Renata Dreos

Synthesis, molecular structure, and characterization in solution of a new series of inorganic and organometallic Co(III) Schiff base complexes

Abstract A new series of inorganic and organometallic cobalt Schiff base complexes containing the tetradentate ligand tmsalen (4,4′,7,7′, tetramethylsalen) have been synthesized. They have been characterized by 1H NMR and UV–Vis spectroscopy and by ESI MS spectrometry, both in coordinating and non-coordinating solvents. Two inorganic complexes [Co(tmsalen)(L)2]ClO4, where L=py (2) and N-MeIm (3), two dimeric organometallic derivatives [RCo(tmsalen)]2 (R=CH3 (4) and CH2CF3 (7)) and one organometallic penta-coordinated species (R=i-Pr (6)) have been structurally characterized. It is noteworthy that the formation of organometallic dimeric and penta-coordinated species occurs even if the synthesis is carried out in presence of py. Solution data confirm the strong tendency to the penta-coordination of the complexes containing the most electron-donating alkyl groups, which maintain penta-coordination even in methanol.

Evidence of the interaction between steric and electronic influence in rhodoximes and cobaloximes. Synthesis of pyRh(DH)2I and X-ray structure of pyRh(DH)2Cl, pyCo(DH)2Cl and pyRh(DH)2I

Abstract The crystal structure of pyRh(DH)2Cl (I) and pyCo(DH)2Cl (II) are reported together with the synthesis and the crystal structure of pyRh(DH)2I (III).I: RhClO4N5C13H19; a=7.5090(8), b=8.588(1), c=14.479(2) A; α=96.45(8), β=87.07(8), γ=76.12(9)°; triclinic P 1 ; Z=2; R=0.022. II: CoClO4N5C13H19; a=14.738(2), b=8.606(1), c=13.369(2) A; β=96.30(1)°; monoclinic Cc; Z=4; R=0.022. III: IRhO4N5C13H19; a=8.875(1), b=14.741(2), c=14.163(3) A; β=97.47(8)°; monoclinic P21/c; Z=4; R=0.031. The Rh-py distance of 2.046(1) A in I, compared to that of 2.079(3) A in III, indicates that I is a slightly better trans-influencing ligand than Cl. The difference in the M-py distances when X=Cl and i-pr is 0.18 A for M=Rh and 0.14 A for M=Co. This result suggests that the interaction between steric and electronic factors is reduced in rhodoximes, owing to the larger size of RhIII.

Diphenylborylated derivatives of organocobaloximes and organorhodoximes: Synthesis, spectroscopic and structural characterisation

Abstract A series of organometallic complexes derived by organocobaloximes and organorhodoximes in which either one or both the hydrogen bridges have been replaced by BPh 2 groups, RM(DH)(DBPh 2 ) N -MeIm and RM((DBPh 2 ) 2 N -MeIm, respectively, have been synthesised and characterised, both in solution and in solid state. 1 H NMR spectra show that they assume different interconverting conformations in solution. With increasing steric bulk of R, the axial phenyls of the BPh 2 group tend to face N -MeIm, forcing the latter in an orientation which is quite unusual in organocobaloximes and causing a lengthening of the Co-N bond. Some possible implications on the strength of the trans Co-C bond are discussed.

New organo-cobalt complexes derived from cobaloximes with one or two diphenylboron moieties in the oxime bridges

Abstract The reaction between methylcobaloxime [CH 3 Co(DH) 2 L] and diphenylborinic anhydride affords derivatives containing either one or two diphenylboron bridges, depending on the ratio of complex: diphenylborinic anhydride. The crystal structures of [CH 3 Co(DH)(DBPh 2 )( N -MeIm)] ( Ib ) and [CH 3 Co(DBPh 2 ) 2 CH 3 OH] ( IId ) show that in Ib the axial phenyl of the BPh 2 moiety faces the axial Me, while in IId the axial phenyls are “trans”. The preferred conformations of these complexes in solution, as inferred from NMR spectra, are analogous to those found in the solid state.

Steric effects in organometallic compounds. A 103Rh NMR study of alkylrhodoximes

Three series of alkylrhodoximes [Rh(Hdmg)2RL] (Hdmg = monoanion of dimethylglyoxime) (L  H2O, R  Me, Et, nPr, nBu, iBu, neoPent; L  py, R  Me, Et, nPr, iPr, nBu, iBu, sBu, tBu, neoPent, adam, CH2Cl, CH2 CH3; L  PPh3, R  Me, Et, nPr, iPr, nBu, iBu, tBu, neoPent, adam) were prepared and characterized by 1H, 13C and 31P NMR spectra; several of the reported compounds are new. The rhodium-103 chemical shifts were measured by (1H, 103Rh)-2D inverse correlation for the complexes with L  H2O and py and by (31P, 103Rh)-{1H}-2D inverse correlation for those with L  PPh3. Rh shielding decreases in the order Et > Me > nBu > i > sBu > neoPent > tBu. Discussion of the shift dependence on the various alkyl parameters allows us to conclude that, in these compounds the R ligand affects rhodium shielding mainly through distortions of the coordination site due to its bulk. The 1J[Rh,P] values reflect the rhodium-phosphine binding interaction.

Kinetics of transfer of coordinated carbanions from cobalt to mercury(II) in two families of model vitamin B12 compounds

Abstract Intermediates are revealed by kinetic studies on the transalkylation by mercury(II) of alkyl- and aryl-aquo-1,3-bis(diacetylmonoximeimino)propanatocobalt(III) mono cations and of alkylaquo- N , N ′-ethylenebis(salicylideneiminato)- cobalt(III).

