Coordinatively Unsaturated Ruthenium Phosphine Half-Sandwich Complexes: Correlations to Structure and Reactivity

Stereoretentive Ligand Exchange Reactions of N-Fused Porphyrin Ruthenium(II) Complexes

The ligand exchange reactions of the ruthenium(II) complex of N-fused tetraphenylporphyrin, Ru(NFp)(CO)₂Cl (2), with various anions were investigated. The chloride ligand of the isomers 2a-c was stereoretentively exchanged with bromide (Br^-), iodide (I^-), and acetate (AcO^-) anions in toluene at 100 °C, structures of which were confirmed by ¹H NMR as well as single crystal X-ray diffraction analysis. The silver (AgOAc, AgOTf) and boron (NaBPh₄) reagents also afforded the corresponding stereoretentive products. On the other hand, the reaction with NaBH₄ afforded the hydride complex Ru(NFp)(CO)₂H (7) with low stereospecificity, showing a higher reactivity of 2c than other isomers. The ligand dissociation mechanism was proposed with the help of theoretical calculations on the plausible five-coordinated intermediates.

Ruthenium-catalyzed nucleophilic fluorination of halobenzenes

The first π-coordination-catalyzed nucleophilic fluorination of unactivated aryl halides has been demonstrated. Chlorobenzene reacts with alkali metal fluorides (CsF, KF) in the presence of a Cp*Ru catalyst at 120-180 °C to give fluorobenzene.

Selective ruthenium-catalyzed hydrochlorination of alkynes: one-step synthesis of vinylchlorides

An unprecedented ruthenium-catalyzed direct and selective alkyne hydrochlorination is reported and leads to vinylchlorides in excellent yields with atom economy. The reaction proceeds at room temperature from terminal alkynes and provides a variety of chloroalkenes. Only the regioisomer resulting from the formal Markovnikov addition is selectively formed. Mechanistic studies show the stereoselective syn addition of HCl to alkynes at room temperature and suggest a chloro hydrido Ru(IV) species as a key intermediate of the reaction.

16-Electron pentadienyl- and cyclopentadienyl-ruthenium half-sandwich complexes with bis(imidazol-2-imine) ligands and their use in catalytic transfer hydrogenation

Ligand exchange from “protonated open ruthenocene” afforded 16-electron ruthenium half-sandwich complexes as efficient transfer hydrogenation catalysts.

Ligand dissociation: planar or pyramidal intermediates?

In organometallic chemistry, ligand dissociation is a key intermediate step in many useful processes. The dissociation of halide from an 18-electron half-sandwich complex (that is, with a single cyclopentadienyl ligand) of the type [CpRu(P-P')Hal] leaves an unsaturated 16-electron intermediate [CpRu(P-P')](+), which is then ready for subsequent addition reactions. Does the intermediate maintain its structure with a vacant site in place of the dissociated ligand, or does it rearrange, either concurrent with its formation or subsequently? In other words, are the 16-electron species planar or pyramidal? The outcome is relevant for chiral-at-metal compounds [CpML(1)L(2)L(3)] because an intermediate [CpML(1)L(2)] retains its chirality with respect to the metal atom as long as it is pyramidal, whereas it loses its chiral information if it becomes planar. In this Account, we address experimental results and theoretical calculations that help illuminate the energetics of structural rearrangements after halide dissociation. The rate-determining step in the halide exchange and racemization reactions of (R(Ru))- and (S(Ru))-[CpRu(P-P')Cl] is the cleavage of the Ru-Cl bond to give pyramidal intermediates (R(Ru))- and (S(Ru))-[CpRu(P-P')](+), which have kept the original metal configurations. These unsaturated intermediates can react with added ligands, such as Br(-) or I(-) (k(2) paths). The substitution products form with retention of the metal configuration. However, the pyramidal intermediates (R(Ru))- and (S(Ru))-[CpRu(P-P')](+) can also invert to their mirror images (k(3) paths). For (R(Ru))- and (S(Ru))-[CpRu(P-P')](+), the barrier of the pyramidal inversion (k(3)) is much higher than that of the halide addition (k(2)). The competition ratio k(3)/k(2) determines how much racemization occurs in a ligand exchange reaction. The competition ratio k(3)/k(2) can be determined from the ratio of the (R(Ru))- and (S(Ru))-products, which is constant throughout the course of the reaction. For compounds like [CpRu(P-P')Hal], k(3)/k(2) is much smaller than 1, resulting in an energy profile that resembles a basilica. These results, established with chiral-at-metal compounds, are supported by calculations that show that 16-electron half-sandwich intermediates with sigma-donating ligands, such as [CpM(NH(3))(2)], adopt planar structures, whereas strongly pi-bonding ligands, as in [CpM(CO)(2)], lead to pyramidal intermediates. The computed activation energies for the pyramidal inversion are on the order of 10 kcal/mol, with the planar species being transition states. The ligand dissociation behavior of 18-electron transition metal complexes is compared with nucleophile dissociation in main group compounds with octet configurations; here we include new computational results. Without exception, unsaturated main group intermediates, such as the carbenium ions formed in S(N)1 reactions, are planar. Our results and analysis help put transition metal chemistry on a firmer mechanistic foundation, and chiral-at-metal compounds are invaluable to this end.

