Isocyanide Ligands Research Articles

Template Synthesis of Tetracarbene Platinum(II) Complexes with Five- and Six-Membered-Ring N-Heterocyclic Carbenes

Reaction of 2 equiv of 2-azidoethyl isocyanide and the tetraphosphine platinum(II) complexes [1a–c](X)2 (a, PR3 = PMe3; b, PR3 = PMe2Ph; c, PR3 = PMePh2) yielded via phosphine substitution and template-controlled cyclization of the isocyanide ligands the trans-di(NH,NH-NHC) complexes [2a–c](X)2. Treatment of [2c](PF6)2 with an additional 2 equiv of 2-azidoethyl isocyanide gave the tetracarbene complex [3](PF6)2, bearing four protic NH,NH-NHC ligands derived from a five-membered heterocycle. The same template synthesis utilizing 3-azidopropyl isocyanide and complex [1c](PF6)2 gave the dicarbene complex [5](PF6)2 and, after addition of 2 equiv more of 3-azidopropyl isocyanide, the tetracarbene complex [6](PF6)2 with four protic NH,NH-NHC ligands derived from a six-membered heterocycle. The intermediate trans-di(NH,NH-NHC) platinum(II) complex [5](PF6)2 also reacts with 2 equiv of 2-azidoethyl isocyanide to give the tetracarbene complex [7](PF6)2, bearing two five-membered-ring NHCs and two six-membered-ring NHCs.

Halide-bridged binuclear HX-splitting catalysts.

Two-electron mixed-valence compounds promote the rearrangement of the two-electron bond photochemically. Such complexes are especially effective at managing the activation of hydrohalic acids (HX). Closed HX-splitting cycles require proton reduction to H2 and halide oxidation to X2 to be both accomplished, the latter of which is thermodynamically and kinetically demanding. Phosphazane-bridged Rh2 catalysts have been especially effective at activating HX via photogenerated ligand-bridged intermediates; such intermediates are analogues of the classical ligand-bridged intermediates proposed in binuclear elimination reactions. Herein, a new family of phosphazane-bridged Rh2 photocatalysts has been developed where the halide-bridged geometry is designed into the ground state. The targeted geometries were accessed by replacing previously used alkyl isocyanides with aryl isocyanide ligands, which provided access to families of Rh2L1 complexes. H2 evolution with Rh2 catalysts typically proceeds via two-electron photoreduction, protonation to afford Rh hydrides, and photochemical H2 evolution. Herein, we have directly observed each of these steps in stoichiometric reactions. Reactivity differences between Rh2 chloride and bromide complexes have been delineated. H2 evolution from both HCl and HBr proceeds with a halide-bridged Rh2 hydride photoresting state. The H2-evolution efficiency of the new family of halide-bridged catalysts is compared to a related catalyst in which ligand-bridged geometries are not stabilized in the molecular ground state, and the new complexes are found to more efficiently facilitate H2 evolution.

Neutral benzoquinolate cyclometalated platinum(II) complexes as precursors in the preparation of luminescent Pt–Ag complexes

