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Recently, several transition metal boryl compounds were characterized, most of them containing the 1,2-phenylenedioxy group (1,2-02C6H4 = cat) as ligand to boron[". In general, these compounds had been obtained by oxidative addition of (cat)BH to complexes of late transition metals or by salt elimination from (cat)BCl and anionic transition metal complexes. Corresponding reactions with diborane(4) derivatives proceed with cleavage of the boron-boron bond and addition of the boron-containing fragments to the metal center, again yielding boryl complexes [*]. In the case of the reaction of several 1,2-dichlorodiboranes with K[(q5-C5H4Me)Mn(SiMePh2)(CO)2] a different reaction was found. The diboranes reacted with formation of binuclear manganese complexes with a bridging borylene group BR (R = NMe2, tBu), and (RBH2)* was found as boron-containing byproduct [']. In this paper we report on the syntheses and structures of the first transition metal-substituted diborane(4) compounds. Results and Discussionwith B2(NMe2j2C12 yields the transition metal diboranyl complexes la, b according to Eq. (1).These compounds were isolated as brown or dark yellow crystals, which can be handled in air for short periods and can be stored under nitrogen at room temperature. In solution both complexes la, b show two charactcristic I'B-NMR shifts 6 = 39.0 and 69.5 and 6 = 40.3 and 62.7, respectively. The signals at higher field are in the same region as the shift of the starting material at 8 = 37.5r41, the signals of the transition metal-substituted boron atoms, however, exhibit the expected low-field shift of 20-30 ppm. The four methyl groups of both compounds bound to nitrogen show four signals in the 'H-and ',C-NMR spectra, respectively, which is due to a restricted rotation with respect to the B-N bond.The X-ray structure analyses reveal that both molecules adopt a C1 symmetry in the crystal. The boron and nitrogen atoms are trigonal-planar-coordinated and both boryl groups are almost perpendicular to each other (dihedral angle for la, b: 92.4 and 92.3", resp.). The B-N distances are in a range of 137.6(3) and 138(1) pm and the B-B distances amount to 168.3(3) and 169(1) pm, respectively. Hence, the geometry of la, b is comparable to other structurally characterized diborane(4) derivatives having two dimethylaminoThe metal boron distances are 209.0(3) and 237.0(8) pm, respectively, thus being 13 and 18 pm longer as for known boryl complexes of iron and tungsten ['].The substitution of one chloro ligand by the [M(Cp)(CO),] group according to Eq. (I) proceeds under mild conditions in good yields. Exchange of the second chlorine, however, fails even in refluxing toluene, obviously for steric reasons.The described compounds are the first examples for diboran(4)yl groups as boron-bound ligands to transition metals. The absence of the catechol group as shbilizing ligand for such boryl complexes opens up the perspectives of investigating the reaction behaviour of metal-coordinated boron which is yet unknown. Possible reactions which are wort...

The new pyridyl‐substituted phosphaferrocene ligands 3 and 6 are prepared by addition of lithiated pyridine or α‐picoline to 2‐formyl‐3,4‐dimethylphosphaferrocene (1). The ligands 3 and 6 react with [Cp*RuCl]4 in THF to give the P,N‐chelate complexes [Cp*RuCl·3] (9) and [Cp*RuCl·6] (10) with high diastereoselectivity. Addition of monodentate ligands like CO or PPh3 to the complexes leads by displacement of the Ru‐bound pyridyl group to the respective carbonyl or phosphane complexes with monodentate P‐coordinated phospha‐ferrocene ligands. Reaction of the ligand 6 with [(C3H5)PdCl]2 and NH4PF6 gives the seven‐membered chelate complex [(C3H5)Pd·6]PF6 (13) which was characterized by X‐ray diffraction. The ligands 3 and 6 were tested in the palladium‐catalyzed asymmetric alkylation of 1,3‐diphenylallyl acetate.

The titanocene vinylidene intermediate [Cp*2TiCCH2] (4) (Cp*, C5(CH3)5), formed by ethylene or methane elimination from Cp*2TiCH2CH2CCH2 (3) and Cp*2Ti(CHCH2)(CH3) (11), respectively, reacts with symmetrical alkynes such as acetylene (12a), 2-butyne (12b), 1,2-diphenylacetylene (12c), 1,2-bis(trimethylsilyl)acetylene (12d), and 1,2-bis(tri-n-butylstannyl)acetylene (12e) by a [2 + 2] cycloaddition to give metallacyclobutenes Cp*2TiCRCRCCH2 (8a−e). When unsymmetrical alkynes are used, such as 2-pentyne (13g), 2,4-hexadiyne (13h), 1,4-diphenyl-1,3-butadiyne (13i), 1-phenyl-1-propyne (13j), or 1-(trimethylsilyl)-2-phenylacetylene (13k), different regioisomers can be isolated. For the reaction products of 4 with 13g and 13j, kinetic and thermodynamic products can be distinguished. In reactions of 1-pentyne (13f) and 4, a 1:1.5 mixture of the [2 + 2] cycloaddition product Cp*2TiCHC(nPr)CCH2 (17f) and the alkyne C−H bond activation product, Cp*2Ti(CHCH2)(C⋮C-nPr) (19f), is formed. By using stronger acidic acetylenes, like phenylacetylene (13l), or terminal acetylenes with bulky substituents, such as 2,2-dimethyl-3-butyne (13m) or (trimethylsilyl)acetylene (13n), the vinyl acetylides Cp*2Ti(CHCH2)(C⋮CR) [R = Ph (19l), t-Bu (19m), SiMe3 (19n)] are isolated in high yields. The structures of Cp*2TiC(CH3)C(CH3)CCH2 (8b) and Cp*2TiC(SiMe3)C(Ph)CCH2 (17k) were determined. The pseudotetrahedral molecules contain planar cyclobutene rings. The X-ray structure of 19l is presented. The regioselectivity of the formation of 17 and its regioisomer 16, using unsymmetrically substituted acetylenes, is attributed to the polarity of the C⋮C bond, on the basis of 13C NMR data. The reactivity of the methylenetitanacyclobutenes depends on the substituents of the alkynes. The formation of trans-poly(acetylene) occurs via 8a with an excess of acetylene. Analogous reactions of 8b,c and substituted alkynes are not successful. The isomerization of the titanacyclobutenes 16 → 17 indicates a cycloreversion. Selective insertion reactions of 8b and 8c with C6H11NC are observed in the TiC(R)C(R) σ-bond opposite the exo-methylene group, forming five-membered rings Cp*2TiC(NC6H11)C(R)C(R)CCH2 [R = Me (25b), Ph (25c)].