Reductive Dimerization of Alkenes and Allenes Enabled by Photochemically Activated Zinc-Zinc Bonded Compounds.

Metal radicals have shown versatile reactivity in modern synthetic chemistry. However, the use of zinc radicals for molecular synthesis has been barely explored. Here, we show that a transient zinc radical can be formed through photoactivation of a zinc-zinc bonded compound, which is able to mediate the selective dimerization of alkenes and allenes. Treatment of dizinc compounds [L2Zn2] [L = CH3C(2,6-iPr2C6H3N)CHC(CH3)(NCH2CH2PR2); R = Ph (LPh) or iPr (LiPr)] with a diverse array of aromatic alkenes under UV irradiation (365 nm) facilely afforded the head-to-head coupling products, i.e., 1,4-dizinciobutanes in high yields. In addition, arylallenes could also be selectively dimerized by the dizinc compound to give 2,5-dizincyl-functionalized 1,5-hexadienes under the same conditions. Control reactions of [LPh2Zn2] in the presence of UV irradiation isolated a zinc phenyl complex and a trimeric zinc phosphide complex resulting from C-P bond cleavage at the tridentate ligand. Reactions of photoactivated dizinc compounds with organic spin traps, i.e., 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 2,2'-bipyridine (2,2'-bpy), successfully isolated zinc radical trapping products [LZnOTEMP] and [LPhZn(2,2'-bpy)·-], respectively. The profile of alkene dimerization was elucidated by density functional theory calculations, which confirmed that a transient zinc radical [LZn·] was initially generated through homolytic Zn-Zn bond cleavage via photoactivation followed by single-electron transfer and radical dimerization. The unique selectivity of the current reaction was also studied computationally.

Electronic Delocalization and σ-Aromaticity in Heterometallic Cluster with Multiple Thorium-Palladium Bonds.

Research on metal-metal bonds involving f-block actinides, such as thorium, lags far behind the well-studied metal-metal bonds of d-block transition metals. The complexes with Th-TM bonds are extremely rare; all previously identified examples have only a single Th-TM bond with the Th center at an invariably +IV oxidation state. Herein, we report a series of Th2Pdn (n = 2, 3, and 6) clusters (complexes 3, 4, and 7) with multiple Th(III)-Pd bonds. Theoretical studies reveal that the Th2Pdn unit allows electronic delocalization and σ aromaticity, leading to unexpected closed-shell singlet structures for these Th(III) species. This electronic delocalization is evident in the highest occupied molecular orbital of Th(III) complexes and facilitates a 2e reduction of alkyne by complex 7, resulting in the formation of 8. Complexes 7 and 8 are distinctive in featuring a Th2Pd6 core with six and eight Th-Pd bonds, respectively, making them the largest known d-f heterometallic clusters exhibiting metal-metal bonding.

Spectroscopic and Computational Evidence of Uranium Dihydrogen Complexes.

Dihydrogen complexation, a phenomenon with robust precedent in the transition metal series, is spectroscopically detected for a uranium(III) complex and thereby extended for the first time to the 5f series. The vacant coordination site and low valence of (C5H4SiMe3)3U prove to be key to the reversible formation of (C5H4SiMe3)3U-H2 (complex 1), and the paramagnetism of the f3 center facilitates the detection of complex 1 by NMR spectroscopy. Density functional theory calculations reveal that the delocalization of the 5f electron density from (C5H4SiMe3)3U onto the side-on dihydrogen ligand is crucial to complex formation, an unusual bonding situation for an actinide acid-base complex. The spectroscopic and computational results are compared to those reported for lanthanide metallocenes to yield insight into the nature of─and future possibilities for─f-element dihydrogen complexation.

Covalency-Driven Differences in the Hydrogenation Chemistry of Lanthanide- and Actinide-Based Frustrated Lewis Pairs.

The electronic organization of Frustrated Lewis Pairs (FLPs) allows them to activate strong bonds in mechanisms that are usually free of redox events at the Lewis acidic site. The unique 6d/5f manifold of uranium could serve as an interesting FLP acceptor site, but to date FLP-like catalysis with actinide ions is unknown. In this paper, the catalytic, FLP-like hydrogenation reactivity of trivalent uranium complexes is explored in the presence of base-stabilized silylenes. Comparison to isoelectronic, isostructural lanthanide and thorium complexes lends insight into the electronic factors governing dihydrogen activation. Mechanistic studies of the uranium- and lanthanide-catalyzed hydrogenations are presented, including discussion of likely intermediates. Computational modeling of the f-element complexes, combined with experimental comparison to p-block Lewis acids, elucidates the relevance of steric hindrance to productive reactivity with dihydrogen. Consideration of the complete experimental and theoretical evidence provides a clear picture of the electronic and steric factors governing dihydrogen activation by these FLPs.

