Cu(II) bis(oxamato) end-grafted poly(amidoamine) dendrimers

Successive treatment of the diethyl ester of 3,4-bis(oxamate)phenylene benzoic acid (3,4-bopbH2Et2OH; ) with [Bu4N]OH and MCl2·nH2O (M = Cu, Ni; n = 2, 6) gave, upon extraction into CH2Cl2, binuclear complexes [Bu4N]4[{M(3,4-bopbO)}2CH2] (, M = Cu, Ni) as novel symmetric methylene diesters. In contrast, subsequent addition of [Bu4N]OH and anhydrous NiCl2 to afforded the very hygroscopic [Bu4N]3[Ni(3,4-bopbO)] () instead. In order to verify reaction conditions to achieve the corresponding carboxamides to - as a crucial step for the synthesis of higher generation dendrimers - was shown to react with RNH2 (R = Me (), Pr ()) to [RNH3][tdqc] (R = Me (), Pr (); tdqc = 1,2,3,4-tetrahydro-2,3-dioxo-6-quinoxaline carboxylate) by rearrangement reactions. Alternatively, if was converted first to 3,4-bopbH2EtF () and treated next with PrNH2, the corresponding carboxamide 3,4-bopbH2Et2NPrH () could be obtained in high yields. The reaction of with [Bu4N]OH and MCl2·nH2O (M = Cu, Ni; n = 2, 6) gave conveniently mononuclear [Bu4N]2[M(3,4-bopbNPrH)] (, M = Cu, Ni). After thus optimizing reaction conditions, for the synthesis of higher-branched bis(oxamato) type complexes the (polyamido)amines (en(II)H2), (den(III)H3), (den(V)H5) and (den(X)H10), possessing two, three, five or ten terminal amino groups, were reacted with appropriate equiv. of to give the corresponding carboxamides en(II)(3,4-bopbH2Et2)2 (), den(III)(3,4-bopbH2Et2)3 (), den(V)(3,4-bopbH2Et2)5 () and den(X)(3,4-bopbH2Et2)10 (). Compounds were converted to the corresponding Cu(II)-containing complexes , which were treated with the corresponding equiv. of [Cu(pmdta)][BF4]2 to afford . Complexes of the series and possess two, three, five or ten end-grafted mononuclear {Cu(3,4-bopb)}(2-) and trinuclear {Cu3(3,4-bopb)(pmdta)2}(2+) complex fragments, respectively. The identities of were established by NMR spectroscopy and ESI-MS measurements. For and , ESI-MS, UV/Vis and ESR studies were applied to confirm the identities of these species. The magnetic properties of the {Cu3(3,4-bopb)(pmdta)2}(2+) end-grafted poly(amidoamine) dendrimers were studied by susceptibility measurements vs. temperature to give J values between -112 () and -118 cm(-1) (), which are typically observed for discrete trinuclear Cu(II)-containing bis(oxamato) type complexes.