We initiated our developments of the α-allylation of ketone 1a and 1-5 cyclooctadiene (2a) exploring Ni(COD)2 and different bulky NHC ligands as catalyst system (Fig. ). Neither IPr or SIPr, the two most popular and commonly used NHC ligands for Ni(0)-catalysis provided any conversion to the expected product at ambient temperature (Entry 1-2). To our delight, by engineering the properties of the ligands, we found that SIPr provided allylation product 3a in 43 % yield and with a 7:1 diastereoselectivity (Entry 3). Longer reaction time did not improve the yield (Entry 4). Acknowledging the relevance of steric bulk at the R 1 -position for reactivity and complex stability, evaluation of SIPr tBu provided yield of 3a (56 % yield) and a slightly lower dr (6.2:1) (Entry 5). We next combined this feature with a dimethyl NHC backbone ( Me IPr tBu ). Notably, this designer NHC gave a significantly improved performance, yielding 3a in 85 % yield and 4.2:1 dr (Entry 6). The octa phenyl congener Me IPr* tBu displayed poor solubility and almost no reactivity was afforded at room temperature (Entry 7). Control experiment demonstrated the essential presence of both nickel precursor and NHC ligand as no trace of product 3a was formed in the absence of either component (Entry 8-9). Subsequently, we investigated the scope of the hydroalkylation (Fig. ). In this respect, a variety of aryl benzyl ketones with of different substitution pattern successfully engaged in the transformation giving the allylation products 3b-3h in moderate to good yields and with a moderate to good diastereoselectivity. The use of 2-methyl indanone (1i) as substrate enabled construction of allylation product 3i with an α-quaternary carbon center provided in good diastereoselectivity. A set of 2-substituted indanones was also subjected to the reaction conditions. Notably, increasing the size of the substituent at the 2-position further increase to the observed diastereoselectivity to up to 12.8:1 dr for 3l. In order to expands the scope of the transformation towards further non-conjugated dienes, a COD-free nickel (0) source is required to mitigate competition between COD and the external diene reactant (Fig. ). Cornella's Ni( tBu stb)3 complex in stable, COD free and the released stilbene does not participate in the reaction . We identified 1,4-cyclohexadiene (2b) as attractive substrate. In this respect, aryl benzyl ketones reacted cleanly providing allylated compounds 4a-4d with good yields and very high diastereoselectivity. Moreover, a series of 2-substituted indanones 1i-1r successfully allowed hydroalkylation of 1,4-cyclohexadiene with generally excellent yields and excellent diastereoselectivities with the minor diastereomer often undetectable. Notably, hindered 2-aryl tetralones with both electronic-donating and electronic-withdrawing aryl groups reacted well and gave access to the corresponding allylated products 4s-4aa in good yields and exquisite diastereoselectivity. Simple acyclic ketones like acetophenone or phenylethyl ketone could be allylated to yielding 4ab and 4ac in moderate yield. Allylation of hindered ketone 1ad required higher temperature and in consequence a diminished diastereoselectivity of 4ad was observed. The approved drug Donepezil (1ae) having a distal basic amino group reacted giving allylated derivative 4ae. Moreover, non-conjugated 2-phenyl 1,4-pentadiene (2c) successfully engaged in the allylation providing products with compound (E)-4af being the most dominant regioisomer. With the fully atom-economic and diastereoselective process of high value, addressing the challenge of enantioselectivity of the transformation would further leverage its utility. Given the success of the above-introduced bulky designer NHC for this reaction and our ongoing activity in the development of structurally related chiral IPhEt NHCs , we evaluated a set of promising chiral NHC for the model transformation with 1b and 2b (Fig. , SI. 4.4) IPhEt versions with the standard chiral side arm and with the dimethyl backbone such as L1 and L2 were incompetent ligands and no desired formation of product 5a was observed. We next applied design knowledge of the diastereoselective process and synthesized ligands with 4-tBu group (L4) or a 4-MeO group (L3). While a very sluggish reaction was observed with L4, L3 provided ketone 5a in 29 % with a 30 % conversion of 1a. Pleasingly 5a was formed with a high dr of 10:1 and a high enantioselectivity of 91:9. Changing the chiral