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17O-labelled tungsten siloxide complexes [WOCl2(OSitBu3)2] (1-Cl) and [WOMe2(OSitBu3)2] (1-Me) were prepared and characterized by 17O MAS NMR, with input from theoretical calculations of NMR parameters. Guidelines linking 17O NMR parameters and the coordination sphere of molecular and silica-grafted tungsten oxo species are proposed. The grafting of 1-Me on SiO2-700 afforded material 2, with surface species [(≡SiO)WOMe2(OSitBu3)] as shown by elemental analysis, IR and 1H and 13C MAS NMR. The DFT calculations of the grafting mechanism are in line with the observed reactivity. They indicate the occurrence of several isomeric species of close energy for the grafted W centers, precluding efficient 17O MAS NMR studies. The lack of catalytic activity in olefin metathesis and ring-opening olefin metathesis polymerization indicates that initiation by α-H elimination is not operative in 2, contrary to related tungsten surface species, which illustrates the crucial influence of the nature of the metal coordination sphere. [ABSTRACT FROM AUTHOR]

The DFS enhancement method as applied to 17O MAS NMR was critically assessed, first on NaPO3, a simple binary glass system, and in a second step, on a series of catalysis-related organometallic molecules and materials. The robustness of DFS was investigated for the wide range of anisotropic parameters (quadrupolar coupling and chemical shift anisotropy) encountered in these samples. Emphasis has been put on the variation of signal enhancements with respect to the DFS final sweep frequency, pulse amplitude and pulse duration, while line shape distortion issues were also addressed. Finally, the robustness of DFS enhancement of the 17O MAS NMR signal is shown through its successful application to silica-supported olefin metathesis catalysts. [ABSTRACT FROM AUTHOR]

Synthesis of cerium yldiide complexes and their reactivity with CO is demonstrated. In the case of the sulphur-tethered yldiide, the ketenyl complex is formed with release of PPh 3 , while Ph 3 PCCO is formed along with a sulfinato ligand in the case of the tosyl-substituted yldiide. Computational analysis shows that this diverging reactivity is due to the stability of the two isomers in the first step of each mechanism.

The synthesis of actinide tetrarhenate complexes completes a series of iridate, osmate, and rhenate polyhydrides, allowing for structural and bonding comparisons to be made. Computational studies examine the bonding interactions, particularly between metals, in these complexes. Several factors─including metal oxidation state, coordination number, and dispersion effects─affect metal-metal distances and covalency in these actinide tetrametallates. Related osmium and rhenium octametallic U 2 M 6 clusters are synthesized and described, and subjected to similar structural and electronic analyses.

We report the synthesis of a heterobimetallic U(III)-Ir species which reacts with CS 2 to form the novel ethanetetrathiolate fragment via hydride insertion and C-C coupling. Computational studies suggest the formation of a radical intermediate, which may couple with another equivalent to form the final product.

Supported metal single atom catalysis is a dynamic research area in catalysis science combining the advantages of homogeneous and heterogeneous catalysis. Understanding the interactions between metal single atoms and the support constitutes a challenge facing the development of such catalysts, since these interactions are essential in optimizing the catalytic performance. For conventional carbon supports, two types of surfaces can contribute to single atom stabilization: the basal planes and the prismatic surface; both of which can be decorated by defects and surface oxygen groups. To date, most studies on carbon-supported single atom catalysts focused on nitrogen-doped carbons, which, unlike classic carbon materials, have a fairly well-defined chemical environment. Herein we report the synthesis, characterization and modeling of rhodium single atom catalysts supported on carbon materials presenting distinct concentrations of surface oxygen groups and basal/prismatic surface area. The influence of these parameters on the speciation of the Rh species, their coordination and ultimately on their catalytic performance in hydrogenation and hydroformylation reactions is analyzed. The results obtained show that catalysis itself is an interesting tool for the fine characterization of these materials, for which the detection of small quantities of metal clusters remains a challenge, even when combining several cutting-edge analytical methods., (© 2024 Wiley-VCH GmbH.)

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 (KC 8 ). 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 N 2 O, 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., (© 2024 Wiley-VCH GmbH.)

A novel Ta/Os heterobimetallic complex, [Ta(CH 2 t Bu) 3 (μ-H) 3 OsCp*], 2, is prepared by protonolysis of Ta(CH t Bu)(CH 2 t Bu) 3 with Cp*OsH 5 . Treatment of 2 and its iridium analogue [Ta(CH 2 t Bu) 3 (μ-H) 2 IrCp*], 1, with CO 2 under mild conditions reveal the efficient cleavage of CO 2 , driven by the formation of a tantalum oxo species in conjunction with CO transfer to the osmium or iridium fragments, to form Cp*Ir(CO)H 2 and Cp*Os(CO)H 3 , respectively. This bimetallic reactivity diverges from more classical CO 2 insertion into metal-X (X = metal, hydride, alkyl) bonds.

