Louise M. Liable-Sands

Platinum-Catalyzed Enantioselective Tandem Alkylation/Arylation of Primary Phosphines. Asymmetric Synthesis of P-Stereogenic 1-Phosphaacenaphthenes

Enantioselective tandem alkylation/arylation of primary phosphines with 1-bromo-8-chloromethylnaphthalene catalyzed by Pt(DuPhos) complexes gave P-stereogenic 1-phosphaacenaphthenes (AcePhos) in up to 74% ee. Diastereoselective formation of four P-C bonds in one pot with bis(primary) phosphines gave C2-symmetric diphosphines, including the o-phenylene derivative DuAcePhos, for which the rac isomer was formed with high enantioselectivity. These reactions, which appear to proceed via an unusual metal-mediated nucleophilic aromatic substitution pathway, yield a new class of heterocycles with potential applications in asymmetric catalysis.

Synthesis, characterization, and ring-opening polymerization of a novel [1]silaferrocenophane with two ferrocenyl substituents at silicon

Abstract Reaction of dichlorodiferrocenylsilane, Fc2SiCl2 (4) (Fc=(η-C5H4)Fe(η-C5H5)), with dilithioferrocene fcLi2·TMEDA (fc=(η-C5H4)2Fe, TMEDA=N,N,N,N-tetramethylethylenediamine) afforded the novel trimetallic [1]silaferrocenophane 5, fcSiFc2, in 77% yield. A single crystal X-ray diffraction study of ferrocenophane 5 showed the presence of significant disorder but revealed that the molecule possesses a highly strained structure where the tilt-angle between the planes of the cyclopentadienyl rings of the ferrocenophane is 20–22°, typical of strained silicon-bridged [1]ferrocenophanes. The Fe⋯Fe distances in 5 are 5.434, 5.537, and 5.687 A, and metal–metal interactions are evident as redox coupling was detected in the cyclic voltammogram of this species. Differential pulse voltammetry resolved three oxidation waves at 0, 0.22, and 0.45 V relative to the ferrocene/ferrocenium couple. Mossbauer spectroscopy proved useful in corroborating the structure of 5, as the two distinct Fe environments present were readily resolved (δ=0.424(5) mm s−1, d, ΔEq=2.242(5) mm s−1, 2 Fe; δ=0.414(5) mm s−1, d, ΔEq=1.930(5) mm s−1, 1 Fe). Further characterization of 5 by IR and Raman spectroscopy was also undertaken. Ring-opening addition of HCl across a strained Si–C bond of 5 afforded chlorotriferrocenylsilane, Fc3SiCl (6), in 81% yield. Subsequent hydrolysis of 6 afforded a silanol Fc3SiOH (7) with three ferrocenyl substituents. Single crystal X-ray diffraction of 7 revealed that the compound crystallizes as hydrogen-bonded dimers. When heated, 5 was found to undergo thermal ring-opening polymerization (ROP) to afford cyclic oligomeric species [fcSiFc2]x (9x, x=2 or 3) and an insoluble polymeric material [fcSiFc2]n (8). Copolymers 10 were obtained when 5 was heated in the presence of dimethyl[1]silaferrocenophane, fcSiMe2 (1a)

Structural Diversity in the Solid‐State Structures of the Rubidium and Cesium Salts of 2,6‐Dimesitylphenylphosphane

A coordination environment reminiscent of a paddle-wheel is exhibited by aryl groups about one of the two cesium ions in CsP(H)Dmp (Dmp=2,6-dimesitylphenyl; structure depicted on the right), which has now been synthesized and is found to exhibit Cs+ {Cs2 [P(H)Dmp]3 }- contact ion pairs in the solid state. In contrast, the analogous rubidium compound displays a Rb4 P4 cube as the central structural motif.

