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Chiral Phosphoramidite Ligands Based on 8‐Chloroquinoline and Their Rhodium(III), Palladium(II), and Platinum(II) Complexes

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.

Hydroformylation of styrene catalyzed by rhodium complexes with 2-diphenylphosphinopyridine

Abstract Mono- and binuclear rhodium complexes containing 2-(diphenylphosphino)pyridine, Ph 2 PPy 2 , as ligand have been examined as catalysts for the hydroformylation of styrene. All the species tested were good catalysts and the formation of the expected aldehydes took place selectively within several hours in mild conditions. The binuclear derivative [(η 5 -C 5 H 5 )Rh 2 (μ-CO)(μ-Ph 2 PPy)(CO)Cl], 1 , was an efficient catalysts only when the reaction was carried out under high pressure, whereas the in situ system obtained by addition of Ph 2 PPY to RhH(CO)(PPh 3 ) 3 , 4 , displayed a pronounced activity even in the low pressure reaction. 31 P{ 1 H} NMR shows that in solution Ph 2 PPy can easily displace one or two moles of PPh 3 from 4 , giving rise to mixed mononuclear phosphine-rhodium complexes that seem likely to be the most active catalytic species.

Synthesis and structural characterization of a new series of ruthenium(II) complexes containing the short bite Ph2PPy ligand. Cooperative effect between the anionic rhodium and cationic ruthenium species in the catalytic hydroformylation of styrene by [Ru(Ph2PPy)3Cl] [Rh(CO)2Cl2]

The reaction of [(C8H12)RuCl2]n with 3 molar equiv. of 2-(diphenylphosphino)pyridine, Ph2PPy, in refluxing methanol, gave [Ru(Ph2PPy)3Cl]Cl (1) and small amount of a red unidentified product. A fac structure in which one of the Ph2PPy is γ1-coordinated and the remaining two are chelated to the ruthenium atom has been assigned to 1 on the basis of 31P{1H} NMR spectra. Solutions of 1 in chlorinated solvents afford the neutral complex [Ru(Ph2PPy)2Cl2] (2). IR and NMR spectra and X-ray analysis indicate that 2 assumes a cis structure in both solution and solid state. Compound 2 crystallizes with two CDCl3 molecules H-bonded to the chlorine atoms of the coordination shell of each ruthenium. Crystal data: triclinic, space group P1, a=10.608(3), b=14.340(4), c=15.570(5) A, α=102.06(2), β=105.48(2), γ=108.16(2)°, Z=2. The structure model was refined up to R=0.066 for 3147 reflections with F⩾8σ(F). At 20 °C and 1 atm, compound 1 adds CO in equilibrium condition affording the dicationic compound [Ru(CO)(Ph2PPy)3]Cl2; this cannot be isolated when operating in CO atmosphere. Treatment of 1 with 2 equiv. of CF3COOAg in dichloromethane gave the corresponding [Ru(Ph2PPY)3(CF3COO)]CF3COO (4) containing a small amount of [Ru(Ph2PPY)2(CF3COO)2] (5). By reacting 1 with [Rh(CO)2Cl]2 or [Ir(CO)2(p-toluidine)Cl] the complexes [Ru(Ph2PPy)3Cl][Rh(CO)2Cl2] (6) and [Ru(Ph2PPy)3Cl][Ir(CO)2Cl2] (7) were obtained. Compounds 6 and 7 were used as catalysts in the hydroformylation of styrene. The hydroformylation reactions were performed in the temperature range 45–100 °C under 20–60 atm of a CO+H2 1:1 mixture and the reaction was generally stopped after 6 h. An almost quantitative conversion of styrene could be obtained under 50–60 atm and 75 °C in 6 h. The chemioselectivity of the reaction is satisfactory; the branched isomer aldehyde predominates in all experiments and its amount increases upon reducing the reaction temperature; at 40 atm the regioselectivity, expressed by the B/L ratio, improves from about 2.3 to 18 operating at 100 and at 45 °C. The most significant result emerges by comparison of the catalytic activity of complexes 1, [Rh(CO)2Cl2]AsPh4 and 6 which shows that the ionic heterobimetallic RuRh complex 6 is much more active than the mononuclear complexes [Ru(Ph2PPy)3Cl]Cl and [Rh(CO)2Cl2]AsPh4. This was explained by a cooperative effect between the anionic rhodium and cationic ruthenium species in complex 6. Compound 7, as a precatalyst, showed only negligible activity.

