Titanatranes Derailed:  Static and Dynamic Triethanolamine Slippage Induced by Polyphenoxide Chelation

Aryloxytitanatranes [N(CH2CH2O)3]Ti[OC6H2-2,4- t Bu2-6-CHPh3 - n (C6H2-3,5- t Bu2-2-OH) n - 1] (1, n = 1; 2, n = 2; 3, n = 3) containing aryloxides derived from substituted triphenylmethanes are formed in high yield in the reactions of the corresponding phenols with tert-butoxytitanatrane [N(CH2CH2O)3]Ti(O t Bu). The aryloxytitanatranes adopt monomeric, trigonal bipyramidal structures, as confirmed by X-ray crystallography for 1 and 2. The compounds with pendant phenol groups display fluxional behavior due to interchange of the bound phenoxide with the free phenol groups, most likely via a mechanism involving displacement of one arm of the nitrilotriethoxide by the dangling phenol group. The amidotitanatrane {[N(CH2CH2O)3]Ti(NEt2)}2 reacts with the bisphenol PhCH(C6H2-3,5- t Bu2-2-OH)2 to give a crystallographically characterized fully metalated cyclic octatitanium complex of the formula {PhCH(C6H2-3,5- t Bu2-2-O)2Ti2[(OCH2CH2)3N]2}4 (4). The structure of 4 reveals a metallamacrocycle (minimum ring size = 28 members) consisting of four repeating unsymmetrical dititanium units. In each dititanium unit, there is an unprecedented slippage of the nitrilotriethoxide ligand such that both triethanolamine nitrogens coordinate to only one of the two titaniums, while the bisphenoxide is coordinated only to the other titanium. The propensity of the polyphenoxide ligands to chelate is attributed to favorable π-bonding interactions attainable in the eight-membered chelate rings.