Group VIII Coordination Chemistry of a Pincer-Type Bis(8-quinolinyl)amido Ligand

This paper provides an entry point to the coordination chemistry of the group VIII chemistry of the bis(8-quinolinyl)amine (BQA) ligand. In this context, mono- and disubstituted BQA complexes of iron, ruthenium, and osmium are described. For example, the low-spin bis-ligated Fe(III) complex [Fe(BQA)2][BPh4] has been prepared via amine addition to FeCl3 in the presence of a base and NaBPh4. Complexes featuring a single BQA ligand are more readily prepared for Ru and Os. Auxiliary ligands featuring a single BQA ligand, along with two other L-type donor ligands, allow for a variety of ligand types to occupy a sixth coordination site. Representative examples include the halide and pseudohalide complexes trans-(BQA)MX(PPh3)2 (M = Ru, Os; X = Cl, Br, N3, OTf), as well as the hydride and alkyl complexes trans-(BQA)RuH(PMe3)2 and trans-(BQA)RuMe(PMe3)2. Electrochemical studies are discussed that help to contextualize the BQA ligand with respect to its neutral counterpart 2,2′,2′′-terpyridine (terpy) in terms of electron-releasing character. Bidentate ligands have been explored in conjunction with the BQA ligand. Thus, the bidentate, monoanionic aryl(8-quinolinyl)amido ligand 3,5-(CF3)2-(C6H3)QA has been installed onto the (BQA)Ru platform to provide (BQA)Ru(3,5-(CF3)2-(C6H3)QA)(PPh3). A bis(phosphino)borate ligand stabilizes the five-coordinate complex [Ph2B(CH2PPh2)2]Ru(BQA). Finally, access to dinitrogen complexes of the types [(BQA)Ru(N2)(PPh3)2][PF6], [(BQA)Ru(N2)(PMe3)2][PF6], and [(BQA)Os(N2)(PPh3)2][PF6] is provided by exposure of the sixth coordination site under a N2 atmosphere

Synthesis of the (Dialkylamino)borate, [Ph_2B(CH_2NMe_2)_2]-, Affords Access to N-Chelated Rhodium(I) Zwitterions

This paper reports the synthesis of the first bis(amino)borate ligand, [Ph_2B(CH_2NMe_2)_2]-, an anionic equivalent of tertiary diamines. Anionic [Ph_2B(CH_2NMe_2)_2] is an excellent bidentate ligand auxiliary and is used to prepare a series of N-chelated, zwitterionic rhodium(I) complexes

Dinitrogen Chemistry from Trigonally Coordinated Iron and Cobalt Platforms

This report establishes that trigonally coordinated “[PhBP^(iPr)_(3)]M” platforms (M = Fe, Co) will support both π-acidic (N_2) and π-basic (NR) ligands at a fourth binding site. The N_2 complexes of iron that are described are the first thoroughly characterized examples to exhibit a 4-coordinate geometry. Methylation of monomeric {Fe^(0)(N_(2))-} and {Co^(0)(N_(2))-} species successfully derivatizes the β-N atom of the coordinated N_(2) ligand and affords the diazenido products {Fe^(II)(N_(2)Me)} and {CoII(N2Me)}, respectively. One-electron oxidation of the mononuclear M^(0)(N_(2))- species produces dinuclear and synthetically versatile M^(I)(N_(2))M^(I) complexes. These latter species provide clean access to the chemistry of the “[PhBP^(iPr)_(3)]M^(I)” subunit. For example, addition of RN_(3) to M^(I)(N_(2))M^(I) results in oxidative nitrene transfer to generate [PhBP^(iPr)_(3)]M_(≡)NR with concomitant N_(2) release

Issues Relevant to C-H Activation at Platinum(II): Comparative Studies between Cationic, Zwitterionic, and Neutral Platinum(II) Compounds in Benzene Solution

Cationic late metal systems are being highly scrutinized due to their propensity to mediate so-called electrophilic C-H activation reactions. This contribution compares the reactivity of highly reactive cationic platinum(II) systems with structurally related but neutral species. Our experimental design exploits isostructural neutral and cationic complexes supported by bis(phosphine) ligands amenable to mechanistic examination in benzene solution. The data presented herein collectively suggests that neutral platinum complexes can be equally if not more reactive towards benzene than their cationic counter-parts. Moreover, a number of unexpected mechanistic distinctions between the two systems arise that help to explain their respective reactivity

Modulation of magnetic behavior via ligand-field effects in the trigonal clusters (PhL)Fe3L*3 (L* = thf, py, PMe2Ph)

Utilizing a hexadentate ligand platform, a series of trinuclear iron clusters (PhL)Fe3L*3 (PhLH6 1⁄4 MeC (CH2NPh-o-NPh)3; L* 1⁄4 tetrahydrofuran (1), pyridine (2), PMePh2 (3)) has been prepared. The phenyl substituents on the ligand sterically prohibit strong iron–iron bonding from occurring but maintain a sufficiently close proximity between iron centers to permit direct interactions. Coordination of the weak-field tetrahydrofuran ligand to the iron centers results in a well-isolated, high-spin S 1⁄4 6 or S 1⁄4 5 ground state, as ascertained through variable-temperature dc magnetic susceptibility and low- temperature magnetization measurements. Replacing the tetrahydrofuran ligands with stronger s-donating pyridine or tertiary phosphine ligands reduces the ground state to S 1⁄4 2 and gives rise to temperature-dependent magnetic susceptibility. In these cases, the magnetic susceptibility cannot be explained as arising simply from superexchange interactions between metal centers through the bridging amide ligands. Rather, the experimental data are best modelled by considering a thermally- induced variation in molecular spin state between S 1⁄4 2 and S 1⁄4 4. Fits to these data provide thermodynamic parameters of DH 1⁄4 406 cm 1 and Tc 1⁄4 187 K for 2 and DH 1⁄4 604 cm 1 and Tc 1⁄4 375 K for 3. The difference in these parameters is consistent with ligand field strength differences between pyridine and phosphine ligands. To rationalize the spin state variation across the series of clusters, we first propose a qualitative model of the Fe3 core electronic structure that considers direct Fe–Fe interactions, arising from direct orbital overlap. We then present a scenario, consistent with the observed magnetic behaviour, in which the s orbitals of the electronic structure are perturbed by substitution of the ancillary ligands.Chemistry and Chemical Biolog

Oxidative Group Transfer to Co(I) Affords a Terminal Co(III) Imido Complex

The synthesis of the first terminal imido complex of cobalt, [PhBP3]CoN-p-tolyl, is reported. Its synthesis proceeds by oxidative group transfer from cobalt(I) upon addition of tolyl azide at room temperature. This species and a related η1-diazoalkane adduct have been structurally characterized. The diamagnetic imido complex [PhBP3]CoN-p-tolyl reacts with CO to liberate isocyanate and the cobalt(I) dicarbonyl complex [PhBP_(3)]Co(CO)_(2)

Expanded redox accessibility via ligand substitution in an octahedral Fe6Br6 cluster

Oxidation of the nominally all-ferrous hexanuclear cluster (HL)2Fe6 with six equivalents of ferrocenium in the presence of bromide ions results in a six-electron oxidation of the Fe6 core to afford the nominally all-ferric cluster (HL)2Fe6Br6. The hexabromide cluster is also structurally characterized in a 4+ core oxidation state. A structural comparison of these two clusters provides an insight into the Fe6 core electronic structure.Chemistry and Chemical Biolog