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Cleavage of Ni-(mu(2)-S)-Ni bridges in dinuclear nickel(II) dithiolate pincer complexes and related reactions.

ABSTRACT: Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble Ni(II) pincer complexes formulated as [Ni(pdmt)](2) and [Ni(pdtc)](2), respectively, with two Ni-(mu(2)-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)](2) + 2L(0,-) --> 2[Ni(pdtc)L](0,-) with an extensive set of nucleophiles to afford planar mononuclear products with L(-) = halide, CN, Me(3)SiO(-), RS(-) and L(0) = Et(3)P and a N-heterocyclic carbene. [Ni(pdmt)](2) is considerably less reactive toward bridge disruption. Cleavage products support several reactions of interest leading to other mononuclear species and to di- and trinuclear complexes. [Ni(pdtc)(OSiMe(3))](1-) deprotonates acetonitrile and acetone to form [Ni(pdtc)(CH(2)R)](1-) (R = CN, COMe). Reaction of [Ni(pdtc)SEt](1-) with Fe(II) yields the thiolate-bridged dimer {[Ni(pdtc)](2)(SEt)}(1-). Refluxing an acetonitrile solution of [Ni(pdtc)SH](1-) in air results in formation of trinuclear [Ni(pdtc)](3)S](2-) containing the rare unsupported Ni(3)(mu(3)-S) bridge core. Reaction of [Ni(pdtc)CN](1-) with [Fe(Me(6)tren)(OTf)](1+) forms the complex [Ni(pdtc)CNFe(Me(6)tren)](1+), the only example of a single Ni-C[triple bond]N-Fe bridge within a molecule. Structures of the various types of reaction products are presented. This work demonstrates the potential utility of bridge cleavage of polynuclear Ni(II) thiolates, an extensive family of compounds, to produce mononuclear products.

SUBMITTER: Huang D

PROVIDER: S-EPMC2878386 | biostudies-literature | 2009 Jul

REPOSITORIES: biostudies-literature

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Cleavage of Ni-(mu(2)-S)-Ni bridges in dinuclear nickel(II) dithiolate pincer complexes and related reactions.

Huang Deguang D Deng Liang L Sun Jibin J Holm R H RH

Inorganic chemistry 20090701 13

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble Ni(II) pincer complexes formulated as [Ni(pdmt)](2) and [Ni(pdtc)](2), respectively, with two Ni-(mu(2)-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)](2) + 2L(0,-) --> 2[Ni(pdtc)L](0,-) with an extensive set of nucleophiles to afford planar mononuclear products with L(-) = halide, CN, Me(3)SiO(-), RS(-) and L(0) = Et(3)P and a N-heterocyc ...[more]

PMID: 19459662

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Project description:Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and Y, at the para-aryl positions. Together with four previously known H(X,Y) ligands, a series of 12 Ni(X,Y)2 complexes were prepared in high yields by a simple one-pot reaction. Six of the 12 derivatives were characterized by single-crystal X-ray diffraction, which showed tetragonally distorted hexacoordinate nickel(II) centers. The nickel(II) complexes exhibit two quasi-reversible one-electron oxidation waves in their cyclic voltammograms, with half-wave potentials that varied over a remarkable 700 mV range with the average of the Hammett ?(p) parameters of the para-aryl X, Y groups. The one- and two-electron oxidized derivatives [Ni(Me,Me)2](BF4)n (n = 1, 2) were prepared synthetically, were characterized by X-band EPR, electronic spectroscopy, and single-crystal X-ray diffraction (for n = 2), and were studied computationally by DFT methods. The dioxidized complex, [Ni(Me,Me)2](BF4)2, is an S = 2 species, with nickel(II) bound to two ligand radicals. The mono-oxidized complex [Ni(Me,Me)2](BF4), prepared by comproportionation, is best described as nickel(II) with one ligand centered radical. Neither the mono- nor the dioxidized derivative shows any substantial electronic coupling between the metal and their bound ligand radicals because of the orthogonal nature of their magnetic orbitals. On the other hand, weak electronic communication occurs between ligands in the mono-oxidized complex as evident from the intervalence charge transfer (IVCT) transition found in the near-IR absorption spectrum. Band shape analysis of the IVCT transition allowed comparisons of the strength of the electronic interaction with that in the related, previously known, Robin-Day class II mixed valence complex, [Ga(Me,Me)2](2+).

Project description:The 15e square-planar complexes [Co(PCPMe-iPr)Cl] (2a) and [Co(PCP-tBu)Cl] (2b), respectively, react readily with NaBH4 to afford complexes [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Co(PCP-tBu)(η2-BH4)] (4b) in high yields, as confirmed by IR spectroscopy, X-ray crystallography, and elemental analysis. The borohydride ligand is symmetrically bound to the cobalt center in η2-fashion. These compounds are paramagnetic with effective magnetic moments of 2.0(1) and 2.1(1) μB consistent with a d7 low-spin system corresponding to one unpaired electron. None of these complexes reacted with CO2 to give formate complexes. For structural and reactivity comparisons, we prepared the analogous Ni(II) borohydride complex [Ni(PCPMe-iPr)(η2-BH4)] (5) via two different synthetic routes. One utilizes [Ni(PCPMe-iPr)Cl] (3) and NaBH4, the second one makes use of the hydride complex [Ni(PCPMe-iPr)H] (6) and BH3·THF. In both cases, 5 is obtained in high yields. In contrast to 4a and 4b, the borohydride ligand is asymmetrically bound to the nickel center but still in an η2-mode. [Ni(PCPMe-iPr)(η2-BH4)] (5) loses readily BH3 at elevated temperatures in the presence of NEt3 to form 6. Complexes 5 and 6 are both diamagnetic and were characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR, IR spectroscopy, and elemental analysis. Additionally, the structure of these compounds was established by X-ray crystallography. Complexes 5 and 6 react with CO2 to give the formate complex [Ni(PCPMe-iPr)(OC(C=O)H] (7). The extrusion of BH3 from [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) with the aid of NH3 to yield the respective hydride complexes [Co(PCPMe-iPr)H] and [Ni(PCPMe-iPr)H] (6) and BH3NH3 was investigated by DFT calculations showing that formation of the Ni hydride is thermodynamically favorable, whereas the formation of the Co(II) hydride, in agreement with the experiment, is unfavorable. The electronic structures and the bonding of the borohydride ligand in [Co(PCPMe-iPr)(η2-BH4)] (4a) and [Ni(PCPMe-iPr)(η2-BH4)] (5) were established by DFT computations.

Dataset Information

Cleavage of Ni-(mu(2)-S)-Ni bridges in dinuclear nickel(II) dithiolate pincer complexes and related reactions.

Publications

Cleavage of Ni-(mu(2)-S)-Ni bridges in dinuclear nickel(II) dithiolate pincer complexes and related reactions.

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