Complexes [Pt(C6F5)(bzq)(CNR)] {R=tBu (1), 2-naphthyl (2), 2,6-Me2Ph (3)} have been prepared by replacement of the labile acetone in [Pt(C6F5)(bzq)(Me2CO)] with the corresponding isocyanide ligand. The structures 1 and 3 (X-ray) confirms their square planar geometry, with the bzq ligand coplanar to the metal plane. The reactions of 1–3 toward AgClO4 lead to the trinuclear complexes [{Pt(C6F5)(bzq)(CNR)}2Ag]ClO4 {R=tBu (4), 2-naphthyl (5)} or the tetranuclear [{Pt(C6F5)(bzq)(CN-2,6-Me2Ph)Ag}2](ClO4)2 (6). The structures of these three polynuclear complexes have been established by X-ray diffraction studies. Two pseudo-polymorphs of 4 (4a and 4b), only differing in the crystallization solvent, have been found. 4a/b and 5 are trinuclear Pt–Ag–Pt complexes with a “sandwich” disposition. In all three cases, two “Pt(C6F5)(bzq)(CNR)” fragments are linked by a silver atom through Pt→Ag bonds of donor acceptor nature and the silver center establishes a short η1 interaction with the Cipso of the bzq ligands. Furthermore, the study of the structure of 6 reveals two “(C6F5)(bzq)(CN-2,6-Me2Ph)PtAg” subunits, each containing a Pt→Ag bond related by an inversion center and held together through η2 interactions established by the silver atom of one unit and one of the aromatic rings of the bzq ligand of the other. The reaction of 1–3 with [Ag(OClO3)(PPh3)] produces [(C6F5)(bzq)(CNR)PtAg(PPh3)]ClO4 {R=tBu, (7), 2-naphthyl (8), 2,6-Me2Ph (9)}. These dinuclear clusters contain a Pt→Ag bond and show dynamic processes in solution (NMR) which involve the rupture and formation of these interactions. The X-ray structure of 7 confirms the presence of a Pt–Ag bond and a η1 interaction with the Cipso of the bzq ligand (2.514(6) Å). All the crystal structures determined show π⋯π interactions of the bzq which stack in a parallel fashion with interplanar distances of ca. 3.3–3.4 Å. In 5 and 6 the aromatic fragments of the isocyanide ligands also take part in these π⋯π interactions. Absorption and emission properties of all the complexes 1–9 have been studied and explained with the aid of TD-DFT theoretical calculations.Compounds 1–9 are not emissive in solution but they are in rigid matrix. In glassy 2-Me-THF or CH2Cl2 at 77K the Pt/Ag compounds 4–9 at any concentration (10−3M, 10−4M, 10−5M) show the same emission spectra as their corresponding starting complexes 1–3, in line with the rupture of the Pt-Ag bonds. In the solid state only the dinuclear compounds [Pt(C6F5)(bzq)(CN-tBu)AgPPh3]ClO4 (7) and [Pt(C6F5)(bzq)(CN-2,6-Me2Ph)AgPPh3]ClO4 (9) together with the tetranuclear complex [{Pt(C6F5)(bzq)(CN-2,6-Me2Ph)Ag}2](ClO4)2 (6) are emissive at room temperature showing bright greenish (7, 9) or yellowish (6) phosphorescence. In all three compounds a significant contribution of M′ orbitals (AgPPh3/Ag) to the frontier orbitals (FO) has been observed, and their main emissions seem to arise from mixed excited states 3ILCT (π–π∗ (bzq))/3MM′LCT (Pt/AgPPh3→bzq) (7, 9) or 3LMM′CT [(bzq)→Pt/Ag]/3ILCT [π–π∗ (bzq)] (6) in nature.

Coupling of Isocyanide and μ-Aminocarbyne Ligands in Diiron Complexes Promoted by Hydride Addition

The diiron μ-aminocarbyne complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(CNR′)(Cp)2][SO3CF3] (R = R′ = Xyl, 2a; R = Xyl, R′ = Me, 2b; R = Xyl, R′ = But, 2c; R = Xyl, R′ = p-C6H4CF3, 2d; R = Me, R′ = Xyl, 2e; Xyl = 2,6-Me2C6H3), containing an isocyanide ligand, have been obtained via CO replacement with the appropriate CNR′ ligand from [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)2(Cp)2][SO3CF3] (R = Xyl, 1a; R = Me, 1b). Compound 2a, upon treatment with NaBH4 and heating at reflux temperature in THF solution, is transformed into the aminocarbene–aldimine [Fe2{μ-η1(C):η1(N)-CN(Me)(Xyl)CH═N(Xyl)}(μ-CO)2(Cp)2] (3) in moderate yield. The reactions occurs via formation of the formimidoyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(H)═NXyl}(Cp)2] (4a), which has been isolated by reacting 2a with NaBH4 at 0 °C. Likewise, the formimidoyl complex [Fe2{μ-CN(Me)(R)}(μ-CO)(CO){C(H)═NR′}(Cp)2] (R = Xyl, R′ = Me, 4b; R = Me, R′ = Xyl, 4c) have been obtained from 2b,e, respectively, upon reaction with NaBH4, but these complexes do not convert into the aminocarbene–aldimine complexes analogous to 3. Reactions of 2a with other nucleophiles have been investigated, without obtaining any product similar to 3. Complex 2a reacts with NaCN or with LiPPh2, resulting in isocyanide displacement and formation of [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(CN)(Cp)2] (5) and [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(PPh2)(Cp)2] (6), respectively. Addition of the organocopper reagent Li2CuCNMe2 to 2a affords the acyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO){C(O)Me}(CNXyl)(Cp)2] (7). The thiocarbyne complex [Fe2{μ-CSMe}(μ-CO)(CO)(CNXyl)(Cp)2][SO3CF3] (8), which shows analogies with 2a, reacts with NaBH4, affording the carbene derivative [Fe2 μ-{C(SMe)(H)}(μ-CO)(CO)(CNXyl)(Cp)2] (9). The molecular structures of 2a and 3 have been determined by X-ray diffraction studies.

