Complexes of formula [RuCl 2 (arene)(κ 1 -dpim)] (dpim ) 2-(diphenylphosphino)-1-methylimidazole) (arene ) p-cymene, 1a; C 6 H 6 , 1b) were prepared by the reaction of [RuCl 2 (pcymene)] 2 or [RuCl 2 (C 6 H 6 )(CH 3 CN)] with dpim. Complexes 1a and 1b were structurally characterized by NMR spectroscopy and X-ray diffraction. The reaction of these precursors with BF 4salts led, in dichloromethane, to cationic complexes of formula [RuCl(arene)(κ 2dpim)]BF 4 (arene ) p-cymene, 2a; C 6 H 6 , 2b). However, in methanol the products were unexpected phosphinite derivatives of the type [RuCl(arene)(HImMe){κ 1 -PPh 2 (OMe)}]A (A ) BF 4 , arene ) p-cymene, 3a; C 6 H 6 , 3b; A ) BPh 4 , arene ) p-cymene, 3d) (ImMe ) methylimidazole). This transformation implies the existence of an easy P-C bond cleavage and phosphine functionalization with methanol at room temperature. The precursors 1a,b or the analogous derivative with 2-(diphenylphosphino)pyridine (PPh 2 py), [RuCl 2 (p-cymene)-(κ 1 -PPh 2 py)], 1c, reacted with HBF 4 to give cationic derivatives by protonation of the imidazole or the pyridine fragment, [RuCl 2 (arene)(κ 1 -PNH)]BF 4 (PNH ) dpimH, arene ) p-cymene, 4a; C 6 H 6 , 4b; PNH ) PPh 2 pyH, arene ) p-cymene, 4c). In these compounds the existence of an asymmetric and bifurcated hydrogen bond NH‚‚‚Cl 2 has been structurally determined (even by X-ray studies for 4a,b). Complexes 2a and 4a also yield the corresponding and analogous phosphinite derivatives in the presence of methanol-d 4 but at a markedly slower rate. NMR and spectrophotometric studies provided information concerning the formation of the phosphinite derivatives. It was concluded that the phosphine is not functionalized if it is not coordinated and that, very probably, a methanol solvatesintermediate between 1a and 2asparticipates in the P-C bond cleavage and allows the aforementioned transformation. Some preliminary catalytic tests involving the transfer hydrogenation of cyclohexanone and the hydrogenation of phenylacetylene have also been carried out.

The preparation of three series of arene Ru(II) half-sandwich compounds with the functional ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) is described. The new cationic derivatives have the general formula [(η6-arene)RuCl(κ2-N,N-dmobpy)]X (arene = benzene, X = Cl– ([1]Cl), BF4 – ([1][BF 4 ]), TsO– ([1]TsO), PF6 – ([1][PF 6 ]); arene = p-cymene (p-cym), X = Cl– ([2]Cl), BF4 – ([2][BF 4 ]), TsO– ([2]TsO), PF6 – ([2][PF 6 ]); arene = 2-phenoxy-1-ethanol (phoxet), X = Cl– ([3]Cl), BF4 – ([3][BF 4 ]), TsO– ([3]TsO), PF6 – ([3][PF 6 ])). The structures of [1]Cl, [1]TsO, [2]TsO, [2][BF 4 ], and [2][PF 6 ] were determined by X-ray crystallography. All of the complexes except the PF6 – salts were water-soluble, and they behaved as active catalysts in two different processes: the transfer hydrogenation of water-soluble and -insoluble ketones to the corresponding alcohols, using HCOONa as the hydrogen source at pH 4, and the oxidation of rac-1-phenylethanol to acetophenone with tBuOOH at pH 7, both in aqueous solution. For the transfer hydrogenation with p-cymene complexes the aqua, formato, and hydride species were detected by means of 1H NMR experiments in D2O. It was found that the cationic hydrido complex was [(η6-p-cymene)RuD(dmobpy)]+. The reversible and pH-dependent formation of the hydroxo derivative was also observed. When the catalytic transfer hydrogenation was performed in D2O, the 1-phenylethanol obtained was selectively deuterated at the benzylic carbon. Mechanistic proposals are also included.

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Keywords: Alkenes / Hydrogenations / N ligands / Phosphanes / RhodiumThe reaction of [Rh 2 (µ-Cl) 2 (COD) 2 ] (COD = 1,5-cyclooctadiene) or [Rh 2 (µ-Cl) 2 (TFB) 2 ] (TFB = tetrafluorobenzobicyclo[2.2.2]octatriene) with the N-donor chelating ligand OP-Py 2 Ph (Py = 2-pyridyl) in the presence of TlBF 4 affords cationic complexes [Rh(diene)(OPPy 2 Ph)](BF 4 ) (1, diene: COD; 2, diene: TFB). Compounds 1 or 2 react with CO to give [Rh(CO) 2 (OPPy 2 Ph)](BF 4 ) (4), which is also obtained by treatment of [Rh 2 (µ-Cl) 2 (CO) 4 ] with OPPy 2 Ph and TlBF 4 . In a similar way, the complexes [Rh(diene)(OPPy 3 )](BF 4 ) (5, diene: COD; 6, diene: TFB) are obtained when using OPPy 3 ; they react with CO to give [Rh 2 (µ-CO) 3 (OPPy 3 ) 2 ](BF 4 ) 2 (9). The [a] 289 behavior of the complexes in solution is reported. The complexes with OPPy 3 , 5 and 6, show equivalence of the three Py groups in their NMR spectra. Complex 5 is square-planar in the solid state, and in solution, and the uncoordinated and coordinated Py groups undergo fast exchange in solution. Complex 6 is pentacoordinated in the solid state and in solution, and its Py groups exchange their coordination sites in a fast topomerization process. The single-crystal X-ray structures of 5 and 6 have been solved. The behavior of 1 and 5 as catalysts in hydrogenation reactions of cyclohexene, acetone, and cyclohexanone is also reported.