Alberto R. Dias

Polymerization with TMA‐protected polar vinyl comonomers. II. Catalyzed by nickel complexes containing α‐diimine‐type ligands

α-Diimine Ni complexes (7, 8) were used as catalyst precursors with MAO in co- and terpolymerization of ethylene/propylene/α-olefins with OH and COOH functional groups. Trimethylaluminium was used to protect the functional group of polar monomers. The presence of 5-hexen-1-ol seems to have no effect on the polymerization rate at all for the N,N′-bis(2,6-diisopropylphenyl) derivative 8 but caused activity decreases of about fivefold in copolymerization and around two times in terpolymerization for the N,N-dimesityl derivative 7. The effect levels off at higher polar comonomer concentration. This system, (7)/MAO, also incorporates well both 10-undecen-1-ol and 10-undecen-1-oic acid. The activities obtained with these α-diimine Ni complexes in co- and terpolymerization are three to twenty times higher than those obtained with group 4 Cp based complexes especially at concentrations of polar monomer in the feed higher than 80 mM.

Polymerization with TMA‐protected polar vinyl comonomers. I. Catalyzed by group 4 metal complexes with η5‐type ligands

This paper describes the use of several kinds of group IV Cp based catalyst systems, in the synthesis of co- and terpolymers of ethylene, propylene and α-olefins endowed with OH and COOH functional groups. The hydroxy monomers used were 5-hexen-1-ol (4) and 10-undecen-1-ol (5) and the carboxy monomer was 10-undecen-1-oic acid (6). The three catalyst systems used were the C 2 symmetric ansa-zirconocene (1) the in-site titanium complex (2) and the non-rigid zirconocene (3), all activated by methylaluminoxane. Trimethylaluminium was used to protect the functional group of polar monomers. The first two catalyst systems suffer similar activity loss in the presence of polar monomer whereas the third one exhibited better tolerance toward the hydroxyolefins. NMR and FTIR spectroscopies were used to characterize the polymerization products. All three catalyst systems afforded functionalized co- and terpolymers by direct polymerization of ethylene/propylene/hydroxy-a-olefins but only the catalyst system (1)/MAO displays appreciable activities for direct polymerization of ethylene, propylene and carboxy-α-olefins.

Hyper-Rayleigh scattering study of η5-monocyclopentadienyl–metal complexes for second order non-linear optical materials

A series of ionic η5-monocyclopentadienyl–metal compounds possessing p-substituted benzonitrile ligands has been studied by hyper-Rayleigh scattering at the fundamental wavelength of 1.064 µm. Upon systematic variation of the metal ion, the first hyperpolarizability β was found to increase along the sequence Co, Ni, Ru, Fe, with about a three-fold increase from Ru to Fe. This yields very high values for the iron complexes, e.g., β=410×10–30 esu for [Fe(η5-C5H5)(dppe)( p-NCC6H4NO2)]+ [PF6 ]– dissolved in methanol. The high β values are attributed to π back-donation resulting in an extension of the conjugated π-system from the FeII organometallic fragment, acting as a good donor group, via the nitrile to the acceptor group NO2 . Complexes with single phenyl rings as conjugated chains perform better than their biphenyl analogues, which is explained in terms of non-planarity of the coordinated biphenyl ligands in solution. By comparing complexes with electron donor and acceptor substituted ligands it is demonstrated that the organometallic moiety can be used as an extremely effective donor group but not as a good acceptor group.

Synthesis, bonding and dynamic behavior of fac-[Mo(II)(CO)2(η3-allyl)] derivatives

Cationic complexes [Mo(η 3 -allyl)(CO) 2 (L–L)L′]PF 6 , (L–L=C 6 H 5 SCH 2 CH 2 SC 6 H 5 , L′=NCCH 3 ( 1 ); bipy, NCCH 3 ( 2 ); py, (NCCH 3 ) 2 ( 3 ); (NCCH 3 ) 3 ( 4 ); dppe, NCCH 3 ( 5 ) and the neutral analogues [Mo(η 3 -allyl)(CO) 2 (L–L)X] (L–L=phen ( 6 ); bipy ( 7 ); X=Br) were synthesized. Complexes 2 , 5 , 6 and 7 were characterized by single crystal X-ray diffraction. Depending on the chelating ligand, these pseudo-octahedral complexes undergo different dynamic processes in solution and NMR spectroscopic evidence was provided for those studies. The structural trends of the limiting structures depicted by these complexes as well as the pathways to their inter-conversion were analyzed by ab initio theoretical calculations. Both NMR data and the calculations showed that for complex 2 the equatorial species predominates at room temperature but that two forms differing only by the conformation of the allyl coexist. Lowering the temperature leads to the appearance of the equatorial–axial isomer.

