Towards Heteroleptic Dicoordinate CuII Complexes

Abstract

In this work we detail our efforts to systematically generate stable dicoordinate Cu^II complexes. Initial experiments via metathesis reactions of a bulky potassium carbazolide (RK) with copper(II) salts indeed yielded a stable product, RCuOTf (1). However, subsequent attempts to grasp systematic synthetic access to complexes of the type RCuX (X=monoanionic ligand) proved difficult as many of the complexes rapidly decomposed in solution. By using triflate-related ligands such as ethyl sulfate and bistriflimide, the additional dicoordinate copper complexes RCuOSO₃ Et (2), [RCu(THF)][Cu(NTf₂ )₂ ] (3) and RCuNTf₂ (4) could be isolated. Spectroscopic indications corroborate more Cu^I than Cu^II character in all RCuX derivatives.

Keywords: EPR; XANES; copper; low-coordinate complexes; steric bulk.

Scheme 1

Dicoordinate Cu^II compounds (Dipp=2,6‐diisopropylphenyl, Dipp^Ad=4‐adamantyl‐Dipp).

Scheme 2

Synthesis of the heteroleptic linear RCuOTf complex (1).

Figure 1

Molecular structure of RCuOTf (1). Ellipsoids for Heteroatoms are set at 50 % probability at 200 K. Selected distances [Å] and angles [°]: N‐Cu 1.8585(11), Cu‐O 1.8669(14), N‐Cu‐O 177.31(5).

Figure 2

EPR spectrum of RCuOTf (1) in hexane solution at ambient temperature (measured top, simulated bottom).

Figure 3

Molecular structure of a) [RCu(THF)][Cu(NTf₂)₂] (3, 150 K) and b) RCuNTf₂ (4, 200 K). Ellipsoids are set at 50 % probability.

Figure 4

Cu−K‐edge XANES spectra of 1–5 and B.