Light-Dependent Reactivity of Heavy Pnictogen Double Bonds.

The chemistry of light dipnictenes has been widely investigated in the last century with remarkable achievements especially for azobenzene derivatives. In contrast, distibenes and dibismuthenes are relatively rare and show very limited reactivity. Herein, we have designed a protocol using visible light to enhance the reactivity of heavy dipnictenes. Exploiting the distinctive π-π* transition, we have been able to isolate unique examples of dipnictene-cobalt complexes. The reactivity of the distibene complex was further exploited using red light in the presence of a diazoolefin to access an unusual four-membered bicyclo[1.1.0]butane analog, containing only a single carbon atom. These findings set the bases to a conceptually new strategy in heavy element double bonds chemistry where visible light is at the front seat of bond activation.

NHC-Supported 2-Sila and 2-Germavinylidenes: Synthesis, Dynamics, First Reactivity and Theoretical Studies.

2-tetrelavinylidenes (C=EH2 ; E=Si, Ge) are according to quantum chemical studies the least stable isomers on the [E,C,2H] potential energy hypersurface isomerizing easily via the trans-bent tetrelaacetylenes HE≡CH to the thermodynamically most stable 1-tetrelavinylidenes (E=CH2 ). Consequently, experimental studies on 2-tetrelavinylidenes (C=ER2 ) and their derivatives are lacking. Herein we report experimental and theoretical studies of the first N-heterocyclic carbene (NHC) supported 2-silavinylidene (NHC)C=SiBr(Tbb) (1-Si: NHC=C[N(Dipp)CH]2 , Dipp=2,6-diisopropylphenyl, Tbb=2,6-bis[bis(trimethylsilyl)methyl]-4-tert-butylphenyl) and the isovalent 2-germavinylidenes (NHC)C=GeBr(R) (1-Ge, 1-GeMind: R=Tbb, Mind (1,1,3,3,5,5,7,7-octamethyl-s-hydrindacene-4-yl)). The NHC-supported 2-tetrelavinylidenes were obtained selectively from the 1,2-dibromoditetrelenes (E)-(R)BrE=EBr(R) using the diazoolefin (NHC)CN2 as vinylidene transfer reagent. 1-E (E=Si, Ge) have a planar vinylidene core, a bent-dicoordinated vinylidene carbon atom (CVNL ), a very short E=CVNL bond and an almost orthogonal orientation of the NHC five-membered ring to the vinylidene core. Quantum chemical analysis of the electronic structures of 1-E suggest a significantly bent 1-tetrelaallene and tetrelyne character. NMR studies shed light into the dynamics of 1-E involving NHC-rotation around the CVNL -CNHC bond with a low activation barrier. Furthermore, the synthetic potential of 1-E is demonstrated by the synthesis and full characterization of the unprecedented NHC-supported bromogermynes BrGe=C(EBr2 Tbb)(NHC) (2-SiGe: E=Si; 2-GeGe: E=Ge).

(NHC)Si═C═N-R: A Two-Coordinated Si0-Isocyanide Compound as Si(NHC) Transfer Reagent.

Experimental and theoretical studies are reported of the first two-coordinated Si0-isocyanide compound (SIDipp)Si═C═N-ArMes (1: SIDipp (NHC) = C[N(Dipp)CH2]2, ArMes = 2,6-dimesitylphenyl), supported by an N-heterocyclic carbene (NHC). A Si atom economic two-step synthesis of 1 involves a 2e reduction of the isocyanide-stabilized silyliumylidene salt [SiBr(CNArMes)(SIDipp)][B(ArF)4] (2[B(ArF)4], ArF = B(C6H3-3,5-(CF3)2)4) with KC8. 2[B(ArF)4] was obtained from SiBr2(SIDipp) after bromide abstraction with an equimolar mixture of Na[B(ArF)4] and ArMesNC. Exact adherence to the stoichiometry is crucial in the latter reaction, since 2[B(ArF)4] reacts with SiBr2(SIDipp) via isocyanide exchange to afford the disilicon(II) salt [Si2Br3(SIDipp)2)][B(ArF)4] (3[B(ArF)4]), the reaction leading to an equilibrium that favors 3[B(ArF)4] (Keq(298 K) = 10.6, ΔH° = -10.6 kJ mol-1; ΔS° = -16.0 J mol-1 K-1). 3[B(ArF)4] was obtained selectively from the 2:1 reaction of SiBr2(SIDipp) with Na[B(ArF)4] and fully characterized. Detailed studies of 1 reveal an intriguing structure featuring a planar CNHC-Si-C-N skeleton with a V-shaped geometry at the dicoordinated Si0 center, a slightly bent Si═C═N core, a CNHC-Si-CCNR 3c-2e out of plane π-bond (HOMO), and an anticlinal conformation of the SIDipp and ArMes substituents leading to axial chirality and the presence of two enantiomers, (Ra)-1 and (Sa)-1. Compound 1 displays structural dynamics in solution, rapidly interconverting the enantiomers. The silacumulene 1 is a potent Si(SIDipp) transfer agent as demonstrated by the synthesis and full characterization of the NHC-supported germasilyne (Z)-(SIDipp)(Cl)Si═GeArMes (4) from 1 and Ge(ArMes)Cl.

