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2-tetrelavinylidenes (C=EH 2 ; 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 2 ). Consequently, experimental studies on 2-tetrelavinylidenes (C=ER 2 ) 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)CN 2 as vinylidene transfer reagent. 1-E (E=Si, Ge) have a planar vinylidene core, a bent-dicoordinated vinylidene carbon atom (C VNL ), a very short E=C VNL 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 C VNL -C NHC 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(EBr 2 Tbb)(NHC) (2-SiGe: E=Si; 2-GeGe: E=Ge)., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

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., (© 2024 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Experimental and theoretical studies are reported of the first two-coordinated Si 0 -isocyanide compound (SIDipp)Si═C═N-Ar Mes ( 1 : SIDipp (NHC) = C[N(Dipp)CH 2 ] 2 , Ar Mes = 2,6-dimesitylphenyl), supported by an N-heterocyclic carbene (NHC). A Si atom economic two-step synthesis of 1 involves a 2 e reduction of the isocyanide-stabilized silyliumylidene salt [SiBr(CNAr Mes )(SIDipp)][B(Ar F ) 4 ] ( 2 [B(Ar F ) 4 ], Ar F = B(C 6 H 3 -3,5-(CF 3 ) 2 ) 4 ) with KC 8 . 2 [B(Ar F ) 4 ] was obtained from SiBr 2 (SIDipp) after bromide abstraction with an equimolar mixture of Na[B(Ar F ) 4 ] and Ar Mes NC. Exact adherence to the stoichiometry is crucial in the latter reaction, since 2 [B(Ar F ) 4 ] reacts with SiBr 2 (SIDipp) via isocyanide exchange to afford the disilicon(II) salt [Si 2 Br 3 (SIDipp) 2 )][B(Ar F ) 4 ] ( 3 [B(Ar F ) 4 ]), the reaction leading to an equilibrium that favors 3 [B(Ar F ) 4 ] ( K eq (298 K) = 10.6, Δ H ° = -10.6 kJ mol -1 ; Δ S ° = -16.0 J mol -1 K -1 ). 3 [B(Ar F ) 4 ] was obtained selectively from the 2:1 reaction of SiBr 2 (SIDipp) with Na[B(Ar F ) 4 ] and fully characterized. Detailed studies of 1 reveal an intriguing structure featuring a planar C NHC -Si-C-N skeleton with a V-shaped geometry at the dicoordinated Si 0 center, a slightly bent Si═C═N core, a C NHC -Si-C CNR 3c-2e out of plane π-bond (HOMO), and an anticlinal conformation of the SIDipp and Ar Mes substituents leading to axial chirality and the presence of two enantiomers, ( R a )- 1 and ( S a )- 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═GeAr Mes ( 4 ) from 1 and Ge(Ar Mes )Cl.

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) 2 MSiC(R 1 )C(R 2 )M(CO) 2 Tp'] (M = Mo, W; R 1 = R 2 = Me or R 1 = H, R 2 = SiMe 3 , Ph; Tp' = κ 3 - 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) 2 M≡Si-M(CO) 2 (PMe 3 )Tp'] with alkynes R 1 C≡CR 2 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 SiC 2 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 SiC 2 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.

A detailed experimental and theoretical analysis is presented of unprecedented molybdenum complexes featuring a linearly coordinated, multiply bonded silicon atom. Reaction of SiBr 2 (SIdipp) (SIdipp = C[N(C 6 H 3 -2,6- iPr 2 )CH 2 ] 2 ) with Na[Tp'Mo(CO) 2 (PMe 3 )] (Na-1) in the ratio 1:2 afforded the reddish-brown metallasilylidyne complex [Tp'(CO) 2 Mo≡Si-Mo(CO) 2 (PMe 3 )Tp'] (Tp' = κ 3 - 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 (PMe 3 ) 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) 2 Mo≡Si-Tbb] (3) was also prepared from Na-1 and the 1,2-dibromodisilene ( E)-Tbb(Br)Si═Si(Br)Tbb (Tbb = C 6 H 2 -2,6-[CH(SiMe 3 ) 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-C Tbb ) = 160.8(1)°). Cyclic voltammetric studies of 2 in diglyme revealed an irreversible reduction of 2 at -1.907 V vs the [Fe(η 5 -C 5 Me 5 ) 2 ] +/0 redox couple. Two-electron reduction of 2 with potassium graphite yielded selectively the 1,3-dimetalla-2-silaallene dianion [Tp'(CO) 2 Mo═Si═Mo(CO) 2 Tp'] 2- (4 2- ), which was isolated as the bright yellow dipotassium salt [K(diglyme)] 2 -4. Single crystal X-ray diffraction analysis revealed a centrosymmetric structure of 4 2- . The Mo-Si bond length of 4 2- (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 4 2- shed light into the electronic structures of these compounds.

