only evidence for a species of composition BS2 has so far come from mass spectrometry and thermal analysi~[~.'~.During our studies on binary and ternary boron sulf i d e~~' .~' we have now obtained a new boron disulfide of molecular formula B8Sib by two different routes. Rapid heating of a B2S,/S mixture (molar ratio 1 : 1.5) to ca. 300 "C at ca. bar in a sealed quartz glass which has been graphitized or protected by a boron nitride coating, in a twozone furnace with a sharp temperature profile (300/1OO "C) leads to deposition of a crystalline product within a narrow region in the colder zone of the reaction tube. The colorless needles are up to 2 mm long, extremely sensitive to hydrolysis, and decompose above 115 " C in a sealed vessel under normal pressure (Nz).The compound [elemental analysis B : S = 1 : 2.01(2)] forms monoclinic crystals (space-group P2,/c), a = 12.158(3), V = 1040.4 A3, pLalL=1.913, pexp=1.90(2) g cm-'. As shown by the complete X-ray structure analysis (1349 diffractometer data, R = 5.5%), solid boron disulfide is made up of discrete exactly planar BsSi6 molecules whose porphine type skeleton contains four 1,2,4,3,5-trithiadiborolane rings linked by sulfur bridges. Figure 1 shows the molecular structure with distances and angles averaged over chemically equivalent bonding parameters. Within the limits of experimental accuracy the molecule has Dlh symmetry (exact symmetry in the crystal is C,). The average B-S bond length (1.811 A)b=4.089 (1), ~=21.961(4) A, @= 107.65(3)", Z = 16 BS2, Fig. I. BXSlh molecule with bond lengths [A] and bond angles (u=0.003 A and 0.1 ', respectively).corresponds approximately to that in B& (1.808 il") and once again, in agreement with the planarity of the molecule, is indicative of strong ( p -p )~ interactions. The significant difference between the two types of B-S bond lengths in the five-membered rings (Fig. 1) provides the first confirmation of the differing T bond orders estimated by CNDO calculations on trithiadiborolane~l~~. The similarity of the structural characteristics to those of dimethyl-and dichloro-1,2,4,3,5trithiadiborolane in the gas phase161 demonstrates the remarkable, substituent-independent constancy of the bonding in the stable five-membered ring.A second synthetic route leading to BsSlb was found in the thioIysis of the halogenated trithiadiborolanes described by Schmidt and SiebertI7]. Thus reaction of 3,5-dibromo-1,2,4,3,5-trithiadiborolane with trithiocarbonic acid as an HZS generatorl'l in dilute CS, solution according to affords the porphine-like B8Si6 in ca. 6% yield along with polymeric (B2S& chains made up of S-linked B2S3 five-membered rings['l. Cyclization can be promoted in the reaction mixture by addition of d X or d9-transition metal compounds; the geometry of the BXSi6 molecule permits formation of interesting transition metal complexes having square-planar coordination of the tetradentate ligand (transannular S . . . S distance in B,S,,,: 4.667 A).In addition to other fragmentation products, the mass spectrum shows B2S; as f...

Several transamination reactions of B2(NMe2)4 (1a) with secondary amines have led to mixed tetraaminodiborane(4) compounds B2(NMe2)4 ‐ n(NR2)n (2–4), and B2(NC5H10)4 (1d) has been characterized by an X‐ray structure analysis which reveals the presence of a rather long B–B bond (1.75 Å). However, tetraaminodiboranes(4) of type R2N(Me2N)B‐B(NMe2)NR2 are more readily accessible from LiNR2 and B2(NMe2)2Cl2. Similarly, amination of B2(NMe2)2Cl2 with N,N'‐dimethylethylenediamine (7) yields B‐[bis(dimethyl‐amino)boryl]‐N,N'‐dimethyl‐1,3,2‐diazaborolidine (8), while reactions with Li(Me)N–CH2–CH2–N(Me)Li (9) lead also to 2,3‐bis(dimethylamino)‐1,4‐dimethyl‐1,4,2,3‐diazadiborinane (10) as the kinetically controlled product. This is further substantiated by the reaction of the B2(NMe2)2Br2 with 9 which gives exclusively the corresponding 1,4,2,3‐diazadiborinane 11. Diborane(4) dihalides B2(NMe2)2X2 (X = Cl, Br) react only in a 1:1 ratio with tmp‐B=N‐CMe3 (13) leading to 14a, b. However, both a 1:1 and a 1:2 methoxyboration of 13 has been observed with B2(OMe)4 with formation of 15 and 16.

