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Piperazine rings are essential motifs frequently found in commercial drugs. However, synthetic methodologies are mainly limited to N-substituted piperazines, preventing structural diversity. Disclosed herein is a straightforward catalytic method for the synthesis of complex C-substituted piperazines based on an uncommon head-to-head coupling of easily prepared imines. This 100% atom-economic process allows the selective formation of a sole diastereoisomer, a broad substrate scope, and a good functional group tolerance employing a bench-stable iridium catalyst under mild reaction conditions. Key to the success is the addition of N-oxides to the reaction mixture, as they notably enhance the catalytic activity and selectivity., The generous financial support from MCIN/AEI/10.13039/501100011033 (PID2020-119512GB-I00) and Gobierno de Aragón/FEDER, EU (GA/FEDER, Reactivity and Catalysis Inorganic Chemistry Group, E50_20D) is gratefully acknowledged. A.M.G. is thankful for Grant IJC2018-035231-I funded by MCIN/AEI/10.13039/501100011033, and L.T. thanks MICIIN/FEDER for an FPI fellowship.

Two-coordinate transition metal complexes are exciting candidates for single-molecule magnets (SMMs) because their highly axial coordination environments lead to sizeable magnetic anisotropy. We report a series of five structurally related two-coordinate Fe(II) m-terphenyl complexes (4-R-2,6-Xyl2C6H2)2Fe [R = tBu (1), SiMe3 (2), H (3), Cl (4), CF3 (5)] where, by changing the functionalisation of the para-substituent (R), we alter their magnetic function. All five complexes are field-induced single-molecule magnets, with relaxation rates that are well-described by a combination of direct and Raman mechanisms. By using more electron donating R groups we were able to slow the rate of magnetic relaxation. Our ab initio calculations predict a large crystal field splitting (>850 cm−1) and sizeable zero-field splitting parameters (ca. −60 cm−1, |E| < 0.2 cm−1) for 1–5. These favourable magnetic properties suggest that m-terphenyl ligands have untapped potential as chemically versatile ligands able to impose highly axial crystal fields., We acknowledge the EPSRC [grant number EP/R004064/1]; the Leverhulme Trust [grant numbers RPG-2014-317; RF-2021-102]; and the University of Nottingham [Hobday Bequest] for financial support of this research.

We report the synthesis, characterization, and electrocatalytic water oxidation activity of two cobalt complexes, (6-FP)Co(NO₃)₂ (1) (6-FP = 8,8′-(1,2-phenylene)diquinoline) and (5-FP)Co(NO₃)₂ (2) (5-FP = 1,2-bis(N-7-azaindolyl)benzene), containing “capping arene” bidentate ligands with nitrogen atom donors. The cobalt complexes 1 and 2 were supported on ordered mesoporous carbon (OMC) by π–π stacking, resulting in heterogenized cobalt materials 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, respectively, and studied for electrocatalytic water oxidation. We find that 6-FP-Co-OMC-1 exhibits an overpotential of 355 mV for a current density of 10 mA cm⁻² and a turnover frequency (TOF) of ∼0.53 s–1 at an overpotential of 400 mV at pH 14. 6-FP-Co-OMC-1 exhibits activity that is ∼1.6 times that of 5-FP-Co-OMC-2, which gives a TOF of 0.32 s⁻¹ at 400 mV overpotential. The structural stability of the single-atom Co site was demonstrated for 6-FP-Co-OMC-1 using X-ray absorption spectroscopy for the molecular complex supported on OMC, but slow degradation in catalyst activity can be attributed to eventual formation of Co oxide clusters. DFT computations of electrocatalytic water oxidation using the molecular complexes as models provide a description of the catalytic mechanism. These studies reveal that the mechanism for O–O bond formation involves an intermediate Coᴵⱽ oxo complex that undergoes an intramolecular reductive O–O coupling to form a Coᴵᴵ–OOH species. Further, the calculations predict that the molecular 6-FP-Co structure is more active for electrocatalytic water oxidation than 5-FP-Co, which is consistent with experimental studies of 6-FP-Co-OMC-1 and 5-FP-Co-OMC-2, highlighting the possibility that the ligand structure influences the catalytic activity of the supported molecular catalysts.

