Dinitrogen Complexes Research Articles

Effects of N2 Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

Distinguishing the reactivity differences between N2 complexes having different binding modes is crucial for the design of effective N2-functionalizing reactions. Here, we compare the reactions of a K-bridged, dinuclear FeNNFe complex with a monomeric Fe(N2) complex where the bimetallic core is broken up by the addition of chelating agents. The new anionic iron(0) dinitrogen complex has enhanced electron density at the distal N atoms of coordinated N2, and though the N2 is not as weakened in this monomeric compound, it is much more reactive toward silylation by (CH3)3SiI (TMSI). Double silylation of N2 gives a three-coordinate iron(III) hydrazido(2-) complex, which is finely balanced between coexisting S = 1/2 and S = 3/2 states that are characterized by crystallography, spectroscopy, and computations. These results give insight into the interdependence between binding modes, alkali dependence, reactivity, and magnetic properties within an iron system that functionalizes N2.

Enhanced Activation of Coordinated Dinitrogen with p-Block Lewis Acids.

This Concept article highlights recent research on Lewis acid adducts of dinitrogen complexes, including our contributions. After a reminder of the early works, it is demonstrated that such kind of species offers a new platform for dinitrogen functionalization as well as valuable models for the understanding of elementary steps of (bio)catalytic cycles. When possible, parallels regarding this mode of activation from the orbital point of view are drawn between the different systems discussed herein.

Cyclometalated Dicarbonyl Ruthenium Catalysts for Transfer Hydrogenation and Hydrogenation of Carbonyl Compounds

The dicarbonyl complex RuCl2(L)2(CO)2 (1) was easily prepared by reaction of ruthenium chloride hydrate with formic acid and L (L = (2,6-Me2C6H3)PPh2) in ethanol at reflux, via the [RuCl2(CO)2]n intermediate. Alternatively, 1 was obtained from [RuCl2(CO)3]2 and L by CO elimination. Reaction of 1 with NEt3 in toluene at reflux afforded the cyclometalated derivative RuCl{(2-CH2-6-MeC6H3)PPh2}(L)(CO)2 (2). A simple one-pot synthesis of 2 was achieved by treatment of RuCl3 hydrate with formic acid, L, and NEt3. The cyclometalated dicarbonyl complexes [Ru{(2-CH2-6-MeC6H3)PPh2}(NN)(CO)2]Cl (NN = ethylenediamine, 3; 2-(aminomethyl)pyridine, 4; (R,R)-1,2-diphenylethane-1,2-diamine, 5) were isolated by reaction of 2 with the corresponding dinitrogen ligand in methanol at reflux. Complexes 1–4 catalyze the transfer hydrogenation (TH) of acetophenone in 2-propanol at reflux (S/C = 1000 and TOF up to 30 000 h–1) with alkali base (1–5 mol %), whereas 5 leads to (S)-1-phenylethanol with 68% ee. The derivatives 1–5 cata...

Magnetism and EPR Studies of Binuclear Ruthenium Hydride Binuclear Species Bearing Redox-Active Ligands.

The binuclear complex {[N3]Ru(H)}2(μ-η1:η1-N2) ([N3] = 2,6-(ArylN═CMe)2C5H3N and Aryl = mesityl or xylyl) contains two formally Ru(I), d7 centers linked by a bridging dinitrogen ligand, although the odd electrons are substantially delocalized onto the redox non-innocent pincer ligands. The complex exhibits paramagnetic behavior in solution, but is diamagnetic in the solid state. This difference is attributed to intermolecular "π-stacking" observed in the solid state, which essentially couples unpaired electrons on each half of the complex to form delocalized 22-center-2-electron covalent bonds. Introduction of a bulky t-butyl group on the ligand pyridine ring prevents this intermolecular association and allows further investigation of the magnetic behavior and electronic structure of the binuclear species. The interaction of the unpaired electrons in the two halves of the complex has been probed with magnetic susceptibility and perpendicular and parallel mode EPR measurements, revealing a weakly antiferromagnetically coupled system with a thermally accessible triplet excited state. In addition, the mixed valent, S = 1/2, {[N3]Ru(H)}(μ-η1:η1-N2){[N3]Ru} system has also been observed via perpendicular mode EPR and was used to quantify the growth of the thermally accessible triplet state of the dihydride complex using parallel mode EPR.

