Synthesis and Transition Metal Complexes of Novel <i>N</i>,<i>N</i>,<i>O</i> Scorpionate Ligands Suitable for Solid Phase Immobilisation

Abstract

Abstract Introduction of an allyl or a hydroxymethyl group to bis(3,5‐dimethylpyrazol‐1‐yl)acetic acid ( 1 ) at the bridging carbon atom leads to the new tripodal N , N , O ligands 2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)pent‐4‐enoic acid (Hbdmpzpen) ( 2 ) and 2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)‐3‐hydroxypropionic acid (Hbdmpzhp) ( 3 ). These ligands exhibit similar chemical behaviour to that of 1 , but they have the additional possibility to be immobilised to a solid phase. Esterification of the hydroxymethyl linker of 3 yields 2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)‐3‐acetatopropionic acid (Hbdmpzap) ( 4 ). The molecular structures of 2 , 3 and 4 all exhibit intramolecular hydrogen bridges. Introduction of a hydroxymethyl group to methyl bis(3,5‐dimethylpyrazol‐1‐yl)acetate ( 5 ) yields methyl2,2‐bis(3,5‐dimethylpyrazol‐1‐yl)‐3‐hydroxypropionate(Mebdmpzhp) ( 6 ), which can be immobilised on Merrifield polymer to yield modified resin P ‐ 6 . To investigate the reactivity of these new ligands, manganese and rhenium complexes of 2 , 3 and 4 have been studied. The molecular structures of the two manganese complexes [Mn(bdmpzpen)(CO) 3 ] ( 7 ) and [Mn(bdmpzap)(CO) 3 ] ( 8 ) have been confirmed by single‐crystal X‐ray structure determination. Saponification of polymer resin P ‐ 6 and subsequent reaction with [ReBr(CO) 5 ] yields rhenium tricarbonyl complexes anchored on Merrifield polymer ( P ‐Re). Solid phase immobilisation of the [Mn(bdmpzpen)(CO) 3 ] ( 7 ) and [Re(bdmpzpen)(CO) 3 ] ( 9 ) complexes on 3‐mercaptopropyl functionalised silica is initialised by AIBN. The tripodal coordination of manganese and rhenium in these functionalised Merrifield resins ( P ‐Re) and silica ( S ‐Mn, S ‐Re) is proven by a single A 1 and two E signals in the IR spectra that are typical for unsymmetrical “piano stool” type carbonyl complexes. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2006)