Recent Advances in the Synthesis of N‐Heteroatom Substituted Imido Complexes Containing a Nitrido Bridge [M=N—E] (M = Group 4, 5 and 6 Metal,E = B,Si, Ge,P, S)

The focus of the current report lies on recent developments of synthetic methods applied to the synthesis of some high‐valent complexes containing the nitrido functionality [N]^3— as a link between a group 4, 5 or 6 transition metal and a main group element E (E = B, Si, Ge, P, S). Emphasis is put on results, that have been obtained within the “Schwerpunktprogramm “Nitridobrücken” funded by the Deutsche Forschungsgemeinschaft. The synthetic methods include condensation reactions of reactive chloro and oxo complexes (M = V, Nb, Ta, Cr, Mo, W) with silylamines, sulfonylamides, with N‐silyl and N‐lithio iminophosphoranes, furthermore methatesis reactions of oxo complexes with N‐sulfonyl sulfinyl amides (M = V, Cr, Mo, W), the oxidative addition of element azides to d² metal centers (M = V, W), and finally transamination reactions of N‐H iminophosphoranes with amido complexes (M = Ti, Sm).     

Polynuclear nitrosyl carbonyl ReI complexes with thiolate and sulfide bridges

The reaction of the complex Re₂(CO)₄(NO)₂Cl₄ (1) with NaSCMe₃ (2) (in THF or MeCN, 65–80°C, 24 h) was studied at different ratios of the reagents (from 1∶2 to 1∶6). At the reagent ratio of 1∶2, the binuclear complex Re₂(CO)₄(NO)₂Cl₂(μ-SCMe₃)₂ (3) was obtained as a mixture ofsyn andanti isomers (3a and3b, respectively) containing Re₂S₂ fragments with different structures (the butterfly-like structure in3a and the planar fragment in3b). When the initials were taken in ratios from 1∶4 to 1∶6, two compounds were isolated: the binuclear complex Re₂(CO)₄(NO)₂(μ-SCMe₃)₂(μ-S)4 (cocrystallized as a mixture ofsyn andanti isomers,4a and4b, respectively) and the triangular cluster Re₃(CO)₃(NO)₃(μ-SCMe₃((μ₃-S)(μ₃-Cl) (5). Apparently, complex4 is formed in the course of isolation as a result of elimination of SR₂ from the unstable tetrathiolate dimer Re₂(CO)₄(NO)₂(SCMe₃)₂(μ-SCMe₃)₂ (6). Cluster5 is the product of the reaction between compounds3 and4. Products of interaction of compound6 with silica gel upon column chromatography of the reaction mixture were studied. Four complexes containing hydroxy and oxo bridging groups, (CO)₂(NO)Re(μ-SCMe₃)₂(μ-OH)Re(SCMe₃)(CO)(NO) (7), (CO)₃(NO)₃RE₃(μ-SCMe₃)₃(μ₃-SCME₃)(μ₃-O) (8), [(CO)₂(NO)₂Re₂(SCMe₃)₂(μ-SCMe₃)₂(μ-OH)][Na(THF)(Et₂O)] (9), and [(CO)₂(NO)₂Re₂(SCMe₃)₂(μ-SCMe₃)₂(μ-OH)]₂−[Na(H₂O)₆][H₅O₂] (10), were isolated. The structures of complexes3, 4, 5, 7, 8, 9, and10 were established by X-ray diffraction study. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1030–1044, May, 1998.     

Ansa-metallocenes with B---N and B---P linkages: the importance of N---HF---C hydrogen bonding in pentafluorophenyl boron compounds

The reaction of Cp′(Cp^B)ZrCl₂ [Cp^B=η⁵-C₅H₄B(C₆F₅)₂] with LiNHCMe₃ gave Cp′(Cp^B)(μ-NHCMe₃)ZrCl, with a constrained-geometry type Cp---B---N chelate ligand. The ¹⁹F-NMR spectrum of the zirconium complexes, as well as that of the titanium analogue, reveals C---FH---N hydrogen bonding to one of the ortho-F atoms of a C₆F₅ ring, strong enough to persist in solution at room temperature. The reaction of Cp′(Cp^B)TiCl₂ with LiPPh₂ affords the Cp---B---P chelate complex Cp′(Cp^B)(μ-PPh₂)TiCl, the first example of a crystallographically characterised Ti(IV) phosphido compound. A ¹⁹F-NMR study of a number of adducts of B(C₆F₅)₃ with prim- and sec-amines demonstrates the importance of intramolecular hydrogen bonding to C₆F₅ in this class of compounds, while there are no such interactions in B(C₆F₅)₃(PHR₂) (R=Cy, Ph). The crystal structures of Cp′(Cp^B)(μ-PPh₂)TiCl, B(C₆F₅)₃(NHMe₂) and B(C₆F₅)₃(PHCy₂) are reported.     

