Complex diamagnetic boron

The proposed structure for the diamagnetic boron complex is as follows 946 [181c] ... 

Covalently bonded sandwiches having five or six decks 78, 79 have been constructed via the reactions of C2B3-endcapped anions with transition metal cations 78,85 the hexadeckers vary in metal composition, in the nature of the substituents on boron (X), in the number of protonated metal centers, and in the number of electrons associated with the metals. Some of these complexes are diamagnetic, but most are paramagnetic with one or two unpaired electrons, in most cases extensively delocalized over the stack as shown by ESR and electrochemical studies.85... 

A number of other hydride complexes have been prepared the purple, diamagnetic hydride [MoH(BH4)(PMe3)4] has been obtained by reaction of NaBH4 with [MoCl3(PMe3)3]. The essentially tram octahedral structure of this molecule has been determined by X-rays as shown in (9) the hydride, the molybdenum and the boron atom of the bidentate BH4 group lie precisely on the intersection of two mirror planes in the molecule.86... 

Replacement of two carbon atoms in nickelocene by boron leads to complex 26 having the ir6/d8 arrangement to which cluster formalism can be applied. The diamagnetic sandwich 26 is isoelectronic with ferrocene... 

Use of the complexation shift as a measure of donor-acceptor interaction is especially treacherous with nuclei other than protons, because chemical shifts of these nuclei are more dependent on the paramagnetic than on the diamagnetic term of the screening tensor (52, 53). Both 19F and 11B resonances of the boron trihalides do shift to high field on complexation, as expected if the complexation shift were due to the increase in electron density on the boron trihalide, and early work indicated that 19F complexation shifts of BF3 could be correlated with enthalpies of formation of the complexes. Although this is true for BF3 adducts of some series of closely related donors (42, 91, 151), such correlations do not occur in other series (169). Table II illustrates that, although there is a tendency for the strongest... 

The NMR spectra were recorded only for diamagnetic cobalt(III) complexes (Table 11). Integral intensities of the signals from cross-linking BO3F group and those from the BF4 counter-ion in the F NMR spectra for boron-capped complexes are in a 1 2 ratio, thus confirming the formula proposed [2],... 

Of particular interest are various complexes formed by organoboron compounds with transition elements. Treatment of the N-lithio-derivative of the S>membered boron-nitrogen heterocycle, 7.28, with anhydrous ferrous chloride yields a dark-brown diamagnetic product, for which the sandwich ferrocene-like structure 7.29, has been proposed. 

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