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Matthias Tamm

Publications and source records attributed to Matthias Tamm.

7 recordsLinked to original sources
PubMed2006

Strong hydrogen bonds in the ionic pair (1,3-diisopropyl-4,5-dimethyl-4-imidazolin-2-ylidene)ammonium trichloro(1,3-diisopropyl-4,5-dimethyl-4-imidazolin-2-ylideneamine)iron(II).

The title compound, (C11H22N3)[FeCl3(C11H21N3)], is one of the rare examples where an isolated ionic pair of the type [A]n+ [EMX3]n- (E is any non-metal, M is any transition metal and X is any halogen) could be structurally characterized. Two short N-H...Cl contacts between the two ammonium H atoms and two of the three Cl atoms of the counter-anion generate a six-membered ring. The third Cl atom is involved in a weaker intramolecular hydrogen bond to the neutral 1,3-diisopropyl-4,5-dimethyl-4-imidazolin-2-ylideneamine ligand.

Journal Article↗
PubMed2005

Imidazolin-2-iminato titanium complexes: synthesis, structure and use in ethylene polymerization catalysis.

The Staudinger reaction of the imidazolin-2-ylidenes, 1,3-di-tert-butylimidazolin-2-ylidene (1a), 1,3-diisopropylimidazolin-2-ylidene (1b), 1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene (1c), 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (1d) and 1,3-bis(2,6-diisopropylphenylimidazolin-2-ylidene (1e), with trimethylsilyl azide furnishes the corresponding N-silylated 2-iminoimidazolines 2a-e, which react with [(eta-C5H5)TiCl3] to afford half-sandwich cyclopentadienyl titanium complexes of the type [CpTi(L)Cl2] (3) (L = imidazolin-2-iminato ligand). Similarly, the reactions of 1,3-di-tert-butyl-2-(trimethylsilylimino)imidazoline (2a) with [(eta-tBuC5H4)TiCl3] results in the formation of [(eta-tBuC5H4)Ti(L)Cl2] (4) (L = 1,3-di-tert-butylimidazolin-2-imide). Bis(1,3-di-tert-butylimidazolin-2-iminato)titanium dichloride (5) is obtained from the reaction of two eq. of 2a with TiCl4. Treatment of 5 with methyllithium results in the formation of the corresponding dimethyl complex [L2Ti(CH3)2] (6), whereas [CpTi(L)(CH3)2] (7) is similarly obtained from 3a. The molecular structures of 3a, 3b, 3c, 3e x C7H8, 4 and 7 are reported revealing linearly coordinated imidazolin-2-iminato ligands together with very short Ti-N bond distances. All dichloro complexes (3a-e, 4 and 5) can be activated with methylaluminoxane (MAO) to give active catalysts for ethylene homopolymerization. In most cases, moderate to high activities are observed together with the formation of high (HMWPE) or even ultra high molecular weight polyethylene (UHMWPE).

Catalysis↗
PubMed2005

Regioselective Si-C bond activation in silicon-bridged ansa-cycloheptatrienyl-cyclopentadienyl complexes.

On treatment with [Pt(PEt3)3], silicon-bridged ansa-cycloheptatrienyl-cyclopentadienyl Ti and V complexes, [1]silatroticenophane and [1]silatrovacenophane, undergo oxidative addition and regioselective insertion of a Pt(PEt3)2 moiety into the silicon-carbon bond to the seven-membered ring; the resulting complexes, [2]platinasilatroticenophane and [2]platinasilatrovacenophane, can be partly used as single-source catalysts for the ring-opening polymerization (ROP) of the original highly strained sandwich molecules.

Journal Article↗
PubMed2004

Titanium complexes with imidazolin-2-iminato ligands.

The reaction of 1,3-di-tert-butylimidazolin-2-ylidene with trimethylsilyl azide furnishes the corresponding N-silylated 2-iminoimidazoline which reacts with titanium(IV) chlorides to yield imidazolin-2-iminato titanium complexes.

Journal Article↗
PubMed2004

Mono- and dinuclear molybdenum complexes with sterically demanding cycloheptatrienyl ligands.

