Synthesis of the first series of rare-earth-metal constrained geometry complexes containing the P-(1-adamantylamino)-P-dimethyl-tetramethyl-cyclopentadienylidene-phosphorane ligand C5Me4PMe2NHAd, {Cp#PN}H, was accomplished. This monoanionic chelate ligand is isoelectronically related to the classical dianionic cyclopentadienyl-silylamine ligand C5Me4HSiMe2NHtBu, {Cp # SiN}H2. The ligand stabilizes dialkyls [{Cp#PN}M(CH2SiMe3)2] (M = Sc, 1; Lu, 2; Y, 3; Sm, 4; Nd, 5; Pr, 6; Ce, 7) over the full range of group 3 and lanthanide cation radii. Results of NMR studies of these crystalline alkyls, XRD molecular structures, and a preliminary study revealing the high catalytic activity of complexes 3–6 in the intramolecular hydroamination/cyclization are reported. The catalytic experiments reveal a trend in activity Lu < Y < Sm < Nd ≤ Pr resembling the trend in rare-earth-metal radii. Interestingly they reveal a distinctive substrate-dependent first-order kinetic profile for all metals investigated. The reaction of the precatalyst 3 with 1.6 equiv of the standard substrate 2,2-dimethylpenten-4-ylamine leads to a fast and selective formation of substrate complex [{Cp#PN}Y(NHCH2CMe2CH2CHCH2)2] (8). Fast cyclization was observed only after addition of more than 2 equiv of amine substrate. A noninsertive mechanism involving a six-membered transition state by a concerted C–N bond formation and N–H bond cleavage at a 3:1 substrate to complex ratio is suggested on the basis of these findings.

A set of lithium phosphonium diylides Li[CH2-PR2-CpX] (9–12; CpX = C5Me4, C5H3 tBu, R = Ph, Me) is presented. Two of the lithium complexes were characterized by means of single-crystal X-ray analysis, revealing a dimeric head-to-tail arrangement in the solid state. The coordination behavior of 9–12 in the liquid phase is solvent dependent. These lithium phosphonium diylides exist as contact ion pairs in benzene and as solvent-separated ion pairs in THF solutions. Phosphonium salts [H3C-PR2-CpXH)]+I– (1–4) are starting materials for the syntheses of the title compounds and exist as mixtures of isomers due to [1,5]-prototropic rearrangements. The dynamic behavior in solution has been investigated. Two different routes allow access to title compounds 9–12. Reactions of 1–4 with 2 equiv of nBuLi give 9–12 in a one-pot synthesis. In an alternative two-step route, dehydrodehalogenation of 1–4 with KH gives the corresponding phosphonium ylides 5–8. Two of these phosphonium ylides were characterized by single-crystal X-ray analysis. In one case two different conformers were obtained.

Cyclopentadienylidene phosphoranes of the general formula Cpx-PR2-CH3 (1a–d) and anionic derivatives thereof have been investigated as ligands in the coordination sphere of zirconium (R = NMe2, tBu, Ph; Cpx = C5H4, C5Me4, C5H2(CMe2)2CH2). The ligand set includes a full series of neutral and mono-, di-, and trianionic phosphonium ylides, which are formed by successive deprotonation of the PCH3 group. The degree of deprotonation can be controlled by choice of the ylides 1a–d and the zirconium precursor. The resulting zirconium complexes have been analyzed by NMR spectroscopy, elemental analyses, and single-crystal X-ray diffraction analyses. Our findings include the first fully characterized zirconium complex bearing a neutral cyclopentadienylidene phosphorane ligand, [Zr(H3C-P(NMe2)2-C5Me4)(CH2SiMe3)Cl3] (3a). New constrained-geometry complexes with chelating Cpx-phosphonio-alkyl ([Zr(CH2-PtBu2-C5H4)R′3]: 4b, R′ = Bn; 4b′, R′ = CH2SiMe3)) and Cpx-phosphonio-alkylidene ligands ([Zr(CH-PR2-Cpx)(CH2SiMe3)2]: 5a, R = NMe2, Cpx = C5Me4; 5c, R = Ph, Cpx = C5H2(CMe2)2CH2; 5d, R = Ph, Cpx = C5Me4) have been isolated and characterized. [Zr(C-PR2-C5Me4)Bn]2 (6a, R = NMe2) is a rare example of a compound featuring a bridging trianionic phosphonium ylide (phosphonio-alkylidyne) ligand.

