Organometallics最新文献

The phenyl-tert-butoxysilanols Ph(tBuO)₂SiOH and Ph₂(tBuO)SiOH were prepared and used for the synthesis of the molybdenum 2,4,6-trimethylbenzylidyne complexes [MesC≡Mo{OSi(OtBu)₂Ph}₃] (1) and [MesC≡Mo{OSi(OtBu)Ph₂}₃] (2) from mer-[MesC≡MoBr₃(dme)] (dme = dimethoxyethane, Mes = 2,4,6-trimethylphenyl). The molecular structures of 1 and 2 were determined by X-ray diffraction analysis, revealing a secondary molybdenum–oxygen interaction and a chelating κ²O,O′ coordination mode of one of the siloxide ligands in the case of 1. Treatment of 1 and 2 with an excess of 3-hexyne (EtC≡CEt) afforded the corresponding propylidyne (EtC≡Mo) complexes, which are in equilibrium with labile metallacyclobutadiene complexes as evidenced by variable-temperature NMR spectroscopy. Single crystals of [(Et₃C₃)Mo{OSi(OtBu)Ph₂}₃] (2-MCBD) have been isolated at low temperature, providing a rare example of a crystallographically characterized molybdenacyclobutadiene. The alkylidyne complexes 1 (n = 1) and 2 (n = 2) complete the series of available alkyne metathesis (pre-)catalysts [RC≡Mo{OSi(OtBu)_3–nPh_n}₃] (n = 0–3), and their catalytic performance in the metathesis of internal and terminal alkynes was investigated and compared, if available, with the previous members of this series (n = 0, 3).

The reaction of (P)AuOTf [P = P(t-Bu)₂o-biphenyl] with the cyclopentadienyl lithium reagents C₅H₅Li, C₅H₄MeLi, and C₅HMe₄Li forms the corresponding gold η¹-cyclopentadienyl complexes (P)Au(η¹-C₅H₅) (3a), (P)Au(η¹-C₅H₄Me) (3b), and (P)Au(η¹-C₅HMe₄) (3c), respectively, in >60% isolated yield. Treatment of complexes 3a or 3b with (P)AuNTf₂ forms the corresponding cationic bis(gold) cyclopentadienyl complexes trans-{[(P)Au]₂(η¹,η¹-cyclopentadien-1,3-yl)}⁺ NTf₂^– (4a) and trans-{[(P)Au]₂(η¹,η¹-methylcyclopentadien-1,3-yl)}⁺ NTf₂^– (4b), respectively, in near-quantitative yield, which were characterized in solution and by X-ray crystallography. Both 4a and 4b undergo migration of the gold atoms about the cyclopentadienyl ring, which is fast on the NMR time scale at −80 °C. In the solid state, the gold atoms of 4a and 4b are positioned on the opposite faces of the cyclopentadienyl ring above and below the C1 and C3 carbon atoms. The reaction of 3c with (P)AuNTf₂ similarly forms the cationic bis(gold) tetramethylcyclopentadienyl complex {[(P)Au]₂(C₅HMe₄)}⁺ NTf₂^– (4c) although the structure of this complex remains obscure. The binding affinity of mono(gold) complexes 3a–3c toward exogenous (P)Au⁺ exceeds that of the corresponding unmetalated cyclopentadienes by more than 3 orders of magnitude. Protodeauration of bis(gold) complexes 4 with acetic acid at −80 °C is >1500 times slower than the protodeauration of the corresponding monogold complexes 3 under identical conditions.

Isolable sulfonium-ylide-stabilized palladium carbene complexes were synthesized through palladium(II)-induced cyclization of 1,2-alkynylarylsulfanes. X-ray crystallographic analysis characterized the maintenance of a palladium +2 oxidation state, with carbene-carbon–palladium bond lengths of 1.95 Å, indicating a partial double-bond character. These endocyclic sulfonium ylide carbenes represent the first characterized and/or isolable examples of this ligand class; such groups were previously proposed as reaction intermediates during cyclization–carbonylation reactions. A variety of palladium(II) complexes bearing sulfonium-ylide carbene ligands, with differing substituents, were synthesized, and the structure and stability of these complexes in solution were analyzed by ¹H and ¹³C NMR spectroscopy, revealing reversibility and a stability dependence on substituents. The chirality of the sulfur heteroatom and the overall properties these ligands provide a potential electronic and steric alternative to existing carbene ligands, which could facilitate the future development of complementary metal-based reactivity.

Zinc benzoates may provide an element of tunability that is not available to their ubiquitous acetate analogues. Unfortunately, the synthesis, speciation, and coordination chemistry of zinc benzoates are less developed than the acetates. In this study, we systematically investigate zinc benzoates to understand their propensity to favor solvate (Zn(O₂CAr)₂(L)₂) or cluster (Zn₄O(O₂CAr)₆) formation as well as their utility as metal complex precursors. The zinc benzoates were found to be Lewis acid catalysts comparable to their acetate counterparts for the formation of oxazolines from esters and amino alcohols.

