Synthesis and structure of a tetra-hedral homoleptic Cu^I complex with xylyl isocyanide

Treatment of the Cu^I precursor [Cu(NCMe)₄]PF₆ with excess (10 equivalents) of relatively bulky xylyl isocyanide formed a tetra-(isocyanide) complex, namely, tetra-kis-(2,6-di-methyl-phenylisocyanide)copper(I) hexa-fluoro-phosphate, [Cu(C₉H₉N)₄]PF₆ or [Cu(CNX-yl)₄]PF₆, in good yield. This is in contrast to the previously reported reactions of Cu^I precursors with approximately three equivalents of xylyl isocyanide, which led selectively to the formation of tris-(isocyanide) complexes. The copper atom lies on a twofold axis and P atom on an inversion centre. The complex was characterized by X-ray crystallography, IR spectroscopy, and ¹H/¹³C {¹H} NMR spectroscopy. In the crystal structure, each individual [Cu(CNX-yl)₄]⁺ mol-ecule demonstrates two pairs of coplanar xylyl isocyanide ligands. This arrangement leads to inter-molecular π-stacking inter-actions between nearby complex mol-ecules.