Walter Weissensteiner

Synthesis and molecular structure of enantiopure 1-(diphenylphosphino)-2,1′-[(1-N,N-dimethylamino)-1,3-propanediyl]-ferrocene and its palladium dichloride complex, a new ligand for enantioselective catalysts

The palladium dichloride complex of (Sc, Sm)-1-(diphenylphosphino)-2,1′-[(1-N,N-dimethylamino)-1,3-propanediyl]-ferrocene (5—PdCl2) has been prepared from enantiopure (S)-1,1′-[(1-N,N-dimethylamino)-1,3-propanediyl]-ferrocene (4) via a highly stereoselective ortho-lithiation followed by reaction with chlorodiphenyl phosphine to give amino phosphine 5, which on treatment with (Ch3CN)2PdCl2 gave the complex 5—PdCl2. Tha absolute configuration of the (-)589-enantiomer of 4 was deduced from the X-ray structure of its tartrate confirming (S)-configuration at the stereogenic center. A conformational analysis including X-ray structure analysis of 5 and 5—PdCl2 as well as empirical force field calculations on 4 and 5 together with NMR data shows strong stereochemical similarities of 5 and 5—PdCl2 with the widely used ligand PPFA and its palladium dichloride complex PPFA-PdCl2.

Synthesis of enantiopure 1,1′-(1-dimethylamino-propanediyl)ferrocene via a highly diastereoselective imine reduction

Abstract 1,1′-(1-Oxo-propanediyl)ferrocene 4 reacts with ( S )-(−)-1-(1-naphthylethyl)amine to give the corresponding syn imine exclusively which undergoes a highly diastereoselective reduction with sodium borohydride to give the diastereomerically pure ( R,S )-( + )-amine 6 . Conversion of 6 leads in three steps to the final product ( R )-( + )-1,1′-(1-dimethylamino-propanediyl)ferrocene 2 in 53% overall yield (based on 4 ) and in >98% e.e. Use of ( S ) - ( − )-1-phenylethylamine as the chiral auxiliary leads to an 84:16 mixture of syn and anti imines. After reduction and separation of the resulting diastereomers the major isomer ( R,S )-(−)- 10 can also be converted to the final product ( R ) - ( + )- 2 in 55% overall yield (based on 4 ) and in >98% e.e.

Platinum complexes of heteroannularly bridged heterobidentate ferrocenyl diphosphine ligands: their molecular structure and their use in catalytic carbonylation reactions

Abstract Platinum complexes PtCl2(L) and PtCl(SnCl3)(L) of the ferrocenyl diphosphine ligands (L) (R,R)-1-diphenylphosphino-2,1′-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene (1), (R,R)-1-diphenylphosphino-2,1′-[(1-dicyclohexylphosphino)-1,3-propanediyl]-ferrocene (2), (R,R)-1-bis(4-fluorophenyl)phosphino-2,1′-[(1-diphenylphosphino)-1,3-propanediyl]-ferrocene (3), have been synthesised. Complexes PtCl2(1) and PtCl2(2) have been structurally characterised by X-ray diffraction. Both the ‘preformed’ and the in situ catalysts have been used in hydroformylations of styrene. At low temperature (below 70°C) and with use of the platinum catalysts the prevailing formation of (R)-2-phenyl-propanal was observed, while at higher temperatures the formation of the (S)-enantiomer was favoured. The palladium catalysts proved to be rather inactive in the hydromethoxycarbonylation of styrene. In the presence of ligand 2 the predominant formation of the linear regioisomer was observed.

A homoannularly bridged hydroxyamino ferrocene as an efficient catalyst for the enantioselective ethylation of aromatic and aliphatic aldehydes.

Abstract Eleven aromatic and aliphatic aldehydes have been alkylated with Et2Zn in the presence of the homoannularly bridged hydroxyamino ferrocene I. The resulting carbinols have e.es varying from 66 to 97%. A mechanistic approach is presented to rationalize the preferred formation of the enantiomer observed.

Carbonylation (hydroformylation and hydroalkoxycarbonylation) of styrene in the presence of transition metal-ferrocene-based aminophosphine systems

Abstract The PtCl2(L)-type platinum complexes of the ferrocenyl ligands, (Sc,Sm)-1-diphenylphosphino-α-N,N-dimethylamino[2,3]tetramethyleneferrocene (1) and (Sc,Sm)-1,1′-bis(diphenylphosphino)-α-N,N-dimethylamino[2,3]tetramethylene ferrocene (2) have been synthesised. Both the ‘preformed’ and in situ catalysts have been used in hydroformylation of styrene. In spite of low enantioselectivities and activities, the ferrocenyl based systems proved to be of interest from theoretical point of view. The ligand influence on regio- and enantioselectivity has been investigated in systems containing either only one of the ferrocenyl ligands or one ferrocenyl ligand together with bdpp ((2S,3S)-2,4-bis(diphenylphosphino)pentane). The coordination of the respective ligands to platinum in the catalytic process can be deduced from results obtained with the ‘mixed ligand system’. The rhodium in situ catalysts containing either 1 or 2 are active in hydroformylation but the ee-s obtained with styrene are low. In the presence of ligand 1, the palladium-catalysed hydromethoxycarbonylation of styrene resulted in the predominant formation of the branched regioisomer, in case of 2 mostly the linear product was formed.