Stabilization of β‐Diketiminato Nickel(I) with Alkaline Metal Halide Entities for Small Molecule Activation

The reduction of the β‐diketiminato nickel(II) halide complex [LtBuNiIIBr] [LtBu = CH(CtBuNdipp)2–, dipp = 2,6‐diisopropylphenyl] with potassium sources proceeds via the initial formation of [(LtBuNiI)x(μ‐Br)xKx] aggregates, which could be isolated and characterized for x = ∞ and 6. The KBr equivalents readily give way to external donors or substrates to be activated at the central nickel(I) atoms. To test, in how far the steric bulk induced by the residues at [LtBu]– influences the formation of the KBr adducts β‐diketiminato ligands with less steric congestion, namely LMe6 and LMe7 [LMe6 = CH(CMeNdmp)2–, LMe7 = CMe(CMeNdmp)2–, dmp = 2,6‐dimethylphenyl] were employed. Through deprotonation of HLMe6 with nBuLi followed by treatment with NiBr2(dme) the nickel(II) precursor compound [LMe6NiII(μ‐Br)2Li(THF)2] was prepared and shown to enter an equilibrium with [(LMe6NiIIBr)2] and LiBr in solution; [(LMe6NiIIBr)2] could be accessed also independently. Syntheses of the complexes [LMe7NiII(μ‐Br)2Li(THF)2] and [(LMe7NiIIBr)2] could be achieved analogously. To test the potential of nickel complexes with the LMe6 and LMe7 ligands for the activation of N2 the thf‐free [(LMe6/7NiIIBr)2] complexes were reduced with potassium in an N2 atmosphere. This led neither to a KBr adduct nor to an N2 complex but to the dimer [(LMe6NiI)2], as the smaller ligands allow an efficient interaction of the central nickel atoms with the aryl rings.

Ultrafast Photophysics of a Dinitrogen-Bridged Molybdenum Complex.

Among the many metal-dinitrogen complexes synthesized, the end-on bridging (μ2, η1, η1-N2) coordination mode is notoriously unreactive for nitrogen fixation. This is principally due to the large activation energy for ground-state nitrogen-element bond formation and motivates exploration of the photoexcited reactivity of this coordination mode. To provide the foundation for this concept, the photophysics of a dinitrogen-bridged molybdenum complex was explored by ultrafast electronic spectroscopies. The complex absorbs light from the UV to near-IR, and the transitions are predominantly of metal-to-ligand charge transfer (MLCT) character. Five excitation wavelengths (440, 520, 610, 730, and 1150 nm) were employed to access MLCT bands, and the dynamics were probed between 430 and 1600 nm. Despite the large energy space occupied by electronic states (ca. 1.2 eV), the dynamics were independent of the excitation wavelength. In the proposed kinetic model, photoexcitation from a Mo-N═N-Mo centered ground state populates the π*-state delocalized over two terpyridine ligands. Due to a large terpyridine-terpyridine spatial separation, electronic localization occurs within 100 fs, augmented by symmetry breaking. The subsequent interplay of internal conversion and intersystem crossing (ISC) populates the lowest 3MLCT state in 2-3 ps. Decay to the ground state occurs either directly or via a thermally activated metal-centered (3MC) trap state having two time constants (10-15 ps, 23-26 ps [298 K]; 103 ps, 612 ps [77 K]). ISC between 1MLCT and 3MLCT involves migration of energized electron density from the terpyridine π* orbitals to the Mo-N═N-Mo core. Implication of the observed dynamics for the potential N-H bond forming reactivity are discussed.

