Reactions with transition metal reagents

This chapter covers the catalytic reactions with transition-metal reagents as Lewis acids consisting of the group 5 to 10 atoms of the periodic table, from vanadium to platinum (Figure 16.1). 

It is well known in organoantimony chemistry that tetraalkyldistibines Sb2R4 tend to react with electrophilic reagents under Sb-Sb bond cleavage.64 This tendency was already observed in reactions with transition metal... 

With transition metal reagents, Cgo undergoes either hydrometalations or forms T] - rather than t] - or Tj -Tt-complexes (see Chapter 7). The latter would be typical reactions for planar aromatics (Scheme 14.2). Conversely, Tj -Tt-complexes can be obtained with fullerene derivatives, where due to a specific addition pattern an isolated cyclopentadienide substructure is present (see Chapter 7) [76-78]. 

Reactions of B5Hg with transition metal reagents can also lead to full incorporation of the metal into the cage skeleton, as discussed in Section 5-6. Among the well-... 

Finally, many reactions of organotin compounds with transition-metal reagents do not lead to isolable or characterizable complexes of the sort included in Table 2. 

This chapter will focus on the nucleophilic addition reactions of transition metal vinylidenes and allyl complexes with Grignard reagents. Reactions with transition metal vinylidenes will be discussed initially, and then a brief review of allyl complexes with Grignard reagents will conclude the chapter. The synthesis and some general reactions of these vinylidene and allyl complexes will be presented. A more detailed description of the chemistry of these metal complexes can be found in the literature [1]. 

Perfluoroalkanes are much less reactive but the classic 1959 work by Tadow in Nature attracted attention by showing that partial reduction to give definite products could occur (equation 26). In this work, perfiuorodecalin (PFD) was reduced to perfluoronaphthalene (PFN) by NaSAr. Since then, several PFD conversions have been reported with transition metal reagents, either via photochemical or thermal routes. " For example, hot sodium oxalate (465 °C) aromatizes perfiuorodecalin to give perfluorotetralin and perfluoronaphthalene (equation 27). Decomposition of solid sodium oxalate at temperatures above 450 °C involves initial formation of elemental carbon that catalyzes the subsequent decomposition of oxalate, leading to the presence of an induction period in the overall decomposition reaction. Prior incipient decomposition of sodium oxalate to carbon and sodium carbonate is necessary for this reagent to effect aromatization. 

Reactions with Transition Metals Forming Carbon-Carbon Bonds. The combination of certain lanthanides and TMS-Br has been found to produce lanthanum halides (LaX n = 2 or 3) that are very active reducing reagents (eq 19). So far, the only metals to be used in these reactions are samarium (Sm) and ytterbium (Yb). In addition to TMS-Br, these reactions have been accomplished using Sm/TMS-Cl/Nal under similar conditions with corr5>arable yields. 

NHC species is remarkably general. Like the formation of the [(NHC)AgX] species itself, subsequent reaction with transition metal precursors can be carried out in air without rigorous purification of solvents, with some exceptions. In an interesting application, Crabtree and co-workers used sequential additions of two different silver NHC reagents in order to synthesize iridium complexes of the formula [(NHC )(NHC )Ir(COD)]. ... 

The iron catalyst was generated in situ upon reaction of iron bis-cyclooctatetraene [= Fe(COT)2] with organometallic reagents and was applied to a limited number of ynamines. However, others were able to follow the route and initiate Diels-Alder reactions with transition metals in low oxidation states. Accordingly, Mach, Klein, and co-workers realized the titanium-catalyzed Diels-Alder reaction of alkynyl silanes for the synthesis of dihydroaromatic intermediates such as 5 (Scheme 13.3) [2],... 

The coordination chemistry of hydrazine is of interest because of its ability to serve as an electron-pair donor. The presence of two free-electron pairs, as in other polybasic ligands, offers the possibility of several different types of coordination toward transition metal ions. The two free-electron pairs allow it to function as a monodentate, bidentate, or bridging ligand, which make hydrazine a preferred ligand. Hydrazine may act both as a ligand or a redox reagent in reactions with transition metals to form complexes. In a comprehensive review by Bottomley, the reaction between hydrazine and transition metals has been investigated in detail and summarized [21]. 

A variety of complexes of the thionyl imide anion [NSO] with both early and late transition-metal complexes have been prepared and structurally characterized. Since both ionic and covalent derivatives of this anion are readily prepared, e.g., K[NSO], McsMNSO (M = Si, Sn) or Hg(NSO)2, metathetical reactions of these reagents with transition-metal halide complexes represent the most general synthetic method for the preparation of these complexes (Eq. 7.10 and 7.11). ... 

Carboxylic esters undergo the conversion C=0— C=CHR (R = primary or secondary alkyl) when treated with RCHBr2, Zn, and TiCl4 in the presence of A,A,A, iV -tetramethylethylenediamine. Metal carbene complexes R2C=ML (L = ligand), where M is a transition metal such as Zr, W, or Ta, have also been used to convert the C=0 of carboxylic esters and lactones to CR2. It is likely that the complex Cp2Ti=CH2 is an intermediate in the reaction with Tebbe s reagent. 

A60. J. P. Candlin, K. A. Taylor, and D. T. Thompson, "Reactions of Transition-Metal Complexes. Elsevier, Amsterdam, 1968. A review of types of reactions of metal complexes (e.g., substitution, combination, redox) reactions with various reagents (e.g., hydrocarbons, halides, carbon monoxide, and isonitrile) and preparation of new stabilised organic systems (e.g., metallocenes, carbenes). Intended for research workers, consequently written at a fairly high level, with emphasis on organometallics. A61. H. J. Keller, NMR-Untersuchungen an Komplexverbindungen. Springer, Berlin, 1970. Expansion of review article 37.1. 

Ph2P(NH2)NP(NH2)Ph2]+Cl, 19, which is prepared by the reaction of Ph2PCl3 and ammonia (136). This synthon has a preformed N-P-N-P-N unit and can be readily cyclized to a six or higher membered ring upon reaction with an appropriate reagent (137). An important application of the use of the Bezman s salt approach has been the synthesis of metallocyclophosphazenes of the type 20, which contain an early transition metal in the framework of the cyclophosphazene skeleton [Fig. 15(A)] (138). A modification of the Bezman s salt to design a chiral synthon allowed the synthesis of an optically pure cyclophosphazene (139). 

Hydrogen transfer reactions from an alcohol to a ketone (typically acetone) to produce a carbonyl compound (the so-caUed Oppenauer-type oxidation ) can be performed under mild and low-toxicity conditions, and with high selectivity when compared to conventional methods for oxidation using chromium and manganese reagents. While the traditional Oppenauer oxidation using aluminum alkoxide is accompanied by various side reactions, several transition-metal-catalyzed Oppenauer-type oxidations have been reported recently [27-29]. However, most of these are limited to the oxidation of secondary alcohols to ketones. 

Zapf, A. Coupling of Aryl and Alkyl Halides With Organoboron Reagents (Suzuki Reaction). In Transition Metals for Organic Synthesis (2nd edn), Beller, M. Bolm, C. eds., 2004, 1, 211-229. Wiley-VCH Weinheim, Germany. (Review). 

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