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The protective pocket of hemocyanin is mimicked by the novel macrocyclic ligand MEPY22PZ (see schematic drawing on the right), which was used to make a Cu2O2 adduct. Proper design of a ligand with azole donors connected by ethylene spacers illustrates how metal–O2 adducts can be stabilized at ambient temperatures and in protic solvents. The purple trans‐μ‐1,2‐CuII‐O2‐CuII species was obtained by oxygenation of the parent CuI compound and by addition of H2O2 and base to the dinuclear CuII complex.

The 22-membered macrocycle, containing four endocyclic pyrazole groups and two exocyclic pyridine groups, viz. (9,22-di(pyridin-2-ylmethyl)-1,4,9,14,17,22,27,28,29,30-decaaza-5,13,18,26-tetramethyl)pentacyclo[24.2.1.1(4,7).1(11,14).1(17,20)]triacontane-5,7(28),11(29),12,18,20(30),24(27),25-octaene (MePy22Pz), has been synthesized in an eleven-step procedure. Two dinuclear copper(II) compounds, viz. [Cu(2)(MePy22Pz)(NO(3))(4)](MeOH)(2) (A) and [Cu(2)(MePy22Pz)(CF(3)SO(3))(2)(H(2)O)(2)](CF(3)SO(3))(2)(MeOH)(2) (B), were prepared with this macrocycle. In both compounds the copper(II) ions are in a square pyramidal N(3)O(2) environment involving a pyrazole nitrogen, a pyridine nitrogen, and a tertiairy amine nitrogen and two oxygen atoms, which stem from two different nitrate anions in compound A and from a triflate anion and a water molecule in compound B. Two of the four pyrazole groups of the macrocycle do not participate in the coordination. The pendent pyridine groups protrude on opposite sides of the macrocycle. Consequently, the copper ions are on different sides of the macrocyclic ring and quite far apart with Cu-Cu distances of 8.668(4) Å in A and 6.814(1) Å in B.

The n e w hafnium complex (q5-C5Me5)Hf(Pri-DAB)CI (Pri-DAB = N,N'-di-isopropyl-l,4-diazabuta-l,3-diene), containing an enediamide ancillary ligand, a precursor t o methyl, propynyl, acyl and hydride derivatives is reported; the structure of [(q5-C5Me5)Hf(Pri-DAB)(y-H)]2 has been determined by X-ray diffraction. J. CHEM. SOC., CHEM. COMMUN., I989 (q5-C5Me5)Hf(diene)C1 --!+ (q5-C5Me5)Hf(Pr'-DAB)C1 (1) 1277 1 ii ... (q5-CSMe5)Hf(Pri-DAB)13C(0)Me (4) [ (qs-C5Mes)Hf(Pri-DAB)(y-H)]2 (5) Scheme 1.

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Die schützende Tasche der Hämocyanins ahmt der neuartige makrocyclische Liganden MEPY22PZ nach, mit dem ein Cu2‐O2‐Addukt hergestellt werden konnte. Der gelungene Entwurf eines Liganden mit ethylenverbrückten Azol‐Donoreinheiten illustriert, wie Metall‐O2‐Addukte bei Raumtemperatur und in protischen Lösungsmitteln stabilisiert werden können. Die purpurfarbene trans‐μ‐1,2‐CuII‐O2‐CuII‐Spezies wurde sowohl durch Umsetzung der CuI‐Stammverbindung mit Disauerstoff als auch durch Zugabe von H2O2/Base zum zweikernigen CuII‐Komplex erhalten.

1981chromatography through a short path of deactivated silica geL9 Thermal reactions were carried out by following the same procedure but strictly excluding light.In summary, a new stereoselective approach to vinyl ethers 3 starting from chromium carbenes having both alkyl and aryl substituents at the carbene carbon and stabilized sulfur ylides has been developed. This novel reaction provides an alternative strategy for constructing 2-acyl enol ethers directly in enolized form, in a process which formally results in the totally site-selective enolization of a 0-keto ester or a 0-diketone. Compounds 3 are in turn not available by using standard Wittig methodology, and the stereoselectivity of the process may be steric in nature. Efforts to extend this methodology to other chromium carbene complexes and to control the stereochemistry in the formation of compounds 3 are now in progress.Acknowledgment. Support for this work under Grant

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