Synthetic Manipulation of Main Group Elements with Transition Metal Isocyanides

With the support of the Chemical Synthesis program in the Division of Chemistry, Professor Joshua S. Figueroa of the University of California, San Diego will study how the chemistry and behavior of main-group elements can be controlled and modulated by transition metal compounds featuring isocyanide supporting groups. The isocyanide supporting groups used in the context of this project provide a protective shield for the chemical interactions between the transition metal and main-group elements.

This shield, in turn, allows for the preparation and isolation of molecules that are usually unstable and difficult to obtain. A specific focus of this award is to use iron isocyanide compounds to study and understand the fundamental properties and chemical reactivity of the diatomic molecules boron monofluoride (BF) and diphosphorus. Boron monofluoride, as a free molecule, is not stable under ambient conditions on account of the extreme bonding polarization.

Similarly, diphosphorus, unlike its lighter analogue dinitrogen, is also not a stable molecule under normal conditions, preferring instead to condense into polyphosphorus solid materials. With the advent of the m-terphenyl isocyanide supporting groups, stable molecules containing both BF and diphosphorus have been prepared. In the course of this award, detailed investigations into the fundamental nature of BF and diphosphorus will be conducted.

These investigations seek to provide answers to basic questions, including 1) how do metal-bound BF and diphosphorus react with other molecules, 2) how do BF and diphosphorus influence the chemical behavior on the metals to which they are bound and, 3) how does the reactivity of metal-bound BF and diphosphorus compare to that of the free, yet unstable, molecules? This project will also focus on the preparation and characterization of other transition-metal-supported main-group element species, with a specific emphasis on generating other unusual or unknown diatomic molecules.

The broader impacts activities will include student research training and mentoring, the development of a hands-on laboratory safety course for incoming graduate students, and mentorship of transfer students.

This project will specifically focus on the synthesis and reactivity of unusual main-group fragments stabilized by transition-metal m-terphenyl isocyanide complexes. Building on recent reports disclosing the synthesis of an iron terminal boron monofluoride (BF) complex, and a mononuclear diphosphorus complex of iron, detailed investigations will be conducted that aim to elucidate the reactivity of these unusual diatomic ligands with exogenous substrates as well as their specific influence on the transition metal centers to which they are bound.

For the terminal BF complex specifically, synthetic studies will be conducted that aim to expand on the pronounced electrophilicity of the boron center, while at the same time detailing reaction profiles that result in the cleavage of the BF unit en route to other metal-boron complexes. In the case of the mononuclear diphosphorus iron complex, its side-on binding mode presents the opportunity to expound upon the fundamental periodic diagonal relationship between phosphorus and carbon.

Accordingly, reactivity studies will be conducted that aim to compare and contrast the reactivity of metal-stabilized diphosphorus with that of acetylene and other substituted alkynes. Specific to these efforts will be an assessment of the scope of Diels-Alder-type reactivity between side-on coordinated diphosphorus and organic dienes. In addition, based on preliminary evidence, the electrophilic character of the side-on coordinated diphosphorus with a range of nucleophilic substrates will be evaluated.

In parallel to investigations into the nature of BF and diphosphorus coordinated to iron, other low-valent transition metal m-terphenyl isocyanide complexes will be prepared and/or studied with respect to their ability to stabilize unusual main-group fragments, with a focus on the preparation of other unstable or unknown diatomic molecules, especially of the heavier p-block elements. An additional emphasis will be placed on the synthesis of BF complexes of other transition metals in an effort to test electronic structure hypotheses on the factors, electronic environment(s) and conditions that are required to stabilize this reactive diatomic molecule.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.