, Si=C and Ge=C compounds are reviewed. This is followed by Si=Si, Ge=Ge, and Ge=Si doubly bonded structures and their isomers. Finally, triply bonded Si==C, Si=Si, and Ge=Ge compounds are briefly considered. 

Sequential Bond Dissociation Energies, D, and Divalent State Stabilization Energies, DSSE, of Monosubstituted Silanes and Methanes ... 

Some of these catalytic cycles lead to products that appear to arise from divalent silylenoid species. However, most of the products that are put forward as evidence of silylenoid species can be formed straightforwardly by simple addition/elimination cycles. Such is the case with the oligomerization of disilanes and the disproportionation of silanes (e.g., R2SiH2). For example, EtsSiSiPh2H is an expected product of the reaction of EtsSiH and Ph2SiH2 via an addition/elimination scheme [cf. Eq. (39)]. 

The molecular sieves with uniform mesopores are attractive substrates for the researches on ion adsorptions. The mesoporous silicas with various pore-connecting topologies have been prepared by templating with surfactant micelles. Grafting technique of silanes introduces funetional groups into the pores of such silicas. Divalent cations, Cu, Zn,... 

Divalent silicon species react with HjO, forming silanes. Dilute aq HF (10%) reacts with SiO or SiO-GeO mixtures producing silanes (SiH, SijH, SijHj, Si Hj, SijHj, Si,H,) or ternary Si-Ge hydrides (SiGeHg, Si GeHg, etc.), respectively. Dimeth-ylsilylene, obtained by photolysis of (MejSi), upon insertion into the OH bonds of HjO yields siloxane ... 

Recently we reported the syntheses of bis(hypersilyl)stannylene and plumbylene, [(Me3Si)3Si]2Sn and [(Me3Si)3Si]2Pb [1], using solvent-free alkali metal derivatives of tris(trimethylsilyl)silane (hypersilane) [2], Based on this success we tried to utilize the same method for the synthesis of the hitherto unknown corresponding germylene and silylene. Thus, bis[bis(trimethylsilyl)amino]-germylene and, as source of divalent silicon, trichlorosilane had been reacted with sodium or lithium hypersilanide in -pentane at -30 to -60°C (Schemes 1 and 2). 

The addition of Grignard reagents to secondary silanes has been catalyzed by low-valent zirconocene compounds (Scheme 23).69 Oxidative addition of an organic halide to the divalent zirconocene occurs following reductive elimination of silane. Using this procedure, silanes can be alkylated in excellent yield. 

Bonn, Reiffenstuhl and Jandik were able to separate a number of divalent metal ions effectively in a single run using an IDA resin [17]. A silica based material (Nucleosil 300-7 of 7 pm diameter. 300 A average pore size) was derivatized with y-glycidoxypropyltrimethoxy silane, then iminodiacetic acid was covalently coupled to the epoxy activated surface. The final material was slurry packed into a 100 x 4.6 mm stainless steel column. A complexing eluent containing 10 mM citric acid plus... 

Divalent titanium has been implicated as a catalyst in several reactions, including silane polymerization (1) and hydrosilation (2). Considerable theoretical effort has therefore been expended recently in analyzing the role of divalent titanium as a catalyst in the hydrosilation and bis-silylation reactions. 

Adsorption of PH3 impurities in silanes on zeolites at low temperatures [29] is the method usually proposed. Cation-exchanged zeolites containing Ag [30] or the divalent ions of Ca [31], Cd [32], or Mn [33,34] were employed. PH3 impurities in halosilane/H2 mixtures can also be removed by adsorption on zeolite [35]. 

Mijatovic et al. (2000) stndied nnmodified and silane-modified nanosilica (5bet=200 m /g) using 2 Si solid-state NMR spectroscopy. The mode of bonding onto the silanol surface (mono- or divalent, seven different surface functionalities) was specified by comparison with chemical shifts from solution. A detailed analysis was performed with respect to products formed via hydrosilylation reactions using a rough quantification of the snrface loading with a signal deconvolution process of the silanol resonances on the Aerosil snrface. Thns, the NMR techniques were mainly used to analyze the chemical structure of whole silica materials or their surface. 

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