Synthesis and structures of selected benzamidinates of Li, Na, Al, Zr and Sn(ii) using the C1-symmetric ligands [N(SiMe3)C(C6H4Me-4 or Ph)NPh]−

Abstract

Several compounds based on the C₁-symmetric ligands [N(R)C(Ar)NPh]⁻ [abbreviated as B¹ (Ar = C₆H₄Me-4) or B² (Ar = Ph), R = SiMe₃] are reported. They are the crystalline metal benzamidinates [Li(µ:κ²-B¹)(OEt₂)]₂ (1), [Al(κ²-B¹)₂Me] (2), [Al(κ²-B¹)₂X] [X = Cl/Me, 1 : 1 (3)], [Sn(κ²-B¹)₂] (4), Zr(κ²-B¹)₂Cl₂ (5), [Zr(κ²-B¹)₃Cl] (6), [Na(µ:κ²-B¹)(tmeda)]₂ (7), K[B¹] (8), Li(B²)(OEt₂) (9) and Zr(κ²-B¹)₃Cl (10) and the known benzamidine Z–H₂NC(C₆H₄Me-4) = NPh (11). They were prepared by (i) insertion of the nitrile 4-MeC₆H₄CN (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)₂Cl (2, 3), SnCl₂ (4) or ZrCl₄ (5, 6), or Li(B²) and ZrCl₄ (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 C₂H₄ under ambient conditions; while 2 was unresponsive, 5 and 6 showed modest activity in the formation of polyethylene.