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

Abstract

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.

Photolytic C-Diazeniumdiolate Disassembly in the β-Diketiminate Complexes [MeLM(O2N2CPh3)] (M = Fe, Co, Cu)

“…It also displays an O , O -κ 2 coordination of the diazeniumdiolate ligand, similar to other four-coordinate Cu diazeniumdiolates. ,, Complex 1 has Co–O1 and Co–O2 bond distances of 1.960(2) and 1.968(1) Å, respectively (Table ), which are understandably shorter than those found in the octahedral Co diazeniumdiolate [K(18-crown-6)][Co(O 2 N 2 CPh 3 ) 3 ], owing to the lower coordination number of 1 . Similarly, the Fe–O1 and Fe–O2 bond distances in complex 2 are shorter than those found in [K(18-crown-6)][Fe(O 2 N 2 CPh 3 ) 3 ] . Complex 3 features Cu–O1 and Cu–O2 bond distances of 1.972(9) and 1.94(1) Å, respectively.…”

“…Ph 3 CH and 9-phenylfluorene were formed in 50 and 43% yields (calculated on the basis of trityl equivalents; Table 2), respectively, while 4 was formed in 91% yield (calculated on the basis of Me L equivalents), according to integration against an internal standard (C 6 Me 6 ). 23,25 no other trityl-containing products were observed in the reaction mixture. Additionally, no other βdiketiminate-containing products were present in the reaction mixture.…”

“…It also displays an O,O-κ 2 coordination of the diazeniumdiolate ligand, similar to other fourcoordinate Cu diazeniumdiolates. 27,28,30 Complex 1 has Co− O1 and Co−O2 bond distances of 1.960(2) and 1.968(1) Å, respectively (Table 1), which are understandably shorter than those found in the octahedral Co diazeniumdiolate [K(18crown-6)][Co(O 2 N 2 CPh 3 ) 3 ], 23 owing to the lower coordination number of 1. Similarly, the Fe−O1 and Fe−O2 bond distances in complex 2 are shorter than those found in [K(18crown-6)][Fe(O 2 N 2 CPh 3 ) 3 ].…”

“…We recently reported the synthesis of a series of triphenylmethyl (trityl) diazeniumdiolate metal complexes, namely, [K­(18-crown-6)]­[M­(O 2 N 2 CPh 3 ) 3 ] (M = Fe, Co, Zn). , As was observed in other C -diazeniumdiolate systems, photolysis of these complexes led to the formation of several reaction products, including NO, N 2 O, Ph 3 CN­( H )­OCPh 3 , Ph 3 CH, and 9-phenylfluorene. Importantly, the observation of N 2 O and Ph 3 CN­( H )­OCPh 3 pointed to incomplete diazeniumdiolate fragmentation, which necessarily limits the yield of NO.…”

“…For example, photolysis or thermolysis of [NH 4 ]­[O 2 N 2 Ph] results in the formation of azoxybenzene in addition to the desired product, NO, whereas oxidation of [NH 4 ]­[O 2 N 2 Ph] results in the formation of NO and nitrosobenzene. , Similarly, hydrolysis of N -(4-methoxybenzyl)­guanidinium diazeniumdiolate at pH 3.1 releases NO, but also N 2 O, N -(4-methoxybenzyl)­urea, N ′-(4-methoxybenzyl)- N -hydroxyguanidine, N -(4-methoxybenzyl)­aminocyanamide, and N ′-(4-methoxybenzyl)- N -nitrosoimine. , Lastly, the diazeniumdiolate-containing siderophore gramibactin generates both NO and the corresponding oxime when photolyzed . The wide range of disassembly pathways and associated reaction products not only renders these reactions inefficient with respect to NO release, but the unknown reaction stoichiometries could make these complexes difficult to advance to the clinic. ,− Nonetheless, it is clear that NO release from C -diazeniumdiolates is possible, − although the yields of NO release are often low. , …”