Polynuclear metal hydride clusters play important roles in various catalytic processes, with most of the reported polynuclear metal hydride clusters adopting a polyhedral three-dimensional structure. Herein, we report the first example of a planar tetranuclear uranium hydride cluster [(CpCMe 2 CMe 2 Cp)U] 4 (μ 2 -H) 4 (μ 3 -H) 4 (U 4 H 8 ). It was synthesized by reacting an ansa-bis(cyclopentadienyl) ligand-supported uranium chloride precursor [(CpCMe 2 CMe 2 Cp)U] 3 (μ 2 -Cl) 3 (μ 3 -Cl) 2 with NaHBEt 3 . The presence of hydrides in U 4 H 8 was confirmed by NMR spectroscopy and its reactivity with phenol and carbon tetrachloride. DFT calculations also facilitated the determination of the hydrides' positions in U 4 H 8 , featuring four bridging μ 2 -H ligands and four face-capping μ 3 -H ligands, with the four U centers arranged in a rhombic geometry. The U 4 H 8 represents not only the first example of planar polynuclear actinide metal hydride cluster but also the uranium hydride cluster with the highest nuclearity reported to date., (© 2024 Wiley-VCH GmbH.)

A salt metathesis synthetic strategy is used to access rare tantalum/coinage metal (Cu, Ag, Au) heterobimetallic complexes. Specifically, complex [Li(THF) 2 ][Ta(C t Bu)(CH 2 t Bu) 3 ], 1 , reacts with (IPr)MCl (M = Cu, Ag, Au, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) to afford the alkylidyne-bridged species [Ta(CH 2 t Bu) 3 (μ-C t Bu)M(IPr)] 2-M . Interestingly, π-bonding of group 11 metals to the Ta─C moiety promotes a rare alkylidyne alkyl to bis-alkylidene tautomerism, in which compounds 2-M are in equilibrium with [Ta(CH t Bu)(CH 2 t Bu) 2 (μ-CH t Bu)M(IPr)] 3-M . This equilibrium was studied in detail using NMR spectroscopy and computational studies. This reveals that the equilibrium position is strongly dependent on the nature of the coinage metal going down the group 11 triad, thus offering a new valuable avenue for controlling this phenomenon. Furthermore, we show that these uncommon bimetallic couples could open attractive opportunities for synergistic reactivity. We notably report an uncommon deoxygenative carbyne transfer to CO 2 resulting in rare examples of coinage metal ketenyl species, ( t BuCCO)M(IPr), 4-M (M = Cu, Ag, Au). In the case of the Ta/Li analogue 1 , the bis(alkylidene) tautomer is not detected, and the reaction with CO 2 does not cleanly yield ketenyl species, which highlights the pivotal role played by the coinage metal partner in controlling these unconventional reactions.

Transition metal multimetallic complexes have seen intense study due to their unique bonding and potential for cooperative reactivity, but actinide-transition metal (An-TM) species are far less understood. We have synthesized uranium- and thorium-osmium heterometallic polyhydride complexes in order to study An-Os bonding and investigate the reactivity of An-Os interactions. Computational studies suggest the presence of a significant bonding interaction between the actinide center and the four coordinated osmium centers supported by bridging hydrides. Upon photolysis, these complexes undergo intramolecular C-H activation with the formation of an Os-Os bond, while the thorium complex may activate an additional C-H bond of the benzene solvent, resulting in a μ-η 1 ,η 1 phenyl ligand across one Th-Os interaction., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Dinitrogen cleavage provides an attractive but poorly studied route to the assembly of multimetallic nitride clusters. Here, we show that the monoelectron reduction of the dinitrogen complex [{U(OC 6 H 2 -Bu t 3 -2,4,6) 3 } 2 (μ-η 2 :η 2 -N 2 )], 1 , allows us to generate, for the first time, a uranium complex presenting a rare triply reduced N 2 moiety ((μ-η 2 :η 2 -N 2 ) •3- ). Importantly, the bound dinitrogen can be further reduced, affording the U 4 N 4 cubane cluster, 3 , and the U 6 N 6 edge-shared cubane cluster, 4 , thus showing that (N 2 ) •3- can be an intermediate in nitride formation. The tetranitride cluster showed high reactivity with electrophiles, yielding ammonia quantitatively upon acid addition and promoting CO cleavage to yield quantitative conversion of nitride into cyanide. These results show that dinitrogen reduction provides a versatile route for the assembly of large highly reactive nitride clusters, with U 6 N 6 providing the first example of a molecular nitride of any metal formed from a complete cleavage of three N 2 molecules.

