Pentamethylcyclopentadienyl Half-Sandwich Diazoalkane Complexes of Ruthenium: Preparation and Reactivity

Abstract

The diazoalkane complexes [Ru(η(5)-C5Me5)(N2CAr1Ar2){P(OR)3}L]BPh4 (1-4) [R = Me, L = P(OMe)3 (1); R = Et, L = P(OEt)3 (2); R = Me, L = PPh3 (3); R = Et, L = PPh3 (4); Ar1 = Ar2 = Ph (a); Ar1 = Ph, Ar2 = p-tolyl (b); Ar1Ar2 = C12H8 (c); Ar1 = Ph, Ar2 = PhC(O) (d)] and [Ru(η(5)-C5Me5){N2C(C12H8)}{PPh(OEt)2}(PPh3)]BPh4 (5c) were prepared by allowing chloro-compounds RuCl(η(5)-C5Me5)[P(OR)3]L to react with the diazoalkane Ar1Ar2CN2 in the presence of NaBPh4. Treatment of complexes 1-4 with H2O afforded 1,2-diazene derivatives [Ru(η(5)-C5Me5)(η(2)-NH═NH){P(OR)3}L]BPh4 (6-9) and ketone Ar1Ar2CO. A reaction path involving nucleophilic attack by H2O on the coordinated diazoalkane is proposed and supported by density functional theory calculations. The complexes were characterized spectroscopically (IR and (1)H, (31)P, (13)C, (15)N NMR) and by X-ray crystal structure determination of [Ru(η(5)-C5Me5)(N2CC12H8){P(OEt)3}2]BPh4 (2c) and [Ru(η(5)-C5Me5)(η(2)-NH═NH){P(OEt)3}2]BPh4 (7).

Selective Reduction of Nitroarenes to Arylamines by the Cooperative Action of Methylhydrazine and a Tris(N-heterocyclic thioamidate) Cobalt(III) Complex

“…The existence of such kind of intermediate species might be responsible for the redox response of C1 with 5 equiv of MeNHNH 2 , which shows a slightly different profile compared to the other two voltammograms, and the Co­(III)/Co­(II) redox potential is positively shifted with respect to C1 (blue line, Figure ). An analogous metal-diezene species has been previously reported in the literature for other transition metal complexes . Besides, the formation of CH 2 NNH 2 has also been detected by 1 H NMR spectroscopy measurements, when 0.02 mmol of methylhydrazine was added into a 0.5 mL CD 3 OD solution containing 0.02 mmol of C1 ; the mixture was stirred for 1 h and then monitored directly by 1 H NMR (Figure S4), therefore, providing another piece of evidence for the proposed pathway …”

“…An analogous metaldiezene species has been previously reported in the literature for other transition metal complexes. 24 Besides, the formation of CH 2 NNH 2 has also been detected by 1 H NMR spectroscopy measurements, when 0.02 mmol of methylhydrazine was added into a 0.5 mL CD 3 OD solution containing 0.02 mmol of C1; the mixture was stirred for 1 h and then monitored directly by 1 H NMR (Figure S4), therefore, providing another piece of evidence for the proposed pathway. 25 Overall, these findings suggest that the formation of a methylhydrazine-coordinated cobalt intermediate species is a crucial step for the catalytic reaction, as it imposes a coordination-induced activation pathway 26 that provides a subsequent electron transfer (ET) between C1 and methylhydrazine, leading to a Co(II) species ([Co]), which takes an active role in the catalytic reaction.…”

Ruthenium Complexes for Catalytic Dehydrogenation of Hydrazine and Transfer Hydrogenation Reactions

“…Whilst we were unable to observe the Ru−H and Ru−diazene intermediates during our investigations, presumably because of the lower stability of these species in the reaction medium, such species are expected to be involved in the dehydrogenation of hydrazine. Notably, X‐ray structure of analogous ruthenium‐diazene species [( η 5 ‐Cp*)Ru( κ 2 ‐HN=NH){P(OEt) 3 } 2 ] + was previously reported by Albertin et al . Also, Hillhouse et al.…”