The interactions of added phenanthroline and triphenylphosphine ligands with the copper(I) tetrahydroborates (phen)Cu(BH,) and (phen)(PPh3)Cu(BH4):: Probing the character of species in solution

Added free ligand, i.e. phenanthroline for (phen)CuBH4 and either phenanthroline or triphenylphosphine for (phen)PPh3CuBH4, causes a progressive change in the mode of attachment of the eta(2)-BH4 moiety from that in the initial complexes to the formation in solution of ionic species of the type [(phen)(2)Cu]+BH4- and [(phen)(PPh3)(2)Cu]+BH4-, respectively. These changes were indicated by: (i) infrared spectroscopy, which showed both a gradual loss of signals attributed to nu(B-H-b) and delta(BH2) and their replacement with spectra typical of ionic BH4- ion; (ii) an increase in the conductance measured that was consistent with a 1:1 electrolyte; (iii) chemical shift changes in the B-11- and P-31-NMR signals associated with the BH4- and PPh3 moieties, respectively and (iv) a relative increase in signal intensities of the ions detected by electrospray mass spectrometry. (C) 1999 Elsevier Science Ltd. All rights reserved.