Chirale Tripod‐Liganden mit Phosphit‐Donorgruppe: Synthese und Komplexchemie

Detection and Characterization of Hydride Ligands in Copper Complexes by Hard X-Ray Spectroscopy

Transition metal complexes, particularly copper hydrides, play an important role in various catalytic processes and molecular inorganic chemistry. This study employs synchrotron hard X-ray spectroscopy to gain insights into the geometric and electronic properties of copper hydrides as potential catalysts for CO2 hydrogenation. The potential of high energy resolution X-ray absorption near-edge structure (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is demonstrated with measurement on Stryker's reagent (Cu6H6) and [Cu3(μ3-H)(dpmppe)2](PF6)2 (Cu3H), alongside a non-hydride copper compound ICu(dtbppOH) (Cuy-I). The XANES analysis reveals that coordination geometries strongly influence the spectra, providing only indirect details about hydride coordination. The VtC-XES analysis exhibits a distinct signal around 8975 eV, offering a diagnostic tool to identify hydride ligands. Theoretical calculations support and extend these findings by comparing hydride-containing complexes with their hydride-free counterparts.

Sterically congested tripodal phosphites: conformational analysis, solid-state polymorphism, metal complexation, and application to the asymmetric hydrosilation of ketones

The synthesis as well as isolation and crystallographic analysis of two solid-state polymorphs of the tripodal ligand tri[2,2',2' '-tris[(2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]ethyl]amine (3) is described. Form I crystallized from ethyl acetate in the space group P2(1)/n with the unit-cell parameters a = 20.070(10) A, b = 17.477(2) A, c = 27.620(3) A, and beta = 93.050(10) degrees, V = 9674.5(14) A(3), and Z = 4. Form II crystallized from a mixture of acetone and toluene in the space group P1 with the unit-cell parameters a = 12.493(1) A, b = 19.701(2) A, c = 21.027(2) A, alpha = 116.23(1) degrees, beta = 100.15(1) degrees, and gamma = 91.07(1) degrees, V = 4542 A(3), and Z = 2. Differences in the relative absolute stereochemistry of the stereoaxes in the seven-membered dibenzo[d,f][1,3,2]dioxaphosphepin ring are discussed. The synthesis and X-ray characterization of enantiomerically pure (S,S,S)-tri[2,2',2' '-tris[(2,4,8,10-tetrakis(1,1-dimethylethyl)dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]propyl]amine [(S,S,S)-7] are reported. Two crystallographically independent molecules exist in the unit cell that cannot be superimposed with each other by either a translation or a symmetry operation. The two solid-state conformers in the unit cell differed predominately by the absolute stereochemistry of the stereoaxes in the seven-membered dibenzo[d,f][1,3,2]dioxaphosphepin ring. The Rh(I)-catalyzed hydrosilation of acetophenone with the chiral ligands (R,R,S)-7 and (S,S,S)-7 showed significant differences in chiral induction. Chiral cooperativity between the stereoaxes and stereocenters in (S,S,S)-7 is observed. The mechanism of the communication between the stereocenters and stereoaxes leading to chiral cooperativity in the stereoselective transition state is suggested to be primarily steric in nature.

Synthesis and coordination studies of new aminoalcohol functionalized tertiary phosphines

The synthesis of two new aminoalcohol functionalized tertiary phosphines o-Ph2PCH2N(H)C6H4(OH) (I) and o-Ph2PCH2N(H)C6H4(CH2OH) (II) are reported. Oxidation with aqueous H2O2 gave the corresponding phosphine oxides o-Ph2P(O)CH2N(H)C6H4(OH) (III) and o-Ph2P(O)CH2N(H)C6H4(CH2OH) (IV) (31P NMR evidence only). The ligating ability of I, II and, in several cases, the known ligand 2,3-Ph2PCH2N(H)C5H3N(OH) (V), was investigated with a range of late transition-metal precursors. Accordingly, reaction of 2 equiv of I (or II) with [MCl2(cod)] (M = Pd or Pt, cod = cycloocta-1,5-diene) gave the corresponding dichloro metal(II) complexes [MCl2(I)2] (M = Pd 1; M = Pt 2) and [MCl2(II)2] (M = Pd 3; M = Pt 4) in which I (and II) P-coordinate. Solution NMR studies reveal that 2 and 4 are exclusively cis whereas 1 and 3 are present as a mixture of cis and (or) trans isomers [4.7:1 (for 1); 2.2:1 (for 3)]. Reaction of 2 equiv of II with [Pt(CH3)2(cod)] gave the neutral complex [Pt(CH3)2(II)2] (5) whose X-ray structure confirmed a cis disposition of "hybrid" ligands. In contrast, reaction of I with [Pt(CH3)2(cod)] gave initially [Pt(CH3)2(I)2] (6) which, upon standing, afforded several products possibly reflecting an increased acidity of the phenolic groups of ligated I. Chloro bridge cleavage reactions of [{Ru(µ-Cl)Cl(p-cymene)}2] or [{Rh(µ-Cl)Cl{C5(CH3)5}}2] with I (or II) proceeds smoothly and gave the mononuclear complexes [RuCl2(p-cymene)I] (7), [RuCl2(p-cymene)II] (8), [RhCl2{C5(CH3)5}I] (9), and [RhCl2{C5(CH3)5}II] (10) in good yield. X-ray crystallography confirms both ruthenium complexes bear P-coordinated I (or II) ligands. Molecules of 7 are linked into linear chains via O-H···Clcoord intermolecular hydrogen bonding, a feature absent in the closely related compound 8. Reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with 1 equiv of I (or II) gave the corresponding gold(I) complexes [AuCl(I)] (11) and [AuCl(II)] (12). Bridge cleavage of the cyclometallated palladium(II) dimers [{Pd(µ-Cl)(C~N)}2] [C~N = C,N-C6H4CH2N(CH3)2, C,N-C10H6N(CH3)2, C,N-C6H4N=NC6H5] with V (or I) gave the neutral complexes [PdCl(C~N)V] (13-15) (or [PdCl(C9H12N)I] (16)), respectively. Chloride abstraction from 13 (or 15) with Ag[BF4] gave the cationic complexes [Pd(C~N)V][BF4] (17) (or 18) in which V P,N pyridyl-chelates to the palladium(II) metal centre. The X-ray structures of 13 and 18 have been determined and confirm the expected coordination environments. An array of intra- and intermolecular H-bonding contacts are also observed. All compounds have been characterized by a combination of spectroscopic and analytical studies.Key words: phosphines, crystal structures, alcohols, precious metals.