Synthesis, crystal structure of ruthenium 1,2-naphthoquinone-1-oxime complex and its mediated C-C coupling reactions of terminal alkynes

Abstract

Substituted decarbonylation reaction of ruthenium 1,2-naphthoquinone-1- oxime (1-nqo) complex, cis-, cis-[Ru{η 2-N(O)C 10-H 6O} 2(CO) 2] (1), with acetonitrile gave cis-, cis-[Ru{η 2-N(O)C 10H 6O} 2(CO) (NCMe)] (2). Complex 2 was fully characterized by 1H NMR, FAB MS, IR spectra and single crystal X-ray analysis. Complex 2 maintains the coordination structure of 1 with the two naphthoquinonic oxygen atoms, as well as the two oximato nitrogen atoms located cis to each other, showing that there is no ligand rearrangement of the 1-nqo ligands during the substitution reaction. The carbonyl group originally trans to the naphthoquinonic oxygen in one 1-nqo ligand is left in its original position [O(5)-Ru-C(1), 174.0(6)°], while the other one originally trans to the oximato group of the other 1-nqo ligand is substituted by NCMe [N(1)-Ru-N(3), 170.6(6)°]. This shows that the carbonyl trans to oximato group is more labile than the one trans to naphthoquinonic O atom towards substitution. This is probably due to the comparatively stronger π back bonding from ruthenium metal to the carbonyl group trans to naphthoquinonic O atom, than the one trans to oximato group, resulting in the comparatively weaker Ru-CO bond for the latter and consequently easier replacement of this carbonyl. Selected coupling of phenylacetylene mediated by 2 gave a single trans-dimerization product 3, while 2 mediated coupling reaction of methyl propiolate produced three products: one trans-dimerization product 4 and two cyclotrimeric products 5 and 6.