Synthesis and structures of selected benzamidinates of Li, Na, Al, Zr and Sn(ii) using the C-symmetric ligands [N(SiMe)C(C HMe-4 or Ph)NPh]

Several compounds based on the C-symmetric ligands [N(R)C(Ar)NPh] [abbreviated as B (Ar = C HMe-4) or B (Ar = Ph), R = SiMe] are reported. They are the crystalline metal benzamidinates [Li(:κ-B)(OEt)] (1), [Al(κ-B)Me] (2), [Al(κ -B)X] [X = Cl/Me, 1: 1 (3)], [Sn(κ-B)] (4), Zr(κ- B)Cl (5), [Zr(κ-B )Cl] (6), [Na(:κ-B)(tmeda) ] (7), K[B] (8), Li(B)(OEt) (9) and Zr(κ-B)Cl (10) and the known benzamidine Z-HNC(CHMe-4) = NPh (11). They were prepared by (i) insertion of the nitrile 4-MeCHCN (1, 7, 8, 11) or PhCN (9) into the appropriate M-N(R′)Ph [R′ = R and M = Li (1, 9), Na (7), K (8)] bond and subsequent hydrolysis for 11 [R′ = H and M = Li], or (ii) a ligand transfer reaction using the lithium amidinate 1 and Al(Me)Cl (2, 3), SnCl (4) or ZrCl (5, 6), or Li(B) and ZrCl (10). The X-ray structures of 1, 2, 3, 4, 6b (i.e. 6·3PhMe), 7 and 11 are presented. Exploratory polymerisation experiments are described, using 2, 5 or 6 as a procatalyst with methylaluminoxane (MAO) (Al: Zr ca. 500: 1) as promoter. Thus toluene solutions were exposed to CH under ambient conditions; while 2 was unresponsive, 5 and 6 showed modest activity in the formation of polyethylene. © The Royal Society of Chemistry 2007.