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Journal ArticleDOI

Metal-Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal.

TL;DR: In this article , the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand was shown to be a potent hydride donor.
Abstract: Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex 1·[Ru]+, comprising a nontrigonal phosphorus chelate (1, P(N(o-N(2-pyridyl)C6H4)2) and an inert metal fragment ([Ru] = (Me5C5)Ru), reacts with NaBH4 to give a metallohydridophosphorane (1H·[Ru]) by P-H bond formation. Complex 1H·[Ru] is revealed to be a potent hydride donor (ΔG°H-,exp < 41 kcal/mol, ΔG°H-,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]+/1H·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.
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TL;DR: The reactivity of pnictinidenes [2,6-(DippN=CH)-6,DippNHCH2)C6H3]E (where E = As (1) or Sb (2)) toward substituted ortho- and para-quinones is reported as mentioned in this paper .
Abstract: The reactivity of pnictinidenes [2-(DippN=CH)-6-(DippNHCH2)C6H3]E (where E = As (1) or Sb (2)) toward substituted ortho- and para-quinones is reported. The central pnictogen atom is easily oxidized by ortho-quinones closing five-membered EO2C2 ring. The oxidized antimony derivatives are stable species, while in the case of arsenic compounds the hydrogen of the pendant amino NHCH2 group cleaves one newly formed As-O bonds leading to the closure of a new azaarsole ring. Furthermore, a heating of these arsenic heterocycles resulted in a C-H bond activation at the NCH2 group involved in this heterocycle followed by a reductive elimination of corresponding catechols and arsinidene [2,6-(DippN=CH)C6H3]As. Using of para-quinones, resulted in the oxidation of the central atom with a concomitant hydrogen migration from NHCH2 group even in the case of the antimony derivatives. The reductive elimination of hydroquinones is in this case feasible for all compounds. Studied compounds were characterized by multi-nuclear NMR, IR and Raman spectroscopy and single-crystal X-ray diffraction analysis. The theoretical study focusing the key compounds and reactions is also included.
Journal ArticleDOI
TL;DR: In this paper, the pyridylmethylaniline proligand (NNLH) is simultaneously deprotonated and 1,4-hydroaluminated by AlH3(NMe2Et) to [(NNLde)AlH(NME 2Et)] (1; NNLde = hydride-inserted dearomatized version of NNL).
Abstract: Dearomatized 1,4-dihydropyridyl motifs are significant in both chemistry and biology for their potential abilities to deliver the stored hydride, driven by rearomatization. Biological cofactors like nicotinamide adenine dinucleotide (NADH) and organic 'hydride sources' like Hantzsch esters are prime examples. An organoaluminum chemistry on a 2-anilidomethylpyridine framework is reported, where such hydride storage and transfer abilities are displayed by the ligand's pyridyl unit. The pyridylmethylaniline proligand (NNLH) is simultaneously deprotonated and 1,4-hydroaluminated by AlH3(NMe2Et) to [(NNLde)AlH(NMe2Et)] (1; NNLde = hydride-inserted dearomatized version of NNL). A hydride abstraction by B(C6F5)3 rearomatizes the pyridyl moiety to give the cationic aluminum hydride [(NNL)AlH(NMe2Et)][HB(C6F5)3] (6). Notably, such chemical non-innocence is priorly unseen in this established ligand class. The hydroalumination mechanism is investigated by isolating the intermediate [(NNL)AlH2] (2) and by control experiments, and is also analyzed by DFT calculation. The results advocate an intriguing 'self-promoting' pathway, which underlines alane's Lewis acid/Brønsted base duality. NMe2Et carrying the alane also plays a crucial role. In contrast, the chemistry between NNLH and AlMe3 is much different, giving only [(NNL)AlMe2] (4) from the adduct [(NNLH)AlMe3] (3) by deprotonation but not a subsequent pyridyl dearomatization in the presence or absence of NMe2Et. This divergence is also justified by DFT analyses.
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Journal ArticleDOI
TL;DR: In this article, the linear quadridentate N2S2 donor ligand 1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-dithiaheptane (bmdhp) forms mono-and di-hydrate 1 : 1 copper(II) complexes which are significantly more stable toward autoreduction than those of the non-methylated analogue.
Abstract: The linear quadridentate N2S2 donor ligand 1,7-bis(N-methylbenzimidazol-2′-yl)-2,6-dithiaheptane (bmdhp) forms mono- and di-hydrate 1 : 1 copper(II) complexes which are significantly more stable toward autoreduction than those of the non-methylated analogue. The deep green monohydrate of the perchlorate salt crystallises as the mononuclear aqua-complex, [Cu(bmdhp)(OH2)][ClO4]2, in the monoclinic space group P21/n, with Z= 4, a= 18.459(3), b= 10.362(2), c= 16.365(3)A, and β= 117.14(1)°. The structure was solved and refined by standard Patterson, Fourier, and least-squares techniques to R= 0.047 and R′= 0.075 for 3 343 independent reflections with l > 2σ(l). The compound consists of [Cu(bmdhp)(OH2)]2+ ions and ClO4– counter ions. The co-ordination around copper is intermediate between trigonal bipyramidal and square pyramidal, with Cu–N distances of 1.950(4) and 1.997(4)A, Cu–O(water) 2.225(4)A, and Cu–S 2.328(1) and 2.337(1)A. In the solid state, the perchlorate dihydrate's co-ordination sphere may be a topoisomer of the monohydrate's. A new angular structural parameter, τ, is defined and proposed as an index of trigonality, as a general descriptor of five-co-ordinate centric molecules. By this criterion, the irregular co-ordination geometry of [Cu(bmdhp)(OH2)]2+ in the solid state is described as being 48% along the pathway of distortion from square pyramidal toward trigonal bipyramidal. In the electronic spectrum of the complex, assignment is made of the S(thioether)→ Cu charge-transfer bands by comparison with those of the colourless complex Zn(bmdhp)(OH)(ClO4). E.s.r. and ligand-field spectra show that the copper(II) compounds adopt a tetragonal structure in donor solvents.

