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Solution-processed and thermally annealed thin films from a series of nalkyl terminated anilino squaraines are systematically investigated regarding their structural and optical properties by means of X-ray diffraction (XRD) and spectroscopic ellipsometry (SE). Their characteristic intense double-hump-shaped absorbance spectra consisting of coupled H-aggregate and intermolecular charge transfer (ICT) resonance bands make them appealing for fundamental light−matter interaction studies, and their environmental sustainability invites for consumer optoelectronic applications. Now, the single-crystal structure of the n-pentyl anilino squaraine (nPSQ) provides a missing link to identify potential odd−even effects with respect to the terminal alkyl chain for bulk crystals. While all single crystals adopt a triclinic unit cell with biaxial dielectric properties, the thin films condense into effectively uniaxial anisotropic thin films. Here, the inherently low sensitivity to the ut-ofplane complex refractive index of SE in reflection is reasonably compensated by adding transmission SE and transmission intensity data. With that, a general picture of the structural and dielectric properties of n-alkyl anilino squaraine thin films is launched, revealing that the terminal alkyl chain length affects the structural and optical properties in a twofold way: we observe a steady change which is superimposed by an anisotropic odd−even effect.

Five ligands with either nitrile or isonitrile metal binding motifs have been synthesized based on the 2,8- or 3,9-disubstituted Troger's base scaffold, respectively. These ligands self-assemble into dinuclear cyclic metallosupramolecular aggregates upon coordination to [(dppp)Pd(OTf)2 ] in a highly diastereoselective manner, by heterochiral self-sorting in a chiral self-discriminating manner as shown by ESI mass spectrometry, NMR spectroscopy, and single crystal XRD analysis. This observation is in contrast to earlier studies with ligands derived from Troger's base that have larger metal binding motifs and bis(nitrile) and bis(isonitrile) ligands based on other rigid dissymmetric cores such as [2.2]paracyclophanes. Thus, the combination of these slim metal binding motifs with the rigid v-shaped 2,8- or 3,9-disubstituted Troger's base scaffolds seems to be especially well preorganized to ensure high-fidelity social self-sorting behavior.

Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties directly connected to a [2.2]paracyclophane backbone with pseudo‐meta substitution pattern have been synthesized. The ligand itself (Lnit) or its precursors (Liso) were resolved by HPLC on a chiral stationary phase and the absolute configuration of the isolated enantiomers was assigned by XRD analysis and/or by comparison of quantum‐chemical simulated and experimental electronic circular dichroism (ECD) spectra. Surprisingly, the resulting metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)2] differ in their composition: whereas Lnit forms dinuclear complexes, Liso exclusively forms trinuclear ones. Furthermore, they also differ in their chiral self‐sorting behavior as (rac)‐Liso undergoes exclusive social self‐sorting leading to a heterochiral assembly, whereas (rac)‐Liso shows a twofold preference for the formation of homochiral complexes in a narcissistic self‐sorting manner as proven by ESI mass spectrometry and NMR spectroscopy. Interestingly, upon crystallization, these discrete aggregates undergo structural transformation to coordination polymers, as evidenced by single‐crystal X‐ray diffraction., Two isostructural ligands with either nitrile (Lnit) or isonitrile (Liso) moieties attached to a [2.2]paracyclophane backbone have been synthesized. Surprisingly, the resulting discrete metallosupramolecular aggregates formed in solution upon coordination of [(dppp)Pd(OTf)2] differ in their composition and in their chiral self‐sorting behavior. Upon crystallization these discrete aggregates undergo structural transformation to coordination polymers.

The synthesis, isolation and structural characterization of the novel heteroleptic copper(I) complexes [Cu(RDABdipp)(LCOOMe)](PF6) (R = H (3), R = Me (4)) incorporating the sterically demanding 1,4-diaza-1,3-butadienes RDABdipp (R = H, Me; dipp = 2,6-diisopropylphenyl) is reported. 3 and 4 were isolated in high yields and spectroscopically characterized. The synthetic strategy includes the in situ reaction of the bis-acetonitrile intermediates [Cu(RDABdipp)(NCMe)2](PF6), (R = H (1), R = Me (2)) with the required amounts of the methyl-2-(pyridin-2-yl)-quinoline-4-carboxylate (LCOOMe) that was used as the ancillary ligand. 3 and 4 are rare examples of heteroleptic copper(I) complexes comprising RDABdipp and an ancillary α-diimine ligand, while 3 is the first crystallographically characterized example of this class of compounds. As a side product during the formation of 3 and 4, the homoleptic complex [Cu(LCOOMe)2](PF6) (5) is detected, that has been independently synthesized, for comparison. All the products were characterized by elemental analysis, FT–IR, UV–Vis and NMR spectroscopy. The molecular structures of 2·CH2Cl2, 3 and 5·CHCl3 were elucidated by single-crystal X-ray diffraction.

