Effect of Azide and Chloride Binding to Diamino-bis(phenolate) Chromium Complexes on CO₂/Cyclohexene Oxide Copolymerization

Abstract

The affinity for nucleophile (azide, N 3 − , and chloride, Cl − ) binding significantly influences the catalytic activity of chromium complexes for the copolymerization of cyclohexene oxide (CHO) and CO 2 . The binding of N 3 − and Cl − to two amino-bis(phenolate) Cr(III) chloride complexes [L1Cr(μ-Cl)] 2 (1) and [L2CrCl(THF)] (2•THF), where L1 = methoxyethylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenolate) and L2 = dimethylaminoethylamino-N,N-bis(2methylene-4,6-di-tert-butylphenolate), were studied by both matrix assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry (MALDI-TOF-MS and ESI-MS, respectively). Upon reaction with [PPN][N 3 ] ([PPN] = bis(triphenylphosphine)iminium), 1 exhibited greater ability to form six-coordinate bis-azide ions [L1Cr(N 3 ) 2 ] − and produced fewer five-coordinate species detected by MS than 2•THF. This corresponded to 2•THF having a significantly faster rate of polymerization with anionic nucleophile cocatalysts than 1. In the presence of 1 equiv of [PPN][N 3 ], 1 showed a slow reaction rate with an induction period of 20 min, whereas 2•THF showed a much faster reaction rate with no induction period. Also, 1 in the presence of 1 equiv of [PPN][Cl] showed faster copolymerization than in the presence of 2 equiv of [PPN][Cl]. The binding of chloride to 1 from addition of [PPN][Cl] was studied by UV−vis spectroscopy, which showed an equilibrium constant of 1.6 × 10 3 M −1 favoring the formation of [L1Cr(Cl) 2 ] − . The ring-opening process of CHO was observed in the mixture of 2•THF/CHO/[PPN][N 3 ] via ESI-MS. Combined with MALDI-TOF-MS of the polymer product obtained within the first 60 min, it was shown that N 3 − preferentially initiates ring-opening of the epoxide in CHO. Upon consumption of N 3− through generation of active polymer chains, the chloride originating from the metal complex can serve as initiator of epoxide ring-opening. This was confirmed by the occurrence of chloride-containing polymers later in the reaction. Taken together, these studies provide mechanistic insight into the copolymerization of CO 2 and epoxide by diamino-bis(phenolate) Cr(III) chloride complexes.

Chromium(III) and Chromium(II) Phenolate Complexes with Bulky Alkylcyclopentadienyl Ligands

“…1 The color changed to deep purple and stirring was continued for 48 h without further change of color.…”

“…Chromium(III) phenolate complexes have been employed in carbon dioxide copolymerization with cyclohexene oxide [1] or with oxetane [2] and in the copolymerization of carbonyl sulfide with epoxides. [3] One of the questions leading to the experiments described in this report is concerned with the oxocyclohexadienyl coordination mode of phenolates, which was among the structural motifs formed from phenolates and iron complexes.…”

Dichiral [4.4.3.01,5]tridecane copper(II) cluster derived from a tripodal ligand having unsymmetrical podands and the linker: Synthesis, structure, surface grafting and catalytic aspects

“…The solvent was removed under reduced pressure to afford a pale yellow solid. (C 14 ), 127.7 (C 21 ), 128.2 (C 12,16,20 ), 129.0 (C 13,15 ), 130.6 (C 22 ), 132.8 (C 5 ), 137.3 (C 11 ), 140.0 (C 23 ), 155.4 (C 1 ), 158.1 (C 19 (2) The tripodal ligand 2 (1.03 mmol, 0.50 g) and sodium methoxide (3.09 mmol, 0.17 g) were dissolved in methanol (50 ml). The solution was stirred for 10 min at room temperature.…”

“…Supporting information-Procedure for the preparation of magnetite nanoparticles (Fe 3 O 4 ), silica encapsulated magnetic nanocores (Fe 3 O 4 @SiO 2 ), aminofunctionalized silica magnetic nanocores (Fe 3 O 4 @SiO 2 / NH 2 ), ORTEP presentation of the asymmetric unit of 2, thermogravimetric analysis of catalyst, energy dispersive X-ray spectrum of (Fe 3 O 4 @SiO 2 /NH 2 ) elemental mapping data, catalytic recyclability data; FT-IR spectrum of the catalyst after the fourth cycle; PXRD data of catalyst after the fourth cycle; spectroscopic data (FT-IR, 1 H, 13…”

“…The most recent contribution of bisphenolate armed [4.4.3.0 1,5 ]tridecane metallatranes as reaction mediators includes copolymerization reactions of CO 2 and cyclohexene oxide, polymerization of methacrylate, hydrophosphination of alkenes, alkynes and heterocumulenes, ring-opening polymerization of L-lactic acid, o-carboxy anhydrides and L-lactide, epoxidation, sulfoxidation and catechol oxidation and cycloaddition of epoxides. [12][13][14][15][16][17][18][19][20][21][22][23][24] The metal centres of metallatrane catalysts are widely distributed among various elements, that is, s-block (K), p-block (Al), d-block (Ti, Zr, Zn, Cr, V, Mo, W) and f-block elements (Y, Yb, Nd, La, Sm). Although bisphenolate atranes of Fe(III), Co(III), Cu(II), Si(IV) and Sn(IV) are known; however, their use in catalysis is rarely reported.…”