Pentacarbonyl(1,4-diisopropyl-1,4-diazabutadiene)chromium: Isolation and Reactivity of the Monodentate Intermediate en Route to Cr(CO)4(iprop-DAB) Chelate Ring Closure

Thermal Ring-Closure Reactions of Pentacarbonylchromium Complexes with Bidentate N−N Ligands Revisited. Elimination of Side Reactions and Elucidation of the Intimate Chelation Mechanism

“…The dab complex was isolated in its nonbridged form. The spectral changes observed for the ring-closure reaction in n -hexane at 150 MPa are in good agreement with those reported before at ambient pressure (see Figure ) . The concentration dependence of the first-order kinetics, monitored at 586 nm, exhibits the same trend as reported above for the dmbpy system (see Figure S3 in the Supporting Information).…”

“…Chromium hexacarbonyl and 4,4‘-dimethyl-2,2‘-bipyridine (dmbpy) were purchased from Aldrich and used as received. The complexes were prepared from Cr(CO) 5 (η 2 -( Z )-cyclooctene) and dab or dmbpy according to the published procedures. − Important to note is the fact that we used considerably more solvent (pentane) in the preparation of the bridged complex than was mentioned in the literature due to the limited solubility of dmbpy. The products were characterized by IR and elemental analysis, and the results were in good agreement with those reported in the literature .…”

“…All manipulations involving the test solutions were carried out under an argon or nitrogen atmosphere in the dark using standard Schlenk techniques. Kinetic data for the chelation reaction at ambient pressure were obtained using a Varian Cary 1.3 or a HP8452A diode array spectrophotometer (ε(Cr(CO) 5 (μ-dmbpy)Cr(CO) 5 (410 nm)) = 5150 L mol -1 cm -1 ; ε(Cr(CO) 4 dmbpy (518 nm)) = 3100 L mol -1 cm -1 ; ε(Cr(CO) 5 dab (405 nm)) = 4450 L mol -1 cm -1 and ε(Cr(CO) 4 dab (586 nm)) = 8140 L mol -1 cm -1 ) . The kinetics at elevated pressure were followed on a modified Varian Cary 1.3 UV−vis spectrophotometer equipped with a thermostated high-pressure cell. , The deoxygenated solutions were introduced into the optical pill-box cell under an argon or nitrogen atmosphere by using a specially designed filling system …”

“…It is in this respect that recent reports in the literature, dealing with the isolation and chelation reactions of (CO) 5 Cr(μ-dmbpy)Cr(CO) 5 and (CO) 5 Cr(dab), where dmbpy = 4,4‘-dimethyl-2,2‘-bipyridine, attracted our attention. − These complexes undergo thermal chelation reactions to produce the chelated tetracarbonyl species via rate-determining extrusion of CO. The authors concluded that these species simulate the intermediates produced in the photoinduced reactions and exhibit properties different from those found before.…”

Preparation and structural characterization of tetracoordinated tungsten(II) diazadiene complexes

“…As a result, the reaction chemistry of this class of diimine ligand with a variety of transition metals has become well established [1,[3][4][5][6][7][8]. Lately, the interest in early transition metal chemistry has focused on group 6 complexes that contain chelating diazadiene ligands [9][10][11][12][13][14][15].…”