Structural systematics of some trinuclear alkynyl and diynyl Group 11 complexes containing dppm [dppm = CH2(PPh2)(2)]

In this review the molecular structures of a series of trinuclear alkynyl and diynyl Group 11 cations [{M-3(mu-dppm)(3)}(X)(n)]((3-n)+) (M = Cu, Ag; n = 1, 2; where X is an alkynyl or diynyl group, an inorganic anion or solvent) are considered from the points of view of (i) the dimensions and geometries of the M-3(P-P)(3) cores, (ii) the conformations of the dppm ligands, and (iii) the attachment of the alkynyl and diynyl ligands. In the crowded [M-3(mu-dppm)(3)](3+) core, the dppm ligands are arranged so that there is always one CH2 group up and two down, to give pseudo mirror symmetry perpendicular to the M-3 plane (crystallographic in some cases). Attachment of the alkynyl or diynyl substituent(s) occurs roughly normal to the M-3 plane; according to their perpendicularity, the C(1) atom may be mu(2) or mu(3). In most cases where only one alkynyl or diynyl ligand is present, a second ligand is also attached to the M-3 core. Unusual and interesting dispositions/conformations of the dppm ligands are widespread, among the mono-diynyl complexes in particular, whereby some phosphorus donor atoms lie at unusual distances out of the M-3 planes, a concomitant of strong agostic interactions between phenyl H atoms and the atoms of the open M-3 face, and weak M center dot center dot center dot M interactions. With one X group, C-H center dot center dot center dot M interactions persist on the other face, with C-H center dot center dot center dot X interactions with the alkyne affecting the inclination of the alkyne and the conformation of the Ph rings. With two substituents (one of which may be a loosely bound anion), similar interactions may occur, accompanied by twisting of the dppm chelate ring to displace P atoms from the M-3 plane. These factors possibly inhibit formation of the bis(diyndiyl) complexes, which are only obtained under more strongly basic conditions. (C) 2017 Elsevier B.V. All rights reserved.