Albrecht Jacobi

Neopentane-Based Tripodal CpL2 Ligands: Synthesis and Reactions of CH3C(CH2-η5-C5H4)(CH2-η1-PPh2)2RuCl; Hindered Rotation of Vinylidene Ligands

The tripodal ligand [CH3C(CH2C5H4)(CH2PPh2)2]– reacts with RuCl2(PPh3)3 to produce CH3C(CH2-η5-C5H4)(CH2-η1-PPh2)2RuCl, [tripodCpL2RuCl], 1. Complex 1 undergoes substitution of the chlorine function with various nucleophiles L′ to produce [tripodCpL2RuL′]+. The carbonyl derivative (L′ = CO) 2, isonitrile (L′ = RNC) 3, nitrile compounds (L′ = RCN) 4, and a tolane adduct (L′ = η2-PhC≡CPh) 5 are obtained when 1 is treated with the appropriate ligands in polar solvents. Halide acceptors (e.g. TlPF6) are generally needed to promote these reactions. The cyanide derivative tripodCpL2RuCN (3a) is alkylated by F3CSO3CH3 to give the isonitrile derivative [tripodCpL2RuCNMe]+3b. Terminal alkynes HC≡CR produce vinylidene compounds [tripodCpL2RuL′]+, where L′ = CCHR (R = tBu, 7b; R = Ph, 7c), or allenylidene derivatives, L′ = CCCPh2 (6), depending on the nature of R (R = CPh2OH for synthesis of 6). Trimethylsilylacetylene gives the parent vinylidene species, L′ = CCH2 (7a), which is transformed to the Fischer-type carbene compound, L′ = C(OMe)Me (8), upon treatment with methanol. The vinylidene species 7 are deprotonated by NaOMe to produce the alkynyl compounds tripodCpL2RuC≡CR (9). Methylation of 9 with F3CSO3CH3 results in the vinylidene derivatives L′ = CC(Me)R (R = tBu, 7d; R = Ph, 7e), having two organic substituents at the terminal carbon centre. For all vinylidene compounds with two different substituents at their terminal carbon atom, hindered rotation of the single-faced vinylidene π-ligand about its Ru–C bond is observed. Analysis by 31P-NMR spectroscopic coalescence measurements as well as line-shape analyses reveals activation enthalpies of around 40 kJmol–1 for this rotation, with small activation entropies of around ±10 Jmol–1K–1. Solid-state structures of nine compounds of the type [tripodCpL2RuL′]+n (n = 0, 1) demonstrate the remarkable conformational rigidity of the tripodCpL2Ru template. They also show that the possible strain imposed by linking the Cp ligand and the two donor groups L in one and the same chelate scaffolding does not appear to impose a serious steric strain on these templates.

RHODIUM COD COMPLEXES OF MIXED DONOR SET TRIPOD LIGANDS : COORDINATION CHEMISTRY AND CATALYSIS

Abstract The reaction of the novel mixed tripod ligands RCH2C(CH2X)(CH2Y)(CH2Z) 1–6 (X, Y, Z=PPh2, NR2, pyrazol-1-yl; R=H, OH) with [RhI(COD)Cl]2 is investigated. The resulting rhodium COD complexes [(1–6)Rh(COD)]PF6, 7 are characterized by NMR spectroscopy, mass spectra and elemental analysis. In addition, X-ray structure analysis is performed on several compounds 7, where in contrast to the behavior of the parent compound triphos [MeC(CH2PPh2)3], the potential tripod ligands 2–6 are found to coordinate in a bidentate mode. {η2-P,O-[HOCH2C(CH2PPh2)(CH2NEt2)2]Rh(COD)]}PF6, 7i exhibits the first structurally characterized example of an intramolecular hydrogen bond between a non-coordinated and a coordinated donor atom. The activities of the complexes 7 as catalyst precursors in the homogeneous hydrogenation of diphenylacetylene and (Z)-α-N-acetamidocinnamic acid are tested and rationalized with respect to a proposed reaction mechanism.