Intermolecular dissociation energies of dispersively bound complexes of aromatics with noble gases and nitrogen

We measured accurate intermolecular dissociation energies D0 of the supersonic jet-cooled complexes of 1-naphthol (1NpOH) with the noble gases Ne, Ar, Kr, and Xe and with N2, using the stimulated-emission pumping resonant two-photon ionization method. The ground-state values D0(S0) for the 1NpOH⋅S complexes with S= Ar, Kr, Xe, and N2 were bracketed to be within ±3.5%; they are 5.67 ± 0.05 kJ/mol for S = Ar, 7.34 ± 0.07 kJ/mol for S = Kr, 10.8 ± 0.28 kJ/mol for S = Xe, 6.67 ± 0.08 kJ/mol for isomer 1 of the 1NpOH⋅N2 complex, and 6.62 ± 0.22 kJ/mol for the corresponding isomer 2. For S = Ne, the upper limit is D0 < 3.36 kJ/mol. The dissociation energies increase by 1%-5% upon S0 → S1 excitation of the complexes. Three dispersion-corrected density functional theory (DFT-D) methods (B97-D3, B3LYP-D3, and ωB97X-D) predict that the most stable form of these complexes involves dispersive binding to the naphthalene "face." A more weakly bound edge isomer is predicted in which the S moiety is H-bonded to the OH group of 1NpOH; however, no edge isomers were observed experimentally. The B97-D3 calculated dissociation energies D0(S0) of the face complexes with Ar, Kr, and N2 agree with the experimental values within <5%, but the D0(S0) for Xe is 12% too low. The B3LYP-D3 and ωB97X-D calculated D0(S0) values exhibit larger deviations to both larger and smaller dissociation energies. For comparison to 1-naphthol, we calculated the D0(S0) of the carbazole complexes with S = Ne, Ar, Kr, Xe, and N2 using the same DFT-D methods. The respective experimental values have been previously determined to be within <2%. Again, the B97-D3 results are in the best overall agreement with experiment.

Coordination of 3‐Methylindole‐Based Tripodal Tetraphosphine Ligands to Iron(+II), Cobalt(+II), and Nickel(+II) and Investigations of their Subsequent Two‐Electron Reduction

We report the coordination chemistry of indole based tripodal tetraphosphine ligands to iron(II), cobalt(II) and nickel(II). These complexes are formed by simple synthetic protocols and were characterized by a combination of spectroscopic techniques and single‐crystal X‐ray analysis. The molecular structures as determined by X‐ray diffraction show that the geometry of the nickel and cobalt complexes are distorted trigonal bipyramidal. The monocationic iron(II) complexes also have distorted trigonal bipyramidal geometries, but the dicationic analogue has an octahedral geometry. Two‐electron reduction of the cobalt(+II) and the nickel(+II) complexes in the presence of N2 did not lead to the coordination of N2. In contrast, two‐electron reduction of the iron(+II) complexes did lead to coordination of dinitrogen to the iron center. The Fe0N2 L1H complex has a trigonal bipyramidal geometry, and the N–N bond length of the coordinated dinitrogen ligand is longer than that of free dinitrogen, indicating that coordination to this iron(0) complex results in activation of the N≡N bond.

A Ruthenium Hydrido Dinitrogen Core Conserved across Multielectron/Multiproton Changes to the Pincer Ligand Backbone.

A series of ruthenium(II) hydrido dinitrogen complexes supported by pincer ligands in different formal oxidation states have been prepared and characterized. Treating a ruthenium dichloride complex supported by the pincer ligand bis(di-tert-butylphosphinoethyl)amine (H-PNP) with reductant or base generates new five-coordinate cis-hydridodinitrogen ruthenium complexes each containing different forms of the pincer ligand. Further ligand transformations provide access to the first isostructural set of complexes featuring all six different forms of the pincer ligand. The conserved cis-hydridodinitrogen structure facilitates characterization of the π-donor, π-acceptor, and/or σ-donor properties of the ligands and assessment of the impact of ligand-centered multielectron/multiproton changes on N2 activation. Crystallographic studies, infrared spectroscopy, and 15N NMR spectroscopy indicate that N2 remains weakly activated in all cases, providing insight into the donor properties of the different pincer ligand states. Ramifications on applications of (pincer)Ru species in catalysis are considered.