Homoleptic Organolanthanum-Catalyzed Carbohalogenation.

Metal-halogen exchange reactions are fundamental processes in chemistry that transform organic halides into organometallic reagents. However, using these reactions to build intricate structures in a cascade manner, especially in a catalytic mode, has been a challenge. In this study, we introduce a homoleptic organolanthanum catalyst to initiate lanthanum-halogen exchange and intramolecular carbohalogenation. The catalytic pathway can be achieved through metal-halogen exchange and carbometalation, followed by the extraction of halogen atoms from starting materials. Our approach offers a flexible and sustainable way to create a variety of useful compounds, showcasing its potential in chemical synthesis.

Hydrogenolysis of Cationic Half-Sandwich Zinc Complexes Containing a Chelating Amine: Facile Cleavage of Zinc-Carbon Bond by Dihydrogen to Give Zinc Hydride Cations.

Cationic half-sandwich zinc complexes containing chelating amines [Cp*Zn(Ln)][BAr4 F] (2 a, Cp*=η3-C5Me5, Ln=N,N,N',N'-tetramethylethylenediamine, TMEDA; 2 b, Ln=N,N,N',N'-tetraethylethylenediamine, TEEDA; 2 c, Cp*=η1-C5Me5, Ln=N,N,N',N'',N''-pentamethyldiethylenetriamine, PMDTA; Ar4 F=(3,5-(CF3)2C6H3)4) reacted with dihydrogen (ca. 2 bar) in THF at 80 °C to give molecular zinc hydride cations [(Ln)ZnH(thf)m][BAr4 F] (3 a,b, m=1; 3 c, m=0) previously reported along with Cp*H. Pseudo first-order kinetics with respect to the concentration of 2 b suggests heterolytic cleavage of dihydrogen by the Zn-Cp* bond, reminiscent of σ-bond metathesis. Hydrogenolysis of the zinc cation 2 b in the presence of benzophenone gave the zinc alkoxide [(TEEDA)Zn(OCHPh2)(thf)][BAr4 F] (5 b). Cation 2 b was shown to catalytically hydrogenate N-benzylideneaniline. The PMDTA complex 2 c underwent C-H bond activation in acetonitrile to give a dinuclear µ-κC,κN-cyanomethyl zinc complex [(PMDTA)Zn(CH2CN)]2[BAr4 F]2 (6 c).

Stabilization and One Electron Reduction of a Silicon Analogue of a Carboxylic Acid Anhydride.

Reaction of the 1,2-disilylenes {(DipAr Am)Si}2 (DipAr Am=[(NDip)2 CAr]- , Dip=2,6-diisopropylphenyl, Ar=4-C6 H4 But (Ar') 1 a or Ph 1 b) and two abnormal N-heterocyclic silylenes, (DipAr Am)SiOCSi{(NDip)2 CAr} (Ar=Ar' 3 a or Ph 3 b) with N2 O led to formation of unprecedented examples of uncoordinated silicon analogues of carboxylic acid anhydrides, (DipAr Am)(O=)SiOSi(=O)(DipAr Am) (Ar=Ar' 2 a or Ph 2 b). Both compounds have been fully characterized, and the mechanism of formation of one explored using DFT calculations. Reduction of sila-acid anhydride 2 a with a dimagnesium(I) compound, [{(Mes Nacnac)Mg}2 ] (Mes Nacnac=[(MesNCMe)2 CH]- , Mes=mesityl), led to the one-electron reduction of the anhydride and formation of a magnesium complex of a sila-acid anhydride radical anion [(Mes Nacnac)Mg{(OSi(DipAr' Am)}2 O] 5. A combination of EPR spectroscopic studies and DFT calculations reveal the unpaired electron to largely reside on one of the amidinate ligands of the complex.

Synthesis and Reactivity of Discrete Europium(II) Hydride Complexes.

