Isomer Dependence in the Assembly and Lability of Silver(I) Trifluoromethanesulfonate Complexes of the Heteroditopic Ligands, 2-, 3-, and 4-[Di(1\u3cem\u3eH\u3c/em\u3e-pyrazolyl)methyl]phenyl(di-\u3cem\u3ep\u3c/em\u3e-tolyl)phosphine

Three isomers of a new heteroditopic ligand that contains a di(1H-pyrazolyl)methyl (−CHpz2) moiety connected to a di(p-tolyl)phosphine group via a para-, meta-, or ortho-phenylene spacer (pL, mL, and oL, respectively) have been synthesized by using a palladium(0)-catalyzed coupling reaction between HP(p-tolyl)2 and the appropriate isomer of (IC6H4)CHpz2. The 1:1 complexes of silver(I) trifluoromethanesulfonate, Ag(OTf), were prepared to examine the nature of ligand coordination and the type of supramolecular isomer (monomeric, cyclic oligomeric, or polymeric) that would be obtained. The single crystal X-ray diffraction studies showed that [Ag(pL)](OTf), 1, and [Ag(mL)](OTf), 2, possessed cyclic dimeric dications, whereas [Ag(oL)](OTf), 3, was a coordination polymer. The polymeric chain in 3 could be disrupted by reaction with triphenylphosphine, and the resulting complex, [Ag(oL)(PPh3)](OTf), 4, possessed a monometallic cation where the ligand was bound to silver in a chelating κ2P,N- coordination mode. The solution structures of 1–4 were probed via a combination of IR, variable-temperature multinuclear (1H, 13C, 31P) NMR spectroscopy, as well as by electron spray ionization (ESI)(+) mass spectrometry. A related complex [Ag(m-IC6H4CHpz2)2](OTf), 5, was also prepared, and its solid-state and solution spectroscopic properties were studied for comparison purposes. These studies suggest that the cyclic structures of 1 and 2 are likely preserved but are dynamic in solution at room temperature. Moreover, both 3 and 4 have dynamic solution structures where 3 is likely extensively dissociated in CH3CN or acetone rather than being polymeric as in the solid state

The Electronic Properties of Ni(PNN) Pincer Complexes Modulate Activity in Catalytic Hydrodehalogenation Reactions

Three chloronickel(II) complexes of PNN‐ pincer ligands with pyrazolyl and diphenylphosphino donors appended to different arms of diarylamido anchors were prepared and fully characterized. The three derivatives (1‐OMe, 1‐Me, 1‐CF3) differ only by the identity of the para‐aryl substituent on the pyrazolyl arm with 1‐OMe being 310 mV easier to oxidize than 1‐CF3. All three complexes are competent catalysts for hydrodehalogenation reactions of 1‐bromooctane and a variety of aryl halides in dimethylacetamide using NaBH4 as both base and hydride source. Comparative studies using diverse substrates showed that catalytic activity correlates with electron donor properties; 1‐OMe was superior to the other two. Deuterium labeling studies verified NaBD4 as the deuteride source and excluded solvent‐assisted radical pathways

Accessing Spin-Crossover Behaviour In Iron(II) Complexes Of N-Confused Scorpionate Ligands

The first examples of a class of N-confused tris(pyrazolyl)methane ‘scorpionate’ ligands have been prepared. The magnetic properties of their iron(II) tetrafluoroborate complexes are dictated by changing one substituent per ligand rather than three as is typical for normal scorpionate ligands

Reaction Chemistry of Silver(I) Trifluoromethanesulfonate Complexes of Nitrogen-Confused \u3cem\u3eC\u3c/em\u3e-Scorpionates

Two new C-scorpionate ligands with a bis(3,5-dimethylpyrazol-1-yl)methyl group bound to the 3 position of either an N-tosyl (TsL*) or an N–H pyrazole (HL*) ring have been prepared. The silver(I) complexes of these new ligands and the two previously reported analogous ligands with unsubstituted bis(pyrazol-1-yl)methyl groups (TsL and HL) in both 1:1 and 2:1 ligand/metal ratios were investigated to explore the effects of ligand sterics on their physical and chemical properties. The structurally characterized derivatives of the type [Ag(L)2](OTf) are four-coordinate, where the confused pyrazolyl is not bound to the metal. On the other hand, three 1:1 complexes [Ag(L)](OTf) had all pyrazolyls bound, while the μ–κ1,κ1-TsL derivative had an unbound confused pyrazolyl. The molecularity of the latter four ranged from polymeric to dimeric to monomeric in the solid with increasing steric bulk of the ligand. The utility of these complexes in stoichiometric ligand-transfer reactions and in styrene aziridination was demonstrated. Thus, tricarbonylmanganese(I) complexes were prepared as kinetically inert models for comparative solution diffusion NMR studies. Also, [Fe(HL)2](OTf)2 was prepared for similar reasons and to compare the effects of anion on spin-crossover properties

A Thallium Mediated Route to \u3cem\u3eσ\u3c/em\u3e-Arylalkynyl Complexes of Bipyridyltricarbonylrhenium(I)

A simple, one-pot preparation of rhenium(I) σ-arylalkynyl complexes is reported using thallium(I) hexafluorophosphate as a halogen abstraction agent. This new route to rhenium σ-alkynyls enjoys higher yields compared to analogous preparations using silver salts by eliminating potential electrochemical degradation pathways

Toward Charge-neutral ‘soft scorpionates’: Coordination Chemistry and Lewis Acid Promoted Isomerization of tris(1-organo-imidazol-2-ylthio)methanes

