Chromium complexes bearing disubstituted organophosphate ligands and their use in ethylene polymerization

The crystal structures of three unusual chromium organophosphate complexes have been determined, namely, bis(μ‐butyl 2,6‐di‐ tert ‐butyl‐4‐methylphenyl hydrogen phosphato‐κ O :κ O ′)di‐μ‐hydroxido‐bis[(butyl 2,6‐di‐ tert ‐butyl‐4‐methylphenyl hydrogen phosphato‐κ O )(butyl 2,6‐di‐ tert ‐butyl‐4‐methylphenyl phosphato‐κ O )chromium]( Cr — Cr ) heptane disolvate or {Cr 2 (μ 2 ‐OH) 2 [μ 2 ‐PO 2 (OBu)(O‐2,6‐ t Bu 2 ‐4‐MeC 6 H 2 )‐κ O :κ O ′] 2 [PO 2 (OBu)(O‐2,6‐ t Bu 2 ‐4‐MeC 6 H 2 )‐κ O ] 2 [HOPO(OBu)(O‐2,6‐ t Bu 2 ‐4‐MeC 6 H 2 )‐κ O ] 2 }·2C 7 H 16 , [Cr 2 (C 19 H 32 O 4 P) 4 (C 19 H 33 O 4 P) 2 (OH) 2 ]·2C 7 H 16 , denoted ( 1 )·2(heptane), [μ‐bis(2,6‐diisopropylphenyl) phosphato‐1κ O :2κ O ′]bis[bis(2,6‐diisopropylphenyl) phosphato]‐1κ O ,2κ O ‐chlorido‐2κ Cl ‐triethanol‐1κ 2 O ,2κ O ‐di‐μ‐ethanolato‐1κ 2 O :2κ 2 O ‐dichromium( Cr — Cr ) ethanol monosolvate or {Cr 2 (μ 2 ‐OEt) 2 [μ 2 ‐PO 2 (O‐2,6‐ i Pr 2 ‐C 6 H 3 ) 2 ‐κ O :κ O ′][PO 2 (O‐2,6‐ i Pr 2 ‐C 6 H 3 ) 2 ‐κ O ] 2 Cl(EtOH) 3 }·EtOH, [Cr 2 (C 2 H 5 O) 2 (C 24 H 34 O 4 P) 3 Cl(C 2 H 6 O) 3 ]·C 2 H 6 O, denoted ( 2 )·EtOH, and di‐μ‐ethanolato‐1κ 2 O :2κ 2 O ‐bis{[bis(2,6‐diisopropylphenyl) hydrogen phosphato‐κ O ][bis(2,6‐diisopropylphenyl) phosphato‐κ O ]chlorido(ethanol‐κ O )chromium}( Cr — Cr ) benzene disolvate or {Cr 2 (μ 2 ‐OEt) 2 [PO 2 (O‐2,6‐ i Pr 2 ‐C 6 H 3 ) 2 ‐κ O ] 2 [HOPO(O‐2,6‐ i Pr 2 ‐C 6 H 3 ) 2 ‐κ O ] 2 Cl 2 (EtOH) 2 }·2C 6 H 6 , [Cr 2 (C 2 H 5 O) 2 (C 24 H 34 O 4 P) 2 (C 24 H 35 O 4 P) 2 Cl 2 (C 2 H 6 O) 2 ]·2C 6 H 6 , denoted ( 3 )·2C 6 H 6 . Complexes ( 1 )–( 3 ) have been synthesized by an exchange reaction between the in‐situ ‐generated corresponding lithium or potassium disubstituted phosphates with CrCl 3 (H 2 O) 6 in ethanol. The subsequent crystallization of ( 1 ) from heptane, ( 2 ) from ethanol and ( 3 ) from an ethanol/benzene mixture allowed us to obtain crystals of ( 1 )·2(heptane), ( 2 )·EtOH and ( 3 )·2C 6 H 6 , whose structures have the monoclinic P 2 1 , orthorhombic P 2 1 2 1 2 1 and triclinic P space groups, respectively. All three complexes have binuclear cores with a single Cr—Cr bond, i.e. Cr 2 O 6 P 2 in ( 1 ), Cr 2 PO 4 in ( 2 ) and Cr 2 O 2 in ( 3 ), where the Cr atoms are in distorted octahedral environments, formally having 16 ē per Cr atom. The complexes have bridging ligands μ 2 ‐OH in ( 1 ) or μ 2 ‐OEt in ( 2 ) and ( 3 ). The organophosphate ligands demonstrate terminal κ O coordination modes in ( 1 )–( 3 ) and bridging μ 2 ‐κ O :κ O ′ coordination modes in ( 1 ) and ( 2 ). All the complexes exhibit hydrogen bonding: two intramolecular O phos …H—O phos interactions in ( 1 ) and ( 3 ) form two {H[PO 2 (O R ) 2 ] 2 } associates; two intramolecular Cl…H—O Et hydrogen bonds additionally stabilize the Cr 2 O 2 core in ( 3 ); two intramolecular O phos …H—O Et interactions and two O…H—O intermolecular hydrogen bonds with a noncoordinating ethanol molecule are observed in ( 2 )·EtOH. The presence of both basic ligands (OH − or OEt − ) and acidic [H(phosphate) 2 ] − associates at the same metal centres in ( 1 ) and ( 3 ) is rather unusual. Complexes may serve as precatalysts for ethylene polymerization under mild conditions, providing polyethylene with a small amount of short‐chain branching. The formation of a small amount of α‐olefins has been detected in this reaction.