Intermolecular C−C Coupling between 1‐Methyl‐1,2,3‐Triazole and 2,2′‐Bipyridine or 1,10‐Phenanthroline in Mo^II Complexes

Abstract

Unsupported 1-methyl-1,2,3-triazole has been coordinated to {Mo(η -methallyl)(CO) (N-N)} (N-N=2,2'-bipyridine, bipy; or 1,10-phenanthroline, phen) fragments, yielding cationic complexes that can be regarded as metalated triazolium salts. Their reactivity towards a strong base led to the deprotonation of the C5-H group of the triazole moiety, followed by an intermolecular nucleophilic attack to the ortho CH group of a bipy or phen ligand affording cyclic, bimetallic dearomatized C-C coupling products. The reaction of the neutral bipy derivative with an acid led to the formation of dihydropyridyl units by protonation of a CH group of the dearomatized rings, the dimeric nature of complexes being mantained upon protonation.

Strongly Electron-Donating Triazolylidene Ligands: Cationic Metal Carbonyl Complexes of 1-Methyl-1,2,3-triazole as Triazolium Surrogates

“…The reactions described above, in the presence of AgOTf, as well as those previously reported consisting of the deprotonation of cationic molybdenum­(II) triazole complexes, suggest a significant difference in the acidity of the C4–H and C5–H groups of the Metz ligand. A natural bond order (NBO) analysis of the non-hydrogen atoms of the Metz ligand of the cation of molybdenum­(II) in compound 1 reveals that the most favorable CH group for deprotonation is C5 because it displays a lower negative NBO charge than C4 (−0.046 vs −0.060), and also this position is less hindered than the C4 for attack by the base.…”

“…The high reactivity of the thus-formed species triggered an intermolecular nucleophilic attack on an o -CH group of a 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) ligand (coordinated to the transition-metal atom), affording cyclic, dearomatized C–C coupling products (Scheme S1). The reaction described above can be considered to be an in situ generation of a strong nucleophile that attacks an electrophile present in the reaction medium, which is a bipy or phen ligand. Taking into account that transition-metal-coordinated bipy or phen in the vast majority of the known complexes do not act as electrophiles and the intermolecular character of the reaction, we reasoned that the presence of a better electrophile counterpart in the reaction medium, such as a metal fragment, would lead to a completely different reactivity pattern.…”

“…We started our studies by reacting equimolar amounts of the compound [Mo­(η 3 -C 4 H 7 )­(bipy)­(CO) 2 (Metz)]­OTf ( 1 ), AgOTf, and the strong base KN­(SiMe 3 ) 2 in tetrahydrofuran (THF) at low temperature (−78 °C). IR ν CO monitoring of the reaction course clearly showed that the outcome was different (ν CO bands at 1952 and 1871 cm –1 ) from that resulting from the same reaction in the absence of AgOTf (ν CO bands at 1936 and 1846 cm –1 ), and compound [Ag­(MetzNHC Mo ) 2 ]­OTf ( 2 ) was obtained as a dark-red microcrystalline solid in good yield (Scheme ). NMR spectra of 2 in CD 2 Cl 2 at 213 K are fully consistent with the formation of a silver­(I) 1,2,3-triazolylidene complex because 1 H NMR shows the signal of only one triazole C H group (at 6.80 ppm) and, even more significantly, 13 C NMR shows the metal–carbene signal as a low-intensity doublet at 158.7 ppm ( J Ag–C = 156.2 Hz).…”

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

“…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.…”

Building C(sp3) Molecular Complexity on 2,2′‐Bipyridine and 1,10‐Phenanthroline in Rhenium Tricarbonyl Complexes

“…Outer‐sphere MeLi addition to coordinated bipy and phen ligands of fac ‐[Re(N‐N)(CO) 3 (PMe 3 )]OTf (N‐N=bipy, phen, Scheme 1 b) complexes [17b] suggests that chelate identity plays a role in the site‐selectivity of the addition. Unfortunately, the target of the few intermolecular additions to metal‐bonded bipy and phen reported were the most electrophilic α‐to‐N positions, [17b, 19] and nucleophilic additions to the β‐to‐N positions remain elusive. Whether or not the nature of the nucleophile can change the site‐selectivity of the addition to metal‐bonded bipy and phen remains unknown.…”