[Ru(HNO)(′pybuS4′)], the First HNO Complex Resulting from Hydride Addition to a NO Complex (′pybuS4′2−=2,6-Bis(2-mercapto- 3,5-di-tert-butylphenylthio)dimethylpyridine(2−))

Abstract

Treatment of the nitrosyl complex [Ru(NO)('pybuS4')]Br (1a) with NaBH4 in CH3OH yielded [Ru(HNO)('pybuS4')](2), which could be completely characterized. The X-ray structure determination of 2 confirmed the N coordination of the HNO ligand. Density functional theory calculations enabled us to assign the nu(NO) IR band of 2, which appears in KBr at 1358cm(-1) and in THF at 1378 cm(-1). The unprecedented hydride addition to nitrosyl complexes yielding HNO complexes fills a white spot on the map of chemical reactions, represents the as yet unknown counterpart to the well-established formyl complex formation from CO complexes and hydrides, and distinctly differs from the formation reaction of [Os(HNO)(CO)Cl2(PPh3)2], the only other HNO complex characterized structurally. The HNO complex 2 is oxidized stepwise by [Cp2Fe]PF6 in the presence of NEt3 and directly by Bronsted acids to give [Ru(NO)('pybuS4')]+ in 2e- oxidations. H+/D+ exchange indicates acidity of the HNO proton.

Coordination chemistry of the HNO ligand with hemes and synthetic coordination complexes

“…The characteristic 1 H NMR signal of Mb-HNO in purified samples does not lose intensity from pH 6 to 10 [51]; and attempts to deprotonate [Ru(HNO)(Ôpy bu S 4 Õ)] with Brønsted bases were unsuccessful [142]. Both compounds do undergo D + /H + exchange, but the mechanism is not directly apparent.…”

“…Likewise, protonation at the terminal oxygen of a metal-bound HNO should lead to a formal reorganization of the bonding: weakening the N-O bond, as has been observed in mNO of [Ru(HNO)(Ôpy bu S 4 Õ)] [142], and a corresponding strengthening of the M-N bond. Such an effect may explain the anomalously high Fe-N bond stretch of Mb-HNO and the comparatively low XANES oxidation energy; strong hydrogen-bonding to the distal histidine might induce such an internal reorganization, and like the alkoxycarbenes, increase the anionic character of the metal.…”

“…For instance, two are generated from hydridic reactions, e.g., reaction of NaBH 4 with [Ru(NO)(Ôpy bu S 4 Õ)] + [142], or with the Fe III -NO of P450nor [92]. The hydridic character of the HNO ligand is apparent in the reaction of [Ru(HNO)(Ôpy bu S 4 Õ)] with Bronsted acids HX ðX ¼ H 2 PO À 3 ; Br À ; CF 3 SO À 3 Þ which results in a two-electron oxidation to [Ru(NO)-(Ôpy bu S 4 Õ)] + , presumably with H 2 evolution.…”

A nitrosyl hydride complex of a heme model [Ru(ttp)(HNO)(1-MeIm)] (ttp=tetratolylporphyrinato dianion)

“…Hillhouse and coworkers [23,31] have previously documented the p-acidity of the HNO ligand in coordination complexes, and we have shown that the related nitrosoarenes (ArNO) are p-acids in [M II (por)(ArNO)]-containing complexes (M ¼ Fe, Ru, Os) [19]. To date, there are four X-ray structural reports of metal-HNO complexes; three of these reveal Nbinding of the HNO ligand attached to the metal (for Os, Ir, Ru) [28,30,31], and one reveals a side-on g 2 binding of the HNO ligand in a Mo complex [33]. The t NO value of 1380 cm À1 in [Ru(ttp)(HNO)(1-MeIm)] suggests that the HNO ligand is N-bound to the Ru center, as this value is similar to the 1306-1332 cm À1 values observed in the related compounds [Ru(por)-(ArNO)(L)] (L ¼ pyridine, 1-MeIm) with N-bound nitrosoarene ligands [34,35].…”

“…There is only one other reported reaction of hydride attack at a metal-NO moiety to give a metal-HNO species [28]. 2 This is surprising, since nucleophilic attack at bound nitrosyls to give related metal-{N(Nu)@O} derivatives are well-known [37].…”