Olefin and Acetylene Complexes

This section deals with the formation as well as substitution of olefin and acetylene complexes. 

Cristiani, D. de Filippo, P. Delano, F. Devillanova, A. Diaz, E. F. Troya, and G. Verani, Inorg. Chim. Acta, 1975, 12, 119. 

The kinetics of addition of tetracyanoethylene (tcne) to rra j -[Rh(R NC)2(PR 8)2l+ (R = /7-MeOCeH4, p-ClCeH4, or CgHn, R = Ph or OPh) have been investigated and found to be first-order in both complex and tcne. Reaction rates increase with increasing solvent polarity in the order THF acetone acetonitrile. This can be explained by formation of a dipolar intermediate (21) in the transition state which 

The kinetics of the reaction are first-order in complex and zero-order in phosphine, and dechelation of cod is proposed as the rate-determining step. Triphenyl phosphite displaces one molecule of l,4-bis(diphenylphosphino)butene (dpb) from [Ni(CO (dpb) J (in which one dpb ligand is unidentate). Significant enhancement of the substitution rate is observed on addition of CF3CO2H and, to a lesser extent, H2SO4, which may indicate that protonation of the complex facilitates the reaction. 

My first incursion into organo-transition metal chemistry occurred because of my interest in chemical bonding. How did olefins with no lone pair of electrons form coordinate bonds to metal atoms The position in 1941 can be read in Keller s review on olefin complexes 54). During the war years I was able to assemble a card index of all references to olefin complexes and I convinced myself that they should be formulated as chelate complexes of, for example, structure (VII) for Zeise s ion if chlorine could bridge metal atoms why should it not bridge carbon to a metal Nature rejected my letter on this topic as being 

Some attempts which I had made in 1946 to obtain PtPh2 or [PtPhJ from the reaction of phenylmagnesium bromide with [ PtCl2(C2H4)2 2] in ether had yielded biphenyl as the only pure solid product, and this served to confirm in my mind the belief that transition metals had no normal organometallic chemistry. I decided then to concentrate on the platinum(II)-olefin complexes. The first question was whether the olefin-metal bond used the d electrons normally involved in the oxidation of platinum(II) to platinum(IV) (valence d electrons) to bind the olefin, as required by such structures as (I), or whether, as was then generally believed, they were olefin coordination compounds formed independently of the presence of d electrons, even by Main Group element ions. 

The bridged compound [Pt2Cl4(C2H4)2] (VI) has rather poor solubility in cold organic solvents, except in ethanol and acetone in which it is not very stable, and I attempted to obtain more soluble platinum(II)-ethylene complexes by introducing trialkylphosphines according to Eq. 

Halogen-bridged platinum(II) complexes of the tertiary phosphines, arsines, etc., were then unknown and they had properties well worth studying for comparison with those of their palladium analogs. Also, they could be oxidized to platinum(IV)-bridged species, and these showed marked instability compared with their platinum(II) analogs. This led me to speculate that the electrons in the f-orbitals of platinum- 

In 1947 Walsh (68) proposed that because the ionization potential of the rr electrons in ethylene and of the lone pair in ammonia are both around 10.5 eV, the it electrons in the olefins should be equally capable of donation to acceptor centers. This implied that olefin complexes should be much more widespread than they were. 

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Olefin and acetylene complexes of Au(I) can be prepared by direct iateraction of the unsaturated compounds with a Au(I) hahde (190,191). The resulting products, however, are not very stable and decompose at low temperatures. Reaction with Au(III) hahdes leads to halogenation of the unsaturated compound and formation of Au(I) complexes or polynuclear complexes with gold ia mixed oxidatioa states. 

Mono-olefin and acetylene complexes of nickel, palladium and platinum... 

Such reactions probably occur through the formation of nickel-olefin and -acetylene complexes, but until recently no stable complex was known. 

The preceding perturbation theory analysis is supported by extended Hiickel calculations by Cusachs and his co-workers (166, 167, 237) on model platinum(II)- and platinum(0)-olefin and -acetylene complexes and Hoffmann and Rossi s extensive analysis of five-coordinate transition metal complexes (194). By using similar arguments, Hoffmann and Rosch (190) predicted that the planar conformation would be energetically preferred for d10 M(C2H4)3 complexes. This geometry has now been established by Stone (214) and his co-workers for the platinum-olefin complex shown in Fig. 12. 

Photochemical reactions have been used for the preparation of various olefin, and acetylene complexes (7). Application to the coordination of dienes as ligands has not been used extensively, so far. In this article the preparative aspects of the photochemistry of carbonyls of the group 6 and group 7 elements and some key derivatives, with the exception of technetium, with conjugated and cumulated dienes will be described. Not only carbonyl substitution reactions by the dienes, but also C—C bond formation, C—H activation, C—H cleavage, and isomerizations due to H shifts, have been observed, thereby leading to various types of complexes. 

Pettit, L. D and Barnes, D. S. The Stability and Structures of Olefin and Acetylene Complexes of Transition Metals. 

The latter is outside the scope of organometallic chemistry, but within the first two topics the work involved three main themes olefin and acetylene complexes, alkyl and aryl complexes, and hydride complexes. As continuous subsidiary themes throughout ran the complex chemistry of tertiary phosphines and such ligands, the nature of the trans effect, and the nature of the coordinate bond. All the work from 1947 to 1969 was carried out in the Butterwick Research Laboratories, later renamed Akers Research Laboratories, of Imperial Chemical Industries Ltd., and I am indebted to that Company and particularly to Mr. R. M. Winter, the Company s Controller of Research, and Sir Wallace Akers, its Director of Research, who in 1947, made available to me the opportunity to develop my research in my own way, in those laboratories. 

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