Tetrakis ligand exchange

Iodotris(2,4-pentanedionato) zirconium (IV) has been prepared by reaction of zirconium (IV) iodide with 2,4-pentanedione in isopropyl ether and by the ligand-exchange reaction between zirconium (IV) iodide and tetrakis(2,4-pentane-dionato)zirconium(IV) in tetrahydrofuran.7 The latter approach, which yields a higher-purity product, is described here. 

Tris- and tetrakis(triaryl phosphite)platinum(O) complexes have been prepared by reduction of platinum(II) phosphite derivatives with hydrazine.5 The tetrakis complexes have also been prepared by ligand exchange processes, and the synthesis described here is based on this latter procedure. The chemistry of platinum phosphite complexes has not been extensively studied. 

Both dipolar and contact contributions are important in glycinate complexes. (166) U(iv) complexes with a-alanine, (167) various amino-acids, (168) ethyl trifluoroacetoacetate, (169) tetrakis-(tetra-ethylammonium)octathiocyanatouranate U(NCS)g(NEt4)4, (170) and -diketones (171, 172) have been examined. In studying the ligand exchange kinetics of the latter complexes (172) the mechanism is considered to involve a ninth coordination site in the U(iv) chelate. 

The Cardiolite kit contains 2-methoxy-isobutyl-isonitrile (MIBI) as a preformed cop-per(I) complex, Cu(MIBI)J-BF4 [tetrakis(2-methoxy-isobutyl-isonitrile)Cu(I)tetra-fluoroborate], which facibtates labeling by ligand exchange at elevated temperature. 

Asymmetric cyclopropanation. The ability to effect ligand exchange between rhodium(II) acetate and various amides has lead to a search for novel, chiral rhodium(II) catalysts for enantioselective cyclopropanation with diazo carbonyl compounds. The most promising to date are prepared from methyl (S)- or (R)-pyroglutamate (1), [dirhodium(ll) tetrakis(methyl 2-pyrrolidone-5-carboxylate)]. Thus these complexes, Rh2[(S)- or (R)-l]4, effect intramolecular cyclopropanation of allylic diazoacetates (2) to give the cyclo-propanated y-lactones 3 in 65 S 94% ee (equation 1). In general, the enantioselectivity is higher in cyclopropanation of (Z)-alkenes. 

In the early 1980 s the existence of tetrakis (monophosphine)Au(I) complexes began to be estabUsbed. Complexes of the type [Au(PR3)4]X were isolated and characterised for the ligands PMes PPha and PMePh2 P NMR solution studies of gold(I) monophosphine complexes in the presence of free PR3 demonstrated that complexes with different Au P ratios undergo rapid ligand exchange above 213... 

Zirconium(IV) and hafnium(IV) tetrakis(tetrahydroborates) M(BH4)4 are of interest as extremely volatile, covalent complexes that contain tridentate BH ligands and exhibit rapid intramolecular exchange of bridging and terminal hydrogen atoms. 4,615 These compounds were prepared initially from NaMF5 (M = Zr or Hf) and excess A1(BH4)3 (equation 53),616 but they are obtained more conveniently from the reaction of the anhydrous metal tetrachloride with excess lithium tetrahydroborate (equation 54), either in the solid state617,618 or in the presence of a small amount of diethyl ether.619... 

Compounds with aliphatic olefins or with diolefins have been easily obtained by reaction of Pt(PPh3)2 with the olefins, octene, n-pentene, butadiene, and cycloocta-1,5-diene 187). They are white, stable to oxidation, and exchange the olefin with other ligands easily. Tetracyanoethylene (C6N4) derivatives of the type Pt(PR3)2(CeN4) (R = Et, Ph) have been obtained recently (7) by different reactions—i.e., from tetrakis(triphenyl-phosphine)-platinum(O) or rans-PtHCl(PR3)2 and tetracyanoethylene, or from Pt(PPh3)2(alkyne) and tetracyanoethylene. The compounds with the latter ligand are always more stable than the compounds with other olefins. 

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