The use of 1,2-dipiperidinoacetylene for the preparation of monometallic diaminoacetylene and homo- or heterobimetallic diaminodicarbene ruthenium(ii) complexes

Abstract

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.