Dinuclear Nickel(II) Complexes of Phenol-Based “End-Off” Compartmental Ligands and Their Urea Adducts Relevant to the Urease Active Site

Two phenol-based compartmental ligands of the “end-off” type, 2,6-bis{N-[2-(dimethylamino)ethyl]iminomethyl}-4-methylphenol (HL1) and 2-{N-[2-(dimethylamino)ethyl]iminomethyl}-6-{N-methyl-N-[2-(dimethylamino)ethyl]aminomethyl}-4-bromophenol (HL2), have been used to form [Ni2(L1)(AcO)(NCS)2(MeOH)] (1), [Ni2(L1)(AcO)2(MeOH)]BPh4 (2), [Ni2(L2)(AcO)(NCS)2(MeOH)] (3), [Ni2(L2)(AcO)2]BPh4 (4), and [Ni2(L2)(NCS)3(MeOH)] (5). X-ray crystallographic studies were done for 2−5. 2: triclinic, space group P1̄, a = 13.613(3) Å, b = 16.475(4) Å, c = 11.307(4) Å, α = 99.90(2)°, β = 104.16(2)°, γ = 109.01(2)°, V = 2253(1) Å3, Z = 2. The complex cation has a dinuclear core triply bridged by the phenolic oxygen of (L1)- and two acetate groups in the syn-syn mode. One Ni has a six-coordinate geometry together with a methanol oxygen. 3: triclinic, space group P1̄, a = 10.167(1) Å, b = 16.119(2) Å, c = 9.472(3) Å, α = 103.53(2)°, β=100.91(1)°, γ = 85.62(1)°, V = 1481(1) Å3, Z = 2. A pair of Ni ions are bridged by the phenolic oxygen of (L2)-, an isothiocyanate nitrogen, and an acetate group. The sixth position of one Ni is occupied by a methanol oxygen and that of the other Ni by isothiocyanate nitrogen. 4: monoclinic, space group P21/n, a = 15.146(2) Å, b = 9.442(3) Å, c = 30.844(2) Å, β = 93.427(9)°, V = 4402(1) Å3, Z = 4. Two Ni ions are bridged by the phenolic oxygen of (L2)- and an acetate group. The Ni bound to the iminic pendant arm is nearly planar whereas the Ni bound to the aminic pendant arm is of six-coordination together with a bidentate acetate group. 5: monoclinic, space group C2/c, a = 26.744(5), b = 10.323(4) Å, c = 21.785(6) Å, β = 94.73(2)°, V = 5993(3) Å3, Z = 8. Two Ni ions are bridged by the phenolic oxygen of (L2)- and an isothiocyanate nitrogen. The Ni bound to the iminic pendant arm is of five-coordination along with an isothiocyanate nitrogen. The Ni bound to the aminic pendant arm has a six-coordinate geometry together with a methanol oxygen and an isothiocyanate nitrogen. 1−5 were examined regarding their ability to bind urea, and 4 and 5 were shown to form [Ni2(L2)(AcO)2(urea)]BPh4 (4‘) and [Ni2(L2)(NCS)3(urea)] (5‘), respectively. 5‘ crystallizes in the monoclinic system, space group P21/n, with a = 11.709(5), b = 15.100(4), c = 17.548(5) Å, β = 95.58(3)°, V = 3087(1) Å3, and Z = 4. Its dinuclear core is very similar to that of 5 except that the methanol of 5 is replaced by a urea molecule.