This paper presents the effect of additives on the mechanism and selectivity of the SmI2-mediated coupling of alkyl halides and ketones. The reaction of 1-iodobutane and 2-octanone was carried out with SmI2 in the absence of cosolvent and in the presence of HMPA, LiBr, and LiCl. The experiments using cosolvent free SmI2 and SmI2−HMPA reductants gave the Barbier product, 5-methyl-5-undecanol predominantly. The same procedure carried out with LiBr as an additive produced the pinacol product, 7,8-dimethyl-7,8-tetradecanediol, exclusively. A careful product analysis of the SmI2-mediated coupling of 1-iodododecane and 2-octanone in the presence of LiBr, LiCl, and HMPA was also performed. The combination of SmI2 and LiBr again produced the pinacol coupling product exclusively and left the 1-iodododecane unreduced. In contrast, the SmI2−HMPA combination gave only the Barbier product. Analysis of the Sm(II) reductants employing cyclic voltammetry and UV−vis spectroscopy coupled with reaction protocol changes and mechanistic studies led to the conclusion that the SmI2-mediated coupling of alkyl halides and carbonyls in the presence of HMPA gives the Barbier product through an outer-sphere electron-transfer process, while the reaction utilizing SmI2 with LiBr or LiCl gives the pinacol product through an inner-sphere reductive coupling of ketones. The results presented herein show that it is possible to alter the reactivity and selectivity of Sm(II) reagents through the choice of additives or cosolvents, primarily by changing the steric bulk around the reductant.

The ability of inorganic cyanometallate polymers to form interesting and useful complexes is well-known. This Account summarizes work, especially in our laboratories, aimed at replicating aspects of this inorganic chemistry in homogeneous solution using organometallic building blocks. A library of molecular organometallic cyanides and Lewis acids, with varying charges and labilities, are shown to give families of neutral and charged cages. Neutral and anionic cages, often molecular boxes, bind larger alkali metals tightly. Cubic frameworks show an unparalleled affinity for cesium cations over potassium cations. Noncubic cages are described including tetrahedranes, defect boxes, trigonal prisms, and hexagonal prisms.

A series of heptametallic cyanide cages are described; they represent soluble analogues of defect-containing cyanometalate solid-state polymers. Reaction of 0.75 equiv of [Cp*Ru(NCMe)3]PF6, Et(4)N[Cp*Rh(CN)3], and 0.25 equiv of CsOTf in MeCN solution produced (Cs subset [CpCo(CN)3]4[Cp*Ru]3)(Cs subset Rh4Ru3). 1H and 133Cs NMR measurements show that Cs subset Rh4Ru3 exists as a single Cs isomer. In contrast, (Cs subset [CpCo(CN)3]4[Cp*Ru]3) (Cs subset Co4Ru3), previously lacking crystallographic characterization, adopts both Cs isomers in solution. In situ ESI-MS studies on the synthesis of Cs subset Rh4Ru3 revealed two Cs-containing intermediates, Cs subset Rh2Ru2+ (1239 m/z) and Cs subset Rh3Ru3+ (1791 m/z), which underscore the participation of Cs+ in the mechanism of cage formation. 133Cs NMR shifts for the cages correlated with the number of CN groups bound to Cs+: Cs subset Co4Ru4+ (delta 1 vs delta 34 for CsOTf), Cs subset Rh4Ru3 where Cs+ is surrounded by ten CN ligands (delta 91), Cs subset Co4Ru3, which consists of isomers with 11 and 10 pi-bonded CNs (delta 42 and delta 89, respectively). Although (K subset [Cp*Rh(CN)3]4[Cp*Ru]3) could not be prepared, (NH4 subset [Cp*Rh(CN)3]4[Cp*Ru]3) (NH4 subset Rh4Ru3) forms readily by NH4+-template cage assembly. IR and NMR measurements indicate that NH4+ binding is weak and that the site symmetry is low. CsOTf quantitatively and rapidly converts NH4 subset Rh4Ru3 into Cs subset Rh4Ru3, demonstrating the kinetic advantages of the M7 cages as ion receptors. Crystallographic characterization of CsCo4Ru3 revealed that it crystallizes in the Cs-(exo)1(endo)2 isomer. In addition to the nine mu-CN ligands, two CN(t) ligands are pi-bonded to Cs+. M subset Rh4Ru3 (M = NH4, Cs) crystallizes as the second Cs isomer, that is, (exo)2(endo)1, wherein only one CN(t) ligand interacts with the included cation. The distorted framework of NH4 subset Rh4Ru3 reflects the smaller ionic radius of NH4+. The protons of NH4+ were located crystallographically, allowing precise determination of the novel NH4...CN interaction. A competition experiment between calix[4]arene-bis(benzocrown-6) and NH4 subset Rh4Ru3 reveals NH4 subset Rh4Ru3 has a higher affinity for cesium.

T he design of molecular containers represents an important component of nanotechnology and has attracted intense interest from synthetic chemists (1-4). Research on molecular containers can realistically be expected to provide highly selective sensors, sorters, and catalysts for numerous applications. A significant challenge in this area is the development of containers that are stereochemically rigid, because rigidity is the basis of sterically governed selectivity. Rigidity, however, is incompatible with much of organic chemistry, and this dichotomy is problematic because organic (and organometallic) chemistry provides the most versatile construction tools for the synthesis of molecular containers. In this contribution, we address this dichotomy, i.e., the incorporation of organic motifs into rigid frameworks. Our approach involves a hybridization of organometallic chemistry and well established precedents in the chemistry of metal cyanides.Cyanometallates are metal complexes with the general formula L l M m (CN) n . The most important cyanometallate is Prussian blue (PB), an inorganic polymer with the formula Fe 7 (CN) 18 (H 2 O) x (x ϳ 15) (5). The synthesis of this useful solid arises from the condensation of [Fe(CN) 6 ] 4Ϫ and Fe(III) salts (Eq. 1).The structure of PB may be roughly described as interconnected cubic cage subunits with Fe vertices linked by cyanide. The PB structure is in fact complicated because the otherwise idealized cubic framework is interrupted by vacancies at the metal positions, these vacancies being occupied by water molecules (6). A building block approach is inherent in Eq. 1, i.e., the use of preassembled [Fe(CN) In recent years we have developed families of molecular cyanometallate ensembles that are synthesized analogously to PB, except that our molecular building blocks are tricyanometallates wherein the three cyanide ligands are mutually cis. Half of the coordination sphere of these tricyanometallates is occupied by a strongly coordinating nondisplaceable coligand. The face-capping coligand inhibits the formation of polymers by minimizing crosslinking but still promotes the formation of three-dimensional structures, which resemble subunits of PB. Particularly effective as face-capping ligands are cyclopentadienyl, C 5 H 5 (Cp), and its pentamethyl analogue, C 5 Me 5 (pentamethylcyclopentadienyl, Cp*). In a proof of concept experiment, we showed that [CpCo (CN

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