Functionalised dien ligands of the type (ArNHCH2CH2)2NR [R = Me, (2-C5H4N)CH2] and their complexes with iron and cobalt halides

The alkylation of (ArHNCH2CH2)2NH with RX [RX = MeI, (2-C5H4N)CH2Cl] under basic conditions gives (ArHNCH2CH2)2NMe (Ar = 2,6-Me2C6H3L1a, 2,4-Me2C6H3L1b) and (ArHNCH2CH2)2{(2-C5H4N)CH2}N (Ar = 2,4,6-Me3C6H2L2a, 2,4-Me2C6H3L2b) in moderate yield, respectively. Alternatively, L1a and L1b can be accessed by the arylation (with Ar–Br) of (H2NCH2CH2)2NMe in the presence of a catalytic quantity of Pd2(dba)3. Treatment of L1 with CoCl2 in n-BuOH gave high-spin [{(ArHNCH2CH2)2NMe}CoCl2] (Ar = 2,6-Me2C6H31a, 2,4-Me2C6H31b) in good yield; no reaction occurred with FeCl2. The molecular structure of 1a reveals a distorted trigonal bipyramidal geometry with the L1a adopting a mer-configuration. Reaction of L2 with MCl2 affords the cobalt and iron complexes, [{ArNHCH2CH2}2{(2-C5H4N)CH2}NMCl2] (M = Co, Ar = 2,4,6-Me3C6H22a, 2,4-Me2C6H32b; M = Fe, Ar = 2,4,6-Me3C6H23a, 2,4-Me2C6H33b); the octahedral frameworks in 2a and 3a are found to be considerably distorted with one of the two M-N(mesityl-substituted) distances noticeably elongated [M-N 2.597(4)–2.795(2) Å]; no such inequivalence is observed in solution at room temperature. On activation with methylaluminoxane, complexes 1a and 1b display some activity for the oligomerisation of ethylene.

The aryl-substituted dien ligand frame has been amenable to functionalisation at the central nitrogen atom allowing access to sterically bulky alkyl- and picolyl-substituted multidentate nitrogen donor ligands; full characterisation of complexes formed from their reactions with iron and cobalt chlorides is reported.Figure optionsDownload as PowerPoint slide