Preparation and Characterization of a Reduced Chromium Complex via Vinyl Oxidative Coupling: Formation of a Self-Activating Catalyst for Selective Ethylene Trimerization

Abstract

Reaction of the divalent [(t-Bu)NP(Ph)(2)N(t-Bu)]CrCl(2)Li(THF)(2) (1) with 1 equiv of vinyl Grignard (CH(2)=CH)MgCl reproducibly afforded the triangulo {π-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr}(2)(μ,μ',η(4),η(4)'-C(4)H(4)){σ-[(t-Bu)N-P(Ph)(2)-N(t-Bu)]Cr} (2) containing a σ-/π-bonded butadiene-diyl unit. The diene-diyl moiety was generated by an oxidative coupling and deprotonation of two vinyl anions. The crystal structure revealed that of the three chromium atoms, each bearing one NPN ligand, two are perpendicularly bonded to the two sides of the π-system of the butadiene-diyl residue in a sort of inverted sandwich type of structure. The third is instead coplanar with the doubly deprotonated C(4) unit and σ-bonded to the two terminal carbon atoms. Despite the appearance as a Cr(II)/Cr(I) mixed valence species, DFT calculations have revealed that the structure of 2 consists of three divalent chromium atoms, while the additional electron resides on the π-system of the bridging organic residue. Complex 2 behaves as a single component selective catalyst for ethylene trimerization.

Selective Ethylene Oligomerization with Chromium Complexes Bearing Pyridine–Phosphine Ligands: Influence of Ligand Structure on Catalytic Behavior

“…31 P NMR (400 MHz, CD 2 Cl 2 ) δ: 50.82 (s). 13 C NMR data were consistent with that reported in the literature.…”

“…31 P NMR (400 MHz, CDCl 3 ) δ: 40.38 (s). 13 PyN(Me)P i Pr 2 (3). Ligand 3 was synthesized similarly to ligand 1, using chlorodiisopropylphosphine (1.6 mL, 10 mmol).…”

“…31 P NMR (400 MHz, CD 2 Cl 2 ) δ: 71.13 (s). 13 PyCH 2 N(Me)PPh 2 (4). A 2.5 M hexane solution of n-BuLi (10 mmol, 4 mL) was added dropwise to a stirred diethyl ether solution (35 mL) of dipyridyl amine (1.7 g, 10 mmol) at −78°C.…”

The Origin of the MNXN Metallacycle Flexibility in the Chelate Iminophosphonamide and Amidinate Transition Metal Complexes

“…However, the chemistry of transition metal iminophosphonamides (NPN) that had been considered to be heteratomic analogs of the corresponding metal amidinates has been developing slowly. Nevertheless, in the last two decades transition metal iminophosphonamides have been reported as active catalysts for alkene polymerization (NiNPN, ZrNPN), 3,4‐selective polymerization of isoprene (rare earth NPN complexes), alkene oligomerization (CrNPN), ethene dimerization (NiNPN),[5c] cyclopropanation and aziridination (CuNPN), as well as for Tsuji–Trost cross‐coupling (PdN 2 P) Recently we have demonstrated that arene ruthenium iminophosphonamide [( p ‐cymene)RuCl{Ph 2 P(N‐ p Tol) 2 }] can efficiently reduce acetophenone under transfer hydrogenation conditions …”

Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra‐High‐Molecular Weight Polyethylene in the Absence of Activators

“…In related work, reaction of divalent Cr(II) complex [( t Bu)NP(Ph) 2 N( t Bu)]CrCl 2 Li(THF) with one equiv. of vinyl Grignard gave a mixed‐valence Cr(I)/Cr(II) butadiene‐diyl complex via a vinyl reductive coupling . Next, reactions of 2 with equimolar amounts of PhCH 2 K or CH 3 MgCl afforded complexes 5 and 6 in 46% and 60% isolated yields, respectively ( Scheme ).…”