Mixture Of Linkage Isomers Research Articles

Linkage Isomerism in Thiophene Cyclometallated Palladium(II) Complexes. Crystal and Molecular Structure of the Isomers [Pd{n‐SC4H2C(H)=NCy}(O2CMe‐O)(PPh3)] (n = 3, 4)

AbstractTreatment of 2‐SC4H3C(H)=NCy, a, or 3‐SC4H3C(H)=NCy, b, with palladium(II) acetate in toluene gave the dinuclear cyclometallated complexes [Pd{n‐SC4H2C(H)=NCy}(O2CMe)]2 (n = 5, 1a; n = 3, 1b; n = 4, 1b′), the latter two as a 1:1 mixture of linkage isomers, whose subsequent reactions produced isomeric mixtures in all cases. Reaction of 1a and 1b, 1b′ with aqueous sodium chloride or bromide yielded the corresponding halide‐bridged complexes [Pd{n‐SC4H2C(H)=NCy}(X)]2 (n = 5: X = Cl, 2a; X = Br, 3a; n = 3,4: X = Cl, 2b, 2b′; X = Br, 3b, 3b′) after metathesis. Reactions of the dinuclear compounds with tertiary phosphines in the appropriate molar ratio gave the mononuclear [Pd{n‐SC4H2C(H)=NCy}(Cl)(PPh3)] (n = 5, 6a; n = 3, 4 4b, 4b′) and [Pd{5‐SC4H2C(H)=NCy}{(Ph2PCH2CH2)2PPh‐P,P,P}](Cl), (5a), and the dinuclear [{Pd[5‐SC4H2C(H)=NCy](O2CMe)}2{μ–Ph2P(CH2)nPPh2}] (n = 2, 7a; n = 3, 8a; n = 4, 9a) complexes. The X‐ray crystal structure of complex 4b, 4b′ is described, establishing the presence of two isomers in the crystal lattice.

Solid-phase synthesis of chiral 3,4-diazaphospholanes and their application to catalytic asymmetric allylic alkylation.

Functionalized chiral diazaphospholanes ligate to a variety of transition metals, yielding chiral, catalytically active, metal complexes. Previous work has established that amino acid derivatization of the carboxyl groups of (R,R)-N,N'-phthaloyl-2,3-(2-carboxyphenyl)-phenyl-3,4-diazaphospholane (1) yields phosphines that are excellent ligands for palladium-catalyzed asymmetric allylic alkylation reactions. Alanine functionalization is particularly effective for allylic alkylation of 1,3-dimethylallyl acetate. Standard Merrifield resins and amino acid coupling methods are used to synthesize the bead-attached phosphine having the topology bead-linker-LAla-(R,R)-1-LAla-OMe, as a 1:1 mixture of linkage isomers. Use of this supported phosphine in Pd-catalyzed asymmetric allylic alkylation yields 92% enantiomeric excess, matching prior solution-phase results. A 20-member collection of amino acid-functionalized phosphines on beads with the topology bead-linker-AA(2)-AA(1)-1-AA(1)-AA(2) was synthesized by using parallel solid-state methods and screened for efficacy in allylic alkylation. Resulting enantioselectivities indicate that the AA(1) position has the strongest effect on the reaction. Catalyst activities can vary widely with the nature of the phosphine ligand and the reaction conditions. Meaningful analysis of intrinsic catalytic activities awaits identification of the structure and abundance of the active catalyst.

Hydridoiridium (III)‐Komplexe mit endständigem und verbrückendem Thio‐ und Selenocyanat 1)

Hydridoiridium(III) Complexes with Terminal and Bridging Thio- and Selenocyanate1) The thio- and selenocyanato complexes (Ph3P)2(CO)(Cl)(H)IrX 1 (X SCN) and 2 (X SeCN) and 2 (X SeCN) have been prepared from the corresponding tetrafluoroborato- and trifluoromethanesulfonato-compounds (X BF4, CF3SO3). The SCN ligand in 1 is S-bonded. 2 was obtained as a mixture of linkage isomers. The reaction of 2 with the tetrafluoroborato-complex (Ph3P)2(CO)(Cl)(H)IrFBF3 gives the salt [(Ph3P)2(OC)(Cl)(H)IrSeCNIr(H)(Cl)(CO)(PPh3)2]+BF which contains the selenocyanate-bridged cation as a mixture of stereoisomers.

ChemInform Abstract: USE OF X‐RAY K‐ABSORPTION SPECTROSCOPY FOR THE DETERMINATION OF BONDING IN THIOCYANATE COMPOUNDS

Abstract X-ray K-absorption edges of sulfur in metal complexes with a thiocyanate group have been investigated in order to find out the mode of coordination of the thiocyanate group in metal complexes. The shapes of the absorption edges revealed that the formation of M-S bonds leads to a characteristic absorption maximum on the low energy side of the edge. The intensity of this band is markedly lowered in thiocyanate complexes containing a mixture of linkage isomers.

Use of x-ray k-absorption spectroscopy for the determination of bonding in thiocyanate compounds

X-ray K-absorption edges of sulfur in metal complexes with a thiocyanate group have been investigated in order to find out the mode of coordination of the thiocyanate group in metal complexes. The shapes of the absorption edges revealed that the formation of M-S bonds leads to a characteristic absorption maximum on the low energy side of the edge. The intensity of this band is markedly lowered in thiocyanate complexes containing a mixture of linkage isomers.

Solvent control of the bonding mode of the co-ordinated thiocyanate ion

CoIII–SCN bonds can be formed in the presence of suitable ligands but, for some ligands, isomerisation occurs in solution to give a mixture of linkage isomers: in contrast to the behaviour observed for thiocyanatopalladium(II) complexes, M–NCS bond formation is promoted in solvents having high dielectric constants.