Synthesis and characterization of η5-monocyclopentadienyl (p-nitrobenzonitrile)ruthenium(II) salts: Second harmonic generation powder efficiencies

Abstract A new family of salts [Ru(η 5 -C 5 H 5 ((+)-(DIOP)( p -NCC 6 H 4 NO 2 )][X] (X = p -CH 3 C 6 H 4 SO 3 − , Cl − , NO 3 − , BF 4 − , PF 6 − , ClO 4 − and CF 3 SO 3 − ), has been synthesized. Variation of the counterion shows that [Ru(η 5 -C 5 H 5 ((+)-(DIOP)( p -NCC 6 H 4 NO 2 )]+ can improve by a factor of 25 the value of second harmonic generation powder efficiency. The relation between 1 H and 13 C NMR spectroscopic data and second harmonic generation values accounts for an electronic interaction between the counterions and π delocalized electronic system on the chromophore.

Organometallic compounds for non-linear optics: Synthesis, reactivity and electrochemistry of chiral η5-monocyclopentadienyl(nitrile)iron complexes

Abstract A new family of compounds of general formula [FeCp ((+)-DIOP)(p-NCC6H4R′)][PF6] (R′ = donor or acceptor group) was synthesized and characterized for non-linear optical properties. Spectroscopic (IR and 1H 13C and 31P NMR) and electrochemical (cyclic voltammetry) studies are consistent with charge-transfer from FeII to coordinated benzonitrile via d-π* back donation. One compound of this family, [FeCp((+)-DIOP)(p-NCC6H4NO2)][PF6] has an SHG value 38 times greater than that of urea.

Enthalpies of formation of cis-azobenzene and trans-azobenzene

The standard ( p ° = 0.1 MPa) molar enthalpy of formation of crystalline trans -azobenzene was determined from its enthalpy of combustion in oxygen at 298.15 K measured by static-bomb calorimetry. The enthalpy of isomerization: Δ isom H ° m (cr, cis → trans )/(kJ · mol −1 ) = -(49.1 ± 1.0), was measured by reaction-solution calorimetry: the isomerization was catalysed by dicyclopentadienyltitanium diiodide in toluene solution. The enthalpy of isomerization in heptane solution: Δ isom H ° m ( trans → cis )/(kJ · mol −1 ) = -(48.9 ± 2.3) when coupled with the enthalpies of solution of the two forms in heptane confirmed the reaction-solution calorimetric value. For the crystalline solids:Δ f H ∘ m ( trans -azobenzene, cr)/(k/J · mol -1 ) = (308.6 ± 1.9),Δ f H ∘ m ( cis -azobenzene, cr)/(k/J · mol -1 ) = (357.7 ± 2.1) The enthalpy of sublimation of trans -azobenzene was determined from the variation of vapour pressure with temperature measured by the Knudsen method: Δ g cr H ° m ( trans -azobenzene)/ (kJ · mol −1 ) = (93.6±1.9).

Thermochemistry of M(η5-C5H5)2Ln complexes (M = Ti, Mo, W)

Abstract The available thermochemical data for the title compounds are summarized and discussed. Metal—ligand bond enthalpies are derived for a variety of ligands through a simple method that involves both the experimental standard enthalpies of formation and theoretical calculations. It is suggested that this method may be used to predict the energetics of new complexes with fair accuracy. In addition, the method provides estimates of meta—ligand stepwise bond dissociation enthalpies. Some of these estimates are compared with recent experimental results obtained for bis (pentamethylcyclopentadienyl) titanium complexes.

Nitrile complexes of dicyclopentadienyl-molybdenum and -tungsten: preparation and reactivity. The structure of di-η5-cyclopentadienyliodoacetonitrile-molybdenum(IV) hexafluorophosphate, [Mo(η5-C5H5)2I(NCCH3)][PF6]

Abstract New complexes of the type [MCp2X(NCR)][PF6] (M = Mo, W; X = SR, halides; R = Me, Et, Ph) have been prepared from [MCp2X2] and TlPF6, NOPF6 or [FeCp2][PF6], in nitrile solvents. Some reactions of these cations with nucleophiles [L] have been studied. With L = PR3 or CO, the complexes [MCp2(SR)L]+ (R = Me, Ph) are formed. [MoCp2(SPh)(NCMe)]+ reacts with NaBH4 to give [MoCp2(SPh)H] and with acetone to give [MoCp2{S(Ph)C(Me)2O}]+. The W complexes [WCp2X(NCR)]+ add NHR′2 to give amidine complexes [WCp2X{HNC(R)Nr′2}]+ (X = SPh, Br). The mode of coordination of the nitriles to the [MoCp2Cl]+ fragment has been studied by EHMO calculations. The molecular structure of [MoCp2I(NCMe)][PF6] has been determined. The crystals are triclinic, space group P 1 , a 7.7989(6), b 10.3044(8), c 10.5565(5) A, α 96.218(4), β 94.466(4), γ 102.697(5)°, V 818.21 A3, Z = 2. The cation has the usual bent bis-metallocene structure, and within this family of complexes is the first reported example of a complex containing a MoI bond.

Estimation of standard enthalpies of formation of crystalline inorganic and organometallic complexes

Abstract Good linear correlations have been found between standard enthalpies of formation of crystalline inorganic and organometallic complexes MXnLm and enthalpies of formation of ligands L or LH in their standard reference state. These correlations may be used to estimate enthalpies of formation of new complexes.