Thioether coordinated metalloenediynes: Syntheses, structures and thermal reactivity comparison

Two novel, thioether containing benzannulated enediyne ligands, 1,2-bis(3-(quinolin-8-ylsulfanyl)prop-1-ynyl)benzene (1), and 1,2-bis(3-(pyridin-2-ylmethylsulfanyl)prop-I-ynyl)benzene (2) have been synthesized and characterized along with their corresponding Cu(I), Ag(I), Cu(II), and Pd(II) metalloenediyne complexes (3-10). Single crystal X-ray structures of the d(10) and d(8) N2S2 complexes show thioether coordination leading to distorted tetrahedral and trans square planar geometries about the metal centers, respectively. Based on their X-ray structures, all complexes are expected to exhibit high Bergman cyclization temperatures (> 200 degrees C), and indeed this is the case for the Cu(I) and Ag(I) complexes (211-218 degrees C). In contrast, the corresponding divalent, tetragonal and trans square planar complexes of Cu(II) and Pd(II) exhibit more facile reactivity and lower solid state Bergman cyclization temperatures (186-190 degrees C) which more closely resemble values expected for cis-complexes. The unusual order in the thermal reactivities of these constructs can be attributed to a previously evaluated mechanism by which weak thioether coordination permits an elevated temperature trans-to-cis geometric rearrangement prior to Bergman cyclization. (c) 2005 Elsevier Ltd. All rights reserved.