Two tris(1-organo-imidazol-2-ylthio)methanes, HC(S-timR)3 (R = organo = methyl, tert-butyl), have been prepared by a triphasic reaction between chloroform, the appropriate heterocycle, and saturated aqueous solutions of Na2CO3, in the presence of a phase transfer agent, (NBu4)(Br). These ligands have been characterized both spectroscopically and by single crystal X-ray diffraction. The reaction chemistry of these potentially N,N,N-tripodal ligands with AgBF4 was also explored where simple 1:1 coordination complexes could be isolated from reactions performed in THF solution at room temperature. The derivative {Ag[HC(S-timMe)3]}(BF4) was structurally characterized which showed that the ligand binds in a μ–κ2N,κ1N-mode to give a coordination polymer with an interesting layered supramolecular structure. Surprisingly, heating CH3CN solutions of the silver complexes at reflux resulted in decomposition of the complex and concomitant isomerization of the ligands to give metal-free tris(3-organo-1-imidazole-2-thione)methane, HC(N-imtR)3; the heretofore elusive charge-neutral analogues of the well-studied ‘soft scorpionate’ TmR− anions. The solution isomerization of HC(S-timR)3 to HC(N-imtR)3 was found to be general, occurring in a variety of solvents with any of a host of different Lewis acids [para-toluenesulfonic acid, KPF6, and M(CO)5Br (M = Mn, Re)] but did not occur by heating in the absence of Lewis acid. The compound HC(N-imtMe)3 exhibited unusually low solubility in common organic solvents. Single crystal X-ray diffraction of HC(N-imtMe)3 revealed a remarkable honeycomb supramolecular structure with ca. 5 Å channels filled with solvent. The robust nature of this solid is a result of strong dipolar stacking interactions of molecules into polymer chains bolstered by concerted π–π and CH–π interactions involving the heterocycles, holding the chains together in the remaining two dimensions

Using Sterics to Promote Reactivity in \u3cem\u3efac\u3c/em\u3e-Re(CO)\u3csub\u3e3\u3c/sub\u3e Complexes of Some ‘Non-Innocent’ NNN-Pincer Ligands

Two new redox active ligands based on di(2-(3-organopyrazolyl)-p-tolyl)amine have been prepared in order to investigate potential effects of steric bulk on the structures, electronic properties, or reactivity of tricarbonylrhenium(I) complexes. Replacing the hydrogens at the 3-pyrazolyl positions with alkyl groups causes significant distortion to the ligand framework due to potential interactions between these groups when bound to a fac-Re(CO)3 moiety. The distortions effectively increase the nucleophilic character of the central amino nitrogen and ligand-centered reactivity of the metal complexes

Janus Scorpionates: Supramolecular Tectons for the Directed Assembly of Hard−Soft Alkali Metallopolymer Chains

A new scorpionate ligand [HB(mtda)3-] containing mercaptothiadiazolyl (mtda) heterocyclic rings with both hard nitrogen donors and soft sulfur donors has been prepared. This new ligand, the Janus scorpionate, is a hybrid of a tris(pyrazolyl)borate and a tris(mercaptoimidazolyl)borate. The differential hard/soft character of the dissimilar donor groups in this bridging ligand was exploited for the controlled solid-state organization of homometallic and heterometallic alkali metal coordination polymers. Remarkably, in the case of sodium, coordination polymers with both acentric (with NaS3N3H kernels) and centric (with alternating NaN6 and NaS6H2 kernels) chains are found in the same crystal (where the centricity is defined by the relative orientations of the B−H bonds of the ligands along the lattice). For the homometallic potassium congener, the larger cation size, compared to sodium, induced significant distortions and favored a polar arrangement of ligands in the resulting coordination polymer chain. An examination of the solid-state structure of the mixed alkali metal salt system revealed that synergistic binding of smaller sodium cations to the nitrogen portion and of the larger potassium cations to the sulfur portion of the ligand minimizes the ligand distortions relative to the homometallic coordination polymer counterparts, a design feature of the ligand that likely assists in thermodynamically driving the self-assembly of the heterometallic chains. The effect of alkali metal complexation on the solution properties of the ligand was studied by comparing NMR chemical shifts, B−H stretching frequencies, and electrochemical properties with those of the noncoordinating tetrabutylammonium salt of the scorpionate. The similarity of these data regardless of cation indicates that the salts are likely dissociated in solution rather than maintaining their solid-state polymeric structures. This data is augmented by the ESI(±) mass spectral data for a series of mixed alkali metal tris(mercaptothiadiazolyl)borates that also indicate that dissociation occurs in solution

Chemical Switching Behaviour of Tricarbonylrhenium(I) Complexes of a New Redox Active ‘Pincer’ Ligand

The structures and optoelectronic properties of tricarbonylrhenium(I) complexes of di(2-pyrazolyl-p-tolyl)amine in its neutral and deprotonated (uninegative amido) form were investigated. Reactions of the complexes with Brønsted acids or bases result in distinctive changes of colour and electrochemical activity owing to the non-innocent nature of the ligand

Manipulating Self-Assembly in Silver(I) Complexes of 1,3-Di-\u3cem\u3eN\u3c/em\u3e-pyrazolylorganyls

Three di-N-pyrazolylorganyls with different conformational flexibilities in the three-atom organyl spacers have been prepared, and the self-assembly properties with AgBF4 have been studied both in solution and in the solid state. All ligands give low-coordinate silver(I) centers that are capable of participating in multiple noncovalent interactions, but only the rigid 1,8-dipyrazolylnaphthalene ligand promotes very short Ag−Ag contacts