1,10-Phenanthroline ring-opening mediated bycis-{Re(CO)₂} complexes

Abstract

Pyridine ring-opening of a metal-coordinated 1,10-phenanthroline has been demonstrated for the first time. The reaction of stable, well-defined cis,trans-[Re(CO)2(N-N)(N-RIm)(PMe3)]OTf [N-N= 2,2’-bipyridine (bipy), N-RIm= N-alkylimidazole] compounds with KN(SiMe3)2, followed by the...

Elucidation of the Pyridine Ring-Opening Mechanism of 2,2′-Bipyridine or 1,10-Phenanthroline Ligands at Re(I) Carbonyl Complexes

“…The experimental reaction of cis,trans-[Re(bipy)(CO) 2 (N-MesIm)(PMe 3 )]OTf (1b) with the equimolar amount of KN(SiMe 3 ) 2 followed by the addition of MeOTf (excess) has been recently published, showing the formation of the ringopening product 7a, which is the experimental analog of intermediate VII_2. 20 The feasibility of the computationally proposed mechanism is strongly supported by the isolation and characterization of compounds 2b and 3b.…”

“…The reaction of cis,trans-[Re(CO) 2 (N-MeIm)(phen)-(PMe 3 )]OTf (R = Me, 1c) with KN(SiMe 3 ) 2 and MeOTf (excess) afforded the phenantroline ring-opening product 7c, as we have already published. 20 It has to be noted that another pyridine ring-opening product had been obtained in this reaction, and it was found to be a product in which the extruded nitrogen becomes both protonated and methylated (8c in Scheme 2), instead of doubly methylated as in 7c. 35 Taking into account the computational results on the mechanism of the ring-opening reaction, it is reasonable to think that in the last step of the reaction, the H 2 N(SiMe 3 ) 2 + ammonium cation, generated in step 3, can be competitive as an electrophile with MeOTf and could lead to a protonation instead of a second methylation.…”

“…As we have briefly mentioned in the Introduction, the addition of a strong base followed by MeOTf (excess) to cis,trans-[Re(CO) 2 (N-N)(N-RIm)(PMe 3 )]OTf (N-N = bipy or phen; N-RIm= N-MeIm or N-MesIm) 27 compounds afforded products resulting from pyridine ring-opening of bipy or phen ligands. 20 It is noteworthy that different regioisomers are obtained depending on the nature of the bidentate ligand, and this fact prompted us to delve deeper into this type of ringopening process.…”

“…In fact, using cis-{Re(CO) reaction without precedents. 20 It is particularly striking that the ring-opening products of bipy or phen ligands display different regiochemistry, so a study of the mechanism of this type of pyridine ring-opening process may lead to extending the knowledge of these very interesting reactions related to HDN processes.…”

“…We have shown that 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) coordinated to cationic fac -rhenium­(I) tricarbonyl fragments are not chemically inert ligands and can undergo, under mild conditions, the addition of internal nucleophiles generated, in most cases, by deprotonation of appropriately positioned coligands. − In the particular case of the deprotonation of 1-methylimidazole (N-MeIm) coordinated to fac -{Re­(bipy)­(CO) 3 }, followed by the action of excess MeOTf, the pyridine ring contraction concomitant with C–N bond scission was obtained ([ A ] in Scheme ). As we have demonstrated more recently, this type of pyridine ring-opening process is favored by more electron-rich cis -rhenium­(I) dicarbonyl complexes, obtained from fac -{Re­(CO) 3 } species by carbonyl substitution by a more σ-donor trimethylphosphane ligand.…”