The bulky ß-diketiminate ligand frameworks [BDIDCHP]- and [BDIDipp/Ar]- (BDI=[HC{C(Me)2N-Dipp/Ar}2]- (Dipp=2,6-diisopropylphenyl (Dipp); Ar=2,6-dicyclohexylphyenyl (DCHP) or 2,4,6-tricyclohexylphyenyl (TCHP)) have been developed for the kinetic stabilisation of the first europium (II) hydride complexes, [(BDIDCHP)Eu(µ-H)]2, [(BDIDipp/DCHP)Eu(µ-H)]2 and [(BDIDipp/TCHP)Eu(µ-H)]2, respectively. These complexes represent the first step beyond the current lanthanide(II) hydrides that are all based on ytterbium. Tuning the steric profile of ß-diketiminate ligands from a symmetrical to unsymmetrical disposition, enhanced solubility and stability in the solution-state. This provides the first opportunity to study the structure and bonding of these novel Eu(II) hydride complexes crystallographically, spectroscopically and computationally, with their preliminary reactivity investigated.

Dihydrogen Cleavage by a Zinc-Zinc Bond of a Heteroleptic Dizinc(I) Cation.

Oxidative addition of dihydrogen across a metal-metal bond to form reactive metal hydrides in homogeneous catalysis is known for transition metals but not for zinc(I)-zinc(I) bond as found in Carmona's eponymous dizinconene [Zn2Cp*2] (Cp* = η5-C5Me5). Dihydrogen reacted with the heteroleptic zinc(I)-zinc(I) bonded cation [(L2)Zn-ZnCp*][BAr4F] (L2 = TMEDA, N,N,N',N'-tetramethylethylenediamine, TEEDA, N,N,N',N'-tetraethylethylenediamine; ArF = 3,5-(CF3)2C6H3) under 2 bar at 80 °C to give the zinc(II) hydride cation [(L2)ZnH(thf)][BAr4F] along with zinc metal and Cp*H derived from the intermediate [Cp*ZnH]. DFT calculations show that the cleavage of dihydrogen occurs through a highly unsymmetrical transition state. Mechanistic studies agree with a heterolytic cleavage of dihydrogen as a result of the cationic charge and unsymmetrical ligand coordination. To explore the existence of zinc(I) hydride, thermally unstable hydridotriphenylborate complexes of zinc(I) [(L2)Zn(HBPh3)-ZnCp*] (L2 = TMEDA, TEEDA; TMPDA, N,N,N',N'-tetramethyl-1,3-propylenediamine) have been prepared by salt metathesis and were shown to undergo fast exchange with both BPh3 and [HBPh3]-.

Panoply of P: An Array of Rhenium-Phosphorus Complexes Generated from a Transition Metal Anion.

We expand upon the synthetic utility of anionic rhenium complex Na[(BDI)ReCp] (1, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-ß-diketiminate) to generate several rhenium-phosphorus complexes. Complex 1 reacts in a metathetical manner with chlorophosphines Ph2PCl, MeNHP-Cl, and OHP-Cl to generate XL-type phosphido complexes 2, 3, and 4, respectively (MeNHP-Cl = 2-chloro-1,3-dimethyl-1,3,2-diazaphospholidine; OHP-Cl = 2-chloro-1,3,2-dioxaphospholane). Crystallographic and computational investigations of phosphido triad 2, 3, and 4 reveal that increasing the electronegativity of the phosphorus substituent (C < N < O) results in a shortening and strengthening of the rhenium-phosphorus bond. Complex 1 reacts with iminophosphane Mes*NPCl (Mes* = 2,4,6-tritert-butylphenyl) to generate linear iminophosphanyl complex 5. In the presence of a suitable halide abstraction reagent, 1 reacts with the dichlorophosphine iPr2NPCl2 to afford cationic phosphinidene complex 6+. Complex 6+ may be reduced by one electron to form 6•, a rare example of a stable, paramagnetic phosphinidene complex. Spectroscopic and structural investigations, as well as computational analyses, are employed to elucidate the influence of the phosphorus substituent on the nature of the rhenium-phosphorus bond in 2 through 6. Furthermore, we examine several common analogies employed to understand metal phosphido, phosphinidene, and iminophosphanyl complexes.

Rare-Earth Metal Complexes Bearing Electrophilic Carbon and Strongly Polarized Metallacyclopropane Moiety: Synthesis and Diverse Reactivity toward Small Molecules.

