Substitution chemistry of MM quadruply bonded complexes (M = Mo or W) supported by the anion of 2-hydroxy-6-methylpyridine

Abstract

The compounds M(2)(mhp)(4), where M = Mo or W and mhp is the anion formed from deprotonation of 2-hydroxy-6-methylpyridine, are shown to react with carboxylic acids RCOOH to give an equilibrium mixture of products M(2)(O(2)CR)(n)(mhp)(4-n) where R = 2-thienyl and phenyl. The equilibrium can be moved in favor of M(2)(O(2)CR)(4) by the addition of excess acid or by the favorable crystallization of these products. The latter provides a facile synthesis of the W(2)(O(2)CR)(4) compound where R = 9-anthracene. Reactions involving 2,4,6-triisopropyl benzoic acid, TiPBH, yield M(2)(TiPB)(2)(mhp)(2) compounds as thermodynamic products. Reactions involving Me(3)OBF(4) (1 and 2 equiv.) yield the complexes Mo(2)(mhp)(3)(CH(3)CN)(2)BF(4) and Mo(2)(mhp)(2)(CH(3)CN)(4)(BF(4))(2), respectively. The latter compound has been structurally characterized and shown to have mirror symmetry with two cis mhp ligands: MoMo = 2.1242(5) A, Mo-O = 2.035(2) A, Mo-N(mhp) = 2.161(2) A, and Mo-N(CH(3)CN) = 2.160(3) and 2.170(3) A. Reactions involving Mo(2)(mhp)(3)(CH(3)CN)(2)(2+) and Mo(2)(mhp)(2)(CH(3)CN)(4)(2+) with (n)Bu(4)NO(2)CMe (1 and 2 equiv.) yield the complexes Mo(2)(mhp)(3)(O(2)CMe) and Mo(2)(mhp)(2)(O(2)CMe)(2) which are shown to be kinetically labile to ligand scrambling. Reactions between Mo(2)(mhp)(3)(CH(3)CN)(2)(+)BF(4)(-) (2 equiv.) and [(n)Bu(4)N(+)](2)[O(2)C-X-CO(2)](2-) yielded dimers of dimers [Mo(2)(mhp)(3)](2)(micro-O(2)C-X-CO(2)] where X = nothing, 2,5- or 3,4-thienyl and 1,4-C(6)H(4). Reactions between Mo(2)(mhp)(2)(CH(3)CN)(4)(2+)(BF(4)(-))(2) and tetra-n-butylammonium oxalate and terephthalate yield compounds [Mo(mhp)(2)bridge](n) which by MALDI-TOF MS are proposed to be a mixture of molecular squares (n = 4) and triangles (n = 3) along with minor products of [Mo(2)(mhp)(3)](2)(bridge) and Mo(2)(mhp)(4) that arise from ligand scrambling.