Controlling the Addition of Metal Centers to a Bis(pyrazolyl)methane Starburst Ligand:  Direct Routes to Mono-, Bi-, and Trimetallic Rhenium(I) Complexes

The bis(pyrazolyl)methane starburst ligand 1,3,5-tris[bis(1-pyrazolyl)methyl]benzene (1,3,5-[CH(pz)2]3C6H3) was prepared by the cobalt-catalyzed condensation reaction between 1,3,5-triformylbenzene and thionyldipyrazole. The addition of Re(CO)5Br to an excess of 1,3,5-[CH(pz)2]3C6H3 resulted in the selective formation of the monometallic complex {1,3,5-[CH(pz)2]C6H3}Re(CO)3Br (1). When 2 equiv of Re(CO)5Br was reacted with 1 equiv of 1,3,5-[CH(pz)2]3C6H3, the bimetallic complex {μ-1,3,5-[CH(pz)2]3C6H3}[Re(CO)3Br]2 (2) was produced as the major product. The trimetallic complex {μ-1,3,5-[CH(pz)2]3C6H3}[Re(CO)3Br]3 (3) was prepared by the reaction of an excess of Re(CO)5Br with 1,3,5-[CH(pz)2]3C6H3. Recrystallization of the complexes from acetone or acetonitrile resulted in the isolation of the crystalline compounds 1, 1·(CH3)2CO, 2·(CH3)2CO, 3·7CH3CN, 3·3(CH3)2CO, and 3·4.5(CH3)2CO. The supramolecular structures of all the complexes are influenced by the 3-fold symmetric, fixed geometry of 1,3,5-[CH(pz)2]3C6H3, and each structure contains intricate networks of molecules, in some cases including alternating layers of complex and solvent molecules, organized through π···π, CH···π, and other hydrogen-bonding interactions.