Is Water a Friend or Foe in Organometallic Chemistry? The Case of Group 13 Organometallic Compounds † HERBERT W. ROESKY* Institut fu ¨r Anorganische Chem ie, Universita ¨t Go ¨ttingen, Tam m annstrasse 4,D-37077 Go ¨ttingen, Germany MRINALINI G. WALAWALKAR AND RAMASWAMY MURUGAVEL Department of Chemistry, Indian Institute of Technology-Bom bay, Powai, Mum bai-400 076, India Received June 22, 2000 ABSTRACT This Account summarizes the recent developments in the hydroly- sis chemistry of Group 13 trialkyl and triaryl compounds. Emphasis has been placed on the results obtained by us on (a) 1 H NMR investigations of controlled hydrolyses of AlMes3 and GaMes3, (b) low-temperature isolation of water adducts of triaryl compounds of aluminum and gallium, (c) synthesis and structural characteriza- tion of new polyhedral alumoxanes and galloxanes, and (d) the search for an easy way to synthesize well-defined crystalline methylalumoxanes by deprotonation of the hydroxides with alkyl- lithium reagents. The systematic studies on the hydrolysis of t Bu 3- Al carried out by Barron et al. are also discussed in order to elucidate the roles of (i) reaction temperature, (ii) solvent medium, and (iii) source of water molecules, in building up hitherto unknown alumoxane clusters. The role of water impurity in organometallic reactions involving a Group 13 alkyl and other ligands (such as silanetriols and phosphorus acids) to build molecular clusters has also been discussed. Introduction Water is a central theme in biological systems and biomolecules. The ability of water to form hydrogen bonds to amino acids results in the self-organization of su- pramolecular assemblies. Further, the OsH‚‚‚O and Os H‚‚‚N interactions are important in OsH bond activation. In contrast, the opening chapters in organometallic chemistry textbooks and monographs emphasize the need for anaerobic conditions and the use of absolutely water- free reaction media for the study of organometallic compounds. This gives the impression that the role of water in organometallic chemistry is different from its role in biochemistry. However, in organometallic compounds, too, the role of water is crucial. Apart from the possible activation of OsH bonds in organometallic hydroxides, structure-directing intermolecular interactions through OsH bonds can also lead to self-organization. To under- stand the so-called water effect in organometallic chem- istry, 1 it is important to investigate in detail the interaction of water with organometallic compounds. The necessity for anaerobic conditions in organome- tallic chemistry was often attributed to the presence of highly reactive MsC bonds. 2 The organometallic com- pounds of s-block elements are highly reactive due to polar M δ+ sC δ- bonds. Among the p-block metal alkyls, Group 14 and Group 15 compounds are comparitively stable due to the increased covalent nature of MsC bonds. On the other hand, the organometallic compounds of Group 13 elements (B, Al, Ga, In, and Tl) occupy a special place within the main group owing to their intermediate reactivity toward water compared to s-block and late p-block organometallic compounds. Interest in the role of water in Group 13 organometallic compounds is two-fold. Recently it has been shown that, rather than being a nuisance, the presence of small amounts of water in the reactions of Group 13 alkyls with other substrates (vide infra) leads to interesting cage structures. 3 Similarly, another interesting aspect of Group 13 organometallic chemistry has been unfolded by delib- erate or adventitious addition of stoichiometric amounts of water to bulky trialkyl compounds of aluminum and gallium (in order to isolate smaller model compounds for alumoxanes). 4 Our interesting explorations, along with those of other workers, on these two aspects of Group 13 organometallic chemistry are presented in this Account. Alumoxanes: A Background Among the above-mentioned aspects of Group 13 orga- nometallic chemistry, more interesting in terms of its usefulness in the chemical industry is the direct controlled reaction of Group 13 alkyls with stoichiometric amounts of water. Compared to the 150-year-old chemistry of hydrolysis of inorganic aluminum salts, the hydrolysis of organometallic compounds of aluminum is relatively new. 4 The products from the partial hydrolysis of alumi- num trialkyls (alkylalumoxanes) were extensively studied in the 1960s as active catalysts in polymerization reac- tions. 5 The recent upsurge in alumoxane chemistry can be traced to the work of Sinn and Kaminsky, who applied methylalumoxane (MAO) as a component of highly active catalysts for the polymerization of ethylene and propy- lene. 6 Interest in the alumoxane chemistry was further increased by subsequent reports on the use of MAO and [Ti(CH 2 Ph) 4 ] for the preparation of syndiotactic polysty- † Dedicated to Professor Oskar Glemser on the occasion of his 90th birthday. Herbert W. Roesky is the Director of the Institute of Inorganic Chemistry, University of Go ¨ ttingen. He is well known through both his scientific publications and science education experiments. His varied research interests in several areas of inorganic chemistry, catalysis, and materials science are evident through his 800 publica- tions. He recently received the ACS Award for Creative Work in Fluorine Chemistry (1999) and the Wilkinson Prize for Creativity in Inorganic Chemistry (2000). Mrinalini G. Walawalkar obtained her Ph.D. from the University of Go ¨ ttingen in 1997. Subsequently, she taught chemistry at UDCT, Mumbai, and was a Scientific Officer at IIT-Bombay. She is presently Alexander-von-Humboldt Fellow at the University of Bochum. She has published over 25 papers including an Account in 1999. Her current research interests are in the area of new materials and catalysis. Ramaswamy Murugavel is Assistant Professor of Chemistry at IIT-Bombay. He has been an Alexander-von-Humboldt Fellow at the University of Go ¨ ttingen (1994- 1996 and 2000). He received the DAE Young Scientist Award in 1999. He has authored more than 50 papers on topics related to main group organometallic chemistry, including two other Accounts in 1996 and 1999. Acc. Chem. Res. 2001, 34, 201-211 10.1021/ar0001158 CCC: $20.00  2001 American Chemical Society VOL. 34, NO. 3, 2001 / ACCOUNTS OF CHEM ICAL RESEARCH 201 Published on Web 01/16/2001