Mononuclear and Binuclear Palladium(II)/Rhenium(I) Complexes Containing a Sterically Hindered Trinucleating Ligand: 2,3,8,9,14,15-Hexamethyl-5,6,11,12,17,18-hexaazatrinaphthalene (hhtn)

Abstract

The trinucleating ligand 2,3,8,9,14,15-hexamethyl-5,6,11,12,17,18-hexaazatrinaphthalene (hhtn), 1, has been obtained in an efficient one-pot synthesis. The reaction of a yellow-green solution of 1 with 1 equiv of Pd-(NCPh)_2Cl_2 gives orange PdCl_2(hhtn), 2, which crystallizes with two independent PdCl_2(hhtn) molecules, a molecule of chlorobenzene, and two molecules of methanol in the triclinic space group P1 with a = 12.949(3) Å, b = 16.625(4) Å, c = 17.062(4) Å, α = 63.00(2)°, β = 71.39(2)°, and γ = 79.78(2)° at 130 K with Z = 4. Refinement of 5551 reflections and 387 parameters yielded R = 0.059 and R_w = 0.060. The structure consists of a nearly square planar PdCl_2(N_2) complex in a highly-distorted hhtn framework. Unfavorable Cl•••H interactions force the PdCl_2 unit out of the hhtn plane by 28.1°. The structure indicates that there are π-π (ligand-ligand) interactions. Reaction of 2 with another equivalent of Pd(NCPh)_2Cl_2 produces the binuclear species (PdCl_2)_2(hhtn), 5. Addition of Re(CO)_5Cl to 1 in refluxing toluene affords deep red crystals of fac-Re(CO)_3Cl(hhtn), 3. Dark red needles of Re(CO)_3Cl(hhtn)•CH_3OH form in the monoclinic space group P2/n with a = 10.515(2) Å, b = 27.123(6) Å, c = 11.385(2) Å, and β = 110.95(2)° at 130 K with Z = 4. Refinement of 5451 reflections and 415 parameters yielded R = 0.052 and R_w = 0.052. The structure features a nearly octahedral Re center that is deflected from the hhtn plane by 19.5°. The hhtn in 3 is less distorted than in 2. Reaction of a dichloromethane solution of 3 with 1 equiv of Pd(NCPh)_2Cl_2 produces the heterobinuclear (Re(CO)_3Cl)(PdCl_2)(hhtn), 4 . Red-brown blocks of 4 cocrystallize with 2.6 molecules of 1,2-dichlorobenzene in the triclinic space group P1 with a = 14.540(4) Å, b = 14.558(3) Å, c = 14.671(4) Å, α = 64.72(2)°, β = 66.00(2)°, and γ = 63.30(2)° at 130 K with Z = 2. Refinement based on full-matrix least squares on F^2 using 8481 reflections and 513 parameters yielded R = 0.061 and R2 = 0.135. The structure includes a nearly octahedral Re and a square planar Pd coordinated to a highly distorted hhtn ligand. The PdCl_2 fragment is bent out of the ligand plane by 40.2°, whereas the Re unit is distorted by only 10.4°. Complex 4 forms π-π stacks exclusively with the 1,2-dichlorobenzene solvate molecules.