Hypervalent Organoselenium(II) Compounds with Organophosphorus Ligands. Crystal and Molecular Structure of [2‐(iPr2NCH2)C6H4]Se[S2PR′2] (R′ = Ph,OiPr)

Redistribution reactions between diorganodiselenides of type [2‐(R₂NCH₂)C₆H₄]₂Se₂ [R = Et, iPr] and bis(diorganophosphinothioyl disulfanes of type [R′₂P(S)S]₂ (R = Ph, OiPr) resulted in the hypervalent [2‐(R₂NCH₂)C₆H₄]SeSP(S)R′₂ [R = Et, R′ = Ph ( 1 ), OiPr ( 2 ); R = iPr, R′ = Ph ( 3 ), OiPr ( 4 )] species. All new compounds were characterized by solution multinuclear NMR spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se) and the solid compounds 1 , 3 , and 4 also by FT‐IR spectroscopy. The crystal and molecular structures of 3 and 4 were determined by single‐crystal X‐ray diffraction. In both compounds the N(1) atom is intramolecularly coordinated to the selenium atom, resulting in T‐shaped coordination arrangements of type (C,N)SeS. The dithio organophosphorus ligands act monodentate in both complexes, which can be described as essentially monomeric species. Weak intermolecular S ··· H contacts could be considered in the crystal of 3 , thus resulting in polymeric zig‐zag chains of R and S isomers, respectively.     

Synthesis and metal complexes of chiral c(2)-symmetric diamino-bisoxazoline ligands

A synthetic route to tetradentate chiral N(4) ligands has been developed with the aim to study the potential of corresponding iron and manganese complexes as catalysts for enantioselective epoxidation. These ligands, which contain two oxazoline rings and two trialkylamino groups as coordinating units, are readily prepared in enantiomerically pure form by the reaction of chiral 2-chloromethyloxazolines with achiral N,N'-dimethylethane-1,2-diamine or chiral (R,R)-N,N'-dimethylcyclohexane-1,2-diamine. The ligands derived from N,N'-dimethylethane-1,2-diamine reacted with anhydrous metal halides MnCl(2) and FeCl(2) in a stereoselective manner to give octahedral mononuclear complexes that have the general formula Delta-[(L)MCl(2)]. In contrast, the ligands derived from N,N'-dimethylcyclohexane-1,2-diamine formed complexes with different coordination modes depending on the diastereomer employed: in one case the metal ion was found to be pentacoordinate, in the other case a hexacoordinated complex was observed. The structure of a series of Fe and Mn complexes was determined by X-ray analysis. The coordination chemistry of these ligands was further studied by X-ray and NMR analyses of the diamagnetic isostructural complexes [(L)ZnCl(2)]. Analogous ionic complexes, which were prepared by removing chloride with silver trifluoromethanesulfonate or hexafluoroantimonate, were tested as catalysts for the epoxidation of olefins.     

New rare earth metal complexes with nitrogen-rich ligands: 5,5'-bitetrazolate and 1,3-bis(tetrazol-5-yl)triazenate-on the borderline between coordination and the formation of salt-like compounds

From the two nitrogen-rich ligands BT(2-) (BT=5,5'-bitetrazole) and BTT(3-) (BTT=1,3-bis(1H-tetrazol-5-yl)triazene), a series of novel rare earth metal complexes were synthesised. For the BT ligand, a vast number of these complexes could be structurally characterised by single-crystal XRD, revealing structures ranging from discrete molecular aggregates to salt-like compounds. The isomorphous complexes [La2(BT)3]14 H2O (1) and [Ce2(BT)3]14 H2O (2) reveal discrete molecules in which one BT(2-) acts as a bridging ligand and two BT groups as chelating ligands. The complexes, [M(BT)(H2O)7]2[BT] x (x) H2O (3-5), (M=Nd (3), Sm (4), and Eu (5)), are also isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT(2-) acts as a chelate ligand for each metal centre. [Tb(H2O)8]2[BT]3 x H2O (6) and [Er(H2O)8](2)[BT](3)x H2O (7) are salt-like compounds that do not exhibit any significant metal-nitrogen contacts. In the BTT-samarium compound 9, discrete molecules were found in which BTT(3-) acts as a tridentate ligand with three Sm--N bonds.     

