Zeise’s compound

I was first made aware of organometallic compounds through reading Modern Aspects of Inorganic Chemistry (1935) by two academics, H. J, Emeleus and J. S. Anderson at Imperial College, London, where I was a student. However, names such as Zeise s compound , Reihlen s butadiene iron tricarbonyl and Hein s polyphenylchromium compounds , none of whose structures were known, remained latent in my memory through over seven years as a nuclear chemist. 

The first metal complex identified as an organometallic compound was a salt, K(C2H4)PtCl3, obtained from reaction of ethylene with platinum (II) chloride by William Zeise in 1825. It was not until much later (1951-1952) that the correct structure of Zeise s compound (see Figure 1) was reported in connection with the structure of a metallocene compound known as ferrocene (see Figure 2). 

In a further discussion of the constitution of alcohol and ether Liebig attacked Dumas etherin theory (see p. 343) and defended the ethyl theory. He also attacked Dumas substitution theory in its application to the formation of chloral (see p. 361). Dumas views, Liebig said, were founded on inexact experiments and he remained silent when his errors were pointed out to him. We should be ready at every moment to change admitted hypotheses for better theories. Since Zeise s compound of platinous chloride and ethylene seemed to support the etherin theory, Liebig recalculated Zeise s analyses to show that the compound contains oxygen and is a compound of ether and not ethylene (etherin). Zeise confirmed that the compound does not contain oxygen. 

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... 

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. 

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. 

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. 

Olefin exchange has been used for the preparation of certain plati-num(II) complexes (67). Thus, trimethylvinylsilane replaces ethylene in Zeise s salt to give the compound K[Cl3Pt(H2C=CHSiMe3)]. The SiMe3 group in this complex is readily cleaved by water (wet acetone) with elimination of hexamethyldisiloxane and regeneration of Zeise s salt, but resists attack by pyridine N-oxide, which instead replaces a chlorine atom (67). 

The first organometallic compound of the transition metals to be characterized (1827) was Zeise s salt, K[(C2H4)PtCl3]-H20 (Fig. 18.1). It forms when K2[PtCl4] in aqueous ethanol is exposed to ethylene (ethene) a dimeric Pt—C2H4 complex with Cl bridges is also formed. In both species, the ethylene is bonded sideways to the platinum(II) center so that the two carbon atoms are equidistant from the metal. This is called the dihapto-or T]2 mode. A ligand such as an allyl radical with three adjacent carbons directly bonded to a metal atom would be trihapto- or t 3, and so on. 

In this molecule ethylene lies in the same plane as the other ligands, unlike the case in Zeise s salt where planarity is sterically prevented. By analogy to a three-membered ring of carbon atoms, this compound may be viewed as a mctallacyclopropane. 

Zeise s salt is obtained as well-formed, yellow, needle-shaped crystals. The compound is stable in the solid state at room temperature and decomposes with loss of ethylene at about 180°C. The chemical, physical, and structural properties have been characterized thoroughly and are described in the literature.9"13... 

One of the earliest organometallic compounds to be isolated was Zeise s salt, K[PtCl3(C2H4)], which contains the anion ... 

Platinum olefin compounds have long been known, the most familiar being Zeise s salt, K(PtCl2C2H4)Cl. The fundamental compound of such... 

In the structure of Zeise s salt, the ethylene occupies the fourth coordination site of the square planar complex with the C C axis perpendicular to the platinum-ligand plane. In this compound, the dsp2 hybridised s orbital of Pt overlaps with / -bonding... 

Although much of the chemistry of organometallics is of recent development, such compounds have been known for many years. Zeise s salt, a metal olefin complex having the formula K[Pt(C2H4)Cl3], was prepared in 1825. The first metal alkyl has been known since 1849 when Frankland prepared diethyl zinc by the reaction... 

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