Dr. Christopher C. Cummins, Chemistry Department, Massachusetts Institute of Technology, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division for the development of new reactions that utilize nitrogen, phosphorus, and arsenic atoms derived directly from the elements. Using complexes in which a nitrogen, phosphorus, or arsenic is triply bonded to a niobium or molybdenum, atom transfer will be used to synthesize organic nitrogen, phosphorus, and arsenic compounds. Routes will be developed for the preparation of reactive diatomic molecules P2, PN, and AsP. Preliminary results suggest that the P2 molecule can be stabilized transiently by binding to the M(CO)5 (M = Cr, Mo, or W) fragment, and that the simple complex (P2)W(CO)5 can be cleanly trapped by organic dienes (double Diels-Alder reactivity of the P?ßP bond), by metal complexes, or by metal-ligand multiple bonds. Similar reactions will be explored with PN and AsP.
The most abundant element in the earth's atmosphere is nitrogen. While nature is able to utilize atmospheric nitrogen in biological systems, modern chemical science is still seeking technologies for the economical usage of elemental nitrogen. This project grows from the recent discovery of molybdenum and niobium compounds that can cleave the nitrogen-nitrogen bond in dinitrogen under mild conditions. In order to utilize this chemistry, the nitrogen atoms derived from metal assisted dinitrogen cleavage will be used to prepare organic nitrogen compounds. In addition, related processes will be devised to use phosphorus and arsenic atoms derived from elemental phosphorus and arsenic, respectively. These results will result in new ways to prepare important classes of organic and inorganic arsenic, phosphorus, and nitrogen compounds. In addition to the scientific results, this project will provide training to a diverse group of undergraduate, graduate, postdoctoral, and visiting senior scientists.
This project has advanced the state-of-the-art for synthesizing compounds containing the group 15 elements nitrogen, phosphorus, and arsenic, when starting from these elements themselves. Goals of the project have included (i) bypassing ammonia as an intermediate in the synthesis of organo-nitrogen compounds from N2, (ii) synthesizing organo-phosphorus compounds from P4 in ways that reduce or eliminate generation of waste, and (iii) synthesis of new binary compounds of these group 15 elements. A defining attribute of one facet of the project was the application of early transition-metal chemistry to the synthesis of group 15 element compounds. Molybdenum chemistry was used to effect N2 cleavage, and to facilitate new synthetic cycles for preparing organo-nitrogen compounds from elemental nitrogen gas. In particular, new reactions were developed for making organic nitrile compounds from N2 in a manner that ultimately exchanges the N--N triple bond for a pair of C--N triple bonds. Niobium chemistry was applied to the synthesis of organo-phosphorus compounds. Activation of elemental phosphorus, in the form of the commodity chemical white phosphorus, by niobium complexes led to new P-containing ligands that could be transferred to organic acceptors. This chemistry led to discovery of diphosphorus as a reactive intermediate that is valuable for its ability to combine with organic diene molecules with creation of four P--C bonds. This diphosphorus chemistry was originally discovered as a consequence of niobium chemistry, but importantly, it has now been extended to photochemical cracking of white phosphorus as an efficient method for direct incorporation of diphosphorus units into organic molecules. Thus we gained practical access to a new class of bicyclic tetra-organo-diphosphane molecules. The niobium methodology also led to a facile synthesis of AsP3, this being a binary molecular compound comprising a 1:3 combination of the elements arsenic and phosphorus. This project supported the graduate education of four new MIT Ph.D. degree recipients who are now going on to careers as chemistry professionals in academia and industry in the United States of America. This project served an ambassador function as it attracted the attention of several international student interns who visited MIT for 3-6 month periods, contributed to the development of the research, and took home an appreciation for group 15 element chemistry in the USA. Videos have been produced and disseminated via the Internet to document the synthesis of key starting materials; this has assisted in transfer of the technology for use in chemical industry and education. We have partnered with chemical industry in seeking efficient methods for synthesis stemming from the commodity chemical white phosphorus.
