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.     

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).     

Oligonary Nitrides and Oxonitrides of Si,P, Al,and B in Combination with Rare Earth or Transition Metals as well as Molecular Precursor Compounds with Nitrido Bridges M‐N‐Si (M = Ti,Zr, Hf,W, Sn)

A novel synthetic approach is presented leading to hitherto unknown nitridosilicates, oxonitridosilicates, oxonitridoaluminosilicates, carbidonitridosilicates, as well as nitridoborates and oxonitridoborates of rare earth elements, alkali, and alkaline earth metals. Typically, the respective metals were reacted with silicon diimide, aluminum nitride, or poly(boron amide imide), respectively, under pure nitrogen atmosphere utilizing a radiofrequency furnace. Usually, the compounds are obtained within short reaction periods as coarsely crystalline products. Zink nitridophosphates of the sodalite structure type were obtained by the reaction of phosphorus nitride imide with zinc or zinc chalcogenides, respectively. Several molecular metal silylamides and imides containing nitridobridges between the metals and silicon were obtained by the reaction of differently chlorinated disilazanes with metal chlorides. During these investigations hitherto unknown bis(trimethylsilyl)ammonium salts have been discovered. Furthermore, we report about the synthesis of N‐silyl metal hydrazides.     

Reactions of Rhenium and Technetium Nitrido Complexes with ER3 Fragments (E = B,Ga, Al,C, P; R = H,Alkyl, Aryl)

Terminal ‘N^3—’ ligands in rhenium and technetium nitrido complexes are sufficiently nucleophilic to react with Lewis acids under formation of nitrido‐bridged compounds. The reactivity of the nucleophilic centre and the nature of the formed compounds are strongly dependent on the Lewis acid and the composition of the metal complex used. Air‐stable compounds with Re≡N‐ER₃ bridges are formed when ER₃ is BR₃ (R = H, Cl, Br, Ethyl, Phenyl, C₆F₅), BCl₂Ph, GaCl₃, CPh₃⁺, or PPh₃. The six‐co‐ordinate rhenium(V) complexes [ReNX₂(PMe₂Ph)₃] (X = Cl, Br), [ReN(X)(Et₂dtc)(PMe₂Ph)₂] (Et₂dtc^— = diethyldithiocarbamate) and [ReN(Et₂dtc)₂(PMe₂Ph)] have been proved to be excellent starting materials for this type of reactions, whereas the five‐co‐ordinate precursors [ReNCl₂(PPh₃)₂], [ReN(Et₂dtc)₂], [ReN{Ph₂P(S)NP(S)Ph₂}₂] or [ReNCl₄]^— only react with the most reactive Lewis bases of the examples mentioned above such as BCl₂Ph or B(C₆F₅)₃. The rhenium‐nitrido bond lengths remain almost unchanged by the adduct formation, whereas a significant decrease of the trans‐influence of the nitrido complexes has been observed as can be seen by a shortening of the corresponding bond lengths or dimerization of five‐co‐ordinate precursors. Electrophilic attack of the Lewis acid to a donor atom of the equatorial co‐ordination sphere of the rhenium complex results in the formation of ‘underco‐ordinate’ metal centres which resemble to di‐, tri or tetrameric units with asymmetric nitrido bridges between each two rhenium atoms. EPR spectroscopy is an excellent tool to reflect the formation of nitrido bridges at the paramagnetic (d¹) [ReNX₄]^— core (X = F, Cl, Br, NCS). The spectral parameters derived for the products of reactions of [ReNCl₄]^— with various boron compounds indicate an increase of the covalency of the equatorial Re‐L bonds as a consequence of the formation of a nitrido bridge. The tendency for the formation of nitrido bridges with Lewis acids is significantly lower for technetium compounds compared to their rhenium analogues. Only a few examples with BH₃ and BPhCl₂ have been established.     

Synthesis of Nitrido(phthalocyaninato)metal(V) Complexes RnPcMN (M = Re,Mo, W) and New Compounds with Nitrido‐Bridges between Rhenium and Elements of the Third Main Group

New tetra‐ and octasubstituted nitrido(phthalocyaninato)metal(V) complexes R_nPcMN (M = Re, Mo, W) were synthesized to obtain soluble nitrido‐bridged phthalocyanines. Phthalocyanines with nitrido bridges between rhenium and boron, aluminium, gallium and indium, respectively, were synthesized from nitrido(tetra‐tert.‐butylphthalocyaninato)rhenium(V) complex, tBu₄PcReN and suitable electrophilic reagents like BCl₃, B(C₆F₅)₃, BPh₃, BEt₃, AlCl₃, GaCl₃, GaBr₃, InCl₃, etc. The nitrido‐bridged compounds prepared show different stabilities depending on the substituents at the boron atom. Additionally, the possibility to increase the nucleophilicity of (C₅H₁₁)₈PcWN by reducing this complex with C₈K was studied. The reaction of the reduced complex with electrophiles, e.g. with tBuMeSiCl, Ph₃SiCl and Me₃GeCl indicates the formation of nitrogen‐bridged complexes.     

