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The facile synthesis of the first stable selenosilanoic acid-base adduct LSi(=Se)OH(dmap) 3 (L = CH[C(Me)NAr]2, Ar = 2,6-iPr2C6H3, dmap = 4-dimethylaminopyridine), the heavier analogue of the thiosilanoic acid adduct LSi(=S)OH(dmap) 1, is reported. Both adducts 1 and 3 react readily with MesCu (Mes = 2,4,6-trimethylphenyl) to form the novel dimeric Cu(I) complexes [LSi(=E)OCu]2 (4: E = S; 5: E = Se) with unprecedented intermolecular Si=E → Cu-O-Si coordination modes. The latter are efficient pre-catalysts for the Cu(I)-mediated aziridination of styrene with PhI=N(Ts) (Ts = tosyl).

In contrast to the well-established chemistry of ketones (R2C=O), the reactivity of the elusive heavier congeners R2E=O (E=Si, Ge, Sn, Pb) is far less explored because of the high polarity of the E=O bonds and hence their tendency to oligomerize with no activation barrier. Very recently, great advances have been achieved in the synthesis of isolable compounds with E=O bonds, including the investigation of donor-stabilized isolable silanones and the first stable "genuine" germanone. These compounds show drastically different reactivities compared to ketones and represent versatile building blocks in silicon-oxygen and germanium-oxygen chemistry. This and other exciting achievements are described in this Minireview., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Synthesis and characterization of the first manganese(II)-containing heavier thiocarboxylate analogues, [L(Dip)Si(=S)OMnL(Dep)] (4; L(Dip)=CH[C(Me)N(2,6-iPr(2)C(6)H(3))](2), L(Dep)=CH[C(Me)N(2,6-Et(2)C(6)H(3))](2)) and [L(Dip)Ge(=S)OMnL(Dep)] (5) are described. They are accessible through reaction of the silicon and germanium analogues of the respective thiocarboxylic acids [L(Dip)E(=S)OH] (E=Si, Ge) with the β-diketiminato (nacnac) manganese(II) hydride precursor [(L(Dep)Mn)(2)(μ-H)(2)] (3) in high yield. The first Mn nacnac hydride 3 has been prepared by the reaction of manganese bromide [(L(Dep)Mn)(2)(μ-Br)(2)] (2) with KBEt(3)H. Compounds 4 and 5 represent the first transition-metal heavier thiocarboxylates with the Si=S and Ge=S functionalities. All new compounds are paramagnetic and were characterized by elemental analysis, IR spectroscopy, MS (EI), and single-crystal X-ray diffraction analyses. Due to the N→E (E=Si, Ge) and E=S→Mn donor-acceptor interaction as well as the carboxylate-like π-electron delocalization within the E(S)O moieties, the E=S double bonds in these compounds are resonance stabilized., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dioxygen activation for the subsequent oxygenation of organic substrates that involves cheap and environmentally friendly chemical elements is at the cutting edge of chemical research. As silicon is a non-toxic and highly oxophilic element, the use of silylenes could be attractive for facile dioxygen activation to give dioxasiliranes with a SiO(2)-peroxo ring as versatile oxo-transfer reagents. However, the latter are elusive species, and have been generated and studied only in argon matrices at -233 degrees C. Recently, it was demonstrated that unstable silicon species can be isolated by applying the concept of donor-acceptor stabilization. We now report the first synthesis and crystallographic characterization of dioxasiliranes stabilized by N-heterocyclic carbenes that feature a three-membered SiO(2)-peroxide ring, isolable at room temperature. Unexpectedly, these can undergo internal oxygen transfer in toluene solution at ambient temperature to give a unique complex of cyclic sila-urea with C=O --> Si=O interaction and the shortest Si=O double-bond distance reported to date.

The strikingly different behavior of the ylide-like, N-heterocyclic silylene LSi: (5: L = CH[(C horizontal lineCH(2))CMe(NAr)(2)]; Ar = 2,6-(i)PrC(6)H(3)) versus its LSi-->Ni(CO)(3) complex 13 to activate E-H bonds (E = S, N) of small molecules is reported. Remarkably, conversion of 5 with hydrogen sulfide leads exclusively to the first isolable silathioformamide, L'Si( horizontal lineS)H (16: L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)) with a donor-supported Si horizontal lineS double bond and four-coordinate silicon. The latter result demonstrates the unusual ambivalent reactivity of 5 by combining two modes of reactivity involving S-H bond activation and subsequent 1,4- and 1,1-addition, respectively. In addition, 5 can serve as a ligand with well-balanced sigma-donor and pi-acceptor capabilities toward transition metals. This has been demonstrated by the isolable [Ni(0)(arene)] complexes 12a-e (arene = Me(n)C(6)H(6-n), n = 0-3), which are ideal precursors for the formation of the corresponding Ni(CO)(3) complex 13. The latter activates a S-H bond in hydrogen sulfide, too, but the presence of the Ni(CO)(3) moiety governs the formation of the complex 17, bearing an unprecedented beta-diketiminate silicon(II) thiol ligand: L'Si(SH): (L' = CH[C(Me)NAr](2); Ar = 2,6-(i)PrC(6)H(3)). Likewise, the Si(II)-->Ni(CO)(3) coordination in 13 steers exclusively 1,4-addition of ammonia, isopropylamine, and phenylhydrazine onto the silylene ligand 5, leading to the corresponding beta-diketiminate silicon(II) amide or hydrazide complexes L'Si(NHR)-->Ni(CO)(3) (23a-c: R = H, (i)Pr, N(H)Ph). IR measurements reveal that the carbonyl stretching frequencies of the Ni(CO)(3) moiety in 23a-c are shifted to even lower wavenumbers in comparison to those of NHCs or phosphines. In other words, the beta-diketiminate silicon(II) amide ligands in 23a-c represent the strongest donors in the series of N-heterocyclic silylenes reported as yet.