Preparation of single-source precursors to nanocrystalline gallium arsenide and gallium antimonide. X-ray crystal structures of [Et2GaAs(SiMe3)2]2, [Et2GaSb(SiMe3)2]2 and Et2b(SiMe3)2 ☆

Abstract The 1:1 mole ratio reaction of Et2GaCl with As(SiMe3)3 leads to the isolation of [Et2GaAs(SiMe3)2]2 (1), while the analogous reaction with Sb(SiMe3)3 results in the formation of [Et2GaSb(SiMe3)2]2 (2). The mixed-pnicogen compound Et2 GaAs(SiMe 3 ) 2 Ga(Et) 2 S b(SiMe3)2 (3) was obtained from both the equilibration of 1 and 2, as well as the 2:1:1 mole ratio reaction of Et2GaCl with As(SiMe3)3 and Sb(SiMe3)3. X-ray crystal structures are reported for 1, 2 and 3, as well as a variable temperature 1H-NMR study of 2 and 3. The dimer 2 was found to exhibit a dimer/trimer equilibrium in solution. Thermolysis of all three compounds results in the formation of GaAs, GaSb or GaAsxSb(1−x) through a β-hydride elimination pathway.

1H nuclear magnetic resonance spin-lattice relaxation, 13C magic-angle-spinning nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and x-ray diffraction of two polymorphs of 2,6-di-tert-butylnaphthalene

Polymorphism, the presence of structurally distinct solid phases of the same chemical species, affords a unique opportunity to evaluate the structural consequences of intermolecular forces. The study of two polymorphs of 2,6-di-tert-butylnaphthalene by single-crystal x-ray diffraction, differential scanning calorimetry (DSC), 13C magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and 1H NMR spin-lattice relaxation provides a picture of the differences in structure and dynamics in these materials. The subtle differences in structure, observed with x-ray diffraction and chemical shifts, strikingly affect the dynamics, as reflected in the relaxation measurements. We analyze the dynamics in terms of both discrete sums and continuous distributions of Poisson processes.

Synthesis and structure of chiral 2,6-bis[(2-carbamoylphenyl)carbamoyl]pyridine ligands

Abstract The synthesis and structure of a series of enantiomerically pure 2,6-bis[(2-carbamoylphenyl)carbamoyl]-pyridine ligands (H22a-c) are described. Appended from the aryl groups are optically active groups which provide a chiral environment around the planar pyridine core. NMR and X-ray diffraction studies show that these ligands contain helical character which is maintained by a network of intramolecular hydrogen bonds. These ligands can bind metal ions through their tridentate diamidato-pyridyl chelate to form optically active metal complexes. The modular design of these ligands offers a variety of chiral environments about the metal chelate that can be useful in the synthesis of metal reagents for asymmetric transformations.

Synthesis and characterization of ring-coupled cyclopentadienyl and indenyl bimetallic derivatives of Cr, Mo and W

Abstract A series of new ring-coupled bimetallic complexesM2(CO)6[η5,η5-C5H4 C(CH3)2 C5H4], where M Cr, Mo, W, was synthesized by reaction of the dianion of the ligand 2,2-bis(cyclopentadienyl)propane and M(CO)3(CH3CN)3, M Cr, Mo, W. Oxidation with acetic acid-Fe(III) produced the bimetallic complexes in moderate yields. Using the same strategy, reactions of Mo(CO)3(CH3CN)3 with the dianion of 2-cyclopentadienyl-2-indenylpropane produced only the dimer[Mo(CO)3[η5-C5H4 C(CH3)2 C9H7]2 in which the indenyl ring was unmetallated. Subsequent detailed studies revealed that the desired dimetalloanion was initially formed, but that the indenyl bound metal was lost upon protonation. Evidence for the mechanism of this demetallation process is presented. The dimetalloanion could be intercepted by methyl iodide to form[Mo(CO)3CH3]2[η5,η5-C5H4 C(CH3)2 (C9H6)]. Synthesis of Mo2(CO)6[η5,η5 C5H4 C(CH3)2−(3-RC9H5)], where R H, CH3, was achieved by aprotic oxidation of the intermediate dimetalloanion by ferricinium tetraphenylborate. The molecular structures of two compounds are reported: Mo2(CO)6[η5,η5 C5H4 C(CH3)2−(3-CH3C9H5)]: triclinic,P1, a = 8.777(3)A˚, b = 9.428(4)A˚, c = 14.915(4)A˚, α = 91.42(3)°, β = 102.04(3)°, γ = 114.69(3)°, V = 1087.9(8)A˚3, Z = 2, R(F) = 3.03%.[Mo(CO)3CH3]2[η5,η5 C5H4 C(CH3)2 (C9H6)]: triclinic,P1, a = 8.298(6)A˚, b = 11.662(6)A˚, c = 13.241(8)A˚, α = 100.28(1)°, β = 93.02(1)°, γ = 99.72(1)°, V = 1238(1)A˚3, Z = 2, R(F) = 3.99%.