The title compound, a tri-aryl-methanol, C 46 H 64 OS 12 Si 3 1 , 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-C ar 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.

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 4 )[Nb(CO) 4 (κ 2 -tmps)] ( 1 ) (tmps = MeSi(CH 2 PMe 2 ) 3 ) with a suitable organotetrel(ii)halide. Compound 1 was obtained from (NMe 4 )[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 [(κ 3 -tmps)(CO) 2 Nb[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(Ar Mes )Cl (E = Ge, Sn; Ar Mes = 2,6-mesitylphenyl) afforded after elimination of (NMe 4 )Cl and two CO ligands the deep magenta colored germylidyne complex [(κ 3 -tmps)(CO) 2 Nb[triple bond, length as m-dash]Ge-Ar Mes ] ( 3-Ge ), and the deep violet, light-sensitive stannylidyne complex [(κ 3 -tmps)(CO) 2 Nb[triple bond, length as m-dash]Sn-Ar Mes ] ( 3-Sn ), respectively. Formation of 3-Sn proceeds via the niobiastannylene [(κ 3 -tmps)(CO) 3 Nb-SnAr Mes ] ( 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 H 2 O afforded upon cleavage of the Nb-Ge triple bond the hydridogermanediol Ge(Ar Mes )H(OH) 2 . Photodecarbonylation of [CpNb(CO) 4 ] (Cp = η 5 -C 5 H 5 ) in the presence of Ge(Ar Mes )Cl afforded the red-orange chlorogermylidene complex [Cp(CO) 3 Nb[double bond, length as m-dash]Ge(Ar Mes )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., (This journal is © The Royal Society of Chemistry 2017.)

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., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)Si II [double bond, length as m-dash]Si 0 (Idipp)][B(Ar F ) 4 ] ( 1H [B(Ar F ) 4 ], Idipp = C[N(C 6 H 3 -2,6- i Pr 2 )CH] 2 , Ar F = C 6 H 3 -3,5-(CF 3 ) 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(Ar F ) 4 ] with KC 8 affords selectively the green, room-temperature stable mixed-valent disilicon(0,I) hydride Si 2 (H)(Idipp) 2 ( 1H ), in which the highly reactive Si 2 H 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., (This journal is © The Royal Society of Chemistry 2016.)

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.

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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient method for the synthesis of the NHC-stabilised Si(i) halides Si 2 X 2 (Idipp) 2 ( 2-X , X = Cl, Br, I; Idipp = C[N(C 6 H 3 -2,6- i Pr 2 )CH] 2 ) was developed, which involves the oxidation of Si 2 (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-C NHC bonds. Iodide abstraction from 2-I by [Li(Et 2 O) 2.5 ][B(C 6 F 5 ) 4 ] selectively afforded the disilicon(i) salt [Si 2 (I)(Idipp) 2 ][B(C 6 F 5 ) 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 [Si 2 (I)(Idipp) 2 ] + ion, which features a Si[double bond, length as m-dash]Si bond between a trigonal planar coordinated Si II atom with a Si-I bond and a two-coordinate Si 0 center carrying a lone pair of electrons. The dynamics of the [Si 2 (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., (This journal is © The Royal Society of Chemistry 2015.)

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(+)., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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.

