Dialkynylated and functionalized alkynylated areneCr(CO)3-complexes—syntheses and structures of carbon rich chromium-complexed benzenes

Racemic tricarbonyl[7-methoxy-2-(η6-phenyl)chromane]chromium(0)

In the title compound, [Cr(C₁₆H₁₆O₂)(CO)₃], the Cr⁰ atom of the Cr(CO)₃ unit is coordinated to the phenyl ring of the flavan ligand in an η⁶ mode, with a normal arene-to-metal distance. The Cr(CO)₃ unit exhibits a three-legged piano-stool conformation, while the dihydro­pyran ring displays a distorted envelope configuration. The phenyl ring is twisted away from the fused ring system by 25.5 (2)°. The meth­oxy group is almost coplanar with the phenyl ring [C_Me—O—C_ar—C_ar torsion angle = 8.46 (2)°]. The crystal packing is stabilized by inter­molecular C—H⋯O inter­actions.

Racemic tricarbonyl[(4a,5,6,7,8,8a-η)-2-phenyl-3,4-dihydro-2H-1-benzopyran]chromium(0)

The title compound, [Cr(C₁₅H₁₄O)(CO)₃], displays a distorted envelope configuration of the dihydro­pyrane ring. The dihedral angle between the phenyl and phenyl­ene rings is 50.63 (4)°. The Cr⁰ atom is coordinated by three CO groups and the phenyl­ene ring of the flavan ligand in an η⁶ mode, with a common arene-to-metal distance

Racemic tricarbonyl(η6-7-methoxyflavan)chromium(0)

In the title compound [systematic name: tricarbonyl(η⁶-7-methoxy-2-phenyl-3,4-dihydro-2H-1-benzopyran)chromium(0)], [Cr(C₁₆H₁₆O₂)(CO)₃], the Cr(CO)₃ unit is coordinated by the phenyl­ene ring of the flavan ligand, exhibiting a three-legged piano-stool conformation, with a point to plane distance of 1.750 (1) Å. The phenyl ring is twisted away from the fused ring system by 36.49 (5)° (r.m.s. deviation = 0.027 Å; fitted atoms are the C₆ ring and the attached fused-ring C and O atoms). The dihydro­pyran ring displays a distorted envelope configuration by displacement of the phenyl-bearing and the adjacent ring C atoms from the fused-ring system plane by 0.356 (2) and 0.402 (2) Å, respectively.

Arene−Chromium Tricarbonyl Complexes in the Pauson−Khand Reaction

[reactions: see text] We show the use of arene-chromium tricarbonyl complexes in intra- and intermolecular Pauson-Khand reactions. Both styrene and ethynylbenzene complexes react with alkynes and olefins. The synthesis of enynes connected through chromium-complexed aromatic rings is developed. The intramolecular Pauson-Khand reaction occurs in a totally diastereoselective manner.

Diastereoselective propargylations with planar chiral chromiumcarbonyl arene complex substituted propargyl cations

The ionization of planar chiral ortho-substituted (arene)Cr(CO)(3)-substituted alpha-propargylic acetates 3 with Lewis acids results in the formation of stable (arene)Cr(CO)(3)-substituted alpha-propargyl cations 4. Subsequent additions of sulfur, nitrogen, oxygen, and pi-carbon nucleophiles to these organometallic electrophiles give rise to the regio- and highly diastereoselective formation of propargyl derivatives 5 in good yields (44-90%; dr = 70:30 to >99:1). The relative stereochemistry of the propargyl acetates 3 and the trapping products 5 was established by several crystal structure analyses, indicating that the cationic propargylations occurred under retention of configuration at the propargylic center. Most important for the diastereoselectivity of the nucleophilic trapping reaction is the configurational stability of the diastereotopic cation 4 as reflected by substituent effects. In situ ionizations according to an S(N)1-mechanism not only result in a considerable loss but also in an inversion of diastereoselectivity.