Photochemical production processes are still extremely rare.With three examples from our own research laboratories illustration is made, how the acceptance of photochemical methodology can be increased. A diastereoselective photocyclisation and two newly designed organometallic photoinitiators succeeded because they overcome drawbacks of conventional operations.

Laser flash photolysis and matrix-isolation techniques were applied to elucidate the photochemistry of the orange complex bis(pentafluoropheny1)titanocene ( = bis(q '-cyclopentadienyl)bis(pentafluorophenyl)titanium-(IV), Cp2Ti1V{C,Fs}2, Cp = q5-C,H,, 1) which is used as a polymerization photo-initiator. The primary photoreaction of 1 is the formation of a highly reactive blue isomer X with unit quantum yield. In carefully dried and degassed benzene solution, the photoisomer X rearranges to starting material 1 with a first-order reaction, k = 5 . 10' s-' at room temperature. X is highly reactive towards H,O, MeOH, acetone, MeCN, MeN02, butane-1,4-diyl diacrylate, 2,2,6,6-tetramethylpiperidine N-oxide, CO, O,, and N2; ahsolute bimolecular rate constants range from lob to 10' M-' . s-'. The primary photoisomerization l-+X is tentatively ascribed to acyclopentadienyl ring slippage from q 5 to a lower hapticity, a process that opens up coordinative unsaturation.Introduction. -Low-valent organotitanium complexes are capable of nitrogen fixation [l] and are well-known as polymerization catalysts [2]. The photoreactions of Ti complexes have been studied rather extensively, and this work has been reviewed [3] but, surprisingly, flash photolysis has so far not been applied to a direct kinetic and spectrographic observation of the relevant reactive intermediates. We have investigated the primary photoprocesses of bis(pentafluoropheny1)titanocene ( = bis(r '-cyclopentadienyl)bis(pentafluorophenyl)titanium(IV), Cp,Ti1V{C,F5),, Cp = 9 '-C,H,, 1) by flash photolysis and matrix-isolation techniques in order to elucidate the mechanism by which 1 acts as a photo-initiator used for integrated circuit fabrication [4-81.

Polymerization methods to manufacture printed and integrated circuits have been studied in great detail. Recently organometallics have been evaluated as photoinitiators for these processes. We discuss the use of organometallic compounds in cationic and radical polymerization initiation.

Methacrylsäurechlorid (I) bildet bei längerem Lagem die cyclischen Dimeren (II), (III) und (IV), die in Form der Amide (V), (VI) und (VII) isoliert werden.

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