Novel Chromium (III) Complexes Containing Imidazole-Based Chelate Ligands with Varying Donor Sets: Synthesis and Reactivity

The syntheses and characterisation of tri- and bi-dentate coordinated chromium(III) and vanadium(III) complexes of the general composition [MCl3(N⁁D⁁N)], [MCl3(N⁁N)]2
{M = Cr, (N⁁D⁁N)
=
(mim)3COCH32a
[mim = 1-methylimidazolyl], (mim)2CHCH2PPh22b, (mim)2CHCH2C(O)But2c, (tBupim)3P 2d
[tBupim = 1-isopropyl-4-tert-butylimidazolyl], (N⁁N)
=
(mim)2CH23e, (mim)2CH2PPh23f, (mim)2CO 3g, (Bzmim)2CO 3h
[Bzmim = 1-methybenzimidazolyl], (tBupim)2CO 3i, (mim)2CNPh 3j; M = V: (N⁁D⁁N)
=
(mim)3COCH35a; (N⁁N)
=
(mim)2CO 5g}, [CrCl3(mim)3]
4k, and [CrCl3(MeTAM)]
6
(MeTAM = 1-methyltriacetylmethane) is described. Crystallisation of 3g from CH3CN/Et2O gave the mononuclear complex [CrCl3{(mim)2CO}(CH3CN)]
3g′. The molecular structure of 3g′ shows the chromium atom is quasi-octahedral, six-coordinate, the three coordinated chlorine atoms disposed mer in the coordination sphere. The electronic spectra of the chromium complexes exhibit d–d transitions typical of a pseudo-octahedral coordinated d3 ion, falling into the region ν14A2g
→
4T2g 600–700 nm and ν24A2g
→
4T1g(F) 430–470 nm, and 10Dq values between 14 400 and 16 700 cm−1. In the presence of MMAO the complexes give active catalyst systems for the conversion of ethylene into 1-alkenes or polymers, with activities and selectivities depending on the electronic and steric factors of the ligand system and the metal centre, respectively.

Synthesis, characterisation and catalytic behaviour of a novel class of chromium(III) and vanadium(III) complexes containing bi- and tri-dentate imidazole chelating ligands: a comparative study

Thermal and structural studies of amide complexes of transition metal(II) chlorides. I: Stoichiometry

Chromium(III)-pyrazole complexes. X-Ray crystal structures, 1H NMR investigation of ligand fluxional behavior and EPR studies

The thermal decomposition in air of several complexes of chromium(III) with imidazole,N-methylimidazole and 2-methylimidazole has been studied with the aid of differential thermal analysis (DTA), thermogravimetry (TG) and derivative thermogravimetry (DTG) in the temperature range 25–600°C. Although the final process of the decomposition gives Cr2O3, there are interesting differences in the complete process of decomposition. The reasons for these differences appear to be related to the trans-effect and to the presence in the imidazole complexes of hydrogen bonds. Enthalpies of the several decomposition reactions have been determined by differential thermal analysis.

M. Sánchez

Papers

Thermochemistry of some complexes of chromium(III) with imidazoles