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Phosphorus-bridged rigid, bent bis(N-heterocyclic) carbenes have not been reported, so far, despite having structural features that could make them interesting ligands in coordination and main group element chemistry. In previous reports, we had demonstrated that tuning of σ3- and σ4-phosphorus environments in planarised bis(NHCs) affects electronic properties and can provide additional coordination sites. Herein, we report on first examples of synthesis and conversion of 1,4-diphosphabarrelene-related compounds into rigid bent, doubly P-bridged bis(NHCs). The formation of main group element adducts with substrates from group 13, 14 and 15 illustrates opportunities to access novel scaffolds and to create nonplanar branching points. DFT calculations reveal the new bis(NHCs) to be good candidates as novel soft/hard ligands with up to four coordination sites. The synthesis of a dinuclear Fe(CO)4 complex is demonstrated. The thermal retro-[4 + 2] cycloaddition was theoretically and experimentally explored for a variety of ionic and zwitterionic 1,4-diphosphabarrelenes, and the generation and trapping of a dinuclear Fe(0) bis(NHC) complex with a tricyclic 1σ2,4 σ2-diphosphinine scaffold is presented. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a series of new cationic gold(i) complexes with hydroxyl-functionalized N-heterocyclic carbene (NHC) ligands is described. They are valuable building blocks for further derivatization: as a first example, coupling with amino acids and a dipeptide, respectively, successfully results in amino acid and peptide conjugates that are hard to obtain by other synthetic routes. [ABSTRACT FROM AUTHOR]

Detailed studies of the reactivity of the NHC-stabilized (NHC = N-heterocyclic carbene) silicon(II) halides SiI2(Idipp) ( 1) and SiClR(IMe4) ( 2- Trip: R = ArTrip; 2- Mes: R = ArMes) towards diazoalkanes and azides are presented (Idipp = C[N(C6H3-2,6- iPr2)CH]2, IMe4 = C[N(Me)CMe]2, ArTrip = C6H3-2,6-Trip2, ArMes = C6H3-2,6-Mes2, Trip = C6H2-2,4,6- iPr3, Mes = C6H2-2,4,6-Me3). Treatment of 1, 2- Trip, and 2- Mes with the diazoalkanes ( p-Tol)2CN2 ( p-Tol = C6H4-4-Me) and ArMesCHN2 afforded the NHC-stabilized silazines SiI2{N2C( p-Tol)2}(Idipp) ( 3) and SiCl R{N2CH(ArMes)}(IMe4) ( 4- Trip: R = ArTrip, 4- Mes: R = ArMes) as orange to yellow solids, respectively. No N2 elimination from the diazoalkanes was observed in these reactions. In comparison, the reactions of 1 or 2- Trip with the covalent azides MesN3 or Me3SiN3, yielded after N2 elimination the yellow to colorless NHC-stabilized silaimines SiI2(NMes)(Idipp) ( 5), Si(ArTrip)Cl(NMes)(IMe4) ( 6) and Si(ArTrip)(N3)(NSiMe3)(IMe4) ( 7), respectively. All compounds were characterized by elemental analyses, FT-IR and multinuclear magnetic resonance spectroscopy. Moreover, the molecular structures of 4- Mes, 5, 6, and 7 were determined by single-crystal X-ray diffraction analyses. [ABSTRACT FROM AUTHOR]

The reaction of Li/Cl phosphinidenoid tungsten(0) complex 2 [R = CH(SiMe3)2] with 1,3,4,5-tetramethylimidazol-2-ylidene ( 3) yielded the zwitterionic phosphaalkene complex 4. A comparative study on chloro- ( 5) or dichloro(organo)phosphane complexes 1 [R = CH(SiMe3)2] and NHC 3 revealed the formation of 4 at ambient temperature. First evidence for the formation of phosphinidenoid complex 7, having a C-Cl imidazolium cation, and its reaction with benzaldehyde to give oxaphosphirane complex 9 are presented. Furthermore, the first example of a formal exchange at the phosphorus center of an oxaphosphirane complex to give zwitterion 4 is demonstrated. [ABSTRACT FROM AUTHOR]

The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the ‘abnormal’ (C4-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented ‘normal’ C2 adduct, Me2IMe → P(Mes)=CPh2 (2). Particularly striking is the asymmetric and weak bonding of the NHC to the P=C moiety in 2. DFT calculations indicate that the P=C natural bond order in 2 (1.54) still reflects significant π-character to the bond (cf. MesP=CPh2: NBO = 1.98). Further computational analysis suggests that π-delocalization into the remote C-phenyl substituents is key to stabilizing the NHC adduct. [ABSTRACT FROM AUTHOR]

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(ArF)4] (ArF=C6H3-3,5-(CF3)2) affords selectively the green radical salt [Si2(Idipp)2][B(ArF)4] ( 1-[B(ArF)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(ArF)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(ArF)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 29Si hyperfine coupling tensors in 1+. EPR studies of 1-B(ArF)4 in liquid solution unraveled a topomerization with a low activation barrier that interconverts the two Si sites in 1+. [ABSTRACT FROM AUTHOR]