Synthesis,Characterization, and X‐ray Structures of Ru3(CO)9(dotpm)(L) Complexes [L = PPh3, P(C6H4Cl‐p)3, and PPh2(C6H4Br‐p)]

The reaction of Ru₃(CO)₁₀(dotpm) ( 1 ) [dotpm = (bis(di‐ortho‐tolylphosphanyl)methane)] and one equivalent of L [L = PPh₃, P(C₆H₄Cl‐p)₃ and PPh₂(C₆H₄Br‐p)] in refluxing n‐hexane afforded a series of derivatives [Ru₃(CO)₉(dotpm)L] ( 2 – 4 ), respectively, in ca. 67–70 % yield. Complexes 2 – 4 were characterized by elemental analysis (CHN), IR, ¹H NMR, ¹³C{¹H} NMR and ³¹P{¹H} NMR spectroscopy. The molecular structures of 2 , 3 , and 4 were established by single‐crystal X‐ray diffraction. The bidentate dotpm and monodentate phosphine ligands occupy equatorial positions with respect to the Ru triangle. The effect of substitution resulted in significant differences in the Ru–Ru and Ru–P bond lengths.     

Ruthenium complexes of substituted hydrazine: new solution- and solid-state binding modes

The methylhydrazine complex [Ru(NH(2)NHMe)(PyP)(2)]Cl(BPh(4)) (PyP=1-[2-(diphenylphosphino)ethyl]pyrazole) was synthesised by addition of methylhydrazine to the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(BPh(4))(2). The methylhydrazine ligand of the ruthenium complex has two different binding modes: side-on (eta(2)-) when the complex is in the solid state and end-on (eta(1)-) when the complex is in solution. The solid-state structure of [Ru(PyP)(2)(NH(2)NHMe)]Cl(BPh(4)) was determined by X-ray crystallography. 2D NMR spectroscopic experiments with (15)N at natural abundance confirmed that in solution the methylhydrazine is bound to the metal centre by only the -NH(2) group and the ruthenium complex retains an octahedral conformation. Hydrazine complexes [RuCl(PyP)(2)(eta(1)-NH(2)NRR')]OSO(2)CF(3) (in which R=H, R'=Ph, R=R'=Me and NRR'=NC(5)H(10)) were formed in situ by the addition of phenylhydrazine, 1,1-dimethylhydrazine and N-aminopiperidine, respectively, to a solution of the bimetallic complex [Ru(mu-Cl)(PyP)(2)](2)(OSO(2)CF(3))(2) in dichloromethane. These substituted hydrazine complexes of ruthenium were shown to exist in an equilibrium mixture with the bimetallic starting material.     

Molecular Structure and Solution Behavior of a Benzonitrile Ligated Silver(I) Complex [Ag(PhCN)2][B(C6F5)4]

The bis(benzonitrile) complex [Ag(PhCN)₂][B(C₆F₅)₄] is synthesized from its tetra(acetonitrile) ligated congener. X‐ray diffraction studies were conducted to compare the bond lengths and angles of the complex in regard with those of other nitrile ligated silver cations with weakly coordinating anions. Vibrational spectra of the solid complex and in (concentrated) benzonitrile solution reveal differences in the strength of benzonitrile‐silver ion interactions.     

Synthesis,Characterization, and Properties of Pentanitrobenzene C6H(NO2)5

The synthesis of the polynitroaromatic compound pentanitrobenzene was re‐examined by modern spectroscopic, structural and physicochemical methods. Originally prepared in 1979, this material could exhibit interesting properties as an oxygen‐rich energetic building block. The energies of formation were calculated with the GAUSSIAN program package and the detonation parameters were predicted using the EXPLO5 computer code. The performance data were determined and compared to the common oxidizer ammonium perchlorate. The crystal structure of pentanitrobenzene was determined by X‐ray crystallography, and those of 2,3,4,6‐tetranitroaniline and styphnic acid (trinitroresorcinol) were re‐determined.     

