Main Group Pentafulvenes: Challenges and Opportunities in Heavy Main Group Isolobal Substitution of Pentafulvene

Heterofulvenes based on isolobal substitution of carbon fragments by (heavier) main group motifs provide a rich source of structurally interesting building blocks with electronic situations that can vastly differ from all-carbon congeners. Group 13, heavier 14 & 16 fulvenes are rare and pose significant stability challenges, while group 15 derivatives, particularly phosphorus and arsenic, have led to many derivatives with intriguing opto-electronic properties.

From phosphanylphosphaalkenes to coordination copper and silver polymers containing P-P bonds

This study was focused on the activation of the CP bond via reactions of Ph2CP-PtBu2 (1) with 1,6-hexanediol and selected dithiols (1,4-butanedithiol, 1,4-benzenedithiol and 1,4-benzenedimethanethiol). These reactions proceed according to a 1,2-addition mechanism, providing new compounds with formulas {(Ph)2(H)C-P-PtBu2}{μ2-(O-(CH2)6-O)}{tBu2P-P-C(H)(Ph)2} (2), {(Ph)2(H)C-P-PtBu2}{μ2-(S-(CH2)4-S)}{tBu2P-P-C(H)(Ph)2} (3a), {(Ph)2(H)C-P-PtBu2}{μ2-(S-C6H4-S)}{tBu2P-P-C(H)(Ph)2} (3b), and {(Ph)2(H)C-P-PtBu2}{μ2-(S-CH2-C6H4-CH2-S)}{tBu2P-P-C(H)(Ph)2} (3c). Next, the reactions of 3a and 3c with metal chlorides led to the growth of desired coordination polymers of copper(I) and silver(I). All the obtained compounds remained stable under atmospheric conditions.

Two complementary approaches for the synthesis and isolation of stable phosphanylphosphaalkenes

A new series of compounds formed in a one-step  reaction (Phospha–Wittig  or phospha–Peterson), containing the CP–P moiety was synthesized and characterized. These species are stable under atmospheric conditions and are resistant to hydrolysis.

Synthesis and characterization of new tetra-substituted porphyrins with exo-donor carboxylic groups as building blocks for supramolecular architectures: Catalytic and structural studies of their metalated derivatives

We report herein the synthesis of the porphyrins 5,10,15,20-tetrakis(4-carboxybiphenyl)-porphyrin (H2TCBP) and 5,10,15,20-tetrakis(4-carboxy-2,6-dimethylbiphenyl)porphyrin (H2TCDMBP) bearing diphenyl units on meso-positions, and of their cobalt and silver derivatives. The silver complexes of H2TCDMBP and of H2TCPP ( H2TCPP = 5 ,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) were investigated by X-ray crystallography and their supramolecular organization elucidated. Co(TCBP) was reacted with copper formate, yielding a polymeric compound that showed a catalytic activity in the benzylic amination of hydrocarbons using arylazide as aminating agent.

Diphosphene and diphosphinylidene

The equilibrium structures of P(2)H(2) isomers and the associated isomerization transition states have been investigated systematically starting from self-consistent-field theory and proceeding to coupled cluster methods using a wide range of basis sets. For each structure, the geometry, energy, dipole moment, harmonic vibrational frequencies, and infrared intensities have been predicted. The global minimum has been confirmed to be planar trans-HPPH diphosphene, lying 3.2 kcal mol(-1) below cis-HPPH with the aug-cc-pVQZ CCSD(T) method upon inclusion of zero-point vibrational energy corrections. Diphosphinylidene, which has the connectivity PPH(2) and C(2v) symmetry, lies 25.2 kcal mol(-1) above the global minimum. The trans-cis isomerization reaction occurs via internal rotation with a barrier of 35.2 kcal mol(-1) using the cc-pVQZ Mk-MRCCSD (2e/2MO) method. This transition state exhibits multireference character and consequently properties were evaluated using CASSCF, MRCI, CASPT2, and Mk-MRCCSD methods with various basis sets. At the aug-cc-pVQZ CCSD(T) level, the transition state for the isomerization reaction between trans-HPPH and diphosphinylidene (planar PPH(2)) is predicted to be nonplanar with a torsional angle of 101.1 degrees . The corresponding barrier is estimated to be 48.2 kcal mol(-1).

