Regioselective C-H bond transformations are potentially the most efficient method for the synthesis of organic molecules. However, the presence of many C-H bonds in organic molecules and the high activation barrier for these reactions make these transformations difficult. Directing groups in the reaction substrate are often used to control regioselectivity, which has been especially successful for the ortho-selective functionalization of aromatic substrates. Here, we describe an iridium-catalysed meta-selective C-H borylation of aromatic compounds using a newly designed catalytic system. The bipyridine-derived ligand that binds iridium contains a pendant urea moiety. A secondary interaction between this urea and a hydrogen-bond acceptor in the substrate places the iridium in close proximity to the meta-C-H bond and thus controls the regioselectivity. (1)H NMR studies and control experiments support the participation of hydrogen bonds in inducing regioselectivity. Reversible direction of the catalyst through hydrogen bonds is a versatile concept for regioselective C-H transformations.

The rhodium-catalyzed synthesis of silafluorenes from biphenylhydrosilanes is described. This highly efficient reaction proceeds via both Si-H and C-H bond activation, producing only H(2) as a side product. Using this method, a ladder-type bis-silicon-bridged p-terphenyl could also be synthesized.

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"Bucky ferrocenes", molecular hybrids of ferrocene and fullerene, have been synthesized in good yield on gram scale by treatment of C(60)HMe(5) or C(70)HMe(3) with [FeCp(CO)(2)](2) and their structures studied with physical methods including X-ray crystallography.

Transition metals of the fourth row are abundant and cheap compared to those of the fifth and sixth rows. Therefore, by introducing new reactivities with fourth-row metal complexes, it might be possible to replace fifth-and sixth-row metals in some fundamental and important reactions. Catalytic Grignard-type addition of nucleophiles to aldehydes is one such reaction. Grignard reagents are usually prepared from organic halides and magnesium metal, [1] but this procedure results in the unwanted formation of stoichiometric amounts of metal salts. One way to solve this problem is to generate the nucleophiles by CÀH bond activation; [2] however, it has been difficult to promote nucleophilic addition after the CÀH activation step. Although nucleophilic addition of species generated by CÀH activation has been reported using ruthenium, [3] rhodium, [4] palladium, [5] and rhenium [6] catalysts, it has been difficult to catalyze such reactions using fourthrow transition-metal complexes. [7] We report herein that 1) complexes of manganese, a fourth-row transition metal, can be employed for CÀH bond activation of aromatic compounds; 2) insertion of aldehydes into CÀH bonds occurs to give benzyl alcohols; and 3) catalytic transformation is achieved with the manganese complex by the addition of Et 3 SiH.We initially investigated stoichiometric CÀH bond activation and insertion of aldehydes with the manganese complex [MnBr(CO) 5 ]. A mixture of 1-methyl-2-phenyl-1H-imidazole (1 a) and [MnBr(CO) 5 ] in toluene was heated at 100 8C for 5 min, at which point a solution of benzaldehyde (2 a) was added. The mixture was heated at reflux for 10 h to give alcohol 3 in 52 % yield (Scheme 1). Although stoichiometric CÀH bond activation and insertion of the aldehyde occured with [MnBr(CO) 5 ], only a trace amount of 3 was produced with a catalytic amount of the manganese complex.To recycle the manganese complex, 2.0 equiv of triethylsilane (4) was added to the reaction mixture from the beginning. As a result, silyl ether 5 a was obtained in 93 % yield with 5 mol % [MnBr(CO) 5 ]. [8,9] We examined the catalytic activity of several metal complexes using the reaction between 1 a, 2 a, and 4 as a probe. A different manganese complex, [Mn 2 (CO) 10 ], showed similar catalytic activities (82 % yield of 5 a). However, the reaction did not proceed at all with the following metal complexes: [MnCl 2 ], [Mn(acac) 3 ] (acac = acetylacetonate), [{ReBr(CO) 3 (thf)} 2 ], [6]

A rhenium complex, [ReBr(CO)3(thf)]2, catalyzes the reaction of an aromatic aldimine with an acetylene to give an indene derivative in a quantitative yield. The reaction proceeds via C-H bond activation, insertion of the acetylene, intramolecular nucleophilic cyclization, and reductive elimination. In contrast to ruthenium and rhodium catalysts, which are usually employed in this type of reaction, the rhenium catalyst promotes the intramolecular nucleophilic cyclization of the alkenylmetal species generated by insertion of the acetylene.

The first copper-catalyzed intramolecular C(sp(3))-H and C(sp(2))-H oxidative amidation has been developed. Using a Cu(OAc)2 catalyst and an Ag2CO3 oxidant in dichloroethane solvent, C(sp(3))-H amidation proceeded at a terminal methyl group, as well as at the internal benzylic position of an alkyl chain. This reaction has a broad substrate scope, and various β-lactams were obtained in excellent yield, even on gram scale. Use of CuCl2 and Ag2CO3 under an O2 atmosphere in dimethyl sulfoxide, however, leads to 2-indolinone selectively by C(sp(2))-H amidation. Kinetic isotope effect (KIE) studies indicated that C-H bond activation is the rate-determining step. The 5-methoxyquinolyl directing group could be removed by oxidation.

A rhenium complex, [ReBr(CO)(3)(thf)](2), catalyzes the reaction of an aromatic aldimine with an isocyanate and an acetylene to give a phthalimidine and an indene derivative in a quantitative yield, respectively. The reactions proceed via C-H bond activation, insertion of the isocyanate or the acetylene, intramolecular nucleophilic cyclization to the aldimine of the generated amido- or alkenyl-rhenium species, and reductive elimination. In contrast to ruthenium and rhodium catalysts, which are usually employed in this type of reaction, the rhenium catalyst promotes the insertion of a polar unsaturated molecule. This occurs more easily than the insertion of a nonpolar unsaturated molecule.