N. John Cooper

Organotransition Metal and Inorganic Chemistry

Research projects within our group are in the broad areas of synthetic and mechanistic organotransition metal and inorganic chemistry, with emphases on developments that have implications for the application of transition metal reagents to organic synthes is, to the development of new inorganic materials with potentially useful electro-optical properties, and to homogeneous and heterogeneous catalysis. Most projects involve the synthesis, purification and characterization of air sensitive compounds, and key analytical techniques include ¹H and ¹³C NMR, IR, EPR and UV-vis spectroscopies, and X-ray crystallography. Mechanistic studies use many of the classical techniques of physical organic chemistry, including trapping of transient intermediates and monitoring the distribution of isotopic labels using IR, ¹H and ¹³C NMR, and mass spectroscopy.

One of the principal focuses for research within the group is the synthesis of highly reduced complexes of the early transition metals with unsaturated ligands such as arenes, cyclopentadienyls, carbenes and isonitriles. Our hypothesis has been that the p-acceptor capabilities of such ligands enable them to form stable complexes with many transition metals in negative oxidation states, and recent successes include the characterization of carbene and h⁴-arene complexes of Cr(-II), isonitrile complexes of Co(-I), Ru(-II) and Mn(-I), and h⁴-arene complexes of Mn(-I).

Our current emphasis in this area is on the way in which low oxidation state metals activate unsaturated ligands, and a particularly important observation has been that 2-electron reduction of [Mn(h⁶-C₆H₆)(CO)₃]⁺, a p-benzene complex of Mn(I), forms a reactive h⁴-arene complex of Mn(-I) in which the benzene ring is the locus of reactivity because reactions on the ring can release the energy stored by the ring distortion. This has lead to the discovery of a number of new C-C bond forming reactions of benzene, including the unprecedented addition of a ketene to the activated arene and the first example (albeit by an indirect route) of [2 + 2] dimerization of benzene.

We are also interested in determining the mechanisms of reactions of hydrocarbon ligands in early transition metal complexes. Our key advance in this area has been the development of a versatile route to tungstenocene complexes in which differential substitution of the cyclopentadienyl ligands renders the metal center chiral, so that the intimate mechanistic details of insertion reactions can be explored by monitoring the stereochemistry at the metal.

Our third area of research is the use of the unique optical and electronic properties of transition metal complexes in electro-optical devices. We are, for example, exploring the use of the wavelength dependent photochromism of d¹-d¹ transition metal dimers with linear oxo bridges in optical memory systems, and are developing syntheses of complexes likely to have unusual and useful non-linear optical properties in which transition metal based donors and acceptors are connected through fused arene bridges.