Two-bond Couplings not Involving Hydrogen

Recently, Hilmersson and co-workers have observed that in heterogeneous aggregates involving lithium amides and alkyllithium compounds, a Juu coupling can be measured between nonequivalent lithium nuclei belonging to a quadrilateral only if the two complementary atoms are carbons. A similar 

An analysis of multipath transmission of spin-spin coupling in cyclic compounds has been made by Wu and Cremer with the help of partially spin-polarized orbital contributions. The calculations have been performed for cyclopropane, cyclopentane, bicydo[1.1.1]pentane and tetrahydrofuran. The authors have shown that the measured and calculated Vcc couplings of cyclopentane and tetrahydrofuran are averages over the pseudorotational motion of these ring molecules where each individual coupling of a conformation passed in the pseudorotation is the sum of different path contributions. 

Carbon-carbon couplings across one, two and three bonds have been reported and discussed by Primer et for a series of cyclobutenones and benzocyc-lobutenones. 

Long-range C-C, C-N and N-N couplings in selectively labelled Ni(II) complexes of the Schiff base derived from (S)-iV-benzylproline(2-benzoylphenyl)am-ide and glycine have been measured by Popkov et al in CDCb solution. Their analysis provided evidence that the donation of electron density from the jt-system of the benzyl ring to the nickel orbitals takes place. 

VcTi couplings between ca. 40 and 65 Hz and Vcti couplings between ca. 35 and 60 Hz have been measured by Claramunt et al. in the solid state C NMR spectra of some thallium (I) tris-(pyrazol-l-yl)borates (thallium scorpionates). 

The Vc-(N)-p couplings measured by Herberhold et for a series of tri(tert-butyl)plumbyl-phosphanes allowed the authors a unequivocal elucidation of the preferred conformation of the amino group with respect to an axis representing the assumed orientation of the lone pair of electrons at the phosphorus atom. A large and positive coupling corresponds to the syn-orientation of the N-C bond with respect to the lone pair of electrons, and a small and of either sign Vc-n-p coupling reflects the anti orientation. 

A two-bond C-P coupling of 10.8 Hz observed by Szafert et al in the spectrum of [(ri -C5Me5)Re(NO)(PPh3)(=C=C=C=C=CAr2)] BF4 provided unequivocal proof of the presence of the P-Re=C fragment. 

Typical trends have been observed in two-bond C-P couplings measured by Sanchez et for two series of the new molybdenum and tungsten carbonyl complexes [M(CO)4(o-Ph2PC6H4-CH=NR)] (M = Mo, W R = Aik), the trans couplings ca. 35 Hz) being significantly larger than the cis ones (3-9 Hz). 

VpF and /ff couplings have been determined by Przyborowski et al from an analysis of the low-temperature spectrum of T-isopropyloamino-T-phenyl-l-methylene-3,3,4,4-tetrafluorocyclopentan-2,5-dione, a member of a newly synthesised series of fluorinated P-enaminoketones. Two-bond F-F 

It has been shown by Edwards et al that a linear correlation exists 

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The catalytic cycle presumably involves the oxidative addition with coupling of two molecules of ethylene to a Ti" species, generating a titanacyclopentane. A 1,3-hydrogen shift across the ring generates 1-butene. Because it does not involve a hydride intermediate that might catalyze a double-bond shift, 1 -butene is stable... 

The formation of a C-C bond resulting from the coupling of two C-H bonds is a particularly attractive target, since the only formal by-product would be hydrogen, or water in an oxidative system. However, substantial hurdles impede the conception of a catalytic arene cross-coupling process that does not involve any substrate pre-activation at all. Aside from issues of reactivity and regioselectivity, the prevention of homo-coupling is a key factor for the development of this important class of reaction. The catalyst must be able to react with one arene in the first step of the catalytic cycle and then invert its selectivity in the second step to react exclusively with a different arene (Scheme 29). 

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