Synthesis, structures, properties, and reactivity of new Group 10 heteroleptic dithiolene complexes
Description
This dissertation is dedicated to the study of the synthesis, crystal structures, properties, and reactivity of heteroleptic metallodithiolene complexes of the Group 10 metals. In this work, we report a systematic survey of the reactivity of [(Ph2C2S2)2M] (M = Ni, Pd, Pt) toward ligand substitution. The upshots of the survey are the clarification of the attributes of the incoming ligand that facilitate ligand displacement, creation of a new set of heteroleptic dithiolene complexes, [M(Ph2C2S2)(C≡NR)2] (M = Ni, Pd, Pt; R = Me, Bn, Cy, tBu, 1-Adamantyl, Ph), and improvement in the efficiency by which mixed-ligand “push-pull” compounds are made. The scope of dithiolene ligand displacement by incoming ligands was expanded beyond the already reported phosphine and diimine ligands. Spectroscopic and physical characterization techniques including S K-edge X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were used in conjunction with DFT computational methods to establish the properties of the compounds prepared in this study. Representative [(Ph2C2S2)Pt(C≡NR)2] (R = aryl) complexes exihibited low temperature luminscence in frozen solvent glasses with relatively long lifetimes. The relevance of the dithiolene redox non-innocence in the ligand substitution mechanism has also been elucidated, thereby giving an insight into the fate of the displaced dithiolene ligand. Redox disproportionation between two radical monoanionic dithiolene ligands leads to the creation of a dithione, which is an enhanced leaving group and an inherently reactive species. When displacement of dithiolene ligand from [(Ph2C2S2)2Ni] was conducted with a twofold excess of C≡NCy, 4,5-diphenyl-1,3-dithiol-2-cyclohexylimine could be isolated. The identification and characterization of this compound is consistent with the creation of dithiobenzil during the ligand substitution. The reactive α-dithione is also capable of undergoing rapid irreversible polymerization, thereby providing the thermodynamic impetus for the dithiolene ligand substitution. Chemical oxidation of [Pt(Ph2C2S2)(C≡NtBu)2] with [N(C6H4Br-4)3][SbCl6] was undertaken to form [Pt(Ph2C2SˉS‧)(C≡NtBu)2]2[SbCl6]2. Structural determination of the dication revealed appreciable shortening and lengthening of C─S and C─C bond distances, respectively, within the dithiolene ligand as compared to the charge-neutral complex, an observation which confirmed the dithiolene ligand as the locus of the redox activity in the heteroleptic monodithiolene complexes. The utility of [M(Ph2C2S2)(C≡NMe)2] (M= Ni, Pd, Pt) as synthons in their own right for heteroleptic compounds not directly attainable by ligand substitution from [M(Ph2C2S2)2] was also explored. The panorama of outcomes when [M(S2C2Ph2)(CNMe)2] (M = Ni2+, Pd2+, Pt2+) are introduced to new ligands intended to substitute for CNMe has been thoroughly defined. The most significant breakthrough was the isolation of the dicyanide complex, [Et4N]2[Ni(S2C2Ph2)(C≡N)2], which is a potentially useful precursor toward cyanide-bridged multimetallic architectures. Finally, the synthesis and structural characterization of multimetallic complexes bridged by bis(diphenylphosphine) ligands and redox active dithiolenes as end capping ligands are described. The electrochemistry study revealed that the dimetallic compounds support reversible oxidation to dications, which likely have singlet diradical - triplet states in close equilibrium. The use of dithiolene ligands as electron spin hosts offers new possibilities for the application of metallodithiolene complexes in molecule-based spintronic devices, such as quantum bits (qubits).