1. Advantages of Chemical Redox Agents 878 2. Disadvantages of Chemical Redox Agents 879 C. Potentials in Nonaqueous Solvents 879 D. Reversible vs Irreversible ET Reagents 879 E. Categorization of Reagent Strength 881 II. Oxidants 881 A. Inorganic 881 1. Metal and Metal Complex Oxidants 881 2. Main Group Oxidants 887 B. Organic 891 1. Radical Cations 891 2. Carbocations 893 3. Cyanocarbons and Related Electron-Rich Compounds 894

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Chemical Redox Agents for Organometallic Chemistry

Synthetic organic chemists enjoy the luxury of having a large collection of reliable reactions at their disposal for preparing small molecules, mesoscopic structures, and polymers. Coordination chemists, on the other hand, are faced with the fact that transition metal chemistry, when normalized for the number of transition metals, has relatively few high-yielding reactions, when compared to the chemistry of carbon, for preparing even small molecule structures. This lack of control is manifested, in large part, in the weak metal-ligand interactions found in coordination complexes as compared with the strong covalent bonds in organic compounds. Weak bonding often translates into many reaction pathways that are not substantially different from an energetic point of view, and therefore, results in poor selectivity. As a result, many coordination chemists in recent years have come to the realization that it may be easier and more productive to develop straightforward and reliable routes to mesoscopic supramolecular structures by capitalizing on the modest collection of high-yielding reactions in coordination chemistry, the directional bonding afforded by metal centers, and strategies aimed at taking advantage of the weak metal bonds found in coordination complexes. Three emerging synthetic strategies, the symmetry-interaction, directional-bonding, and weak-link synthetic approaches, all use metal centers as structural building blocks to rationally assemble molecular components into supramolecular metallocyclophanes. These three approaches are discussed herein, and the fundamental principles underlying each as well as their capabilities are compared and contrasted.

Strategies for the Construction of Supramolecular Compounds through Coordination Chemistry

Crown ethers: sensors for ions and molecular scaffolds for materials and biological models.

Iron-catalyzed hydroxyl radical formation. Stringent requirement for free iron coordination site.

The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals—nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl—so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).

Playing with organic radicals as building blocks for functional molecular materials

(n = 2-5; HB(Me,pz),- = hydrotris(3,5-dimethylpyrazoly1)borate) have been synthesized and characterized by spectroscopic methods. All contain the redox-active (MO(NO))~+ moiety incorporated in an unusually large chelate ring which forms a cyclic polyether structure. Cyclic voltammetric studies of these compounds reveal a reduction process at ca. -1.3 V (SCE) which is shifted to more anodic potentials in the presence of an equimolar concentration of sodium ions. At higher concentrations, decomposition is associated with the reduction process. In the case where n = 3, 1:l complexes with Li+, Na+, and K+ have been isolated. The molecular structure of [Mo(NO)(HB(Me2pz)3)(OCH2(CH20CH2)3CH20)] has been determined by X-ray diffraction methods. The compound crystallizes in the orthorhombic space group Pbca (No. 61) with eight molecules in a cell of dimensions a = 16.937 (3), b = 15.143 (4), and c = 22.034 (8) A. Full-matrix least-squares refinement gives final R, R, on Fof 0.051,0.079 for 3063 observed [F > 5u(F)] data, This structure confirms the presence of a 14-membered chelate ring (Md = 1.903 (4) and 1.910 (4) A; 0-Mo-0 = 101.0 (2)O) and a linear nitric oxide ligand (Mo-N-O = 177.9 (5)'; N-O = 1.190 (6) A). The cyclic polyether ring is extended away from the bulky HB(Me2pz), ligand.

Redox-responsive molybdenum mononitrosyl complexes incorporating cyclic polyether cation binding sites and x-ray crystal structure of [Mo(NO){HB(3,5-Me2C3N2H)3}{OCH2(CH2OCH2)3CH2O}]

