Transition metal complexes with p-radical ligand(s) can serve as intermediates in diversified metalloenzymatic transformations. The elucidation of the active site of galactose oxidase which employs the CuII/I and tyrosyl radical redox couples to drive the 2e- oxidation of primary alcohols to their corresponding aldehydes, has prompted the synthesis and characterization of CuII complexes that contain coordinating redox-active ligands. Ligands with variable oxidation states have earned the designation as noninnocent or redox active due to their interesting electronic structures. Transition metal compounds may perform chemical transformations by utilizing redox processes of the noninnocent ligands as reservoirs of electrons. O2 activation mediated by transition metal ions is of importance in stoichiometric and catalytic transformations of organic substrates in biological processes. Numerous environmental benign aerobic oxidations performed by biological and synthetic metal compounds use copper and iron. Although {MO2}(M= Ni, Pd) intermediates have in fact been inferred to be highly active species in several C-H bond transformations, the knowledge on nickel-dioxygen complexes and C-H fictionalisations by such intermediates are still comparatively scarce. MII (M= Ni, Pd)complexes are generally inert toward O2. The study will demonstrate how redox noninnocence of the ligand enforces O2 activation at the MII (M = Ni, Pd) site which subsequently involved in C-H bond activation. An emerging concept of 'oxidation & addition' compared to the known concept of oxidative-addition will be presented. Furthermore, a notable rare example of redox-active ligand based organometallic compound is [CoIII(LISQ)2(CH2CN)] where C-H bond activation of CH3CN lead to the synthesis of above mentioned compound. Thus, the glaring omission of noninnocent ligandbased late transition metal organometallic complex inspired us to synthesize p-radical containing transition metal complex with organometallic {M-Ph} species which is subjected to structural, spectroscopic and DFT characterizations. Herein, we present synthesis of such unusual transition metal complexes that contain coordinating redox active ligands, characterizations by single-crystal X-ray, CV, spectroscopic (NMR, UV-VIS, EPR), DFT and the reactivity of the noninnocent ligand based {M-O2�-} (M= Ni, Pd) intermediates which lead to unexpected facile C-H functionalisations of alcohol to aldehyde, P-C bond activation at ambient condition.

The guilty verdict: Bio-inspired chemical transformations

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.