AbstractBis(amino)cyclodiphosph(III)azanes cis‐[(RNH)(PN‐tBu)]2, R = 2,6‐iPr2C6H3 (2), 2‐tBuC6H4 (3), 2‐CF3C6H4 (4), 2,5‐tBu2C6H3 (5), Ph2CH (6), 2,4‐Me2C6H3 (7), 2,6‐Et2C6H3 (8), have been synthesized in the presence of Et3N by a nucleophilic substitution reaction of cis‐(ClPN‐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‐Me2C6H3N)(PN‐tBu)]2Li2(THF)2. The crystal structure of cis‐[(2,4‐Me2C6H3N)(PN‐tBu)]2Li2(THF)2 (9) consists of a heterocube of two lithium atoms, two nitrogen atoms and a cyclodiphosph(III)azane ring. Transmetallation of Li compounds by TiCl4 was unselective and led to a complex mixture of products. The direct reaction of cis‐bis(amino)cyclodiphosph(III)azanes with Ti(NMe2)4 is the most efficient method to prepare the corresponding titanium(IV) bis‐amido complexes cis‐[(RN)(PNtBu)]2Ti(NMe2)2 (11a, 12a, 14a, 15a). In the solid state, cis‐[(PhN)(PN‐tBu)]2Ti(NMe2)2 (11a) adopts a highly distorted trigonal‐bipyramidal configuration at the metal center. These bis‐amido titanium(IV) complexes have been subsequently transformed into the dichlorides cis‐[(RN)(PN‐tBu)]2TiCl2 (12−15) with Me3SiCl. After MAO activation the complexes possess moderate catalytic activity in ethene polymerization and produce linear polyethylene with molar masses of up to 2.6 × 106 g/mol and with narrow polydispersities. The catalytic activity and polymer properties depend strongly on the bulkiness of the ligand substituents; cis‐[(2,6‐iPr2C6H3N)(PN‐tBu)]2TiCl2 (14) gave the highest activity (231 kg PE/molcat × bar × h). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)