Lewis acidic antimony compounds

FIA is defined as the amount of energy released upon binding a fluoride ion in the gas phase.

[7] Lewis acidic antimony complexes with a variety of oxidation states and coordination numbers are known.

Although stibanes have a lone pair electrons, their antibonding orbitals with electron-withdrawing substituents renders them Lewis acidic.

However, as shown in the electrostatic potential map of Sb(C6F5)3, only one site is accessible to Lewis bases due to the asymmetric arrangement of the three aryl rings.

[9] Sb2(o-catecholate)2(μ-O) (2) had been predicted that a Lewis base would bind to two antimony centers in a bridging manner.

First, rotational freedom around the bridge oxygen disrupts the Lewis base binding between two antimony centers.

Second, intramolecular interactions between oxygen at catecholate and antimony competes with external Lewis base binding.

Short Sb–C bond distances of 2.095(2) Å and a tetrahedral space group in the crystal proves that isolated [Sb(C6F5)4]+ is completely free of external electron donors.

In detail, the LUMO can be assigned to as localized orbital on stiborafluorene moiety with larger nodes at the 9-position (Sb).

This cooperativity is supported by the Sb-(μ-F)-Sb moiety in solid state structure of F− binding bisantimony compound 9.

[19] Strongly acidic antimony compounds catalyze organic transformations such as the transfer hydrogenation and the Ritter reaction.

Owing to the strong σ-accepting ability of dicationic Sb ligand, a gold-antimony complex can catalyze styrene polymerization and hydroamination after being activated by AgNTf2.

NBO of Sb(C 6 F 5 ) 3 -P(O)Ph 3 adduct describing donor–acceptor interaction between lp(O) and σ*(Sb-C 6 F 5 ). [ 7 ]
Electrostatic potential map of (right) Sb(C 6 F 5 ) 3 and (left) Sb(C 6 F 5 ) 3 ( o -O 2 C 6 Cl 4 ). High electrostatic potential (blue region in the map) means partial positive charge. [ 7 ]
FIA indicates fluoride ion affinity. δ indicates the 31 P NMR shift of OPEt 3 adducts ( Gutmann–Beckett method ). The chemical shift of OPEt 3 is 51.0 ppm (in CH 2 Cl 2 ), 51.2 ppm (in CHCl 3 ), and 47.6 ppm (in DFB (difluorobenzene)).
IBO of Sb-(η 5 -Cp*) bondings in [Sb(tol)(Cp*)] 2+ ( 1 ). [ 9 ]
Contour plots of the Laplacian of the electron density of (left) ( o -C 6 H 4 (PPh 2 )[Sb(C 6 F 5 ) 2 (O 2 C 6 Cl 4 )] and (right) o -C 6 H 4 (PPh 2 )[(SbPh 2 (O 2 C 6 Cl 4 )]. Blue dots are the bcp and brown lines are the bond paths. [ 17 ]
Electrostatic potential map of a bisantimony(V) complex ( 9 ). Partial positive charges at antimony centers facing each other. [ 16 ]
Fluoride binding turns on emission. [ 14 ]
Examples of catalytic activity of Lewis acidic antimony compounds in (top) hydrogenation of quinoline using Hantzsch ester and (bottom) Ritter reaction. [ 7 ]
Examples of Z-type ligand antimony compounds. Strong electron donation from gold to antimony decreases electron density on the Au center and the Au–Sb complex catalyzes (top) hydroamination and (bottom) polymerization of olefin. [ 21 ]