Alkyl dehydrogenation in a Rh(I) complex via an isolated agostic intermediate

A well-characterised 14-electron rhodium phosphine complex, [Rh(PiPr3)3][BArF4], which contains a beta-CH agostic interaction, is observed to undergo spontaneous dehydrogenation to afford [Rh(PiPr3)2(PiPr2(C3H5))][BArF4]; calculations on a model system show that while C-H activation is equally accessible from the beta-CH agostic species or an alternative gamma-CH agostic isomer, subsequent beta-H-transfer can only be achieved along pathways originating from the beta-CH agostic form.

Coordinatively Unsaturated Semisandwich Complexes of Ruthenium with Phosphinoamine Ligands and Related Species: A Complex Containing (R,R)-1,2-Bis((diisopropylphosphino)amino)cyclohexane in a New Coordination Form κ3P,P‘,N-η2-P,N

The syntheses of the chloro complexes [Ru(eta5-C5R5)Cl(L)] (R = H, Me; L = phosphinoamine ligand) (1a-d) have been carried out by reaction of [(eta5-C5H5)RuCl(PPh3)2] or {(eta5-C5Me5)RuCl}4 with the corresponding phosphinoamine (R,R)-1,2-bis((diisopropylphosphino)amino)cyclohexane), R,R-dippach, or 1,2-bis(((diisopropylphosphino)amino)ethane), dippae. The chloride abstraction reactions from these compounds lead to different products depending on the starting chlorocomplex and the reaction conditions. Under argon atmosphere, chloride abstraction from [(eta5-C5Me5)RuCl(R,R-dippach)] with NaBAr'4 yields the compound [(eta5-C5Me5)Ru(kappa3P,P'-(R,R)-dippach)][BAr'4] (2b) which exhibits a three-membered ring Ru-N-P by a new coordination form of this phosphinoamine. However, under the same conditions the reaction starting from [(eta5-C5Me5)RuCl(dippae)] yields the unsaturated 16 electron complex [(eta5-C5Me5)Ru(dippae)][BAr'4] (2d). The bonding modes of R,R-dippach and dippae ligands have been analyzed by DFT calculations. The possibility of tridentate P,N,P-coordination of the phosphinoamide ligand to a fragment [(eta5-C5Me5)Ru]+ is always present, but only the presence of a cyclohexane unit in the ligand framework converts this bonding mode in a more favorable option than the usual P,P-coordination. Dinitrogen [(eta5-C5R5)Ru(N2)(L)][BAr'4] (3a-d) and dioxygen complexes [(eta5-C5H5)Ru(O2)(R,R-dippach)][BPh4] (4a) and [(eta5-C5Me5)Ru(O2)(L)][BPh4] (4b,d) have been prepared by chloride abstraction under dinitrogen or dioxygen atmosphere, respectively. The presence of 16 electron [(eta5-C5H5)Ru(R,R-dippach)]+ species in fluorobenzene solutions of the corresponding dinitrogen or dioxygen complexes in conjunction with the presence of [BAr'4]- gave in some cases a small fraction of [Ru(eta5-C5H5)(eta6-C6H5F)][BAr'4] (5a), which has been isolated and characterized by X-ray diffraction.