99mTc-labeled vasopressin peptide as a radiopharmaceutical for small-cell lung cancer (SCLC) diagnosis.

The 99mTc-labeled conjugates of the vasopressin (AVP) peptide and of its analogue d(CH2)5[D-Tyr(Et2)-Ile4-Eda9]AVP (AVP(an)) have been synthesized using the technetium complexes with tetradentate tripodal chelator (the tris(2-mercaptoethyl)amine (NS3)) and the monodentate isocyanide ligand (CN-peptide). The conjugates exhibit high stability in the presence of 100 times the molar excess of standard amino acids cysteine or histidine and also satisfactory stability in human serum. The 99mTc(NS3)(CN-AVP) and 99mTc(NS3)(CN-AVP(an)) ability of binding to small-cell lung cancer (SCLC) cell line H69 was studied in vitro. The results suggest that the novel vasopressin conjugate 99mTc(NS3)(CN-AVP(an)) is a desirable compound for imaging oncogene receptors overexpressed in SCLC cells and can be an important basis for further consideration the conjugate as a potential diagnostic radiopharmaceutical for patients suffering from small-cell lung cancer.

Coupling of trifluoromethyl isocyanide ligands in binuclear iron carbonyl complexes

The trifluoromethyl isocyanide ligand, CF3NC is of interest in being a strong back-bonding ligand similar to carbon monoxide. Furthermore, Lentz and coworkers have shown that free CF3NC is stable enough in the free state at low temperatures to use as a reagent for the synthesis of metal complexes. In this connection the binuclear (CF3NC)2Fe2(CO)n (n=7, 6, 5) and mononuclear (CF3NC)Fe(CO)n (n=4, 3) have been studied by density functional theory. Coupling of CF3NC ligands to form a bridging η2,η2-μ-CF3NCCNCF3 ligand is predicted to occur in the lowest energy binuclear (CF3NC)2Fe2(CO)n (n=6, 5) structures. A similarly coupled Fe2(CO)7(η2,η2-μ-CF3NCCNCF3) structure is also found for (CF3NC)2Fe2(CO)7. However, this structure lies ∼11kcal/mol in energy above the lowest energy Fe2(CO)6(μ-CO)(μ-CF3CN)2 isomer having separate bridging CF3NC ligands analogous to the well-known triply bridged Fe2(CO)9 structure. The mononuclear derivative (CF3NC)Fe(CO)4 is shown to be similar to Fe(CO)4(CS) in having equatorial and axially substituted trigonal bipyramidal isomers of nearly identical energies within 1kcal/mol. The binuclear (CF3NC)2Fe2(CO)n (n=7, 6) derivatives are predicted to be viable toward dissociation into the mononuclear fragments (CF3NC)Fe(CO)m (m=4 and/or 3) by substantial energies exceeding 29kcal/mol.

Stoichiometric carbon–carbon bond formation mediated by well defined Nb(III) complexes

The discovery of a Nb-mediated double coupling of terminal alkynes and carbon monoxide is reported. The Nb(III) complex (BDI)Nb(NtBu)(CO)2 reacts with two equivalents of t-butylacetylene to form a metal-bound yne-one-ene moiety resulting from coupling of CO to two equivalents of the terminal alkyne. Additionally, Z-alkene and α,β-unsaturated imine formation from hydrogenolysis of an internal alkyne bound complex in the presence of an isocyanide ligand is described. 1H NMR spectroscopy and synthesis of a bromide analog support the involvement of an alkenyl iminyl ligand intermediate.

{N,N'-Bis-[2-(di-phenyl-phosphan-yl)ethan-1-yl-idene]ethyl-enedi-amine}bromido-(p-toluene-sulfonyl-methyl isocyanide)iron(II) tetra-phenyl-borate.

In the title compound, [FeBr(C9H9NO2S)(C30H30N2P2)][B(C6H5)4], the FeII ion is in a distorted octa­hedral CBrN2P2 coordination geometry with a P—Fe—P angle of 109.95 (3)°. The relative orientation of the p-toluene­sulfonyl­methyl isocyanide ligand is defined by the C—S—C—N torsion angle of 67.1 (2)°. In the crystal, pairs of weak C—H⋯O hydrogen bonds connect the cations into inversion dimers, forming R 2 2(8) rings.

