Dario Drommi

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.

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.

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.

Steric effects of the 2-(diphenylphosphino)pyridine bridging ligand in the synthesis of binuclear palladium(II) complexes

Treatment of [Pd{CH2C(CH3)CH2}(Ph2PPy)Cl] (Ph2PPy = 2-(diphenylphosphino)pyridine) with cis-[Pd(tBuNC)2Cl2] in dichloromethane affords the mixed isocyanide-tertiary phosphine complex cis-[Pd(tBuNC)Ph2PPy)Cl2], in which the Ph2PPy is a monodentate P-donor, and [{Pd[CH2C(CH3)CH2]Cl}2]. The steric effects of the Ph2PPy bridging ligand in determining the reaction course is discussed. The complex cis-[Pd(tBuNC)(Ph2PPy)Cl2] was crystallographically characterized: P21/n, a = 15.143(2), b = 9.527(1), c = 17.517(4) A, β = 113.96(1)°, V= 2309.4(7) A3, Z = 4. The final R value was 0.044, Rw= 0.046 for the 3078 reflections with I > 3σ(I).

Formation of Metallamacrocycles from Palladium(II), Platinum(II) and Copper(I) Complexes and the Ditopic Ligands [{p‐(Ph2PO)C6H4}2CMe2], [{2‐Ph2PO‐3,5‐(Me3C)2C6H2}2S], [{p‐[(C10H6O)2PO]C6H4}2CMe2]

The new ligands bis(phosphinito) [{2-Ph2PO-3,5-(Me3C)2C6H2}2S] (4) and chiral bis(phosphite) [{p-[(C10H6O)2PO]C6H4}2CMe2] (5) were synthesised and their reactions with palladium(II), platinum(II), copper(I) substrates were studied. The ligand 3 [{p-(Ph2PO)C6H4}2CMe2], previously reported by us, was also used in the same reactions. Ligands 3 and 5 formed 28-membered metallamacrocycles while ligand 4 afforded the analogous compound only in the reaction with the copper(I) substrate. In the reaction of 3 with [Pd(PhCN)2Cl2] the metallamacrocycle [PdCl2(μ-3)]2 (6) or the oligomer [Pd2Cl4(μ-3)]n (7) were formed, depending on the molar ratio used. The reaction of 3 with [Pd(η3-C3H5)Cl]2 afforded compound {[Pd(η3-C3H5)Cl]2(μ-3)} (8). The allylpalladium macrocycle [Pd(η3-C3H5)(μ-3)]2[OTf]2 (9) was obtained by treating a solution of 8 in THF with AgCF3SO3. The reactions of ligand 3 with [Pt(COD)I2] or [Cu(NCCH3)4]BF4 led to the formation of metallamacrocycles [PtI2(μ-3)]2 (10) and [Cu2(μ-3)2][BF4]2·2CH3CN (11), respectively. The structure of 10 was also elucidated by X-ray analysis. Reactions of 4 with palladium(II) and platinum(II) complexes afforded a mixture of two very different compounds in almost an equimolar ratio. An X-ray analysis established that one is a mononuclear compound, formed by modification of the ligand 4, containing a P,S-chelate, namely {PdCl2{[2-Ph2PO-3,5(Me3C)2C6H2][3,5-(Me3C)2C6H2OH]S}] (12). The reaction between [Cu(NCCH3)4]BF4 and 4 afforded the ionic metallamacrocycle [Cu(μ-4)][BF4]2·2CH3CN (14). In compound 10, the size of the central cavity formed by the bridging ligand 3 was determined.

Mixed phosphito–phosphonato rhodium(I) complexes

O,O′-3,3′-Di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl-2,2′-diyl phosphonate (HL)I was prepared by hydrolysis of (3,3′-di-tert-butyl-5,5′-dimethoxy-1,1′-biphenyl-2,2′-diyl)phosphorus chloride. Its tautomeric equilibrium with the corresponding phosphite form was completely shifted toward the phosphonate form. The reaction of I with the solvato complex [Rh(C8H12)(thf)2]ClO4(C8H12= cycloocta-1,5-diene, thf = tetrahydrofuran), in thf, in the molar ratio 2 : 1, afforded the rhodium(I) complex [Rh(HL)L(C8H12)] containing I co-ordinated both as a phosphonate and phosphite ligand. Carbon monoxide replaces the C8H12 ligand of 1 to afford the corresponding dicarbonyl species 2. The latter was better obtained by treating [Rh(acac)(CO)2](acac = acetylacetonate) with I, in benzene solution, in the molar ratio 1 : 2. The 31P-{1H} NMR spectra indicate for 1 and 2 the existence either of a P–OH to PO proton-exchange process faster than the NMR time-scale or of a symmetrical O ⋯ H ⋯ O bridge. The existence of a symmetrical O ⋯ H ⋯ O bridge was confirmed by treating 2 with BF3·Et2O. The acidic character of the hydrogen of the O ⋯ H ⋯ O framework was also confirmed treating 2 with NaOH. The reaction of the resulting anionic species with the solvato species [Rh(C8H12)(thf)2]ClO4 afforded a binuclear dirhodium(I) zwitterionic compound [Rh2L2(C8H12)2] containing bridging phosphonate ligands both bonded to a rhodium(I) centre through the phosphorus atoms and to the other one through the oxygen atoms. Attempts to crystallize 1 from a dilute diethyl ether–dichloromethane (4 : 1) solution also afforded the binuclear complex in low yield. Its crystal structure has been determined by single-crystal X-ray diffraction. Under catalytic hydroformylation conditions, the complexes lose the phosphorus-containing moieties to give the catalyst [RhH(CO)4].