Desorption/ionization on porous silicon mass spectrometry (DIOS-MS) is a novel method for generating and analyzing gas-phase ions that employs direct laser vaporization. The structure and physicochemical properties of the porous silicon surfaces are crucial to DIOS-MS performance and are controlled by the selection of silicon and the electrochemical etching conditions. Porous silicon generation and DIOS signals were examined as a function of silicon crystal orientation, resistivity, etching solution, etching current density, etching time, and irradiation. Pre-and postetching conditions were also examined for their effect on DIOS signal as were chemical modifications to examine stability with respect to surface oxidation. Pore size and other physical characteristics were examined by scanning electron microscopy and Fourier transform infrared spectroscopy, and correlated with DIOS-MS signal. Porous silicon surfaces optimized for DIOS response were examined for their applicability to quantitative analysis, organic reaction monitoring, post-source decay mass spectrometry, and chromatography.

This communication reports the synthesis and activity of four racemic mixtures of bis (benzamidinate) group-4 complexes, cis-[p-R′C 6 H 4 (4)) as precatalysts for the stereoregular polymerization of propylene. These complexes catalyze the stereoregular polymerization of propylene only under pressure in CH 2 Cl 2 , producing polypropylene with very large isotacticities (mmmm % ) ∼95-98), high melting points (140-154°C ).a Methylaluminoxane, solvent removed from a 20% solution in toluene (Schering) at 25°C /10 -6 Torr. b Grams of total polymer/mole of Zr‚h. c By viscosimeter technique in 1,2,4-trichlorobenzene at 130°C (K ) 1.37 × 10 -2 ; R ) 0.7). d An additional low molecular weight oily fraction was separated from the solid. e The polypropylene is obtained as an elastomer (Tg).

The chiral lithium (-)-trimethylsilylmyrtanyl amide reacts with benzonitrile yielding the chiral benzamidinate lithium ligand ([N-trimethylsilyl][N′-myrtanyl]benzamidinate Li‚TMEDA (TMEDA ) tetramethylethylenediamine), [N(R*)-C-N]Li. An X-ray study shows that the ligand has a distorted tetrahedral environment in which the lithium atom is arranged symmetrically between the two benzamidinate and the two TMEDA nitrogen atoms. Equimolar addition of). An X-ray study of 1 shows that it has an octahedral structure with the oxygen atom and one chlorine atom at the apical positions. [N(R*)-C-N] 3 ZrCl‚toluene (2) can be prepared in a manner related to that employed to synthesize 1. An X-ray study of 2 shows that it has a capped octahedral geometry with the three trimethylsilyl groups in a cis position with respect to the chlorine atom and the other three myrtanyl groups arranged on the opposite side of the chlorine. Addition of MeLi‚LiBr to complex 2 yields [N(R*)-C-N] 3 ZrMe (3) which is obtained as cocrystalline with complex 2. The X-ray structure of the cocrystalline mixture is similar to that of the chloride complex 2 exhibiting a Zr-Me distance of 2.469(10) Å. Complex 1 is an active catalyst, under pressure, for the polymerization of propylene producing elastomeric polypropylene and for the syndiotactic polymerization of styrene. Complex 2 was found to be active for the highly stereospecific polymerization of propylene.

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A novel and efficient one-pot synthesis of trismetallated olefins is described by using the diisopropyloxy(h 2 -propene)titanium derivative.The synthesis of polysubstituted olefins in a single-pot operation from common starting material is still the object of continuing vigorous research 1 . Among several strategies, the synthesis and reactivity of 1,1-dimetalloalkenes with a large variety of metals (dilithium 2 , aluminum and titanium 3 , aluminum and zirconium 3 , zinc and zirconium 4 , zinc and boron 5 , copper and boron 5 , copper and zirconium 4 , lithium and boron 6 , zinc and zinc 7 and finally boron and zirconium 8 ) were used as a source of tri-and tetra-substituted olefins. In this context, we have already reported the allylmetallation of alkynyl metals 9 leading to sp 2 1,1-bismetallic derivatives in good overall yield 10 . These geminate bis-anions react selectively with two different electrophiles 10 and can be a source of chiral a,a'-disubstituted alkynes 10c . However, in the course of our studies on the synthesis and reactivity of polymetallated alkenes, we needed a more general preparation of these reagents allowing the access to a variety of carbon skeletons. Our attention was drawn by the pioneering work of Sato et al who demonstrated that various disubstituted alkynes react with diisopropyloxy(h 2 -propene)titanium 1 11 , readily generated by the reaction of Ti(OiPr) 4 with 2 equiv. of iPrMgX, to give the corresponding titanacyclopropene derivatives. Although terminal alkynes failed to participate in the present reaction, the use of this lowvalent titanium alkoxide reagent was successfully applied to several systems 12 . The same type of intermediate as 1 had previously been used for the synthesis of cyclopropanols 13,14 and cyclopropylamines 15 . Inspired by this work, we were pleased to find that the ligand exchange of the low-valent titanium alkoxide can be performed with a metallated alkyne 16 to give the corresponding metallated titanacyclopropene. Our initial attempts consisted in adding alkynyl metal derivatives to the preformed Ti II complex 1 (Scheme 1).However, this new strategy was only moderately successful since the overall chemical yield of the polymetallated olefin was strongly dependent on the nature of the alkynyl metal and on the experimental conditions. Indeed, starting from alkynyllithium (M = Li) or alkynylmagnesium bromide (M = MgBr), the desired product was not obtained in the former case and only in 20% yield in the latter one. The best cases were the alkynyltitanium triisopropoxide (M = Ti(OiPr) 3 , 41% yield) and either the alkynylzinc bromide (M = ZnBr, 65% yield) or alkynyl-alkylzinc (M = ZnBu, 68% yield). Unfortunately, even in these last three cases, it was very difficult in our hands to get reproducible results (i.e. for the alkynylzinc bromide the yield was varying from 25% to 70%). These fluctuations were attributed to the possible instability of the preformed lowvalent titanium alkoxide 1 under these Grignard-type experimental conditions 17 , and also to the r...