Aufbau von Heterocyclen durch [4 + 2]-Cycloaddition vonÜbergangsmetall-koordinierten Heteroolefinen mit Butadienen: zur Regioselektivität der Cycloaddition

(Pentamethylcyclopentadienyl)selenium Derivatives. 5.1 Bis(pentamethylcyclopentadienyl)selenium and Its Reactions with Transition-Metal Carbonyls

“…The bond lengths in the M(CO) 5 fragments are normal and show typical shortening of the M-C bond trans to the non-carbonyl ligand. There appear to be no comparable data available for chromium selenide complexes, but the W-Se distance (2.671 Å) is similar to that in [W(CO) 5 -(SeCPh 2 CH 2 CMedCMeCH 2 )] (2.674 Å) 28 and only slightly shorter than that in [W(CO) 5 {Se(SnMe 3 ) 2 }] (2.736 Å). 29 Each selenium atom is bonded to a single carbon of one C 5 Me 5 ring, the Se-C distances (average 2.036, 2.028 Å) being the longest thus far reported, much larger than the sum of the covalent radii (1.930 Å).…”

“…The bond lengths in the M(CO) 5 fragments are normal and show typical shortening of the M−C bond trans to the non-carbonyl ligand. There appear to be no comparable data available for chromium selenide complexes, but the W−Se distance (2.671 Å) is similar to that in [W(CO) 5 (SeCPh 2 CH 2 CMeCMeCH 2 )] (2.674 Å) and only slightly shorter than that in [W(CO) 5 {Se(SnMe 3 ) 2 }] (2.736 Å) .…”

Metal-Assisted Cycloaddition Reactions in Organotransition Metal Chemistry

“…532,534,[536][537][538][539][540][541] An example is given in eq 87. When unsymmetrically substituted dienes are used, 542 both isomeric cycloadducts are obtained with regioselectivities ranging from 2.4:1 to 19:1. The kinetics have also been studied.…”

“…They have been used as convenient sources of CS, CSe, and CTe bonds to synthesize heterocyclics via [4+2] cycloaddition reactions with a variety of open chain and cyclic dienes. ,,− An example is given in eq 87. When unsymmetrically substituted dienes are used, both isomeric cycloadducts are obtained with regioselectivities ranging from 2.4:1 to 19:1. The kinetics have also been studied .…”

Pentamethylcyclopentadienylselenium derivatives: synthesis and X-ray crystal structures of [M(CO)5{Se2(σ-C5Me5)2}](M = Cr, W)

“…2.671(1), W-C( 1) 2.022 (10), W-C(2) 1.968 (11), W-C(3) 2.032 (12), tive, is not unprecedented. The reduction of a selenide to a diselenide, within the coordination sphere of a transition metal, is however completely new.…”