The preparation of olefin-transition metal complexes

of C=C groups bound, = n Name of olefin Metals which form complexes with the olefin 

The treatment of many metal salts either in solution or in the solid state may give smooth addition of the olefin to the complex. The famous Zeise s salt, first isolated in 1827 [16], is prepared by bubbling ethylene through an aqueous solution of potassium tetrachloroplatinate(Il) from which the yellow crystals of the complex, K+[C2H4PtCh] .H20, are precipitated. The reaction is catalysed by tin(Il) chloride [17], The bis-ethylene rhodium complex, 1.1, is similarly prepared [18]. 

Aqueous solutions of silver nitrate or perchlorate also react rapidly with olefins. It has been noted that the addition of fiuoroboric acid to silver nitrate gives a surprisingly large increase in ethylene adsorption and it was suggested that this may be due to a lowering of the degree of hydration of the silver ion in solution [1. Non-aqueous solvents such as alcohols, acetone or acetic acid have been used in these reactions and, in the case of hydrolytically unstable complexes such as C5H6AgC104, benzene or ether solutions are used [20]. 

The butadiene complexes of the copper(l) halides are prepared by the direct reaction of anhydrous copper(I) halides with butadiene at —10°, in the absence of solvents [21]. Also, the complexes [Olefin PdCh] , where the olefin is straight chain, may be prepared by direct interaction at room temperature of palladium dichloride and the olefin in a liquid state [2Ia]. 

Many metal carbonyls undergo easy replacement of some of their carbon monoxide ligands. Direct reaction between the olefin and the metal carbonyl frequently occurs at room temperature or at slightly higher temperatures, e.g. 

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