Organometallics最新文献

An osmaborane featuring a planar [B₄H₈]^2– ring has been synthesized and structurallycharacterized.Prolonged thermolysis of the intermediate generated from the reactionof [Os(PPh₃)₃Cl₂] (1) with dppf [dppf = 1,1′-Bis(diphenylphosphino) ferrocene]in the presence of excess [BH₃·THF] afforded [Os(dppf)H₂(η⁴–B₄H₈)] (2) along with [H(dppf)OsB₅H₁₀] (3) and [{HOs(dppf)}₂(μ-H)B₄H₇] (4). Complex 2 contains a planar[B₄H₈]^2– ring and is an osmiumanalog of pentaborane(9). Complex 3 is the osmium analogof hexaborane(10). On the other hand, complex 4 adoptsa nido monocapped square pyramidal geometry whichis structurally analogous to [{HOs(PPh₃)₂}₂(μ-H)B₄H₇] (5), obtainedfrom the prolonged thermolysis of [Os(PPh₃)₃Cl₂] (1) with excess of [BH₃·THF]alongside the earlier reported [Os(PPh₃)₂H₂(η⁴–B₄H₈)] (I) and [H(PPh₃)₂OsB₅H₁₀] (II). Surprisingly, no analogous productswere obtained using dppm [dppm = 1,2-bis(diphenylphosphino)methane]and dppe [dppe = 1,2-bis(diphenylphosphino)ethane]. All synthesizedmolecules were characterized through multinuclear NMR and IR spectroscopyand mass spectrometry. Single-crystal X-ray diffraction analyses ofclusters 2 and 5 established their solid-statestructures, while theoretical investigations elucidated the bondingin 2. In addition, comparative electrochemical studiesof 2 and I were carried out to examine electroniccommunication and to assess the influence of the redox-active dppfligand on the electronic properties of the complex.

Reaction of 2 equiv of Bestmann’s ylide, Ph₃PCCO,with the Th(IV) metallacycle, [Th{N(R)(SiMe₂CH₂)}(NR₂)₂] (R= SiMe₃), results in formation of [Th{N(R)(SiMe₂CHC(C(H)PPh₃)O}(NR₂)₂(OCCPPh₃)] (1). The first equivalent of phosphoranylideneketene insertsinto the Th–C bond, which is accompanied by a 1,3-H shift toform an η³-oxy-allyl fragment. The second equivalentof Ph₃PCCO coordinates to the metal center in a κ-Ofashion. Reaction of [AnCl(NR₂)₃] (An = U, Th)with 1 equiv of Ph₃PCCO results in the formation of [AnCl(NR₂)₃(OCCPPh₃)] (An =U, 2; Th, 3) in good yields. In both cases,the phosphoranylideneketene coordinates to the metal center in a κ-Ofashion. Complexes 1, 2, and 3 were characterized by NMR and IR spectroscopies and X-ray crystallography.They represent the first reported actinide phosphoranylideneketenecomplexes.

The synthesis of iridium and ruthenium complexes bearinga uracil-derivedN-heterocyclic carbene (NHC) ligand is reported herein, and theirapplication for the reduction of NAD+ is described. The synthesisemploys two different synthetic pathways, yielding both abnormal andnormal NHC complexes, with iridium demonstrating a strong preferencefor the abnormal coordination mode. The catalytic performance of thecomplexes was evaluated for the reduction of NAD⁺ to NADHusing formic acid as a proton source. The iridium complexes significantlyoutperform their ruthenium analogs, which are essentially inactiveand show signs of instability. Among the iridium complexes, normalNHC 5 exhibits superior catalytic activity, robustness,and reduced susceptibility to substrate inhibition compared with itsabnormal counterpart.