Enhancing catalytic activity through synergic effects is a current challenge in homogeneous catalysis. In addition to the well-established metal–metal and metal–ligand cooperation, we showcase here an example of self-activation by the substrate in controlling the catalytic activity of the two-coordinate iron complex [Fe(2,6-Xyl2C6H3)2] (1, Xyl = 2,6-Me2C6H3). This behavior was observed for aryl acetylenes in their regioselective cyclotrimerization to 1,2,4-(aryl)-benzenes. Two kinetically distinct regimes are observed dependent upon the substrate-to-catalyst ratio ([RC≡CH]0/[1]0), referred to as the low ([RC≡CH]0/[1]0 < 40) and high ([RC≡CH]0/[1]0 > 40) regimes. Both showed sigmoidal kinetic response, with positive Hill indices of 1.85 and 3.62, respectively, and nonlinear Lineweaver–Burk replots with an upward curvature, which supports positive substrate cooperativity. Moreover, two alkyne molecules participate in the low regime, whereas up to four are involved in the high regime. The second-order rate dependence on 1 indicates that binuclear complexes are the catalytically competent species in both regimes, with that in the high one being 6 times faster than that involved in the low one. Moreover, Eyring plot analyses revealed two different catalytic cycles, with a rate-determining step more endergonic in the low regime than in the high one, but with a more ordered transition state in the high regime than in the low one., The generous financial support from MCIN/AEI/10.13039/501100011033 (PID2020-119512GB-I00) and Gobierno de Aragón/FEDER, UE (GA/FEDER, Inorganic molecular architecture and applications Group, E50_23R) is gratefully acknowledged. A.M.G. thanks grant IJC2018-035231-I funded by MCIN/AEI/10.13039/501100011033. D.L.K. thanks The Leverhulme Trust (RF-2021-102 and RPG-2021-183) for funding.

Ruthenium complexes of hemilabile phosphinocarboxamide ligands, and their use to form metallacycles using halide abstraction/deprotonation reactions are reported. Thus, [Ru(p-cym){PPh2C(=O)NHR}Cl2; R = iPr (1), Ph (2), p-tol (3)] and [Ru(p-cym){PPh2C(=O)N(R)C(=O)N(H)R}Cl2; R = Ph (4), p-tol (5)] were synthesized from [(p-cym)RuCl2]2 (p-cym = para-cymene) and phosphinocarboxamides or phosphinodicarboxamides, respectively. Single crystal X-ray diffraction measurements on 1–5 reveal coordination to ruthenium through the phosphorus donor, with an intramolecular hydrogen bond between the amine-bound proton and a metal-bound chloride. Six-membered metallacycles formed by halide abstraction/deprotonation of complexes 4 and 5 afforded [Ru(p-cym){κ2-P,N-PPh2C(=O)N(R)C(=O)NR}Cl] [R = Ph (6), p-tol (7)]. These species exist as a mixture of two rotational isomers in solution, as demonstrated by NMR spectroscopy.

Electrochemical methods are coupled with chemical oxidant-based analytical strategies to evaluate the oxidative reactivity of the platinum(II) diimine complex (bpy)PtII(CH3)2 (bpy = 2,2′-bipyridine...

Herein we report the synthesis of three heteroleptic first‐row transition metal(II) complexes containing carbazolido NNN pincer ligands and conversion to the corresponding metal(I)‐carbonyl complexes via a reductive carbonylation route. These complexes are precatalysts for the hydrophosphination of activated alkenes, affording a cobalt‐catalysed hydrophosphination process that solely and selectively yields the β addition (anti‐Markovnikov) product. The scope of this transformation has been investigated using a variety of activated alkenes. Isolation and characterisation of substrate‐coordinated intermediates reveal available coordination sites, which provide insight into the proposed catalytic cycle., This work was supported by the Engineering and Physical Sciences Research Council [grant number EP/R004064/1]; The Leverhulme Trust [grant number RPG‐2014‐317]; CONACYT (Mexican Council for Science and Technology) [grant number CVU 600474] and the University of Nottingham.

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A two-coordinate Fe(II) m-terphenyl complex acts as a precatalyst for the hydroamination of isocyanates, affording urea and biuret derivatives, with product selectivity accomplished via modificatio...

