The research project highlighted in this thesis utilizes a systematic synthetic protocol for synthesis of multimetallic dithiolene complexes. Monometallic dithiolene complexes are widely studied and easy to synthesize, whereas, multimetallic dithiolene complexes are rare. The synthetic protocols available in the literature for trimetallic complexes are not well developed and often lack control over specific product formation. Therefore we devised a convergent approach for the synthesis of multimetallic dithiolene complexes with a high degree of control over product formation.
Recently, we have used 1,3-dithiole-2-one (R2C2S 2C=O) and 1,2-di-n-alkyltin complexs (R2S 2C2SnR'2) as protected forms of dithiolene ligands for synthesis of mono-, di- and trimetallic dithiolene complexes. Dimetallic compounds [(P-P)M(S2C6H2S2)M(P-P)] (M = Ni, Pd; (P-P) = chelating bis(phosphine)) are prepared from O=CS 2C6H2S2C=O or nBu2SnS2C6H2S 2SnnBu2, which are protected forms of 1,2,4,5-benzenetetrathiolate (btt). Selective monodeprotections of O=CS2C6H2S2C=O or nBu 2SnS2C6H2S2Sn nBu2 lead to [(P-P)Ni(S2C6H 2S2C=O)] or [(P-P)Ni(S2C6H2S 2SnnBu2)]; the former is used to prepare trimetallic compounds [(dcpe)Ni(S2C6H 2S2)M(S2C6H2S2)Ni(dcpe)] (M = Ni or Pt; dcpe = 1,2-bis(dicyclohexylphosphino)ethane), in which, 1,2,4,5-benzenetetrathiolate acts as the connector. Dimetallic compounds of type [(R2C 2S2)M((PPh2)2C6H2(PPh 2)2)M(S2C2R2)] (M = Ni, Pd, Pt; R = CH3, CH3O-p-C6H 4) are prepared from R2C2S2SnR' 2 and Cl2M((PPh2)2C6H 2(PPh2)2)MCl2, in which 1,2,4,5-tetrakis(diphenylphosphino)benzene (tppb) acts as the connector. Both classes of dimetallic compounds (btt- and tppb-bridged) are redox active and display two oxidation processes, of which the first is generally reversible. The tppb-bridged dimetallic complexes are characterized by two simultaneous 1e- oxidations, whereas the btt-bridged dimetallic complexes are characterized by single 1e- oxidation processes. Electrochemical studies reveal that 1,2,4,5-benzenetetrathiolate is the redox-active moiety in the btt-linked compounds, while in the tppb-linked compounds, 1,2,4,5-tetrakis(diphenylphosphino)benzene ligand is effectively an insulator between redox active metallodithiolene fragments.
Structural identification of [(dcpe)Ni(S2C6H 2S2)Ni(dcpe)][BArF24] reveals appreciable shortening and lengthening of C–S and C–C bond distances, respectively, within the tetrathioarene fragment compared to charge-neutral [(dcpe)Ni(S2C 6H2S2)Ni(dcpe)], indicating this to be the redox active moiety. Near IR spectroscopy upon solution-generated cations ([(dcpe)Ni(S 2C6H2S2)Ni(dcpe)]+ and [(R2C2S2)M((PPh2)2C 6H2(PPh2)2)M(S2C2R 2)]+ M = Ni, Pd, Pt; R = CH3O-p-C 6H4) and upon the neutral trinickel complex reveals multiple intense absorptions in the 700-1400 nm region.
The reaction of P4S10 with acyloins, RC(O)CH(OH)R, in refluxing dioxane, followed by the addition of alkylating agents, forms dithiolene thiophosphoryl thiolate compounds, (R2C2S 2)P(S)(SR´), which are readily isolated and purified. Deprotection of ((H3CO-p-C6H4)2 C2S2)P(S)(SMe) in MeO-/MeOH, followed by addition of NiCl2˙6H2O and then I2, produces square planar [Ni(S2C2(C6H4- p-OCH3)2)2] in 93% yield.