Reactions of Nitridotechnetium(V) Complexes with Boranes

Nitrido bridges between technetium and boron were formed during reactions of [TcN(PMe₂Ph)(Et₂dtc)₂] (Et₂dtc^? = diethyldithiocarbamate) and BH₃ or BPhCl₂ at low temperatures. X‐Ray structure determinations show that the products contain almost linear Tc–N–B bonds with Tc–N distances which are only slightly lengthened with respect to the triple bonds in the precursor molecule. However, a significant lengthening of the Tc–S bond trans to the nitrido ligand is detected by the decrease of the structural trans influence of “N^3?”N. The compounds are instable and decompose at room temperature under cleavage of the N–B bonds. A reaction between [TcNCl₂(PPh₃)₂] and BCl₃ does not yield a product with a nitrido bridge. Prolonged heating in dichloromethane results in decomposition of the technetium complex and the formation of (HPPh₃)₂[TcCl₆]. Hydrogen bonds are established between the complex anion and each two counter ions.     

Nitrido Complexes of Transition Metals

In the past decade new syntheses and numerous structural determinations have enlivened studies in the still relatively young field of nitrido-transition-metal complexes. Aside from the terminal function of the nitrido ligand M?N:, this group also occurs as linear μ₂-bridging ligand in symmetric and asymmetric coordination; examples are known with almost right-angled bridge function; and, finally, it also functions as μ₃-bridging ligand. Accordingly, the fresh impulses given to synthetic chemistry by nitrido complexes are also many-sided: such complexes are used, inter alia, for the preparation of phosphaniminato and thionitrosyl complexes as well as for the synthesis of metallaheterocycles of the type MN₃S₂ and MN₃P₂ with delocalized π-systems. In technetium chemistry complexes with terminal nitrido group are employed as radiopharmaceuticals, and, owing to the strong trans influence of the M?N: group, nitrido complexes of molybdenum are suitable as catalysts in olefin metathesis. Finally, nitrido complexes are also of wide interest in theoretical studies.     

Gemischtligand-Komplexe des Rheniums. IV. Die Reaktion von [ReNCl2(Me2PhP)3] mit Dithiocarbamaten. Kristallstrukturen von trans-Chloro-dimethyldithiocarbamato-bis(dimethylphenylphosphan) nitridorhenium(V), [ReN(Cl)(Me2PhP)2(Me2dtc)], und Bis(diethyldithiocarbamato)(dimethylphenylphosphan)nitridorhenium(V), [ReN(Me2PhP)(Et2dtc)2]

Mixed-Ligand Complexes of Rhenium IV. The Reaction of [ReNCl₂(Me₂PhP)₃] with Dithiocarbamates. X-Ray Crystal Structures of trans-Chloro-dimethyldithiocarbamato-bis(dimethylphenylphosphine) nitridorhenium(V), [ReN(Cl)(Me₂PhP)₂(Me₂dtc)], and Bis(diethyldithiocarbamato)(dimethylphenylphosphine)nitridorhenium(V), [ReN(Cl)(Me₂PhP)(Et₂dtc)₂] [ReNCl₂(Me₂PhP)₃] reacts with dialkyldithiocarbamates, R₂dtc^?, under a stepwise ligand exchange. Final products of these reactions are the well-known [ReN(R₂dtc)₂] bischelates. Intermediatelly, however, complexes of the general formulae [ReN(Cl)(Me₂PhP)₂(R₂dtc)] and [ReN(Me₂PhP)(R₂dtc)₂] can be isolated. Representatives have been structurally characterized. [ReN(Cl)(Me₂PhP)₂(Me₂dtc)] crystallizes monoclinic in the space group P2₁/c, Z = 4. The dimensions of the unit cell are a = 13.071(3); b = 11.622(1); c = 15.667(3) Å; β = 97.09(1)°. The rhenium atom has a distorted octahedral environment; the Re≡N bond length is 1.71(1) Å. The Re? Cl bond distance is markedly lengthened (2.665(2) Å) as a consequence of the strong trans labilizing influence of the coordinated nitrido ligand. [ReN(Me₂PhP)(Et₂dtc)₂] crystallizes monoclinic in the space group P2₁/c, Z = 4, a = 17.262(3); b = 14.915(2); c = 9.888(2); β = 76.35(8)°. The equatorial coordination sphere is occupied by one phosphorus atom and three sulphur atoms. One of the dithiocarbamate ligands is coordinated bidentately; the second one with two distinct Re? S bond lengths. The Re? S(4) distance is 2.7983(2) Å which can be discussed as a weak interaction with the metal.     