Terthienyl-Based Redox-Switchable Hemilabile Ligands: Transition Metal Polymeric Complexes with Electrochemically Tunable or Switchable Coordination Environments?

By controlling the extent of oxidation of the polymeric forms of the new class of isolable, polymerizable terthienyl Ru(II) complexes 1, one can modulate both the binding strength of the polymer backbone for Ru(II) and the electronic nature of the bound metal centers.

4,5-Bis(diphenylthiophosphinoyl)-1,2,3-triazole, LT-S2: a new varidentate ligand containing diphenylthiophosphinoyl moieties

Abstract The novel ligand 4,5-bis(diphenylthiophosphinoyl)-1,2,3-triazole, LT-S2H, has been synthesized, converted to the triethylamine salt, and to the palladium complexes Pd[LT-S2]2 and Pd[LT-S2][η3-methallyl]. Structures of LT-S2H, of its 2-acetyl derivative, of Pd[LT-S2]2 and Pd[LT-S2][η3-methallyl] were determined by X-ray crystallography. In the last two complexes the LT-S2 ligand was N,S-bonded.

Multimodal Study of Secondary Interactions in Cp*Ir Complexes of Imidazolylphosphines Bearing an NH Group

Hydrogen bonding phenomena are explored using a combination of X-ray diffraction, NMR and IR spectroscopy, and DFT calculations. Three imidazolylphosphines R(2)PImH (ImH = imidazol-2-yl, R = t-butyl, i-propyl, phenyl, 1a-1c) and control phosphine (i-Pr)(2)PhP (1d) lacking an imidazole were used to make a series of complexes of the form Cp*Ir(L(1))(L(2))(phosphine). In addition, in order to suppress intermolecular interactions with either imidazole nitrogen, 1e, a di(isopropyl)imidazolyl analogue of 1b was made along with its doubly (15)N-labeled isotopomer to explore bonding interactions at each imidazole nitrogen. A modest enhancement of transfer hydrogenation rate was seen when an imidazolylphosphine ligand 1b was used. Dichloro complexes (L(1) = L(2) = Cl, 2a-2c,2e) showed intramolecular hydrogen bonding as revealed by four X-ray structures and various NMR and IR data. Significantly, hydride chloride complexes [L(1) = H, L(2) = Cl, 3a-3c and 3e-((15)N)(2)] showed stronger hydrogen bonding to chloride than hydride, though the solid-state structure of 3b evinced intramolecular Ir-H...H-N bonding reinforced by intermolecular N...H-N bonding between unhindered imidazoles. These results are compared to literature examples, which show variations in preferred hydrogen bonding to hydride, halide, CO, and NO ligands. Surprising differences were seen between the dichloro complex 2b with isopropyl groups on phosphorus, which appeared to exist as a mixture of two conformers, and related complex 2a with tert-butyl groups on phosphorus, which exists in chlorinated solvents as a mixture of conformer 2a-endo and chelate 5a-Cl, the product of ionization of one chloride ligand. This difference became apparent only through a series of experiments, especially (15)N chemical shift data from 2D (1)H-(15)N correlation. The results highlight the difficulty of characterizing hemilabile, bifunctional complexes and the importance of innocent ligand substituents in determining structure and dynamics.