The reaction of 2-telluraphthalide, C8H6OTe, with [Fe3(CO)12] gave as the major characterised species compound 1, [C6H4CH2TeFe(CO)3]2. An iron atom has inserted into the telluracyclic ring, and it is probable that one co-ordinated CO ligand arises from the initially organic carbonyl group. X-Ray single crystal investigations revealed a dimeric structure containing an Fe2Te2 core. The reaction of 2-telluraphthalic anhydride, C8H4O2Te, with [Fe3(CO)12] gave a known, but unexpected, organic product phthalide, C8H6O2. X-Ray crystallography confirmed its isolation; the main feature of interest is the significant double bond character of C(8)–O(1) at 1.352(4) A. 2-Selenaphthalic anhydride, C8H4O2Se, gave intractable products on reaction with [Fe3(CO)12], but 2-selenaphthalide, C8H6OSe, on reaction with the carbonyl gave a major product 2, [Fe(CO)3{C6H4CH2SeFe(CO)3}] and a minor product 3, [Fe(CO)2{η6-C6H4CH2SeFe2(CO)6}] which is an intermediate in the formation of 2. Compound 2 was shown by X-ray methods to be very similar to 1 except that the 18 electron rule is satisfied by co-ordination of an Fe(CO)3 moiety, rather than by dimerisation. Compound 3, also studied by X-ray crystallography, differs from 2 mainly in the addition of an η6-bonded Fe(CO)2 moiety, but the selenaferrole ring is more distorted. It is proposed that comparative studies of reactions of selenium and tellurium compounds with [Fe3(CO)12] may assist the development of an understanding of the complex reaction pathways.

The reactions of heterocyclic organotellurium and selenium compounds with triiron dodecacarbonyl

The crystal structures of 1-allyl-1-bromo-3,4-benzo-1-telluracyclopentane [C8H8Te(C3H5)Br], 1-phenacyl-1-bromo-3,4-benzo-1-telluracyclopentane [C8H8Te(C8H7O)Br] and 1-deuteromethyl-1-iodo-3,4-benzo-1-telluracyclopentane [C8H8Te(CD3)I]; the trans effect in organotellurium bromides and iodides☆

The tridentate ligand 2-[Ph2P(CH2)3NCH]C6H4OH (HL), which contains both ‘hard’ and ‘soft’ potential donor atoms, has been synthesized. Single-crystal X-ray diffraction studies show that, in the solid state, this ligand adopts a structure in which the oxygen and nitrogen atoms are linked by an intramolecular hydrogen bond. The reaction of this material with [ReOCl4]– to form [ReOCl2L] leads to the replacement of the proton in this hydrogen bond by rhenium(V), and the folding of the trimethylene chain to bring the phosphorus atom [Re–P 2.442(5)A] into a position which allows the ligand to bind facially to the {ReO}3+ moiety through all three donor atoms. The co-ordination site trans to the ReO oxygen [Re–O = 1.711 (13)A] is occupied by the phenolic oxygen [Re–O = 1.965(13)A] and the rhenium atom has a distorted octahedral co-ordination environment.

Syntheses and molecular structures of the tridentate phosphine ligand 2-[Ph2P(CH2)3NCH]C6H4OH (HL) and its rhenium(V) complex [ReOCl2L]·0.25CH2Cl2

The crystal structures of the 1-methyl-3,4-benzo-1-telluracyclopentane and 1-phenyl-1-telluracyclopentane cations in their tetraphenylborate salts, C8H8TeMe+ BPh4− and C4H8TePh+ BPh4−

Thomas A. Hamor

Papers

Redox-responsive molybdenum mononitrosyl complexes incorporating cyclic polyether cation binding sites and x-ray crystal structure of [Mo(NO){HB(3,5-Me2C3N2H)3}{OCH2(CH2OCH2)3CH2O}]

The reactions of heterocyclic organotellurium and selenium compounds with triiron dodecacarbonyl

The crystal structures of 1-allyl-1-bromo-3,4-benzo-1-telluracyclopentane [C8H8Te(C3H5)Br], 1-phenacyl-1-bromo-3,4-benzo-1-telluracyclopentane [C8H8Te(C8H7O)Br] and 1-deuteromethyl-1-iodo-3,4-benzo-1-telluracyclopentane [C8H8Te(CD3)I]; the trans effect in organotellurium bromides and iodides☆

Syntheses and molecular structures of the tridentate phosphine ligand 2-[Ph2P(CH2)3NCH]C6H4OH (HL) and its rhenium(V) complex [ReOCl2L]·0.25CH2Cl2

The crystal structures of the 1-methyl-3,4-benzo-1-telluracyclopentane and 1-phenyl-1-telluracyclopentane cations in their tetraphenylborate salts, C8H8TeMe+ BPh4− and C4H8TePh+ BPh4−