Organometallics最新文献

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η⁴–η⁶), less is known about the chemistry of their η² analogues. Herein, we describe a general method for synthesizing 5,6-η²-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe₃)}. This study includes detailed spectroscopic and crystallographic data for the η²-dihydropyridine and η²-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers.

Aminocarbonylation of alkynes with organic amines as an attractive straightforward protocol for the synthesis of high-value-added α,β-unsaturated amides is highly in demand, which is highly dependent on the performance of Pd catalysts modified by the elaborately designed ligands with various stereoelectronic properties. Herein, the bis-P,N,P-hybrid ligands (L2–L4) were successfully synthesized by using low-cost and easily handleable bis(2-chloroethyl)amine hydrochloride as the starting material. The complexation of L2 with Pd(CF₃COO)₂ could afford a stable binuclear complex L2 with an ideal centrosymmetric configuration, which proved that L2 served as the bis-P,P-bidental chelating ligand. It was found that L2-modified Pd(CF₃COO)₂ (or Pd-L2) could catalyze aminocarbonylation of phenylacetylene with aniline free of any additive and organic solvent, affording the branched product N,2-diphenylacrylamide (3a) with 100% regio-selectivity in the isolated yield of 90%. However, the generality of the developed L2-Pd(CF₃COO)₂ catalytic system is very limited.

In this study, we explored the reaction mechanism of Ni-NHC-catalyzed 1,2-bis-silylation of internal alkynes, comparing and discussing the reactivity and stability of various Ni-NHC catalysts. The following conclusions were drawn: (1) The reaction mechanism of 1,2-bis-silylation of internal alkynes remains consistent across different catalyst structures, highlighting that the substrate is the primary factor influencing the catalyst’s existence form; (2) Among various Ni-NHC catalysts, [Ni(NHC)₂] emerges as the most stable structure, while [Ni(NHC)(η²-COD)] exhibits the highest catalytic activity. This underscores the significance of maintaining M-(η²-COD) ligand bonding for enhancing the catalytic activity of the catalysts.

Palladium hydrides are ubiquitous during organometallic reactions. However, synthesis of catalytically active Pd–H from precatalytic Pd, as in Pd–H-catalyzed enyne cycloisomerization, is often thermodynamically unfavorable, producing very little Pd–H. Therefore, the Pd loadings required are often high due to the small amount of active catalyst present. We investigated the oxidative addition of weak acids to Pd(0) complexes in an attempt to increase [Pd–H] and shorten reaction times. Pd(PCy₃)₂ reacts with 1,1’-binaphthyl-2,2’-diol (BINOL) and acetic acid reversibly, to produce Pd–H. We measure the equilibrium constants and show that the rate of the cycloisomerization of 1 increases at higher [ROH]. By increasing [ROH], we can lower the Pd(PPh₃)₄ loading by 50 times with reasonable reaction times. BINOL-derived phosphoric acids, such as S-TRIP, gave irreversible oxidative additions to Pd(PCy₃)₂ and also resulted in high enantioselectivities. This work demonstrates that it is possible to use the Pd more efficiently in such reactions by maintaining a high concentration of the weak acid in the reaction, resulting in higher concentrations of the catalytically active Pd–H species. More broadly, we show that for reactions involving in situ formation of active catalytic intermediates, both the number of equivalents of ligands and their concentration are important for improving catalytic activity.

Reactions of the title complexes and n-BuLi (1.5 equiv, –45 °C) afford functional equivalents of the deprotonated species trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_nLi (n = 2–4), as assayed by subsequent additions of MeI or Me₃SiCl to give trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_nMe (66–52%) or trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)_nSiMe₃ (63–49%). However, ³¹P NMR data suggest more complicated mechanistic scenarios, and small amounts of the hydride complex trans-(C₆F₅)(p-tol₃P)₂PtH (independently synthesized from the chloride complex, AgClO₄, and NaBH₄) are detected in most cases. Analogous sequences involving trans-(C₆F₅)(p-tol₃P)₂Pt(C≡C)₂H and benzyl bromide, D₂O, or W(CO)₆/Me₃O⁺ BF₄^– similarly afford products with Pt(C≡C)₂Bn, Pt(C≡C)₂D, or Pt(C≡C)₂C(OCH₃)═W(CO)₅ linkages. The crystal structures of the tungsten and corresponding SiMe₃ adduct, the three Pt(C≡C)_nMe species, and hydride complex are determined.

Treatment of [Sn(NMe₂)₂]₂ (1) with R–I (where R = Et, ⁱPr, Me₃SiCH₂, F₃CH₂C, and F₃C) yields the monoalkyltin amides (RSn(NMe₂)₃) (3–7) and the stannous iodide/amide dimer [ISn(NMe₂)]₂ (2) as major products. The monoalkyl stannic amides (3–7) are light-sensitive liquids which are sufficiently volatile (<1% residual mass by TGA) for use as ALD/CVD precursors. The oxidative addition of R–I to a Sn(II) center, followed by exchange of a stannic iodide with unreacted 1, is supported by the solid-state structural analysis of crystalline [ⁱPrSn(NMe₂)₂I]₂ (9) and [ISn(NMe₂)]₂ (2). The stannous iodide byproduct (2) is independently synthesized from stoichiometric amounts of SnI₂ and [Sn(NMe₂)₂]₂. Heating solutions of ⁱPrSn(NMe₂)₃ (4) and ⁱPr–I produces nominal quantities (∼10%) or NⁱPrMe₂ and 9; demonstrating RSn(NMe₂)₃ sensitivity toward alkyl iodides via Sn(IV)–NMe₂ bond cleavage. The modified synthesis and light-sensitivity of [Sn(NMe₂)₂]₂ (1) are also discussed. Multinuclear NMR, solid-state structural analysis, and thermogravimetric differential scanning calorimetry (TGA-DSC) experiments are described.

The synthesis of ethane-1,2-diyl-bis(diarylphosphane oxides) and -phosphanes, containing bulky ortho-substituted P-bound aryl groups, poses severe challenges, such as drastic reaction conditions and low yields. A potassium base-mediated hydrophosphorylation of phenylacetylene with dimesitylphosphane oxide (Mes₂P(O)H) yields an E/Z mixture of alkenyl-dimesitylphosphane oxide. The bulky mesityl group hampers the addition of a second diarylphosphane oxide. Contrary to this expected addition of a phosphane oxide across an alkyne yielding an alkenylphosphane oxide, the potassium base-mediated reaction of trimethylsilyl acetylene with Mes₂P(O)H yields ethane-1,2-diyl-bis(dimesitylphosphane oxide) (2b); surprisingly, the TMS group is substituted by a hydrogen atom via a rather complex reaction mechanism. Excess TMS-C≡CH (5 equiv), ethereal solvents, soft alkali metal catalysts, and large catalyst loadings of 30 mol % are highly beneficial. Furthermore, at least one ortho-position must be alkylated, whereas very bulky aryl groups pose no obstacle. Di(n-alkyl)phosphane oxides and diphenylphosphane oxide do not show the described conversion but react completely different. Alternatively, ethane-1,2-diyl-bis(diarylphosphane oxides) are accessible via a metathetical approach of calcium acetylide CaC₂ with diarylphosphane oxide in a superbasic solvent. Reduction of these phosphane oxides (2) to phosphanes (3) offers a library of bulky bidentate ligands for coordination chemistry at hard (e.g., Y³⁺) and soft metal ions (e.g., Pd²⁺).