ORGANOCHROMIUM PI-COMPLEXES .3. PREPARATION AND REACTIONS OF BIS(ETA-3-ALLYL)CHROMIUM(II) COMPLEXES

Cr(PR3)2Cl2 (PR3 = PMe3, PMe2Ph, PPh2Me), Cr(Me2PC2H4PMe2)2Cl2, and [Cr(Pr(i)2PC2H4PPr(i)2)Cl2]2 react with 2-propenylmagnesium chloride or 2-methyl-2-propenylmagnesium chloride to give thermolabile (eta-3-allyl)2Cr(PR3)2 and (eta-3-allyl)2Cr(R2PC2H4PR2) compounds. In contrast, the final product of the reaction between Cr(PMe3)2Cl2 and 2-butenylmagnesium chloride contains an eta-2,eta-2-bonded dimethyldiallyl group derived from the reductive coupling of two eta-3-1-MeC3H4 fragments. (eta-3-C3H5)2Cr(PMe3)2 reacts with 2-butyne with alkyne insertion into an eta-3-allyl group to give a compound containing both eta-3-allyl and eta-1,eta-2-4-methyl-1,4-hexadienyl groups. The structures of these paramagnetic organochromium(II) compounds have been confirmed by X-ray structural determinations of three examples, viz. (eta-3-C3H5)2Cr(PMe2PH)2 (2) (a = 8.894 (4) angstrom, b = 27.56 (1) angstrom, c = 9.355 (3) angstrom, beta = 107.64 (3)-degrees, space group P2(1)/n, Z = 4), (eta-3-C3H5)2Cr(Pr(i)2PC2H4PPr(i)2) (6) (a = 9.171 (1) angstrom, b = 15.936 (2) angstrom, c = 15.368 (1) angstrom, beta = 102.22 (1)-degrees, space group P2(1)/n, Z = 4) and (eta-3-C3H5)(eta-1,eta-2-4-methyl-1,4-hexadienyl)Cr(PMe3)2 (9) (a = 9.299 (5) angstrom, b = 14.474 (8) angstrom, c = 13.916 (5) angstrom, space group P2(1)2(1)2(1), Z = 4).