Structural control in palladium(II)-catalyzed enantioselective allylic alkylation by new chiral phosphine-phosphite and pyridine-phosphite ligands

Abstract The ligands 6-[(diphenylphosphanyl)methoxy]-4,8-di-tert-butyl-2,10-dimethoxy-5,7-dioxa-6-phosphadibenzo[a,c]cycloheptene, 1, (S)-4-[(diphenylphosphanyl)methoxy]-3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4a′]dinaphthalene, (S)-2, and (S)-4-[(diphenylphosphanyl)methoxy]-2,6-bis-trimethylsilanyl-3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalene, (S)-3, (S)-2-(3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxymethyl)pyridine, (S)-4, and (S)-2-(3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxy)pyridine, (S)-5, have been easily prepared. The cationic complexes [Pd(η3-C3H5)(L-L′)]CF3SO3 (L–L′=1–(S)-5) and [Pd(η3-PhCHCHCHPh)(L–L′)]CF3SO3 (L–L′=(S)-2–(S)-4) were synthesized by conventional methods starting from the complexes [Pd(η3-C3H5)Cl]2 and [Pd(η3-PhCHCHCHPh)Cl]2, respectively. The behavior in solution of all the π-allyl- and π-phenylallyl-(L–L′)palladium derivatives 6–14 was studied by 1H, 31P{1H}, 13C{1H} NMR and 2D-NOESY spectroscopy. As concerns the ligands (S)-4 and (S)-5, a satisfactory analysis of the structures in solution was possible only for palladium–allyl complexes [Pd(η3-C3H5)((S)-4)]CF3SO3, 11, and [Pd(η3-C3H5)((S)-5)]CF3SO3, 12, since the corresponding species [Pd(η3-PhCHCHCHPh)((S)-4)]CF3SO3, 13, and [Pd(η3-PhCHCHCHPh)((S)-5)]CF3SO3, 14, revealed low stability in solution for a long time. The new ligands (S)-2–(S)-5 were tested in the palladium-catalyzed enantioselective substitution of (1,3-diphenyl-1,2-propenyl)acetate by dimethylmalonate. The precatalyst [Pd(η3-C3H5)((S)-2)]CF3SO3 afforded the allyl substituted product in good yield (95%) and acceptable enantioselectivities (71% e.e. in the S form). A similar result was achieved with the precatalyst [Pd(η3-C3H5)((S)-3)]CF3SO3. The nucleophilic attack of the malonate occurred preferentially at allylic carbon far from the binaphthalene moiety, namely trans to the phosphite group. When the complexes containing ligands (S)-4 and (S)-5 were used as precatalysts, the product was obtained as a racemic mixture in high yield. The number of the configurational isomers of the Pd-allyl intermediates present in solution in the allylic alkylation and the relative concentrations are considered a determining factor for the enantioselectivity of the process.

Enantioselective hydroformylation with the chiral bidentate P,N-ligand 2-[1-(1S,2S,5R)-(–)menthoxydiphenylphosphino]pyridine cationic rhodium(I) complexes

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

Mononuclear(η6-arene)ruthenium(II) and (η5-pentamethllcyclopentadienyl)rhodium(III) and binuclear ruthenium(II)-platimum(II) and ruthenium(II)-rhodium(I) complexes containing 2-(diphenylphosphino)pyridine

Abstract The isoelectronic complexes [(η 6 -C 6 H 6 )Ru(Ph) 2 PPyCl 2 ] ( 1 ) and [(η 5 Me 5 )Rh(Ph 5 PPy)Cl 2 ] ( 3 ) in which 2-(diphenylphosphino)pyridine (Ph 2 PPy) is P-monodentate , have been obtained by treating the complexes [{(η 6 -C 6 H 6 )RuCl 2 } 2 ], and [{(η 5 -C 5 Me 5 )RhCl 2 } 2 ], respectively, with Ph 2 PPy in the molar ratio 1:1, Coordination of the pyridine nitrogen atom to metal in 1 and 3 has been achieved by removing one chloride with AgPF 6 . By this route the cationic complexes [(η 6 -C 6 H 6 )Ru(Ph 2 PPy)Cl]PF 6 ( 2 ) and [(η 5 -C 5 Me 5 )Rh(Ph 2 PPy)Cl]PF 6 ( 4 ) in which the Ph 2 PPy is chelating, have been obtained. The reaction of [(η 6 -C 6 Me 6 Ru(Ph 2 PPy)Cl 2 ] ( 1 ) with cis -[Pt(DMSO) 2 Cl 2 ] in CH 2 Cl 2 gives the ionic binuclear complex [(η 6 -C 6 Me 6 )Ru(Ph 2 PPy)(μ-Cl)Pt(DMSO)Cl 2 ]Cl ( 5a ) which was also obtained as the [PF 6 ] − salt, 5b . 1 H and 31 P{ 1 H} NMR spectra support structures for 5a and 5b with the Ph 2 PPy chelated to ruthenium(II) and a chloride bridging to platinum(II). The DMSO is S-bonded and the geometry at platinum(II) is cis . Upon attempted reaction of 1 with cis -[Pd( t BuNC) 2 Cl 2 ] in CH 2 Cl 2 at room temperature, the reagents were recovered unchanged after 7 h. The reactions of [(η 5 -C 5 Me 5 )Rh(Ph 2 PPy)Cl 2 ] ( 3 ) with cis -[Pd( t BuNC) 2 Cl 2 ] and cis -[Pt(DMSO) 2 Cl 2 ] afford the known cis -[Pd( t BuNC)(Ph 2 PPy)Cl 2 ] and cis -[Pt(DMSO)(Ph 2 PPy)Cl 2 ], together with {[(η 5 -C 5 Me 5 )RhCl 2 } 2 ]. The reaction of [{(C 8 H 12 )RuCl 2 } n ] with [(η 5 -C 5 H 5 )Rh(CO)(Ph 2 PPy)] in CH 2 Cl 2 in the molar ratio 1:1, is very complex. We have separated [(C 8 H 12 )RuCl((μ-Cl(μ-Ph 2 PPy)Rh(η 5 -C 5 H 5 )] ( 6 ) by chromatography column. The bridging Ph 2 PPy is P-bonded to the rhodium(I). On allowing CH 2 Cl 2 solution of 6 to stand, crystals of the rhodium(III) complex [(η 5 -C 5 H 5 )RhCl 2 (Ph 2 PPy)] ( 7 ) are formed. Probably a very slow intramolecular redox process involving the Ru II Rh I species 6 is responsible of the formation of 7 . In the complex, the 2-(diphenylphosphino)pyridine is monodentate, coordinating through phosphorus.

