“...but besides Europe the majority of exciting results originates from the United States and China.”

Such review articles are often highly cited, provided that they cover hot topics of significant current interest. Organometallic compounds of the rare earth elements offer very promising applications in the fields of catalysis and materials science. Thus the article was most likely cited not only by chemists but also by researchers working in these particular areas.

It provides a comprehensive account of a rapidly developing field and summarizes new discoveries made by research groups all over the world. Of course, our own work is also included. Besides Europe, the majority of exciting results have originated from the United States and China.

The lanthanides form the largest group of naturally occurring elements in the Periodic Table. Although not always obvious to the general public, lanthanide compounds find numerous important applications such as in lasers (neodymium), and as phosphors in color TV tubes (europium) or MRI scans (gadolinium). The subject area, organolanthanide complexes, has its major impact in the field of catalysis, e.g., in the catalytic manufacture of various important industrial polymers.

We became interested in the organometallic chemistry of the lanthanides—or rare earths, as they are often termed—almost 20 years ago. One of the co-authors of this review, Prof. Dr. Herbert Schumann of the Technische Universität Berlin, is perhaps the pioneer researcher in this area, as someone who stimulated the work of numerous other research groups.

We and others observed that this particular group of elements displays unique reactivities unprecedented for any other metals. In part, we initiated the new direction summarized in this review article. The compounds compiled in this review offer a tremendous variety of possible structures and applications.

Unlike many heavy metals, the lanthanide elements are generally non-toxic. As a long-term consideration, the development of organolanthanide catalysts, e.g., for the industrial production of polymers, is an important contribution to a true "green chemistry."