Chelated Bis-N-heterocyclic Carbene Platinum and Palladium Units as Tunable Components of Multinuclear Complexes

Heterometallic trinuclear M2M′ complexes (M = Rh, Ir; M′ = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)2{M′(bisNHC-Cn-R)}(μ3-S)2](BPh4)2 (M = Rh, Ir; M′ = Pt, Pd; bisNHC-Cn-R = methylene-, ethylene-, or propylene-bridged bis(N-alkyl-imidazolylidene)), were synthesized by reacting bis(hydrosulfido)platinum(II) or palladium(II) complexs with bisNHC-Cn-R and hydroxo-bridged dinuclear complexes [(MCp*)2(μ-OH)3](BPh4), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M2M′ complexes with a variety of alkylene bridges in bisNHC-Cn-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or pal...