Halide Complexes with Donor Ligands

Actinide halides and oxyhalides are known to form numerous complexes with oxygen and nitrogen donor ligands and the preparation and properties of such compounds have recently been reviewed (12, 13). Relatively few protactinium halide complexes are known, but this situation reflects the lack of research rather than a tendency not to form complexes. However, there is sufficient information available for certain ligands to permit a comparison with the behavior of other actinide halides, and to illustrate the similarities and differences observed with the tetrahalides of thorium to plutonium inclusive and, to a lesser extent, with the protactinium and uranium pentahalides. 

Protactinium pentachloride (42) and pentabromide (43) form both 1 1 and 1 2 complexes with phosphine oxides, the former being analogous to those formed by niobium, tantalum, and uranium pentahalides (26, 42, 43). Unlike niobium and tantalum pentachloride (42, 64) however, they do not react with excess triphenylphosphine oxide (TPPO) to form 

otactinium(IV) and (V) Halide Complexes with Donor Ligands 

A-Dimethylacetamide (DMA) forms a 1 3 complex with protactinium pentabromide (23), but its reaction with other pentahalides has not been studied. 

Like other actinide tetrahalides, protactinium tetrachloride and tetrabromide form stable complexes with phosphine oxides (48, 55) and iV, iV-dimethylacetamide (24), but the tetrachloride-dimethyl sulfoxide 

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Complexes with halide and hydride donor ligands 979... 

Transition metal complexes are cationic, neutral or anionic species in which a transition metal is coordinated by ligands. A classical or Werner complex is one formed by 2 metal in a positive oxidation state with donor ligands such as H20, NH3, or halide ions. 

Mercury(II) reacts with phosphines to form 1 1 or 1 2 complexes of the general type HgLX2, where X is an anionic ligand such as halide or nitrate. The values of the coupling constants are useful in elucidating the structures of these compounds. Complexes with bidentate ligands that contain phosphorous and group 16 donor atoms (S, Se) are also known. These have been characterized by P, Se, and Se, and Hg NMR spectroscopy and by electrochemical... 

A step towards more realistic systems in the context of the Heck reaction was taken by Herrmann s group [10]. They have studied the mechanism and activation barriers of oxidative addition of vinyl halides and halobenzenes to Pd° complexes with simple ligands of varying donor/acceptor characteristics (eq. (10)). 

Reaction of [Mo02Cl2(THF)2] (X = Cl or Br) with Tp yielded [MoC>2Cl(Tp)]. The turnover frequency of this complex in olefin epoxidation, with f-butyl hydroperoxide as oxidizing agent, is reported in the middle of the range observed for [M0O2X2L2] complexes (X = halide, L = N-donor ligands).58... 

A vast array of complex ions, predominantly with halide or nitrogen donor ligands, are water-soluble. Exchange and kinetic studies have been made with many of these because of interest in (a) trans-effects, especially with square Pt11, (h) differences in substitution mechanisms between the ions of the three transition-metal series, and (c) the unusually rapid electron-transfer processes with heavy-metal complex ions. 

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