Synthesis and Characterization of Bimetallic Copper(I) Complexes Supported by a Hexadentate Naphthyridine-Based Macrocycle Ligand

Herein, we report the synthesis, characterization, and binding properties of a new ligand, <i>N</i>,<i>N</i>'-di-<i>tert</i>-butyl-3,7-diaza-1,5(2,7)-1,8-naphthyridinacyclooctaphane (^<b>tBu</b><b>N6</b>), with copper (I), Cu^I, centers. We demonstrate the flexibility and the ability of ^<b>tBu</b><b>N6</b> to adopt various conformations in solution and when coordinated to Cu^Icenters. NMR studies exhibit the labile coordination nature of Cu^I. However, the lability of the complexes is blocked by counterion exchange, which enables the use of less coordinating solvents such as tetrahydrofuran (THF) and avoids using acetonitrile. Thus, the exchange of [BF₄]^- with tetrakis 3,5-bis(trifluoromethyl)phenyl borate, [B(Ar^F)₄]^-, in <b>1·BF</b>_<b>4</b>, [Cu₂(MeCN)₂(^tBuN6)][BF₄], generates <b>1·B(Ar</b>^<b>F</b><b>)</b>_<b>4</b>, which is stable in THF and reacts under a CO atmosphere to generate a <i>syn,syn</i> bis(carbonyl) complex. This complex is sufficiently stable in solution under CO and Ar atmosphere to be characterized by NMR and IR spectroscopy, the latter revealing two stretching bands for the CO bound to the Cu^I-centers at 2102 and 2088 cm^-1.