Distibine diarsine

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

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... 

A large number of nickel(II) complexes with bidentate tertiary phosphines and arsines have been prepared and characterized since the initial reports on o-phenylenebisdimethylarsine and 1,2-bisdiphenylphosphinoethane (Table 64 XVIII, III) by Chatt and Mann,1267 and Wymore and Bailar126 respectively. The most common diphosphines, diarsines, distibines and mixed donor ligands are collected in Table 64 and selected nickel(II) complexes are reported in Table 65. 

No diarsines or diphosphines show thermochromic behavior similar to that of the distibines and dibismuthines. For example, in the series of dipnictogen compounds A, B, and C illustrated in Scheme 6, the thermochromic distibines and dibismuthines correspond to nonthermochromic diarsines and diphosphines. Structural data are available to compare the three diarsines 51 (46), 52 (57), and 53 (5S) with the corresponding distibines 22 (25,26), 36 (37), and 30 (22). Diarsines 52 and 53 crystallize in gauche conformations as opposed to the trans-staggered conformation of the distibines. In neither case are there intermolecular As---As contacts shorter than 4 A. However, the lack of conformational correspondence makes any comparison tenuous. 

Diarsine and distibine ligands. The n bond in ligands of the type RE = ER (E = P, As, Sb) is naturally very reactive but may be protected by a side-on coordination to a transition metal atom. The ligand is -bound with a bond order of approximately 1.5. Therefore, arsenic and antimony coordinate either via the lone-pair of electrons as a... 

The electrochemical reduction of the tetra-substituted diarsines, distibines and disbis-muthines (Ph2MMPh2) has been studied in some detail (cf Section IV.A) whereas studies of the electrochemical oxidation of these compounds are rather sparse. Table 16 presents reported chemically irreversible oxidation potentials for these dimers. 

Distibines and dibismuthines (RjMMRj M = Sb, Bi) react with diarsines (R j AsAsRj) to give equilibrium mixtures of RjMAsR j (equation 93 ... 

Diarsines (R2ASASR2) react easily with diphosphines, distibines and dibismuthines (R jMMR j M = P, Sb, Bi) to give equilibrium mixtures containing R2AsMR j (equation 146 3). 

A number of simple diarsines have been structurally investigated and, although individual molecules are similar to those of the corresponding distibines, the diarsines do not show the extended chain structures and consequent thermochromism often found for the latter. The geometry at the two arsenic atoms is pyramidal, though the angles at arsenic can be asymmetric. The substituents occupy anti (gauche) conformations and in some cases the molecules have imposed Cj symmetry. Parameters for four of the compounds are summarized in Table 2. 

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