Synthesis,Structure and Reactivity of Sulfur-Rich Cyclopentadienyl-Transition Metal Complexes: Sulfur Chemistry from an Organometallic Point of View

Metal-sulfur centers play an important role in the activity of metalloproteins in enzymatic catalysis and the activity of metal sulfides as heterogeneous catalysts. The systematic search for M? S model compounds led to the discovery of an interesting and novel structural chemistry, which stems from the numerous coordination possibilities of sulfur ligands. The intention of this review article is to present and outline new approaches to sulfur chemistry from the organometallic point of view. Reactive cyclopentadienyl-transition metal fragments incorporate elemental sulfur to give polynuclear sulfur-rich complexes, which can contain either mono-, di- or polysulfido ligands or several such ligands in combined form. The versatile structural chemistry of the complexes formed and their reactivity towards organic, inorganic and organometallic compounds are discussed, and examples of some simple and rational procedures for their synthesis starting from cyclopentadienylcarbonyl- and cyclopentadienylhydrido-complexes are outlined. Their reactivity is manifested in numerous metal- and ligandcentered reactions. Finally the, albeit far less extensive, complex chemistry of the other chalcogens (O, Se, Te) is also considered for comparison, thus providing a more detailed survey of particular aspects of this area of chemistry.     

Phosphorus Ylides in the Coordination Sphere of Transition Metals: An Inventory

Phosphorus ylides are not only classical reagents in organic chemistry, but also play an increasingly important role as novel components in organometallic compounds. These metallic “ylide complexes” are either synthesized from “preformed ylides” and coordination compounds by addition or substitution, on the building block principle, or they are formed, in sometimes complicated reactions, from phosphanes, metal complexes, and C₁ substrates in the coordination sphere of the metals. The resulting metal-carbon bonds are greatly modified in their properties by the immediate presence of the phosphonium center and often belong to the most stable of M-C structural units. The metal can come from any group of the periodic table, including the lanthanoids and actinoids. Numerous preparative and structural studies are gradually enabling us to gain an overall picture of the scope of this area of research.     

Cyclooligomerization with Transition Metal Catalysts

This report is concerned not only with the syntheses of new ring systems and the preparation of derivatives of known rings but also with new types of catalysts based upon, e. g., nickel, iron, molybdenum, manganese, and palladium. The broad applicability of the methylene insertion reaction as a method for identifying mono- and di-methyl-substituted eight-, ten-, and twelve-membered rings is also demonstrated. A further section is concerned with the possible mechanism of C? C bond formation in transition metal complexes; several earlier suggestions have been revised in the light of new experimental data. In addition, experimental results are discussed which indicate that the reactivity and selectivity of the complexes formed by the nickel-ligand catalyst and olefins or alkynes depend upon the structure of the ligands.     

Methods for the Synthesis of μ-Hydrocarbon Transition Metal Complexes without Metal–Metal Bonds

Transition metal complexes in which hydrocarbons serve as σ,σ-, σ,π- or π,π-bound bridging ligands are currently of great interest. This review presents efficient and directed syntheses for such compounds, which often have very aesthetic structures. These reactions are among the most important reaction types in modern organometallic chemistry. They can be a useful aid for the synthesis of tailor-made compounds, for example, for models of catalytic processes and, specifically, for the construction of heterometallic compounds. We will discuss reactions of electrophilic complexes with nucleophilic ones, numerous transformations of (functionalized) hydrocarbons with metal complexes, the currently very topical complexes with bridging acetylide and carbide ligands, and organometallic polymers, which can be expected to have interesting and novel materials properties. Chisholm

1 M. H. Chisholm, Polyhedron 1988 , 7, 757–1077.

has described the importance of these complexes as follows: “Central to the development of polynuclear and cluster chemistry are bridging ligands and central to organometallic chemistry are metal–carbon bonds. Thus bridging ligands hold a pivotal role ins the development of Binuclear and polynuclear organometallic chemistry”.     

