Complexes having platinum to metal dative bonds

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It has been shown that the occupied d_<z^2> orbital of a d^8 transition metal ion with square-planar coordination geometry can act as a potential donor to another metal ion (M) resulting in a dative M(d^8)→M bond. In this study we synthesize complexes having short unsupported Pt(II)→M dative bonds by using platinum(II) complexes with carbon σ-donor ligands which exert a strong ligand field.(1) From a mixture of [Pt(phpy)_2] (Hphpy = phenylpyridine) and AgClO_4 in acetone, a helical chain complex, [{Pt(phpy)_2}2{Ag(acetone)}2]_n(ClO_4)_<2n>・acetone_n, was obtained, which consists of alternate stacking of [Pt(phpy)_2] and Ag(acetone)^+ connected by platinum to silver dative bond and has large diameter (2.3 nm) of helix.(2) When the silver source contains a a relatively coordinative NO_3^-, tetranuclear Pt_2Ag_2 the rhombus cluster complex [{Pt(phpy)_2}2{Ag(NO_3)}2]・CH_3CN was obtained. The cluster core has a 4-center 2-electron bond that includes not only the platinum to silver dative bonds but also a silver-silver bond.(3) When the rhodium dimer [Rh_2(CF_3COO)_4] was used as an acceptor, the tetranuclear Pt→Rh_2←Pt complex [{Rh_2(CF_3COO)_4}{Pt(phpy)_2}2] was obtained in which the platinum complexes coordinate to axial sites of rhodium dimer. The cluster has both platinum to silver dative bonds and a rhodium-rhodium single bond.These results show not only that platinum complexes in a strong ligand field can make a strong platinum to metal dative bond, but also that the metal-metal dative bond is useful for making large cluster complexes.