Synthesis, coordination chemistry and polymerfixation of the tripod-ligand HOC6H4CH2C(CH2PPh2)3

Abstract Starting from 4-methoxybenzylmalonic ester MeOC6H4CH2CH(COOEt)2, the synthesis of the tripod-ligand HOC6H4CH2C(CH2PPh2)3, 12, functionalized with a phenolic group at its backbone, is achieved in a few steps. Ether derivatives of 12 show the normal coordination behavior of RC(CH2PPh2)3. Thus MeOC6H4CH2C(CH2PPh2)3 forms the complexes [7·Fe(NCMe)3] (BF4)2 (8) and 7·Mo(CO)3 (9). The phenolate derived from 12 by deprotonation reacts with the CH2Cl groups of Merrifield resin to form covalently polymer fixed 12 with high efficiency. The polymer bound tripod ligands undergo tripod typical coordination reactions. In addition to the usual spectroscopic and analytical techniques, X-ray analyses of derivatives of 12 as well as of 8 and 9 are used to identify the products.

(η5-C5H4SiMe3)2Ti(CC–SiMe2–CCSiMe3)2: a unique entry to monomeric and oligomeric alkyne–copper(I) and alkyne–silver(I) halides

Abstract The reaction of [Ti]Cl2 (1) {[Ti](η5-C5H4SiMe3)2Ti} with two equivalents of LiCC–SiMe2–CCSiMe3 (2) produces [Ti](CC–SiMe2–CCSiMe3)2 (3). On treatment with [MX] (M=Cu: 4a X=Cl, 4b X=Br; M=Ag: 5a X=Cl, 5b X=Br) the tweezer complexes {[Ti](CC–SiMe2–CCSiMe3)2}MX (M=Cu: 6a X=Cl, 6b X=Br; M=Ag: 7a X=Cl, 7b X=Br) are formed in which the Ti–CC–Si units are η2-coordinated to a monomeric copper(I) or silver(I) halide moiety. When 6b is further reacted with [CuBr] (4b), oligomeric {[Ti](CC–SiMe2–CCSiMe3)2(CuBr)3}n (8) is formed. This molecule contains a (η2-TiCCSi)2CuBr entity next to two (η2-SiCCSi)CuBr moieties, of which the latter building blocks are responsible for the oligomeric structure. In addition, 8 can be prepared by the direct reaction of 3 with an excess of 4b, respectively. However, when an excess of [AgX] is used, the only formed products are 7; no polymeric material is obtained. A Group 11 metal exchange reaction is noticed, when 7a or 7b are reacted with [CuX]: depending on the amount of [CuX] used, monomeric 6 or oligomeric 8 is produced. An explanation is given by a better bonding synergysmus for the alkyne-to-copper interaction. The result of the X-ray structure analysis of compound 7b is reported. The compound 7b crystallizes in the monoclinic space group C2/c with cell constants a=25.097(8), b=11.327(3), c=19.014(6) A, β=122.36(3)°, V=4566(2) A3 and Z=4. The compound 7b contains a monomeric (η2-alkyne)2AgBr moiety in which the silver(I) center possesses a trigonal-planar environment, caused by the η2-coordinated TiCCSi units as well as a η1-bonded bromine atom. However this differs from the behavior of compounds 6 and 7 in solution, where all four CC building blocks of the TiCCSi as well as the SiCCSi units are complexed by the transition metal entities MX (M=Cu, Ag X=Cl, Br).