Utility of Lithium in Rare-Earth Metal Reduction Reactions to Form Nontraditional Ln2+ Complexes and Unusual [Li(2.2.2-cryptand)]1+ Cations.

The utility of lithium compared to other alkali metals in generating Ln2+ rare-earth metal complexes via reduction of Ln3+ precursors in reactions abbreviated as LnA3/M (Ln = rare-earth metal; A = anionic ligand; M = alkali metal) is described. Lithium reduction of Cp'3Ln (Cp' = C5H4SiMe3; Ln = Y, Tb, Dy, Ho) under Ar in the presence of 2.2.2-cryptand (crypt) forms new examples of crystallographically characterizable Ln2+ complexes of these metals, [Li(crypt)][Cp'3Ln]. In each complex, lithium is found in an N2O4 donor atom coordination geometry that is unusual for the cryptand ligand. Magnetic susceptibility data on these new examples of nontraditional divalent lanthanide complexes are consistent with 4fn5d1 electronic configurations. The Dy and Ho complexes have exceptionally high single-ion magnetic moments, 11.35 and 11.67 μB, respectively. Lithium reduction of Cp'3Y under N2 at -35 °C forms the Y2+ complex (Cp'3Y)1-, which reduces dinitrogen upon warming to room temperature to generate the (N2)2- complex [Cp'2Y(THF)]2(μ-η2:η2-N2). These results provide insight on the factors that lead to reduced dinitrogen complexes and/or stable divalent lanthanide complexes as a function of the specific reducing agent and conditions.

Nitrogen Fixation Catalyzed by Transition Metal Complexes: Recent Developments

The structures and reactivity of various catalytic model systems of nitrogenase are reviewed. Firstly, the Schrock cycle is discussed as an example of a nitrogen‐fixing system for which the mechanism has been elucidated both experimentally and theoretically. Then a series of mononuclear iron complexes based on tetradentate ligands of the type EP3 (E = Si, C, B) is discussed. These systems both serve as highly active catalysts for the synthesis of ammonia from N2 and provide important insights into the role of the ligand situated in the position trans to coordinated N2. In addition, new cobalt, iron, ruthenium, and osmium complexes that display catalytic conversion of N2 into ammonia are discussed. As an alternative to the mononuclear systems, the synthesis and catalytic activity of dinuclear Mo0–dinitrogen complexes supported by terminal pincer ligands are reviewed. The available mechanistic scenarios disagree on the question of whether or not the complex dissociates during the catalytic cycle. Furthermore, a new dinuclear iron system that is active in synthetic nitrogen fixation and exhibits a further activity increase under irradiation is reviewed. The implications of the results obtained with all of these systems with respect to the reactivity of nitrogenase are discussed.

Bis(dinitrogen)cobalt(-1) Complexes with NHC Ligation: Synthesis, Characterization, and Their Dinitrogen Functionalization Reactions Affording Side-on Bound Diazene Complexes.

Late-transition-metal-based catalysts are widely used in N2 fixation reactions, but the reactivity of late-transition-metal N2 complexes, besides iron N2 complexes, has remained poorly understood as their N2 complexes were thought to be labile and hard to functionalize. By employing a monodentate N-heterocyclic carbene (NHC), 1,3-dicyclohexylimidazol-2-ylidene (ICy) as ligand, the cobalt(0)- and cobalt(-1)-N2 complexes, [(ICy)3Co(N2)] (1) and [(ICy)2Co(N2)2M]n (M = K, 2a; Rb, 2b; Cs, 2c), respectively, were synthesized from the stepwise reduction of (ICy)3CoCl by the corresponding alkaline metals under a N2 atmosphere. Complexes 2a-c in their solid states adopt polymeric structures. The N-N distances (1.145(6)-1.162(5) Å) and small N-N infrared stretchings (ca. 1800 and 1900 cm-1) suggest the strong N2 activation of the end-on N2 ligands in 2a-c. One electron oxidation of 1 by [Cp2Fe][BF4] gave the cobalt(I) complex devoid of N2 ligand [(ICy)3Co][BF4] (3). The bis(dinitrogen)cobalt(-1) complexes 2a-c undergo protonation reaction with triflic acid to give N2H4 in 24-30% yields (relative to cobalt). Complexes 2a-c could also react with silyl halides to afford diazene complexes [(ICy)2Co(η2-R3SiNNSiR3)] (R = Me, 6a; Et, 6b) that are the first diazene complexes of late transition metals prepared from N2 functionalization. Characterization data, in combination with calculation results, suggest the electronic structures of the diazene complexes as low-spin cobalt(II) complexes containing dianionic ligand [η2-R3SiNNSiR3]2-. Complexes 1, 2a-c, 6a, 6b, and (ICy)2CoCl2 proved to be effective catalysts for the reductive silylation of N2 to afford N(SiMe3)3. These NHC-cobalt catalysts display comparable turnover numbers (ca. 120) that exceed the reported 3d metal catalysts. The fine performance of the NHC-cobalt complexes in the stoichiometric and catalytic N2-functionalization reactions points out the utility of low-valent low-coordinate group 9 metal species for N2 fixation.

