Synthesis and Characterization of MoOI2(PMe3)3 and Use of MoOX2(PMe3)3 (X = Cl, I) in Controlled Radical Polymerization

Complex MoOCl2(PMe3)3 smoothly reacts with NaI in acetone to produce MoOI2(PMe3)3 in good yields. The geometry of the compound is mer-cis octahedral, that is, identical to that of the dichloride precursor, as shown by NMR spectroscopy and by an X-ray crystallographic study. Electrochemical investigations of MoOX2(PMe3)3 show irreversible oxidation waves at Ep,a = +0.18 and +0.39 V for X = Cl and I, respectively. A study of the halide exchange between MoOCl2(PMe3)3 and NaI, or between MoOI2(PMe3)3 and Bu4NCl, shows two equilibrated isomers for the mixed halide intermediate MoOICl(PMe3)3. The diiodide complex rapidly exchanges the iodo ligands with chloride upon dissolution in chloroform at room temperature, and with bromide from (1-bromoethyl)benzene (BEB) under more forcing conditions. The equilibrium favors the softer halide (I) on C and the harder one (Cl or Br) on MoIV. Both oxido compounds catalyze the atom transfer radical polymerization (ATRP) of styrene in combination with the BEB initiator, yielding polymers with quite narrow molecular weight distributions (down to 1.11). The apparent polymerization rate constant is approximately doubled in the presence of 1 equiv. of the Al(OiPr)3 cocatalyst. On the other hand, the system is not capable of efficiently controlling the radical chain growth for methyl acrylate polymerization. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

[1]  S. Maria,et al.  An experimental and computational study on the effect of Al(OiPr)3 on atom-transfer radical polymerization and on the catalyst-dormant-chain halogen exchange. , 2005, Chemistry.

[2]  S. Maria,et al.  The radical trap in atom transfer radical polymerization need not be thermodynamically stable. A study of the MoX(3)(PMe(3))(3) catalysts. , 2005, Journal of the American Chemical Society.

[3]  R. Poli,et al.  Al(OPr i)3-catalysed halogen exchange processes of relevance to atom transfer radical polymerization: the effect depends on the metal electronic structure. , 2004, Chemical communications.

[4]  D. Haddleton,et al.  Controlled radical polymerization of alkyl acrylates and styrene using a half-sandwich molybdenum(III) complex containing diazadiene ligands , 2003 .

[5]  L. Bronstein,et al.  Atom Transfer Radical Polymerization with Ti(III) Halides and Alkoxides , 2003 .

[6]  David J. Williams,et al.  Four-coordinate iron complexes bearing alpha-diimine ligands: efficient catalysts for atom transfer radical polymerisation (ATRP). , 2002, Chemical communications.

[7]  M. Sawamoto,et al.  Metal-catalyzed living radical polymerization. , 2001, Chemical reviews.

[8]  K. Matyjaszewski,et al.  Atom transfer radical polymerization. , 2001, Chemical reviews.

[9]  J. Claverie,et al.  Radical polymerization of styrene controlled by half-sandwich Mo(III)/Mo(IV) couples: all basic mechanisms are possible. , 2001, Journal of the American Chemical Society.

[10]  R. Poli,et al.  Improved Preparations of Molybdenum Coordination Compounds from Tetrachlorobis(diethyl ether)molybdenum(IV) , 2001 .

[11]  Zhe‐wen Han,et al.  A new complex catalytic system CuX/bpy/Al(OR)3 for atom transfer radical polymerization , 2000 .

[12]  M. Sawamoto,et al.  Metal Alkoxides as Additives for Ruthenium(II)-Catalyzed Living Radical Polymerization1 , 2000 .

[13]  M. Sawamoto,et al.  FeCp(CO)2I: A Phosphine-Free Half-Metallocene-Type Iron(II) Catalyst for Living Radical Polymerization of Styrene1 , 1999 .

[14]  M. Sawamoto,et al.  Living radical polymerization of methyl methacrylate with a zerovalent nickel complex, Ni(PPh3)41 , 1999 .

[15]  Agustín Galindo,et al.  Synthesis and characterization of dioxocomplexes of molybdenum with (η-C5H5)Co{P(O)(OEt)2}3, C5H4(SiMe3) and 1,3-C5H3(SiMe3)2 ligands. X-ray crystal structure of [(η-C5H5)Co{P(O)(OEt)2}3]MoO2Cl , 1999 .

[16]  M. Sawamoto,et al.  Re(V)-Mediated Living Radical Polymerization of Styrene:1 ReO2I(PPh3)2/R−I Initiating Systems , 1999 .

[17]  Maria Cristina Burla,et al.  SIR97: a new tool for crystal structure determination and refinement , 1999 .

[18]  Louis J. Farrugia,et al.  ORTEP-3 for Windows - a version of ORTEP-III with a Graphical User Interface (GUI) , 1997 .

[19]  M. Sawamoto,et al.  Nickel-Mediated Living Radical Polymerization of Methyl Methacrylate1 , 1997 .

[20]  P. Fanwick,et al.  Crystal structure of base-free [MoOI4]− , 1995 .

[21]  H. Kraatz,et al.  Pentamethylcyclopentadienyl)molybdenum bromides and iodides , 1994 .

[22]  A. Rheingold,et al.  A reinvestigation of the molecular structures of cis-mer-MoOCl2(PR3)3 : do bond-stretch isomers really exist ? , 1991 .

[23]  F. Cotton,et al.  Low-valent molybdenum carbonyl complexes as an entry to octahedral MoI3L3 complexes. Synthesis and x-ray molecular structure of triiodotris(tetrahydrofuran)molybdenum , 1987 .

[24]  H. D. Flack,et al.  Least-squares absolute-structure refinement. Practical experience and ancillary calculations , 1985 .

[25]  H. Flack,et al.  On enantiomorph‐polarity estimation , 1983 .

[26]  G. Wilkinson,et al.  Mononuclear and dinuclear tertiary phosphine molybdenum complexes. oxo-molybdenum(IV), dinuclear Mo2Cl4L4 and related derivatives , 1984 .

[27]  James E. Huheey,et al.  Inorganic chemistry; principles of structure and reactivity , 1972 .