To better define scandium(II) reduction chemistry andto studyligand effects on the hyperfine coupling to ⁴⁵Sc in theEPR spectra of Sc(II) complexes, which could be useful in the designof qubits based on nd¹ electronic configurations, the reductionof bis(cyclopentadienyl) scandium(III) iodide complexes in the presenceof isocyanide ligands has been examined. Both pentamethyl- and tetramethylcyclopentadienylcomplexes have been examined with isocyanides CNR, where R = 2,6-dimethylphenyl(Xylyl), 1-naphthyl (Naph), and 2,6-diisopropylphenyl (Dipp). Thesynthesis and structures of the isocyanide adducts of Sc(III) metalloceneiodides, Cp^x₂ScI(CNR) [Cp^x = C₅Me₅ (Cp*) and C₅Me₄H (Cp^tet)] are described as well as EPR data on the Sc(II) productsformed by reduction of Cp^x₂ScI in the presenceof CNR. A more direct synthetic route to the Sc(II) complex, Cp*₂Sc(CNXylyl)₂, is reported. New Sc(III) complexesobtained from these reactions are also described including [Cp^tet₂Sc(μ-CN)]₄ which is the firstcrystallographically characterized Sc complex containing (CN)^1– cyanide ligands, as well as products with two andthree coupled isocyanides, Cp^tet₂Sc(XylylNCCNXylyl)ScCp^tet₂, Cp^tet₂Sc(C₂₇N₃H₂₈), and Cp^x₂Sc(C₃₃N₃H₂₂). In addition, the [Cp*₂Sc(CNXylyl)₂]¹⁺ cation was isolated as the(BPh₄)^1– salt for comparison with theSc(II) analog, Cp*₂Sc(CNXylyl)₂, and the unexpectedorganometallic aquo adducts, [Cp^tet₂Sc(H₂O)₂][I][THF] and Cp^tet₂Sc(OH)(H₂O), were fortuitously crystallized.

Palladium-catalyzeddehydrogenation of formic acid underhomogeneousconditions is rare. In most cases, decomposition of palladium complexesis observed under the reaction conditions. In this study, bis(phosphinite)-supportedpalladium(II) complexes, {2,6-(R₂PO)₂C₆H₃}PdX [R = ⁱPr, ^tBu; X = H (1a–b),OCHO (2a–b)], were examined for catalyticformic acid dehydrogenation (FAD). Their derivative complexes, {2,6-(R₂PO)₂C₆H₃}PdCH₃ (3a–b), were found to be precatalysts.During catalysis, complex degradation was observed; however, by optimizingthe reaction conditions (80 °C, ethanol), a homogeneous and additive-freeprocedure for FAD was achieved. Alcohols and dihydrogen were identifiedas the possible sources of catalyst decomposition. Mechanistic investigationsreveal that the protonation of {2,6-(R₂PO)₂C₆H₃}PdH (1a–b)is both kinetically and thermodynamically favored, which drives FADwhile suppressing catalyst degradation pathways. It was found thatthe sterically crowded {2,6-(^tBu₂PO)₂C₆H₃}PdCH₃ (3b) is a more effective catalyst compared to {2,6-(ⁱPr₂PO)₂C₆H₃}PdCH₃ (3a). Experimental data show thatCO₂ elimination, the rate-limiting step of the catalyticcycle, occurs more rapidly from {2,6-(^tBu₂PO)₂C₆H₃}PdOCHO (2b) than from {2,6-(ⁱPr₂PO)₂C₆H₃}PdOCHO (2a), thereby accelerating the overall reaction rate.

R₂Zn compounds prepared by the conventional method (reactionof 2 eq RMgCl with ZnCl₂ in Et₂O, followed byfiltration to remove MgCl₂) are often unsuitable for certainorganic and polymer syntheses─particularly coordinative chaintransfer polymerization (CCTP)─due to residual impurities.Herein, we disclose a convenient, safe, scalable, and cost-effectivemethod for the preparation of high-purity R₂Zn that performseffectively in CCTP. In this approach, RMgCl, generated in Et₂O or the less hazardous (CH₃O)₂CH₂, are reacted with ZnCl₂. Subsequent removal ofthe ether solvent affords a residue containing both the desired R₂Zn product and dried MgCl₂ byproduct. The driedMgCl₂ acts as an impurity scrubber during the hexane extractionstep, enabling isolation of highly pure R₂Zn compounds.Using this method, [CH₂═C(R)C₆H₄(CH₂)_x]₂Zn [1 (x = 3, R = H); 2 (x = 3, R = Me); 3 (x = 2,R = H); 4 (x = 2, R = Me)] was efficientlysynthesized. These reagents enabled the formation of high yields ofCH₂═C(R)C₆H₄(CH₂)_x-[(CH(R)CH₂)]_n-Zn-[(CH₂CH(R))]_n-(CH₂)_xC₆H₄C(R)═CH₂ in CCTP. GPC, ¹H NMR,and rotational rheology analyses of the resulting polymers indicatethat a fraction of the styrene units in 1 and 3 is incorporated into the polymer backbone, leading to higher-molecular-weightmaterials with long-chain branching.

