Organometallics最新文献

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⁺).

Four-coordinate aryl borafluorenes with boron–oxygen and boron–nitrogen dative bonds can exhibit very large fluorescence Stokes shifts. The large Stokes shifts are hypothesized to arise from cleavage of the boron-donor dative bond in the excited state, via a mechanism called bond-cleavage-induced intramolecular charge transfer (BICT). The primary goal of this current investigation is to directly observe the BICT state by performing transient absorption spectroscopy (TAS) on four-coordinate borafluorenes, which have improved optical stability. A novel four-coordinate aryl borafluorene was synthesized which features a dative B–O bond and two tert-butyl moieties on the aryl ring. TAS of the new borafluorene is consistent with the existence of a single, three-coordinate species in the excited state, as predicted by the BICT hypothesis. The TAS data is supported by fluorescence lifetime measurements and DFT calculations.

Rh complexes of a tridentate PPP ligand bearing 1,2-pyrrolediyl linkers have been prepared, including examples with the central P donor being either a phosphine or a phosphide. Three bimetallic Rh complexes containing the diamandoid Rh₂P₂ core (P = phosphido) have been structurally and spectroscopically characterized. The Rh–Rh interaction in these three dimers was examined by way of structural comparisons and DFT investigations.

Palladium complexes are emerging as potential antitumor compounds. Recent experimental evidence suggests that the mechanism of action of some organopalladium derivatives might involve the target of proteins such as Thioredoxin Reductase (TrxR). In this work, we investigate different possible chemical mechanisms of interaction between selected palladium(II)-η³-allyl complexes and thiolates or selenolates, which are key functional groups present in the catalytic pocket of TrxR. Our investigation, focusing on both anionic and cationic complexes, suggests that in all cases, the interaction between the organopalladium species and chalcogenolates occurs via a ligand exchange reaction, which leads to the formation of a new Pd–S or Pd–Se bond. Allyl substitution, which takes place with the formation of a new C–S or C–Se bond, always appears to be the least favored reaction, from both the kinetic and thermodynamic points of view.

Hydrogenolysis of less reactive carbonyl compounds such as urethanes and ureas is a challenging but promising transformation to utilize new chemical feedstocks, such as plastic waste and carbon dioxide fixation products. In these transformations, pincer-type complexes consisting of Ru and Mn have been intensively investigated but catalyst design with bidentate ligand systems has rarely been explored. We report here the synthesis of a Mn complex supported by a PN bidentate ligand consisting of phosphino and pyrrolido coordination sites, the molecular structure of which has been fully characterized. The Mn complex catalyzed the hydrogenolysis of urethanes and ureas. In the case of the hydrogenolysis of 1,3-diphenylurea, formanilide was obtained as a product. In addition, the present Mn complex did not promote the hydrogenation of carboxamides, showing a unique reactivity that preferentially reduces urethanes and ureas over carboxamides, in contrast to the general reactivity order of carbonyl compounds.