Binding of Amino-Dialkylated Adenines to Rhenium(III) and Rhenium(IV) Centers.

Amino-dialkylated adenines R(2)AdH (R = Me, Et) react with ReCl(3)(MeCN)(PPh(3))(2) to form mer,cis-ReCl(3)(R(2)AdH)(2)(PPh(3)) complexes. Attempts to protonate the coordinated adenine with HCl led to the oxidized trans-ReCl(4)(R(2)AdH)(PPh(3)) compounds. In both types of complexes, the purine binds via the N3 site of the six-membered ring and makes an intramolecular N9-H.Cl hydrogen bond with a chloride ligand. A material of composition ReCl(4)(R(2)AdH)(MeCN) was obtained by reacting R(2)AdH with cis-ReCl(4)(MeCN)(2). It turned out to be a ReCl(4)[R(2)AdC(Me)=NH] complex containing a cyclic amidine ligand resulting from the insertion of the acetonitrile C&tbd1;N group in the N9-H bond of the N3-coordinated adenine unit. Crystal structures were determined for one compound of each type: ReCl(3)(Me(2)AdH)(2)(PPh(3)).2C(6)H(5)CH(3), triclinic, P&onemacr;, a = 14.181(2) Å, b = 17.591(3) Å, c = 19.015(5) Å, alpha = 76.66(2) degrees, beta = 86.80(2) degrees, gamma = 87.02(1) degrees, Z = 4, R = 0.0606; ReCl(4)(Me(2)AdH)(PPh(3)), triclinic, P&onemacr;, a = 10.391(4) Å, b = 10.801(5) Å, c = 13.651(6) Å, alpha = 89.64(4) degrees, beta = 83.49(3) degrees, gamma = 65.14(4) degrees, Z = 2, R = 0.0432; ReCl(4)[Me(2)AdC(Me)=NH].C(6)H(6).CH(2)Cl(2), monoclinic, P2(1)/c, a = 13.941(3) Å, b = 13.656(3) Å, c = 12.874(2) Å, beta = 105.47(2) degrees, Z = 4, R = 0.0406. Most of the signals in the (1)H NMR spectra of these paramagnetic species could be assigned.