Planar Tetracoordinated Silicon (ptSi): Room-Temperature Stable Compounds Containing Anti-van't Hoff/Le Bel Silicon.

While a variety of compounds containing planar tetracoordinated carbon (ptC), the so-called anti-van't Hoff/Le Bel carbon, are known experimentally, stable systems containing planar tetracoordinated silicon (ptSi) are barely known. As part of our studies on the application of stereoelectronically well-defined transition-metal fragments to stabilize silicon in unprecedented bonding modes, we report herein the synthesis and full characterization of a series of thermally stable complexes of the general formula [Tp'(CO)2MSiC(R1)C(R2)M(CO)2Tp'] (M = Mo, W; R1 = R2 = Me or R1 = H, R2 = SiMe3, Ph; Tp' = κ3-N,N',N″-hydridotris(3,5-dimethylpyrazolyl)borate), which incorporate a ptSi atom in addition to two ptC atoms. The complexes were obtained by reacting the metallasilylidyne complexes [Tp'(CO)2M≡Si-M(CO)2(PMe3)Tp'] with alkynes R1C≡CR2 and were comprehensively analyzed by experimental studies and quantum chemical calculations. The analyses revealed that the ptSi atom is embedded in a tricyclic trapezoidal core featuring one internal SiC2 and two outer M-Si-C three-membered rings, which are fused via two Si-C bonds. The structural peculiarities evoked by the presence of an anti-van't Hoff/Le Bel ptSi center, such as the short M-Si bonds, a nearly linear M-Si-M spine, long M-C bonds, and the presence of two planar tetracoordinated carbon atoms were elucidated by a detailed analysis of the electronic structure, suggesting that one factor for the stabilization of the ptSi geometry is the aromaticity of the central SiC2 ring having two delocalized π electrons. Remarkably, the results further indicate the existence of both anti-van't Hoff/Le Bel carbon and silicon centers next to each other in the isolated complexes.

Tris[2,2,6,6-tetra-methyl-8-(tri-methyl-sil-yl)benzo[1,2-d;4,5-d']bis-(1,3-di-thiol)-4-yl]methanol diethyl ether monosolvate.

The title compound, a tri-aryl-methanol, C46H64OS12Si31, was synthesized via li-thia-tion of tris-2,2,6,6-tetra-methyl-benzo[1,2-d;4,5-d']bis-[1,3]di-thiol-4-yl-methanol, 2, and electrophilic quenching with tri-methyl-silyl chloride. The current crystal structure reveals information about the reactivity of this compound and compares well with the structure reported for the unsubstituted parent compound 2 [Driesschaert et al. (2012 ▸). Eur. J. Org. Chem.33, 6517-6525]. The title compound 1 forms mol-ecular propellers and crystallizes in P [Formula: see text], featuring an unusually long Si-Car bond of 1.910 (3) Å. Moreover, the geometry at the central quaternary carbon is rather trigonal-pyramidal than tetra-hedral due to vast intra-molecular stress. One tri-methyl-silyl group is disordered over two positions in a 0.504 (4):0.496 (4) ratio and one S atom is disordered over two positions in a 0.509 (7):0.491 (7) ratio. The contribution of disordered diethyl ether solvent mol-ecule(s) was removed using the PLATON SQUEEZE (Spek, 2015 ▸) solvent masking procedure. These solvent mol-ecules are not considered in the given chemical formula and other crystal data.

