Alkoxo and Aryloxo Derivatives of Metals Elsevier, 2001 Author: D.C. Bradley, R.C. Mehrotra, I.P. Rothwell and A. Singh ISBN: 978-0-12-124140-7 Foreword, Page xi 1 - Introduction, Pages 1-2 2 - Homometallic Alkoxides, Pages 3-181 3 - Heterometallic Alkoxides, Pages 183-228 4 - X-Ray Crystal Structures of Alkoxo Metal Compounds, Pages 229-382 5 - Metal Oxo-alkoxides, Pages 383-443 6 - Metal Aryloxides, Pages 445-669 7 - Industrial Applications, Pages 671-686 Index, Pages 687-704 Foreword The value of a book may well be judged by the number of times a person has to buy it, for, while many books once read gather dust upon a shelf, those more often sought can sometimes be seldom found. Over 20 years ago, I was fortunate to receive a complimentary copy of “Metal Alkoxides” by Bradley, Mehrotra and Gaur. As one interested in alkoxide metal chemistry, this proved a valuable reference for me and my research group. In fact, I had to purchase two subsequent copies and probably would have purchased more were it not for the fact that the book became out of print and unavailable except through the library. Now I have received the galley proofs of the second edition entitled “Alkoxo and Aryloxo Derivatives of Metals”byBradley, Mehrotra, Rothwell and Singh. After 20 years, virtually every field of chemistry must have changed to the extent that a new edition would be appropriate. However, it is unlikely that any field of chemistry, save computational chemistry, will have changed as much as that of the chemistry of metal alkoxides and aryloxides during the period 1978–2000. The explosion of interest in metal alkoxides has arisen primarily for two reasons. First and foremost, we have witnessed the tremendous growth of materials chemistry spurred on by the discovery of high temperature superconducting oxides and by the increasingly important role of other metal oxides to technology. Metal alkoxides, mixed metal alkoxides and their related complexes have played an essential role in the development of new routes to these materials either by sol-gel or chemical vapor deposition techniques. In a second area of almost equal magnitude, we have seen the growth of a new area of organometallic chemistry and catalysis supported by alkoxide or aryloxide ancillary ligands. As a consequence of these major changes in chemistry, virtually any issue of a current chemistry journal will feature articles dealing with metal alkoxides and aryloxides. Thus, although the present book owes its origins, and to some extent its format, to the first edition, its content is largely new. For example, while the first edition reported on but a handful of structurally characterized metal alkoxides, this second edition carries a whole chapter dealing with this topic, a chapter with over 500 references to publications. The second edition is therefore most timely, if not somewhat overdue, and will be a most valuable reference work for this rapidly expanding field of chemistry. I only hope that I can hold on to my copy more successfully than I did in the first instance. Malcolm H. Chisholm FRS Distinguished Professor of Mathematical and Physical Sciences The Ohio State University Department of Chemistry Columbus, OH 43210-1185 USA January 2001 1 Introduction In 1978 the book entitled “Metal Alkoxides” was published. 