Predicting the enantioselectivity of the copper-catalysed cyclopropanation of alkenes by using quantitative quadrant-diagram representations of the catalysts.

We present a new methodology to predict the enantioselectivity of asymmetric catalysis based on quantitative quadrant-diagram representations of the catalysts and quantitative structure-selectivity relationship (QSSR) modelling. To account for quadrant occupation, we used two types of molecular steric descriptors: the Taft-Charton steric parameter (ν(Charton)) and the distance-weighted volume (V(W) ). By assigning the value of the steric descriptors to each of the positions of the quadrant diagram, we generated the independent variables to build the multidimensional QSSR models.

Theoretical studies of asymmetric hydroformylation using the Rh-(R,S)-BINAPHOS catalyst--origin of coordination preferences and stereoinduction.

We have undertaken theoretical investigations of the asymmetric hydroformylation of styrene by the [Rh{(R,S)-BINAPHOS}(CO)(2)H] catalyst, focusing on the origin of the ligand coordination preferences and stereoinduction. We evaluated the different factors governing the preference of the BINAPHOS ligand to coordinate with the phosphane moiety at the equatorial site and the phosphite moiety at the apical site. The donor-acceptor interactions, obtained using a modified version of energy decomposition analysis (EDA) based on orbital deletion, favour the phosphite moiety at the equatorial site.

Ammonia activation by μ3-alkylidyne fragments supported on a titanium molecular oxide model.

Ammonolysis of the μ(3)-alkylidyne derivatives [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-CR)] [R = H (1), Me (2)] produces a trinuclear oxonitride species, [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ(3)-N)] (3), via methane or ethane elimination, respectively. During the course of the reaction, the intermediates amido μ-alkylidene [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-CHR)(NH(2))] [(R = H (4), Me (5)] and μ-imido ethyl species [{Ti(η(5)-C(5)Me(5))(μ-O)}(3)(μ-NH)Et] (6) were characterized and/or isolated. This achievement constitutes an example of characterization of the three steps of successive activation of N-H bonds in ammonia within the same transition-metal molecular system.