Synthesis and molecular structures of palladium and platinum complexes of PTFA: models of Grignard cross-coupling catalysts

Abstract A number of palladium(O) and palladium(II) as well as platinum(O) and platinum(II) complexes of (η5-cyclopentadienyl)-(η5-4-endo-N,N-dimethylamino-3-diphenylphosphino-4,5,6,7-tetrahydro-1H-idenyl)iron (PTFA) of the type (PTFA)M(0)(alkene) and (PTFA)M(II)(R)X, (M = Pd, Pt; alkene = dibenzylideneacetone, maleic anhydride, fumaronitrile and tetracyanoethylene; R = CH3, Ph and PhCH2; X = Cl, Br and I) have been synthesized as models of Grignard cross-coupling catalysts. All complexes were prepared either by proper ligand exchange or via oxidative addition reactions. A comparison of the X-ray structures of five complexes ((PTFA)Pd(fumaronitrile), 4, (PTFA)PdCl2, 8, (PTFA)Pd(Ph)I, 10, (PTFA)Pt(tetracyanoethylene), 6, and (PTFA)Pt(CH3)Cl, 13) showed that, in contrast to complexes of 2-(1-N,N-dimethylaminoethyl)-1-diphenylphosphino-ferrocene (PTFA), the overall molecular structures of PTFA complexes are comparable; they neither strongly depend on the oxidation state of the metal nor the type of additional ligands coordinated to the metal. Compound 4, C32H32FeN3PPd · CH2Cl2, crystallizes in the monoclinic space group P21/c (no. 14), with a = 19.237(2), b = 9.0737(10), c = 17.917(3), A , β = 96.458(11)°, V = 3107.6(7) A 3 , Z = 4 . The structure refinement converged to R1 = 0.0579 for 3832 F0 > 4q (F0) and wR2 = 0.1276 for all unique data, S = 0.94. Compound 6, C34H30FeN5PPt·C4H10, crystallizes in the triclinic space group P 1 , with a a = 11.845(3), b = 12.120(4), c = 12.979(3) A , α = 81.68(2)δ, β = 82.06(2)°, γ = 68.11(3)°, V = 1703.6(8) A 3 , Z = 2 . The structure refinement converged to R1 = 0.0402 for 6459 F0 > 4q(F0 and wR2 = 0.1076 for all 7235 unique data, S = 1.04. Compound 13, C29H33ClFeNPPt, crystallizes in the monoclinic space group P21/c (no. 14), with a = 16.122(2), b = 10.1608(11), c = 21.716(3) A , β = 132.202(11)°, V = 2635.2(5) A 3 , Z = 4 . The structure refinement converged to R1 = 0.0322 for 3846 F0 > 4q (F0) and wR2 = 0.0734 for all unique data, S = 1.03.

Rhodium catalysed enantioselective hydroboration of alkenylboronic esters with catecholborane

Abstract Alkenylboronic esters such as ( E )-2-(2-phenylethenyl)-1,3,2-dioxaborolane were subjected to catalytic hydroboration with catecholborane and with use of neutral and cationic rhodium complexes modified by various diphosphine ligands. The resulting 1,2-diboryl intermediate was oxidised with alkaline hydrogen peroxide to give the corresponding 1,2-diol with enantioselectivities up to 79 % e.e.

O-Methylephedrine: a highly efficient ortho-directing group in the synthesis of enantiopure 1,2-disubstituted ferrocene derivatives

Abstract ortho -Lithiation of N -ferrocenylmethyl- O -methylephedrine (98% d.e.) and reaction with electrophiles followed by nucleophilic replacement of the chiral auxiliary O -methylephedrine leads to 1,2-disubstituted enantiopure ferrocenyl derivatives.

A straightforward and modular synthesis of enantiopure C2- and C1-symmetrical 2,2′′-phosphino-1,1′′-biferrocenes

Abstract A new practical and highly flexible synthesis of enantiopure C2- and C1-symmetrical 2,2′′-phosphino-1,1′′-biferrocenes is presented. The structural properties of two of their PdCl2 complexes and preliminary Ru-catalysed hydrogenations using the biferrocene ligands, giving enantioselectivities of up to 82%, are described.

The triphenylphosphine cone angle and restricted rotation about the chromium-phosphorus bond in dicarbonyl(η6-hexa-alkylbenzene)(triphenyl-phosphine)chromium(0) complexes. Crystal and molecular structure of dicarbonyl(η6-hexa-n-propylbenzene)(triphenylphosphine)chromium(0)

The variable-temperature 90.56.MHz 13C-{1H} n.m.r. spectra of dicarbonyl(η6-benzene)(triphenylphosphine)chromium(0), (1), dicarbonyl(η6-hexamethylbenzene)(triphenylphosphine)chromium(0), (2), dicarbonyl(η6-hexaethylbenzene)(triphenylphosphine)chromium(0), (3), and dicarbonyl(η6-hexa-n-propylbenzene)(triphenylphosphine)chromium(0), (4), have been observed and a decoalescence in the triphenylphosphine subspectra of (2), (3), and (4), with ΔG200‡ca. 38 kJ mol–1, attributed to restricted rotation about the chromium–phosphorus bond. The steric requirements for intramolecular rotations for these complexes are visualised as two cones with a common apex at the centre of the chromium atom. The crystal and molecular structure of (4) has been determined and the co-ordinated hexa-n-propylbenzene has been found to adopt an all-distal alkyl group conformation.