60]Fullerene–porphyrin–ferrocene triad self-assembled monolayers (SAMs) for photovoltaic applications

A new triad array, C60–triosmium cluster-zinc porphyrin–ferrocene complex 1, Os3C60ZnPFc, was prepared by the decarbonylation of Os3(CO)9(μ3-η2:η2:η2-C60) (9) and subsequent reaction with an isocyanide ligand containing porphyrin and ferrocene. This novel triad array exhibits well-defined and stable electrochemical properties in solution due to a robust bonding mode between the C60 and the triosmium cluster. Compound 2, Os3C60SiZnPFc was prepared in a manner similar to that of compound 1 from Os3(CO)8(CN(CH2)3Si(OEt)3)(μ3-η2:η2:η2-C60) (10) and an isocyanide ligand containing porphyrin and ferrocene. The SAM of triad 2 (2/ITO) was fabricated by immersion of an ITO electrode into a chlorobenzene solution of 2 and diazabicyclooctane (2:1 equiv.), and characterized by UV–Vis absorption spectroscopy and cyclic voltammetry. The triad SAM exhibited ideal, well-defined electrochemical responses and high stability due to the stable C60 π-delocalized system via a linkage with the metal cluster center as well as a robust bonding mode. The photoelectrochemical properties of the 2/ITO triad were investigated by a standard three-electrode system in the presence of an ascorbic acid sacrificial electron donor. Reproducible photocurrent was generated by excitation of the porphyrin moiety in the triad SAM with visible light.

Synthesis, Characterization, and Photophysical Study of Luminescent Rhenium(I) Diimine Complexes with Various Types of N-Heterocyclic Carbene Ligands

A series of luminescent Re(I) diimine complexes with various types of N-heterocyclic carbene (NHC) ligands has been synthesized through the reaction between isocyano Re(I) diimine complexes with different nucleophiles. These Re(I) NHC complexes were characterized by (1)H and (13)C NMR and IR spectroscopy, mass spectrometry, and elemental analysis. One of the precursor complexes fac-{Re(CO)3[CN(H)C6H4-2-O]2Br} and five of the Re(I) diimine complexes with different types of NHC ligands were also structurally characterized by X-ray crystallography. In the preparation of these Re(I) NHC complexes, it is found that the reactivity of the isocyanide ligands in the synthetic complex precursors is significantly affected by the electronic nature of the trans ligand. All these complexes displayed (3)MLCT [dπ(Re) → π*(N-N)] phosphorescence in degassed CH2Cl2 and CH3CN solutions at room temperature. Through the study of the photophysical and electrochemical properties of these Re(I) NHC complexes, the electronic properties of different types of NHC ligands were investigated.

Ligand Dynamics of tert-Butyl Isocyanide Oxido Complexes of Molybdenum(IV)

The six-coordinate molybdenum(IV) oxido isocyanide complex 1 [Δ,Λ-OC-6-2-3-[MoO(N(p)∩N(i))2(CN(t)Bu)]; N(p)∩N(i) = 4-tert-butylphenyl(pyrrolato-2-ylmethylene)amine] is obtained in diastereomerically pure form in the solid state, as revealed by single-crystal X-ray diffraction. In solution, this stereoisomer equilibrates with the Δ,Λ-OC-6-2-4 diastereomer 2 at ambient temperature. The stereochemistry of both isomers has been elucidated by NMR, IR, and UV/vis spectroscopy in combination with density functional theory (DFT)/polarizable continuum model and time-dependent DFT calculations. The isomerization 1 → 2 is suggested to proceed via a dissociative trigonal twist with dissociation of the imine nitrogen donor N(i) of one chelate ligand (hemilabile ligand) rather than dissociation of the monodentate isocyanide ligand. The isomerization barrier has been experimentally determined as 91 and 95 kJ mol(-1) in tetrahydrofuran and toluene, respectively.

