S-halogen bonds

The broken bonds (boldface = dissociated atom) BDEs (boldface = recommended data reference in parentheses) Methods (reference in parentheses)  

Sulfur hexafluoride anion F-SFg (Also see Chapter 27) 42.5 2.9 178 12 CID 2003LOB/CHE 

Methyldipheny lphosphino-1 -thione S=PMePh2 91 381 Calorimetry 1998CAP/W1X 

---

Because sulfur is in the second row of the periodic table it forms many types of compounds not vailable to oxygen. Compounds with S-S and S-halogen bonds arc quite stable and can be isolated, unlike the unstable and often explosive O-halogen and 0-0 compounds. Sulfur has d orbitals so it can have oxidation states of 2, 4, or 6 and coordination numbers from 0 to 7. Here is a selection of compounds. 

There have been a few reports dealing with 1,2-thiazines bearing a halogen substituent at the 1 position <9lMi 606-01, 92CB581, 93CB1529). The S-halogen bond in a 1,2-thiazine is hydrolytically labile. 

C-H bonds aliphatic, 129 aromatic, 129, 131 di-sulfonyl, 130 C-S bonds, 442 N-H bonds, 374, 376 N-N bonds, 440 N-S bonds, 421 O-C bonds, 364 S-halogen bonds, 446 S-O bonds, 363-364 Sulfonic acids RSO3H O-H bonds, 261 O-S bonds, 363 Sulfoxides RSOR ... 

C-H bonds, 129 S-C bonds, 442 S-H bonds, 428 S-halogen bonds, 446, 447, 448 S-O bonds, 364 Sulfur clusters/complexes, 917 anions, 1331-1341 cations, 1325-1331 neutrals, 1323-1324... 

The E2 mechanism is a concerted process m which the carbon-hydrogen and carbon-halogen bonds both break m the same elementary step What if these bonds break m separate steps s... 

The carbon-halogen bonds of aryl halides are both shorter and stronger than the carbon-halogen bonds of alkyl halides In this respect as well as m their chemical behavior they resemble vinyl halides more than alkyl halides A hybridization effect seems to be responsible because as the data m Table 23 1 indicate similar patterns are seen for both carbon-hydrogen bonds and carbon-halogen bonds An increase m s... 

The strength of their carbon-halogen bonds causes aryl halides to react very slowly in reactions in which carbon-halogen bond cleavage is rate determining as m nude ophilic substitution for example Later m this chapter we will see examples of such reactions that do take place at reasonable rates but proceed by mechanisms distinctly dif ferent from the classical S l and 8 2 pathways... 

It will be convenient to describe first the binary. sulfur nitrides SjN,. and then the related cationic and anionic species, S,Nv. The sulfur imides and other cyclic S-N compounds will then be discus.sed and this will be followed by sections on S-N-halogen and S-N-O compounds. Several compounds which feature i.solated S<—N, S-N, S = N and S=N bonds have already been mentioned in the. section on SF4 e.g. F4S NC,H, F5S-NF2. F2S = NCF3, and FiS=N (p. 687). Flowever. many SN compounds do not lend themselves to simple bond diagrams, - and formal oxidation states are often unhelpful or even misleading. 

R.A. More O Ferrall, in The Chemistry of the Carbon-Halogen Bond, S. Patai, Ed. Wiley-Interscience, Part 2, Chapter 9,609-675, (1973). 

Bonds become weaker as we move down the periodic table. Compare C—O and C—S or the four carbon-halogen bonds. This is a consequence of the first generalization, since bond distances must increa.se as we go down the periodic table because the number of inner electrons increases. 

The reactivity shown in Scheme 3 results from the low bond dissociation energy (BDE) of the P-H bond [11] k=l.2 10 M s for the H-transfer from R02P(0)H to a primary C-centered radical) and the fast halogen-atom transfer from a C-halogen bond to a phosphonyl radical [9,12] (fc=4 10 M s for f-Bu-Br and k=83 10 M s for Cl3C-Br). Piettre et al. [13] pointed out that these chain reactions were even more efficient when dialkylthiophosphites and the corresponding dialkylphosphinothioyl radicals were involved. 

We shall show both from experimental evidence about gas-phase complexes and, to a lesser extent, from the results of electronic structure calculations that a parallel definition of the intermolecular halogen bond is appropriate The halogen bond is an attractive interaction between a halogen atom X and an atom or a group of atoms in different molecule(s), when there is evidence of bond formation. ... 

---