Sterically demanding cycloheptatrienylium (tropylium) salts of the type (1,3,5-C7H4R3)BF4 [R = t-Bu, (3a)BF4; R = SiMe3, (3b)BF4] have been prepared from the corresponding 1,3,5-trisubstituted benzene derivatives 1 by ring expansion with diazomethane followed by hydride abstraction with triphenylcarbenium tetrafluoroborate, (Ph3C)BF4. Complexation can be achieved by arene exchange and Mo(CO)3 group transfer employing [(eta6-p-xylene)Mo(CO)3] (4) to yield the cationic complexes (5)BF4. In refluxing mesitylene, [(eta7-C7H4t-Bu3)Mo(CO)3]BF4, (5a)BF4, undergoes CO substitution to furnish the mesitylene sandwich complex (6a)BF4. A cyclic voltammetric study reveals that this complex exhibits a reversible one-electron oxidation to the dicationic 17e complex 6a2+, which can also be accessed by chemical oxidation with AgBF4. On the contrary, the reduction of 6a+ is irreversible and does not yield a stable 19e complex 6a. To study the fate of the reduced 19e form, (5a)BF4 was treated with Na2Hg to diastereoselectively afford the C-C coupled bicycloheptatriene complex 7a. Paramagnetic, dinuclear complexes of the type [(eta7-C7H4R3)Mo(mu-Cl)3Mo(eta7-C7H4R3)] (8) have been obtained from the reaction of (5)BF4 with Me3SiCl. These can be regarded as mixed-valence Mo(0)/Mo(+I) compounds with a metal-metal bond order of 0.5. Cyclic voltammetric studies reveal that both complexes 8a and 8b undergo reversible one-electron oxidation as well as reduction. Treatment with one equivalent of ferrocenium hexafluorophosphate leads to removal of the unpaired electron and formation of the diamagnetic complexes (8)PF6. Theoretical DFT calculations have been carried out to further elucidate the bonding in these systems. In addition, the X-ray crystal structures of (5b)BF4, (6a)BF4 x CH2Cl2, (6a)(BF4)2 x (acetone)2, 7a x CH2Cl2, 8a x 0.5C6H14, and (8a)PF6 x Et2O are reported.

Crystallography, X-Ray↗
PubMed2002

Molybdenum complexes with linked cycloheptatrienyl-phenolate ligands.

The tropylium salt (2-hydroxy-3,5-dimethylphenyl)cycloheptatrienylium tetrafluoroborate (3) has been synthesized in three steps from THP-protected 2,4-dimethylphenol and tropylium tetrafluoroborate, (C(7)H(7))BF(4). In CH(2)Cl(2) solution, the unexpected formation of tricyclic 2,4-dimethylbenzo[b]cyclohepta[d]furanylium tetrafluoroborate (5) has been observed, which must have formed from 3 by loss of H(2). 5 was characterized by an X-ray crystal structure determination and could independently be synthesized by treatment of 3 with NaHCO(3) to give 2,4-dimethylbenzo[b]cyclohepta[d]furan (4) followed by acidification with HBF(4).Et(2)O. The arene transfer reaction of 3 with [(eta-p-xylene)Mo(CO)(3)] furnished the cycloheptatrienyl complex [(HOC(6)H(2)Me(2)-eta(7)-C(7)H(6))Mo(CO)(3)]BF(4) (6), which could be converted into the chiral chelate complexes [(OC6H2Me2-eta7-C7H6)Mo(CO)(PR3)](9a, R = Ph; 9b, R = c-C(6)H(11); 9c, i-Pr) by subsequent treatment with NaI, PR(3), and NaH. The linked cycloheptatienyl-phenolate ligand in 9a could be protonated at the coordinated oxygen atom employing HBF(4).Et(2)O to yield [(HOC6H2Me2-eta7-C7H6)Mo(CO)(PPh3)]-BF4 (10). In 10, the appended phenol group is coordinated in a hemilabile fashion, which allowed the introduction of 2,6-dimethylphenyl isocyanide and CO and formation of complexes [(HOC(6)H(2)Me(2)-eta(7)-C(7)H(6))Mo(CO)(PPh(3))L]BF(4) (11, L = XyNC; 12, L = CO). On thermal reaction of [(HOC(6)H(2)Me(2)-eta(7)-C(7)H(6))Mo(CO)(2)I] (7) with dppe, the addition of the diphosphine was observed together with the simultaneous formation of the molydenum-oxygen bond to yield [(OC6H2Me2-eta3-C7H6)Mo(CO)2(dppe)] (13), in which the cycloheptatrienyl ring has reduced its hapticity from seven to three. The pseudooctahedral complex 13 exhibits an interesting fluxional behavior in solution, which has been studied by means of variable-temperature (31)P and (1)H NMR spectroscopy. A eta(3) --> eta(7) hapticity reversion could be achieved by UV irradiation of a solution of 13 in THF to give the electron-rich complex [(OC6H2Me2-eta7-C7H6)Mo(dppe)] (14). 14 was readily oxidized with ferrocenium hexafluorophosphate, and the resulting paramagnetic monocationic complex 15 has been studied by means of ESR spectroscopy and X-ray diffraction. In addition, the X-ray crystal structures of complexes 9a, 10.2CH(2)Cl(2), 12, and 13 are reported.

Journal Article↗