We report a trinuclear copper(II) complex, [(DAM)Cu3(μ3-O)][Cl]4 (1, DAM = dodecaaza macrotetracycle), as a homogeneous electrocatalyst for water oxidation to dioxygen in phosphate-buffered solutions at pH 7.0, 8.1, and 11.5. Electrocatalytic water oxidation at pH 7 occurs at an overpotential of 550 mV with a turnover frequency of ∼19 s–1 at 1.5 V vs NHE. Controlled potential electrolysis (CPE) experiments at pH 11.5 over 3 h at 1.2 V and at pH 8.1 for 40 min at 1.37 V vs NHE confirm the evolution of dioxygen with Faradaic efficiencies of 81% and 45%, respectively. Rinse tests conducted after CPE studies provide evidence for the homogeneous nature of the catalysis. The linear dependence of the current density on the catalyst concentration indicates a likely first-order dependence on the Cu precatalyst 1, while kinetic isotope studies (H2O versus D2O) point to involvement of a proton in or preceding the rate-determining step. Rotating ring-disk electrode measurements at pH 8.1 and 11.2 show no evidence of H2O2 formation and support selectivity to form dioxygen. Freeze-quench electron paramagnetic resonance studies during electrolysis provide evidence for the formation of a molecular copper intermediate. Experimental and computational studies support a key role of the phosphate as an acceptor base. Moreover, density functional theory calculations highlight the importance of second-sphere interactions and the role of the nitrogen-based ligands to facilitate proton transfer processes.

Olefin hydrophosphanation is an attractive route for the atom-economical synthesis of functionalized phosphanes. This reaction involves the formation of P–C and H–C bonds. Thus, complexes that contain both hydrido and phosphanido functionalities are of great interest for the development of effective and fast catalysts. Herein, we showcase the excellent activity of one of them, [Rh(Tp)H(PMe3)(PPh2)] (1), in the hydrophosphanation of a wide range of olefins. In addition to the required nucleophilicity of the phosphanido moiety to accomplish the P–C bond formation, the key role of the hydride ligand in 1 has been disclosed by both experimental results and DFT calculations. An additional Rh–H···C stabilization in some intermediates or transition states favors the hydrogen transfer reaction from rhodium to carbon to form the H–C bond. Further support for our proposal arises from the poor activity exhibited by the related chloride complex [Rh(Tp)Cl(PMe3)(PPh2)] as well as from stoichiometric and kinetic studies., The generous financial support from AEI/FEDER, UE (CTQ2017-83421-P), Gobierno de Aragón/FEDER, UE (GA/FEDER, Inorganic Molecular Architecture Group E08_17R) is gratefully acknowledged. A.M.G. and V.V.-I. thank MINECO/FEDER for a JdC contract and a FPI fellowship, respectively. The Centro de Supercomputación de Galicia (CESGA) is also gratefully acknowledged for generous allocation of time.

The effect of para-substitution upon the structural and electronic properties of a series of m-terphenyl lithium complexes [R–Ar#–Li]2 (R = t-Bu 1, SiMe32, H 3, Cl 4, CF35; where R–Ar# = 2,6-{2,6-Xyl}2-4-R-C6H2 and 2,6-Xyl = 2,6-Me2C6H3) has been investigated. X-ray crystallography reveals the complexes to be structurally similar, with little variation in C–M–C bond lengths and angles across the series. However, in-depth NMR spectroscopic studies reveal notable electronic differences, showing a linear correlation between the 7Li{1H} NMR chemical shifts of the para-substituted complexes and their Hammett constants. The flanking methyl protons exhibit a similar electronic shift in the 1H NMR spectra, which has been rationalised by the presence of through-space Li⋯H interactions, as evidenced by two-dimensional 7Li–1H heteronuclear Overhauser spectroscopy (HOESY). In both cases, electron-withdrawing substituents are found to cause an upfield peak shift. A computational analysis is employed to account for these trends., We acknowledge the EPSRC [grant number EP/R004064/1], the Leverhulme Trust [grant number RPG-2014-317], and the University of Nottingham for financial support of this research. We also thank the University of Nottingham Analytical Services Team for elemental analyses, mass spectrometry, and NMR spectroscopy measurements. We are also grateful for access to the University of Nottingham's Augusta High Performance Computing service. AMT is grateful for support from the European Research Council under H2020/ERC Consolidator Grant “topDFT” (Grant No. 772259).

