Nickel, complex from chlorophyll

In addition to hydrocarbons, petroleum also contains compounds that consist of nitrogen, oxygen, and sulfur (in the minority) as well as trace amounts of metals such as vanadium, nickel, iron, and copper. Porphyrins, the major organometaUic compounds present in petroleum, are large, complex cyclic carbon structures derived from chlorophyll and characterized by the ability to contain a central metal atom (trace metals are commonly found within these compounds). 

The problem of the origin of the metal-porphyrins is closely related to that of the origin of petroleum and is oie of the most basic and interesting questions of petroleum geochemistry. The most probable conclusion seems to be that the nickel and vanadium porphyrin complexes are formed by metal exchange reactions from animal and/or plant metabolic pigments such as hemoglobin and chlorophyll. 

The first two of these compounds occur at sufficiently high concentrations in some crudes to enable production of them from petroleum. Benzonitrile has also been detected [6]. Much of the trace metal content of petroleums, in particular vanadium and nickel, is present in association with petroporphy-rins, which are polycyclic pyrroles closely related in structure to the hemes and chlorophylls. These materials are examples of the more complex nitrogen heterocycles to be found in petroleum. These particular heterocycles with their complexed metal atoms contribute much to our present knowledge of the original biogenesis of the petroleum hydrocarbons [6]. 

Figure 3.4 nickel ethylenediamine complex reacts with acetone to form a nirrin, the four planar positions of the JVz " " bonds templating the reaction. In evolutionary terms, such reactions permitted great strides forward, as simple molecules such as the two above immediately became corrins surrounding the cobalt of vitamin B12 chlorophyll if magnesium and haem if ferrous was at the centre (from R.W. Hay, in An Introduction to Bio-inorganic Chemistry , ed. D.R. Williams, by permission of the Publishers,... 

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