Synthesis of the first P(V)-bridged bis(NHC) ligand 7 was achieved via deprotonation of P(V)-functionalized bis(imidazolium) salt 6, which was obtained via oxidative desulfurization of bis(imidazole-2-thion-4-yl)-phosphane 2. Bis(imidazolium) salt 6 was also employed to synthesize the corresponding silver complex 8. All new products were firmly established by spectroscopic and spectrometric methods as well as elemental analysis and, in addition, X-ray crystal structure analysis in the case of 3. [ABSTRACT FROM AUTHOR]

Chromium-pyrenylcarbenes accessible from halopyrene precursors undergo benzannulation upon gentle warming with 3-hexyne to give hydroquinoid benzopyrene-Cr(CO)3 complexes. Kinetic benzannulation product 3 rearranges into thermodynamic haptotropomer 4 at 70 °C in octafluorotoluene under first-order kinetics. Further complexation of 3 by Cr(NH3)3(CO)3 affords syn and anti dinuclear chromium-benzopyrene complexes. Bidirectional extension of the benzannulation protocol results in the formation of syn and anti dibenzopyrene-dichromium complexes, which are structurally characterized by X-ray analysis. [ABSTRACT FROM AUTHOR]

The article presents a study which examines the synthesis of a novel imidazolium phosphanide zwitterion and its conversion into an atomic imidazol-2-ylidene derivatives. It states that the inversely polarized ylidic compounds II and IV show the same aromaticity. It also mentions that zwitterionic species can formally described as an adduct of an abnormal N-heterocyclic carbenes (NHC) and a phosphinidene.

The article focuses on the study which illustrates the N-Heterocyclic Carbene (NHC) complexes of Si²+ and SiI+ based on the exchange of NHC ligands at Si11. The study is investigated by single-crystal X-ray crystallography, nuclear magnetic resonance (NMR) spectra, and topological analysis. Results show that the NHC complex salts of Si²+ and SiI can increase the synthetic potential of NHC-SiX2.

The article discusses the coordination chemistry of silicon(II). It states that the Si2+ are high reactive and two-valence-electron species which were generated in laser-induced plasmas as well as studied by microwave spectroscopy and photoabsorption. It mentions that the exchange of N-heterocyclic carbenes (NHC) ligands at the centers of Si(II) provides access to unprecedented dicationic NHC complexes.

A novel method to prepare SiCp*2 (1) (Cp* = C5Me5) is presented involving the reaction of N-heterocyclic carbene (NHC)-stabilized SiII halides SiX2(NHC) (X = Cl, Br) with 2 equiv of KCp*. This route is a superior alternative to the laborious, multistep synthesis of 1 presently known and provides via the selective protonolysis of 1 with [H(Et2O)2][B(C6F5)4] facile access to [Si(η5-Cp*)][B(C6F5)4] (2) in multigram scale and high yield. Reaction of 2 with the tailored metallate Na[TpMeMo(CO)2(PMe3)] afforded the unprecedented silylidyne complex [TpMe(CO)2MoSi(η³-Cp*)] (3; TpMe = κ³-N,N',N"-hydridotris(3,5-dimethyl-1-pyrazolyl)borate). Single crystal X-ray diffraction and spectroscopic studies in combination with quantum chemical calculations shed light on the unique bonding situation of 3 featuring a delocalized Mo-Si bond with partial triple bond character and a Cp* substituent, which is η³-coordinated to silicon. [ABSTRACT FROM AUTHOR]

Protonation and alkylation of (ldipp)Si=Si- (idipp) ( l) afforded the mixed-valent disilicon(l)-borates [(Idipp)(R)SiII=Si0(Idipp)][B(ArF)4] (lR[B(ArF)4]; R = H, Me, Et; ArF = 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 multinudear NMR spectroscopy. Dynamic NMR studies in solution revealed a degenerate isomerization (topomerization) of the "σ-bonded" tautomers of 1H[B- (ArF)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 lH[B(ArF)4] provides the first example of a reversible 1,2-H migration along a Si=Si bond observed in a molecular system. In contrast, lMe[B(ArF)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(O) borates lM[BAr4] (M = Li, Ar = C6F5; M = Na, Ar = ArF) as brown, air-sensitive solids. Single-crystal X-ray diffraction analyses and NMR spectroscopic studies of lM[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. [ABSTRACT FROM AUTHOR]

The article discusses the coordination chemistry of silicon(II). It states that the Si2+ are high reactive and two-valence-electron species which were generated in laser-induced plasmas as well as studied by microwave spectroscopy and photoabsorption. It mentions that the exchange of N-heterocyclic carbenes (NHC) ligands at the centers of Si(II) provides access to unprecedented dicationic NHC complexes.

The article focuses on the study which illustrates the N-Heterocyclic Carbene (NHC) complexes of Si²+ and SiI+ based on the exchange of NHC ligands at Si11. The study is investigated by single-crystal X-ray crystallography, nuclear magnetic resonance (NMR) spectra, and topological analysis. Results show that the NHC complex salts of Si²+ and SiI can increase the synthetic potential of NHC-SiX2.