Asymptotic Behaviour of Convolution Semigroups

In this paper, necessary and sufficient conditions are given for U * μ^*n to converge uniformly on the real axis; here $\mu$ is a nonsingular probability measure on ℝ, and U is a Banach space valued L^∞-function. A connection to uniform convergence of Cesaro mean values is shown. By applying the results to extended orbits of bounded C_0-semigroups on a Banach space X one can relate both kernel and range of the respective generator with those of the derivative operator on L^∞(X). Ergodic theorems and consequences for subordinated semigroups, in particular for holomorphic semigroups, are deduced.     

Redox chemistry of the triplet complex (PNP)Co(I)

Reaction of PNPCo, where PNP is (tBu2PCH2SiMe2)2N-, with the persistent radical galvinoxyl, G, gives PNPCoIIG, a nonplanar S = 3/2 species. Reaction with PhCH2Cl or with 0.5 mol I2 gives PNPCoX (X = Cl or I, respectively), but additional I2, seeking CoIII, gives instead oxidation at phosphorus: (tBu2P(I)CH2SiMe2NSiMe2CH2PtBu2)CoI2. Hydrogen-atom transfer reagents fail to give PNPCoH, but H2 gives instead PNPCo(H)2, a result rationalized thermodynamically based on DFT calculations. Multiple equiv of PhSiH3 give a product of Co(V), where N/SiPh and P/Si bonds have formed. N2CH(SiMe3) gives a 1:1 adduct of PNPCo, whose metric parameters suggest partial oxidation above CoI; N2CHPh gives a 1:1 adduct but with very different spectroscopic features. PhN3 reacts fast, via several intermediates detected below 0 degrees C, to finally release N2 and form a CoI product where one phosphorus has been oxidized, PN(P=NPh)Co. Whereas PNPCo(N3) resists loss of N2 on heating, one electron oxidation gives a rapid loss of N2, and the remaining nitride nitrogen is quickly incorporated into the chelate ligand, giving [tBu2PCH2SiMe2NSiMe2NP(tBu2)=CH2Co]. O2 or PhI=O generally gives products where one or both phosphorus centers are converted to its oxide, bonded to cobalt.     

Solution,Crystal and in Silico Structures of the Organometallic Vitamin B12-Derivative Acetylcobalamin and of its Novel Rhodium-Analogue Acetylrhodibalamin

The natural vitamin B₁₂-derivatives are intriguing complexes of cobalt that entrap the metal within the strikingly skewed and ring-contracted corrin ligand. Here, we describe the synthesis of the Rh(III)-corrin acetylrhodibalamin ( AcRhbl ) from biotechnologically produced metal-free hydrogenobyric acid and analyze the effect of the replacement of the cobalt-center of the organometallic vitamin B₁₂-derivative acetylcobalamin ( AcCbl ) with its group-IX homologue rhodium, to give AcRhbl . The structures of AcCbl and AcRhbl were thoroughly analyzed in aqueous solution, in crystals and by in silico methods, in order to gain detailed insights into the structural adaptations to the two homologous metals. Indeed, the common, nucleotide-appended corrin-ligand in these two metal corrins features extensive structural similarity. Thus, the rhodium-corrin AcRhbl joins the small group of B₁₂-mimics classified as ‘antivitamins B₁₂’, isostructural metal analogues of the natural cobalt-corrins that hold significant potential in biological and biomedical applications as selective inhibitors of key cellular processes.     

Energy Transport in Dichroic Metallo-organic Crystals: Selective Inclusion of Spatially Resolved Arrays of Donor and Acceptor Dyes in Different Nanochannels**

In this study, the precise positioning and alignment of arrays of two different guest molecules in a crystalline host matrix has been engineered and resulted in new optically active materials. Sub-nm differences in the diameters of two types of 1D channels are sufficient for size-selective inclusion of dyes. Energy transport occurs between the arrays of different dyes that are included in parallel-positioned nanochannels by Förster resonance energy transfer (FRET). The color of individual micro-sized crystals are dependent on their relative position under polarized light. This angular-dependent behavior is a result of the geometrically constrained orientation of the dyes by the crystallographic packing of the host matrix and is concentration dependent.     