Ab initio potential and rotational spectra of the CO-N2 complex.

Ab initio calculations of the intermolecular potential energy surface (PES) of CO-N2 have been carried out using the closed-shell single- and double-excitation coupled cluster approach with a non-iterative perturbative treatment of triple excitations method and the augmented correlation-consistent quadruple-zeta (aug-cc-pVQZ) basis set supplemented with midbond functions. The global minimum (De = 117.35 cm-1) of the four-dimensional PES corresponds to an approximately T-shaped structure with the N2 subunit forming the leg and CO the top. The bound rovibrational levels of the CO-N2 complex were calculated for total angular momenta J = 0-8 on this intermolecular potential surface. The calculated dissociation energies D0 are 75.60 and 76.79 cm-1 for the ortho-N2 (A-symmetry) and para-N2 (B-symmetry) nuclear spin modifications of CO-N2, respectively. Guided by these bound state calculations, a new millimeter-wave survey for the CO-N2 complex in the frequency range of 110-145 GHz was performed using the intracavity OROTRON jet spectrometer. Transitions not previously observed were detected and assigned to the subbands connecting the K = 0 and 1, (jCO, jN2 ) = (1, 0) states with a new K = 1, (jCO, jN2 ) = (2, 0) state. Finally, the measured rotational energy levels of the CO-N2 complex were compared to the theoretical bound state results, thus providing a critical test of the quality of the PES presented. The computed rovibrational wave functions were analyzed to characterize the nature of the different bound states observed for the two nuclear spin species of CO-N2.

A Noncovalent Binding Strategy to Capture Noble Gases, Hydrogen and Nitrogen.

A molecular design strategy to develop receptor systems for the entrapment of noble gases, H2 and N2 is described using M06L-D3/6-311++G(d,p)//M06L/6-311++G(d,p) DFT method. These receptors made with two-, three-, four- and five-fluorinated benzene cores, linked with methelene units viz. RI , RII , RIII and RIV as well as the corresponding non-fluorinated hydrocarbons viz. RIH , RIIH , RIIIH and RIVH show a steady and significant increase in binding energy (Eint ) with increase in the number of aromatic rings in the receptor. A stabilizing "cage effect" is observed in the cyclophane type receptors RIV and RIVH which is 26-48% of total Eint for all except the larger sized Kr, Xe and N2 complexes. Eint of RIV …He, RIV …Ne, RIV …Ar, RIV …Kr, RIV …H2 and RIV …N2 is 4.89, 7.03, 6.49, 6.19, 8.57 and 8.17 kcal/mol, respectively which is 5- to9-fold higher than that of hexafluorobenzene. Similarly, compared to benzene, multiple fold increase in Eint is observed for RIVH receptors with noble gases, H2 and N2 . Fluorination of the aromatic core has no significant impact on Eint (∼ ±0.5 kcal/mol) for most of the systems with a notable exception of the cage receptor RIV for N2 where fluorination improves Eint by 1.61 kcal/mol. The Eint of the cage receptors may be projected as one of the highest interaction energy ranges reported for noble gases, H2 and N2 for a neutral carbon framework. Synthesis of such systems is promising in the study of molecules in confined environment. © 2018 Wiley Periodicals, Inc.