Linearly Two-Coordinated Silicon: Transition Metal Complexes with the Functional Groups M≡Si-M and M═Si═M.

A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr2(SIdipp) (SIdipp = C[N(C6H3-2,6- iPr2)CH2]2) with Na[Tp'Mo(CO)2(PMe3)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)2Mo≡Si-Mo(CO)2(PMe3)Tp'] (Tp' = κ3- N, N', N″-hydridotris(3,5-dimethylpyrazolyl)borate) (2), in which an almost linearly coordinated silicon atom (∠(Mo1-Si-Mo2) = 162.93(7)°) is bridging the 15VE metal fragment Tp'Mo(CO)2 with the 17VE metal fragment Tp'Mo(CO)2(PMe3) via a short Mo1-Si bond (2.287(2) Å) and a considerably longer Mo2-Si bond (2.438(2) Å), respectively. The reddish-orange silylidyne complex [Tp'(CO)2Mo≡Si-Tbb] (3) was also prepared from Na-1 and the 1,2-dibromodisilene ( E)-Tbb(Br)Si═Si(Br)Tbb (Tbb = C6H2-2,6-[CH(SiMe3)2]2-4- tBu) and contains as 2 a short Mo-Si bond (2.2614(9) Å) to an almost linearly coordinated Si atom (∠(Mo-Si-CTbb) = 160.8(1)°). Cyclic voltammetric studies of 2 in diglyme revealed an irreversible reduction of 2 at -1.907 V vs the [Fe(η5-C5Me5)2]+/0 redox couple. Two-electron reduction of 2 with potassium graphite yielded selectively the 1,3-dimetalla-2-silaallene dianion [Tp'(CO)2Mo═Si═Mo(CO)2Tp']2- (42-), which was isolated as the bright yellow dipotassium salt [K(diglyme)]2-4. Single crystal X-ray diffraction analysis revealed a centrosymmetric structure of 42-. The Mo-Si bond length of 42- (2.3494(2) Å) compares well with those of Mo-Si double bonds and lies in-between the Mo1-Si triple bond and Mo2-Si single bond length of 2. Compounds 2, 3 and [K(diglyme)2]-4 were characterized by elemental analyses, IR and multinuclear NMR spectroscopy. Comparative ELF (electron localization function), NBO (natural bond orbital) and NRT (natural resonance theory) analyses of 2, 3 and 42- shed light into the electronic structures of these compounds.

The Femtochemistry of a Ferracyclobutadiene.

The eminent role of metallacyclobutadienes as catalytic intermediates in organic synthesis and polymer chemistry is widely acknowledged. In contrast, their photochemistry is as yet entirely unexplored. Herein, the photo-induced primary processes of a ferracyclobutadiene tricarbonyl complex in solution are revealed by femtosecond mid-infrared spectroscopy. The time-resolved vibrational spectra expose an ultrafast substitution of a basal CO ligand by a solvent molecule in a consecutive dissociation-association mechanism. Following optical excitation, the system relaxes non-radiatively to the triplet ground state from which a CO is expelled. Since the triplet state is bound with respect to Fe-CO cleavage, the dissociation can only occur from vibrationally excited states. The excitation energy, vibrational relaxation, and intersystem crossing to the singlet ground state control the primary quantum yield for formation of the ferracyclic dicarbonyl-solvent product complex.

Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]E-R] (E = Si, Ge, Sn; tmps = MeSi(CH2PMe2)3; R = aryl).

