An investigation of the photoinitiated cationic ring-opening polymerizations of various epoxy monomers was conducted using real-time infrared spectroscopy and optical pyrometry. Several types of behavior were observed and interpreted on the basis of the relative stabilities of the secondary and tertiary oxonium ion intermediates that are generated during the ring-opening polymerization of these monomers. Based on the mechanistic interpretations proposed, attempts were made to accelerate the photopolymerizations of epoxy monomers that undergo overall slow reaction as a result of the presence of an induction period. Three general methods were effective for the acceleration of the photopolymerizations of these and other epoxy monomers:  (1) carrying out the photopolymerizations at higher temperatures, (2) copolymerization with more reactive monomers, and (3) the use of free radical photoinitiators.

Investigation of the Reactivity of Epoxide Monomers in Photoinitiated Cationic Polymerization

We show that bis(aminophosphine) complexes of the type [M(R1R2N(CH2)nPPh2)2]2+, M = Pt(II) or Pd(II), can exist in chelate ring-closed and ring-opened forms both in the solid state and in aqueous solution. The equilibrium between them in solution can be controlled by the nature of the groups R1 and R2 (H, Me, Bz, cyclohexyl), by the bridge length n, and by the pH and Cl− concentration. X-Ray crystal structures are reported for the ring-closed complexes cis-[Pt(H2N(CH2)2PPh2-P,N)2]Cl2, cis-[Pt(H2N(CH2)3PPh2-P,N)2]Cl2, and cis-[Pt(Me(H)N(CH2)2PPh2-P,N)2][HCl2]2,
the mono-ring-opened complex cis-[Pd(Me2N(CH2)2PPh2-N,P)Cl(Me2NH(CH2)2PPh2-P)](NO3)2, the di-ring-opened complex cis-[Pt(Me2N(CH2)3PPh2-P)2Cl2], and, for comparison, the monochelate cis-[Pd(Me2N(CH2)3PPh2-N,P)Cl2]. These square-planar complexes exhibit varying degrees of distortion and variable M–N bond lengths dependent not only on the trans influence of P but also on steric effects within the complex. pH-induced chelate ring-opening of cis-[Pt(Me2N(CH2)2PPh2-P,N)2]Cl2 had an associated pK value of 6.9. In contrast, complexes with R1 and R2 = H, n = 2
or 3 or R1 = H and R2 = Me, n = 2, are more difficult to ring-open. Thus the complexes cis-[Pt(Me(H)N(CH2)2PPh2-P,N)2]Cl2 and cis-[Pt(H2N(CH2)3PPh2-P,N)2]Cl2, had associated pK values of 2.1 and 2.9, respectively. These aminophosphine complexes may exhibit anticancer activity by two mechanisms: by disrupting mitochondrial membrane potentials as bis-chelated (ring-closed) lipophilic cations, or by direct binding to DNA bases as ring-opened complexes.

Control of aminophosphine chelate ring-opening in Pt(II) and Pd(II) complexes: potential dual-mode anticancer agents

The preparation and structures of a variety of oxonium ion tetrachloroaurate(III) salts isolated from aqua regia are reported. The new compounds are [(H5O2)2(12-crown-4)2][AuCl4]2 (1), [(H7O3)(15-c...

Oxonium ions from aqua regia: isolation by hydrogen bonding to crown ethers.

