The intercalation of Li into micro-and nanocrystalline anatase xerogel powders using n-butyllithium and various preparation conditions has been studied by 6 Li and 7 Li solidstate NMR and X-ray absorption spectroscopy. The orthorhombic lithium titanate phase which forms for Li/Ti < 0.56 undergoes further structural modification as the Li/Ti ratio increases to 0.70. NMR shows the existence of one type of lithium environment in microcrystalline samples when Li/Ti e 0.30 and two lithium environments when Li/Ti > 0.30. These two lithium environments are assigned to Li + ions in similar structural sites that are uncoupled (species A) and weakly coupled (species B) to conduction band electrons. Nanocrystalline anatase samples produced by sol-gel methods differ from microcrystalline anatase in that the proportion of species A is greater. NMR further suggests that the coordination number of species A cannot be greater than five while no definite conclusions could be reached from NMR concerning species B. Titanium K-edge X-ray absorption near edge structure (XANES) provides a method of monitoring changes in electronic structure as Li is intercalated. Extended X-ray absorption fine structure (EXAFS) analysis provides information on the Ti local environment which changes considerably with the degree of intercalation in microcrystalline samples. For nanocrystalline anatase samples greater amounts of intercalation can be achieved which dramatically affects both the XANES and the EXAFS.

Rhodium(I) catalysts formed by the two chiral chelating six-membered ring diphosphines, 2,4-bis(diphenylphosphino)pentane (skewphos) and l,3-bis(diphenylphosphino)butane (chairphos), are efficient catalysts for the hydrogenation of amino acid precursors. The two chiral phosphines differ in that skewphos probably adopts a chiral conformation whereas chairphos probably adopts an achiral conformation. As a consequence the former generally gives high optical yields whereas the latter is ineffective as a chiral catalyst. This comparison evidences the importance of ring conformations in determining optical yields. The mechanism of asymmetric hydrogenation is discussed, and a number of particular and general conclusions are drawn which may prove useful in predicting optical yields from asymmetric synthesis.

Sodium amalgam reduction of NiC1(C6H4Br-2)(Cy2PCHzCHzPCyz)-0.5THF (6) (Cy = cyclohexyl, C6H1,) gives a mononuclear nickel(0) complex, Ni(qz-C6H4)(Cy3PCHzCHzPCy2) (3), which has been characterized by microanalysis, by mass, infrared, and NMR ('H, ' C, 31P) spectroscopy, and by single-crystal X-ray structural analysis. Crystals of 3 are orthorhombic, space group Pbca, with a = 16.068 (1) A, b = 17.189 (1) A, c = 22.358 (1) A, and 2 = 8. The structure was solved by heavy-atom methods and refined by least-squares methods to R = 0.035 and R, = 0.055 for 4203 independent reflections. The molecule consists of a central nickel atom coordinated by a symmetric q2-benzyne ligand [Ni-C(l) = 1.870 (4) A, Ni-C(2) = 1.868 (4) A the coordination geometry being close to trigonal planar. The coordinated C-C bond length of 1.332 (6) k is significantly larger than those observed in alkyne complexes of zerovalent nickel and latinum. The remaining C-C bonds of the six-membered ring are almost equal in length (average 1.385 i), consistent with a delocalized aromatic structure for the benzyne ligand. Complex 3 reacts with iodine and methyl iodide at room temperature to give, respectively, the 2-iodophenyl and o-tolyl complexes NiI(C6H4Y-2)(CyzPCHzCHzPCyz) (Y = I (71, Me (8)). Carbon dioxide, ethylene, and dimethyl acetylenedicarboxylate insert into the nickel-benzyne bond of 3 to give the nickelacycles Ni(C6H4COO)-(CyzPCHzCH2PCyz) (lo), Ni(CH2CHzC6H4-o)(CyzPCHzCHzPCyz) (111, and Ni(C(C02Me)=C-(COzMe)C6~4-o)(CyzPCH~cH~Pcyz) (12), respectively, whereas diphenylacetylene displaces benzyne to give Ni(PhCd!Ph)(CyzPCHzCHzPCyz) (13). Crystals of 11 are monoclinic, space group P2,/n, with a = 15.792 (6) A, b = 17.471 (6) A, c = 12.104 (4) A, p = 104.09 ( 2 ) O , and 2 = 4. The structure was solvedand refined as for 3 to R = 0.070 and R, = 0.071 for 2379 independent reflections. The nickel atom is coordinated in an approximately planar arrangement by the bidentate di(tertiary phosphine) and by two carbon atoms of a five-membered, half-chair-shaped chelate ring, the Ni-C(ary1) and Ni-C(alky1) bond lengths being 1.951 (12) and 1.988 (12) A, respectively. , .

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