As in ferrocene, the C5H5 ligand of (2) can be replaced with c6H6/AICl3 to give the red-violet triple-decker salt (3) which is sensitive to hydrolysis. Its thermolysis at 14O0C/O.1 torr affords a low yield of the orange-red tetradecker complex ( 4 ) , m.p.: dark coloration above 155"C, decomposition at The IR spectrum of ( 4 ) contains three strong bands at 2033, 1955, and 1944cm-' (in C2C14) showing a significant shift relative to the C O stretching vibrations of the tripledecker [(C0)3Mn.(Z).Mn(C0)3] (2021, 1966, 1956cm-', in C Z C~~) [~~] .The F D mass spectrum exhibits an isotopic pattern for the molecular ion [(C0)3MnL]2Fe+ [L=(l)] (Irel= 100 based on "B4) which is due to the presence of four boron atoms. Apart from M' (12), the following principal fragments are observed at 70eV: {M-3CO}+ (50), {Mn2L2Fe}+ (16), {MnLFe-28)" (8),MnL+ (4),L+ (12),(C2H5)2C2BCH: (100).The structure of the complex ( 4 ) is confirmed by X-ray structure analysisE6]. Both of the independent molecules in the triclinic unit cell have a center of inversion (Fe); they differ in the conformation of the substituents on the planar (kO.01 x 10-I0m) CzB2S rings. Owing to the center of inversion these rings have a mutual transoid arrangement whereas they are staggered (each rotated 90") in the comparable tripledecker sandwich (C2B2S)3C02[71. The bond lengths of the bifacially coordinated ring atoms are lengthened in a typical manner relative to the corresponding distances in unifacially coordinated C2B2S ringsL8] (average values: B-S 1.928(7), B-C 1.544(9), C-C (1.477 (9)). The F c M n distances are 3.408(1) and 3.391(1) 10-"m.We attribute this first example of trans orientation of neighboring CzBzS rings to formation of two #-electron systems in the central (C2B2S)2Fe sandwich. Two equivalent approaches can be adopted in describing the bonding in ( 4 ) . According to the x6/d6-8 ( 4 ) is the first member of the tetradecker family with 42-48 valence electrons; four planes of ligands (two C2B2S rings as #-electron donors and two (CO), groups as 06-electron donors) are held together by three d6 metal ions. According to the closo approach[gb], ( 4 ) can be regarded as a double cluster of two pentagonal bipyramids with a common Fe apex; 2 n + 2 = 16 skeletal electrons are necessary to hold the C2B2SMnFe clusters together; they are provided by C(2 x 3), B(2 x 2), S(4), Mn( l), and Fe( 1).
ProcedureA mixture of ( I ) (0.85g, 5.12mmol), Mn2(CO)lo (1.49g, 3.84mmol) and [C5H5Fe(C0)2]2 (1.35g, 3.84mmol) in 20ml mesitylene is heated under nitrogen for 0.5h at 165°C. After removal of solvent the residue is taken up in hexane and chromatographed on dry silica gel (Woelm 100-200). The first band contains Mn2(CO)lo and some [(C0)3Mn.(l ).Mn(C0)3], the second band green (2) (0.82 g; best yield in analogous reactions 37 %).A mixture of (2) (0.25g, 0.58mmol) and AlC13 (0.25g, 1.87mmol) in benzene (20ml) is stirred under nitrogen for 0.5 h at 90°C. Reddish-violet (3) precipitates out. On heating (3) (0.2 g, 0.33 mol) to 140-16OoC/0.1 torr a yellow-brown sub...
