C—Te cross-coupling

SCHEME 20.58 Cu-catalyzed synthesis of aryl alkyl tellurides. 

TRANSITION METAL-MEDIATED CARBON-HETEROATOM CROSS-COUPLING 

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First, Suzuki and coworkers reported Cul-mediated synthesis of diaryl tellurides via C—Te cross-coupling of aryl iodides with benzene teUurolate ions [194]. Catalytic protocol has been subsequently developed using Cul/l,10-phenanthroline L80 for the coupling of aryl iodides with organotellurolates [195] (Scheme 20.58). Further improvement was achieved in the coupling of ditellurides with boronic acid derivatives using copper-based catalytic systems, Cul-bpy [166], CuCl-bpy [196], and CuSO -5H2O/l,10-phenanthroline [197]. 

Comparing this with the data in Table 1, the real situation is found to be between the cases " a and " c of Hund coupling, but case (6) docs not correspond exactly to any one of the Hund cases. Now we evaluate the exchange ion-atom interaction potential A(i ) on the basis of the formula for the resonant charge exchange cross section (Te,r ill the case of the transition of s—electron [4, 14, 15]... 

Beletskaya IP, Ananikov VP. Transition-metal-catalyzed C S, C Se, and C Te bond formation via cross-coupling and atom-economic addition reactions. Chem. Rev. 2011 111 1596-1636. 

Fio. 9.3.4 Excitation with a surface coil of 9 mm diameter in a Bo gradient of the order of lOT/m by the NMR-MOUSE (a) Series train of CPMG echoes from a carbon-black filled SBR section of an intact car tyre with a steel belt. A fit of the echo envelope with an exponential decay function yields a transverse relaxation time Ti [Eidl]. (b) Variation of the pulse duration in an a — te/l — Ta — ts/ i- pulse sequence for different rf frequencies. For each frequency maxima and minima are observed which define the nominal 90° and 180° pulse widths. With decreasing rf frequency the distance of the sensitive volume from the rf coil increases. A frequency of 17.5 MHz correspond to depths of 0-0.5 mm, 16MHz to 0.5-1.0mm, and 16.5 MHz to 1.0-1.5 mm into the sample [Gut3], (c) Hahn- and solid-echo envelopes for a sample of carbon-black filled cross-linked SBR. The Hahn-echo decay is faster because of residual dipolar couplings which are partially refocused by the solid-echo [Gut3]. (d) Multi-echo excitation. 

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