Mono- and Dinuclear Manganese Carbonyls Supported by 1,8-Disubstituted (L = Py, SMe, SH) Anthracene Ligand Scaffolds

Presented herein is a synthetic scheme to generate symmetric and asymmetric ligands based on a 1,8-disubstituted anthracene scaffold. The metal-binding scaffolds were prepared by aryl chloride activation of 1,8-dichloroanthracene using Suzuki-type couplings facilitated by [Pd(dba)(2)] as a Pd source; the choice of cocatalyst (XPhos or SPhos) yielded symmetrically or asymmetrically substituted scaffolds (respectively): namely, Anth-S(Me)2 (3), Anth-N2 (4), and Anth-NSMe (6). The ligands exhibit a nonplanar geometry in the solid state (X-ray), owing to steric hindrance between the anthracene scaffold and the coupled aryl units. To determine the flexibility and binding characteristics of the anthracene-based ligands, the symmetric scaffolds were complexed with [Mn(CO)(5)Br] to afford the mononuclear species [(Anth-SMe2)Mn(CO)(3)Br] (8) and [(Anth-N2)Mn(CO)(3)Br] (9), in which the donor moieties chelate the Mn center in a cis fashion. The asymmetric ligand Anth-NSMe (6) binds preferentially through the py moieties, affording the bis-ligated complex RAnth-NSMe)(2)Mn(CO)(3)Br] (10), wherein the thioether-S donors remain unbound. Alternatively, deprotection of the thioether in 6 affords the free thiol ligand Anth-NSH (7), which more readily binds the Mn center. Complexation of 7 ultimately affords the mixed-valence Mn-I/Mn-II dimer of formula [(Anth-NS)(3)Mn-2(CO)(3)] (11), which exhibits a fac-{Mn(CO)(3)} unit supported by a triad of bridging thiolates, which are in turn ligated to a supporting Mn(II) center (EPR: vertical bar D vertical bar = 0.053 cm(-1), E/vertical bar D vertical bar = 0.3, A(iso) = 150 MHz). All of the metal complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy and NMR/EPR measurements all of which demonstrate that the meta-linked, anthracene-based ligand scaffold is a viable approach for the coordination of metal carbonyls.