Aryl C(sp2)-X Coupling (X = C, N, O, Cl) and Facile Control of N-Mono- and N,N-Diarylation of Primary Alkylamines at a Pt(IV) Center

Photoinduced Reductive C-O Couplings from Unsymmetrical Bis-Cyclometalated Pt(IV) Dicarboxylato Complexes

Unsymmetrical bis-cyclometalated dicarboxylato complexes (OC-6-32)-[Pt(tpy)2(O2CR)2] [tpy = cyclometalated 2-(p-tolyl)pyridine, R = t-Bu (1), Me (2), Ph (3), CF3 (4)], are obtained from the reaction of cis-[Pt(tpy)2] with the appropriate PhI(O2CR)2 reagent. Treatment of complexes of this type with different carboxylates (R'CO2-) results in the formation of mixed-carboxylato derivatives, namely (OC-6-43)-[Pt(tpy)2(O2CMe)(O2CR')] [R' = t-Bu (5), CF3 (6), Ph (7)], (OC-6-34)-[Pt(tpy)2(O2CCF3)(O2CR')] [R' = t-Bu (8), Me (9), Ph (10)], and (OC-6-34)-[Pt(tpy)2(O2C-t-Bu)(O2CMe)] (11). Irradiation of 1-3 and 5-11 with UV light (365 nm) in MeCN gives 5-methyl-2-(2-pyridyl)phenyl pivalate (12), 5-methyl-2-(2-pyridyl)phenyl acetate (13) or 5-methyl-2-(2-pyridyl)phenyl benzoate (14) as the major photoproduct from most complexes, resulting from a reductive C-O coupling between a tpy ligand and a carboxylato ligand. Cyclometalation of 12-14 at the ensuing Pt(II) species to produce cis-[Pt(tpy)(tpyO2CR/R')], reduction to cis-[Pt(tpy)2] and isomerization to (OC-6-33)-[Pt(tpy)2(O2CR/R')2] are identified as secondary processes in most cases. In contrast, complex 4 exclusively photoisomerizes to (OC-6-33)-[Pt(tpy)2(O2CCF3)2] (4'). The C-O couplings are favored for the most electron-rich carboxylato ligands and occur predominantly from the carboxylato trans to N. Consistent with this, a computational study reveals that the lowest singlet and triplet LMCT excited states result from electronic transitions to a dσ* orbital distributed along the N-Pt-O axis, which would trigger the observed processes.

Quantum chemical package Jaguar: A survey of recent developments and unique features

This paper is dedicated to the quantum chemical package Jaguar, which is commercial software developed and distributed by Schrödinger, Inc. We discuss Jaguar's scientific features that are relevant to chemical research as well as describe those aspects of the program that are pertinent to the user interface, the organization of the computer code, and its maintenance and testing. Among the scientific topics that feature prominently in this paper are the quantum chemical methods grounded in the pseudospectral approach. A number of multistep workflows dependent on Jaguar are covered: prediction of protonation equilibria in aqueous solutions (particularly calculations of tautomeric stability and pKa), reactivity predictions based on automated transition state search, assembly of Boltzmann-averaged spectra such as vibrational and electronic circular dichroism, as well as nuclear magnetic resonance. Discussed also are quantum chemical calculations that are oriented toward materials science applications, in particular, prediction of properties of optoelectronic materials and organic semiconductors, and molecular catalyst design. The topic of treatment of conformations inevitably comes up in real world research projects and is considered as part of all the workflows mentioned above. In addition, we examine the role of machine learning methods in quantum chemical calculations performed by Jaguar, from auxiliary functions that return the approximate calculation runtime in a user interface, to prediction of actual molecular properties. The current work is second in a series of reviews of Jaguar, the first having been published more than ten years ago. Thus, this paper serves as a rare milestone on the path that is being traversed by Jaguar's development in more than thirty years of its existence.

Organometallic Oxidative Addition Complexes for S-Arylation of Free Cysteines

Development of bioconjugation strategies to efficiently modify biomolecules is of key importance for fundamental and translational scientific studies. Cysteine S-arylation is an approach which is becoming more popular due to generally rapid kinetics and high chemoselectivity, as well as the strong covalently bonded S-aryl linkage created in these processes. Organometallic approaches to cysteine S-arylation have been explored that feature many advantages compared to their more traditional organic counterparts. In this Viewpoint, progress in the use of Au(III) and Pd(II) oxidative addition (OA) complexes for stoichiometric cysteine S-arylation is presented and discussed. A focus is placed on understanding the rapid kinetics of these reactions under mild conditions, as well as the ability to generate biomolecular heterostructures. Potential avenues for further exploration are addressed and usefulness of these methods to the practitioner are emphasized in the discussion.

