Synthesis, Structures, Characterization, Dynamic Behavior, and Reactions of Novel Late Transition Metal(II) 1-Azaallyls

Abstract

A series of homoleptic late transition metal(II) 1-azaallyl compounds ([M(L)2] {L = η3-N(SiMe3)C(tBu)CH(C6H4Me-4), M = Fe (5), Co (6), or Ni (7)}, [M(L1)2] {L1 = η3-N(SiMe3)C(Ph)CH(SiMe3), M = Ni (8) or Pd (9)}, [M(L2)2] {L2 = η3-N(SiMe3)C(tBu)CH(SiMe3), M = Fe (10) or Co (11)}, or [M(L3)2] {L3 = η1-N(SiMe3)C(tBu)CH(C10H7-1), M = Fe (12)} have been prepared by reactions of anhydrous late transition metal halides {MX2 = FeBr2, CoCl2, [NiBr2(dme)], or [PdCl2(cod)]} with the appropriate lithium or potassium 1-azallyl KL (1), [LiL1(thf)]2 (2), [LiL2]2 (3), or KL3 (4) in a 1:2 molar ratio. The heteroleptic 1-azallylnickel(II) complex Ni(η3-C3H5)(L3) (13) was prepared from [{Ni(η3-C3H5)(μ-Br)}2] with a stoichiometric amount of the 1-azaallylpotassium reagent KL3 (4). Single-crystal X-ray analysis revealed the 1-azaallyl to be bonded to the metal center in an η3-NCC mode in the mononuclear compounds 5−8 and 10, whereas in 12 the 1-azallyl is N-bound in the κ1-enamido fashion. The iron(II) (5, 10, and 12) and cobalt(II) (6 and 11) compounds are paramagnetic and have magnetic moments in the range 5.01−5.61 μB and 2.73−3.01 μB, respectively, characteristic of a high-spin d6 and low-spin d7 electronic configuration, respectively. The diamagnetic group 10 metal 1-azaallyl compounds (7−9 and 13) were fully characterized by multinuclear NMR spectroscopy and were found to be a mixture of isomers. Several NOE, two-dimensional, and saturation transfer NMR spectroscopic experiments were used to elucidate the nature of the three isomers. Variable-temperature and variable-temperature saturation transfer NMR spectroscopic experiments showed the isomers of each of compounds 7−9 to be involved in a dynamic process. Electrochemical and oxidation studies on compounds 5 and 6 are reported, as are α-olefin oligomerization reactions catalyzed by 13 with MAO or B(C6F5)3.