We present the formation of a series of chiral metallacycles and metallacages by the use of a BINOL-derived dicarboxylate as a donor that is capable of affording a variety of coordination angles between its two Lewis basic sites. Two squares, two rhomboids, two tetragonal prisms, and one hexagonal prism were successfully formed when the chiral dicarboxylate donor self-assembled with one of four ditopic Pt(II) complexes, including two bimetallic 180° Pt-based acceptors, a 120° bimetallic Pt-based acceptor, and a 90° mononuclear Pt-based acceptor. Their structures were well characterized by (31)P{(1)H} NMR, ESI-MS, CD, and optical rotation analyses.

Zn-mediated reduction of readily accessible dialkyl oxalates derived from tertiary alcohols provides an efficient approach to C−O bond fragmentation and alkyl radical formation. With MgCl 2 as the indispensable additive and Ni as the promoter, trapping the radical with activated alkenes and aryl−Ni intermediates allows for the generation of alkylated and arylated all-carbon quaternary centers.

Conspectus Transition metal catalyzed cross-electrophile coupling of alkyl electrophiles has evolved into a privileged strategy that permits the facile construction of valuable C­(sp3)–C bonds. Numerous elegant Ni-catalyzed coupling methods, for example, arylation, allylation, acylation, and vinylation of primary and secondary alkyl halides have been developed. This prior work has provided important mechanistic insights into the selectivity and reactivity of the coupling partners, which are largely dictated by both the catalysts and the reactants. In spite of the advances made to date, a number of challenging issues remain, including (1) achieving stereoselective syntheses of C–C bonds that rely primarily on functionalized or activated alkyl precursors, (2) diversifying the electrophiles, and (3) gaining insights into the underlying reaction mechanisms. In this Account, we summarize a number of Ni- and Fe-catalyzed reductive C–C bond forming methods developed in our laboratory, which have allowed us to couple activated, sterically hindered tertiary alkyl and C­(sp3)–O bond electrophiles and to access methylated and trifluoromethylated products, esters, C-glycosides, and quaternary carbon centers. We will begin with a brief discussion of Ni-catalyzed chemoselective construction of unactivated alkyl–alkyl bonds, with focus on the effects of ligands and reductants, along with leaving group-directed reactivities of alkyl halides, and the role they play in promoting the reductive coupling of activated electrophiles, including methyl, trifluoromethyl, and glycosyl electrophiles, and chloroformates. Matching the reactivities of these electrophiles with suitable coupling partners is considered essential for success; this is something that can be tuned by means of appropriate Ni catalysts. Second, we will detail how tuning the steric and electronic effects of nickel catalysts with labile pyridine-type ligands and additives (primarily MgCl2) permits effective creation of arylated all-carbon quaternary centers through the coupling of aryl halides with sterically encumbered tertiary alkyl halides. In contrast, the use of bulkier bipyridine and terpyridine ligands permits the incorporation of relative small-sized acyl and allyl groups into acylated and allylated all-carbon quaternary centers. Finally, we will show how the knowledge gained with halide electrophiles enabled us to develop methods that permit the coupling of tertiary alkyl oxalates with allyl, aryl, and vinyl electrophiles, wherein Barton C–O bond radical fragmentation is mediated by Zn and MgCl2 and promoted by Ni catalysts. The same protocol is applicable to the arylation of secondary alkyl oxalates derived from α-hydroxyl carbonyl substrates, which involves the formation of relatively stable α-carbonyl carbon centered radicals. Thus, this Account not only summarizes synthetic methods that allow formation of valuable C–C bonds using challenging electrophiles but also provides insight into the relationship between the structure and reactivity of the substrates a...

The formation of catenated systems can be simplified greatly if one or more rings are generated via self-assembly. Herein we exploit the orthogonality of coordination-driven self-assembly and crown-ether host-guest complexation to obtain a [4]molecular necklace and a [7]molecular necklace based on a well-developed recognition motif of 1,2-bis(pyridinium)ethane/dibenzo[24]crown-8. By adapting the bis(pyridinium) motif into the backbone of a donor building block, the resulting semirigid dipyridyl species can serve both as a structural element in the formation of metallacycles and as a site for subsequent host-guest chemistry. The pseudolinear nature of the donor precursor lends itself to the formation of triangular and hexagonal central metallacycles based on the complementary acceptor unit used. This exemplary system organizes up to 18 molecules from three unique species in solution to afford a single supramolecular ensemble.

Exchange bias phenomena are observed in the bulk polycrystalline Ni49.5Mn34.5In16 alloy in which ferromagnetic and antiferromagnetic phases coexist in the martensitic state. Both the exchange bias field and coercivity are strongly dependent on temperature. The training effect of the exchange bias is found to be very small in the present alloy and can be explained by the depinning of uncompensated antiferromagnet spins. These results suggest that the ferromagnetic and antiferromagnetic domains couple at the interfaces and as a result induce the exchange bias. Such behavior is an addition to the multifunctional properties of the Ni49.5Mn34.5In16 ferromagnetic shape memory alloy.