The [221] cycloaddition of two alkynes and carbon monoxide in the presence of pentacarbonyliron represents a useful method for the construction of five-membered ring systems. [1, 2] Applications of the resulting tricarbonyl(h 4 -cyclopentadienone)iron complexes to organic synthesis are feasible by demetalation to the free cyclopentadienones. This transformation was achieved by oxidation with trimethylamine Noxide. [1,3] Recently we reported a novel method for the demetalation of tricarbonyl(diene)iron complexes by a photolytically induced exchange of the carbonyl ligands by acetonitrile. [4] Herein we describe an alternative procedure for the ligand exchange at tricarbonyl(h 4 -cyclopentadienone)iron complexes and the subsequent demetalation in the air.Tricarbonyl(h 4 -cyclopentadienone)iron complexes undergo a transformation similar to the Hieber reaction. [5] Thus, reaction of complex 1 a with aqueous NaOH in THF leads to an equilibrium of the corresponding hydrido complexes 2 a and 4 a in a ratio of about 13:1 (Scheme 1). Tricarbonyl(cyclohexa-1,3-diene)iron complexes are inert under these conditions. Addition of H 3 PO 4 affords 2 a in 94 % yield, while reaction with NaH shifts the equilibrium towards the salt 4 a Scheme 1. a) 1m NaOH/THF (1/2); b) C 5 H 11 I; c) H 3 PO 4 ; d) air, daylight, Et 2 O/THF, Na 2 S 2 O 3 , Celite, 3 h; e) NaH, Et 2 O/THF.(82 % yield). Reaction of the hydrido complex 2 a with 1-iodopentane provides the iodo complex 3 a in 98 % yield. A related transformation is reported for the hydrido complex [CpFe(CO) 2 H]. [6] The addition of 1-iodopentane after the reaction of 1 a with NaOH affords an equilibrium of the iodo complexes 3 a and 5 a that is shifted again by addition of H 3 PO 4 or NaH, respectively. Preparation of the iodo complex 3 a without isolation of the intermediate hydrido complex 2 a increases the yield (98 % based on complex 1 a).The 13 C NMR and the IR data of the hydrido complex 2 a and the iodo complex 3 a suggest an h 5 -coordinated hydroxycyclopentadienyl ligand for both compounds. [7] A characteristic structural feature of the hydrido complex 2 a is the unsymmetrical arrangement of the coligands, which is apparent from two CO signals in the 13 C NMR spectrum. This assignment was confirmed by an X-ray structure determination of complex 2 a (Figure 1), [8] which shows an h 5 -coordinated hydroxycyclopentadienyl ligand and a C1ÀO1 bond length of 1.366 . [9] A loss of C S symmetry was also found for the hydrido complex 4 a from the 13 C NMR spectrum, which exhibits the two signals for the carbonyl ligands and a peak at d 170.13 for C1. [7] Figure 1. Molecular structure of 2 a in the crystal. Selected bond lengths []: FeÀC1 2.

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COMMUNICATIONS lenylmetal species without the involvement of chirality transfer or destruction of the allenyl enantiomer. This should become a powerful strategy for the asymmetric synthesis of allenic compounds from racemic allenyl-/propargylmetal species. Experimental SectionTo a solution of the phosphate (0.5 mmol). [Pd(PPh,),] (29 mg. 0.025 mmol. 5 mol%), and the chiral alcohol (0.55 mmol) in anhydrous THF (2.5 mL) was added a 0.1 M solution of samarium(l1) iodide in THF (10 mL, 1.0 mmol) at room temperature under an argon atmosphere. After stirring for 10 min. the reaction mixture was quenched with saturated NH,CI. Standard workup followed by silica gel chromatography afforded the allenic ester 2.