A titanocene‐catalyzed regiodivergent radical arylation is described that allows access to either enantiomerically pure tetrahydroquinolines or indolines from a common starting material. The regioselectivity of epoxide opening that results in the high selectivity of heterocycle formation is controlled by two factors, the absolute configuration of the enantiopure ligands of the (C5H4R)2TiX2 catalyst and the inorganic ligand X (X=Cl, OTs). The overall reaction is atom‐economical and constitutes a radical Friedel–Crafts alkylation., Indolines and tetrahydroquinolines are formed from the same substrates by titanocene catalysis. The absolute configuration of the cyclopentadienyl ligand and the inorganic ligand determine the regioselectivity of the ring opening and diastereoselectivity of tje radical arylation in the regiodivergent radical arylation of epoxides.

The modification of amino acids leads to valuable building blocks for the synthesis of bioactive compounds. By keeping the amino group protected, the carboxylic acid functionality can be converted in two steps into an imidazole moiety via a Davidson-like heterocyclization. This reaction allows for a combinatorial approach, in which two positions at the heterocycle can be modified. Herein, we report the synthesis of such imidazole derivatives by employing N-protected cyclohexylalanine as the starting material. Different α-halo ketones were used and two points of diversity, positions 4 and 5, were examined. The structure of the final imidazole derivatives was confirmed by three X-ray crystal structure analyses and their protease inhibiting activities were evaluated.

While P(v) 1,2-oxaphosphetanes were investigated in great detail over the past decades, the knowledge about P(v) 1,2-thiaphosphetanes is rather scarce, and P(iii) derivatives are unknown. Herein, we present the synthesis of the first P(iii) complex derivatives formed in the coordination sphere of group 6 metals and, additionally, the first unligated P(iii) 1,2-thiaphosphetanes. The latter display an unusually low HOMO-LUMO gap thus constituting excellent candidates for redox-cycling organocatalysts.

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.

Synthesis of the first tricyclic bis(carbenes) with facially opposed imidazole-2-ylidenes and two linking phosphorus centres in different oxidation states is presented using a modular, high-yield synthetic route. The formation of homo bimetallic coinage metal(i) complexes provides a first glimpse on their potential use.

In this study we describe the one-pot and high yield synthesis of the ruthenium(II) complex cis-dichloride [RuCl2(PPh3)2(L1)] (L1 = 4-methyl-2-(2′-pyridyl)quinoline) (1). The solid state structure of L1 is described. The catalytic activity of 1 in the transfer hydrogenation of various ketones by 2-propanol at 82 °C, has been studied and compared with the activity of the known catalyst precursors cis-[RuCl2(PPh3)2(L2)] (L2 = 2-(2'-pyridyl)quinoline) (2), cis-[RuCl2(PPh3)2(L3)] (L3 = 2-(2′-pyridyl)quinoxaline) (3) and cis-[RuCl2(PPh3)2(bipy)] (bipy = 2,2′-bipyridine) (4). The ruthenium monohydride complex [RuHCl(PPh3)2(L3)] 3-H (Cl cis to H) was prepared from the reaction of 3 with 2.5 equivalents of a KOiPr solution. Reaction of 3 with 10 equivalents of KOiPr yields the cis-[RuH2(PPh3)2(L3)] (3-H2). Treatment of 1, 2 and 4 with KOiPr (in excess) affords the ruthenium cis-dihydride complexes [RuH2(PPh3)2(L1)] (1-H2), [RuH2(PPh3)2(L2)] (2-H2) and [RuH2(PPh3)2(bipy)] (4-H2). The formation of 1-H2, 2-H2, 3-H2 and 4-H2 is supported by NMR spectroscopic data. The cis-dihydrides 1-H2 to 4-H2 catalyze successfully the transfer hydrogenation of benzophenone to benzhydrol in the absence of a base, suggesting that presumably the active catalyst is a ruthenium dihydride complex (RuH2). Catalyst 1 has been potentially recovered and reused at least four times.

