The synthesis of a heterodinucleating ligand LH2 (LH2 = (E)-3-(((2,7-di-tert-butyl-9,9-dimethyl-5-((pyridin-2-ylmethylene)amino)-9H-xanthen-4-yl)amino)methyl)benzene-1,2-diol) was undertaken toward a functional model of the bimetallic active site found in Mo-Cu carbon monoxide dehydrogenase (Mo-Cu CODH), and to understand the origins of heterobimetallic cooperativity exhibited by the enzyme. LH2 features a hard potentially dianionic catechol chelate for binding Mo(vi) and a soft iminopyridine chelate for binding Cu(i). Treatment of LH2 with either Cu(i) or M(vi) (M = Mo, W) sources leads to the anticipated site-selective incorporation of the respective metals. While both [CuI(LH2)]+ and [MVIO3(L)]2- complexes are stable in the solid state, [MVIO3(L)]2- complexes disproportionate in solution to give [MVIO2(L)2](NEt4)2 complexes, with [MVIO4]2- as the by-product. The incorporation of BOTH Mo(vi) and Cu(i) into L forms a highly reactive heterobimetallic complex [MoVIO3CuI(L)](NEt4)2, whose formation and reactivity was interrogated via1H NMR/UV-vis spectroscopy and DFT calculations. These studies reveal that the combination of the two metals triggers oxidation reactivity, in which a nucleophilic Mo(vi) trioxo attacks Cu(i)-bound imine. The major product of the reaction is a crystallographically characterized molybdenum(vi) complex [Mo(L')O2](NEt4) coordinated by a modified ligand L' that contains a new C-O bond in place of the imine functionality. This observed hydroxylation reactivity is consistent with the postulated first step of Mo-Cu CODH (nucleophilic attack of the Mo(vi)-oxo on the Cu(i)-bound electrophilic CO) and xanthine oxidoreductase (nucleophilic attack of Mo(vi)-oxo on the electrophilic xanthine carbon).
A mononuclear magnesium complex Mg(OCtBu2Ph)2(THF)2 catalyzes the active polymerization of cyclic esters and alternating co-polymerization of epoxides with cyclic anhydrides.
In an effort to probe the feasibility of a model of Mo-Cu CODH (CODH = carbon monoxide dehydrogenase) lacking a bridging sulfido group, the new heterodinucleating ligand LH 2 was designed and its Cu(I)/Mo(VI) reactivity was investigated. LH 2 ((E)-3-(((5-(bis(pyridin-2-ylmethyl)amino)-2,7-di-tert-butyl-9,9-dimethyl-9H-xanthen-4-yl)imino)methyl)benzene-1,2-diol) features two different chelating positions bridged by a xanthene linker: bis(pyridyl)amine for Cu(I) and catecholate for Mo(VI). LH 2 was synthesized via the initial protection of one of the amine positions, followed by two consecutive alkylations of the second position, deprotection, and condensation to attach the catechol functionality. LH 2 was found to exhibit dynamic cooperativity between two reactive sites mediated by H-bonding of the catechol protons. In the free ligand, catechol protons exhibit H-bonding with imine (intramolecular) and with pyridine (intermolecular in the solid state). The reaction of LH 2 with [Cu-(NCMe) 4 ] + led to the tetradentate coordination of Cu(I) via all nitrogen donors of the ligand, including the imine. Cu(I) complexes were characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), X-ray crystallography, and DFT calculations. Cu(I) coordination to the imine disrupted H-bonding and caused rotation away from the catechol arm. The reaction of the Cu(I) complex [Cu(LH 2 )] + with a variety of monodentate ligands X (PPh 3 , Cl − , SCN − , CN − ) released the metal from coordination to the imine, thereby restoring imine H-bonding with the catechol proton. The second catechol proton engages in H-bonding with Cu−X (X = Cl, CN, SCN), which can be intermolecular (XRD) or intramolecular (DFT). The reaction of LH 2 with molybdate [MoO 4 ] 2− led to incorporation of [Mo VI O 3 ] at the catecholate position, producing [MoO 3 (L)] 2− . Similarly, the reaction of [Cu(LH 2 )] + with [MoO 4 ] 2− formed the heterodinuclear complex [CuMoO 3 (L)] − . Both complexes were characterized by multinuclear NMR, UV−vis, and HRMS. HRMS in both cases confirmed the constitution of the complexes, containing molecular ions with the expected isotopic distribution.
Di-zinc complexes of a new dinucleating xanthene-based bis(iminophenolate) ligand have been synthesized, and their coordination chemistry and lactide polymerization activity have been investigated.
4,4'-Methylene diphenyl diisocyanate (MDI) is an industrially crucial compound, being one of the most utilized linkers in the polyurethane industry. However, its long-term stability is limited due to dimerization to form insoluble uretdione. Herein we demonstrate an organometallic "catchstore-release" concept aiming at improving the long-term chemical stability of MDI. Treatment of MDI with two equivalents of selected N-heterocyclic carbenes (NHC) forms stable MDIÀ NHC adducts. Treatment of the adducts with CuCl forms metastable di-Cu I complexes that undergo decomposi-tion to re-form MDI (up to 85 %), along with CuÀ NHC complexes. The yield of re-formed MDI can be improved (up to 95 %) by the release of the NHC ligands in the form of thiourea; this prevents subsequent MDI dimerization/polymerization by the carbenes. Furthermore, the need to separate MDI from the reaction mixture can be eliminated by the direct reaction of MDIÀ NHC complexes with alcohols (as models for diols), that form dicarbamate (as a model for polyurethane) quantitatively.
4,4’‐Methylene diphenyl diisocyanate (4,4’‐MDI) is a key diisocyanate linker in the production of polyurethanes. 4,4’‐MDI is thermally unstable, undergoing dimerization to unreactive and insoluble uretdione. The “catch–store–release” strategy presented in the Research Article by S. Groysman and co‐workers (DOI: 10.1002/chem.202300924) allows 4,4’‐MDI to be stabilized in the form of an imidazolium amidate that is produced by the coordination of two equivalents of N‐heterocyclic carbene. The complex can be released by heating with CuCl (with or without sulfur); this forms a CuI carbene/urea complex and restores MDI. Artwork by the authors with help from Mary Iverson.
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