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.

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

2-tetrelavinylidenes (C=EH; 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=CH). Consequently, experimental studies on 2-tetrelavinylidenes (C=ER) 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], 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)).

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)MSiC(R)C(R)M(CO)Tp'] (M = Mo, W; R = R = Me or R = H, R = SiMe, Ph; Tp' = κ-,',″-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)M≡Si-M(CO)(PMe)Tp'] with alkynes RC≡CR and were comprehensively analyzed by experimental studies and quantum chemical calculations.

Triple bonds of niobium with silicon, germaniun and tin: the tetrylidyne complexes [(κ-tmps)(CO)Nb[triple bond, length as m-dash]E-R] (E = Si, Ge, Sn; tmps = MeSi(CHPMe); 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 (NMe)[Nb(CO)(κ-tmps)] () (tmps = MeSi(CHPMe)) with a suitable organotetrel(ii)halide. Compound was obtained from (NMe)[Nb(CO)] and the triphosphane tmps by photodecarbonylation.

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

The title compound, a tri-aryl-methanol, CHOSSi, was synthesized li-thia-tion of tris-2,2,6,6-tetra-methyl-benzo[1,2-;4,5-']bis-[1,3]di-thiol-4-yl-methanol, , 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 [Driesschaert (2012 ▸). , 6517-6525].

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 SiBr(SIdipp) (SIdipp = C[N(CH-2,6- iPr)CH]) with Na[Tp'Mo(CO)(PMe)] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO)Mo≡Si-Mo(CO)(PMe)Tp'] (Tp' = κ- 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) with the 17VE metal fragment Tp'Mo(CO)(PMe) via a short Mo1-Si bond (2.

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 SiH radical supported by two N-heterocyclic carbenes.

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)Si[double bond, length as m-dash]Si(Idipp)][B(Ar)] ([B(Ar)], Idipp = C[N(CH-2,6-Pr)CH], Ar = CH-3,5-(CF)) reveal a reversible one-electron reduction at a low redox potential ( = -2.15 V Fc/Fc). Chemical reduction of [B(Ar)] with KC affords selectively the green, room-temperature stable mixed-valent disilicon(0,I) hydride Si(H)(Idipp) (), in which the highly reactive SiH molecule is trapped between two N-heterocyclic carbenes (NHCs).

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.

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

An efficient method for the synthesis of the NHC-stabilised Si(i) halides SiX(Idipp) (, X = Cl, Br, I; Idipp = C[N(CH-2,6-Pr)CH]) was developed, which involves the oxidation of Si(Idipp) () with 1,2-dihaloethanes. Halogenation of is a diastereoselective reaction leading exclusively to a racemic mixture of the and enantiomers of . Compounds and were characterised by single-crystal X-ray crystallography and multinuclear NMR spectroscopy, and their electronic structures were analysed by quantum chemical methods.

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.

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.

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.

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.

[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).

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.

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.

Rhenium-germanium triple bonds: syntheses and reactions of the germylidyne complexes mer-[X2(PMe3)3Re≡Ge-R] (X=Cl, I, H; R=m-terphenyl).

A general approach to the first compounds that contain rhenium-germanium triple and double bonds is reported. Heating [ReCl(PMe3)5] (1) with the arylgermanium(II) chloride GeCl(C6H3-2,6-Trip2) (2; Trip=2,4,6-triisopropylphenyl) results in the germylidyne complex mer-[Cl2 (PMe3)3Re≡Ge-C6H3-2,6-Trip2] (4) upon PMe3 elimination. An equilibrium that is dependent on the PMe3 concentration exists between complexes 1 and 4.

The photochemistry of [Fe(III)N3(cyclam-ac)]PF6 at 266 nm.

The photochemistry of iron azido complexes is quite challenging and poorly understood. For example, the photochemical decomposition of [Fe(III)N(3)(cyclam-ac)]PF(6) ([1]PF(6)), where cyclam-ac represents the 1,4,8,11-tetraazacyclotetradecane-1-acetate ligand, has been shown to be wavelength-dependent, leading either to the rare high-valent iron(V) nitrido complex [Fe(V)N(cyclam-ac)]PF(6) ([3]PF(6)) after cleavage of the azide N(α)-N(β) bond, or to a photoreduced Fe(II) species after Fe-N(azide) bond homolysis. The mechanistic details of this intriguing reactivity have never been studied in detail.

Ultrafast primary processes of an iron-(III) azido complex in solution induced with 266 nm light.

The ultrafast photo-induced primary processes of the iron-(III) azido complex, [Fe(III)N(3)(cyclam-acetato)] PF(6) (1), in acetonitrile solution at room temperature were studied using femtosecond spectroscopy with ultraviolet (UV) excitation and mid-infrared (MIR) detection. Following the absorption of a 266 nm photon, the complex undergoes an internal conversion back to the electronic doublet ground state at a time scale below 2 ps. Subsequently, the electronic ground state vibrationally cools with a characteristic time constant of 13 ps.