New Bulky Bis(amino)cyclodiphosph(III)azanes and Their Titanium(IV) Complexes:Synthesis,Structures and Ethene Polymerization Studies

摘要

Bis(amino)cyclodiphosph(III) azanes cis-[(RNH)(PN-tBu)]_2,R=2,6-iPr_2C_6H_3 (2),2-tBuC_6H_4 (3),2-CF_3C_6H_4 (4),2,5-tBu_2C_6H_3 (5),Ph_2CH (6),2,4-Me_2C_6H_3 (7),2,5-Et_2C_6H_3 (8),have been synthesized in the presence of Et_3N by a nucleophilic substitution reaction of cis-(CIPN-tBu)_2 (1) with the corresponding bulky aryl and alkylamines.The bis(amino)-cyclodiphosph(III)azanes 2-8 adopt the thermodynamically stable cis-configuration -a prerequisite for efficient metal complex formation.Deprotonation of bis(amino)cyclodiphosph(III)azanes with nBuLi slowly afforded the corresponding salts,cis-[(2,4-Me_2C_6H_3N)(PN-tBu)]_2Li_2(THF)_2.The crystal structure of cis-[(2,4-Me_2C_6H_3N)(PN-tBu)]_2Li(THF)_2 (9) consists of a heterocube of two lithium atoms,two nitrogen atoms and a cyclodiphosph(III)azene ring.Transmetallation of Li compounds by TiCl_4 was unselective and led to a complex mixture or products.The direct reaction of cis-bis(amino)cyclodiphosph(III)azenes wtih Ti(NMe_2)_4 is the most efficient method to prepare the corresponding titanium(IV) bis-amido complexes cis-[(RN)(PNtBn)]_2Ti(NME_2)_2 (11a,12a,14a,15a).In the solid state,cis-[(PhN)(PN-tBu)]_2Ti(NMe_2)_2 (11a) adopts a highly distorted trigonal-bipyramidal configuration at the metal center.These bis-amindo titanium(IV) complexes have been subsequently transformed into the dichlorides cis[(RN)(PN-tBu)_2]TiCl_2 (12-15) with Me_3SiCl.After MAO activation the complexes possess moderate catalytic activity in ethene polymerization and produce linear polyethylene with molar massess of up to 2.6X10~6 g/mol and with narrow polydispersities.The catalytic activity and polymer properties depend strongly on the bulkiness of the ligand substituents;cis-[(2,6-iPr_2C_6H_3N)(PN-tBu)]_2TiCl_2(14) gave the highest activity (231 kg PE/mol_(cat)XbarXh).