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New compounds of the general formulas [M(Ar-BIAN)(2)]BF(4) and [M(Ar-BIAN)(NCMe)(2)]BF(4), where M=Cu(1) or Ag(1) and Ar-BIAN = bis(aryl)acenaphthenequinonediimine, were synthesized by the direct reaction of [Cu(NCMe)(4)]BF(4) or [Ag(NCMe)(4)]BF(4) with the corresponding Ar-BIAN ligand in dried CH(2)Cl(2). The synthesized compounds are [M(o, d, p-Me(3)C(6)H(2)-BIAN)(2)]BF(4) where M = Cu(1) (1) and Ag(1) (2), [M(o,d-iPr(2)C(6)H(3)-BIAN)(NCMe)(2)]BF(4) where M = Cu(1) (3) and Ag(1) (4), and [Ag(o,d-iPr(2)C(6)H(3)-BIAN)(2)]BF(4) (5). The crystal structures of compounds 1-3 and 5 were solved by singlecrystal X-ray diffraction. In all cases copper(I) or silver(I) are in a distorted tetrahedron that is constructed from the four nitrogen atoms of the two a-diimine ligands or, in 3, from one a-diimine ligand and two acetonitrile molecules. All compounds were characterized by elemental analyses, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and IR, UV-vis, and (1)H NMR spectroscopy. The analysis of the molecular geometry and the energetic changes for the formation reactions of the complexes, in a CH(2)Cl(2) solution, were evaluated by density functional theory calculations and compared with the experimental results.

The reactivity of mono-substituted HC=CR (R =Ph. a; CH2OH, b; CH2CH2CH2CH3, c) and di-substituted RC=CR (R = CH2CH3, d; CO2CH3, e; Ph. f) acetylenes was studied in supercritical carbon dioxide (scCO(2)) using the easily available complex CpCo(CO)(2) as catalyst. The reaction of phenylacetylene produced a mixture of the isomeric cyclotrimers 1,3,5- (2a) and 1.2,4-triphenylbenzene (2a '). in a 1:5 ratio, and traces of cobaltcyclopentadienone complexes CPCO(eta (4)-C4H2[Ph](2)CO) (6a, mixture of isomers). The possible product formed by the incorporation of CO, to alkynes, i.e. diphenylpyrone (7a) was not observed. The reaction of the cobaltacyclopentadiene complex CpCo(1.4-sigma -C-4[Ph](4))(PPh)(3) (8f), in scCO(2), was performed. No insertion of CO2 into the Co-C a-bond to form tetraphenylpyrone (7f) by reductive elimination was observed, instead the cobaItcyclobutadiene Complex CpCo(eta (4)-C-4[Ph](4)) (9f) was formed. In the reactions with other alkynes, lower yields were obtained in general, except in the cyclotrimerisation of the highly activated alkyne, propargyl alcohol (b). Reaction of the non-activated alkynes, 1-hexyne (c) and 3-hexyne (d), produced complex mixtures of cobalt complexes in low yield in which the alkyne was coordinated to cobalt. Finally, the highly hindered diphenylacetylene (f) gave a mixture of the known Complexes CpCo(eta (4)-C-4[Ph](4)) (9f) and CpCo(eta (4)- C-4[Ph](4)CO) (6f) in agreement with the results observed in conventional organic solvents. (C) 2001 Elsevier Science B.V, All rights reserved.

The deactivation reaction of the [CoCp(1,4-sigma-C(4)-[Ph](4))PPh(3)] catalyst for the cyclotrimerization of acetylenes has been kinetico-mechanistically studied under different temperature, pressure, and solvent conditions. The results indicate a dramatic change in mechanism from conventional to ionic liquid solvents due to the polarity of the medium.

