MOLECULAR ASSEMBLIES CONTAINING UNSUPPORTED [FE-III-(MU(2)ETA(2)-RCO(2))-CU-II] BRIDGES

Formate is an inhibitor of cytochrome oxidases and also effects conver sion of the bovine heart enzyme from the ''fast'' to the ''slow'' cyan ide-binding form. The molecular basis of these effects is unknown; one possibility is that formate inserts as a bridge into the binuclear he me alpha(3)-Cu-B site, impeding the binding of dioxygen or cyanide. Co nsequently, Fe-Cu-carboxylate interactions are a matter of current int erest. We have initiated an examination of such interactions by the sy nthesis of the first examples of [Fe-III-(mu(2):eta(2)-RCO(2))-Cu-II] bridges, minimally represented by Fe-III-L + Cu-II-O(2)CR --> [Fe-III- (RCO(2))-Cu-II] + L. A series of Cu(II) precursor complexes and solvat e forms have been prepared and their structures determined, including [Cu(Me(5)dien)(O2CH)](+) (3), [Cu(Me(5)dien)(O2CH)(MeOH)](+) (4), [Cu( Me(6)tren)(O2CH)](+) (5), and [Cu(Me(5)dien)(OAc)](+) (6). [4](ClO4) w as obtained in monoclinic space group P2(1)/n with a = 8.166(3) Angstr om, b = 15.119(5) Angstrom, c = 15.070(4) Angstrom, beta = 104.65(2)de grees, and Z = 4. [5](ClO4)/[6](ClO4) crystallize in orthorhombic spac e groups Pmma/Pna2(1) with a = 16.788(2)/14.928(5) Angstrom, b = 9.542 (1)/9.341(4) Angstrom, c = 12.911(1)/12.554(4) Angstrom, and Z = 4/4. In all cases, the carboxylate ligand is terminal and is bound in a syn orientation. Also prepared for the purpose of structural comparison w as [Fe-(OEP)(O2CH)], which occurred in monoclinic space group P2(1)/c with a = 13.342(2) Angstrom, b = 13.621(2) Angstrom, c = 19.333(2) Ang strom, beta = 106.12(2)degrees, and Z = 4. The desired bridges were st abilized in the assemblies [(OEP)Fe(O2CH)Cu(Me(5)dien)(OClO3)](+) (9), [(OEP)Fe(OAc)Cu(Me(5)dien)](2+) (10), and {(OEP)Fe[(O2CH)Cu(Me(6)tren )](2)}(3+) (11), which were prepared by the reaction of 3, 6, and 5, r espectively, with [Fe(OEP)(OClO3)] in acetone or dichloromethane. [9]( ClO4)/[10](ClO4)(2) . CH2Cl2 crystallize in triclinic space group P1 w ith a = 9.016(3)/13.777-(3) Angstrom, b = 15.377(5)/13.847(3) Angstrom , c = 19.253(53/17.608(4) Angstrom, alpha = 78.12(3)/96.82(3)degrees, beta = 86.30(4)/108.06(3)degrees, gamma = 76.23(3)/114.32(3)degrees, a nd Z = 2/2. Each assembly contains a [Fe-III-(RCO(2))-Cu-II] bridge bu t with the differing orientations anti-anti (9) and syn-anti (10, 11). The compound [11](ClO4)(2)(SbF6) occurs in orthorhombic space group P bcn with a = 12.517(6) Angstrom, b = 29.45(1) Angstrom, c = 21.569(8) Angstrom, and Z = 4. Complex 11 is trinuclear; the Fe(III) site has tw o axial formate ligands with bond distances indicative of a high-spin configuration. Structural features of 9-11 are discussed and are consi dered in relation to the possible insertion of formate into the binucl ear sites of two oxidases whose structures were recently determined. T he present results contribute to the series of molecular assemblies wi th the bridge groups [Fe-III-X-Cu-II], X = O2-, OH-, and RCO(2)(-), al l with a common high-spin heme, thereby allowing an examination of ele ctronic structure as dependent on the bridging atom or group and bridg e structure. (Me(5)dien = 1,1,4,7,7-pentamethyldiethylenetriamine; Me( 6)tren = tris(2-(dimethyl-amino)ethyl)amine; OEP = octaethylporphyrina te(2-).)