1 It contained over one thousand references and attempted to summarize most of what was known about metal alkoxides up to that time. A striking feature was the dearth of X-ray crystal struc- tures and so structural aspects necessarily involved speculation based on the results of molecular weight determinations, combined where possible with spectroscopic data. The intervening years have witnessed a spectacular advance in our knowledge of the chemistry of the metal alkoxides, a development which has been driven primarily by research activity resulting from the realization that these compounds have great potential as precursors for the deposition of metal oxide films for microelectronic device applications and in bulk for producing new ceramic materials. Simultaneously a tremendous advance occurred in X-ray crystallography with the advent of computer- controlled automated diffractometers and with improvements in the techniques for growing and mounting single crystals of the air sensitive metal alkoxides. Consequently the number of structures solved has become so large that in this book a separate chapter with over 500 references has been devoted to crystal structures with much of the data summarized in tabular form. In addition, considerable advances have been made in the synthesis and characterization of a range of new alkoxides of the alkali metals, alkaline earths, yttrium and the lanthanides which together with other new developments has led to a chapter on Homometallic Alkoxides containing well over 1000 references. Similarly the chapter on Heterometallic Alkoxides (previously described as Double Metal Alkoxides) has been expanded to include many novel compounds, with particular emphasis on the recently authenticated species containing two, three and even four different metals in one molecule. Another area that has expanded in recent years concerns the Industrial Applications of metal alkoxides. Besides the previously mentioned deposition of metal oxides in the microelectronic and ceramics industries there have also been major developments in the catalytic activity of early transition metal alkoxo compounds in several important homogeneous reactions. This has stimulated a growing interest in the mechanisms of reactions catalysed by metal alkoxides. Metal Oxo Alkoxides are implicated as intermediates in the hydrolysis of metal alkoxides to metal oxides and their importance in the sol–gel process has led to much research activity in this area. Accordingly we have allocated a whole chapter to the Metal Oxo Alkoxides. In the 1978 book very little space was devoted to metal aryloxides because this area had received scant attention, but the intervening years have seen a resurgence of activity involving the synthesis and characterization of many novel compounds and 2 Alkoxo and Aryloxo Derivatives of Metals studies on their catalytic activity. Therefore we have added a separate chapter dealing with this important topic. In this book we are giving the relevant references at the end of the seven chap- ters rather than placing them all at the end of the text in the hope that this will be more convenient for the reader. Finally, the authors acknowledge their indebtedness to all of their former research students, postdoctoral assistants, and colleagues for their invaluable contributions to the research which has provided much of the information collected in this publication. REFERENCE 1. D.C. Bradley, R.C. Mehrotra, and D.P. Gaur, Metal Alkoxides, Academic Press, London (1978). 