The synthesis and characterization of the first heterobinuclear tetraphosphorus complexes 3a and 3b with a [Si(mu,eta(2:2)-P(4))Ni] core are reported. The latter result from conversion of the silylene-activated P(4) ligand LSiP(4) (1; L = CH[(C horizontal lineCH(2))CMe][N(2,6-(i)Pr(2)C(6)H(3))](2)) with the beta-diketiminatonickel(I) complexes [(L'Ni)(2).toluene] (L' = CH[CMeN(2,6-iPr(2)C(6)H(3))](2)) and [(L''Ni)(2).toluene] (L'' = CH[CMeN(2,6-Et(2)C(6)H(3))](2)), respectively. Unexpectedly, the complexes 3a and 3b feature a [Si(mu,eta(2:2)-P(4))Ni] core with nickel(I) centers as shown by X-ray diffraction analysis, electron paramagnetic resonance, and magnetic measurements. The latter prove that the products are paramagnetic both in the solid state and in solution because of the presence of tetrahedral nickel(I) sites.

New types of metal‐free white phosphorus (P4) activation are reported. While the phosphine‐silylene‐substituted dicarborane 1, CB‐SiP (CB=ortho‐C,C′‐C2B10H10, Si=PhC(tBuN)2Si, P=P[N(tBu)CH2]2), activates white phosphorus in a 2 : 1 molar ratio to yield the P5‐chain containing species 2, the analogous bis(silylene)‐substituted compound 3, CB‐Si2, reacts with P4 in the molar ratio of 2 : 1 to furnish the first isolable 1,3‐diphospha‐2,4‐disilabutadiene (Si=P−Si=P‐containing) compound 4. For the latter reaction, two intermediates having a CB‐Si2P4 and CB‐Si2P2 core could be observed by multinuclear NMR spectroscopy. The compounds 2 and 4 were characterized including single‐crystal X‐ray diffraction analyses. Their electronic structures and mechanisms were investigated by density functional theory calculations. [ABSTRACT FROM AUTHOR]

The reactivity of the 1,4‐substituted bis(silylenyl)terphenylene 1, 1,4‐[ortho‐(LSi)C6H4]2C6H4, (L=RC(NtBu)2, R=Ph, Mes) towards CS2 is reported. It results in a dearomatization of the phenylene ring, affording the 1,3‐substituted cyclohexadiene derivative 2. According to DFT calculations, a transient silene containing a Si=C bond capable of π(C=C) addition at the aromatic phenylene ring is a key intermediate. In contrast, addition of CS2 to the biphenyl‐substituted mono‐silylene ortho‐(LSi)C6H4‐C6H53 leaves the aromatic π‐system intact and forms, in a [1+2] cycloaddition reaction, the corresponding thiasilirane 4 with a three‐membered SiSC ring. Further experimental studies led to the isolation of the novel mesoionic five‐membered Si2S2C heterocycle 6, which reacts with CS2 under C−C bond formation. All isolated new compounds were fully characterized and their molecular structures determined by single‐crystal X‐ray diffraction analyses. [ABSTRACT FROM AUTHOR]

In stark contrast to the reactivity of the bis-silylenyl dicarborane CB–Si2 (1) [CB = ortho-C,C′-C2B10H10, Si = PhC(tBuN)2Si] towards O2, N2O, and CO2, yielding the same dioxygenation product CB–Si2O2 (2) with a four-membered 1,3,2,4-disiladioxetane ring, the activation of the latter small molecules with the phosphanyl-silylenyl-functionalised CB–SiP (3) {P＝P[N(tBu)CH2]2} affords with O2 the CB–Si(＝O)P(＝O) silanone-phosphine oxide (4), with N2O the CB–Si(＝O)P silanone-phosphine (5), and with CO2 the CB–Si(O2C＝O)P silicon carbonate-phosphine (6) and CB–C(＝O)OSiOP ester (7), respectively. [ABSTRACT FROM AUTHOR]