Dedicated in Memoriam to Professor Dr. Pascual Royo., The reactions of the rhodium(I) and iridium(I) complexes [M(PhBP3)(C2H4)(NCMe)] (PhBP3=PhB(CH2PPh2)3−) with alkynes have resulted in the synthesis of a new family of pseudo‐tetrahedral complexes, [M(PhBP3)(RC≡CR′)] (M=Rh, Ir), which contain the alkyne as a four‐electron donor. The reactions of these unusual compounds with two‐electron donors (L=PMe3, CNtBu) produced a change in the “donicity” of the alkyne from a 4e− to a 2e− donor to give five‐coordinate complexes. These were the final products with the iridium complexes, whereas further reactions took place with the rhodium complexes. In particular, C(sp)−H bond activation of the alkyne occurred leading to hydrido alkynyl complexes. This process is essential for the further reactivity of the alkynes, and if the alkyne itself was used as reagent, E‐enyne complexes were obtained. As a consequence of this chemistry, we show that the complex [Rh(PhBP3)(C2H4)(NCMe)] is a very efficient pre‐catalyst for the regioselective di‐ and trimerization of terminal alkynes to E‐enynes and benzene derivatives, respectively. Interestingly, acetonitrile significantly enhanced the catalytic activity by facilitating the C(sp)−H bond activation step. A hydrometalation mechanism to account for these experimental observations is proposed., The generous financial support from the MINECO/FEDER (Projects CTQ2014‐53033‐P and CTQ2017‐83421‐P, C.T.) and the Gobierno de Aragón/FEDER (GA/FEDER, Inorganic Molecular Architecture Group E08_17R; C.T.) is gratefully acknowledged.

Group 1 salts containing carbazolido NNN pincer ligands are precatalysts for the dehydrogenation of Me2NH·BH3. NMR monitoring and DOSY studies show a heavy dependence on the metal and solvent, allowing in some cases selective formation of dehydrogenation products consistent with hydrogen liberation.

Two- and three-coordinate manganese m-terphenyl complexes are precatalysts for the dehydrogenation of dimethylamine-borane (Me2NH·BH3) affording one equivalent of molecular hydrogen and half an equivalent of [Me2N–BH2]2. Experimental studies into the nature of the catalyst indicate that small changes in the coordination environment give rise to significant differences in the reaction mechanism, occurring through a homogeneous mechanism for two-coordinate precatalysts, whilst for the three-coordinate species a heterogeneous mechanism takes place where nanoparticles are responsible for the catalysis.

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The first transition metal catalyzed hydrophosphination of isocyanates is presented. The use of low-coordinate iron(II) precatalysts leads to an unprecedented catalytic double insertion of isocyanates into the P−H bond of diphenylphosphine to yield phosphinodicarboxamides [Ph2PC(=O)N(R)C(=O)N(H)R], a new family of derivatized organophosphorus compounds. This remarkable result can be attributed to the low-coordinate nature of the iron(II) centers whose inherent electron deficiency enables a Lewis-acid mechanism in which a combination of the steric pocket of the metal center and substrate size determines the reaction products and regioselectivity.

A magnesium complex (1) featuring a bidentate aminopyridinato ligand is a remarkably selective catalyst for the dehydrocoupling of amine‐boranes. This reaction proceeds to completion with low catalyst loadings (1 mol %) under mild conditions (60 °C), exceeding previously reported s‐block systems in terms of selectivity, rate, and turnover number (TON). Mechanistic studies by in situ NMR analysis reveals the reaction to be first order in both catalyst and substrate. A reaction mechanism is proposed to account for these findings, with the high TON of the catalyst attributed to the bidentate nature of the ligand, which allows for reversible deprotonation of the substrate and regeneration of 1 as a stable resting state.

A magnesium complex (1) featuring a bidentate aminopyridinato ligand is a remarkably selective catalyst for the dehydrocoupling of amine-boranes. This reaction proceeds to completion with low catalyst loadings (1 mol %) under mild conditions (60 °C), exceeding previously reported s-block systems in terms of selectivity, rate, and turnover number (TON). Mechanistic studies by in situ NMR analysis reveals the reaction to be first order in both catalyst and substrate. A reaction mechanism is proposed to account for these findings, with the high TON of the catalyst attributed to the bidentate nature of the ligand, which allows for reversible deprotonation of the substrate and regeneration of 1 as a stable resting state.

