Structure-property relationships of photofunctional diiridium(II) complexes with tetracationic charge and an unsupported Ir-Ir bond.

In contrast to the extensively studied dirhodium(II) complexes and iridium(III) complexes, neutral or dicationic dinuclear iridium(II) complexes with an unsupported ligand are underdeveloped. Here, a series of tetracationic dinuclear iridium(II) complexes, featuring the unsupported Ir(II)-Ir(II) single bond with long bond distances (2.8942(4)-2.9731(4) Å), are synthesized and structurally characterized. Interestingly, compared to the previous unsupported neutral or dicationic diiridium(II) complexes, our DFT and high-level DLPNO-CCSD(T) results found the largest binding energy in these tetracationic complexes even with the long Ir(II)-Ir(II) bond. Our study further reveals that London dispersion interactions enhance the stability cooperatively and significantly to overcome the strong electrostatic repulsion between two half dicationic metal fragments. This class of complexes also exhibit photoluminescence in solution and solid states, which, to our knowledge, represents the first example of this unsupported dinuclear iridium(II) system. In addition, their photoreactivity involving the generation of iridium(II) radical monomer from homolytic cleavage was also explored. The experimental results of photophysical and photochemical behaviours were also correlated with computational studies.

Synthesis and X-ray characterization of 15- and 16-vertex closo-carboranes.

Carboranes are a class of carbon-boron molecular clusters with three-dimensional aromaticity, and inherent robustness. These endowments enable carboranes as valuable building blocks for applications ranging from functional materials to pharmaceuticals. Thus, the chemistry of carboranes has received tremendous research interest, and significant progress has been made in the past decades. However, many attempts to the synthesis of carboranes with more than 14 vertices had been unsuccessful since the report of a 14-vertex carborane in 2005. The question arises as to whether these long sought-after molecules exist. We describe in this article the synthesis and structural characterization of 15- and 16-vertex closo-carboranes as well as 16-vertex ruthenacarborane. Such a success relies on the introduction of silyl groups to both cage carbons, stabilizing the corresponding nido-carborane dianions and promoting the capitation reaction with HBBr2·SMe2. This work would shed some light on the preparation of carboranes with 17 vertices or more, and open the door for studying supercarborane chemistry.

Phosphine-catalyzed cage carbon functionalization of o-carborane: facile synthesis of alkenylcarboranes.

A phosphine-catalyzed alkenylation reaction of o-carborane with electron-deficient alkynes at the C-H vertex of the o-carborane cage has been developed, which led to the preparation of a series of 1-alkenyl-o-carboranes in moderate to very good yields with excellent regio- and stereoselectivity. This highly efficient and simple method represents the first example of organophosphine catalyzed C-H functionalization of o-carborane.

Cholesterol side chain analogs but not its ether analogs possess cholesterol-lowering activity.

Cholesterol analogs can be used to treat hypercholesterolemia. The present study was to test the effects of cholesteryl 3ß-ethoxy (CE) and cholesteryl 3ß-methoxy (CM) on plasma total cholesterol (TC) compared with that of ß-sitosterol (SI) in hamsters fed a high cholesterol diet. CM and CE are the methoxy and ethoxy analogs of cholesterol while SI is an analog of cholesterol having an additional ethyl group on the side chain. Results showed that SI at a dose of 0.1% could effectively reduce plasma TC by 18%. The analysis of sterols in the plasma and liver did not detect the presence of SI, proving that it was poorly absorbed in the intestine. In contrast, both CE and CM had no effect on plasma TC. However, CE and CM were found to accumulate in both plasma and liver, indicating that they could be well absorbed in the intestine. It was therefore concluded that analogs having different side chains possessed plasma TC-lowering activity, while analogs or derivatives on the hydroxyl group had no hypocholesterolemic activity.

Capsaicinoids but not their analogue capsinoids lower plasma cholesterol and possess beneficial vascular activity.

Capsaicinoids exist in chili peppers, whereas capsinoids are present in some sweet peppers. The present study investigated the effects of capsaicinoids and capsinoids on plasma lipids, relaxation of the aorta, atherosclerotic plaque development, and fecal sterol excretion in hamsters fed a high-cholesterol diet. Five groups of male hamsters were given the control diet or one of the four experimental diets containing 1.3 mmol of capsaicinoids (NL), 2.6 mmol of capsaicinoids (NH), 1.3 mmol of capsinoids (OL), or 2.6 mmol of capsinoids (OH), respectively. Results showed capsaicinoids but not capsinoids could decrease plasma total cholesterol (TC), reduce the formation of atherosclerotic plaque, and relax the aortic artery. This was accompanied by a 28-175% increase in fecal excretion of acidic sterols in hamsters fed the diets containing capsaicinoids. Similarly, capsaicinoids but not capsinoids could decrease the pad weights of epididymal and prerenal adipose tissues. It was concluded that capsaicinoids but not capsinoids could favorably modulate plasma lipids and possess beneficial vascular activity.

Synthesis and structural characterization of 14-vertex germa-, stanna-, and plumba-carboranes.

