Structure cristalline et conformation moléculaire du (1-3,3a,8a-η)-(dimethyl-5,7 4H-cyclohepta[c]thiophene)chrome tricarbonyle

Abstract

The crystal structure of (1-3,3a,8a-r/)(5,7-dimethyl-4H-cyclohepta[c]thiophene)tricarbonylchromium has been determined by X-ray diffraction. The complex crystallizes in the monoclinic system, space group P21/c. Unit-cell dimensions are a = 6.75, b = 10"93, c= 19"33/~, ,8= 100 ° Y, Z= 4. The tricarbonyl chromium group is fixed on the thiophene ring. The conformation of the latter is different from that in the free ligand and the tropilidene ring has a 'boat' conformation. R= 0"059 for 552 reflexions.

Structure and properties of tricarbonyl(2-5:9,10-.eta.-9-methylenebicyclo[4.2.1]nona-2,4,7-triene)chromium(0). New chromium-olefin stereochemistry

“…6 (2)°a re observed at C(sp3) centers. While the butadiene moiety is almost planar (see Table VII for least-squares planes), atoms C (19) and C( 14) are substantially out of this plane (see also Figure 3). As a result of this twist, the hydrogen atoms H(ll), H(12), H(13), and H( 14) are significantly displaced from the butadiene plane toward the chromium atom, whereas for the methylene group the hydrogen atoms show the more usual small displacement away from the metal.…”

“…Almost all olefin complexes of the M(CO)3 species have involved conjugated trienes3-10 or pseudotriene systems. [11][12][13][14][15][18][19][20][21][22][23][24] The single exception appears to be the butadiene-olefin complex (5,6-dimethylenebicyclo[2.2.1]hept-2-ene)Mo(CO)3.17 In no instance has coordination of an olefin perpendicular to other coordinated olefins been structurally characterized for the M(CO)3 systems; furthermore, we know of only several structures where this geometry is found-an RuCl(triolefin)25 and a PtCl2(diolefin)26 species.…”