Synthetic and mechanistic studies on ruthenium dicarbonyl complexes containing PhP(CH2CH2CH2PCy2)2 (Cyttp) ligand

A synthetic and mechanistic study is reported on ligand substitution and other reactions of six-coordinate ruthenium(II) carbonyl complexes containing tridentate PhP(CH2CH2CH2PCy2)(2) (Cyttp). Carbonylation of cis-mer-Ru(OSO2CF3)(2)(CO)(Cyttp) (1) affords [cis-mer-Ru(OSO2CF3)(CO)(2)(Cyttp)]O3SCF3 (2(O3SCF3)) and, on longer reaction times, [cis-mer-Ru(solvent)(CO)(2)(Cyttp)] (O3SCF3)(2) (solvent = acetone, THF, methanol). 2(O3SCF3) reacts with each of NaF, LiCl, LiBr, NaI, and LiHBEt3 to yield [cis-mer-RuX(CO)(2)(Cyttp)](+) (X = F (3) Cl (4), Br (5), I (6), H (7)), isolated as 3-7(BPh4). These conversions proceed with high stereospecificity to afford only a single isomer of the product that is assigned a structure in which the Ph group of Cyttp points toward the CO trans to X (anti when X = F, Cl, Br, or 1; syn when X = H). Treatment of 2(O3SCF3) with NaOMe and CO generates the methoxycarbonyl complex [cis-mer-Ru(CO2Me)(CO)(2)(Cyttp)](+) (8), whereas addition of excess n-BuLi to 2(O3SCF3) in THF under CO affords mer-RU(CO)(2)(Cyttp) (9). The two C-13 isotopomers [cis-mer-Ru(OSO2CF3)(CO)((CO)-C-13)(Cyttp)]O3SCF3 (2'(O3SCF3): (CO)-C-13 trans to P-C; 2"(O3SCF3): (CO)-C-13 cis to all P donors) were synthesized by appropriate adaptations of known transformations and used in mechanistic studies of reactions with each of LiHBEt3, NaOMOCO, and n-BuLi. Whereas LiHBEt3 reacts with 2'(O3SCF3) and 2"(O3SCF3) to replace triflate by hydride without any scrambling of the carbonyl ligands, the corresponding reactions of NaOMe-CO are more complex. The methoxide combines with the CO cis to triflate in 2, and the resultant methoxycarbonyl ligand ends up positioned trans to the incoming CO in 8. A mechanism is proposed for this transformation. Finally, treatment of either 2'(O3SCF3) or 2"(O3SCF3) with an excess of n-BuLi leads to the formation of the same two ruthenium(0) isomers of mer-Ru(CO)((CO)-C-13)(Cyttp). These products represent. to our knowledge, the first example of a syn-anti pair of isomers of a five-coordinate metal complex. (c) 2005 Elsevier B.V. All rights reserved.