PPNCl Research Articles

Influence of the Metal (Al, Cr, and Co) and the Substituents of the Porphyrin in Controlling the Reactions Involved in the Copolymerization of Propylene Oxide and Carbon Dioxide by Porphyrin Metal(III) Complexes. 2. Chromium Chemistry

The reactivities of chromium(III) complexes LCrX, where L = 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), and 2,3,7,8,12,13,17,18-octaethylporphyrin (OEP) and X = Cl or OH, have been studied with respect to their ability to homopolymerize propylene oxide (PO) and copolymerize PO and CO(2) to yield polypropylene oxide (PPO) and polypropylene carbonate (PPC) or propylene carbonate (PC), respectively, with and without the presence of a cocatalyst, namely, 4-dimethylaminopyridine (DMAP) or PPN(+)Cl(-) (bis(triphenylphosphine)iminium chloride). The homopolymerization is notably faster (TOF ≈ 2000 h(-1) at room temperature) than copolymerization, which commonly leads to ether-rich polymers. Studies of kinetics reveal that for TPPCr(OH) with DMAP (1 equiv) the propagation reaction rate is first order in [Cr] with excess PO. With PPN(+)Cl(-) as a cocatalyst the reaction order in [Cr] and [Cl(-)] is complicated by the presence of two growing chains, and the presence of excess [Cl(-)] facilitates the formation of PC by two different backbiting mechanisms. The fixation of CO(2) is promoted by [Cl(-)] but is not greatly influenced by CO(2) pressure (1-50 bar). The reactions and polymers have been monitored by UV-visible spectroscopy, react-IR, GPC, ESI, and MALDI TOF, and NMR ((1)H, (13)C{(1)H}) spectroscopy. Notable differences are seen in these reactions when compared with earlier studies by Darensbourg et al. with salen chromium(III) systems and related aluminum(III) porphyrins.

Thermal Stability, Decomposition Paths, and Ph/Ph Exchange Reactions of [(Ph3P)2Pd(Ph)X] (X = I, Br, Cl, F, and HF2)

Complexes of the type [(Ph3P)2Pd(Ph)X], where X = I (1), Br (2), Cl (3), F (4), and HF2 (5), possess different thermal stability and reactivity toward the Pd−Ph/P−Ph exchange reactions. While 1 decomposed (16 h) in toluene at 110 °C to [Ph4P]I, Pd metal, and Ph3P, complexes 2 and 3 exhibited no sign of decomposition under these conditions. Kinetic studies of the aryl−aryl exchange reactions of [(Ph3P)2Pd(C6D5)X] in benzene-d6 demonstrated that the rate of exchange decreases in the order 1 > 2 > 3, the observed rate constant ratio, kI:kBr:kCl, in benzene at 75 °C being ca. 100:4:1 for 1-d5, 2-d5, and 3-d5. The exchange was facilitated by a decrease in the concentration of the complex, polar media, and a Lewis acid, e.g., Et2O·BF3. Unlike [Bu4N]PF6, which speeded up the exchange reaction of 2-d5, [Bu4N]Br inhibited it due to the formation of anionic four-coordinate [(Ph3P)Pd(C6D5)Br2]-. The latter and its iodo analogue were generated in dichloromethane and benzene upon addition of [Bu4N]X or PPN Cl to [(Ph3P)2Pd2(Ph)2(μ-X)2] (X = I, Br, or Cl) and characterized in solution by 1H and 31P NMR spectral data. The mechanism of the aryl−aryl exchange reactions of [(Ph3P)2Pd(C6D5)X] in noncoordinating solvents of low polarity may not require Pd−X ionization but rather involves phosphine dissociation, the ease of which decreases in the order X = I > Br > Cl, as suggested by crystallographic data. Two mechanisms govern the thermal reactions of [(Ph3P)2Pd(Ph)F], 4. One of them is similar to the aryl−aryl exchange and decomposition path for 1−3, involving a tight ion pair intermediate, [Ph4P][(Ph3P)PdF], within which two processes were shown to occur. At 75 °C, the C−P oxidative addition restores the original neutral complex (4). At 90 °C, reversible fluoride transfer from Pd to the phosphonium cation resulted in the formation of covalent [Ph4PF] and [(Ph3P)Pd], which was trapped by PhI to produce [(Ph3P)2Pd2(Ph)2(μ-I)2]. The other decomposition path of 4 leads to the formation of [(Ph3P)3Pd], Pd, Ph2, Ph3PF2, and Ph2P−PPh2 as main products. Unlike the aryl−aryl exchange, this decomposition reaction is not inhibited by free phosphine. The formation of biphenyl was shown to occur due to PdPh/PPh coupling on the metal center. Mechanisms accounting for the formation of these products are proposed and discussed. The facile (4 h at 75 °C) thermal decomposition of [(Ph3P)2Pd(Ph)(FHF)] (5) in benzene resulted in the clean formation of PhH, Ph3PF2, Pd metal, and [(Ph3P)3Pd].

