Dianion complexes

Figure 7.10. X-ray structure of dianion 16 shown in two different views (a) ORTEP representation of two dianions complexed with four lithium ions and two molecules of THF, also excluding the toluene molecules found in the crystal, (b) View of the complex without the phenyl groups. (Adapted from ref 64.)...

This sequence has been proposed as a novel approach to olefin separation and purification. Ffowever, there is disagreement about the reversibility of the reaction because it has been shown that irreversible reduction to the dianionic complex occurs through an ECE process.1082 A convenient new route to 1,2-enedithiolate complexes of Ni has been reported, which starts from the bisfhydrosulfldo) complex [Ni(dppe)(SFI)2] and various a-bromoketoues(heterocycle-C(0)CH2Br). 

Complex [Ni(468)] is formed with Ni11 salts and the amine-thiolate ligand, or by reduction of the corresponding Schiff base complex with NaBH4-[Ni(468)] is easily deprotonated to form the dianionic complex, which is subsequently oxidized to the monoanion. On the other hand, the dianionic complex reacts with CH3I to form the fourfold methylated octahedral complex (469).1305 Since without preceding deprotonation only the S-donors are methylated, the complex with twofold amine methyla-tion must be synthesized via protection and subsequent deprotection of the S-donors.1306... 

Figure 15 The reaction of Pd11 salts with two equivalents of dipeptide ester in methanol in the presence of NaOMe as base results in dianionic complexes, which can be isolated by precipitation with suitable cations.

Figure 22 Structures of the hexameric sodium hydrazide 317 and the mixed mono- and dianionic complex 318. Hydrogen atoms have been omitted for clarity.

Organoytterbium chemistry has been developed in the last 20 years, although the development rate is much slower than the other lanthanides like samarium or cerium. Dianionic complexes that are produced from the reaction of ytterbium with diaryl ketones react with various kinds of electrophiles including carbon-heteroatom unsaturated bonds.35 Phenylytterbium iodide, a Grignard-type reagent, is known to have reactivity toward carbon dioxide,36 aldehydes, ketones,37,37 and carboxylic acid derivatives38,3811 to form the corresponding adducts respectively. 

Organometal diamides RM(NR2)2 have also been studied. As an example, the reaction of (Me2N)2Sb(CH2)3Sb(NMe2)2 with 2-NHLiR (R = pyridyl) generating the dianion complex l,3-[(RNLi)Sb]2 (/r-NR)(CH2)3(RNHLi)3THF is shown in Scheme 18.222... 

Hoppe D, Marr F, Bruggemann M (2003) Enantioselective Synthesis by Lithiation Adjacent to Oxygen and Electrophile Incorporation. 5 61-138 Hou Z, Wakatsuki Y (1999) Reactions of Ketones with Low-Valent Lanthanides Isolation and Reactivity of Lanthanide Ketyl and Ketone Dianion Complexes. 2 233-253 Hoveyda AH (1998) Catalytic Ring-Closing Metathesis and the Development of Enantioselective Processes. 1 105-132 Huang M, see Wu GG (2004) 6 1-36... 

Reaction of (34) with the bidentate sulfur ligand isotrithionedithiol (H2dmit, (278)) produced a dianionic complex. The reaction of (278) in which the thiol groups were deprotected in situ prior to the substitution reaction with [TcNClJ in acetonitrile gave a 45% yield of [TcN(dmit)2] ... 

Polarographic and cycKc voltammetric studies showed the formation of dianions, with one of the dianionic complexes exhibiting further chemical reactivity. Bulk electrolysis and infrared spectroelectro-chemistry were used to confirm the decomposition of the dianionic tetranuclear clusters to stable tricobalt anions. 

The iron-molybdenum and iron-tungsten analogs are prepared in precisely the same manner with comparative yields of pure product. Well-formed crystals of [PPN]+ salts of the dinuclear dianion may be obtained by layering diethyl ether onto a concentrated CH3CN solution of dianion complex. 

The complex [W Se2C2(CF3)2 3] has also been prepared123 and like its sulfur analogue, it undergoes two reversible one-electron reductions. The dianionic complex was isolated as the tetrabutylammonium salt. 

Further examples of Bi2 clusters in this class are the anionic and dianionic complexes [Bi2Fe3(CO)9], 2 (130 and 131), reported by Whitmire (128) as resulting from sequential one-electron reduction of 126 with sodium amalgam, and the dibismuth-tetrairon dianion [Bi2Fe4(CO)I3]2 (132) obtained from... 

A wide range of metal dithiolene complexes have been prepared and their electrical conduction properties reported.111-114 They include neutral, monoanion and dianion complexes with a variety of substituents on the ligand (R = Ph, Me, CN, H, CF3) and a variety of cations. The choice of cation has often been determined by the desire to obtain easily crystallized products and has resulted in the use of rather bulky substituted ammonium salts. The compounds behave as semiconductors with relatively low conductivities at room temperature. It has been shown that the monoanion complexes are considerably more conducting than either the corresponding neutral complex or the dianion, and Rosseinsky and Malpas have proposed that this is related to the ease of disproportionation.113... 

It has been demonstrated625 that ytterbium-aromatic imine dianion complexes can act as effective catalysts for the isomerization of terminal alkynes to internal alk-2-ynes. Isomerization of acetylenic pentafluorophenyl esters in the presence of phosphines has been found to give rise to activated dienoic acids, which have been coupled directly with amines (and alcohols) in a simple one-pot procedure626 (see Scheme 124). 

The reaction product of ytterbium metal with benzophenone in a 1 1 molar ratio could be determined by an X-ray structure [278]. The benzophenone dianion unsymmetrically bridges the ytterbium atoms in the HMPA solvate [Yb(OCPh2)2(HMPA)2]2. The aryl oxygen forms a Yb-O bond with a typical terminal bond length (Table 18), but also donates to the other ytterbium. A Yb-C a-bond involving the a-C-atom (2.59(5) A) balances the charge at Yb (II). Reaction of the dianionic complex with four equivalents of phenol HOC6H3tBu2-2,6-Me-4 afforded the mononuclear aryloxide complex Yb(OAr)2(HMPA)2 (Sect. 4.2) [72],... 

An example of rj5 bonding type is evident in the case of the bis(germole dianion) complex [K4(18-crown-6)]3[C4Me4Ge]2 (Figure 7)21. 

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