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

Copper complexes of the new ligands1a LPiv
and LRAmR‘ 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(CH3CN)]X (L =
LHAmMe,
X = ClO4; L = LPiv, X =
CF3SO3) revealed typical 4-coordinate
geometries with the amide dangling free, while
those of the Cu(II) compounds [LCuCl]X (L =
LHAmMe, X = ClO4; L = LMeAmH, X
= PF6) and
[LPivCu(O3SCF3)]O3SCF3 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
[LMeAmR‘Cu(CO)]SbF6
(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).