Formation of thermally unstable complexes [Mn(CO)2CpMe(R2PO-TEMP)] (Cp = cyclopentadienyl; Me = methyl; TEMP = 2,2,6,6-tetramethyl-piperidin-1-oxyl) is presented in this experimental and theoretical study; in case of R = Cy 31P NMR spectroscopic evidence is provided. Mechanistic details of the product formation and decomposition, due to a homolytic O–N bond cleavage, are revealed by high-level density functional theory calculations. Insights into stability and spin density distribution of transient phosphanoxyl complexes [Mn(CO)2CpMe(R2PO·)] and preliminary results on the acidity of related complexes [Mn(CO)2CpMe(R2P–OH)] and [W(CO)5(R2P–OH)] toward TEMP–H are presented.

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) A) and a considerably longer Mo2–Si bond (2.438(2) A), 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) A) to an almost linearly coordinated Si atom (∠(Mo–Si–CTbb) = 160.8(1)°). Cyclic voltamme...

A combined theoretical and experimental study on the formation and reactivity of a P-OTEMP (P-bound TEMPO (TEMPO=2,2,6,6-tetramethyl-piperidin-1-oxyl)) substituted 1,3,2-diazaphospholane W(CO)5 complex is presented, including DFT-based mechanistic details. The complex possesses a thermally labile O-N bond that cleaves homolytically yielding the transient 1,3,2-diazaphospholane-2-oxyl complex [(CO)5 W(R2 PO. )], which acts as a radical initiator for styrene polymerization under ambient conditions.

Facile stereo- and regioselective ring opening of the oxaphosphirane complex A is presented using small molecules with differently polar E–H bonds (HCl, H2O, and NH3). The synthetic potential of the thus obtained novel 1,2-bifunctional ligands B is illustrated in cyclocondensation reactions, leading to the novel heterocyclic P-ligands C.

The syntheses of a formazan and a verdazyl radical are reported along with their crystal structures, UV–Vis spectra, and the EPR spectrum of the radical. In addition, the isolation of a possible by-product was achieved., The title compounds, C19H15BrN4, C20H16BrN4 and C20H15BrN4, are nitro­gen-rich organic compounds that are related by their synthesis. The verdazyl radical, in which stacking leads to anti­ferromagnetic inter­actions, was reported previously [Iwase et al. (2013 ▸). Phys. Rev. B, 88, 184431]. For this compound, improved structural data and spectroscopic data are presented. The other two compounds have been crystallized for the first time and form stacks of dimers, roughly along the a-axis direction of the crystal. The formazan mol­ecule shows signs of rapid intra­molecular H-atom exchange typical for this class of compounds and spectroscopic data are provided in addition to the crystal structure. The triazole compound appears to be a side-product of the verdazyl synthesis.

Metallosupramolecular systems heavily rely on the correct choice of ligands to obtain materials with desired properties. Engaging this problem, we present three ligand systems and six of their mono- and dinuclear complexes, based on the subcomponent self-assembly approach using electron-deficient pyridylcarbaldehyde building blocks. The properties are examined in solution by NMR and UV-vis spectroscopy and CV measurements as well as in solid state by single crystal X-ray diffraction analysis. Ultimately, the choice of ligands allows for fine-tuning of the electronic properties of the metal centers, complex-to-complex transformations, as well as establishing distinct anion-π-interaction motifs.

Structural diffraction analysis of an anilino squaraine with branched isobutyl side chains shows crystallization into two polymorphic structures in the bulk and in spin-casted thin films. We observe multipeaked and pleochroic absorption spectra being blue-(red)-shifted for the monoclinic (orthorhombic) polymorph. We understand the packing as Coulombic molecular H- (J)-aggregates supporting Davydov splitting. Pictures of projected Davydov components in oriented thin films fit well to polarization resolved spectro-microscopy and crossed-polarized light microscopy investigations. By comparison with literature on anilino squaraines with linear alkyl side chains, we point out a general trend for steering the thin film excitonic properties by simple side chain and/or processing condition variation. Combined with the ability to locally probe the direction of transition dipole moments, this adds value to the rational design of functional thin films for optoelectronic applications, especially envisioning ultrastrong light-matter interactions.

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.

