Bonding and Reactivity in Low-Valent Dinickel Complexes

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

Bonding and Reactivity in Low-Valent Dinickel Complexes A remarkable property of nickel compounds is their ability to break strong chemical bonds. Indeed, some proteins contain nickel centers that react with carbon dioxide, which has very strong bonds. Catalysts based on nickel are widely used in energy-related chemistry. The research project led by Professor Joseph P. Sadighi at the Georgia Institute of Technology builds on these themes of strong bonds and energy-relevance. The project focuses on pairs of nickel atoms. The nickel atoms are linked in pairs using bridging atoms or bridging groups. The linkers that are explored in this work include hydrogen, nonmetallic elements, or another metal. The project examines bridging centers that are weakly bonded to each nickel center. These unusually weak bonds should make the complexes sufficiently stable to be isolated, yet unstable enough to be highly reactive. A deeper understanding of these compounds is providing insights into the design of catalysts for breaking strong bonds. The graduate and undergraduate researchers who carry out this research are introduced to concepts of bonding and reactivity, and to an array of synthetic and spectroscopic techniques. The group also participates in a Georgia Tech program to recruit high school students from demographics underrepresented in science. The students are introduced to research through a summer and then through the academic year. This training prepares students to contribute to the future of science in the United States as teachers, or as researchers in academic, industrial, or government laboratories. The PI has extensive contacts with currently serving or recently transitioned veterans, and provides advice and encouragement to those returning to full-time study. Nickel has been the subject of remarkable recent advances in metal-element bonding, and in bond-breaking and bond-forming reactions that enable catalysis. This research presents architectures derived from the interaction of two nickel(0) centers with a Lewis acid to form a bridging ligand. When the Lewis acid is a proton, this interaction creates a rare linear hydride bridge; The [Ni---H---Ni]+ core is held together by a three-center, four-electron bond, analogous to that in the bifluoride ion. One aim is the synthesis of a series of related hydride-bridged dinickel complexes, enabling an assessment of the hydridic character of the bridging hydrogen, and a detailed study of the complex's reactivity toward the C-CN bonds of nitriles. Another aim explores the formation of bridges derived from Lewis-acidic main group species such as carbocations, boranes, alanes, or organometallic fragments. Finally, the insertion of copper(I) or gold(I) cations between the nickel centers would afford heterometallic systems with a single net bond across three metal centers. The hypothesis underpinning these aims is that the [Ni---E---Ni] ensembles are sufficiently stable for isolation or characterization, yet display reactivity distinct from that of mononickel complexes [Ni-E], nickel alone, or the bridging element alone. Students who work on this project learn concepts of bonding and chemical synthesis. They acquire technical skills in the preparation of air-sensitive complexes. They are trained in analysis using modern instrumentation. These researchers include graduate students, undergraduates, and high school students. The program identifies underrepresented minority students interested in scientific research. This training prepares students for technical careers in education, research, and industry. In another form of outreach, Professor Sadighi advises fellow veterans on their return to full-time study. 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.