INSIGHTS into the structures adopted by titanocalix[6 and 8]arenes and their use in the ring opening polymerization of cyclic esters

摘要

Interaction of p-tert-butylcalix[6]areneH(6), (LH6)-H-1, with [TiCl4] afforded the complex [Ti2Cl3(MeCN)(2)(OH2)((LH)-H-1)][Ti2Cl3(MeCN)(3)((LH)-H-1)]center dot 4.5MeCN (1 center dot 4.5MeCN), in which two pseudo-octahedral titanium centres are bound to one calix[6]arene. A similar reaction but employing THF resulted in the THF ring-opened product [Ti4Cl2(mu(3)-O)(2)(NCMe)(2)(L)(2)(O(CH2)(4)Cl)(2)]center dot 4MeCN (2 center dot 4MeCN), where LH4= p-tert-butylcalix[4]areneH(4). Interaction of L(1)H(6)with [TiF4] (3 equiv.) led, after work-up, to the complex [(TiF)(2)(mu-F)(LH)-H-1](2)center dot 6.5MeCN (3 center dot 6.5MeCN). Treatment of p-tert-butylcalix[8]areneH(8), (LH8)-H-2, with [TiCl4] led to the isolation of the complex [(TiCl)(2)(TiClNCMe)(2)(mu(3)-O)(2)(L-2)]center dot 1.5MeCN (4 center dot 1.5MeCN). From a similar reaction, a co-crystallized complex [Ti4O2Cl4(MeCN)(2)(L-2)][Ti3Cl6(MeCN)(5)(OH2)((LH2)-H-2)]center dot H2O center dot 11MeCN (5 center dot H2O 11MeCN) was isolated. Extension of the L(2)H(8)chemistry to [TiBr4] afforded, depending on the stoichiometry, the complexes [(TiBr)(2)(TiBrNCMe)(2)(mu(3)-O)(2)(L-2)]center dot 6MeCN (6 center dot 6MeCN) or [[Ti(NCMe)(2)Br](2)[Ti(O)Br-2(NCMe)](L-2)]center dot 7.5MeCN (7 center dot 7.5MeCN), whilst use of [TiF4] afforded complexes containing Ca(2+)and Na+, thought to originate from drying agents, namely [Ti8CaF20(OH2)Na-2(MeCN)(4)(L-2)(2)]center dot 14MeCN (8 center dot 14MeCN), [Na(MeCN)(2)][Ti8CaF20NaO16(L-2)(2)]center dot 7MeCN (9 center dot 7MeCN) or [Na](6)[Ti8F20Na(MeCN)(2)(L-2)][Ti8F20Na(MeCN)(0.5)(L-2)]center dot 15.5(C2H3N) (10 center dot 15.5MeCN). In the case of [TiI4], the ladder [(TiI)(2)(TiINCMe)(2)(mu(3)-O)(2)(L-2)]center dot 7.25CH(2)Cl(2)(11 center dot 7.25CH(2)Cl(2)) was isolated. These complexes have been screened for their potential to act as catalysts in the ring opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL), delta-valerolactone (delta-VL) andrac-lactide (r-LA), both in air and N-2. For epsilon-CL and delta-VL, moderate activity at 130 degrees C over 24 h was observed for1,9and11; forr-LA, only1exhibited reasonable activity. In the case of the co-polymerization of epsilon-CL with delta-VL, the complexes1and11afforded reasonable conversions and low molecular weight polymers, whilst4,6, and9were less effective. None of the complexes proved to be active in the co-polymerization of epsilon-CL andr-LA under the conditions employed herein.