Se-X bonds

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

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Although the path (a) has been verified by a stoichiometric reaction [23], the details of exact reaction mechanism remain unsettled. Triggered by this publication [and the Pd-catalyzed doublethiolation of alkynes described in Eq. (7.7) in Section 7-3], a number of transition metal-catalyzed additions of S-X or Se-X bonds to C-C unsaturated organic compounds started to be published. In 1994, BackvaU et al. applied the Pd(OAc)2-catalyzed hydrothiolation to conjugated enynes and obtained 17,... 

This reaction typifies the two possibilities of reaction routes for M-catalyzed addition of an S-X (or Se-X) bond to alkyne (a) oxidative addition of the S-X bond to M(0) to form 94, (b) insertion of alkyne into either the M-S or M-X bond to provide 95 or 96 (c) C-X or C-S bond-forming reductive elimination to give 97 (Scheme 7-21). Comparable reaction sequences are also discussed when the Chalk-Harrod mechanism is compared with the modified Chalk-Harrod mechanism in hydrosily-lations [1,3]. The palladium-catalyzed thioboratiori, that is, addition of an S-B bond to an alkyne was reported by Miyaura and Suzuki et al. to furnish the cis-adducts 98 with the sulfur bound to the internal carbon and the boron center to the terminal carbon (Eq. 7.61) [62]. 

T-shaped Y- E-X 3c-4e interactions occur by the attack of Y at E of polar E-X bonds. Such interactions are usually highly unsymmetric.17,43 However, the N-E-X bonds are close to symmetric in some cases. Singh and co-workers reported such interactions. Table 2 shows the bond distances and the deferences from the sum of covalent radii in 19 (E = Se), together with the angles.44 The N-E-X (E = Se) bonds are rather typical 3c-4e for X of halogens, especially for X = I. The Y-E- -X character shown in 19A contributes to the interactions in substantial amount, although the distances are affected by the nature of the Se-X bonds. Similar interactions are reported.45 48... 

The Se-X bonds (X=C1 and Br) in 48 are examined by stabilizing through the coordination of X, in which the negative charge brought by X- is neutralized by the ammonium group.69... 

Fig. 1. Schematic view of Se chemical shift ranges in compounds containing C-Se-X bonds.

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