A facile synthesis and isolation of pristine silicon tetrakis(trifluoromethanesulfonate), Si(OTf)4, is reported, acting as the first neutral silicon‐based Lewis superacid suitable towards soft and hard Lewis bases. Its OTf groups have a dual function: they are excellent leaving groups and modulate the degree of reactivity towards soft and hard Lewis bases. Exposed to soft Lewis donors, Si(OTf)4 leads to [L2Si(OTf)4] complexes (L=isocyanide, thioether and carbonyl compounds) with retention of all Si−OTf bonds. In contrast, it can cleave C−X bonds (X=F, Cl) of hard organic Lewis bases with a high tendency to form SiX4 (X=F, Cl) after halide/triflate exchange. Most notable, Si(OTf)4 allows a gentle oxydefluorination of mono‐ and bis(trifluoromethyl)benzenes, resulting in the formation of the corresponding benzoylium species, which are stabilized by the weakly coordinating [Si(OTf)6] dianion. [ABSTRACT FROM AUTHOR]

Molecular silicon polycations of the types R2Si2+ and RSi3+ (R=H, organic groups) are elusive Lewis superacids and currently unknown in the condensed phase. Here, we report the synthesis of a series of isolable terpyridine‐stabilized R2Si2+ and RSi3+ complexes, [R2Si(terpy)]2+ (R=Ph 12+; R2=C12H822+, (CH2)332+) and [RSi(terpy)]3+ (R=Ph 43+, cyclohexyl 53+, m‐xylyl 63+), in form of their triflate salts. The stabilization of the latter is achieved through higher coordination and to the expense of reduced fluoride‐ion affinities, but a significant level of Lewis superacidity is nonetheless retained as verified by theory and experiment. The complexes activate C(sp3)−F bonds, as showcased by stoichiometric fluoride abstraction from 1‐fluoroadamantane (AdF) and the catalytic hydrodefluorination of AdF. The formation of the crystalline adducts [2(F)]+ and [5(H)]2+ documents in particular the high reactivity towards fluoride and hydride donors. [ABSTRACT FROM AUTHOR]

The versatile cycloaddition chemistry of the Si−Ni multiple bond in the acyclic (amido)(chloro)silylene→Ni0 complex 1, [(TMSL)ClSi→Ni(NHC)2] (TMSL=N(SiMe3)Dipp; Dipp=2,6‐iPr2C6H4; NHC=C[(iPr)NC(Me)]2), toward unsaturated organic substrates is reported, which is both reminiscent of and expanding on the reactivity patterns of classical Fischer and Schrock carbene–metal complexes. Thus, 1:1 reaction of 1 with aldehydes, imines, alkynes, and even alkenes proceed to yield [2+2] cycloaddition products, leading to a range of four‐membered metallasilacycles. This cycloaddition is in fact reversible for ethylene, whereas addition of an excess of this olefin leads to quantitative sp2‐CH bond activation, via a 1‐nickela‐4‐silacyclohexane intermediate. These results have been supported by DFT calculations giving insights into key mechanistic aspects. [ABSTRACT FROM AUTHOR]

Facile oxygenation of the acyclic amido-chlorosilylene bis(N-heterocyclic carbene) Ni0 complex [{N(Dipp)(SiMe3)ClSi:→Ni(NHC)2] ( 1; Dipp=2,6-iPr2C6H4; N-heterocyclic carbene=C[(iPr)NC(Me)]2) with N2O furnishes the first Si-metalated iminosilane, [DippN=Si(OSiMe3)Ni(Cl)(NHC)2] ( 3), in a rearrangement cascade. Markedly, the formation of 3 proceeds via the silanone (Si=O)-Ni π-complex 2 as the initial product, which was predicted by DFT calculations and observed spectroscopically. The Si=O and Si=N moieties in 2 and 3, respectively, show remarkable hydroboration reactivity towards H−B bonds of boranes, in the former case corroborating the proposed formation of a (Si=O)-Ni π-complex at low temperature. [ABSTRACT FROM AUTHOR]

The first 16 valence electron [bis(NHC)](silylene)Ni0 complex 1, [(TMSL)ClSi:→Ni(NHC)2], bearing the acyclic amido-chlorosilylene (TMSL)ClSi: (TMSL=N(SiMe3)Dipp; Dipp=2,6-Pri2C6H4) and two NHC ligands (N-heterocyclic carbene=:C[(Pri)NC(Me)]2) was synthesized in high yield and structurally characterized. Compound 1 is capable of facile dihydrogen activation under ambient conditions to give the corresponding HSi-NiH complex 2. Most notably, 1 reacts with catechol borane to afford the unprecedented hydroborylene-coordinated (chloro)(silyl)nickel(II) complex 3, {[cat(TMSL)Si](Cl)Ni←:BH(NHC)2}, via the cleavage of two B−O bonds and simultaneous formation of two Si−O bonds. The mechanism for the formation of 3 was rationalized by means of DFT calculations, which highlight the powerful synergistic effects of the Si:→Ni moiety in the breaking of incredibly strong B−O bonds. [ABSTRACT FROM AUTHOR]