3 SiCl. According to X-ray structure analyses, the ditrielanes contain two planar groups R 2 EE which are orthogonal to each other (R = R*; angle REER ca. 90°) or nearly orthogonal (R = RЈ; angle REER ca. 80°). All compounds are deeply colored. The λ max value of the visible absorption shifts with increasing atomic number of E and with the increasing angle between the R 2 EE planes to longer wavelengths (ruby R− besides the mentioned ditrielanes − are presented.In fact, except for the compounds dealt with in this publication, only three other examples of silyl-ditrielanes, namely [(Me 3 Si) 3 Si] 4 E 2 with E ϭ Ga, [9] In, [10] Tl [11] have been published to date. On the other hand, some organyland aminyl-ditrielanes R 4 E 2 are known with R ϭ

The novel neutral gallium cluster compounds [Ga18R*8] (1) and [Ga22R*8] (2) are obtained by warming up a metastable solution of gallium(I) bromide in THF/C6H5CH3 after addition of equimolar amounts of supersilyl sodium NaR* from -78 degrees C to room temperature (R* = SitBu3 = supersilyl). From X-ray structure analyses, the observed arrangements of the 18 and 22 Ga atoms in 1 and 2, respectively, are comparable with an 18 atom section of the beta-Ga modification, or show at least some kind of relationship to a 22 atom section of the Ga-III modification. This allows a description of both the clusters as metalloid. The topology of the atoms in 2 is also well explained by the Wade-Mingos rules as an eightfold capped closo-Ga14 cluster, whereby the Ga atoms of Ga14 occupy the center and the corners of a cuboctahedron with one Ga3 face replaced by a Ga4 face. Some concepts are presented about the formation mechanism, the cluster growth, and the metalloid character of the two Ga cluster compounds.

A disproportionation process of a metastable AlCl solution with a simultaneous ligand exchange-Cl is substituted by N(SiMe(3))(2)-leads to a [Al(69)[N(SiMe(3))(2)](18)](3-) cluster compound that can be regarded as an intermediate on the way to bulk metal formation. The cluster was characterized by an X-ray crystal structural analysis. Regarding its structure and the packing within the crystal, this metalloid cluster with 4 times more Al atoms than ligands is compared to the [Al(77)N(SiMe(3))(2)](20)](2-) cluster that has been published four years ago. Although there is a similar packing density of the Al atoms in both clusters as well as in Al metal, the X-ray structural analysis shows significant differences in topology and distance proportions. The differences between these-at a first glance almost identical-Al clusters demonstrate that results of physical measuring, e.g., of nanostructured surfaces which carry supposedly identical cluster species, have to be interpreted with great caution.

The 1,4-diaryl-1-azabuta-1,3-diene-catalyzed complexation of cyclohexa-1,3-diene with either nonacarbonyldiiron or pentacarbonyliron is reported to provide high yields of the tricarbonyl(η4-cyclohexa-1,3-diene)iron complex. This procedure enables exploitation of both tricarbonyliron fragments of nonacarbonyldiiron for the complexation of dienes for the first time. Using 12.5 mol % of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene and optimized reaction conditions (nonacarbonyldiiron, dimethoxyethane, reflux, 16.5 h, or pentacarbonyliron, dioxane, reflux, 45 h), a quantitative catalytic complexation of cyclohexa-1,3-diene is feasible with both reagents. An extensive study with a broad range of 1,4-diaryl-1-azabuta-1,3-dienes shows that the efficiency of the catalysts strongly depends on the substituents of the two aryl rings. Remarkably high activities are found for those catalysts deriving from condensation of cinnamaldehyde and ortho-methoxy-substituted arylamines. A hexacarbonyldiiron complex of 1-(4-methoxyphenyl)-4-phenyl-1-azabuta-1,3-diene is obtained as a byproduct of the catalytic complexation and is structurally confirmed by X-ray crystallography. A mechanism supported by the experimental findings is proposed.

The reactions of lithiated diphosphanes with transition metal chlorides constitute a new general entry to phosphinophosphinidene complexes: the reaction of Cp2ZrCl2(Cp = C5H5) with tBu2P-P(SiMe3)Li (molar ratio approximately 1:1) yields [mu-(1,2:2-eta-tBu2P=P)[Zr(Cl)Cp2]2]; the reaction of Cp2ZrCl2 with tBu2P-P(SiMe3)Li (molar ratio approximately 1:2) and an excess of PPhMe2 in DME yields the first terminally bonded phosphinophosphinidene complex, [[Zr(PPhMe2)Cp2](eta1-P-PtBu2)].