The majority of commodity plastics and materials are derived from petroleum-based chemicals, illustrating the strong dependence on products derived from non-renewable energy sources. As the most accessible, renewable form of carbon (in comparison to CO2), lignocellulosic biomass (defined as organic matter available on a renewable basis) has been acknowledged as the most logical carbon-based feedstock for a variety of materials such as biofuels and chemicals. This Review focuses on methods developed to synthesize polymers derived from lignin, monolignols, and lignin-derived chemicals. Major topics include the structure and processing of lignocellulosic biomass to lignin, polymers utilizing lignin as a macromonomer, synthesis of monomers and polymers from monolignols, and polymers from lignin-derived chemicals, such as vanillin.

The divalent calcium and ytterbium compounds M(C(SiHMe(2))(3))(2)THF(2) contain beta-agostic SiH groups, as determined by spectroscopy and crystallography. Upon thermolysis, HC(SiHMe(2))(3) is formed. However, the SiH groups are hydridic. The compounds M(C(SiHMe(2))(3))(2)THF(2) react with 1 and 2 equiv of the Lewis acid B(C(6)F(5))(3) to form MC(SiHMe(2))(3)HB(C(6)F(5))(3))THF(2) and M(HB(C(6)F(5))(3))(2)THF(2), respectively. These species contain the anion [HB(C(6)F(5))(3)](-) from hydride abstraction rather than [(Me(2)HSi)(3)CB(C(6)F(5))(3)](-) from alkyl abstraction. The 1,3-disilacyclobutane byproduct initially suggested beta-elimination [as the dimer of the silene Me(2)Si horizontal lineC(SiHMe(2))(2)], but the other products and reaction stoichiometry rule out that pathway. Additionally, Yb(C(SiHMe(2))(3))(2)THF(2) and the weak Lewis acid BPh(3) react rapidly and also give the H-abstracted products. Despite the strong hydridic character of the SiH groups and the low-coordinate, Lewis acidic metal center in M(C(SiHMe(2))(3)THF(2) compounds, beta-elimination is not an observed reaction pathway.

Local Identifier(s): UCPMS ID: 1604555eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. Abstract:We report a discovery that perfunctionalized icosahedral dodecaborate clusters of the type B12(OCH2Ar)12 (Ar = Ph or C6F5) can undergo photo-excitation with visible light, leading to a new class of metal-free photooxidants. Excitation in these species occurs as a result of the charge transfer between low-lying orbitals located on the benzyl substituents and an unoccupied orbital delocalized throughout the boron cluster core. Here we show how these species, photo-excited with a benchtop blue LED source, can exhibit excited-state reduction potentials as high as 3 V and can participate in electron-transfer processes with a broad range of styrene monomers, initiating their polymerization. Initiation is observed in cases of both electron-rich and electron-deficient styrene monomers at cluster loadings as low as 0.005 mol%. Furthermore, photo-excitation of B12(OCH2C6F5)12 in the presence of a less activated olefin such as isobutylene results in the production of highly branched poly(isobutylene). This work introduces a new class of air-stable, metal-free photo-redox reagents capable of mediating chemical transformations.

A series of organometallic compounds containing the tris(dimethylsilyl)methyl ligand are described. The potassium carbanions KC(SiHMe2)3 and {KC(SiHMe2)3TMEDA}2 are synthesized by deprotonation of the hydrocarbon HC(SiHMe2)3 with potassium benzyl. {KC(SiHMe2)3TMEDA}2 crystallizes as a dimer with two types of three-center-two-electron K-H-Si interactions: side-on coordination of SiH (∠K-H-Si = 102(2)°) and more obtuse K-H-Si structures (∠K-H-Si ≈ 150°). The divalent calcium and ytterbium compounds M{C(SiHMe2)3}2L (M = Ca, Yb; L = 2THF, TMEDA) are prepared from MI2 and 2 equiv of KC(SiHMe2)3. Low 1JSiH coupling constants in the NMR spectra, low-energy νSiH bands in the IR spectra, and short M-Si distances and small M-C-Si angles in the crystal structures suggest β-agostic interactions on each C(SiHMe2)3 ligand. The IR assignments of M{C(SiHMe2)3}2L (L = 2THF, TMEDA) are supported by DFT calculations. The compounds M{C(SiHMe2)3}2L react with 1 or 2 equiv of B(C6F5)3 to give the 1,3-disilacyclobutane {Me2SiC(SiHMe2)2}2 and MC(SiHMe2)3HB(C6F5)3L or M{HB(C6F5)3}2L, respectively. In addition, M{C(SiHMe2)3}2L compounds react with BPh3 to give β-H abstracted products. The compounds M{C(SiHMe2)3}2THF2 react with SiMe3I to yield Me3SiH and disilacyclobutane as the products of β-H abstraction, while M{C(SiHMe2)3}2TMEDA and Me3SiI form a mixture of Me3SiH and the alkylation product Me3SiC(SiHMe2)3 in a 1:3 ratio.