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO) 2 Mn(N 2 )] (1, Cp=η 5 -cyclopentadienyl, C 5 H 5 ) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N 2 )MnCOPh]Li (3) that is stable only below -40 °C. Full characterization of 3 (including single crystal X-ray diffraction) was performed. This complex decomposes quickly above -20 °C with N 2 loss to give a phenylate complex [Cp(CO) 2 MnPh]Li (2). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO) 2 MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so-far unique behavior of the N 2 ligand in 1. DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal-coordinated N 2 remains to be demonstrated., (© 2023 Wiley-VCH GmbH.)

This work reports the synthesis, characterization, and reactivity of the first example of a well-defined zinc α-diazoalkyl complex. Treatment of zinc(I)-zinc(I) bonded compound L 2 Zn 2 [L=CH 3 C(2,6- i Pr 2 C 6 H 3 N)CHC(CH 3 )(NCH 2 CH 2 PPh 2 )] or zinc(II) hydride LZnH with trimethylsilyldiazomethane affords zinc diazoalkyl complex LZnC(N 2 )SiMe 3 . This complex liberates N 2 in the presence of a nickel catalyst to form an α-zincated phosphorus ylide by reacting with the pendant phosphine. It selectively undergoes formal [3+2] cycloaddition with CO 2 or CO to form the corresponding product with a five-membered heterocyclic core. Notably, the use of CO in such a [3+2] cycloaddition reaction is unprecedented, reflecting a novel CO reaction mode., (© 2023 Wiley-VCH Verlag GmbH.)

A guanidinato-stabilized binuclear yttrium carbyne complex [(PhCH 2 ) 2 NC(NC 6 H 3 i Pr 2 -2,6) 2 ] 2 Y 2 (μ 2 -Me)(AlMe 3 ) 2 (μ 4 -CH) (1) was synthesized via C-H bond activation and its versatile reactivities were investigated. Complex 1 underwent σ-bond metathesis with PhSSPh and nucleophilic addition with PhCN to form the corresponding yttrium thiolate complex 3 and aza-allyl complex 4 respectively. Additionally, the rare yttrium carbide complex 5 was also prepared by treatment of complex 1 with S 8 . Interestingly, in the reaction with PhNCS, the C[double bond, length as m-dash]S double bond was cleaved, followed by C-H bond activation to give the yttrium sulfide complex 7 with a ketenimine dianion ligand. Unexpectedly, the reaction of complex 1 with CO (1 atm) resulted in deoxygenative coupling of CO, to afford mono- or dioxo-yttrium complexes at different temperatures. The mechanism of the possible formation processes of complexes 3 and 9 was elucidated by DFT calculations., Competing Interests: The authors declare no conflict of interest., (This journal is © The Royal Society of Chemistry.)

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH 2 (NR 3 ){N(SiMe 3 ) 2 }] (NR 3 =NMe 3 or N-methylpiperidine (NMP)), with β-diketiminato dimagnesium(I) reagents, [{( Ar Nacnac)Mg} 2 ] ( Ar Nacnac=[HC(MeCNAr) 2 ] - , Ar=mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al 6 H 8 (NR 3 ) 2 {Mg( Ar Nacnac)} 4 ], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al 6 cores, having zero-valent Al axial sites and mono-valent AlH 2 - equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg-Al bonded magnesio-aluminate complexes, [( Ar Nacnac)(Me 3 N)Mg-Al(μ-H) 3 [{Mg( Ar Nacnac)} 2 (μ-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al 6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

17 O-labelled tungsten siloxide complexes [WOCl 2 (OSi t Bu 3 ) 2 ] (1-Cl) and [WOMe 2 (OSi t Bu 3 ) 2 ] (1-Me) were prepared and characterized by 17 O MAS NMR, with input from theoretical calculations of NMR parameters. Guidelines linking 17 O NMR parameters and the coordination sphere of molecular and silica-grafted tungsten oxo species are proposed. The grafting of 1-Me on SiO 2-700 afforded material 2, with surface species [(SiO)WOMe 2 (OSi t Bu 3 )] as shown by elemental analysis, IR and 1 H and 13 C MAS NMR. The DFT calculations of the grafting mechanism are in line with the observed reactivity. They indicate the occurrence of several isomeric species of close energy for the grafted W centers, precluding efficient 17 O MAS NMR studies. The lack of catalytic activity in olefin metathesis and ring-opening olefin metathesis polymerization indicates that initiation by α-H elimination is not operative in 2, contrary to related tungsten surface species, which illustrates the crucial influence of the nature of the metal coordination sphere.

