Lamoreaux catalyst

In a first step the epoxy-functionalized siloxanes were prepared by hydrosilylation, with allyl glycidyl ether and Lamoreaux catalyst (Pt catalyst resulting from HjPtClg.H O in octanol), at 130-145°C for 4-lOh. The reaction is quantitative. 

The first step, as shown in equation 3, is a solventless process involving the hydrosilylation of DAM with trichlorosilane (TCS) in the presence of Lamoreaux catalyst (chloroplatinic acid in excess octanol). As noted above, since DAM inhibits platinum catalyzed hydrosilylation, the reaction requires elevated temperatures (> 40 °C). However, the low boiling point of TCS (31.9 °C) and the thermal instability of DAM necessitate reaction temperatures not to exceed 110 °C. Thus higher levels of platinum had been used to overcome these limitations, but inevitably results in increased coloration and cost of the final product. 

Whereas water-soluble rhodium complexes catalyze the biphasic hydrogenation of various unsaturated substrates but rapidly form colloids, the addition of yd-CD has been shown to lead to efficient homogeneous catalytic systems [40]. For instance, in the absence of transfer agent, as reported by Larpent et al. [41], maleic acid is completely transformed in 83 h instead of a reaction time of 17 h with yd-CD. Similarly, the hydrosilylation reaction of an alkene catalyzed by a platinum precursor can be notably accelerated by the presence of yd-CD the case of a Lamoreaux Pt Pl catalyst is more spectacular since the yield can reach 100% in 12 min, whereas no transformation of the substrate occurs in 24 h in the absence of yd-CD [42]. 

Amongst catalyst modifications that achieve purely rate effects, two reports are noteworthy. One is the hydrosilation rate enhancement in the presence of j -cyclodextrins, for Karstedt s catalyst Pt2(s ym-tetramethyldivinyldisiloxane)3] and Lamoreaux s catalyst. Lamoreaux s catalyst (prepared from H2PtCl6 and 1-octanol), showed the most dramatic rate accelerations. The second instance of rate moderation is reported by Endo and collaborators. They report the use of isocyanides in just 2 1 molar ratio with Pt, to dramatically suppress hydrosilation of vinylsilane (with EtsSiH) or vinyl-terminated siloxane with methylhydrogensiloxane copolymer until 60-70 °C. Above this temperature, rapid hydrosilation occurs. This is in contrast with traditional cure inhibitors where a large excess of inhibitor (relative to Pt), typically alkynols or maleates, is needed to prevent premature cure. 

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