Insertion into E-H Bonds

A widely developed methodology to create E-M compounds has been the insertion of metal fragments into E-H bonds. In some cases simple 

When treated with arsine, Cp Mn(CO)2(THF) gives [Cp Mn(CO)2]2 AsH, which converts into [/a-(Cp )Mn(CO)2]2As2 with elimination of H2 246,247 xhiS contrasts with the reaction of the analogous nonsubstituted cyclopentadienyl complex, which under similar circumstances yields [CpMn(CO)2]4As2.246,247 To achieve selectivity in the synthesis of the sensi- 

The ruthenium sulfoximido complex HRu3(C0)9 NS(0)MePh is of note because it formally has two electrons fewer than the normal tetrahedral structure [Eq. (64)].170 Upon addition of CO it is converted into an electron-precise /a-imido complex [Eq. (65)170]. 

Multidecker M2E3 complexes are most often obtained by treating M2+ ions and tripodal ligands with elemental phosphorus or arsenic. If PhAsH2 

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Green and coworkers (5-8) have shown in a series of studies that photogenerated tungstenocene behaves as. an organometallic car-bene and readily inserts into C-H bonds of a variety of solvent molecules, e.g., eq 3 (5). 

Insertion of the Si=N bond into polar bonds is the most used reaction for the characterization of very reactive and transient silanimines. Especially, the reaction with alcohols is often the first reaction to be carried out with silicon-nitrogen multiple bond systems. Other reagents used for insertion reactions are amines, water and alkoxysilanes (equation 269)300,303,306,311,351-353. The insertion into E—X bonds (E = Si, Ge, Sn X = Cl, OR, NR2, N3) has been shown earlier in this review for the insertion into the Si—N bond of silyl azides310,351. A reaction reported is the insertion of 678 into the C—H... 

The complications that occasionally arise in the use of diazoalkanes reflect the possible further reactions of carbene ligands, which will be dealt with subsequently, e.g. insertion into adjacent M-H or M-halide bonds and the formation of bimetallic complexes supported by bridging carbene ligands. In some cases, transition metals may catalyse reactions of diazoalkanes, leading to products which are suggestive of the reactions of free carbenes, i.e. dimerization, addition to alkenes (cyclo-propanation) and insertion into C-H bonds (Figure 5.9). In such cases, however, the actual mechanism does not involve free carbenes but rather transient diazoalkane/carbene complexes. This is supported by the obser-... 

Insertion into C—H bonds of the ligands as well as formation of metallacycles (i.e., metallaoxiranes and 1,2,4-metalladioxolanes) according to Eqs. (2)-(4), depending on the coordination sphere and reaction conditions. All metallaoxiranes and 1,2,4-metalladioxolanes are listed in Tables VII and VIII. Three-membered rings have been synthesized by reaction of metal... 

Triplet electronic-state carbenes react similarly. Singlet carbenes insert into substrate-H bonds, e.g. ... 

The experimental observations favoring this proposal are the following (i) the regioselectivities for nickel-catalyzed hydroaluminations differ significantly from those obtained from the uncatalyzed process e.g. equation 11) (ii) certain hindered alkenes do not undergo uncatalyzed hydroalumination under conditions where the nickel-catalyzed reaction is essentially complete (e.g. equation 39) (iii) nickel(O) complexes have been shown to insert into A1—H bonds to yield R2A1-N1—H intermediates (equation 40) and (iv) such Al-Ni—H intermediates react with A1—H bonds, with the rate depending upon sub-... 

The ring opening of cyclopropencs to vinylcarbenes has been described in detail (Houben-Weyl, Vol. E19b, p94). In many cases these carbenes undergo rapid intramolecular reactions in other examples, the carbene may be trapped by insertion into C-H bonds, e.g. reaction of 1,1 7. >58. >59 2.84... 

SiMcj, may be conveniently generated by photolysis of o c/o-Si6Me,2, and this method has been used in the study of its insertion into Si—H bonds (e.g. in Me3SiH), Si—O bonds e.g. MejSiOEt)/ and into HCl. In low-temperature matrices it has been shown that SiMej may be converted by visible light (A = 450nm) into MeHSi = CH2. Annealing the photolysed matrix yields (4b). 

Other insertions into M-H bonds of paramagnetic complexes have been proposed to occur during the reactions of a few saturated hydride complexes with electron poor acetylenes, the first step being an electron transfer process. A characteristic of this mechanism is an E- rather than Z-addition stereochemistry. Examples of this phenomenon have been described for PtHjLj (L = tertiary phosphine) [139], Cp2ReH and CP2WH2 [140]. 

As mentioned in Section 8.1, carbenes easily undergo insertion into O-H bonds. At an early date, Kerr et al. (1967) found that in the photolysis of diazomethane- er butanol mixtures insertion is eleven times faster at O - H than at C - H bonds. The relative rates of ether formation for methanol, ethanol, 2-propanol, and tert-butanol are 2.01 1.95 1.37 1.00. Before that investigation, Kirmse (1963) postulated that diphenylcarbene is protonated to form the diphenylmethyl carbocation, which, as a strong electrophile, adds to the alcoholate anion (or to the alcohol followed by deprotonation) forming the ether (8-26 a). Bethell et al. (1969, 1971), however, favored an electrophilic attack of diphenylcarbene at the O-atom, i. e., an ylide intermediate on the basis of isotope effects (8-26 b). Finally, a concerted process via the transition state 8.39 may be feasible (8-26 c). 

Transition metal-catalysed methods for carbenoid insertion into C-H bonds remain well documented. The asymmetric intramolecular Cu(II)-catalysed C-H insertion reactions of (i) a-diazo-/ -keto esters and phosphonates and (ii) a-diazo sulfones have been described. One can note that the optimal reaction conditions have been found to be quite similar regardless of the nature of the carbenoid precursor the best conditions featured CUCI2 as Cu(II)-source, bis(oxazoline) (68) as chiral ligand and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate (i.e., NaBARF) as additive. Under the so-optimized reaction conditions, each of these carbenoid sources have been eonverted into five-membered cyclopentanone-based derivatives (69), whereas a-sulfonyl diazo esters (70) have led to six-membered cyclic compounds (71), thus featuring a distinct but well-known selectivity. In a related work, the asymmetric C-H insertion cyclization of (70) to (71) has also been achieved under Rh(II)-catalysis, using a combination of Rh2(5-pttl)4 (72) as chiral catalyst and menthyl ester as chiral auxiliary. As already mentioned in the previous section, allene-containing substrates (49) have been shown to undergo an intramolecular C-H insertion process under Rh(II)-catalysis. ... 

Triphenylsilane heated 2-4 hrs. with phenyl (bromodichloromethyl) mercury in benzene at ca. 80° until thin layer chromatography shows that all of the mercurial has been consumed triphenyl (dichloromethyl) silane. Y 90%. F. e., also insertion into G-H bonds, s. D. Seyferth and J. M. Burlitch, Am. Soc. 85, 2067 (1963). 

These carbene (or alkylidene) complexes are used for various transformations. Known reactions of these complexes are (a) alkene metathesis, (b) alkene cyclopropanation, (c) carbonyl alkenation, (d) insertion into C-H, N-H and O-H bonds, (e) ylide formation and (f) dimerization. The reactivity of these complexes can be tuned by varying the metal, oxidation state or ligands. Nowadays carbene complexes with cumulated double bonds have also been synthesized and investigated [45-49] as well as carbene cluster compounds, which will not be discussed here [50]. 

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

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