Zeise s salt

Zeise s salt, K[PtCl3(C2H4)]. A ff-elhylene complex, the first such complex isolated. 

The neutral m do-borane B Hio (structure 10) has a basal B-B bond (see p. 159) and this enables it to act as a ligand by displacing ethene from Zeise s salt (p. 930). 

A common property of coordinated alkenes is their susceptibility to attack by nucleophiles such as OH , OMe , MeC02, and Cl , and it has long been known that Zeise s salt is slowly attacked by non-acidic water to give MeCHO and Pt metal, while corresponding Pd complexes are even more reactive. This forms the basis of the Wacker process (developed by J. Smidt and his colleagues at Wacker Chemie, 1959-60) for converting ethene (ethylene) into ethanal (acetaldehyde) — see Panel overleaf. 

The adoption of a planar structure in these adducts, rather than the sterically more favourable tetrahedral one, is in keeping with a platinum(II) oxidation state. The side-on bonding of the 02 molecule is believed to involve two components, as in Zeise s salt (Figure 3.18). 

Although Zeise s salt is a complex of a 7r-bonding ligand, this compound must be included in an account of the chemistry of these metals, if only as... 

Figure 3.63 Platinum-alkene bonding in Zeise s salt. (Reproduced with permission from S.A. Cotton and F.A. Hart, The Heavy Transition Elements, Macmillan Press Ltd, 1975, p. 126.)...

FIGURE 16.10 The structure and bonding in the anion of Zeise s salt. A cr-bond results from the overlap of a dsp2 hybrid orbital on the metal and the 7T orbital on ethylene. Back donation from a d orbital on the metal to the -k orbital on ethylene gives some 7r bonding (shown in (c)). 

Coordination compounds have been produced by a variety of techniques for at least two centuries. Zeise s salt, K[Pt(C2H4)Cl3], dates from the early 1800s, and Werner s classic syntheses of cobalt complexes were described over a century ago. Synthetic techniques used to prepare coordination compounds range from simply mixing the reactants to employing nonaqueous solvent chemistry. In this section, a brief overview of some types of general synthetic procedures will be presented. In Chapter 21, a survey of the organometallic chemistry of transition metals will be presented, and additional preparative methods for complexes of that type will be described there. 

Some alkenes will react with metal salts to give complexes that involve electron donation from the double bond. A classic case of this type is the formation of Zeise s salt. However, if the alkene has... 

Probably the first metal alkene complex was Zeise s salt, K[Pt(C2H4)Cl3] or the bridged compound [PtCl2(C2H4)]2. These compounds were first prepared by Zeise in about 1825. The palladium analogs of these compounds are also now known. A large number of metal alkene complexes are known, and some of the chemistry of these materials will be described here. 

FIGURE 21.8 The 7r bonding that occurs between ethylene and Pt in Zeise s salt. 

In this case, the bond between the carbon atoms is about the same as it is for a C-C single bond. Moreover, unlike the anion of Zeise s salt, the carbon atoms are in the plane formed by platinum and the other ligands. Clearly, this represents a significant difference from the usual alkene complexes. In essence, a three-membered C-P-C ring is formed. It appears in this case that the ability of the... 

Since the early work dealing with Zeise s salt, many complexes have been prepared with the formula [PtL(C2H4)X2], where L = quinoline, pyridine, or ammonia and X=C1 , Br , I, or N()2. Similar compounds have been prepared that contain other alkenes than C2H4. Many of the complexes containing dienes, trienes, and tetraenes as ligands also contain carbonyl ligands. In fact, metal carbonyls are frequently starting complexes from which alkene complexes are obtained by substitution reactions. 

This method is the one of those that can be used to prepare the ethylene complex known as Zeise s salt, K[Pt(C2H4)Cl3]. Actually, the dimer [Pt(C2H4)Cl2]2 is obtained first and the potassium salt is obtained by treating a concentrated solution of the dimer with KC1. 

The classic synthesis of Zeise s salt, K[Pt(C2H4)Cl3], is an example of this type of reaction ... 

The basis for this method lies in the fact that complexes of different olefins have different stabilities. For several common olefins, the order of stability of complexes analogous to Zeise s salt is... 

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