Diphenylamine‐Substituted Osmanaphthalyne Complexes: Structural, Bonding, and Redox Properties of Unusual Donor–Bridge–Acceptor Systems

Abstract

Diarylamine‐substituted osmanaphthalyne complexes that feature two redox centers linked by the rigid skeleton of the metallacycle (C^C+), specifically, [OsCl2(PPh3)2{(C^C+)NAr2}][BF4−] (Ar=Ph (1 a), p‐MeOPh (1 b)) and their open‐ring precursors [OsHCl2(PPh3)2{(≡C−C(PPh3+)=CHPh)NR2}][BF4−] (Ar=Ph (2 a), p‐MeOPh (2 b)), were successfully synthesized and characterized by 1H, 13C, and 31P NMR spectroscopy, ESI‐MS, and elemental analysis. The solid‐state molecular structures of complexes 1 a and 2 a were ascertained by single‐crystal X‐ray diffraction. The Os≡C bond length in both complexes 1 a and 2 a fell within the range reported for similar osmanaphthalynes and osmium carbyne complexes, respectively. The structural parameters determined for complex 1 a, which were successfully reproduced by theoretical calculations, point to a π‐delocalized metallacycle structure. The purple color of compounds 1 a and b was explained by the diarylamine→Os(metallacycle) charge‐transfer absorption in the visible region. The neutral, one‐electron‐oxidized and one‐electron‐reduced states of compounds 1 a, b, and a reference complex that lacked the diarylamine substituent, [OsCl2(PPh3)2{(C^C+)}][BF4−] (1′), were investigated by cyclic and square‐wave voltammetry, UV/Vis/NIR spectroelectrochemistry, and DFT calculations. The spin density in singly oxidized complexes [1 a]+ and [1 b]+ predominantly resided on the aminyl segment, with osmium involvement controlled by the diphenylamine substitution. Spin density in stable, singly‐reduced [1′]− was distributed mainly over the osmanaphthalyne metallacycle.

Nucleophilic Reactions of Osmanaphthalynes with PMe3 and H2O

“…In its 1 H NMR spectrum, a signal at δ ≈1.10 ppm may be ascribed to the trimethylphosphine protons, and a signal at δ =13.34 ppm in the 31 P{ 1 H} NMR spectrum may be attributed to the triphenylphosphonium group (PPh 3 + ). A signal at δ ≈267 ppm in the 13 C{ 1 H} NMR spectrum is close to those previously reported for cyclic metal carbynes [19–21] . Based on the reaction system and the results of elemental analysis and high‐resolution mass spectrometry, we preliminarily concluded that complex [ 1 (OCH 3 )]′ is the product of substitution of one triphenylphosphine ligand of complex 1 (OCH 3 ) by a trimethylphosphine ligand.…”

“…The synthetic route to complex 1 (OCH 3 ) and its precursor 3 (OCH 3 ) is shown in Scheme 2 (Experimental Section). Complexes 1 (OCH 3 ) and 3(OCH 3 ) were both obtained as green solids, as reported in our previous publication [19] . The Os−H hydride ligand was confirmed by the signal of the chemical shift at −6.11 ppm in the 1 H NMR spectrum and the structure of the osmium carbyne was supported by the resonance at δ =250.4 ppm in the 13 C{ 1 H} NMR spectrum.…”

“…The parameters for [1(OCH 3 )]' are similar to those described above for 1(OCH 3 ) and others reported in the literature. [19][20][21] This result is consistent with our expectation that the introduction of trimethylphosphine offers less steric protection of the Os�C bond in 1(OCH 3 ), such that this complex should be more susceptible to attack by other nucleophiles. Water in the solvent attacks the Os�C bond as another nucleophilic reagent, thereby opening the osmanaphthalyne ring to afford the above-mentioned osmium complexes as the final products.…”

“…Complexes 1(OCH 3 ) and 3(OCH 3 ) were both obtained as green solids, as reported in our previous publication. [19] The OsÀ H hydride ligand was confirmed by the signal of the chemical shift at À 6.11 ppm in the 1 H NMR spectrum and the structure of the osmium carbyne was supported by the resonance at δ = 250.4 ppm in the 13 C{ 1 H} NMR spectrum. Similarly, NMR data for complex 1(OCH 3 ) were also consistent with those reported for osmanaphthalynes.…”

“…A signal at δ � 267 ppm in the 13 C{ 1 H} NMR spectrum is close to those previously reported for cyclic metal carbynes. [19][20][21] Based on the reaction system and the results of elemental analysis and high-resolution mass spectrometry, we preliminarily concluded that complex [1(OCH 3 )]' is the product of substitution of one triphenylphosphine ligand of complex 1(OCH 3 ) by a trimethylphosphine ligand. This speculation was supported by subsequent X-ray diffraction analysis.…”