Metallacyclopropanes are highly strained and very reactive organometallics; the rare-earth metal complexes bearing both highly reactive electrophilic carbon and strongly polarized metallacyclopropanes are extremely rare. This type of rare-earth metal complexes (κ2-L)RE(η2-C2B10H10)·(THF)3 [L = 1-(2-N-C5H10NCH2CH2)-3-(2,6-iPr2C6H3N═CH)-C8H4N, RE = Lu(1a), Yb(1b), Er(1c), Y(1d), Dy(1e)] bearing the indol-2-yl electrophilic carbon and carboryne-based strongly polarized metallacyclopropanes have been synthesized. Structures of complexes 1 are further confirmed by single-crystal X-ray diffraction and DFT theoretical calculations. It is found that complexes 1 have remarkable reactivity toward different polar unsaturated small molecules, elemental sulfur, and selenium to provide different products (2-15) through the selective reactions of the RE-Ccage, and RE-C2-ind bonds with the given small molecules, respectively. The reactivities of these complexes are different from those of the reported rare-earth metallacyclopropenes and d-block metal-carborynes.

Anti-Selective Carbosilylation: Nickel-Catalyzed Multicomponent Reaction of Solid Me3SiZnI.

The stereodefined and highly substituted vinylsilanes are essential building blocks for constructing complex organic molecules. Transition metal-mediated silylmetalation of alkynes was developed to overcome the limitations of conventional hydrosilylations; however, a very limited study was carried out to utilize transient vinylmetal species in cross-coupling reactions. Moreover, they produce syn-adduct, and the anti-selective cross-coupling is still unknown and highly desired. Silylzinc reagents are highly functional group tolerant, however, their synthesis from pyrophoric silyllithium and dissolved lithium salts hampers cross-coupling reactions. Our novel solid silylzinc reagents circumvent these constraints are employed in the anti-selective synthesis of vinylsilanes via a multi-component reaction involving Me3SiZnI, terminal alkynes, and activated alkyl halides. An intensive computational and experimental investigation of the mechanism reveals an equilibrium between the intermediate syn- and anti-adducts; the greater barrier at the single electron reduction of alkyl halides and the thermodynamic stability of the Ni(III) adduct determine the anti-selectivity.

Two-Electron Redox Reactivity of Thorium Supported by Redox-Active Tripodal Frameworks.

The high stability of the + IVoxidation state limits thorium redox reactivity. Here we report the synthesis and the redox reactivity of two Th(IV) complexes supported by the arene-tethered tris(siloxide) tripodal ligands [(KOSiR2 Ar)3 -arene)]. The two-electron reduction of these Th(IV) complexes generates the doubly reduced [KTh((OSi(Ot Bu)2 Ar)3 -arene)(THF)2 ] (2OtBu ) and [K(2.2.2-cryptand)][Th((OSiPh2 Ar)3 -arene)(THF)2 ](2Ph -crypt) where the formal oxidation state of Th is +II. Structural and computational studies indicate that the reduction occurred at the arene anchor of the ligand. The robust tripodal frameworks store in the arene anchor two electrons that become available at the metal center for the two-electron reduction of a broad range of substrates (N2 O, COT, CHT, Ph2 N2 , Ph3 PS and O2 ) while retaining the ligand framework. This work shows that arene-tethered tris(siloxide) tripodal ligands allow implementation of two-electron redox chemistry at the thorium center while retaining the ligand framework unchanged.

Dinitrogen Reduction and Functionalization by a Siloxide Supported Thulium-Potassium Complex for the formation of Ammonia or Hydrazine Derivatives.

The dinitrogen (N2) chemistry of lanthanides remains less developed compared to the d-block metals and lanthanide-promoted N2 functionalization chemistry in well-defined lanthanide complexes remains elusive. Here we report the synthesis and characterization (SQUID, EPR, DFT, X-Ray) of the siloxide supported heterobimetallic (Tm/K) complexes [{KTm(OSi(OtBu)3)3}2(µ-η2:η2-N2)] (1) and [K3{Tm(OSi(OtBu)3)3}2(µ-η2:η2-N2)] (2). Complex 2 provides a rare example of a metal complex of the triply reduced N23- radical. The structure of 2 differs from the few previously reported N23- complexes as it presents two Tm and three K cations binding the N23- radical, facilitating N2 functionalization. Notably, the K3Tm2-bound N23- moiety reacts with excess H+ to form NH4Cl in 18% yield, and with MeOTf at room temperature to yield the dimethyl hydrazido complex [K2{Tm(OSi(OtBu)3)3}2(µ-(CH3)NN(CH3))] (3). Protonolysis of 3yields MeHN-NMeH·2HCl in 18 % yield.