Development of catalytic nitrogen fixation using transition metal-dinitrogen complexes under mild reaction conditions.

This paper describes our recent progress in catalytic nitrogen fixation using transition metal-dinitrogen complexes as catalysts. Our research group has recently developed novel reaction systems for the catalytic transformation of molecular dinitrogen into ammonia and hydrazine using molybdenum-, iron-, cobalt- and vanadium-dinitrogen complexes under mild reaction conditions. The new findings presented in this paper may provide a new approach to the development of economical nitrogen fixation to replace the energy-consuming Haber-Bosch process.

Synthesis and reactivity of an N-triphos Mo(0) dinitrogen complex.

The preparation and reactivity of a novel molybdenum dinitrogen complex supported by a nitrogen-centred tripodal phosphine ligand (N-triphos, N(CH2PPh2)3, NP3Ph) are reported. Reaction of N-triphos with [MoX3(THF)3] (X = Cl, Br, I) gave the Mo(iii) complex [MoX3(κ2-NP3Ph)(THF)] (1), where bidentate N-triphos coordination was observed. Reduction of this complex in the presence of dppm (bis(diphenylphosphino)methane) gave the dinitrogen complex [Mo(N2)(dppm)(κ3-NP3Ph)] (2), which exhibits moderate dinitrogen activation. An additional hydride complex, [Mo(H)2(dppm)(κ3-NP3Ph)] (4), was produced either as a minor side product during the reduction step, or as a major product by direct hydrogenation of the dinitrogen complex 2. The reactivity of the dinitrogen complex 2 with a range of Lewis acids was also investigated. At low temperatures, protic or borane Lewis acids (H+, BBr3 and tris(pentafluorophenyl)borane (BCF)) were found to coordinate to the apical nitrogen atom of the N-triphos ligand, with no conclusive evidence of any functionalisation of the dinitrogen ligand. Alkali metal Lewis acid addition to 2 resulted in the unexpected rearrangement of the N-triphos ligand to form [Mo(dppm)(PMePh2)(PCP)][B(C6F5)4] (7), where PCP, [Ph2PCNHCH2PPh2] is the carbenic ligand formed upon rearrangement from the reaction of 2 with M[B(C6F5)4] (M = Li, Na or K). Single crystal X-ray diffraction of complexes 1, 2, 4 and 7 provided structural confirmation of the N-triphos molybdenum complexes described.

Ab initio study of the CO-N2 complex: a new highly accurate intermolecular potential energy surface and rovibrational spectrum.

A new, highly accurate ab initio ground-state intermolecular potential-energy surface (IPES) for the CO-N2 complex is presented. Thousands of interaction energies calculated with the CCSD(T) method and Dunning's aug-cc-pVQZ basis set extended with midbond functions were fitted to an analytical function. The global minimum of the potential is characterized by an almost T-shaped structure and has an energy of -118.2 cm-1. The symmetry-adapted Lanczos algorithm was used to compute rovibrational energies (up to J = 20) on the new IPES. The RMSE with respect to experiment was found to be on the order of 0.038 cm-1 which confirms the very high accuracy of the potential. This level of agreement is among the best reported in the literature for weakly bound systems and considerably improves on those of previously published potentials.

Intermolecular configurations dominated by quadrupole-quadrupole electrostatic interactions: explicit correlation treatment of the five-dimensional potential energy surface and infrared spectra for the CO-N2 complex.

