The reaction chemistry of transition-metal diphenylphosphorus complexes with organoaluminum compounds. The synthesis, characterization, and crystal and molecular structure of Cr(CO)5[PPh2(CH2)4OAl(CH 2SiMe3)2], an example of THF cleavage

Article abstract of DOI:10.1021/om50003a011

Metathetical and small molecule elimination reactions between appropriate transition-metal carbonyl diphenylphosphorus complexes and organoaluminum compounds have been investigated as synthetic routes to transition-metal derivatives of amphoteric ligands. The synthesis, characterization, and properties of the starting compounds for the metathetical reactions M(CO)₅PPh₂K·n(dioxane) (M = Cr, W, n = 2; M = Mo, n = 1) from M(CO)₅PPh₂H and KH are described. All data confirm that the dioxane molecules in these complexes retain their identity as cyclic ethers. Subsequent reactions of Cr(CO)₅PPh₂K·2(dioxane) with AlR₂Br (R = Br, Me, Et, CH₂SiMe₃) in THF lead to the formation of high yields of fully characterized compounds with the empirical formula Cr(CO)₅[PPh₂(CH₂)₄OAlR₂]. The (CH₂)₄O unit arises from the cleavage of the THF molecule. No THF-aluminum adducts are observed. The compound Cr(CO)₅-[PPh₂(CH₂)₄OAl(CH ₂SiMe₃)₂] which incorporates a new amphoteric ligand has also been characterized by an X-ray structural study. The crystal is composed of dimeric units of formula [Cr(CO)₅[PPh₂-(CH₂)₄OAl(CH ₂SiMe₃)₂]]₂ which are in the centrosymmetric monoclinic space group P2₁/n with a = 11.939 (3) A?, b = 14.940 (A?), c = 21.014 (5) A?, β= 102.88 (2)°, V = 3654 A?³, Z = 2 (dimeric units), and mol wt 1301.5. Diffraction data (20(max) = 35°, Mo Kα radiation) were collected with a Syntex P2₁ automated four-circle diffractometer, the structure was solved by Patterson and difference-Fourier techniques, and the model was refined to R_F = 9.2% and R_wF = 8.2% for 1515 reflections with |F_o| > 3σ(|F_o|). The dimeric molecule lies on an inversion center. Each octahedral (OC)₅CrPPh₂- fragment is linked by an -(CH₂)₄O-unit (formed by cleavage of THF) to the two Al(CH₂SiMe₃)₂ fragments. The central Al-O-Al-O ring is strictly planar, with obtuse Al-O-Al angles of 100.3 (6)° and acute O-Al-O angles of 79.7 (5)°. The second route to chromium derivatives of amphoteric aluminum-phosphorus ligands, small molecule elimination reactions between Cr(CO)₅PPh₂H and AlMe₃ or AlMe₂H, does not lead to compounds with Cr-P-Al bonds. Our observations suggest that the major site of reaction for the aluminum compounds is the carbonyl ligand.