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 [(CH812)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 eta1-coordinated and the remaining two are chelated to the ruthenium atom has been assigned to 1 on the basis of P-31{H-1} 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 P1BAR, a = 10.608(3), b = 14.340(4), c = 15.570(5) angstrom, alpha = 102.06(2), beta = 105.48(2), gamma = 108.16(2)degrees, Z = 2. The structure model was refined up to R = 0.066 for 3147 reflections with F greater-than-or-equal-to 8sigma(F). At 20-degrees-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)2C]2] (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-degrees-C under 20-60 atm of a CO + H-2 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-degrees-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-degrees-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.