Reactions of New Organoplatinum(II) and -(IV) Complexes of 1,4-Diaza-1,3-butadienes with Light and Electrons. Emission vs Photochemistry and the Electronic Structures of Ground, Reduced, Oxidized, and Low-Lying Charge-Transfer Excited States
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Organometallics 17 (2): 237--247 (1998)

Complexes between the 1,4-disubstituted 1,4-diaza-1,3-butadiene chelate ligands RN:CHCH:NR (R-DAB; R = alkyl, aryl) and the organoplatinum fragments PtMe2, PtMe4, and PtMes2 (Mes = mesityl) were prepd. and characterized with respect to their electronic structures. All compds. are distinguished by low-energy charge-transfer transitions to low-lying p* orbitals of the R-DAB ligands, either from metal d orbitals (PtII) or from metal-carbon s bond combinations (PtIV). These spectral assignments are supported by DFT calcns. on model complexes between HN:CHCH:NH and PtMe2 or PtMe4. The calcns. also reproduce the structural results for the complex between CyN:CHCH:NCy and PtMe4, which exhibits significantly longer Pt-C bonds to the axial Me groups. The distinct solvatochromism of the long-wavelength transitions is described, as are the UV/vis spectroelectrochem. results for reversible redn. to PtIV(R-DAB.bul.-) or PtII(R-DAB.bul.-) species (no evidence for a PtI state). In contrast, the oxidn. is electrochem. irreversible except for the dimesitylplatinum compds. The electrochem. potentials of corresponding PtMe2 and PtMe4 compds. are very similar, demonstrating that the binding of two addnl. Me carbanions compensates for the effect of the higher metal oxidn. state. While the organoplatinum(II) species are emissive, the tetramethylplatinum(IV) complexes are photoreactive and undergo metal-to-ligand Me transfer reactions-in agreement with the structurally confirmed weaker bonding to the axial Me groups. on SciFinder(R)
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