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Despite the well-established tradition of organomagnesium reagents, lit-tIe attention was given to the heavier congeners, until very recently. Since the 1990s, researchers have intensified their efforts in the quest for sterically demanding ligand frameworks capable of preventing classic decomposition re› actions of Ae organometallics. Sterically demanding N -donors have become increasingly popular owing to their ability (i) to provide stable metal-donor interactions and (ii) to achieve kinetic stabilisation of the complex via steric crowding around the metal centre. This has led to reports which challenge the common knowledge of the Ae metals. Group 2 complexes have also found applications as stoichiometric reagents, catalysts and as precursors for MOCVD techniques. The work here discussed is aimed at investigating the use of aminopy› ridinate, amidinate and carbazolyl ligands in the stabilisation of novel Ae coordination compounds. Several synthetic procedures have been employed: (i) precursors for metathetical reactivity with Group 2 halides have been obtained from the reaction between the preligands and KH or K[N(SiMe3)2] (13, 12-18, 31-34); (ii) metathesis reactions between potassium salts and MgI2 or CaI2 afforded homoleptic (4-7), heteroleptic (35-38) and hetero› bimetallic compounds (8 and 9); (iii) organoelimination reactions between the preligands and (nBuhMg led to the isolation of homoleptic (4 and 5, 19-24) and heteroleptic magnesium complexes (25) ; (iv) reactions be› tween amidines and MeMgI afforded heteroleptic magnesium halides (28-30) and a rare homometallic magnesium inverse crown ether complex (26); (v) aminopyridines were employed in co-complexation reactions with nBuLi and (nBuhMg, affording the magnesiate complexes lOa and lOb; (vi) the metathesis reaction between the l,l-di-Grignard complex CH2(MgBr)2 and 1 produced the rare methylene bridged magnesium derivative 11. All the compounds herein reported were characterised via analytical and spectroscopic techniques. NMR characterisations in solution of amidinate Group 1 and Group 2 derivatives highlighted the presence of rotational bar› riers for some of these compounds. Moreover, several molecular structures of potassium (14 and 15, 31 and 33), magnesium (19, 21-24, 26-30, 35-38) , calcium (7) and heterobimetallic compounds (8, lOa and lOb) were obtained.

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Hexafluoroacetone readily adds to primary and secondary arsines to form arsino-1,1,1,3,3,3-hexafluoro-propanols and to tetramethyldiarsine to form a moderately stable 1:1 complex at 20° . Trimethylarsine affords a 1:1 complex with hexafluoroacetone at 0° although the complex is completely dissociated at 20°. Trimethylsilahe, trimethylgermane, and trimethyltin hydride react with hexaf luoroacetone to form 1,1,1, 3, 3, 3,-hexaf luoropropoxy derivatives and to dialkyltin dihydrides to form the bis(hexafluoropropoxy) derivatives. Addition of a second mole of hexafluoroacetone to form 1:1 complexes with propoxygermane and propoxysilane occurs at 20°in the presence of excess hexafluoroacetone. The analogous 1:1 tin complex can be isolated and is stable at 25°. Dimethylbis (1,1,1 ,3, 3, 3-hexaf luoropropoxy) tin gives a stable complex containing two moles of hexafluoroacetone. The structures of the arsine- and Group IV- hexafluoroacetone complexes and some of their reactions are discussed. The fluorocycloolefins, perfluorocyclobutene and 1,2-dichlorotetrafluorocyclobutene react with secondary arsines to give arsinocyclobutene derivatives. Perfluorocyclobutene affords the 1:1 adduct when heated with trimethylsilane and trimethylgermane. Trimethyltin hydride adds to perfluorocyclobutene at 20°to form the 1:1 adduct which subsequently slowly decomposes to trimethyltin fluoride. The reaction-of Group IV hydrides with 1, 2-dichlorotetraf luorocyclobutene affords a number of products the nature of which varies with the Group IV metal or metalloid. Thus the reaction of the dichlorocyclobutene with triethyltin hydride gives only triethyltin chloride, with trimethylsilane chlorotrimethylsilane and 1-chlorotetraf luorocyclobutyl-2-trimethylsilane are obtained,and with trimethylgermane reaction gives a variety of cyclobutenyl and cyclobutylgermanes as well as chlorotrimethylgermane. The configuration and conformation of the cyclobutyl derivatives of the Group IV elements are established from an analysis of their ¹H n.m.r. spectra. Hexafluorobut-2-yne adds quantitatively to tin hydrides at 20° to afford the 1,1,1,4,4,4-hexafluorobutenyl derivatives. Hexamethylditin, tetrakis (trifluoromethyl) diarsine, trimethylsilane and triethylgermane add to hexafluorobut-2-yne on ultraviolet irradiation to give 1:1 adducts. The 1:1 trimethylsilane-hexafluorobut-2-yne adduct also forms at 235°. Trimethyltin hydride and 1,1,1,-trifluoropropyne react slowly at 20° to afford the 1:1 adduct. A study of the isomer distribution of the 1:1 acetylene adducts indicates in all cases a predominant formation of the transisomer. Trimethylsilane catalyzes the conversion of trans-1,1,1,4,4,4-hexafluorobutenyltrimethylsilane to the cis-isomer and trimethyltin hydride catalyzes the conversion of cis-1,1,1-trifluoropropenyl-3-trimethyltin to the trans-isomer. The diadducts (CH₃) ₃SiCHCF3-CH(CF₃)Si(CH₃)₃ and ((CH₃)₃Sn)₂CHCH₂CF₃, are also obtained simultaneously with the formation of the respective 1:1 adducts although they are not formed by addition of the hydrides to the 1:1 adducts. / Science, Faculty of / Chemistry, Department of / Graduate

Triphenyl-, trimethyl- and dimethyltin(IV), and trimethylantimony(V) derivatives of a wide variety of acids, including those of very strong acids, as well as derivatives of a transition metal oxyanion, were synthesized. Their structural characteristics in the solid state, under strictly anhydrous conditions, were determined from their infrared spectra. These spectroscopic results can only be interpreted in terms of a very strong interaction between the organometal group and the corresponding anionic group, and provide strong evidence for coordination or partial covalent bonding between the organometal group and the anionic group. Contrary to earlier reports, no evidence is found for the existence of free R₃Sn⁺ , R2Sn²⁺ or R₃Sb²⁺ cations in the solid state. / Science, Faculty of / Chemistry, Department of / Graduate