Ni -complexes

Meta.1 Complexes. The importance of Ni complexes is based on their effectiveness as quenchers for singlet oxygen. Of disadvantage is their low colorfastness and their lower ir-reflectance compared to cyanine dyes (qv) therefore they are used in combination with suitable dyes. Numerous complexes are described in the Hterature, primarily tetrathiolate complexes of Pt or Ni, eg, dithiolatonickel complexes (3). Well known is the practical use of a combination of ben2othia2ole dyes with nickel thiol complexes in WORM disks (Ricoh, TDK) (17). 

Extensive efforts have been made to develop catalyst systems to control the stereochemistry, addition site, and other properties of the final polymers. Among the most prominant ones are transition metal-based catalysts including Ziegler or Ziegler-Natta type catalysts. The metals most frequentiy studied are Ti (203,204), Mo (205), Co (206-208), Cr (206-208), Ni (209,210), V (205), Nd (211-215), and other lanthanides (216). Of these, Ti, Co, and Ni complexes have been used commercially. It has long been recognized that by varying the catalyst compositions, the trans/cis ratio for 1,4-additions can be controlled quite selectively (204). Catalysts have also been developed to control the ratio of 1,4- to 1,2-additions within the polymers (203). 

OPTICAL DENSITY DIFFERENTIATION FOR THE MIXTURES OF Cu, Zn, Co, Ni COMPLEXES WITH 4-(2-PYRIDYLAZO)-RESORCINOL... 

TROST - CHEN Decarboxylation Ni complex catalyzed decarboxylation of dicarboxylic acid anbydndes to form alkenes. 

Na2S04, filter, evaporate and distil the residue under reduced pressure [Bredereck et al. Chem Ber 90 1837 1957). The Ni complex [Ni(SCH2C02Et)2] recrystallised twice from EtOH gives crystals which became black when dried in a vacuum over H2SO4, m 104-105° [Dranet and Cefola J Am Chem Soc 76 1975 1954]. 

The use of liquid NH3 to prepare compounds of elements in unusual (low) oxidation states is exemplified by the successive reduction of K2[Ni(CN)4] with Na/Hg in the presence of an excess of CN the dark-red dimeric Ni complex K4[Ni2(CN)6] is first formed and this can be further reduced to the yellow Ni° complex K4[Ni(CN)4]. The corresponding complexes [Pd(CN)4]" and [Pt(CN)4]" can be prepared similarly, though there is no evidence in these latter systems for the formation of the M dimer. A ditertiaiyphosphine complex of Pd° has also been prepared ... 

The oxygen-bridging mode (v) is less common but occurs together with modes (iii) and (iv) in the following centrosymmetrieal trimeric Ni complex and related compounds. 

This is undoubtedly the most prolific oxidation state for this group of elements. The stereochemistry of Ni" has been a topic of continuing interest (see Panel), and kinetic and mechanistic studies on complexes of Pd" and Pt" have likewise been of major importance. It will be convenient to treat Ni" complexes first and then those of Pd" and Pt"... 

A partial explanation, at least, can be provided for the relative abundances and ease of formation of the above stereochemical varieties of Ni complexes. It can be seen from Table 26.6 that the CFSEs of the d configuration, unlike those of the d configuration (e.g. Co ), favour an... 

Polymerization of alkynes by Ni" complexes produces a variety of products which depend on conditions and especially on the particular nickel complex used. If, for instance, O-donor ligands such as acetylacetone or salicaldehyde are employed in a solvent such as tetrahydrofuran or dioxan, 4 coordination sites are available and cyclotetramerization occurs to give mainly cyclo-octatetraene (cot). If a less-labile ligand such as PPhj is incorporated, the coordination sites required for tetramerization are not available and cyclic trimerization to benzene predominates (Fig. A). These syntheses are amenable to extensive variation and adaptation. Substituted ring systems can be obtained from the appropriately substituted alkynes while linear polymers can also be produced. 

Scheme 5.2-6 Synthesis of a deuterated analogue of the square-planar Ni-complex (i -4-...

Ionic liquid Composition of the ionic liquid (molar ratio) Ni-complex Activity (kgg(Ni)- b-v Product DMB/ M2P/nH < >... 

