2-Nickelaoxetanes have been frequently invoked as reactive intermediates in catalytic reactions of epoxides using nickel, but have never been isolated or experimentally observed in these transformations. Herein, we report the preparation of a series of well-defined nickelaoxetanes formed via the oxidative addition of nickel(0) with epoxides featuring ketones. The stereochemistry of the products is retained, which has not yet been reported for nickelaoxetanes. Theoretical calculations support a bimetallic ring-opening/closing pathway over a concerted oxidative addition. Initial reactivity studies of a nickelaoxetane demonstrated protonolysis, oxidatively induced reductive elimination, deoxygenation, and elimination reactions when treated with the appropriate reagents.

Amidate-supported two- and three-coordinate Ni complexes were synthesized by reduction of the corresponding Ni precursors. A dramatic change in binding mode is observed upon reduction from Ni to Ni . The Ni derivatives include an unprecedented Ni bis(C-H) agostic complex and a two-coordinate Ni complex.

Selective reductive elimination of ethane (Csp(3)-Csp(3) RE) was observed following bromide abstraction and subsequent thermolysis of a Pt(IV) complex bearing both Csp(3)- and Csp(2)-hybridized hydrocarbyl ligands. Through a comparative experimental and theoretical study with two other Pt(IV) complexes featuring greater conformational flexibility of the ligand scaffold, we show that the rigidity of a meridionally coordinating ligand raises the barrier for Csp(2)-Csp(3) RE, resulting in unprecedented reactivity.

Described is as ystematic comparison of factors impacting the relative rates and selectivities of C(sp 3 ) À Ca nd C(sp 3 )ÀObond-forming reactions at high-valent Ni as afunction of oxidation state.T wo Ni complexes are compared: ac ationic octahedral Ni IV complex ligated by tris(pyrazolyl)borate and ac ationic octahedral Ni III complex ligated by tris(pyrazolyl)methane.K ey features of reactivity/selectivity are revealed:1 )C(sp 3 ) À C(sp 2 )b ond-forming reductive elimination occurs from both centers,b ut the Ni III complex reacts up to 300-fold faster than the Ni IV ,d epending on the reaction conditions.T he relative reactivity is proposed to derive from ligand dissociation kinetics,w hich vary as af unction of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO À ), the Ni IV complex exclusively undergoes C(sp 3 ) À OAcb ond formation, while the Ni III analogue forms the C(sp 3 )ÀC(sp 2 )c oupled product selectively.This difference is rationalized based on the electrophilicity of the respective MÀC(sp 3 )b onds,a nd thus their relative reactivity towards outer-sphere S N 2-type bond-forming reactions.

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