Comprehensive Summary The sustainable development of synthetic reactions catalyzed by earth‐abundant metals is one of the principal goals in homogeneous catalysis. However, so far most of the protocols are still plagued by sophisticated ligands, hazardous activators, high catalyst loading (1—10 mol%) and/or multistep synthesis of the metal complexes in the process development. Consequently, the development of earth‐abundant metal catalysts with high activity from commercially available metal salts is highly desirable for practical utilization of base metal catalyzed synthetic methodology. Herein, we report the catalyst generated in situ from a mixture of catalytic amounts of Ni(acac)2 (as low as 0.005 mol%) and CsF, which is found highly active for Markovnikov‐selective hydroboration of vinylarenes, including 1,1‐disubstituted vinylarenes and internal olefins, affording a wide range of secondary and tertiary alkyl boronates in excellent yields. Mechanistic experiments indicate that the key to the success of this catalysis is the use of CsF, which in combination with pinacolborane acts as an effective activator for Ni(acac)2, probably generating metastable Ni nanoparticles in situ that demonstrate high activity in the catalytic hydroboration (TON up to 18800).

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