The selective, Ni-catalyzed, biphasic dimerization of 1-butene to linear octenes has been studied in the author s group. A catalytic system well loiown for its ability to form linear dimers from 1-butene in conventional organic solvents - namely the square-planar Ni-complex (q-4-cycloocten-l-yl](l,l,l,5,5,5,-hexafluoro-2,4-pen-tanedionato-0,0 )nickel [(H-COD)Ni(hfacac)] [103] - was therefore used in chloroaluminate ionic liquids. 

Figure 5.2-7 The cationic Ni-complex [(mall)Ni(dppmo)][SbFg] as used for the diphasic oligomerization of ethylene to a-olefins in, for example, [BMIM][PFg].

In addition to the neutral nickel/phosphine complexes used in the Shell Higher Olefins Process (SHOP), cationic Ni-complexes such as [(mall)Ni(dppmo)][SbF6] (see Figure 5.2-7) have attracted some attention as highly selective and highly active catalysts for ethylene oligomerization to HAOs [106]. 

However, all attempts to carry out biphasic ethylene oligomerization with this cationic catalyst in traditional organic solvents, such as 1,4-butanediol (as used in the SHOP) resulted in almost complete catalyst deactivation by the solvent. This reflects the much higher electrophilicity of the cationic complex [(mall)Ni(dppmo)] [SbFg] in relation to the neutral Ni-complexes used in the SHOP. 

The fact that ionic liquids with weakly coordinating anions can combine, in a unique manner, relatively high polarity with low nucleophilicity allows biphasic catalysis with highly electrophilic, cationic Ni-complexes to be carried out for the first time [26]. 

PMMA finds ordn usage in several areas in ballistic or impact shields for missiles or airplanes also as windows, windshields or canopies in aircraft (Refs 7 and 22) as a Laser Q switch host using an organic Ni complex dye (Ref 22) and in proplnts as fuel (with A1 and NG as cofuels — Ref 20) and Amm perchlorate or K perchlorate as oxidizers (Refs 2, 4, 8—11, 13,14 16—20). Also see under Aeroplex Propellants in Vol 1, A108-R and under Composite Propellants in Vol 3, C464-L to C474-L Refs 1) Beil 2, [398] and (1279 1283 ... 

Bis-tert-butylthioquinoxaline (53) afforded the Ni complex (54) with loss of 2-methylpropene (55) (NiCl2, trace HCl, Me0CH2CH20H, reflux, 12 h 78%). ... 

A Ru—Si complex 169), a cobaloxime derivative 216a), a Ni complex 216), and the reported Pd compound (obtained in an impure state) 158) have also been made [Eqs. (20)-(23)]. 

The first electrochemical H2 generation catalyzed by a hetero-nuclear Fe-Ni complex [Ni(L)Fe2(CO)g] (27) [L - = (CH3C6H3S2)2(CH2)3 ] (Fig. 9) with tri-fluoroacetic acid was reported by Schoder and coworkers in 2006 [211]. Based on their electrochemical behavior, spectroscopic data, and DFT calculations of 27, an EECC mechanism was mled out and therefore an ECCE or ECEC mechanism involving the formation of Fe°-H and Ni -H intermediates is likely. In this cycle, six catalytic turnovers were achieved. This value is comparable to those for... 

In 2009, Rauchfuss and coworkers succeeded in the synthesis of the Fe- i-H-Ni complex [(CO)3Fe(pdt)(p-H)Ni(dppe)]BF4 28 (pdt = 1,3-propanedithiolate, dppe = 1,2-C2H4(PPh2)2) as a model for [NiFeJ-hydrogenases (Scheme 64) [212]. The structure of 28 was characterized by X-ray crystallographic analysis. This is the first example of an Fe-Ni thiolato hydride complex. Evolution of H2 by electrochemical reduction of CF3CO2H (pXa = 12.65) was observed in the presence of the catalytic amounts of 28. 

Reductions of various Co(ni) complexes by Fe(II) have been studied under high pressures . The motivation for performing such experiments resides in the possibility that the volume of activation (AF ), like the entropy of activation, might be a criterion for distinguishing between inner- and outer-sphere reactions. For reactions of the type... 

Despite the lability of Fe(ni) complexes, Haim and Sutin have been able to study the rapid reductions of some Co(III) complexes by Fe(fr) and identify the primary Fe(III) products. A flow apparatus, described by Dulz and Sutin", enabled the rate of formation and decay of the spectra of the Fe(III) products... 

Metal-ligand vibrations have been identified using metal isotopes, e.g. the Ni—P stretching band which appears at 273.4 cm for NiCl2(PEt3)2 is shifted to 267.5 cm" for the Ni complex. 

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