A systematic, efficient approach to first complexes containing a triple bond between niobium and the elements silicon, germanium or tin is reported. The approach involves a metathetical exchange of the niobium-centered nucleophile (NMe4)[Nb(CO)4(κ2-tmps)] (1) (tmps = MeSi(CH2PMe2)3) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe4)[Nb(CO)6] and the triphosphane tmps by photodecarbonylation. Reaction of 1 with the disilene E-Tbb(Br)Si[double bond, length as m-dash]Si(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Si-Tbb] (2-Si, Tbb = 4-tert-butyl-2,6-bis(bis(trimethylsilyl)methyl)phenyl). Similarly, treatment of 1 with E(ArMes)Cl (E = Ge, Sn; ArMes = 2,6-mesitylphenyl) afforded after elimination of (NMe4)Cl and two CO ligands the deep magenta colored germylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Ge-ArMes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(κ3-tmps)(CO)2Nb[triple bond, length as m-dash]Sn-ArMes] (3-Sn), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ3-tmps)(CO)3Nb-SnArMes] (4-Sn), which was detected by IR and NMR spectroscopy. The niobium tetrylidyne complexes 2-Si, 3-Ge and 3-Sn were fully characterized and their solid-state structures determined by single-crystal X-ray diffraction studies. All complexes feature an almost linear tetrel coordination and the shortest Nb-E bond lengths (d(Nb-Si) = 232.7(2) pm; d(Nb-Ge) = 235.79(4) pm; d(Nb-Sn) = 253.3(1) pm) reported to date. Reaction of 3-Ge with a large excess of H2O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(ArMes)H(OH)2. Photodecarbonylation of [CpNb(CO)4] (Cp = η5-C5H5) in the presence of Ge(ArMes)Cl afforded the red-orange chlorogermylidene complex [Cp(CO)3Nb[double bond, length as m-dash]Ge(ArMes)Cl] (5-Ge). The molecular structure of 5-Ge features an upright conformation of the germylidene ligand, a trigonal-planar coordinated Ge atom, and a Nb-Ge double bond length of 251.78(6) pm, which lies in-between the Nb-Ge triple bond length of 3-Ge (235.79(4) pm) and a Nb-Ge single bond length (267.3 pm). Cyclic voltammetric studies of 2-Si, 3-Ge, and 3-Sn reveal several electron-transfer steps. One-electron oxidation and reduction of the germylidyne complex of 3-Ge in THF are electrochemically reversible suggesting that both the radical cation and radical anion of 3-Ge are accessible species in solution.

Addition of Small Electrophiles to N-Heterocyclic-Carbene-Stabilized Disilicon(0): A Revisit of the Isolobal Concept in Low-Valent Silicon Chemistry.

Protonation and alkylation of (Idipp)Si═Si(Idipp) (1) afforded the mixed-valent disilicon(I)-borates [(Idipp)(R)Si(II)═Si(0)(Idipp)][B(Ar(F))4] (1R[B(Ar(F))4]; R = H, Me, Et; Ar(F) = C6H3-3,5-(CF3)2; Idipp = C[N(C6H3-2,6-iPr2)CH]2) as red to orange colored, highly air-sensitive solids, which were characterized by single-crystal X-ray diffraction, IR spectroscopy and multinuclear NMR spectroscopy. Dynamic NMR studies in solution revealed a degenerate isomerization (topomerization) of the "σ-bonded" tautomers of 1H[B(Ar(F))4], which proceeds according to quantum chemical calculations via a NHC-stabilized (NHC = N-heterocyclic carbene) disilahydronium ion ("π-bonded" isomer) and is reminiscent of the degenerate rearrangement of carbenium ions formed upon protonation of olefins. The topomerization of 1H[B(Ar(F))4] provides the first example of a reversible 1,2-H migration along a Si═Si bond observed in a molecular system. In contrast, 1Me[B(Ar(F))4] adopts a "rigid" structure in solution due to the higher energy required for the interconversion of the "σ-bonded" isomer into a putative NHC-stabilized disilamethonium ion. Addition of alkali metal borates to 1 afforded the alkali metal disilicon(0) borates 1M[BAr4] (M = Li, Ar = C6F5; M = Na, Ar = Ar(F)) as brown, air-sensitive solids. Single-crystal X-ray diffraction analyses and NMR spectroscopic studies of 1M[BAr4] suggest in concert with quantum chemical calculations that encapsulation of the alkali metal cations in the cavity of 1 predominantly occurs via electrostatic cation-π interactions with the Si═Si π-bond and the peripheral NHC aryl rings. Displacement of the [Si(NHC)] fragments by the isolobal fragments [PR] and [SiR](-) interrelates the cations [(NHC)(R)Si═Si(NHC)](+) to a series of familiar, multiply bonded Si and P compounds as verified by analyses of their electronic structures.

The Si2H radical supported by two N-heterocyclic carbenes.

