Structures and Spectral Properties of Iron(II), Cobalt(II), and Copper(II) Complexes Involving 2-(Dimethylamino)-4(3H)-pteridinone

Abstract

With a view to understanding the pterin cofactor-metal ion interactions, some divalent transition metal complexes containing 2-(dimethylamino)-4(3H)-pteridinone (NDMP), M(NDMP) 2 (CH 3 OH) 2 (M ) Fe(II) (1), Co(II) (2), Cu(II) (3)) and Fe(NDMP) 2 Cl 2 (4), have been prepared and investigated by magnetic, spectroscopic, and X-ray diffraction methods. Complexes 1, 2, and 4 were found to be in a typical high-spin state, and complex 3 was found to be in a d x 2 -y 2 ground state. Complexes 1-3 were structurally determined. [Fe(NDMP) 2 (CH 3 OH) 2 ]‚2CH 3 -OH (1) crystallizes in the triclinic system, space group P1 h, with a ) 8.54 (1) (2) is isomorphous with 1 with a ) 8.4753 (6) Å, b ) 9.430(1) Å, c ) 8.3695(5) Å, R ) 95.885(7)°, ) 98.412(6)°, γ ) 79.421(8)°, V ) 648.48 Å 3 , and Z ) 2. [Cu(NDMP) 2 (CH 3 OH) 2 ] (3) crystallizes in the monoclinic system, space group P2 1 /a, with a ) 8.428(1) Å, b ) 14.3857(8) Å, c ) 8.9570(8) Å, ) 95.225(8)°, V ) 1081.5 Å 3 , and Z ) 4. The final R and R w values are 0.042 and 0.033 for 1, 0.056 and 0.040 for 2, and 0.040 and 0.018 for 3, respectively. The geometries around the metal ions are essentially the same, and each metal ion is octahedrally coordinated with 4-carbonyl oxygens and 5-nitrogens of NDMP molecules in the equatorial positions and two methanol molecules in the axial positions. The Fe(II) complexes 1 and 4 exhibited an absorption band centered at 568 nm ( ) 1900 M -1 cm -1 ) in DMF and a peak at 674 nm in the reflectance spectrum, respectively, both of which are assigned to a charge transfer. This and other spectroscopic and structural properties have been comparatively discussed.

Metal complexes with non-innocent ligands

“…A considerable metal 3 ligand charge transfer and stabilisation of ruthenium, copper and rhenium complexes with the reduced ligand were established by cyclic voltammetry and UV-Vis spectroscopy in the visible region. 157 Iridium, 158 copper, 159 ± 162 iron(II), 160 cobalt(II) 160 and zinc 161 complexes with pterin and pteridine were studied by spectroscopic and electrochemical methods and characterised by X-ray diffraction.…”

A Ruthenium Pterin Complex Showing Proton‐Coupled Electron Transfer: Synthesis and Characterization

“…Along this line, many pterin‐metal complexes have been reported to model Mo‐co,9 tungstopterins,10, 11 and copper‐containing pterin‐dependent enzymes 12. The coordination chemistry of ruthenium pterin complexes has also been investigated 13–15. However, the PCET process of metal pterin complexes has yet to be clarified.…”

“…In addition, the imidate nitrogen atoms forms hydrogen bonds with a water molecule of crystallization (N8⋅⋅⋅O8, 2.927(9) Å; not shown). The imidate coordination has been observed in [M(NDMP − ) 2 (MeOH) 2 ] (M=Fe, Co, Ni; HNDMP=2‐dimethylamino‐4(3 H )‐pteridinone)13 and [Cu(tppb)(pterin)] (tbbp=tris(3‐phenylpyrazolyl)hydroborate) 19. In contrast, Yamauchi and co‐workers have reported that Hdmdmp coordinates to a Cu II center in [Cu(NO 3 ) 2 (Hdmdmp) 2 ]20 as a neutral ligand and Burgmayer et al have also demonstrated that the amide is not deprotonated upon coordination in their Mo VI pterin complexes 9.…”

A Ruthenium Pterin Complex Showing Proton‐Coupled Electron Transfer: Synthesis and Characterization

“…[12] The coordination chemistry of ruthenium pterin complexes has also been investigated. [13][14][15] However, the PCET process of metal pterin complexes has yet to be clarified. The lack of the crystal structures together with low stability in redox processes of metal complexes with pterin ligands has precluded elucidation of the PCET mechanism of metal pterin complexes.…”

“…In addition, the imidate nitrogen atoms forms hydrogen bonds with a water molecule of crystallization (N8···O8, 2.927(9) ; not shown). The imidate coordination has been observed in [M(NDMP À ) 2 (MeOH) 2 ] (M = Fe, Co, Ni; HNDMP = 2-dimethylamino-4(3H)-pteridinone) [13] and [Cu(tppb)(pterin)] (tbbp = tris(3-phenylpyrazolyl)hydroborate). [19] This difference probably stems from the interactions of pterins with metal d orbitals and the Lewis acidity of the Ru-TPA unit, in which three pyridine moieties act as p acceptors to increase the acidity on the metal center which facilitates the deprotonation of Hdmdmp, and which results in the imidate binding.…”