Oxidative Addition of E-H (E=C, N) Bonds to Transient Uranium(II) Centers.

Two-electron oxidative addition is one of the most important elementary reactions for d-block transition metals but it is uncommon for f-block elements. Here, we report the first examples of intermolecular oxidative addition of E-H (E=C, N) bonds to uranium(II) centers. The transient U(II) species was formed in-situ by reducing a heterometallic cluster featuring U(IV)-Pd(0) bonds with potassium-graphite (KC8). Oxidative addition of C-H or N-H bonds to the U(II) centers was observed when this transient U(II) species was treated with benzene, carbazole or 1-adamantylamine, respectively. The U(II) centers could also react with tetracene, biphenylene or N2O, leading to the formation of arene reduced U(IV) products and uranyl(VI) species via two- or four-electron processes. This study demonstrates that the intermolecular two-electron oxidative addition reactions are viable for actinide elements.

Multielectron Redox Chemistry of Uranium by Accessing the +II Oxidation State and Enabling Reduction to a U(I) Synthon.

The synthesis of molecular uranium complexes in oxidation states lower than +3 remains a challenge despite the interest for their multielectron transfer reactivity and electronic structures. Herein, we report the one- and two-electron reduction of a U(III) complex supported by an arene-tethered tris(siloxide) tripodal ligand leading to the mono-reduced complexes, [K(THF)U((OSi(OtBu)2Ar)3-arene)(THF)] (2) and [K(2.2.2-cryptand)][U((OSi(OtBu)2Ar)3-arene)(THF)] (2-crypt), and to the di-reduced U(I) synthons, [K2(THF)3U((OSi(OtBu)2Ar)3-arene)]∞ (3) and [(K(2.2.2-cryptand))]2[U((OSi(OtBu)2Ar)3-arene)] (3-crypt). EPR and UV/vis/NIR spectroscopies, magnetic, cyclic voltammetry, and computational studies provide strong evidence that complex 2-crypt is best described as a U(II), where the U(II) is stabilized by δ-bonding interactions between the arene anchor and the uranium frontier orbitals, whereas complexes 3 and 3-crypt are best described as having a U(III) ion supported by the di-reduced arene anchor. Three quasi-reversible redox waves at E1/2 = -3.27, -2.45, and -1.71 V were identified by cyclic voltammetry studies and were assigned to the U(IV)/U(III), U(III)/U(II), and U(II)/U(III)-(arene)2- redox couples. The ability of complexes 2 and 3 in transferring two- and three-electrons, respectively, to oxidizing substrates was confirmed by the reaction of 2 with azobenzene (PhNNPh), leading to the U(IV) complex, [K(Et2O)U((OSi(OtBu)2Ar)3-arene)(PhNNPh)(THF)] (4), and of complex 3 with cycloheptatriene, yielding the U(IV) complex, [(K(Et2O)2)U((OSi(OtBu)2Ar)3-arene)(η7-C7H7)]∞ (6). These results demonstrate that the arene-tethered tris(siloxide) tripodal ligand provides an excellent platform for accessing low-valent uranium chemistry while implementing multielectron transfer pathways as shown by the reactivity of complex 3, which provides the third example of a U(I) synthon.

Heterobimetallic Hydrides with a Germanium(II)-Zinc Bond.

In the presence of TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine), zinc dihydride reacted with germanium(II) compounds (BDI-H)Ge (1) and [(BDI)Ge][B(3,5-(CF3 )2 C6 H3 )4 ] (3) (BDI-H = HC{(C=CH2 )(CMe)(NAr)2 }, BDI = [HC(CMeNAr)2 ]; Ar = 2,6-i Pr2 C6 H3 ) by formal insertion of the germanium(II) center into the Zn-H bond of polymeric [ZnH2 ]n to give neutral and cationic zincagermane with a H-Ge-Zn-H core [(BDI-H)Ge(H)-(H)Zn(tmeda)] (2) and [(BDI)Ge(H)-(H)Zn(tmeda)][B(3,5-(CF3 )2 C6 H3 )4 ] (4), respectively. Compound 2 eliminated [ZnH2 ] giving diamido germylene 1 at 60 °C. Compound 2 and deuterated analogue 2-d2 exchanged with [ZnH2 ]n and [ZnD2 ]n in the presence of TMEDA to give a mixture of 2 and 2-d2 . Compounds 2 and 4 reacted with carbon dioxide (1 bar) at room temperature to form zincagermane diformate [(BDI-H)Ge(OCHO)-(OCHO)Zn(tmeda)] (5) and formate bridged digermylene [({BDI}Ge)2 (µ-OCHO)]+ [B(C6 H3 (CF3 )2 )4 ] (6) along with zinc formate [(tmeda)Zn(µ-OCHO)3 Zn(tmeda)][B(C6 H3 (CF3 )2 )4 ] (7), respectively. The hydridic nature of the Ge-H and Zn-H bonds in 2 and 4 was probed by reactions with Brönsted and Lewis acids.

