Synthesis and ethylene trimerisation capability of new chromium(ii) and chromium(iii) heteroscorpionate complexes

Abstract

Reaction of (Me(2)pz)(2)CHSiMe(2)N(H)R (R = (i)Pr or Ph) or (Me(2)pz)(2)CHSiMe(2)NMe(2) with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(3) (R(1) = H, R(2) = (i)Pr (10) or Ph (11); R(1) = R(2) = Me (15)) or Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(2)(THF) (R(1) = H, R(2) = (i)Pr (12) or Ph (13); R(1) = R(2) = Me (16)), respectively. Compounds 10 and 11 were crystallographically characterized and the magnetic behaviour of all the new compounds was evaluated using SQUID magnetometry. Reaction of CrCl(3)(THF)(3) with Li{C(Me(2)pz)(3)}(THF) gave the zwitterionic complex Cr{C(Me(2)pz)(3)}Cl(2)(THF) (17) containing an apical carbanion. Reaction of the analogous phenol-based ligand (Me(2)pz)(2)CHArOH (ArO = 2-O-3,5-C(6)H(2)(t)Bu(2)) with CrCl(3)(THF)(3) gave Cr{(Me(2)pz)(2)CHArOH}Cl(3) (19) whereas the corresponding reaction with CrCl(2)(THF)(2) unexpectedly gave the Cr(III) phenolate derivative Cr{(Me(2)pz)(2)CHArO}Cl(2)(THF) (20) which could also be prepared from CrCl(3)(THF)(3) and the sodiated ligand [Na{(Me(2)pz)(2)CHArO}(THF)](2). Reaction of the corresponding ether (Me(2)pz)(2)CHArOMe with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHArOMe}Cl(3) (23) and Cr{(Me(2)pz)(2)CHArOMe}Cl(2)(THF) (24), respectively. The catalytic performance in ethylene oligomerisation/polymerisation of all of the new Cr(II) and Cr(III) complexes was evaluated. Most of the complexes showed high activity, but produced a Schultz-Flory distribution of alpha-olefins. Compound 23 had an exceptionally low alpha-value of 0.37 and showed a preference for 1-hexene and 1-octene formation. While replacing a secondary amine (10-13) for a tertiary amine (15-16) resulted in loss of catalytic activity, replacing a phenol (19) for an anisole (23) group afforded a more selective and more active catalyst. Changing from MAO to DIBAL-O as cocatalyst induced a switch in selectivity to ethylene polymerisation.

Rapid Synthesis of a Functional Resin‐Supported Scorpionate and Its Copper(I, II), Rhodium(I), and Chromium(III) Complexes

“…This substitutional inertness of TpCr III centers is also supported by similarly slow and confirmed single chloro ligand‐substitution reaction for TpCrCl 3 – with pyridine. [19b] Two hours of reflux in acetonitrile/pyridine (17 % v/v pyridine) produced only the single substitution product, TpCrCl 2 (py), an analytically pure and structurally characterized red‐violet solid. Interestingly, its visible spectrum (in CH 3 CN: λ max = 412 nm, 554 nm),[19b] is essentially the same as was measured here for ammoniated [BdTpCrCl 3 ]Na.…”

“…[19b] Two hours of reflux in acetonitrile/pyridine (17 % v/v pyridine) produced only the single substitution product, TpCrCl 2 (py), an analytically pure and structurally characterized red‐violet solid. Interestingly, its visible spectrum (in CH 3 CN: λ max = 412 nm, 554 nm),[19b] is essentially the same as was measured here for ammoniated [BdTpCrCl 3 ]Na. This strongly suggests that the purple ammoniated solid (Figure ) can be formulated as [BdPhTpCrCl 2 (NH 3 )](NaCl).…”

“…Consequently, rhodium(I) was chosen because of its demonstrated catalytic polymerization of phenylacetylene whose deep red‐orange color would provide a visual assay of the catalytic effectiveness of the supported metal system. Chromium(III) was chosen, because the general substitutional inertness of this d 3 metal ion provided a robust first‐row metal ion platform for confirmatory ligand‐substitution reactions . Finally copper(I and II) were chosen because of the activity of Tp R Cu I toward binding small molecules with spectroscopic handles (e.g.…”

Oligomerization of Olefins

“…to produce the corresponding cationic dinuclear Cr(II) complex and Me 2 AlX adduct of Cr(III)Cl 2 Me complex (Scheme 5.6i). Duchateau and Mountford also studied Cr catalysts with various heteroscorpionate ligand, including bis(pyrazolyl)methane with pendant secondary and tertiary amine donors as well as phenol and phenyl ether donors [104]. Most of the complexes show improved activity compared to the complex with tris(pyrazolyl)methane ligand (up to 3,250 g (mmol Cr) -1 h -1 ).…”

Synthesis of Bis(benzotriazol-1-yl)methane Derivatives by Cobalt-Catalyzed Formation of C-C Bonds

“…A reaction mechanism was subsequently proposed [2,3], indicating the crucial role of the coordination of the metal centre to the free nitrogen atoms for the activation of the N-C(O) bonds in the bis(pyrazol-1-yl)methanone skeleton. The synthetic approach was then extended by other research groups to functionalized aldehydes [4][5][6][7][8], with the aim of preparing pyrazole-based ligands to be applied in coordination [9][10][11][12][13][14][15][16][17], bioinorganic [18][19][20][21], organometallic chemistry and homogeneous catalysis [22][23][24][25][26][27][28].…”