We report on the synthesis and characterization of 25−70 Å diameter amine-capped gold nanocrystals. In particular, we show how these particles can be prepared by a simple procedure and confirm the particle composition (including the identity of the amine surface passivant) through several materials characterization techniques that include infrared spectroscopy, nuclear magnetic resonance spectroscopy, ultraviolet−visible spectroscopy, mass spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis. All physical characterizations are consistent with a charge−neutral amine/gold surface interaction described by a weak covalent bond. The stability of the particles appears to be largely kinetic, rather than thermodynamic, in nature. Comparison of these nanocrystals to amines adsorbed onto bulk Au surfaces indicates that the stability of the nanocrystal/amine system is a finite-size effect.

atoms in the step 3 + 5."". b, 91 (3) It is obvious from Table 1 that for the Coe and NiO complexes of 4-octyne both steps, i.e., C-H bond activation andligand detachment, are subject to a kinetic isotope effect. For the ligand detachment 3 -5 the data for 1 b and 1 d permit the estimation of an isotope effect kH/kD = 1.10 (per deuterium) for either CoO or Nie. The C-H bond activation step 2 + 3 (or, less likely, I-Me -+ 4) is associated with slightly differing kH/kD values of 1.25 and 1.36 for Coo and Nie, respectively.f'O] Obviously, the various transition-metal ions cause a switching in regard to the bottleneck of the multistep event which is shown in Scheme 1 in a simplified manner.As indicated in Figure 3 , a quite remarkable inverse relationship exists between the magnitude of the kinetic isotope [R hC I LzI CPhzNz ": CzH,Ph-H 6a

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1-Butadienyl)platinum(11) complexes can be obtained by reaction of [Pt(C2H4)(PPh3)2] with either chloroprene or 4-chloro-3-methylbuta-1,2-diene. Treatment of these complexes with AgPF6 provides direct access to the cationic r?3-butadlenyl complexes [Ptlv3-CH2:C(R):C:CH2}(PPh3)2] [PFe] (R = H, Me), which surprisingly are attacked by the soft carbon nucleophile 2] at the central carbon atom of the allylic moiety to form methyleneplatlnacyclobutanes. These are unusual molecules that on thermolysis afford Pt(0) methylenecyclopropane complexes.