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Transition metal complexes of diazenes, XXV: Photochemical substitution reactions of group VIb dimetallaheterocycles
Author(s) -
Holzmeier Peter,
Görner Helmut,
Knoch Falk,
Kisch Horst
Publication year - 1989
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19891220813
Subject(s) - chemistry , denticity , metal carbonyl , ligand (biochemistry) , photochemistry , chromium , medicinal chemistry , transition metal , substitution reaction , hexamethylphosphoramide , metal , quantum yield , homoleptic , crystallography , crystal structure , organic chemistry , catalysis , biochemistry , physics , receptor , quantum mechanics , fluorescence
Irradiation of the dimetallacycles (CO) 4 M(μ‐PMD) 2 M(CO) 4 ( 1 ) (M = Cr, Mo, W; PMD = pentamethylenediazirine) in the presence of bidentate nitrogen ligands LL (2,2′‐bipyridine, 1,4‐di‐ tert ‐butyl‐1,4‐diazabutadiene, N , N , N ′, N ′‐tetramethylethylenediamine) leads to (LL)M(CO) 4 ( 2 ) by cleavage of the metal–diazirine bonds. The quantum yield for the disappearance of the starting compound is 0.056 and 0.0063 when the chromium complex is excited within its metal‐centered or CTML band at 368 and 445 nm, respectively. Much lower values, 0.0001 and 0.00009, are found upon CTML excitation of the molybdenum and tungsten complexes, respectively. Contrary to this reaction, irradiation of the chromium complex 1a in the presence of the bidentate phosphorus ligand dppe, 1,2‐bis(diphenylphosphino)ethane, leads to (CO) 3 Cr(μ‐PMD) 2 (μ‐dppe)Cr(CO) 2 ( 4a ) by substitution of carbon monoxide. X‐ray structural analysis reveals that the planar Cr 2 N 4 dimetallacycle present in 1 does not change its geometry upon introduction of the third bridging ligand. UV‐VIS reaction spectroscopy and laser flash photolysis indicate that in both reactions CO elimination is the primary photochemical step, followed by monodentate coordination. The successive chelation step occurs at the same chromium atom in the case of nitrogen ligands but at the other atom in the case of the phosphorus ligand. The CTML energy decreases when one and two CO ligands are substituted by triphenylphosphine and dppe, respectively.