The ability of the bicyclic guanidinates hpp- and hpp*- (anions of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, hppH, and 3,3,7,7-tetramethyl-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine, hpp*H) to stabilize lower-valent metal centers in dinuclear compounds has been well documented in the literature, with hpp*- shown to be the stronger donor by Cotton, et al. We have studied how this charge donation to the metal, formally a ligand-to-metal charge transfer (LMCT), can be examined structurally and spectroscopically in mononuclear mid-transition metal hpp- and hpp*- complexes. [Re(O)(hpp)2]+Cl– and [Re(O)(hpp*)2]+Cl– (Re(V), d2), and W(O)(hpp)2Cl2, and W(O)(hpp*)2Cl2 (W(VI), d0), have been synthesized and characterized. [Re(18O)(hpp)2]+Cl–and W(18O)(hpp)2Cl2 have been prepared for metal-oxo vibrational assignment. We have tested the utility of the terminal M=O IR stretch as a reporter of metal electron density. We will discuss our attempts to synthesize d0 Ta(O)(hpp)2Cl for comparison to the d2 Re compounds. DFT calculations have been performed on these complexes in order to understand the orbitals involved in M=O bonding, and the comparative contributions of hpp- and hpp*- in electron donation to M.

Using the terminal metal-oxo bond as a reporter of electron donation from bicyclic guanidinate ligands to mid transition metals

253rd National Meeting (2017)

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