Pulled Molecular Strings and Stacked Molecular Decks: Chelate‐Ring Formation vs. Metal–Metal Bridging in Dicopper<scp>(I)</scp> Complexes of 2,2′‐Bipyrimidine with Diphosphine Ligands of Variable Polymethylene Chain Length

Abstract

Abstract The “self‐assembly” reaction between bischelating 2,2′‐bipyrimidine, metallic copper, Cu 2+ , and two equivalents of bidentate Ph 2 P(CH 2 ) n PPh 2 produces crystallographically characterized dinuclear complexes with a [Cu 1 (μ‐bpym)‐Cu 1 ] 2+ core and chelating ( n = 5; type I ) or bridging diphosphine ligands ( n = 6, 8; type II ). Structures II may be designated as “inverse cryptate” arrangements. The structural data of the solids and the spectroscopic results for the dissolved species indicate a strained configuration in the case of complex [(μ‐bpym)Cu 2 {μ‐Ph 2 P‐(CH 2 ) n ] 2+ ( 6 ) with n = 6. Once the polymethylene chain length is reduced one notch further to n = 5 ( 5 ), the diphosphines can no longer bridge but help to form eight‐membered chelate rings (structure I ). In this complex there is a distortion towards a trigonal‐pyramidal coordination geometry at the copper(I) centers, which is supported by the formation of an “organic sandwich” arrangement between the central bpym acceptor and two phosphino phenyl rings.