Effect of ancillary ligand structure on the catalytic activity were investigated. The use of Sc-1 without substitution at para-position of phenyl group in the NHI ligand resulted into lower reactivity with a slightly higher E/Z ratio (entry 2, 82% yield, 6.3:1 E/Z). Changing 4,5-dimethyl groups on the skeleton of imidazolin-2-imine ring to 4,5-dihydrogen afforded 90% yield with the same E/Z ratio (entry 3). No better results were given when the substituent at paraposition of phenyl group in the NHI ligand was changed from i Pr to 1-adamantyl group (entry 4, Sc-4, 95% yield, 5:1 E/Z). Remarkably, increasing the steric hindrance of 2,6substituents of phenyl group in imidazolin-2-iminato ligand was benefit to the E/Z ratio of allylic alkylation product D1 (entries 5-7). Switching the catalyst precursor Sc-3 to Sc-5 with 2,6-(3-pentanyl)2 substituents led to higher E/Z ratio albeit with reduced reactivity (entry 5 vs. entry 2, 73% yield, 9.1:1 E/Z ratio). Further increase the steric hindrance of 2,6-positions (Sc-6 and Sc-7) provided excellent E/Z ratio of the desired product with moderate yield (entries 6 and 7, 51% yield and 45% yield, respectively). It should be noted that varied amount of homo-coupling product C1 was formed in all cases (for more details, see SI, page S20). Sc-8 with [TMSCH2] -basic group and other rare-earth metalbased complexes, such as Y-1, Gd-1 and Lu-1 were tested as well, no desired product was detected (entries 8 and 9). Notably, performing the reaction without either [Sc] or [Ph3C][B(C6F5)4] led to no reaction (See SI, page S22-23 for more details), suggesting that cationic NHI-Sc(III) alkyl complex was the percussor of catalytically active species. The influence of amine additives was evaluated (entries 10 and 11). High E/Z ratio was afforded after the addition of 1-admantylamine or CyNMe2 in the reaction system, however, the reactivity was decreased to some extent (40% yield and 58% yield, >19:1 E/Z). Under the standard conditions, the addition of THF (10 mol%) prohibited the formation of cross-coupling product D1. However, the dimerization product C1 was afforded in 9% yield and >19:1 E/Z (entry 12). Carrying out the reaction at lower temperature or decreasing the catalyst loading resulted into low yield of the related product (entries 13 and 14, 71% yield and 89% yield, respectively). Decreasing the amount of A1 (0.1 mmol) led to the desired product D1 in moderate yield and maintained E/Z ratio along with trace amount of C1 (entry 15). Commercially available sodium bis(trimethylsilyl)amide (NaHMDS), which was efficient for the addition of aldimine with allylbenzene, 3a could not promote the allylic alkylation of β-methylstyrene with styrene at all. , -methylstyrenes with different alkyl or alkenyl substituents at the para-and ortho-position of phenyl ring were all compatible in the current system, yielding the related cross-coupling products (D1-D8) in 31-99% yields and 1:3.4-10:1 E/Z ratio along with trace amount of homodimerization products. Generally, the reactions of 2substituted -methylstyrenes A3 and A4 afforded Z-D3 and Z-D4 as the major products. For the reaction of 1,4-di(prop-1-en-1-yl)benzene, one of the two allylic positions underwent the reaction, delivering the related allylic alkylation product D7 in 99% yield with 10:1 E/Z. Notably, -methylstyrenes A9-A11 with heteroatom containing groups, such as C6H5O, MeS and NMe2 were suitable substrates, allylic alkylation reaction rather than heteroatom-directed C-H alkylation 5 took place, providing the related alkene cross-coupling products D9-D11 in moderate to good yield with high E/Z ratio (69-80% yields, 3.3:1->19:1 E/Z). Moreover, the current reaction system was compatible with halogen substituted -methylstyrenes A12-A19 (23-86% yields, 9:1->19:1 E/Z). From orthohalogen substitute -methylstyrenes to para-halogen substituted ones, their reaction activity decreased gradually (D16-D18) probably due to the strong halogen affinity of the rare-earth metal ion. 17 -Ethylstyrene, -propylstyrene and -benzylstyrene were amenable to the reaction, producing the related allylic alkylation adducts D20-D22 in medium yield (23-70% yields) with excellent E/Z ratio (>19:1). Besides -methylstyrenes derivatives, the reaction with internal aliphatic substituted alkenes were feasible as well, although the reactivity decreased (D23-D25, 35-52% yields, >19:1 E/Z). When but-2-en-1-ylbenzene was subjected into the standard conditions, the cross-coupling product D25 (32% yield, >19:1 E/Z) was generated along with alkene migration/addition product D20 (20% yield, >19:1 E/Z). To our delight, trisubstituted alkene, for example, (cyclobutylidenemethyl)benzene, transformed into the product D26 under the standard conditions in 99% yield with 3.3:1 E/Z. The use of steric bulky Sc-6 or Sc-7 significantly improved the E/Z ratio albeit with moderate reactivity (70% yield and 37% yield, >19:1 E/Z).