2 Homometallic Alkoxides 1 INTRODUCTION Metal alkoxides [M(OR) x ] n (where M D metal or metalloid of valency x;RD simple alkyl, substituted alkyl, or alkenyl group; and n D degree of molecular association), may be deemed to be formed by the replacement of the hydroxylic hydrogen of an alcohol (ROH) by a metal(loid) atom. Historically, the first homoleptic alkoxo derivatives of elements such as boron and silicon had been described 1,2 as early as 1846, but later progress in the alkoxide chemistry of only half a dozen metals was rather slow and sporadic till the 1950s; since then the chemistry of alkoxides of almost all the metals in the periodic table has been systematically investigated. With a few exceptions, systematic investigations on the structural aspects of metal alkoxides till the mid-1980s 3–10 were limited to studies on molecular association, volatility, chemical reactivity, and spectroscopic (IR, NMR and electronic) as well as magnetic properties. It is only since the early 1980s that definitive X-ray structural elucidation has become feasible and increasingly revealing. The rapidly advancing applications 11–16 of metal alkoxides for synthesis of ceramic materials by sol–gel/MOCVD (metallo-organic chemical vapour deposition) processes (Chapter 7) have more recently given a new impetus to intensive investigations on synthetic, reactivity (including hydrolytic), structural, and mass-spectroscopic aspects of oxo-alkoxide species. 17–21 Some of the exciting developments since 1990 in metal alkoxide chemistry have been focussing on the synthesis and structural characterization of novel derivatives involving special types of alkoxo groups such as (i) sterically demanding monodentate (OBu t , OCHPr i 2 , OCHBu t 2 ,OCMeEtPr i , OCBu t 3 ) as well as multidentate (OCR 0 CH 2 OPr i  2 ) (R 0 D Bu t or CF 3 ), OCR 00 2 CH 2 X(R 00 D Me or Et, X D OMe, OEt, NMe 2 ) ligands, 21–24 (ii) fluorinated tertiary alkoxo (OCMeCF 3  2 ,OCMe 2 CF 3 ,OCCF 3  3 , etc.) moie- ties, 21–23 and (iii) ligands containing intramolecularly coordinating substituents (OCBu t 2 CH 2 PMe 2 ,OCH 2 CH 2 X(XD OMe, OEt, OBu n ,NR 2 ,PR 2 )). 21,22 Compared to simple alkoxo groups, most of these chelating/sterically demanding ligands possess the inherent advantages of enhancing the solubility and volatility of the products by lowering their nuclearities owing to steric factors and intramolecular coordination. Solubility and volatility are the two key properties of metal alkoxides which provide convenient methods for their purification as well as making them suitable precursors for high-purity metal oxide-based ceramic materials. It is noteworthy that the homoleptic platinum group metal (Ru, Rh, Pd, Os, Ir, Pt) alkoxides are kinetically more labile possibly owing to ˇ-hydrogen elimination 9,10,21 4 Alkoxo and Aryloxo Derivatives of Metals type reaction(s) (Eq. 2.1): M—OCHR 0 R 00  ! M—H C R 0 R 00 C D O # M C 1 2 H 2 2.1 These, therefore, are not generally isolable under ambient conditions unless special types of chelating alkoxo ligands 21 are used. Although single crystal X-ray studies presented considerable difficulties in the earlier stages, 25 the development of more sophisticated X-ray diffraction techniques has led to the structural elucidation of a number of homo- and heteroleptic alkoxides 17–23 and actual identification of many interesting metal oxo-alkoxide systems (Chapter 4). In this chapter we shall discuss the synthesis, 3,4,26 chemistry and properties of homometallic alkoxides with more emphasis on homoleptic alkoxides [M(OR) x ] n and M(OR) x .L n with occasional references to metal oxo-alkoxides MO y OR x 2y and metal halide alkoxides M(OR) xy X y .L z (where x D valency of metal, L D neutral donor ligand, X D halide, and n, y and z are integers). The discussion will generally exclude organometallic alkoxides and a considerable range of metal-organic compounds containing alkoxo groups, as in these systems the alkoxo groups play only a subsidiary role in determining the nature of the molecule. 