PYRAZOLE AS A DONOR FUNCTION IN NEOPENTANE-BASED TRIPOD LIGANDS RCH2C(CH2PYRAZOL-1-YL)3-N(CH2PR2)N : SYNTHESIS AND COORDINATION CHEMISTRY

The chlorine functions of CH3C(CH2Cl)3, 1, may be replaced by pyrazolyl (pz) as well as imidazolyl (im) residues under the conditions of nucleophilic substitution leading to tripodal ligands CH3C(CH2X)3, X = pz, 2; X = im, 3. As a means of introducing two nitrogen donors and one phosphorus donor into a tripod ligand, substitution of the Br and OMs functions in O(CH2)2C(CH2Br)(CH2OMs), 8, by nitrogen nucleophiles and subsequent cleavage of the oxetane ring by a phosphide nucleophile to give HOCH2C(CH2PPh2)(CH2X)2 has been developed, furnishing 10a (X = pz) and 10d (X = NEt2), respectively. For the synthesis of 10a, K-pz was used as the nucleophile, while 10d was prepared using azide in the initial step, which then had to be transformed into NEt2 in two subsequent steps. The nucleophugic functions of the oxetane 8 undergo selective substitution by K-pz and KPPh2 in THF to produce O(CH2)2C(CH2PPh2)(CH2pz), 9b. Phosphide cleavage of the oxetane function leads to HOCH2C(CH2PPh2)(CH2PR2)(CH2pz), R = Ph, 10b; R = 3,5-Me2(C6H3), 10c. – The tris(pyrazolyl) tripod ligand 2 reacts with (MeCN)3Mo(CO)3to give 2 · Mo(CO)3(MeCN), 12a, in which only two of the three donor functions are coordinated. Upon reaction with 10a, the same reagent gives 10a · Mo(CO)4, 12b, with one pyrazolyl coordinated and the other involved in intramolecular hydrogen bonding to the CH2OH function (N···H–O distance 280 pm). Blocking of the OH function of 10a by etherification, i.e. to form EtOCH2C(CH2PPh2)(CH2pz)2, 11, does not dramatically affect the coordination capabilities with 11 · Mo(CO)3(MeCN), 12d, being formed upon treatment with (MeCN)3Mo(CO)3. Again only one pz function is coordinated to the metal. Bidentate coordination by two phosphorus donors of 10c is observed in 10c · Mo(CO)3(MeCN), 12d. The dangling arm pz donor function and the CH2OH group are intermolecularly hydrogen-bonded in this case. When the bulky P[3,5-Me2(C6H3)]2 substituent of 10c is replaced by the less sterically demanding PPh2 donor in 10b, η3-coordination is finally observed with the formation of 10b · Mo(CO)3, 13. The coordination capabilities of the new ligands are rationalized in terms of the size (six-, seven-, and eight-membered rings) and interference of the chelate cycles. All compounds have been characterized by the usual analytical and spectroscopic methods, with a complete assignment of the NMR data achieved by a combination of 2D-NMR techniques in some cases. The structures of the coordination compounds have additionally been deduced by X-ray methods.

Novel Dinucleating Ligand Systems Containing Two Adjacent Coordination Compartments of the Potential Triamidoamine-Type - Nickel(II) and Cobalt(II) Coordination Chemistry

The preparation of novel dinucleating pyrazolate ligands H5L3 - H5L8 carrying chelating side arms with appending secondary amine functions is reported. Following different synthetic routes, either CH2CF3, C6H2F3 , or C6F5 moieties can be introduced as substituents at the terminal nitrogen atoms. These systems are reminiscent of two coupled coordination compartments of the potential triamidoamine-type. Crystallographic analyses of a series of bimetallic complexes of the CH2CF3 -substituted ligand H5L4 with NiCl2 and CoCI2 reveal manifold coordination modes in the solid state, resulting from the facile detachment of a single or several N-donor sites from the metal centers. Coordination number sets {4/6} (in H5L4Co2Cl4) and {5/6} (in H4L4Ni2Cl3, H4L4Co2 Cl3 and H5L4Ni2Cl4) are thus observed. In the non-deprotonated H5L-type systems the remaining protons are found to be scavenged by a pyrazolate-N (in H5L4Ni2Cl4) or an amine function of a ligand side arm (in H5L4Co2Cl4).