New tricyclic hexacoordinated phosphoranes 1-6 with internal NfP coordination containing ring sizes varying from five to eight membered have been synthesized by oxidative addition of a quinone or a diol to a cyclic phosphite.

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Zirconium tetrachloride reacted with C2H4(Ph2P=NSiMe3)2-1,2 1 under C–H activation to give the NCN chelate complex ZrCl3{?3-N,C,N'-C2H3(Ph2P=NSiMe3)2}, while the reaction with C5H3N(Ph2P=NSiMe3)2-2,6 gave an N-donor adduct. Cp*TiCl3 reacts with trimethylsilyliminophosphines under dehalosilylation in all cases. In contrast to 1, the potentially C–N chelating benzylphosphinimine (4-ButC6H4CH2)Ph2P=NSiMe3 undergoes dehalosilylation with TiCl4 in preference to C–H activation, while prolonged reflux with ZrCl4 affords the salt [4-ButC6H4CH2P(Ph)2NHSiMe3]2[Zr2Cl10]. The molecular structures of the latter, ZrCl3{C2H3(Ph2PNSiMe3)2}, C5H3N(Ph2P=NTiCl2Cp*)2-2,6, and TiCl2Cp*{N=PPh2CH2C6H4But-4} have been determined by X-ray diffraction

Metalation of the bulky phosphinimine 4-MeC 6 H 4 CH(SiMe 3 )P(Ph) 2 dNSiMe 3 (1) with n-butyllithium followed by recrystallization from benzene affords [Li{4-MeC 6 H 4 C(SiMe 3 )P-(Ph) 2 dNSiMe 3 }] 2 (3), while Li(THF) 2 {4-MeC 6 H 4 C(SiMe 3 )P(Ph) 2 dNSiMe 3 } (2) is formed in the presence of THF. Similarly, treatment of the N-mesityl compound 4-Bu t C 6 H 4 CH(SiMe 3 )P-(Ph) 2 dNC 6 H 2 Me 3 -2,4,6 (4) with Bu n Li in the presence of THF produced Li(THF) 2 {4-Bu t C 6 H 4 C-(SiMe 3 )P(Ph) 2 dNC 6 H 2 Me 3 -2,4,6} (5), while lithiation of the new phosphorus ylid 4-Bu t C 6 H 4 -CH 2 P(Ph) 2 {dC(SiMe 3 )C 6 H 4 Bu t -4} (6) afforded Li(THF) 2 {4-Bu t C 6 H 4 CHP(Ph) 2 C(SiMe 3 )C 6 H 4 -Bu t -4} (7). The solid-state structures of 2, 3, 5, and 7 were determined. Whereas the anion in 2 acts simply as a C-N chelate, the MeC 6 H 4 moieties in the dimeric compound 3 are η 6 -bonded. On the other hand, compound 5 contains an aryl substituent that is η 1 -coordinated to Li + via its ipso-carbon, while the ylid anion 7 displays an unusual η 1 -coordination to one ortho-C atom of a strongly tilted arene ring. The results demonstrate the surprisingly variable coordination behavior of aryl-substituted [CPN]and [CPC]anions and the importance of aryl substituents in stabilizing electron-deficient metal centers.

Aminophosphoranes 2 and 4-9 with a cyclohexylamino substituent and ring sizes varying from five to eight have been synthesized by oxidative addition reactions of cyclic aminophosphites with diols or 1,2-diketones. The reactivities of these phosphoranes are compared with those of the corresponding cyclic aminophosphites. The difference in hydrolytic pathways between amino- and analogous phenoxyphosphoranes is discussed. X-ray structures of two sets of compounds, (a) (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O) (1) and (C(6)H(11)NH)P(OCH(2)CMe(2)CH(2)O)(1,2-O(2)C(6)Cl(4)) (2) and (b) (C(6)H(11)NH)P{O-(t-Bu)(2)C(6)H(2))(2)CH(2)} (3) and (C(6)H(11)NH)P{(O-(t-Bu)(2)C(6)H(2))(2)CH(2)}(1,2-O(2)C(6)H(4)).(1)/(2)Et(2)O (4.(1)/(2)Et(2)O) have been determined and geometrical parameters compared between the P(III) and the corresponding P(V) compounds. In 1, the six-membered ring has a chair conformation with the amino group axial; in 2, the six-membered ring is located apical-equatorial in a trigonal bipyramidal geometry and has a boat conformation. The eight-membered ring has a boat-chair conformation in 3, whereas the same ring has a tub conformation in 4.

The highly contagious nature of Covid-19 attracted us to this challenging area of research, mainly because the disease is spreading very fast and until now, no effective method of a safe treatment or a vaccine is developed. A library of novel 1,2,3-triazoles based 1,2,4-triazole, 1,3,4-oxadiazole and/or 1,3,4-thiadiazole scaffolds were designed and successfully synthesized. Different spectroscopic tools efficiently characterized all the newly synthesized hybrid molecules. An interesting finding is that some of the newly designed compounds revealed two isomeric forms. The ratio is affected by the size of the attached group as well as the type of the heteroatom forming the side ring attached to the central 1,2,3-triazole ring. The experimental spectroscopic data is in agreement with the DFT calculations at B3LYP 6-31G (d,p) with regard to the geometrical conformation of the prepared compounds. The DFT results revealed that the stability of one isomeric form over the other in the range of 0.057-0.161 Kcal mol À 1 . A docking study was performed using PyRx and AutoDockVina to investigate the activity of the prepared 1,2,3-triazoles as antiviral agents. Bond affinity scores of the 1,2,3-triazole derivatives were detected in the range of À 6.0 to À 8.8 kcal/ mol showing binding to the active sites of the 6LU7 protease and hence could be anticipated to inhibit the activity of the enzyme. Verification of the docking results was performed using the M pro alignment of coronaviruses substrate-binding pockets of COVID-19 against the ligands. As per these results, it can be proposed that the title hybrid molecules are acceptable candidates against COVID-19 for possible medicinal agents.

Treatment of the N-P ligand ArPN(SiMe3)2 with TiCl4 affords the imido-bridged binuclear titanium complex [TiCl2(THF)(micro-NArP)]2 (ArP = m-C6H4PR2) which reacts with Ni(0) or Pd(ii) to give heterotrinuclear compounds, while activation with methylaluminoxane generates a new type of imido-based ethene polymerisation catalyst that is tolerant of -PR2 functional groups.

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