Heterometallic Clusters with Cerium-Transition-Metal Bonding Supported by Nitrogen-Phosphorus Ligands.

Ligands are known to play a crucial role in the construction of complexes with metal-metal bonds. Compared with metal-metal bonds involving d-block transition metals, knowledge of the metal-metal bonds involving f-block rare-earth metals still lags far behind. Herein, we report a series of complexes with cerium-transition-metal bonds, which are supported by two kinds of nitrogen-phosphorus ligands N[CH2CH2NHPiPr2]3 (VI) and PyNHCH2PPh2 (VII). The reactions of zerovalent group 10 metal precursors, Pd(PPh3)4 and Pt(PPh3)4, with the cerium complex supported by VI generate heterometallic clusters [N{CH2CH2NPiPr2}3Ce(µ-M)]2 (M = Pd, 2 and M = Pt, 3) featuring four Ce-M bonds; meanwhile, the bimetallic species [(PyNCH2PPh2)3Ce-M] (M = Ni, 5; M = Pd, 6; and M = Pt, 7) with a single Ce-M bond were isolated from the reactions of the cerium precursor 4 supported by VII with Ni(COD)2, Pd(PPh3)4, or Pt(PPh3)4, respectively. These complexes represent the first example of species with an RE-M bond between Ce and group 10 metals, and 2 and 3 contain the largest number of RE-M donor/acceptor interactions ever to have been observed in a molecule.

Quest for Active Species in Al/B-Catalyzed CO2 Hydrosilylation.

We demonstrate the catalytic role of aluminum and boron centers in aluminum borohydride [(2-Me2CH2C6H4)(C6H5)Al(µ-H)2B(C6H5)2] (6) during carbon dioxide (CO2) hydrosilylation. Preliminary investigations into CO2 reduction using [(2-Me2NCH2C6H4)(H)Al(µ-H)]2 (1) and [Ph3C][B(3,5-C6H3Cl2)4] (2) in the presence of Et3SiH and PhSiH3 resulted in CH2(OSiR3)2 and CH3OSiR3, which serve as formaldehyde and methanol surrogates, respectively. In pursuit of identifying the active catalytic species, three compounds, B(3,5-C6H3Cl2)3 (3), [(2-Me2NCH2C6H4)(3,5-C6H3Cl2)Al(µ-H)2B(3,5-C6H3Cl2)2] (4), and [(2-Me2NCH2C6H4)2Al(THF)][B(3,5-C6H3Cl2)4] (5), were isolated. Among compounds 2-5, the highest catalytic conversion was achieved by 4. Further, 4 and 6 were prepared in a straightforward method by treating 1 with 3 and BPh3, respectively. 6 was found to be in equilibrium with 1 and BPh3, thus making the catalytic process of 6 more efficient than that of 4. Computational investigations inferred that CO2 reduction occurs across the Al-H bond, while Si-H activation occurs through a concerted mechanism involving an in situ generated aluminum formate species and BPh3.

Coordination and Activation of N2 at Low-Valent Magnesium using a Heterobimetallic Approach: Synthesis and Reactivity of a Masked Dimagnesium Diradical.

The activation of dinitrogen (N2 ) by transition metals is central to the highly energy intensive, heterogeneous Haber-Bosch process. Considerable progress has been made towards more sustainable homogeneous activations of N2 with d- and f-block metals, though little success has been had with main group metals. Here we report that the reduction of a bulky magnesium(II) amide [(TCHP NON)Mg] (TCHP NON=4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) with 5 % w/w K/KI yields the magnesium-N2 complex [{K(TCHP NON)Mg}2 (µ-N2 )]. DFT calculations and experimental data show that the dinitrogen unit in the complex has been reduced to the N2 2- dianion, via a transient anionic magnesium(I) radical. The compound readily reductively activates CO, H2 and C2 H4 , in reactions in which it acts as a masked dimagnesium(I) diradical.