Square-planar complexes of the type RZMX (M = Pt or Pd), containing the terdentate ligand 2,6-(Me,NCH,),C,H,, undergo with Me1 (M = Pt, X = BF,) oxidative addition and consecutive reductive elimination resulting in the formation of the complex BF,-[IPtgR-Me]+ in which the C-aryl centre, a t which C-C coupling has occurred, is bonded to the cationic Pt-centre by a novel Pt-to-C-interaction.

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A series of new and known Rh(1) complexes [ Rh(R2P(CH2),PR2),)Y and [ Rh(diene)(R2P(CH2),PR,)1Y (R = Me, Et, Ph, C,F,, C,H,CF,; Y = C1, CIO,, PF,, BF,, OSO,CF,; diene = norbornadiene, cyclooctadiene) were prepared and their lo3Rh NMR spectra were recorded on a 100-MHz spectrometer by using inverse two-dimensional "P, 'oBRh{*H} NMR. This technique provides quick access to "' Rh NMR data (2-8 h for cu. 0.1 M samples) when dealing with Rh-phosphine complexes. The Io3Rh NMR data are discussed. All G(103Rh) of the cationic Rh(1) complexes appear at the lower frequency end of the Rh(1) range, i.e. between -1350 and +ZOO ppm, which is in agreement with the fact that the Rh shift is determined by up and with a large AE in square-planar d8 complexes. The relative change in AE between complexes is not large and the changes in paramagnetic shift for these complexes are essentially determined by their relative adonor capacities. G(lo3Rh) shows an inverse correlation with S("P), which was rationalized by invoking the chelate ring size containing the Rh centre and the bidentate phosphine ligands.

An in vitro pH-cycling experiment was completed to determine the effect of the timing of fluoride toothpaste application on de- and remineralization. Both initially sound enamel and artificially produced enamel lesions were subjected to a pH-cycling scheme. The lesions were either formed in an undersaturated calcium-phosphate-fluoride-acetate system (CPF lesions) or in a MHDP-containing lactate buffer (MHDP lesions). The two systems produced subsurface demineralization which differed in porosity, depth and surface layer characteristics. Changes in the enamel mineral content were assessed either by microhardness evaluation of the specimens at the end of the cycling period or by calcium uptake and loss during the pH-cycling period. The results show that a fluoride dentifrice treatment is very effective in inhibiting lesion formation in initially sound enamel as well as in inhibiting lesion progression. The latter was found to be primarily due to a significant decrease in mineral loss during the demineralization cycles. This observation was made irrespective of the timing of the fluoride dentifrice treatment, which was either given before or after the demineralization challenge. For the CPF lesions this inhibition was between 40 and 50%, while the corresponding value for the MDHP lesions was 15–30%. Differences between the two lesion types were also found in the dentifrice effect on lesion remineralization. In the case of the CPF lesions a small inhibition of mineral deposition was observed, while in MHDP lesions the fluoride treatment enhanced the remineralization. These observed differences are explained in terms of the differences in characteristics between these two types of lesions.