Of platinum olefin complexes

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence  

The method described below provides a more reliable synthetic route to this compound. 

Li2CgHg + Pt(C8H12)Cl2 + C8H12 - Pt(CsH12)2 + 2LiCl + C8H8 Procedure 

Dichloro(l,5-cyclooctadiene)platinum(II) may be prepared from hexachloro-platinic acid,3 by heating bis(benzonitrile)dichloroplatinum(II)4 in 1,5-cyclo- 

Ethylene (C.P. grade) may be used directly from the cylinder without further pruification. 

---

My last comment concerns the reaction of palladium olefin complexes with carbon monoxide discovered by Tsuji. I agree that this is most likely to proceed by an insertion rather than an ionic mechanism. Chloride attack on coordinated olefin is rare however. Chloride ion is an inhibitor, for example in the palladous chloride catalyzed hydration of ethylene (0). I, therefore, wondered whether carbon monoxide was affecting the ease with which chloride attacks olefin. One can postulate that carbon monoxide participates in this insertion either as a gas phase reactant or by first forming a carbonyl olefin complex. Such complexes of the noble metals were unknown, but examining the reaction between carbon monoxide and the halogen bridged olefin complexes of platinum revealed that they are formed very readily... 

In addition to the complexes of platinum(II), a number of olefin complexes of platinum(O) have been prepared. Chatt, Shaw, and Williams (103) have described the complex (olefin)bis(triphenylphosphine)-platinum(O) prepared by reaction of the olefin at 60°C with cis-dichloro-bis(triphenylphosphine)platinum(Il) in ethyl alcohol containing hydrazine hydrate. The complex was formed only with ethylene complex (C2H4)Pt[P(CgH5)3]2 has been prepared (121) by reduction of the corresponding oxygen complex with sodium borohydride in the presence of the olefin. 

The olefin complexes of platinum(II) resemble those of rhodium(I) in being very effective catalysts for addition of silanes to olefinic compounds (66). The following results have been found for the hydrosilylation of hexene-1 ... 

At this point we seem to have come a long way from the chemistry of Joe Chatt. Is there really a connection between the stability of olefin complexes of platinum(ii) and the semi-conducting properties of GaAs In this short review I have tried to show that there is a direct relationship between the two. The class... 

It has recently been shown 90> that the olefin tetracyanoethylene, (CN)2C= C(CN)2, can displace phenylacetylene from the bis-triphenylacetylene from the bis-triphenylphosphine platinum(O) complex, the first time such a reaction has been achieved. Preparative work on olefin complexes of platinum(0) of the same type has also shown that electron-withdrawing substituents on the olefin increase the stability of the complex, e.g. trans-4,4-dinitrostilbene forms a more stable complex than trans-stilbene itself 86L... 

---