The synthesis, characterization, and solid-state structure of bulky alkoxy- and aryloxy-supported yttrium polynuclear hydrides are reported. Hydrogenolysis of the supertrityl alkoxy anchored yttrium dialkyl, Y(OTr*)(CH 2 SiMe 3 ) 2 (THF) 2 ( 1 ) (Tr* = tris(3,5-di- tert -butylphenyl)methyl), resulted in the clean conversion to the tetranuclear dihydride, [Y(OTr*)H 2 (THF)] 4 ( 1a ). X-ray analysis revealed a highly symmetrical structure ( 4 ̅ site symmetry) with the four Y atoms located on the corners of a compressed tetrahedron, each bonded to an OTr* and tetrahydrofuran (THF) ligand and the cluster held together by four face-capping, μ 3 -H, and four edge-bridging, μ 2 -H, hydrides. DFT calculations on the full system with and without THF, but also on model systems, clearly show that the structural preference for complex 1a is controlled by the presence and coordination of THF molecules. Contrary to the exclusive formation of the tetranuclear dihydride, hydrogenolysis of the bulky aryloxy yttrium dialkyl, Y(OAr*)(CH 2 SiMe 3 ) 2 (THF) 2 ( 2 ) (Ar* = 3,5-di- tert -butylphenyl) gave a mixture of the analogous tetranuclear 2a and trinuclear, [Y 3 (OAr*) 4 H 5 (THF) 4 ], polyhydride, 2b . Similar results, i.e., a mixture of tetra-/tri-nuclear products, were obtained from hydrogenolysis of the even bulkier Y(OAr Ad2,Me )(CH 2 SiMe 3 ) 2 (THF) 2 compound. Experimental conditions were established to optimize the production of either the tetra- or trinuclear products. X-ray structure of 2b revealed a triangular array of three yttrium atoms with two face-capping μ 3 -H and three edge-bridging μ 2 -H hydrides, with one yttrium bonded to two aryloxy ligands while the other two have a complement of one aryloxy and two THF ligands; the solid-state structure is close to being C 2 symmetric, with the C 2 axis running through the unique Y and unique μ 2 -H hydride. As opposed to 2a , which shows distinct 1 H NMR resonances for μ 3 / μ 2 -H (δ = 5.83/6.35 ppm, respectively), no hydride signals for 2b were observed at room temperature, indicating hydride exchange on the NMR time scale. Their presence and assignment were secured at -40 °C from 1 H SST (spin saturation) experiment.

The palladium-catalyzed annulation reaction of alkynes enables an attractive approach to siloles. Their access from silirenes and terminal alkynes proved rather general, involving reactive intermediates that have remained elusive to date. Starting from 1,2-bis(3-thienyl)silirene as a source of photochromic siloles, the mechanism of the annulation reaction has been revisited, and palladasilacyclobutenes resulting from the activation of the silirene could be isolated and thoroughly characterized (NMR, X-ray, and DFT). Their role as reactive intermediates and their fate in the course of the reaction were also studied in situ. In combination with in-depth DFT calculations, a clearer picture of the mechanism and the reactive key species is disclosed.

