Keywords: Homogeneous catalysis / Iridium / Hydrogen bonds / Hydride ligands / Cooperative effectsWe have synthesized a series of organometallic oxime complexes as novel metal-ligand cooperating bifunctional catalysts. The reaction of [{Cp*IrCl(μ 2 -Cl)} 2 ] with ketoximes in the presence of sodium acetate afforded the half-sandwich chlorido iridium complexes 6 bearing a C-N chelate oxime ligand with a protic OH group in the β-position to the metal. Complex 6a, derived from acetophenone oxime, reacted with silver triflate to give the triflate complex 7 and cationic nitrile complex 8 depending upon the reaction solvent. Complexes 6 also reacted with a base in dichloromethane to afford the oximato-bridged dinuclear complexes 9, which were con-

Catalytic intramolecular cyclization of nonactivated aminoalkene with functional group compatibility provides an atom-economical and concise route to valuable nitrogen-containing heterocycles yet remains a challenge. In this paper, we report the detailed substrate scope and mechanism of catalytic intramolecular hydroamination with a half-sandwich-type iridium pyrazolato complex we have recently developed. This metal−ligand bifunctional catalyst promoted the hydroamination of various primary and secondary aminoalkenes at mild temperatures (50−110 °C) without side reactions such as oxidative amination. Cyclization of secondary aminoalkenes containing ester, cyano, bromo, and hydroxy groups occurred with maintenance of these functional groups, while the reactions of aminoalkenes bearing allylic substituents proceeded with a perfect diastereoselectivity. Catalyst optimization revealed that the proton-responsive functional group at the position β to the metal is crucial to efficient catalytic turnover. Kinetic analysis indicated a highly ordered transition state associated with N−H bond cleavage in the rate-determining step. On the basis of these data along with the stoichiometric reactions and DFT calculations, we propose an unprecedented metal−ligand cooperating mechanism, in which cyclization occurs through syn addition of the amino group to the coordinated olefin bond with the aid of the Brønsted basic pyrazolato ligand.

A reaction of [{Cp*IrCl(μ-Cl)}2] (Cp* = η5-C5(CH3)5) with 1-(pyridin-2-yl)ethanone oxime (PyNOH) afforded the cationic oxime complex [Cp*IrCl(PyNOH)]Cl (3) with an acidic OH group at the β-position to the metal center. Complex 3 underwent reversible deprotonation to give the corresponding oximato complex [Cp*IrCl(PyNO)] (4), while treatment of 3 with silver triflate in acetonitrile led to the formation of the dicationic complex [Cp*Ir(PyNOH)(CH3CN)][OTf]2 (5, OTf = OSO2CF3). The detailed structures of 3–5 have been determined by X-ray crystallography.

A reaction of [{Cp*Ru(μ3-Cl)}4] (Cp*: η5-C5(CH3)5) with 5-phenyl-3-(2-pyridyl)-1H-pyrazole (PhpypzH) afforded a chelating pyrazole complex [Cp*RuCl(PhpypzH)] (2) bearing an NH proton at the β-position to the metal. Treatment of 2 with an equimolar amount of silver nitrite followed by anion exchange with KOTf (OTf: OSO2CF3) gave the pyrazolato–nitrosyl complex [Cp*Ru(NO)(Phpypz)](OTf) (3) through a proton shift from the pyrazole ligand to the nitrite ion. In contrast, simple ligand exchange took place in the reaction of silver nitrite and [Cp*RuCl(bipy)] (bipy: 2,2′-bipyridine) without the protic chelate ligand to give the nitro complex [Cp*Ru(NO2-κN)(bipy)] (4). Protonation of 4 with triflic acid led to the formation of the nitrosyl complex [Cp*Ru(NO)(bipy)](OTf)2 (5). The pyrazolato complex 3 was also obtained by the reaction of [Cp*Ru(NO)Cl2] with PhpypzH and KOTf in water. Reversible protonation of 3 resulted in the formation of the dicationic pyrazole complex [Cp*Ru(NO)(PhpypzH)](OTf)2 (6). The detailed structures of 2–4 and 6 have been determined by X-ray crystallography.

Metal-ligand bifunctional molecular catalysts, in which the ligand cooperates in the substrate binding and activation through secondary interactions, such as hydrogen bonding and proton transfer, have attracted increased attention in synthetic organic chemistry. Among the most successful examples are the Noyoris hydrogenation and Noyori and Ikariyas transfer-hydrogenation catalysts; these catalysts have chelate amine ligands to provide a protic NH group at the a-position to the metal (Scheme 1a,b). [1, 2] The nitrogen ligand works as a hydrogen-bond donor to the substrate in the protonated amine form, and as an internal Brønsted base in the deprotonated amido form, to realize efficient catalytic reactions . Both amine and amido complexes are isolable in some cases, allowing for detailed mechanistic investigations. Shvos catalyst [3] and Milsteins pincer-type complexes [4] (Scheme 1c,d) represent an additional class of bifunctional catalysts, in which an operationally protic group is situated at a place more distant from the metal. As an extension of our extensive studies on the bifunctional chelate amine complexes, such as Scheme 1b,e, [2, 5,6] we recently synthesized a chelating N-heterocyclic carbene (NHC) complex, 1, bearing a protic b-NH group and revealed facile C À O bond cleavage of allyl alcohol, which was ascribed to the metal-NH bifunction.[7] Still, bifunctional catalysis based on the b-NH group in ligated N-heteroaromatics remains in its infancy if compared with the a-NH analogues. For example, full characterization of interconvertible couples linked with the reversible addition of H 2 or pronucleophiles has rarely been achieved for the protic NHC complexes [7][8][9] and for the related, and more accessible, pyrazole-based chelate complexes. [10][11][12] We report here the C À N chelating protic pyrazole complex 2, which is isoelectronic with 1, as a new entry of b-NH-based bifunctional catalysts (Scheme 1g). The welldefined deprotonation-reprotonation network involving 2, as well as catalytic hydroamination with 2 is described.[13]The chloro-pyrazole complex 2 was readily obtained by acetate-promoted cyclometalation [6, 14] of 3,5-diphenylpyrazole [Eq. (1)