Syntheses, Structural Characterization, and Kinetic Investigations of Metalla[3]triangulanes: Isoelectronic Nickel(0) and Copper(I) Complexes with Bicyclopropylidene (bcp) and Dicyclopropylacetylene (dcpa) as Ligands

Abstract

The kinetics of the reactions between [Ni(bipy)(COD)] and bicyclopropylidene (bcp), dicyclopropylacetylene (dcpa) and 1,4-dimethoxy-2-butyne (dmbu) were investigated using stopped-flow techniques. Similar to previous studies the results support an associative mechanism (activation parameters for bcp: ΔH # = 46 � 2 kJ • mol À 1 and ΔS # = À 69 � 8 J • mol À 1 • K À 1) and therefore allowed to postulate a more general reaction mechanism for the reaction pathway. The products, the nickel(0) complexes [Ni(bipy)(bcp)] and [Ni(bipy)(dcpa)], could be structurally characterized and the molecular structures are presented. In addition, the corresponding copper(I) complexes [Cu(bipy)(bcp)]PF 6 and [Cu(bipy)(dcpa)]PF 6 were also structurally characterized and their reactivity towards dioxygen was investigated. A detailed discussion of the structural properties and comparisons to similar literature-known olefinic complexes with transition metals are presented.

Electrocatalytic Semihydrogenation of Alkynes with [Ni(bpy)3]2+

“…We thus conclude that the complex evolved from the doubly reduced Ni and alkyne 1 is formulated as [Ni­(bpy) 1 ] 0 ( Ni-I ) (Figure ), consistent with previous literature reports . This intermediate is best described as a Ni­(II) nickelacyclopropene complex. , The in situ UV-SEC electrolysis of Ni and 1 at an applied potential of −1.93 V Fc (Figure S39) evolves charge-transfer bands (at 438 and 695 nm) in spectral regions reported for the formation of nickelacyclopropene [Ni­(bpy)­(alkyne)] fragments …”

“…33 This intermediate is best described as a Ni(II) nickelacyclopropene complex. 41,42 The in situ UV-SEC electrolysis of Ni and 1 at an applied potential of −1.93 V Fc (Figure S39) evolves chargetransfer bands (at 438 and 695 nm) in spectral regions reported for the formation of nickelacyclopropene [Ni(bpy)-(alkyne)] fragments. 41 Moreover, the corresponding IR-SEC experiment using alkyne 2 (to avoid overlay with the solvent signature) produces a band at 1924 cm −1 (Figure S40).…”

“…41,42 The in situ UV-SEC electrolysis of Ni and 1 at an applied potential of −1.93 V Fc (Figure S39) evolves chargetransfer bands (at 438 and 695 nm) in spectral regions reported for the formation of nickelacyclopropene [Ni(bpy)-(alkyne)] fragments. 41 Moreover, the corresponding IR-SEC experiment using alkyne 2 (to avoid overlay with the solvent signature) produces a band at 1924 cm −1 (Figure S40). When only BA is added to the reaction mixture, the twoelectron-reduction wave of Ni is only marginally affected with regard to peak potential and current density (Figure S5).…”

Electrocatalysis with Molecular Transition-Metal Complexes for Reductive Organic Synthesis

“…In the presence of an alkyne (e.g., 4-octyne), , electrochemical observations suggest that a fast ligand exchange follows the reduction to [Ni 0 (bpy) 2 ] and affords a formal [Ni 0 (bpy)­(alkyne)] complex (Figure ). The structure of this intermediate is supported by isolated [Ni 0 (bpy)­(alkyne)] samples, − which display a square planar geometry and are best described as Ni­(II) cyclopropene compounds. The electrochemical behavior of [Ni II (bpy) 3 ] 2+ under only CO 2 indicates that the reduction to Ni(0) triggers the formation of a Ni–CO 2 adduct, while electrocatalytic CO 2 reduction occurs with [Ni II (bpy) 3 ] 2+ at potentials more negative than the ones explored here.…”

“…The reactivity is in general lower with the alkenes than with the corresponding alkynes, because of a weaker affinity of the C=C bond for the reduced Ni(0) complex. 101 In that case, the in situ made [Ni II (pmdta)Br 2 ] system (typically 10 mol %) was primarily investigated. 88 While nonactivated aliphatic alkenes (e.g., ethylene, 1-octene, or 1,7-octadiene) proved unreactive, benzylic olefins (e.g., (α/β-methyl)styrene) could be transformed with moderate performance (typically 25–70% conversion and 50–80% FE).…”