RETRACTED: Substitution reactions of diiron dithiolate complexes with phosphine or isocyanide ligands

This article has been retracted: please see Elsevier Policy on Article Withdrawal ( http://www.elsevier.com/locate/withdrawalpolicy ). This article has been retracted at the request of the Author, for the following reasons. Firstly, some of the work reported as new in this paper, was previously conducted by someone else, and is now published by Li-Cheng Song, et al. (Eur. J. Inorg. Chem 2014, 1886-1895, http://onlinelibrary.wiley.com/doi/10.1002/ejic.201301553/suppinfo ). Secondly, the synthetic method used and the proposed mechanism for the formation of several of the compounds, are similar to those previously reported by Prof. Li-Cheng Song. Finally, portions of the manuscript are worded identically to those in manuscripts that have been published by Prof. Li-Cheng Song.

Strong electron-donating metalla-N-heterocyclic carbenes

By choosing the appropriate coupling reactions an isocyanide ligand in complex [Fe(Cp)(CO)(CNxylyl)2](+) is transformed into either a conventional NHC or into a metalla-N-heterocyclic carbene (MNHC), with the stretching frequencies of the CO and CNR ligands attached to the iron center demonstrating the stronger electron-donating ability of the metal-containing carbenes.

Binuclear cobalt carbonyl complexes of the strong π-acceptor trifluoromethyl isocyanide

The cobalt carbonyl complexes (CF3NC)2Co2(CO)n (n=7, 6, 5, 4) and (CF3NC)Co(CO)n(n=4, 3, 2) of the strongly π-accepting trifluoromethyl isocyanide ligand have been investigated by density functional theory. The lowest energy (CF3NC)2Co2(CO)6 structures are doubly bridged structures with the global minimum having two bridging CF3NC ligands. The lowest energy unbridged (CF3NC)2Co2(CO)6 structure lies ∼19kcal/mol in energy above this global minimum. This differs from unsubstituted Co2(CO)8 for which the doubly bridged and unbridged isomers have similar energies so both can be observed experimentally. The lowest energy structures of the formally unsaturated (CF3NC)2Co2(CO)n (n=5, 4) derivatives are also doubly bridged structures. Bridging CF3NC groups are energetically preferred over bridging CO groups. Four-electron donor bridging η2-μ-CF3NC groups are found in higher energy structures. Coupling of CF3NC groups to form a coordinated bis(trifluoromethyldiimine) ligand, CF3NCCNCF3 is observed in carbonyl-rich (CF3NC)2Co2(CO)7 structures. However, such (CF3NC)2Co2(CO)7 structures do not appear to be viable since CO dissociation from the lowest energy such structure to give (CF3NC)2Co2(CO)6 is predicted to be essentially thermoneutral.

Chloro- and Trifluoromethyl-Substituted Flanking-Ring m-Terphenyl Isocyanides: η6-Arene Binding to Zero-Valent Molybdenum Centers and Comparison to Alkyl-Substituted Derivatives

Presented herein are synthetic and structural studies exploring the propensity of m-terphenyl isocyanide ligands to provide flanking-ring η(6)-arene interactions to zerovalent molybdenum centers. The alkyl-substituted m-terphenyl isocyanides CNAr(Mes2) and CNAr(Dipp2) (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3; Ar(Dipp2) = 2,6-(2,6-(i-Pr)2C6H3)2C6H3) react with Mo(η(6)-napthalene)2 in a 3:1 ratio to form tris-isocyanide η(6)-arene Mo complexes, in which a flanking mesityl or 2,6-diisopropylphenyl group, respectively, of one isocyanide ligand is bound to the zerovalent molybdenum center. Thermal stability and reactivity studies show that these flanking ring η(6)-arene interactions are particularly robust. To weaken or prevent formation of a flanking-ring η(6)-arene interaction, and to potentially provide access to the coordinatively unsaturated [Mo(CNAr(R))3] fragment, the new halo-substituted m-terphenyl isocyanides CNAr(Clips2) and CNAr(DArF2) (Ar(Clips) = 2,6-(2,6-Cl2C6H3)2(4-t-Bu)C6H2; Ar(DArF2) = 2,6-(3,5-(CF3)2C6H3)2C6H3) have been prepared. Relative to their alkyl-substituted counterparts, synthetic and structural studies demonstrate that the flanking aryl rings of CNAr(Clips2) and CNAr(DArF2) display a lower tendency toward η(6)-binding. In the case of CNAr(DArF2), it is shown that an η(6)-bound 3,5-bis(trifluoromethyl)phenyl group can be displaced from a zerovalent molybdenum center by three molecules of acetonitrile. This observation suggests that the CNAr(DArF2) ligand effectively masks low-valent metal centers in a fashion that provides access to low-coordinate isocyano targets such as [Mo(CNAr(R))3]. A series of Mo(CO)3(CNAr(R))3 complexes were also prepared to compare the relative π-acidities of CNAr(Mes2), CNAr(Clips2), and CNAr(DArF2). It is found that CNAr(DArF2) shows increased π-acidity relative to CNAr(Mes2) and CNAr(Clips2), despite the fact that its electron-withdrawing CF3 groups are fairly distal to the terminal isocyano unit.