Complexes of Multifunctional Phosphorus Ligands. Rhenium(V) Complexes of the Multidentate Phenoxyphosphine Ligands Bis(o-trimethylsilyloxyphenyl)phenylphosphine and Tris(o-trimethylsilyloxyphenyl)phosphine. Stepwise Elimination of Me(3)SiX (X = Cl, OEt) from the Metal-Ligand System.

The silylated aryloxo ligands bis(o-silyloxyphenyl)phenylphosphine (abbreviated PhP{OT}(2)) and tris(o-trimethylsilyloxyphenyl)phosphine (abbreviated P{OT}(3), where T = Me(3)Si) were prepared. Complexation reactions with O=ReCl(2)(OEt)(PPh(3))(2) and O=ReCl(3)(PPh(3))(2) proceed by displacement of one PPh(3) and the subsequent stepwise replacement of the OEt and/or Cl substituents. The new complex Re(O)Cl(2)[kappa(2)-(P,O)-(PhP{O}{OT})](PPh(3)), formed by elimination of Me(3)SiOEt, exists in diastereomeric cis and trans forms. Elimination of a second equivalent of Me(3)SiCl gives Re(O)Cl[kappa(3)-(P,O,O)-(PhP{O}(2))](PPh(3)). Similarly P{OT}(3) converts Re(O)Cl(2)(OEt)(PPh(3))(2) to ReOCl(2)[kappa(2)-(P,O)-(P{O}{OT}(2))](PPh(3)) (5) (structurally characterized as 5.0.875CH(2)Cl(2)): crystal data; triclinic P&onemacr;, a = 14.302(4) Å, b = 18.734(2) Å, c = 17.639(4) Å, alpha = 80.950(12) degrees, beta = 80.12(2) degrees, gamma = 81.76(2) degrees, Z = 4. Final R(1) and wR(2) values are 0.0852 and 0.1525, respectively on F(o)(2) > 2sigma(F(o)(2)) data (or 0.1948 and 0.2019 on all data). The phenoxy phosphine ligand in 5 is bound via P and one O to Re. The P atoms are mutually cis to each other and to the terminal oxygen on Re. Two ortho-trimethylsiloxy substituted phenyl rings dangle from the coordinated phosphorus atom. Complex 5 can be converted to Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OT})](PPh(3)) (6) by treatment with PPN(+) Cl(-) and 6 was also obtained by direct reaction of Re(O)Cl(3)(PPh(3))(2) with P{OT}(3) at higher temperatures. The complex 6 has been structurally characterized: crystal data triclinic, P&onemacr;, a = 10.1509(6) Å, b = 12.1123(8) Å, c = 16.2142(14) Å, alpha = 97.851(7) degrees, beta = 94.852(7) degrees, gamma = 96.889(6) degrees, Z = 2. Final R(1) and wR(2) values were 0.0303 and 0.0721 on F(o)(2) > 2sigma(F(o)(2)) data (or 0.0348 and 0.0742 on all data). The phenoxyphosphine ligand in 6 is bound facially to Re through P and two of the phenoxy oxygens. The Ph(3)P group and terminal oxygen atoms are cis to the oxygen atoms of the phenoxy ligands and the Cl lies trans to P. One trimethylsiloxyphenol group dangles. Careful hydrolysis of 6 gave Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OH})](PPh(3)) which was also formed during complexation reactions in moist solvent. Solution (31)P{(1)H} NMR demonstrated cis- or trans-(P,P) geometry for the complexes, which was confirmed in the two aforementioned cases by structure determinations.

The trans influence of F, Cl, Br and I ligands in a series of square-planar Pd(II) complexes. Relative affinities of halide anions for the metal centre in trans-[(Ph 3P) 2Pd(Ph)X

Single crystal X-ray diffraction studies of trans-[(Ph 3P) 2Pd(Ph)X] (X = F ( 1), Cl ( 2), Br ( 3), and I ( 4) were carried out. The four structures split in two isostructural and isomorphous groups, namely orthorhombic for 1 and 2 (space group Pbca, Z = 8) and triclinic for 3 and 4 (space group P-1, Z = 2). According to the PdC bond length, the trans influence of X within these pairs follows the trend Cl>F and 1>Br. However, the trans influence of Cl is slightly stronger than that of Br. Both structural and 13C NMR studies revealed that electron-donating effects of (Ph 3P) 2PdX increase along the series X=I<Br<Cl<F, in accord with the previously reported ‘halogen anomaly’ phenomenon. Relative affinities of X − for the Pd centre in [(Ph 3P) 2Pd(Ph)] − were studied by 31P NMR in rigorously anhydrous CH 2Cl 2 solutions, and equilibrium constants and ΔG values were obtained for all possible combinations. The sequence F − > Cl − > Br − > I − is characteristic of halide preference for the Pd complexes. Dissolving 1 and PPN Cl in dry CH 2Cl 2 resulted in the release of ‘naked’ F − which fluorinated the solvent smoothly to give a mixture of CH 2ClF and CH 2F 2 in high yield. When chloroform was used instead of CH 2Cl 2, dichlorocarbene was generated slowly, forming the corresponding cyclopropane in the presence of styrene. All observations were rationalized successfully in terms of the filled/filled effect and push/pull interactions.