Unexpected Carbon-Carbon Coupling between Organic Cyanides and an Isopropyl β-Carbon in a Hafnium Ene Diamide Complex

A reaction sequence involving two hydrogen transfers and a C-C coupling on the β-carbon of an isopropyl group leads to formation of a new dianionic tridentate ligand in the reaction of the ene diamide complex Cp*Hf(σ2,π-iPr-DAB)Cl (1; Cp* = η5-C5Me5, iPr-DAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene) with organic cyanides. The product Cp*Hf [iPrNCH=CHNC(Me)=CHC(tBu)=NH]Cl was structurally characterized (Pbca, a = 13.454 (1) Å, b = 11.470 (1) Å, c = 31.297 (2) Å, 100 K). The reaction sequence is probably initiated by the transfer of the iPr α-H atom to a coordinated cyanide. Such a hydrogen transfer was observed in the reaction of 1 with ketones, producing the ene imine alkoxide complexes Cp*Hf[iPrNCH=CHN=CMe2](OCHR2)Cl, which were identified by NMR spectroscopy

Activation of sp3-CH Bonds in a Mono(pentamethylcyclopentadienyl)yttrium Complex. X-ray Crystal Structures and Dynamic Behavior of Cp*Y(o-C6H4CH2NMe2)2 and Cp*Y[o-C6H4CH2NMe(CH2-μ)][μ-o-C6H4CH2NMe(CH2-μ)]YCp*[THF]

Reaction of Y(o-C6H4CH2NMe2)3 (1) with Cp*H gives Cp*Y(o-C6H4CH2NMe2)2 (2), which crystallizes in the monoclinic space group P21/n (No. 14) with a = 18.607 (4) Å, b = 15.633 (3) Å, c = 8.861 (3) Å, β = 102.73 (3)°, and Z = 4. Least-squares refinement with 3006 independent reflections (F > 4.0σ(F)) led to a final RF (wR) of 0.053 (0.068). The molecular structure consists of monomeric Cp*Y(o-C6H4CH2NMe2)2 units with a regularly bonded Cp* ligand (Y-Ct = 2.367 (3) Å), equal Y-C(aryl) distances (2.479 (6) and 2.471 (6) Å), and both nitrogen atoms coordinated to yttrium (Y-N distances = 2.568 (5) and 2.506 (6) Å). Short intramolecular Y···H distances (Y···H(181) = 3.00 (6) Å, Y···H(183) = 3.13 (9) Å) indicate agostic interactions. The long N(2)-C(18) bond (1.55 (1) Å) and the short Y···C(18) distance (3.202 (8) Å) indicate an Y···C-N agostic interaction. Thermolysis of 2 in THF gives Cp*Y[o-C6H4CH2NMe(CH2-μ)][μ-o-C6H4CH2NMe(CH2-μ)]YCp*[THF] (3) and N,N-dimethylbenzylamine. Compound 3 crystallizes in the monoclinic space group P21/c (No. 14) with a = 17.004 (1) Å, b = 13.962 (1) Å, c = 20.129 (3) Å, β = 92.94 (1)°, and Z = 4. Least-squares refinement with 4578 independent reflections (F > 5.0σ(F)) led to a final RF (wR) of 0.065 (0.070). The molecule consists of two Cp*Y fragments (Y(1)-Ct(1) = 2.420 (6) Å, Y(2)-Ct(2) = 2.414 (5) Å), bridged by two methylene carbon atoms (Y(1)-C(9) = 2.591 (10) Å, Y(2)-C(9) = 2.527 (9) Å, Y(1)-C(18) = 2.622 (10) Å, Y(2)-C(18) = 2.532 (10) Å) and one aryl carbon atom (Y(1)-C(1) = 2.702 (8) Å, Y(2)-C(1) = 2.547 (9) Å). The remaining aryl group is not bridging (Y(1)-C(10) = 2.441 (8) Å). Asymmetry in 3 is caused by THF coordination (Y(2)-O = 2.446 (5) Å). Thermolysis of 2 can be explained by dissociation of an Y-N dative bond followed by activation of an agostic C-H bond

Calix[4]arene dimers; self-assembly via hydrogen bonding at the upper rim

The X-ray structure determination of calix[4]arenedicarboxylic acid unequivocally proves the self-assembled dimeric structure in the solid state. Also in apolar solvents two calix[4]arene molecules are connected via carboxylic acid moieties at the upper rim. NMR studies show that in polar solvents the calix[4]arenedicarboxylic acid is present as a monomer with a pinched cone conformation that differs from the dimeric structure in apolar solvents. \u

Unexpected Carbon-Carbon Coupling between Organic Cyanides and an Isopropyl β-Carbon in a Hafnium Ene Diamide Complex

A reaction sequence involving two hydrogen transfers and a C-C coupling on the β-carbon of an isopropyl group leads to formation of a new dianionic tridentate ligand in the reaction of the ene diamide complex Cp*Hf(σ2,π-iPr-DAB)Cl (1; Cp* = η5-C5Me5, iPr-DAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene) with organic cyanides. The product Cp*Hf [iPrNCH=CHNC(Me)=CHC(tBu)=NH]Cl was structurally characterized (Pbca, a = 13.454 (1) Å, b = 11.470 (1) Å, c = 31.297 (2) Å, 100 K). The reaction sequence is probably initiated by the transfer of the iPr α-H atom to a coordinated cyanide. Such a hydrogen transfer was observed in the reaction of 1 with ketones, producing the ene imine alkoxide complexes Cp*Hf[iPrNCH=CHN=CMe2](OCHR2)Cl, which were identified by NMR spectroscopy.

