Dibismuthines

Unlike many distibines and dibismuthines, diarsines do not appear to exhibit thermochromic effects (105). 

The secondary bismuthides discussed herein are useful for preparing several types of organobismuth compounds, eg, tertiary bismuthines and dibismuthines. 

Dibismuthines. Only about a do2en tetraalkyl- and tetraaryldibismuthines are known (135). These compounds can be obtained by the reaction of a sodium dialkyl- or diarylbismuthide and a 1,2-dihaloethane (66—69) ... 

Dibismuthines tend to be thermally unstable. Thus tetramethyldibismuthine [82783-70-8] C4H22Bi2, decomposes at 25°C to yield trimethylbismuthine and metallic bismuth (66) ... 

Tetraethyldibismuthine [81956-27-6], CgH2QBi2, undergoes a similar reaction at 40°C (67). At 0°C this dibismuthine as well as tetra-4-tolyldibismuthine [114245-28-2], C2gH2gBi2, (105) decompose to form dark polymeric soHds ... 

Dibismuthines are very sensitive to oxidation. Thus tetramethyldibismuthine fumes ia air, and tetraphenyldibismuthine ia toluene solution rapidly absorbs oxygen. Under controlled conditions, dibismuthines react with chalcogens resulting ia cleavage of the bismuth—bismuth bond and iasertion of a chalcogen atom (105,138,140—142) ... 

Syntheses and Solid State Structures of Group 13-Distibine and -Dibismuthine Bisadducts... 

Scheme 5. Synthesis of tetraalkyldistibine and-dibismuthine bisadducts [R3M2][E2R4]...

The so-prepared compounds are stable in the pure form, whereas they easily undergo consecutive reactions in solution under cleavage of the E—E bond (see Sect. 3.1). Four tetraalkyldistibine (32-35) and two -dibismuthine bisadducts (36 and 37) have been structurally characterized (Table 8). 

Structures 5 and 6 display the solid state structures of two representative distibine and dibismuthine adducts. The ligands bound to the central Sb and Bi atoms adopt a staggered conformation in relation to one another, with the bulky M(t-Bu)3 groups arranged in a trans-position. This is likely due to repulsive steric interactions. The central Sb—Sb [281.1(1) 32 283.9(1) pm 35] and Bi—Bi bond distances [298.3(1) 36 and 298.4(1) pm 37] are almost unchanged compared to the uncomplexed distibines and dibismuthines, as can be seen... 

Reactions of tetraalkyldistibines and -dibismuthines with trialkylalanes and -gallanes yield bisadducts of the type [R3M]2[E2R4]. These compounds are stable in the solid state, while they easily undergo consecutive reactions in solution. Completely alkyl-substituted heterocycles [R2MER x are formed under cleavage of the Sb—Sb bond, as was demonstrated for two Ga—Sb heterocycles. 

An intermolecular analog of this inter-ring pnictogen bonding is found in the thermochromic distibines and dibismuthines.45 For example, 2,2, 5,5 -tetramethylbistibole (87) crystallizes so that the Sb atoms are aligned in chains with close contacts between the Sb atoms of adjacent molecules. It seems more than coincidental that the intermolecular contacts in 87 occur at virtually the same distance as the intramolecular contacts in 29. See Figure 3. 

An alternative preparative route to R2QER acid esters (Q = P, As, Sb, Bi E = S, Se, Te) of interest due to its generally applicability to all the heavier group 15 and 16 elements, is the dismutation reaction between diorganodichalco-genides and tetraorgano-diphosphines, -diarsines, -distibines or -dibismuthines (Equation 17).2... 

In sharp contrast to the intensely studied reactions of dipenteles with transition metal compounds, reactions with group 13 metal compounds are almost unknown. Only two diphosphine-borane bisadducts of Type C ([H3B]2[Me4P2], [H2(Br)B]2[Me4P2]) have been synthesized and structurally characterized65 but no diarsine, distibine or dibismuthine adducts. We, therefore, became interested in the synthesis of such compounds, focusing... 

TABLE XV Bond Lengths [pm] and Angles [°] of Dibismuthine Adducts and Pure Dibismuthines ... 

Dibismuth ditellurium selenide, 4 25 Dibismuth ditellurium sulfide, 4 25 Dibismuthenes, 4 30-31 Dibismuthines, 4 29-30 Diblock copolymers, 7 646 23 367 Diborane, 13 619, 632, 634 Diborane(6), 4 141, 142, 184-185 bonding, 4 181 economic aspects, 4 228 physical properties of, 4 184t Diboron dioxide, 4 242t Diboron trioxide, 4 242t, 246 Dibromamine, 13 103 Dibromamine-B, 13 109 N, N-Dibromamines, 13 105 Dibromamine-T, 13 109 Dibromanine, 4 319 Dibromine oxide, 4 332... 

Figure 5 Structures of GaBu 3 adducts of a distibine 104 and a dibismuthine 106.

Many distibines and dibismuthines have lighter colors in solutions or melts than in the solid state. Crystals of these thermochromic distibines or dibismuthines consist of linear chains of the dimetal compounds with short intermolecular metal-metal contacts. Delocalization of electrons along the chains is possibly responsible for the bathochromic shift between fluid and solid phases. Usually, the /raor-conformation is adopted by the tetraorganodimetal compounds in the solid state. (CF3)4As2 shows the /ra r-conformation also in the gas phase. Photoelectrospectroscopic measurements on Me4Sb2 revealed the presence of gauche- (12%) and trans- (88%) conformed in the gas phase.52... 

---