The donor strengths of the following triarylphosphine ligands P(Ar)(2)(Ar') (Ar = Ar' = 4-Me3SiC6H4, 1b; 4-Me3CC6H4, 1d; 4-F3CC6H4, 1e; Ar = C6H5, Ar' = 4-Me3SiC6H4, 1c) have been evaluated experimentally and theoretically. The measurements of the J(P-Se) coupling constants of the corresponding synthesised selenides Se=P(Ar)(2)(Ar'), 2b, c and the DFT calculation of the energies of the phosphine lone-pair ( HOMO) reveal insignificant influence on the electronic properties of the substituted phosphines when the trimethylsilyl group is attached to the aryl ring, in marked contrast to the strong electronic effect of the trifluoromethyl group. These triarylphosphine ligands P(Ar)(2)(Ar') reacted with (eta(5)-C5H5)Co(CO)(2), (eta(5)-C5H5)Co(CO)I-2 or PdCl2 to yield the new compounds (eta(5)-C5H5)Co(CO)[P(Ar)(2)(Ar')], 3b, d; (eta(5)-C5H5)COI[P(Ar)(2)(Ar')], 4b-e; and PdCl2[P(Ar)(2)(Ar')](2), 5b, c, respectively. These complexes have been characterized and their spectroscopic properties compared with those reported for the known triphenylphosphine complexes. Again, the contrast of the P-31 NMR and C-13 NMR chemical shifts or C-O or M-Cl stretching frequencies, when applied, does not show an important electronic effect on the metal complex of the trimethylsilyl substituted phosphines with respect to P(C6H5)(3) derivatives. Solubility measurements of complexes 3a and 3b in scCO(2) were performed. We conclude that Me3Si groups on the triarylphosphine improve the solubility of the corresponding metal complex in scCO(2).

The electrochemical behavior of the species [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I] and [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+) in ACN solutions, at 25 degrees C, is described. The kinetic analysis of the cyclic voltammetry curves indicates that the introduction of one electron in the former complex is concerted with the dissociation of the Co-I bond. The ensuing radical undergoes fast solvation to yield the solvato complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](.), which then acts as an efficient electron donor toward the starting material with the formation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+); finally, the cation is electroreduced at the working potentials to conclude an overall autocatalytic sequence. The solvato complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](.), formed as a product of the above reduction process, can be reversibly reduced to the corresponding anion at more negative potentials. Confirmation of the above mechanism and of the fact that the solvato complex can act as a solution electron donor toward the starting material was obtained by studying the electrochemical behavior of the solvato complex itself and through calculations aimed to better define the dissociative electron-transfer process to [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I]. The dissociation of the metal-halide bond in the neutral complex [Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)I], with the formation of[Co(eta(5)-C5H5)(eta(3)-2-MeC3H4)(ACN)](+), was also found to occur spontaneously, in the bulk, through the observation of a progressive change of the cyclic voltammetric pattern. Support for the occurrence of the reaction between the starting complex and the solvent was confirmed by conductivity and spectroscopic measurements, which allowed the rate constant for the homogeneous solvolysis to be determined.

Rhodium complexes modified by simple trialkylphosphines can be used to carry out homogeneous hydroformylation in supercritical carbon dioxide (scCO(2)). The catalyst derived from PEt3 is more active and slightly more selective for the linear products in scCO2 than in toluene, and under the same reaction conditions [100degreesC, 40 bar of CO/H-2 (1:1)] P(OPri)(3) is also an effective ligand giving good catalyst solubility and activity. Other ligands such as PPh3, POct(3), PCy3, and P(4-C6H4But)(3) are less effective because of the low solubility of their rhodium complexes in scCO(2). P(4-C6H4SiMe3)(n) Ph3-n (n = 3 or 1) and P(OPh)(3) impart activity despite their complexes only being poorly soluble in scCO(2). Under subcritical conditions, using PEt3 as the ligand, C7-alcohols from hydrogenation of the first formed aldehydes are the main products whilst above a total pressure of 200 bar, where the solution remains supercritical (monophasic) throughout the reaction, aldehydes are obtained with 97% selectivity. High pressure IR studies in scCO(2) using PEt3 as the ligand are reported.