Divalent cobalt and copper coordination complexes of κ2-N, O-derivatives of (Z)-1-R-2-(2′-oxazolin-2′-yl)-eth-1-en-1-ates: Structure and reactivity patterns

Abstract

The synthesis and characterisation of a small library of Co and Cu derivatives (29 examples) incorporating the (Z)-1-R 1 -2-(4',4'-R 2 -2'-oxazolin-2'-yl)-eth-1-en-1-ate (L: R 1 = alkyl or aryl; R 2 = H or Me) skeleton is described. This work includes six new derivatives of "Tohda's Ligands". In the case where R 2 = H, solid-state stable Co(II) materials of formula Co(κ 2 -N,O-L)2 could, in some cases, be obtained following base-induced deprotonation of L+H and treatment with hydrated CoX2 salts. These complexes display redox induced solution decomposition behaviour giving Co(κ 2 -N,O-L)3 as one isolable product. Stable Cu(II) complexes could only be obtained in the case of for R 1 = Ph and R 2 = H. In the case of R 2 = Me, distorted tetrahedral Co(II) compounds (also Co(κ 2 -N,O-L)2) are obtained as above (twelve examples). Square planar derivatives of Cu(II), of similar stoichiometry, are likewise isolated (eleven new examples). In contrast to the R 2 = H reactions, all of these latter materials were found to be air-stable in solution or the solid phase. In total, 18 complexes have been characterised by single crystal X-ray diffraction. Molecular modelling (PM6(tm) and DFT) are also used to elucidate the molecular properties of selected complexes. Only a single Co complex (R 1 = t-butyl and R 2 = Me) of the library displays reversible one-electron redox properties.

Synthesis, Characterization, and Catalytic Exploration of Mononuclear Mo(VI) Dioxido Complexes of (Z)-1-R-2-(4′,4′-Dimethyl-2′-oxazolin-2′-yl)-eth-1-en-1-ates

“…The straightforward reaction of readily available cis-MoO 2 (acac) 2 to give the desired air-stable materials occurred in the absence of an added base, a situation that is typically required to produce reaction conditions necessary to coordinate the enolate fragment obtained from LH. Hence, these Mo 6+ -based materials formed more readily when compared to most of the Ni 2+ , Co 2+ , Cu 2+ , and Ir + complexes reported previously [9,[11][12][13]. Molecular modeling (Section 2.2) suggested that the likely ligand orientation around a mononuclear Mo 6+ center was that of isomer III (Scheme 3).…”

“…Thus far, we have only observed the κ 2 -N,O bonding motif following formal H + loss from LH; hence, metal-bound enolate anions (L − ) are found within the metal coordination sphere. This has been shown in the chemistry of Co 2+/3+ , Cu 2+ [9,11], Ni 2+ [12], and Ir +/3+ [13], in addition to main group examples [14]. Herein, we detail our exploration into the reactivity of formally Mo 6+ metal centers with LH derivatives, as the reactivity of these compounds with Group 6 metals is currently completely unexplored.…”