A Cobotic, Digitally Controlled Schlenk-line Unlocks Access to Elusive Lewis-Base Stabilised Copper Bis(Disilylamides)

Abstract

Silylamides are important ligands in coordination chemistry for their ability to stabilise low coordination numbers and provide soluble, and even volatile, metal complexes. Such compounds provide valuable insights into the fundamental bonding and reactivity of their respective metals. Despite the wealth of homo- and heteroleptic hexamethyldisilazide complexes of divalent 3d ions (Sc-Ni, Zn), attempts to access the corresponding divalent copper complexes have yielded only Cu(I) species. Herein, we demonstrate the stabilisation and isolation of a formally Cu(II) bis-hexamethyldisilazide which was achieved by implementing novel digital chemistry tools. In order to successfully isolate (DMAP)Cu^II(N{SiMe₃}₂)₂ (DMAP = N,N-dimethylaminopyridine), we investigated the roles of the co-ligand and silylamide transfer reagent in the kinetics of its formation. Crucial to these studies was our newly developed "cobotic" Schlenk line which provides digital control of the atmosphere under which we conduct our highly reactive syntheses. In digitising Schlenk-line handling, we have improved synthetic productivity by creating protocols for automated inertisation, solvent evaporation, liquid handling and crystallisation all while capturing reaction log data. Importantly, our Cu silylamide synthesis provides a case study showing that our cobotics approach allows for the discovery and isolation of unstable species which may remain elusive by traditional manual or fully autonomous methodologies.

Keywords: Automation; Copper(II); Digital chemistry; Inert atmosphere; Silylamide.

Figure 1

A summary of the known first‐row transition metal silylamide complexes and the relative reduction potentials of their respective M(II) ions. Notably nickel analogues can be stabilised by solvent coordination. The stability of the first‐row transition metal bis(hexamethyldisilazide) complexes closely follows the reduction potential of the divalent oxidation state (grey). Ar = 2,6‐diisopropyl, X = Br; N″ = N(SiMe₃)₂.

Figure 2

Top: Autoschlenk; middle: Raspberry Pi GUI; bottom: Workflow for newly developed functionalities which exploit digital vacuum gauge feedback.

Figure 3

Synthesis of DMAP adducts of copper triflate salts (1a‐b) using Autoschlenk functions Cycle, Transfer and Evaporate.

Figure 4

a) Proposed mechanism for the synthesis and degradation of DMAPCuN”₂ (2). b) Cobotic method of synthesis and isolation of 2 showing the X‐ray crystal structure of isolated material. H‐atoms removed for clarity. Cu1‐N2: 1.8819(18) Å; Cu1‐N1: 1.952(3) Å