Substitution, cage functionalization, and oxidation of the charge-compensated triruthenium monocarbollide cluster complex [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8]

The compound [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)6}-closo-2,1-RuCB10H8] 1a reacts with PMe3 or PCy3(Cy = cyclo-C6H11) to give the structurally different species [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)5(PMe3)}-closo-2,1-RuCB10H8] 4 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)5(PCy3)}-closo-2,1-RuCB10H8]5, respectively. A symmetrically disubstituted product [1-SMe2-2,2-(CO)2-7,11-(mu-H)2-2,7,11-{Ru2(CO)4(PMe3)2}-closo-2,1-RuCB10H8] 6 is obtained using an excess of PMe3. In contrast, the chelating diphosphines 1,1'-(PPh2)2-Fe(eta-C5H4)2 and 1,2-(PPh2)2-closo-1,2-C2B10H10 react with 1a to yield oxidative-insertion species [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(micro-[1',1''-(PPh2)2-Fe(eta-C5H4)2])(CO)4}-closo-2,1-RuCB10H8] 7 and [1-SMe2-2,2-(CO)2-11-(mu-H)-2,7,11-{Ru2(mu-H)(CO)4(1',2'-(PPh2)2-closo-1',2'-C2B10H10)}-closo-2,1-RuCB10H8] 8, respectively. In toluene at reflux temperatures, 1a with Bu(t)SSBu(t) gives [1-SMe2-2,2-(CO)2-7-(mu-SBu(t))-11-(mu-H)-2,7,11-{Ru2(mu-H)(mu-SBu(t))(CO)4}-closo-2,1-RuCB10H8] 9, and with Bu(t)C [triple bond] CH gives [1-SMe2-2,2-(CO)2-7-{mu:eta2-(E)-CH=C(H)Bu(t)}-11-{mu:eta2-(E)-CH=C(H)Bu(t)}-2,7,11-{Ru2(CO)5}-closo-2,1-RuCB10H8] 10. In the latter, two alkyne groups have inserted into cage B-H groups, with one of the resulting B-vinyl moieties involved in a C-H...Ru agostic bond. Oxidation of 1a with I2 or HgCl2 affords the mononuclear ruthenium complex [1-SMe2-2,2,2-(CO)3-closo-2,1-RuCB10H10] 11.

Multifunctional Behavior by a Bis-(phosphinimino)methanide Ligand: η2- vs η3-coordination vs Bronsted Basicity

The reaction of [(Cymene)RuCl2]2 with the chelate LiHC(PPh2NPh)2 occurs to remove both chloride ligands, to furnish a cationic Ru(II) complex with the monoanionic ligand bound eta3, through two N and an sp3 carbon. This cation is also produced from the conjugate acid of the ligand H2C(PPh2NPh)2 because this molecule can serve as a Brønsted base, to deprotonate the acidic carbon of another molecule of H2C(PPh2NPh)2. DFT calculations show an energy surface where (Cymene)RuHC(PPh2NPh)2L is more stable with a Ru-CH(PPh2NPh)2 bond and with L = Cl- or MeCN not coordinated to Ru, than to an eta2-HC(PPh2NPh)2 structure with coordinated L; this is tested experimentally. The greater tendency for this ligand to be coordinated eta3 vs analogous diketiminates is discussed. The nucleophilicity of Cgamma in structure 1, vs that of donors L = Cl- or MeCN, is evaluated to understand the preference of the bis(phosphinimino)methanide to be bidentate or tridentate.