Synthesis and structures of the ytterbium(II)beta-diketiminates [Yb{N(SiMe_3)C(R~2)C(H)C(R~4)N(SiMe_3)}_2](R~2 = R~4 = Ph,c_6H_4Me-4,or C_6H_4Ph-4;or R~2 = C_6H_4Me-4,R~4 = 1-adamantyl)

摘要

Crystalline,homoleptic mononuclear ytterbium(II)P-diketiminates [Yb{N(SiMe_3)C(R~2)C(H)C(R~4)N(SiMe_3)}_2](R~2 = R~4 = Ph 1,R~2 = R~4 = Tol 2,R~2 = R~4 = Dph 3,or R~2 = Tol and R~4 = Ad 4)(Tol = C_6H_4Me-4,Dph = C_6H_4Ph-4,Ad = 1-adamantyl)have been prepared.They have a characteristic ~171Yb{~1H} chemical shift in the region S 2650 ± 200 relative to [Yb(eta~5-C_5Me_5)_2(thf)],although for 2 and 3 this was only observed at low temperatures,indicative of a fast fluxional process at ambient temperature;data recorded ealier for 1 are shown to have been in error.The ~1H NMR spectra of 4 showed that two isomers were present in toluene solution,in a ratio of ca.3 :2,which interconverted on the spin saturation transfer scale of ca.1 s~(-1).NOE data are presented for each of 1-4;these led to(i)assignments of the two types of SiMe_3 groups(adjacent to Tol or Ad)and(II)the conclusion that the two isomers are conformers,one of which probably corresponds to that found in the crystal.The molecular structures of each of 1,3 and 4 have the ytterbium in a distorted tetrahedral environment,the two ligand planes(1 and 3)or boats(including the Yb atom,4)approximate to being either orthogonal(1 and 3)or parallel(4).The ligand-to-metal bonding is close to kappa~2(1,3)or eta~5(4)and the ligands are both pi-delocalised(1,3)or only one of them in 4.