F. Faraone

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.

Some reations of the (π-C5H5)Rh(CO)L (L=CO, PPh3) complexes

The reactions of the complexes CpRh(CO)L (Cp = cycclopentadienyl; L = CO, PPh3) with Hl, ClCH2CN and C6H5SO2 l have been investigated. Inboth cases the reaction with hydrogen chloride gives products which do not contain the cyclopentadcienyl ring. Chloroa etonitrile reacts only with CpRh(CO)PPh3, and gives the cationic complex [CpRh(CO)(CH2CN)PPh3]+, which has been isolated and characterized. The sulphonyl chloride 6H5SO2l reacts with CpRh(CO)PPh3 to give a product which had not been fully identified and with CpRh(CO)2 to give CpRh (O)(C6H5SO2)Cl.

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.

Synthesis of Phosphonito,N and Phosphito,N ligands based on quinolines and (R)-binaphthol or substituted biphenol and of their rhodium(I), palladium(II) and platinum(II) complexes

Abstract The new Phosphonito,N ligands 8-(4,8-di-tert-butyl-1,11-dimethoxy-5,7-dioxa-6-phospha-dibenzo[a,c]cyclohepten-6-yl)-quinoline (2a), and (R)-8-(3,5-dioxa-4-phospha-cyclohepta-[2,1-a;3,4-a′]dinaphthalen-4-yl)-quinoline ((R)-2b), were readily prepared starting from 8-(bis-diethylamino-phosphine)-quinoline (1), as a key intermediate, and 2,2′-dihydroxy-5,5′-dimethoxy-3,3′-di-tert-butylbiphenyl or (R)-binaphthol, respectively. The Phosphito,N ligand, 8-(4,8-di-tert-butyl-1,11-dimethoxy-5,7-dioxa-6-phospha-dibenzo[a,c]cyclohepten-6-yloxy)-quinoline (3a), was obtained by reacting equimolar amounts of 8-hydroxyquinoline and the phosphorochloridite derived from 3,3′-di-tert-butyl-2,2′-dihydroxy-5,5′-dimethoxybiphenyl, in toluene in the presence of NEt3. The corresponding Phosphito,N-ligand, 8-(3,5-dioxa-4-phospha-cyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxy)-quinoline (R)-(3b), was obtained similarly using the phosphorochloridite derived from (R)-binaphthol. A systematic study of the coordination abilities of 2–3 to rhodium(I), palladium(II) and platinum(II) precursors has been carried out. Crystal structures of the complexes [Pt(3a)I2] (7a), and [Pd(2a)Cl2] (8a), are reported. The reactions of the chiral ligands (R)-2b and (R)-3b with [Rh(acac)(CO)2] lead to [Rh(acac)(R-2b)] (10), and [Rh(acac)(R-3b)] (11), respectively. Under hydroformylation conditions, displacement of the chiral ligands in both complexes 10 and 11 takes place, even in the presence of an excess of free ligand, leading to achiral hydrido-carbonyl rhodium complexes.

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.

Effect of chelating vs. bridging coordination of chiral short-bite P–X–P (X = C, N, O) ligands in enantioselective palladium-catalysed allylic substitution reactions

The chiral short-bite ligands (Ra,Ra)-bis(dinaphthylphosphonito)methane, (Ra,Ra)-1, (Ra,Ra)-bis-dinaphthylpyrophosphite, (Ra,Ra)-2, (Sc)-bis(diphenylphosphino)-sec-butylamine, (Sc)-3, (Ra,Ra)-bis(dinaphthylphosphonito)phenylamine, (Ra,Ra)-4a, (Ra,Ra,Sc)-bis(dinaphthylphosphonito)-sec-butylamine, (Ra,Ra,Sc)-4b, and (Ra,Sc)-(dinaphthylphosphonito)(diphenylphosphino)-sec-butylamine, (Ra,Sc)-5, have been synthesised. The cationic palladium-allyl mononuclear chelate, [Pd(eta3-PhCHCHCHPh)(mu-L-Lshort-bite)]PF6 [L-Lshort-bite=(Sc)-3, (Ra,Ra)-4a, (Ra,Ra,Sc)-4b and (Ra,Sc)-5 for complexes, and, respectively] and binuclear bridged [Pd(eta3-PhCHCHCHPh)(mu-Ra,Ra-2)]2(PF6)2, 12, have been isolated. The short-bite chiral ligands synthesised have been tested in the palladium-allyl catalysed substitution reaction of 1,3-diphenylallyl acetate with dimethyl malonate. The catalytic system was studied, in solution, by a multinuclear NMR technique. In the catalytically active species formed with (Ra,Ra)-2 ligand, [Pd(eta3-PhCHCHCHPh)(Ra,Ra-2)]2(PF6)2, 12, the palladium(II) centres are bridged by two ligands which are forced to adopt a nearly cis-coordination to allow coordination of the allyl-moiety. Semiempirical calculations on a biphenyl-model molecule, similar to the species 12, indicate that this situation induces a strain and rigid conformation in the chiral ligands, which produce differences in the terminal allyl carbon atoms. As consequence, the catalytic product was obtained with an enantiomeric excess of 57.1% in the S form. A low e.e. value was obtained when the (Ra,Ra)-1, (Sc)-3, (Ra,Ra)-4a, (Ra,Ra,Sc)-4b and (Ra,Sc)-5 ligands have been tested in the same palladium-catalysed reaction.