Selective P–O bond activation of 1,2-oxaphosphetane complexes [(OC)5W(P{CH(SiMe3)2}CH2CRR′O)] (R/R′ = H/H (1a), H/CH3 (1b), H/CF3 (1c), CF3/CF3 (1d)) was achieved using different Bronsted acids. In case of acids with nucleophilic anions, such as HCl and HBF4·OEt2, the corresponding halophosphane complexes [(OC)5W(XP{CH(SiMe3)2}CH2CRR′OH] (X = Cl (2a–c), F (3c,d)) resulted as ring-opened products; 2b could be closed again with tBuLi/12-crown-4. In contrast, trifluoromethanesulfonic acid could be used to initiate either a ring-opening hydrolysis with a subsequent cleavage of the P–M bond to yield PH(O){CH(SiMe3)2}{CH2C(CF3)2OH} (7) or, in the presence of nitriles, a ring expansion yielding [(OC)5W(P{CH(SiMe3)2}CH2CH2OCR═N)] (R = CH3 (5a), Ph (5b), C(CH3)3 (5c)). P–O bond cleavage in 1a was achieved using the Lewis acidic catechol(chloro)borane to give [(OC)5W(P{CH(SiMe3)2}CH2CH(CH3)OBcat}Cl)] (8; cat = catechol).

A new bis(salicylimine) ligand based on the Tröger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordination to zinc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates as proven by XRD analysis and via comparison of experimental ECD spectra with those simulated with quantum-chemical methods. When the racemic ligand was used, self-assembly occurs under narcissistic self-sorting resulting in the formation of a racemic pair of helicates as revealed by NMR spectroscopy and XRD analysis.

Investigations on the reactivity of the transiently formed phosphanoxyl complex [(CO)5W(Ph2PO•)], thermally generated from [(CO)5W(Ph2PO-TEMP)] in toluene, is presented. Apart from self-reactions, trapping of this radical complex was achieved using group 14 hydrides Ph3EH (E = Si, Ge, Sn), leading to new phosphane complexes possessing a P–O–EPh3 bonding motif and the corresponding TEMP-H as byproduct. Reaction pathways, derived from DFT calculations, clearly revealed the intermediacy of various open-shell complexes; EPR measurements showed the presence of radicals, but unfortunately interpretation was not achieved.

Two different classes of aza analogues of 9,9'-spirobifluorenes have been synthesized. These were obtained by either furnishing the spirobifluorene with additional pyridyl moieties or by installing the aza function directly into the spirobifluorene core. These structurally rigid compounds were then evaluated as affinity materials for quartz crystal microbalances and proved to be highly potent for the detection of volatile organic compounds.

The synthesis and full characterization of the NHC-stabilized tungstenochlorostannylene [Cp*(CO)3W–SnCl(Idipp)] (1Sn), the NHC-stabilized chlorogermylidyne complex [Cp*(CO)2W═GeCl(Idipp)] (2), the tungsten germylidyne complex salt [Cp*(CO)2W≡Ge(Idipp)][B(C6H3-3,5-(CF3)2)4] (3), and the cationic metallostannylene [Cp*(CO)3W–Sn(Idipp)][Al(OC(CF3)3)4] (4Sn) are reported (Idipp = 2,3-dihydro-1,3-bis(2,6-diisopropylphenyl)-1H-imidazol-2-ylidene, Cp* = η5-C5Me5). Metathetical exchange of SnCl2(Idipp) with Li[Cp*W(CO)3] afforded selectively 1Sn. Photolytic decarbonylation of the Ge analogue [Cp*(CO)3W–GeCl(Idipp)] (1Ge) afforded the NHC-stabilized chlorogermylidyne complex (2), featuring a trigonal-planar coordinated germanium center and a W–Ge double bond (W–Ge 2.3496(5) A). Chloride abstraction from 2 with Na[B(C6H3-3,5-(CF3)2)4] yielded the germylidyne complex salt 3, which contains an almost linear W–Ge–C1 linkage (angle at Ge = 168.7(1)°) and a W–Ge triple bond (2.2813(4) A). Chloride elimination from 1Ge a...

Syntheses of 1,1′-bifunctional aminophosphane complexes 3–10 was achieved by reacting Li/Cl phosphinidenoid complex 2 (R = CPh3) with secondary (Me2NH, Et2NH, Bn2NH, pyrrolidine, and piperidine), primary amines (EtNH2 and allyl amine), and ammonia. Furthermore, regioselective N-silylation of 11 (R = Me) was achieved using MeLi and Me3SiCl to give complex 12. In contrast, treatment of complex 6 with KHMDS in the presence of 18-crown-6 yielded K/NMe2 phosphinidenoid complex 13 subsequently reacted with MeI to give P–Me substituted 14. Complex 5 was deprotonated with KHMDS in the presence of 18-crown-6 and reacted with [Ph3C]BF4 to yield complex 17 via single-electron transfer reaction and P,C-heterocoupling. Finally, selective P–N bond cleavage was achieved by treating complex 18 (R = t-Bu) with HCl(g) to afford chlorophosphane complex 19.

