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 10 H 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. 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] [2]. [2] Complex 2 was characterized by 1H NMR, FAB MS, IR spectra and single crystal X ray analysis. Complex 2 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 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 more changes than 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.