Given potential ramificationsin catalysis, exploringredox cyclingat heavy main group centers is attracting renewed interest. In thiscontext, this study explores how chalcogen bonding interactions caninfluence the oxidative addition of o-chloranil tothe Te(II) center of diaryltellurides. Using a series of diaryltelluridesfunctionalized by ortho-methylene-dimethylamino or-methyl ether functionalities, we show that the formation of a chalcogenbond between the donor atom and the tellurium center drives the oxidationreaction, as confirmed by the isolation and structural characterizationof the corresponding Te(IV) monocatecholates. Furthermore, this studyalso shows that these tetravalent tellurium derivatives react withan additional equivalent of o-chloranil to affordhexachloro-dibenzo[1,4]dioxine-2,3-dione, a known compound, and thecorresponding Te(IV) dichlorides. Lastly, this work also documentsthe facile reductions of the Te(IV) dichlorides into their Te(II)diaryl precursors using dithiothreitol or DTT.

Dinuclear iridium complexes supported by a 1,8-naphthyl-bridgedpyridine diimine (PDI) ligand exhibit pronounced metal–metalcooperativity (MMC) in the acceptorless dehydrogenation of methanol.Whereas the corresponding mononuclear analogues are inert, the diiridiummethoxido intermediate undergoes clean conversion to a carbonyl–dihydridecomplex via cooperative C–H activation of a coordinated formaldehydefragment. Structural characterization by X-ray crystallography andmultinuclear NMR spectroscopy, combined with isotopic labeling, establishthe methoxide origin of the carbonyl ligand. Variable-temperatureNMR studies reveal dynamic hydride exchange consistent with a low-barrierη²-H₂ transition state. Computationalanalysis identifies two competing pathways─a Meerwein-Ponndorf-Verley-typeroute and an organometallic α-C–H activation pathway─withcomparable activation barriers (∼26 kcal·mol^–1). Both involve transient Ir–Ir distance contraction.These results demonstrate that metal–metal proximity enablescooperative bond activation inaccessible to mononuclear analoguesand provide design principles for bimetallic alcohol dehydrogenation.

A series of bis(phosphine)cobalt carbonyl complexeswere preparedand investigated in situ using cyclic voltammetry, ¹H, ³¹P, and ⁵⁹Co NMR spectroscopy (includingDOSY), and IR spectroscopy. X-ray diffraction analysis on isolatedsingle crystals confirmed that complex speciation was highly dependenton the nature of the bis(phosphine) and ligand-to-metal stoichiometry.Reactions of [Co₂(CO)₈] with 1,2-bis(dicyclohexylphosphino)ethane(DCyPE) and 1,2-bis(diphenylphosphino)benzene (DPPBz) led todisproportionation of the precursor, affording cationic κ²-Co(I) bis(phosphine) complexes with Co(−I) tetracarbonylcobaltate counteranions. In contrast, ferrocenyl bis(phosphine) ligands1,1′-bis(diphenylphosphino)ferrocene (DPPF), 1,1′-bis(di-isopropylphosphino)ferrocene(DⁱPrPF), and 1,1′-bis(dicyclohexylphosphino)ferrocene(DCyPF), displayed different reactivity. DⁱPrPF and DCyPFappeared to form polymeric species at 1:1 ligand-to-metal ratios butfavored the formation of discrete neutral dinuclear complexes of thetype [(μ²-L)Co₂(CO)₆] when0.5 equiv of ligand was employed. Reaction of [Co₂(CO)₈] with DPPF yielded a significantly larger molecular assembly.Single-crystal X-ray diffraction revealed an unprecedented metallocyclicstructure comprising six cobalt tricarbonyl centers interconnectedby four bridging DPPF ligands.