Cyclophanes—13: Crystal and molecular structure of [2.2][2,5]furano(1,4)naphthalenophane

The crystal and molecular structure of [2.2](2,5)furano(1,4)naphthalenophane (1) was determined by X-ray crystallography. The molecule exists in the anti-conformation and the study represents the first instance in which the structural features of a naphthalenoid ring within a cyclophane were determined. Crystals of cyclophane 1 are orthorhombic, space group Pbca, with a = 7.859(2). b = 11.482(3) and c = 28.818(8) Å. While the nonbridged portion of the naphthalenoid ring is planar, the portion which is bridged to the furanoid ring through its 1 and 4 C atoms is puckered and boat-shaped. These C atoms are positioned 14° out of the plane of the other four C atoms of this ring. The furanoid ring is essentially planar but is not parallel to the naphthalenoid ring. It is inclined 22° to the least squares plane of the bridged portion of the naphthalenoid ring. This angle of inclination staggers the atoms of the furanoid and bridged naphthalenoid ring and positions the 3 and 4 C atoms, the 2 and 5 C atoms and the 0 atom of the furanoid ring 3.4. 2.9 and 2.6 Å. respectively, from the least squares plane of the bridged portion of the naphthalenoid ring. While the internal angles around the bridging C atoms α- to the naphthalenoid ring are 109°, those α- to the furanoid ring are 113°. In addition unusually large bond angles ($\text{\$}\text{?}$137°) at the 2 and 5 C atoms of the furanoid ring, external to the ring, are also observed. The distortions are considered with respect to the strain within the cyclophane macrocycle and are compared with other similar systems.     

Facile oxidative addition of N-C and N-H bonds to monovalent rhodium and iridium

An investigation of room-temperature oxidative addition of N-C and N-H bonds to RhI and IrI in solution and in the solid state is presented. The rigid, product-adapted framework of the pincer bis(ortho-phosphinoaryl)amine (PNP) ligand may contribute to the ease of the N-C and N-H cleavage. The migration of Me from N of the coordinated amine moiety to Rh proceeds with near-zero entropy of activation in solution. In the solid state, this transformation is a crystal-to-crystal reaction, transforming only one of the two independent molecules of (PN(Me)P)RhCl into (PNP)Rh(Me)Cl.     

Activation of CO2 by a heterobimetallic Zr/Co complex

At room temperature, the early/late heterobimetallic complex Co((i)Pr(2)PNMes)(3)Zr(THF) has been shown to oxidatively add CO(2), generating (OC)Co((i)Pr(2)PNMes)(2)(μ-O)Zr((i)Pr(2)PNMes). This compound can be further reduced under varying conditions to generate either the Zr oxoanion (THF)(3)Na-O-Zr(MesNP(i)Pr(2))(3)Co(CO) or the Zr carbonate complex (THF)(4)Na(2)(CO(3))-Zr(MesNP(i)Pr(2))(3)Co(CO). Additionally, reactivity of the CO(2)-derived product has been observed with PhSiH(3) to generate the Co-hydride/Zr-siloxide product (OC)(H)Co((i)Pr(2)PNMes)(3)ZrOSiH(2)Ph.     

Skeletal change in the PNP pincer ligand leads to a highly regioselective alkyne dimerization catalyst

A Rh complex of a bulky diarylamino-based PNP pincer ligand is a robust catalyst for the dimerization of terminal alkynes and highly selective for the trans-enyne product.     

ESR and Theoretical Studies of Bis-Benzene-1, 2-Diselenolate Nickel and Related Complexes

Abstract

ESR and theoretical studies of the transition metal complexes of [Co and Ni (Se₂C₆H₄)₂]^? (n-C₄H₉)₄N⁺ are reported and compared with closely related systems. Room temperature single crystal X-ray studies reveal the Nickel complex is orthorhombic. ESR studies of the polycrystalline powders of the Ni complex as a function of temperature from 108 K to room temperature show a series of spectral envelopes which can arise only from a paramagnetic site which possesses axial symmetry. At ca 160 K, there is an abrupt change in the value of the principal components of the anisotropic g-tensor of the Ni complex which is discussed. Low temperature ESR studies of polycrystalline samples of the ground state triplet Cobalt complex which is isomorphous with the Nickel complex reveal an orthorhombic g-tensor. From the field position of the half-field resonance, it is possible to calculate a mean separation, of the two electrons which make up the triplet state, of 4.3 (±0.5) A.     

Addition of H2 Across a Cobalt–Phosphorus Bond

Addition of H₂ across the cobalt–phosphorus bond of (PPP)CoPMe₃ ( 3 ) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP^?) donor. The chlorophosphine Co^II complex (PP^ClP)CoCl₂ ( 2 ) can be generated through coordination of the chlorophosphine ligand (PP^ClP, 1 ) to CoCl₂. Subsequent reduction of 2 with KC₈ in the presence of PMe₃ generates (PPP)CoPMe₃ ( 3 ), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H₂ to complex 3 cleanly affords (PP^HP)Co(H)PMe₃ ( 4 ), in which H₂ has ultimately been added across the metal–phosphorus bond. Complex 4 was characterized spectroscopically and using computational methods to predict its geometry.     

Formal synthesis of (+/-)-platensimycin

[reaction: see text] Reductive alkylation of 5-methoxy-1-tetralone (6) with 2,3-dibromopropene gave an equilibrium mixture of bicyclic diones 7 (51%) and 8 (35%). Radical cyclization of 7 afforded tricyclic dione 5 (84%), which was reduced, cyclized, and dehydrated to give tetracyclic alkene 13 in 63% yield. Allylic oxidation of 13 with SeO2 and activated MnO2 afforded enone 2 in 85% yield, thereby completing a short formal synthesis of (+/-)-platensimycin.     

Covalent palladium-zinc bonds and their reactivity

Photolysis of ((F)PNP)Pd-Et in the presence of Et(2)Zn leads to the formation of ((F)PNP)Pd-Zn-Pd(PNP(F)), the first example of a compound with a covalent Pd-Zn bond.