selector side arms from phenyl (L3) to 4-tBu-phenyl (L5) significantly boosted the reactivity with conservation of diastereo-and enantioselectivity. Additional reaction parameters like solvent, temperature and nickel source were optimized (SI. 4.4). Finally, to bypass the need of the free carbene, in situ generation from 3 mol% L5•HBF4, 3 mol% tBuOK and 3 mol% Ni( tBu stb)3 in cyclopentyl methyl ether (CPME) provided adequate reactivity providing (R,R)-5a in 85 % yield, 16:1 dr and 92:8 er. The scope of enantioselective hydroalkylation was then investigated (Fig. ). Bulkier substituents at the 2-position of the indanones (5i-5l) increased both enantioselectivities (95:5 er) and diastereoselectivities (>20:1). 5-Methyl (1m) or 6-fluoro indanone (1o) gave desired allylated products in excellent yield, diastereo-and enantioselectivity. Diminished enantioselectivity was observed for the allylation of ketone 1r reflecting its very hindered access to the carbonyl group. Acyclic benzyl phenyl ketone 1a with the possibility of E/Z isomers of the nickel enolate gave moderate enantioselectivity. However, the excellent diastereoselectivity of >20:1 of the process was retained. The transformation with 1,5-COD delivered 7i with high enantioselectivities but a low diastereoselectivity. Subsequently, a series of 2-aryl substituted tetralones having electron-donating or electronwithdrawing groups reacted well yielding corresponding allylated products 8s-8z with excellent diastereoselectivities and enantioselectivities. Notably, substrate 1w with a PMP group increased the enantiomeric ratio to 99:1 er. Crystal structures of products 6a, 8s, 8t, and 8w unequivocally allowed determination of the relative and absolute configurations formed in the allylation process. To obtain some insights on mechanism, we synthesized and crystallized arene-bound Me IPr tBuligated nickel complex 9 (Fig. ) . It has a buried volume of 46.8 % and the influence of its p-tbutyl groups on are clearly visible on the plotted steric map (SI. 5.2). Notably, 9 proved to be a competent catalyst giving 3i in 65 % yield and 6.3:1 diastereoselectivity under standard conditions. Although 9 is rather labile, its advantage is the absence of any acceptor olefin that would directly quench any potential nickel hydride making it unlikely observable by planned NMR studies. Indeed, mixing complex 9 and ketone 1i in d -toluene led to a new signal at -26.64 ppm at -80 °C, matching shifts of reported Ni(II) hydrides . The shift of this signal is temperature dependent, an effect that was previously as well observed for iron hydrides (Fig. & SI. 5.4) . As expected, a mixture of complex 8 and labeled ketone D-1i did not form the described nickel hydride signal (SI. 5.5). Tentatively, the signal of the observed hydride species was assigned to structure 10. Monitoring a mixture of Ni(COD)2, Me IPr tBu and ketone 1i revealed that the nickel hydride signal is significantly smaller (SI. 5.6). This finding can be attributed due to the presence of two equivalents of COD able react with nickel hydrides. Moreover, small amounts of 3i were already detectable at 20 °C. This observation can be either explained by the reaction of COD with nickel hydride or alternatively an ongoing LLHT pathway. Exposing a mixture of indanones D-1i and 1l to 10 mol% of complex 9 caused a strong deuterium cross-over. No cross-over was observed in the absence of 9 (Fig. ). Reaction of D-1i with COD gave D-3i with deuterium transfer on all but the vinylic and allylic positions of the cyclooctene portion (Fig. ), in line with a β-hydride elimination chain-walking mechanism . Furthermore, we observe a hydrogen/deuterium exchange between ketone D-1i and olefin 2d. This finding indicates that the nickel hydride insertion or LLHT can successfully engage simple terminal mono-olefins (Fig. ). However, the high energy barrier of a straight C(sp 3 )-C(sp 3 ) reductive elimination seams out of reach with the current catalyst system. Parallel reactions of 1b and D-1b show no significant primary kinetic isotope effect (KD/KH = 1.10), suggesting that the C-H bond cleavage is not involved in the rate-determining step (SI. 5.10). However, the observed diastereoselectivity for D-3i is lower than the one for 3i (4:1 vs 6.4:1). No epimerization occurs under the reaction conditions over time. In contrast, we observed a slow erosion of the dr of 3a dropping from 8.0:1 to 4.2:1 in 24 h due to presence of a remaining enolizable carbonyl group in 3a (SI. 5.11).