Versatile N2S2 nickel-dithiolates as mono- and bridging bidentate, S-donor ligands to gold(i)

Abstract

Development of square planar cis-dithiolate nickel complexes as metallo S-donor ligands focuses on the synthesis and structures of gold(I) heterometallic clusters derived from assemblage with three NiN₂S₂ complexes: Ni(bme-daco), Ni(bme-dach) and Ni(ema)²⁻ (bme-daco = (bismercaptoethanediazacyclooctane); bme-dach = bismercaptoethanediazacycloheptane; and ema = N,N′-ethylenebis-2-mercaptoacetamide). With Ph₃PAuCl as the gold source, examples of simple S-aurolation retaining the PPh₃ on Au⁺ were obtained for [{Ni(bme-daco)}AuPPh₃]⁺Cl⁻ and [{Ni(ema)}₂Au₄(PPh₃)₄], where the latter complex demonstrated unsupported aurophilic interactions between [{Ni(ema)}Au₂(PPh₃)₂] units in its X-ray crystal structure (Au–Au = 3.054 and 3.127 Å). Three compounds containing fully-supported digold units with Au–Au distances in the aurophilic range of 3.11 to 3.13 Å were found as stair-step structures in which planar NiN₂S₂ step treads are connected by planar S₂Au₂S₂ risers at ca. 90°: [{Ni(bme-daco)}₂Au₂]²⁺(Cl⁻)₂; [{Ni(bme-dach)}₂Au₂]²⁺(Cl⁻)₂; and (Et₄N⁺)₂[{Ni(ema)}₂Au₂]²⁻. Electrochemical data from cyclic voltammograms demonstrated a positive shift in Ni^II/I couples for the [{NiN₂S₂}_xAu_y] complexes as compared to the NiN₂S₂ precursors and a ca. 700 mV decrease in communication between multiple NiN₂S₂ units as compared to [{NiN₂S₂}₂Ni]²⁺ analogues in slant chair conformation. The analogy between NiN₂S₂ metallodithiolate ligands and diphosphine ligands holds here as in other examples of inorganic and organometallic complexes.