The synthesis of the unprecedented monomeric SiII selenide complex (bis-NHC)Si=Se→GaCl3 2 (bis-NHC=bis-N heterocyclic carbene, H2C[{NC(H)=C(H)N(Dipp)}C:]2, Dipp=2,6-iPr2C6H3), bearing the elusive SiSe ligand as a heavy CO homologue by the reaction of the silylone-GaCl3 adduct (bis-NHC)Si→GaCl3 1 with elemental selenium in acetonitrile, is reported. The similar conversion of 1 with excess selenium conducted in THF afforded the SiSe2 complex (bis-NHC)Si(=Se)Se→GaCl3 3. Remarkably, the reaction of 1 with Te=P( nBu)3 as a gentle Te transfer reagent led to the isolation of the monomeric SiTe2 complex (bis-NHC)SiTe2 4, the first structurally characterized Lewis acid free heavy CO2 homologue complex. The isolated compounds 2, 3, and 4 have been fully characterized, including single-crystal X-ray diffraction analyses. Their electronic structures and spectroscopic data have also been studied by quantum-chemical calculations. [ABSTRACT FROM AUTHOR]

C−H Borylation of arenes has been a subject of great interest recently because of its atom-economy and the wide applicability of borylated products in value-added synthesis. A new bis(silylene)cobalt(II) complex bearing a bis( N-heterocyclic silylene)-pyridine pincer ligand (SiNSi) has been synthesized and structurally characterized. It enabled the regioselective catalytic C−H borylation of pyridines, furans, and fluorinated arenes. Notably, it exhibited complementary regioselectivity for the borylation of fluorinated arenes compared to previously known catalytic systems, demonstrating that N-heterocyclic silylene donors have enormous potential in metal-catalyzed catalytic applications. [ABSTRACT FROM AUTHOR]

For the first time, a significant boost in catalytic activity in the rhodium-catalysed hydroformylation of an alkene by using a bidentate bis(N-heterocyclic silylene) ligand is reported. This is shown by the hydroformylation of styrene at 30 bar CO/H2 pressure in the presence of [HRh(CO)(PPh3)3] with an excess of the ferrocenediyl-based bis-NHSi ligand 4, [({η5-C5H4{PhC(NtBu)2}Si})2Fe], which results in superior catalytic activity, compared with the bidentate diphosphines DPPF (3a) and xantphos (3b). In contrast, the hydroformylation of styrene in the presence of [HRh(CO)(PPh3)3] with excesses of the monodentate NHSi ligands [{PhC(NtBu)2}SiNMe2] (1) and [{C2H2(NtBu)2}Si:] (2) at 30 bar CO/H2 pressure revealed considerably slower conversion to the aldehyde products than [HRh(CO)(PPh3)3], with or without an excess of PPh3, showing catalyst deactivation. Surprisingly, the germanium analogue of 4 is shown to be virtually catalytically inactive. The superior activity of 4, compared with the xantphos-containing benchmark system, is rationalized on the basis of solution NMR spectroscopic studies, and the comparative catalyst cycles are elucidated using density functional theory (DFT) methods. The latter quantum-chemical studies explain very well the favourable energy pathway for the hydroformylation of styrene using 4 versus xantphos. [ABSTRACT FROM AUTHOR]

The first isolable molecular silicon dicarbonate complex (bis-NHC)Si(CO3)2 2 (bis-NHC=H2C[{NC(H)=C(H)N(Dipp)}C:]2, Dipp=2,6-iPr2C6H3) was synthesized by facile reaction of the bis-N-heterocyclic carbene stabilized silylone (bis-NHC)Si 1, bearing a zero-valent silicon atom, with carbon dioxide. The monomeric silicon dioxide complex (bis-NHC)SiO2 3 supported by the bis-NHC ligand was proposed as a key intermediate resulting from double oxygenation of the zero-valent silicon atom in 1 by two molar equivalents of CO2 under liberation of CO; its subsequent Lewis acid-base reaction with CO2 leads to 2 which has been fully characterized including an single-crystal X-ray diffraction analysis. Its electronic structure, spectroscopic data and the thermochemistry of the formation have been studied quantum-chemically. [ABSTRACT FROM AUTHOR]

The synthesis, reactivity, and electronic structure of the unique germylone iron carbonyl complex [SiNSi]Ge0→Fe(CO)4 is reported. The compound was obtained in 49 % yield from the reaction of the bis(N-heterocyclic silylenyl)pyridine pincer ligand SiNSi (1,6-C5NH3-[EtNSi(NtBu)2CPh]2) with GeCl2⋅(dioxane) to give the corresponding chlorogermyliumylidene chloride precursor [SiNSi]GeIICl+ Cl−, which was further reduced with K2Fe(CO)4. Single-crystal X-ray diffraction analysis of [SiNSi]Ge→Fe(CO)4 revealed that the Ge0 center adopts a trigonal-pyramidal geometry with a Si-Ge-Si angle of 95.66(2)°. Remarkably, one of the SiII donor atoms in the complex is five-coordinated because of additional (pyridine)N→Si coordination. Unexpectedly, the reaction of [SiNSi]Ge→Fe(CO)4 with GeCl2⋅(dioxane) (one molar equivalent) yielded the first push-pull germylone-germylene donor-acceptor complex, [SiNSi]Ge→GeCl2→Fe(CO)4 through the insertion of GeCl2 into the dative Ge0→Fe bond. The electronic features of the new compounds were investigated by DFT calculations. [ABSTRACT FROM AUTHOR]

