Heterotrimetallic Assemblies with 1,2,4,5-Tetrakis(diphenylphosphino)benzene Bridges: Constructs for Controlling the Separation and Spatial Orientation of Redox-Active Metallodithiolene Groups.

Metallodithiolene complexes of the type [(RCS)M(η-tpbz)] [R = CN, Ph, or -anisyl; M = Ni, Pd, or Pt; tpbz = 1,2,4,5-tetrakis(diphenylphosphino)benzene] chelate transition metals ions to form trimetallic arrays [[(RCS)M(tpbz)]M'], where M' is square planar Pt, tetrahedral Cu, Ag, or Au, or octahedral {ReBr(CO)}/{Re(CO)}. Forcing conditions (190 °C reflux in decalin, 72 h) are demanded for the Re compounds. With third-row metals at the nexus, the compounds are stable to air. Twelve members of the set have been characterized by X-ray diffraction and reveal dithiolene centroid-centroid distances ranging from 22.4 to 24.0 Å. Folding around each tpbz intrachelate P···P axis such that the MP/M'P planes meet the tpbz PCP mean plane at non-zero values gives rise to core topologies that appear "S-like" or herringbone-like for M' = Pt or {ReBr(CO)}/{Re(CO)}. Calculations reveal that departure from idealized // symmetries is induced by steric crowding between Ph groups and that dynamic, fluxional behavior is pertinent to the solution phase because multiple, lower-symmetry minima of comparable energy exist. Spectroscopically, the formation of the trimetallic arrays is marked by a shift of the open end P nuclear magnetic resonance signal from approximately -14.5 ppm to approximately +41, approximately +20.5, and approximately +28.5 ppm for M' = Pt, Au, and {ReBr(CO)}/{Re(CO)}, respectively. Electrochemically, dithiolene-based oxidations are observed for the R = Ph and M' = Pt or Au compounds but at potentials that are anodically shifted relative to charge-neutral [(RCS)M]. The compounds reported clarify the possibilities for the synthesis of assemblies in which weakly coupled spins may be created in their modular (RCS)M and M' parts.