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. Removal of the volatile PMe3 shifts the equilibrium towards complex 4, whereas treatment of 4 with an excess of PMe3 gives a 1:1 mixture of 1 and the PMe3 adduct of 2, GeCl(C6H3-2,6-Trip2)(PMe3) (2-PMe3). Adduct 2-PMe3 can be selectively obtained by addition of PMe3 to chlorogermylidene 2. The NMR spectroscopic data for 2-PMe3 indicate an equilibrium between 2-PMe3 and its dissociation products, 2 and PMe3 , which is shifted far towards the adduct site at ambient temperature. NMR spectroscopic monitoring of the reaction of complex 1 with 2 and the reaction of complex 4 with PMe3 revealed the formation of two key intermediates, which were identified to be the chlorogermylidene complexes cis/trans-[Cl(PMe3)4 Re=Ge(Cl)C6H3-2,6-Trip2] (cis/trans-3) by using NMR spectroscopy. Labile chlorogermylidene complexes cis/trans-3 can be also generated from trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9) and (nBu4N)Cl at low temperature, and decompose at ambient temperature to give a mixture of complexes 1 and 4. Complex 4 reacts with LiI to give the diiodido derivative mer-[I2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (5), which undergoes a metathetical iodide/hydride exchange with Na(BEt3H) to give the dihydrido germylidyne complex mer-[H2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (6). Carbonylation of 4 induces a chloride migration from rhenium to the germanium atom to afford the chlorogermylidene complex mer-[Cl(CO)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (7). Similarly, MeNC converts complex 4 into the methylisocyanide analogue mer-[Cl(MeNC)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (8). Chloride abstraction from 4 by NaBPh4 in the presence of PMe3 gives the cationic germylidyne complex trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9). Heating complex 4 with cis-[Mo(PMe3)4(N2)2] induces a germylidyne ligand transfer from rhenium to molybdenum to afford the germylidyne complex trans-[Cl(PMe3)4Mo≡Ge-C6H3-2,6-Trip2] (10). All new compounds were fully characterized and their molecular structures studied by X-ray crystallography, which led to the first experimentally determined Re-Ge triple- and double-bond lengths., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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. A homolytic bond cleavage was also observed by the appearance of ground state azide radicals, which were identified by their asymmetric stretching vibration at 1659 cm(-1). The azide radical recombines in a geminate fashion with the iron containing fragment within 20 ps. The cage escape leading to well separated fragments after homolytic Fe-N bond breakage was found to occur with a quantum yield of 35%. Finally, non-geminate recombination at nanosecond time scales was seen to further reduce the photolytic quantum yield to below 20% at a wavelength of 266 nm., (This journal is © the Owner Societies 2012)

