Oxidative cyclization of tetrafluoroethylene (TFE) and ethylene with Ni(0) resulted in the formation of a five-membered nickelacycle. In the presence of PPh 3 as an auxiliary ligand, the partially fluorinated five-membered nickelacycle was isolated and the structure was determined by X-ray analysis. This nickelacycle was found not only to react stoichiometrically with enones to give a cross-trimerization product but also to be a key reaction intermediate in the Ni(0)-catalyzed cotrimerization of TFE and ethylene, leading to 5,5,6,6tetrafluoro-1-hexene.

Oxygen-containing organic compounds, such as ethers, carboxylates, and carbamates, have recently received increasing attention because of their newly discovered applications as electrophiles in cross-coupling reactions via transition metal-catalyzed C-O bond activation. However, no cycloaddition reaction involving their C-O bond activation has been demonstrated thus far. The present study developed a Ni(0)-catalyzed unique [3+2] cycloaddition reaction of α,β-unsaturated phenyl esters with alkynes in (i)PrOH to yield cyclopentenone derivatives.

Stoichiometric treatment of Ni(cod) 2 with ethyl cyclopropylideneacetate (ECPA) in the presence of PCy 3 resulted in an unpredicted formation of a Ni(0) complex bearing an (E,E)-1,2-bis(exo-alkylidene)cyclohexane ligand, which stemmed from the [3 þ 3] cyclodimerization of ECPA. The reaction could be expanded to a Ni(0)-catalyzed [3 þ 3] cyclodimerization reaction of ester-substituted methylenecyclopropanes, giving the corresponding cyclohexane derivatives in excellent yields.Methylenecyclopropanes (MCPs) are strained reactive molecules, and transition-metal-catalyzed cyclodimerization or cycloaddition reactions of MCPs have provided an atomefficient, powerful strategy for the synthesis of a variety of cyclic compounds. 1 Nickel(0) is also known to catalyze cyclodimerization reactions of MCPs to afford cyclobutane and cyclopentane derivatives via [2 þ 2] and [3 þ 2] cyclodimerizations, respectively (Chart 1). 2-4 Pioneering work on the cyclodimerization of methylenecyclopropane in the presence of Ni(cod) 2 , giving a mixture of dispiro[2.1.2.1]octane ([2 þ 2] product) and 5-methylenespiro[2.4]heptane ([3 þ 2] product), was reported by Binger. 2a The usage of maleic anhydride as an additive with the Ni(0) catalyst was found to be effective for the selective formation of the [3 þ 2] cyclodimerization product, 2c whereas the introduction of tertiary phosphines into the Ni(0) catalytic system resulted in the preferential formation of MCP trimers. 2b Interestingly, employing dialkyl fumarates as the solvent in the Ni-catalyzed reaction was devised to give another dimer, 1,3-dimethylenecyclohexane, as a minor product. 2c The selective [3 þ 2] cyclodimerization of methylenecyclopropane, on the other hand, was also caused by treating with Pd(0) catalyst. 3 In contrast, the limiting studies of cyclodimerization reactions of substituted MCPs have been described thus far: the cyclodimerization of 1-methylene-2-vinylcyclopropane with Pd(0) catalysts was reported by Binger, 4a and the reaction of ethyl cyclopropylideneacetates in the presence of Ni catalysts was developed by Saito. 4b Although a number of the cyclodimerizations of MCPs have been reported as described above, there is a very limiting example for [3 þ 3] cyclodimerization in which two proximal C-C bonds are cleaved (Chart 1). 4b In these related reactions, some attempts to confirm the reaction intermediates have been made. Based on the isolation and characterization of a nickelacyclopentane intermediate (Chart 1, A) by using (bipy)Ni(cod) as a Ni (0) precursor, oxidative cyclization of methylenecyclopropane with Ni(0) has been regarded as a key reaction step. 5 The C-C bond cleavage of the cyclopropane ring could be achieved via β-carbon elimination of A, which is known as a "cyclopropyl-butenyl rearrangement", during the catalytic reaction. Another possibility was proposed that the oxidative addition of a proximal bond to Ni(0) took place at the initial stage of the reaction to give 2-methylene-1-nickelacyclobutane (Chart 1, B), while the corresponding interm...

As an effort to integrate natural products chemistry and coordination chemistry, a diastereomeric pair of chiral alkaloidal manifolds composed of a bispyrrolidinoindoline (BPI) framework was designed and synthesized to generate luminescent Eu III complexes with switchable chiroptical properties. The C 2 -symmetric alkaloidal manifolds were linked with bis(benzimidazolyl)pyridine (BBIPy) as an achiral metal-binding component through substituents installed at the stereogenic 2/2′ positions of the BPI manifolds. The resulting diastereomeric pair of ligands, syn-L1 and anti-L2, allow pseudomirror symmetrical presentation of the metal-binding BBIPy units due to the stereogenic centers on the alkaloidal manifold. The ligand syn-L1 induces intramolecular coordination to form the 1:1 complex Eu III (syn-L1) composed of a single stranded metal helicate which exhibits a negative split Cotton effect. In contrast, the ligand anti-L2 led to a supramolecular assembly comprising the 2:2 complex Eu III 2 (anti-L2) 2 consisting of a bimetallic double-stranded helicate which shows a positive split Cotton effect. Thus, the sp 3 stereogenic centers in the BPI manifolds play pivotal roles in controlling both metal−ligand equilibria and chiralityswitching of luminescent Eu III complexes. This approach, which exploits diastereomeric natural product-based manifolds, provides a relatively unexplored means for diversifying metal coordination modes and for controlling the chiroptical properties of the resultant luminescent lanthanoid complexes.