2,8-lanostadiene

The title salt, C(20)H(42)N(4)S(2) (2+)·2ClO(4) (-), was obtained from the reaction of bis-(diethyl-amino)-carbeniumdithio-carboxyl-ate, (Et(2)N)(2)C(2)S(2), with Fe(ClO(4))(2)·6H(2)O in CH(2)Cl(2). The title compound, in which one of the S atoms of (Et(2)N)(2)C(2)S(2) is bound to a 1,1-bis-(diethyl-amino)-ethane moiety, has two carbenium C atoms, and the charge compensation is provided by two perchlorate anions. The N(2)C-CS(2) bond length is 1.512 (4) Å, corresponding to a C-C single bond, and the dihedral angle between N(2)C- and -CS(2) planes [72.0 (2)°] is smaller than that of (Et(2)N)(2)C(2)S(2) [82.0 (1)°]. The crystal structure features C-H⋯S hydrogen bonds.

We study two metal-free catalysts for the reduction of CO2 with four different hydroboranes and try to identify mechanistically relevant intermediate species. The catalysts are the phosphinoborane Ph2P(CH2)2BBN (1), easily accessible in a one-step synthesis from diphenyl(vinyl)phosphine and 9-borabicyclo[3.3.1]nonane (H-BBN), and its formaldehyde adduct Ph2P(CH2)2BBN(CH2O) (2), detected in the catalytic reduction of CO2 with 1 as the catalyst but properly prepared from compound 1 and p-formaldehyde. Reduction of CO2 with H-BBN gave mixtures of CH2(OBBN)2 (A) and CH3OBBN (B) using both catalysts. Stoichiometric and kinetic studies allowed us to unveil the key role played in this reaction by the formaldehyde adduct 2 and other formaldehyde-formate species, such as the polymeric BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2) (3) and the bisformate macrocycle BBN(CH2)2(Ph2P)(CH2O)BBN(HCO2)BBN(HCO2) (4), whose structures were confirmed by diffractometric analysis. Reduction of CO2 with catecholborane (HBcat) led to MeOBcat (C) exclusively. Another key intermediate was identified in the reaction of 2 with the borane and CO2, this being the bisformaldehyde-formate macrocycle (HCO2){BBN(CH2)2(Ph2P)(CH2O)}2Bcat (5), which was also structurally characterized by X-ray analysis. In contrast, using pinacolborane (HBpin) as the reductant with catalysts 1 and 2 usually led to mixtures of mono-, di-, and trihydroboration products HCO2Bpin (D), CH2(OBpin)2 (E), and CH3OBpin (F). Stoichiometric studies allowed us to detect another formaldehyde-formate species, (HCO2)BBN(CH2)2(Ph2P)(CH2O)Bpin (6), which may play an important role in the catalytic reaction. Finally, only the formaldehyde adduct 2 turned out to be active in the catalytic hydroboration of CO2 using BH3·SMe2 as the reductant, yielding a mixture of two methanol-level products, [(OMe)BO]3 (G, major product) and B(OMe)3 (H, minor product). In this transformation, the Lewis adduct (BH3)Ph2P(CH2)2BBN was identified as the resting state of the catalyst, whereas an intermediate tentatively formulated as the Lewis adduct of compound 2 and BH3 was detected in solution in a stoichiometric experiment and is likely to be mechanistically relevant for the catalytic reaction.

In the title compound, C19H17Cl2N3O2, there are three mol-ecules (A, B and C) in the asymmetric unit and each differs in the conformation adopted. As a result of steric repulsion, the amide group is rotated with respect to both the dichloro-phenyl and 2,3-dihydro-1H-pyrazol-4-yl rings, making dihedral angles of 44.5 (2) and 56.2 (2)°, respectively in A, 51.1 (2) and 54.1 (2)° in B, and 53.8 (2) and 54.6 (2)° in C. The dihedral angles between the dichloro-phenyl and 2,3-dihydro-1H-pyrazol-4-yl rings are 54.8 (2), 76.2 (2) and 77.5 (2)° in mol-ecules A, B and C, respectively, while the 2,3-dihydro-1H-pyrazol-4-yl and phenyl rings make dihedral angles of 45.3 (2), 51.2 (2) and 42.8 (2)°, respectively. In the crystal, two of the mol-ecules are linked through N-H⋯O hydrogen bonding to an adjoining mol-ecule, forming dimers of the R2(2)(10) type, while the third mol-ecule forms such dimers with itself. C-H⋯O inter-actions link the dimers.