Spectral and Structural Characterization of Amidate-Bridged Platinum−Thallium Complexes with Strong Metal−Metal Bonds

The reactions of [Pt(NH3)2(NHCOtBu)2] and TlX3 (X = NO3-, Cl-, CF3CO2-) yielded dinuclear [{Pt(ONO2)(NH3)2(NHCOtBu)}Tl(ONO2)2(MeOH)] (2) and trinuclear complexes [{PtX(RNH2)2(NHCOtBu)2}2Tl]+ [X = NO3- (3), Cl-
(5), CF3CO2- (6)], which were spectroscopically and structurally 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 (1JPtTl), 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 PtIII. 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 PtIII 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.