The feasibility of oxidative addition of the P−H bond of PHPh2 to a series of rhodium complexes to give mononuclear hydrido‐phosphanido complexes has been analyzed. Three main scenarios have been found depending on the nature of the L ligand added to [Rh(Tp)(C2H4)(PHPh2)] (Tp= hydridotris(pyrazolyl)borate): i) clean and quantitative reactions to terminal hydrido‐phosphanido complexes [RhTp(H)(PPh2)(L)] (L=PMe3, PMe2Ph and PHPh2), ii) equilibria between RhI and RhIII species: [RhTp(H)(PPh2)(L)]⇄[RhTp(PHPh2)(L)] (L=PMePh2, PPh3) and iii) a simple ethylene replacement to give the rhodium(I) complexes [Rh(κ2‐Tp)(L)(PHPh2)] (L=NHCs‐type ligands). The position of the P−H oxidative addition–reductive elimination equilibrium is mainly determined by sterics influencing the entropy contribution of the reaction. When ethylene was used as a ligand, the unique rhodaphosphacyclobutane complex [Rh(Tp)(η1‐Et)(κC,P‐CH2CH2PPh2)] was obtained. DFT calculations revealed that the reaction proceeds through the rate limiting oxidative addition of the P−H bond, followed by a low‐barrier sequence of reaction steps involving ethylene insertion into the Rh−H and Rh−P bonds. In addition, oxidative addition of the P−H bond in OPHPh2 to [Rh(Tp)(C2H4)(PHPh2)] gave the related hydride complex [RhTp(H)(PHPh2)(POPh2)], but ethyl complexes resulted from hydride insertion into the Rh−ethylene bond in the reaction with [Rh(Tp)(C2H4)2]., The generous financial support from AEI/FEDER, UE (CTQ2017‐83421‐P, C.T.), Gobierno de Aragón/FEDER (GA/FEDER, Inorganic Molecular Architecture Group E08_17R; C.T.) and the Netherlands Organization for Scientific Research (NWO) (TOP Grant 716.015.001, B.dB) is gratefully acknowledged. V.V. thanks MINECO/FEDER for an FPI fellowship.

Two- and three-coordinate m-terphenyl complexes of manganese and iron are efficient catalysts for the selective cyclotrimerisation of primary aliphatic isocyanates affording isocyanurates in short reaction times and under mild conditions.

The TBPY-5 rhodium complex [(PhBP 3)Rh(CH 2=CH 2)(NCMe)] (1; PhBP 3 = PhB(CH 2PPh 2) 3), which contains ethylene in the equatorial plane and a labile acetonitrile ligand at one of the axial positions, provides a simple entry into the chemistry of the fac-[P 3Rh] scaffold. DFT calculations using the model compound [(MeB(CH 2PMe 2) 3)Rh(CH 2=CH 2)(NCMe)] (1′) reproduce well the crystallographic geometry of 1 and converge to the isolated conformer, in which the strong π back-donation from the metal to the π* orbital of ethylene fixes it coplanar with the equatorial plane. Oxidation of 1 is electrochemically irreversible (at 0.080 V vs SCE), and 1 was effectively oxidized with [Cp 2Fe] + in acetonitrile to [(PhBP 3)Rh(NCMe) 3] 2+. Reaction of 1 with hydrogen in toluene gives the dihydride [(PhBP 3)Rh(H) 2(NCMe)] (3), which loses acetonitrile to give the insoluble hydride [{(PhBP 3)Rh(H)(μ-H)} 2] (4), while 1 in THF with BHT (2,6-bis(1,1-dimethylethyl)-4-methylphenol) results in the mixed-valence paramagnetic hydride [{(PhBP 3)Rh} 2(μ-H) 3] (5). Complexes 1 and 3 react with oxygen to give the dinuclear complex [{(PhBP 3)Rh(μ-O 2)} 2]. The kinetic products from the protonation of complex 1 with carboxylic acids were found to be the ethyl complexes [(PhBP 3)Rh(η 1-C 2H 5)(κ 2-O 2CR)] (R = Ph, Me), which establish an equilibrium in solution with the corresponding hydride complexes [(PhBP 3)Rh(H)(κ 2-O 2CR)] (R = Ph, Me) and free ethylene. These equilibria can be shifted to the desired compound working under either an atmosphere of ethylene or vacuum. Sequential protonation of 1 and 3 with HBF 4 in acetonitrile gave cleanly the cationic hydride complex [(PhBP 3)Rh(H)(NCMe) 2]BF 4 first and then [(PhBP 3)Rh(NCMe) 3](BF 4) 2 and hydrogen. Other electrophiles such as MeOTf react immediately with 1 at one phosphorus atom to give the alkylated (P-methyl) complex [{PhB(PMe)P 2}Rh(κ 2-O 2SOCF 3)]. © 2012 American Chemical Society., This research was supported by the MICINN/FEDER (Projects CTQ2008-03860 and CTQ2011-22516, Spain) and Gobierno de Aragón/FSE (Group E70, Spain). A.M.G. and S.J. thank Gobierno de Aragón for a fellowship.

