Alkane activation, progress

Although it is clear that alkane activation is possible, the work done so far using soft metals as catalyst has not produced a reaction that converts alkanes into useful products. Nor does it point very clearly in the direction where progress will be made. It may be that studies on dimeric and cluster compounds, on polyhydrides, or on transition metal alkyls will indicate the paths to be explored. The work using hard catalysts is at present very limited and can be expected to be developed much further in future years. 

In the subsequent section, we shall suggest how a more comprehensive view of selective oxidations can foster progress in alkane activation. This will be illustrated by some of our recent results. 

The chemistry of all of these molecules is fascinating but, concentrating on the origins of life, a detailed look at the organic species is appropriate to see what molecules are present and how they might have been formed. The only alkane detected directly in the ISM is methane but this is due to the problem of detection. All alkanes are non-polar and so do not have a pure rotation spectrum. However, there is one allowed vibration of methane that is infrared active and with the low moment of inertia of methane the vibration-rotation spectrum can be observed and a rotational progression identifies the molecule with confidence. 

Activation of Alkanes The selective oxidation of these unreactive hydrocarbons continues to receive attention. Progress in this area is reported by Matsumura, et al, Driscoll, et oL, Banares and Fierro, Erdohelyi, et oL, Owens, et al, and Khouw, et al. 

The discovery of titanium substituted ZSM-5 (TS-1) and ZSM-11 (TS-2) have led to remarkable progress in oxidation catalysis (1,2). These materials catalyze the oxidation of various organic substrates using aqueous hydrogen peroxide as oxidant. For example, TS-1 is now used commercially for the hydroxylation of phenol to hydroquinone and catechol (/). Additionally, TS-1 has also shown activity for the oxidation of alkanes at temperatures below 1()0 °C (3,4). 

Much progress has been made in understanding the catalytic activity of zeolites for several type of reactions. The number of reactions catalyzed by zeolites has been extended, and new multi-component polyfunctional catalysts with specific properties have been developed. In addition to cracking and hydrocracking, reactions such as n-alkane isomerization, low temperature isomerization of aromatic C8 hydrocarbons, and disproportionation of toluene are industrially performed over zeolite-containing catalysts. Moreover, introduction of various compounds (C02, HCl) into reaction mixtures allows one to control the intensity and selectivity of the reactions. There are many reviews on the catalytic behavior of zeolites and even more original papers and patents. This review emphasizes the results, achievements, and trends which we consider to be most important. 

To summarize, N20 studies have contributed significantly to a better understanding of the activation mechanism of lower alkanes. This facilitates progress in the oxidation by 02, which is being made step by step [49-51]. 

The first activation of an alkane C-H bond was described in 1969 [29]. Three decades were to pass until the development of the current catalytic procedures for dehydrogenation and C-O, C-C, and C-B bond-forming reactions. Progress has been slow. Nevertheless, significant advances in catalyst research were achieved in the 1990s, aided by the development of improved metal ligands and the increased understanding of the mechanism of transition metal-catalyzed C-H activation reactions. Further improvements of catalytic cycles are nec-... 

As these examples show there has been considerable progress in achieving the goal of finding efficient methods to selectively oxidize alkanes. There have been also several promising reports on transition metal complexes which are able to insert into non activated C-H bonds at very low temperatures. 

---