Coordination chemistry of [2 + 2] Schiff-base macrocycles derived from the dianilines [(2-NHCH)X] (X = CHCH, O): structural studies and ROP capability towards cyclic esters

Reaction of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-CH-1,3-(CH)][CHCH(2-CHN)]}(R = Me, LH;tBu, LH) with FeBrafforded the complexes [FeBr(LH)][(FeBr)O]·2MeCN (1·2MeCN), [FeBr(LH)][X] (X = 0.5(FeBr)O,2·0.5MeCN, X = Br,3·5.5MeCN), respectively. Reaction of LHwith [KFe(OtBu)(THF)] (formedin situfrom FeBrand KOtBu), following work-up, led to the isolation of the complex [Fe(L)(LH)]·3MeCN (4·3MeCN), whilst with [CuBr] afforded [CuBr(LH)][CuBr]·2MeCN (5·2MeCN). Attempts to form mixed Co/Ti species by reaction of [CoBrL][CoBr(NCMe)] with TiClresulted in [LH][CoBr]·2MeCN (6·2MeCN). Use of the related oxy-bridged Schiff-base macrocycles {[2-(OH)-5-(R)-CH-1,3-(CH)][O(2-CHN)]}(R = Me, LH;tBu, LH) with CoBrled to the isolation of the complexes [(CoBr)(L)]·2CHO (7·2CHO), [Co(NCMe)(LH)][CoBr]·5MeCN (8·5MeCN), [Co(NCMe)][CoBr(MeCN)]·2MeCN (9·2MeCN). For comparative structural/polymerisation studies, the complexes {CoBr(NCMe)L}·2MeCN (10·2MeCN) and [Co(NCMe)L][CoBr(NCMe)](11), [FeBr(NCMe)L]·2MeCN (12·2MeCN) where LH = 2,6-(CHO)-4-tBu-CHOH, as well as the chelate-free salt [Fe(NCMe)][FeBrOFeBr] (13) have been isolated and structurally characterized. The ability of these complexes to act as catalysts for the ring opening polymerisation (ROP) of ε-caprolactone (ε-CL) and δ-valerolactone (δ-VL) was investigated, as well as co-polymerisation of ε-CL withrac-lactide (r-LA) andvice versa.