Ethylene insertion into Rh-H bonds in complexes bearing an anionic fac-triphosphane ligand gives hydrido complexes, β-agostic species, or noninteracting ethyl derivatives depending on the reaction conditions. Several chemical equilibria between these species have been analyzed by NMR and DFT calculations, which revealed that they are mainly controlled by the entropy. Moreover, β-agostic species were found to be lower in enthalpy than the corresponding hydride-ethylene complexes, probably due to the steric pressure exerted by the bulky fac-triphosphane ligand., The generous financial support from MICINN/FEDER (Project CTQ2011-22516), MINECO/FEDER (Project CTQ2014-53033-P), and Gobierno de Aragon/FSE (GA/FSE, Inorganic Molecular Architecture Group, E70) is gratefully acknowledged. A.M.G. thanks GA/FSE for a fellowship.

Complexes with terminal phosphanido (M-PR2) functionalities are believed to be crucial intermediates in new catalytic processes involving the formation of P-P and P-C bonds. We showcase here the isolation and characterization of mononuclear phosphanide rhodium complexes ([RhTp(H)(PR2)L]) that result from the oxidative addition of secondary phosphanes, a reaction that was also explored computationally. These compounds are active catalysts for the dehydrocoupling of PHPh2 to Ph2P-PPh2. The hydrophosphination of dimethyl maleate and the unactivated olefin ethylene is also reported. Reliable evidence for the prominent role of mononuclear phosphanido rhodium species in these reactions is also provided., The generous financial support from MICINN/FEDER (Project CTQ2011-22516), Gobierno de Aragón/FSE (GA/FSE, Inorganic Molecular Architecture Group, E70), and NWO-CW (VICI project 016.122.613; BdB) is gratefully acknowledged. A.M.G. and A.L.S. thank Gobierno de Aragón and MEC, respectively, for fellowships.

A combination of four-electron donors, such as alkynes, with strongly donating and strong-field scorpionate ligands is appropriate to create pseudotetrahedral rhodium(I) environments, as found in [Rh(PhBP3)(HCCPh)], which promotes HC bond activation and CC coupling reactions under very smooth conditions., The generous financial support from MICINN/FEDER (Project CTQ2011-22516), Gobierno de Aragón/FSE (GA/FSE, Inorganic Molecular Architecture Group, E70), and GA-La Caixa (Project 2012/GA LC 057) are gratefully acknowledged. A. M. Geer thanks GA for a PhD fellowship and A. Julián thanks GA-LC for a P.I. contract.

Compounds of the late transition metals with M≡X multiple bonds (X=CR2, NR, O) represent a synthetic challenge, partly overcome by preparative chemists, but with noticeable gaps in the second- and third-row elements. For example, there are no isolated examples of terminal imido rhodium complexes known to date. Described herein is the isolation, characterization, and some preliminary reactivity studies of the first rhodium complexes [Rh(PhBP3)(NR)] (PhBP3=PhB{CH2PPh2}3) with a multiple and terminal RhN bond. These imido compounds result from reactions of organic azides with the corresponding rhodium(I) complex having a labile ligand, and display a pseudo-tetrahedral core geometry with an almost linear Rh-N-C arrangement [177.5(2)°] and a short Rh-N bond [1.780(2) Å]. We also show that the Rh-N bond undergoes protonation at the nitrogen atom or addition of H2, and also engages in nitrene-group transfer and cycloaddition reactions., The generous financial support from MICINN/FEDER (Project CTQ2011-22516) and Gobierno de Aragón/FSE (GA/FSE, Inorganic Molecular Architecture Group, E70), are gratefully acknowledged. A.M.G. thanks the Gobierno de Aragón for a fellowship.