Organometallics最新文献

A preparation of [⁹⁹TcH(CO)₅] as a neat liquid or as a solution in a hydrocarbon solvent by treatment of [⁹⁹TcBr(CO)₅] with Na[BH₄] in an organic solvent–water mixture is presented. [⁹⁹TcH(CO)₅] was characterized by ¹H and ⁹⁹Tc NMR spectroscopy, IR spectroscopy, and EI MS. The reactivity of [⁹⁹TcH(CO)₅] was studied. It reacts readily with strong acids such as HClO₄ and F₃CCOOH to form [⁹⁹Tc(ClO₄)(CO)₅] and [⁹⁹Tc(O₂C–CF₃)(CO)₅], respectively, but does not react with weak acids such as HCOOH. [⁹⁹TcH(CO)₅] is moderately resistant to atmospheric oxygen in solution and is more air-sensitive in the neat form, gradually transforming into [⁹⁹Tc₃H(CO)₁₄]. The metal–hydrogen bond in [⁹⁹TcH(CO)₅] is oxidized with I₂ to form [⁹⁹TcI(CO)₅]. The oxidation pathway with molecular iodine differs from the ones observed for typical hydrides or acids and is rather characteristic for low-polarity covalent compounds. The carbonyl groups of [⁹⁹TcH(CO)₅] are quite resistant to substitutions by σ-donor ligands. To promote such substitutions, the Tc–H bond should be oxidatively cleaved. Unusual technetium carbonyl complexes, [(μ₃-CO₃)(⁹⁹Tc(bipy)(CO)₃)₃]⁹⁹TcO₄ and [⁹⁹Tc(phen)₂(CO)₂]⁹⁹TcO₄, are formed in the reactions of [⁹⁹TcH(CO)₅] with 2,2′-bipyridine and 1,10-phenanthroline in air. [⁹⁹Tc(phen)₂(CO)₂]⁺ is the first example of a technetium(I) dicarbonyl complex stabilized by ligands with weak π-acceptor properties.

Photolyses of trans-Fe(CO)₃(As((CH₂)_n)₃As) (n = a, 10; b, 12; c, 14) in the presence of PMe₃, or reactions of trans-[Fe(CO)₂(NO)(As((CH₂)_n)₃As)]⁺ BF₄^– and n-Bu₄N⁺ Cl^–, afford the air stable title complexes As((CH₂)_n)₃As (8a–c) in 79–34% yields. With 8a, the in, in and out, out isomers are separable and each is crystallographically characterized. With 8b,c, the isomers rapidly interconvert by homeomorphic isomerization, but each crystallizes (contrathermodynamically) as an out, out isomer. Reactions of 8c with H₂O₂ or 8b with BH₃ give 8c·2O or 8b·2BH₃, respectively (85–94%). Reactions of 8c with MCl₂ (M = Pt, Pd, Ni), Rh(CO)(Cl), and Fe(CO)₃ sources afford the corresponding cage-like complexes trans-ML_n(As((CH₂)₁₄)₃As) (86–51%). The crystal structures of 8c·2O and the PtCl₂ and PdCl₂ adducts are determined and compared to those of 8a–c and diphosphorus analogs. The corresponding distibine Sb((CH₂)₁₄)₃Sb is analogously prepared, but precursors necessary for the bismuth analog could not be accessed due to the diminished BiR₃ Lewis basicity.

Ir-catalyzed C–H borylations of fluorinated and cyanated arenes with high meta-to-F/CN are described. Use of a dipyridyl hydrazone framework as the ancillary ligand and pinacolborane (HBpin) as the functionalizing reagent generates catalysts that are significantly more active and selective than 4,4′-di-tert-butyl-2,2′-bipyridine (dtbpy) for both electron-deficient and electron-rich substrates. Investigation of the ligand framework resulted in the observation of formal N-borylation of the hydrazone by HBpin, as evidenced by NMR spectroscopy and X-ray crystallography. Subsequent stoichiometric reactions of this adduct with an iridium precatalyst revealed the formation of an unusual Ir^I hydrazido. Isolation and use of this hydrazido reproduce the selectivity of in situ generated catalysts, suggesting that it leads to formation of the active species.

