Frustrated Pairs

Recall from Section 1.9 that the Lewis acid and base in a frustrated pair are too bulky or otherwise sterically constrained to bond with each other but the cleft between them acts like an enzyme active site and promotes remarkable chemical reactions, perhaps none more so than the activation of dihydrogen at or below room temperature. Two representative reactions mediated by P,B-based FLPs are as follows ... 

We now return to our kitchen sink filled with warm water, to which we add a few drops of a surfactant. When we insert a frustrated pair in water, the polar head is happy, whereas the aliphatic chain is miserable. One way to improve this state of affairs is to place the molecule at the water/air interface (Figure 8.3). This strategy allows us to realize what is referred to as a monolayer of surface density (where E is the surface area per polar head). 

Even more effective in hydrogen activation are frustrated Lewis pairs [220] containing NHCs as Lewis bases. In 2008 two research groups reported the activation of hydrogen by frustrated Lewis pairs made up from a suitably Af,A -substituted NHC and B(CgF5)3 (Fig. 30) [221, 222]. The corresponding reaction of the frustrated Lewis pair with primary and secondary alkyl amines resulted in the formation of aminoboranes [222]. 

As Rosenkreutz wryly observes with a certain measure of sangfroid, we had all been thoroughly foxed... and we had to be reconciled with the Virgin s practical joke. Immediately following this sexual practical joke, chance pairs us, the frustrated Bachelors must witness a play within in a play, and. 

CT-VPP-REDOR) or the pulse duration fp (CT-VPD-REDOR) then produces CT-REDOR curves, from which the second moment may be evaluated with distinctively superior accuracy as compared to the values obtained from a parabolic fit to the conventional REDOR data. When restricting the experiment to short dipolar evolution times, the two-spin approximation may be applied for the data analysis, which proves to be especially attractive for amorphous solids, for which the exact spin geometry is unknovm. The data presented on the model compoimds illustrate the various facets of CT-REDOR NMR spectroscopy. First application examples, namely, the evaluation of the heteronuclear Li-Ti dipolar couplings within the garnet structure of Li5La3Nb20i2, the determi-nation of the intemuclear B- P distance in frustrated Lewis pairs, the analysis of Na- F dipolar interaction in fluormica or Na- P... 

In the framework of Frustrated Lewis Pairs, Erker also investigated the hydroboration of a-alkenyl-phosphines with HB(C6F5)2.52/53 Starting from dimesityl(vinyl)phosphine, the CH2CH2-bridged PB 40a was first... 

For example, if the BN bond were to break during the dehydrohalogenation process amine bases could be chosen that selectively capture a proton while the halogenated boron species remains uncoordinated due to steric hindrance. This concept is related to the recently published frustrated Lewis pair concept used for hydrogen activation by sterically demanding borane and amine species [104]. 

To control access to the cabinet, a solenoid lock and thumbwheel can be installed on the door of the field cabinet and wired to input/output points on the controller. The access code is specified by the system programmer and should be a pair of combinations that will be easy for the maintenance workers to remember. Upon entry of the correct code or a process instability, the solenoid will be de-energized to permit entry. This arrangement makes it unnecessary for production personnel to know the access code, and the unlock algorithm detailed in the figure uses a 10-s timer to frustrate clever operators. 

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