Cristina G. de Azevedo

Nucleophilic and electrophilic reactions of C5 cyclo-polyenes coordinated to the [CpMoL2]n+ fragment (n = 1,2; L = 1/2dppe, PMe3, P(OMe)3, CO)

Abstract Reaction of several nucleophiles (R−) with the dications [Cp2MoL2]2+ (L = CO, PMe3, dppe) produces the cyclopentadiene complexes [CpMo(η4-C5H5R)L2]+ (L = dppe, R = H, CH3, CH2CN, CH2PPh3, SMe; L = CO, R = H, CH3, SPh, PMe3; L = PMe3, R = H). Excess nucleophiles only produces regio and stereospecific double addition to one Cp ring in the case of H− forming CpMo(η3-C5H7)L2 (L = CO, PMe3, dppe). [CpMo(η4-C5H6)L2]+ reacts with LiCuMe2 to give CpMo(η3-C5H6Me)L2 (L = dppe, CO) and [Cp′Mo(η4-C5H6)(CO)2]+ reacts with NaSPh and PMe3 to give Cp′Mo(η3-C5H6SPh)(CO)2 (Cp′ = Cp, indenyl) and [CpMo(η3-C5H6PMe3)(CO)2]BF4 respectively. The structure of the exclusively formed conformers endo-[CpMo(η4-C5H6)(dppe)]PF6 and endo-CpMo(η3-C5H7)(dppe) was determined by NMR and X-ray crystallography and analyzed by EHMO calculations. The reverse H− abstractions from [CpMo(η4-C5H6)L2]+ and CpMo(η3-C5H7)L2 with Ph3C+ are specific in all cases except for CpMo(η3C5H7)(dppe) which gives oxidative decomposition to [Cp2Mo(dppe)]2− and [CpMo(dppe)2]2+. All the complexes [CpMo(η4-C5H5R)L2]+ and CpMo(η3-C5H7)L2 (L = CO1, PMe3, dppe) as well as their C6 ring congeners [CpMo(η4-C6H8)(CO)2]+ and CpMo(η3-C6H9)(CO)2 have irreversible cyclovoltammograms. Nucleophilic attacks of Me3NO/NCMe and PMe3 to [CpMo(η4-C6H8)(CO)2]+ gave [CpMo(η4-C6H8)(NCMe)2]BF4 and [CpMo(η3-C6H8PMe3)(CO)2]BF4 respectively. Both were crystallographically characterized.

Molecular structure, bonding, and reactions of Mo(η5-C5H5)2 derivatives containing phosphorus ligands. Crystal structures of [Mo(η5-C5H5)2H(PPh3)]I · 12H2O and [Mo(η5-C5H5)2(CH3)(PPh3)][PF6]

Abstract The oxidative addition reactions of [Mo(η5-C5H5)2(PPh3)], prepared by deprotonation of [Mo(η5-C5H5)2H(PPh3)][PF6] with HCl, CH3I, (CH3)3SiCl and (C2H5)2S2 are described. Two of the complexes obtained have been characterized by single crystal X-ray diffraction studies, viz: [Mo(η2-C5H5)2H(PPh3)]I.1/2H2O (1a) and [Mo(η5-C5H5)2(CH3)(PPh3)][PF6] (3). In complex 1a, the MoH and MoP bond lengths are 1.74(8) and 2.501(4) A, and the HMoP angle is 77(2)°, while in complex 3 the MoC and MoP bond lengths are 2.269(7) and 2.526(4) A and the CMoP angle is 84.1(2)°. Molecular orbital and steric energy calculations have been carried out for some model complexes in order to throw light on their geometrical preferences and to evaluate the influence of a bulky ligand in association with a small hydride on the overall geometry of the molecule.

