Selenols , addition

Using pyridine as solvent for Pd(OAc)2phenyl selenol addition to alkynes resulted in better regioselectivities and yields (although in some cases the yields were not very high) [150]. Most likely, pyridine facilitated the formation of soluble Pd complexes in this catalytic system. 

Like the three-coordinate aluminum and gallium alkoxides, the corresponding thiolates, selenolates, and tellurolates require very bulky substituents at the chalcogen atom to ensure a low metal coordination number. In addition, the steric requirements associated with the preservation of the low coordination number at the metal are increased by the longer M—S and M—Se bond lengths. The ten examples of low-coordinate,... 

Nickel-selenium coordination compounds have received attention in recent years, because a unique Ni-selenocysteine interaction was revealed in the active site of [FeNiSe]-hydrogenases.1083,1084 Of particular interest in this regard are mixed CO/selenolate complexes. Distorted square planar (393) was prepared from [CpNi(CO)]2, PhSeSePh, and [Fe(CO)3(SePh)3] and provides the first example of CO bound to a square planar Ni11 center in thiolate/selenolate environment.1085,1086 Upon addition of RSSR, species of the series [Ni(CO)(SR) (SePh)3 ] are formed. //(CO) ranges from 2,023 cm-1 to 2,043 cm-1 and is regarded as a spectroscopic reference for the CO binding site in [NiFeSe] hydrogenases. 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

The oxidative addition reaction of the type shown in Equation (9) were used to prepare some of the first selenolate and tellurolate complexes still used today. 

The lO-E-4 chalcogen(IV) species diphenylselenium(IV) dibromide (1, Fig. 1) and diphenyltellurium(IV) dibromide (2, Fig. 1) oxidize thiophenol to diphenyl disulfide in nearly quantitative yield as shown in equations (13) and (14). Tellurium(IV) dihalides 6-11 also oxidize thiophenol to diphenyl disulfide and benzene selenol to diphenyl diselenide. Similarly, the 12-Te-5 molecule dioxatellurapentalene 45 (Fig. 19) is a mild oxidant for ethylmercaptan, thiophenol, and benzene selenol giving diethyl disulfide, diphenyl disulfide, and diphenyl diselenide in essentially quantitative yield. As shown in equation (15), 1,1,5,5,9,9-hexachloro-1,5,9-tritelluracyclododecane oxidizes six molecules of thiophenol to diphenyl disulfide and 1,5,9-tritelluracyclododecane in 90% yield. In contrast, 12-Te-5 pertellurane 44 and 12-Se-5 perselenane 46 do not oxidize thiophenol to diphenyl disulfide. Instead, these molecules undergo a nucleophilic addition of thiophenol followed by cleavage of the tellurium-carbon or selenium-carbon bond. ... 

Example 2, in addition to oxyselenide formation, carbo- and heteroseleno cycliza-tion, A -PSP can be used to generate selenides from alcohols and selenol esters from carboxylic acids, respectively, in the presence of a stoichiometric amount of n-Bu,P. ... 

Nucleophilic additions of alcohols, amines, thiols, and selenols to Group 8 buta-trienylidene intermediates [M]=C=C=C=CR2 have also been used in the preparation of stable heteroatom-conjugated allenylidene complexes. Thus, activation of trimethylsilyl-l,3-butadiyne HC=C-C=CSiMe3 by the iron(II) complex [FeClCp (dppe)], in methanol and in the presence of NaBPh4, resulted in the high-yield formation of the methoxy-allenylidene [FeCp =C=C=C(OMe)Me ... 

The syntheses of 2-ketobenzo[ >]selenophene (134) (76JCS(P1)2452) and its benzo[c] counterpart (135) (64BSB491, 81JHC343) both depend on intramolecular acylation of an intermediary selenol, while in the benzo[Z>]selenophene (137) preparation from (136) the ring closure depends upon the intramolecular addition of the intermediary selenol to the carbonyl group (70BSB235). 

There are several reviews that enumerate the many methods that effect the addition of H—SeR to C—C multiple bonds.558,559 Of these, only a few methods involve true electrophilic additions of selenols to C—C multiple bonds. High yields of the Markovnikov product are reported when the relatively acidic... 

Diethyl zinc undergoes enantioselective addition to 2-pyridinecarbaldeyde in 91% ee in the presence of 0.5 mol% optically pure diselenide 68 in toluene at room temperature <2003OL2635> (Equation 48). The reaction is postulated to proceed by in situ formation of a chiral zinc selenolate formed by nucleophilic attack of Et2Zn on diselenide 68. 

Thiols may react in analogous fashion, e.g., their addition to Ru(CO)2L3 gives RuH(SR)(CO)2L2 (L = PPh3) a hydrido selenolate species is also known.40... 

The oxidative addition of chalcogen-chalcogen bonds in RE—ER is widely applied in transition metal chemistry and is often a useful route for the preparation of thiolates, selenolates and, to a more limited extent, tellurolates. The oxidative addition of X2 = HO—OH and PhC(0)0—0C(0)Ph is also known and, in the case of Ptu complexes, gives predominantly trans products 47... 

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