Reaction of the arylchlorosilylene-NHC adduct ArSi(NHC)Cl [Ar = 2,6-Trip2C6H3; NHC = (MeC)2(NMe)2C:] 1 with one molar equiv of lithium diphenylphosphanide affords the first stable NHC-stabilized acyclic phosphinosilylene adduct 2 (ArSi(NHC)PPh2), which could be structurally characterized. Compound 2, when reacted with one molar equiv selenium and sulfur, affords the silanechalco-genones 4a and 4b (ArSi(NHC)(=E)PPh2, 4a: E = Se, 4b: E = S), respectively. Conversion of 2 with an excess of Se and S, through additional insertion of one chalcogen atom into the Si-P bond, leads to 3 a and 3 b (Ar-Si(NHC)(=E)-E-P(=E)Ph2, 3a: E = Se, 3b: E = S), respectively. Additionally, the exposure of 2 to N2O or CO2 yielded the isolable NHC-stabilized silanone 4c, Ar(NHC)(Ph2P)Si=O. [ABSTRACT FROM AUTHOR]

The reaction of the arylchlorosilylene-NHC adduct ArSi(NHC)Cl [Ar=2,6-Trip2-C6H3; NHC=(MeC)2(NMe)2C] 1 with one molar equiv of LiPH2.dme (dme=1,2-dimethoxyethane) affords the first 1,2-dihydrophosphasilene adduct 2 (ArSi(NHC)(H)=PH). The latter is labile in solution and can undergo head-to-tail dimerization to give [ArSi(H)PH]2 3 and "free" NHC. Further stabilization of 2 by complexation with {W(CO)5} affords the isolable 1,2-dihydrophosphasilene-tungsten complex 4 [ArSi(NHC)(H)=P(H)W(CO)5]. Additionally, the new 1-silyl-2-hydrophosphasilene ArSi(NHC)(H)=PSiMe3 5 could be synthesized and structurally characterized. DFT studies confirmed that the Si=P bond in 2 and 4 is mostly zwitterionic with drastically decreased double-bond character. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the first bis-N-heterocyclic carbene stabilized monomeric silicon disulfide (bis-NHC)SiS2 2 (bis-NHC=H2C[{NC(H)C(H)N(Dipp)}C:]2, Dipp=2,6- iPr2C6H3) is reported. Compound 2 is prepared in 89 % yield from the reaction of the zero-valent silicon complex (′silylone′) 1 [(bis-NHC)Si] with elemental sulfur. Compound 2 can react with GaCl3 in acetonitrile to give the corresponding (bis-NHC)Si(S)S→GaCl3 Lewis acid-base adduct 3 in 91 % yield. Compound 3 is also accessible through the reaction of the unprecedented silylone-GaCl3 adduct [(bis-NHC)Si→GaCl3] 4 with elemental sulfur. Compounds 2, 3, and 4 could be isolated and characterized by elemental analyses, HR-MS, IR, 13C- and 29Si-NMR spectroscopy. The structures of 3 and 4 could be determined by single-crystal X-ray diffraction analyses. DFT-derived bonding analyses of 2 and 3 exhibited highly polar SiS bonds with moderate pπ-pπ bonding character. [ABSTRACT FROM AUTHOR]

The NiII-mediated tautomerization of the N-heterocyclic hydrosilylcarbene L2Si(H)(CH2)NHC 1, where L2=CH(CCH2)(CMe)(NAr)2, Ar=2,6- iPr2C6H3; NHC=3,4,5-trimethylimidazol-2-yliden-6-yl, leads to the first N-heterocyclic silylene (NHSi)-carbene (NHC) chelate ligand in the dibromo nickel(II) complex [L1Si:(CH2)(NHC)NiBr2] 2 (L1=CH(MeCNAr)2). Reduction of 2 with KC8 in the presence of PMe3 as an auxiliary ligand afforded, depending on the reaction time, the N-heterocyclic silyl-NHC bromo NiII complex [L2Si(CH2)NHCNiBr(PMe3)] 3 and the unique Ni0 complex [η2(Si-H){L2Si(H)(CH2)NHC}Ni(PMe3)2] 4 featuring an agostic SiH→Ni bonding interaction. When 1,2-bis(dimethylphosphino)ethane (DMPE) was employed as an exogenous ligand, the first NHSi-NHC chelate-ligand-stabilized Ni0 complex [L1Si:(CH2)NHCNi(dmpe)] 5 could be isolated. Moreover, the dicarbonyl Ni0 complex 6, [L1Si:(CH2)NHCNi(CO)2], is easily accessible by the reduction of 2 with K(BHEt3) under a CO atmosphere. The complexes were spectroscopically and structurally characterized. Furthermore, complex 2 can serve as an efficient precatalyst for Kumada-Corriu-type cross-coupling reactions. [ABSTRACT FROM AUTHOR]

