STRUCTURES OF (ETA(6)-BENZENE DIMETHYLACETAL)CHROMIUM TRICARBONYL AND(ETA(6)-BENZENE DIETHYLACETAL)CHROMIUM TRICARBONYL - STRUCTURAL EVIDENCE FOR THE NEAR-ELECTRONEUTRALITY OF THE DIALKYLACETAL SUBSTITUENT

The structures of the (benzene dialkylacetal)tricarbonyl chromium comp lexes [eta(6)-C6H5-CH(OR)(2)]Cr(CO)(3) (R = Met, 1; Et, 2), are report ed. The compounds were examined as part of a study of the conformation s of the tripodal tricarbonylchromium group. For [eta(6)-C6H5-CH(OMe)( 2)]Cr(CO)3, 1, monoclinic, P2(1)/c (# 14), a = 15.235(1) Angstrom, b = 6.5304(5) Angstrom, c = 12.702(1) Angstrom, beta = 103.197(1)degrees, Z = 4. For [eta(6)-C6H5-CH(OEt)(2)]Cr(CO)(3), 2, monoclinic, P2(1)/c (# 14), a = 9.859(3) Angstrom, b = 10.547(3) Angstrom, c = 15.138(3) A ngstrom, beta = 108.42(2)degrees, Z = 4. The data show that the molecu les adopt the expected ''three-legged piano stool'' structure. The car bonyl ligands in 1 adopt an eclipsed arrangement with respect to the a rene ring and its substituent, while those in 2 are staggered. These c onformations are consistent with the notion that the acetal substituen t behaves largely as an electroneutral group, or at most as a weak ele ctronic acceptor.