Synthesis and Reaction Chemistry of Sb(ECH2CH2NMe2)3 (E = O,S)

The antimony aminoalkoxide and aminothiolates Sb(ECH₂CH₂NMe₂)₃ [E = O ( 1 ), S ( 2 )] were synthesized and their ability to form adducts with other metal moieties investigated. Compound 1 forms 1:1 adducts with NiI₂ ( 3 ) and M(acac)₂ [M = Cd ( 4 ), Ni ( 5 )], while 2 undergoes ligand exchange with AlMe₃ to afford Me₂AlSCH₂CH₂NMe₂ ( 6 ). The structures of 2 – 4 and 6 were determined. Compound 2 incorporates three S, N‐chelating ligands though the interaction with nitrogen is weaker than in analogous alkoxide complexes. Product 3 reveals one iodine has migrated from nickel to antimony, and all three alkoxide ligands bridge the two metals through μ₂‐O atoms. In contrast, in 4 , only one alkoxide links the antimony and cadmium. Compound 6 adopts the same structure, a chelating S,N ligand generating a tetrahedral center at aluminum, as known tBu₂AlSCH₂CH₂NR₂ species (R = Me, Et).     

Homoleptic copper(I) arylthiolates as a new class of p-type charge carriers: structures and charge mobility studies

Polymeric homoleptic copper(I) arylthiolates [Cu(p-SC(6)H(4)-X)](infinity) (X=CH(3) (1), H (2), CH(3)O (3), tBu (4), CF(3) (5), NO(2) (6), and COOH (7)) have been prepared as insoluble crystalline solids in good yields (75-95 %). Structure determinations by powder X-ray diffraction analysis have revealed that 1-3 and 6 form polymers of infinite chain length, with the copper atoms bridged by arylthiolate ligands. Weak intra-chain pi***pi stacking interactions are present in 1-3, as evidenced by the distances (3.210 A in 1, 3.016 A in 2, 3.401 A in 3) between the mean planes of neighboring phenyl rings. In the structure of 6, the intra-chain pi***pi interactions (d=3.711 A) are insignificant and the chain polymers are associated through weak, non-covalent C-H...O hydrogen-bonding interactions (d=2.586 A). Samples of 1-7 in their polycrystalline forms proved to be thermally stable at 200-300 degrees C; their respective decomposition temperatures are around 100 degrees C higher than that of the aliphatic analogue [Cu(SCH(3))](infinity). Data from in situ variable-temperature X-ray diffractometry measurements indicated that the structures of both 1 and 7 are thermally more robust than that of [Cu(SCH(3))](infinity). TEM analysis revealed that the solid samples of 1-5 and [Cu(SCH(3))](infinity) contained homogeneously dispersed crystalline nanorods with widths of 20-250 nm, whereas smaller plate-like nanocrystals were found for 6 and 7. SAED data showed that the chain polymers of 1-3 and [Cu(SCH(3))](infinity) similarly extend along the long axes of their nanorods. The nanorods of 1-5 and [Cu(SCH(3))](infinity) have been found to exhibit p-type field-effect transistor behavior, with charge mobility (micro) values of 10(-2)-10(-5) cm(2) V(-1) s(-1). Polycrystalline solid samples of 6 and 7 each showed a low charge mobility (<10(-6) cm(2) V(-1) s(-1)). The charge mobility values of field-effect transistors made from crystalline nanorods of 1-3 and [Cu(SCH(3))](infinity) could be correlated with their unique chain-like copper-sulfur networks, with the para-substituent of the arylthiolate ligand influencing the charge-transport properties.     

Pd(II) and Pt(II) complexes of 2-(2'-pyridyl)-4,6-diphenylphosphinine: synthesis, structure, and reactivity

The coordination chemistry of the bidentate P,N hybrid ligand 2-(2'-pyridyl)-4,6-diphenylphosphinine (1) towards Pd(II) and Pt(II) has been investigated. The molecular structures of the complexes [PdCl(2)(1)] and [PtCl(2)(1)] were determined by X-ray diffraction, representing the first crystallographically characterized λ(3)-phosphinine-Pd(II) and -Pt(II) complexes. Both complexes reacted with methanol at the P=C double bond at an elevated temperature, leading to the corresponding products [MCl(2)(1H·OCH(3))]. The molecular structure of [PdCl(2)(1H·OCH(3))] was determined crystallographically and revealed that the reaction with methanol proceeds selectively by syn addition and exclusively to one of the P=C double bonds. Strikingly, the reaction of [PdCl(2)(1H·OCH(3))] with the chelating diphosphine DPEphos at room temperature in CH(2)Cl(2) led quantitatively to [PdCl(2)(DPEphos)] and phosphinine 1 by elimination of CH(3)OH and rearomatization of the phosphorus heterocycle.     

