Hapto

DOtz KH, Wenzel B, Jahr HC (2004) Chromium-Templated Benzannulation and Hapto-tropic Metal Migration. 248 63-103... 

An interesting class of reactions includes the activation of furan derivatives by their hapto coordination to a rhenium centre. Harman and co-workers have made a number of contributions to this field,303-305 with a particularly significant paper that appeared in 2003 (Scheme 68).306 Harman and co-workers also reported on the activation of non-heteroaromatics, such as benzene and naphthalene.307-309... 

Kl. Kluthe, R., and Isliker, H., Isolierung von Serumhaptoglobinen als Hapto-globin-Hamoglobin-Komplex durch Zinkfallung und Saulenchromatographie. Hellj. Physiol, et Pharmacol. Acta 18, 1 (1960). 

Following a number of stable Si-N silylenes301 and the stable hapto bonded silylene decamethylsilicocene (Me5C5)2Si 107,265 Kira et al. have described the preparation of the first stable sigma-bonded dialkylsilylene,... 

Further Increases in the number of electrons associated with the main-group fragment are realized In the halides, C5H5X (X=F, Cl). The global minimum for both molecules is and this geometry is strongly preferred over any multl-hapto structure. 

Reaction of the mono-hapto bis-allyl complex 57b with NaOEt in EtOH gave allyl group hydrogenation yielding [lr(cod)Br(NHC3)j (55d, NHC3=1,3-... 

Examples of reductive cluster-opening and oxidative cluster-closing reactions are common in the chemistry of metal-hydrocarbon tt complexes. For example, bases convert nido- (hexa-hapto)arene-manganese tricarbonyl complexes into aracAno(pentahapto)-7T-cyclohexadienyl complexes 129,130, 217) ... 

This exemplifies a quite general reaction in organometallic chemistry, the cluster-opening conversion of an w-hapto ligand into an ( — 1 )-hapto ligand by addition of a nucleophile X . The converse, cluster-closing conversion accompanies removal of X . 

The magnitude of the chemical shift anisotropy depends on the bonding situation and the nucleus gyromagnetic ratio. Since the bonds formed by lithium in organolithium compounds or other lithiated systems are mainly ionic, the anisotropy of the lithium chemical shift is generally small. It is more pronounced for Li than for Li. Li spectra are dominated by the quadrupolar effect and the CSA contribution to the Li lineshape is often negligible. Exceptions are compounds with poly-hapto bound lithium, such as... 

The molybdenum-acyl enolate 4 has been characterized spectroscopically by NMR and has been reported to exist as a single (observable) isomer88. Extended Hiickel calculations on model complexes suggest that a conformation similar to A is most favorable for enolates such as 488. The deprotonated di-hapto acyl ligand may also be described as a 2-(C,0)-ketene ligand both the ketene and enolate terminology appear in the literature. 

Reaction of achiral biscyclopentadienyl zirconium-( /2-acyl-C,0) complexes, such as la and lb, with sodium hexamethyldisilazide generates the di-hapto enolates 2a and 2b91. Enolate 2b is believed to adopt a Z geomeLry, only one isomer was observable by H-NMR spectroscopy (d.r. >98 2). 

B. Diorganomagnesium Compounds Containing Multi-hapto-bonded... 

F. Donor-Acceptor Complexes of Diorganomagnesium Compounds with Multi-hapto-bonded Groups... 

So far, only multi-hapto-bonded groups have been considered that contain a cyclic unsaturated functionality. It appeared that linear conjugated unsaturated functionalities are also capable of being involved in such multi-hapto interactions. 

Another type of ligand, capable of forming multi-hapto interactions with metals, are boron and boron-carbon cage compounds of which in particular the carboranes have been used extensively in organometallic chemistry . The structures in the solid state of a few magnesacarboranes have been determined by X-ray crystallographic studies. 

B. Diorganozinc Compounds Containing Multi-hapto Bonded Groups... 

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