The conversion of C1 feedstock molecules such as CO into commodity chemicals is a desirable, but challenging, endeavour. When the U(iii) complex, [(C 5 Me 5 ) 2 U(O-2,6- t Bu 2 -4-MeC 6 H 2 )], is exposed to 1 atm of CO, only coordination is observed by IR spectroscopy as well as X-ray crystallography, unveiling a rare structurally characterized f element carbonyl. However, using [(C 5 Me 5 ) 2 (MesO)U (THF)], Mes = 2,4,6-Me 3 C 6 H 2 , reaction with CO forms the bridging ethynediolate species, [{(C 5 Me 5 ) 2 (MesO)U} 2 (μ 2 -OCCO)]. While ethynediolate complexes are known, their reactivity has not been reported in much detail to afford further functionalization. For example, addition of more CO to the ethynediolate complex with heating forms a ketene carboxylate, [{(C 5 Me 5 ) 2 (MesO)U} 2 ( μ 2 : κ 2 : η 1 -C 3 O 3 )], which can be further reacted with CO 2 to yield a ketene dicarboxylate complex, [{(C 5 Me 5 ) 2 (MesO)U} 2 ( μ 2 : κ 2 : κ 2 -C 4 O 5 )]. Since the ethynediolate showed reactivity with more CO, we explored its reactivity further. A [2 + 2] cycloaddition is observed with diphenylketene to yield [{(C 5 Me 5 ) 2 U} 2 (OC(CPh 2 )C([double bond, length as m-dash]O)CO)] with concomitant formation of [(C 5 Me 5 ) 2 U(OMes) 2 ]. Surprisingly, reaction with SO 2 shows rare S-O bond cleavage to yield the unusual [(O 2 CC(O)(SO)] 2- bridging ligand between two U(iv) centres. All complexes have been characterized using spectroscopic and structural methods, and the reaction of the ethynediolate with CO to form the ketene carboxylate has been investigated computationally as well as the reaction with SO 2 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Reaction of the potassium pentamethylcyclopentadienyl iridate tris-hydride K[IrCp*H 3 ] with UCl 4 and ThCl 4 (DME) 2 led to the complete replacement of the halide ligands to generate multimetallic complexes U{(μ-H) 3 IrCp*} 4 (1) and Th{[(μ-H 2 )(H)IrCp*] 2 [(μ-H) 3 IrCp*] 2 } (2), respectively. These analogues feature a significant discrepancy in hydride bonding modes; 1 contains twelve bridging hydrides while 2 contains ten bridging hydrides and two terminal, Ir-bound hydrides. Use of a U(iii) starting material, UI 3 (1,4-dioxane) 1.5 , resulted in the octanuclear complex {U[(μ 2 -H 3 )IrCp*] 2 [(μ 3 -H 2 )IrCp*]} 2 (3). Computational studies indicate significant bonding character between U/Th and Ir in 1 and 2, with f-orbital involvement in the singly-occupied molecular orbitals of the uranium species 1. In addition, these studies attribute the variation in hydride bonding between 1 and 2 to differences in dispersion effects., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The search for new ligands capable of modifying the metal nanoparticle (MNP) catalytic behavior is of increasing interest. Herein we present the first example of RuNPs stabilized with non-planar heptagon-containing saddle-shaped nanographenes (Ru@1 and Ru@2). The resemblance to graphene-supported MNPs makes these non-planar nanographene-stabilized RuNPs very attractive systems to further investigate graphene-metal interactions. A combined theoretical/experimental study allowed us to explore the coordination modes and dynamics of these nanographenes at the Ru surface. The curvature of these saddle-shaped nanographenes makes them efficient MNP stabilizers. The resulting RuNPs were found to be highly active catalysts for the hydrogenation of aromatics, including platform molecules derived from biomass ( i.e. HMF) or liquid organic hydrogen carriers ( i.e. N -indole). A significant ligand effect was observed since a minor modification on the hept-HBC structure (C[double bond, length as m-dash]CH 2 instead of C[double bond, length as m-dash]O) was reflected in a substantial increase in the MNP activity. Finally, the stability of these canopied RuNPs was investigated by multiple addition experiments, proving to be stable catalysts for at least 96 h., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The synthesis of metallic nanoparticles (MNP) with high surface area and controlled shape is of paramount importance to increase their catalytic performance. The detailed growing process of NP is mostly unknown and understanding the specific steps would pave the way for a rational synthesis of the desired MNP. Here we take advantage of the stabilization properties exerted by the tetragonal prismatic supramolecular nanocapsule 8·(BArF) 8 to develop a synthetic methodology for sub-nanometric RuNP (0.6-0.7 nm). The catalytic properties of these sub-nanometric nanoparticles were tested on the hydrogenation of styrene, obtaining excellent selectivity for the hydrogenation of the alkene moiety. In addition, the encapsulation of [Ru 5 ] clusters inside the nanocapsule is strikingly observed in most of the experimental conditions, as ascertained by HR-MS. Moreover, a thorough DFT study enlightens the nature of the [Ru 5 ] clusters as tb-Ru 5 H 2 (η 6 -PhH) 2 (η 6 -pyz) 3 (2) trapped by two arene moieties of the clip, or as tb-Ru 5 H 2 (η 1 -pyz) 6 (η 6 -pyz) 3 (3) trapped between the two Zn-porphyrin units of the nanocapsule. Both options fulfill the Wade-Mingos counting rules, i.e. 72 CVEs for the closo tb. The trapped [Ru 5 ] metallic clusters are proposed to be the first-grown seeds of subsequent formation of the subnanometric RuNP. Moreover, the double role of the nanocapsule in stabilising ∼0.7 nm NPs and also in hosting ultra-small Ru clusters, is unprecedented and may pave the way towards the synthesis of ultra-small metallic clusters for catalytic purposes.

