New Iminophosphonamide Chromium(II) Complexes as Highly Active Polymer-Free Ethylene Oligomerization Catalysts

The reactions of the deprotonated form of cis -{[(μ-N)( t -Bu)] 2 PN(H)( o -OMeC 6 H 4 )] 2 } ( a ) with either CrCl 2 (THF) 2 or CrCl 3 (THF) 3 afforded the corresponding dimeric Cr(II) and monomeric Cr(III) complexes { cis- [(μ-N)( t -Bu)] 2 [PN( o -MeOC 6 H 4 )] 2 Cr} 2 ( 1a ) and cis- [(μ-N)( t -Bu)] 2 [PN-2-MeOC 6 H 4 ] 2 CrCl ( 2a ). By replacing the ligand’s o -OMeC 6 H 4 groups with less-crowded CH 2 CH 2 N( i -Pr) 2 functionalities and reacting the deprotonated form of cis -{[(μ-N)( t -Bu)] 2 [PN(H)CH 2 CH 2 N( i -Pr) 2 )] 2 } ( b ) with CrCl 2 (THF) 2, the dimetallic, divalent { cis- [(μ-N)( t -Bu)] 2 [PNCH 2 CH 2 N( i -Pr) 2 )] 2 Cr} 2 ( 1b ) was obtained in crystalline form. Upon activation with MAO, both 1a and 1b afforded highly active, polyethylene-free ethylene oligomerization catalysts. Complex 2a is instead catalytically inactive.