A New Route to Coordination Complexes of Nitroxyl (HNO) via Insertion Reactions of Nitrosonium Triflate with Transition-Metal Hydrides

Abstract

Nitrosonium triflate reacts with cold methylene chloride solutions of mer,trans-ReH(CO)3(PPh3)2 (1) with 1,1-insertion of NO+ into the Re-H bond to give the orange nitroxyl complex [mer,trans-Re(NH=O)(CO)3(PPh3)2][SO3CF3] (3) in 86% isolated yield. Use of [NO][PF6] or [NO][BF4] gives analogous insertion products at low temperature, which decompose on warning to ambient temperature to the fluoride complex mer,trans-ReF(CO)3(PPh3)2 (4). A related 1,1-insertion is observed in the reaction of 1 with [PhN2][PF6] in acetone that affords the yellow-orange phenyldiazene salt [mer,trans-Re(NH=NPh)(CO)3(PPh3)2][PF6] (2), which has been characterized by X-ray crystallographic methods. The methyl derivative mer,trans-Re(CH3)(CO)3(PPh3)2 (5) also undergoes a 1,1-insertion reaction with [NO][SO3CF3] to give the nitrosomethane adduct [mer,trans-Re{N(CH3)=O}(CO)3(PPh3)2][SO3CF3] (6) as red crystals in 75% yield. The nitroxyl complex [cis,trans-OsBr(NH=O)(CO)2(PPh3)2][SO3CF3] (8) can be similarly prepared as orange crystals in 52% yield by reaction of cis,trans-OsHBr(CO)2(PPh3)2 (7) with [NO][SO3CF3] in cold methylene chloride solution.

The Reaction of White Phosphorus with NO+/NO2+[Al(ORF)4]−: The [P4NO]+ Cluster Formed by an Unexpected Nitrosonium Insertion

“…The insertion of NO + into a main-group E À E bond to give the E À N(O) À E fragment is unprecedented. [16] The nature of [P 4 NO] + was established by solution and solid-state NMR, IR, and Raman spectroscopy and mass spectrometry and is consistent with quantum-chemical calculations, as is also the weight balance of the reaction.Preliminary experiments were conducted at 203 K, but due to the poor solubility of white phosphorus, the reaction mixture was warmed to 298 K. The initially colorless mixture turns dark red until one of the starting materials is consumed; thereafter the color turns pale yellow. If the entire reaction is carried out at room temperature, the red color disappears within 10 s. The 31 P NMR spectrum of the yellow product in CD 2 Cl 2 (Figure 1 a) shows two triplets at À232 and + 360 ppm (integration 1:1) with a 1 J PP coupling constant of À160 Hz that is reminiscent of P 5 X 2 + .…”

“…The insertion of NO + into a main-group E À E bond to give the E À N(O) À E fragment is unprecedented. [16] The nature of [P 4 NO] + was established by solution and solid-state NMR, IR, and Raman spectroscopy and mass spectrometry and is consistent with quantum-chemical calculations, as is also the weight balance of the reaction.…”

Reactivity of iron(II)-bound nitrosyl hydride (HNO, nitroxyl) in aqueous solution

“…Well characterized complexes with HNO and NO -as ligands have been prepared in the last decade, noticeably with d 6 low-spin metals such as Ru II [25][26][27][28], Os II [27,[29][30][31], Re I [31][32][33], Ir III [29] (for HNO), and with Co III [34][35][36][37][38], Cr III [39][40][41], Pt IV [42], Ru II [27], and Fe II [43][44][45][46][47] (for NO -), generally by using chelating macrocyclic coligands (viz., with porphyrins, aza-macrocycles, and thioether binding species) [24]. In general, a main drawback relates to the low solubility in water and the very limited presence of iron complexes.…”

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

“…2 This is surprising, since nucleophilic attack at bound nitrosyls to give related metal-{N(Nu)@O} derivatives are well-known [37]. Other methods to generate metal-HNO complexes involve (i) formal protonation of bound NO [22,23,[29][30][31][38][39][40], (ii) proton abstraction from coordinated H 2 NO [33], (iii) oxidation of bound hydroxylamine [27], (iv) formal coupling of a H-atom with the NO ligand in a metal nitrosyl radical complex [24], and (v) NO þ insertion into metal-hydride bonds [26]. In addition, the [Ru(ttp)(H-NO)(1-MeIm)] complex is air-and thermally sensitive.…”