Reaction of N-Heterocyclic Silylenes with Thioketone: Formation of Silicon-Sulfur Three (Si-C-S)- and Five (Si-C-C-C-S)-Membered Ring Systems

Azhakar R, Ghadwal R, Roesky HW, et al. Reaction of N-Heterocyclic Silylenes with Thioketone: Formation of Silicon-Sulfur Three (Si-C-S)- and Five (Si-C-C-C-S)-Membered Ring Systems. Chemistry - A European Journal. 2013;19(11):3715-3720.Three‐ and five‐membered rings that bear the (Si‐C‐S) and (Si‐C‐C‐C‐S) unit have been synthesized by the reactions of LSiCl (1; L=PhC(NtBu)2) and L′Si (2; L′=CH{(CCH2)(CMe)(2,6‐iPr2C6H3N)2}) with the thioketone 4,4′‐bis(dimethylamino)thiobenzophenone. Treatment of 4,4′‐bis(dimethylamino)thiobenzophenone with LSiCl at room temperature furnished the [1+2]‐cycloaddition product silathiacyclopropane 3. However, reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′Si at low temperature afforded a [1+4]‐cycloaddition to yield the five‐membered ring product 4. Compounds 3 and 4 were characterized by NMR spectroscopy, EIMS, and elemental analysis. The molecular structures of 3 and 4 were unambiguously established by single‐crystal X‐ray structural analysis. The room‐temperature reaction of 4,4′‐bis(dimethylamino)thiobenzophenone with L′Si resulted in products 4 and 5, in which 4 is the dearomatized product and 5 is formed under the 1,3‐migration of a hydrogen atom from the aromatic phenyl ring to the carbon atom of the CS unit. Furthermore, the optimized structures of probable products were investigated by using DFT calculations

New structural forms of organostannoxane macrocycle networks

The reaction of pyrazole-3,5-dicarboxylic acid with dibenzyltin dichloride in the presence of potassium hydroxide affords a novel 2D network containing rectangular box type hexatin units interconnected by two Bz<SUB>2</SUB>SnCl bridging groups. Hydrolysis of the latter affords a polymeric tape containing alternate hexatin macrocycle and tetratin ladder motifs

Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)<SUB>2</SUB>(Co(NO<SUB>3</SUB>)}Cl] (L' = N<SUB>3</SUB>P<SUB>3</SUB>(OC<SUB>5</SUB>H<SUB>4</SUB>N)<SUB>5</SUB>(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a &#951; 5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an &#951; 1-N1 fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (&#951; 3-nongem-N3), while the other zinc ion is tetracoordinate(&#951; 2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2&#183;6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens)

Dichlorosilylene: A High Temperature Transient Species to an Indispensable Building Block

Ghadwal R, Azhakar R, Roesky HW. Dichlorosilylene: A High Temperature Transient Species to an Indispensable Building Block. Accounts of Chemical Research. 2012;46(2):444-456.Isolating stable compounds with low-valent main group elements have long been an attractive research topic, because several of these compounds can mimic transition metals in activating small molecules. In addition, compounds with heavier low-valent main group elements have fundamentally different electronic properties when compared with their lighter congeners. Among group 14 elements, the heavier analogues of carbenes (R2C:) such as silylenes (R2Si:), germylenes (R2Ge:), stannylenes (R2Sn:), and plumbylenes (R2Pb:) are the most studied species with low-valent elements. The first stable carbene and silylene species were isolated as N-heterocycles. Among the dichlorides of group 14 elements, CCl2 and SiCl2 are highly reactive intermediates and play an important role in many chemical transformations. GeCl2 can be stabilized as a dioxane adduct, whereas SnCl2 and PbCl2 are available as stable compounds. In the Siemens process, which produces electronic grade silicon by thermal decomposition of HSiCl3 at 1150 °C, chemists proposed dichlorosilylene (SiCl2) as an intermediate, which further dissociates to Si and SiCl4. Similarly, base induced disproportionation of HSiCl3 or Si2Cl6 to SiCl2 is a known reaction. Trapping these products in situ with organic substrates suggested the mechanism for this reaction. In addition, West and co-workers reported a polymeric trans-chain like perchloropolysilane (SiCl2)n. However, the isolation of a stable free monomeric dichlorosilylene remained a challenge. The first successful attempt of taming SiCl2 was the isolation of monochlorosilylene PhC(NtBu)2SiCl supported by an amidinate ligand in 2006. In 2009, we succeeded in isolating N-heterocyclic carbene (NHC) stabilized dichlorosilylene (NHC)SiCl2 with a three coordinate silicon atom. (The NHC is 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) or 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes).) Notably, this method allows for the almost quantitative synthesis of (NHC)SiCl2 without using any hazardous reducing agents. Dehydrochlorination of HSiCl3 with NHC under mild reaction conditions produces (NHC)SiCl2. We can separate the insoluble side product (NHC)HCl readily and recycle it to form NHC. The high yield and facile access to dichlorosilylene allow us to explore its chemistry to a greater extent. In this Account, we describe the results using (NHC)SiCl2 primarily from our laboratory, including findings by other researchers. We emphasize the novel silicon compounds, which supposedly existed only as short-lived species. We also discuss silaoxirane, silaimine with tricoordinate silicon atom, silaisonitrile, and silaformyl chloride. In analogy with N-heterocyclic silylenes (NHSis), oxidative addition reactions of organic substrates with (NHC)SiCl2 produce Si(IV) compounds. The presence of the chloro-substituents both on (NHC)SiCl2 and its products allows metathesis reactions to produce novel silicon compounds with new functionality. These substituents also offer the possibility to synthesize interesting compounds with low-valent silicon by further reduction. Coordination of NHC to the silicon increases the acidity of the backbone protons on the imidazole ring, and therefore (NHC)SiCl2 can functionalize NHC at the C-4 or C-5 position