Synthesis, structure and reactivity of bidentate 2-ketopyrrolyl cobalt(III) phosphonates and phosphinates

Article abstract of DOI:10.1016/S0020-1693(96)05184-5

Bidentate N,O complexes (η⁵-C₅R₅)Co(R′C(O)-C ₄H₃N)(I) (3) are prepared by treating in situ produced 2-acyl-pyrrolyl anion (R′C(O)-C₄H₃N^-, 2α,β; α (R′ = H), β (R′ = Me)) with (η⁵-C₅R₅)Co(CO)(I)₂ (1a,b; a (R = H), b (R = Me)) in THF. Reaction of 3 with P-donor ligands (PMe₃, P(OMe)₃ and PPh(OMe)₂) results in simple halide substitution to give [(η⁵-C₅R₅)Co(R′C(O)-C ₄H₃N)(P-donor)]⁺I^- (4-6). The PMe₃ product (4) is readily isolated, however facile Arbuzov dealkylation of the phosphite (5) and phosphonite (6) salts gives dimethyl phosphonates, (η⁵-C₅R₅)Co(R′C(O)-C ₄H₃N)(P(O)(OMe)₂) (7), and mixtures of diastereomeric methyl phenylphosphinates, (η⁵-C₅R₅)Co(R′C(O)-C ₄H₃N)(P(O)Ph(OMe)) (8), respectively. Intermediate phosphite and phosphonite complexes [(η⁵-C₅R₅)Co(R′C(O)-C ₄H₃N)(PR″(OMe)₂)]⁺I ^- (5, 6; R″ = OMe, Ph) were directly observed by ¹H NMR in acetone-d₆ at room temperature in several cases. The molecular structures of complexes 3bβ and 7bβ were determined by X-ray diffraction. 3bβ crystallizes in the orthorhombic system with a = 16.809(3), 6 = 13.755(5), c = 7.535(2) A, V = 1742(1) A³, Z = 4. Although the coordination geometry of 3bβ was determined, disorder problems in the selected crystal prevented refinement of the diffraction data to give meaningful structural parameters. 7bβ crystallizes in the monoclinic system, space group P2₁/c (No. 14) with a = 12.183(1), b = 10.100(2), c = 16.915(2) A, β = 106.559(9)°, V = 1995.1(4) A³, Z = 4 and R = 0.036 (R_w = 0.039) for 2716 reflections with I > 3.00σ(I). Conformation preferences for metallophosphonates and phosphinates 7 and 8, determined from solid state and solution (¹H nOed) data, are analyzed using molecular modeling (MM+) and extended Hueckel calculations.