title: 1,2-Bis{(pentafluorophenyl)phenylphosphino}ethane:  A Probe for Configurational Stability in Three-Legged Piano Stool Complexes

authors: Nieuwenhuyzen, Mark

subjects: chemistry

abstract: The pentafluorophenyl-substituted diphosphine (C₆F₅)PhPCH₂CH₂PPh(C₆F₅) has been prepared, as a 1:1.7 mixture of rac (1a) and meso (1b) isomers, in four steps from dppe. The reaction between [Cp*RhCl(μ-Cl)]2 and 1 in the presence of tetrafluoroborate yielded a mixture of racemic diastereoisomers of [Cp*RhCl(κP,κP-1a)][BF₄] (4a•BF₄) and trans and cis isomers of [Cp*RhCl(κP,κP-1b)][BF₄] (4b•BF₄ and 4c•BF₄, respectively). On addition of Proton Sponge, 4a and 4c, in which at least one pentafluorophenyl group is close to the pentamethylcyclopentadienyl ligand, underwent rapid dehydrofluorinative carbon−carbon coupling giving trans- and cis-[{η⁵,κP,κP-C₅Me₄CH₂C₆F₄-2-PPhCH₂CH₂PPh(C₆F₅)}RhCl]⁺ (5 and 6), respectively. The latter underwent further dehydrofluorinative carbon−carbon coupling to give two isomers of [{η⁵,κP,κP-C₅Me₃[CH₂C₆F₄-2-PPhCH₂]₂}RhCl]+ (7). Isomerization of 4b to 4c was observed in chloroform and dimethlysulfoxide. Neither isomerization of 4a to 4b or 4c nor isomerization of 5 to 6 was observed at ambient or elevated temperature in dimethyl sulfoxide. The results provide the first evidence that complexes of η⁵,κP,κL-cyclopentadienyl-phosphine-donor ligands are configurationally stable at high temperature.

text: 1,2-Bis{(pentafluorophenyl)phenylphosphino}ethane:  A Probe for Configurational Stability in Three-Legged Piano Stool Complexes The pentafluorophenyl-substituted diphosphine (C₆F₅)PhPCH₂CH₂PPh(C₆F₅) has been prepared, as a 1:1.7 mixture of rac (1a) and meso (1b) isomers, in four steps from dppe. The reaction between [Cp*RhCl(μ-Cl)]2 and 1 in the presence of tetrafluoroborate yielded a mixture of racemic diastereoisomers of [Cp*RhCl(κP,κP-1a)][BF₄] (4a•BF₄) and trans and cis isomers of [Cp*RhCl(κP,κP-1b)][BF₄] (4b•BF₄ and 4c•BF₄, respectively). On addition of Proton Sponge, 4a and 4c, in which at least one pentafluorophenyl group is close to the pentamethylcyclopentadienyl ligand, underwent rapid dehydrofluorinative carbon−carbon coupling giving trans- and cis-[{η⁵,κP,κP-C₅Me₄CH₂C₆F₄-2-PPhCH₂CH₂PPh(C₆F₅)}RhCl]⁺ (5 and 6), respectively. The latter underwent further dehydrofluorinative carbon−carbon coupling to give two isomers of [{η⁵,κP,κP-C₅Me₃[CH₂C₆F₄-2-PPhCH₂]₂}RhCl]+ (7). Isomerization of 4b to 4c was observed in chloroform and dimethlysulfoxide. Neither isomerization of 4a to 4b or 4c nor isomerization of 5 to 6 was observed at ambient or elevated temperature in dimethyl sulfoxide. The results provide the first evidence that complexes of η⁵,κP,κL-cyclopentadienyl-phosphine-donor ligands are configurationally stable at high temperature.

year: 2006

title: Review: The effect of temperature on enzyme activity: new insights and their implications

authors: Daniel, Roy M.

subjects: Equilibrium Model

abstract: The two established thermal properties of enzymes are their activation energy and their thermal stability. Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active-inactive transition, in addition to an irreversible thermal inactivation. Two new thermal parameters, T eq and ΔH eq, describe the active–inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We review here the Model itself, methods for the determination of T eq and ΔH eq, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology.

text: Review: The effect of temperature on enzyme activity: new insights and their implications The two established thermal properties of enzymes are their activation energy and their thermal stability. Arising from careful measurements of the thermal behaviour of enzymes, a new model, the Equilibrium Model, has been developed to explain more fully the effects of temperature on enzymes. The model describes the effect of temperature on enzyme activity in terms of a rapidly reversible active-inactive transition, in addition to an irreversible thermal inactivation. Two new thermal parameters, T eq and ΔH eq, describe the active–inactive transition, and enable a complete description of the effect of temperature on enzyme activity. We review here the Model itself, methods for the determination of T eq and ΔH eq, and the implications of the Model for the environmental adaptation and evolution of enzymes, and for biotechnology.

year: 2007

title: Māori language resources and Māori initiatives for teaching and learning te reo Māori

authors: Greensill, Hineitimoana

abstract: As the most southerly member of the Polynesian languages, a sub-group of the widespread Austronesian language family (Harlow, 2007), te reo Māori has been the subject of substantial analysis, documentation, and analyses of its structure since first contact with Captain Cook in 1769 (Whaanga & Greensill, 2014). The history, trials and tribulations of te reo Māori in Aotearoa have been well documented (see, for example, Reedy, 2000; Spolsky, 2005; Waitangi Tribunal, 1986, 2011). The various reasons for the language’s decline has been an area of ongoing debate and critique by academics, researchers, linguists, language activists, parliamentarians and Māori in recent times (see, for example, Bauer, 2008; Benton, 2015; Higgins, Rewi, & Olsen-Reeder, 2014; Rata, 2007; Winitana, 2011).

text: Māori language resources and Māori initiatives for teaching and learning te reo Māori As the most southerly member of the Polynesian languages, a sub-group of the widespread Austronesian language family (Harlow, 2007), te reo Māori has been the subject of substantial analysis, documentation, and analyses of its structure since first contact with Captain Cook in 1769 (Whaanga & Greensill, 2014). The history, trials and tribulations of te reo Māori in Aotearoa have been well documented (see, for example, Reedy, 2000; Spolsky, 2005; Waitangi Tribunal, 1986, 2011). The various reasons for the language’s decline has been an area of ongoing debate and critique by academics, researchers, linguists, language activists, parliamentarians and Māori in recent times (see, for example, Bauer, 2008; Benton, 2015; Higgins, Rewi, & Olsen-Reeder, 2014; Rata, 2007; Winitana, 2011).

year: 2017