Cationic Nickel(II)-Catalyzed Hydrosilylation of Alkenes: Role of P, N-Type Ligand Scaffold on Selectivity and Reactivity

Abstract

Seven structurally similar cationic nickel(II)−alkyl complexes were synthesized by using a series of P, N ligands, and their reactivity was explored in the hydrosilylation of alkenes. More electron-rich phosphines enhanced the overall reactivity of the transformation; in contrast, groups on the imine donor had little impact. Overall, these catalysts displayed reactivity and selectivity that was previously unknown or very rare in nickel-catalyzed hydrosilylation. In reactions with Ph 2 SiH 2 , 1,2-disubstituted vinylarenes showed complete benzylic selectivity for silane addition, whereas terminal selectivity was observed for 1,1-disubstituted alkenes. The related PhSiH 3 led to exclusively Markovnikov selectivity for monosubstituted vinylarenes with no competing double addition observed. Mechanistic investigations supported the hypothesis that a Ni−H functions as the active species in this catalytic hydrosilylation, which in turn also showed catalytic competence for the silane redistribution reaction, especially with sterically unhindered silanes.

(NHC)Ni(0)-Catalyzed Branched-Selective Alkene Hydrosilylation with Secondary and Tertiary Silanes

“…Even fewer examples enabling activation of 2°silanes have been reported. 32,52,57,58,60,98,99 To our knowledge, examples with 3°silanes are limited to the (pincer)Co-catalyzed hydrosilylation of 1-octene using (EtO) 3 SiH 73 and the ([P∼C]-chelate)Co-catalyzed hydrosilylation of styrene with Ph 3 SiH and Me(EtO) 2 SiH. 58 A significant challenge remaining in base-metal-catalyzed alkene hydrosilylation is the synthesis of branched hydrosilylation products using 3°silanes with alkyl-, aryl-, alkoxy-, or chloro-substituents (Figure 1b).…”

The Influence of Silane Steric Bulk on the Formation and Dynamic Behavior of Silyl Palladium Hydrides

“…In hydrosilylation reactions, the steric hindrance of silane substituents is observed to impact the regio- and stereoselectivity of the reaction for a wide range of metal catalysts including Pt, − Pd, − Ni, Rh, − and other late transition metals. − Nonetheless, despite the proposed role of silane steric hindrance in transformations involving silyl metal hydride intermediates, focused studies on the impact of silane steric bulk in oxidative addition with late transition metals are scarce. In examples of oxidative addition using Ni, , Pd, − and Pt complexes, − tertiary silanes are observed to yield discrete silyl metal hydrides, while reacting the same complexes with secondary or primary silanes gives metal bis­(silyl) species; however, some silyl metal hydride complexes of Pd and Pt have been isolated from very bulky primary silanes. ,, In contrast, systematic variation of silane substituents in the oxidative addition of tertiary silanes to Rh complexes reveal a pronounced decrease in the rate of oxidative addition (and stability of the formed products) with increasing steric bulk at silicon. , Deeper understanding of the impact of silane steric bulk on the formation and stability of silyl metal complexes is necessary to more fully understand hydrosilylation reactions.…”

“…60−64 Late-stage modification of polysiloxanes and polybutadiene by transition metal-catalyzed hydrosilylation is hindered by sterically large substituents at silicon. 65−73 In hydrosilylation reactions, the steric hindrance of silane substituents is observed to impact the regio-and stereoselectivity of the reaction for a wide range of metal catalysts including Pt, 74−79 Pd, 80−83 Ni, 84 Rh, 85−92 and other late transition metals. 93−98 Nonetheless, despite the proposed role of silane steric hindrance in transformations involving silyl metal hydride intermediates, focused studies on the impact of silane steric bulk in oxidative addition with late transition metals are scarce.…”

Synthesis of aryl cobalt and iron complexes and their catalytic activity on hydrosilylation of alkenes

“…In recent years, there are more and more reports on alkene hydrosilylation catalyzed by base metals such as iron, [4][5][6][7][8][9] cobalt [9][10][11][12][13][14][15][16][17] and nickel. [18][19][20][21][22] However, in the construction of a ligand skeleton, most catalysts are metal complexes supported by bidentate ligands 6,16,20 or pincer ligands ([NNN], 7,18,19 [NNP] 4,5 [CNC] 11 and [PSiP] 13,14 ). The metal complexes supported by monodentate ligands are rarely reported.…”