Syntheses, Structures, and Coordination Chemistry of Phosphole-Containing Hybrid Calixphyrins:  Promising Macrocyclic P,N₂,X-Mixed Donor Ligands for Designing Reactive Transition-Metal Complexes

Abstract

The syntheses, structures, and coordination chemistry of phosphole-containing hybrid calixphyrins (P,N2,X-hybrid calixphyrins) and the catalytic activities of their transition-metal complexes are reported. The 5,10-porphodimethene type 14pi-P,(NH)2,X- and 16pi-P,N2,X-hybrid calixphyrins (X = O, S, NH) are prepared via acid-promoted dehydrative condensation between a sigma4-phosphatripyrrane and the corresponding 2,5-bis[hydroxy(phenyl)methyl]heteroles followed by DDQ oxidation. Both spectroscopic and crystallographic data of the hybrid calixphyrins have revealed that the conformation and size of the macrocyclic platforms as well as the oxidation state of the -conjugated pyrrole-heterole-pyrrole (N-X-N) units vary considerably depending on the combination of heteroles. The sigma3-P,(NH)2,S- and sigma3-P,N2,S-hybrids react with Pd(OAc)2 and Pd(dba)2, respectively, to afford the same Pd(II)-P,N2,S-hybrid complex, in which the calixphyrin platform is regarded as a dianionic ligand. In the complexation with [RhCl(CO)2]2 in dichloromethane, the sigma3-P,N2,S-hybrid behaves as a neutral ligand to afford an ionic Rh(I)-P,N2,S-hybrid complex, whereas the sigma3-P,N2,NH-hybrid behaves as an anionic ligand to produce Rh(III)-P,N3-hybrid complexes. In the latter reaction, it is likely that a neutral Rh(I)-P,N3-hybrid complex, generated as a highly nucleophilic intermediate, undergoes C-Cl bond activation of the solvent. The complexation of AuCl(SMe2) with the sigma3-P,N2,X-hybrids (X = S, NH) leads to the formation of the corresponding Au(I)-monophosphine complexes. The spectral data and crystal structures of these metal complexes exhibit the hemilabile nature of the phosphole-containing hybrid calixphyrin platforms derived from the flexible phosphole unit and the redox active N-X-N units. The hybrid calixphyrin-palladium and -rhodium complexes catalyze the Heck reaction and hydrosilylations, respectively, implying that the metal center in the core is capable of activating the substrates under appropriate reaction conditions. The present results demonstrate the potential utility of the phosphole-containing hybrid calixphyrins as a new class of macrocyclic P,N2,X-mixed donor ligands for designing highly reactive transition-metal complexes.

Revealing substituent effects on the electronic structure and planarity of Ni-porphyrins

“…The most unusual and intriguing result of this substitution is strong deformation of the resulting NiP(P) 4 , which attains bowl-like shape, with the ${\text{C}}_{\text{m}}{-\text{Ni}-\text{C}}_{\text{m}}^{\prime }$ angles being about 21° smaller than in the parent NiP (see Tables 1 and 9). This is in line with the results obtained previously in theoretical [81,82,84–90] and experimental [82–90] studies of phosphaporphyrins [82–89], phosphacalixphyrins [83,85,89,90] and phosphacalixpyrroles [85] where deviations from planarity were found as well, although in our case they are much more pronounced. The Ni—P and P—C α bond distances are considerably longer than the Ni—N and N—C α bond distances, by ca.…”

“…In 2003 Delaere and Nguyen [81] reported the DFT study of the structural and optical properties of the P-porphyrins with one or two P-atoms. Matano, Nakabuchi, Imahori and co-workers [82–89] reported syntheses and characterization of various phosphaporphyrins [82–89], phosphacalixphyrins [83,85,89,90] and phosphacalixpyrroles [85] with only one pyrrole nitrogen replaced by P-atom. Several metal complexes were studied as well [82,87,90].…”

Protonation‐Induced Formation of a Stable Singlet Biradicaloid Derived from a Modified Sapphyrin Analogue

“…This result implies that the protonation crucially contributes to the formation of [1·3 H] 3+ ( Figure S13 in the Supporting Information). [21] Considering that expanded quinoidal oligothiophenes [15d,g] with terminal dicyanomethylene groups have singlet biradicaloid character in the ground state, it is reasonable to conclude that the p-conjugated form of [1·3 H] 3+ could be represented by the resonance of the closed-shell quinoid KekulØ structure and the biradicaloid form (Scheme S2 in the Supporting Information). The switchable tripyrrin subunit of [1·3 H] 3+ might be a thermodynamically more favorable singlet biradical form relative to the singlet KekulØ structure.…”

Phosphorus Heterocycles

“…Extensive 18p cyclic delocalization in these structures has been demonstrated by NMR and DFT calculations. The coordination chemistry of these new macrocycles has been studied extensively [242][243][244].…”