Facile synthesis of Fe(NO)2L2 compounds, where L=phosphines and phosphites

NO and N2O Release from the Trityl Diazeniumdiolate Complexes [M(O2N2CPh3)3]- (M = Fe, Co)

Reaction of MBr₂ with 3 equiv of [K(18-crown-6)][O₂N₂CPh₃] generates the trityl diazeniumdiolate complexes [K(18-crown-6)][M(O₂N₂CPh₃)₃] (M = Co, 2; Fe, 3) in good yields. Irradiation of 2 and 3 using 371 nm light led to NO formation in 10 and 1% yields (calculated assuming a maximum of 6 equiv of NO produced per complex), respectively. N₂O was also formed during the photolysis of 2, in 63% yield, whereas photolysis of 3 led to the formation of N₂O, as well as Ph₃CN(H)OCPh₃, in 37 and 5% yields, respectively. These products are indicative of diazeniumdiolate fragmentation via both C-N and N-N bond cleavage pathways. In contrast, oxidation of complexes 2 and 3 with 1.2 equiv of [Ag(MeCN)₄][PF₆] led to N₂O formation but no NO formation, suggesting that diazeniumdiolate fragmentation occurs exclusively via C-N bond cleavage under these conditions. While the photolytic yields of NO are modest, they represent a 10- to 100-fold increase compared to the previously reported Zn congener, suggesting that the presence of a redox-active metal center favors NO formation upon trityl diazeniumdiolate fragmentation.

Detection and Characterization of Hydride Ligands in Iron Complexes by High-Resolution Hard X-ray Spectroscopy and Implications for Catalytic Processes

Two hydride catalysts [Fe(CO)(dppp)H(NO)] (dppp = 1,3-bis(diphenylphosphino)propane) and [Fe(CO)H(NO)(PPh₃)₂] in comparison with nonhydride analogues [Fe(dppe)(NO)₂] (dppe = 1,3-bis(diphenylphosphino)ethane) and [Fe(NO)₂(PPh₃)₂] are investigated with a combination of valence-to-core X-ray emission spectroscopy (VtC-XES) and high-energy resolution fluorescence detected X-ray absorption near-edge structure (HERFD-XANES). To fully understand the experiments and to obtain precise information about molecular levels being involved in the spectral signals, time-dependent density functional theory (TD-DFT) calculations and ground state density functional theory (DFT) calculations are necessary. An excellent agreement between experiment and theory allows the identification of particular spectral signals of the Fe-H group. Antibonding Fe-H interactions clearly contribute to pre-edge signals in HERFD-XANES spectra, while bonding Fe-H interactions cause characteristic signatures in the VtC-XES spectra. The sensitivity of both methods with respect to the Fe-H distance is demonstrated by a scanning simulation approach. The results open the way to study metal hydride complexes in situ, their formation, and their fate during catalytic reactions, using high-resolution XANES and valence-to-core X-ray emission spectroscopy.

Syntheses of Iron(0) Complexes of Symmetrical Trialkylphosphines with Three Terminal Vinyl Groups, P((CH2)mCH=CH2)3

Reactions of (BDA)Fe(CO)3 (BDA = benzylideneacetone) and P((CH2)mCH=CH2)3 (1; m = 4, a; 5, b; 6, c; 7, d; 8, e) give the trigonal bipyramidal bis(phosphine) complexes trans-Fe(CO)3(P((CH2)mCH=CH2)3)2 (2a–e) as moderately air-sensitive yellow-orange oils in 60–75 % yields after workup. These and NO+BF4– react to give the cationic iron dicarbonyl nitrosyl complexes trans-[Fe(CO)2(NO)(P((CH2)mCH=CH2)3)2]+BF4– (3a–e; orange oils, 88–98 %). Further substitution is effected with n-Bu4N+X– (X = Cl, Br, I, or CN) to give trans-Fe(CO)(NO)(X)(P((CH2)mCH=CH2)3)2 (4a–e-X; red oils, 73–93 %). The NMR (1H, 13C, 31P) and IR properties of these adducts, which provide precursors to gyroscope-like complexes by intramolecular C=C metatheses, are analysed in detail.