Removal of Ruthenium Using a Silica Gel Supported Reagent

A solid-supported isocyanide ligand was developed to destroy active metathesis catalysts and to remove ruthenium byproducts from metathesis reactions. This method was able to significantly reduce the concentration of residual ruthenium from the organic products of several alkene and ene-yne metathesis reactions, under a variety of different conditions.

Synthesis and X-ray studies of ruthenium(II) complexes containing hydrazine and benzyl isocyanide ligands

The reaction of the polymeric species [{RuCl2(COD)}x] (1; x > 2; COD = cyclo-octa-1,5-diene) and hydrazine hydrate in methanol under reflux gave a pale pink solution from which the salt [Ru(COD)(N2H4)4][BPh4]2.CH3OH (2) was isolated on addition of NaBPh4. Treatment of 2 in refluxing acetone in the presence of the ligand benzyl isocyanide give a complex of stoichiometry [Ru(NH2N=CMe2)2(PhCH2NC)4][BPh4]2 (3) on the substitution of the labile COD ligand. The two compounds have been characterized by elemental analyses, IR and NMR measurements and single-crystal X-ray diffraction studies. The ruthenium in both compounds has a distorted octahedral coordination geometry. KEY WORDS: Cycloocta-1,5-diene, Hydrazine hydrate, Isocyanide, Ruthenium Bull. Chem. Soc. Ethiop. 2013, 27(3), 405-411.DOI: http://dx.doi.org/10.4314/bcse.v27i3.9

A ladder polysilane as a template for folding palladium nanosheets

Although discrete nano-sized compounds consisting of a monolayer sheet of multiple atoms have attracted much attention, monolayer transition metal nanosheets are difficult to access. Here we report a template synthesis of the folding metal nanosheet (2) consisting of 11 palladium atoms by treatment of a ladder polysilane, decaisopropylbicyclo[2.2.0]hexasilane (1), with Pd(CN(t)Bu)2. Crystallographic analysis reveals that the compound is composed of two monolayer Pd7 sheets sharing three palladium atoms at the junction. Each Pd atom is stabilized by Pd-Si σ-bonds, Pd-Pd bonds and coordination of isocyanides. Ligand exchange of 2 from CN(t)Bu to CN(2,4,6-Me3-C6H2) is accompanied by structural rearrangement, leading to the formation of another folding Pd11 nanosheet (3) consisting of two edge-sharing Pd7 sheets. The shapes of the Pd7 sheets as well as the dihedral angle between the two Pd7 sheets are dependent on the substituent of the isocyanide ligand.

Synthesis, radiochemistry and stability of the conjugates of technetium-99m complexes with Substance P

Two types of technetium-99m complexes: (i) with the Hynic ligand linked to Substance P(1–11) and (ii) of the type ‘4 + 1’ consisting of tetradentate tripodal chelator tris(2-mercaptoethyl)-amine and monodentate isocyanide ligand previously coupled with Substance P(1–11), have been prepared on the n.c.a. scale. The obtained conjugates exhibit different lipophilicity and high stability in neutral aqueous solutions, even in the presence of excess concentration of histidine/cysteine competitive standard ligands. The conjugate (99mTc(NS3)(CN))2–SP containing two technetium-99m species in the molecule may be expected to be an extremely good diagnostic radiopharmaceutical.

Dinitrogen Borylation with Group 4 Metallocene Complexes

AbstractBorylation of hafno‐ and zirconocene complexes [(η5‐C5H2‐1,2,4‐Me3)2M]2(μ2,η2,η2‐N2), containing strongly activated dinitrogen ligands, with pinacolborane (HBPin) resulted in N–B and M–H bond formation. Treatment of the borylated products with carbon monoxide triggered N–N bond scission with concomitant N–C bond formation to produce μ‐borylimido and μ‐formamidido fragments. Conversely, addition of tBuNC resulted in insertion of the isocyanide ligand into the M–H bonds and furnished the corresponding η2‐iminoacylhafnocene complexes.