This work provides a facile access to a series of triangular [Zn 2 M] (M = group 10 and 11 metals) clusters. Treatment of Zn-Zn-bonded compounds [ L Zn-Zn L ] ( L = CH 3 C(2,6- i Pr 2 C 6 H 3 N)CHC(CH 3 )(NCH 2 CH 2 PR 2 ); R = Ph, i Pr) with zero-valent transition-metal reagents selectively afforded the corresponding triangular clusters [Zn 2 M], where M = Ni(0), Pd(0), and Pt(0). Notably, the isoelectronic triangular clusters [Zn 2 M] + , where M = Ag(I) and Cu(I), could also be obtained by reactions of [LZn-ZnL] with AgOTf and CuOTf, respectively. The [Zn 2 Ag] + complex containing elusive Zn-Ag bonds was investigated by density functional theory analysis, showing a 3c-2e bonding feature in the metallic ring. The electrochemical behaviors of [Zn 2 M] complexes were examined and revealed the donation of electron density from the Zn-Zn σ-bond to the metal centers. Reaction of the [Zn 2 Ni] complex with isocyanide gave heterometallic species by coordination of isocyanide to the nickel center, keeping the trimetallic ring core structure intact. In contrast, the Zn-Zn bond was rapidly cleaved upon treatment of the [Zn 2 Ni] complex with dihydrogen or phenyl acetylene, generating the hydride- or acetylide-bridged heterotrimetallic complex.

We report an original alkane elimination approach, entailing the protonolysis of triisobutylaluminum by the acidic hydrides from Cp*IrH 4 . This strategy allows access to a series of well-defined tri- and tetranuclear iridium aluminum polyhydride clusters, depending on the stoichiometry: [Cp*IrH 3 Al( i Bu) 2 ] 2 ( 1 ), [Cp*IrH 2 Al( i Bu)] 2 ( 2 ), [(Cp*IrH 3 ) 2 Al( i Bu)] ( 3 ), and [(Cp*IrH 3 ) 3 Al] ( 4 ). Contrary to most transition-metal aluminohydride complexes, which can be considered as [AlH x +3 ] x- aluminates and LnM + moieties, the situation here is reversed: These complexes have original structures that are best described as [Cp*IrH x ] n - iridate units surrounding cationic Al(III) fragments. This is corroborated by reactivity studies, which show that the hydrides are always retained at the iridium sites and that the [Cp*IrH 3 ] - moieties are labile and can be transmetalated to yield potassium ([KIrCp*H 3 ], 8 ) or silver (([AgIrCp*H 3 ] n , 10 ) derivatives of potential synthetic interest. DFT calculations show that the bonding situation can vary in these systems, from 3-center 2-electron hydride-bridged Lewis adducts of the form Ir-H⇀Al to direct polarized metal-metal interaction from donation of d -electrons of Ir to the Al metal, and both types of interactions take place to some extent in each of these clusters.

Breslow intermediates are very often elusive species whose application in frustrated Lewis pair (FLP) chemistry is unprecedented. Described herein is the use of a masked form of an O-borylated Breslow (OBB) intermediate that performs FLP-type activation of the carbonyl function of five different benzaldehyde derivatives with complete diastereoselectivity. The resulting compounds are characterised in solution by NMR spectroscopy (compounds 4-8) and in solid state by X-ray diffraction analysis (compounds 4-6). A combined kinetic and theoretical investigation reveals the associative nature of the rate determining step and suggests that the OBB intermediate part is never released during the whole process., (© 2021 Wiley-VCH GmbH.)

The direct access to (mesityl)(alkyl)haloboranes (Mes(Alk)BX) (X = Br, Cl) from mesitylborane dimer and vinyl halides is presented. The involved hydroboration reaction results in the transfer of the halogen atom from the carbon of the starting material to the boron in the final product. The reactivity of the obtained Mes(Alk)BX has been evaluated for the synthesis of the bipyridyl boronium cations and 2-arylpyridine derived boron N^C-chelates. The formation mechanism of Mes(Alk)BX is apprended by DFT-calculations which shows that their formation involves two concomitant pathways derived from the regioslectivity of the hydroboration reaction.

This work reports the first catalyzed synthesis of d-block metal-metal bonded complexes. The treatment of terminal zinc hydrides [LZnH] [L = CH 3 C(2,6- i Pr 2 C 6 H 3 N)CHC(CH 3 )(N(CH 2 ) n CH 2 PR 2 ); n = 1, 2; R = Ph, i Pr] in the presence of 5 mol% Ni(CO) 2 (PPh 3 ) 2 afforded Zn(I)-Zn(I) bonded compounds [L 2 Zn 2 ] in high isolated yields with concomitant elimination of dihydrogen. Stoichiometric reactions, kinetic studies and DFT calculations were conducted to elucidate the reaction mechanism.