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. Here, the photochemistry of 1 in acetonitrile solution at room temperature has been investigated using step-scan and rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy following a 266 nm, 10 ns pulsed laser excitation. Using carbon monoxide as a quencher for the primary iron-containing photochemical product, it is shown that 266 nm excitation of 1 results exclusively in the cleavage of the Fe-N(azide) bond, as was suspected from earlier steady-state irradiation studies. In argon-purged solutions of [1]PF(6), the solvent-stabilized complex cation [Fe(II)(CH(3)CN)(cyclam-ac)](+) (2red) together with the azide radical (N(3)(.)) is formed with a relative yield of 80%, as evidenced by the appearance of their characteristic vibrational resonances. Strikingly, step-scan experiments with a higher time resolution reveal the formation of azide anions (N(3)(-)) during the first 500 ns after photolysis, with a yield of 20%. These azide ions can subsequently react thermally with 2red to form [Fe(II)N(3)(cyclam-ac)] (1red) as a secondary product of the photochemical decomposition of 1. Molecular oxygen was further used to quench 1red and 2red to form what seems to be the elusive complex [Fe(O(2))(cyclam-ac)](+) (6)., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient method for the synthesis of the first N-heterocyclic carbene (NHC)-stabilized halosilylidyne complexes is reported that starts from SiBr(4). In the first step, SiBr(4) was treated with one equivalent of the N-heterocyclic carbene 1,3-bis[2,6-bis(isopropyl)phenyl]imidazolidin-2-ylidene (SIdipp) to give the 4,5-dihydroimidazolium salt [SiBr(3)(SIdipp)]Br (1-Br), which then was reduced with potassium graphite to afford the silicon(II) dibromide-NHC adduct SiBr(2)(SIdipp)(2-Br) in good yields. Heating 2-Br with Li[CpCr(CO)(3)] afforded the complex [Cp(CO)(2)Cr=SiBr(SIdipp)] (3-Br) upon elimination of CO. Complex 3-Br features a trigonal-planar-coordinated silicon center and a very short CrSi double bond. Similarly, the reaction of SiCl(2)(SIdipp) (2-Cl) with Li[CpCr(CO)(3)] gave the analogous chloro derivative [Cp(CO)(2)Cr=SiCl(SIdipp)] (3-Cl). Complex 3-Br undergoes an NHC exchange with 1,3-dihydro-4,5-dimethyl-1,3-bis(isopropyl)-2H-imidazol-2-ylidene (IMe(2)iPr(2)) to give the complex [Cp(CO)(2)CrSiBr(IMe(2)iPr(2))(2)] (4-Br). Compound 4-Br features a distorted-tetrahedral four-coordinate silicon center. Bromide abstraction occurs readily from 4-Br with Li[B(C(6)F(5))(4)] to give the putative silylidene complex salt [Cp(CO)(2)Cr=Si(IMe(2)iPr(2))(2)][B(C(6)F(5))(4)], which irreversibly dimerizes by means of an Si-promoted electrophilic activation of one carbonyl oxygen atom to yield the dinuclear siloxycarbyne complex [Cp(CO)Cr{(μ-CO)Si(IMe(2)iPr(2))(2)}(2-)Cr(CO)Cp][B(C(6)F(5))(4)](2) (5). All compounds were fully characterized, and the molecular structures of 2-Br-5-Br were determined by single-crystal X-ray diffraction. DFT calculations of 3-Br and 3-Cl and their carbene dissociation products [Cp(CO)(2)Cr=Si-X] (X=Cl, Br) were carried out, and the electronic structures of 3-Br, 3-Cl and [Cp(CO)(2)Cr=Si-X] were analyzed by the natural bond orbital method in combination with natural resonance theory., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The first N-heterocyclic carbene adducts of arylchlorosilylenes are reported and compared with the homologous germanium compounds. The arylsilicon(II) chlorides SiArCl(Im-Me(4)) [Ar=C(6)H(3)-2,6-Mes(2) (Mes=C(6)H(2)-2,4,6-Me(3)), C(6)H(3)-2,6-Trip(2) (Trip=C(6)H(2)-2,4,6-iPr(3))] were obtained selectively on dehydrochlorination of the arylchlorosilanes SiArHCl(2) with 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me(4)). The analogous arylgermanium(II) chlorides GeArCl(Im-Me(4)) were prepared by metathetical exchange of GeCl(2)(Im-Me(4)) with LiC(6)H(3)-2,6-Mes(2) or addition of Im-Me(4) to GeCl(C(6)H(3)-2,6-Trip(2)). All compounds were fully characterized. Density functional calculations on ECl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)), where E=Si, Ge, at different levels of theory show very good agreement between calculated and experimental bonding parameters, and NBO analyses reveal similar electronic structures of the two aryltetrel(II) chlorides. The low gas-phase Gibbs free energy of bond dissociation of SiCl(C(6)H(3)-2,6-Trip(2))(Im-Me(4)) (Delta(calcd) degrees=28.1 kJ mol(-1)) suggests that the carbene adducts SiArCl(Im-Me(4)) may be valuable transfer reagents of the arylsilicon(II) chlorides SiArCl.

Reduction of [Cr(N(3)N)] (1) [(N(3)N)(3)(-) = ((SiMe(3)NCH(2)CH(2))(3)N)(3)(-)] with sodium powder in THF affords the yellow, extremely air-sensitive amidochromate(II) [Na(THF)(2)Cr(N(3)N)] (2) in good yield. Complex 2 has an effective magnetic moment of 5.1 mu(B) indicative of a d(4) high-spin electronic configuration. (1)H NMR spectroscopy in solution and single-crystal X-ray crystallography show that compound 2 is composed of idealized C(s) symmetric contact ion pairs, in which trigonal-monopyramidal [Cr(II)(N(3)N)](-) anions are linked to the [Na(THF)(2)](+) countercations by two bridging amide ligands. DFT calculations of 1, 2, and the anion [Cr(N(3)N)](-) at the RI-BP86/TZVPP level of theory provide in combination with extended Hückel calculations a rationale for the observed structural changes from 1 to 2.

The reaction of SiCl4 with an excess of (PPN)N3 (PPN+ = [(Ph3P)2N]+) affords selectively (PPN)2[Si(N3)6] (1). Simultaneous thermal analysis (TG-DTA) shows that the hexaazidosilicate salt is remarkably stable, melting at Tonex = 214 degrees C. Melting of 1 is followed by two distinct exothermic decomposition processes at Ton = 256 and 321 degrees C, the first one involving elimination of N2 and the second one degradation of the PPN cations and evolution of Si(N3)4, N2, and some HN3. The crystal structure of 1 consists of discrete PPN+ cations and S2 symmetric [Si(N3)6]2- anions, which have a very rare, octahedral SiN6 framework and the highest nitrogen content (90%) among the hexaazidometallates reported so far. The IR, Raman, 29Si, and 14N NMR spectra of 1 in CH3CN suggest in combination with the calculated spectra the presence of intact [Si(N3)6]2--anions of S6 symmetry in solution. Geometry optimizations with various methods and basis sets show an S6 symmetric structure to be the most stable [Si(N3)6]2- isomer, the calculated bonding parameters comparing well with the experimental values.