This article reports the synthesis and structures of several 14-vertex germa-, stanna-, and plumba-carboranes of the MC2B11 system. The reaction of GeCl2·dioxane, SnCl2 or Pb(OAc)2 with [8,9-(CH2)3-8,9-C2B11H11][Na2] in THF gave, after recrystallization from bidentate ligands such as bipyridine, 4,4'-dimethyl-2,2'-bipyridine, phenantroline and 1,2-bis(diphenylphosphino)ethane (dppe), eight 14-vertex p-block metallacarboranes 2,3-(CH2)3-1-(2',2''-bipyridine)-1,2,3-GeC2B11H11 (1), 2,3-(CH2)3-1-(4',4''-dimethyl-bipyridine)-1,2,3-GeC2B11H11 (2), 2,3-(CH2)3-1-(1',10'-phenantroline)-1,2,3-GeC2B11H11 (3), 2,3-(CH2)3-1-(2',2''-bipyridine)-1,2,3-SnC2B11H11 (4), 2,3-(CH2)3-1-(4',4''-dimethyl-bipyridine)-1,2,3-SnC2B11H11 (5), 2,3-(CH2)3-1-(1',10'-phenantroline)-1,2,3-SnC2B11H11 (6), 2,3-(CH2)3-1-(dppe)-1,2,3-SnC2B11H11 (7) and 2,3-(CH2)3-1-(2',2''-bipyridine)-1,2,3-PbC2B11H11 (8) in high isolated yields. Single-crystal X-ray analyses reveal that they adopt a distorted-bicapped-hexagonal antiprism geometry, in which the p-block metal atom slips away from the above center of the C2B4 bonding face towards the boron side, leading to an η(4) bonding mode. The results suggest that [nido-8,9-(CH2)3-8,9-C2B11H11](2-) is a redox inactive species and a good π-ligand for transition metals and p-block elements.

Reactions of 13-vertex carboranes with strong bases: synthesis and structural characterization of carborane monoanions with exo-π bonding.

Several monoanions of 13-vertex carboranes were prepared in high yields from the reactions of C,C'-linked 13-vertex carboranes with tBuOK or NaH in dry THF at room temperature. These monoanions were characterized by various spectroscopic methods, elemental analysis, and single-crystal X-ray diffraction. The results showed substantial double-bond character between the cage-carbon atom and the exo vicinal carbon atom, thus leading to charge delocalization into the cage. As a result, the atom-atom distances within the cage were elongated, with one broken C-B bond. However, the cage geometry of the monoanions remained very similar to that of their corresponding neutral 13-vertex closo-carboranes. These monoanions represent the first examples of 13-vertex carboranes with exo-π bonding to hypercarbon atoms.

Reaction of o-carboranes with sterically demanding N-heterocyclic carbene: synthesis and structural characterization of 1 : 1 adducts.

Several nido-carborane-carbene 1 : 1 adducts were prepared in very high yields from the reaction of o-carboranes with 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene in dry THF at room temperature. Single-crystal X-ray analyses reveal that they are zwitterionic salts consisting of a nido carborane cage and imidazolium moiety that are linked by a five-coordinate boron atom. They are inert toward carbenes, but sensitive toward moisture and water, leading to the formation of deboration products, nido-C(2)B(9) ions. These results shed light on the deboration reaction mechanism of o-carboranes.

Reaction of a 14-vertex carborane with nucleophiles: formation of nido-C(2)B(12), nido-C(2)B(11,) and closo-CB(11) carborane anions.

Nucleophilic reactions of a 14-vertex closo-carborane are reported. 2,3-(CH(2))(3)-2,3-C(2)B(12)H(12) (1) reacts with MeOH at 70 degrees C to give closo-CB(11) anions [1,2-(CH(2))(3)CH(OMe)-1-CB(11)H(10)](-) ([2a](-)), [1,2-(CH(2))(2)CH(OMe)CH(2)-1-CB(11)H(10)](-) ([2b](-)), and [1,2-(CH(2))(2)CH horizontal lineCH-1-CB(11)H(10)](-) ([2c](-)). It is suggested that [2c](-) is an intermediate for the isomerization from [2a](-) to [2b](-). Treatment of 1 with MeOH/Me(3)N, (t)BuOK or LiNMe(2) affords nido-C(2)B(12) species [8,9-(CH(2))(3)-mu-11,12-(Nu)BH-8,9-C(2)B(11)H(11)](-) (Nu = MeO ([3a](-)), (t)BuO ([3b](-)), and Me(2)N ([3c](-))). In the presence of acid such as HCl, anions [3](-) are converted to 1. However, [3](-) undergo deboration reaction, in the presence of bases, to generate a nido-C(2)B(11) anion [8,9-(CH(2))(3)-8,9-C(2)B(11)H(12)](-) ([4](-)) that can also be formed directly from the reaction of 1 with excess CsF or piperidine. Mechanistic studies show that [3a](-) is the first intermediate in the reaction of 1 with MeOH and [4](-) is unlikely an intermediate.