Nickel complexes monodentate

Even if the C104 ion is commonly believed to experience a scarce tendency to act as a ligand, nonetheless coordination of perchlorate as a monodentate ligand through an oxygen atom has been proposed in a number of nickel complexes containing alkylamines,1676 pyridine and substituted pyridines,1677-1680 arylamines such as aniline and substituted anilines,1681 phosphine and arsine oxides1682,1683 (Table 84). 

Reactions of 250 with four electrophiles are recorded in Scheme 31. In general, the products are more stable than those from complexes with monodentate ligands. Reaction of 249 with CS2, 249 or 250 with alkynes, and 249-251 with ethylene gives products in which the C6H8 has been lost but its fate has not been determined attempts to trap free cyclohexyne failed.93 Loss of the organic ligand appears to occur more readily in nickel complexes than in those with platinum. 

Allyl complexes of nickel with monodentate phosphines, e.g., (22-XXXIII), are highly active catalysts for the dimerization of propene.130 Nickel hydride species... 

The biphosphite ligands, (5) and (6), react with [(cod)2Ni] to form nickel complexes of type (7). Nickel phosphite complexes are catalysts in the hydrocyanation of butadiene complex (7) is more robust than the monodentate phosphite analogs. ... 

There are only a few examples of complexes of monodentate SB ligands. One of them is the SB PhCH=NMe which acts as a monodentate ligand in a Pd complex.7 Another example is provided by the SB Ph3P=CHC(=NPh)Ph which coordinates in a monodentate manner in a nickel complex.35... 

In addition to the nickel complexes discussed above the interaction of complexes Cu° [H4](X )l1, Cu [H4](X )l2, Fe°I [H4](Me)Ll Y and Cr [H4](Me)Ll Y (Y = monodentate anion) with dioxygen in aerated acetone was also studied. It was found that these complexes are obviously not dehydrogenated, since the vis spectra were stable for long periods of time. 

Tremendous effort has been made to develop ligands that control and improve the selectivity, stability, and reactivity of palladium and nickel complexes for cross coupling. Initially, ligandless palladium complexes and triphenylphosphine-palladium complexes were used for these processes. Subsequently, bidentate ligands and monodentate ligands have been developed that possess particular electronic and steric properties that increase reaction rates, scope, and turnover numbers. 

The [2 + 2] reaction also occurs for stained olefins 49 and 50, giving only the exo cycloadducts (Scheme 25). It was thought that the reaction proceeds via the exo metallacyclopentane intermediate Y arising from monodentate coordination to the exo face of the bicyclic olefins. The similarity in the electronic spectra of nickel complexes of these olefins to those of the complex of norbomene, which was known to coordinate on the exo face, supports this mechanism. 

Metal ion complexation rates have been studied by the T-jump method. ° Divalent nickel and cobalt have coordination numbers of 6, so they can form complexes ML with monodentate ligands L with n = 1—6 or with bidentate ligands, n = 1-3. The ligands are Bronsted bases, and only the conjugate base form undergoes coordination with the metal ion. The complex formation reaction is then... 

Monodentate dipolarophiles such as acrolein, methacrolein, and a-bromoacrolein could be successfully utilized in the l ,J -DBFOX/Ph-transition metal complex-catalyzed asymmetric nitrone cycloadditions [76]. The reactions of N-benzylideneani-line N-oxide with acrolein in the presence of the nickel(II) aqua complex R,R-DBF0X/Ph-Ni(C104)2 3H20 (10mol%) and MS 4 A produced a mixture of two regioisomers (5-formyl/4-formyl regioisomers ca 3 1). However, enantio-... 

Other dichloro(ditertiary phosphine)nickel(II) complexes (see Table VI) catalyze both hydrosilylation and H/Cl exchange, but analogous complexes containing monodentate phosphine ligands or bidentate amine groups are essentially inactive (173). 

With P-donors a variety of different structures are formed. Two complexes (359a,b) with a five-coordinate square pyramidal geometry and one S-donor in the apical position are reported.934,933 In a related complex (360) the nickel center reveals a distorted square planar geometry, because one xanthate ligand switched to a monodentate coordination mode. 6 By reaction of [NiL2] complexes with Ph2P(CH2)2P(Ph)(CH2)2PPh2, compound (362) is formed, which consists of a five-coordinate cation and a hexacoordinate anion. 7... 

Catalytic homogeneous hydrogenation of cyclohexene has been claimed for simple systems such as nickel(II) acetylacetonate [39] or a nickel-chloride complex with two monodentate amines [40]. The latter complex was used as comparison for a heterogeneous catalyst obtained by impregnation of the complex on y-alu-mina [40]. SCRs of 100 were used at 30 atm. H2 and temperatures up to 100°C, resulting in conversions of only 20-35% after 1 h. 

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