Synthesis and characterization of mu,mu '-M(B5H8)(2) (M = Cd, Hg and Zn): a reassignment of the NMR spectra for 2,3-mu-metalloderivatives of pentaborane(9)

The series of compounds mu,mu'-M(B5H8)(2), where M = Cd (I), Zn (II), or Hg (III), has been prepared from the reaction between K(B5H8) and the metal c hloride in THF at low temperatures. The species were characterized by multi nuclear NMR spectroscopy, elemental analysis and mass spectrometry. The NMR spectral assignments were confirmed using B-11{H-1} selective decoupling e xperiments and heteronuclear B-11-H-1 chemical shift correlation spectrosco py. The results appeared to be in conflict with the earlier assignment of t he B-11-NMR spectra for 2,3-mu -metalloderivatives of pentaborane(9) which appear in the literature. For systems with an electrophilic group replacing a bridging H atom in B5H9, the B atoms most shifted in the B-11-NMR spectr um, which appear at the lower field, were assigned to the ones closest to t he metal group. Our results for I-m suggested that the assignment was rever sed, that is the higher held resonance is the one closest to the metal grou p. Thus, we reexamined the spectra of a series of related compounds includi ng 2,3-mu -SnPPh3(B5H8), mu,mu'-SnPh2(B5H8), mu ,1'-SnPh2(B5H8), other Sn s pecies and 2,3-mu -Cu(dppe)B5H8. In all cases our assignments were in accor d with those for I-III and we suggest that this is general for all such B5H 9 derivatives. (C) 2000 Elsevier Science B.V. All rights reserved.