High Selectivity in Csp2-Csp2 versus Csp3-O Reductive Elimination from Cycloplatinated(IV) Complexes

The cycloplatinated(IV) complexes trans-[Pt(p-MeC6H4)(C∧N)(OAc)2(H2O)] (C∧N = benzo[h]quinolate, bhq, 2a, and 2-phenylpyridinate, ppy, 2b) were prepared by reacting the corresponding [Pt(p-MeC6H4)(C∧N)(SMe2)] precursors with PhI(OAc)2 through an oxidative addition (OA) reaction. Thermolysis of 2a at 65 °C generates cis-[Pt(κ1N-10-(p-MeC6H4)-bhq)(OAc)2(H2O)], 3a, which is the product of a Csp2Ar-Csp2bhq reductive elimination (RE). The observed coupling reaction is significantly different from the previously reported analogous thermolysis of trans-[PtMe(C∧N)(OAc)2(H2O)] (C∧N = bhq, 2c, and ppy, 2d) that selectively releases Me-OAc (C-O RE). The density functional theory (DFT) calculations and experimental observations reveal that the Csp2Ar-Csp2bhq coupling reaction occurs through the dissociation of a coordinated water ligand. This in turn is followed by the concomitant bond forming and bond breaking process via a three-center ring transition state, in contrast to the Csp3Me-OAc coupling, which had taken place by an outer sphere SN2 type RE reaction in methyl complexes.

Photoinduced Reductive C-C and C-Heteroatom Couplings from Bis-cyclometalated Pt(IV) Alkynyl Complexes

Unsymmetrical dicarboxylato complexes [Pt(tpy)2(O2CR)2] [tpy = cyclometalated 2-(p-tolyl)pyridine, R = Me, CF3] react with the terminal alkynes 4-methoxyphenylacetylene, phenylacetylene, 4-(trifluoromethyl)phenylacetylene or 3,5-difluorophenylacetylene in the presence of a base to produce complexes mer-[Pt(tpy)2(O2CR)(CCAr)], in which the metalated carbon atoms are in a meridional arrangement. Irradiation of the trifluoroacetato derivatives with a 365 nm LED source leads to isomerization to the facial complexes, which can be converted to chlorido derivatives upon reaction with NH4Cl. In contrast, irradiation of the acetato derivatives leads to four different processes, namely, reduction to cis-[Pt(tpy)2], annulations involving one of the tpy ligands and the Cα and Cβ atoms of the alkynyl to give benzoquinolizinium derivatives, isomerization to the facial geometry, or C-O couplings between the acetato ligand and one tpy. The first two processes are favored by the presence of electron-donating groups on the alkynyl, whereas electron-withdrawing groups favor the last two. Irradiation of complexes fac-[Pt(tpy)2(O2CCF3)(CCAr)] with a medium-pressure Hg UV lamp leads to a reductive C-C coupling involving the alkynyl Cα atom and one of the tpy ligands to give pyridoisoindolium derivatives, except for the methoxyphenylacetylide derivative, which is photostable. On the basis of TDDFT calculations, the photoreactivity of the mer complexes is attributed to 3LLCT [π(alkynyl) → π*(tpy)] excited states for annulations or 3LMCT [π(alkynyl) → dσ*] excited states for the rest of the processes, which are accessible through thermal population from 3LC(tpy) states. The C-C couplings from the fac complexes are attributed to photoreactive pentacoordinate intermediates.

Selective Stepwise Arylation of Unprotected Peptides by PtIV Complexes

LPtIV F(Aryl) complexes bearing a bulky bidentate 2-[bis(adamant-1-yl)phosphino]phenoxide ligand (L) demonstrate excellent reactivity and selectivity in the arylation of X-H (X=S, N) bonds of amino acid residues in unprotected peptides under mild, including aqueous, conditions. Stepwise addition of these complexes allowed a convenient one-pot introduction of different aromatic groups in the X-H bonds of Cys and N terminus. PtIV reagents can also be used to further arylate N-H bonds in Lys and Trp providing access to peptides bearing multiple aromatic groups.