Theoretical Studies of Inorganic Compounds. 27 Quantum Chemical Investigations of Transition Metal Nitrido Complexes with a TM‐N‐E Linkage (E = Main Group Element)

It is reported about quantum chemical DFT calculations of various transition metal (TM) nitrido complexes which contain a TM‐N‐E linkage. The goal is to elucidate the nature of the TM‐N‐E bonding situation with modern quantum chemical tools. Five comparative investigations have been carried out. (a) Comparison of the N‐donor ability in the nitrido complexes Cl₃W‐N‐ECl_n where ECl_n = NaCl, MgCl₂, AlCl₃. (b) Comparative analysis of the bonding situation in Cl₄W‐N‐X where X = Na, MgCl, AlCl₂, SiCl₃, PCl₂, SCl, Cl. (c) Comparison of the structure and bonding in Cl₅W‐NPH₃, Cl₅W‐OPH₃⁺, Cl₄W‐(NPH₃)(OPH₃)⁺. (d) Comparative analysis of the bonding situation in Cl₅Ta‐OPH₃, Cl₅W‐NPH₃, Cl₅Re‐CPH₃. (e) Energy decomposition analysis of the bonding of the isolobal ligands NPH₃ and Cp with WCl₅.     

Synthesis,Structure and Reactivity of PH‐Phosphoraneiminato‐ and Iminophosphoraneiminato Group 4 Transition‐Metal Complexes

The versatile coordination chemistry of the well‐investigated phosphoraneiminato‐ligand R₃PN^— ( I ) was extended by the successive introduction of protons to the phosphorus atom. The position of the resulting equilibrium between the NH‐phosphanylamido‐ [R₂P‐NH^—] and the PH‐phosphoraneiminato‐form [R₂HP=N^—] is affected by the Lewis acidity of the coordinated metal fragment. Experimental studies on complexes with various substitution patterns at the group 4 metal center R₂HP=N[M] ( II ) were unambiguously confirmed by DFT‐calculations. The isolation of group 4 PH‐dihydrido‐phosphoraneiminato‐complexes RH₂P‐N[M] ( III ) is prevented by the low thermodynamic stability of the target molecules, also supported by the results of ab initio calculations. However, an access to the by then unknown transition‐metal substituted iminophosphanes RP=N[M] ( IV ) was verified for the first time. Within extensive studies on the coordination chemistry of bis(imino)phosphoranes RP(=NR′)(=NR″), several species of group 4 complexes R(R′N=)P=N[M] ( V ) were isolated and structurally characterized. In this case, investigations on the NH/PH‐tautomerism were performed exclusively on theoretical level, because the required educts are experimentally non‐accessible due to their kinetic instability.     

过渡金属十一钨锆酸钾的合成及鉴定

缺位杂多阴离子XW₁₁O₃₉(X=Si,P,As,Ge)能与过渡金属阳离子M生成MXW₁₁O₃₉,在该混配杂多阴离子中,过渡金属原子占据缺位的八面体位置^[1].为深入了解其配位方式,我们合成并鉴定了未见报道的K_n[MZrW₁₁O₃₉(H₂O)]·xH₂O(M为第一过渡系金属).     

Influence of Ligands on the Activity and Specificity of Soluble Transition Metal Catalysts

The reaction of a covalently σ-bonded ligand (alkyl group, hydrogen) with a molecule (olefin, CO) attached to the transition metal by a coordinate bond is the essence of many catalytic processes. The influence of the other ligands in the complex on this reaction is discussed in the present article. Various ways in which the ligands can act, e.g. by electronic effects via the σ and π electron systems of the complex and by steric effects, are first described separately and then illustrated by examples.     

Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands

It has been long known that certain transition metal sulfides dissolve in aqueous ammonium polysulfide. Although it was assumed that they thereby formed metal polysulfides, attention was first paid to such compounds only a few years ago. In recent years a host of new complexes with polysulfido chelate ligands have been isolated and characterized. The complexes are of interest not only regarding their structure and reactivity but also in view of their potential uses; they can be used for the directed preparation of sulfur rings of a given size, and there are indications that they will find applications in catalysis.     

Asymmetric Syntheses with the Aid of Homogeneous Transition Metal Catalysts

The progress made in the field of homogeneous catalysis during the last five to six years has led, inter alia, to the development of highly selective catalysts for asymmetric syntheses. Homogeneous asymmetric hydrogenation, using well defined transition metal catalysts, may be achieved with optical yields of 85 to 90% or more. Catalytic reactions, in which the chiral centers are generated by C? C bond formation, can result in optical yields of 70 to 80%. The hydrogenation catalysts consist primarily of rhodium(I) complexes containing “Homer phosphanes”, phosphanes with chiral C atoms, or optically active amides. Catalysts which induce optical activity through the formation of C? C bonds have been developed from π-allylnickel halides, Lewis acids, and phosphanes containing chiral C atoms. The results obtained signify a breakthrough in an area of catalysis previously restricted to syntheses involving enzymes.     

