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

Mono benzoxazine appended N-capped amino bis(disubstitutedphenol) ligands [II(a-c)] upon reaction with (VO)-O-V(OEt)(3) in a 1 : 1 molar ratio in EtOH/MeOH give [{(VO)-O-V}en(3,5-dtbb)(3)] (1), [{(VO)-O-V}en(3-tb,5-mb)(3)] (2) and [{(VO)-O-V}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 [(MO2)-O-VI(acac)(2)] (M=Mo or W; Hacac=acetylacetone) reacts with II(a-c), these ligands retain their identity and form cis-[(MO2)-O-VI] complexes, [{(MoO2)-O-VI}{en(3,5-dtbb)(2)(6,8-dtbbenzox)}] (4), [{(MoO2)-O-VI}{en(3-tb,5-mb)(2)(6-tb,8-mbbenzox)}] (5) and [{(MoO2)-O-VI}{en(3,5-dmb)(2)(6,8-dmbenzox)}] (6), [{(WO2)-O-VI}{en(3,5-dtbb)(2)(6,8-dtbbenzox)}] (7), and [{(WO2)-O-VI}{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 [{(WO2)-O-VI}{en(3,5-dmb)(3)}] (10), similar to complexes 1-3. Complex [{(WO2)-O-VI}{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 [(MO2)-O-VI(acac)(2)] (M=Mo or W) in MeOH and give salan type complexes [((MO2)-O-VI)en(3,5-dtbb)(2)] [M=Mo (11), M=W (14)], [((MO2)-O-VI)en(3-tb,5-mb)(4)] [M=Mo (12), M=W (15)] and [((MO2)-O-VI)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.

Automated summary

This study synthesized a series of transition metal complexes, some of which exhibited catalytic activity and were used as catalysts for various organic reactions.