The reaction of the ynediamine 1,2-dipiperidinoacetylene (1) with [(η2-COE)Cr(CO)5], [(THF)W(CO)5] and [RuCl2(η6-cymene)]2 afforded homobimetallic complexes 2a, 2b and 3, in which the diaminoacetylene 1 acts as a bis(aminocarbene) ligand by bridging two complex fragments Cr(CO)5 (in 2a), W(CO)5 (in 2b) and RuCl2(η6-cymene) (in 3). The reaction of 1 with [RuCl2(PPh3)3] gave trans-[(1)RuCl(PPh3)2]Cl, [4]Cl, in which the alkyne 1 coordinates as a 4-electron donor ligand. The cation 4 represents a rare example of a square-planar Ru(II) complex with a low-spin ground state (S = 0), and its stability can be ascribed to the strong alkyne-metal π-interaction as confirmed by DFT calculations. Treatment with one or two equivalents of NaBPh4 in acetonitrile gave [4]BPh4 and the dicationic [(1)Ru(PPh3)2(CH3CN)2](BPh4)2, [5](BPh4)2. [4]Cl can be used for the preparation of heterobimetallic Ru-Pd bis(aminocarbene) complexes by reaction with [(MeCN)2PdCl2], resulting in the formation of bimetallic 6 and tetrametallic 7.
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