Sonochemistry organometallic

In 1981, the first report on the sonochemistry of discrete organometallic complexes demonstrated the effect of ultrasound on iron carbonyls in alkane solutions (174). The transition metal carbonyls were chosen for these initial studies because their thermal and photochemical reactivities have been well characterized. The comparison among the thermal, photochemical, and sonochemical reactions of Fe(CO)5 provides an excellent example of the unique chemistry which homogeneous cavitation can 

In addition to clusterification, ligand substitution also occurs for Fe(CO)5, and in fact for most metal carbonyls. This has proved useful as a mechanistic probe of the reactive species formed during cavitation. Sonica-tion of Fe(CO)5 in the presence of phosphines or phosphites produces Fe(CO)5 L (n = 1,2, and 3). The ratio of these products is independent of length of sonication the multiply substituted products increase with increasing initial [L] Fe(CO)4L is not sonochemically converted to Fe(CO)3L2 on the timescale of its production from Fe(CO)5. These observations are consistent with the same primary sonochemical event 

Sonochemical ligand substitution readily occurs with a variety of other metal carbonyls, as shown in Table IV. In all cases, multiple ligand substitution originates directly from the parent carbonyl. The rates of sonochemical ligand substitution of the various metal carbonyls follow their relative volatilities, as predicted from the nature of the cavitational collapse. 

Another recent example of sonochemical substitution is in the preparation of 7r-allyllactone(tricarbonyl)iron complexes, which are useful synthetic intermediates in the synthesis of lactones and lactams (185). Upon 

The sonolysis of Mn2(CO)10 makes for an interesting comparison (186), since either metal-metal (as in photolysis) (187) or metal-carbon (as in moderate temperature thermolysis) (188) bond breakage could occur. Ligand substitution will occur from either route producing the axially di-substituted Mn2(CO)8L2. Using benzyl chloride as a trap for the possible intermediacy of Mn(CO)5, the sonochemical substitution of Mn2(CO)10 has been shown to follow the thermal, rather than the photochemical, pathway of dissociative CO loss. 

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The purpose of this chapter will be to serve as a critical introduction to the nature and origin of the chemical effects of ultrasound. We will focus on organo-transition metal sonochemistry as a case study. There will be no attempt to be comprehensive, since recent, exhaustive reviews on both organometallic sonochemistry Q) and the synthetic applications of ultrasound (2) have been published, and a full monograph on the chemical, physical and biological effects of ultrasound is in press (3). 

However, the domain of choice for these reductive processes is undoubtedly the preparation of organometallic reagents. After the initial work reported by Renaud, a second paper appeared in 1959, on the preparation of phenylsodium from ultrasonically activated sodium and chlorobenzene. These initial reports can be seen as the initial steps towards modem organometallic sonochemistry. 

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