Treatment of [CrCl3(THF)3] with slightly more than 1 equiv of Li3(N3N) [(N3N)(3-) = ((Me3SiNCH2CH2)3N)(3-)] affords the triamidoamine complex [Cr(N3N)] (1) in 75% yield. 1 is oxidized by PhICl2, CuCl2, or AgCl to give the chromium(IV) complex [Cr(N3N)Cl] (2) in moderate yields. Alternatively, complex 2 is obtained directly from [CrCl3(THF)3] in 50% yield after treatment with 0.5 equiv of Li3(N3N). Both compounds are high-spin complexes bearing three and two unpaired electrons, respectively. Their molecular structures are described revealing a trigonal monopyramidal and trigonal bipyramidal coordination geometry of the chromium center, respectively.

We report the synthesis and characterization of the first eta(3)-1,3,5-trimethyl-1,3,5-triazacyclohexane (Me(3)TAC) alkoxo complexes. Dehydration of [Co(H(2)O)(6)](X)(2) with 2,2-dimethoxypropane or HC(OMe)(3) and subsequent treatment with Me(3)TAC results in the formation of the methoxo cube fragment clusters [{(Me(3)TAC)Co}(3)(OMe)(4)](X)(2) (X = B(C(6)F(5))(4) (2a) and B(m-C(6)H(3)(CF(3))(2))(4) (2b)). 2a crystallizes in the triclinic space group P&onemacr; (a = 13.857(2) Å, b = 16.843(3) Å, c = 19.318(2) Å, alpha = 79.23(2) degrees, beta = 76.855(13) degrees, gamma = 70.10(2) degrees, Z = 2) and 2b in the monoclinic space group P2(1) (a = 12.710(3) Å, b = 23.251(3) Å, c = 18.702(4) Å, beta = 101.16(2) degrees, Z = 2). The cations contain a {Co(3)(OMe)(4)} cube fragment core with an eta(3)-Me(3)TAC bonded to each cobalt atom. Me(3)TAC is bonded unsymmetrically due to hydrogen-bonding interactions with the anions. This broken symmetry can also be observed as solvent-, anion-, and H/D isotope-dependent splitting of the signals in (1)H and (2)H NMR. A byproduct of the reaction is the protonated Me(3)TAC. The analogous monoacid adduct Me(3)TAC.HCl has been characterized by X-ray crystallography (orthorhombic space group Pbca, a = 11.0366(9) Å, b = 12.2986(6) Å, c = 13.9949(7) Å, Z = 8).

Azurin*, a by-product of heterologous expression of the gene encoding the blue copper protein azurin from Pseudomonas aeruginosa in Escherichia coli, was characterized by chemical analysis and electrospray ionization mass spectrometry, and its structure determined by X-ray crystallography. It was shown that azurin* is native azurin with its copper atom replaced by zinc in the metal binding site. Zinc is probably incorporated in the apo-protein after its expression and transport into the periplasm. Holo-azurin can be reconstituted from azurin* by prolonged exposure of the protein to high copper ion concentrations or unfolding of the protein and refolding in the presence of copper ions. An X-ray crystallographic analysis of azurin* at 0.21-nm resolution revealed that the overall structure of azurin is not perturbed by the metal exchange. However, the geometry of the co-ordination sphere changes from trigonal bipyramidal in the case of copper azurin to distorted tetrahedral for the zinc protein. The copper ligand Met121 is no longer co-ordinated to zinc which adopts a position close to the carbonyl oxygen atom from residue Gly45. The polypeptide structure surrounding the metal site undergoes moderate reorganization upon zinc binding. The largest displacement observed is for the carbonyl oxygen from residue Gly45, which is involved in copper and zinc binding. It moves by 0.03 nm towards the zinc, thereby reducing its distance to the metal from 0.29 nm in the copper protein to 0.23 nm in the derivative.