A Proton-Induced N-1 to η²Migration of the Fluxional Pyrazine in the [Ru^II(hedta)(pz)]^-Complex

Abstract

[Ru(II)(hedta)(D(2)O)](-), hedta(3)(-) = N-(hydroxyethyl)ethylenediaminetriacetate, reacts with pyrazine in D(2)O at 25 degrees C to yield several isomers and </=20% of the pyrazine-bridged binuclear complex. Two isomers of 56.2% combined abundance have differentiated alpha (near) and beta (remote) (1)H NMR pyrazine resonances at 9.09 ppm (alpha or H2, H6 pair) and 8.33 ppm (beta or H3, H5 pair). The other isomer of ca. 24% abundance exhibits only a singlet at 8.76 ppm, indicative of fluxional pyrazine movement from N-1 to N-4. This is believed to be the cis-polar isomer. Within 24 h the differentiated isomers convert to the fluxional isomer, which remains fluxional in 50% D(2)O/50% CD(3)OD down to 237 K. The fluxional isomer has all equivalent (13)C NMR resonances at 152.44 ppm, 5.18 ppm downfield of free pyrazine. Comparison with the bridged binuclear ion {[Ru(hedta)](2)(pz)}(2)(-) revealed fortuitously similar shifts; the (1)H NMR spectrum shows a singlet at 8.76 ppm, and the (13)C NMR spectrum, a singlet at 152.40 ppm. These species have different electrochemical signatures, however, with the 1:1 fluxional complex having a Ru(II/III) wave at 0.20 V that shifts to 0.35 V upon protonation of the N-4 position, whereas the binuclear complex has two waves at 0.18 and 0.33 V which are independent of pH. (1)H NMR indicates stereochemically rigid coordination of 2-methylpyrazine (2-CH(3)pz) at N-4 with the 2-CH(3) position remote in the major species (65.5%) and at N-2 with the 2-CH(3) site adjacent (34.4%) in the lesser isomer. The proton resonances are as follows. Remote isomer (N-4): H2, 8.22 ppm; H3, 8.97 ppm; H5, 8.88 ppm; CH(3), 2.53 ppm. Adjacent (N-1) isomer: H2, 8.73 ppm; H3, 8.42 ppm, H5, 8.50 ppm; CH(3), 2.45 ppm. A slow conversion of the strained adjacent isomer to the remote isomer is observed. Remote and adjacent isomers were also prepared for [(NH(3))(5)Ru(2-CH(3)pz)](2+) in 87.7% and 12.3% yield. Protonation of [Ru(hedta)(pz)](-) yields nonfluxional complexes: a major species (63%) bound eta(2)(1,2) with four complicated resonance patterns at 8.72, 8.57, 8.00, and 7.91 ppm, each signal having across-the-ring couplings which require couplings to at least two different ring protons and a minor N-1-coordinated N-4 protonated species (16%) with alpha and beta proton pairs resonating at 8.81 and 8.25 ppm. An eta(2)(2,3) isomer is also detectable (20%) which has four types of (1)H resonances at 9.51, 9.01, 8.85, and 8.15 ppm. The weakened sigma bonding from pzH(+) and enhanced pi-acceptor capacity power of pzH(+) combine to induce a switch in coordination to either eta(2)(1,2) or eta(2)(2,3).

A New Generation of π-Basic Dearomatization Agents

“…The pentaammineosmium(II) metal fragment is not unique in its ability to bind aromatic molecules in a η 2 fashion, with d 10 Cu(I), − Ag(I), Pt(0), , and Ni(0), − d 2 Ta(III) − and Nb(III), d 8 Rh(I) − and Ru(0), and d 6 Ru(II) , and Re(I) − complexes having been reported . What distinguishes the pentaammineosmium(II) fragment is its ability to form thermally stable complexes of a wide range of aromatic molecules and to subsequently activate these molecules toward reactions with electrophiles.…”

Reactions of [Ru(CO)3Cl2]2 with aromatic nitrogen donor ligands in alcoholic media

“…Thermal ellipsoids are drawn with 50% probability. Selected bond lengths (Å) and angles (deg): Ru(1)-Cl(1), 2.389(2); Ru(1)-C(1), 1.932(9); Ru(1)-C(3),1.927(11); Ru(1)-C(2), 1.916(9); Ru(1)-N(1), 2.111 (7); Ru(1)-N(2), 2.093 (7); C(1)-O(1), 1.124(10); C(2)-O(2), 1.126(10); C(3)-O(3), 1.131 (11); Ru(2)-Cl(5), 2.406(2); Ru(2)-Cl(6), 2.406(2); Ru(2)-Cl(7), 2.429(2); Ru(2)-C(7), 1.885(11); Ru(2)-C(5), 1.885(10); Ru(2)-C(6), 1.910(9); C(5)-O(5), 1.131 (11); C(6)-O(6), 1.117 (11); C(7)-O(7), 1.147(11); C(2)-Ru(1)-C(1), 88.6(3); C(3)-Ru(1)-Cl(1), 177.8 (3); N(2)-Ru(1)-N(1), 78.3(3); C(7)-Ru(2)-Cl (7), 177.8(3); Cl(6)-Ru(2)-Cl(5), 90.68 (8); C(5)-Ru(2)-C(6) 94.3 (4).…”

“…883.15 (11) 871.04 (8) 3749.5 (11) 888.53 (19) 980.12 (5) 3472.94 (12) 936.53(7) 7.9376 (7) 11.5515 (5) 7.8430(4) 9.9701 (1) 9.0489 (3) 5.8397 (1) 10.5068 (4) 11.8381 (8) 10.1009 (7) 8.8475 (6) 19.4565 (3) 8.8532 (3) 17.9940 (7) 12.6438 (5) 17.4631 (14) 21.7720 (14) 13.0089 (7) 12.5721 (2) 13.9097 (2) 9.7215 (4) 65.935 (2…”

Coordination of Two High-Affinity Hexamer Peptides to Copper(II) and Palladium(II) Models of the Peptide−Metal Chelation Site on IMAC Resins

“…The 300 MHz NMR spectra were obtained on Bruker 300AF spectrometers for samples in D 2 O referenced to DSS (0.00 ppm) at 25 °C by following prior procedures for other Pt II , Pd II , and Ru II aminocarboxylate complexes. − …”