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A series of diarylamido phosphine ligands of the type N-(2-dihydrocarbylphosphinophenyl)-2,6-dialkylanilide 1a-d have been prepared and employed to investigate the coordination chemistry of zinc. Protonolysis of ZnMe2 with one equivalent of N-(2-diphenylphosphinophenyl)-2,6-dimethylaniline (H[1a]) produced a mixture of [1a]ZnMe (2a) and Zn[1a]2 (4a), whereas that involving ZnEt2 gave exclusively the three-coordinate [1a]ZnEt (3a). In contrast, treatment of ZnR2 (R = Me, Et) with N-(2-diphenylphosphinophenyl)-2,6-diisopropylaniline (H[1b]), N-(2-diisopropylphosphinophenyl)-2,6-dimethylaniline (H[1c]), or N-(2-diisopropylphosphinophenyl)-2,6-diisopropylaniline (H[1d]) under similar conditions generated quantitatively the corresponding three-coordinate zinc methyl 2b-d and zinc ethyl 3b-d. The bis-ligand complexes 4a,b,d were isolated by either protonolysis of alkyls 2-3 with one equivalent of H[1] or metathesis of ZnX2 (X = Cl, OAc) with the corresponding lithium derivatives 5. Attempts to prepare [1a-d]ZnX (X = Cl, OAc) were not successful regardless of stoichiometry of the starting materials employed. Alcoholysis of zinc alkyls 2-3 led undesirably to protonation on the amido nitrogen donor of 1, highlighting perhaps its higher basicity than alkyls. The reaction of ZnCl2 with H[1c] generated the phosphorus-bound adduct {H[1c]ZnCl(mu-Cl)}2 (6c). Interestingly, attempts to deprotonate 6c with n-BuLi produced unexpectedly the alkylated product [1c]Zn(n-Bu) (7c) instead of [1c]ZnCl; analogous reactions employing NEt3 led to Lewis base substitution to give H[1c] and [ZnCl2(NEt3)]2. Structural characterization of all new compounds was achieved by multi-nuclear NMR spectroscopy (1H, 13C, 31P, and 7Li) and X-ray crystallography (2c-d, 3c, 4d, 5c-d, and 6c) where appropriate. On the basis of the NMR and X-ray data, in combination with the synthetic investigations, the steric nature of these amido phosphine ligands is recognized to follow the order of 1a < 1b < 1c < 1d. Interestingly, zinc alkyls 2-3 are all active initiators for catalytic ring-opening polymerization of ε-caprolactone whereas the bis-ligand complexes 4 are not.

Background: Recent advances in liquid chromatography-mass spectrometry (LC-MS) technology have led to more effective approaches for measuring changes in peptide/protein abundances in biological samples. Label-free LC-MS methods have been used for extraction of quantitative information and for detection of differentially abundant peptides/proteins. However, difference detection by analysis of data derived from label-free LC-MS methods requires various preprocessing steps including filtering, baseline correction, peak detection, alignment, and normalization. Although several specialized tools have been developed to analyze LC-MS data, determining the most appropriate computational pipeline remains challenging partly due to lack of established gold standards. Results: The work in this paper is an initial study to develop a simple model with "presence" or "absence" condition using spike-in experiments and to be able to identify these "true differences" using available software tools. In addition to the preprocessing pipelines, choosing appropriate statistical tests and determining critical values are important. We observe that individual statistical tests could lead to different results due to different assumptions and employed metrics. It is therefore preferable to incorporate several statistical tests for either exploration or confirmation purpose. Conclusions: The LC-MS data from our spike-in experiment can be used for developing and optimizing LC-MS data preprocessing algorithms and to evaluate workflows implemented in existing software tools. Our current work is a stepping stone towards optimizing LC-MS data acquisition and testing the accuracy and validity of computational tools for difference detection in future studies that will be focused on spiking peptides of diverse physicochemical properties in different concentrations to better represent biomarker discovery of differentially abundant peptides/proteins.

A series of divalent nickel complexes containing diarylamido phosphine ligands of the type (o-ArNC 6 H 4 PR 2 ) − (1a, Ar = 2,6-C 6 H 3 Me 2 , R = Ph; 1b, Ar = 2,6-C 6 H 3 iPr 2 , R = Ph; 1c, Ar = 2,6-C 6 H 3 Me 2 , R = iPr; 1d, Ar = 2,6-C 6 H 3 iPr 2 , R = iPr) have been prepared and structurally characterized. The dimeric nickel chloride derivatives {[1b−d]Ni(μ-Cl)} 2 (2b−d) were isolated as brick red microcrystals in high yields from the reactions of NiCl 2 (DME) with either Li[1b−d](solv) x or H[1b−d] in the presence of NEt 3 . Similar reactions employing [1a] − , however, generated homoleptic Ni[1a] 2 (3a) as paramagnetic, dark red prisms in high yield. Addition of trimethylphosphine to red solutions of 2b,c in THF at room temperature afforded emerald crystals of [1b,c]NiCl(PMe 3 ) (4b,c).Interestingly, solution NMR spectroscopic and X-ray crystallographic data of these PMe 3 adducts reveal the exclusive formation of cis-4b and trans-4c, as defined by the mutual orientation of the two phosphorus donors incorporated. Metathetical reactions of 4b,c with RMgCl (R = Me, CH 2 SiMe 3 , Ph) in THF at −35°C produced high yields of red or brownish red crystalline [1b,c]NiR(PMe 3 ) (R = Me (5b,c), CH 2 SiMe 3 (6b,c), Ph (7b,c)). Analogous reactions of 4c with EtMgCl or nBuMgCl, however, led instead to the isolation of the hydrido species [1c]NiH(PMe 3 ) (8c) in quantitative yield. Solution NMR data of the methyl complexes 5b,c indicate the presence of both cis and trans isomers; the major component of 5b is cis whereas that of 5c is trans. In contrast, complexes 6b,c, 7b,c, and 8c all exist exclusively in the trans form. The chloro complexes 2b−d are all active catalyst precursors for Kumada couplings under mild conditions. In particular, this catalysis is compatible with alkyl nucleophiles that contain β-hydrogen atoms, even in reactions with chlorobenzene. The X-ray structures of 2d, 3a, 4c, 5c, 6b,c, 7c, and 8c are presented.