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)SiII[double bond, length as m-dash]Si0(Idipp)][B(ArF)4] (1H[B(ArF)4], Idipp = C[N(C6H3-2,6-iPr2)CH]2, ArF = C6H3-3,5-(CF3)2) reveal a reversible one-electron reduction at a low redox potential (E 1/2 = -2.15 V vs. Fc+/Fc). Chemical reduction of 1H[B(ArF)4] with KC8 affords selectively the green, room-temperature stable mixed-valent disilicon(0,I) hydride Si2(H)(Idipp)2 (1H), in which the highly reactive Si2H molecule is trapped between two N-heterocyclic carbenes (NHCs). The molecular and electronic structure of 1H was investigated by a combination of experimental and theoretical methods and reveals the presence of a π-type radical featuring a terminal bonded H atom at a flattened trigonal pyramidal coordinated Si center, that is connected via a Si-Si bond to a bent two-coordinated Si center carrying a lone pair of electrons. The unpaired electron occupies the Si[double bond, length as m-dash]Si π* orbital leading to a formal Si-Si bond order of 1.5. Extensive delocalization of the spin density occurs via conjugation with the coplanar arranged NHC rings with the higher spin density lying on the site of the two-coordinated silicon atom.

Photochemistry of a Puckered Ferracyclobutadiene in Liquid Solution Studied by Time-Resolved Fourier-Transform Infrared Spectroscopy.

Flash photolysis combined with step-scan and rapid-scan Fourier-transform infrared spectroscopy was carried out to explore the photochemistry of a puckered, quasi-square pyramidal ferracyclobutadiene, [Fe{κ(2) -C3 (NEt2 )3 }(CO)3 ]BF4 ([1]BF4 ), that features three additional carbonyl ligands in the metal coordination sphere. In liquid solution at room temperature, an excitation with λ=355 nm light resulted in the loss of one CO ligand, which is cleaved from a basal metal-coordination site. Within the time resolution of the experiment, a solvent molecule promptly refills the resultant vacancy at the coordinatively unsaturated metal center. In the weakly interacting liquid, dichloromethane, the counterion of the complex is subsequently able to substitute the solvent in the coordination sphere of the iron center, thereby forming as a stable product a neutral dicarbonyl tetrafluoroborato iron(0) species containing a four-membered ferracycle.

One-Electron Oxidation of a Disilicon(0) Compound: An Experimental and Theoretical Study of [Si2](+) Trapped by N-Heterocyclic Carbenes.

One-electron oxidation of the disilicon(0) compound Si2(Idipp)2 (1, Idipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with [Fe(C5Me5)2][B(Ar(F))4] (Ar(F) = C6H3-3,5-(CF3)2) affords selectively the green radical salt [Si2(Idipp)2][B(Ar(F))4] (1-[B(Ar(F))4). Oxidation of the centrosymmetric 1 occurs reversibly at a low redox potential (E1/2 = -1.250 V vs. Fc(+)/Fc), and is accompanied by considerable structural changes as shown by single-crystal X-ray structural analysis of 1-B(Ar(F))4. These include a shortening of the Si-Si bond, a widening of the Si-Si-CNHC angles, and a lowering of the symmetry, leading to a quite different conformation of the NHC substituents at the two inequivalent Si sites in 1(+). Comparative quantum chemical calculations of 1 and 1(+) indicate that electron ejection occurs from the symmetric (n+) combination of the Si lone pairs (HOMO). EPR studies of 1-B(Ar(F))4 in frozen solution verified the inequivalency of the two Si sites observed in the solid-state, and point in agreement with the theoretical results to an almost equal distribution of the spin density over the two Si atoms, leading to quite similar (29)Si hyperfine coupling tensors in 1(+). EPR studies of 1-B(Ar(F))4 in liquid solution unraveled a topomerization with a low activation barrier that interconverts the two Si sites in 1(+).

Si=Si Double Bonds: Synthesis of an NHC-Stabilized Disilavinylidene.

An efficient two-step synthesis of the first NHC-stabilized disilavinylidene (Z)-(SIdipp)Si=Si(Br)Tbb (2; SIdipp=C[N(C6H3-2,6-iPr2)CH2]2, Tbb=C6H2-2,6-[CH(SiMe3)2]2-4-tBu, NHC=N-heterocyclic carbene) is reported. The first step of the procedure involved a 2:1 reaction of SiBr2(SIdipp) with the 1,2-dibromodisilene (E)-Tbb(Br)Si=Si(Br)Tbb at 100 °C, which afforded selectively an unprecedented NHC-stabilized bromo(silyl)silylene, namely SiBr(SiBr2Tbb)(SIdipp) (1). Alternatively, compound 1 could be obtained from the 2:1 reaction of SiBr2(SIdipp) with LiTbb at low temperature. 1 was then selectively reduced with C8K to give the NHC-stabilized disilavinylidene 2. Both low-valent silicon compounds were comprehensively characterized by X-ray diffraction analysis, multinuclear NMR spectroscopy, and elemental analyses. Additionally, the electronic structure of 2 was studied by various quantum-chemical methods.