Reaction of MCl(3).nH(2)O (M = La, Eu) with 18-crown-6 in HCl/toluene affords the crystalline oxonium complexes (H(9)O(4))[LaCl(2)(H(2)O)(18-crown-6)]Cl(2) (1) and (H(3)O)[EuCl(H(2)O)(2)(18-crown-6)]Cl(2) (2). In complex 1 the H(9)O(4)(+) cation is of the unusual linear chain type with O.O contacts of 2.560(9), 2.430(9), and 2.483(9) A. The analogous reaction with YbCl(3).6H(2)O results in the isolation of the known species (H(5)O(2))[H(3)O.(18-crown-6)]Cl(2). Analogous reaction of YbCl(3).6H(2)O with 15-crown-5 gives [Yb(H(2)O)(8)]Cl(3).(15-crown-5) (5). Reaction of uranyl acetate with 15-crown-5 within a toluene/HCl mixture results in the formation of a yellow liquid clathrate layer from which crystals of (H(5)O(2))[UO(2)(H(2)O)(2)Cl(3)].2(15-crown-5) (6) are deposited. The H(5)O(2)(+) ion in this material exhibits a particularly short O.O separation of 2.371(8) A. On standing, loss of HCl results in the transformation of 6 into a species of empirical formula [UO(2)(H(2)O)(3)Cl(2)].(15-crown-5) (7) which has been shown by X-ray crystallography to contain 16 unique uranium complexes, arranged in infinite hydrogen-bonded chains in the solid state. Crystal data for 1: monoclinic, P2(1)/c, a = 7.6950(2) A, b = 21.2160(16) A, c = 15.8650(10) A, beta = 92.866(2) degrees, V = 2586.8(3) A(3), Z = 4. 2: orthorhombic, Pbn2(1), a = 10.2267(6) A, b = 14.7231(9) A, c = 29.8565(18) A, V = 4495.5(5) A(3), Z = 4. 5: monoclinic, P2(1)/n, a = 9.1740(3) A, b = 17.1900(3) A, c = 15.2450(5) A, beta = 92.643(2) degrees, V = 2401.60(12) A(3), Z = 4. 6: orthorhombic, Pmcn, a = 12.1740(5) A, b = 14.7740(7) A, c = 18.4920(11) A, V = 3325.9(3) A(3), Z = 4. 7: trigonal, P3(2), a = 35.3500(2) A, c = 21.3755(2) A, V = 23 132.7(3) A(3), Z = 48.

Formation of Lanthanide and Actinide Oxonium Ion Complexes with Crown Ethers from a Liquid Clathrate Medium

Oxonium ions (H+·(H2O)n) can be stabilised and isolated in the solid state by using crown ethers of differing sizes. Crown ethers can act as very good hydrogen bond acceptors for the binding of oxonium ions. It has been reasonably well established that 18C6 binds the H3O+ oxonium ion almost selectively in the cavity of the crown, while for the smaller crown ethers 12C4 and 15C5 the macrocycles generally span successive oxonium ions of varying nuclearity (H3O+, H5O2+, H7O3+ and H9O4+) to form hydrogen bonded polymers. Crown ethers larger than 18C6, e.g. 21C7 and 24C8 can bind H5O2+ ions on the face of the crowns, while 30C10 appears to prefer two molecules of H3O+ in the cavity. It is the intention of this perspective to review the literature involving the solid state interactions of crown ether complexes involving oxonium ions.

Crown ethers as stabilising ligands for oxonium ions

The interaction of the oxonium ion, H/sub 3/O/sup +/, with polar solvents has been extensively reviewed in the broader context of hydrogen bonding The first report of a complex of H/sub 3/O/sup +/ and a macrocycle was an infrared spectroscopic study in 1972 More recently several reports have appeared This has proved to be a method of isolation of H/sub 3/O/sup +/ from higher hydrated species, H/sub 3/O/sup +/ coordinated to macrocycles have been reported, one which lends strong support for pyramidal H/sub 3/O/sup +/, and one which may be interpreted in terms of planar H/sub 3/O/sup +/ In the extensive literature of the oxonium ion, evidence for the species in aromatic solution has not bee presented Here the authors report that the oxonium ion coordinated to 18-crown-6 does indeed have a stable existence in aromatic media

The oxonium cation in aromatic solvents. Synthesis, structure, and solution behavior of [H3O+.cntdot.18-crown-6][Cl-H-Cl]

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The oxonium cation in aromatic solvents. Synthesis, structure, and solution behavior of [H3O+.cntdot.18-crown-6][Cl-H-Cl]