Arsine oxides, nickel complexes

Numerous nickel(II) complexes with a variety of phosphine and arsine oxides have been reported, but only a few X-ray crystal structures have been determined. In some cases the structures assigned to the complexes are not completely certain.1800 A selection of nickel(II) complexes is reported in Table 86. 

Unlike the tertiary phosphine and arsine oxides which form a variety of nickel complexes with peculiar properties, tertiary arsine sulfides and, particularly, tertiary phosphine sulfides... 

Even if the ClOl" ion is commonly believed to experience a scarce tendency to act as a ligand, nonetheless coordination of perchlorate as a monodentate ligand throng an oxygen atom has been proposed in a number of nickel complexes containing alkylamines, pyridine and substituted pyridines, arylamines such as aniline and substituted anilines, phosphine and arsine oxides (Table 84). 

The reaction of fluoroalkenes with nickel(O) phosphine and arsine complexes may also result in the dimerization of the fluoroalkene and in the formation, for example, of octafluoro-nickelacyclopentane complexes [Ni(ER3)2(CF2)4] (E = P, As), which contain the nickel atom in the formal oxidation state +2., 55 A similar reaction also occurs when [N PPhj QtFj reacts... 

The earliest examples of higher oxidation states of nickel were given in 19133021 and the first nickel(III) complex, Ni(PEt3)2Br3, was isolated by Jensen in 1936. 2 In 1907 Hall reported the occurrence of nickel(IV) in a heteropolymolybdate,3023 and in 1951 Nyholm described the synthesis of a nickel(IV) complex with the chelating arsine o -phenylenebisdimethylarsine (diars).3024 In the last 15 years the chemistry of nickel(III) and nickel(IV) complexes has largely developed due to the use of electrochemical methods of synthesis. 

The pale yellow [Ni(PEt3)4] is also tetrahedral but with some distortion. In sharp contrast to nickel, palladium forms no simple carbonyl, Pt(CO)4 is prepared only by matrix isolation at very low temperatures and reports of K4[M(CN)4] (M = Pd, Pt) may well refer to hydrido complexes in any event they are very unstable. The chemistry of these two metals in the zero oxidation state is in fact essentially that of their phosphine and arsine complexes and was initiated by L. Malatesta and his school in the 1950s. Compounds of the type [M(PR3)4], of which [Pt(PPh3)4] has been most thoroughly studied, are in general yellow, air-stable solids or liquids obtained by reducing complexes in H2O or H20/EtOH solutions with hydrazine or sodium borohydride. They are tetrahedral molecules whose most important property is their readiness to dissociate in solution to form... 

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