Si=P double bonds: experimental and theoretical study of an NHC-stabilized phosphasilenylidene.

An experimental and theoretical study of the first compound featuring a Si=P bond to a two-coordinate silicon atom is reported. The NHC-stabilized phosphasilenylidene (IDipp)Si=PMes* (IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, Mes*=2,4,6-tBu3 C6 H2 ) was prepared by SiMe3 Cl elimination from SiCl2 (IDipp) and LiP(Mes*)SiMe3 and characterized by X-ray crystallography, NMR spectroscopy, cyclic voltammetry, and UV/Vis spectroscopy. It has a planar trans-bent geometry with a short Si=P distance of 2.1188(7)Å and acute bonding angles at Si (96.90(6)°) and P (95.38(6)°). The bonding parameters indicate the presence of a Si=P bond with a lone electron pair of high s-character at Si and P, in agreement with natural bond orbital (NBO) analysis. Comparative cyclic voltammetric and UV/Vis spectroscopic experiments of this compound, the disilicon(0) compound (IDipp)Si=Si(IDipp), and the diphosphene Mes*P=PMes* reveal, in combination with quantum chemical calculations, the isolobal relationship of the three double-bond systems.

Silicon(i) chemistry: the NHC-stabilised silicon(i) halides Si2X2(Idipp)2 (X = Br, I) and the disilicon(i)-iodido cation [Si2(I)(Idipp)2].

An efficient method for the synthesis of the NHC-stabilised Si(i) halides Si2X2(Idipp)2 (2-X, X = Cl, Br, I; Idipp = C[N(C6H3-2,6-iPr2)CH]2) was developed, which involves the oxidation of Si2(Idipp)2 (1) with 1,2-dihaloethanes. Halogenation of 1 is a diastereoselective reaction leading exclusively to a racemic mixture of the RR and SS enantiomers of 2-X. Compounds 2-Br and 2-I were characterised by single-crystal X-ray crystallography and multinuclear NMR spectroscopy, and their electronic structures were analysed by quantum chemical methods. Dynamic NMR spectroscopy unraveled a fluxional process of 2-Br and 2-I in solution, which involved a hindered rotation of the NHC groups about the Si-CNHC bonds. Iodide abstraction from 2-I by [Li(Et2O)2.5][B(C6F5)4] selectively afforded the disilicon(i) salt [Si2(I)(Idipp)2][B(C6F5)4] (3). X-ray crystallography and variable-temperature NMR spectroscopy of 3 in combination with quantum chemical calculations shed light on the ground-state geometric and electronic structure of the [Si2(I)(Idipp)2]+ ion, which features a Si[double bond, length as m-dash]Si bond between a trigonal planar coordinated SiII atom with a Si-I bond and a two-coordinate Si0 center carrying a lone pair of electrons. The dynamics of the [Si2(I)(Idipp)2]+ ion were studied in solution by variable-temperature NMR spectroscopy and they involve a topomerisation, which proceeds according to quantum theory via a disilaiodonium intermediate ("π-bonded" isomer) and exchanges the two heterotopic Si sites.

[2+2+1] cycloadditions of bis(dialkylamino)acetylenes with SiI2(Idip): syntheses and reactivity studies of unprecedented 2,3,4,5-tetraamino-1 H-siloles.

