1,3-Dipolar Cycloaddition to the Fe−XC Fragment 18. Chemoselectivity in the Addition of Activated Alkynes across the Fe−OC Fragment vs the Fe−NC Fragment in Chelate (α-Imino ester)tricarbonyliron Complexes

Abstract

In situ prepared chelate complexes Fe(CO) 3 (R 1 NdC(R 2 )C(R 3 )dO) (R 1 ) alkyl, R 2 ) H, R 3 ) O-alkyl) (7a-j) react with dimethyl acetylenedicarboxylate (DMAD) via a 1,3-dipolar cycloaddition reaction to form four products as a result of cycloaddition to both the Fe-Od C and the Fe-NdC fragments. The main product is the Fe(CO) 3 (butenolide) complex (10), which results from cycloaddition to the Fe-OdC fragment, indicating that this fragment is more reactive than the Fe-NdC fragment. Complexes 10, 11, 13, and 15 have been characterized by spectroscopy (IR, 1 H and 13 C NMR, FD-mass) and by elemental analyses. The molecular structures of all four types of complexes (10d, 11a, 13c, and 15h) have been established by single-crystal X-ray diffraction. The product formation and distribution is determined by both the R 1 and the R 3 substituents. Reaction with the less activated alkyne methyl propynoate (MP) results, in a slow reaction, exclusively in cycloaddition to the Fe-OdC fragment with formation of two products depending on the additional ligand offered. Uptake of an additional CO ligand leads to the Fe(CO) 3 (butenolide) complex 16, which is formed exclusively as one of the possible regioisomers with the former ketone carbon atom C-C connected to the ester-substituted alkyne carbon atom. When MP also acts as an additional ligand, the tricyclic complexes 20 are formed, which consist of three five-membered rings. Complexes 20 are also obtained in almost quantitative yield by irradiation of 16 in the presence of MP. Similarly, complexes 19 are obtained by irradiation of 10 in the presence of MP. The molecular structure has been confirmed by an X-ray structure determination of 19c. When complexes 10 are refluxed in THF and subsequently reacted with water at room temperature, the organic butenolide derivatives 21 with an exocyclic enamine function are obtained. The molecular structure has been established by an X-ray structure determination of 21c. Reaction of 10 under 50 bar of CO pressure at 115 °C results in the liberation of the intact butenolide heterocycles (22) together with some side products. Scheme 1. Reactions of Fe(CO) 2 L(R-DAB), Fe(CO) 3 (r-imino ketone), and Ru(CO) 3 (R-DAB) with the Electron-Deficient Alkynes DMAD and MP

1,3-Dipolar cycloaddition to the FeSC fragment 20. Preparation and properties of carbonyliron complexes of di-thiooxamide. Reactivity of the mononuclear (di-thiooxamide)Fe(CO)3 towards dimethyl acetylenedicarboxylate

“…The molecular structure of 11a is confirmed by a single crystal X-ray structure determination. Closely related complexes have been observed in the in situ 1,3-dipolar cycloaddition reactions of Fe(CO) 3 (L) (L =a-iminoketone [57], a-iminoester [58]) with DMAD (cf. Fig.…”

“…Fig. 7) resulting in Fe 2 (CO) 5 (OIB) [58] (A) and Fe 2 (CO) 5 (OPP) [57] (B) complexes. Reaction of Table 5 Selected bond distances (A , ) and angles (°) for 10a (e.s.d.s in parentheses)…”

Reactions of a quintuply bonded chromium dimer with alkynes

“…In transition metal chemistry, the compounds most closely related to 3 are Fru¨hauf's products of 1,3 dipolar additions across M-XQC bonds (X = O, S, N). [19][20][21][22][23][24][25] In main group chemistry, the reversible addition of alkynes to dinuclear gallium complexes of a chelating diamide provides a recent analogue. 26 However, what makes 3 unique is the apparent retention of its metal-metal multiple bond.…”

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

“…Furthermore, the central bond of the former alkyne (C1−C2 = 1.354(8) Å) is reduced to a double bond. The olato oxygen O5 is coordinated to iron by a bond of 1.944(4) Å, which compares well with the Fe−O bond length in Fe 2 (CO) 5 [ i PrNC(H)C(OMe)(O)C(CO 2 Me)C(CO 2 Me)] and Fe 2 (CO) 6 [CEtCEt(CO 2 )] . The rather short Fe−C19 bond of 1.742(6) Å reflects the electron-donating capacity of both the DPPE phosphorus atoms, which enhances π-back-donation to this carbonyl.…”