The stabilization of the labile, zwitterionic 'half-parent' phosphasilene 4 L′SiPH (L′=CH[(CCH2)CMe(NAr)2]; Ar=2,6- iPr2C6H3) could now be accomplished by coordination with two different donor ligands (4-dimethylaminopyridine (DMAP) and 1,3,4,5-tetramethylimidazol-2-ylidene), affording the adducts 8 and 9, respectively. The DMAP-stabilized zwitterionic 'half-parent' phosphasilene 8 is capable of transferring the elusive parent phosphinidene moiety (:PH) to an unsaturated organic substrate, in analogy to the 'free' phosphasilene 4. Furthermore, compounds 4 and 8 show an unusual reactivity of the SiP moiety towards small molecules. They are capable of adding dimethylzinc and of activating the SH bonds in H2S and the NH bonds in ammonia and several organoamines. Interestingly, the DMAP donor ligand of 8 has the propensity to act as a leaving group at the phosphasilene during the reaction. Accordingly, treatment of 8 with H2S affords, under liberation of DMAP, the unprecedented thiosilanoic phosphane LSiS(PH2) 16 (L=HC(CMe[2,6- iPr2C6H3N])2). Compounds 4 and 8 react with ammonia both affording L′Si(NH2)PH2 17, respectively. In addition, the reaction of 8 with isoproylamine, p-toluidine, and pentafluorophenylhydrazine lead to the corresponding phosphanylsilanes L′Si(PH2)NHR (R= iPr 18 a; R=C6H5CH3 18 b, R=NH(C6F5) 18 c), respectively. [ABSTRACT FROM AUTHOR]

King of donor: The chelating bis(carbene) 1 enabled the synthesis of the new silyliumylidene salt 2. This salt can be dechlorinated with sodium naphthalenide to give the first cyclic siladicarbene 3, which bears a single Si0 atom with strikingly high basicity. The small C‐Si‐C angle of 89.1° and the average CSi distance of 1.869 Å are consistent with results from theoretical calculations, which revealed that 3 is best described as a silylone. [ABSTRACT FROM AUTHOR]

In contrast to the well-established chemistry of ketones (R2CO), the reactivity of the elusive heavier congeners R2EO (E=Si, Ge, Sn, Pb) is far less explored because of the high polarity of the EO bonds and hence their tendency to oligomerize with no activation barrier. Very recently, great advances have been achieved in the synthesis of isolable compounds with EO bonds, including the investigation of donor-stabilized isolable silanones and the first stable 'genuine' germanone. These compounds show drastically different reactivities compared to ketones and represent versatile building blocks in silicon-oxygen and germanium-oxygen chemistry. This and other exciting achievements are described in this Minireview. [ABSTRACT FROM AUTHOR]

A series of unprecedented bis-silylene titanium(II) complexes of the type [(η5-C5H5)2Ti(LSiX)2] (L=PhC(N tBu)2; X=Cl, CH3, H) has been prepared using a phosphane elimination strategy. Treatment of the [(η5-C5H5)2Ti(PMe3)2] precursor ( 1) with two molar equivalents of the N-heterocyclic chlorosilylene LSiCl ( 2), results in [(η5-C5H5)2Ti(LSiCl)2] ( 3) with concomitant PMe3 elimination. The presence of a SiCl bond in 3 enabled further functionalization at the silicon(II) center. Accordingly, a salt metathesis reaction of 3 with two equivalents of MeLi results in [(η5-C5H5)2Ti(LSiMe)2] ( 4). Similarly, the reaction of 3 with two equivalents of LiBHEt3 results in [(η5-C5H5)2Ti(LSiH)2] ( 5), which represents the first example of a bis-(hydridosilylene) metal complex. All complexes were fully characterized and the structures of 3 and 4 elucidated by single-crystal X-ray diffraction analysis. DFT calculations of complexes 3- 5 were also carried out to assess the nature of the titanium-silicon bonds. Two σ and one π-type molecular orbital, delocalized over the Si-Ti-Si framework, are observed. [ABSTRACT FROM AUTHOR]

Synthesis and characterization of the first manganese(II)-containing heavier thiocarboxylate analogues, [LDipSi(S)OMnLDep] ( 4; LDip=CH[C(Me)N(2,6- iPr2C6H3)]2, LDep=CH[C(Me)N(2,6-Et2C6H3)]2) and [LDipGe(S)OMnLDep] ( 5) are described. They are accessible through reaction of the silicon and germanium analogues of the respective thiocarboxylic acids [LDipE(S)OH] (E=Si, Ge) with the β-diketiminato (nacnac) manganese(II) hydride precursor [(LDepMn)2(μ-H)2] ( 3) in high yield. The first Mn nacnac hydride 3 has been prepared by the reaction of manganese bromide [(LDepMn)2(μ-Br)2] ( 2) with KBEt3H. Compounds 4 and 5 represent the first transition-metal heavier thiocarboxylates with the SiS and GeS functionalities. All new compounds are paramagnetic and were characterized by elemental analysis, IR spectroscopy, MS (EI), and single-crystal X-ray diffraction analyses. Due to the N→E (E=Si, Ge) and E=S→Mn donor-acceptor interaction as well as the carboxylate-like π-electron delocalization within the E(S)O moieties, the ES double bonds in these compounds are resonance stabilized. [ABSTRACT FROM AUTHOR]