Amido- and imido-ethylpyridine titanium complexes. Crystal structure of {Ti[NCH2CH2py]Cl2(THF)}2

Abstract Compounds of general formula N(R 1 )(R 2 )CH 2 CH 2 py (py=C 5 H 4 N; R 1 =R 2 =SiMe 3 , 1a ; R 1 =H, R 2 =Si t BuMe 2 , 1b ; R 1 =SiMe 3 , R 2 =Si t BuMe 2 , 1c ; R 1 =SiMe 3 , R 2 =Ph, 5 ) were synthesised. They readily reacted with TiCl 4 to afford the corresponding amidoaminotrichlorides {Ti[N(R 2 )(CH 2 CH 2 py)]Cl 3 } (R 2 =SiMe 3 , 2a ; R 2 =Si t BuMe 2 , 2b ; R 2 =Ph, 6 ). The related imido derivatives {Ti[N(CH 2 CH 2 py)]Cl 2 } n ( 3b ) and {Ti[N(CH 2 CH 2 py)](L)Cl 2 } 2 (L=THF, 3c ; PMe 3 , 3d ) were isolated upon heating and reaction with L, respectively. Reaction of 6 with THF afforded the corresponding adduct, {Ti[N(Ph)(CH 2 CH 2 py)](THF)Cl 3 } ( 7 ). Compound 3b reacted with LiNMe 2 to give asymmetrical {Ti 2 [N(CH 2 CH 2 py)][N(CH 2 CH 2 py)]′Cl 4 } ( 4a ). Compound {CpTi[N(CH 2 CH 2 py)]Cl} n ( 4b ), was formed when 3b reacted with NaCp. Analogous studies with 2a and 6 led to Cp 2 TiCl 2 . {Cp 2 Ti 2 [μ-N(Ph)]Cl 2 } ( 8 ) was isolated as the product of CpTiCl 3 and Na[N(Ph)CH 2 CH 2 py]. The molecular structure of 3c was determined by X-ray single crystal diffraction.

Studies on molybdenocene derivatives: Reactions of [Cp2Mo(η2-NCMe)] and preparation of alkyl hydride complexes. Crystal structure of [Cp2Mo(PMe3)]

Abstract Reaction of [Cp 2 Mo(η 2 -NCMe)] ( 1 ) with PMe 3 affords [CP 2 Mo(PMe 3 )] ( 2 ), which is readily alkylated go give [Cp 2 MoR(PMe 3 )]PF 6 ( 3a , R = Me; 3b , R = Et). The crystal structure of 2 shows tricoordination around the Mo atom. Cyclic voltammetry of 3a and 3b and the analogues [Cp 2 MoR(CNMe)]I, ( 4a , R = Me; 4b , R = Et) and [Cp 2 MoMe(PPh 3 )]PF 6 ( 7 ) shows one reversible one-electron oxidation, but the potential is independent of R, in contrast to the complexes [Cp 2 MoR 2 ]. Oxidative addition of Et 2 S 2 , Ph 2 Se 2 or (PhCOO) 2 to 1 yields [Cp 2 Mo(ER) 2 ] (E = O, S or Se). The molybdenocene alkyl hydrides [Cp 2 Mo(H)Me] ( 5 ) and [Cp 2 MoH(CH 2 PPh 3 )]I·THF ( 6 ) are prepared from [Cp 2 MoHI]. Thermal decomposition of 6 as well as reaction Of [Cp 2 MoMe 2 ] + with Ph 3 C . provide evidence for transient formation of the methylidene complex [Cp 2 MoH(CH 2 )] + .

Zirconium indenylamido complexes: synthesis and reactivity: Crystal structure of [Zr(Ind)2(NC3H6)2]

