Spectral and structural characterization of amidate-bridged platinum-thallium complexes with strong metal-metal bonds

The reactions of [Pt(NH₃)₂(NHCO^tBu) ₂] and TlX₃ (X = NO₃^-, Cl ^-, CF₃CO₂^-) yielded dinuclear [{Pt(ONO₂)(NH₃)₂-(NHCO^tBu)} Tl(ONO₂)₂(MeOH)] (2) and trinuclear complexes [{PtX(RNH₂)₂(NHCO^tBu)₂} ₂Tl]⁺ [X = NO₃^- (3), Cl^- (5), CF₃CO₂^- (6)], which were spectroscopically and etructurally characterized. Strong Pt-Tl interaction in the complexes in solutions was indicated by both ¹⁹⁵Pt and ²⁰⁵Tl NMR spectra, which exhibit very large one-bond spin-spin coupling constants between the heteronuclei (¹J_PtTl), 146.8 and 88.84 kHz for 2 and 3, respectively. Both the X-ray photoelectron spectra and the ¹⁹⁵Pt chemical shifts reveal that the complexes have Pt centers whose oxidation states are close to that of Pt^III. Characterization of these complexes by X-ray diffraction analysis confirms that the Pt and Tl atoms are held together by very short Pt-Tl bonds and are supported by the bridging amidate ligands. The Pt-Tl bonds are shorter than 2.6 Å, indicating a strong metal-metal attraction between these two metals. Compound 2 was found to activate the C-H bond of acetone to yield a platinum(IV) acetonate complex. This reactivity corresponds to the property of Pt^III complexes. Density functional theory calculations were able to reproduce the large magnitude of the metal-metal spin-spin coupling constants. The couplings are sensitive to the computational model because of a delicate balance of metal 6s contributions in the frontier orbitals. The computational analysis reveals the role of the axial ligands in the magnitude of the coupling constants.