mer‐[Cr(CO)₃(η⁴‐norbornadien)(η²‐ethen)]: eine Schlüsselverbindung zum mechanistischen Verständnis der photokatalytischen Dien‐Hydrierung mit Carbonylchrom‐Komplexen

Abstract

Die katalytisch aktiven Spezies, die bei der photoinduzierten Hydrierung von Norbornadien (NBD) zu Nortricyclen und Norbornen führen, sind die Komplexfragmente fac‐bzw. mer‐[Cr(CO)3(η4‐nbd)]. Dies läßt sich daraus folgern, daß die Produktverteilung mit 1 als Katalysator derjenigen der bereits bekannten photoinduzierten Katalyse mit [Cr(CO)4(η4‐nbd)] als Startkomplex, auch in bezug auf Druckabhängigkeit und Markierung mit Deuterium, entspricht.

Dissociative CO Photosubstitution in M(CO)4(1,4-diazabutadiene) Complexes (M = W, Mo) by an Olefin Affording Novel fac-M(CO)3(1,4-diazabutadiene)(η2-olefin) Derivatives

“…Olefin ligands have not yet been examined in this respect, although a few M(CO) 3 (α-diimine)(η 2 -olefin) and M(CO) 2 (α-diimine)(η 2 -olefin) 2 complexes are known. − However, these compounds were prepared via nonphotochemical routes and no UV−vis spectral data were reported. This lack of information, along with our continued interest in the photochemical synthesis and structural aspects of olefin-substituted group 6 metal carbonyls, − led us to launch an exploratory investigation into the photolytic behavior of M(CO) 4 (α-diimine) complexes in the presence of an olefin. In this paper we report on the photoinduced reaction of M(CO) 4 (iprop-dab) (M = W, Mo; iprop-dab = 1,4-diisopropyl-1,4-diazabuta-1,3-diene) with ( E )-cyclooctene (eco) and on the structure and properties of the resulting M(CO) 3 (iprop-dab)(η 2 -eco) products.…”

Photocatalytic Hydrosilylation of Conjugated Dienes with Triethylsilane in the Presence of Cr(CO)6

“…The catalytic process as such does not require the action of light, once the active species containing the repeating Cr(CO) 3 unit has been generated. This is evident from experiments without irradiation in which Cr(CO) 3 (η 4 -norbornadiene)(η 2 -ethene), photogenerated from Cr(CO) 4 (η 4 -norbornadiene) in ethene-saturated solution at -50 °C, 25 serves as a source of the active catalyst. The ethene complex was previously employed to simulate the generation of the active catalyst in the photocatalytic hydrogenation 25 and hydrosilylation 26 of norbornadiene, whereby the weakly bound ethene plays the role of a stand-in ligand which is readily lost at ambient temperature.…”

“…This is evident from experiments without irradiation in which Cr(CO) 3 (η 4 -norbornadiene)(η 2 -ethene), photogenerated from Cr(CO) 4 (η 4 -norbornadiene) in ethene-saturated solution at -50 °C, 25 serves as a source of the active catalyst. The ethene complex was previously employed to simulate the generation of the active catalyst in the photocatalytic hydrogenation 25 and hydrosilylation 26 of norbornadiene, whereby the weakly bound ethene plays the role of a stand-in ligand which is readily lost at ambient temperature. This way, hundreds of hydrosilylation turnovers have been achieved in the dark by warming this complex to ambient temperature in the presence of a sufficiently large excess of norbornadiene and triethylsilane.…”

“…Method e. A cold solution (−30 °C) of 1,3-cyclohexadiene ( 6 ) (3.7 mL, 40 mmol), triethylsilane (6.4 mL, 40 mmol), Cr(CO) 3 (η 4 -norbornadiene)(η 2 -ethene) (ca. 1.8 mmol, in situ generated), and n -octane (2.0223 g, internal standard for GC) in n -hexane (200 mL) was warmed to room temperature and stirred for 100 min, at which time the triethylsilane was no longer detectable in the IR spectrum. GC and GC−MS analyses of the samples drawn during the catalytic run showed the gradual consumption of the starting material with concomitant formation of (triethylsilyl)norbornene (identified by GC−MS, M + = m / e 208; 97 mg, 0.47 mmol), 16a (72% ultimate yield) and 16b (12% ultimate yield).…”

“…The dienes (except 1,3-butadiene) 30 were commercially available (Fluka) and distilled before used. Tetracarbonyl(η 4 -1,3-butadiene)chromium(0) 13 and tricarbonyl(η 4 -norbornadiene)(η 2 -ethene)chromium(0) 25 were prepared according to the literature procedures.…”