Complex-forming reactions Document

Consistent Data-Recording Procedures. Clear procedures for recording all pertinent data from the experiment must be developed and documented, and unambiguous data recording forms estabUshed. These should include provisions not only for recording the values of the measured responses and the desired experimental conditions, but also the conditions that resulted, if these differ from those plaimed. It is generally preferable to use the values of the actual conditions in the statistical analysis of the experimental results. For example, if a test was supposed to have been conducted at 150°C but was mn at 148.3°C, the actual temperature would be used in the analysis. In experimentation with industrial processes, process equiUbrium should be reached before the responses are measured. This is particularly important when complex chemical reactions are involved. 

Reaction 6 has been documented for H2Rh(02C0H)(PCy3)2 (16).) Other IR bands at 1580(s) and 1235(m) cm"1 that result from the solution C02 reactions could arise from a C02 complex (54), a formate complex formed via C02 insertion into Rh-H (16), or even a bicarbonate formed via Reaction 7, which has been documented again for a rhodium/PCy3 system (16). 

Carbene complexes have also been shown to undergo a-hydrogen elimination, in this case to form alkylidyne complexes. This reaction is much less common than the reaction of alkyl complexes to form alkylidenes, but a few examples are well documented. Two examples of this transformation are shown in Equations 10.39 and 10.40. Schrock reported the first direct observation of this transformation (Equation 10.39). ° In this first example, an isolated carbene complex converted to an alkylidyne hydride complex upon abstraction of a chloride ligand with trimethylaluminum. In a second example, a double C-H activation process by two sequential a-hydrogen elimination reactions converts the starting tungsten-methyl complex in Equation 10.40 into a methylidyne complex. ... 

There are only a few weU-documented examples of catalysis by metal clusters, and not many are to be expected as most metal clusters are fragile and fragment to give metal complexes or aggregate to give metal under reaction conditions (39). However, the metal carbonyl clusters are conceptually important because they form a bridge between catalysts commonly used in solution, ie, transition-metal complexes with single metal atoms, and catalysts commonly used on surfaces, ie, small metal particles or clusters. 

Unlike the case of the Ni-catalyzed reaction, which afforded the branched thioester (Eq. 7.1), the PdCl2(PPh3)3/SnCl2-catalyzed reaction with 1-alkyne and 1-alkene predominantly provided terminal thioester 6 in up to 61% yield in preference to 7. In 1983, a similar hydrothiocarboxylation of an alkene was also documented by using a Pd(OAc)2/P( -Pr)3 catalyst system with t-BuSH to form 8 in up to 79% yield (Eq. 7.6) [16]. It was mentioned in the patent that the Pt-complex also possessed catalyhc activity for the transformation, although the yield of product was unsatisfactory. In 1984, the hydrothiocarboxylation of a 1,3-diene catalyzed by Co2(CO)g in pyridine was also reported in a patent [17]. In 1986, Alper et al. reported that a similar transformation to the one shown in Eq. (7.3) can be realized under much milder reaction conditions in the presence of a 1,3-diene [18], and the carboxylic ester 10 was produced using an aqueous alcohol as solvent (Eq. 7.7) [19]. 

The potential synthetic utility of titanium-based olefin metathesis and related reactions is evident from the extensive documentation outlined above. Titanium carbene complexes react with organic molecules possessing a carbon—carbon or carbon—oxygen double bond to produce, as metathesis products, a variety of acyclic and cyclic unsaturated compounds. Furthermore, the four-membered titanacydes formed by the reactions of the carbene complexes with alkynes or nitriles serve as useful reagents for the preparation of functionalized compounds. Since various types of titanium carbene complexes and their equivalents are now readily available, these reactions constitute convenient tools available to synthetic chemists. 

Oxamborolidenes. There are noteworthy advances in the design, synthesis, and study of amino acid-derived oxazaborolidene complexes as catalysts for the Mukaiyama aldol addition. Corey has documented the use of complex 1 prepared from A-tosyl (S)-tryptophan in enantioselective Mukaiyama aldol addition reactions [5]. The addition of aryl or alkyl methyl ketones 2a-b proceeded with aromatic as well as aliphatic aldehydes, giving adducts in 56-100% yields and up to 93% ee (Scheme 8B2.1, Table 8B2.1). The use of 1-trimethylsilyloxycyclopentene 3 as well as dienolsilane 4 has been examined. Thus, for example, the cyclopentanone adduct with benzaldehyde 5 (R = Ph) was isolated as a 94 6 mixture of diastereomers favoring the syn diastereomer, which was formed with 92% ee, Dienolate adducts 6 were isolated with up to 82% ee it is important that these were shown to afford the corresponding dihydropyrones upon treatment with trifuoroacetic acid. Thus this process not only allows access to aldol addition adducts, but also the products of hetero Diels-Alder cycloaddition reactions. 

Catalysis with Ti(IV) Complexes and Boronates. Carreira has documented the addition of dienolsilane 105 to a broad range of aldehydes [28], Enolization of the commercially available acetone-ketene adduct 104 with LDA, followed by quenching with chlorotrimethyl silane, gave 105 in 78% yield as a clear colorless liquid that can be conveniently purified by distillation (Eq. 8B2.24). The addition reactions are conducted at 23°C utilizing 5 mol % 72 to give adducts with up to 94% ee (Eq. 8B2.25, Table 8B2.13). The aldol adducts 106 were isolated fully protected as the corresponding 0-silyl ethers with the P-keto ester masked in the form of a dioxinone. 

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