Tripodal tris-tacn and tris-dpa platforms for assembling phosphate-templated trimetallic centers.

Multidentate tripodal ligands, N(CH2-m-C6H4-CH2tacn)3 (L1) and N(CH2-o-C6H4-CH2N(CH2py)2)3 (L2), have been devised for assembling high-nuclearity metal clusters. By using the same tripodal platform with different ligand appendages, either triazacyclononanes or dipicolylamines, and functionalizing either the ortho or the meta positions on the tris(xylyl) linker arms, discrete trimetal phosphate units of relevance to phosphate-metabolizing trimetallic centers in biology were prepared. Four such compounds, [(Cu(II)Cl)3(HPO4)L1](PF6) (1), [(Cu(II)Cl)3(HAsO4)L1](PF6) (2), Na2[Mn(III)6Mn(II)2(H2O)2(HPO4)6(PO4)4(L1)2] (3), and [Co(II)3(H2PO4)Cl2(MeCN)L2](PF6)3 (4), all containing three metal centers bound to a central phosphate or arsenate unit bridging oxygen atoms, have been synthesized and structurally characterized. These results demonstrate the propensity of this novel tripodal ligand platform, in the presence of phosphate or arsenate, to assemble {M3(EO4)} units and thus structurally mimic trimetallic active sites of proteins involved in phosphate metabolism. Reactivity studies reveal that the tricopper complex 1 is more efficient than monocopper analogues in catalyzing the hydrolysis of 4-nitrophenyl phosphate.