Synthesis, formation constants and structures of ternary copper(I) complexes with 1,10-phenanthroline and alkynes

Abstract

Ternary copper(I) complexes with alkynes and 1,10-phenanthroline (phen) have been prepared and characterized by their formation constants, IR spectra, ¹H and ¹³C NMR spectra. The structures of three complexes, [Cu(phen)(HCCR)]ClO₄(R = H 1, Ph 2 or CO₂Et 3) have been determined using single-crystal X-ray methods. Each copper atom in all three complexes is co-ordinated to two nitrogen atoms of phen and an alkyne molecule in a trigonal-planar arrangement. The alkyne is sideways bonded onto the copper atom. The CC bond distances of 1.190(7)(1), 1.218(13)(2) and 1.193(10)Å(3) are slightly longer than those of the free alkynes and indicate that π back donation from copper to the alkyne is weak. The reduction of the CC stretching frequency for metal–alkyne complexes is correlated to the acetylenic bend-back angles and the lenghthening of the CC distance of the alkyne upon co-ordination. The copper–carbon and –nitrogen distances for 1 and 2 are essentially the same as those for the corresponding olefin complexes.