Three organometallic ligand scaffolds resulting from the insertion of 1-adamantyl isonitrile (C≡NAd; Ad = C₁₀H₁₅) into titanium neopentylidene complexes, [(PNP)Ti═CH^tBu(X)] are described herein. Treatment of the titanium neopentylidene complex (PNP)Ti═CH^tBu(OTf) (1-OTf, PNP^– = N[2-PⁱPr₂-4-methylphenyl]₂^–, OTf = trifluoromethanesulfonate^–) with one equivalent of C≡NAd leads to the formation of a titanium η²-C,N-ketenimine, (PNP)Ti(η²-C,N-AdNCCH^tBu)(OTf) (2-OTf). However, when the titanium neopentylidene neopentyl complex (PNP)Ti═CH^tBu(CH₂^tBu) (1-Np) is added one equivalent of C≡NAd, a titanium neopentylidene κ¹-N-vinylamido complex (PNP)Ti═CH^tBu(κ¹-N-AdNCHCH^tBu) (3) is formed. In contrast, the titanium neopentylidene methyl complex (PNP)Ti═CH^tBu(CH₃) (1-Me) reacts with one equivalent of C≡NAd to produce a rare chelating κ²-C,N-azaalleneyl ligand, in the complex (PNP)Ti(κ²-C,N-AdNCC^tBu) (4), with concurrent extrusion of methane. Independently, it is shown that treatment of 2-OTf with one equivalent of neopentyl lithium (LiNp, Np^– = CH₂^tBu) or a half equivalent of dimethyl magnesium (MgMe₂) smoothly forms complex 3 or 4, respectively, and suggests that the η²-C,N-ketenimine ligand in 2-OTf might be an intermediate ligand enroute to the neopentylidene κ¹-N-vinylamido or κ²-C,N-azaalleneyl complexes. Complexes 2-OTf, 3 and 4 have been structurally and spectroscopically characterized and a proposed mechanism for the formation of complexes 3 and 4 is also described.

Zinc benzoates may provide an element of tunability that is not available to their ubiquitous acetate analogues. Unfortunately, the synthesis, speciation, and coordination chemistry of zinc benzoates are less developed than the acetates. In this study, we systematically investigate zinc benzoates to understand their propensity to favor solvate (Zn(O₂CAr)₂(L)₂) or cluster (Zn₄O(O₂CAr)₆) formation as well as their utility as metal complex precursors. The zinc benzoates were found to be Lewis acid catalysts comparable to their acetate counterparts for the formation of oxazolines from esters and amino alcohols.

A series of chiral pincer iridium complexes supported by oxazoline-containing P^CCN-type ligands were synthesized. Among them, the (^tBuP^CCN^tBu)IrHCl complex bearing sterically bulky tBu groups both at the P atom and on the oxazoline ring exhibits high efficiency and enantioselectivity for the asymmetric dual dehydrogenative silylation of C(sp³)–H bonds. This reaction provides an enantioselective approach to oxa-spirosilanes with a stereogenic silicon center from readily available diarylsilanes.

Fluorinated borates have been widely used as innocent and weakly coordinating counteranions. Among those, [BAr^F₄]⁻ ([B(C₆H₃-3,5-(CF₃)₂)₄]⁻) occupies a prominent position due to the robustness of its B–C carbon bonds. Herein, we investigate C–B bond cleavage in the [BAr^F₄]⁻ anion mediated by cationic gold fragments of type [Au(PMe₂Ar′)]⁺, where Ar′ stands for bulky terphenyl (C₆H₃-2,6-Ar₂) substituents. In addition, we have exploited the stoichiometric B–C bond cleavage to construct a catalytic cycle for the synthesis of boranes under acidic conditions.

The oxidative functionalization of aromatic sp² C–H bonds to C–O bonds is a difficult transformation. For main-group metals, the oxyfunctionalization step of a metal-aryl bond is generally slow and potentially problematic if carried out in a relatively strong acid solvent where protonation could prevent oxyfunctionalization. In this work, we experimentally and computationally analyzed the oxyfunctionalization reaction of (Ph)₃Bi^V(TFA)₂ (TFA = trifluoroacetate) in a trifluoroacetic acid (TFAH) solvent. Experiments showed a single oxyfunctionalization product phenyl TFA (PhTFA) and two equivalents of benzene. Explicit/continuum solvent density functional theory calculations revealed that a direct intramolecular reductive functionalization pathway is lower in energy than radical or ionic pathways, and surprisingly from (Ph)₃Bi^V(TFA)₂, the reductive functionalization pathway is potentially competitive with protonation. In contrast, for (Ph)₂Bi^V(TFA)₃ oxyfunctionalization is significantly lower in energy than protonation. For Bi^III-phenyl intermediates, redox neutral protonation is significantly lower in energy than a second functionalization. We also examined the oxyfunctionalization versus protonation of Bi^V-phenyl complexes with a coordinated biphenyl ligand and a coordinated biphenyl sulfone ligand, which both resulted in oxyfunctionalization. For the biphenyl ligand complex, a protonation-first mechanism is proposed, while for the biphenyl sulfone ligand, an oxyfunctionalization first mechanism is consistent with both calculations and experiments.