Dibenzo[a,e]pentalene (DBP) is a low-bandgap organic semiconductor. A versatile synthetic route to DBPs substituted with aryl or alkyl groups in the 5,10-positions and electron-donating or -accepting functionalities in the 2,7-positions is described. Six donor- or acceptor-functionalized DBP derivatives were synthesized that show amphoteric redox behavior and band gaps around 2 eV. Through choice of the 2,7-substituents, the HOMO/LUMO energy levels and band gaps can be adjusted within a range of up to 0.6 eV. In the solid state, the DBP derivatives assume herringbone-type packing structures.

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)SiSi(Br)Tbb in the presence of 4-dimethylaminopyridine afforded selectively the red-brown silylidyne complex [(κ3-tmps)(CO)2NbSi–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)2NbGe–ArMes] (3-Ge), and the deep violet, light-sensitive stannylidyne complex [(κ3-tmps)(CO)2NbSn–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)3NbGe(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.

A novel ambiguous reactivity of Li/Cl phosphinidenoid complexes under redox conditions is described. The outcome of the reaction with hexafluoroacetone is highly dependent on the P-substituent as fluoride substitution occurred in the case of R = CPh3 and C5Me5via a radical pathway, whereas for R = CH(SiMe3)2 a complex having a novel 1,2-diol-type P-ligand was obtained via a closed-shell pathway. DFT calculations reveal a new SET pathway starting with a noncovalent π-hole complex between the phosphinidenoid anion and hexafluoroacetone followed by an elimination of LiF. The second, closed-shell reaction course is strongly influenced by a noncovalent O⋯Si interaction established after the initial nucleophilic attack.

The transiently generated electrophilic terminal phosphinidene complex [(CO)5WPCH(SiMe3)2] reacted with allyl halides (X = F, Cl, Br) in toluene resulting in the formation of stable C–X insertion products 3a–c and diastereomeric phosphirane complexes 4a,a′,b,b′ as well as methylenephosphirane complex 5 as observed by 31P{1H} NMR spectroscopy. DFT calculations revealed that a novel rearrangement of transient phosphirane complexes is responsible involving C → P X atom transfer.

8-Arylethynylxanthine derivatives are potent, selective adenosine A2A receptor antagonists, which represent (potential) therapeutics for Parkinson&rsquo, s disease, Alzheimer&rsquo, s dementia, and the immunotherapy of cancer. 6-Amino-5-amidouracil derivatives are important precursors for the synthesis of such xanthines. We noticed an unexpected duplication of NMR signals in many of these uracil derivatives. Here, we present a detailed analytical study of structurally diverse 6-amino-5-carboxamidouracils employing dynamic and two-dimensional NMR spectroscopy, density functional theory calculations, and X-ray analysis to explain the unexpected properties of these valuable drug intermediates.

The 5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine derivative BIM-46174 has received attention as Gα(q) inhibitor. We conducted structural reductions to monocyclic and bicyclic substructures to explore the chemical space of BIM fragments and to gain insights into the pharmacophore of BIM-type Gα(q) inhibitors. Two piperazin-2-one-containing fragments and a small library of bicyclic lactams featuring fused pyrazine and diazepine rings were synthesized and evaluated. The results of a second messenger-based cellular assay indicate that the entire BIM structure is required for efficient Gα(q) inhibition.

Substituted xanthine derivatives are important bioactive molecules. Herein we report on a new, practical synthesis of 6-amino-5-carboxamidouracils, the main building blocks for the preparation of 8-substituted xanthines, by condensation of 5,6-diaminouracil derivatives and various carboxylic acids using the recently developed non-hazardous coupling reagent COMU (1-[(1-(cyano-2-ethoxy-2-oxoethylideneaminooxy)dimethylaminomorpholinomethylene)]methanaminium hexafluorophosphate). Optimized reaction conditions led to the precipitation of pure products after only 5 to 10 min of reaction time. The method tolerates a variety of substituted 5,6-diaminouracil and carboxylic acid derivatives as starting compounds resulting in most cases in more than 80% isolated yield. Regioselectivity of the reaction yielding only the 5-carboxamido-, but not the 6-carboxamidouracil derivatives, was unambiguously confirmed by single X-ray crystallography and multidimensional NMR experiments. The described method represents a convenient, fast access to direct precursors of 8-substituted xanthines under mild conditions without the necessity of hazardous coupling or chlorinating reagents.

