Synthetic salt metathesis

Amidinate- and guanidinate-substituted boron halides are normally prepared using the two standard synthetic routes, i.e., salt-metathesis between suitable... 

The synthesis, structures, and reactivity of neutral and cationic mono- and bis(guanidinato)zirconium(rV) complexes have been studied in detail. Either salt-metathesis using preformed lithium guanidinates or carbodiimide insertion of zirconium amides can be employed. Typical examples for these two main synthetic routes are illustrated in Schemes 73 and 74. Various cr-alkyl complexes and cationic species derived from these precursors have been prepared and structurally characterized. 

In addition to the two widely used synthetic routes (i.e., salt metathesis and elimination) discussed above, there are two unique approaches effectively leading to mono-Cp alkyl complexes in one step. The first utilizes a bis(Cp) complex precursor, Cp2ZrCl2, to react with 3 equiv. of LiBun, yielding a 1 1 mixture CpZr(Bun)3 and CpLi via a facile... 

Anhydrous lanthanide halides are ionic substances with high melting points which take up water immediately when exposed to air to form hydrates (r>Br >Ch) [48]. Straightforward synthetic access and a favorable complexation/solva-tion behavior make the lanthanide halides the most common precursors in organolanthanide chemistry. Many important Ln-X bonds (X=C, Si, Ge, Sn, N, P, As, Sb, Bi, O, S, Se, Te) can be generated via simple salt metathesis reactions [4,8]. The so-called ammonium chloride route either starting from the lanthanide oxides or... 

Chemical differences between imide and sulfide ligand types, however, are substantive and dictate synthetic tactics. In ionic form, N-anions are considerably more basic than sulfur anions [e.g. in DMSO PhNH2, = 30.6 PhSH, 10.3) and, when coordinated to weak-field iron, the former remain more reactive than the latter. Furthermore, redox transformations coupled to weak-field iron are much more accessible with sulfur than nitrogen. As a result, imide ligation is introduced in Scheme 5.9 by protolysis rather than the salt-metathesis or redox routes typical in Fe-S chemistry. Protolysis requires iron precursors with reactive ligands as latent bases the relative instability of these complexes forces the incorporation of imide (or equivalent N-anions) early in the synthetic sequence. 

A -Heterocychc carbenes (24.64) have become important ligands in organometallic chemistry, a notable example being Grubbs second generation catalyst (24.67). Synthetic routes to A -heterocyclic carbene complexes (which are stable to air) typically involve salt metathesis or elimination reactions. Reaction 24.103 shows the use of a 1,3-dialkylimi-dazolium salt as a precursor, and scheme 24.104 illustrates conversions relevant to Grubbs catalysts (see below). 

Two different synthetic approaches were used to prepare complex 9a (Scheme 5.3). The aminolysis approach, modeled after the method developed by Jordan and coworkers. afforded 9b with a higher selectivity for the rac isomer rac.meso ratio of 7 1) than the salt metathesis route to form 9a (rac.meso ratio of 3 2). 

There are a number of synthetic pathways to trivalent rare earth siloxides and their Lewis base adducts such as salt metathesis, transesterification, acid-base chemistry, and silanolysis. Less frequently used are insertions of organo rare earth complexes into cychc and linear sUoxanes and CO2 insertion into rare earth silylamides. Transesterification is a common route for the preparation of stericaUy less-hindered early transition metal trialkyl siloxides and involves... 

The linking of two electronically different transition metal centers to give a dinuclear complex containing a highly polar metal-metal bond may be achieved by several basic synthetic strategies. The most widely used method is the simple salt metathesis, which for early-late heterodinudear complexes involves the reaction of an early (high-valent) transition metal halide with an alkali metal salt of an anionic late (low-valent) transition metal complex (mostly carbonyl metalates). Two examples of this method, including the reaction of a dihalide with a dianionic metal carbonylate, are summarized in Scheme 4.1. 

The development of the heavy alkaline-earth metal bis(bis(trimethylsilyl)amides, M[N(SiMe3)2]2(thf)2, has been instrumental in the use of the transaminadOTi route as a viable and dependable synthetic route towards the preparadmi of alkaline-earth metal compounds. The amides, M[N(SiMe3)2]2(thf)2, can be prepared via salt metathesis involving treatment of the metal halides with alkali metal amide (Ca-Ba) [182, 183]. The heavier metal (Sr, Ba) amides can also be obtained by direct metallation in liquid, anhydrous ammonia (Sr and Ba) [83,90,91, 184-187]. 

This first plan for a decarboxylative cross-coupling carried with it certain weaknesses for potential industrial applications. It was to be expected that the salt metathesis between alkali metal carboxylates and late transition metal halides would be thermodynamically disfavored. We expected the formation of a palladium benzoate complex i from palladium bromide complexes c and potassium benzoate (g) to proceed well only in the presence of a stoichiometric quantity of silver to capture bromide ions [27]. However, we did not like the idea of using stoichiometric quantities of silver salts or of expensive aiyl triflates in the place of aryl halides. Finally, the published substrate scope of the oxidative Heck reactimi led to concerns that palladium catalysts mediate the decarboxylation rally of a narrow range of carboxylates, precluding use of this reaction as a general synthetic strategy. 

Metathesis reactions between iV-chloramines and silver nitrite in alkaline solution are reported to give the silver salt of the corresponding primary nitramine. The method is of little synthetic value. ... 

As part of an investigation into new synthetic routes to the important acyclic nucleoside class of antiviral drugs, the cross metathesis of 9-allyl-6-chloropurine with 2,2-dimethyl-4-vinyl-l,3-dioxolane was attempted <2003TL9177>. The reaction was confounded by the coordination of the ruthenium metathesis catalyst with the purine heterocyclic nitrogens. This was overcome to some extent by using the /i-toluenesulfonic acid or hydrogen chloride salts of the... 

---