Selenolates bonding

These reactions could proceed either via (1) insertion of the alkyne or the allene into the M-Se bonds, and (2) C-H bond-forming reductive elimination (or protolysis by selenol) or via (1) insertion of the alkyne or the aUene into the M-H bond, and (2) C-Se bond-forming reductive elimination. 

Hydrozirconation of terminal alkynes R-C=CH (R= aryl, alkyl) with 1 affords terminally ( )-Zr-substituted alkenes with high efficiency and excellent stereochemical and regiochemical control (>98%). These alkenylzirconocene complexes are of particular interest for synthetic use [136, 143, 144]. Moreover, beside the electropositive halogen sources [145] and heteroatom electrophiles [3] used in the pioneering studies to directly cleave the Zr-C bond, ( )-vinyl-Zr complexes were recently transformed into a number of other trans-functionalized alkenes such as ( )-vinyl-sul-fides[146], vinylic selenol esters [147], vinyl-sulfones [148], vinyl-iodonium [149], vinyl-(R0)2P(0) [150], and vinilic tellurides [143]. 

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,... 

Metal-Sulfur, -Selenium, and -Tellurium Bond Lengths, M—E—C Angles, and Torsion Angles for Three-Coordinate Aluminum, Gallium, and Indium Thiolates, Selenolates and Tellurolates", and Related Compounds... 

Treatment of tetrahydroberberine (26) with sodium benzenethiolate (48) or -selenolate (49) in the presence of ruthenium catalyst afforded the C-14—N bond cleavage products 51 or 52 with a phenylthio or phenylseleno group at C-14 (Scheme 12). The latter was converted to the 10-membered amino olefin 53 on treatment with m-chloroperbenzoic acid. 

In the second step of this reaction the O—O bond of H2O2 is cleaved. During this process, one hydroxyl fragment (0 11) is transferred to the selenolate anion (R—Se-) to form selenenic acid (R—SeO1 II), while simultaneously the second... 

In (393), the average Ni—Se distance is 231.7(2) pm.1085 Simple tetrahedral [Ni(SePh)4]2 has been prepared by reaction of NiCl2-4H20 with LiSePh.1087,1088 An excess of selenolate has to be used to prevent formation of [Ni(SePh)2]8. The PPh4+ salt is stable in air for several hours. Its average Ni—Se bond lengths (240.1(3) pm) are longer than in the homoleptic square planar systems. 

The starting material is always the chalcogenol and, consequently, is more used for thiols than selenols and tellurols. There are several types of reactions depending if the starting materials are metal hydrides (hydrogen elimination), complexes with M C (alkane elimination), M-N (transamination), or M-O (hydrolysis) bonds. 

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. ... 

Methyl-metal bond cleavage also occurred in the reactions of gold(I), gold(III), and platinum(II) compounds with thiols and selenols (207-209). The reactions of gold(I) and platinum(II) complexes were much faster than those of gold(III), due to the operation of a radical chain mechanism in the former cases. For the reactions with diphenylphosphine, however, the following order of reactivity was found (209) ... 

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... 

An example of adding selenols to triple bonds in a Markovnikov fashion is the reaction of selenophenol and 1-hexyne (equation 310).562... 

Carbonsulfur bonds can be formed by the reaction of elemental sulfur with a lithio derivative, as illustrated by the preparation of thiophene-2-thiol 446. If dialkyl or diaryl disulfides are used as reagents to introduce sulfur, then alkyl or aryl sulfides are formed sulfinic acids are available by reaction of lithium derivatives with sulfur dioxide. In the pyrrole series, a 2-thiol and the corresponding selenol can be prepared via reaction of 2-lithio-l-methylpyrrole with sulfur or selenium, then trapping with Me3SiCl leading to the 2-Me3SiX-substituted derivatives <1997T13079>. 

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