Cycloaddition of Coordinated Diazoalkanes to Ethene To Yield 3H-Pyrazole Derivatives

Abstract

Diazoalkane complexes [Ru(η 5 -C 5 H 5 )-(N 2 CAr1Ar2)(PPh 3 )L]BPh 4 (1, 2; Ar1 = Ph, Ar2 = p-tolyl; Ar1Ar2 = C 12 H 8 ; L = P(OMe) 3 , P(OEt) 3 ) were prepared by allowing compounds RuCl(η 5 -C 5 H 5 )(PPh 3 )L to react with diazoalkane in ethanol. Treatment of complexes 1 and 2 with ethylene under mild conditions (1 atm, room temperature) led not only to the ethylene complexes [Ru(η 5 -C 5 H 5 )(η 2 -CH 2  CH 2 )(PPh 3 )L]BPh 4 (5, 6) but also to dipolar (3 + 2) cycloaddition, affording the 3H-pyrazole derivatives [Ru(η 5 -C 5 H 5 ){η 1 -NNC(Ar1Ar2)CH 2 CH 2 }(PPh 3 )L]BPh 4 (3, 4).The propylene complexes [Ru(η 5 -C 5 H 5 )(η 2 -CH 3 CHCH 2 )(PPh 3 )L]BPh 4 (7, 8) were also prepared. The compounds were characterized by spectroscopy and by X-ray crystal structure determinations of 2a, 3b, and 7.

Preparation of Diazoalkane Complexes of Ruthenium and Their Cyclization Reactions with Alkenes and Alkynes

“…Both bis­(triphenylphosphine) [Ru­(η 5 -C 5 H 5 )­(PPh 3 ) 2 ] + and mixed-ligand [Ru­(η 5 -C 5 H 5 )­(PPh 3 )­(L)] + fragments (L = phosphites, tert- butyl isocyanide) are able to stabilize diazoalkane complexes 1 – 5 , which were isolated as solids stable in air and in solution of polar organic solvents, where they behave as 1:1 electrolytes . Analytical and spectroscopic data (IR and NMR) confirm the proposed formulation, which was further supported by an X-ray crystal structure determination of [Ru­(η 5 -C 5 H 5 )­{N 2 C­(Ph)­( p- tolyl)}­(PPh 3 )­{P­(OEt) 3 }]­BPh 4 ( 3b ).…”

“…Good analytical data were obtained for both 4,5-dihydro-3Hpyrazole (6−9) and η 2 -alkene derivatives (10−14), which were all isolated as yellow or orange solids, stable in air and in solution of polar organic solvents, where they behave as 1:1 electrolytes. 23 Infrared and NMR spectra support the proposed formulations, which were further confirmed by an X-ray crystal structure At room temperature, the proton spectra of ethylene complexes [Ru(η 5 -C 5 H 5 )(η 2 -CH 2 CH 2 )(PPh 3 )(L)]BPh 4 (11−13) show two multiplets at 3.07−2.99 and 2.65−2.71 ppm, but only one triplet at 2.97 ppm appears for [Ru(η 5 -C 5 H 5 )(η 2 -CH 2  CH 2 )(PPh 3 ) 2 ]BPh 4 (10); they were attributed to the protons of the coordinated ethylene. Lowering the sample temperature caused some variations in the spectra, but ethylene peaks were still broadened even at −90 °C, suggesting that rotation of CH 2 CH 2 still occurred at this temperature.…”

“…Instead, relatively few data have been reported on the reactivity of coordinate diazoalkane, 1,6−9 including the formation of dinitrogen complexes [M]−N 2 , 8f N−N bond cleavage, 8k and reduction of the coordinated N 2 CAr1Ar2 ligand. 8i However, no example of cyclization of coordinated diazoalkane had ever been reported until we found 10 that the half-sandwich complexes [Ru(η 5 -C 5 H 5 )-(N 2 CAr1Ar2)(PPh 3 ){P(OR) 3 }]BPh 4 can undergo unprecedented (3 + 2) cycloaddition of a metal-bonded diazoalkane to ethylene, yielding 4,5-dihydro-3H-pyrazole derivatives. These interesting preliminary results prompted us to extend our research and study to activated alkenes and alkynes, as well as to the influence of ancillary ligands on the cyclization reaction.…”

“…Found: C,76.36;H,6.19;N,4.02. (10). In a 25 mL threenecked round-bottomed flask were placed a solid sample of the chloro complex RuCl(η 5 -C 5 H 5 )(PPh 3 ) 2 (0.109 g, 0.15 mmol), an excess of NaBPh 4 (0.3 mmol, 0.103 g), and 4 mL of ethanol.…”

Preparation of Azine Complexes of Ruthenium(II)

“…Coordination of the Cp ligand (ring slippage 0.052 Å) deals Ru‐C bond lengths and a distance from the ruthenium atom to the centroid in the usual range (see Table ) for this kind of piano‐stool structures. Also the Ru‐P bond lengths, either for the phosphine (P1), either for the phosphite (P2), are in the usual range (see Table ); they do not justify more comments …”