Time-dependent density functional theory study of cobalt corrinoids: Electronically excited states of methylcobalamin

Time-dependent density functional theory (TDDFT) has been applied to the analysis of the electronic spectra of methylcobalamin (MeCbl) and its derivative in which the trans axial base was replaced by a water molecule (MeCbi[Single Bond]H(2)O). The latter corresponds to the situation encountered in strongly acidic solutions. The study primarily focuses on the accuracy of two functionals, the hybrid B3LYP and the gradient corrected BP86, in dealing with the electronic excitations. The high resolution crystal structure of MeCbl was the source of the initial coordinates. To generate the initial structures, the full MeCbl was simplified by replacing the corrin side chains by H atoms. The vertical excitation energies, together with the corresponding oscillator strengths, were calculated at the optimized BP86 and B3LYP structures of the ground electronic state of the complexes. The NBO analysis shows that the B3LYP functional gives a bonding description of the ground state as a more polarized covalent bond compared to that given by BP86. The latter functional has more covalent bonding and is thus more appropriate for modeling the axial bonding properties. To validate the accuracy of the present TDDFT analysis, the computed excitations were directly compared to the absorption spectra of MeCbl. In order to obtain a reliable agreement between experiment and theory, the two-parameter scaling technique was introduced, which compensates differently the low-energy and high-energy excitations. Electronic excitations strongly depend on the choice of the functional. Transitions involving corrin pi-->pi(*) excitations are better described by the B3LYP functional while transitions associated with metal-to-ligand (dpi-->pi(*)d) excitations are better described by BP86. These differences can be associated with the different bonding descriptions obtained by B3LYP and BP86.

Synthesis and structure of borylated organocobaloximes containing neutral nitrile ligands

Abstract The syntheses of the organometallic complexes RCo(DBPh2)2(MeCN), where R = Me (1), n-Pr (2), trans-β-styryl (β-Sty, 3), and MeCo (DBPh2)2TCNE (4) are described. The complexes were characterized by X-ray crystallography. Compound 1 is monoclinic, space group P2 1 /n, a = 9.081(2), b = 14.491(3), c = 14.178(3) A , β = 95.35(2)°, Z = 2, R = 0.053 compound 2 is monoclinic, space group P2 1 /a, a = 18.973(6), b = 9.369(2), c = 21.059(6) A , β = 106.65(2)°, Z = 4, R = 0.079 ; compound 3 is monoclinic, space group P2 1 /n, a = 15.130(2), b = 16.055(3), c = 15.591(3) A , β = 91.70(1)°, Z = 0.071 ; compound 4 is triclinic, space group P I , a = 15.390(6), b = 15.529(7), c = 18.038(7) A , α = 107.44(2)°, β = 103.54(2)°, γ = 101.19(2)°, Z = 4, R = 0.058 . Compound 1 is found to have an up-down conformation of the equatorial ligand, with one phenyl group facing the Me axial ligand and the other facing the axial MeCN ligand, whereas compounds 2–4 in the solid state show the down-down conformation, with the two axial phenyls of the equatorial ligand facing the neutral one. The present results sshow that the conformation adopted by these complexes is determined primarily by the difference in bulk between the axial ligands. When the bulk of R is similar to that of L. the π = π interactions become the conformational driving force.

Time-dependent density functional theory study of cobalt corrinoids: Electronically excited states of coenzyme B12

The analysis of the electronic spectra of adenosylcobalamin (AdoCbl) and its derivative in which the trans axial base was replaced by a water molecule (AdoCbi–H2O) has been performed by means of time-dependent density functional theory (TDDFT). The latter corresponds to the situation encountered in strongly acidic conditions. The TDDFT electronic transitions and oscillator strengths were calculated at the optimized B3LYP and BP86 ground state equilibrium geometries. A comparison of the orbital energy diagrams obtained with the B3LYP and BP86 functionals reveals a different orbital order and composition of the highest occupied and lowest unoccupied molecular orbitals. In B3LYP the lowest-energy transitions are of π∕d→π*, π∕d→σ*, and π∕d→d characters while in the case of BP86 they are mainly d∕π→π* and d→π*. The long range charge transfer transitions involving excitations from adenine π orbitals to antibonding corrin π* orbital can be observed at low energies, especially in BP86 results. Calculated electron...

Self-Assembly of Cobaloximes and Rhodoximes with 3-Aminophenylboronic Acid: A Molecular Triangle and a Polymer

The reactions of methylaquacobaloxime and ethylaquacobaloxime with 3-aminophenylboronic acid in water produce supramolecular triangles 3a and 3b respectively, through the reaction of boron with the oxime oxygens of the alkylcobaloxime and the coordination of pyridine to cobalt. The reaction is reversible and strongly pH dependent. The complexes 3a and 3b precipitate immediately from the solution at pH 7, but dissolve quickly at both acidic (below 4) and basic (above 9) pH values. The aggregates are re-formed by readjusting the pH to neutrality and the precipitation-dissolution cycle may be repeated several times without an apparent decrease in yield. The complexes were fully characterised by 1H and 13C NMR spectroscopy. The X-ray structure shows that the neutral chiral supramolecule 3a is a triangle of cobalt atoms with an approximate C3 symmetry. The side of the triangle is about 9.5 A. The ring closure is ensured by the torsion angles around the B−C and C−NH2 bonds, which vary in the range 25−30° and 97−109°, respectively. The reaction of methylaquarhodoxime with 3-aminophenylboronic acid in water at pH 7 results in the displacement of H2O by 3-aminophenylboronic acid only. The polymeric form 4 precipitates from CD3OD in the NMR tube with time. The X-ray structure shows that 4 is a polymeric species with a zig-zag chain arrangement, with Rh···Rh distances of 9.2 A. The chain arrangement is characterized by torsion angles around the B−C and C-NH2 bonds of 61° and 92°, respectively. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)