The chiral P-N* ligands [(S)-2-(dimethylamino)-3-phenylpropyl]diphenylphosphine, (S)-phephos, 1, [(S)-2-)-chiraldphos, 4, reacted with [Ru(η 6 -arene)Cl 2 ] 2 (arene = p-cymene, benzene or hexamethylbenzene), in dichloromethane or tetrahydrofuran solution, affording the corresponding [Ru(η 6 -arene)-(P-N*)Cl 2 ] complexes, 5, in which the P-N* acts as a monodentate P-bonded ligand. In methanol the same reactions easily afforded the corresponding chelate complexes [Ru(η 6 -arene)(P-N*)Cl]Cl. Using ligands 1-3, when the arene is p-cymene, 90 : 10 diastereomeric mixtures of the cationic complexes have been obtained while only one diastereomer was formed in the corresponding reactions when the arene is benzene or hexamethylbenzene. The determination of the absolute configuration of the major products as R Ru ,S C diastereoisomers was made from the crystal structure and CD spectra comparison of the complex (R Ru ,S C )-[Ru(η 6 -p-MeC 6 H 4 Pr i )-(S-phglyphos)Cl]BF 4 . Complexes [Ru(η 6 -arene)(P-N*)Cl]Cl were also obtained by adding small amounts of methanol to solutions of [Ru(η 6 -arene)(P-N*)Cl 2 ] in chloroform. A kinetic study, in CDCl 3 solution containing variable amounts of methanol, on the chelation process in the neutral species [Ru(η 6 -arene)(P-N*)Cl 2 ] showed first-order behaviour of the k obs values with the nucleophile (methanol) concentration. The pseudo-first-order rate constants are ascribed to replacement of Cl Ϫ by a molecule of methanol. A reaction mechanism is proposed.

Cationic rhodium(1) complexes containing the new chiral bidentate P,N ligand 2-[l-(1 S,2S,5R)-(-)menthoxydiphenylphosphinolpyridine are prepared and used successfully in the enantioselective hydroformylation of olefinic substrates, styrene, 2-vinylnaphthalene, methylacrylate and vinylacetate.

The new chiral ligands 2‐butyl‐8‐chloro‐1‐(4,8‐di‐tert‐butyl‐2,10‐dimethoxy‐5,7‐dioxa‐6‐phosphadibenzo[a,c]cyclohepten‐6‐yl)‐1,2‐dihydroquinoline (BIPHENPHOSHQUIN, 3) and 2‐butyl‐8‐chloro‐1‐(3,5‐dioxa‐4‐phosphacyclohepta[2,1‐a;3,4‐a′]dinaphthalen‐4‐yl)‐1,2‐dihydroquinoline (BINAPHOSHQUIN, 4; 4a: SaRC, 4b: SaSC) have been synthesized starting from the rigid backbone of 8‐chloroquinoline. The reactions of 3 and 4 with rhodium(I), palladium(II), and platinum(II) substrates are reported. The reaction of 3 with [Rh(CO)2Cl]2 in a 2:1 molar ratio in hexane afforded a binuclear chloro‐bridged rhodium(III) species by intramolecular oxidative addition of the C–Cl bond of ligand 3 across the rhodium(I) centers. The rhodium(III) complex 5, incorporating the enantiomers SaRC‐3 and RaSC‐3, has been fully characterized by X‐ray diffractometry. Reactions of [Pd(PhCN)2Cl2] with the ligands 3 and 4a in 1:2 molar ratio in toluene afforded the products cis‐[Pd(3)2Cl2] (9) and cis‐[Pd(4a)2Cl2] (10). Similarly, reaction of [Pt(COD)I2] with 4a in a 1:2 molar ratio afforded the complex cis‐[Pt(4a)2I2] (11). An X‐ray analysis has been carried out to obtain information on the effect of the ligand 4a on the overall structure of 11.

The complex trans-[Ir(CO)Cl(Ph2PPy)2] (1; Ph2PPy = 2-(diphenylphosphino)pyridine) was obtained in good yield from the reaction of [Ir(p-toluidine)(CO)2Cl] with Ph2PPy. It has a square-planar geometry, as does the analogous Vaska complex, with two monodentate Ph2PPy ligands P-bonded to the iridium(I) center. Compound 1 exhibits a reactivity reminiscent of Vaska's complex; in fact, it adds SO2, halogens, HCl, and CH3I. The addition of HCl to 1 initially occurs at the pyridine nitrogen atoms of the pendant Ph2PPy and subsequently at the iridium(I) center, affording [Ir(CO)H(Cl)2(Ph2PPyH)2][Cl]2 (6). The addition of a benzene solution of [Pd(PhCN)2Cl2] to a solution of 1 in the same solvent yielded, nearly quantitatively, the IrIIPdI complex [IrPd(CO)Cl3(μ-Ph2PPy)2] (8). The reaction of 1 with HgCl2, in benzene, in a 1:1 molar ratio afforded the binuclear complex [Ir(CO)Cl2(μ-Ph2PPy)2HgCl] (9). Using a 1:2 molar ratio the product [Ir(CO)Cl2(HgCl2)(μ-Ph2PPy)2HgCl]·2CH2Cl2 (10) was obtained. Compounds 8 and 10 were also characterized by a single-crystal X-ray diffraction analysis. The reaction of 1 with [Cu(NCCH3)4]BF4 afforded, almost quantitatively, the ionic compound [Ir(CO)Cl(μ-Ph2PPy)2Cu]BF4 (11) as an orange solid. The compound [Ir(CO)Cl(μ-Ph2PPy)2Tl]PF6 (12) obtained from the reaction of 1 with TlPF6, shows the Ir−Tl bonding and is luminescent in frozen CH2Cl2 solution at 77 K with a lifetime of 5 ns (±10%). As opposed to analogous compounds, in the bimetallic complexes 8−12 the bridging Ph2PPy ligands assume a head-to-head structure. The aim of the work was to obtain some insight into the beneficial effect of catalytic precursors containing the pendant Ph2PPy ligand in the hydroformylation catalytic cycle. Using complex 1 as a precatalyst in the hydroformylation of styrene, at 80 °C and under 80 atm of CO/H2 (1:1) pressure, the rate of the catalytic process increases significantly with respect to that observed with Vaska's complex, making clear a favorable effect of the pendant Ph2PPy ligand. However, the chemoselectivity of the process was low. A scheme of the catalytic cycle is proposed. The new aspects of the catalytic cycle are:  (i) the protonation under equilibrium conditions of one of the two pyridine nitrogen atoms of the pendant Ph2PPy ligands in the reductive elimination of HCl from the dihydride−iridium(III) species formed by oxidative addition of H2 to 1 and (ii) protonolysis, by the proton coordinated to the pyridine nitrogen atom, of the acyl or σ-alkyl groups present in the intermediates formed in the reaction pathway. Unexpectedly, 11 and 12 exhibit catalytic activity comparable with that of 1. This occurs because under the experimental conditions used the Cu−N or Tl−N bonds are broken, giving 1.

No abstract