Synthesis And Dynamic Behaviour Of New Metallo-based Sterically Overcrowded Alkenes

The synthesis and crystal and molecular structures of novel metallo-based sterically overcrowded alkenes are reported and dynamic H-1 NMR studies reveals that the isomerization barriers are dramatically increased on metal coordination

9,10-Dimetallatriptycenes of group 14: a structural study

From ortho-phenylenemagnesium (1), 9-phenyl-9-germa-10-silatriptycene (5) was prepared via a simple one pot procedure. The previously prepared 9-methyl-10-phenyl-9,10-digermatriptycene (4) and 5 are the first germanium-containing 9,10-dimetallatriptycenes to be structurally characterised. The availability of these structural data allows a comparative discussion of 9,10-dimetallatriptycenes of Group 14

Formation and Molecular Structure of Permethylyttrocene Methyl Tetrahydrofuranate

The reaction of Cp*2YCl · THF with MeLi in THF at -80 °C gives the monomeric Cp*2YMe · THF (1), which has been characterized by spectroscopy, elemental analyses and a single crystal X-ray diffraction study. Complex 1 crystallizes in the orthorhombic space group Pnam with lattice parameters a 17.881(4), b 8.621(2), c 15.095(3) Å, Z = 4, and Dcalc 1.274 g cm-3. Least-squares refinement using 1056 independent observed reflections and 117 parameters gave a final R value of 0.071. The Y-C(σ) bond distance is 2.44(2) Å. IR and NMR spectra indicate an agostic interaction between the metal center and one of the C-H bonds of the methyl ligand, but this could not be confirmed by the X-ray structure determination owing to disorder.

Synthesis of Pt compounds containing chiral (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole) as ligand and their use in asymmetric hydroformylation of styrene derivatives

Unlike bis(diphenyl)phosphine derivatives in general, (2S,4S)-pentane-2,4-diyl-bis(5H-dibenzo[b]phosphindole), S,S-BDBPP, gives a trans oligomeric compound [PtCl2(S,S-BDBPP)]n, 1, in reaction with dichloro-Pt precursors such as PtCl2(PhCN)2, PtCl2(CH3CN)2 and PtCl2(COD) at room temperature. Compound 1, which could be readily isolated, slowly rearranges in solutions at room temperature to the expected cis-monomer PtCl2(S,S-BDBPP), 3. Heating or the presence of PtCl2(COD) accelerates the transformation of compound 1 to 3. SnCl2 adducts of both compounds, trans-[PtCl(SnCl3)(S,S-BDBPP)]n, 2, and cis-PtCl(SnCl3)(S,S-BDBPP), 4, as well as the known cis-PtCl(SnCl3)(S,S-BDPP), 5, (S,S-BDPP = (2S,4S)-2,4-bis(dipbenylphosphino)pentane) have been tested as catalysts in the asymmetric hydroformylation of p-isobutylstyrene. The phenyl analog 5 provides up to 75% e.e. but moderate yields to chiral 2-(4-isobutylphenyl)-2-propanal. Compared to this, the regioselectivity to the branched aldehyde is remarkably increased; however, the enantioselectivity is drastically decreased by the use of both dibenzophosphole derivatives 2 and 4. The similarities in the selectivities provided by 2 and 4 indicate that the trans oligomer 2 transforms to the cis-monomer 4 during the catalytic process. X-ray crystal structure determination of compound 3 shows a half-chair conformation for the chelate ring with a symmetric arrangement of dibenzophosphole groups. Besides a preference for the latter achiral conformation, the planar structure of the dibenzophosphole groups can also be considered as reason for the moderate enantioselectivities provided by 4.

CCDC 123213: Experimental Crystal Structure Determination

Related Article: W.P.Mul, C.J.Elsevier, M.A.Vuurman, W.J.J.Smeets, A.L.Spek, J.L.de Boer|1997|J.Organomet.Chem.|532|89|doi:10.1016/S0022-328X(96)06808-8,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

CCDC 123212: Experimental Crystal Structure Determination

Related Article: W.P.Mul, C.J.Elsevier, M.A.Vuurman, W.J.J.Smeets, A.L.Spek, J.L.de Boer|1997|J.Organomet.Chem.|532|89|doi:10.1016/S0022-328X(96)06808-8,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.