B—S Bonds

H2S reacts with BXg (X = Cl, Br, or I) to give the new substitution products BXgSH, BX(SH)2, and B(SH)a(+ HX). These are unstable and cyclize to (BSSH)a or (BSX)a- In the case of BBrg the ratios of reactants, and the temperatures, can be controlled to yield any one of the 3 initial products in high yield, so that either (BSSH)a or (BSBr)a may be obtained rapidly and selectively. (BSCl)a can best be prepared by dissolving (BSSH)a in liquid BCI3, and (BSI)a by the action of H2S on solid Bla. 

A vibrational assignment has been proposed for the molecules BX2SH (where X = Cl, Br, or I), and a normal-co-ordinate analysis was carried out, using force-constant data derived from BX2CI systems.  

Stoicheiometric quantities of KSR -I- BaH give (in THF solution) the thermally stable salts K+[RS(BHa)2l . Treatment of these with anhydrous acids, BgHg, or I2 gives //-RS-BaHg in moderate yield, thus  

BS2 molecules (formed by heating ZnS-B mixtures) may be trapped in neon matrices at 4 Transitions due to theA Il - X Ug and systems may be observed and these, together with matrix- and gas-phase i.r. data, lead to the following molecular constants for BS2. 24 012, 

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The first examples of sulfur-containing iminoboranes have been obtained by the 1,2-addition of the B—S bond of (alkylthio)diorganoboranes to acetonitrile 3S>. 

Eq. (40) proceeds at extremely slow rate leading to the assumption that the reaction involves the B-S bond rather than the B-Cl bond. This event has been substantiated by UB n.m.r. spectroscopy of a dimeric monothioalkylborane (c.f. Sect. VIII.2) 33). 

A DFT study reveals that the thioboration reaction proceeds via a metathesis-like pathway between Pd-G and S-B bonds forming Pd-S and G-B bonds, rather than an oxidative addition of the B-S bond to the Pd(0) complex (Scheme 74).284... 

In comparison with the hydroboration and diborafion reactions, thioboration reactions are relatively limited. In 1993, Suzuki and co-workers reported the Pd(0)-catalyzed addition of 9-(alkylthio)-9-BBN (BBN = borabicyclo [3.3.1] nonane) derivatives to terminal alkynes to produce (alkylthio)boranes, which are known as versatile reagents to introduce alkylthio groups into organic molecules [21], Experimental results indicate that the thioboration reactions, specific to terminal alkynes, are preferentially catalyzed by Pd(0) complexes, e.g. Pd(PPh3)4, producing (thioboryl)alkene products, in which the Z-isomers are dominant. A mechanism proposed by Suzuki and co-workers for the reactions involves an oxidative addition of the B-S bond to the Pd(0) complex, the insertion of an alkyne into the Pd-B or Pd-S bond, and the reductive elimination of the (thioboryl)alkene product. 

In 1998, Morokuma and co-workers carried out density functional calculations on the following model reaction, Pd(PH3)2 + C2H2 + (OCH2)2B-SH Pd(PH3)2 + (OCH2)2B-CH=CH-SH, to study the detailed reaction mechanism [24], The theoretical studies suggest that the reaction mechanism involves a metathesis-like process, instead of an oxidative addition, in breaking the B-S bond of the substrate. The reason for not having an... 

The aminoboranes containing NR2 groups do not form neutral complexes because the B—N bond possesses a higher n order than B—O and B—S bonds. In contrast, the pyrazol-l-yl and pyrrol-l-yl boranes with sp2 nitrogens bonded to the boron do give stable amine complexes... 

These reactions usually proceed more slowly than the reactions of the corresponding alcohols or phenols with boron halides. In some cases, where direct reaction is too slow, the lead or mercury derivatives of thiols are used. Attempts to use the reactions of thiols with diboron trisulfide to prepare trialkylthioboranes have usually been unsuccessful, although analogous reactions with oxygen compounds are commonly used to prepare trialkoxyboranes. Formation of B-S bonds... 

The slightly yellow compounds 10a,b are very air- and moisture-sensitive due to its B-Cl and B-S bonds. 10b reacts with a excess of HsB thf to yield the nufo-thiacarborane lib and traces of the 2,3-dihydro-l,2,5-thiadiborole 12b, identified by MS. 

There have been no measurements reported for HBO which provide direct experimental information on its structure. However, the millimeter-wave spectra of the related species HBS (14) have been observed. These results show that this molecule is linear and has a B S bond length which is 0.01 A less than that for BS (1). We assume a similar decrease in r (B 0) for the HBO-BO pair,... 

The Pd(0)-catalyzed addition of the B-S bond to alkynes (thioboration) regio- and stereoselectively produces (Z)-2-(organothio)-l-alkenylboron reagents (Scheme 2-25) [63]. Tlie addition of (tetraalkoxy)diboron to alkynes to give cw-bis(boryl)alkenes (diboration) is catalyzed by a platinum(O) catalyst [34]. 

In (a) and (c) there would be no great difference between the characters of the A-S and B—S bonds in a particular compound, while in (b) the B and S atoms form a covalent complex which may be finite or infinite in one, two, or three dimensions. By analogy with oxides we should describe (a) and (c) as complex sulphides and (b) as thio-salts. Compounds of type (c) are not found in oxy-compounds, and moreover the criterion for isomorphous replacement is different from that applicable to complex oxides because of the more ionic character of the bonding in the latter. In ionic compounds the possibility of isomorphous replacement depends largely on ionic radius, and the chemical properties of a particular ion are of minor importance. So we find the following ions replacing one another in oxide structures Fe, Mg , Mn , Zn, in positions of octahedral coordination, while Na" " more often replaces Ca (which has approximately the same size) than K , to which it is more closely related chemically. In sulphides, on the other hand, the criterion is the formation of the same number of directed bonds, and we find atoms such as Cu, Fe, Mo, Sn, Ag, and Hg replacing Zn in zinc-blende and closely related structures. 

Photoelectron spectra have been reported for a series of methylthio- and methoxy-boranes Me3 BXB(X = SMe or OMe).247 These were compared and assigned using modified CNDO/2 calculations. Substituent effects and chemical shifts (8 B) were consistent with significant tt-contributions to the B—S bond. 

Compounds of Group 13. Proton NMR spectra and ab initio calculations were used to probe conformational equilibria of 2,5-substituted 1,3,2-dioxaborinane molecules.994 A dynamic NMR study of [2,6-bis(ethyl-thiomethyl)phenyl]diethylborane shows rapid dissociation of the intramolecular B S bond.995... 

Methods to produce B—C, B—P, B—N and B—S bonds in boron clusters, including metaUacarboranes 13CSR3318. 

The formation of an insertion product of diphenylketene into the B-S bond in trimethyl thioborate is evidenced by the isolation of Ph2CHCOSMe after hydrolysis Insertion of ketene into C-H, C-0 and C-Cl bonds is also encountered. For example, reaction of triphenylmethyl chloride with ketene in a nonpolar solvent, in the presence of aluminum chloride, affords the insertion product 336. In nitrobenzene, the reaction proceeds without the added catalyst . 

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