In Silico Olefin Metathesis with Ru‐Based Catalysts Containing N‐Heterocyclic Carbenes Bearing C60 Fullerenes

Density functional theory calculations have been used to explore the potential of Ru‐based complexes with 1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene (SIMes) ligand backbone ( A ) being modified in silico by the insertion of a C₆₀ molecule ( B and C ), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A , B , and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron‐withdrawing N‐heterocyclic carbene improves the performance of unannulated complex A . The efficiency of complex B is only surpassed by complex A when the backbone of the N‐heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic‐donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A . Overall, this study indicates that such Ru‐based complexes B and C might have the potential to be effective olefin metathesis catalysts.     

A generalized complexity measure based on Rényi entropy

Phase drift is an inherent problem in one-way phase-encoded quantum key distribution (QKD) systems. Although combining passive with active phase compensation (APC) processes can effectively compensate for the phase drift, the security problems brought about by these processes are rarely considered. In this paper, we point out a security hole in the APC process and put forward a corresponding attack scheme. Under our proposed attack, the quantum bit error rate (QBER) of the QKD can be close to zero for some conditions. However, under the same conditions the ratio r of the key “0” and the key “1” which Bob (the legal communicators Alice and Bob) gets is no longer 1:1 but 2:1, which may expose Eve (the eavesdropper). In order to solve this problem, we modify the resend strategy of the attack scheme, which can force r to reach 1 and the QBER to be lower than the tolerable QBER.     

Cationic Platinum(II) σ‐SiH Complexes in Carbon Dioxide Hydrosilation

The low‐electron‐count cationic platinum complex [Pt(ItBu’)(ItBu)][BAr^F], 1 , interacts with primary and secondary silanes to form the corresponding σ‐SiH complexes. According to DFT calculations, the most stable coordination mode is the uncommon η¹‐SiH. The reaction of 1 with Et₂SiH₂ leads to the X‐ray structurally characterized 14‐electron Pt^II species [Pt(SiEt₂H)(ItBu)₂][BAr^F], 2 , which is stabilized by an agostic interaction. Complexes 1 , 2 , and the hydride [Pt(H)(ItBu)₂][BAr^F], 3 , catalyze the hydrosilation of CO₂, leading to the exclusive formation of the corresponding silyl formates at room temperature.     

The Challenge of Deciphering Linkage Isomers in Mixtures of Oligomeric Complexes Derived from 9‐Methyladenine and trans‐(NH3)2PtII Units

Metal coordination to N9‐substituted adenines, such as the model nucleobase 9‐methyladenine (9MeA), under neutral or weakly acidic pH conditions in water preferably occurs at N1 and/or N7. This leads, not only to mononuclear linkage isomers with N1 or N7 binding, but also to species that involve both N1 and N7 metal binding in the form of dinuclear or oligomeric species. Application of a trans‐(NH₃)₂Pt^II unit and restriction of metal coordination to the N1 and N7 sites and the size of the oligomer to four metal entities generates over 50 possible isomers, which display different feasible connectivities. Slowly interconverting rotamers are not included in this number. Based on ¹H NMR spectroscopic analysis, a qualitative assessment of the spectroscopic features of N1,N7‐bridged species was attempted. By studying the solution behavior of selected isolated and structurally characterized compounds, such as trans‐[PtCl(9MeA‐N7)(NH₃)₂]ClO₄ ? 2H₂O or trans,trans‐[{PtCl(NH₃)₂}₂(9MeA‐N1,N7)][ClO₄]₂ ? H₂O, and also by application of a 9MeA complex with an (NH₃)₃Pt^II entity at N7, [Pt(9MeA‐N7)(NH₃)₃][NO₃]₂, which blocks further cross‐link formation at the N7 site, basic NMR spectroscopic signatures of N1,N7‐bridged Pt^II complexes were identified. Among others, the trinuclear complex trans‐[Pt(NH₃)₂{μ‐(N1‐9MeA‐N7)Pt(NH₃)₃}₂][ClO₄]₆ ? 2H₂O was crystallized and its rotational isomerism in aqueous solution was studied by NMR spectroscopy and DFT calculations. Interestingly, simultaneous Pt^II coordination to N1 and N7 acidifies the exocyclic amino group of the two 9MeA ligands sufficiently to permit replacement of one proton each by a bridging heterometal ion, Hg^II or Cu^II, under mild conditions in water.