2 METHODS OF SYNTHESIS Metal alkoxides in general are highly moisture-sensitive. Stringent precautions are, therefore, essential during their synthesis and handling; these involve drying of all reagents, solvents, apparatus, and the environment above the reactants and products. Provided that these precautions are taken, the preparation of metal alkoxides, although sometimes tedious and time consuming, is relatively straightforward. The method employed for the synthesis 3,4,8,17,21 of any metal/metalloid alkoxide depends generally on the electronegativity of the element concerned. Highly elec- tropositive metals with valencies up to three (alkali metals, alkaline earth metals, and lanthanides) react directly with alcohols liberating hydrogen and forming the corre- sponding metal alkoxides. The reactions of alcohols with less electropositive metals such as magnesium and aluminium, require a catalyst (I 2 or HgCl 2 ) for successful synthesis of their alkoxides. The electrochemical synthesis of metal alkoxides by anodic dissolution of metals (Sc, Y, Ti, Zr, Nb, Ta, Fe, Co, Ni, Cu, Pb) and even metalloids (Si, Ge) in dry alcohols in the presence of a conducting electrolyte (e.g. tetrabutylam- monium bromide) appears to offer a promising procedure (Section 2.2) of considerable utility. It may be worthwhile to mention at this stage that the metal atom vapour tech- nique, which has shown exciting results in organometallics, may emerge as one of the potential synthetic routes for metal alkoxides also in future. For the synthesis of metalloid (B, Si) alkoxides, the method generally employed consists of the reaction of their covalent halides (usually chlorides) with an appropriate alcohol. However, the replacement of chloride by the alkoxo group(s) does not appear to proceed to completion, when the central element is comparatively more electropositive. In such cases (e.g. titanium, niobium, iron, lanthanides, thorium) excluding the strongly electropositive s-block metals, the replacement of halide could in general be pushed Homometallic Alkoxides 5 to completion by the presence of bases such as ammonia, pyridine, or alkali metal alkoxides. Another generally applicable method, particularly in the case of electronegative elements, is the esterification of their oxyacids or oxides (acid anhydrides) with alcohols (Section 2.6), and removing the water produced in the reaction continuously. In addition to the above, alcoholysis or transesterification reactions of metal alkox- ides themselves have been widely used for obtaining the targeted homo- and heteroleptic alkoxide derivatives of the same metal. Since the 1960s, the replacement reactions of metal dialkylamides with alcohols has provided a highly convenient and versatile route (Section 2.9) for the synthesis of homoleptic alkoxides of a number of metals, particularly in their lower valency states. The metal–hydrogen and metal–carbon bond cleavage reactions have also been exploited in some instances (Section 2.10.2). The following pages present a brief summary of the general methods used for the synthesis of metal and metalloid alkoxides applicable to specific systems. Tables 2.1 and 2.2 in Section 2.1 (pp. 6–14) list some illustrative compounds along with their preparative routes and characterization techniques. 2.1 Reactions of Metals with Alcohols (Method A) The facility of the direct reaction of a metal with an alcohol depends on both the electropositive nature of the metal and the ramification of the alcohol concerned. In view of the very feeble acidic character of nonfluorinated alcohols [even weaker than that of water: pK a values (in parentheses) of some alcohols are CH 3 OH(15.8), CH 3 CH 2 OH(15.9), CH 3  2 CHOH(17.1), CH 3  3 COH(19.2), CF 3 CH 2 OH(12.8), CH 3 CF 3  2 COH(9.6), CF 3  2 CHOH(9.3),  CF 3  3 COH(5.4)], this route is more facile with lower aliphatic and fluorinated alcohols. 