Synthese und Kristallstruktur des Nitrido-Oxalato-Osmats PPh4{Na(15-Krone-5)[OsNCl3(C2O4)]}

Synthesis and Crystal Structure of the Nitrido Oxalato Osmate PPh₄{Na(15-Crown-5)[OsNCl₃(C₂O₄)]} The title compound has been prepared by slow reaction of PPh₄[OsNCl₄] with sodium oxalate in boiling dichloromethane in the presence of 15-crown-5, forming violet crystals, which were characterized by an X-ray structure determination. Space group P2₁/c, Z = 4, 4 769 observed unique reflections, R = 0.035. Lattice dimensions at –80°C: a = 1 931.4, b = 1 178.7, c = 1 764.1 pm, β = 99.39°. The structure consists of PPh₄⁺ ions and ion pairs {Na(15-crown-5)[OsNCl₃(C₂O₄)]}^?, in which the osmium atom is distortedly octahedrally coordinated by the nitrido ligand, by three chlorine atoms, and by two oxygen atoms of the oxalato group. The remaining oxygen atoms of the oxalato ligand are coordinated to the sodium atom, which, together with the five oxygen atoms of the crown ether molecule, gets coordination number seven.     

Homo- and hetero-bridged mixed-valence dinuclear complexes which contain the fragment ‘Rh(C6F5)3’

The reaction of the anionic mononuclear rhodium complex [Rh(C₆F₅)₃Cl(Hpz)]^t- (Hpz = pyrazole, C₃H₄N₂) with methoxo or acetylacetonate complexes of Rh or Ir led to the heterodinuclear anionic compounds [(C₆F₅)₃Rh(μ-Cl)(μ-pz)M(L₂)] [M = Rh, L₂ = cyclo-octa-1,5-diene, COD (1), tetrafluorobenzobarrelene, TFB (2) or (CO)₂ (4); M = Ir, L₂ = COD (3)]. The complex [Rh(C₆F₅)₃(Hbim)]⁻ (5) has been prepared by treating [Rh(C₆F₅)₃(acac)]⁻ with H₂bim (acac = acetylacetonate; H₂bim = 2,2′-biimidazole). Complex 5 also reacts with Rh or Ir methoxo, or with Pd acetylacetonate, complexes affording the heterodinuclear complexes [(C₆F₅)₃Rh(μ-bim)M(L₂)]⁻ [M = Rh, L₂ = COD (6) or TFB (7); M = Ir, L₂ = COD (8); M = Pd, L₂ = η³-C₃H₅ (9)]. With [Rh(acac)(CO)₂], complex 5 yields the tetranuclear complex [{(C₆F₅)₃Rh(μ-bim)Rh(CO)₂}₂]₂₋. Homodinuclear Rh^III derivatives [{Rh(C₆F₅)₃}₂(μ-L)₂]^·- [L₂ = OH, pz (11); OH, S^tBu (12); OH, SPh (13); bim (14)] have been obtained by substitution of one or both hydroxo groups of the dianion [{Rh(C₆F₅)₃(μ-OH)}₂]²⁻ by the corresponding ligands. The reaction of [Rh(C₆F₅)₃(Et₂O)_x] with [PdX₂(COD)] produces neutral heterodinuclear compounds [(C₆F₅)₃Rh(μ-X)₂Pd(COD)] [X = Cl (15); Br (16)]. The anionic complexes 1–14 have been isolated as the benzyltriphenylphosphonium (PBzPh₃⁺) salts.     

Linking polythiophene chains with vinylene‐bridges: A way to improve charge transport in polymer field‐effect transistors

A series of novel branched polythiophene derivatives bearing different densities of vinylene‐bridges as linking chains were synthesized by a general synthetic strategy. The organic field‐effect transistors, which were fabricated by spin‐coating the polymer solutions onto octadecyltrichlorosilane‐modified SiO₂/Si substrates with top‐contact configuration, afforded a high mobility of 8.0 × 10^?3 cm² V^?1 s^?1 with an on/off ratio greater than 10⁴ and a threshold voltage of about ?3 V in saturation regime. The devices based on these polymers possessed better performance than those of polymers without conjugated bridges and polymers with longer conjugated bridges. These results demonstrated that the combination of conjugated polythiophene backbones and vinylene‐bridges would improve the carrier mobility. As an emerging class of conjugated materials, polymers with vinylene‐bridges as linking chains would open up new opportunities in organic electronics, and their applications in organic electronics are promising. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1381–1392, 2009     

Engineering Models for Numerical Analysis of Composite Bending Members∗

Abstract

ABSTRACT The two-step numerical analysis of a composite beam structure is presented in this paper. The first step, based on the idea of dividing the cross section into laminas, leads to the estimation of the moment-curvature relation for different types of cross sections used in composite beams. The second step adopts this constitutive relation, which is expressed in the space of generalized stresses and strains, into finite element nonlinear code. Some numerical examples are given, to show the agreement of numerical calculations with results of the authors' experiments, when the shrinkage of a concrete encasement and stresses due to welding processes in steel beams are considered. In addition, the numerical concept presented here seems to reduce the sensitivity of the final results obtained to finite element discretization error.