Sulphur bonding

In many cases, it has been found that 7r-bonding ligands favour S-bonding. In a complex with both N- and S-bonded thiocyanate (Figure 3.74) the N-bonded group is trans to P while the sulphur-bonded thiocyanate is trans to the harder nitrogen ( anti-symbiosis ). 

Some aspects of the reactivity of metal ion-sulphur bonds. C. G. Kuehn and S. S. Isied, Prog. Inorg. Chem., 1980, 27,153-221 (317). 

Jones and coworkers200 found that a variety of sulphenic acids may be generated by thermolysis of the readily available /J-cyanosulphoxides (equation 81) and observed their highly regiospecific addition also to non-conjugated alkynes (Table 12). As expected for a pericyclic mechanism, the reaction afforded the product of a stereospecific cis-addition. However, the regioselectivity of the addition suggests that the partial carbon-sulphur bond in the transition state 148 is polarized in such a way that the carbon atom has some cationic character (equation 82). 

In all the desulphonylation reactions discussed in Sections III.B and III.C the sulphur is lost from the starting sulphone and is reduced in the process simultaneously, the former carbon-sulphur bond is either reduced to a C—H bond or is converted into a C=C bond. The reactions described in this section have the common thread that the sulphur atom is lost with reduction at sulphur, but the carbon atom is converted directly into a carbonyl group. Formally, these reactions offer a route from alkyl halides to aldehydes or ketones. 

Several studies confirm an ortho effect leading to a dominating aryl sulphur bond cleavage. For example, the introduction of a bulky ortho substituent17 will provide the formation of the aliphatic sulphinic acid. A series of cyclic sulphones was studied18,19 at the mercury cathode and the results (see Table 2) appear to be fully in agreement with those expected when considering the preliminary works presented above. 

Sulphuranes - see also Dialkoxysulphuranes, Oxysulphuranes as intermediates 406 Sulphur bonding 484-493 Sulphur-containing groups, stereoelectronic effects of 584-594 Sulphur dioxide addition to 215-217 extrusion of 137, 140, 141, 158, 163, 397-402, 801, 805, 962, 1098 Sulphur monoxide, extrusion of 397-402 Sulphur trioxide, reactions of 217, 218 Sultenes, as intermediates 743 Sultines 679, 943 as photolytic products 881, 882... 

The oxygen-(I) and sulphur-bonded(II) isomers of thiosulphatopentaam-minecobalt(lll)... 

Reactions (6), (7) and (9) occur with substitution-labile oxidants and (6), (7) and (8) with substitution-inert oxidants. It is postulated that the species (MS03)" involves metal-oxygen coordination for labile M", and metal-sulphur coordination for inert M". The latter mode is thought to prevent sulphur-sulphur bond formation. 

The closely related dichloroethylenediamine platinum(II) was found to be slightly better than PtCll- as a heavy atom. A platinum-sulphur bond to methionine 29 is formed according to current analysis (now confirmed). The platinum cannot be removed by washing the crystal in sharp contrast to the reversible binding of other metal complexes. ... 

Hydrogenolysis of carbon-sulphur bonds (desulphurization) is carried out with Raney nickel. 

Hydrogenolysis of carbon-halogen and carbon-sulphur bonds... 

Homogeneous reductive cleavage of the sulphur-sulphur bond in some diphenyl disulphides by electron transfer from added radical-anions in the solution illustrate points from the two previous paragraphs [32], Rate data for two diphenyl disulphides are given in Figure 4.6. The variation in electron transfer rate with electron... 

One carbon-sulphur bond in dithioacetals can be preferentially cleaved because of stabilization of the intermediate carbon radical by an adjacent sulphur substituent [62]. 

Dialkyl sulphones are not reducible at a mercury cathode. Aryl alkyl and diaryl sulphones are however reduced with cleavage of a carbon-sulphur bond. Polaro-graphic half-wave potentials for this process are given in Table 5.6. One-electron addition in aprotic media to phenyl methyl sulphone [66] and to diphenyl sulphone [67] leads in both cases to a delocalised radical-anion in which the sulphone grorqj can be described as contributing a vacant symmetrical dx-orbital to the conjugated system. Phenyl methyl sulphone radical-anion is prepared and characterised in liq-... 

Electrochemical reduction of aryl sulphones in methanol leads to cleavage of one carbon-sulphur bond in a two-electron process. Alkyl aryl sulphones with an electron donating substituent in the aryl ring give the arenesulphinic acid and an alkane [68, 69]. Methyl phenyl sulphone and alkyl aryl sulphones with an electron withdrawing substituent in the aryl ring are cleaved to the substituted arene and the alkylsulphinic acid [70], see Scheme 5.2. In addition, a bulky orfAo-substituent such as tert.-butyl favours cleavage to the arene and alkanesulphinic acid [71]. 

Benzene mono- di- and tri-sulphonic acids are stable towards electrochemical reduction. More highly sulphonated compounds undergo a two-electron cleavage of a carbon-sulphur bond with elimination of sulphurous acid [82]. Thus benzene-hexa-sulphonic acid 14, in aqueous solution at pH 8, shows three two-electron po-larographic waves with half-wave potentials -1.00, -1.45 and 1.65 V vs. see, due to the sequential loss of substituents. The half-wave potentials are independent of pH. 

Some benzenesulphonic acids with an electron withdrawing carboxyl group in the ring will also undergo carbon-sulphur bond cleavage [83]. 

One synthetic route to methyl ketones involves the cleavage of carbon-sulphur bonds in either sulphoxides or sulphones using aluminium amalgam as the electron... 

The sulphonyl chloride 23 is proposed as a protecting group for the Gabriel synthesis of secondary amines from primary amines. At the deprotecting stage, carbon-sulphur bond cleavage is achieved using zinc and acid as the electron source [109]. 

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