2.1.1 s-Block Metals 2.1.1.1 Group 1 metals (Li, Na, K, Rb, Cs) The more electropositive alkali metals react vigorously with alcohols by replacement of the hydroxylic hydrogen (Eq. 2.2): M C 1 C yROH  ! 1 n [MOR.yROH] n C 1 2 H 2 " 2.2 M D Li,Na,K,Rb,Cs;RD Me, Et, Pr i , Bu t ; 3,6,26,27 y D 0. M D Li; R D Bu t , CMe 2 Ph; 28 y D 0. M D K, Rb, Cs; R D Bu t ; 29 y D 1. M D K, Rb; R D Bu t ; 29 y D 0. The alkali metals react spontaneously with sterically compact aliphatic alcohols (MeOH, EtOH, etc.) and the speed of the reaction increases with atomic number of the metal, Li < Na < K < Rb < Cs, corresponding to a decrease in ionization potential of the alkali metals. The ramification of the alkyl group is also important, as shown by the 6 Alkoxo and Aryloxo Derivatives of Metals Table 2.1 Examples of some homoleptic alkoxides Method of Characterization Compound 1 preparation 2 techniques 3 Reference Group 1 [LiOMe] 1 A X-ray 28a [LiOBu t ] 6 AIR; 1 H, 13 C, 7 Li NMR; MW 28 [LiOCMe 2 Ph] 6 AIR; 1 H, 13 C, 7 Li NMR; MW; X-ray 28 [LiOCBu t 3 ] 2 J-2 1 H, 13 C, 7 Li NMR; X-ray 396 [LiOCBu t 3 thf] 2 J-2 X-ray 230 [LiOCBu t 2 CH 2 PMe 2 ] 2 J-3 1 H, 13 C, 7 Li, 31 P NMR; X-ray 22 [LiOCBu t 2 CH 2 PPh 2 ] 2 J-3 1 H, 13 C, 7 Li, 31 P NMR; X-ray 422 [LiOCBu t 2 CH 2 PPh 2 ] 2 Bu t 2 CO J-3 1 H, 13 C, 7 Li, 31 P NMR; X-ray 422 [MOMe] 1 (M D Na,K,Rb,Cs) A X-ray a, b, c, d [NaOBu t ] 6 A X-ray e, f [NaOBu t ] 9 A X-ray e [MOBu t .HOBu t ] 1 M D K, Rb) AIR; 1 H, 13 CNMR; MW; X-ray 29 [MOBu t ] 4 M D K, Rb, Cs A 1 H, 13 CNMR; X-ray 29, g [NafOCHCF 3  2 g] 4 J-2 IR; 1 H, 19 FNMR; X-ray 397 Group 2 [BeOMe 2 ] n E-3, J-2 IR 214, 385 [BeOBu t  2 ] 3 J-2 IR; 1 H NMR; MW 385 [BeOCEt 3  2 ] 2 J-2 IR; 1 H NMR; MW 385 [BeOCMe 2 CH 2 OMe 2 ] 2 IIR; 1 H NMR; MS 340 [BeOCEt 2 CH 2 OMe 2 ] 2 IIR; 1 H NMR; MS 340 [BefOCCF 3 g 2 ] 3 .OEt 2 E-2 1 H, 19 F NMR; MW 396 MgOMe 2 .3.5MeOH A X-ray 38 [Ca-ORORthf] 2 .toluene 2 E-2 IR; 1 H, 13 CNMR; X-ray 147 [CaOR 2 thf 3 ].THF E-2 IR; 1 H, 13 CNMR; X-ray 147 CafOCCF 3  3 g 2 A 19 F NMR 47, 53, 340 Ca 3 OCHBu t 2  6 I 53, 340 Ca 2 [OCBu t CH 2 OPr i  2 ] 4 I IR; MS; X-ray 53, 340 Ca[OCBu t CH 2 OPr i CH 2 CH 2 NEt 2 ] 2 I IR; MS 53, 340 Ca 9 OC 2 H 4 OMe 18 HOC 2 H 4 OMe 2 AIR; 1 H, 13 CNMR; X-ray 50 Sr[OCCF 3  3 ] 2 A 19 FNMR 47 Sr 2 [OCBu t CH 2 OPr i  2 ] 4 I IR; MS 53, 340 BaOBu t  2 A 1 HNMR 47 BaOCEt 3  2 A 1 HNMR 47 BaOCMeEtPr i  2 A 1 HNMR 47 Homometallic Alkoxides 7 Table 2.1 (Continued ) Method of Characterization Compound 1 preparation 2 techniques 3 Reference BaOCHBu t 2  2 A 1 HNMR 47 Ba[OCHCF 3  2 ] 2 A 19 FNMR 47 Ba[OCCF 3  3 ] 2 A 19 FNMR 47 [BaOBu t  2 HOBu t  2 ] 4 I 1 H, 13 CNMR; X-ray 549 Ba 2 [OCBu t CH 2 OEt 2 ] 4 E-2 53, 340 Ba 2 [OCBu t CH 2 OPr i  2 ] 4 A, I IR; MS 53, 340 Ba 2 OCPh 3  4 thf 3 A 1 H, 13 CNMR; X-ray 48 Ba[OCH 2 CH 2  x CH 3 ] 2 (x D 2, 3) AIR; 1 H, 13 CNMR; MS 52 Scandium, Yttrium, and Lanthanides [ScfOCHCF 3  2 g 3 NH 3  2 ] 2 IIR; 1 H, 19 FNMR; MS; X-ray 349 LnOPr i  3 Ln D Y, Pr, Nd, Sm, Eu, Gd,Tb,Dy,Ho,Et,Tm,Yb,Lu AIR; 1 HNMR(Y, La, Lu); UV-Vis (Pr, Nd, Sm, Ho, Er) 55 LnOPr i  3 Ln D Y, Dy, Yb AIR; 1 HNMR (Ln D Y) 54 LnOPr i  3 Ln D Pr, Nd E-2 MW 153 LnOR 3 Ln D Pr, Nd; R D Bu n ,Bu i ,Bu s ,Bu t ,Am n , Am t ,Pr n CH(Me), Pr n CMe 2 G MW 153 GdOPr i  3 E-2 IR; MW 157 ErOPr i  3 E-2 IR; MW 157 LnOMe 3 Ln D Gd, Er E-3 IR 157 HoOPr i  3 E-2 MW 158 [YfOCHCF 3  2 g 3 thf 3 ] I IR; MS; X-ray 349 [YfOCMe 2 CF 3 g 3 ] n I 1 H, 19 F NMR 349a [YfOCMe 2 CF 3 g 3 thf 2.5 ]I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 g 3 ] n I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 g 3 NH 3  0.5 ]I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 g 3 NH 3  3 ]I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 gthf 3 ]I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 g 3 OEt 2  0.33 ]I 1 H, 19 F, 89 Y NMR 349a fYfOCMeCF 3  2 g 3 diglymeg I 1 H, 19 F, 89 Y NMR 349a [YfOCMeCF 3  2 g 3 HOBu t  3 ]I 1 H, 19 F, 89 Y NMR 349a fYOCHCF 3  2 g 3 NH 3  0.5 ]I 1 H, 19 F, 89 Y NMR 349a [YfOCHCF 3  2 g 3 thf 3 ]I 1 H, 19 F, 89 Y NMR 349a [Y 3 OBu t  9 HOBu t  2 ]IIR; 1 H, 13 C, 89 Y NMR; MS 345 [Y 3 OAm t  9 HOAm t  2 ]IIR; 1 H, 13 C, 89 Y NMR; MS 345 (continued overleaf ) 8 Alkoxo and Aryloxo Derivatives of Metals Table 2.1 (Continued ) Method of Characterization Compound 1 preparation 2 techniques 3 Reference [YOR 3 ] 2 R D CMe 2 Pr i ,CMeEtPr i ,CEt 3 IIR; 1 H, 13 C, 89 Y NMR; MS 345 [YOC 2 H 4 OMe 3 ] 10 AIR; 1 H, 13 CNMR; X-ray 57 [La 3 OBu t  9 HOBu t  2 ]I 1 H, 13 CNMR;MS; X-ray 345 [LaOR 3 ] 2 R D CMe 2 Pr i ,CMeEtPr i I 1 H, 13 C NMR; MS 345 [La 3 OBu t  9 thf 2 ]E-2 1 H, 13 CNMR; X-ray 160 [LaOCPh 3  3 ] 2 IIR; 1 H, 13 CNMR; X-ray 346 [LafOCMeCF 3  2 g 3 thf 3 ]IIR; 1 H, 13 CNMR; MS; X-ray 349c La 4 OCH 2 Bu t  12 IIR; 1 H, 13 CNMR; X-ray 348a [CeOPr i  4 .Pr i OH] 2 E-1 MW 143 E-2 1 H, 13 CNMR; X-ray 460 CeOCBu t 3  3 I MW 344 [CeOCHBu t 2  3 ] 2 150 Ž C, vacuum X-ray 344 CeOR 4 R D Me, Et, Pr n ,Bu n ,Bu i , CH 2 Bu t G MW 143 CeOBu t  4 thf 2 E-2 IR; 1 H, 13 C NMR 164 [PrfOCMeCF 3  2 g 3 NH 3  2 ] 2 I IR; MS; X-ray 349 [PrfOCMeCF 3  2 g 3 NH 3  4 ]IIR; 1 H NMR; X-ray 349b [PrfOCMe 2 CF 3 g 3 ] 3 I IR; MS; X-ray 349 [NdOCBu t 3  3 thf]IIR; 1 H NMR; X-ray 959 Nd 4 OCH 2 Bu t  12 IIR; 1 H NMR; X-ray 348a Nd 2 OCHPr i 2  6 thf 2 IIR; 1 H NMR; X-ray 348 [NdOPr i  3 .Pr i OH] 4 AIR 56 [EufOCMeCF 3  2 g 3 ] n I IR 349b [Eu 2 fOCMeCF 3  2 g 6 NH 3  2 ] I IR 349b [EufOCMeCF 3  2 g 3 thf 3 ]I 1 H, 19 F NMR; MS 349c [EufOCMeCF 3  2 g 3 diglyme]I 1 H, 19 F NMR; MS 349c [LuOCMe 2 CH 2 OMe 3 ] 2 IIR; 1 H, 13 CNMR; MS; X-ray 355 Actinides [ThOPr i  4 ] n E-2 MW 141 [ThOEt 4 ] n G MW 141 [ThOR 4 ] n G MW 143 R D Bu n ,Pent n ,CH 2 Bu t 143 R D CMe 3 ,CMe 2 Et, CMeEt 2 , CMe 2 Pr n ,CMe 2 Pr i ,CEt 3 , CMeEtPr n , CMeEt,Pr i 141a Th 4 OPr i  16 Py 2 E-2 IR; 1 H, 13 CNMR; X-ray 165 Th 2 OCHEt 2  8 Py J-3 IR; 1 H, 13 CNMR; X-ray 165 [ThOBu t  4 Py 2 ] E-2 IR; 1 H NMR; X-ray 398 [...]... whereas (iv) heterobimetallic alkoxides like NaAl(OR)4 and KZr2 (OR)9 tend to be formed with excess of alkali alkoxides 22 Alkoxo and Aryloxo Derivatives of Metals 2.5.1 The Ammonia Method (E-1) The addition of a base, typically ammonia, to mixtures of metal(loid) halides and alcohols allows the synthesis of homoleptic alkoxides for a wide range of metals and metalloids Anhydrous ammonia appears to have... fluorinated) and/ or donor-functionalized alkoxo ligands is an attractive strategy for the design and synthesis of hydrocarbon-soluble and volatile derivatives (Table 2.1) In this context the use of lithium derivatives of such ligands,21 which are conveniently prepared by the interaction of an alcohol with butyllithium, has played an important role For example, the reactions of LiOR (R D a sterically demanding... 