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 SiClR{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.

Wahrend fur Phosphaalkene und Phosphane die Teilnahme an [4+n]-Cycloadditionen bekannt ist, sind P-C-Einfachbindungen diesbezuglich inert. Wir stellen hier Reaktionen von Oxaphosphirankomplexen mit Tetrachlor-ortho-benzochinon (TOB) vor, die eine Reaktion an der endocyclichen P-C-Bindung zeigen, welche stereoselektiv zu Benzo-1,3,6,2-trioxaphosphepinkomplexen fuhrt. DFT-Rechnungen auf hochstem Niveau liefern Hinweise darauf, dass das endgultige Produkt aus einer Sequenz dreier konsekutiver Schritte stammt, die einen ditopischen Van-der-Waals-Komplex beinhalten.

While phosphaalkenes and phosphanes are known to participate in [4+n] cycloaddition reactions, P-C single bonds are inert in this respect. Herein, reactions of oxaphosphirane complexes with tetrachloro-ortho-benzoquinone are presented that reveal a stereoselective reaction of the endocyclic P-C bond to afford benzo-1,3,6,2-trioxaphosphepine complexes. High-level DFT calculations provide evidence that the final product is derived from a sequence of three consecutive steps involving a ditopic van der Waals complex.

Synthesis of 1,1′-bifunctional aminophosphane complexes 3 a–e was achieved by the reaction of Li/Cl phosphinidenoid complex 2 with various primary amines (R=Me, iPr, tBu, Cy, Ph). Deprotonation of complex 3 a (R=Me) with potassium hexamethyldisilazide yielded a mixture of K/NHMe phosphinidenoid complex 4 a and potassium phosphanylamido complex 4 a′. Treatment of complex 3 c (R=tBu) and e (R=Ph) with KHMDS afforded the first examples of K/NHR phosphinidenoid complexes 4 c and e. The reaction of complex 3 c with 2 molar equivalents of KHMDS followed by PhPCl2 afforded complexes 5 c,c′, which possess a P2N-ring ligand. All complexes were characterized by NMR, IR, MS, and microanalysis, and additionally, complexes 3 b–e and 5 c′ were scrutinized by single-crystal X-ray crystallography.

Synthetic investigations towards spiroconjugated ketones and derivatives thereof are presented. These studies led to the development of a short procedure for the synthesis of spiroconjugated tetraketone 1 in two steps with 10 % overall yield and the first-time synthesis of spirocyclic trindone 2. The optoelectronic properties of these compounds based on spectroscopic and electrochemical measurements in combination with DFT calculations as well as their molecular structures in the solid state are presented and discussed.

Recently, the first synthetic route to 1,2-oxaphosphetane complexes was described, but the formation of too many isomers was a clear drawback and hampered further studies. Herein, we present significant advances with this problem using trifluoromethyl epoxide (4), 1,1′-bis(trifluoromethyl) epoxide (5), and differently substituted Li/Cl phosphinidenoid complexes 1–3 (R = CH(SiMe3)2, CPh3, C5Me5), thus giving 1,2-oxaphosphetane complexes 6–10 with high selectivity.

Cyclic voltammetric studies of the hydridodisilicon(0,II) borate [(Idipp)(H)SiIISi0(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 (E1/2 = −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 SiSi 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.

The proton-catalyzed transformation of 2-thioureidobenzonitriles to 4-acylimino-4H-3,1-benzothiazines was accomplished by treatment with carboxylic anhydrides, acid chlorides or alkyl chloroformates. The reaction involves a cyclization to 4-imino-3,1-benzothiazinium salts, whose thioimidate structure is trapped by a subsequent reaction with the acyl donor. 2-Ureidobenzonitriles do not undergo such an intermolecular tandem reaction. The different reaction behavior of both types of substrates was verified by NMR monitoring and employing 18O-enriched water.

The reaction of MesP=CPh2 with the least sterically demanding N-heterocyclic carbene (NHC = IMe) results in formation of the 'abnormal' (C(4)-substituted) 4-phosphino-NHC (1). In contrast, reaction with Me2IMe gives the unprecedented 'normal' C(2) 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.