Abstract Reactions of [ZrInd(NMe2)3] (1) with Me3SiCl afforded [ZrInd(NMe2)2Cl] (2), [ZrInd(NMe2)Cl2] (3) and [ZrIndCl3]n (4) in high yields (≥90%). [ZrIndCl3(dme)] (5) was obtained either from 4 and dme or by a one-pot reaction from [ZrInd(NMe2)3], Me3SiCl and dme. Treatment of [ZrInd(NMe2)2Cl] with LiMe gave [ZrInd(NMe2)2Me] (6), and in similar reaction conditions [ZrInd2Me2] (10) was obtained from [ZrInd(NMe2)Cl2]. Whereas the reaction of 2 with LiN(H)tBu produced {[ZrInd(NMe2)2[N(H)tBu]} (7), the addition of LiN(H)tBu to [TiInd(NMe2)2Cl] afforded [Ti(NMe2)2(μ-NtBu)]2 (9) in quantitative yield. {TiInd(NMe2)2[N(H)tBu]} was identified by NMR as an intermediate in the synthesis of 9, and two isomeric forms corresponding to the parallel (8a) and perpendicular (8b) orientations of the indenyl and N(H)tBu ligands were characterised. The addition of an excess of azetidine to 1 gave [ZrInd2(NC3H6)2] (11), the molecular structure of which was determined by X-ray crystallography. Preliminary studies showed that 3–methylaluminoxane (MAO) polymerises ethylene and propylene, whereas [TiInd(NMe2)Cl2], 12–MAO, only polymerises ethylene.

Binding of vanadium to human serum transferrin - voltammetric and spectrometric studies

Previous studies generally agree that in the blood serum vanadium is transported mainly by human serum transferrin (hTF). In this work through the combined use of electrochemical techniques, matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry and small-angle X-ray scattering (SAXS) data it is confirmed that both VIV and VV bind to apo-hTF and holo-hTF. The electrochemical behavior of solutions containing vanadate(V) solutions at pH=7.0, analyzed by using two different voltammetric techniques, with different time windows, at a mercury electrode, Differential Pulse Polarography (DPP) and Cyclic Voltammetry (CV), is consistent with a stepwise reduction of VV→VIV and VIV→VII. Globally the voltammetric data are consistent with the formation of 2:1 complexes in the case of the system VV-apo-hTF and both 1:1 and 2:1 complexes in the case of VV-holo-hTF; the corresponding conditional formation constants were estimated. MALDI-TOF mass spectrometric data carried out with samples of VIVOSO4 and apo-hTF and of NH4VVO3 with both apo-hTF and holo-hTF with V:hTF ratios of 3:1 are consistent with the binding of vanadium to the proteins. Additionally the SAXS data suggest that both VIVOSO4 and NaVVO3 can effectively interact with human apo-transferrin, but for holo-hTF no clear evidence was obtained supporting the existence or the absence of protein-ligand interactions. This latter data suggest that the conformation of holo-hTF does not change in the presence of either VIVOSO4 or NH4VVO3. Therefore, it is anticipated that VIV or VV bound to holo-hTF may be efficiently up-taken by the cells through receptor-mediated endocytosis of hTF.

Titanium indenyldimethylamido complexes: synthesis, characterisation and theoretical calculations. Crystal structure of [Ti(η5-Ind)(NMe2)Cl2]

Reactions of Ti(Ind)Cl3, 1, with LiNMe2 afforded the corresponding titanium indenyldimethylamido complexes Ti(Ind)(NMe2)Cl2, 2, Ti(Ind)(NMe2)2Cl, 3, and Ti(Ind)(NMe2)3, 4, depending on the reaction conditions. Treatment of 2 and 3 with LiMe yielded Ti(Ind)(NMe2)Me2, 5, and Ti(Ind)(NMe2)2Me, 6, respectively. Chloride metathesis reactions of Ti(Ind)(NMe2)2Cl with Me3SiCH2MgCl, LiCCPh and LiCCSiMe3 gave Ti(Ind)(NMe2)2(CH2SiMe3), 7, Ti(Ind)(NMe2)2(CCPh), 8 and Ti(Ind)(NMe2)2(CCSiMe3), 9. The solid-state molecular structure of 2 was determined. 1H and 13C NMR data and DFT calculations (full geometry optimisations) showed that the indenyl ring remains approximately planar and exhibits an η5 co-ordination mode in all the complexes. The amido groups have a preference for binding in the way that favours π bonding to the titanium. Even in the trisamido complex the indenyl remains η5, π bonding to the ring being preferred to that from the amides.