Twisting the phenyls in aryl diphosphenes (Ar-P=P-Ar). Significant impact upon lowest energy excited states

Aryl diphosphenes (Ar-P=P-Ar) possess features that may make them useful in photonic devices, including the possibility for photochemical E-Z isomerization. Development of good models guided by computations is hampered by poor correspondence between predicted and experimental UV/vis absorption spectra. A hypothesis that the phenyl twist angle (i.e., PPCC torsion) accounts for this discrepancy is explored, with positive findings. DFT and TDDFT (B3LYP) were applied to the phenyl-P=P-phenyl (Ph-P=P-Ph) model compound over a range of phenyl twist angles, and to the Ph-P=P-Ph cores of two crystallographically characterized diphosphenes: bis-(2,4,6-tBu(3)C(6)H(2))-diphosphene (Mes*-P=P-Mes*) and bis-(2,6-Mes(2)C(6)H(3))-diphosphene (Dmp-P=P-Dmp). A shallow PES is observed for the model diphosphene: the full range of phenyl twist angles is accessible for under 5 kcal/mol. The Kohn-Sham orbitals (KS-MOs) exhibit stabilization and mixing of the two highest energy frontier orbitals: the n(+) and pi localized primarily on the -P=P- unit. A simple, single-configuration model based upon this symmetry-breaking is shown to be consistent with the major features of the measured UV/vis spectra of several diphosphenes. Detailed evaluation of singlet excitations, transition energies and oscillator strengths with TDDFT showed that the lowest energy transition (S(1) <-- S(0)) does not always correspond to the LUMO <-- HOMO configuration. Coupling between the phenyl rings and central -P=P- destabilizes the pi-pi* dominated state. Hence, the S(1) is always n(+)-pi* in nature, even with a pi-type HOMO. This coupling of the ring and -P=P- pi systems engenders complexity in the UV/vis absorption region, and may be the origin of the variety of photobehaviors observed in diphosphenes.

Theoretical study on the phenyl torsional potentials of trans-diphenyldiphosphene

The phenyl torsional potentials of trans-diphenyldiphosphene ( trans-phosphobenzene; t-DPP), which is an analogue of trans-azobenzene ( t-AZB), have been examined by means of ab initio complete active space self-consistent field (CASSCF) calculations. Though the electronic structures of t-DPP are similar to those of t-AZB, the phenyl torsional potentials are different from each other. In S 0, the potential energy curve of t-DPP has double minima at nonplanar conformations with C 2 and C i symmetries, while that of t-AZB has only minimum at a planar conformation with C 2 h . In S 1, the phenyl torsion of t-AZB is impeded from a planar geometry more than that in S 0. On the other hand, the phenyl torsion of t-DPP is promoted so that the phenyl groups are perpendicularly twisted against the PP double bond around the Franck-Condon region. Comments on the experimental findings of realistic diphosphenes protected by bulky substituents are also made.

Photochemical E−Z Isomerization of meta-Terphenyl-Protected Phosphaalkenes and Structural Characterizations

A series of phosphaalkenes, E-ArP=C(H)Ar' (Ar = 2,6-Mes2C6H3, Ar' = Ph (1a); Ar = 2,6-Mes2C6H3, Ar' = p-C6H4Br (2a); Ar = 4-Br-2,6-Mes2C6H2, Ar' = Ph (3a); Ar = 4-Br-2,6-Mes2C6H2, Ar' = p-C6H4Br (4a)) have been prepared by phospha-Wittig reactions and characterized. Exposure of these materials either to room light over an extended period of time (days) or to UV light (hours) produced equilibrium mixtures of the E and Z isomers (1b-4b) as indicated by 1H and 31P NMR spectroscopy. The structures of compounds 4a and 4b were determined by single-crystal X-ray diffraction methods. Variable-temperature (1)H NMR studies of 4b indicate hindered rotation about the P-CAr bond, with DeltaH(double dagger) = 13.8 kcal/mol and DeltaS(double dagger) = 1.3 eu. The electronic structures of E- and Z-PhP=C(H)Ph have been examined using density functional theory.