The design and synthesis of a rigid carbazole trianionic pincer ligand and its tungsten alkylidene [CBZ-ONO]WCH t Bu(O t Bu) (3) and anionic alkylidyne {Ph 3 PCH 3 }{[CBZ-ONO]WC t Bu(O t Bu)} (4) complexes are reported. Designed to maximize the inorganic enamine effect by constraining the N atom lone pair, the carbazole ligand achieves high planarity. However, the orbital overlap remains similar to that of the flexible ligand [CF 3 −ONO]H 3 (1). The neutral alkylidyne complex could not be synthesized. The complexes were characterized by multinuclear NMR spectroscopy, combustion analysis, mass spectrometry, and single-crystal Xray diffraction. DFT calculations reveal an inorganic enamine orbital overlap within the alkylidyne complexes bearing both the rigid and flexible ligands.
This work outlines an approach to creating a catalyst for cyclic polymer synthesis using readily available materials in only one or two steps. Combining commercially available molybdenum-alkylidene 1 with two equivalents of ene-ol proligand 2 rapidly produces, in quantitative yield ( 1 H NMR spectroscopy), the double tethered metallacyclobutane complex 3. Characterized by variable temperature NMR studies and nuclear Overhauser effect spectroscopy (NOESY) experiments, complex 3 exhibits fluxional behavior in solution. Determined by single crystal X-ray diffraction, the solid-state structure of complex 3 reveals metrical parameters indicating that the metallacyclobutane is not predicted to undergo rapid retro-cycloaddition. However, complex 3 is a precatalyst for the polymerization of norbornene to produce cyclic polynorbornene. An NMR spectrum of a test polymerization indicates that only a small fraction of the precatalyst is activated upon exposure to monomer. Quantifying the active catalyst is possible by measuring vinyl resonances that appear in the 1 H NMR spectrum. The vinyl resonances are attributable to the release of one of the tethers upon norbornene addition. Confirmation of the polymer cyclic topology comes from gel permeation chromatography (GPC), dynamic light scattering (DLS), and intrinsic viscosity (η) measurements. The double tethered metallacyclobutane complex is a novel design for catalytic cyclic polymer synthesis. The synthetic approach suggests that catalyst tuning is possible by a choice of the commercial alkylidene and alteration of the ene-ol proligand.Article pubs.acs.org/JACS
Two equivalents of 1-benzyl-3-bromoethylbenzimidazolium bromide couple with NaSe to produce the first selenoether bridged bis-benzimidazolium salt (LH)Br. The nitrate (LH)(NO) and tetrafluoroborate (LH)(BF) salts were also synthesized from (LH)Br. The reaction of Hg(OAc) with (LH)Br gave the first pseudo pincer carbene mercury complex, [Hg(L-κC)][HgBr] (C1). Different complexes of Pd(ii) with selenoether bridged carbene were obtained using (LH)Br and (LH)(NO). Syntheses of these complexes were dependent on the counter anion and the temperature. Thus, the pincer type ionic complex [PdBr(L-κCSeC)]Br (C2) was isolated at 80 °C and the pseudo pincer type neutral complex cis-[PdBr(L-κC)] (C3) was isolated at room temperature from (LH)Br and Pd(OAc) in DMSO. The nitrate precursor (LH)(NO) on palladation with Pd(OAc) afforded [Pd(L-κCCSeC)]NO (C4) showing an unprecedented intramolecular metallation at the ortho position of the benzyl wingtip of the benzimidazole moiety. The ligand salts and metal complexes have been characterized using HRMS, heteronuclear NMR and IR spectroscopy. Single crystal X-ray structures of the ligand salts (LH)Br and (LH)(BF) and complexes C1-C4 have also been elucidated. Complex C2 showed good activity for C-C coupling in the mono-Heck reaction of methyl acrylate and arylbromides. Interestingly, the less common bis-arylation was also observed with deactivated arylbromides as the result of double-Heck coupling.
Reported is the hydrolysis of ah omogeneous Mo-nitride complex bearing at rianionic pincer-type ligand to produce ammonia.T reating the anionic [(ONO)]Mo N(OtBu)]Ph 3 PCH 3 with two equivalents of water produces ammonia and the dioxo complex [(ONO)]MoO 2 ]Ph 3 PCH 3 . X-Ray crystal structures of the starting nitrido complex and product dioxo complex are presented. Evidencef or ammonia release comes fromG C-MS and deuterium-labelling studies. Ther eactioni sp resented in the context of a two-stage solar thermochemical dinitrogen fixation process as the solid-state nitride hydrolysis step.[a] J.
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