Efficient New Synthetic Route to Bidentate, Monomeric Cyclopentadienyl-Amide Complexes of Group 4 Transition Metals: Synthesis and Characterization of the Zirconium and Hafnium Complexes [{η5

The synthesis of the amine-substituted cyclopentadiene C5H5CH2CH2CH2N(H)Me (2, HCpNH) is described. The reaction of 2 with M(NMe2)4 (M = Zr, Hf) gives the ring-closed species [M(η5:σ-C5H4CH2CH2CH2NMe)(NMe2)2] (M(CpN)(NMe2)2; M = Zr (3), Hf (4)) in high yields (60-95%). Aminolysis of 3 and 4 with 2 equiv of Me2NH·HX (X = Cl, I) provides a route to amine adducts of the dihalide complexes [M(CpN)X2(NHMe2)] (M = Zr, X = Cl (5), I (6); M = Hf, X = I (7)). Aminolysis of 3 with 1 equiv of Me2NH·HI gives the mixed amido-iodide [Zr(CpN)I(NMe2)] (8). The dichloride 5 is an excellent precursor to alkyl complexes; thus, reaction of 5 with C6H5CH2MgCl (2 equiv) gives [Zr(CpN)(CH2Ph)2] (9), that of 5 with Me3SiCH2Li gives [Zr(CpN)(CH2SiMe3)2] (10), and that of 5 with C6H5CH2MgCl (1 equiv) gives the mixed complex [Zr(CpN)(CH2Ph)Cl] (11). The 1H and 13C NMR data for 9 and 10 are discussed in terms of η2-benzyl (9) and agostic (10) interactions in these formally 14-valence-electron compounds. The reaction of 5 with LiBH4 gives [Zr(CpN)(η3-BH4)2] (13). Aminolysis of 3 with cyclopentadiene gives [Zr(CpN)(η-C5H5)(NMe2)] (14), while 3 also reacts with phenylacetylene to give the poorly stable bis(acetylide) [Zr(CpN)(CCPh)2] (15). Compound 11 has been characterized as a benzene-d6 solvate by X-ray crystallography: (C32H40Cl2N2Zr2)0.5(C6D6), Mr = 437.17, monoclinic, P21/c, a = 11.649(1) Å, b = 10.360(1) Å, c = 17.802(1) Å, βi = 106.750(4)°, V = 2057.3(3) Å3, Z = 4, Dx = 1.411 g cm-3, λ(Mo Kα) = 0.710 73 Å, μ = 6.6 cm-1, F(000) = 888, T = 295 K, and RF = 0.035 for 3691 unique observed reflections with I ≥ 2.5σ(I) and 260 parameters. The crystal structure consists of dimer molecules of 11, obeying symmetry 1 and coupled by two bridging Cl atoms, with two different Zr-Cl distances of 2.6288(8) and 2.6797(9) Å, respectively.