Oxazoles revisited: On the nature of binding of benzoxazole and 2-methylbenzoxazole with the zinc and palladium halides

Abstract

A synthetic and structural (X-ray) investigation into the bonding modes of benzoxazole (box) and 2-methylbenzoxazole (Mebox) ligands with halide precursors of Zn and Pd has been undertaken to clarify earlier discrepancies concerning the nature of the bonding mode(s) of the two azoles. In four structurally characterised examples, all contain the title ligands in a κ(1)N bonding motif. Calculations at the density functional level (DFT) of theory (B3LYP) confirm the ground state stability of this class of coordination for several hypothetical Pd and Zn (gas phase) compounds. The attempt to obtain suitable crystalline material of PdCl(2)(box)(2) (i.e., 5) leads to substantial complex degradation. One minor product of this process has been identified (X-ray) as the diarylformamidinato complex C(26)H(22)N(4)O(4)Pd, presumably formed via a complex combination of the decomposition products of both free box and 5.

Conformational Heterogeneity and the Role of the C(2)–H Donor in Mono- and Dihydrated Clusters of Benzoxazole

“…BOX is an imidazole analogue in which the N–H group is substituted by an O atom. The molecule possesses three H bond acceptors, namely, N, O, and delocalized π electrons, as well as an activated C(2)–H as the only potential H-bond donor. , In heterocyclic aromatic molecules where the lone pairs of the O atom are effectively delocalized by π-conjugation such as furan, anisole, and benzofuran, the H-bond accepting ability is often seen to be weakened to the limit of a π acceptor. This is manifested in various experimental findings such as the N–H···π hydrogen bond being favored over N–H···O in the indole–furan complex, the smaller red-shift of the H-bonded OH stretching vibration in hydrated anisole compared to hydrated 2-phenylethanol, and the coexistence of O–H···O and O–H···π isomers in the jet-cooled complexes of benzofuran with water and methanol .…”

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

“…Our reasoning for the production of the materials described above stems from our long standing interest in both fundamental structural elucidation [7][8][9][10][42][43] and catalysis [8,13,17,[20][21][22][23] with azole-containing transition metal (TM) complexes. Divalent Co and Cu compounds are well-known precursors for selective olefin polymerisation, in some cases under Atom Transfer Radical Polymerisation (ATRP) conditions.…”

“…[1][2][3][4][5][6] In this regard, our research interests are primarily focused on the use of azole heterocycles for a variety of topics within coordination chemistry. These areas include fundamental structural studies, [7][8][9][10] metal-mediated polymerization, [11] catalysts for selective C-C bond formation (e.g., Suzuki-Miyaura coupling), [12,13] and medicinal chemistry. [17] Recently, we have turned our attention to a class of azole metalbinding agents that we call Tohda's Ligands (Figure 1).…”

Palladium-catalyzed direct arylation of benzoxazoles with unactivated simple arenes

“…8 Herein, we report that the Pd-catalyzed C-H-C-H cross-coupling between C-H acidic benzoxazoles and simple arenes can be achieved by increasing the difference of C-H acidity between two cross-coupling partners, providing a straightforward and high-yielding approach to 2-arylbenzoxazoles. 9,10 Palladium-catalyzed direct arylation of benzoxazoles with simple arenes via twofold C-H activation must be addressed with two inherent difficulties: first, excessive amount of azoles (relative to Pd catalyst) can strongly ligate the palladium center via nitrogen atoms, 11 which attenuates the electrophilicity of the palladium center and hence interferes with the C-H activation of simple arenes; second, 2-arylbenzoxazoles, the products from this cross-coupling reaction, have a tendency to trap the palladium catalyst in the cyclopalladated complex form to block the catalysis process. 12 Furthermore, benzoxazole itself is liable to oxidative homocoupling 13a and decomposition under oxidative conditions.…”