2.81 Preparation of organometal alkoxides of germanium,253 – 255 tin,256 – 266 and lead267,268 have also been described by the reactions of an appropriate organometal oxide or hydroxide with alcohols The reaction between an organometal oxide and a dialkyl 32 Alkoxo and Aryloxo Derivatives of Metals carbonate has also been found to yield the corresponding organometal alkoxides of tin261 and mercury.269... available for the varying reactivity of different metal chlorides with alcohols, it is interesting to note that final products of similar compositions have been isolated in the reactions of tetraalkoxides of these metals with HCl For example, the reaction of Ti OPri 4 with HCl leads finally to Ti OPri 2 Cl2 Pri OH (Section 4.11.2) 20 Alkoxo and Aryloxo Derivatives of Metals Specific intermediate products... of the metal(loid) The tendency for the formation of heterobimetallic alkoxides with alkali metals, 179,180,195 has generally restricted the applicability of this procedure for the synthesis of homometallic alkoxides of many of these metals, except in cases where the heterobimetallic alkoxides are thermally labile and dissociate to yield the corresponding volatile homometallic alkoxides of p-block metals. .. rather unusual and intriguing in view of the general trends of metal alkoxide chemistry and are somewhat at variance with the earlier findings (mainly on isopropoxide derivatives) from the research groups of Mehrotra103,148 – 150,156 – 158 and Mazdiyasni.54,55 Also, although most of the 1:3 reactions of lanthanide trichlorides and alkali alkoxides (mainly methoxides, ethoxides, isopropoxides and even 2methoxyethoxides57... or alkyl with donor functionalities) with metal halides yield derivatives generally with unprecedented structural and reactivity features The synthesis of such soluble derivatives is generally carried out in Et2 O or THF solvents, in which LiCl tends to be precipitated (Eqs 2.70–2.74): 30 Alkoxo and Aryloxo Derivatives of Metals Homoleptic derivatives MClx thf C x LiOR Et2 O or THF L ! 1 [M OR m x L... to the alkali metals and monovalent thallium as well as boron, silicon, and arsenic This might be due to the high lattice energies of oxides of higher valency metals In view of the importance of alkoxysilanes and alkoxysiloxanes as precursors for glasses and ceramic materials, a process of obtaining these from portland cement and silicate minerals was described in 1990.251 Under the mild reaction conditions... excess 2KOH 2 28 Alkoxo and Aryloxo Derivatives of Metals PtCl2(NCBut)2 + 2 R′′2PCH2CRR′OH (i) NaOH in MeOH Pt(OCRR′CH2PR′′2)2.(H2O)x (ii) xH2O 2.62 R D R0 D H, R00 D Ph, x D 0 or 1;178 R D R0 D Me, R00 D Ph, x D 0178 2.5.2.4 p-Block elements Meerwein and Bersin179 investigated the reaction of sodium ethoxide with an alcoholic solution of aluminium trichloride and isolated a product of composition NaAl(OEt)4... thermal decomposition (Section 2.1), typically by a ˇ-hydrogen elimination pathway However, with the use of some special (fluorinated and/ or donor-functionalized) type of alkoxo ligands,21 the synthesis of hydrocarbonsoluble and monomeric alkoxides of later transition metals including palladium(II) and platinum(II) can be achieved (Eqs 2.59–2.62): cis- R3 P 2 MCl2 C 2NaOCH CF3 2 ! cis- R3 P 2 MfOCH CH3 . of the alkali metals. The ramification of the alkyl group is also important, as shown by the 6 Alkoxo and Aryloxo Derivatives of Metals Table 2.1 Examples of some homoleptic alkoxides Method of. intervening years have seen a resurgence of activity involving the synthesis and characterization of many novel compounds and 2 Alkoxo and Aryloxo Derivatives of Metals studies on their catalytic activity Pr n ,Bu n , MeCH 2 CH 2 CH 2 (and its isomers), MeCH 2 CH 2 CH 2 CH 2 (and its isomers) E-1, G MW 280, 312, 469 (continued overleaf ) 10 Alkoxo and Aryloxo Derivatives of Metals Table 2.1 (Continued ) Method of Characterization Compound 1 preparation 2 techniques 3 Reference [NbOPr i  5 ] 2 B,