Synthesis and Copper Coordination Chemistry of Hindered 1,4,7-Triazacyclononane Ligands with Amide Appendages

Copper complexes of the new ligands<sup>1a</sup> L<sup>Piv</sup> and L<sup>RAmR‘</sup> that comprise 1,4-diisopropyl-1,4,7-triazacyclononanes linked to secondary and tertiary amide groups were prepared and characterized, with a particular view toward evaluating amide structural, spectroscopic, and potential hydrogen-bonding influences of relevance to ongoing copper−dioxygen reactivity studies. X-ray crystal structures of the Cu(I) complexes [LCu(CH<sub>3</sub>CN)]X (L = L<sup>HAmMe</sup>, X = ClO<sub>4</sub>; L = L<sup>Piv</sup>, X = CF<sub>3</sub>SO<sub>3</sub>) revealed typical 4-coordinate geometries with the amide dangling free, while those of the Cu(II) compounds [LCuCl]X (L = L<sup>HAmMe</sup>, X = ClO<sub>4</sub>; L = L<sup>MeAmH</sup>, X = PF<sub>6</sub>) and [L<sup>Piv</sup>Cu(O<sub>3</sub>SCF<sub>3</sub>)]O<sub>3</sub>SCF<sub>3</sub> showed 5-coordinate square pyramidal geometries with the amide coordinated to the metal via its carbonyl oxygen atom. Analysis of FTIR spectra of the aforementioned compounds and the carbon monoxide adducts [L<sup>MeAmR‘</sup>Cu(CO)]SbF<sub>6</sub> (R‘ = H or Me) allowed (i) identification of signatures of amide structural features, hydrogen bonding, and metal coordination and (ii) classification of the amide ligands as generally electron withdrawing relative to alkyl-substituted counterparts (e.g., 1,4,7-triisopropyl-1,4,7-triazacyclononane).