The P + -transfer abilities of 1,1,1,3,3,3-hexakis(dimethylamino)-triphosphenium tetraphenylborate were investigated. Reaction with Schwartz reagent lead to the first planar tetracoordinated phosphonium salt P[ZrCp 2 H] 4 + BPh 4 + . The theoretical background of this unusual planar geometry at the phosphorus atom is discussed. The first arsenic analogue [As(P(NMe 2 ) 3 )2] + BPh 4 - of the respective triphosphenium salt was prepared, which surprisingly can act as a P + - and As + -transfer reagent at the same time. Furthermore, the synthesis of perstannylated ([(Me 3 Sn) 4 E]OSO 2 CF 3 , E = N, P) and persilylated ([(Me 3 Si) 4 E] + B(C 6 F 5 ) 4 - , E = P, As) onium ions of nitrogen, phosphorus, and arsenic are reported, which are potential starting materials for an independent access to E[ZrCp 2 X] 4 salts. [ABSTRACT FROM AUTHOR]

The back cover of the 2017 edition of the journal "Angewandte Chemie" is presented.

Going for silicon: Although silicon is the second most abundant chemical element of the earth crust, it took mankind quite some time (more than 100 years) to uncover and develop its chemistry to the level of being indispensable in today's chemical technology. Find out more about this exciting subject in this special themed issue of Chemistry—A European Journal. [ABSTRACT FROM AUTHOR]

The article offers information about a study that has discovered the synthesis of the novel silylenes including heterofulvene-like stable silylene and its kinetic product, which represents two new types of metastable divalent silicon compounds with unique reactivity. Such study is undertaken due to the importance of the synthesis of isolable silylene derivatives or the molecular compounds of divalent and dicoordinate silicon in contemporary silicon chemistry.

A rare pearl of a neutral silicon atom in the formal oxidation state zero seems to evolve best in the oyster‐like coordination environment of a bidentate N‐heterocyclic carbene ligand. In their Communication on page 7147 ff., M. Driess and co‐workers present the strikingly facile formation of this silicon pearl, which belongs to the novel class of theoretically predicted compounds termed silylones. (Graphics: Wernerwerke.) [ABSTRACT FROM AUTHOR]

The reactivity of the 1,4‐substituted bis(silylenyl)terphenylene 1, 1,4‐[ortho‐(LSi)C6H4]2C6H4, (L=RC(NtBu)2, R=Ph, Mes) towards CS2 is reported. It results in a dearomatization of the phenylene ring, affording the 1,3‐substituted cyclohexadiene derivative 2. According to DFT calculations, a transient silene containing a Si=C bond capable of π(C=C) addition at the aromatic phenylene ring is a key intermediate. In contrast, addition of CS2 to the biphenyl‐substituted mono‐silylene ortho‐(LSi)C6H4‐C6H5 3 leaves the aromatic π‐system intact and forms, in a [1+2] cycloaddition reaction, the corresponding thiasilirane 4 with a three‐membered SiSC ring. Further experimental studies led to the isolation of the novel mesoionic five‐membered Si2S2C heterocycle 6, which reacts with CS2 under C−C bond formation. All isolated new compounds were fully characterized and their molecular structures determined by single‐crystal X‐ray diffraction analyses. [ABSTRACT FROM AUTHOR]

In stark contrast to the reactivity of the bis-silylenyl dicarborane CB–Si2 (1) [CB = ortho-C,C′-C2B10H10, Si = PhC(tBuN)2Si] towards O2, N2O, and CO2, yielding the same dioxygenation product CB–Si2O2 (2) with a four-membered 1,3,2,4-disiladioxetane ring, the activation of the latter small molecules with the phosphanyl-silylenyl-functionalised CB–SiP (3) {P＝P[N(tBu)CH2]2} affords with O2 the CB–Si(＝O)P(＝O) silanone-phosphine oxide (4), with N2O the CB–Si(＝O)P silanone-phosphine (5), and with CO2 the CB–Si(O2C＝O)P silicon carbonate-phosphine (6) and CB–C(＝O)OSiOP ester (7), respectively. [ABSTRACT FROM AUTHOR]

Electronic structure of the six-membered unsaturated N-heterocyclic silylene 1 was investigated by the experimental (Raman, IR, UV–vis) and theoretical methods of optical spectroscopy. The results obtained along with the refined NICS data confirm π-conjugated but not aromatic character of molecule 1 with its trans -diene fragment and participation of the vacant p z orbital of Si II atom in the conjugated system. [ABSTRACT FROM AUTHOR]

The present review highlights the role of N-heterocyclic silylene (NHSi) ligands, the silicon analogues of N-heterocyclic carbenes (NHCs), utilized in various catalytic organic transformations. The application of such novel ligands coordinated by different metal sites offers massive opportunities in organic synthesis. Despite significant advances in the synthesis of NHSi-based metal complexes, the use of these compounds in organic methodologies is still in its initial stages. Since NHSi ligands promote the σ donor-ability of phosphines and even that of NHCs, they can facilitate catalytic events by lowering the energy barrier of the rate limiting steps such as oxidative additions. This encourages scientists to utilize NHSi-metal complexes in exploiting catalyzed reactions and to revisit and improve various existing organic methodologies. This is demonstrated in several showcases of organic transformations including the Heck coupling, Suzuki coupling, alkyne and ketone hydrosilylation, amide reduction, cyclotrimerization of alkynes (in the absence and the presence of an organo cyanide), and Sonogashira cross-coupling reactions. The latter represents a novel and unexpected steering function of NHSi-based systems in homogeneous catalysis. [ABSTRACT FROM AUTHOR]

