1,3-Dipolar Cycloaddition to the Fe−OC Fragment. 19. Synthesis and Properties of Fe(CO)2(PR3)(R1NC(R2)−C(R3)O) and Fe(CO)(Ph2PCH2CH2PPh2)(R1NC(R2)−C(R3)O) and Their Reactivity toward Dipolarophiles. First X-ray Crystal Structure of the Initial Bicyclo[2.2.1] Adduct

Complexes 7ak − an, 7bk, bm [(R 1 N C(R 2 )−C(R 3 ) O)Fe(CO) 2 PR 3 a: R 1 = t Bu, R 2 = H, R 3 = Ph; b: R 1 = Me, R 2 = Ph, R 3 = Ph; k: R = OMe; l: R = Ph; m: R = Et; n: R = n Pr], and 7ao, bo [(R 1 N C(R 2 )−C(R 3 ) O)Fe(CO)Ph 2 PCH 2 CH 2 PPh 2 ] have been prepared by substitution of CO in the respective tricarbonyl complexes 1a, b at room temperature. Various dynamic processes have been investigated by 13 C and 31 P NMR. On the IR time scale, complex 7bk exists in two distinct isomeric forms. Complexes 7 have been characterized by IR, UV−vis, and 1 H, 13 C, and 31 P NMR spectroscopy. Surprisingly, in the 1,3-dipolar cycloaddition reaction of complexes 7 with the dipolarophiles dimethyl acetylenedicarboxylate (DMAD, v ), methyl propynoate ( w ), phenyl acetylene ( x ), and p -methoxyphenyl-isothiocyanate ( y ) the bicyclic ferra[2.2.1] complexes 8, i.e., the initial cycloadducts, are stable and isolable. With dimethyl maleate ( z ) it is formed reversibly. Complexes 8 containing one phosphorus ligand are formed as two non-interconverting isomers. The molecular structure of 8aov, C 45 H 45 FeNO 6 P 2, has been determined by single-crystal X-ray diffraction. In pentane, the initial cycloadduct ( 8bv ) of the tricarbonyl 1b with DMAD is insoluble and precipitates. In solution above −30 °C 8bv reacts further by insertion of CO into the Fe−O bond to the Fe(CO) 3 (butenolide) complex 10bv . No intermediates can be detected by 1 H, 13 C, and IR monitoring. The other complexes 8 do not insert CO and slowly decompose on stirring at room temperature in THF. From the decomposition of complexes 8 with α-iminoketone a, the organic compound 11a can be isolated. The cycloaddition reaction of 1a with DMAD ( v ) in the presence of PR 3 ( k: R = OMe; l: R = Ph) results without detectable intermediates in the formation of the Fe(CO) 2 PR 3 (butenolide) complexes 10akv, alv. They are formed as three and two non-interconverting isomers, respectively. Reaction of 8bv with PEt 3 also results in the formation of the butenolide complex 10bmv; however, here the PEt 3 ligand occupies exclusively one of the equatorial positions. An explanation for the isomeric ratios of complexes 8 and 10 is discussed.