Influence of the metal orbital occupancy and principal quantum number on organoazide (RN3) conversion to transition-metal imide complexes

The reaction of phenyl azide with (PNP)Ni, where PNP = ( (t)Bu 2PCH 2SiMe 2) 2N (-), promptly evolves N 2 and forms a P=N bond in the product (PNP=NPh)Ni (I). A similar reaction with (PNP)FeCl proceeds to form a P=N bond but without N 2 evolution, to furnish (PNP=N-N=NPh)FeCl. An analogous reaction with (PNP)RuCl occurs with a more dramatic redox change at the metal (and N 2 evolution), to give the salt composed of (PNP)Ru(NPh) (+) and (PNP)RuCl 3 (-), together with equimolar (PNP)Ru(NPh). The contrast among these results is used to deduce what conditions favor N 2 loss and oxidative incorporation of the NPh fragment from PhN 3 into a metal complex.     

P=N bond formation via incomplete N-atom transfer from a ferrous amide precursor

Incomplete N-atom transfer from Fe to P is observed when the ferrous amide complex (PNP)Fe(dbabh) (PNP-=N[2-P(iPr)2-4-methylphenyl]2, dbabh=2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene), prepared from salt metathesis of (PNP)FeCl and Li(dbabh), is thermolyzed at 70 degrees C over 48 h in C6D6. Several plausible reaction pathways resulting from the transformation of (PNP)Fe(dbabh) are discussed, including the possibility of an Fe(IV) nitride as an intermediate.     

Nitrogen-ligated iron complexes: photolytic approach to the FeN+ moiety

The synthesis of (PNP)FeCl, (PNP)Fe[NH(xylyl)], and (PNP)FeN3 are reported(PNP = (tBu2PCH2SiMe2)2N-). While the azide is thermally stable, it is photosensitive to lose N2 and form [(PNPN)Fe]2,in which the nitride ligand has formed a double bond to one phosphorus, and this N bridges to a second iron to form a 2-fold symmetric dimer. The reaction energy to form the (undetected) monomeric [eta3- tBu2PCH2SiMe2NSiMe2CH2PtBu2N]Fe is -15.9 kcal/mol, so this PIII --> PV oxidation is favorable. The eta2 version of this same species is less stable by 23.7 kcal/mol, which shows that the loss of one P--> Fe bond is caused by dimerization, and therefore, it does not precede and cause dimerization. A comparison is made to Ru analogs.     

Influence of the d-Electron Count on CO binding by three-coordinate [(tBu2PCH2SiMe2)2N]Fe, -Co, and -Ni

Reduction of (PNP)MCl [PNP = ((t)Bu(2)PCH(2)SiMe(2))(2)N] with Mg gives three-coordinate, T-shaped (PNP)M for M = Fe(S = 3/2) and Ni. Their reactivity was tested toward CO; Ni binds one CO, but only reversibly (i.e., CO is completely lost in vacuum), and has a CO stretching frequency showing effective back-donation by NiI. The structure of (PNP)Ni(CO) is intermediate between planar and tetrahedral, in contrast to the planar d8 analogue, (PNP)Co(CO). This structural reorganization on carbonylation changes the singly occupied molecular orbital from having negligible phosphorus character [no P hyperfine structure in the electron paramagnetic resonance (EPR) spectrum of (PNP)Ni] to having enough P character to have a triplet structure in the EPR spectrum of the CO. The presence of one fewer electron in (PNP)Fe (vs the Co analogue) leads to binding of two CO, and (PNP)Fe(CO)(2) is characterized as a spin doublet with square-pyramidal structure. Density functional theory calculations strengthen the understanding of the structural and spectroscopic changes along this dn series (n = 7-9).