A new, highly redox‐active chromophore ligand, H2(anthraphen) (1), containing two o‐phenylenediamine‐linked anthraquinone imine units has been synthesized in a three‐step synthesis and fully characterized by X‐ray crystallography, UV/Vis spectroscopy, and cyclic voltammetry. The dark‐red dye 1 shows molar extinction coefficients of up to 47000 L mol–1 cm–1 and four reversible reduction processes. This dianionic N2O2 ligand, with a significantly extended π system, offers a salphen‐like binding cavity for metal coordination, as has been demonstrated by the synthesis of [K2(anthraphen)] (2) and the transition‐metal complexes of TiIV (3), VIV (4), FeII (5), FeIII (6), CoII (7), NiII (8), CuII (9), PdII (10), PtII (11), and ZnII (12). These metal chromophores have colors ranging from dark‐red, violet, green to black. Their optical and electrochemical properties were investigated and compared with those of the diprotic ligand. Coordination led to an increase in the molar extinction coefficients up to 66400 L mol–1 cm–1 in the case of [V(anthraphen)O] (4), broadening of the absorption bands in the visible‐light region as well as a redshift of the lowest‐energy absorption band. The lowest‐energy absorption observed for these complexes to date is for [Ni(anthraphen)] (8) at 784 nm. The metal chromophores exhibit up to five fully reversible oxidation and reduction processes.

Base‐catalysed condensation of Ph2P–C5H5 (1) with an excess of acetone leads to a fulvene‐like diphenyl(4,4,6‐trimethyl‐4,5‐dihydropentalen‐2‐yl)phosphane Ph2P‐C11H13 (3) as a product of double condensation. Carbometallation of 3 with MeLi, followed by aqueous work‐up, results in formation of a new cyclopentadienylphosphane bearing a highly sterically demanding, anellated 1,1,3,3‐tetramethylcyclopentane moiety (4, Ph2P‐CpTMH). It reacts with chalcogene oxidants (H2O2, S8, Se) to form the corresponding phosphane chalcogenides Ph2P(=X)CpTMH, X = O (5), S (6), Se (7) in high yields. Quaternization of 4 with MeI gives the phosphonium salt 8 as a single isomer in high yield. Dehydrohalogenation of 8 by reaction with nBuLi gives CpTM‐phosphonium ylide Ph2P(CpTM)Me (9). An alternative protocol towards 9 that includes deprotonation of 8 with benzylpotassium followed by P‐alkylation is superior and gives 9 in more than 95 % yield. Staudinger reaction of 4 with tBuN3 gives onlyP‐amino‐cyclopentadienylidenephosphorane Ph2P(CpTM)NHtBu (10), whereas with Me3SiN3 only the tautomeric P‐imino‐cyclopentadienylphosphane Ph2P(NSiMe3)CpTMH (11) was isolated. Hydrolysis of 11 with wet MeCN leads to the new parent P‐amino‐cyclopentadienylidenephosphorane Ph2P‐(CpTM)NH2 (12). Treatment of 4 with benzylpotassium followed by transmetallation with FeCl2 leads to the sterically most crowded ferrocenyl‐bisphosphane [{Ph2P‐CpTM}2Fe] (13, dppfTM) in high yield. Its X‐ray diffraction analysis reveals an anti‐orientation of phosphane functionalities at both cyclopentadienyl rings. However, upon reaction of dppfTM with [PdCl2(MeCN)2], a constrained syn‐orientation is achieved in the product [{dppfTM}PdCl2] (14). Halogen exchange by reaction of 14 with NaI leads to the corresponding [{dppfTM}PdI2] (15). Molecular structures of 4, 9, 13 and 15 have been confirmed by XRD studies.