Facile reaction of the model urease complex [Ni2(OAc)3(urea)(tmen)2][OTf] (A) with acetohydroxamic acid (AHA) gives the monobridged hydroxamate complex (I) [Ni2(OAc)2(AA)(urea)(tmen)2][OTf] with a Ni−Ni distance of 3.434(1) Å compared to that of 3.5 Å in urease (OAc, CH3COO-; tmen, N,N,N‘,N‘-tetramethylethylenediamine; OTf, CF3SO3; AHA, acetohydroxamic acid; AA, acetohydroxamate anion). I is a close model of one proposed mode of urease inhibition by hydroxamic acids, recently observed in the acetohydroxamate-inhibited C319A variant of Klebsiella aerogenes urease. Reaction of [Ni2(OH2)(OAc)4(tmen)2] (B) with AHA gives the dibridged hydroxamate complex (II) [Ni2(OAc)(AA)2(tmen)2][OAc] with a Ni−Ni distance of 3.005(1) Å. Infrared spectroscopic studies provide evidence for the bridging acetate groups undergoing carboxylate shifts thereby assisting replacement of acetate by hydroxamate. Both I and II show ferromagnetic exchange coupling.

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Combinatorial parallel synthesis has led to the rapid generation of a single-compound library of novel fluorinated quaterphenyls. Subsequent automated screening revealed liquid crystalline (LC) behaviour and gave qualitative relationships of molecular structures and solid state properties.

Depending on the reaction conditions, excited chloranil ( 3 CA) and cis-cyclooctene (cis-CO) furnished three types of products, which all contain carbocyclic four-membered rings. The illumination of a solution in benzene by light bulbs gave rise to the all-cis 1:1 cycloadduct (11a) in 76 % yield. On its part, this compound reacted with cis-CO under the action of better sources for UV light with the formation of three isomeric 1:2 cycloadducts. Two of them underwent a photochemical dechlorination leading to a cyclobutene derivative. Albeit rather sluggishly, 3 CA and trans-cyclooctene (trans-CO) brought about an unsymmetrical 1:1 and a 1:2 cycloadduct. By contrast, excited 11a reacted smoothly with trans-CO and afforded a 72 % yield of the unsymmetrical 1:2 cy-

Solutions of chloranil (CA) in benzene were irradiated in the presence of Moore's hydrocarbon (MH) and 2-norcarene (NC). These reactions brought about four common products, namely 2,3,5,6-tetrachlorohydroquinone (TCH) and three 1 : 1 cycloadducts, whose C7H10 subunits were reorganised in comparison to the skeletons of MH and NC. As the fifth product, a norcar-3-en-2-yl ether of TCH was formed in the case of NC, whereas MH gave rise to a substance having the structure of the diastereomeric bis(endo-2-norcaryl) ethers of TCH. A control experiment demonstrated that this substance is also produced from MH and TCH without irradiation. In view of the known addition of acids onto MH to give norcaranes substituted in position 2 and the known acid-catalysed isomerisation of MH to NC, it seems obvious that TCH was the only genuine product of the photoreaction of CA with MH. Being an acid, TCH then not only took up two equivalents of MH furnishing the bisethers referred to but also catalysed the rearrangement of MH to NC, which served as a substrate for excited CA to yield the three 1 : 1 cycloadducts mentioned.

The rapid solution phase synthesis of novel liquid crystalline materials is demonstrated by utilising combinatorial and parallel methods for the preparation of a library of 225 differently fluorinated 4,4"-dipropyl-p-quaterphenyls. Chemical diversity was introduced into the growing oligomers via a convergent synthetic sequence of iodinations and Suzuki cross-couplings by using various fluorinated phenyl building blocks. A highly efficient rapid parallel purification method was developed that provided HPLC-pure library members in amounts sufficient for the characterization of bulk properties.

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