Influence of Coordination Geometry on the Ring Opening of Benzoxazine: Oxidovanadium(V), Dioxidomolybdenum(VI) and Dioxidotungsten(VI) Complexes of Benzoxazine Based Ligands and their Bio Inspired Catalytic Applications

Abstract

AbstractMono benzoxazine appended N‐capped amino bis(disubstitutedphenol) ligands [II(a–c)] upon reaction with VVO(OEt)3 in a 1 : 1 molar ratio in EtOH/MeOH give [{VVO}en(3,5‐dtbb)3] (1), [{VVO}en(3‐tb,5‐mb)3] (2) and [{VVO}en(3,5‐dmb)3] (3). During the reaction, the benzoxazine ring opens with the loss of methylene group and the newly formed ligands, N,N‐bis(2‐hydroxy‐3,5‐disubstitutedbenzyl)‐N’‐2‐hydroxy‐3,5‐disubstituted benzyledene‐1,2‐diaminoethane [III(a–c)], behave as tribasic pentadentate in these complexes. Under similar conditions, when [MVIO2(acac)2] (M=Mo or W; Hacac=acetylacetone) reacts with II(a–c), these ligands retain their identity and form cis‐[MVIO2] complexes, [{MoVIO2}{en(3,5‐dtbb)2(6,8‐dtbbenzox)}] (4), [{MoVIO2}{en(3‐tb,5‐mb)2(6‐tb,8‐mbbenzox)}] (5) and [{MoVIO2}{en(3,5‐dmb)2(6,8‐dmbenzox)}] (6), [{WVIO2}{en(3,5‐dtbb)2(6,8‐dtbbenzox)}] (7), and [{WVIO2}{en(3‐tb,5‐mb)2(6‐tb,8‐mbbenzox)}] (8). However, the benzoxazine ring ruptures in case of ligand IIc under these conditions and form [{WVIO2}{en(3,5‐dmb)3}] (10), similar to complexes 1–3. Complex [{WVIO2}{en(3,5‐dmb)2(6,8‐dmbenzox)}] (9), having structure similar to 4–8, could only be obtained when the reaction was carried out in toluene. Not only 9, even complexes 4–8 can be isolated in toluene. Rupturing of both benzoxazine rings has also been experienced when ligands 1,2‐bis(6,8‐disubstitutedbenzo[e][1,3]oxazin‐3(4H)‐yl)ethane [I(a–c)] react with [MVIO2(acac)2] (M=Mo or W) in MeOH and give salan type complexes [(MVIO2)en(3,5‐dtbb)2] [M=Mo (11), M=W (14)], [(MVIO2)en(3‐tb,5‐mb)4] [M=Mo (12), M=W (15)] and [(MVIO2)en(3,5‐dmb)4] [M=Mo (13), M=W (16)]. Complexes 1–9 have been used as catalyst for the multicomponent Biginelli reaction for the synthesis of 3,4‐dihydropyrimidin‐2(1H)‐ones (DHPMs) and oxidative bromination of phenol derivatives.