Nucleophilic substitution of B–H is an important strategy for the synthesis of carborane derivatives. Although the intermolecular B–H nucleophilic substitution has been widely explored, intramolecular B–H nucleophilic substitution has rarely been reported. Herein, we synthesized a novel carborane-fused N-heteroaromatic through a transition-metal-free reaction between carboranyl lithium and 2,3-dichloroquinoxaline. Two intermolecular C–Cl nucleophilic substitutions and one intramolecular B–H nucleophilic substitution with carboranyl lithium were involved in this transformation. Instead of the most electron-deficient B(3)–H vertex, the B–H nucleophilic substitution selectively occurred on the B(4)–H vertex. This method provides a new method for the synthesis of carborane-fused ring compounds.

Although secondary coordination sphere effects on catalytic active sites are widely appreciated, the influence of such interactions on (hetero)binuclear active sites has not been examined comprehensively. Here, the influence of cyclodextrin encapsulation on the (NHC)Cu-FeCp(CO)₂ moiety, which is known to be catalytically active in several transformations, is analyzed in detail. Compared to free (NHC)CuFp complexes (Fp = FeCp(CO)₂), encapsulated (NHC)CuFp complexes were found to shift from resembling Fe(0) toward having Fe(II) character according to Mössbauer and IR spectroscopies. According to DFT modeling, this change in electronic structure is correlated to the pyramidalization of the Fp fragment away from a planar orientation and to the disruption of semibridging CO interactions typically found in (NHC)CuFp complexes. The latter change can be attributed, in part, to the presence of contra-electrostatic C–H···Cu anagostic interactions that outcompete semibridging Cu···CO interactions due to geometric constraints. These combined factors result in Fe(II)-like substitution reactivity of one of the CO ligands that is enabled only within the supramolecular architecture. The data presented herein provide understanding of how (hetero)binuclear reaction centers, especially those involving CO ligands, are influenced by partially covalent interactions from beyond the primary coordination sphere.

Dinuclear Ru(II) complexes [(p-cymene)₂(RuCl)₂L¹]2X (X = BF₄ (Ru1); X = PF₆ (Ru2)) and mononuclear [(p-cymene)(RuCl)L²]BF₄ (Ru3) (where L¹ = N,N′-(3,3′,5,5′-tetraisopropyl-[1,1′-biphenyl]-4,4′-diyl)bis(1-(pyridin-2-yl)methanimine); L² = N-(2,6-diisopropyl-phenyl)-1-(pyridin-2-yl)-methanimine) have been synthesized and characterized by spectroscopic and analytical techniques. Dinuclear Ru1 and Ru2 orchestrate direct transformation of 2-nitrobenzyl alcohols to quinolines under mild conditions with significant efficiency even when employed at a minimal catalyst loading of 0.1 mol %. Proportional experiments carried out with the corresponding mononuclear complex Ru3 by keeping the Ru content the same (0.2 mol % of Ru3) reveal superior activity by the bimetallic system Ru1 for the one-pot quinoline synthesis. Late-stage functionalization of bioactive steroids and scale-up synthesis demonstrate the practical applicability of the present catalyst system. A probable mechanism of this conversion is proposed based on trapping of many of the intermediates by ESI-mass spectroscopy. These mechanistic studies have further been substantiated by ReactIR studies by monitoring the progress of the reaction in real time.

[2]Ferrocenophanes bridged by a carbon and a heteroatom were targeted in the hope that such an asymmetric bridge gives rise to monomers suitable for ring-opening polymerization. Three strained sandwich compounds with bridging C–Si (13^SiMe2), C–P (13^PPh), or C–B (13^BMes) moieties were prepared using a lithium–bromine exchange followed by a common salt-metathesis reaction. Single-crystal X-ray structural analyses revealed an increase of the degree of Cp ring tilting, commonly expressed as the α angle, from 12.58(9) (13^SiMe2) to 16.63(2) (13^PPh) to 19.66(11)° (13^BMes). Despite being strained, all three species turned out to be resistant toward thermal ring-opening polymerization. The characterization of the three [2]ferrocenophanes by one- and two-dimensional ¹H NMR spectroscopy disclosed that Cp protons in α position to the bridging elements are deshielded relative to Cp protons in the β position. Experimental assignments were supported by DFT calculations of chemical shifts. The determined order of α and β Cp protons is opposite to that known for [1]ferrocenophanes. Using a set of known [n]ferrocenophanes (n = 1, 2) with significant tilted Cp rings, DFT calculations revealed that both families exhibit a different order of Cp peaks in ¹H NMR spectra.