Two-electron reduction of the amidate-supported U(III) mono(arene) complex U(TDA) 3 ( 2 ) with KC 8 yields the anionic bis(arene) complex [K[2.2.2]cryptand][U(TDA) 2 ] ( 3 ) (TDA = N -(2,6-di-isopropylphenyl)pivalamido). EPR spectroscopy, magnetic susceptibility measurements, and calculations using DFT as well as multireference CASSCF methods all provide strong evidence that the electronic structure of 3 is best represented as a 5f 4 U(II) metal center bound to a monoreduced arene ligand. Reactivity studies show 3 reacts as a U(I) synthon by behaving as a two-electron reductant toward I 2 to form the dinuclear U(III)-U(III) triiodide species [K[2.2.2]cryptand][(UI(TDA) 2 ) 2 (μ-I)] ( 6 ) and as a three-electron reductant toward cycloheptatriene (CHT) to form the U(IV) complex [K[2.2.2]cryptand][U(η 7 -C 7 H 7 )(TDA) 2 (THF)] ( 7 ). The reaction of 3 with cyclooctatetraene (COT) generates a mixture of the U(III) anion [K[2.2.2]cryptand][U(TDA) 4 ] ( 1-crypt ) and U(COT) 2 , while the addition of COT to complex 2 instead yields the dinuclear U(IV)-U(IV) inverse sandwich complex [U(TDA) 3 ] 2 (μ-η 8 :η 3 -C 8 H 8 ) ( 8 ). Two-electron reduction of the homoleptic Th(IV) amidate complex Th(TDA) 4 ( 4 ) with KC 8 gives the mono(arene) complex [K[2.2.2]cryptand][Th(TDA) 3 (THF)] ( 5 ). The C-C bond lengths and torsion angles in the bound arene of 5 suggest a direduced arene bound to a Th(IV) metal center; this conclusion is supported by DFT calculations.

Hydrogenolysis of the half-sandwich penta-arylcycopentadienyl-supported rare-earth metal dibenzyl complexes [(Cp Ar5 )Ln(p-CH 2 -C 6 H 4 -Me) 2 (THF)] (Cp Ar5 = C 5 Ar 5 , Ar = 3,5- i Pr 2 -C 6 H 3 ; Ln = Sc, La) afforded a bimetallic scandium complex [(Cp Ar5 )Sc(H)(μ-OC 4 H 9 )] 2 (2) with two terminal hydrido ligands, and a double-sandwich bimetallic lanthanum hydride complex [(Cp Ar5 )La(μ-H)] 2 (4) bearing the reduced Cp Ar5 ligand. DFT calculations were conducted to elucidate the reaction profiles.

An efficient tandem hydrosilylation of CO2, which uses a combination of a simple, homoleptic lanthanum aryloxide and B(C6F5)3, was performed. Use of a less sterically hindered silane led to an exclusive reduction of CO2 to CH4, with a turnover frequency of up to 6000 h-1 at room temperature. The catalytic system is robust, and 19 400 turnovers could be achieved with 0.005 mol% loading of lanthanum. The reaction outcome depended highly on the nature of the silane reductant used. Selective production of the formaldehyde equivalent, i.e., bis(silyl)acetal, without over-reduction, was observed when a sterically bulky silane was used. The reaction mechanism was elucidated by stoichiometric reactions and DFT calculations.

We have prepared and characterized a series of unprecedented group 6-group 11, N 2 -bridged, heterobimetallic [ML 4 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )Au(NHC)] + complexes (M = Mo, W, L 2 = diphosphine) by treatment of trans -[ML 4 (N 2 ) 2 ] with a cationic gold(I) complex [Au(NHC)] + . The adducts are very labile in solution and in the solid, especially in the case of molybdenum, and decomposition pathways are likely initiated by electron transfers from the zerovalent group 6 atom to gold. Spectroscopic and structural parameters point to the fact that the gold adducts are very similar to Lewis pairs formed out of strong main-group Lewis acids (LA) and low-valent, end-on dinitrogen complexes, with a bent M-N-N-Au motif. To verify how far the analogy goes, we computed the electronic structures of [W(depe) 2 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )AuNHC] + ( 10 W + ) and [W(depe) 2 (η 1 -N 2 )(μ-η 1 :η 1 -N 2 )B(C 6 F 5 ) 3 ] ( 11 W ). A careful analysis of the frontier orbitals of both compounds shows that a filled orbital resulting from the combination of the π* orbital of the bridging N 2 with a d orbital of the group 6 metal overlaps in 10 W + with an empty sd hybrid orbital at gold, whereas in 11 W with an sp 3 hybrid orbital at boron. The bent N-N-LA arrangement maximizes these interactions, providing a similar level of N 2 "push-pull" activation in the two compounds. In the gold case, the HOMO-2 orbital is further delocalized to the empty carbenic p orbital, and an NBO analysis suggests an important electrostatic component in the μ-N 2 -[Au(NHC)] + bond.