A novel method for the synthesis of 1H-siloles is presented. It involves a [2+2+1] cycloaddition of the ynediamines R2N-C≡C-NR2 (R = Me, Et) with SiI2(Idip) (Idip = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) to afford the orange-colored, highly water-sensitive 1,1-diiodo-2,3,4,5-tetraamino-1H-siloles SiI2{C4(NR2)4} (1-I: R = Me; 2-I R = Et). Treatment of 2-I with an excess of SiBr4 afforded after I/Br exchange the 1,1-dibromo-1H-silole SiBr2{C4(NEt2)4} (2-Br). The 1H-siloles 1-I, 2-I, and 2-Br were fully characterized and their molecular structures determined by single-crystal X-ray diffraction. The compounds feature a slightly twisted five-membered silacyclopenta-2,4-diene ring and a double/single C-C bond alternation in the diene fragment. Reaction of 2-I with the N-heterocyclic carbene IMe4 (IMe4 = 1,3,4,5-tetramethylimidazolin-2-ylidene) leads, after displacement of the iodide groups, to the unprecedented diiodide salt [Si(IMe4)2{C4(NEt2)4}](I)2 (3), containing a 1H-silole dication with a four-coordinate Si(IV) center. The crystal structure of 3 reveals similar bonding characteristics for the dicationic 1H-silole to those of the neutral 1H-siloles 1-I-2-Br. Two-electron reduction of 3 with C8K affords, after elimination of one IMe4 group, the thermolabile, carbene-stabilized 1-silacyclopentadien-1-ylidene Si{C4(NEt2)4}(IMe4) (4), which was characterized by elemental analysis and (1)H, (13)C{(1)H}, and (29)Si{(1)H} NMR spectroscopies.

Silicon-oxygen double bonds: a stable silanone with a trigonal-planar coordinated silicon center.

SiO in a complex: The first silanone that is stable at room temperature (3) is reported. The two-step synthesis involves carbonylation of the silylidyne complex 1 to give the chromiosilylene 2, followed by oxidation of 2 with N2 O. Silanone 3 features a polar, short SiO bond (1.526(3) Å) to a trigonal-planar-coordinated silicon center and reacts with water to give the dihydroxysilyl complex.

Observing the formation and the reactivity of an octahedral iron(V) nitrido complex in real time.

Give me five: Time-resolved Fourier-transform IR spectroscopy is used to time-resolve the formation and the reaction dynamics of a fourfold symmetrical nitrido iron(V) complex (light blue C, red Fe, blue N) in liquid solution under physiological and technologically relevant conditions.

Manganese-tin triple bonds: a new synthetic route to the manganese stannylidyne complex cation trans-[H(dmpe)2Mn≡Sn(C6H3-2,6-Mes2)]+ (dmpe = Me2PCH2CH2PMe2, Mes = 2,4,6-trimethylphenyl).

A new approach to the first complex featuring a manganese-tin triple bond that takes advantage of the propensity of dihydrogen complexes to eliminate H2 is reported. Reaction of the 18-valence-electron manganese dihydrogen hydride complex [MnH(η(2)-H2)(dmpe)2] (1) (dmpe = Me2PCH2CH2PMe2) with the organotin(II) chloride SnCl(C6H3-2,6-Mes2) (Mes = 2,4,6-trimethylphenyl) selectively afforded by H2 elimination the chlorostannylidene complex trans-[H(dmpe)2Mn═Sn(Cl)(C6H3-2,6-Mes2)] (2), which upon treatment with Na[B(C6H3-3,5-(CF3)2)4] and Li[Al(OC(CF3)3)4] was transformed quantitatively into the stannylidyne complex salts trans-[H(dmpe)2Mn≡Sn(C6H3-2,6-Mes2)]A [A = B(C6H3-3,5-(CF3)2)4 (3a), Al(OC(CF3)3)4 (3b)]. Complexes 2 and 3a/3b were fully characterized, and the structures of 2 and 3a were determined by single-crystal X-ray diffraction. Complex 2 features the shortest Mn-Sn double bond reported to date, a large Mn-Sn-Caryl bond angle, and a long Sn-Cl bond of the trigonal-planar-coordinated tin center. These bonding features can be rationalized in valence-bond terms by a strong contribution of the triply bonded resonance structure [LnMn≡SnR]Cl and were verified by a natural resonance theory (NRT) analysis of the electron density of the DFT-minimized structure of 2. Complex 3a features the shortest Mn-Sn bond reported to date and a linearly coordinated tin atom. Natural bond order and NRT analyses of the electronic structure of the complex cation in 3a/3b suggested a highly polar Mn-Sn triple bond with a 65% ionic contribution to the NRT Mn-Sn bond order of 2.25. Complex 3a undergoes reversible one-electron reduction, suggesting that open-shell stannylidyne complexes might be accessible using strong reducing agents.