The article describes the synthesis of the NHC-silylene adduct 2 containing a highly nucleophilic Si(II) site, which undergoes remarkably facile oxygenation with N2O to yield the first isolable NHC-supported silanone 3. According to the authors, the Si NMR spectrum 2 exhibits a significant shielding for the donor-supported Si(II) nucleus. Moreover, it reveals that Si NMR spectrum also exhibits a remarkable shift for the Si nucleus in 3.

The article reports on the first example of NHSi and related donor-stabilized silylene ligands generated in the coordination sphere of a metal. Accordingly, its donor/acceptor properties can be tuned to cover a wide range from NHC- and organophosphine. Moreover, it reveals that the CO stretching frequencies of the Ni(CO)3 moiety in the novel complexes were utilized as an ideal probe of the donor/acceptor strength of the novel NHSi ligands.

New types of metal‐free white phosphorus (P4) activation are reported. While the phosphine‐silylene‐substituted dicarborane 1, CB‐SiP (CB=ortho‐C,C′‐C2B10H10, Si=PhC(tBuN)2Si, P=P[N(tBu)CH2]2), activates white phosphorus in a 2 : 1 molar ratio to yield the P5‐chain containing species 2, the analogous bis(silylene)‐substituted compound 3, CB‐Si2, reacts with P4 in the molar ratio of 2 : 1 to furnish the first isolable 1,3‐diphospha‐2,4‐disilabutadiene (Si=P−Si=P‐containing) compound 4. For the latter reaction, two intermediates having a CB‐Si2P4 and CB‐Si2P2 core could be observed by multinuclear NMR spectroscopy. The compounds 2 and 4 were characterized including single‐crystal X‐ray diffraction analyses. Their electronic structures and mechanisms were investigated by density functional theory calculations. [ABSTRACT FROM AUTHOR]

The electronic structures and nature of silicon-chalcogen double bonds Si=X (X = 0, S) with four-coordinate silicon in the unique silanoic silylester 2 and silanoic thioester 3 have been investigated for the first time, by 29Si solid state NMR measurements and detailed DFT and ab initio calculations. 29Si solid state NMR spectroscopy of the precursor silylene 1 was also carried out. The experimental and computational study of 2 and 3, which was also supported by a detailed computational study of smaller model systems with Si=O and Si=S bonds, provides a deeper understanding of the isotropic and tensor components of their NMR chemical shifts. The general agreement between the experimental NMR spectra and the calculations strongly support our previous NMR assignment deduced from experiment. The calculations revealed that in 2 δ(29Si(=O))iso is shifted upfield relative to H2Si=O by as much as 175 ppm; the substituents are responsible for Ca. 100 ppm of this shift, while the remaining upfield shift is caused by change in the coordination number from three to four at the Si=O moiety. The change in coordination number leads to a nearly cylindrical symmetry in the plane which is perpendicular to the Si=O molecular axis (δ11≈δ22), in contrast to the significant anisotropy found in this plane in typical doubly bonded compounds. The Change in r(Si=O) or in the degree of pyramidality at the Si=O center which accompanies the change in coordination number has practically no effect on the chemical shift. δ(29Si(=S))iso in 3 is shifted downfield significantly relative to that in 2, and a similar trend is found in smaller models with Si=S vs those with Si=O subunits. This downfield shift can be explained by the smaller σ-π* energy difference in the Si=S bond, relative to that of the Si=O bond. The NMR measurements of 2 and 3 having a four-coordinate silicon-chalcogen moiety, and the calculations of their tensor components, their bond polarities, and their Wiberg bond indices revealed that the Si=X moieties in both 2 and 3 have a significant π(Si=X) character; yet, in both molecules there is a substantial contribution from a zwitterionic Si+-X resonance structure, which is more pronounced [ABSTRACT FROM AUTHOR]

The first isolable oxygen-bridged bis-silylene 1 has been synthesized by facile dehydrochloration of the corresponding disiloxane [LSiH(Cl)-O-SiH(Cl)L] precursor [L = PhC(NtBu)2] with LiN(SiMe3)2. Compound 1 contains three-coordinate, pyra- midal Si(II) atoms in a bent disiloxane-like moiety and reacts readily with [Ni(COD)2] to afford the unique bis-silylene oxide nickel complex 3. [ABSTRACT FROM AUTHOR]

The article describes the first silanoic silylester 2 and the striking cyclodisiloxane 4 which is the outcomes of convenient oxygenation of the siloxysilylene. The exposure of a brown solution of the siloxysilylene 1 in toluene to nitrogen oxide at 178 degree Celsius has resulted to a gradual decoloration. Moreover, compound 4 shows a unique type of cyclodisiloxane which results by a remarkably clean dioxygenation process of a stable silylene with oxygen.