A thorough understanding of the intermolecular configurations of van der Waals complexes is a great challenge due to their weak interactions, floppiness and anharmonic nature. Although high-resolution microwave or infrared spectroscopy provides one of the most direct and precise pieces of experimental evidence, the origin and key role in determining such intermolecular configurations of a van der Waals system strongly depend on its highly accurate potential energy surface (PES) and a detailed analysis of its ro-vibrational wavefunctions. Here, a new five-dimensional potential energy surface for the van der Waals complex of CO-N2 which explicitly incorporates the dependence on the stretch coordinate of the CO monomer is generated using the explicitly correlated couple cluster (CCSD(T)-F12) method in conjunction with a large basis set. Analytic four-dimensional PESs are obtained by the least-squares fitting of vibrationally averaged interaction energies for v = 0 and v = 1 to the Morse/Long-Range potential mode (VMLR). These fits to 7966 points have root-mean-square deviations (RMSD) of 0.131 cm-1 and 0.129 cm-1 for v = 0 and v = 1, respectively, with only 315 parameters. Energy decomposition analysis is carried out, and it reveals that the dominant factor in controlling intermolecular configurations is quadrupole-quadrupole electrostatic interactions. Moreover, the rovibrational levels and wave functions are obtained for the first time. The predicted infrared transitions and intensities for the ortho-N2-CO complex as well as the calculated energy levels for para-N2-CO are in good agreement with the available experimental data with RMSD discrepancies smaller than 0.068 cm-1. The calculated infrared band origin shift associated with the fundamental band frequency of CO is -0.721 cm-1 for ortho-N2-CO which is in excellent agreement with the experimental value of -0.739 cm-1. The agreement with experimental values validates the high quality of the PESs and enhances our confidence to explain the observed mystery lines around 2163 cm-1.

Dinitrogen functionalization at a ditantalum center. Balancing N2 displacement and N2 functionalization in the reaction of coordinated N2 with CS2.

The reaction of carbon disulfide (CS2) with the side-on end-on dinitrogen complex ([NPNSi]Ta)2(μ-η1:η2-N2)(μ-H)2 (1) (where [NPNSi] = [PhP(CH2SiMe2NPh)2]) has been studied and shown to generate two products, the ratio of which depends on the concentration of added carbon disulfide. At high concentrations of CS2, N-N bond cleavage and functionalization occur to generate a ditantalum complex with an isothiocyanato ligand N-bound to Ta along with bridging sulfido and nitrido moieties. At lower concentrations of CS2, less dinitrogen functionalization is observed; instead, N2 is displaced and the CS2 molecule is completely disassembled to generate a ditantalum derivative with bridging methylene and two sulfide moieties. Kinetic and DFT studies have been performed and provide clues about the product ratio and mechanistic information and shed light on why N2 functionalization is challenging.

Preparation and reactivity of half-sandwich organic azide complexes of osmium.

Organic azide complexes [Os(η5-C5H5)(κ1-N3R)(PPh3){P(OR1)3}]BPh4 (1, 2) [R = CH2C6H5 (a), CH2C6H4-4-CH3 (b), CH(CH3)C6H5 (c), C6H5 (d); R1 = Me (1), Et (2)] were prepared by allowing bromo-compounds [OsBr(η5-C5H5)(PPh3){P(OR1)3}] to react first with AgOTf and then with an excess of azide in toluene. Benzylazide complexes reacted in solution leading to imine derivatives [Os(η5-C5H5){κ1-NH[double bond, length as m-dash]C(R2)Ar}(PPh3){P(OR1)3}]BPh4 (3, 4) [R2 = H (a, b), CH3 (c); Ar = C6H5, C6H4-4-CH3; R1 = Me (3), Et (4)]. Phenylazide, on the other hand, reacted in solution affording the dinuclear dinitrogen complex [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5). Depending on the nature of the R substituent, the reaction of the p-cymene complex [OsCl2(η6-p-cymene)(PPh3){P(OEt)3}] with RN3 yielded imine [OsCl(η6-p-cymene){κ1-NH[double bond, length as m-dash]C(H)Ar}{P(OEt)3}]BPh4 (6) (Ar = C6H4-4-CH3) and amine derivatives [OsCl(η6-p-cymene)(κ1-NH2C6H5){P(OEt)3}]BPh4 (7). The complexes were characterised spectroscopically (IR, 1H, 31P, 15N NMR) and by the X-ray crystal structure determination of [{Os(η5-C5H5)(PPh3)[P(OMe)3]}2(μ-N2)](BPh4)2 (5).