New Transition Metal Clusters with Ligands from Main Groups Five and Six

In both physics and chemistry, increased attention is being paid to metal clusters. One reason for this attitude is furnished by the surprising results that have been obtained from studies of the preparation, structural characterization and physical and chemical properties of the clusters. Whereas investigations of cluster reactivity are at present generally limited to three- or four-membered clusters, successful syntheses of clusters with many more metal atoms have recently been designed. These substances occupy an intermediate position between solid state chemistry and the chemistry of metal complexes. This review presents a versatile method for synthesizing metal clusters: the reaction of complexes of transition metal halides with silylated compounds such as E(SiMe₃)₂ (E = S, Se, Te) and E′R(SiMe₃)₂ (R = Ph, Me, Et; E′ = P, As, Sb). Although some of the compounds thus formed have already been prepared by other routes, the method affords ready access to both small and large transition metal clusters with unusual structures and valence electron concentrations; a variety of reactions in the ligand sphere are also possible.     

Electron－rich Polynuclear Transition Metal Clusters：Ⅰ． The Clusters with Chalcogen Bridges and Phosphine Ligands

Ｅｌｅｃｔｒｏｎ－ｒｉｃｈＰｏｌｙｎｕｃｌｅａｒＴｒａｎｓｉｔｉｏｎＭｅｔａｌＣｌｕｓｔｅｒｓ：Ⅰ．ＴｈｅＣｌｕｓｔｅｒｓｗｉｔｈＣｈａｌｃｏｇｅｎＢｒｉｄｇｅｓａｎｄＰｈｏｓｐｈｉｎｅＬｉｇａｎｄｓＨｏｎｇＭａｏ－Ｃｈｕｎ；ＪｉａｎｇＦｅｉ－Ｌｏｎ...     

Oxidation of Alkenes and Sulfides with Transition Metal Catalysts

Alkenes and sulfides were oxidized with transition-metal catalysts. The oxidant sources include molecular dioxygen, air and iodosylbenzene. The metal ions Mn(III), Fe(III), Co(II) and Ni(II) were used. The Catalysts 1-18 of 1,3-dioxo-, β-ketoimine- or salen-types were prepared and their efficacy was examined. 1,2-Dihydronaphthalene is most efficiently epoxidized with O₂/Me₂CHCHO or PhIO in the presence of Mn(III)-salen catalysts. The Ni(II)-, Co(II)- and Fe(III)-catalysts of either β-ketoimine- or salen-types are useful for epoxidation of styrene, (E)-stilbene and (E)-benzalacetone in the O₂/Me₂HCHO system; these epoxidations are stereospecific without formation of corresponding diastereomeric epoxides. Oxidation of methyl p-tolyl sulfide with O₂/Me₂CHCHO is facilitated by the 1,3-dioxo-catalyst Co(II)-1. Monooxidation is achieved with Me₂CHCHO in equimolar proportions to give the corresponding sulfoxide, whereas overoxidation is realized with excess Me₂CHCHO to give the sulfone. These epoxidation and sulfide oxidations all occur at 25 °C and are complete in less than a day.     

Preparation and spectroscopic characterization of novel cyclodiphosph(V)azane of N(1)-2-pyrimidinylsulfanilamide complexes. Magnetic, thermal and biological activity studies

Hexachlorocyclophosph(V)azane of sulfadiazine, (sulfupyrimidine) [N(1)-2-pyrimidinylsulfanilamide] (H2L1), was prepared and reacted with sulfur and glycine to give (H2L2) and (H2L3) ligands, respectively. The prepared ligands; H2L1, H2L2 and H2L3, react in 1:2 [ligands]:[metal ions] molar ratio with transition metals to give coloured complexes in a relatively good yields. The complexes were characterized using different physicochemical techniques, namely elemental analyses, IR, UV-vis, mass, 1H NMR, molar conductance, magnetic, solid reflectance and thermal analysis. The spectral data reveal that all the ligands behave as neutral bidentate ligands and coordinated to the metal ions via pyrimidine-N and enolic sulfonamide OH. The molar conductance data reveal that the complexes are non-electrolytes while UV-vis, solid reflectance and magnetic moment data have been shown that the complexes have octahedral geometry. The thermal behaviour of the complexes is studied and the thermodynamic activation parameters are calculated. The ligands and their complexes show high to moderate bactericidal activity.