Borole, pentaphenyl

Borole, pentaphenyl-, stability, 56, 375 Boron complexes, of acyltetramic acids,... 

Borole (IV in Figure 14) has been used to synthesize a plethora of sandwich and half-sandwich stmctures it is the bora analog of cyclopentadiene. Borole is an antiaromatic system see Antiaromatic Compound), and only the blue pentaphenyl derivative has been prepared. The general route to borole complexes consists of complexation under dehydrogenation of 2- or 3-borolenes, which are prepared from [Mg(butadiene)]x and RBX2. Thus, the heating of either isomer of borolene with Co2(CO)g produces [(borole)Co(CO)2]2 (47) (equation 60) from which further cobalt borole complexes are prepared (equation 61). CpCo(borole) (48) can be made from (47) by Cp transfer from the labile 20-electron nickelocene (equation 61). Pyrolysis of (48) at 160-180 °C gives a triple-decker complex (49) in nearly quantitative yield, which in turn can be cleaved by Cp into (48) and the bis(borole)cobaltate anion (50 ) (Scheme 34). 

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