Formation of stable carbides during CO bond dissociation on small ruthenium nanoparticles (RuNPs) is demonstrated, both by means of DFT calculations and by solid state 13 C NMR techniques. Theoretical calculations of chemical shifts in several model clusters are employed in order to secure experimental spectroscopic assignations for surface ruthenium carbides. Mechanistic DFT investigations, carried out on a realistic Ru 55 nanoparticle model (∼1 nm) in terms of size, structure and surface composition, reveal that ruthenium carbides are obtained during CO hydrogenation. Calculations also indicate that carbide formation via hydrogen-assisted hydroxymethylidyne (COH) pathways is exothermic and occurs at reasonable kinetic cost on standard sites of the RuNPs, such as 4-fold ones on flat terraces, and not only in steps as previously suggested. Another novel outcome of the DFT mechanistic study consists of the possible formation of μ 6 ruthenium carbides in the tip-B 5 site, similar examples being known only for molecular ruthenium clusters. Moreover, based on DFT energies, the possible rearrangement of the surface metal atoms around the same tip-site results in a μ-Ru atom coordinated to the remaining RuNP moiety, reminiscent of a pseudo-octahedral metal center on the NP surface.

Main-group metal calcium-mediated alkylpyridine benzylic C(sp 3 )-H activation and functionalization have been achieved. The reaction of a calcium hydride complex [{( DIPP nacnac)CaH(thf)} 2 ] ( DIPP nacnac = CH{(CMe)(2,6- i Pr 2 -C 6 H 3 N)} 2 ) with two equivalents of 2,6-lutidine rapidly yields a monomeric calcium alkyl complex with the release of dihydrogen. A hydride/carbon-bridged binuclear calcium complex [{( DIPP nacnac)Ca} 2 (μ-H){2-Me-6-(μ-CH 2 )-Py}(thf)] is obtained from an equimolar treatment of calcium hydride and 2,6-lutidine that is readily converted into mono- or binuclear calcium alkyl complexes upon subsequent addition of 2,6-lutidine. DFT calculations and kinetic studies are conducted to determine their reaction profiles. More significantly, this calcium hydride complex catalyzes regioselective benzylic C-H bond addition of alkylpyridines to a variety of alkenes, affording linear or branched alkylated pyridine derivatives.

The iridium tetrahydride complex Cp*IrH 4 reacts with a range of isobutylaluminum derivatives of general formula Al( i Bu) x (OAr) 3- x ( x = 1, 2) to give the unusual iridium aluminum species [Cp*IrH 3 Al( i Bu)(OAr)] ( 1 ) via a reductive elimination route. The Lewis acidity of the Al atom in complex 1 is confirmed by the coordination of pyridine, leading to the adduct [Cp*IrH 3 Al( i Bu)(OAr)(Py)] ( 2 ). Spectroscopic, crystallographic, and computational data support the description of these heterobimetallic complexes 1 and 2 as featuring strongly polarized Al(III) δ+ -Ir(III) δ- interactions. Reactivity studies demonstrate that the binding of a Lewis base to Al does not quench the reactivity of the Ir-Al motif and that both species 1 and 2 promote the cooperative reductive cleavage of a range of heteroallenes. Specifically, complex 2 promotes the decarbonylation of CO 2 and AdNCO, leading to CO (trapped as Cp*IrH 2 (CO)) and the alkylaluminum oxo ([( i Bu)(OAr)Al(Py)] 2 (μ-O) ( 3 )) and ureate ({Al(OAr)( i Bu)[κ 2 -(N,O)AdNC(O)NHAd]} ( 4 )) species, respectively. The bridged amidinate species Cp*IrH 2 (μ-CyNC(H)NCy)Al( i Bu)(OAr) ( 5 ) is formed in the reaction of 2 with dicyclohexylcarbodiimine. Mechanistic investigations via DFT support cooperative heterobimetallic bond activation processes.

A rare heterobimetallic oxidative addition of X-H (X = C, O) bonds is reported. DFT suggests that steric constraints around the bimetallic core play a critical role to synergistically activate C-H bonds across the two metals and thus explains the exceptional H/D exchange catalytic activity of unhindered surface organometallic Ta/Ir species observed experimentally.

The reduction of U(VI) to U(IV) is rare, especially in one step, and not observed electrochemically as a one-wave, two-electron couple. Here, we demonstrate that reduction of the uranium(VI) bis(imido) complex, (C 5 Me 5 ) 2 U[═N(4-O i PrC 6 H 4 )] 2 , is readily accomplished with Al(C 5 Me 5 ), forming the bridging uranium(IV)/aluminum(III) imido complex (C 5 Me 5 ) 2 U[μ 2 -N(4-O i PrC 6 H 4 )] 2 Al(C 5 Me 5 ). The structure and bonding of the bridging imido complex is examined with electrochemical measurements in tandem with density functional theory calculations.