A Direct Route to Halogenated Arsaborane Clusters: Crystal Structure of 3,4,5,6‐Tetrachloro‐1,2‐diarsa‐closo‐hexaborane(4)

Abstract

Copyrolysis of BzC14 and AsC1, at 330 "C leads to the forma-the products. At temperatures above 400 "C and higher tion of closo-1,2-As2B4C14 (1) and further products the mass B2C14/AsC13 ratios the formation of AszBloCllo is preferred to spectral evidence of which suggests that they are perchlorithat of smaller arsaboranes. A single-crystal X-ray study of 1 nated arsaboranes AsZB5Cl5, As4B8C16, and AszBloCllo. The confirmed that, consistent with its 14-skeletal electron count, pyrolysis temperature and the molar ratio of the reactants the arsaborane adopts a slightly distorted octahedral strucexert an essential influence on the type and distribution of ture with the arsenic atoms in adjacent cis positions.There are only very few boranes known so far containing two arsenic atoms in the polyhedral framework. They were synthesized by a reaction involving two arsenic insertions into decaborane in the presence of a base to yield clos0-1,2-As~B~~H~~['~~~. Derived thereof are closo-1 ,2-As2BloH812[3] and nido-7,8-As,B9H,['l. However, aside from l l -or 12-vertex arsaboranes there are no examples where arsenic atoms are part of frameworks deriving from smaller boron compounds.In this paper we report on the first direct method of combining arsenic and boron species starting from molecules with 2-center 2-electron bonds to yield several previously unknown small-and medium-sized polyhedral diarsaboranes with chlorine ligands attached to the boron atoms. Results and DiscussionRecently, we have reported on the thermal disproportionation of tetrahalodiboranes(4) BzX4 in the presence of the coreactants PX3, CX4, or C2X4 (X = C1, Br). Stable polyhedral heteroboranes such as clos0-1,2-P,B~C1~[~1(2), ~loso-l,2-P~B~Br~[~I, and C2BnXn+2 (n = 5-8)r6] could be obtained in case the reaction took place in the vapor phase. In order to apply this method to the preparation of heteroboranes aside from phospha-and carbaboranes we studied the copyrolyses of B2Cl4 with various other volatile main group halides.Preliminary attempts to prepare arsaboranes via copyrolysis of B2C14 with AsC13 under corresponding conditions in a single-flask reactor failed. Thereby trichloroarsane is reduced almost quantitatively by tetrachlorodiborane(4) to elemental arsenic and trichloroborane (eq. 1). This redox reaction already occurs in the mixture at room temperature. However, if B2C14 and AsCI3 are condensed into two separate flasks which are connected by a tube, and the reactants are transferred into a preheated oven immediately after sealing, simultaneous vaporization and pyrolysis partly suppress the redox reaction to give new arsaborane clusters. The reaction mixture can be sublimed fractionally. The components were identified by mass spectrometry as As2B4CI4 (I), B9C19, AS&Cl6, and -only in traces -as As2BSCIs. The remaining low-volatile residue contains As2BlDCl10 and elemental arsenic.The formation of A s~B~~C I~~ is favored compared to smaller arsaboranes when the pyrolysis is performed at higher temperatures. By increasing both the molar ratio B2Cld...

Syntheses and Crystal Structures of Brominated Polyhedral Arsa- and Phosphaboranes

“…Since each signal exhibits more than one cross peak, this allows only the 1,2‐conformation. Consistent with the assignments previously made for 1,2‐As 2 B 10 Cl 10 ,[3b] 2 contains boron atoms B4,5,7,11 and B8,10 that are directly linked to all other boron sites. Thus, the signal with a relative intensity of four at 0.6 ppm is assigned to B4,5,7,11 and the signal at δ = –1.6 ppm to B8,10.…”

“…The previous study of the co‐pyrolysis of B 2 Cl 4 with AsCl 3 at 330 °C was found to only produce the polyhedral arsaborane closo ‐1,2‐As 2 B 4 Cl 4 . [3a] However, when the thermolysis reaction was carried out using more severe conditions (450 °C), production of the arsaboranes closo ‐1,2‐As 2 B 10 Cl 10 and conjuncto ‐(As 2 B 4 Cl 3 ) 2 was also observed. [3b]…”

“…[3a] However, when the thermolysis reaction was carried out using more severe conditions (450 °C), production of the arsaboranes closo ‐1,2‐As 2 B 10 Cl 10 and conjuncto ‐(As 2 B 4 Cl 3 ) 2 was also observed. [3b]…”

“…Apart from the carboranes, examples of small‐sized neutral heteroboranes with closo ‐deltahedral structures are rare . To our knowledge, the only examples which have been reported so far include the perhalogenated octahedral group‐15 pnictogenaboranes closo ‐1,2‐ Pn 2 B 4 X 4 ( Pn = P, X = Cl, Br;[2a, b], Pn = As, X = Cl)[3a] and conjuncto ‐( Pn 2 B 4 X 3 ) 2 ( Pn = P, X = Cl, Br;[2c, d], Pn = As, X = Cl)[3b] or the group‐16 chalcogenaborane closo ‐ Se B 5 Cl 5 , respectively . They are prepared by co‐pyrolysis reactions of diboron tetrahalide B 2 X 4 and main‐group halides of elements with an electronegativity at least as high as boron, as described in previous works .…”

“…To our knowledge, the only examples which have been reported so far include the perhalogenated octahedral group‐15 pnictogenaboranes closo ‐1,2‐ Pn 2 B 4 X 4 ( Pn = P, X = Cl, Br;[2a, b], Pn = As, X = Cl)[3a] and conjuncto ‐( Pn 2 B 4 X 3 ) 2 ( Pn = P, X = Cl, Br;[2c, d], Pn = As, X = Cl)[3b] or the group‐16 chalcogenaborane closo ‐ Se B 5 Cl 5 , respectively . They are prepared by co‐pyrolysis reactions of diboron tetrahalide B 2 X 4 and main‐group halides of elements with an electronegativity at least as high as boron, as described in previous works . Obviously, similar to the “electron hyperdeficient” boron subhalides B n X n , which exhibit closo ‐deltahedral structures regardless of their 2 n skeletal electron counts, the halogen ligands exert a strong influence on the stability and the 1,2‐geometry of these small clusters, since neither the corresponding parent hydrogen compounds, nor 1,6‐isomers have been observed.…”