Rhodium(I), Palladium(II), and Platinum(II) Complexes Containing New Mixed Phosphane−Phosphite Ligands − Effect of the Catalytic System Stability on the Enantioselective Hydroformylation of Styrene

The new mixed phosphane−phosphite ligands 1 and 2, derived from 3,3′-di-tert-butyl-2,2′-dihydroxy-5,5′-dimethoxybiphenyl and (S)-binaphthol, respectively, reacted with [Rh(COD)(THF)2]CF3SO3 to give the compounds [Rh(COD)(1)]CF3SO3 and [Rh(COD)(2)]CF3SO3 in which the ligands 1 and (S)-2 are chelated to the rhodium centre. The reaction with [Rh(CO)2Cl]2 gave two different products, [Rh(CO)2(L)Cl] and [Rh(CO)(L)Cl] [L = 1 and (S)-2], containing L as a chelate. On the basis of the IR and NMR spectroscopic data, the proposed structure of the pentacoordinate species is a trigonal bipyramide in which the phosphane−phosphite ligand assumes an equatorial-axial coordination. The reactions of 1 and 2 with [Pd(C6H5CN)2Cl2] and [Pt(COD)I2] gave the corresponding compounds [Pd(L)Cl2] and [Pt(L)I2] in which the ligands are chelated to the metal centre. The crystal structure of the chloroform solvate of [Pd(L)Cl2] was fully characterised by an X-ray study. The chiral ligands (S)-2 and (S)-3 [derived from the ortho-bis(trimethylsilyl)-substituted (S)-binaphthol] were tested in the hydroformylation of styrene. The results obtained were discussed in light of the catalytic system stability.

New chiral amino-phosphoramidite and bisphosphoramidite ligands derived from (R, R)-1,2-diaminocyclohexane: application in Cu-catalyzed asymmetric conjugate addition of diethylzinc to 2-cyclohexenone

Abstract New bidentate amino-phosphoroamidite and diphosphoroamidite ligands derived from inexpensive (R,R)-1,2-diaminocyclohexane have been synthesized and screened in the Cu-catalyzed asymmetric conjugate addition of Et2Zn to 2-cyclohexenone. The highest 74% ee value was reached with the N,N′-dimethyl substituted P,N-ligand and Cu(OAc)2·H2O.

New phosphoramidite and phosphito-N chiral ligands based on 8-substituted quinolines and (S)-binaphthol; applications in the Cu-catalyzed enantioselective conjugate addition of diethylzinc to 2-cyclohexen-1-one

Abstract The copper(II)-catalyzed enantioselective conjugate addition of diethylzinc to 2-cyclohexen-1-one, in the presence of phosphoramidite and of phosphito-N chiral ligands, derived from 8-chloroquinoline or 8-hydroxyquinoline and ( S )-4-chloro-3,5-dioxa-4-phosphacyclohepta[2,1- a ;3,4- a ′]binaphthalene, resulted in ee s of 70 and 51%, respectively.

Steric and chelate ring size effects on the enantioselectivity in palladium-catalyzed allylic alkylation with new chiral P,N-ligands

Abstract New chiral P,N-ligands derived from substituted pyridine and (S)-2,2′-binaphthol phosphorochloridite have been prepared and tested in asymmetric palladium-catalyzed allylic alkylations. The enantioselectivity was poorly dependent on the pyridine substituent, instead, a chelate ring size effect was apparent.