Octahedral adducts of dichlorosilane with substituted pyridines: synthesis, reactivity and a comparison of their structures and (29)si NMR chemical shifts

H(2)SiCl(2) and substituted pyridines (Rpy) form adducts of the type all-trans-SiH(2*)Cl(2)2 Rpy. Pyridines with substituents in the 4- (CH(3), C(2)H(5), H(2)C=CH, (CH(3))(3)C, (CH(3))(2)N) and 3-positions (Br) give the colourless solids 1 a-f. The reaction with pyrazine results in the first 1:2 adduct (2) of H(2)SiCl(2) with an electron-deficient heteroaromatic compound. Treatment of 1 d and 1 e with CHCl(3) yields the ionic complexes [SiH(2)(Rpy)(4)]Cl(2*)6 CHCl(3) (Rpy=4-methylpyridine (3 d) and 4-ethylpyridine (3 e)). All products are investigated by single-crystal X-ray diffraction and (29)Si CP/MAS NMR spectroscopy. The Si atoms are found to be situated on centres of symmetry (inversion, rotation), and the Si-N distances vary between 193.3 pm for 1 c (4-(dimethylamino)pyridine complex) and 197.3 pm for 2. Interestingly, the pyridine moieties are coplanar and nearly in an eclipsed position with respect to the SiH(2) units, except for the ethyl-substituted derivative 1 e, which shows a more staggered conformation in the solid state. Calculation of the energy profile for the rotation of one pyridine ring indicates two minima that are separated by only 1.2 kJ mol(-1) and a maximum barrier of 12.5 kJ mol(-1). The (29)Si NMR chemical shifts (delta(iso)) range from -145.2 to -152.2 ppm and correlate with the electron density at the Si atoms, in other words with the +I and +M effects of the substituents. Again, compound 1 e is an exception and shows the highest shielding. The bonding situation at the Si atoms and the (29)Si NMR tensor components are analysed by quantum chemical methods at the density functional theory level. The natural bond orbital analysis indicates polar covalent Si-H bonds and very polar Si-Cl bonds, with the highest bond polarisation being observed for the Si-N interaction, which must be considered a donor-acceptor interaction. An analysis of the topological properties of the electron distribution (AIM) suggests a Lewis structure, thereby supporting this bonding situation.     

Computational (DFT) and Experimental (EXAFS) Study of the Interaction of [Ir(IMes)(H)2(L)3] with Substrates and Co‐substrates Relevant for SABRE in Dilute Systems

Signal amplification by reversible exchange (SABRE) is an emerging hyperpolarization method in NMR spectroscopy, in which hyperpolarization is transferred through the scalar coupling network of para‐hydrogen derived hydrides in a metal complex to a reversibly bound substrate. Substrates can even be hyperpolarized at concentrations below that of the metal complex by addition of a suitable co‐substrate. Here we investigate the catalytic system used for trace detection in NMR spectroscopy with [Ir(IMes)(H)₂(L)₃]⁺ (IMes=1,3‐dimesitylimidazol‐2‐ylidene) as catalyst, pyridine as a substrate and 1‐methyl‐1,2,3‐triazole as co‐substrate in great detail. With density functional theory (DFT), validated by extended X‐ray absorption fine structure (EXAFS) experiments, we provide explanations for the relative abundance of the observed metal complexes, as well as their contribution to SABRE. We have established that the interaction between iridium and ligands cis to IMes is weaker than that with the trans ligand, and that in mixed complexes with pyridine and triazole, the latter preferentially takes up the trans position.     

Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study

Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes [Pd(O₃SCH₃)(L‐L)][O₃SCH₃] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O₃SCH₃)(L‐ L)][O₃SCH₃], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism.     

Isolable tris(alkyne) and bis(alkyne) complexes of gold(I)

Golden trefoils: Tris(alkyne)gold complex [(coct)(3)Au][SbF(6)] (see picture; 1-SbF(6)) can be synthesized from cyclooctyne (coct) and AuSbF(6) generated in situ. Treatment of AuCl with cyclooctyne led to the bis(alkyne)gold complex [Au(coct)(2)Cl] (2). DFT analysis indicates that the cyclooctyne ligands are net electron donors in 1 but overall electron acceptors in 2. AuSbF(6) is shown to mediate [2+2+2] cycloaddition reactions of alkynes.