A Convenient Synthesis of Diboron TetrabromideTetramethoxydiborane(4) and boron tribromide react at ambient temperature with formation of diboron tetrabromide (yield 50%). methyl bromide and diboron trioxide.This makes B2Br4 readily accessible for further studies.Dibortetrahalogenide kdnnen eine Schlusselfunktion in der Organobor-Chemie ubernehmen, wie ihre stereospezifische cis-Addition an Acetylene und Olefine zu 1 ,2-Diborylderivaten2), die Ringoffnung von Cyclopropanen zu 1,3-Diborylpropanen?) oder die Synthese von Thiadiborolenen und anderer Heterocyclen4) belegen. Gleiches gilt fur Subverbindungen des Bors, etwa den Zugang zu Tetrab~rtetrahalogeniden~) und weiteren polyedrischen Bor(I)-Species6), deren Chemie noch wenig untersucht ist. Voraussetzung dafur ist allerdings eine einfache Synthese von Dibortetrahalogeniden.1925 entdeckten Srock und Mitarbb.') das an Luft selbstentzundliche BzCb, das in geringen Mengen bei der elektrischen Entladung zwischen Zinkelektroden durch fliissiges Bortrichlorid anfiel. Die Einfuhrung von Hg-Elektroden und die Entladung durch gasformiges Bortrichlorid brachten eine wesentliche Ausbeutesteigerung und ermoglichten die Entwicklung eines kontinuierlichen Verfahrens*). Aber erst die Reaktion von Kupferatomen mi1 BC1, unter Anwendung der Cokondensationstechnik fuhrte zur weiteren Ausbeutesteigerung und bedeutete zugleich einen wesentlichen methodischen Fort~chritt~). Jedoch erfordern alle diese Verfahren und andere, hier nicht genannte, einen relativ hohen apparativen Aufwand.Versuche, Dibortetrahalogenide iiber metathetische Reaktionen aus einfachen Ausgangsverbindungen zu gewinnen, liefern z. T. gute Ausbeuten, setzten sich aber als praparative Verfahren nicht durch. Dies gilt etwa fur die Darstellung von Diborterrafluorid aus (BO), oder Bz(OR)., mit Schwefeltetrafluorid'O) oder die Umsetzung von (BO), mit Bortrichlorid") (Ausbeuten bis 50% a n B2F4 oder 13% an B2Cb). RO, ,OR Br, / B r RO' OR Br' B r B-B, + 4 BBr, -B-B, 4 ROBBr, 1 2 3 ROBBr, -B203 + 3 R B r + BBr, R = CH, ( 2 ) Wir fanden nun, daL3 das bei Raumtemperatur flussige Dibortetrabromid (2), das bisher durch Umhalogenierung von B2C4 mit BBr3 dargestellt wurde, durch Einwirkung von Bortribromid auf Chem.

Boron compounds of type (alkyl)2B—B(alkyl)2, which have been sought for more than 40 years, have been independently synthesized by two research teams almost simultaneously and by the same pathway. Stepwise replacement of the methoxy groups of (1) by alkyl groups gave the tetraalkyldiboranes (4), (5) (RMe), and (6) (R=tBuCh2). Tetra‐tert‐butyldiborane could not be prepared, while the silylborane (7), RSiMe3, could.

Einen B6‐Ring in Sesselkonformation enthält die Titelverbindung (1), die aus Destillationsrückständen bei der Enthalogenierung von [(CH3)2N]2BCl kristallisiert. (1) ist der erste Homocyclus des Bors und zugleich die erste Bor(I)‐Verbindung ohne Elektronenmangel.