Synthesis and anion coordination chemistry of novel mono- and bifunctional borylmetallocenes

The synthesis, characterisation and anion binding properties of a series of bifunctional boryl-substituted ferrocene systems, and monofunctional boryl-substituted ferrocene and cymantrene systems are reported. Thus, the bis-borylated ferrocene systems: Fe rj5-C5H4B(OR)2 2 and Fe n5-C5H4Bcat 2 where (OR)2 = OCH(Ph)CH(Ph)0 (la) or OCH2CH(2-napthyl)0 (5a), and cat = catecholate (2a), 3,5-di-terr-butylcatecholate (3a), or 3-methoxycatecholate (4a) and the mono-borylated ferrocenes and cymantrenes (t 5-C5H5)Fe r 5-C5H4B(OR) 2 (lb), -n.5-C5H4B(OR)2 Mn(CO) 3 (7), (n5-C5H5)Fe n5-C5H4Bcat (2b), and n5-C5H4Bcat Mn(CO)3 (8) where (OR) 2 = OCH(Ph)CH(Ph)0 and cat = catecholate have been synthesised and characterised by NMR, UV/Vis and IR spectroscopy, mass spectrometry, elemental microanalysis, and in most cases by X-ray diffraction. Electrochemical analyses of all ferrocene-based compounds has demonstrated the electronic and redox properties associated with boryl-substituted metallocenes, and allowed a comparison to be made between mono- and disubstituted systems. The anion binding characteristics of the borylated metallocenes and half-sandwich compounds have been probed by spectroscopic (including NMR, UV/Vis, fluorescence and IR spectroscopy) and electrochemical techniques, revealing a specific affinity for binding of the fluoride ion. Binding is shown to occur through monodentate coordination of fluoride, even for the bifunctional Lewis acids such that two equivalents of the anion are bound by the ferrocenyl-host system. In particular, the bis-borylferrocene receptors display remarkable behaviour on complexation of two equivalents of fluoride, such that a colorimetric response is observed on fluoride binding, attributable to the redox chemistry of the ferrocene moiety to which the binding site is covalentfy linked. The synthesis, characterisation and potential hydrogen fluoride binding capabilities of mixed Lewis acidic boron-Lewis basic nitrogen containing systems are also presented here. Both (ri5-C5H 5)Fe ri5-C5H4B(OCH2CH2)NCH 3 (9a) and (n5- C5H5)Fe r 5-C5H 4B(OR)2 where (OR)2 = OCH2CH(CH 2NC5Hi0)O (10a) have been synthesised and characterised by standard techniques, and the former shown by X-ray diffraction to display an intramolecular N-B dative bond. In addition to these newly synthesised Lewis acid-Lewis base-containing systems, hydrogen fluoride binding studies involving the literature compound 2-(AAdimethylaminomethyl)ferrocene boronic acid (11a) are also presented. Analyses of the reactions of different hydrogen fluoride sources with these three compounds have been performed via NMR spectroscopy, electrochemistry, and in the cases of 9a and 11a, by X-ray crystallography. The results indicate that HF treatment of 9a and 10a, causes B-0 bond cleavage leading to loss of the amine function. The Lewis basic component is preserved in the treatment of 10a with HF, however, leading to formation of an HF adduct