Organometallics最新文献

Densityfunctional theory (DFT) calculations were performed toevaluate the relative efficiencies of Nb-, Mo-, and W-based Schrock-typealkylidene complexes (1–11) in olefinmetathesis. The study reveals that catalytic efficiency is stronglygoverned by the electrostatic nature of the M–C bond. A largerelectrostatic contribution imparts greater ionic and polarizable characterto the metal–carbene interaction, facilitating electron redistributionduring olefin coordination and promoting efficient metallacyclobutaneformation in the Chauvin mechanism. W-based complexes, particularly(7), (9), and (11), exhibitshorter M–C bonds, higher ν(M–C) frequencies,larger WBIs, and stronger orbital stabilization, indicating highlystabilized and more covalent metal–carbene interactions. Incontrast, Mo complex (1) shows a larger electrostaticcontribution, longer M–C bond distance, smaller charge separation,lower WBI, and lower steric congestion, indicating a more ionic andreadily polarizable Mo–C interaction favorable for catalyticturnover. EDA, %VBur, and mechanistic analyses further demonstratethat although W complex (11) is thermodynamically morestable, its greater covalent stabilization and steric congestion reducecatalytic efficiency, whereas Mo complex (1) exhibitsmore favorable energetics for four-membered TS formation and is themost catalytically efficient system among the complexes studied herein,in accordance with experimental reports.

A new trigonallysymmetric ligand scaffold is reported from thereaction of tris(2-aminoethyl)amine (TREN) and methyl trifluoroacetate.Deprotonation and metalation with iron(II) yields a trigonal monopyramidalferrate that bears an open coordination site surrounded by C–Fmotifs. The weak-field ligand environment promoted by the fluorinatedamidate donors leads to distinctive behaviors that are apparent inreactions with π-acids such as CO and tert-butylisocyanide.As shown by structural, spectroscopic, and computational studies,the trifluoromethyl substituents lead to an attenuation of π-backbondingcapabilities, while also labilizing the Fe–N_amidate bonds. While no tractable reactivity with O₂ occurs,the ferrate irreversibly coordinates NO to yield a high-spin {FeNO}⁷ complex.

A stereo- and regioselective Fe(II)-catalyzed hydroborationofboth terminal and internal alkynes with pinacolborane (HBpin) is described.The hydroboration reaction is in all cases highly syn-selective. The reaction requires no additives and proceeds witha catalyst loading of 1–2 mol % at 45–55 °C. Anactive pre-catalyst is the bench-stable alkyl Fe(II) complex [Fe(PCP^CH2-iPr)(CH₂CH₂CH₃)(CO)₂]. This complex reacts with an excess ofHBpin to form the Fe(II) pinacolborane complex [Fe(PCP^CH2-iPr)(κ²-H₂BPin)(CO)],which is an equally active pre-catalyst but more difficult to handle,as it decomposes in the absence of substrates. Both pre-catalystsafford the highly reactive hydride catalyst [Fe(PCP^CH2-iPr)(H)(CO)] under catalytic conditions. A broad varietyof aromatic and aliphatic alkynes were efficiently and selectivelyborylated. Mechanistic insights are provided based on experimentaldata and DFT calculations.

In contrast to alkoxidesalts, siloxide salts MOSiR₃ (M = Na, Li) can be used togood effect as activators for B₂pin₂ in theiron-catalyzed borylation of aryl chloridesubstrates, in many cases giving results comparable to or better thanthose obtained previously with highly pyrophoric ^tBuLi acting as an activator. Preliminary mechanistic investigationsreveal a protracted induction period, most likely associated withprecatalyst reduction, and these also suggest that the NaOSi^tBuMe-activated B₂pin₂ isnot as reducing as the equivalent ^tBuLi-activatedspecies.

We report the synthesis and photophysical characterizationof twospirofluorene xanthene-functionalized benzimidazolylidene platinum(II)complexes with bis(3-methylpyrazolyl)borate and bis(3-trifluoromethylpyrazolyl)borateauxiliary ligands. Both complexes were synthesized from a μ-chloro-bridgedbimetallic intermediate in 40% and 72% yields. Photophysical investigationsrevealed green-blue emission with CIE coordinates of (0.16; 0.23)and (0.17; 0.27), and photoluminescence quantum yields of 63% and58%.

Bis(pinacolato)diboron (B₂pin₂)is a widelyused diboron reagent for the installation of modular boryl groupsand is generally regarded as bench stable. Here we show that traceimpurities can initiate an autocatalytic process that promotes oxidativedecomposition of B₂pin₂ in the solid state.Once initiated, this process renders B₂pin₂ susceptibleto reaction with molecular oxygen and HO–Bpin, leading to degradationof bulk material. Notably, decomposition propagates under closed containerconditions but is suppressed in loosely capped containers, consistentwith the involvement of volatile components in the degradation process.These findings reveal an unexpected vulnerability in a widely usedboron reagent and establish practical guidelines for its storage andhandling.

The polarized andunsaturated Sb–O bond of stibine oxidesexhibits a combination of electrophilicity at the antimony atom andnucleophilicity at the oxygen atom. Here, we explore the consequentability of Mes₃SbO compounds to undergo 1,2-addition chemistrywith carboxylic, sulfonic, and phosphinic acid anhydrides to affordstiboranes of the type Mes₃SbX₂. With the bulkierstibine oxide Dipp₃SbO, reaction with triflic anhydridepermits in situ preparation of Dipp₃Sb(OTf)₂, which crystallized as the stibonium triflate salt. This reactivityalso enables the disaggregation of the polymeric stibine oxide (Ph₃SbO)_n under mild conditions, providing an alternativesynthetic route to Ph₃SbX₂ products.

A prior report (Inorg. Chim. Acta 2011, 376, 118–122)detailed the use of “[Ni(THF)₆][(BF₄)₂]” to prepare [(dtbe)Ni(μ-F)]₂[BF₄]₂ (dtbe = 1,2-bis(di-tert-butylphosphino)ethane)using a DCM/THF (1:1) solvent system. Herewe describe a procedure that affords [Ni(THF)₄(BF₄)₂] in the solid-state, and note that reaction of [Ni(THF)₄(BF₄)₂] with the similar phosphine dcpe(dcpe = 1,2-bis(dicyclohexylphosphino)ethane) only produces [(dcpe)Ni(μ-F)]₂[BF₄]₂ when run in thoroughly driedTHF solvent. If a 1:1 mixture of DCM/THF solvents is used as previouslydescribed, the bridging chloride derivative [(dcpe)Ni(μ-Cl)]₂[BF₄]₂ is formed. Moreover, we showthat bridging fluorides of [(dcpe)Ni(μ-F)]₂[BF₄]₂ can be short-lived in solution, reacting withthe medium to produce unexpected products.

Metalloxiranes are mechanistically relevant intermediatesin carbonylfunctionalization by metals. Herein, we investigate carbonyl activationusing a nickel complex supported by a diphosphine ligand bearing apendent Lewis-acidic monoborane. Reaction of this ambiphilic systemwith a series of carbonyl substrates affords nickeloxiranes whoseisomeric distributions and relative energies were examined experimentallyand computationally through density functional theory. Despite theproximity of borane functionality, the nickeloxiranes derived frombenzophenone and acetophenone exhibited no definitive evidence forintra- or intermolecular O→B interactions. In contrast, thebenzaldehyde analogue displayed a well-defined noncovalent O→Binteraction in both the solution and solid states. These findingsprovide insights into the factors governing carbonyl activation byambiphilic nickel systems.