7,886 citations

Journal ArticleDOI
TL;DR: The NBO 6.0 as mentioned in this paper is a new version of the NBO that provides novel "link-free" interactivity with host electronic structure systems, improved search algorithms and labeling conventions, and new analysis options that significantly extend the range of chemical applications.
Abstract: We describe principal features of the newly released version, NBO 6.0, of the natural bond orbital analysis program, that provides novel “link-free” interactivity with host electronic structure systems, improved search algorithms and labeling conventions for a broader range of chemical species, and new analysis options that significantly extend the range of chemical applications. We sketch the motivation and implementation of program changes and describe newer analysis options with illustrative applications. © 2013 Wiley Periodicals, Inc.

1,154 citations

Journal ArticleDOI
TL;DR: Examples of MLC in which both the metal and the ligand are chemically modified during bond activation and 2) Bond activation results in immediate changes in the 1st coordination sphere involving the cooperating ligand, even if the reactive center at the ligands is not directly bound to the metal.
Abstract: Metal-ligand cooperation (MLC) has become an important concept in catalysis by transition metal complexes both in synthetic and biological systems. MLC implies that both the metal and the ligand are directly involved in bond activation processes, by contrast to "classical" transition metal catalysis where the ligand (e.g. phosphine) acts as a spectator, while all key transformations occur at the metal center. In this Review, we will discuss examples of MLC in which 1) both the metal and the ligand are chemically modified during bond activation and 2) bond activation results in immediate changes in the 1st coordination sphere involving the cooperating ligand, even if the reactive center at the ligand is not directly bound to the metal (e.g. via tautomerization). The role of MLC in enabling effective catalysis as well as in catalyst deactivation reactions will be discussed.

846 citations

Journal ArticleDOI
TL;DR: In this paper, the authors highlight the use of non-innocent redox active ligands in catalysis and highlight four main application strategies of redox-active ligands: oxidation/reduction of the ligand to tune the electronic properties (i.e., Lewis acidity/basicity) of the metal.
Abstract: In this (tutorial overview) perspective we highlight the use of “redox non-innocent” ligands in catalysis. Two main types of reactivity in which the redox non-innocent ligand is involved can be specified: (A) The redox active ligand participates in the catalytic cycle only by accepting/donating electrons, and (B) the ligand actively participates in the formation/breaking of substrate covalent bonds. On the basis of these two types of behavior, four main application strategies of redox-active ligands in catalysis can be distinguished: The first strategy (I) involves oxidation/reduction of the ligand to tune the electronic properties (i.e., Lewis acidity/basicity) of the metal. In the second approach (II) the ligand is used as an electron reservoir. This allows multiple-electron transformations for metal complexes that are reluctant to such transformations otherwise (e.g., because the metal would need to accommodate an uncommon, high-energy oxidation state). This includes examples of (first row) transition ...

822 citations